Deep eutectic solvents (DESs) are regarded as a new class of green solvents because of their unique properties such as easy synthesis, low cost, environmental friendliness, low volatility, high dissolution power, high biodegradability, and feasibility of structural design. DESs have been widely applied for the separation of mixtures as alternatives to conventional solvents. A DES usually consists of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA). HBAs include amides, thiourea, amines, imidazole, azole, alcohols, acids and phenol. HBAs include quaternary ammonium salts, quaternary phosphonium salts, imidazolium-based salts, dication based salts, inner salts, and molecular imidazole and its analogues. Therefore, there are numerous DESs available for use in different applications. With an in-depth understanding of the common and novel properties of DESs, researchers have prepared and applied DESs to various types of separations. We first introduce the composition of DESs, including various HBDs and HBAs frequently used in the literature. Second, the properties of DESs, including phase diagrams, melting points, density, viscosity, and conductivity, are summarized. Third, recent applications of DESs in the separation of mixtures are reviewed, including the absorption of acidic gases (CO₂, SO₂ and H₂S), the extraction of bioactive compounds, extraction of sulfur-and nitrogen-containing compounds from fuel oils, extraction of phenolic compounds from oils, separation of mixtures of aromatic and aliphatic compounds, separation of alcohol and water mixtures, removal of glycerol from biodiesel, separation of alcohol and ester mixtures, removal of radioactive nuclear contaminants, and separation of isomer mixtures of benzene carboxylic acids. DESs are used in two ways for the separation of mixtures. (1) A DES prepared in advance is used as a solvent to separate a component from a mixture by selective dissolution or absorption of specific compound(s), such as the absorption of SO₂ using betaine+ethylene glycol DES. Here, DESs are used like traditional solvents. (2) A DES is formed in situ during the separation of mixtures by adding a HBA to a mixture containing one or more HBDs, such as the removal of phenol from an oil mixture using choline chloride, where a phenol+choline chloride DES is formed during the separation process and the formed DES does not dissolve in the oil phase. Although various DESs have been broadly developed for the separation of mixtures, research continues in the field of DESs, including analysis of the physicochemical properties of DES, especially during extraction or absorption, development of functional DESs for high-efficiency separations, development of efficient methods to regenerate DESs, and combined use of DESs with other techniques to improve separation processes. This article describes general trends in the development of DESs for separation and evaluates the problematic or challenging aspects of DESs in the separation of mixtures.

Graphyne is a rapidly rising star material of carbon allotropes containing only sp and sp² hybridized carbon atoms forming extended two-dimensional layers. In particular, graphdiyne is an important member of graphyne family. With unique nanotopological pores, two-dimensional layered conjugated frameworks, and excellent semiconducting and optical properties, graphdiyne has displayed distinct superiorities in the fields of energy storage, electrocatalysis, photocatalysis, nonlinear optics, electronics, gas separation, etc. Therefore, the synthesis of high-quality graphdiyne is highly required to fulfill its potentially extraordinary applications. Furthermore, the development of a standardized and systematic set of characterization procedures is an urgent need, and would be based on intrinsic samples. However, there are still obvious barriers to synthesizing this new-born carbon allotrope that can be mainly considered as follows. The selection and stability of monomers is essential for synthesis. The synthesis process in solution also suffers from an annoying problem of the relatively free rotation possible about the alkyne-aryl single bonds, which leads to the coexistence and rapid equilibration of coplanar and twisted structures. Furthermore, the limited reaction conversion and side reactions also lead to a confusion of configuration.

In this review, we primarily focus on the state-of-the-art progress of the synthetic strategies for graphdiyne. First, we give a brief introduction about the structure of graphyne and graphdiyne. We subsequently discuss in detail the recent developments in synthetic methods that can mainly be divided into three aspects: total organic synthesis, on-surface covalent reaction, and polymerization in a solution phase. In particular, much progress in solution polymerization has been achieved since in-situ polymerization on Cu surface was reported in 2010. Liquid/liquid interface, gas/liquid interface, and surface template were also employed for confined reaction, and contribute significantly to the synthesis of a graphdiyne film. Through such strategies, graphdiyne with a well-defined structure and diverse morphologies could be achieved successfully. Finally, the opportunities and challenges for the synthesis of graphdiyne are prospected. A more rational design is desired in terms of monomer modification and reaction regulation.

The frequency of oil-spill accidents and industrial wastewater discharges have caused severe water pollution, not only resulting in huge economic losses but also threatening the ecological system. Recently, researchers have developed different types of materials with special wettability (such as superhydrophobicity or superoleophobicity) and used them successfully for oil-water separation. Superhydrophobic and superoleophobic surfaces can generally be obtained by designing the surface geometric micro-topography and chemical composition of solid materials. Endowing porous materials with reverse super-wettability to water and oil using various microfabrication technologies is the key to separate oil-water mixtures. In this review we initially identify the significance of fabricating oil/water-separating materials and achieving effective separations. Then, the typical theoretical principles underlying surface wettability are briefly introduced. According to the difference in surface wettabilities toward water and oil, we classify the current oil-water separating materials into three categories: (ⅰ) superhydrophobic/superoleophilic materials, (ⅱ) superoleophobic/ superhydrophilic materials, and (ⅲ) smart-response materials with switchable wettability. This review summarizes the representative research work for each of these materials, including their fabrication methods, principle and process of oil-water separation, and main characteristics and applications. Finally, existing problems, challenges, and future prospects of this fast-growing field of special wettability porous materials for the separation of oil-water mixtures are discussed.

Numerous real space functions have been purposed so far for unveiling chemically interesting molecular electronic structure characteristics, such as chemical bonds, lone pairs, and multicenter electronic conjugations. Among these analysis methods, electron localization function (ELF), Laplacian of electron density (∇²ρ), and deformation density (ρ_def) were widely employed in practical research work. It is well known that the analysis of total molecular electron density is not sufficient for revealing much information about the molecular electronic structure like the above-mentioned methods. However, in this work, using several instances and by comparing with the ELF, ∇²ρ, and ρ_def values, we show that it is possible to explore molecular electronic structure characteristics if one solely focuses on investigating the valence electron density distribution. It is found that for most cases, analysis of the very simple valence electron density conveys analogous information as ELF, ∇²ρ and ρ_def analyses, with additional advantage of reduced computational complexity. We hope that this work will bring chemists' attention to the high importance of valence electron density, which has been largely ignored for a long time. It should also be noticed that the valence electron density analysis is not free from drawbacks, and when this method is unable to provide an informative picture, one has to use other analysis methods.

In recent years, deep eutectic solvents (DESs) have attracted considerable attention. They have been applied in many fields such as dissolution and separation, electrochemistry, materials preparation, reaction, and catalysis. The DESs are generally formed by the hydrogen bonding interactions between hydrogen-bond donors (HBDs) and acceptors (HBAs). Knowledge of the thermal stability of DESs is very important for their application at high temperatures. However, there have been relatively few studies on the thermal stability of DESs. Herein, a systematic investigation on the thermal stability of 40 DESs was carried out using thermal gravimetric analysis (TGA), and the onset decomposition temperatures (T_onset) of these solvents were obtained. The most important conclusion drawn from this work is that the thermal behavior of DESs is quite different from that of ionic liquids. The anions or cations of ionic liquids decompose first, followed by the decomposition of the opposite ion at elevated temperatures. On the other hand, the DESs generally first decompose to HBDs and HBAs at high temperatures through the weakening of the hydrogen bond interactions. Subsequently, the HBDs with relatively low boiling points or poor stabilities undergo volatilization or decomposition; the HBAs also undergo volatilization or decomposition but at a higher temperature. For example, the most commonly used HBA choline chloride (ChCl) begins to decompose at around 250 ℃. The hydrogen bond plays an important role in the thermal stability of DESs. It hinders the "escape" of molecules and requires greater energy to break than pure HBAs and HBDs, which causes the T_onset of DESs to shift to higher temperatures. Note that the thermal stability of HBDs has a crucial effect on the T_onset of DESs. The HBDs would decompose or volatilize first during TGA because of their relatively poor thermal stability or lower boiling points. The more stable the HBDs are, the greater would be the T_onset values of the corresponding DESs. Further, the effects of anions on HBAs, molar ratio of HBAs to HBDs, and heating rate in fast scan TGA have been discussed. As the heating rate increased, the TGA curves of DESs shifted to higher temperatures gradually, and the temperature hysteretic effect became prominent when the rate reached 10 ℃?min?1. From an industrial application point of view, there is an overestimation of the onset decomposition temperatures of DESs by T_onset, so the long-term stability of DESs was investigated at the end of the study. This study could help understand the thermal behavior of DESs (progressive decomposition) and provide guidance for designing DESs with appropriate thermal stability for practical applications.

Organic-inorganic perovskite solar cells (PSCs) have become one of the most promising solar cells, as the power conversion efficiency (PCE) has increased from less than 5% in 2009 to certified values of over 22%. In the typical PSC device architecture, hole transport materials that can effectively extract and transmit holes from the active layer to the counter electrode (HTMs) are indispensable. The well-known small molecule 2, 2', 7, 7'-tetrakis-(N, N-di-4-methoxy-phenyl amino)-9, 9'-spirobifluorene (spiro-OMeTAD) is the best choice for optimal perovskite device performance. Nevertheless, there is a consensus that spiro-OMeTAD by itself is not stable enough for long-term use in devices due to the sophisticated oxidation process associated with undesired ion migration/interactions. It has been found that spiro-OMeTAD can significantly contribute to the overall cost of materials required for the PSC manufacturing, thus its market price makes its use in large-scale production costly. Besides, another main drawback of spiro-OMeTAD is its poor reproducibility.

To engineer HTMs that are considerably cheaper and more reproducible than spiro-OMeTAD, shorter reaction schemes with simple purification procedures are required. Furthermore, HTMs must possess a number of other qualities, including excellent charge transporting properties, good energy matching with the perovskite, transparency to solar radiation, a large Stokes shift, good solubility in organic solvents, morphologically stable film formation, and others. To date, hundreds of new organic semiconductor molecules have been synthesized for use as HTMs in perovskite solar cells. Successful examples include azomethine derivatives, branched methoxydiphenylamine-substituted fluorine derivatives, enamine derivatives, and many others. Some of these have been incorporated as HTMs in complete, functional PSCs capable of matching the performance of the best-performing PSCs prepared using spiro-OMeTAD while showing even better stability.

In light of these results, we describe the advances made in the synthesis of HTMs that have been tested in perovskite solar cells, and give an overview of the molecular engineering of HTMs. Meanwhile, we highlight the effects of molecular structure on PCE and device stability of PSCs. This review is organized as follows. In the first part, we give a general introduction to the development of PSCs. In the second part, we focus on the introduction of the perovskite structure, device architecture, and relevant work principles in detail. In the third part, we discuss all kinds of molecular HTMs applied in PSCs. Special emphasis is placed on the relationship between HTM molecular structure and device function. Last but not least, we point out some existing challenges, suggest possible routes for further HTM design, and provide some conclusions.

With solar, wind, and other types of renewable energy incorporated into electrical grids and with the construction of smart grids, energy storage technology has become essential to optimize energy utilization. Due primarily to its abundance and low cost, aqueous rechargeable sodium-ion batteries (ARSBs) have received increasing attention in the field of electrochemical energy storage technology, and represent a promising alternative to energy storage in future power grids. However, because of the limitations of the thermodynamics of electrochemical processes in water, reactions in aqueous solution are more complicated compared to an organic system. Many parameters must be taken into account in an aqueous system, such as electrolyte concentration, dissolved oxygen content, and pH. As a result, it is challenging to select an appropriate electrode material, whose capacity, electrochemical potential, adaptability, and even catalytic effect may seriously affect the battery performance and hamper its application. Therefore, the development of advanced electrode materials, which can suppress side reactions of the battery and have good electrochemical performance, has become the focus of ARSB research. This paper briefly discusses the characteristics of ARSBs and summarizes the latest research progress in the development of electrode materials, including oxides, polyanionic compounds, Prussian blue analogues, and organics. This review also discusses the challenges remaining in the development of ARSBs, and suggests several ways to solve them, such as by using multivalent ions, hybridized electrolytes, etc., and speculates about future research directions. The studies and concepts discussed herein will advance the development of ARSBs and promote the optimization of energy utilization.

Borophene, a boron analogue of graphene, exhibits a rich variety of chemical and physical properties. Here, we provide an intensive overview of recent progress in theoretical modeling and experimental synthesis of borophene. In particular, we analyze the influence of substrate, growth temperature, and precursor on the selectivity of boron nucleation. While three-dimensional (3D) bulk boron is more stable than a two-dimensional (2D) boron sheet, the nucleation barrier determined by the growth process controls the formation of the material and it depends on the specific growth environment. Theoretical studies have shown that a metal substrate can play an important role in stabilizing 2D boron clusters over their 3D form, resulting in the kinetically favored growth of 2D boron on the substrate even though the 2D boron clusters will be overwhelmingly less stable than the 3D form with increasing cluster size. Ag and Cu substrates have proven to be particularly suitable for achieving this preference. Guided by theoretical works and perhaps original insights, experimentalists from two independent groups have successfully synthesized 2D boron sheets on silver substrates by depositing ultra-high purity boron onto a clean Ag (111) surface under high vacuum conditions. Moreover, the borophene samples were found to exhibit the same atomic structure previously predicted to be preferred on this substrate. Besides the substrate, the growth temperature is also key to the final product. When the temperature is too low, boron growth cannot overcome the nucleation barrier of the 2D structure. As a result, boron clusters or amorphous boron structures are likely to be formed. In contrast, an excessively high growth temperature will steer the growth to overcome the nucleation barrier of 3D boron, possibly yielding boron nanofilms with finite thickness. Therefore, the growth temperature needs to be carefully controlled, so that the free energy of boron growth will be located between the nucleation barriers of the 3D and 2D forms. Some impurity elements found in synthetic source materials, such as hydrogen and oxygen, can also impact boron nucleation. The existence of these elements may alter the competition between 2D and 3D structures during the nucleation process. More importantly, hydrogen and oxygen can passivate the dangling bonds on the surface of a 3D boron structure, lowering its surface energy, and therefore, impairing the nucleation of 2D boron structures. At present, molecular beam epitaxy (MBE) is the only method with which borophene has been successfully synthesized. Yet this method is very expensive, suffers from low yield, and is constrained to small sample sizes. Thus, exploring the growth of borophene via chemical vapor deposition (CVD) on different substrates is critically important for realizing the great potential of borophene in various applications. By discussing possible growth conditions and atomistic mechanisms of borophene nucleation as well as theoretical methods for modeling and simulations, we suggest prospects for chemical vapor deposition growth of borophene on selected substrates. This work aims to offer useful guidance for chemical synthesis of large-area, high-quality borophenes and promote their practical applications.

Graphdiyne features sp and sp² hybridized carbon atoms. The direct natural band gap and Dirac cone structure for graphdiyne are believed to originated from inhomogeneous π-bonding of differently hybridized carbon atoms and overlap of carbon 2p_z orbitals. The special electronic structures and pore structures of graphdiyne are responsible for its potential and important applications in the fields of information technology, electronics, energy, catalysis, and optoelectronics. Recent basic and applied research studies of graphdiyne have led to important results; as a result, graphdiyne has become a new research field for carbon materials. The high activity of acetylenic units in graphdiyne provides a good platform for chemical modification and doping. Several approaches have been developed to modify the band gap of graphdiyne, including invoking strain, BN-doping, preparing nanoribbons, and hydrogenation, leading to a new graphdiyne (GDY) or graphyne (GY) derivatives. In this review, we summarize the recent progress in nonmetallic heteroatom doping, especially by nitrogen, boron, or oxygen; by modifying metal atoms for tuning electronic/spintronic properties, enhancing water splitting performance, and applying dye-sensitized solar cells and catalysts; and by surface functionalization of graphdiyne via hydrogenation, hydroxylation, and halogenation to adjust the band gap. Hence, it can be surmised that the electronic structures of graphdiynes can be tuned for specific applications. These results suggest that graphdiynes can be more advantageous than grapheme for tailoring energy band gaps for application in nanoelectronics. We also discuss the influence of doping and functionalization on the electronic properties of graphdiyne and their effects on the synergistic enhancement of photoelectrocatalytic performance. We hope that the deep and wide application of these new materials in many fields such as energy transfer and storage, catalyst, electronics, gas separation, and spintronics will draw much attention and become a widely focused research direction.

Graphdiyne(GDY) is a new booming carbon material with a highly π-conjugatedstructure that consists of sp-and sp²-hybridizedcarbon atoms. Due to the diverse compositions of the carbon atoms, GDYs can bedivided into several forms based on their structure and periodicity. Until2010, γ-GDY has been successfully synthesized and becomes a new member of thecarbon family. Many researchers have subsequently devoted their attention tothe study of GDY. Compared to the traditional carbon materials, GDY exhibits aunique carbon network and electronic structure, thereby attracting considerableattention in a variety of fields. With the development of its syntheticchemistry, many types of GDY with different structures have been synthesizedand characterized. The characterization of their micromorphology is crucial forstudying the synthesis procedure and understanding the properties of GDYmaterials. At present, the developed method can characterize GDY morphology, crystal structure, and thechemical bonds of the carbon atoms. Specifically, the morphology and thicknessof GDY can be evaluated by scanning electron microscopy, transmission electronmicroscopy, and atomic force microscopy. The crystal structure can beinvestigated using X-ray diffraction and high-resolution transmission electronmicroscopy. The chemical bonding of the carbon atoms can be analyzed by Ramanspectroscopy, X-ray photoelectron spectroscopy, Fourier transforminfrared (FT-IR) spectroscopy, C-13 nuclear magnetic resonance (¹³C NMR), UV-visible (UV-Vis) absorption spectroscopy, etc. However, methods for therapid and nondestructive characterization of the highly crystalline graphdiyneare still absent, restricting the study of the intrinsic properties of GDY. Dueto the unique electronic and porous structure of GDY, it has been the focus ofextensive investigations in the field of catalysis. As a result of itsfavorable electronic structure and good capability for transferringphotoexcited electrons and holes, GDY can enhance light absorption andfacilitate the separation of photoexcited charge carriers in semiconductors andthereby significantly promote their photocatalytic performance. In addition, GDY can be modified using foreign elements, providing an ideal platform toprepare a highly active catalyst for the hydrogen evolution reaction, oxygenevolution reaction, oxygen reduction reaction, etc. Furthermore, GDY can besynthesized on arbitrary substrates in a three-dimensional nanosheet arraystructure, which can provide a large number of channels for the transfer ofelectrons and a large contact area with the reactant, which is beneficial inelectrocatalytic reactions. This review focused on the recent developments incharacterization methods as well as the photo and electrocatalysis applicationsof GDY, and elaborated the opportunities and challenges for the investigationof GDY in the future.

Intrinsically conductive polymers are a class of exciting materials since they combine the advantages of both metals and plastics. But their application is limited due to the issues related to their electronic properties, stability and processibility. For example, although polyacetylene can have electrical conductivity comparable to metals, it degrades fast in air. Most of the conductive polymers in the conductive state, such as polypyrrole and polythiophene, cannot be dispersed in any solvent and cannot be turned to a melt. It is thus difficult to process them into thin films with good quality, while thin films with good quality are important for many applications. In terms of the materials processing, polyaniline (PANi) and poly(3, 4-ethylenedioxythiophene) (PEDOT) have gained great attention. PANi doped with some large cations can be dispersed in some toxic organic solvents, and poly(3, 4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) can be dispersed in water and some polar organic solvents. But the PANi and PEDOT:PSS films prepared from their solutions are usually low. Recently, great progress was made in improving the properties of intrinsically conductive polymers. The conductivity of PEDOT:PSS can be enhanced from 10^-1 S·cm^-1 to > 4000 S·cm^-1 through the so-called "secondary doping". The high conductivity together with the solution processibility enables the application of conductive polymers in many areas, such as electrodes and thermoelectric conversion. In addition, due to their electrochemical activity, conductive polymers or their composites with inorganic materials can have high capacity of charge storage. Conductive polymers can also be added into the electrodes of batteries, because they can facilitate the charge transport and alleviate the large volume change problem of silicon electrode of batteries. It has been demonstrated that conductive polymers can have important application in many areas, such as transparent electrode, stretchable electrode, neural interfaces, thermoelectric conversion and energy storage system. This article provides a brief review on the enhancement of the electrical conductivity of intrinsically conductive polymers and their application as electrodes and in thermoelectric conversion, supercapacitors and batteries.

Electrochemicalenergy storage devices are becoming increasingly important in modern societyfor efficient energy storage. The use of these devices is mainly dependent onthe electrode materials. As a newly discovered carbon allotrope, graphdiyne(GDY) is a two-dimensional full-carbon material. Its wide interlayer distance(0.365 nm), large specific surface area, special three-dimensional porousstructure (18-C hexagon pores), and high conductivity make it a potentialelectrode material in energy storage devices. In this paper, based on thefacile synthesis method and the unique porous structure of GDY, theapplications of GDY in energy storage devices have been discussed in detailfrom the aspects of both theoretical predictions and recent experimentaldevelopments. The Li/Na migration and storage in mono-layered and bulk GDYindicate that GDY-based batteries have excellent theoretical Li/Na storagecapacity. The maximal Li storage capacity in mono-layered GDY is LiC₃(744 mAh∙g^-1). The experimental Li storage capacity of GDY issimilar to theoretical predictions. The experimental Li storage capacity of athick GDY film is close to that of mono-layered GDY' (744 mAh∙g^-1).A thin GDY film with double-side storage model has two-times the Li storagecapacity (1480 mAh∙g^-1) of mono-layered GDY. Powder GDY has lower Listorage capacity than GDY film. The maximal Na storage capacity in GDYcorresponds to NaC_5.14 (316 mAh∙g^-1), and mono-layeredGDY possesses higher theoretical Na storage capacity (NaC_2.57). Theexperimental Na storage capacity (261 mAh∙g^-1) is similar to itstheoretical value. Besides, GDY as electrode material, applied in metal-sulfurbatteries, presents excellent electrochemical performance (in Li-S battery: 0.1C, 949.2 mAh∙g^-1; in Mg-S battery: 50 mA∙g^-1, 458.9 mAh∙g^-1).This ingenious design presents a new way for the preparation of carbon-loadedsulfur. GDY electrode material is also successfully used in supercapacitors, including the traditional supercapacitor, Li-ion capacitors, and Na-ioncapacitors. The traditional supercapacitor with GDY as the electrode material showsgood double layer capacitance and pseudo-capacitance. Both Li-ion capacitor(100.3 W∙kg^-1, 110.7 Wh∙kg^-1) and Na-ion capacitor (300W∙kg^-1, 182.3 Wh∙kg^-1) possess high power and energydensities. Moreover, the effects of synthesis of GDY nanostructure, heattreatment of GDY, and atom-doping in GDY on the performance of electrochemicalenergy storage will be introduced and discussed. The results indicate that GDYhas great potential for application in different energy storage devices as anefficient electrode material.

Vitamin E compounds are biologically active and are frequently used as antioxidants. The demand for Vitamin E compounds has increased significantly in recent years, and at present, more than 80% of the market demand for Vitamin E is fulfilled by its synthetic counterparts. Therefore, it is imperative to increase the production of Vitamin E. Vitamin E compounds contain tocopherol and tocotrienol derivatives, and α-tocopherol, which dominates the sound, is the most biologically active. This review covers the methods of preparation of α-tocopherol, focusing on the synthesis routes, chemical reactions, and corresponding catalysts. The synthesis of Vitamin E, including preparation of 2, 3, 5-trimethylhydroquinone (TMHQ), preparation of isophytol, and condensation of TMHQ and isophytol are discussed in detail. The disadvantages and issues related to the preparation methods are also included. In general, the preparation of TMHQ comprises three steps: (1) methylation of m-cresol to 2, 3, 6-trimethylphenol, (2) oxidation of 2, 3, 6-trimethylphenol to 2, 3, 5-trimethylbenzoquione (TMBQ), and (3) hydrogenation of TMBQ to TMHQ. Recently, a novel and attractive method using isophorone, which can be produced by self-condensation of acetone, as a source for synthesizing TMHQ has been developed. Among these procedures, it is important to attain high selectivity in the oxidative reactions, including oxidation of 2, 3, 6-trimethylphenol and isophorone (α-isophorone or β-isophorone), and to replace H₂O₂, a common oxidant, by oxygen or air. One of the methods of preparation of isophytol using citral as a source has been abandoned because of shortage of oil of litsea cubeba, which is a natural source of citral. Linalool, produced from 6-methyl-5-hepten-2-one, is a key intermediate in the main process of preparation of isophytol. Both BASF SE and Roche have developed effective methods for the preparation of 6-methyl-5-hepten-2-one, respectively. Semi-hydrogenation of alkynols plays a key role in the whole process. The selectivity, especially at high conversion is directly related to the profit; therefore, it is of great importance for industries. The condensation of TMHQ and isophytol is essentially a Friedel-Crafts alkylation reaction catalyzed by acids. Similar reactions include methylation of m-cresol. Bronsted acids are usually effective for these reactions; however, it is difficult to recover these catalysts from the homogeneous systems. Therefore solid acid has a great potential in this area and it is also a promising topic to reduce the loss of acid sites when using acid-immobilized catalysts. The supply of various sources of the reactants and the local policy need to be considered while choosing an appropriate method for the preparation of Vitamin E.

Organic-inorganic hybrid perovskites have attracted substantial attention due to their outstanding performance in solar energy conversion and optoelectronic applications. However, the poor stability of organic lead halide perovskites (APbX₃, A: organic cations; X: halide anions) hinders their practical application. Compositional engineering, optimizing the concentration of different A and/or X, is one of the most effective ways to enhance the stability of APbX₃. In particular, mixing formamidinium (FA) and methylammonium (MA) cations has been widely investigated. Here, we performed first-principles calculations to systematically investigate the structures and optical properties of FA_1-xMA_xPbI₃. We obtained several stable crystal structures of FA_1-xMA_xPbI₃ in the cubic phase for different ratios of FA and MA cations. By analyzing the structures of these mixed cation perovskites, we revealed that the lattice parameters decreased linearly with increasing concentration of MA cations, which was consistent with previous experimental results. For APbX₃ perovskites, the Goldschmidt tolerance factor has been shown to be an effective index for predicting the stability. The mixing of organic cations is an effective method for adjusting this factor and thus the stability of these perovskite materials. In this work, the formation energy difference (∆E) was calculated and our results showed that mixing of FA and MA cations could increase the thermodynamic stability compared to pure FAPbI₃ and MAPbI₃. FA_0.5MA_0.5PbI₃ was found to be the most stable of all composites investigated. Furthermore, the band gap decreased with increasing proportion of FA cations, indicating an effective strategy for extending the absorption range of organic-inorganic hybrid perovskites into the infra-red region of the solar spectrum. By analyzing the Pb―I bond lengths for different FA : MA ratios, we showed that the decrease of band gap mainly comes from the increase of the maximum valence band energy. In addition, the effective masses were similar, irrespective of the cation mixture, indicating that the mixing of organic cations does not affect the carrier transport mechanism in this material. Density of states (DOS) analysis revealed that the DOS of valence band edge increased with increasing proportion of FA cations, enhancing transitions between the valence and conduction bands. Finally, detailed analysis of the optical absorption coefficients of all composition was performed; the absorption spectra were blue shifted with increasing MA cation concentration. These results demonstrated the possibility of controlling the optoelectronic properties of organometallic lead halide perovskites by mixing FA and MA cations and hence, further improving the efficiency of perovskite solar cells.

As new types of carbon nanomaterials, carbon quantum dots (CQDs) have received widespread attention for their potential applications in optoelectronic device owing to their unique properties such as long hot-electron lifetime, high electron mobility, tunable bandgap, strong stable florescence, solution-processability, stability, non-toxicity, and low cost. Correspondingly, there has been several interesting developments in researches focusing on CQDs. In this review, we will present an update the on the latest research on the synthesis, morphology, structural characteristics, and optoelectronic properties of CQDs. The latter are determined by quantum confinement effect and surface defects. Using bottom-up synthesis methods, CQDs with higher crystallinity and less surface defects could be obtained by accurately designing the precursors and reaction conditions. The structures could be characterized by high-resolution transmission electron microscopy. Secondly, the latest progress on photoelectric devices, including light-emitting diodes (LEDs), solar cells (SCs), and photodetectors (PDs), are summarized in detail. CQDs-based LEDs are divided into photoluminescence (PL) and electroluminescence (EL) LEDs owing to their different excitation modes. Recently, PL LEDs leveled with developed QDs-based LEDs in both luminous efficiency and color rendering index (CRI). With the discovery of their bandgap emission, CQDs overcame carrier injection, which is determined by surface defects and molecule states, and presented excellent potential in EL applications. Moreover, their broad absorption in the ultraviolet-to-visible light range and high electron mobility make CQDs preferable for improving energy conversion efficiency of SCs and responsivity of PDs. Finally, we delineate current challenges on studying CQDs. Its indefinite fluorescence mechanism and structural characterizations limit the development of CQDs. Furthermore, large-scale synthesis methods for CQDs with high quantum yields and crystallinity are not yet established, which hinders their utility in optoelectronic devices. Moreover, CQDs with narrow emission bandwidth (full width at half maximum, FWHM ≤ 35 nm) still do not exist, which restrains their applications in display and laser. Hence, researches on CQDs-based optoelectronic applications are still in the first stages of development. We hope that this review will indicate future directions and encourage critical thinking to elicit new discoveries on CQDs from both fundamental and applied researches. Consequently, the potential of environment-friendly CQDs can be realized in optoelectronics and more areas.

The electronic structures, deformation potential, electron-phonon couplings (EPCs), and intrinsic charge transport of layered systems — the sp +sp² hybridized carbon allotropes, graphynes (GYs) and graphdiynes (GDYs), as well as sp² + sp³ hybridized structure with buckling, such as stanine — have been investigated theoretically. Computational studies showed that, similar to graphene, some GYs can possess Dirac cones (such as α-, β-, and 6, 6, 12-GYs), and that the electronic properties of GYs and GDYs can be tuned by cutting into nanoribbons with different widths and edge morphologies. Focusing on the features of Dirac cones, band structure engineering can provide a clue for tuning electronic transport in 2D carbon-based materials. Based on the Boltzmann transport equation and the deformation potential approximation (DPA), the charge carrier mobilities in GYs and GDYs were predicted to be as high as 10⁴–10⁵ cm²·V^-1·s^-1 at room temperature. Interestingly, due to lower EPC strength and longer relaxation time, the charge carrier mobility in 6, 6, 12-GY with double Dirac cones structure was found to be even larger than that of graphene at room temperature. The unique electronic properties and high mobilities of GYs and GDYs make them highly promising candidates for applications in next generation nanoelectronics. Additionally, through the full evaluation of the EPC by density functional perturbation theory (DFPT) and Wannier interpolation, the EPCs with different phonon branches and wave-vectors as well as charge carrier mobilities for graphene, GYs and stanene have been discussed. This showed that the longitudinal acoustic (LA) phonon scattering in the long wavelength limit is the main scattering mechanism for GYs and graphene, and thus the DPA is applicable. Due to stronger LA phonon scattering, the electron mobilities (∼10⁴ cm²·V^-1·s^-1) of α-GYs and γ-GYs were predicted to be one order of magnitude smaller than that of graphene at room temperature by full evaluation of the EPC. However, the DPA would fail if there was buckling in the honeycomb structure and the planar symmetry was broken (absence of σ_h), such as in stanene, where the inter-valley scatterings from the out-of-plane acoustic (ZA) and transverse acoustic (TA) phonons dominate the carrier transport process and limit the electron mobilities to be (2–3) × 10³ cm²·V^-1·s^-1 at room temperature. In addition to our calculations, others have also found that the main scattering mechanisms in layered systems with buckling, such as silicene and germanene, are ZA and TA phonons. Thus, these results give us new insights into the role of EPCs and the limitation of the DPA for carrier transport in layered systems. They also indicate that the carrier mobilities of systems without σ_h-symmetry can be improved by suppressing the out-of-plane vibrations, for example by clamping by a substrate.

Polymer solar cells (PSCs) with bulk heterojunction (BHJ) structures have seen rapid development in recent years. In comparison with their inorganic counterparts, PSCs have some advantages such as low cost, light weight, solution processability, and good mechanical flexibility. However, improvement of the power conversion efficiency (PCE) of PSCs is required for commercial applications. In order to achieve high-performance PSCs, active layers, including donor polymers and acceptors, are very important. Several design principles for conjugated donor polymers in PSCs have emerged, including optimization of the conjugated backbone, side-chains, and substituents. In the past few decades, various classes of electron-donating polymers have been reported for PSCs. Among them, quinoxaline (Qx) is a unique building block for the construction of different optoelectronic polymers because of its planar, rigid, and conjugated structure. Qx derivatives have proven interesting and have been widely employed in many fields. Qx-based conjugated polymers (or small molecules) can be easily modified to match with ball-like fullerene derivatives such as PCBM ([6, 6]-phenyl-C₆₁ or C₇₁-butyric acid methyl ester) or weak crystalline non-fullerene acceptors such as 2, 2'-[[6, 6, 12, 12-tetrakis(4-hexylphenyl)-6, 12, -dihydrodithieno[2, 3-d:2', 3'-d']-s-indaceno[1, 2-b:5, 6-b']dithiophene-2, 8-diyl]bis[methylidyne(3-oxo-1H-indene-2, 1(3H)-diylidene)]]bispropanedinitrile (ITIC). Herein, we synthesized a Qx-based polymer with asymmetric side-chains (TPQ-1). The molecular weight, optical properties, molecular energy levels, and mobilities of TPQ-1 were investigated. Furthermore, the blend morphologies and photovoltaic properties of TPQ-1 using a strong crystalline non-fullerene (NF) acceptor (o-IDTBR) were systematically explored. The photovoltaic performance of TPQ-1 and its symmetric side-chain counterpart, HFQx-T, was compared. The introduction of asymmetric side-chains led to a favorable phase separation when blended with o-IDTBR. As expected, the TPQ-1:o-IDTBR-based devices exhibited a high PCE of 8.6% after thermal annealing (TA). In contrast, the HFQx-T:o-IDTBR-based devices showed a moderate PCE of 5.7%, moreover, the PCE was decreased to 4.6% after TA treatment. More importantly, a low bandgap material, PTB7-Th, was specifically selected as a third component to mix with the TPQ-1:o-IDTBR blend to form highly-efficient ternary PSCs. At an optimal weight ratio (15%) of PTB7-Th addition, a PCE of 9.6% was achieved. In the systems that were investigated, TPQ-1 demonstrated significantly better photovoltaic properties than the HFQx-T-based devices. These results indicate that Qx-based polymers with asymmetric side chains have a bright future in photovoltaic devices.

Quantitative correlation of several theoretical electrophilicity measures over different families of organic compounds are examined relative to the experimental values of Mayr et al. Notably, the ability to predict these values accurately will help to elucidate the reactivity and selectivity trends observed in charge-transfer reactions. A crucial advantage of this theoretical approach is that it provides this information without the need of experiments, which are often demanding and time-consuming. Here, two different types of electrophilicity measures were analyzed. First, models derived from conceptual density functional theory (c-DFT), including Parr's original proposal and further generalizations of this index, are investigated. For instance, the approaches of Gázquez et al. and Chamorro et al. are considered, whereby it is possible to distinguish between processes in which a molecule gains or loses electrons. Further, we also explored two novel electrophilicity definitions. On one hand, the potential of environmental perturbations to affect electron incorporation into a system is analyzed in terms of recent developments in c-DFT. These studies highlight the importance of considering the molecular surroundings when a consistent description of chemical reactivity is needed. On the other hand, we test a new definition of electrophilicity that is free from inconsistencies (so-called thermodynamic electrophilicity). This approach is based on Parr's pioneering insights, though it corrects issues present in the standard working expression for the calculation of electrophilicity. Additionally, we use machine-learning tools (i.e., symbolic regression) to identify the models that best fit the experimental values. In this way, the best possible description of the electrophilicity values in terms of different electronic structure quantities is obtained. Overall, this straightforward approach enables one to obtain good correlations between the theoretical and experimental quantities by using the simple, yet powerful, interpretative advantage of c-DFT methods. In general, we observed that the correlations found at the HF/6-31G(d) level of theory are of semi-quantitative value. To obtain more accurate results, we showed that working with families of compounds with similar functional groups is indispensable.

In the past decade, perovskite solar cells (Pero-SCs) have attracted a great deal of attention owing to their soaring power conversion efficiency (PCE), up to 22.7% in 2017. In p-i-n type Pero-SCs, one of the most commonly used hole transport layer (HTL) materials is poly(3, 4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT: PSS), which possesses a high coverage and an extremely smooth surface. However, the inferior electrical conductivity (or large series resistance) and lower work function (WF) of PEDOT:PSS relative to many other HTL materials limits the open-circuit voltages of Pero-SCs. Furthermore, the hygroscopic property and the acidic nature of PEDOT:PSS can readily cause the degradation of perovskite, and thereby affect the long-term stability of Pero-SCs. The abovementioned disadvantages can hinder the application of PEDOT:PSS in high-performance and stable Pero-SCs; therefore, many efforts have been made to modify PEDOT:PSS to prevent these disadvantages, for instance, adding various organic solvents, surfactants, salts, or acids to PEDOT:PSS as dopants. In this paper, we report a simple codoping method to modify PEDOT:PSS, i.e., employing L-3, 4-dihydroxyphenylalanine (DOPA) and dimethyl sulfoxide (DMSO) as codopants in PEDOT:PSS, and applying it as a HTL in p-i-n type Pero-SCs. Herein, DOPA and DMSO were mixed separately with PEDOT:PSS to obtain HTLs for comparison. The DMSO-doped PEDOT:PSS improved the conductivity of the PEDOT:PSS film, while the DOPA-doped PEDOT:PSS tuned the WF of the PEDOT:PSS film. Hence, codoping of DMSO and DOPA not only allows for a good match of the energy levels between PEDOT:PSS and the perovskite but also leads to an improvement in the conductivity of PEDOT:PSS. The champion PCE of the Pero-SCs increased from 13.35% to 17.54% after DOPA and DMSO were codoped in PEDOT:PSS. Owing to their aligned energy levels and enhanced charge transportation, the detailed photovoltaic parameters were greatly improved. Scanning electron microscope and X-ray diffraction were used to characterize the morphological change and crystallinity of the perovskite films. Morphological characterization also revealed that the density of grain boundaries in the perovskite films decreased, which should alleviate the charge recombination occurring in the photoactive layer. Both steady-state photoluminescence (PL) and time-resolved PL characterizations were carried out, and they indicated that nonradiative recombination increased for the perovskite films prepared on the doped PEDOT:PSS films. This result explains the improved short-circuit current density. Electrochemical impedance spectroscopy was employed to determine the resistances of the solar cells. The results are consistent with device performance and that reflected in the PL spectra.

In recent years, organic solar cells (OSCs) have attracted increasing attention, and the power conversion efficiency (PCE) of OSCs has markedly improved. To enhance the photovoltaic properties of OSCs, it is important to develop the donor materials in the light-harvesting layer, which mainly include conjugated polymers and small molecules (SMs). Compared with polymeric materials, small-molecule materials have been widely investigated for their superior characteristics, such as well-defined molecular structures that can provide good batch-to-batch reproducibility. In this work, we synthesized three SM donor materials with theacceptor-donor-acceptor (A-D-A) structure by employing the trialkylthienyl-substituted benzodithiophene (TriBDT-T) unit as the D-core unit, and rhodanine (RN), cyano-rhodanine (RCN), and 1, 3-indanone (IDO) as the A end groups, respectively. The optical properties, molecular energy levels, and thermogravimetic characteristics of the three SMs were studied; moreover, the blend morphologies and photovoltaic properties of the devices by employing the non-fullerene (NF) acceptor, IT-4F, were systematically investigated. The results showed that 1) the three SMs exhibit good thermal stabilities as evinced by thermogravimetric analysis (TGA), and all decomposition temperatures exceeded 410 ℃; 2) They all exhibit strong and broad absorption in the visible light range (300–700 nm), and show similar molar extinction coefficients; 3) the HOMO levels are -5.47 eV, -5.54 eV, and -5.44 eV for RN, RCN, and IDO, respectively, implying the clear influence of the different end groups for the energy levels of the A-D-A-type SMs; the slight differences in the optical and electrochemical properties of the corresponding donor material could be attributed to the different electron-withdrawing ability of the A-type end groups. When studying the photovoltaic properties, interestingly, the RN:IT-4F blend was found to form fibrillar-like aggregates with appropriate size, and the corresponding devices exhibited desirable short circuit current (J_sc) and thus the highest PCE value of 9.25%; however, large-size aggregates were formed in the RCN:IT-4F and IDO:IT-4F blend films, resulting in a much lower J_sc and fill factor (FF), and the PCE of the corresponding devices were only around 6%. In summary, by introducing RN, RCN, and IDO as the A units, we synthesized a class of TriBDT-T based A-D-A type SMs. This study shows that terminal A units exert influence on the absorption spectra, molecular energy level, and morphologies after blending with the acceptor material, and hence, the corresponding devices exhibit significant differences in photovoltaic performance. This work also provides useful information for the molecular design of SM donor materials.

Microorganisms exploit extracellular electron transfer (EET) with external minerals during their growth. This process is accompanied by the conversion of chemical energy. Direct electron transfer (DET) from the microorganisms to solid electron acceptors via membrane-bound cytochrome c enzymes or conductive nanowires/pili has been reported. In previous studies, mediated electron transfer (MET) has also been demonstrated to occur through electrochemically active metabolites acting as redox mediators. The microorganisms with EET capabilities have been harnessed for bioelectrochemical systems (BESs) in the bioremediation of environmental contaminants and the production of biofuels and nanomaterials. Electron transfer at the electrode biofilm/solution interface is one of the core phenomena occurring in BESs. The study of the redox reactions occurring in the microenvironment of the biofilm should elucidate the mechanism of microbial EET, which will then help improve the electron transfer efficiency of BESs. The composition of a biofilm is complex and contains many redox secreta and extracellular polymeric substances. Therefore, the specific current generated from the DET or MET pathways cannot be solely detected using classic electrochemical methods. In the present study, the interfacial electron transfer of Shewanella oneidensis MR-1 on an ITO surface was investigated. Cyclic voltammetry (CV) was first applied to study the redox properties of Shewanella and its interaction with ferrocenylmethanol (FcMeOH), which served as an exogenous electron mediator. The cyclic voltammograms showed that the oxidation current of S. oneidensis MR-1 was dramatically enhanced in the presence of 0.01 mmol·L^-1 FcMeOH compared to a control, i.e. bacterium-free ITO. This can be explained by the ability of S. oneidensis MR-1 to reduce FcMeOH⁺ during the positive scan. These results also showed that FcMeOH was a good redox mediator and capable of transferring electrons between the electrode and the bacterial cells. In addition, using the penetration mode in scanning electrochemical microscopy, the current generated from the MET by FcMeOH was collected using a microelectrode. Examination of the approaching curve showed that the current started to increase when the tip was approaching the solution/biofilm interface, providing positive feedback for the FcMeOH-mediated electron transfer between the microelectrode and the bacterial cells. The electrode biofilm/solution microenvironment was also detected, showing the thickness of the solution/biofilm to be 500 μm and the thickness of the biofilm to be 1100 μm. This study indicates that scanning electrochemical microscopy can be used in studying microbial MET. It also provides insight into the electron transfer mechanism of the microbial metabolism from a physical chemistry perspective.

Solution-processed bulk-heterojunction organic solar cells (BHJ-OSCs), with their advantages of light weight, low cost, and easy fabrication, are a photovoltaic technology with practical potentials. In BHJ-OSCs, the exciton dissociation and charge transport are highly sensitive to the molecular packing pattern and phase separation morphology in the active layer. On the other hand, when using photovoltaic small molecules (SMs), the purity can be controlled due to their well-defined chemical structure, and therefore there is better reproducibility in device performance. Especially, the non-fullerene acceptors are easier to tune in their light absorption and energy level. Hence, there has been considerable interest in small non-fullerene SM organic solar cells (NF-SM-OSCs). Although these cells have the dual advantages of non-fullerene acceptor materials and SMs, the fabrication of high-efficiency cells still possess great challenges. For example, efficient photovoltaic SMs typically possess an acceptor-donor-acceptor (A-D-A) structure that causes intrinsic anisotropy, making it more complicated to modulate and control the morphology of the nanoscale active layer. In this article, we will summarize recent advances in high-performance NF-SM-OSCs, and present an introduction of the specific requirements for SM donors in the small NF-SM-OSCs. We first summarize our works on SM donors with the A-D-A structure. The trialkylthienyl-substituted benzodithiophene (TriBDT-T) unit is employed as the D-core unit, and the A end groups include rhodanine (RN), cyano-rhodanine (RCN), and 1, 3-indanone (IDO). The band gap (E_g) of these compounds is about 2.0 eV, with the low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. First, NF-SM-OSCs with DRTB-T and a non-fullerene acceptor (IDIC) were constructed. The morphology of the active layer was fine-tuned by solvent vapor annealing (SVA), leading to the formation of the desired interconnected nanoscale structure. Our results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) non-fullerene SM acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs. We also studied the molecular orientation optimization from the aspect of molecular design. We designed and synthesized a group of SM compounds having identical π-conjugated backbones and end groups with different alkyl chain lengths. Since these compounds have identical photoelectric properties, they allow us to focus on the significant influence of the end alkyl chains on the molecular orientation and intermolecular aggregation behavior in solid-state films. Characterization of the DRTB-T-CX films using 2D grazing incidence wide-angle X-ray scattering (GIWAXS) revealed an obvious transition of orientation from edge-on to face-on relative to the substrate when the end alkyl chain is lengthened. This demonstrates that the length of the end alkyl chain can be used to modify the molecular orientation. A DRTB-T-C4/IT-4F-based device achieved a maximum power conversion efficiency (PCE) of up to 11.24%, which is the best performance reported for state-of-the-art NF-SM-OSCs. On this basis, the challenges and prospects of NF-SM-OSCs are discussed.

As a new member of the carbon allotrope family, graphdiynes (GDs)consist of both sp-and sp²-hybridized carbon atoms, possessing unique π-conjugated carbon skeletons and expanded 18C-hexagonalpores in two dimensions. In contrast with the zero band gap graphene (GR), GDis a semiconductor with a direct band gap of 1.22 eV calculated according tothe density functional theory (DFT) using the HSE06 method; this makes it apotential semiconductor material that can supplant silicon in the integratedcircuit industry. Moreover, owing to the presence of diacetylenic linkagesbetween its hexagonal carbon rings, GD shows electron-deficient properties, which lead to its electron-accepting tendency. Graphdiynes exhibit unusualsemiconducting properties with excellent charge mobilities and electrontransport properties that are associated with its distinct topological andelectronic structures. Graphdiynes play the role of not only electron-acceptorsthat efficiently collect the electrons from other materials but also electron-donorsthat inject electrons into other systems, thus exhibiting excellentelectron-transfer enhancement characteristics. The unique electron-transferenhancement property of GDs inspired us to summarize the interactions betweenGDs and other materials including metal oxides, metal nano-particles, andorganic molecules. In this review paper, we first introduce the TiO₂/GDnanocomposite, because the linking of GDs and titania nanoparticles (P25) throughthe Ti—O—Cbond sets an important precedent for exploring the electron-transfer behaviors involvingGDs and the metal oxide. These results indicate that the GDs can act asacceptors of the photogenerated electrons in the TiO₂/GD system, effectively suppressing charge recombination and resulting in excellent photocatalyticproperties. Nevertheless, the GDs in CdSe quantum dots (QDs)/GD composites areable to collect photogenerated holes from the QDs and perform as promising hole-transfermaterials in the photoelectrochemical cell for water splitting. As a result, the interactions between GDs and various metal compounds should be explored todeeply understand the electron-transfer properties of GDs. Furthermore, GDs canbe also used as electron donors to reduce PdCl₄^2- toPd nanoparticles that can subsequently be used for the electroless depositionof highly dispersed Pd nanoparticles. Based on electrostatic potential surfaceanalysis over the Pt₂/GD, GDs can attract the electron cloud fromthe Pt nanoparticles and produce a positive polarization of the metal atomsurface. However, due to its large π-conjugated system, GD can alsocollect and transfer electrons from the electrode under a bias voltage, making ita new type of electrocatalyst material, especially for single-atom catalysts.The interactions between GDs and metal particles/clusters/atoms have attracted thebroad attention of the rapidly developing field of single-atom catalysis.Finally, research on the interactions between GDs and organic molecules, especially biomolecules, is still in its infancy and requires development. In summary, we overview the recent research progress on GD and its enhanced ability forelectron transfer in this review paper, including metal oxides/GD, metalnano-particles/GD, polymers/GD, and organic molecules/GD, from bothexperimental and theoretical perspectives, and emphasize the interactions andelectron-transfer enhancement properties. It is expected that this review canpromote the development and applications of GD chemistry.

Carbon atoms can bond together in different molecular configurations leading to different carbon allotropes including diamond, fullerene, carbon nanotubes, graphene, and graphdiyne that are widely used or explored in a number of fields. Carbon dots (CDs), which are generally surface-passivated carbon nanoparticles less than 10 nm in size, are other new members of carbon allotropes. CDs were serendipitously discovered in 2004 during the electrophoresis purification of single-walled carbon nanotubes. Similar to their popular older cousins, fullerenes, carbon nanotubes, and graphene, CDs have drawn much attention in the past decade and have gradually become a rising star because of the advantages of chemical inertness, high abundance, good biocompatibility, and low toxicity. Interestingly, CDs typically display excitation-energy- and size-dependent fluorescent behavior. Depending on their structures, the fluorescence from CDs is either attributed to the quantum-confinement effect and conjugated π-domains of the carbogenic core (intrinsic states), or determined by the hybridization of the carbon skeleton and the connected chemical groups (surface states). Compared with the traditional semiconductors, quantum dots, and their organic dye counterparts, fluorescent CDs possess not only excellent optical properties and small-size effect, but also the advantages of low-cost synthesis, good photo-bleaching resistance, tunable band gaps, and surface functionalities. For these reasons, CDs are considered to be emergent nanolights for bio-imaging, sensing, and optoelectronic devices. Additionally, CDs feature abundant structural defects at their surface and edges, excellent light-harvesting capability, and photo-induced electron-transfer ability, thus facilitating their applications in photocatalysis and energy storage and conversions. To date, remarkable progress has been achieved in terms of synthetic approaches, properties, and applications of CDs. This review aims to classify the different types of CDs, based on the structures of their carbogenic cores, and to describe their structural characteristics in terms of synthesis approaches. Two well-established strategies for synthesizing CDs, the top-down and bottom-up routes, are highlighted. The diverse potential applications, in the bio-imaging and diagnosis, sensing, catalysis, optoelectronics, and energy-storage fields, of CDs with different structures and physicochemical properties, are summarized, covering the issues of surface modification, heteroatom doping, and hybrids made by combining CDs with other species such as metals, metal oxides, and biological molecules. The challenges and opportunities for the future development of CDs are also briefly outlined.

The increasing anthropogenic emission of CO₂ leads to global warming, to address which three strategies can be considered: (1) decrease fossil fuel consumption through increased utilization efficiency and lower per capita consumption; (2) replace fossil fuels with renewable energy sources like wind, tidal, solar, and biomass energies; (3) utilize CO₂ efficiently. Despite efforts to reduce energy use and increase the use of carbon-neutral biofuels, it seems that fossil fuels will continue to be a major energy source for the next few decades. Tremendous effort is therefore being focused on developing effective technologies for CO₂ capture and transformation. In particular, the transformation of CO₂ into fuels and chemicals via reduction with renewable hydrogen is a promising strategy for mitigating global warming and energy supply problems. The hydrogenation of CO₂, especially to C₂₊ hydrocarbons and oxygenates, has sparked growing interest. The C₂₊ species can be used as entry platform chemicals for existing value chains, thus providing more advantages than C₁ compounds. However, optimizing catalyst design by integrating multifunctionalities for both CO₂ activation and C-C coupling remains an ongoing challenge. Here, we provide a timely review on the recent progress that has been made in the hydrogenation of CO₂ to higher-order alkanes, olefins, and alcohols by various heterogeneous catalysts. The thermodynamics and kinetics, as well as possible reaction pathways for CO₂ hydrogenation, are discussed. The hydrogenation of CO₂ to hydrocarbons usually involves the initial generation of CO via a reverse water-gas shift (RWGS) reaction followed by hydrogenation of the CO intermediate. The RWGS reaction proceeds through a redox route and an associative pathway. "CH_x" insertion (carbide-type) and "CO" insertion are two proposed mechanisms for this Fischer-Tropsch-like synthesis. Fe-or Co-based catalysts have been widely used to catalyze the hydrogenation of CO₂ to C₂₊ hydrocarbons via the CO intermediate. C₂₊ hydrocarbons can also be obtained by combining CH₃OH synthesis with the methanol-to-hydrocarbon process (MTH). This reaction pathway has been realized over bifunctional systems comprising a CH₃OH synthesis catalyst and an MTH catalyst. Alternatively, CO₂ hydrogenation can occur via a RWGS reaction to the CO intermediate, and subsequent formation of higher alcohols from syngas. Higher alcohols (mostly CH₃CH₂OH) have been produced by using a hybrid tandem catalyst. Understanding of the activation mechanism, precise C-C coupling, and synergy control between the two active components requires further research. In the final part, we describe the future challenges and opportunities in heterogeneous catalysis of CO₂ hydrogenation. The combination of calculations (precise theoretical models) and experiments (in-situ spectroscopic techniques) will facilitate the design of advanced catalysts to achieve both high CO₂ conversion and C₂₊ product selectivity.

Although a large variety of aromatic systems have been unveiled in the literature, justifying their origin of stability and understanding their nature of aromaticity is still an unaccomplished task. In this work, using tools recently developed by us within the density functional reactivity theory framework, where we employ simple density functionals to quantify molecular structural and reactivity properties, we examine the aromaticity concept from a different perspective. Using six quantities from the information-theoretic approach, namely, the Shannon entropy, Fisher information, Ghosh-Berkowitz-Parr entropy, Onicescu information energy, information gain, and relative Rényi entropy, and four aromaticity descriptors, namely, the aromatic stabilization energy (ASE) index, the harmonic oscillator model of aromaticity (HOMA) index, the aromatic fluctuation (FLU) index, and the nucleus-independent chemical shift (NICS) index, we systematically examined the correlations between substituted fulvene derivatives fused with one, two, and three benzene rings. Among the 14 benzofulvene derivatives studied in this work, there were seven single-fused, four double-fused, and three triple-fused benzofulvene derivatives. Our results show that the aromaticity indexes are often well correlated with one another. The same is true for information-theoretic quantities. Moreover, these correlations are valid across all series of benzofulvene derivatives with different ring structures. The cross-correlations between information-theoretic quantities and aromaticity indexes were usually strong. However, two completely opposite patterns were observed; as a consequence, these correlations are not valid across all series of benzofulvene derivatives. The nature of these correlations depends on the nature of the ring structure. The two groups of systems, each obeying the same cross-correlation patterns, have a total number of 4n + 2 and 4n π electrons, respectively, which are in agreement with Hückel's rule of aromaticity and antiaromaticity. Compared with the results obtained for systems without a benzene fused ring, the correlation patterns of these quantities were always found to be the same, both with and without fused benzene rings. This suggests that, despite benzene's aromaticity, its fusion with a fulvene moiety does not modify the aromaticity and antiaromaticity of the fulvene ring. These results confirm that the fusion of benzene rings with a fulvene moiety has no influence on the aromatic nature of the fulvene moiety. Thus, the aromaticity and antiaromaticity of benzene-fused fulvene derivatives are solely determined by the fulvene moiety. These results should provide a new understanding of the origin and nature of aromaticity and antiaromaticity.

Heterogeneous catalysts are usually synthesized by the conventional wet-chemistry methods, including wet-impregnation, ion exchange, and deposition-precipitation. With the development of catalyst synthesis, great progress has been made in many industrially important catalytic processes. However, these catalytic materials often have very complex structures along with poor uniformity of active sites. Such heterogeneity of active site structures significantly decreases catalytic performance, especially in terms of selectivity, and hinders atomic-level understanding of structure-activity relationships. Moreover, loss of exposed active components by sintering or leaching under harsh reaction conditions causes considerable catalyst deactivation. It is desirable to develop a facile method to tune catalyst active site structures, as well as their local chemical environments on the atomic level, thereby facilitating reaction mechanisms understanding and rational design of catalysts with high stability.

Atomic layer deposition (ALD), a gas-phase technique for thin film growth, has emerged as an alternative method to synthesize heterogeneous catalysts. Like chemical vapor deposition (CVD), ALD relies on a sequence of molecular-level, self-limiting surface reactions between the vapors of precursor molecules and a substrate. This unique character makes it possible to deposit various catalytic materials uniformly on a high-surface-area support with nearly atomic precision. By tuning the number, sequence, and types of ALD cycles, bottom-up precise construction of catalytic architectures on a support can be achieved.

In this review, we focus on the design and synthesis of supported metal catalysts using ALD. We first review strategies developed to precisely tailor the size, composition, and structures of metal nanoparticles (NPs) using ALD. Catalytic performances of these ALD metal catalysts are also discussed and compared to conventional catalysts. We highlight synthetic strategies for synthesis of metal single-atom catalysts and bottom-up precise synthesis of dimeric metal catalysts. Their impact on catalysis is discussed. We demonstrate that metal oxide ALD on metal NPs can enhance catalytic activity, selectivity, and especially stability. In particular, we show that site-selective blocking of metal NPs with an oxide overcoat improves selectivity and contributes to an understanding of the distinct functionalities of the low-and high-coordination sites in catalytic reactions on the atomic level. Next, we discuss an effective method to construct bifunctional catalysts via precisely-controlled addition of a secondary functionality using ALD. Finally, we summarize the advantages of ALD for the advanced design and synthesis of catalysts and discuss the challenges and opportunities of scaling up ALD catalyst synthesis for practical applications.

Carbon quantum dots (CQDs) are emerging as the new-generation light absorber for solar energy conversion. However, the low photosensitization efficiency of CQDs is one of the current bottlenecks impeding their large-scale practical applications in photocatalysis. Therefore, developing a facile approach for the engineering and functionalization of CQDs-based composites to improve the photosensitization efficiency of CQDs is highly desirable. On account of the abundant functional groups, especially oxygen-containing functional groups such as carbonyl, carboxyl, and hydroxyl present on their surface, CQDs can be readily combined with various organic molecules or polymers as a surface passivation component to reduce the nonradioactive surface recombination of photo-generated charge carriers, thus enabling the CQDs to exhibit strong photoluminescence in the visible and near-infrared spectral regions. Consequently, polymer passivation has been demonstrated as an ideal strategy to make it accessible for improving the sensitization efficiency of CQDs in photocatalytic applications. Branched polyethylenimine (BPEI) is one of polymers that contains a high density of amine groups and exhibits high electron mobility, which can be used as an electron injection material at the interface of nanomaterials. Besides, the BPEI polymer with amino groups exhibiting positive charge has been utilized for designing heterogeneous catalysts by an electrostatic self-assembly strategy. Therefore, BPEI is expected to modify the surface of inorganic oxides semiconductor to enhance the photosensitization efficiency of CQDs under visible light. However, to date, the study in this regard has been still unavailable. In this work, we developed a facile approach to engineer well-distributed CQDs via electrostatic interaction on BPEI passivated TiO₂ composites (BTC) as photocatalysts. The BTC composites with an optimal loading of 5% (w, mass fraction) CQDs outperformed the TiO₂/CQDs (TC) composite and referential BPEI/SiO₂/CQDs (BSC) composites for the photoreduction of 4-nitroaniline under visible light irradiation. The structure of the fabricated BTC composites was systematically investigated by the combined use of structural and spectral characterizations, demonstrating that the photosensitizer CQDs contacted well with the BPEI modified TiO₂ nanoparticles. The comparison characterizations revealed that BPEI facilitated the dissociation and transfer of excitons as an electron transfer channel. The as-prepared BTC composites benefited from the favorable interfacial contact and effective transfer of photo-generated charge carriers, and thus manifested superior photocatalytic activity to the TC composite. It is expected that this strategy would be extended to other wide band gap semiconductor photocatalyst systems and open up new possibilities in designing efficient CQDs-based semiconductor artificial light harvesting systems by interfacial optimization.

A series of MnO_x-CeO₂ with different Mn contents was prepared using CeBTC-MOF as the sacrificial template. These constituted a new kind of porous crystalline materials assembled by cerium as metal ions and 1, 3, 5-benzenetricarboxylic acid as organic ligands. The composite oxides exhibited good redox properties and were tested as catalysts in the oxidation of toluene. To obtain insight into the structure-activity relationship of the catalysts, the samples were characterized using powder X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis (TG), elemental analysis (EA), inductively coupled plasma-optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and UV-Vis diffuse reflectance spectroscopy. Studies of the CeBTC-MOF template showed that the metal-organic framework could be completely decomposed at a calcination temperature of 300 ℃. Therefore, CeBTC-MOF decomposed and generated CO₂ and H₂O during the calcination process. The gas molecule spilled out from the structure to form the interior void space. The spilling out could be controlled by varying the calcination temperature. This regulated the quantity and size of the interior void, which in turn made the surface area controllable. The secondary building unit of CeBTC-MOF was oxidized to nano-sized crystalline particles, which exhibited outstanding interfacial contact. SEM and TEM results showed that the composite oxides prepared by pyrolysis of the CeBTC-MOF template exhibited rod-shaped nanocrystalline particles. While introducing Mn into MOF, part of Mn entered the ceria lattice to form solid solution and the remaining Mn was dispersed on CeO₂ surface. The elemental mappings revealed a well-proportioned distribution of Mn, which confirmed the successful formation of bimetallic metal oxides using the MOF-template method. All the samples exhibited sizes and shapes similar to their parent MOFs. As for catalytic activity, all the composite oxides showed better performances than pure CeO₂ for catalytic oxidation of toluene. This could be attributed to higher concentration of oxygen vacancies, which was characterized by Raman spectroscopy. In addition, the XPS results indicated that Mn⁴⁺/(Mn²⁺+Mn³⁺), Ce⁴⁺/Ce³⁺, O_latt (lattice oxygen), and O_sur(surface oxygen) all participated in the redox process during catalytic oxidation of toluene, which helped elucidate the mechanism at a micro level.

Interestingly, the catalytic activity did not improve further when the Mn content of the composite oxides reached 5%. This could be ascribed to two different states of the dispersed Mn: monolayer dispersion state and crystalline phase. The strong interaction between ceria oxides and dispersed Mn species played an important role in affecting catalytic activity. The results showed the presence of a monolayer dispersion threshold (6.2%), confirmed by XPS characterization, which was in accordance with all the characterization results; it was proved that this threshold had a significant impact on the catalytic activity. When the dispersed Mn content was lower than the monolayer dispersion threshold, Mn reacted with the surface CeO₂ in the form of an incorporation model, leading to charge transfer and higher concentration of oxygen vacancies, which in turn effectively promoted the catalytic performance. When the dispersed Mn content exceeded the monolayer dispersion threshold, Mn₃O₄ was formed on the CeO₂ surface; this disrupted the promotion of catalytic activity, which explains the same catalytic activity of all the samples (5% MnO_x-CeO₂, 8% MnO_x-CeO₂, and 10% MnO_x-CeO₂).

This successful formation of bimetallic metal oxides using CeBTC-MOF template indicated that composite oxide synthesis was feasible using the MOF template method. To obtain high catalyst performance of these composite oxides, it was important to control the metal content at the level of the monolayer dispersion threshold.

Alloy metal nanoclusters (NCs), including bimetallic and multimetallic clusters, have recently emerged as a novel class of multifunctional nanomaterials. They are widely used in catalysis, optical sensing, and biological imaging due to their excellent physicochemical properties such as unique electronic structure, ultrasmall size, strong photoluminescence, and rich surface chemistry. Although much progress has been made in the development of NCs, a major challenge in the synthesis of the relevant multifunctional nanomaterial is to achieve the synthetic methodological breakthrough, especially for controlling the synthesis and structure of NCs with atomic precision. It is evident that by realizing controlled synthesis and structural regulation at the atomic scale, we can better understand and tune the fundamental properties of NCs for efficient use in various application areas; this could also shed light on the development of new functionalized nanomaterials. Most of the recent research on the controlled synthesis and structural characterization of metal clusters with atomic precision has focused on monometallic NCs, and significant progress has been realized with respect to alloy metal NCs. A number of synthetic strategies have been developed for synthesizing high-quality alloy NCs with well-defined compositions, sizes, and architectures. In this review, we have highlighted some recent advances in strategies for the precise synthesis of ligands-protected alloy metal NCs, especially thiolate-stabilized gold-based alloy NCs. We classified the synthetic strategies for alloy NCs into several strategies, which include one-pot synthesis, metal exchange, ligand exchange, chemical etching, intercluster reactions, surface motif exchange reaction, and in situ two-phase ligand exchange strategy. One-pot synthesis is facile and widely used as a synthetic strategy for monodisperse alloy NCs with well-defined compositions, sizes, architectures, and surface chemistries. However, the alloy NCs obtained through the one-pot strategy often exhibits a relatively somber fluorescence. Therefore, other synthesis strategies have been exploited that can fabricate alloy NCs exhibiting strong photoluminescence. Among them, the surface motif exchange reaction is expected to be extended to the fabrication of new binary alloy NCs with precise alloy sites to broaden the physicochemical properties of the NCs; intercluster reactions has been explored as an emerging and efficient strategy to fabricate atomically precise alloy NCs. It is noted that the two or multiple metal species incorporated in a single alloy NC usually show unexpected synergistic properties like adjustable electronic structures and strong photoluminescence. Such unique properties have rapidly motivated the research community to use alloy NCs in many applications such as catalysis, biosensors, and biomedicine.

As a potential substitute for commercial lithium ion batteries (LIBs), sodium ion batteries (NIBs) have attracted increasing interest during the last decade. However, compared to the LIBs, the sluggish kinetics of sodium ion diffusion in NIBs due to its larger ionic radius results in deteriorated electrochemical performances, which hinders the future development and application of NIBs. Therefore, exploring anode materials that exhibit a novel kinetic mechanism is desired. Recently, extremely rapid kinetics has been realized by introducing the pseudocapacitance effect into battery systems; this effect generally refers to faradaic charge-transfer reactions, including surface or near-surface redox reactions, and fast bulk ion intercalation. To obtain a pseudocapacitance effect in battery systems, the critical step involves the rational design of a two-dimensional structure with a high conductivity. In this regard, the bimetallic sulfide thiospinel NiCo₂S₄ stands out by virtue of its high conductivity (1.25 × 10⁶ S·m^-1) at room temperature, which is at least two orders of magnitude higher than that of the oxide counterpart (NiCo₂O₄). Herein, NiCo₂S₄ hexagonal nanosheets with a large lateral dimension of ~2 μm and thickness ~30 nm have been successfully synthesized through coprecipitation followed by a vapor sulfidation method. As the anode material in NIBs, the NiCo₂S₄ nanosheets deliver a reversible capacity of 387 mAh·g^-1 after 60 cycles at a current density of 1000 mA·g^-1. Additionally, the NiCo₂S₄ nanosheets exhibit high reversible capacities of 542, 398, 347, 300, and 217 mAh·g^-1 at the current densities 200, 400, 800, 1000, and 2000 mA·g^-1, respectively. Ex situ X-ray diffraction analysis has been employed to reveal that the sodium ion storage process is a result of a combined Na⁺ intercalation and conversion reaction between Na⁺ and NiCo₂S₄. Further quantitative analysis of the kinetics has verified the extrinsic pseudocapacitance mechanism of the Na⁺ storage process, in which the capacitive contribution enlarges as the current density increases. The observed capacitive contribution of NiCo₂S₄ electrode is as high as 71% at a scan rate of 0.4 mV·s^-1. This is closely attributed to the modified thin-sheet structure of NiCo₂S₄ and hybridization with graphene that account for the superior high-rate performance with long-term cyclability. These intriguing results shed light on a new strategy for the structural design of electrode materials for advanced NIBs. Moreover, this vapor transformation route can be extended to the preparation of other transition metal disulfides with high electrochemical activities, such as FeCo₂S₄, ZnCo₂S₄, CuCo₂S₄, etc.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention owing to their high absorption coefficient and ambipolar charge transport properties. With only several years of development, the power conversion efficiency (PCE) has increased from 3.8% to 22.7%. In general, PSCs have two types of structural architecture: mesoporous and planar. The latter possesses higher potential for commercialization due to its simpler structure and fabrication process, especially the inverted planar structure, which possesses negligible hysteresis. In an inverted PSC, the electron transport materials (ETM) are deposited on a perovskite film. Only a few ETMs can be used for inverted PSCs as the perovskite film is easily damaged by the solvent used to dissolve the ETM. Furthermore, the energy levels of the ETM should be well aligned with that of the perovskites. Normally it is difficult to use inorganic ETMs as they require high temperatures for the annealing process to improve the electron conductivity; the perovskite film cannot sustain these high temperatures. To date, the fullerene derivative, [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM), is the most commonly used organic ETM for high efficiency inverted planar PSCs. However, the high manufacturing cost due to its complex synthesis retards the industrialization of the PSCs. Here, we introduce a fullerene pyrrolidine derivative, N-methyl-2-pentyl-[60]fullerene pyrrolidine (NMPFP), synthesized via the Prato reaction of C₆₀ directly with cheap hexanal and sarcosine. Then the NMPFP electron transport layer (ETL) was prepared by a simple solution process. The properties of the resulting NMPFP ETLs were characterized using UV-Vis absorption spectroscopy, cyclic voltammetry measurements, atomic force microscopy, and conductivity test. From the results of the UV-Vis absorption spectroscopy and cyclic voltammetry measurements, the LUMO level of NMPFP ETL was calculated to be 0.2 eV higher than that of the PCBM ETL. This contributes to a higher open-circuit photovoltage. In addition, the NMPFP film presented higher conductivity than the PCBM film. Thus, the photo-generated charge carriers in the perovskite films should be transported more efficiently to the NMPFP electron transport layer (ETL) than to the PCBM ETL. This was confirmed by the results of the steady-state photoluminescence spectroscopy. Finally, the NMPFP as an alternative low-cost ETL was employed in an inverted planar PSC to evaluate the device performance. The device made with the NMPFP ETL yielded an efficiency of 13.83% with negligible hysteresis, which is comparable to the PCBM counterpart devices. Moreover, since stability is another important parameter retarding the commercialization of PSCs, the stability of the PCBM and NMPFP base PSCs were investigated and compared. It was found that the NMPFP devices possessed significantly improved stability due to the higher hydrophobicity of the NMPFP. In conclusion, this research demonstrates that NMPFP is a promising ETL to replace PCBM for the industrialization of cheap, efficient and stable inverted planar PSCs.

Catalytic CO₂ hydrogenation to methanol is a promising route to mitigate the negative effects of anthropogenic CO₂. To develop an efficient Pd/ZnO catalyst, increasing the contact between Pd and ZnO is of the utmost importance, because "naked" Pd favors CO production via the reverse water-gas shift path. Here, we have utilized a ZnO@ZIF-8 core-shell structure to synthesize Pd/ZnO catalysts via Pd immobilization and calcination. The merit of this method is that the porous outer layer can offer abundant "guest rooms" for Pd, ensuring intimate contact between Pd and the post-generated ZnO. The synthesized Pd/ZnO catalysts (PZZ8-T, T denotes the temperature of calcination in degree Celsius) is compared with a ZnO nanorod-immobilized Pd catalyst (PZ). When the catalytic reaction was performed at lower reaction temperatures (250, 270, and 290 ℃), the highest methanol space time yield (STY) and highest STY per Pd achieved by PZ at 290 ℃ were 0.465 g g_cat^-1 h^-1 and 13.0 g g_Pd^-1 h^-1, respectively. However, all the PZZ8-T catalysts exhibited methanol selectivity values greater than 67.0% at 290 ℃, in sharp contrast to a methanol selectivity value of 32.8% for PZ at the same temperature. Thus, we performed additional investigations of the PZZ8-T catalysts at 310 and 360 ℃, which are unusually high temperatures for CO₂ hydrogenation to methanol because the required endothermic reaction is expected to be severely inhibited at such high temperatures. Interestingly, the PZZ8-T catalysts were observed to achieve a methanol selectivity value of approximately 60% at 310 ℃, and PZZ8-400 was observed to maintain a methanol selectivity value of 51.9% even at a temperature of 360 ℃. Thus, PZZ8-400 attains the highest methanol STY of 0.571 g g_cat^-1 h^-1at 310 ℃. For a better understanding of the structure-performance relationship, we characterized the catalysts using different techniques, focusing especially on the surface properties. X-ray photoelectron spectroscopy (XPS) results indicated a linear relationship between the methanol selectivity and the surface PdZn : Pd ratio, proving that the surface PdZn phase is the active site for CO₂ hydrogenation to methanol. Furthermore, analysis of the XPS O 1s spectrum together with the electronic paramagnetic resonance results revealed that both, the oxygen vacancy as well as the ZnO polar surface, played important roles in CO₂ activation. Chemisorption techniques provided further quantitative and qualitative information regarding the Pd-ZnO interface that is closely related to the CO₂ conversion rate. We believe that our results can provide insight into the catalytic reaction of CO₂ hydrogenation from the perspective of surface science. In addition, this work is an illustrative example of the use of novel chemical structures in the fabrication of superior catalysts using a traditional formula.

Electric double-layer capacitors (EDLCs) are advanced electrochemical devices that have attracted tremendous attention because of their high power density, ultra-fast charging/discharging rate, and superior lifespan. A major challenge is how to further improve their energy density. At present, a large number of research efforts are primarily focusing on engineering the morphology and microstructure of electrodes to achieve better performance, for example, enlarging the specific surface area and designing the pore size. More importantly, wettability plays a crucial role in maximizing the effective utilization and accessibility of electrode materials. However, its primary mechanisms/phenomena are still partially resolved. Here, we explore the effects of wettability on the charging dynamics of EDLCs using molecular dynamics (MD) simulations. Typically, hydrophobic graphene (GP) and hydrophilic copper (Cu) are employed as the electrode materials. Differential capacitances (C_D) as a function of electrode potentials (ϕ) are computed by means of Poisson and Gaussian equation calculations. Simulation results show that during the charging process of EDLCs, the differential capacitances of hydrophobic GP are insensitive to the electrode potentials. However, superhydrophilic Cu electrode exhibits an asymmetric U-shaped C_D–ϕ curve, in which the capacitance at the negative polarization can be ~5.77 times greater than that of the positive counterpart. Such an unusual behavior is obviously different with the conventional Gouy-Chapman-Stern theory (i.e., symmetric U-shaped), room temperature ionic liquids (i.e., camel-, or bell-shaped), and hydrophobic counterpart, which is closely correlated with the free energy barrier distributions. Compared with the positive polarization or hydrophobic case, the energy barriers near the negative hydrophilic electrodes are remarkably suppressed, which benefits ion populations at the interface and enables the convenient orientation or distribution of ions to shield the external electric fields from electrodes, thereby yielding higher differential capacitances. With differentiating the ion charge density, the as-obtained C_D–ϕ curves are well resembled, quantitatively establishing the correlations between EDL microstructures and differential capacitances. Besides, we also point out that enhancing the wettability could significantly decrease the EDL thickness from ~1.0 nm (hydrophobic) to ~0.5 nm (hydrophilic). In the end, we demonstrate that wetting property also impacts a prominent role in the charge storage behavior of EDLCs, transforming the charging mechanism dominated by counter-ion adsorption and ion exchange (hydrophobic) to pure counter-ion adsorption (hydrophilic). The as-obtained insights highlight the significance of wettability in regulating charging dynamics and mechanisms, providing useful guidelines for precisely controlling the wetting property of electrode materials for advanced charge storage of EDLCs.

Cu/ZnO/Al₂O₃ is one of the most widely used catalysts in industrial methanol synthesis. However, the reaction mechanism and the nature of the active sites on the catalyst for this reaction are still under debate. Thus, detailed information is needed to understand the catalytic processes occurring on the surface of this catalyst. H₂ is one of the reaction gases in methanol synthesis. Studies of the activation and dissociation behaviors of H₂ on ZnO surfaces are of great importance in understanding the catalytic mechanism of methanol synthesis. In this work, the activation and dissociation processes of H₂ on a ZnO(10${\rm{\bar 1}}$0) single crystal surface were investigated in-situ using ambient-pressure X-ray photoelectron spectroscopy (APXPS) and scanning tunneling microscopy (STM), two powerful surface characterization techniques. In the APXPS experiments, results indicated the formation of hydroxyl (OH) species on the ZnO single crystal surface at room temperature in 0.3 mbar (1 mbar = 100 Pa) H₂ atmosphere. Meanwhile, STM measurements showed that the ZnO surface was reconstructed from a (1×1) to a (2×1) structure upon introduction of H₂. These observations revealed adsorption behaviors of H₂ the same as those of atomic H on a ZnO(10${\rm{\bar 1}}$0) surface as seen in previous studies, which could be evidence of the dissociative adsorption of H₂ on a ZnO surface. However, H₂O adsorption on ZnO surfaces can also result in the formation of OH species, which can be observed using XPS. The STM results show that the exposure of H₂O also leads to the reconstruction from a (1×1) to a (2×1) structure on the ZnO(10${\rm{\bar 1}}$0) surface upon H₂ introduction. Hence, it is necessary to exclude the influence of H₂O in this work, because there may be trace amounts of H₂O in the H₂ gas. Therefore, we performed a comparative study of H₂ and H₂O on ZnO(10${\rm{\bar 1}}$0) single crystal surface. A downward band bending of 0.3 eV was observed on the ZnO surface in 0.3 mbar H₂ atmosphere using APXPS, while negligible band bending was shown in the case of the H₂O atmosphere. Moreover, thermal stability studies revealed that the OH group formed in the H₂ atmosphere desorbed at a higher temperature than the one resulting from H₂O adsorption, meaning that the two OH groups formed on the ZnO surface were different. Results in this work provide evidence of the dissociative adsorption of H₂ on the ZnO(10${\rm{\bar 1}}$0) surface at room temperature and atmospheric pressure. This is in contrast to previous findings, in which no H₂ dissociation on a ZnO(10${\rm{\bar 1}}$0) surface under ultra-high vacuum conditions was observed, indicating that the activation of H₂ on ZnO surfaces is a pressure dependent process.

Nonadiabatic processes widely exist in photochemistry and photophysics. The theoretical treatment of nonadiabatic processes is an important challenge in theoretical chemistry. In nonadiabatic dynamics, the well-known "Born-Oppenheimer approximation" breaks down due to the involvement of strong nuclear-electronic coupled motions. Hence, the development of a theoretical framework is required for the proper treatment of nonadiabatic dynamics. The fewest-switches trajectory surface-hopping method developed by Tully is one of the most widely used methods in the treatment of nonadiabatic processes because of its rather simple numerical implementation. In this approach, the nuclear degrees of freedom are propagated on the potential energy surface of an electronic state using the classical equations of motion, while the electronic degrees of freedom are propagated along the same trajectory according to the time-dependent Schr?dinger equation. Nonadiabatic effects are included by allowing sudden hops between different potential energy surfaces. After averaging over many trajectories, a reasonable description of nonadiabatic dynamics is achieved at low computational cost. Particularly, when we combine the trajectory surface-hopping dynamics with on-the-fly molecular dynamics, it is possible to describe the nonadiabatic dynamics of realistic polyatomic molecular systems at a fully atomic level with all degrees of freedom included. After the introduction of hybrid multiscale methods, the simulation of photochemistry in solutions and in biological systems becomes possible. The simulation results provide important information concerning the nonadiabatic dynamics of realistic polyatomic systems, such as excited-state lifetime, major active molecular motions, reaction channels, and branching ratio. This review article summarizes some progresses in this field. After briefly introducing the basic theory of widely used fewest switches surface-hopping dynamics methods, we mainly focus on several numerical details in the implementation of on-the-fly fewest switches surface-hopping dynamics. The seamless combination of surface-hopping dynamics and electronic-structure calculations is emphasized in this review, rather than an exhaustive discussion of rigorous nonadiabatic dynamics theories. Numerical methods to estimate nonadiabatic coupling terms are discussed, which allow us to perform the trajectory surface-hopping calculations when the nonadiabatic coupling vectors are not available in the electronic structure calculations. Several important issues, such as decoherence corrections, diabatic or adiabatic representations, and initial sampling methods are discussed in detail. We also summarize the theoretical treatment of the nonadiabatic dynamics of some interesting molecular systems, which include the photostability of DNA, photo-isomerization of organic systems, photochemistry of transition metal complexes, and photovoltaics. Finally, we discuss the theoretical challenges of this direct dynamics approach and provide an outlook of this field from our personal perspective.

Two new coordination polymers, namely, [[Zn₂(TTR4A)(L)₂]·DMF·4H₂O]_n (compound 1) and [[Co(TTR4A)Cl₂]·DMA·H₂O]_n (compound 2), have been synthesized under solvothermal conditions (TTR4A = tetrakis(1, 2, 4-triazol-ylmethylresorcin[4]arene), L = 4, 4'-biphenyldicarboxylic acid, DMF = N, N-dimethylformamide and DMA = N, N-dimethylacetamide). Crystal structures of the coordination compounds 1 and 2 were determined by single-crystal X-ray diffraction analyses, and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, and thermogravimetric analyses. In coordination compound 1, four L ligands bridge four adjacent Zn(Ⅱ) atoms to generate macrocyclic Zn₄L₄ units, which are further linked by the TTR4A ligands into a one-dimensional chain structure. In coordination compound 2, four 1, 2, 4-triazole groups of each TTR4A ligand bridge four Co(Ⅱ) atoms to form a two-dimensional layer structure. Furthermore, studies on the luminescent properties of compound 1 in solid state at room temperature reveal that it exhibits an intense emission peak. Luminescent-sensing detections for Fe³⁺, Cr₂O₇²⁻, and nitrobenzene solvents were also investigated by using compound 1 as the potential luminescent sensor.

The global energy shortage has led to vigorous research for the development of new energy technologies in all countries to cope with the energy crisis and to meet the demand for green energy. In this regard, the development of new battery systems with high energy densities has become the current research hotspot. Lithium-sulfur battery is considered as a promising candidate due to its high energy density and low cost. However, it suffers from the insulating nature of sulfur and the shuttle effect of polysulfide, which hinder its practical application. Selenium (Se), as a congener element of sulfur, possesses electrochemical properties similar to sulfur. Lithium-selenium batteries have attracted considerable research attention due to the high electronic conductivity of selenium and high volumetric capacity. The conductivity of Se (1 × 10^-3 S·m^-1) is ~24 orders of magnitude higher than that of sulfur (5 × 10^-28 S·m^-1), providing much better electron transportation in cathode, leading to fast electrochemical reaction and high utilization of Se. Moreover, Se is compatible with cheap carbonate-based electrolytes, which could greatly reduce the cost. Lithium-selenium batteries also have much higher theoretical volumetric and gravimetric capacities (3253 mAh·cm^-3 and 675 mAh·g^-1, respectively) than those of commercial lithium-ion batteries such as LiCoO₂/graphite and LiFePO₄/graphite systems. Volumetric capacity is a more important requirement than gravimetric capacity for a battery, especially for applications in electric vehicles and portable electronic devices, because they have limited space for accommodating batteries. Thus, research on lithium-selenium batteries with high volumetric capacities is of great significance for these volume-sensitive applications. However, the electrochemical performance of current lithium-selenium batteries is not satisfactory. Several key problems must be solved, including shuttle effect, electrolyte compatibility, volume change during cycling, capacity fading, and low coulombic efficiency. In recent years, widespread research has been conducted to address these problems and considerable progress has been made. This review summarizes the status of research on lithium-selenium batteries, and focuses on the recent progress in the research of selenium-carbon cathode materials. The advantages and disadvantages of lithium-selenium batteries are discussed in detail. The performance-structure relationship is analyzed from the perspective of different dimensional structures, including one-dimensional nanofibers and nanowires, two-dimensional nanosheets, composite films and scaffolds, three-dimensional hollow structures, solid structures, and freestanding structures (spheres, nanobelts, nanotubes, microcubes etc.). Other types of selenium-based cathodes, including metal selenides and heterocyclic selenium-sulfur (Se_xS_y), are also described. The compatible electrolytes and functional interlayers for lithium-selenium batteries are also discussed. The reaction mechanisms of lithium-selenium batteries and their relationship with various electrolytes are summarized. Finally, the future perspective of lithium-selenium batteries is proposed.

The growth and structural properties of ZnO thin films on both Au(111) and Cu(111) surfaces were studied using either NO₂ or O₂ as oxidizing agent. The results indicate that NO₂ promotes the formation of well-ordered ZnO thin films on both Au(111) and Cu(111). The stoichiometric ZnO thin films obtained on these two surfaces exhibit a flattened and non-polar ZnO(0001) structure. It is shown that on Au(111), the growth of bilayer ZnO nanostructures (NSs) is favored during the deposition of Zn in presence of NO₂ at 300 K, whereas both monolayer and bilayer ZnO NSs could be observed when Zn is deposited at elevated temperatures under a NO₂ atmosphere. The growth of bilayer ZnO NSs is caused by the stronger interaction between two ZnO layers than between ZnO and Au(111) surface. In contrast, the growth of monolayer ZnO NSs involves a kinetically controlled process. ZnO thin films covering the Au(111) surface exhibits a multilayer thickness, which is consistent with the growth kinetics of ZnO NSs. Besides, the use of O₂ as oxidizing agent could lead to the formation of sub-stoichiometric ZnO_x structures. The growth of full layers of ZnO on Cu(111) has been a difficult task, mainly because of the interdiffusion of Zn promoted by the strong interaction between Cu and Zn and the formation of Cu surface oxides by the oxidation of Cu(111). We overcome this problem by using NO₂ as oxidizing agent to form well-ordered ZnO thin films covering the Cu(111) surface. The surface of the well-ordered ZnO thin films on Cu(111) displays mainly a moiré pattern, which suggests a (3 × 3) ZnO superlattice supported on a (4 × 4) supercell of Cu(111). The observation of this superstructure provides a direct experimental evidence for the recently proposed structural model of ZnO on Cu(111), which suggests that this superstructure exhibits the minimal strain. Our studies suggested that the surface structures of ZnO thin films could change depending on the oxidation level or the oxidant used. The oxidation of Cu(111) could also become a key factor for the growth of ZnO. When Cu(111) is pre-oxidized to form copper surface oxides, the growth mode of ZnO_x is altered and single-site Zn could be confined into the lattice of copper surface oxides. Our studies show that the growth of ZnO is promoted by inhibiting the diffusion of Zn into metal substrates and preventing the formation of sub-stoichiometric ZnO_x. In short, the use of an atomic oxygen source is advantageous to the growth of ZnO thin films on Au(111) and Cu(111) surfaces.

Since the successful synthesis of graphdiyne, graphynes have emerged as an active field in carbon materials research.Hydrogen-substituted graphyne, structurally similar to graphynes, is a kind of two-dimensional (2D) carbon-rich material composed of sp²-hybridized carbon and hydrogen from phenyl groups and sp-hybridized carbon from ethynyl linkages.The large pore size in the molecular structure of hydrogen-substituted graphyne aids the diffusion of ions and molecules.In this work, hydrogen-substituted graphyne was synthesized by a facile mechanochemical route.Calcium carbide (CaC₂) was employed as the precursor of sp-hybridized carbon and 1, 3, 5 tribromobenzene (PhBr₃) as that of sp²-hybridized carbon and hydrogen.Hydrogen-substituted graphyne was directly obtained via the cross-coupling reaction performed by ball milling under vacuum and the impurities were removed by dilute nitric acid and benzene.Mechanochemistry is a mature technology for the simple and high-yield synthesis of nanostructured materials.The composition of the as-prepared hydrogen-substituted graphyne was confirmed by Raman and ¹H solid-state nuclear magnetic spectroscopies.Energy-dispersive X-ray (EDX) spectrum and X-ray diffraction (XRD) patterns indicated that the purity and crystallinity of the prepared samples are high, which was further confirmed by the corresponding selected area electron diffraction (SAED) patterns.Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images illustrated that samples had nanosheet structure with a layer-to-layer distance of 0.35 nm.However, owing to the lack of a substrate, the nanosheets reunite to form irregular microparticles, as shown in the scanning electron microscopy (SEM) images.Twin structure was found in the as-prepared samples, which might be relevant to the mechanochemical process.The samples were used to prepare electrodes for the photoelectrochemical and electrochemical catalytic analysis.The open circuit potential under chopped irradiation of the electrode showed that the as-prepared hydrogen-substituted graphyne was a p-type semiconductor.The band gap was calculated to be 2.30 eV by UV-Vis diffused reflectance (UV-Vis DRS) spectroscopy.The electrocatalytic properties of the sample were determined using a three-electrode cell in a neutral solution (Na₂SO₄, 0.5 mol·L⁻¹).The onset overpotential for hydrogen evolution was −0.17 V; however, the Tafel slope was too large (1088.4 mV·dec⁻¹), which restricted application in electrocatalytic hydrogen evolution.On the other hand, the overpotential for oxygen evolution reaction was only 0.04 V and the Tafel slope was 70.0 mV·dec⁻¹, making applications in electrocatalytic oxygen evolution and photocatalysis possible.This strategy opens a new avenue for preparing graphyne with good electrochemical properties using readily available precursors under mild conditions.

The molten salt CO₂ capture and electrochemical transformation (MSCC-ET) process is a potentially efficient method for CO₂ utilization, which can convert CO₂ into value-added carbon and oxygen with a current density of 100–1000 mA cm^-2. The electrolytic carbon (EC) prepared through the MSCC-ET process is highly electrically conductive and forms flexible microstructures. These structures show excellent adsorption ability towards environmental pollutants and high energy storage capacity when used in supercapacitors. Although the morphology, structure, and application of EC prepared under different electrolysis conditions have been previously reported, their intrinsic electrochemical properties have not yet been elucidated. Powder microelectrodes (PMEs) are useful for studying the electrochemical kinetics of various powdery materials. In this study, we systematically investigated the electrochemical properties of ECs obtained using molten Li₂CO₃-Na₂CO₃-K₂CO₃ under different temperature and electrolysis voltage conditions by cyclic voltammetry (CV) with a carbon powder microelectrode in 10 mmol L^-1 Na₂SO₄. The electrochemical behavior of the EC obtained at 450 ℃ and a cell voltage of 4.5 V (450 ℃-4.5 V-EC) differs significantly from that of other carbon materials, i.e., multi-walled carbon nanotubes, graphene, graphite, and acetylene black. In addition to a much larger charging-discharging capacity, unusual hysteresis of the charge/discharge current response of ECs in the negative potential region (-0.6 to -0.2 V vs SCE) was observed. This phenomenon was eliminated by annealing the material under Ar at 550 ℃, demonstrating that the unique electrochemical behavior of ECs is closely related to the oxygen-containing groups on its surface. Furthermore, CVs of EC-PME were compared in solutions with different pH, Na₂SO₄ concentrations, and other ions. The pH of the solution did not affect the CVs, excluding a redox mechanism involving the surface functional groups. Hysteresis was weakened by a certain degree at slower potential sweep speeds (< 10 mV s^-1) or in higher concentrations of electrolyte (100 mmol L^-1 Na₂SO₄). The onset potential for discharging was negatively shifted in electrolytes with a larger cation ((NH₄)₂SO₄) and was unaffected by larger anions (Na₂S₂O₈). This indicates that the hysteresis is more likely related to the specific adsorption of cations, caused by the unique surface properties of EC. It should be noted that the specific surface area and oxygen concentration of EC can be adjusted by the electrolysis temperature and cell voltage. Generally, the Brunauer–Emmett–Teller (BET) specific surface area and oxygen content decrease with increasing temperature and the BET-area increases with increasing cell voltage. The CVs of ECs prepared at different cell voltages were similar, but the adsorption capacity decreased for those prepared at higher temperatures (550 and 650 ℃). Interestingly, the specific capacitance of the ECs is much higher at negative potentials (-0.6 to 0 V vs. SCE) than that at positive potentials (0 to 0.6 V vs. SCE). Therefore, it is anticipated that a better capacitance performance can be achieved when the ECs are used as a negative electrode material in supercapacitors.

Organic solar cells (OSCs) have received widespread attention for their advantages of cheap, light, flexible characteristics and roll-to-roll printing technology. However, the efficiencies of OSCs are still lower than 50% of the theoretical Shockley-Queisser detailed-balance efficiency limit. Consequently, to further improve device performance, it is significant to develop molecular design strategies to lower the energy loss and enhance the utilization of absorbed photons. From the molecular design aspects, down-shifting energy levels is an effective way to lowering the energy loss in order to obtain a high open circuit voltage, and optimizing the morphology is an efficient approach to lowering the fill factor and current density loss. Introduction of fluorine atom in molecules is an effective molecular design strategy to realize both above-mentioned requirements. In this review, starting from the characteristics of fluorine atoms, we summarized the fluorination effects on adjusting molecular levels. Whether the fluorine attached to the donor units, acceptor units or π-bridge units, it could efficiently downshift the energy levels. However, fluorinating the molecular backbone affects the energy levels more significantly than fluorinating the side chains of the two-dimensional structures. The introduction of fluorine is also an effective approach to optimize molecular packing and morphology. Generally, whether the fluorine attached to the donor units, acceptor units or π-bridge units, it can effectively increase molecular coherence length, decrease π–π stacking distance, and enhance domain purity. However, there is a saturation of the fluorine on the backbone, further introduction of the fluorine can accelerate molecular aggregation and induce disorder. In addition, the position of fluorination is important. In this review, we also briefly discuss the fluorination strategy for representative and high-efficiency photovoltaic material designs, including small molecule, polymer, and non-fullerene OSCs, mainly focusing on improving efficiency by reducing the efficiency losses. Fluorination is advantageous only for OSCs with high HOMO energy levels or poor molecular packing; otherwise, it can compromise device performance. OSCs based on narrow band-gap non-fullerene acceptors with low energy loss show promise for highly efficient device performance. Fluorination provides an effective means to fine-tune energy levels and form ideal microstructures to further reduce the efficiency loss and achieve a breakthrough in device performance.

The thermal decomposition of condensed CL-20 was investigated using reactive force field molecular dynamics (ReaxFF MD) simulations of a super cell containing 128 CL-20 molecules at 800–3000 K. The VARxMD code previously developed by our group is used for detailed reaction analysis. Various intermediates and comprehensive reaction pathways in the thermal decomposition of CL-20 were obtained. Nitrogen oxides are the major initial decomposition products, generated in a sequence of NO₂, NO₃, NO, and N₂O. NO₂ is the most abundant primary product and is gradually consumed in subsequent secondary reactions to form other nitrogen oxides. NO₃ is the second most abundant intermediate in the early stages of CL-20 thermolysis. However, it is unstable and quickly decomposes at high temperatures, while other nitrogen oxides remain. At all temperatures, the unimolecular pathways of N―NO₂ bond cleavage and ring-opening C―N bond scission dominate the initial decomposition of condensed CL-20. The cleavage of the N―NO₂ bond is greatly enhanced at high temperatures, but scission of the C―N bond is not as favorable. A bimolecular pathway of oxygen-abstraction by NO₂ to generate NO₃ is observed in the initial decomposition steps of CL-20, which should be considered as one of the major pathways for CL-20 decomposition at low temperatures. After the initiation of CL-20 decomposition, fragments with different ring structures are formed from a series of bond-breaking reactions. Analysis of the ring structure evolution indicates that the pyrazine derivatives of fused tricycles and bicycles are early intermediates in the decomposition process, which further decompose to single ring pyrazine. Pyrazine is the most stable ring structure obtained in the simulations of CL-20 thermolysis, supporting the proposed existence of pyrazine in Py-GC/MS experiments. The single imidazole ring is unstable and decomposes quickly in the early stages of CL-20 thermolysis. Many C₄ and C₂ intermediates are observed after the initial fragmentation, but eventually convert into stable products. The distribution of the final products (N₂, H₂O, CO₂, and H₂) obtained in ReaxFF MD simulation of CL-20 thermolysis at 3000 K quantitatively agrees with the results of the CL-20 detonation experiment. The comprehensive understanding of CL-20 thermolysis obtained through this study suggests that ReaxFF MD simulation, combined with the reaction analysis capability of VARxMD, would be a promising method for obtaining deeper insight into the complex chemistry of energetic materials exposed to thermal stimuli.

In recent years, the successful preparation of single-layer graphene, MoS₂, and other two-dimensional materials has started a new era of two-dimensional materials.The potential applications of two-dimensional materials in emerging electronics have drawn widespread attention.Two-dimensional carbon materials, with their unique properties, have become the research hotspot of condensed matter physics, nanoelectronics, and biological medicine.The remarkable success in preparing graphene provides additional possibilities for developing sensitive biodevices and medicine systems.However, graphene is gapless and thus is unsuitable for building nanoelectronic devices or biosensors due to the too low on/off current ratio.More than 20 years ago, graphyne and its family (viz.graphdiyne, graphyne-3, etc.), as hypothetical C allotropes, were theoretically predicted to be semiconductors with a layered structure.Recently, graphdiyne was successfully synthesized on the surface of copper via a cross-coupling reaction using hexaethynylbenzene.Graphdiyne, as a new two-dimensional carbon material with semiconductor properties and a unique porous structure, is more advantageous than graphene for nanoelectronic and biosensing applications.As the first discovered semiconducting two-dimensional carbon material, with independent intellectual property rights in China, graphdiyne has great research significance.Compared with graphene, graphdiyne has a unique structure with larger pores composed of high π-conjugated acetylenic bonds, which may facilitate strong adsorption to biomolecules.Therefore, further research is needed to reveal how the physical properties of graphdiyne can be modulated effectively to meet the requirements of practical applications.The interaction between biological molecules and materials is an important subject of research in condensed matter physics and materials science.Detailed understanding of the interactions between graphdiyne and small molecules may facilitate the development of advanced biological applications such as biosensors for the detection of biomolecules and living cells, drug delivery systems, and cell imaging technologies.In sensitive analysis, the ultimate goal is to achieve reliable detection of trace amounts of molecules.In this work, first-principles calculations were employed to investigate the electronic structure of graphdiyne nanoribbons and the adsorption of graphdiyne to small molecules.To improve the chemical response of graphdiyne to single molecules, we considered modifying graphdiyne by doping 3d transition metal atoms.We chose Sc and Ti, which have the largest adsorption energies on graphdiyne, and studied the room-temperature stabilities of Sc-and Ti-doped graphdiyne and the possibility of using Sc-and Ti-doped graphdiyne as materials for molecular sensing.Finally, we investigated the interaction between graphdiyne and amino acid molecules and discovered that the dispersion force plays a large role in the interaction.The influence of amino acids on the electronic transport properties of graphdiyne was also studied, and the potential applications of graphdiyne to biosensors were investigated.

A complex reaction, such as combustion, polymerization, and zeolite synthesis, involves a large number of elementary reactions and chemical species. Given a set of elementary reactions, the apparent reaction rates, population of chemical species, and energy distribution as functions of time can be derived using deterministic or stochastic kinetic models. However, for many complex reactions, the corresponding elementary reactions are unknown. Molecular dynamics (MD) simulation, which is based on forces calculated by using either quantum mechanical methods or pre-parameterized reactive force fields, offers a possibility to probe the reaction mechanism from the first principles. Unfortunately, most reactions take place on timescales far above that of molecular simulation, which is considered to be a well-known rare event problem. The molecules may undergo numerous collisions and follow many pathways to find a favorable route to react. Often, the simulation trajectory can be trapped in a local minimum separated from others by high free-energy barriers; thus, crossing these barriers requires prohibitively long simulation times. Due to this timescale limitation, simulations are often conducted on very small systems or at unrealistically high temperatures, which might hinder their validity. In order to model complex reactions under conditions comparable with those of the experiments, enhanced sampling techniques are required. The replica exchange molecular dynamics (REMD) is one of the most popular enhance sampling techniques. By running multiple replicas of a simulation system using one or several controlling variables and exchanging the replicas according to the Metropolis acceptance rule, the phase space can be explored more efficiently. However, most published work on the REMD method focuses on the conformational changes of biological molecules or simple reactions that can be described by a reaction coordinate. The optimized parameters of such simulations may not be suitable for simulations of complex reactions, in which the energy changes are much more dramatic than those associated with conformational changes and the hundreds elementary reactions through numerous pathways are unknown prior to the simulations. Therefore, it is necessary to investigate how to use the REMD method efficiently for the simulation of complex reactions. In this work, we examined the REMD method using temperature (T-REMD) and Hamiltonian (H-REMD) as the controlling variable respectively. In order to quantitatively validate the simulation results against direct simulations and analytic solutions, we performed the study based on a simple replacement reaction (A + BC = AB + C) with variable energy barrier heights and reaction energies described using the ReaxFF functional forms. The aim was to optimize the simulation parameters including number, sequence, and swap frequency of the replicas. The T-REMD method was found to be efficient for modeling exothermic reactions of modest reaction energy (< 3 kcal∙mol^-1) or activation energy (ca. < 20 kcal∙mol^-1). The efficiency was severely impaired for reactions with high activation and reaction energies. The analysis of the simulation trajectory revealed that the problem was intrinsic and could not be solved by adjusting the simulation parameters since the phase space sampled using T-REMD was localized in the region favored by high (artificial for speed-up) temperatures, which is different from the region favored by low (experimental) temperatures. This issue was aggravated in the case of endothermic reactions. On the other hand, the H-REMD run on a series of potential surfaces having different activation energies was demonstrated to be remarkably robust. Since the energy barrier only reduces the reaction rates, while the phase space controlled by the reaction energy differences remains unchanged at a fixed temperature, excellent results were obtained with fewer replicas by using H-REMD. It is evident that H-REMD is a more suitable method for the simulation of complex reactions.

Atomically precise nanoclusters form an important class of functional materials that have recently attracted research interest for their unique properties and easily tunable surface functionalities. Core-shell nanomaterials with precise structural information can be produced to better understand the structure–property relationships for different applications. Polyoxo-titanium clusters (PTCs) are such a kind of nanomaterial for different functional applications in catalysis, photovoltaics, ceramics, etc. However, the high bandgap of semiconductive PTCs is the limiting factor in their practical solar application in the visible region of sunlight. The development of PTCs with different surface-bound ligands is an emerging area of research in the design and synthesis of core-shell nanoclusters with reduced bandgaps. It has been extensively reported that the polynuclear growth of PTCs requires molecular-level water supply in reactions. Moreover, it is important to identify more environment-friendly synthetic methods. Deep eutectic-solvothermal (DES) synthesis is an emerging green method for the synthesis of different crystalline materials. The hygroscopic nature of DES should enhance the provision of water during polynuclear growth of nanoclusters. Hence, we chose to synthesize different kinds of PTCs using DES as solvent. Two nanoclusters, Zr-oxo (PTC-65) and Zr/Ti-oxo (PTC-66) clusters having surface-bound 1, 10-phenanthroline (1, 10-phn) and phenol ligands, were successfully synthesized using this approach; 1, 10-phn was employed as the precursor in the synthetic reaction, and phenol was not employed directly in the chemical reaction, but was supplied from the DES solvent used in the reaction. In the presence of chromophoric ligands, 1, 10-phn and phenol are believed to enhance the light absorption properties of the resulting functional nanomaterials. Their crystal structure revealed that they form core-shell mimics with Zr-oxo and Ti/Zr-oxo core units having surface-bound shell ligands. Based on their different structural characteristics, photocatalytic hydrogen evolution studies were performed on these two functional materials using an aqueous solution of H₂O (50 mL)/triethanol amine (10 mL). Interestingly, PTC-65 formed a turbid solution, whereas PTC-66 formed a clear solution. The possible reasons for their different dispersion behaviors are widely discussed, with emphasis on their structure–property relationships. This study provides a potential tool for the homogenization of Ti-O materials to improve their photocatalytic activities. Moreover, the success of our work confirms that deep eutectic-solvothermal synthesis can be an effective method for cluster preparation. Many other interesting polynuclear complexes like polyoxometalates, chalcogenides, and noble-metal clusters could be obtained by this synthetic methodology.

In this perspective, we review the chemical information encoded in electron density and other ingredients used in semilocal functionals. This information is usually looked at from the functional point of view: the exchange density or the enhancement factor are discussed in terms of the reduced density gradient. However, what parts of a molecule do these 3D functions represent? We look at these quantities in real space, aiming to understand the electronic structure information they encode and provide an insight from the quantum chemical topology (QCT). Generalized gradient approximations (GGAs) provide information about the presence of chemical interactions, whereas meta-GGAs can differentiate between the different bonding types. By merging these two techniques, we show new insight into the failures of semilocal functionals owing to three main errors: fractional charges, fractional spins, and non-covalent interactions. We build on simple models. We also analyze the delocalization error in hydrogen chains, showing the ability of QCT to reveal the delocalization error introduced by semilocal functionals. Then, we show how the analysis of localization can help understand the fractional spin error in alkali atoms, and how it can be used to correct it. Finally, we show that the poor description of GGAs of isodesmic reactions in alkanes is due to 1, 3-interactions.

Lithium-ion batteries (LIBs) possess many virtues, such as low weight, a high energy density, and a long service life, and are regarded as an essential component of a low-carbon economy. Nowadays, LIBs are widely used in consumer electronics, as well as military and aviation products, and are the focus of significant research in the emerging field of energy materials. The cathode material is one of the most important parts of the LIB; its electrochemical performance plays an important role in the battery voltage, power/energy density, cycle life, and safety. LiFePO₄ is a superior cathode material compared to spinel manganite (LiMn₂O₄) and layered lithium nickel-cobalt-manganese oxide (LiMO₂ (M = Mn, Co, Ni)), and LiFePO₄ has many advantages, such as excellent thermal stability, cycling performance, economic viability, and environmental friendliness. The theoretical diffusion coefficient of LiFePO₄ is 10⁻⁸ cm²∙s⁻¹, which is sufficient for Li⁺ de-intercalation in nanoparticles. However, the one-dimensional transport channels are easily blocked by structural defects, resulting in a lower diffusion coefficient and poor rate performance. The electronic conductivity of LiFePO₄ is about 10⁻⁸ S∙cm⁻¹, and this also limits the rate performance. Moreover, the low-temperature performance, low yield, and patent problems are also significant problems facing LiFePO₄. In contrast, the stability and cost are not significant limitations to more extensive applications; rather, it is the energy density and power density that must be improved. To meet the above demands, in-depth research on the factors affecting the electrochemical performance of LiFePO₄ is required. Many factors affect the electrochemical performance of LiFePO₄, such as the synthetic method, particle size, electrolyte environment, electrode structure, and temperature. Based on the current state of research into LiFePO₄, we have focused our review on the following three aspects: the characteristics of the nanoparticles, interface environment of the material, and the electrode structure. Finally, we summarize the relationship between the structure and electrochemical performance of LiFePO₄ cathode materials: (1) the bulk phase characteristics of the material (phase structure, doping, nanocrystallization, defects, and lithium-ion transport mechanism), (2) interface structure and interface reconstruction under different electrolyte environments, and (3) the electrode structure. Our conclusions have great significance for future research.

Water is involved in many important physical, chemical, and biological phenomena. However, not much is known about water at the nanoscale level, such as about its radiolysis and condensation, because of the experimental difficulties of imaging liquid at such a length-scale. The newly developed graphene liquid cell (GLC) technique facilitates imaging dynamic events in a liquid medium with unprecedented resolution while sustaining the most realistic liquid condition achievable under electron-beam irradiation. The graphene liquid cell was fabricated by the wet transfer of monolayer graphene synthesized by chemical vapor deposition to a graphene-supported transmission electron microscope (TEM) grid, and the water islands were naturally captured during the wet transfer process. Compared with traditional, commercial silicon nitride cells, the fabrication of graphene liquid cells required higher expertise and thus related research reports are limited. Here, we used graphene liquid cells for in situ TEM observation of dynamic behaviors of entrapped water between two layers of graphene. The radiolysis and condensation processes of water could be modulated by controlling the electron dose rate. We showed that a high electron dose rate yields supersaturated concentration of gas molecules in a liquid system, and the excess gas then dissolve out in the form of a series of nanobubbles at a low dose rate. From The quantitative and statistical analyses of the dynamic processes of the confined liquid showed that the growth of the nanobubbles is limited by interface reactions and the newly formed nanobubble inhibits the growth of the existing one. The gas molecules inside the nanobubbles are in a "dense gas" phase and the density number ratio of the gas molecules inside each nanobubble decreases during the growth process of each nanobubble. The total number of gas molecules increases approximately linearly with time. A fixed middle dose rate leads to the condensation of droplets, with repeat growth/dissolution processes on the inner wall of graphene. The contact angles at the water-graphene interface are less than 90°, suggesting that the scrolled graphene is hydrophilic. Using in situ GLC-TEM imaging, we directly observed the dynamic processes involved in beam-induced bubble formation in liquid and nanodroplet condensation from vapor at the preferential sites. Some unexpected and so-far undiscovered phenomena involving both nanobubbles and nanodroplets were observed and investigated in detail, which increased our knowledge on the behaviors of the nanoconfined liquid. Our results presented here would serve as an important reference to understand the vapor/liquid interface transition in a nanoconfined space and electron-water interactions in liquid cell TEM. The experiment and method reported here may help find further applications of the new graphene liquid cell technique. The use of graphene liquid cell will also help a wide range of studies on reactions and process dynamics in material science and biochemistry that either have not been explored or need more detailed understanding.

Ternary blends have been considered as an effective approach to improve power conversion efficiency (PCE) of organic solar cells (OSCs). Among them, the fullerene-containing ternary OSCs have been studied extensively, and their PCEs are as high as over 14%. However, all non-fullerene acceptor ternary OSCs are still limited by their relatively lower PCEs. In this work, we used wide-bandgap benzodithiophene-difluorobenzotriazole copolymer FTAZ as the donor, low-bandgap fused-ring electron acceptor (FREA), fused tris(thieno- thiophene) end-capped by fluorinated 1, 1-dicyanomethylene-3-indanone (FOIC) as acceptor, and two medium-bandgap FREAs, indaceno-dithiophene end- capped by 1, 1-dicyanomethylene-3-indanone (IDT-IC) and indacenodithiophene end-capped by 1, 1-dicyanomethylene-3-benzoindanone (IDT-NC), as the third components to fabricate the ternary blends FTAZ:FOIC:IDT-IC and FTAZ:FOIC:IDT-NC, and investigated the effects of the third components on the performance of ternary OSCs. Both IDT-IC and IDT-NC are based on the same indacenodithiophene core but contain different terminal groups (phenyl and naphthyl). Relative to IDT-IC with phenyl terminal groups, IDT-NC with naphthyl terminal groups has extended π-conjugation, down-shifted lowest unoccupied molecular orbital (LUMO), red-shifted absorption and higher electron mobility. The binary devices based on the FTAZ:FOIC, FTAZ:IDT-IC and FTAZ:IDT-NC blends exhibit PCEs of 9.73%, 7.48% and 7.68%, respectively. Compared with corresponding binary devices, both ternary devices based on FTAZ:FOIC:IDT-IC and FTAZ:FOIC:IDT-NC exhibit better photovoltaic performances. When the IDT-IC weight ratio in acceptors is 50%, the FTAZ:FOIC:IDT-IC ternary devices exhibit the best PCE of 11.2%. The ternary-blend OSCs yield simultaneously improved open-circuit voltage (V_OC), short-circuit current density (J_SC) and fill factor (FF) compared with the binary devices based on FTAZ:FOIC. The higher V_OC is attributed to the higher LUMO energy level of IDT-IC compared with FOIC. The improved J_SC is attributed to the complementary absorption of FOIC and IDT-IC. The introduction of IDT-IC improves blend morphology and charge transport, leading to higher FF. The FTAZ:FOIC:IDT-NC system yields a higher PCE of 10.4% relative to the binary devices based on FTAZ:FOIC as the active layer. However, the PCE of the FTAZ:FOIC:IDT-NC-based ternary devices is lower than that of the FTAZ:FOIC:IDT-IC-based ternary devices. Compared with the binary devices based on FTAZ:FOIC, in FTAZ:FOIC:IDT-NC-based ternary devices, as the ratio of the third component increases, the V_OC increases due to the higher LUMO energy level of IDT-NC, the FF increases due to optimized morphology and improved charge transport, while the J_SC decreases due to the overlapped absorption of FOIC and IDT-NC. The terminal groups in the third components affect the performance of the ternary OSCs. The lower LUMO. energy level of IDT-NC is responsible for the lower V_OC of the FTAZ:FOIC:IDT-NC devices. The red-shifted absorption of IDT-NC leads to the overlapping of the absorption spectra of IDT-NC and FOIC and lower J_SC. On the other hand, replacing the phenyl terminal groups by the naphthyl terminal groups influences the π-π packing and charge transport. The FTAZ:FOIC:IDT-NC blend exhibits higher electron mobility and more balanced charge transport than FTAZ:FOIC:IDT-IC, leading to a higher FF.

The development of the photocatalytic production of hydrogen from water splitting has attracted immense attention in recent years. CdS is a potential photocatalyst with a visible light response, though it still suffers from a limited activity for hydrogen production due to the fast recombination of photo-induced electron/hole pairs and the low reaction rate of hydrogen evolution on the surface. Studies on the effect of CdS surface structure and properties on hydrogen production are still very limited. In this work, we prepared three CdS nanocrystals with different morphologies: long rod, short rod, and triangular plate. The prepared samples were well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). From the results of TEM, XRD and XPS, we find that the three CdS nanocrystals with different morphologies were successfully synthesized. From the PL spectra, we conclude that the area of exposed nonpolar surface and degree of surface defects increase with an increase in aspect ratio. We also performed the photocatalytic hydrogen production reaction using the three CdS crystals. Long rod-like CdS (lr-CdS) exhibits the highest photocatalytic activity, with a hydrogen production rate of 482 μmol·h^-1·g^-1, which is 2.6 times that of short rod-like CdS (sr-CdS) (183 μmol·h^-1·g^-1) and 8.8 times that of triangular plate-like CdS (tp-CdS, 55 μmol h^-1·g^-1). It is found that lr-CdS shows a higher hydrogen production rate than sr-CdS and tp-CdS. We find that the hydrogen production rate is related to the degree of surface defects. Surface defects can trap the photo-induced electrons/holes, thus decreasing their probability of recombination. In addition, these defects can be used to anchor Pd particles to form a heterojunction structure that facilitates the separation of photo-induced charges. Therefore, we also compared three CdS/Pd nanocrystals synthesized with the three abovementioned morphologies with respect to hydrogen production. With 1% (w, mass fraction) Pd, the hydrogen production rate was greatly enhanced compared to all the CdS catalysts. Compared to the unpromoted CdS, the reaction rate is enhanced 43.1, 10.7 and 6.0 times over those of sr-CdS, lr-CdS and tp-CdS, respectively. Notably, the hydrogen production rate with short rod-like CdS/Pd reaches 7884 μmol·h^-1·g^-1, which can be favorably compared with the ever-increasing values reported in the literature. Hopefully, this work provides knowledge on the effect of crystal surface structure and properties on photocatalysis.

The construction of a photo-controllable artificial molecular machine capable of realizing the light-driven motion on a molecular scale and of performing a specific function is a fascinating topic in supramolecular chemistry. The bistable switchable molecule, azobenzene (AZO), has been introduced into the supramolecular architecture as a key building block, owing to its efficient and reversible trans (E)-cis (Z) photoisomerization. The binding strength of the dibenzo[24]crown-8 (DB24C8) host and dialkylammonium-based rod-like guest consisting of an AZO moiety and the Z$\to $E photoisomerization process in an interlocked host-guest complex have been investigated by the density functional theory (DFT) calculations and the reactive molecular dynamics (RMD) simulations by considering both torsion and inversion paths. The strong host-guest binding strength provides a necessary premise to stabilize the complex during the E-Z photoisomerization of the AZO unit, which is a terminal stopper to control the directional motion of the guest. A stronger binding strength for the Z isomer can be induced by the stronger hydrogen-bonding interaction. The steric effect is introduced into the Z isomer to force the ring slipping exclusively over the cyclopentyl terminal (pseudostopper). The host-guest complexation has a slight effect on the conformation of the AZO functional subunit for the two isomers. The faster Z$\to $E photoisomerization process within the picosecond timescale is kinetically more favored than the dethreading of the ring through the pseudostopper subunit of the rod. After isomerization, a structure relaxation is observed for the crown ether ring within 500 ps. The flexible backbone of the crown ether ring is helpful in realizing steady and stable host-guest recognition during photoisomerization. Moreover, the orthogonality of the site-specific binding interaction is revealed by the similar binding energies obtained at similar hydrogen bonding recognition sites for various interlocked host-guest supramolecular systems although the constituents of the guests are different from each other. The introduction of two stereoisomers of the AZO subunit has little influence on the other conformations of guest subunits. These results are useful for the rational design of more sophisticated stimuli-controlled artificial molecular machines.

The electrocatalytic reduction of CO₂ to C₂H₄ is a topic of great interest. It is known that the preparation of efficient catalysts for this transformation is the key factor that determines the yield of C₂H₄. In this study, we prepared 1-octyl-3-methylimidazole functionalized graphite sheets (ILGS) in a facile manner by the electro-exfoliation of pure graphite rod in an aqueous solution of 1-octyl-3-methylimidazolium chloride (OmimCl : H₂O = 1 : 5, V/V) at 10 V. They were then dispersed in an aqueous solution of copper chloride and sodium citrate. Subsequent reduction with sodium borohydride led to the formation of a composite comprised of cuprous oxide supported on Omim-functionalized graphite sheets (Cu₂O/ILGS). This composite was found to be an efficient catalyst for the electroreduction of carbon dioxide to ethylene. The as-made materials were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD). The TEM images showed that the ILGS were composed of multiple layers of graphene. The XRD pattern and Raman spectrum indicated that the surface of the ILGS possessed several defects. In the electro-exfoliation process, the defects in the ILGS were modified in situ by covalent bonding with Omim groups, which was also confirmed by XPS. The Cu₂O nanoparticles with an average diameter of 5 nm were uniformly distributed on the surface of the ILGS because the Omim groups grafted to the graphite sheets acted as anchors and prevented their aggregation by the steric effect. The electrocatalytic activities of Cu₂O/ILGS for CO₂ reduction were measured at different voltages in 0.1 mol L^–1 KHCO₃ aqueous solution under ambient temperature and pressure. These experiments showed that the catalytic performance of the Cu₂O/ILGS composite was determined by cuprous oxide, while the ILGS displayed nearly no catalytic activity in the electroreduction of carbon dioxide. The faradaic efficiency of hydrogen and carbon dioxide reduction products changed with the reaction time because of the reduction of Cu₂O to Cu under the electroreduction conditions. The faradaic efficiency of ethylene was ~14.8% at –1.3 V (versus reversible hydrogen electrode). The performance of Cu₂O/ILGS in the catalytic electroreduction of carbon dioxide was attributed to the stabilization of the Cu₂O nanoparticles by the nest-like microstructures in the Cu₂O/ILGS composite.

ZnO is an ideal material for ultraviolet (UV) detection due to its wide direct-bandgap, high exciton binding energy, and high internal photoconductive gain.However, ZnO UV detectors have the disadvantages of slow response speed and low detectivity.Graphdiyne (GD) is a novel carbonaceous allotrope, and possesses excellent electronic performance in air.In this study, the metal-semiconductor-metal (MSM) structured lateral ZnO UV detectors were prepared, and GD was employed to modify the ZnO surface.The effects of GD deposited 1–3 times (viz.1T, 2T, and 3T GD) on the performance of ZnO ultraviolet detector were carefully investigated.The results show that the dark current of the bare ZnO detector is 24 μA under a bias of 10 V, while that of the graphdiyne-modified detector is ~0.34 μA (about two orders of magnitude reduction).The dark current remains almost the same for the 1T, 2T and 3T GD films.The photocurrents of 1–3T GD-modified detectors were 0.21, 0.32, 0.27 mA, respectively.The device modified with 2T GD displays the highest photocurrent, which is significantly enhanced in comparison to the unmodified device (0.08 mA) under a 365-nm UV radiation of 100 μW·cm⁻².Meanwhile, the responsivity and detectivity are improved remarkably.Under a bias of 10 V, the 2T-GD-modified detector displays high responsivity of 1759 A·W⁻¹ and detectivity of 4.23×10¹⁵ Jones.The detectivity is thus far the highest for ZnO UV detectors prepared by the sol-gel method.The improved performance of the GD-modified detector is attributed to the p-n junction formed between the GD and the ZnO film.At dark, the p-n junction is formed between the ZnO film and the GD, which greatly decreases the dark current of the detector.Under UV illumination, photogenerated holes accumulate in the GD, reducing electron-hole recombination; thus, the photocurrent is significantly increased.Furthermore, desorption and absorption of oxygen on the ZnO surface are much reduced due to the GD attached on the ZnO surface, thus improving the response speed of the detector.However, the intensive distribution of GD slightly hinders the UV absorption of ZnO thin films, reducing the responsivity of the detector.Careful optimization shows that the use of 2T GD gives the best output, and the corresponding ZnO UV detector exhibits very good performance.Overall, this study demonstrates that using GD can effectively improve the performance of ZnO UV detector.

The structure of low-temperature α-Cu₂Se, which is of great importance for understanding the mechanism of the significant increase in thermoelectric performance during the α-β phase transition of Cu₂Se, has still not been fully solved. Because it is restricted by the quality of polycrystal and powder specimens and the accuracy of characterization methods such as the conventional transmission electron microscopy (TEM) and X-ray diffraction (XRD), direct observation with atomic-scale resolution to reveal the structural details has not been realized, although electron diffraction and high-resolution transmission electron microscopy (HRTEM) studies have indicated the complexity of the α-Cu₂Se layered structure. Owing to developments in the focused ion beam (FIB) milling preparation method, high-quality single crystalline specimens with specific crystallographic orientations can be prepared to ensure that atomic-resolution images along a specific orientation can be acquired. Furthermore, the developments in aberration correction technology in TEM and scanning transmission electron microscopy (STEM) allow us to observe the subtle details of structural variation and evolution. Herein, we report, for the first time, the atomic-resolution high-angle annular dark field (HAADF) images acquired along the $ {{\left[ \bar{1}\bar{1}2 \right]}_{\text{c}}}$ axis of α-Cu₂Se using spherical-aberration (C_s)-corrected STEM from FIB-prepared single crystalline specimens. The observations revealed that the complex structure is generated by ordered fluctuations of Se atoms with various forms, including that some of the Se atoms on the two sides of the Cu deficiency layer get closer to each other than the others and the neighboring Cu deficiency layers have different forms of ordered Se fluctuations. These characteristics can only be observed along the $ {{\left[ \bar{1}\bar{1}2 \right]}_{\text{c}}}$ axis, while these details were not visible in a previous study along the $ <\bar{1}10{{>}_{\text{c}}} $ axis or in our results obtained along the ${{\left[ \bar{1}01 \right]}_{\text{c}}} $ axis. By combining the electron diffraction patterns, several models of the unit cell variants were established, including the two-layer and four-layer cells (both have two different shapes) and the two-layer variants with and without central symmetry. These variants can also transform into each other, and an α-Cu₂Se crystal can be formed through the random assembly of these variants. Using the program QSTEM, the corresponding HAADF images of these variants were simulated. The simulation results were similar to the experimental HAADF images and reflected most of the observed details, including the different forms of the ordered fluctuations of Se atoms and the dispersion of Cu atoms, which indicates that our structure models of α-Cu₂Se are reasonable. This work provides new critical information for thoroughly understanding the structure of α-Cu₂Se and the α-β phase transition of Cu₂Se.

We present the atomic structure of thiolate-protected hollow Au nanosphere (HAuNS), Au₆₀(SR)₂₀, with high symmetry and stability based on the grand unified model (GUM; Nat. Commun. 2016, 7, 13574) and density-functional theory (DFT) calculations. Using C₂₀ fullerene (with I_h symmetry) as a template, 20 tetrahedral Au₄ units were used to replace the C atoms of C₂₀, and three Au atoms of each Au₄ were fused with three neighboring Au₄ units by sharing one Au atom to form an icosahedral Au₅₀ fullerene cage as the inner core. Subsequently, the unfused Au atom in each Au₄ was bonded with the [―RS―Au―SR―] staple to form the completely hollow Au₆₀(SR)₂₀ nanosphere. Therefore, the Au₆₀(SR)₂₀ is composed of an icosahedral Au₅₀ fullerene hollow cage (constructed by fusing 20 tetrahedral Au₄ units) with 10 [―RS―Au―SR―] staples, obeying the "divide and protect" rule. Each Au₄ unit has 2e valence electrons, namely, the tetrahedral Au₄(2e) elementary block in the grand unified model. The DFT calculations showed that this hollow Au₆₀(SR)₂₀ nanosphere had a large HOMO–LUMO (HOMO: the highest occupied molecular orbital; LUMO: the lowest unoccupied molecular orbital) gap (1.3 eV) and a negative nucleus-independent chemical shift (NICS) value (−5) at the center of the hollow cage, indicating its high chemical stability. Furthermore, the NICS values in the center of the tetrahedral Au₄ units were much more negative than that in the center of the hollow cage, revealing that the overall stability of Au₆₀(SR)₂₀ likely stemmed from the local stability of each tetrahedral Au₄ unit. The harmonic vibrational frequencies were all positive, suggesting that the HAuNS corresponded to the local minimum of the potential energy surface. In addition, the bilayer HAuNS was designed by fusing the tetrahedral Au₄ layers, indicating the feasibility of tuning the thickness of the shell of HAuNS. In bilayer HAuNS, each tetrahedral Au₄ unit in the first layer shared four Au atoms, while those in the second layer shared one Au atom. The other three Au atoms of each tetrahedral unit bonded with the SR groups, demonstrating that each tetrahedral Au₄ unit has 2e valence electrons (namely the tetrahedral Au₄(2e) elementary block in GUM). The HOMO-LUMO gap of the bilayer Au₁₄₀(SH)₆₀ nanosphere is 1.5 eV, indicating its chemical stability. The thicknesses of the shells in monolayer and bilayer HAuNS are about 0.2 and 0.4 nm, respectively. This process could be easily understood in terms of the local stabilities of the tetrahedral Au₄(2e) elementary block in GUM. Finally, the design of larger HAuNS, Au₁₈₀(SR)₆₀, has also been presented. The HOMO-LUMO gap of Au₁₈₀(SH)₆₀ was 0.9 eV, which showed that it was also a stable HAuNS. This work provides a new strategy to controllably design the HAuNS.

Carbon dioxide is a green C₁ resource that can be efficiently recycled by catalytic transformation into value-added chemicals. Formamides are important intermediates and solvents that are used extensively in pharmaceutical, daily-chemical, and petrochemical industry. Therefore, it is worthwhile to synthesize formamides with CO₂ and amines. In this review, the main advancements in the synthesis of formamides by using CO₂ as the C₁ feedstock with noble metal catalysts (Ir, Pd, Pt, Ru, Rh, etc.), non-noble metal catalysts (Ni, Mo, Cu, Fe, Co, Zn, Al, etc.), organocatalysts, and catalyst-free systems have been summarized. In addition, the role of the reducing agents such as H₂, silanes, and boranes involved in these transformations has also been reviewed. In addition, the reaction mechanisms with the different catalyst systems have been discussed.

Non-fullerene electron acceptors have attracted enormous attention of the research community owing to their advantages of optoelectronic and chemical tunabilities for promoting high-performance polymer solar cells (PSCs). Among them, fused-ring electron acceptors (FREAs) are the most popular ones with the good structural planarity and rigidity, which successfully boost the power conversion efficiencies (PCEs) of PSCs to over 14%. In considering the cost-control of future scale-up applications, it is also worthwhile to explore novel structures that are easy to synthesize and still maintain the advantages of FREAs. In this work, we design and synthesize a new electron acceptor with an unfused backbone, 5, 5'-((2, 5-bis((2-hexyldecyl)oxy)-1, 4-phenylene)bis(thiophene-2-yl))bis(methanylylidene)) bis(3-oxo-2, 3-dihydro-1H-indene-2, 1-diylidene))dimal-ononitrile (ICTP), which contains two thiophenes and one alkoxy benzene as the core and 2-(3-oxo-2, 3-dihydroinden-1-ylidene) malononitrile (IC) as the terminal groups. The synthetic route to ICTP involves only three steps, with high yields. Density functional theory calculations indicate that the non-covalent interactions, O…H and O…S, help reinforce the space conformation between the central core and the terminals. ICTP shows broad and strong absorption in the long-wavelength range between 500 and 760 nm. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of ICTP were measured to be -5.56 and -3.84 eV by cyclic voltammetry. The suitable absorption and energy levels make ICTP a good acceptor candidate for medium bandgap polymer donors. The best devices based on PBDB-T:ICTP showed a PCE of 4.43%, with an open circuit voltage (V_OC) of 0.97 V, a short circuit current density (J_SC) of 8.29 mA∙cm^-2, and a fill factor (FF) of 0.55, after adding 1% 1, 8-diiodooctane (DIO) as the solvent additive. Atomic force microscopy revealed that DIO could ameliorate the strong aggregation in the blended film and lead to a smoother film surface. The hole and electron mobilities of the optimized device were measured to be 9.64 and 2.03 × 10^-5 cm²∙V^-1∙s^-1, respectively, by the space-charge-limited current method. The relatively low mobilities might be responsible for the moderate PCE. Further studies can be performed to enlarge the conjugation length by including more aromatic rings. This study provides a simple strategy to design non-fullerene acceptors and a valuable reference for the future development of PSCs.

Cu has been widely used as a substrate material for graphene growth. To understand the atomistic mechanism of growth, an efficient and accurate method for describing Cu-C interactions is necessary, which is the prerequisite of any possible large-scale molecular simulation studies. The semi-empirical density-functional tight-binding (DFTB) method has a solid basis from the density functional theory (DFT) and is believed to be a good tool for achieving a balance between efficiency and accuracy. However, existing DFTB parameters cannot provide a reasonable description of the Cu surface structure. At the same time, DFTB parameters for Cu-C interactions are not available. Therefore, it is highly desirable to develop a set of DFTB parameters that can describe the Cu-C system, especially for surface reactions. In this study, a parametrization for Cu-C systems within the self-consistent-charge DFTB (SCC-DFTB) framework is performed. One-center parameters, including on-site energy, Hubbard, and spin parameters, are obtained from DFT calculations on free atoms. Two-center parameters can be calculated based on atomic wavefunctions. The remaining repulsive potential is obtained as the best compromise to describe different kinds of systems. Test calculations on Cu surfaces and Cu-or C atom-adsorbed Cu surfaces indicate that the obtained parameters can generate reasonable geometric structures and energetics. Based on this parameter set, carbon dimerization on the Cu(111) surface has been investigated via molecular dynamics simulations. Since they are the feeding species for graphene growth, it is important to understand how carbon dimers are formed on the Cu surface. It is difficult to observe carbon dimerization in brute-force MD simulations even at high temperatures, because of the surface structure distortion. To study the dimerization mechanism, metadynamics simulations are performed. Our simulations suggest that carbon atoms will rotate around the bridging Cu atom after a bridging metal structure is formed, which eventually leads to the dimer formation. The free energy barrier for dimerization at 1300 K is about 0.9 eV. The results presented here provide useful insights for understanding graphene growth.

Atomically precise pieces of metallic matter with nanometer dimensions, which are called nanoclusters, have attracted special research interest as a frontier in nanoscience research. These nanoclusters exhibit unique properties that make them suitable for widespread applications in fields like medical treatments and catalysis. Studies in nanoclusters have been greatly benefited from the use of advanced instrumentation, especially adaptation of mass spectrometry (e.g., matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and electrospray ionization mass spectrometry (ESI MS)). However, mass spectrometry could not elucidate the bonding between metals and ligands; therefore, single-crystal X-ray diffraction (SC-XRD) analysis has been used. SC-XRD is significant for the development of the nanocluster range in terms of revealing the precise structure of nanoclusters and fully understanding the structure-property relationship. Furthermore, understanding the nature of nanocluster surface has provided possibility to embellish nanocluster surface and to improve their performance. Nowadays, alloy nanoclusters play an important role in catalysis, biology, and materials science. Researchers have synthesized and predicted the alloy structure composed of silver and nickel in ultra-small size (Ag₄Ni₂(DMSA)_4, (DMSA = meso-2, 3-dimercaptosuccinic acid)). However, no precise crystal structure has been reported. Herein, we report the crystal structure of the Ag-Ni alloy nanocluster Ag₄Ni₂(SPhMe₂)₈. The structure was further confirmed by SC-XRD, X-ray photoelectron spectroscopy (XPS), MALDI-TOF MS, ESI MS and thermo gravimetric analysis (TGA) measurements. The stability experiment suggested that the Ag₄Ni₂ nanocluster could be stable in ultra-small sizes. This research on Ag-Ni alloy nanoclusters will contribute to the understanding of the alloy in ultra-small sizes. Specifically, based on the structure determination by SC-XRD, the structure of Ag₄Ni₂(SPhMe₂)₈ could be divided into three layers: upper and lower layers with Ni(SPhMe₂)₄ complexes constituting a parallelogram, and the middle layer with four silver atoms constituting a parallelogram like a sandwich. The Ag―Ni, Ag―S and Ni―S bond distances were 0.31–0.32, 0.23–0.24, and 0.22–0.23 nm, respectively. XPS analyses revealed that the Ag/Ni/S atomic ratio was 5.19/2.55/10.28, consistent with the corresponding expected ratio of 4/2/8 in Ag₄Ni₂(SPhMe₂)₈. In addition, the Ag 3d_3/2 and Ag 3d_5/2 binding energy peaks were located at 375.0 and 369.0 eV, respectively, and the Ni 2p_1/2 and Ni 2p_3/2 are located at 871.50 and 853.90 eV, respectively. Moreover, combined with ESI, the Ag 3d_3/2 and Ag 3d_5/2 binding energies of Ag₄Ni₂(SPhMe₂)₈ were close to the +1 valences, according to previous reports. Meanwhile, the spectra of Ag₄Ni₂(SPhMe₂)₈ illustrated that the valence of nickel was +2. Additionally, the MALDI-TOF mass spectrum was in good agreement with the ESI results. Weight loss upon heating was used to confirm the percentage of organic material in nanoclusters (66.31% weight loss was observed in TGA, consistent with the 66.67% loss calculated according to the formula). In the liquid state, the UV-Vis spectra showed no change after exposure to oxygen for a few weeks. Meanwhile, we used UV-Vis spectroscopy at temperatures under 80 ℃ to test the stability of the Ag₄Ni₂(SPhMe₂)₈. The absorption peaks were almost identical with each other, suggesting high stability of the Ag₄Ni₂(SPhMe₂)₈. Our study proves that small-sized alloy also has the possibility of diversification, which will play an important role in the synthesis of alloy nanoclusters. Moreover, this research on Ag-Ni alloy nanoclusters will contribute to the understanding of alloys in ultra-small sizes.

Over the past two decades, bulk heterojunction polymer solar cells (PSCs) have attracted significant attention owing to their potential applications in the mass fabrication of flexible device panels by roll-to-roll printing. To improve the photovoltaic performance of PSCs, much effort has been devoted to the optimization of properties of donor-acceptor (D-A) type polymer donor materials. Until now, the development of high-performance donor polymers is mainly dependent on the design and synthesis of binary polymers with a regular D/A alternating skeleton. Compared to binary polymers, random terpolymers with three different donor or acceptor monomer units possess synergetic effects of their inherent properties, such as optical absorption ability, energy levels, crystallinity, charge mobility, and morphological compatibility with the n-OS acceptors with suitable adjustment of the molar ratio of the three monomers. However, the irregularity in the polymer backbone of the random terpolymers may have an adverse effect on molecular packing, crystallinity, and charge mobility. Therefore, design and synthesis of high-performance terpolymers for PSCs is a challenging task. In this study, a series of wide bandgap random terpolymers PSBTZ-80, PSBTZ-60, and PSBTZ-40 based on alkylthiothienyl substituted benzodithiophene as the donor unit and two weak electron-deficient acceptor units of 5, 6-difluorobenzotriazole (FBTz) and thiazolothiazole (TTz) were designed and synthesized for PSC applications. The optical, electrochemical, molecular packing, and photovoltaic properties of the polymers were effectively modulated by varying the FBTz:TTz molar ratio. Therefore, the PSC based on PSBTZ-60 as the donor material and narrow bandgap small molecule 3, 9-bis(2-methylene-(3-(1, 1-dicyanomethylene)-indanone))-5, 5, 11, 11-tetrakis(4-hexyl-phenyl)-dithieno[2, 3-d:2', 3'-d']-s-indaceno[1, 2-b:5, 6-b']di thiophene) (ITIC) as the acceptor, processed using halogen-free solvents, exhibited high power conversion efficiency (PCE) of 10.3% with high open-circuit voltage (V_oc) of 0.91 V, improved short-circuit current density (J_sc) of 18.0 mA∙cm⁻², and fill factor (FF) of 62.7%, which are superior to those of PSCs based on binary polymers PSBZ (a PCE of 8.1%, V_oc of 0.89 V, J_sc of 14.7 mA∙cm⁻², and FF of 61.5%) and PSTZ (a PCE of 8.5%, V_oc of 0.96 V, J_sc of 14.9 mA∙cm⁻², and FF of 59.1%). These results indicate that random terpolymerization is a simple and practical strategy for the development of high-performance polymer photovoltaic materials.

DNA can adopt a diverse range of structural conformations, including duplexes, triplexes, and quadruplexes. Among these structures, G-quadruplexes have attracted much more attention of researchers. For G-rich DNA sequences, they can fold into multiple G-quadruplex conformations, such as parallel, antiparallel, or hybrid, and the exact conformation is influenced by G-rich DNA sequence, strand concentration, and binding cations. Among the factors influencing the G-quadruplex conformation and stability, cations played a really important role. Numerous studies have reported cation-dependent stability and topological changes of G-quadruplexes; however, most of studies have focused on the effect of individual cation (such as charge, radii, or hydration, etc.), and only few have assessed the effect of competition between cations at different concentrations. Actually, most biological and aqueous systems contained multiple cations and each of the cations had very different concentrations. Thus, investigation of the competitions between different cations (at different concentrations) for binding with G-quadruplexes and their effects on polymorphism of G-quadruplex is critical, which would improve our understanding of the roles of G-quadruplexes and assist us in further exploring their potential applications in biochemical, biomedical, and environmental systems. Under this situation, we focused on K⁺- and Pb²⁺-stabilized G-quadruplex, two major cations that are usually used to stabilize G-quadruplex. It has been shown that for a given G-quadruplex forming DNA sequence, Pb²⁺-stabilized G-quadruplex was more stable than K⁺-stabilized G-quadruplex, and Pb²⁺ could substitute K⁺ in K⁺-stabilized G-quadruplex. However, the concentrations of K⁺ that allow such a substitution are not completely studied. Previous studies have used G-quadruplex-based fluorescent, colorimetric, and electrochemical sensors for detecting Pb²⁺, and these methods show excellent selectivity for Pb²⁺ over K⁺. Although G-quadruplex-based Pb²⁺ sensors were developed, their applications in real samples containing K⁺ were greatly limited. Thus, how K⁺ and Pb²⁺ compete for binding to G-quadruplex and how K⁺ concentrations affect the stability of Pb²⁺-stabilized G-quadruplex remain elusive. In this study, eight G-rich DNA sequences were selected to investigate the effect of K⁺ concentration on Pb²⁺-stabilized G-quadruplex. Previous studies have established that the presence of K⁺ cannot alter the stability of Pb²⁺-stabilized G-quadruplex. In contrast to this, our results indicated that K⁺ could induce a conformational switch in Pb²⁺-stabilized T2TT (G-rich DNA sequence, forming G-quadruplex in the presence of Pb²⁺), and further replace Pb²⁺ in Pb²⁺-stabilized T2TT and transform it into 2K⁺-stabilized T2TT, which is strictly K⁺ concentration-dependent. Importantly, such a conformational switch could be observed for other seven selected G-rich sequences as well. Therefore, our findings provide a new insight into the exchange and competition of cations in G-quadruplex.

Catalytic hydrogenation of CO₂ to methanol is an important chemical process owing to its contribution in alleviating the impacts of the greenhouse effect and in realizing the requirement for renewable energy sources. Owing to their excellent synergic functionalities and unique optoelectronic as well as catalytic properties, transition metal/ZnO (M/ZnO) nanocomposites have been widely used as catalysts for this reaction in recent years. Development of size-controlled synthesis of metal/oxide complexes is highly desirable. Further, because it is extremely difficult to achieve the strong-metal-support-interaction (SMSI) effect when the M/ZnO nanocomposites are prepared via physical methods, the use of chemical methods is more favorable for the fabrication of multi-component catalysts. However, because of the requirement for an extra H₂ reduction step to obtain the active metallic phase (M) and surfactants to control the size of nanoparticles, most M/ZnO nanocomposites undergo two- or multi-step synthesis, which is disadvantageous for the stable catalytic performance of the M/ZnO nanocomposites. In this work, we demonstrate facile one-pot synthesis of M/ZnO (M = Pd, Au, Ag, and Cu) nanocomposites in refluxed ethylene glycol as a solvent, without using any surfactants. During the synthesis process, Pd and ZnO species can stabilize each other from further aggregation by reducing their individual surface energies, thereby achieving size control of particles. Besides, NaHCO₃ serves as a size-control tool for Pd nanoparticles by adjusting the alkaline conditions. Ethylene glycol serves as a mild reducing agent and solvent owing to its capacity to reduce Pd ions to generate Pd crystals. The nucleation and growth of Pd particles are achieved by thermal reduction, while the ZnO nanocrystals are formed by thermal decomposition of Zn(OAc)₂. X-ray diffraction patterns of the M/ZnO and ZnO were analyzed to study the phase of the nanocomposites, and the results show that no impurity phase was detected. Transmission electron microscopy (TEM) was used to study the morphology and structural properties. In addition, X-ray photoelectron spectroscopy analysis was performed to further confirm the formation of M/ZnO hybrid materials, and the results confirm SMSI between Pd and ZnO. Inductively coupled plasma mass spectrometry was used to check the actual elemental compositions, and the results show that the detected atomic ratios of Pd/Zn were consistent with the values in the theoretical recipe. To investigate the effects of the Pd/Zn molar ratios and the added amount of NaHCO₃ on Pd size, the average sizes of Pd particles were calculated, and the results were confirmed by TEM observation. The Cu/ZnO/Al₂O₃ composite is a widely known catalyst for hydrogenation of CO₂ to methanol, and other M/ZnO composites are also catalytic for this reaction. Therefore, different M/ZnO hybrids were further studied as catalysts for hydrogenation of CO₂ to methanol, among which Pd/ZnO (1 : 9) demonstrated the best performance (30% CO₂ conversion, 69% methanol selectivity, and 421.9 g_methanol·(kg catalyst·h)^-1 at 240 ℃ and 5 MPa. The outstanding catalytic performance may be explained by the following two factors: first, Pd is a good catalyst for the dissociation of H₂ to give active H atoms, and second, SMSI between Pd and ZnO favors the formation of surface oxygen vacancies on ZnO. Moreover, most M/ZnO composites exhibit excellent performance in methanol selectivity, especially the Au/ZnO catalyst, which has the highest methanol selectivity (82%) despite having the lowest CO₂ conversion. Hopefully, this work would provide a simple route for synthesis of M/ZnO nanocomposites with clean surfaces for catalysis.

The self-assembly behavior of block copolymers and their assembled micellar morphologies have attracted considerable attention because of their potential applications in biomedicine, drug delivery, and catalysis. Herein we report that CO₂-expanded liquids (CXLs) facilitate the morphology control of the self-assembled aggregates (SAAs) of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) formed in CO₂-expanded toluene. It is found that the anti-solvent effect of CXLs can successfully regulate the self-assembly behavior of the copolymer PS-b-P4VP. The difference in amphiphilicity between PS and P4VP block is reduced with increasing pressure of CO₂-expanded toluene owing to the anti-solvent effect of CO₂. In addition, this diminished difference may influence the interfacial tension at the P4VP core-PS corona interface, which triggers a morphological change of the aggregate. The SAA structures are dependent on both CXL pressure and copolymer composition under the experimental conditions implemented in this work. The morphological evolution of the SAAs in CXLs exhibits remarkable pressure dependence. As the pressure increases, the SAA structure of PS₁₆₈-b-P4VP₄₂₀ transits from primarily spheres (0.1 MPa) to mostly interconnected rods (6.35 MPa), the SAA of PS₇₉₀-b-P4VP₂₆₃ evolves from small vesicles (0.1 MPa) to large compound vesicles (LCVs, 6.35 MPa), whereas the PS₁₅₃-b-P4VP₁₅₃₀ counterpart switches from large compound micelles (LCMs, 0.1 MPa) to mainly large compound vesicles (LCVs, 6.35 MPa). Moreover, transmission electron microscopy (TEM) data on constant copolymer composition implies that the packing parameter p of the SAAs increases with the CXLs pressure. Especially, under the experimental conditions employed in this work, we find that the major factor controlling the SAA shape in conventional toluene is the copolymer composition, while in CO₂-expanded toluene, the dominant factor controlling the SAA morphology might be the varying contact area between shell-forming segment PS and the CXLs with increasing pressure. This work proves that the CXL method facilitates the modulation of morphology of the SAAs, and opens a green route for the development of new nano-functional materials.

The development of efficient catalysts for the hydrogenation of CO₂ to formic acid (FA) or formate has attracted significant interest as it can address the increasingly severe energy crisis and environmental problems. One of the most efficient methods to transform CO₂ to FA is catalytic homogeneous hydrogenation using noble metal catalysts based on Ir, Ru, and Rh. In our previous work, we demonstrated that the activity of CO₂ hydrogenation via direct addition of hydride to CO₂ on Ir(Ⅲ) and Ru(Ⅱ) complexes was determined by the nature of the metal-hydride bond. These complexes could react with the highly stable CO₂ molecule because they contain the same distinct metal-hydride bond formed from the mixing of the sd² hybrid orbital of metal with the 1s orbital of H, and evidently, this property can be influenced by the trans ligand. Since boryl ligands exhibit a strong trans influence, we proposed that introducing such ligands may enhance the activity of the Ru―H bond by weakening it as a result of the trans influence. In this work, we designed two potential catalysts, namely, Ru-PNP-HBcat and Ru-PNP-HBpin, which were based on the Ru(PNP)(CO)H₂ (PNP = 2, 6-bis(dialkylphosphinomethyl)pyridine) complex, and computationally investigated their reactivity toward CO₂ hydrogenation. Bcat and Bpin (cat = catecholate, pin = pinacolate) are among the most popular boryl ligands in transition metal boryl complexes and have been widely applied in catalytic reactions. Our optimization results revealed that the complexes modified by boryl ligands possessed a longer Ru―H bond. Similarly, natural bond orbital (NBO) charge analysis indicated that the nucleophilic character of the hydride in Ru-PNP-HBcat and Ru-PNP-HBpin was higher as compared to that in Ru-PNP-H₂. NBO analysis of the nature of Ru―H bond indicated that these complexes also followed the law of the bonding of Ru―H bond proved in the previous works (Bull. Chem. Soc. Jpn. 2011, 84 (10), 1039; Bull. Chem. Soc. Jpn. 2016, 89 (8), 905), and the d orbital contribution of the Ru atom in Ru-PNP-HBcat and Ru-PNP-HBpin was smaller than that in Ru-PNP-H₂. Consequently, the Ru-PNP-HBcat and Ru-PNP-HBpin complexes were more active than Ru-PNP-H₂ for the direct hydride addition to CO₂ because of the lower activation energy barrier, i.e., from 29.3 kJ∙mol^-1 down to 24.7 and 23.4 kJ∙mol^-1, respectively. In order to further verify our proposed catalyst-design strategy for CO₂ hydrogenation, the free energy barriers of the complete pathway for the hydrogenation of CO₂ to formate catalyzed by complexes Ru-PNP-H₂, Ru-PNP-HBcat, and Ru-PNP-HBpin were calculated to be 76.2, 67.8, and 54.4 kJ∙mol^-1, respectively, indicating the highest activity of Ru-PNP-HBpin. Thus, the reactivity of Ru catalysts for CO₂ hydrogenation could be tailored by the strong trans influence of the boryl ligands and the nature of the Ru―H bond.

Small-sized zeolite ZSM-5 for a wide SiO₂/Al₂O₃ ratio range was prepared using a small amount of colloidal silicalite-1 as the active seeds. The thus-prepared small-sized ZSM-5 samples have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption analysis, temperature-programmed ammonium desorption (NH₃-TPD) analysis, and adsorbed pyridine infrared spectroscopy (Py-IR). The use of the active silicalite-1 seeds was effective in directing the reaction towards the formation of the MFI phase, avoiding the impure phases and reducing the crystal sizes. The prepared sample exhibited aggregated morphologies when a lower ratio of starting batch SiO₂/Al₂O₃ (SiO₂/Al₂O₃ ratio = 30) was used. The aggregates, with the size of ~500 nm, were formed with nano-sized primary crystals 50 nm in size, possessing large external surface area (84.9 m²·g⁻¹) and secondary pore volume (0.22 cm³·g⁻¹) and relatively regular mesopores. Different morphologies could be observed when the SiO₂/Al₂O₃ ratio was increased (SiO₂/Al₂O₃ ratio = 60–120). ZSM-5 with the size of 200 nm could be prepared, with the external surface area and the secondary pore volume being ~60 m²·g⁻¹ and 0.10 cm³·g⁻¹, respectively. It should be highlighted that all the prepared samples could be directly ion-exchanged to obtain the acidic H-form samples without complete blocking of the micropores due to the low dose of the organic structure-directing agent. The obtained acidic H-form samples exhibited acidic properties similar to the samples ion-exchanged after calcination and the conventional ZSM-5 possessing similar SiO₂/Al₂O₃ ratio, showing catalytic performance comparative to the catalytic conversion of methanol to olefins. Compared with conventional methods, this method largely reduced the use of organic templates and avoided the subsequent combustion before ion-exchange. The method is green and cost-effective, possessing wide potentials in the industrial processes.

In recent years, non-fullerene small molecule acceptors for organic solar cells (OSCs) have attracted much research attention. Among them, perylene diimide (PDI) and its derivatives are widely investigated due to their excellent electron mobility, high electron affinity, thermal and photochemical stability, and the feasibility with which they can be chemically modified. However, the utilization of PDIs in OSCs still lags behind that of fullerenes. This is mainly because the PDI-based acceptors possess strong π–π stacking, and therefore they are inclined to form large aggregates in bulk heterojunction (BHJ) active layers. Structural modification of PDIs by disrupting their planarity plays a vital role for the application of these novel acceptors in high-performance OSCs. In this review, progresses in PDI-based small molecule acceptors for BHJ OSCs in the past three years are summarized. This work focuses on the development of molecular structures and the optimization of the power conversion efficiency (PCE) of devices. The modifications in the molecular structures are introduced according to the active PDI reaction sites, including the bay positions, ortho positions, and imide positions, to disturb the planarity and construct twisted configurations. Modifications at the bay positions are considered to be the most common and efficient; they may form PDI multimers such as dimers, trimers, and tetramers possessing quasi-3D nonplanar structures. The progress in such modifications is discussed at length. Substitutions at the imide positions are chemically simple but less effective in changing the planarity of the molecular backbone. Nevertheless, they may alter the solubility of the molecules, the film morphology, and thereby the efficiency of the devices. Functionalization of ortho positions can also effectively improve the performance of devices, but they are synthetically difficult. For conjugated PDI molecules fused at the bay positions, the properties of exciton diffusion, charge mobility and charge separation, and thereby the device performance, may be modulated by the molecular planarity, the number of the fusing unit, and the axis direction, which in turn determine the packing modes and the extent of π-extension. In summary, the photoelectric properties of PDI-based acceptors can be adjusted via various modification methods, and the relationships between the molecular structure and photovoltaic performances should be further explored.

In recent years, Au nanoclusters have attracted much attention as new nanomaterials, which contain several to two hundred Au atoms and are protected by ligands. The structures and properties of Au nanoclusters are usually sensitive to the particle size due to quantum confinement effect. Au nanoclusters have been applied to different fields, such as optical properties, catalysis, and biology. There are two common methods for the synthesis of atomically precise Au nanoclusters: "size focusing" and "ligand exchange". Although a series of Au nanocluster have been obtained via "size focusing" and "ligand exchange", obtaining high yield of such Au nanoclusters is a challenge. Au₂₁(S-Adam)₁₅ was previously synthesized via etching Au₁₈ nanoclusters with excess thiols, and its crystal structure was determined by X-ray diffraction crystallography; however, the yield of Au nanoclusters was low. In this study, we prepared Au₂₁(S-Adam)₁₅ in high yield via conversion of Au₂₃(S-Adam)₁₆ to Au₂₁(S-Adam)₁₅. Firstly, Au₂₃(S-Adam)₁₆ nanoclusters were synthesized using adamantanethiols(HS-Adam) as the protecting ligand and HAuCl₄ as the gold resource in ethyl acetate solvent. Au₂₃(S-Adam)₁₆ were further etched with excess thiols at room temperature. After reacting for 30 min, highly pure Au₂₁(S-Adam)₁₅, with high yield of ~20% based on HAuCl₄ precursor, were successfully prepared. Au₂₃(S-Adam)₁₆ and Au₂₁(S-Adam)₁₅ were characterized by electrospray ionization (ESI), UV-Vis absorption spectroscopy, matrix-assisted laser desorption ionization (MALDI) mass spectrometry, and thermogravimetric analysis (TGA). ESI-MS and UV-Vis spectra confirm the high purity of the Au₂₃(S-Adam)₁₆. After conversion, UV-Vis spectra show the absorption peaks of Au₂₁(S-Adam)₁₅ at 700, 540, 435 and 380 nm. The MALDI-MS of Au₂₁(S-Adam)₁₅ shows several peaks at 6502, 6471, 6106, 5411, and 5048, assigned to Au₂₁(S-Adam)₁₄S, Au₂₁(S-Adam)₁₄, Au₂₀(S-Adam)₁₃, Au₁₉(S-Adam)₁₀, and Au₁₈(S-Adam)₉, respectively. The fragments of Au nanoclusters were produced by the strong laser intensity, which easily removes carbon tails from HS-Adam. Thermogravimetric analysis (TGA) was also performed to check the purity of Au₂₁(S-Adam)₁₅ nanoclusters. The TGA curve shows a weight loss of 42% (expected value, 38%). UV-Vis absorption spectroscopy was performed to track the conversion of Au₂₃(S-Adam)₁₆ to Au₂₁(S-Adam)₁₅. It was found that Au₂₃(S-Adam)₁₆ can convert to Au₂₁(S-Adam)₁₅ with a conversion efficiency of up to 97%, using excess thiols at room temperature within 30 min. In general, we successfully synthesized highly pure Au₂₁(S-Adam)₁₅ nanoclusters, with high yield of ∼20% based on HAuCl₄, by etching Au₂₃(S-Adam)₁₆ with excess thiols at room temperature.

o-Thioquinones can undergo either [2+4] or [4+2] cycloaddition reactions with acyclic dienes. To illustrate the bonding processes in these cycloadditions, the natural orbital Fukui function (NOFF) and bonding reactivity descriptor have been employed. The electrophilicity of a bond or an orbital in the o-thioquinone as well as in the acyclic diene has been found using the NOFF, which suggests that electron transfer takes place from an electron-donating bonding orbital to an electron-accepting antibonding/bonding orbital, leading to the cyclic product via the formation of a circular loop and two covalent bonds. The bonding reactivity descriptor shows that covalent bonds readily form between atom k1 of one molecule with a large f_k1⁺ value and atom k2 of another molecule with a large f_k2^- value. Both the NOFF and the bonding reactivity descriptor are efficient tools for interpreting the mechanism underlying the [2+4] and [4+2] cycloaddition between o-thioquinones and acyclic dienes.

In this study, the influence of an external electric field (EEF) on the vibrational spectra of an imidazolium-based ionic liquid, 1-ethyl-3-methylimidazolium hexfluorophosphate (EMIMPF₆), in the wavenumber range from 0 to 4000 cm⁻¹ was probed by molecular dynamics (MD) simulation at 350 K. The results showed that the experimentally obtained spectrum could be reproduced by the calculated vibrational bands (VBs) in the wavenumber range from 400 to 4000 cm⁻¹ using MD simulation without any EEF. When the EEF applied increased from 0 to 9 V·nm⁻¹, the VB intensities at 50.0 and 199.8 cm⁻¹ increased continuously and then tended to be saturated, while the VB intensities from 400 to 4000 cm⁻¹ decrease and eventually disappear. Moreover, the VB at 50.0 cm⁻¹ was red-shifted to ~16.7 cm⁻¹ and then increased to 33.3 cm⁻¹ as the EEF was increased from 0 to 2 and then to 3 V·nm⁻¹ and higher. The VB at 3396.6 cm⁻¹ was redshifted to ~16.7 cm⁻¹ and then increased to 33.3 cm⁻¹ as the EEF was increased from 0 to 3 and then to 4 V·nm⁻¹ and higher; however, the position of other VBs from 0 to 4000 cm⁻¹ remain almost unchanged. Based on further analysis of the simulation results and previously reported studies, for the VB at 50.0 cm⁻¹, the increasing EEF enhances the polarity between cations and anions; thus, the difference in dipole moment between the cations and the anions increases, which continually increases the VB intensity until saturation is reached. For the VB at 199.8 cm⁻¹, the increasing EEF intensifies the twisting of the ethyl chain, which enhances the VB intensity until saturation. For the other VBs from 400 to 4000 cm⁻¹, the increasing EEF makes the orientation of the cations and anions in EMIMPF₆ more consistent; thus, it can be conjectured that such consistent orientation may weaken the VB intensities and can even make them disappear. The redshift of VB at 50.0 cm⁻¹ may occur because the EEF breaks the distribution of the electrostatic field inside EMIMPF₆ and then weakens the interactions between cations and anions. The redshift of VB at 3396.6 cm⁻¹ may be attributed to the EEF weakening the stretching vibration of the hydrogen bonds formed between the N atoms and the acidic hydrogen atoms on the cationic imidazolium rings. The EEF does not change the positions of the other VBs because the inherent stretching, bending, and rocking vibration of functional groups are not affected by the EEF.

Nucleobases (guanine (G), adenine (A), thymine (T), cytosine (C), and uracil (U)) are important constituents of nucleic acids, which carry genetic information in all living organisms, and play vital roles in structure formation, functionalization, and biological catalytic processes. The principle of complementary base pairing is significant in the high-fidelity replication of DNA and RNA. In addition to their specific recognition, the interaction between bases and other reactants, such as metals, salts, and certain small molecules, may cause distinct effects. Specifically, the interactions between bases and certain metal atoms or ions could damage nucleic acids, inducing gene mutation and even carcinogenesis. In the meantime, nanoscale devices based on metal-DNA interactions have become the focus of research in nanotechnology. Therefore, extensive researches on the interactions between metals and bases and the corresponding mechanism are of great importance and may make improvements in the fields of both biochemistry and nanotechnology. Scanning tunneling microscopy (STM) is a powerful tool for effectively resolving nanostructures in real space and on the atomic scale under ultrahigh vacuum (UHV) conditions. Moreover, density functional theory (DFT) calculations could help elucidate the reaction pathways and their mechanisms. In this review, we summarize the distinct interactions between bases (including their derivatives) and various metal species (comprising alkali, alkaline earth, and transition metals) derived from metal sources and the corresponding salts on the Au(111) substrate reported recently based on the results obtained by a combination of above two methods. In general, bases afford N and/or O binding sites to interact with metal atoms, resulting in various motifs via coordination or electrostatic interactions, and form intermolecular hydrogen bonds to stabilize the whole system. On the basis of high-resolution STM images and DFT calculations, structural models and the possible reaction pathways are proposed, and their underlying mechanisms, which reveal the nature of the interactions, are thus obtained. Among them, we summarize the construction of G-quartet structures with different kinds of central metals like Na, K, and Ca, which are directly introduced by salts, and their relative stabilities are compared. In addition, salts can provide not only metal cations but also halogen anions in modulating the structure formation with bases. The halogen species enable the regulation of metal-organic motifs and induce phase transition by locating at specific hydrogen-rich sites. Moreover, reversible structural transformations of metal-organic nanostructures are realized owing to the intrinsic dynamic characteristic of coordination bonds, together with the coordination priority and diversity. Furthermore, the controllable scission and seamless stitching of metal-organic clusters, which contain two types of hierarchical interactions, have been successfully achieved through STM manipulations. Finally, this review offers a thorough comprehension on the interaction between bases and metals on Au(111) and provide fundamental insights into controllable fabrication of nanostructures of DNA bases. We also admit the limitation involved in detecting biological processes by on-surface model system, and speculate on future studies that would use more complicated biomolecules together with other technologies.

The Keggin type heteropolyacids (HPAs) have attracted increasing attention due to their strong Bronsted acidity and excellent redox properties, which could play an important role in accelerating the conversion of bio-derived molecules. In this work, heteropolyacid (HPA, H₄PMo₁₁VO₄₀) encapsulated by silica was synthesized by a sol-gel method and a sequential silylation technique (HPA@SiO₂-N₂-S). The as-synthesized material was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The FT-IR spectra show that the HPA anions preserved their Keggin structure when incorporated into the catalyst. The XRD patterns show that HPA molecules are uniformly dispersed within the silica network. The SEM and TEM images confirm that the catalyst was composed of spherical nanometer-sized particles. The porous properties of the catalysts measured by the N₂ adsorption-desorption isotherms indicate that the Brunauer, Emmett and Teller (BET) surface area of pure SiO₂ was 287 m²·g^-1, but upon encapsulation of HPA into the silica matrix, a lower surface area (245 m²·g^-1) was measured for the resulting material. In addition, the pore diameter was reduced after silylation. Furthermore, the hydrophobicity of the catalysts was investigated by the measurement of contact angle (CA) with water. The SiO₂ and SiO₂/HPA catalysts were completely hydrophilic and the contact angle was close to 0°. However, the contact angle of the silylated catalyst was determined to be 137°, indicating that the silylation procedure significantly increased the hydrophobicity of the catalyst. The as-prepared catalysts were also used as heterogeneous catalysts for the selective oxidation of glycerol. The prepared material exhibited excellent catalytic activity towards glycerol oxidation, in which the glycerol can be selectively transformed into formic acid (ca. 70% selectivity) and glycolic acid (ca. 27% selectivity) using H₂O₂ as an oxidant under mild reaction conditions. The effect of the silylation procedure on the recyclability of catalyst was also investigated in this work. The characterizations described above indicated that silylation procedure can significantly increase the hydrophobicity and limit the pore sizes, resulting in high leach-resistance towards HPA, thus improving the recyclability of the silica-encapsulated HPA catalyst, as compared to the SiO₂/HPA catalyst prepared with the conventional impregnation method. Furthermore, the conversion in the second catalytic run is even higher than that of the initial run, which is likely because more active sites are exposed after the first run. The catalyst can be reused for at least five cycles without any leaching of HPA. The spent catalyst did not undergo structural changes, as revealed by FT-IR, XRD, and SEM characterization. Moreover, it was found that the strong Bronsted acid additives played a crucial role in the catalytic oxidation of glycerol.

The rational design of naphthalimide derivatives, which can target specific DNA sequences and secondary structural DNA, is important for developing potential anticancer drugs. In this work, the naphthalimide-imidazole conjugate (3) and its alkylated derivatives (4a–c) were synthesized, and characterized by ¹H NMR, ¹³C NMR, and mass spectrometry (MS). The interactions of these compounds with calf thymus DNA (CT DNA) and G-quadruplex DNA were investigated by UV-Vis spectroscopy, fluorescence spectroscopy, circular dichroism, and fluorescence resonance energy transfer (FRET). The studies revealed that the naphthalimides with imidazolium displayed higher affinity towards CT DNA than those with the imidazole moiety, suggesting that the electrostatic interaction plays an important role in the interactions between the naphthalimide and the DNA duplex. All of the obtained naphthalimide derivatives possessed high affinity (K_a > 4 × 10⁶ L·mol^-1) towards the telomeric G-quadruplex, and exhibited more than 30-fold selectivity for the quadruplex versus CT DNA. The viscosity of CT DNA increased upon addition of the naphthalimides, suggesting that the latter could bind to the former via a classical intercalation mode. FRET results indicated that the compounds 3 and 4a–c stabilized the structure of the telomeric G-quadruplex by increasing its melting temperature by 5.8, 10.7, 8.4, and 7.8 ℃, respectively. CD spectral results suggested that the telomeric G-quadruplex maintained a mixture of antiparallel and parallel conformation in the presence of the naphthalimide derivatives (3 and 4a–c) in a buffer containing K⁺. The fluorescence intensity of the naphthalimide derivatives 3 and 4a, b with octylimidazolium was significantly enhanced upon interaction with the G-quadruplex, which could be attributed to the immersion of naphthalimide moieties in the hydrophobic region of the G-quadruplex. However, the fluorescence of compound 4c with hexadecylimidazolium increased only slightly upon addition of the G-quadruplex. Molecular docking studies indicated that the naphthalimide derivatives were associated with the loop and groove of the human telomeric G-quadruplex via hydrophobic interactions. A hydrogen bond was formed between the imidazole group in compound 3 and the guanine residue DG16. The phosphate group from the G-quadruplex backbone pointed to the imidazolium moiety of 4a–c, suggesting that the electrostatic interactions also played an important role. Being fluorescent, the cellular localization of 3 and 4a–c could be conveniently tracked by fluorescence imaging. The results showed that compounds 4a–c, which contained the imidazolium moiety, were mainly localized in the nucleus after 4.0 h of incubation, while compound 3 with the imidazole moiety was partially localized in the nucleus. The enhancement of the nuclear localization of 4a–c may be attributed to the positive charge in 4a–c and their higher DNA affinity. Based on the MTT assay results, it was concluded that compounds 4a–c displayed much stronger cytotoxic activity against breast cancer cells than 3. Furthermore, compounds 4a and 4b selectively inhibited the A549 cells over normal human lung fibroblast MRC-5 cells, with high anticancer activity. These results indicated that the G-quadruplex binding affinity and anticancer activity of naphthalimide could be modulated by conjugation with the imidazole moiety.

Benefitting from high-temperature operating conditions, solid oxide fuel cells (SOFCs) exhibit high electricity efficiency and can be coupled with conventional engines such as gas turbines, to achieve cascaded energy utilization. However, high temperature inevitably accelerates material deterioration, and simultaneously complicates the on-line diagnosis of SOFCs. Electrochemical impedance spectroscopy (EIS) is a mature on-line testing technology that is been widely used in SOFC research. Using EIS analyses, researchers can clearly determine the ohmic resistance of pure ion/electron conduction and the magnitude of the polarization impedance of electrochemical processes or diffusion. However, the lack of decomposition of polarization impedance constitutes a limitation for the deeper understanding of SOFC operation. To better utilize information-rich EIS, this work used a typical Ni-Y₂O₃ stabilized zirconia (Ni-YSZ) anode-supported SOFC and designed a complete set of impedance tests by modifying the test temperature, anode operating atmosphere, and cathode operating atmosphere. In addition, this study combined two advanced impedance spectrum analysis methods: the analysis of differences in impedance spectra (ADIS) and distribution of relaxation time (DRT) methods to allow for a deeper comprehension of the impedance spectrum and obtain the characteristic frequency of each process in the SOFC. Based on the characteristic frequency obtained by the spectral decomposition, this study analyzed and explained the physical or (electro-) chemical origins of the impedance in each frequency band. In addition, the equivalent circuit method (ECM) was adopted to fit the SOFC impedance spectra by 6 (RQ) parallel circuits to summarize the impedance distribution. The ADIS method was more convenient than the DRT method and could be used to initially determine the range of characteristic frequencies. However, it failed to provide a clear decomposition for the high-frequency region of the impedance spectrum. The DRT method can yield a good decomposition of a single impedance spectrum, and the characteristic frequency of Ni-YSZ SOFC was separated into ~2, ~20, ~30, 1 × 10³-1.5 × 10³, 2 × 10³-4 × 10³, and ~4 × 10⁴ Hz regions. The highest frequency (~4 × 10⁴) region was dominated by charge transfer impedance at the YSZ/GDC (gadolinia doped ceria) or LSCF/GDC interface. Peaks at 2 × 10³-4 × 10³ and 1 × 10³-1.5 × 10³ Hz correspond to the H₂ electrochemical reaction at the Ni/YSZ/H₂ boundary and O₂ reduction at the LSCF/O₂ boundary, respectively. The impedance at lower frequencies can be explained by diffusion polarization impedance. In this study, ~20 Hz corresponds to the cathode diffusion impedance, and ~30 Hz corresponds to the anode diffusion resistance. At a frequency of ~2 Hz, the impedance magnitude is influenced by both cathode and anode diffusion. The results of this study combined three methods (ADIS, DRT, and ECM) for SOFC impedance investigations, and lays a foundation for future studies regarding SOFC performance degradation and degradation characteristics based on DRT analysis.

Crystalline silver cluster compounds are highly interesting owing to their intriguing structure and potential technological application in luminescence, semiconductivity, and as precursors for nonlinear optical materials. Typically, the synthesis of silver clusters involves the use of protecting ligands such as thiolates, phosphines, and alkynes, which have been found to be critical for cluster size and shape tuning. Among these nanoclusters, pentacosanuclear silver clusters (Ag₂₅) have only been reported with either thiolate ligands or phosphine ligands, while those bearing mixed protecting ligands are rather rare. In the course of our exploration of novel silver clusters, a new silver thiolate precursor (ⁱPrC₆H₄SAg)_n was used to construct nanosized silver clusters. In the presence of 1, 3-bis(diphenyphosphino)propane (dppp) and CF₃SO₃Ag, the pentacosanuclear silver cluster [Ag₂₅(SC₆H₄Prⁱ)₁₈(dppp)₆](CF₃SO₃)₇·CH₃CN (designated as Ag₂₅, HSC₆H₄Prⁱ = 4-t-isopropylthiophenol) ligated both by thiolate and phosphine ligands was obtained under ultrasonic reaction conditions. Yellow block crystals were isolated from the solution, whose molecular structure was elucidated by single-crystal X-ray analysis. The skeleton of the Ag₂₅ cluster comprises a sandwich-like motif containing two structurally very similar cylinders sharing a metal-cluster plane. The core of each cylinder presents the overall shape of a twisted hexagonal cylinder made of two connected Ag₃S₃ units, with six sulfur atoms and six silver atoms alternating on a puckered drum-like surface. The metal-cluster plane contains one type of pure-Ag tetragons showing significant Ag…Ag argentophilic interactions. The optical properties of Ag₂₅ were investigated in the solid state. A band gap of ~2.5 eV was estimated for Ag₂₅ from the optical absorption spectrum, suggesting this cluster to be a potential wide-gap semiconductor. This Ag₂₅ cluster was also found to emit green luminescence at λ = 505 nm and room temperature.

Selective molecular permeation through two-dimensional nanopores is of great importance for nanoporous graphene membranes. In this study, we investigate the selective permeation characteristics of gas molecules through a nitrogen-and hydrogen-modified graphene nanopore using molecular dynamics simulations. We reveal the mechanisms of selective molecular permeation from the aspects of molecular size and structure, pore configuration, and interactions between gas molecules and graphene. The results show that the permeances of different molecules are different, and the following order is observed in our study: H₂O > H₂S > CO₂ > N₂ > CH₄. Molecular permeance is related to the molecular size, mass, and molecular density on the graphene surface. The molecular permeation rate is inversely proportional to the molecular mass based on gas kinetic theory, while the molecular density on the graphene surface exerts a positive effect on molecular permeation. The permeance of H₂O molecules is the highest owing to their smallest diameter, while the permeance of CH₄ molecules is the lowest owing to their biggest diameter; in these cases, the molecular size is a dominating factor. For H₂S and CO₂ molecules, the diameters of H₂S molecules are larger than those of CO₂ molecules, but the interactions between H₂S molecules and graphene are stronger, resulting in a stronger permeation ability of H₂S molecules. Between CO₂ and N₂ molecules, CO₂ molecules show higher permeation rates owing to smaller diameters and stronger interactions with graphene. The graphene surface also shows nonuniform molecular density distribution owing to molecular permeation through graphene nanopores. Because of the doped nitrogen atoms, the CH₄ molecules prefer to permeate from the left and right sides of the graphene nanopore, while the other molecules prefer to permeate from the center of the nanopore owing to their small diameters. For the molecules that show stronger interactions with graphene, the molecular density on the graphene surface is higher; accordingly, the residence time on the graphene surface is longer and the experience time period during permeation is also longer. The mechanisms identified in this study can provide theoretical guidelines for the application of graphene-based membranes. In addition, the permeance of gas molecules in the graphene nanopore adopted in this study is on the order of 10^-3 mol·s^-1·m^-2·Pa^-1, and the selectivity of other molecules relative to CH₄ molecules is also high, showing that the membranes based on this type of nanopore can be employed in natural gas processing and other separation industries.

Three kinds of novel coordination compounds [Re³⁺-C] (Re = La, Gd, Er; C = Catechin) were synthesized by the liquid-phase method, and characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV) spectrophotometry, X-ray photoelectron spectroscopy (XPS), and coordination number determination. The results indicated that the coordination number of the complexes is 8. Moreover, the antibacterial activities of Re³⁺-C against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella were evaluated by the Oxford cup, minimum inhibition concentration (MIC), and minimum bactericidal concentration (MBC) approaches. Compared with Re³⁺ and C, the as-prepared complexes exhibited excellent antimicrobial activity toward the four strains. The MIC of Gd³⁺-C to these food-borne bacteria was 1.550, 0.0968, 0.775, and 1.550 μmol·mL⁻¹, respectively, while the corresponding MBC values were 3.100, 0.194, 1.550, and 1.550 μmol·mL⁻¹. It is clear that the Gd³⁺-C complex showed the best antibacterial and germicidal activity against S. aureus.

Ni-based catalysts have been widely used in many important industrial heterogeneous processes such as hydrogenation and steam reforming owing to their sufficiently high activity yet significantly lower cost than that of alternative precious-metal-based catalysts. However, nickel catalysts are susceptible to deactivation. Understanding the adsorption and activation behavior of small molecules on the model catalyst surface is important to optimize the catalytic performance. Although many studies have been carried out in recent years, the initial oxidation process of nickel surface is still not fully understood, and the influence of the adsorption sequence of CO and O₂ and their co-adsorption is controversial. In this study, the surface oxygen species on Ni(111) and the co-adsorption of CO and O₂ were explored using high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). HREELS can provide useful information about the surface structure, surface-adsorbed species, adsorption sites, and interactions between surface oxygen species and CO on the surface. The results showed that there were two kinds of oxygen species after the oxidation of Ni(111), and the energy loss peaks at 54–58 meV were ascribed to surface chemisorbed oxygen species, and the peak at 69 meV to surface nickel oxide. The chemisorbed oxygen at low coverage displayed a LEED pattern of (2×2), revealing the formation of an ordered surface structure. As the amount of oxygen increased, the energy loss peak at 54 meV shifted to 58 meV. At an O₂ partial pressure of 1×10^-8 Torr (1 Torr = 133.32 Pa), the AES ratio of O/Ni remained almost unchanged after dosing 48 L, which indicated that the surface nickel oxide was relatively stable. The surface chemisorbed oxygen species was less stable, which could change to surface nickel oxide after annealing in vacuum. CO adsorbed on Ni(111) at room temperature with tri-hollow and a-top sites. Upon annealing in vacuum, a-top CO weakened first and then disappeared completely at 520 K, whereas tri-hollow CO was much more stable. The pre-adsorption of CO could suppress O₂ adsorption and oxidation of the Ni(111) surface. The presence of oxygen could then gradually remove and replace CO with O₂. The surface oxygen species preferred the tri-hollow sites, resulting in more a-top adsorbed CO during the co-adsorption of CO and oxygen. The surface chemisorbed oxygen species were more active and could react with CO at room temperature; however, the surface nickel oxide was less active, and could only be reduced at a higher temperature and higher partial pressure of CO.

Graphdiyne(GDY) is a novel carbon allotrope containing sp-and sp²-hybridized carbon atoms.Because of GDY's special structure, theoretical studies have predicted Li storage as dense as 744 mAh∙g⁻¹ in the form of LiC₃, representing twice the specific capacity of graphite.Previous studies have reported that GDY film, bulk GDY, N-doped graphdiyne, and similar materials exhibit high specific capacity, excellent rate performance, and long cycle life when used as anode materials in lithium ion batteries(LIBs).The flat(sp²-and sp-hybridized) carbon networks endow GDY with extensive π-conjunction and uniformly distributed pores, which allow π–π interactions between GDY and organic conjugated molecules to construct a GDY/organic conjugated molecule hybrid material for high-performance anodes with in LIBs.Anode materials with higher specific capacity, better rate performance, and longer cycle life still present an important challenge in LIBs.Nitrogen doping of GDY is one of the effective ways to improve the performance of LIBs.Nitrogen doping of GDY has been achieved by annealing at high temperature in an ammonia atmosphere.The resulting material shows enhanced electrochemical properties due to the creation of numerous heteroatomic defects and active sites.Herein, we have developed a new method based on supramolecular chemistry for preparing N-doped GDY(graphdiyne/porphine) with π–π interactions between graphdiyne and organic conjugated molecules.As opposed to previously reported graphdiyne films, the as-prepared graphdiyne/porphine film can be used as an anode for LIBs without any binders or conducting agents.The resulting anode delivers a high capacity of 1000 mAh∙g⁻¹ and exhibits excellent performance and cycle stability, suggesting that the high rate capability and long cycle life are due to the large amount of active sites provided by porphine for lithium storage.Galvanostatic measurements were performed for 5 cycles each, and retentions of 915.4, 778.9, 675.9, 553.6, and 375.2 mAh∙g⁻¹ were obtained at current densities of 100, 200, 500, 1000, and 2000 mA∙g⁻¹, respectively.When the current density was reset to 50 mA∙g⁻¹, the capacity reached 900 mA∙g⁻¹, indicating excellent structural stability during the high-rate measurements.Excellent cyclic stability with a retention of 1000 mAh∙g⁻¹ at 50 mA∙g⁻¹ after 50 cycles was obtained for LIB applications, which results from the unique hierarchical porosity due to the presence of butadiyne linkages.The unique hierarchical structure of the GDY/porphine film was not destroyed after 50 charge/discharge cycles at 50 mA∙g⁻¹, which suggested high structural stability.The competitive lithium storage values provide promising potential for the development of high-performance LIBs.This strategy opens an avenue for designing N-doped graphdiyne with tunable electronic properties under mild conditions.

Metal nanoclusters (MNCs), as a new type of nano-material, possess excellent properties such as facile synthesis, strong light stability, low toxicity, excellent biocompatibility, and high luminous efficiency. Aggregation-induced emission (AIE), which can enhance the luminescence properties of MNCs, has resulted in MNCs attracting significant attention. In this thesis, L-glutathione (GSH)-protected copper nanoclusters (GS@CuNCs) were prepared by a "one-pot" method in aqueous solution without additional reducing agents. The GS@CuNCs were characterized by UV-Vis absorption spectroscopy and fluorescence spectroscopy. Upon excitation at 370 nm, the fluorescence spectrum of GS@CuNCs displayed the maximum emission peak at 610 nm. The as-prepared CuNCs generate a striking fluorescence intensity via aggregation-induced emission (AIE). The AIE property of GS@CuNCs was examined for the aggregates in different organic solvents, such as ethanol, methanol, and dimethylformamide. Since the aggregation degree was controlled by the content of organic solvent, we further measured the fluorescence intensity of GS@CuNCs in different volume ratios of a water-ethanol mixture solution. The fluorescence intensity of GS@CuNCs exhibited an approximately 30-fold increase at 85% of ethanol content, as compared to that in aqueous solution. A possible mechanism may be that intramolecular motions are restricted in ethanol, resulting in a significant increase of fluorescence intensity. Moreover, only very weak emissions were recorded for the CuNC dispersion in aqueous solution; however, an apparent luminescence enhancement was observed in both luminescence spectra and by naked eyes under UV light, with a gradual increase in the ethanol content in the water-ethanol mixture from 0% to 85%. Additionally, we developed a new selective and sensitive turn-on fluorescent sensor for the detection of trivalent aluminum ions (Al³⁺) based on cation-induced aggregation methods. Among the 15 types of metal cations studied, only Al³⁺ visibly increased the fluorescence emission of the GS@CuNCs. These results indicated that the GS@CuNCs were highly selective to Al³⁺ than other metal ions, which may result from the electrostatic and coordination interactions between the trivalent aluminum ions and monovalent carboxylic anions from GSH in the CuNCs. The response of the probe to Al³⁺ exhibited a good linear range of 2–20 μmol·L^-1 and the detection limit was 33 nmol·L^-1. Thus, the weak fluorescence intensity of CuNCs was increased markedly by the AIE of Al³⁺, and could construct an interesting fluorescent platform for sensing aluminum ions. The property of AIE of GS@CuNCs may expand the potential applications of nanocluster materials to biosensors and cell imaging.

Carbon-based non-precious metal catalysts, represented by pyrolyzed Fe/N/C, are the most promising catalysts to replace platinum for the oxygen reduction reaction (ORR). Therefore, further improvement of their performance will be significant for commercialization of proton exchange membrane fuel cells. Unveiling the nature of active sites at the atomic scale paves the way for rational designs of Fe/N/C catalysts with high activity and durability. Herein, we review the advances in the active site structure of carbon-based non-precious metal catalysts. Three types of active sites are discussed in the order of their ORR activity, namely, iron/nitrogen-containing sites, nitrogen-containing sites, and carbon defects. In the iron/nitrogen-containing sites, some of iron atoms are amorphous and positioned in a porphyrin-like plane structure with single-iron-atom coordinated to nitrogen. Iron in porphyrin-like sites is believed to directly bind to dioxygen with electron transfer from e_g-orbitals (d_z²) of iron to antibonding orbitals of dioxygen. Factors governing the energy level of e_g-orbitals (d_z²) are certainly effected the ORR activity, including coordination number, atom type, axial ligand effect and electron-donating/withdrawing capability of the carbon matrix. The structures of porphyrin-like iron centers are described as four-coordinate FeN₄, five-coordinate N-FeN₂₊₂, O₂-FeN₄C₁₂ and Fe-N₂₊₂ bridging two graphene edges. Moreover, some highly active sites are proposed with basic N-group or defective carbon neighboring the Fe-N center. It is worth noting that surface probing is a powerful tool to identify porphyrin-like iron sites, as well as to estimate its density and turnover frequency. The prospect of surface probe is combined with spectroscopy techniques that will be tremendously helpful in providing further insights of pyrolyzed Fe/N/C. Besides the iron in porphyrin-like sites, other iron atoms are incorporated into crystalline iron nanoparticles and clusters, which are speculated to facilitate electron transfer from nitrogen-doped carbon to dioxygen. However, the role of crystalline iron remains uncertain, because conflicting experimental results are often observed when crystalline iron is removed. Nonetheless, it is undoubted that the iron doping highly boosts the ORR activity of carbon-based catalysts. The next category consists of the nitrogen-containing sites. Various models have been developed to describe the nitrogen-doping carbon catalysts. These include synthesis of planar nitrogen by the layer-by-layer space-confined method, controlled-synthesis of nitrogen on highly-oriented pyrolytic graphite, and selective graft of acetyl group on pyridinic-nitrogen. Strong evidences from models of nitrogen-doping carbon catalysts identify the ortho-carbon atom of the pyridinic ring is the reactive site. The last sites, dopant-free defective carbon, are also found to contribute to ORR. Exploring and summarizing the active sites of pyrolyzed Fe/N/C deepen our understanding of the structure-performance relationship and paves the way for new synthetic strategies. It is expected that the activity as well as stability of pyrolyzed Fe/N/C can be further improved, by exploring the active sites and the ORR mechanism.

X-ray scattering measurements were performed on 1.0 mol·dm^-3 RbCl and CsCl aqueous solutions. The X-ray structure factors were subjected to empirical potential structure refinement to extract detailed structural information on hydrated Cl^-, Rb⁺, Cs⁺, and ion association, as well as bulk water, in terms of the individual site-site pair correlation functions, coordination number distributions, and spatial density functions (three-dimensional structure). Cl^- is found to have a relatively stable six-fold coordination of water molecules with a Cl^--H₂O distance of 0.321 nm, and without a significant cation effect on its local structure. Rb⁺ is surrounded on an average by 7.3 ± 1.4 water molecules with a Rb⁺-H₂O distance of 0.297 nm, whereas 8.4 ± 1.6 water molecules hydrate Cs⁺ at a Cs⁺-H₂O distance of 0.312 nm. It is likely that Rb⁺ has a stronger hydration shell than Cs⁺, as evidenced by the presence of the second hydration shell of the former. Contact ion-pairs are partially formed in both solutions and characterized by the Rb⁺-Cl^- and Cs⁺-Cl^- distances of 0.324 nm and 0.336 nm. The solvent-separated ion pairs for both ions are discernible at around 0.6 nm. Rb⁺ has a stronger electrostatic interaction and hence a relatively stronger ion association with Cl^- than Cs⁺.

Over the past decade, significant progress has been made in theoretical and experimental research in the field of chemical reaction dynamics, moving from triatomic reactions to larger polyatomic reactions. This has challenged the theoretical and computational approaches to polyatomic reaction dynamics in two major areas: the potential energy surface and the dynamics. Highly accurate potential energy surfaces are essential for achieving accurate dynamical information in quantum dynamics calculations. The increased number of degrees of freedom in larger systems poses a significant challenge to the accurate construction of potential energy surfaces. Recently, there has been substantial progress in the development of potential energy surfaces for polyatomic reactive systems. In this article, we review the recent developments made by our group in constructing highly accurately fitted potential energy surfaces for polyatomic reactive systems, based on a neural network approach. A key advantage of the neural network approach is its more faithful representation of the ab initio points. We recently proposed a systematic procedure, based on neural network fitting, for the construction of accurate potential energy surfaces with very small root mean square errors. Based on the neural network approach, we successfully developed potential energy surfaces for polyatomic reactions in the gas phase, including the reactive systems OH₃, HOCO, and CH₅, and the dissociation of gas-phase molecules on metal surfaces, such as H₂O on the Cu(111) surface. These potential energy surfaces were fitted to an unprecedented level of accuracy, representing the most accurate potential energy surfaces calculated for these systems, and were rigorously tested using quantum dynamics calculations. The quantum dynamics calculations based on these potential energy surfaces produce accurate results, which are in good agreement with experiments. We have also proposed a new method for developing permutationally invariant potential energy surfaces, named fundamental-invariant neural networks. Mathematically, fundamental invariants are used to finitely generate the permutation-invariant polynomial ring; thus, fundamental-invariant neural networks can approximate any function to arbitrary accuracy. The use of fundamental invariants minimizes the size of the input permutation-invariant polynomials, which reduces the evaluation time for potential energy calculations, especially for polyatomic systems. Potential energy surfaces for OH₃ and CH₄ were constructed using fundamental-invariant neural networks, with their accuracies confirmed by full-dimensional quantum dynamics and bound-state calculations. These developments in the construction of highly accurate potential energy surfaces are expected to extend the theoretical study of reaction dynamics to larger and more complex systems.

In the last few decades, noble metal nanoparticles (MNP) have been widely used as imaging probes, in the field of bio-imaging, due to their localized surface plasmon resonance (LSPR) phenomenon. Compared to fluorescent probes, MNP imaging exhibits high sensitivity and outstanding signal-to-noise ratio, while the particle itself has good photostability; this makes the MNP probe the perfect candidate for long-term imaging. Currently the most popular MNP imaging and analysis method employs a dark-field microscope with a spectroscope. Since most dark-field microscopes use halogen lamp or mercury lamp as their illumination source, the illumination intensity and wavelength spectrum are limited. Both camera and spectroscopy require longer exposure time to collect sufficient scattering signal to generate a reasonable quality image and scattering spectrum. The narrow illumination spectrum also limits the size of the MNP that can be used (larger-diameter MNP tend to scatter in the near-infrared region). Therefore, a high-intensity and wide-spectrum illumination source is urgently needed in MNP imaging. In this study, we custom-designed a multi-mode dark field microscope by using a supercontinuum laser, comprising of a lightsheet illumination mode for wide-field imaging and a back focus mode for live spectrum analysis, as its illumination source. The total output of the supercontinuum laser was 2 W. Since it was a coherent illumination source it could be focused by the microscope objective to a near diffraction limit area for sufficient intensity. Moreover, since its wavelength spectrum was between 450 nm and 2200 nm, which covered most of the visible and near infrared region, it made the detection of the large-diameter MNP single particle possible. In the back-focus mode, the supercontinuum laser first passed through an annular filter and then entered the objective from the microscope back port. In the lightsheet illumination mode, the laser was focused by a 400-mm cylindrical concave mirror to create a "sheet" and illuminate the sample from its side. In both the illumination modes, the illumination radiation was blocked from the camera to obtain the dark field illumination effect. By using a multi-mode dark field microscope, we could observe a 30-nm-diameter MNP single particle with a color CCD camera in its lightsheet illumination mode and a spectrum time resolution of 1 ms in its back-focus illumination mode. This custom-designed microscope could not only be used to study the MNP single particle in living cells, but more importantly, its application could also be potentially extended to all the MNP-probe-based cell imaging.

The average diameter and size distribution of dispersed-phase droplets are important factors affecting the properties of emulsions, and the changes in these parameters with time and environment can be used to evaluate the emulsion stability. Traditional size characterization methods such as dynamic light scattering (DLS) are not applicable to highly concentrated emulsions. Herein, we report an imaging-based method to measure the droplet size in highly concentrated emulsions. This method comprises three steps: 1) emulsions are labeled with a fluorescent dye, 2) three optical slices with a certain distance between two adjacent focal plans are measured sequentially via confocal laser scanning microscopy, 3) the sizes of dispersed-phase droplets are determined from the apparent diameters of droplets in the optical slices. When the apparent diameter of a droplet in the three optical slices increases or decreases monotonically, droplet diameter is calculated according to the following equations: D_C1–2 = {D₂² +[(D₁² − D₂²)/4δ_z + δ_z]²}^1/2 or D_C2–3 = {D₃² + [(D₂² – D₃²)/4δ_z + δ_z]²}^1/2, where D₁, D₂, D₃ is the apparent diameter of the droplet measured from the consecutively-obtained optical slices 1−3, respectively; D_C1–2 represents the calculated diameter of the droplet from the slices 1 and 2, and D_C2–3 is that from the slices 2 and 3, and δ_z is the distance between two focal planes of the adjacent optical slices. To avoid an obvious interference from the droplet movement, we use the equation 2|D_C1–2− D_C2–3|/(D_C1–2 + D_C2–3) = X, where a smaller X value indicates a less extent of movement during measurement, and that the calculated average diameter (D_C1–2 + D_C2–3)/2 is closer to the measured size of the droplet. The experimental results showed that when X was 15%, the difference between the calculated and measured diameters was about 10%. When X was less than 15%, the calculated average droplet diameter was adopted as an effective diameter. However, when the condition D₁= D₂ ≥ D₃ (or D₃ = D₂≥ D₁) was met, D₂ was used as the effective droplet diameter. The present method combines the advantages of fluorescent labeling, double optical slices analysis, and a strategy for eliminating the error caused by droplet movement. The stability of highly concentrated emulsions (oil volume percentage: 60%−80%), prepared by mixing a crude oil model mixture containing n-decane, naphthaline, decalin, and tetraphenylporphyrin (92.3%, 4.1%, 3.6%, and 0.1‰ by mass, respectively) with aqueous solutions containing surfactants, was studied with the proposed method. The experimental results indicated that the present method allowed for the effective and accurate measurement of the anti-coalescence stability of emulsion dispersed-phase droplets. In contrast, the widely adopted "bottle test" method could not provide accurate information on the anti-coalescence stability of the dispersed phase droplets.

Perovskite CH₃NH₃PbI₃ is an ionic crystal with suitable band gap and conductivity for optoelectronic applications. The sensitivity of the CH₃NH₃PbI₃ crystal and its derivatives to chemical composition, film-forming process, and even moisture lead to difficulties in evaluating its electronic structure and redox behavior using electrochemical techniques. Nevertheless, full understanding of the electrochemical behavior of the perovskite crystal is certainly beneficial for tuning its redox properties and chemical stability, especially for device fabrication. We show that the band structure of CH₃NH₃PbI₃ can be successfully evaluated based on electrochemical square wave voltammetry. The energy level of the bottom of the conduction band of the perovskite crystal was determined directly from the onset reduction potential with reference to the onset oxidation potential of ferrocene, and estimated to be −3.56 eV; the top of the valence band, at –5.07 eV, was determined indirectly after taking into consideration the bandgap, because the oxidation current of the iodide ions shields that corresponding to the valence band of the CH₃NH₃PbI₃ crystal. The overlap of the oxidation currents from the iodide ions and the valence band of the crystal suggests that there are excess iodide ions in CH₃NH₃PbI₃ not involved in the development of the valence band. In addition, the alternating current (AC) impedance spectra of CH₃NH₃PbI₃ indicate that the iodide ions are not completely immobilized. These imply that the defects in the crystal are related to the iodide ions to a large extent. The electrochemistry of CH₃NH₃PbI₃ in an organic electrolyte reveals its coupling degradation during the redox processes in square wave and cyclic voltammetry. The degradation reactions result from the reduction of lead ions and oxidation of iodide ions in the perovskite crystal. In electrochemical reduction, along with the reduction that occurs in the conduction band, the lead ions in the crystal are reduced to metallic lead, which introduces a phase change in the crystal, as revealed in cyclic voltammetry; the metallic lead can be re-oxidized electrochemically. In the case of electrochemical oxidation, the iodide ions, as well as the valence band of CH₃NH₃PbI₃, lose electrons. The electrochemically generated iodine diffuses into the organic electrolyte gradually, which results in the loss of iodide ions in the crystal. Such loss of iodide ions continues during the cyclic redox reaction. Apparently, the electrochemical investigations on perovskite CH₃NH₃PbI₃ show that the crystal is extremely reactive during the redox process; attention should be paid on controlling the excess iodide ions and the irreversible phase change resulting from the oxidation of lead ions.

In the past decade, fossil fuel resources have been exploited and utilized extensively, which could lead to increasing environmental crises, like greenhouse effect, water pollution, etc. Accordingly, many coping strategies have been put forward, such as water electrolysis, metal-air batteries, fuel cell, etc. Among the strategies mentioned above, water electrolysis is one of the most promising. Water splitting, which can achieve sustainable hydrogen production, is a favorable strategy due to the abundance of water resources. Splitting of water includes two half reactions integral to its operation: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, its practical application is mainly impeded by the sluggish anode reaction. Simultaneously, noble metal oxides (IrO₂ and RuO₂) and Pt-based catalysts have been recognized as typical OER catalysts; however, the scarcity of noble metals greatly limits their development. Hence, designing an alternative electrocatalyst plays a vital role in the development of OER. However, exploring a highly active electrocatalyst for OER is still difficult. Herein, a miraculous construction of a tree-like array of NiS/Ni₃S₂ heterostructure, which is directly grown on Ni foam substrate, is synthesized via one-step hydrothermal process. Since NiS and Ni₃S₂ have shown great OER performance in previous investigations, this novel NiS-Ni₃S₂/Nikel foam (NF) heterostructure array has tremendous potential as a practical OER catalyst. Upon application in OER, the NiS-Ni₃S₂/NF heterostructure array catalyst exhibits excellent activity and stability. More specifically, this novel tree-like NiS-Ni₃S₂ heterostructure array shows extremely low overpotential (269 mV to achieve a current density of 10 mA·cm^-2) and small Tafel slope for OER. It also shows extraordinary stability in alkaline electrolytes. Compared with the Ni₃S₂ nanorods array, the NiS-Ni₃S₂ heterostructure array has a synergistic effect that can improve the OER performance. Due to the secondary structure (Ni₃S₂ nanosheets), the tree-like NiS-Ni₃S₂ array provides more active sites could have higher specific surface area. The greater activity of the NiS/Ni₃S₂ heterostructure may also stem from the tight conjunction between tree-like NiS/Ni₃S₂ and the Ni foam substrate, which is beneficial for electronic transmission. Hydroxy groups can accumulate in large amounts on the surface of the tree-like array, and it also generates some Ni-based oxides that are favorable to OER. Moreover, the synergistic effect of such heterostructure can intrinsically improve the OER activity. The unique tree-like NiS-Ni₃S₂ heterostructure array has great potential as an alternative OER electrocatalyst.

In the past decade, gold nanoclusters of atomic precision have been demonstrated as novel and promising materials for potential applications in catalysis and biotechnology because of their optical properties and photovoltaics. The Au₃₆(SR)₂₄ nanocluster is one of the most well-known clusters, which is directly converted from the Au₃₈(SR)₂₄ cluster through a "ligand-exchange" process. It consists of an Au₂₈ kernel with a truncated face-centered cubic (FCC) framework exposing the (111) and (100) facets. Here we report a simple protocol to prepare Au₃₆(SR)₂₄ nanoclusters, ligated by aliphatic and aromatic thiolate ligands (SR = SPh, SC₆H₄CH₃, SCH(CH₃)Ph, and SC₁₀H₇) via a "size-focusing" process. First, polydisperse Au nanoparticles were synthesized and isolated, and then reacted under harsh conditions in the presence of excess thiol ligands at relatively high etching temperatures (80 ℃). The as-synthesized Au₃₆(SR)₂₄ nanoclusters were characterized and analyzed by UV-Vis absorption spectroscopy, electrospray ionization (ESI), and matrix-assisted laser desorption ionization (MALDI) mass spectrometry, as well as thermogravimetric analysis (TGA). All the Au₃₆(SR)₂₄ nanoclusters showed two step-like optical absorption peaks at ~370 and 580 nm in the UV-vis spectra. Only one strong set of nanocluster-ion peaks centered at an m/z of 10517.0 was observed in the ESI mass spectrum of the Au₃₆(SCH(CH₃)Ph)₂₄ nanocluster. This could be assigned to the [Au₃₆(SCH(CH₃)Ph)₂₄Cs]⁺ species, and was a strong indicator of the high purity of the as-obtained Au₃₆ cluster samples produced on a small scale. The TGA profile showed 31.67% organic weight loss of the nanocluster, matching well with the expected theoretical value of 31.71%. The Au-SR bond in the gold nanoclusters was broken at ~180 ℃ in a normal air atmosphere. Fragments of the Au₃₆(SR)₂₄ clusters capped with different thiolate ligands, which were mainly caused by the strong laser intensity during the analysis, were detected in the MALDI mass spectra. This interesting phenomenon was also observed in the case of Au₂₅(SR)₁₈, and could be due to the inherent properties of the Au-SR bond on the surface of the gold nanoclusters. Finally, the optical properties of the Au₃₆(SR)₂₄ nanoclusters were found to be influenced by the capping thiolate ligands. Compared to the UV-Vis spectrum of the Au₃₆(SCH(CH₃)Ph)₂₄ cluster, the optical spectra of the other three Au₃₆ clusters were red-shifted (~3 nm for Au₃₆(SPh)₂₄, 5 nm for Au₃₆(SC₆H₄CH₃)₂₄, and 13 nm for the (Au₃₆(SNap)₂₄ clusters). This shift could be explained by the electron transfer occurring from the electron-rich aromatic ligands to the Au kernel. The electron transfer capacity followed the order ―SNap > ―SC₆H₄CH₃ > ―SPh > ―SCH(CH₃)Ph. Overall, this study demonstrates the effectiveness and promising application of ligand engineering for tailoring the electronic properties of Au nanoclusters.

The hole injection layer (HIL) plays a significant role in determining the performances of organic light-emitting diodes (OLEDs), especially when hole transport materials with deep highest occupied molecular orbital levels (HOMOs) are employed. Intensive efforts have been devoted to exploring novel hole injection materials with good solution-processing abilities in recent years. In this study, the solution-processed molybdenum trioxide (s-MoO₃) is prepared via an ultra-facile method. Three different s-MoO₃ layers prepared by three different methods, viz. layers annealed at 150 ℃ (s-MoO₃ (150)), layers annealed at 150 ℃ and then processed in UV-ozone for 15 min (s-MoO₃ (150, UVO)), and layers processed in UV-ozone for 15 min without annealing (s-MoO₃ (UVO)), are obtained to investigate their influences on hole injection. The device with the s-MoO₃ (150) layer has the lowest current density and the largest driving voltage, showing poor hole injection ability. In contrast, with the s-MoO₃ (150, UVO) layer as HIL, the OLED produces a greatly enhanced current and sharply reduced driving voltage, comparable to the device using vacuum-evaporated MoO₃. Similar results are obtained for the device with the s-MoO₃ (UVO) film, suggesting that high-temperature annealing is not essential for the s-MoO₃ film with UV-ozone treatment. Hole injection efficiencies of MoO₃ films are quantitatively characterized by analyzing the space-charge-limited current of hole-only devices; the hole injection efficiencies of s-MoO₃ (150, UVO) and s-MoO₃ (UVO)-based devices are ~0.1, far exceeding that of the s-MoO₃ (150)-based device (10⁻⁵). XPS analysis is performed to detect the impact of the above treatments on the surface electronic properties of the s-MoO₃ films. A typical characteristic of Mo⁵⁺ species is obtained for the s-MoO₃ (150) film and a high-binding-energy shoulder appears in the O 1s peak of the s-MoO₃ (150) film, indicating the existence of oxygen vacancies and oxygen adsorbed at the surface of s-MoO₃ (150) film. When UV-ozone treatment is applied to this s-MoO₃ (150) film, it produces a decrease of Mo⁵⁺ state and elimination of oxygen-rich adsorbates, resulting in MoO₃ stoichiometry similar to that of the vacuum-evaporated MoO₃ film. Consequently, a maximum current efficiency of 48.3 cd∙A⁻¹ is realized with the optimized UV-ozone treated s-MoO₃ HIL. It This UV-ozone treated s-MoO₃ should have widespread applications in low-cost solution-processed OLEDs as an excellent hole injection layer.

Organic dyes, especially the harmful cationic dye methyl orange (MO), are emerging pollutants. The development of new materials for their efficient adsorption and removal is thus of great significance. Porous organic polymers (POPs) such as hyper-cross-linked polymers, covalent organic frameworks, conjugated microporous polymers, and polymers with intrinsic microporosity are a new class of materials constructed from organic molecular building blocks. To design POPs both with good porosity and task-specific functionalization is still a critical challenge. In this study, we have demonstrated a simple one-step method for the synthesis of the hyper-cross-linked aromatic triazine porous polymer (HAPP) via the Friedel-Crafts reaction. The resultant porous polymer was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, elemental analysis (EA), thermo-gravimetric analysis (TGA), solid-state ¹³C nuclear magnetic resonance (¹³C NMR), and nitrogen adsorption-desorption isotherms. The results show that HAPP is a rough, irregular morphology, porous organic polymer that is amorphous in nature. The novel polymer showed high Brunauer-Emmett-Teller surface area (of up to 104.36 m²∙g⁻¹), porosity, and physicochemical stability. Owing to the presence of N heteroatom pore surfaces in the network, the material exhibited a maximum adsorption capacity of 249.3 mg∙g⁻¹ for MO from aqueous solutions at room temperature. This is higher than that of some reported porous materials under the same conditions. To explain this phenomenon more clearly, theoretical quantum calculations were performed via the DFT method using Gaussian 09 software and Multiwfn version 3.4.1. It is performed to analyze the properties and electrostatic potential (ESP) of the HAPP monomer and MO. The results indicated that the N heteroatom of HAPP can easily develop strong interactions with MO, supporting the efficient adsorption of MO. The parameters studied include the physical and chemical properties of adsorption, pH, contact time, and initial concentrations. The percentage of MO removal increased as the pH was increased from 2 to 4. The optimum pH required for maximum adsorption was found to be 5.6. Adsorption kinetics data were modeled using the pseudo-first-order and pseudo-second-order models. The results indicate that the second-order model best describes the kinetic adsorption data. The adsorption isotherms revealed a good fit with the Langmuir model. More importantly, the HAPP can be regenerated effectively and recycled at least five times without significant loss of adsorption capacity. Therefore, it is believed that HAPPs with hierarchical porous structures, high surface areas, and physicochemical stability are promising candidates for the purification and treatment of dyes in solution.

The Hofmeister ion effect is a very interesting but elusive phenomenon, the importance of which is revealed in self-assembly, ion recognition, and protein folding regulation. With an increasing number of studies suggesting that interactions between ions and solutes play a role in the Hofmeister ion effect, the nature of the Hofmeister phenomenon becomes more debatable. Yet, it is not clear whether the Hofmeister ion effect is a local effect or bulk effect that can reach beyond many hydration shells, where specific interactions between ions and solutes play key roles. In order to further explore this, we applied proton nuclear magnetic resonance (¹H-NMR) spectroscopy to study the effects of specific ions on the local environment around N, N-dimethylpropionamide (NDA) and N-isopropylisobutyramide (NPA), which are the model compounds for poly(2-ethyl-2-oxazoline) and poly(N-isopropylacrylamide), respectively. These polymers are important bio-engineering materials that possess thermoresponsive properties and are also subject to specific ion effects. By correlating the changes in chemical shifts of the two methyl groups on either side of the amide bond, it was found that the Hofmeister ion effects on NPA were more anisotropic than on NDA, and that the cationic effects were more anisotropic than the anionic effects on NPA. These results indicated that the effects of specific ions were almost identical for all methyl groups of NDA. On the other hand, NPA is a larger molecule; thus, not all of its methyl groups were subjected to the specific ion effects to the same extent. The calculation of the electrostatic potential surfaces of NDA and NPA suggested that these observations on the Hofmeister ion effects might be due to steric hindrance, and that the observations on the cationic effects might be due to the interactions between cations and NPA being stronger than the interactions between anions and NPA. This would explain why the highly charged cations caused a significant anisotropicity. Additionally, we found that the chemical shift of the water protons (Δδ_H2O) of conventional kosmotropic anions was larger than zero, which suggested a stronger HB and more charge transfer between water and these anions. The Δδ_H2O of conventional chaotropic anions was less than zero. Despite the different solutes, the results were indifferent in both NDA and NPA solutions. Surprisingly, the Δδ_H2O of Cl^- at concentrations lower than 1 mol∙L^-1 was zero, thus becoming the benchmark between chaotropes and kosmotropes. These results suggested a quantitative measurement of kosmotropicity/chaotropicity, where the anion would be kosmotropic if its Δδ_H2O were higher than that of Cl^- and chaotropic for the opposing condition. Moreover, the results showed that the effects of the cations on the water structure were minimal, which was consistent with minimal charge transfer between the cations and water. The overall results of this study suggest that the Hofmeister ion effect is a global effect, while local interactions of ions with solutes also play a key role.

In modern advanced internal combustion engines such as homogeneous compression ignition engine (HCCI) and reactivity controlled compression ignition engine (RCCI), turbulence/chemistry interactions have a dramatic influence on the combustion efficiency. In particular, the low-temperature fuel chemistry and two-stage ignition of large hydrocarbon fuels can significantly affect the turbulent flame regimes and propagation. The turbulent flame propagation and flame structure of a turbulent premixed n-heptane/air flame is simulated in a slot, i.e., reactor-assisted turbulent slot (RATS) burner. In the center, a premixed n-heptane/air gas mixture flows out from the burner, exiting into the surrounding atmosphere. In order to maintain a high Reynolds number for the flame, a pilot flame consisting of stoichiometric methane/air is applied. The GRI3.0 mechanism for methane/air mixture is adopted. A three-dimensional (3D) numerical simulation model is established based on OpenFOAM reactingFoam solver. A reduced kinetic mechanism of n-heptane consisting of 44 species and 112 reactions is employed, which is validated against the detailed mechanism with regard to the ignition delay time over a wide range of the initial temperature, equivalence ratio, and pressure. Then, the effects of the reactant temperature (ranging from 450 to 700 K), inlet velocity (6 m·s⁻¹ and 10 m·s⁻¹), and pre-flame flow residence time (100 ms and 60 ms) on the turbulent flame combustion of the n-heptane/air mixture with an equivalent ratio of 0.6, are investigated by performing 3D simulations. Twelve cases are considered and analyzed based on the flow residence time and ignition delay time. The 2D span-wise temperature contour is used to show that when the ignition Da number and fuel reactivity increase, the flame temperature increases and the flame height decreases, indicating a stronger turbulent burning velocity (S_T). The results coincide well with experiment results and indicate that the extent of fuel oxidation is affected by the reactant temperature and inlet velocity during the low-temperature ignition stage, since the ratio between the ignition delay time and flow residence time plays an important role. Moreover, a quantitative analysis is performed on the flame front. The intermediate species CH is used to mark the thin reaction zone, and the turbulent burning velocity is obtained. Two branches of turbulent burning velocities verified the upper and lower limits and are consistent with the fitting correlation of S_T/S_L from a previous semi-implicit expression by Won et al. (2014), in which S_L is laminar burning velocity. In the upper limit, the fuel decomposes and produces a large amount of intermediate species like CH₂O in the pre-heat zone, which subsequently increases the turbulent burning velocity. While in the lower limit in which the flow residence time is shorter than the first ignition delay time, it shows a smaller turbulent burning velocity and a thin reaction zone, which is in chemically-frozen-flow regime. A transitional regime between the low- to high-temperature ignition regimes is also identified, where the ignition delay time is comparable with the heated flow residence time before the flame was produced. With an increase in the reactant temperature, the turbulent flame gradually changes from the chemically frozen flow regime to the low-temperature ignition regime. When the temperature is higher than a certain value, the low-temperature ignition will not happen again and the flame will be classified as being in the high-temperature ignition regime.

Ethylene carbonate (EC) liquid and its vapor-liquid interface were investigated using a combination of molecular dynamics (MD) simulation and vibrational IR, Raman and sum frequency generation (SFG) spectroscopies. The MD simulation was performed with a flexible and polarizable model of the EC molecule newly developed for the computation of vibrational spectra. The internal vibration of the model was described on the basis of the harmonic couplings of vibrational modes, including the anharmonicity and Fermi resonance coupling of C＝O stretching. The polarizable model was represented by the charge response kernel (CRK), which is based on ab initio molecular orbital calculations and can be readily applied to other systems. The flexible and polarizable model can also accurately reproduce the structural and thermodynamic properties of EC liquid. Meanwhile, a comprehensive set of vibrational spectra of EC liquid, including the IR and Raman spectra of the bulk liquid as well as the SFG spectra of the liquid interface, were experimentally measured and reported. The set of experimental vibrational spectra provided valuable information for validating the model, and the MD simulation using the model comprehensively elucidates the observed vibrational IR, Raman, and SFG spectra of EC liquid. Further MD analysis of the interface region revealed that EC molecules tend to orientate themselves with the C＝O bond parallel to the interface. The MD simulation explains the positive Im[$ \chi ^{(2)}$](ssp) band of the C＝O stretching region in the SFG spectrum in terms of the preferential orientation of EC molecules at the interface. This work also elucidates the distinct lineshapes of the C＝O stretching band in the IR, Raman, and SFG spectra. The lineshapes of the C＝O band are split by the Fermi resonance of the C＝O fundamental and the overtone of skeletal stretching. The Fermi resonance of C＝O stretching was fully analyzed using the empirical potential parameter shift analysis (EPSA) method. The apparently different lineshapes of the C＝O stretching band in the IR, Raman, and SFG spectra were attributed to the frequency shift of the C＝O fundamental in different solvation environments in the bulk liquid and at the interface. This work proposes a systematic procedure for investigating the interface structure and SFG spectra, including general modeling procedure based on ab initio calculations, validation of the model using available experimental data, and simultaneous analysis of molecular orientation and SFG spectra through MD trajectories. The proposed procedure provides microscopic information on the EC interface in this study, and can be further applied to investigate other interface systems, such as liquid-liquid and solid-liquid interfaces.

Recently, non-fullerene small molecular acceptors (NFSMAs) have received great attention because of their broad and strong absorption spectra and stable active layer morphology when compared with traditional fullerene acceptors. The most widely used strategy to design NFSMAs is through A-D-A type molecules, in which an electron-rich core unit (D) is flanked by two electron-deficient units (A). In order to fine-tune the absorption spectra, energy levels, and photovoltaic properties of NFSMAs, great efforts have been made to modify the conjugated backbone of A-D-A type molecule acceptors. In a previous work, we developed a small molecular electron acceptor, namely MBN-Ph, with an A-D-A structure and an organoboron core unit. MBN-Ph exhibited distinctive absorption spectra with two absorption bands in short- and long-wavelength regions. It is known that side chains or substituents on small molecular electron acceptors can also play an important role in the molecular properties and photovoltaic performance of bulk heterojunction organic solar cells (OSCs). In this work, we report an A-D-A type organoboron compound (MBN-Th) bearing a thienyl substituent on the boron atom, which can be used as an electron acceptor for OSCs. The lowest unoccupied molecular orbital (LUMO) of MBN-Th delocalized on the entire backbone, while the highest occupied molecular orbital (HOMO) localized on the core unit. The unique electronic structure of MBN-Th resulted in two strong absorption peaks at 490 and 726 nm, which indicate a wide absorption spectrum and superior sunlight harvesting capability. Compared with the phenyl substituent, the thienyl group led to an unchanged LUMO energy level, low-lying HOMO energy level by 0.1 eV, and blue-shifted absorption spectrum by 20 nm. OSCs with MBN-Th as an electron acceptor showed a power conversion efficiency of 4.21% and a wide photoresponse from 300 to 850 nm. Our results indicate that the substitution of the boron atom with a thienyl group is an effective strategy to tune the electronic structure of organoboron compounds for applications as electron acceptors in OSCs.