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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

It is a widespread concern that the extensive use of antibiotics has caused not only harm to the human body but also heavy environmental pollution. Because of its high efficiency and universal applicability, adsorption technology has significant application potential for the removal of antibiotics. The development of new adsorbents is critical for high-efficiency adsorption treatment. In recent years, the excellent physical, chemical, and adsorption properties of graphene have made it an important antibiotic adsorbent. The high specific surface area and large number of pores of graphene provide many adsorption sites for antibiotics. In addition, the conjugated structure makes graphene relatively electronegative, which also affects adsorption. Due to the limitations of graphene and the increasing requirements for efficiency and stability of graphene adsorbents, a variety of graphene-based adsorbents have been developed to solve the issues of graphene agglomeration in aqueous solutions, poor graphene dispersibility, and poor adsorption performance. Thus far, there has not been a systematic review on the design, synthesis, and adsorption mechanism of graphene-based composites for the removal of antibiotics in aqueous solutions. The design and preparation methods for magnetic graphene adsorbents, polymer/graphene adsorbents, three-dimensional graphene gels, graphene/biochar adsorbents, and graphene-based adsorbents for catalytic degradation of antibiotics are also reviewed. We show the synthesis and design concepts of various graphene-based adsorbents, as well as their different physical and chemical properties and adsorption performance, so that we can distinguish and select different graphene-based adsorbents. We also discuss the design of adsorbents for different kinds of antibiotic contaminants to provide guidance to future researchers for choosing the appropriate design methods based on the antibiotic type. These graphene-based adsorbents can also be extended to the adsorption of various pollutants, which is of great significance for environmental protection. The main adsorption mechanism of antibiotics on graphene-based adsorbents in aqueous solutions is expounded. The cyclic structure of graphene determines the interaction between graphene and antibiotics, such as π–π and cation–π interactions. The numerous oxygen-containing functional groups on the surface of graphene oxide (GO) provide more possibilities for the design of graphene composites. Finally, the future development of graphene-based adsorbents for the removal of antibiotics in aqueous solutions is discussed. We recommend the design of highly-efficient, broad-spectrum, and selective adsorbents for high adsorption performance for multiple antibiotic contaminants in the environment. We also address the regeneration and disposal of graphene-based sorbents and promote green, harmless, and resource-based disposal.

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.

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.

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.

Since the rediscovery of black phosphorus as a fascinating two-dimensional material, other two-dimensional materials comprising group V_A elements have attracted tremendous interest, such as antimonene. Since 2015, besides intensive research efforts on the atomic structures, electronic properties and synthesis methods of antimonene, scientists have conducted applied researches on semiconductor and nonlinear optical devices, molecular adsorption and thermoelectric applications based on antimonene. In addition, antimonene quantum dots (SbQDs) as derivatives of antimonene, have also been studied recently, and their potential applications in photothermal therapy have been reported. To further explore the unique properties and potential applicationsof SbQDs, it is important tosynthesize large amounts of high-quality SbQDs. In this work, antimonene samples were prepared by sonication-assisted liquid exfoliation method. Antimony powders (200 mg) were dispersed in 200 mL water, C₂H₅OH and 1-methyl-2-pyrrolidone (NMP) solvents separately and sonicated for 10 h at a power of 180 W. Thereafter, the suspensions were centrifuged at 6000 r∙min^-1 for 20 min, and the supernatant containing antimonene samples were decanted and characterized. The dispersion concentration of antimonene samples in the three solvents (water, C₂H₅OH and NMP) were measured as 0.57, 1.04, and 4.27 µg∙mL^-1, respectively. However, the antimonene concentrations in water, C₂H₅OH and NMP dropped by 73.7%, 30.8% and 10.5%, respectively, after standing for 96 h. Thus, antimonene dispersed in NMP demonstrated the highest concentration and best stability, which indicates that NMP is more suitable for antimonene exfoliation. Furthermore, transmission electron microscopy (TEM) studies revealed that only the samples prepared in NMP were morphologically quantum dots, while antimonene samples obtained in the other two solvents were mainly nanosheets. The obtained SbQDs in NMP had a lateral size of approximately 3.0 nm. High-resolution transmission electron microscope (HRTEM) also confirmed the good crystal quality of theobtained SbQDs. In addition, we measured the turbidities of antimonene dispersed in those three solvents at various concentrations. As theoretically predicted, the turbidity of antimonne dispersions linearly depends on the concentraion; thus, the antimonene concentrations can be calculated by measuring the turbidity through an optical method. Thus, this study provides a high-throughput, nondestructive method for determining antimonene dispersion concentration, which will faciliate further research in this area.

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.

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.

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.

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.

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.

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.

Morin is a natural flavonoid compound extracted from the bark of mulberry, orange, and other fruit trees. Serum albumin (SA) is the most abundant carrier protein in animal plasma, as well as the most common soluble protein in the circulatory system. The study of the binding behavior of Morin and the characteristics of the binding of Morin to SA would help in further elucidating its transport process and mechanism of action in vivo at the molecular level. Herein, the thermodynamics of the interaction between bovine serum albumin (BSA) and Morin was investigated by fluorescence, UV-Vis absorbance, CD, and molecular modeling under physiological conditions. The quenching constants (K_SV) decreased as the temperature increased, indicating that the fluorescence quenching of BSA by Morin was a static process. The static quenching mechanism was further supported by the measurement of the UV-vis spectra of the BSA-Morin system. Based on the van't Hoff equation, the ΔH^Ɵ, ΔS^Ɵ, and ΔG^Ɵ were calculated to be around −81.20 kJ·mol⁻¹, −181.01 J·mol⁻¹·K⁻¹, and −27.19 kJ·mol⁻¹, respectively. The negative ΔG^Ɵ value indicated that the interaction between Morin and BSA was a spontaneous process. The hydrogen bonds and van der Waals force played a predominant role in the binding process. Our data indicate that Morin binds solely with the BSA molecule. The apparent binding constant of the Morin-BSA system reached the order of 10⁴, which further confirmed the strong binding between Morin and BSA. This indicates that serum albumin can store and transport Morin molecules in the body, enabling them to reach the action site through blood circulation; thus, they can exert their physiological and biochemical effects. By using the fluorescence resonance energy transfer theory and the molecular simulation method, we found that Morin bound at Site Ⅱ in the hydrophobic cavity of the substructure domain IIIA of BSA, and the average distance between the two tryptophan residues and Morin was 3.09 nm. The synchronous fluorescence spectrum also revealed that Morin was far away from the two tryptophans of BSA, and therefore, cannot change the spatial structure near tryptophan. The CD spectra demonstrated that the α-helix content of BSA decreased from 59.5% to 53.9% after its interaction with Morin, while the disordered structure increased from 20.6% to 23.7%. The best-fitted docking poses reveal that Morin mainly contacted with the side-chains of surrounding hydrophobic amino acid residues. In addition, the generation of hydrogen bonds between hydroxyl groups on Morin molecules and the side-chains of R413 and K437 can be observed. These results provide basic knowledge for understanding the pharmacology of Morin, and useful guidance for designing, modifying, and screening flavonoid drug molecules.

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.

Environmentally friendly and renewable energy technologies, such as fuel cells and metal-air batteries, hold great promise for solving current energy and environmental challenges. The oxygen reduction reaction (ORR) plays a pivotal role in this top-drawer question. However, the sluggish kinetics of the ORR and prohibitive costs limit the global scalability of such devices. Traditionally, platinum-based electrocatalysts exhibit the best performance for ORRs in both acid and alkaline electrolytes. However, to significantly reduce the cost and realize sustainable development, utilization of Pt must be replaced or significantly reduced in the ORR cathode for fuel cell applications. Therefore, developing earth-abundant and high-performance non-precious metal catalysts (NPMCs) for ORR is of critical importance for the commercialization of fuel cells. In comparison to traditional catalysts, metal-organic frameworks (MOFs) are ideal precursors that integrate metal, nitrogen, and carbon functionalities together into one ordered 3D crystal structure. MOFs, assembled by secondary building of units comprised of metals and organic linkers with strong bonding, have received significant research attention because they possess permanent porosity, a three-dimensional (3D) structure, and can be prepared using a diversity of metals and organic linkers. High surface area, and microporous carbon materials can be easily obtained by carbonization of MOFs at high temperatures. In particular, MOF-derived carbon nanocomposites, which were prepared from transition metals, and have the form M-N-C (M = Fe or Co), have demonstrated remarkably improved catalytic activity and stability. Herein, we report an NPMC material consisting of Fe₃C nanoparticles encapsulated in mesoporous N-doped carbon (Fe-N-C), synthesized by a simple strategy involving physical mixing of MIL-100(Fe) with glucose and urea, and subsequent pyrolysis under inert atmosphere. The strong interaction between metal atoms and nitrogen atoms is beneficial in generating more active sites, and sites with a higher intrinsic catalytic activity, via carbonization. The as-obtained catalysts exhibit remarkable ORR activity in alkaline media, with the best catalyst (Fe-N-C-900, which is synthesized at 900 ℃) featuring a more positive onset potential (0.96 V vs the reversible hydrogen electrode (RHE)), a more positive half-wave potential (0.83 V vs RHE), a much higher diffusion limiting current density (6.28 mA·cm^-2) and a larger electron-transfer number (n), even at low overpotentials, compared with other contrast materials. Fe-N-C-900's excellent catalytic activity and stability in ORR are due to its large BET surface area, its large total pore volume, its nitrogen dopants, its active Fe₃C nanoparticles and the cooperative effects among its reactive functionalities.

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.

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.

Two-dimensional transition metal dichalcogenides (TMDs) possess the potential to be widely applied in optoelectronic devices, sensors, photocatalysis, and many other fields because of their intrinsic physical, chemical, and mechanical properties. Generally, the van der Waals (vdW) heterostructures fabricated from these TMDs exhibit excellent electronic properties. However, the spectral responses of most vdW heterostructures are limited by the inherent band gaps; it is thus essential to tune the band gaps for specific applications. In this paper, we performed a first-principles theoretical study on the structures and properties of WX₂ (X = S, Se, Te), as well as the vdW heterostructures WS₂/WSe₂, WS₂/WTe₂, and WSe₂/WTe₂. The impacts of the number of layers on the properties of WX₂ and the strain on the band gaps of vdW heterostructures were demonstrated. We found that every monolayer WX₂ (X = S, Se, Te) is a direct gap semiconductor, and as the number of layers increases, their band gaps decrease and they become indirect bandgap semiconductors. The spin-orbit coupling (SOC) effect on their band structures is significant and can decrease the band gap by approximately 300 meV compared with those that do no incorporate SOC effects. The properties of WX₂ can be accurately described by the HSE06 + SOC approach. WS₂/WSe₂, WS₂/WTe₂, and WSe₂/WTe₂ heterostructures are direct gap semiconductors with band gaps of 1.10, 0.32, and 0.61 eV, respectively. These three heterostructures exhibit type-II band alignments, which facilitate photo-induced electron-hole separation. In addition, they have quite small electron and hole effective masses, indicating that the separated electrons and holes can move very quickly to reduce the recombination rate of electrons and holes. There is an explicit red-shift of the optical absorption spectra of the three heterostructures compared with those of the monolayer components, and the most obvious redshift occurs in WSe₂/WTe_2. Both uniaxial and biaxial strains can alter the band gaps of these vdW heterostructures. Once the strain exceeds 4%, a transition from semiconductor to metal characteristics occurs. This work provides a way to tune the electronic properties and band gaps of vdW heterostructures for incorporation in high-performance optoelectronic devices.

Interactions between surfactants and small organic molecules not only enhance the surface activity of the surfactants and induce aggregate transitions in them, but also improve the solubility and stability of the organic molecules. Understanding the interaction between surfactants and small molecules will help in widening the scope of application of surfactants. Folic acid, a member of the vitamin B family, has a pteridine ring, para-aminobenzoic acid, and glutamic acid, and is crucial for many reactions inside the human body. The unique structure of folic acid also facilitates the preparation of functional materials such as liquid crystals and gels. However, the poor solubility and precipitation of folic acid limit its applications. Therefore, it is essential to improve the solubility and stability of folic acid. Surfactants are efficient in solubilizing and stabilizing small molecules. The interactions of folic acid with four types of surfactants, namely, an anionic surfactant, sodium dodecyl sulfate (SDS); a cationic surfactant, dodecyl trimethylammonium bromide (DTAB); a cationic ammonium gemini surfactant, 12-6-12; and a cationic ammonium trimeric surfactant, 12-3-12-3-12; have been investigated at pH 7.0 by surface tension measurements, ultraviolet-visible (UV) absorption spectroscopy, dynamic light scattering, isothermal titration calorimetry, and nuclear magnetic resonance spectroscopy. At pH 7.0, the carboxylic acid groups of folic acid are deprotonated, so each folic acid molecule carries two negative charges. The addition of a small amount of folic acid sharply reduces the critical micelle concentration (CMC) of cationic surfactants and their surface tension at the CMC. However, the surface activity and aggregation of SDS show only minimal changes with the introduction of folic acid. In addition, the photodegradation of folic acid in the presence of different surfactants is studied by fluorescence and UV absorption spectroscopy. When irradiated with UV light, folic acid undergoes rapid degradation in aqueous solution, in the absence of any surfactants. In contrast, the degradation is greatly suppressed in the presence of surfactants. The extent of suppression by cationic surfactants is more significant than that by the anionic surfactant. The residual folic acid concentration increases from nearly 0 in the absence of any surfactant to 43%, 89%, 96%, and 96% in the presence of SDS, DTAB, 12-6-12, and 12-3-12-3-12, respectively, in the concentration range studied. The amount of surfactant required to prevent the degradation decreases with an increase in the degree of oligomerization of the cationic surfactants. The greater number of binding sites and hydrophobic tails in the gemini and oligomeric surfactants result in much stronger electrostatic and hydrophobic interactions with folic acid. In addition, the close and compact packing in these surfactant molecules prevents folic acid from coming in contact with oxygen, thereby retaining its stability and preserving its properties. This work provides a new methodology for regulating the surface activity of the surfactants and their aggregation in the presence of small functional molecules, which in turn improves the stability of the small molecules that are otherwise unstable.

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.

Because of broad potential applications in sensing, drug delivery, and molecular motors, two-dimensional (2D), flexible, responsive Janus materials have attracted considerable interest recently in many fields. Unfortunately, the molecular-level responsive deformation of these 2D Janus nanomaterials is still not clearly understood. Hence, investigating the influence factor and responsiveness of the deformation of the 2D flexible responsive Janus nanomaterials should be helpful to deepen our understanding of the deformation mechanism and may provide valuable information in the design and synthesis of novel functional 2D Janus nanomaterials. Therefore, a mesoscopic simulation method, dissipative particle dynamics simulation, based on coarse-grained models, is employed in this work to systematically investigate the effect of the chain length difference between grafted polymers within two compartments of each individual Janus nanosheet and the effect of solvent selectivity difference of these two compartments on the deformation of the polymer-grafted Janus nanosheet. Although the coarse-grained model within this simulation is relatively crude, it is still valid to provide a qualitative image of the deformation of the polymer-grafted Janus nanosheet. Furthermore, we find two basic principles: (1) with increasing length difference between grafted polymers on the two opposite surfaces, the nanosheet will bear an entropy-driven deformation with increasing curvature; (2) the solvent will preferentially wet the polymer layer with better compatibility, and such a swelling effect may also provide a driving force for the deformation process. Owing to the interplay of conformational entropy and mixing enthalpy, the equilibrium structures of the polymer-grafted Janus nanosheet result in several interesting structures, such as a tube-like structure with a hydrophobic outer surface, an envelope-like structure, and a bowl-like structure, with tuning of the chain length and solvent compatibility of grafted polymers. Additionally, an unusually tube-like structure with a hydrophobic outer surface has been observed for a relatively weak solvent selectivity, which may provide us a novel method to transfer materials into the incompatible environment and therefore has potential applications in many areas, such as controllable drug delivery and release, and industrial and medical detection. Our theoretical results first provide a fundamental insight into the controllable deformation of the flexible Janus nanosheet, which can then help in the design and synthesis of novel Janus nanodevices for potential applications in pharmaceuticals and biomedicine. Bearing the limited of the computational capabilities, our model Janus nanosheets are relatively small, which are not direct mappings from real system. We hope that a systematic simulation study on this topic would be possible soon with the rapid developments in computer technology and simulation methods, and this would provide an exhaustive and universal methodology to guide experimental studies and applications.

Recently, non-fullerene polymer solar cells (NPSCs) have been developed rapidly because of the flexible energy-level variability and excellent optical absorption properties of non-fullerene electron acceptors. Among them, fused-ring electron acceptors (FREAs) with acceptor-donor- acceptor (A-D-A) structures have been extensively exploited in high-performance NPSCs. These FREAs often employ central aromatic fused rings attached to several rigid side-chains and flanked by two electron-deficient terminals. Many efforts have focused on the modification of the central flat conjugated backbone in order to gain broad and strong absorption and dense stacking. However, the preparation of such FREAs is relatively complex, especially for large fused-ring structures. In a previous work, we provided a simple and useful method to extend the effective conjugation length and broaden the absorption spectrum of the acceptor by noncovalent intramolecular interactions. On this basis, in this work, we have designed and synthesized a new A-D-A-type FREA (ITOIC-2Cl) that uses 4, 9-dihydro-s-indaceno[1, 2-b:5, 6-b']dithiophene (IDT) as a central donor unit, bis(alkoxy)-substituted thiophene rings as conformational locking π-bridges between the donor and acceptor units, and cyanoindanones modified with two high-electron-affinity chlorine atoms as end-capping acceptor units. On one hand, we can attain good backbone planarity in the solid state via the noncovalent conformational locking induced by sulfur−oxygen (S···O) and oxygen−hydrogen (CH···O) interactions, which are not strong enough to lock the coplanar conformation in solution, thus simultaneously endowing ITOIC-2Cl with good solubility. On the other hand, we can enhance the intramolecular charge transfer by enhancing the electron deficiency of the terminal groups. The optical and electrochemical properties of ITOIC-2Cl were systematically explored. Moreover, in combination with the donor polymer of [(2, 6-(4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1, 2-b:4, 5-b']dithiophene))-alt-(5, 5-(1', 3'-di-2-thienyl-5', 7'-bis(2-ethylhexyl)benzo[1', 2'-c:4', 5'-c']dithiophene-4, 8-dione))] (PBDB-T), the photovoltaic performances of the devices and the corresponding blend morphologies were studied. ITOIC-2Cl exhibited a broad absorption spectrum up to 900 nm, which is beneficial for broad harvesting of photons across the visible and NIR region. The PBDB-T:ITOIC-2Cl-based blend films exhibited favorable fibrous nanostructures with appropriate nanoscale phase separation, verified by atomic force microscopy and transmission electron microscopy characterizations. This morphology is beneficial for charge transport. Through the space-charge-limited current measurement, the PBDB-T:ITOIC-2Cl-based device exhibited the high hole/electron mobility of 1.85 × 10⁻⁴/1.19 × 10⁻⁴ cm²∙V⁻¹∙s⁻¹. The PBDB-T:ITOIC-2Cl-based devices obtained a high power conversion efficiency of 9.37%, with an open-circuit voltage (V_oc) of 0.886 V, short-circuit current (J_sc) of 17.09 mA cm⁻², and a fill factor (FF) of 61.8%. These results thus demonstrate the efficacy of the proposed strategy for designing high-performance non-fullerene FREAs.

Fluoride contamination of water is a problem worldwide and has caused great concern. Our study focused on the removal of fluorides from aqueous solutions using newly prepared and regenerated activated alumina. To obtain a suitable adsorbent, industrial boehmite was calcined from 573 K to 1473 K and the sample was characterized. The X-ray diffraction patterns showed that the sample was transformed to γ-alumina (activated alumina) at temperatures from 773 K to 1173 K, and the BET dates showed that the specific surface area of the sample decreased gradually from the temperature of 773 K to 1173 K. In our study, the activated alumina calcined from 773 K to 973 K was selected as the defluoridation adsorbent, and dynamic adsorption was employed for the removal of fluorides from aqueous solutions. The breakthrough curves demonstrated that the adsorption capacity of the adsorbent decreased with increasing calcination temperature. To investigate the effect of initial fluoride concentration on the adsorption capacity, 15 mg·L^-1, 20 mg·L^-1, and 25 mg·L^-1 fluoride solutions were selected as the initial aqueous fluoride solution. As a result, the capacity of the adsorbent increased gradually with the increase in the initial fluoride concentration. In order to improve the capacity, we also studied the regeneration process in our experiment. When the activated alumina was saturated by the fluorides, it was regenerated with a NaOH solution (pH = 13.0, 13.3, 13.5) and activated with a HCl solution (0.1 mol·L^-1). By a comparison of the five desorption and Al³⁺ dissolution rates during the regeneration process, it was determined that the NaOH solution with pH 13.0 was the most suitable desorption agent. An analysis of the nitrogen adsorption-desorption isotherm showed that its sharpness was almost unchanged after regeneration, which indicated that the pore structure of the adsorbent was not destroyed during this process. The change in the specific surface area and isoelectric point for the five-times regenerated adsorbent were important impact factors for fluoride adsorption. The specific surface area of the regenerated adsorbent increased, and the study of the zeta potential demonstrated that the isoelectric point also increased after regeneration. To observe the adsorption effect of regenerated activated alumina, we performed an adsorption experiment after each regeneration. The breakthrough curves demonstrated that the regenerated activated alumina exhibited faster saturation and increased adsorption capacity compared to fresh activated alumina. To elucidate the adsorption mechanism, IR spectroscopy was employed to characterize the O―H band of the adsorbent. The change in the Al―O―H content of the activated alumina during regeneration was the main factor impacting the fluoride adsorption capacity of the activated alumina.

Supercapacitors, advanced electrochemical devices, have attracted great interest due to their extraordinary properties, such as high power density, fast charging or discharging rate, and ultra-long cycle life. Currently, great efforts have been devoted to increasing their moderate energy density (typically < 5 Wh·kg^-1). Especially, room temperature ionic liquids (RTILs) have been considered as a promising electrolyte for further improving supercapacitor's performances owing to their large voltage window, high thermal stability, and wide working temperature range. However, RTILs suffer from the high viscosity and poor conductivity stemming from their strong cation–anion interactions. In this work, we investigate the influences of solvent on the capacitive performance within RTIL-based supercapacitors. Activated graphene powders are employed as the electrode active materials, and 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF₄) is chosen as the electrolyte because of the wide applications in electrochemical energy storage. The mole fraction of BMIMBF₄ (ρ_IL) in electrolytes can be regulated with adjusting the ratio of acetonitrile solvents (AN). Electrochemical measurements suggest that the solvent effects on the charge storage capability of supercapacitors depend strongly on the applied scan rate or current density. Specifically, at a lower scan rate of 10 mV·s^-1, solvent exhibits a negligible influence on the electrochemical performance; however, at an elevated scan rate of 200 mV·s^-1, solvent addition could prominently enhance the capacitance by ~2 folds. These results can resolve the controversial solvent effects reported in previous simulation and experimental studies. To interpret the as-obtained results, we further explore the solvent effects on the dynamic properties of electrolytes. It is found that solvent can effectively reduce the strong ion–ion interactions within pristine RTILs, thus decreasing the viscosity by ~29 times. Further electrical impedance spectroscopy tests suggest that the addition of solvent is able to significantly suppress the series resistance (by ~5.5 times) and dielectric relaxation time (by ~6.3 times), which thereby improves the rate capability of supercapacitors. We demonstrate that the maximum specific energy and power density of supercapacitor (ρ_IL = 0.25) are calculated to be 65.2 Wh·kg^-1 at 1 A·g^-1 and 18066.6 W·kg^-1 at 20 A·g^-1, respectively, among the best performances in the state-of-art literatures. More importantly, under an elevated working temperature of 50, its energy density can reach up to 85.5 Wh·kg^-1 at 1 A·g^-1, which is much higher than that of aqueous or organic solution based supercapacitors (< 10 Wh·kg^-1) and lead-acid battery (20–35 Wh·kg^-1), comparable to that of Ni metal hydride (40–100 Wh·kg^-1) and lithium-ion battery (80–150 Wh·kg^-1).

CeO₂-based catalysts are promising for use in various important chemical reactions involving CO₂, such as the dry reforming of methane to produce synthesis gas and methanol. CeO₂ has a superior ability to store and release oxygen, which can improve the catalytic performance by suppressing the formation of coke. Although the adsorption and activation behavior of CO₂ on the CeO₂ surface has been extensively investigated in recent years, the intermediate species formed from CO₂ on ceria has not been clearly identified. The reactivity of the ceria surface to CO₂ has been reported to be tuned by introducing CaO, which increases the number of basic sites for the ceria-based catalysts. However, the mechanism by which Ca²⁺ ions affect CO₂ decomposition is still debated. In this study, the morphologies and electronic properties of stoichiometric CeO₂(111), partially reduced CeO_2-x(111) (0 < x < 0.5), and calcium-doped ceria model catalysts, as well as their interactions with CO₂, were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, and synchrotron radiation photoemission spectroscopy. Stoichiometric CeO₂(111) and partially reduced CeO_2-x(111) films were epitaxially grown on a Cu(111) surface. STM images show that the stoichiometric CeO₂ film exhibits large, flat terraces that completely cover the Cu(111) surface. The reduced CeO_2-x film also has a flat surface and an ordered structure, but dark spaces are observed on the film. Different Ca-doped ceria films were prepared by physical vapor deposition of metallic Ca on CeO₂(111) at room temperature and subsequent annealing to 600 or 800 K in ultrahigh vacuum. The different preparation procedures produce samples with various surface components, oxidation states, and structures. Our results indicate that the deposition of metallic Ca on CeO₂ at room temperature leads to a partial reduction of Ce from the +4 to the +3 state, accompanied by the oxidation of Ca to Ca²⁺. Large CaO nanofilms are observed on CeO₂ upon annealing to 600 K. However, small CaO nanoislands appear near the step edges and more Ca²⁺ ions migrate into the subsurface of CeO₂ upon annealing to 800 K. In addition, different surface-adsorbed species are identified after CO₂ adsorption on ceria (CeO₂ and reduced CeO_2-x) and Ca-doped ceria films. CO₂ adsorption on the stoichiometric CeO₂ and partially reduced CeO_2-x surfaces leads to the formation of surface carboxylate. Moreover, the surface carboxylate species is more easily formed on reduced CeO_2-x with enhanced thermal stability than on stoichiometric CeO₂. On Ca-doped ceria films, the presence of Ca²⁺ ions is observed to be beneficial for CO₂ adsorption; further, the carbonate species is identified.

The fabrication of high-efficiency organic solar cells requires a cathode interlayer (CIF) having multiple properties such as forming an ohmic contact with the active layer, high electron conductivity, low-density traps, and hole blocking. These roles can be more completely fulfilled by using a suitable binary blended CIF rather than a single molecule based CIF. In this article, we present the roles by using binary blended PDINO (amino N-oxide perylene diimide) and QPhPBr (tetraphenylphosphonium bromide) as the CIF to fabricate fullerene-free polymer solar cells (PSCs) with PBDB-T:IDTBR, a new donor: acceptor combination, as the active layer. The high-lying lowest unoccupied molecular orbital of the acceptor and the low-lying highest occupied molecular orbital (HOMO) of the polymer with small driving force (the donor-acceptor HOMO-HOMO energy offset, ∆HOMO) for the hole transfer, both result in a high open circuit voltage (V_oc). Moreover, our strategy to insert a dual mixed solution of CIF over the blended active layer better facilitates the role, which significantly improves charge extraction and collection, leading to the high V_oc, short-circuit current density (J_sc), and fill factor (FF) observed in comparison to a single CIF material. It was observed that the power conversion efficiency (PCE) increases to 8.27%, with a high V_oc of 1.0 V, using a binary mixture of CBL. Such tremendous improvements in V_oc using well known polymer donors have not been reported till date in binary solar cell systems. This idea demonstrates that the minimum energy loss because of the small ∆HOMO of the D-A combination and the use of a dual mixed layer of CBL together present the future prospects of non-fullerene photovoltaic devices for researchers.

Bile acid salts, which are regarded as anionic steroid biosurfactants, have been widely used in the preparation of novel nanomaterials owing to their special amphiphilic skeleton structure, unique physical and chemical properties, good biocompatibility, and environmental friendliness. They can participate in the supramolecular self-assembly to form ordered aggregates in solution, and can be used as a template for the preparation of micro and nanomaterials. In this manuscript, we present an overview of our research work based on the effect of bile salts on the self-assembly of micro and nanomaterials along with related research done worldwide. The first section introduces the effect of small biological molecules such as amino acids, on the aggregation behavior of bile salts, wherein the interaction between amino acids and cholate has been studied extensively. Many in vivo and in vitro studies have been carried out mainly focusing on solutions and interfaces. Second part of this manuscript summarizes the research progress on the construction of supramolecular gels based on bile salts, including amino acids, rare earth salts, Graphene Oxide (GO), and surfactants. Cholic acid sodium, sodium deoxycholic acid, and lithocholic acid sodium cholic acid salt have special steroidal parent skeleton, which is much more complicated than the alkane surfactant, enabling them to self-assemble to form gel via non-covalent interactions such as van der Waals force, hydrogen bonding, and hydrophobic effect. Also addition of small molecules and other organic/inorganic fillers can increase the mechanical strength of the gels. Last part describes the formation of micro and nanomaterials by self-assembly in presence of bile salts, especially about their interaction with dye molecules, wherein the formed complex usually has novel and ordered microstructures. The interaction between surfactants and dye molecules are mainly driven by electrostatic forces, hydrogen bonding, and van der Waals force. Dye molecules are considered to be an ideal substrate for constructing functional nanomaterials and as biosurfactant, bile salts are often used to assist in the synthesis of micro and nanomaterials. In order to get a more comprehensive and in-depth understanding of the preparation of micro and nanomaterials in presence of bile salts, this article provides a solid foundation to explore future applications. Although the participation of bile salts in supramolecular self-assembly and in the preparation of various functional nanomaterials has not been studied much, the current research focuses on the template function of bile salt and ionic self-assembly. However, the biological and physiological aspects of bile salts are low; therefore the function of bile salts still needs to be probed.

Li-S batteries are considered promising next-generation energy storage systems because they offer high theoretical specific capacity (1675 mAh∙g⁻¹), high energy density (2600 Wh∙kg⁻¹), environmental friendliness, and low cost. However, large-scale commercial applications are hindered by the low electrical conductivity of S, high volume expansion ratio, and high solubility of intermediate polysulfides in organic electrolytes. Li-Se batteries using Se as the cathode material have high discharge rates, good cyclic performance, high electrical conductivities, high output voltages, and high volumetric capacity densities, and therefore, they are potential alternatives to Li-S systems. Recently, covalent organic frameworks (COFs) have emerged as new porous crystalline materials with large specific surface areas, high porosities, low densities, good thermal stabilities, and controllable structures. Therefore, COFs have wide potential applicability in the fields of gas adsorption, heterogeneous catalysis, energy storage, and drug delivery. Based on the above analysis, a simple core-shell multiwalled carbon nanotube (MWCNT)/1, 3, 5-triformylphloroglucinol (Tp)-phenylenediamine (Pa) COF nanocomposite (MWCNT@TpPa-COF) was prepared by growing a TpPa-COF on MWCNTs through a simple solvothermal reaction. The MWCNT@TpPa-COF high-performance cathode material realizes the first application of a COF in Li-Se batteries. The MWCNTs can encapsulate Se, limit the diffusion of polyselenides (Li₂Se_n, 3 ≤ n ≤ 8), and provide rapid electron conduction and ion transmission. In addition, the π-π interaction between MWCNTs and COFs promotes COF growth and distribution on the MWCNTs, thereby forming core-shell MWCNT@TpPa-COF nanocomposites, which can further increase the loading of Se. Measurements via field-emission scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy confirmed the successful combination of MWCNTs and COFs. The rich micro- and mesoporous hierarchical structure provides the MWCNT@TpPa-COF nanocomposites with initial specific discharge capacities reaching 463.5 mAh∙g⁻¹ at the current density of 3C (1C = 675 mA∙g⁻¹). Cells utilizing the nanocomposite electrodes maintained 99% Coulombic efficiency, with the average cyclic capacitive loss of 0.14% after 500 cycles. In addition, electrochemical impedance spectroscopy, cyclic voltammetry, and multiple-rate cycling analyses support the excellent electrochemical performance of the proposed cathode material. This work provides a promising new prospect for the future development of rechargeable Li-Se batteries utilizing new COF-based cathode materials.

Molecular electronics has been the subject of increasing interest since 1974. Although it describes the utilization of single molecules as active components of electrical devices, molecular electronics remains a fundamental subject to date. Considering that the length of a single molecule is typically several nanometers, the electrical characterization of a probe molecule is a significant experimental challenge. A metal/molecule/metal junction can bridge the gap between nanometer-sized molecules and the macroscopic measuring circuit and is, thus, generally considered as the most common prototype in molecular electronics. For the fabrication and characterization of single-molecule junctions, break junction methods, which include the mechanically controllable break junction (MCBJ) technique and the scanning tunneling microscopy-break junction (STM-BJ) technique, were proposed at the turn of the century and have been developed rapidly in recent years. These methods are widely employed in the experimental study of charge transport through single-molecule junctions and provide a platform to investigate the physical and chemical processes at the single-molecule level. In this review, we mainly focus on MCBJ and STM-BJ techniques applicable for single-molecule conductance measurement and highlight the progress of these techniques in the context of identification and modulation of chemical reactions and evaluation of their reaction kinetics at the single-molecule level. We begin by presenting the operation principles of MCBJ and STM-BJ and stating their brief comparison. Subsequently, we summarize the recent advances in modulating single-molecule chemical reactions. In this regard, we introduce several examples that involve changing the environmental solution, applying an external electrical field, and resorting to electrochemical gating. Next, we overview the application of the break junction techniques in the investigation of reaction kinetics at the single-molecule level. In this section, we also present a brief introduction to studies on single-molecule reaction kinetics using graphene-based nanogaps, wherein conventional metallic electrodes were replaced by graphene electrodes. Furthermore, we discuss the combination of break junction techniques and surface-enhanced Raman spectroscopy for detecting single-molecule reactions occurring at nanometer-scale separation. We discuss the historical development of this combined method and present the latest advancement explaining the origin of the low conductance of 1, 4-benzenedithiol, which is a topic of significant concern in single-molecule electronics. Finally, we discuss some future issues in molecular electronics, including the expansion from simple molecules to complex molecular systems and the introduction of multi-physical fields into single-molecule junctions. Moreover, we provide a list of critical characterization tools in molecular electronics and discuss their potential applications.

As reported previously, rhodanine and thiazolidine-2, 4-dione units have been widely used as the terminal group to construct the efficient non-fullerene small molecular acceptors with the structure of A₁-A₂-D-A₂-A₁. Compared with the acceptor using thiazolidine-2, 4-dione unit as the terminal group, the acceptor with rhodanine unit as the terminal electron-withdrawing group usually showed the improved short circuit current density (J_sc) and fill factor (FF) as well as the higher power conversion efficiency (PCE), regardless of the lower open circuit voltage (V_oc). However, the causes of difference are still not very clear. Therefore, in this work, an unsymmetrical organic acceptor (IDT-2) has been designed and synthesized with rhodanine and thiazolidine- 2, 4-dione units as the electron-withdrawing terminal groups to connect an indacenodithiophene (IDT) central core, respectively. By comparing with the two analogues of the symmetrical organic acceptors based on rhodamine unit (IDT-1) or thiazolidine-2, 4-dione unit (IDT-3) as the terminal group, the structure-property relationship has been investigated for this series of acceptors. It is found that as two rhodamine terminal groups are replaced step by step with the thiazolidine-2, 4-dione unit from IDT-1 to IDT-3, the ICT absorption of these small molecular acceptors is significantly blue-shifted from 633 (soln)/656 (film), 618/645 to 603/625 nm, and the corresponding optical band gap (E_g^opt) is also gradually widened from 1.68, 1.71 to 1.77 eV for IDT-1, IDT-2 and IDT-3, respectively, which can be attributed to the introduction of thiazolidine-2, 4-dione unit to reduce the stability of quinoid structure of the conjugation backbone. At the same time, the LUMO/HOMO (the lowest unoccupied molecular orbital/the highest occupied molecular orbital) energy levels of the molecules are gradually uplifted to be -3.62/-5.58, -3.60/-5.56, and -3.57/-5.53 eV, respectively, which is generally beneficial for the improvement of the V_oc due to the upshifted LUMO energy levels of the acceptors. Considering the complementary absorption and well-matched energy levels of the donor and acceptor, the regioregular poly(3-hexylthiophene) (P3HT) has been chosen as a donor to fabricate the devices with three small molecular acceptors, respectively, and the corresponding photovoltaic performances have been evaluated and compared. The device based on IDT-1 with two rhodamine terminal groups gives the best PCE of 4.52% with the lowest V_oc of 0.87 V, the highest FF of 70.66% and J_sc of 7.37 mA·cm^-2, while the device based on IDT-3 with two thiazolidine-2, 4-dione terminal groups shows the poorest PCE of 3.40% with the highest V_oc of 0.98 V but the lowest FF of 59.70% and J_sc of 5.82 mA·cm^-2. As for IDT-2 with an unsymmetrical structure, it contains a thiazolidine-2, 4-dione terminal group and a rhodamine terminal group at the two sides of the molecule. It can be seen that the IDT-2 based device just shows a PCE of 4.07% with a V_oc of 0.91 V, a FF of 64.65% and a J_sc of 6.81 mA·cm^-2, all of which are between those of the devices based on IDT-1 and IDT-3. These results indicate that the thiazolidine-2, 4-dione unit is an effective terminal group to enhance the V_oc of the device but is not beneficial to the improvement of the J_sc and FF. Furthermore, when designing the structure of the acceptors, it is very important to maintain the balance of all the three parameters to maximize the PCE in the OSCs.

Surfactant molecules, when dispersed in solution, have been shown to spontaneously form aggregates. Our previous studies on molecular dynamics (MD) calculations have shown that ionic sodium dodecyl sulfate molecules quickly aggregated even when the aggregation number is small. The aggregation rate, however, decreased for larger aggregation numbers. In addition, studies have shown that micelle formation was not completed even after a 100 ns-long MD run (Chem. Phys. Lett. 2016, 646, 36). Herein, we analyze the free energy change of micelle formation based on chemical species model combined with molecular dynamics calculations. First, the free energy landscape of the aggregation, ΔG_i+j^†, where two aggregates with sizes i and j associate to form the (i + j)-mer, was investigated using the free energy of micelle formation of the i-mer, G_i^†, which was obtained through MD calculations. The calculated ΔG_i+j^† was negative for all the aggregations where the sum of DS ions in the two aggregates was 60 or less. From the viewpoint of chemical equilibrium, aggregation to the stable micelle is desired. Further, the free energy profile along possible aggregation pathways was investigated, starting from small aggregates and ending with the complete thermodynamically stable micelles in solution. The free energy profiles, G(l, k), of the aggregates at l-th aggregation path and k-th state were evaluated by the formation free energy $\sum\limits_i {{n_i}\left( {l, k} \right)G_i^\dagger } $ and the free energy of mixing $\sum\limits_i {{n_i}(l, k){k_B}Tln({n_i}(l, k)/n(l, k))} $, where n_i(l, k) is the number of i-mer in the system at the l-th aggregation path and k-th state, with $n\left( {l, k} \right) = \sum\limits_i {{n_i}\left( {l, k} \right)} $. All the aggregation pathways were obtained from the initial state of 12 pentamers to the stable micelle with i = 60. All the calculated G(l, k) values monotonically decreased with increasing k. This indicates that there are no free energy barriers along the pathways. Hence, the slowdown is not due to the thermodynamic stability of the aggregates, but rather the kinetics that inhibit the association of the fragments. The time required for a collision between aggregates, one of the kinetic factors, was evaluated using the fast passage time, t_FPT. The calculated t_FPT was about 20 ns for the aggregates with N = 31. Therefore, if aggregation is a diffusion-controlled process, it should be completed within the 100 ns-simulation. However, aggregation does not occur due to the free energy barrier between the aggregates, that is, the repulsive force acting on them. This may be caused by electrostatic repulsions produced by the overlap of the electric double layers, which are formed by the negative charge of the hydrophilic groups and counter sodium ions on the surface of the aggregates.

With the development of non-fullerene small-molecule acceptors, non-fullerene polymer solar cells (PSCs) have garnered increased attention due to their high performance. While photons are absorbed and converted to free charge carriers in the active layer, the donor and acceptor materials both play a critical role in determining the performance of PSCs. Among the various conjugated-polymer donor materials, polythiophene (PT) derivatives such as poly(3-hexylthiophene), have attracted considerable interest due to their high hole mobility and simple synthesis. However, there are limited studies on the applications of PT derivatives in non-fullerene PSCs. Fabrication of highly efficient non-fullerene PSCs utilizing PT derivatives as the donor is a challenging topic. In this study, a new PT derivative, poly[5, 5′-4, 4′-bis(2-butyloctylsulphanyl)-2, 2′-bithiophene-alt-5, 5′-4, 4′-difluoro-2, 2′-bithiophene] (PBSBT-2F), with alkylthio groups and fluorination was synthesized for use as the donor in non-fullerene PSC applications. The absorption spectra, electrochemical properties, molecular packing, and photovoltaic properties of PBSBT-2F were investigated and compared with those of poly(3-hexylthiophene) (P3HT). The polymer exhibited a wide bandgap of 1.82 eV, a deep highest occupied molecular orbital (HOMO) of -5.02 eV, and an ordered molecular packing structure. Following this observation, PSCs based on a blend of PBSBT-2F as the donor and 3, 9-bis(2-methylene-(3-(1, 1-dicyanomethylene)-indanone)-5, 5, 11, 11-tetrakis(4-hexylphenyl)-dithieno-[2, 3-d:2′, 3′-d′]-s-indaceno[1, 2-b:5, 6-b′]dithiophene (ITIC) as the acceptor were fabricated. The absorption spectra were collected and the energy levels were found to be well matched. These devices exhibited a power conversion efficiency (PCE) of 6.7% with an open-circuit voltage (V_OC) of 0.75 V, a short-circuit current density (J_SC) of 13.5 mA·cm^-2, and a fill factor (FF) of 66.6%. These properties were superior to those of P3HT (1.2%) under the optimal conditions. This result indicates that PBSBT-2F is a promising donor material for non-fullerene PSCs.

In this study, a localized surface plasmon resonance (LSPR) fiber probe modified with Ag nanoparticles (NPs) was developed. The LSPR fiber probe not only serves as a reaction substrate for plasmonic catalysis, but also detects in situ surface-enhanced Raman spectroscopy (SERS) signals from the reaction product, thereby achieving the integration of the plasmonic catalysis reactions and SERS signal detection. To fabricate the LSPR probe, plasmonic Ag NPs were first self-assembled on the surface of the fiber probe with assistance by the amination and silanization of (3-aminopropyl) trimethoxysilane (APTMS) molecules. p-Aminothiophenol (PATP) was chosen as a model molecule for plasmonic catalytic reaction. By regulating the self-assembly time of the Ag NPs, a uniform distributed monolayer of Ag NPs was formed on the surface of the probe, with which excellent plasmonic catalysis effects and SERS signal collection from the reaction product of 4, 4′-dimercaptoazobenzene (DMAB) were achieved. It was found that the characteristic SERS signal of the plasmonic catalytic reaction product DMAB obtained from internal excitation and collection was 12.8 times more intense than that from the external excitation and collection under the same laser intensity conditions, demonstrating that the internal excitation and collection method was advantageous in the plasmonic catalysis and SERS signal detection. The LSPR fiber probe was demonstrably qualified to quantitatively detect the concentrations of PATP solutions in the concentration ranges 10⁻⁴–10⁻⁸ mol∙L⁻¹. Using the LSPR fiber probe, we also realized an in situ kinetics study of the PATP coupling reaction enhanced by plasmonic catalysis. The results showed that the Ag NP-based LSPR fiber probe with internal excitation and collection modes had the advantages of high sensitivity, low cost, facile preparation, and most importantly, applicability to in situ detection in a flexible manner with less damage to the samples. The preliminary study also indicated that it was feasible to combine the LSPR fiber probe with near-field scanning optical microscopy, not only to obtain morphological images of the surface but also to simultaneously perform the plasmonic catalysis reaction and the detection of micro-domains of the surface. This permitted the acquisition of a two-dimensional distributional assessment of surface reactions by the plasmonic catalysis.

The controllability of metal adatoms has been attracting ever-growing attention because the metal species in particular single-atom metals can play an important role in various surface processes, including heterogeneous catalytic reactions. On the other hand, organic self-assembly films have been regarded as an efficient and versatile bottom-up method to fabricate surface nanostructures, whose functionality and periodicity can be highly designable. In this work, we have developed a novel strategy to steer the generation and distribution of metal adatoms by combining the surface self-assemblies with exposure to small inorganic gaseous molecules. More specifically, we have prepared a honeycomb structure of melem (triamino-s-heptazine) on the Au(111) surface based on a well-structured hydrogen bonding network. The achieved melem self-assembly contains periodic hexagonal pores having diameters as large as around 1 nm. More importantly, the peripheries of the nanopores are decorated with heterocyclic N atoms that can probably form strong interactions with the metal species. Upon exposing the melem self-assembly to a CO atmosphere at room temperature, a fair number of Au adatoms were produced and trapped inside the nanopores encircled by the melem molecules. Single or clustered Au vacancies were concomitantly formed that were also trapped by the melem pores and stabilized by the surrounding molecules, as confirmed by high-resolution scanning tunneling microscopy (STM) images. Both types of added species showed positive correlations with the CO exposure and saturated at around 0.01 monolayer. In addition, owing to the large pore size, as well as the presence of multiple docking sites inside the nanopores, more than one Au adatom can reside in a melem nanopore; they can be distributed in a variety of configurations for bi-Au (two Au adatoms) and tri-Au (three Au adatoms) species, whose population can be manipulated with the CO exposure. Moreover, control experiments demonstrated that these CO-induced Au species, including the adatoms and vacancies, can survive annealing treatments up to the temperature at which the melem molecules start to desorb, indicating a substantial thermal stability. The formed Au species may hold great potential for serving as active sites for surface reactions. More interestingly, the bi-Au and tri-Au species have moderate Au-Au intervals, and can be potentially active for certain structurally sensitive bimolecular reactions. Considering all these aspects, we believe that this work presents a fresh approach to utilizing organic self-assembly films and has demonstrated a rather novel strategy for preparing various single-atom metal species on substrate surfaces.

Normal alkyl sp³C―H bonds are ubiquitous in compounds such as methane, linear alkanes, and cycloalkanes that are not linked directly to heteroatoms or other functional groups. These unactivated bonds are not broken readily under mild conditions because their bond dissociation energy values are high and acidity values are low. Moreover, in the radical processes at high temperatures, reaction selectivity is not good for an alkane substrate with various alkyl sp³C―H bonds, which is commonly methyl < 1° < 2° < 3°. In the past five decades, C―H activation by transition-metal species to give C-metal bonds under mild conditions was intensively studied; all efforts were undertaken to provide new methods that can be applied in both chemical synthesis and chemical industry. However, the effective transformations of inert C―H bonds, particularly alkyl sp³C―H bonds, without the assistance of directing groups have been rarely investigated. This review focuses on the functionalization of normal alkyl sp³C―H bonds, such as methyl and primary sp³C―H bonds, via electrophilic activation or oxidative addition by using homogenous transition-metal catalysts, which are two main strategies in the study of inert C―H activation. The selectivity on C―H bond is methyl > 1° > 2° > 3° in both the reactions. Neither heterogeneous catalysis nor biocatalysis is mentioned in this review. Some remarkable progress is described on the study of reaction mechanisms and the establishment of novel reactions. For example, several selective oxidations of methane or linear alkanes have been introduced to afford new C―O, C―Cl, or even C―C bonds in the presence of Pt or Pd catalysts. The Shilov chemistry, which combines electrophilic activation of the C―H bond by the transition-metal complex, oxidation of the transition-metal intermediate, and nucleophilic substitution of organometallic species, has been emphasized in these reactions. Other transition-metal catalysts including Rh, Ir, Re, and W have been employed successfully in the carbonylation, borylation, and dehydrogenation of alkanes at moderate temperatures. The reaction pathways normally involve oxidative addition of the C―H bond with the transition-metal complex followed by insertion-elimination, reductive elimination, or β-H elimination. In the cascade reactions consisting of dehydrogenation of alkanes and addition of alkenes, new C―C or C―Si bonds can also be formed at terminal sites of linear alkanes. However, most of the above-mentioned reactions are still under investigation because of limited scope of the substrate, excess loading of the alkane, low efficiency of the catalyst, and high cost of the reaction operation. Breakthroughs in this promising field of alkane functionalization are possible when new concepts and technology are realized and applied.

With the increasing energy demands and the limited petroleum reserves, it is highly desirable to produce fuels and chemicals from non-petroleum feedstocks, such as coal, natural gas and biomass. Catalytic conversion of C₁ resources (CO, CO₂, CH₃OH, CH₄, etc.) affords various products and attracts increasing attention from both academia and industries. Methane and methanol are important C₁ feedstocks in the production of fuels and chemicals. In order to obtain high selectivity for the target product, it is necessary to control the activation of C―H bonds in methane and methanol. However, this remains a great challenge. Although the traditional thermal catalytic conversion of methane and methanol has been developed over decades, there are still some disadvantages associated with the catalytic process, such as harsh reaction conditions, high energy consumption, and low selectivity. Photocatalysis, which is driven by photoenergy, can compensate for the Gibbs free energy. In the photocatalytic reactions, semiconductor photocatalysts absorb photons and generate electrons and holes in their conduction and valence bands, respectively, to accelerate the reaction rate. The position of the conduction band determines the oxidation capacity, and the bandgap determines the light absorption property. Normally, the oxidation capacity of photocatalysts is regulated by choosing semiconductors with a suitable bandgap or anions/cations doping. Fabrication of heterojunction and loading metalsare recognized as effective methods to promote the separation of electron-hole pairs and improve the photocatalytic efficiency. In contrast to thermal catalysis, photocatalysis can be carried out under mild reaction conditions with low energy consumption. Recently, photocatalysis has been considered an attractive route for the efficient conversion of methane and methanol to fuels and chemicals. Partial oxidation of methane, which is necessary to avoid the formation of byproducts, can be achieved by adjusting the wavelength and intensity of the light and the oxidation capacity of the photocatalysts. In addition, light-induced plasmon resonance improves the efficiency of methane conversion by forming an intrinsic high-energy magnetic field that can polarize methane. In methanol conversion, the C―H bond can be selectively activated, instead of the O―H bond, by light irradiation. Therefore, C―C coupling can be realized for the production of various value-added chemicals from methanol. This review summarizes the recent advances in the photocatalytic conversion of methane and methanol including the reactions of reforming, oxidation, and coupling. Perspectives and challenges for further research on the photocatalytic conversion of methane and methanol are also discussed.

A polymer-surfactant complex is significant in understanding the interactions between amphiphilic molecules and has great potential for use in a vast number of industries. In addition, the stimuli-responsive polymer-surfactant complex represents a hot research topic for the colloid community. However, the use of CO₂ gas to tune their interaction and the corresponding morphological change in the polymer-surfactant complex has been less documented. In this work, the commercially available triblock copolymer Pluronic F127 was used as a starting material and the macromolecular initiator Br-F127-Br was synthesized via esterification. Then, the pentablock copolymer poly(2-(diethylamino)ethyl methacrylate))-block-F127-block-poly(2-(diethylamino)ethyl methacrylate)) (PDEAEAM-b-F127-b-PDEAEMA) was prepared via atom transfer radical polymerization (ATRP) of Br-F127-Br and the monomer 2-(diethylamino)ethyl methacrylate. Both Br-F127-Br and PDEAEAM-b-F127-b-PDEAEMA were characterized by FT-IR and ¹H NMR spectroscopies as well as gel permeation chromatography (GPC). The results indicated that both Br-F127-Br and PDEAEAM-b-F127-b-PDEAEMA were synthesized successfully. The CO₂-responsive behavior of the pentablock copolymer was examined by tracking the changes in pH and electrical conductivity of the polymer solution after alternatingly bubbling CO₂ and N₂. It was found that cyclic streaming of CO₂/N₂ could alter the pH of the polymer solution between 7.2 and 5.3, leading to the protonation degree of PDEAEAM-b-F127-b-PDEAEMA varying between 0.26 and 0.96; this in turn varied the electrical conductivity of the polymer solution between 19.4 μS∙cm⁻¹ and 70.6 μS∙cm⁻¹. The reversible changes in pH and electrical conductivity of the polymer solution indicate the good CO₂-stimuli responsiveness of PDEAEAM-b-F127-b-PDEAEMA. The interaction of PDEAEAM-b-F127-b-PDEAEMA with an anionic fluorocarbon surfactant potassium nonafluoro-1-butanesulfonate (C₄F₉SO₃K) with and without CO₂ was studied by ultraviolet-visible absorption spectrometry (UV-Vis), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The transmittance of the mixed solution of PDEAEAM-b-F127-b-PDEAEMA and C₄F₉SO₃K could be varied between 84% and 52% in the absence and presence of CO₂, indicating the formation of aggregates with different sizes. The DLS results showed that the size of aggregates could be modified reversibly between tens of nanometers and several micrometers by bubbling CO₂ and replacing CO₂ by N₂. The TEM image revealed the reversible morphological transition of the aggregates from spherical to wormlike micelles after bubbling CO₂. The carbonic acid formed from CO₂ and water can protonate the PDEAEMA in the pentablock copolymer to form PDEAEMA·H⁺, and thus the interaction between the pentablock copolymer and C₄F₉SO₃K becomes strong. When CO₂ is replaced by N₂, PDEAEMA·H⁺ reverts to PDEAEMA, and the interaction becomes weak once again. It can therefore be concluded that the protonation/deprotonation process of the pentablock copolymer can be controlled by bubbling CO₂/N₂. The protonation/deprotonation process can "switch" the electrostatic attraction of PDEAEAM-b-F127-b-PDEAEMA to C₄F₉SO₃K, thereby tuning the hydrophilic-lipophilic balance (HLB) of the polymer-surfactant complex reversibly, leading to the reversible morphological transition of the aggregates. The strategy of CO₂-controllable morphological alteration of a polymer–surfactant complex opens a new avenue for preparing gas-sensitive soft materials.

Molybdenum carbide is regarded as an excellent substitute for Pt-based catalysts in the hydrogen evolution reaction (HER), owing to its low cost, superior catalytic performance, and long-term stability. In this work, salt-sealed molybdenum carbide was prepared using sodium molybdate and 2, 6-diaminopyridine as the reactive raw materials, followed by continuous salt sealing and calcination of the precursor under an inert atmosphere. The morphology, composition and structure of salt-sealed molybdenum carbide were determined by scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicate that salt-sealed molybdenum carbide has irregular morphology and includes nanoparticles and nanorods. A comparison of the TEM images of Mo₂C with salt sealing (Mo₂C/SS) and Mo₂C without salt sealing (Mo₂C) indicates that Mo₂C/SS exhibits a smaller particle size. This suggests that salt sealing can efficiently avoid particle aggregation. The Brunauer-Emmett- Teller (BET) specific surface area of the catalysts was obtained from nitrogen adsorption/desorption isotherms. The increase in BET surface area from 2.55 to 8.14 m²·g⁻¹ after salt sealing provides evidence for the formation of pores in the product. The results of XRD, EDS and XPS analyses show that Mo₂C/SS has an orthorhombic crystal structure with molybdenum oxides on the surface, which may originate from surface oxidation. Considering the results of XPS and the turnover frequency (TOF) calculation, we can conclude that the formation of pores via salt sealing contributes to the exposure of more active sites, while simultaneously enlarging the contact area with oxygen. Therefore, higher molybdenum oxide content is generated on the surface, resulting in a lower proportion of active centers (molybdenum carbides) on the catalyst surface. Furthermore, the pseudocapacitance generated by the faradaic reaction of molybdenum oxides is superimposed on the double-layer capacitance of Mo₂C catalysts, which increases the double layer capacitance. Since the effect of pseudo-capacitance on Mo₂C/SS is more significant, the TOF number declines after salt sealing. Compared with Mo₂C, Mo₂C/SS exhibits three features that promote HER mass activity: (1) the generation of large quantities of pores via salt sealing leads to an increase in the BET surface area and exposure of more active sites, which is beneficial for improving HER performance; (2) the porous structure and enlarged surface area pave the way for effective mass and charge transfer; (3) the decrease of the Tafel slope from 145 to 88 mV·dec⁻¹. In summary, salt-sealed Mo₂C exhibited enhanced HER activity with an overpotential of 175 mV to achieve a current density of 10 mA·cm⁻². The Tafel slope for HER on salt-sealed Mo₂C is 88 mV·dec⁻¹. This can be considered as the proof of the Volmer-Heyrovsky mechanism with electrochemical desorption as the rate-determining step.

With the rapid development of science and technology, various nanomaterials have continually emerged to meet human needs. As a newly emerging class of nanomaterials, two-dimensional (2D) materials have received wide attention recently in energy storage, catalysis, sensing and biomedicine due to their unique features such as good mechanical property, high specific surface area, excellent thermal and electrical conductivity. Biomacromolecules are the special organic molecules with various biological activities which exist extensively in every aspect of human life. When 2D materials meet biomacromolecules to display their own unique advantages, more opportunities and challenges have arisen for the exploitation and fabrication of novel nanomaterials with unique electrical, mechanical, biological properties and specific functions. In recent years, extensive research has been carried out with outstanding achievement thus the combination of 2D materials and biomacromolecules becomes a new hotspot. There were generally two binding interactions between 2D materials and biomacromolecules, namely non-covalent binding (electrostatic interaction, hydrophobic effect, π–π stacking, van der Waals interaction) and covalent binding (special chemical reactions between the functional groups of 2D materials and biomacromolecules). In addition, due to the excellent photothermal conversion performance, 2D materials could exhibit a non-contact interaction to biomacromolecules through the photo-thermal effect which has greatly broadened their applications. Up to now, numerous studies have clearly revealed the binding and effect mechanism and the research will be more focused on expanding the scope and application. Currently, the combination of 2D materials and biomacromolecules has widely involved in many cutting-edge applications such as flexible device, biosensor, smart skin, drug delivery, antibacterial, disease therapy and so on. Although a lot of progress has been made, several highlight open questions still need to be urgently addressed, such as the production cost of 2D materials, biological activity of biomacromolecules, stability and biocompatibility of 2D/biomacromolecule nanomaterials. This review summarizes the interactions between some typical 2D materials (i.e. graphene, graphene oxide, nitrogen-doped graphene, molybdenum disulfide, phosphorene, silylene and germanene) and biomacromolecules (i.e. silk protein, lysozyme, bovine serum albumin, bovine hemoglobin, ovalbumin, villin, bovine fibrinogen, DNA/RNA, glucose oxidase and chitosan) and focuses on the recent progress of some typical applications (i.e. engineering application, disease therapy and antibacterial). The non-covalent and covalent bindings of 2D materials and biomacromolecules are discussed in detail, and the applications of the combination of 2D materials and biomacromolecules in engineering and bioscience have been reviewed. Finally, the challenges for the future development of 2D materials and biomacromolecules are also briefly proposed.

Perovskite is widely used as catalyst supports because of its flexible composition, good redox performance, and excellent thermal stability. However, the use of perovskite oxides as catalyst supports has two disadvantages: low surface area due to synthesizing the perovskite structure at high temperatures, and native perovskite surfaces preferentially have A-sites instead of catalytically active sites. On the other hand, interaction between the support and metal affects the size and valence state of noble metals. Therefore, perovskite oxides with different structures were prepared and were used to support Au catalysts, in order to obtain excellent catalytic activity and high stability. Specifically, stoichiometric LaMnO₃ and nonstoichiometric LaMn_1.2O₃ perovskites were prepared by the ethylene glycol sol-gel method, and then the LaMnO₃-AE oxide was prepared by treating LaMnO₃ perovskite with dilute nitric acid. The perovskite-supported Au catalyst was prepared by the deposition precipitation method and its catalytic activity for CO oxidation was evaluated. Using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H₂ temperature-programmed reduction (H₂-TPR), it was found that LaMnO₃ and LaMn_1.2O₃ perovskite carriers were beneficial for the dispersion of Au; however, the Au nanoparticle size significantly increased with increasing calcination temperature, indicating poor Au thermal stability. In contrast, LaMnO₃ perovskite (LaMnO₃-AE) etched by nitric acid is not conducive to dispersion of Au, but it is beneficial for improving the thermal stability of Au. Au was always maintained in the zero-valence state after calcination at different temperature. H₂-TPR results revealed that the reducibility of the catalysts changed largely after thermal treatment at high temperatures, and was mainly influenced by the agglomeration of Au nanoparticles. Although the reducibility of the Au/LaMnO₃-AE catalyst calcined at 250 ℃ is lower than that of Au/LaMn_1.2O₃ and Au/LaMnO₃ catalysts calcined at the same temperature, the former exhibited higher reducibility when the catalyst was calcined at high temperatures (500 and 900 ℃). In the CO oxidation reaction, the catalytic activity of all the prepared catalysts decreased when the calcination temperature was increased from 250 to 500, 700, and 900 ℃. However, the catalytic activity of the Au/LaMn_1.2O₃ catalyst was significantly higher than those of LaMnO₃- and LaMnO₃-AE-supported Au catalyst, when calcination temperature was below 500 ℃, while the activity of the Au/LaMnO₃-AE catalyst was significantly higher than those of the Au/LaMnO₃ and Au/LaMn_1.2O₃ catalysts when the calcination temperature was more than 700 ℃. As shown in characterization results, after the catalyst was calcined at high temperatures (700 and 900 ℃), the Au nanoparticle size on the Au/LaMnO₃-AE catalyst was lower than those on Au/LaMnO₃ and Au/LaMn_1.2O₃ catalysts, leading to high reducibility and catalytic activity of the Au/LaMnO₃-AE catalyst. The Au/LaMnO₃-AE catalyst also exhibited high stability in CO oxidation. The catalytic activity of the Au/LaMnO₃-AE catalyst can be maintained for 20 h at 130 ℃.

In the emerging field of nanoscience, tubular structures have been attracting remarkable interest due to their well-defined geometry, high specific area, and exceptional physical and chemical properties. Among them, oriented ZnO tubular arrays are regarded as promising candidates for various applications such as optoelectronics, solar cells, sensors, field emission, piezoelectrics, and catalysis. Although template-directed and selective dissolution synthesizing strategies are commonly used to prepare ZnO nanotubes, repeatability and large scale preparation are still challenging. In this study, ZnO nanotube arrays were controllably prepared by tuning the hydrothermal parameters, without the use of any additives. The mechanism underlying the self-conversion of ZnO nanorods to nanotubes was comprehensively studied based on the surface energy theory. It has been proved that the metastable top surface of the ZnO nanorods dissolves preferentially to reach a stable state during the hydrothermal growth. The specific surface energy of different crystal faces of ZnO nanorods was calculated using molecular dynamics simulation. The top surface of the ZnO nanorod, the Zn-terminated [0001] face, demonstrated much higher surface free energy than did the lateral faces, which indicated that the self-dissolution of top face (002) is energetically favorable. The self-conversion behavior of ZnO nanorod arrays with different diameters was specifically investigated by adjusting the initial precursor concentration, density of the crystal seed layers, and growth time. The dissolution-crystallization equilibrium concentration, determined by crystal surface energy, was found to be a key factor for the formation of the tubular structure. Notably, the critical equilibrium conditions for the self-conversion of ZnO nanorods to nanotubes, including zinc ion concentration and pH, have been identified by studying parameters corresponding to the dissolution-crystallization equilibrium for the metastable top surface of the ZnO nanorods. The preparation of the ZnO nanotube arrays was successfully accelerated and simplified via two-step procedure: (1) preparation of ZnO nanorod arrays and (2) self-conversion of ZnO nanorods to nanotubes. The preparation method based on the self-conversion mechanism from rods to tubes for polar oxides is simpler and more easily controllable as compared to the reported methods involving variety of additives. Because of the advantages of adaptability to a wide range of substrates, excellent conducting properties, and filling ability, the prepared ZnO nanotube array films were used in encapsulating phase-change materials. The encapsulated phase-change material exhibited excellent heat storage/release properties and heat conductivities. This indicates the potential application of precision devices for temperature control.

Self-aggregated quaternary ammonium polysulfone (aQAPS) is a high-performance alkaline polymer electrolyte that has been applied in alkaline polymer electrolyte fuel cells (APEFCs). For a long time, N, N-dimethyl formamide (DMF) has been considered the best solvent to dissolve aQAPS, but the high boiling point of DMF makes it hard to remove from the electrodes, which potentially poisons the electrocatalysts. Our recent experiments have shown that although aQAPS is unable to dissolve in ethanol, n-propanol, or water, it can dissolve in the mixture of these alcohols and water. This peculiar dissolution behavior significantly facilitates the fabrication of the membrane electrode assembly (MEA) for APEFCs, even though it has not been understood. In this work, atomistic molecular dynamics (MD) simulations were employed to study the dissolution behavior of aQAPS in different solvents, including water, methanol, ethanol, n-propanol, DMF, and the mixture of these non-aqueous solvents and water. The conformation of the aQAPS chain in pure solvents agreed well with the dissolution behavior observed in the experiments, even though in the water-containing mixed solvents, the aQAPS chain tended to be in a more contracted state. The simulations further revealed that the water component in the mixed solvents played dual roles. On one hand, the hydrocarbon chain of aQAPS was compressed to a contracted state upon the addition of water, because of the hydrophobic effect. On the other hand, water can drive the dissociation of the counterion (Cl^{–­ ­ ­} ), which led to an enhancement in the solute-solvent interaction energy and thus facilitated the dissolution of aQAPS. In most mixed solvents, the compensation of these two interactions resulted in a general increase in the total solute-solvent interaction energy; therefore, the addition of water was energetically favorable for the dissolution of aQAPS. This study not only furthers our fundamental understanding of the dissolution behavior of polyelectrolytes but also is technologically significant for the development of better APEFCs.

Owing to the scarcity of platinum, it is of high importance to develop electrodes with low platinum metal loading and to thereby improve the utilization of Pt for the commercialization of proton-exchange membrane fuel cells (PEMFCs). In comparison to conventional high-platinum electrodes, the thickness of the catalyst layer (CL) is thinner and the interatomic Pt spacing is larger for the low-Pt loading electrodes. The distribution of electrolyte ionomer and the electrode morphology, which are strongly influenced by the solvents used in the fabrication process, are therefore increasingly important factors for achieving high performance in the membrane electrode assembly (MEA). In this work, different solvents with various dielectric constants and evaporation rates were used to prepare the inks for low-Pt loading cathode (0.1 mg·cm^-2) fabrication. First, the inks were fabricated by dispersing the catalyst and ionomer in different solvents which were then coated onto carbon paper to prepare the gas diffusion electrodes. The anode and cathode electrodes were then hot-pressed together with the Nafion membrane to produce the MEAs. The results showed a mixture of isopropanol-water (4:1) yielded the best-performing MEA during the single-cell tests compared to the other solvents tested. In order to elucidate the relationship between the performance of MEAs and the solvents, the structure and the surface morphology of the CL and the distribution of Nafion ionomer in the CL was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A comparison of the SEM and TEM images of representative samples indicated that the best performing electrode had a much improved homogeneity in the surface morphology as well as the dispersion of catalyst and ionomer. This was because of the moderate evaporation rate and better dispersion, caused by the increased hydrogen bonding and high dielectric constant, respectively. The results from dynamic light scattering (DLS) showed that the size of the catalyst and ionomer aggregates are influenced by the solvents. It is suggested that larger aggregates might help the formation of holes in the CL for gas diffusion and water removal, with the optimum size found to be around 400–800 nm. In conclusion, the MEA fabricated from the isopropanol-water solvent exhibited a significantly increased power density (1.79 W·cm^-2), and the utilization of Pt was increased to approximately 0.047 mg·W^-1, which is among the best-performing fuel cells reported to date.

Currently, worldwide attention is focused on controlling the continually increasing emissions of greenhouse gases, especially carbon dioxide. To this end, a number of investigations have been carried out to convert the carbon dioxide molecules into value-added chemicals. As carbon dioxide is thermodynamically stable, it is necessary to develop an efficient carbon dioxide utilization method for future scaled-up applications. Recently, several approaches, such as electrocatalysis, thermolysis, and non-thermal plasma, have been utilized to achieve carbon dioxide conversion. Among them, non-thermal plasma, which contains chemically active species such as high-energy electrons, ions, atoms, and excited gas molecules, has the potential to achieve high energy efficiency without catalysts near room temperature. Here, we used radio-frequency (RF) discharge plasma, which exhibits the non-thermal feature, to explore the decomposition behavior of carbon dioxide in non-thermal plasma. We studied the ionization and decomposition behaviors of CO₂ and CO₂-H₂ mixtures in plasma at low gas pressure. The non-thermal plasma was realized by our custom-made inductively coupled RF plasma research system. The reaction products were analyzed by on-line quadrupole mass spectrometry (differentially pumped), while the plasma status was monitored using an in situ real-time optical emission spectrometer. Plasma parameters (such as the electron temperature and ion density), which can be tuned by utilizing different discharge conditions, played significant roles in the carbon dioxide dissociation process in non-thermal plasma. In this study, the conversion ratio and energy efficiency of pure carbon dioxide plasma were investigated at different values of power supply and gas flow. Subsequently, the effect of H₂ on CO₂ decomposition was studied with varying H₂ contents. Results showed that the carbon dioxide molecules were rapidly ionized and partially decomposed into CO and oxygen in the RF field. With increasing RF power, the conversion ratio of carbon dioxide increased, while the energy efficiency decreased. A maximum conversion ratio of 77.6% was achieved. It was found that the addition of hydrogen could substantially reduce the time required to attain the equilibrium of the carbon dioxide decomposition reaction. With increasing H₂ content, the conversion ratio of CO₂ decreased initially and then increased. The ionization state of H₂ and the consumption of oxygen owing to CO₂ decomposition were the main reasons for the V-shape plot of the CO₂ conversion ratio. In summary, this study investigates the influence of power supply, feed gas flow, and added hydrogen gas content, on the carbon dioxide decomposition behavior in non-thermal RF discharge plasma.

With the development of synthetic chemistry, more and more efficient catalysts are exploited to activate inert chemical bonds and organic molecules. In the synthetic chemistry, catalysts play an important role, scientists are paying more and more attention to the design and synthesis of catalysts. The majority of catalysts in homogeneous catalytic systems belong to mononuclear active species. In addition to the development of catalysis science, major research is also being conducted on the development of the coordination environment for metal centers to increase their catalytic ability and thereby create enhanced catalytic processes. The catalytic activity of dinuclear catalysts varies from those of mononuclear catalysts. Due to the synergistic effect between the two metal centers, the catalytic activity of dinuclear catalytic systems exhibits particular performance characteristics. The first row of elements in group Ⅷ of the periodic table, Fe, Co, and Ni, are also known as the ferrous group. These metals have drawn attention in recent years because of their relatively low price, stable structure, commercial availability, and ability to catalyze various type of reactions. Homodinuclear ferrous group metal complexes are applied in a wide variety of reactions, including hydroboration, hydrosilylation, cross-coupling reactions, asymmetric 1, 4-addition, asymmetric Mannich reactions, CO₂ activation, copolymerization, and alkyne cyclotrimerizations. Compared with mononuclear metal catalytic systems, there are currently relatively few types of homogenous catalytic systems that are catalyzed by bimetal catalysts. However, such catalytic systems possess significant advantages over mononuclear catalytic systems. For example, the catalytic activity and reaction selectivity of dinuclear metal catalytic systems are far superior, the reaction conditions milder, and the operations required simpler. However, research on the mechanisms of dinuclear metal catalytic systems is still insufficient. For example, the interaction between metals and substrates requires further investigation. This review focusses on the synthesis and characterization of homodinuclear bimetallic iron complexes. The application of homodinuclear iron, cobalt, and nickel complexes in homogeneous catalytic systems is introduced and summarized in detail. Finally, the challenges for the future development of homogeneous catalytic systems that utilize homodinuclear bimetallic iron complexes are outlined.

Graphitic carbon nitride (g-CN), as a nonmetal semiconductor material, has been widely used in various fields, such as photocatalysis, electrocatalysis, batteries, light-emitting diodes, and solar cells, owing to its unique electronic and photophysical properties. However, the application of g-CN in practical devices remains limited because of the difficulties in fabricating g-CN films of high quality. In this work, we report a method for preparing a g-CN film with high optical quality on a substrate of indium tin oxide (ITO) glass and/or soda lime (NaCa) glass by using melamine as a precursor. First, we prepared the bulk g-CN from melamine in a muffle furnace via thermal polymerization. Then, we fabricated the g-CN film on the ITO and/or NaCa glass substrate with fine-milled, bulk g-CN in a tube furnace using thermal vapor deposition. With this two-step method, a yellow, transparent g-CN film with high optical quality was successfully fabricated on both the ITO and/or NaCa glass substrates. To check the quality of the film, we used scanning electron microscopy (SEM) to study the morphology of the fabricated g-CN film on the ITO glass substrate. Both the high-resolution and low-resolution SEM image results show that the obtained g-CN film on the ITO glass substrate had a homogeneous and dense structure without a corrugated surface, illustrating that it had good surface roughness. Then, we investigated the thickness and surface roughness of the g-CN film via atomic force microscopy (AFM). The AFM results show that the thickness of the g-CN film deposited on the ITO glass substrate was around 300 nm and that the surface roughness of the g-CN film deposited on the ITO glass substrate was less than 40 nm. To verify the chemical composition of the obtained g-CN film on the ITO glass substrate, we performed X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectroscopy (EDS) analyses. Both the XPS and EDS results demonstrate that the chemical composition of the g-CN film deposited on the ITO glass substrate was similar to that of bulk g-CN powder. More importantly, we determined the band structure for the g-CN film deposited on the ITO glass substrate by using a combination of steady-state absorption and high-resolution valence band XPS analysis. It was found that the determined band structure for the g-CN film deposited on the ITO glass substrate was close to that of bulk g-CN powder, also indicating that its chemical composition was similar to that of bulk g-CN. Meanwhile, we also found that the prepared g-CN film on the ITO glass substrate effectively degraded methylene blue dye under Xe lamp irradiation, which was similar to the effect of bulk g-CN powder. All analyses performed demonstrate that the two-step method presented in this study could successfully fabricate a g-CN film with high optical quality. In addition, we also analyzed the fluorescence lifetime of the g-CN film deposited on the ITO glass substrate by using a homemade time-correlated single-photon counting apparatus and found that it was much shorter than that of bulk g-CN.

Dimethyl ether (DME) is considered a promising energy source and clean fuel for the next generation, with its high hydrogen content, and non-toxicity compared with methanol. In addition, it is easy to store and transport. DME steam reforming (SR) has received considerable attention for its applicability in the production of hydrogen for fuel cell applications. Generally, DME SR consists of two steps: DME hydrolysis and methanol SR. DME hydrolysis often occurs on an acidic catalyst, such as γ-Al₂O₃. Methanol SR in Cu-based catalysts requires both Cu⁰ and Cu⁺ as the active sites; moreover, the relative ratios of Cu⁰ and Cu⁺ can influence the catalytic performance. In addition, the byproduct of CO also commonly exists in DME SR, and a small amount of CO can poison Pt electrodes of fuel cells. Therefore, it is necessary to reduce the concentration of the generated CO in DME SR. Herein, using an ammonia-evaporation method, we synthesized a Cu/SiO₂ catalyst, which can simultaneously generate the dual copper species of Cu⁰ and Cu⁺ by reduction. After modification with Ga₂O₃, the xGa-Cu/SiO₂ catalysts show much improved catalytic activity and decreased CO selectivity. The Cu/SiO₂ catalyst shows a DME conversion of 90.7% and CO selectivity of 11.5% at 380 ℃. The 5Ga-Cu/SiO₂ catalyst, with a loading amount of Ga₂O₃ of 5% (w, based on the weight of Cu), shows the best performance, with a DME conversion of 99.8% and CO selectivity of 4.8% under the same conditions. The measurement of apparent activation energies shows that the addition of Ga₂O₃ cannot change the reaction path. By multiple characterization methods, we demonstrated that the improved performance can be ascribed to the following two aspects. First, our characterization results show that the loaded Ga₂O₃ is highly dispersed on the Cu/SiO₂ catalyst, which can increase the interaction between Ga and Cu species. This can not only improve the dispersion of copper species (Cu⁰ and Cu⁺) on the catalysts, but can also adjust the ratios of Cu⁺/(Cu⁰ + Cu⁺). The H₂ production rate shows a typical volcano curve owing to the ratio of Cu⁺/(Cu⁰ + Cu⁺), and reaches a maximum of 5.02 mol·g^-1·h^-1 at Cu⁺/(Cu⁰ + Cu⁺) = 0.5 for the 5Ga-Cu/SiO₂ catalyst. We conclude that the interaction between Ga and Cu species and the synergistic effect between Cu⁰ and Cu⁺ result in the promoted catalytic activity for DME SR. Second, by using a temperature-programmed surface reaction (TPSR), we showed that the addition of Ga₂O₃ can efficiently promote the water–gas shift reaction, thereby reducing the CO selectivity in DME SR. Thus, Ga₂O₃ suppresses the generation of CO, leading to the low CO selectivity and high CO₂ selectivity. In summary, the Ga₂O₃-modified Cu/SiO₂ catalyst yields reformates with low CO selectivity and high catalytic activity for DME SR. Our work provides a novel approach to designing a highly efficient Cu-based catalyst for catalytic SR systems.

Leucine zipper-functionalized liposomes are promising drug carriers for cancer treatment because of their unique thermosensitivity. The leucine zippers, which consist of two α-helical polypeptides that dimerize in parallel, have characteristic heptad repeats (represented by [abcdefg]_n). A leucine residue was observed periodically at site "d" to stabilize the dimerization of the two polypeptides through inter-chain hydrophobic interactions. As the temperature increased, the inter-chain hydrophobic interactions became weaker, eventually triggering the dissociation of the leucine zippers. Due to the unique nature of the temperature response, leucine zippers are useful for developing novel lipid-peptide vesicles for drug delivery because they allow for better control and optimization of drug release under mild hyperthermia. The base sequence of the leucine zipper peptides used in our lab for the functionalize liposomal carrier is [VAQLEVK-VAQLESK-VSKLESK-VSSLESK]. Our recent experiments revealed that modifying this peptide at the N-terminus with distinct functional groups can change the physicochemical properties of the lipopeptides, and eventually affect the liposomes' phase transition behaviors. Four leucine zipper-structured lipopeptides with distinct head groups, viz. ALA, C3CO, C5CO, and POCH, were studied computationally to examine the influence of the molecular structures on the phase transition behaviors of lipopeptides. A series of computational techniques including quantum mechanics (QM) calculations, implicit solvation replica exchange molecular dynamics (REMD) simulations, dihedral principal component analysis (dPCA), and dictionary of protein secondary structure (DSSP) methods, and the conventional explicit solvation molecular dynamics (MD) simulations were applied in this work. First, QM calculations were conducted to obtain the partial charges of some modified head groups. Implicit-solvent REMD simulations were then performed to study the effect of temperature on the folded conformations of the leucine zipper peptides. The dPCA method was used to simulate trajectories to identify representative structures of the peptides at various temperatures, and the DSSP method was used to determine conformation transitions of the four lipopeptides ALA, C3CO, C5CO, and POCH at 324.8, 312.1, 319.1, and 319.4 K, respectively. The thermostability of the lipopeptide dimers in the lipid DPPC bilayer was studied in the conventional explicit solvent MD simulations. Finally, we conducted a deep analysis on the area per lipid and the electron-density profile for the DPPC bilayer to explore the folding and unfolding processes of the lipopeptides in the liposomes to better understand the underlying phase transition mechanisms of the thermosensitive liposomes. On this basis, we could further improve the thermosensitivity of the leucine zipper-structured lipopeptides, thereby facilitating the development of liposomal drug delivery techniques in the future.

Dye-sensitized solar cells (DSSCs) are one of the most promising renewable energy technologies. Charge transfer and charge transport are pivotal processes in DSSCs, which govern solar energy capture and conversion. These processes can be probed using modern electronic structure methods. Because of the heterogeneity and complexity of the local environment of a chromophore in DSSCs (such as solvatochromism and chromophore aggregation), a part of the solvation environment should be treated explicitly during the calculation. However, because of the high computational cost and unfavorable scaling with the number of electrons of high-level quantum mechanical methods, approaches to explicitly treat the local environment need careful consideration. Two problems must be tackled to reduce computational cost. First, the number of configurations representing the solvent distribution should be limited as much as possible. Second, the size of the explicit region should be kept relatively small. The purpose of this study is to develop efficient computational approaches to select representative configurations and to limit the explicit solvent region to reduce the computational cost for later (higher-level) quantum mechanical calculations. For this purpose, an ensemble of solvent configurations around a 1-methyl-8-oxyquinolinium betaine (QB) dye molecule was generated using Monte Carlo simulations and molecular mechanics force fields. Then, a fitness function was developed using data from inexpensive electronic structure calculations to reduce the number of configurations. Specific solvent molecules were also selected for explicit treatment based on a distance criterion, and those not selected were treated as background charges. The configurations and solvent molecules selected proved to be good representatives of the entire ensemble; thus, expensive electronic structure calculations need to be performed only on this subset of the system, which significantly reduces the computational cost.