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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Two-dimensional (2D) layered materials have garnered increasing interest in the past few years due to their unique structures and novel properties. These 2D layered materials with atomic thicknesses cover metals, semiconductors, and insulators, including graphene, black phosphorus (BP), transition metal dichalcogenides (TMDs) and hexagonal boron nitride (BN). Their bandgaps are usually tunable by changing the number of layers and the thicknesses. These 2D material are also sensitive to changes in the surrounding environment, e. g. changes in temperature, pressure, and illumination. Particularly, most 2D materials have high absorption coefficients. Owing to their excellent performance in electronics and optoelectronics and their potential for further development, many optoelectronic devices based on 2D materials, such as photodetectors, have been manufactured and widely used. In this paper, the latest progress of photodetectors based on 2D materials has been outlined. We introduce some 2D materials and their preparation methods, and the mechanisms of photodetectors based on 2D materials, i. e. photovoltaic effect, photoconductive effect, photogating effect, photothermoelectric effect and bolometric effect, have been discussed. Next, we summarize the parameters used to evaluate the performance of photodetectors, including photoresponsivity, external quantum efficiency, internal quantum efficiency, photoconductive gain, signal-to-noise ratio, noise-equivalent power, response time, cutoff frequency, linear dynamic range, and specific detectivity. We also report some recent studies on photodetectors based on 2D materials; among the 2D materials used in these studies, graphene, TMDs, and BP are the most widely used. Many methods have been proposed to improve the performances of photodetectors based on 2D materials, such as doping, designing novel structures, changing the dielectric layer, modifying the contact between channel and electrodes, controlling the surface and the interface, etc. Compared to single 2D materials, heterostructures composed of different 2D materials are more promising for use in photodetectors because they combine materials with different properties, which makes it possible to obtain photodetectors with desired and enhanced performances. Thus, we present some van der Waals heterojunctions and their applications in photodetectors. Finally, we provide a brief summary of the full article and an outlook for future development.

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.

As a new 2D material with excellent chemical stability, good electric conductivity, and high specific surface area, graphene has been widely used in energy storage and conversion devices. However, 2D graphene layers are easily stacked, which may significantly reduce the surface area and degrade the excellent electrical properties of graphene. To avoid this, one of the most effective methods is to construct 3D graphene (3DG) with specific porous microstructures. Chemical vapor deposition (CVD) is an important method for the synthesis of high-quality 3DG, where templates play a defining role in controlling the structure and cost of 3DG. Metallic materials with 3D microstructures, such as nickel foam, have proven to be useful as substrates for the growth of high-quality 3DG. However, metal substrates are usually expensive, and the pickling solution generated after etching may cause environmental problems. Therefore, non-metallic substrate materials with lower costs have been investigated for the preparation of 3DG. Herein, we developed a novel template material, mammal bone ashes, for the CVD preparation of 3DG. Mammal bone ash is an inexpensive and abundant biomass hydroxyapatite. During the high-temperature CVD reaction, the bone ash powders were slightly sintered to form a continuous porous structure with graphene coating. The morphology of 3DG is inherited from the microstructure of bone ash templates. After removing the bone ash template with hydrochloric acid, the template-grown 3DG was obtained with a unique bicontinuous structure, i.e. both the graphene framework and the void space were continuous. In addition, the pickling solution of the bone ash templates after etching was exactly the same as that for the raw materials for the production of phosphoric acid to achieve high atom utilization. We further optimized the graphitization degrees, layer number, and porous morphology of 3DGs. The microstructure evolution of 3DG is highly relevant to the layer thickness and uniformity of graphene layers. A short growth time would lead to a non-uniform and thin layer of graphene, which is not able to support a complex 3D porous structure. In contrast, a uniform graphene layer with proper thickness is capable of forming a robust 3D architecture. In addition, the facile CVD method can be extended to a series of metal phosphate templates, including tricalcium phosphate [Ca₃(PO₄)₂], trimagnesium phosphate [Mg₃(PO₄)₂], and aluminum phosphate [AlPO₄]. 3DG with bicontinuous morphology is promising as a conductive frame material in electrochemical energy storage devices. As an illustration, high-performance Li-S batteries were fabricated by the uniform composition of an S cathode on 3DG. In comparison with heavily stacked 2D graphene sheets in reduced graphene oxide / S composite, the non-flat structure of 3DGs remained unchanged even after the harsh melt-diffusion process of high-viscosity liquid sulfur. The resulting 3DG/S cathode delivered a high specific capacity of ~550 mAh∙g^-1 at a high current rate (2C). Our work opens an avenue to the low-cost and high-utility production of 3D graphene, which could be integrated with the well-developed phosphorus chemical industry.

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.

Two-dimensional (2D) materials, led by graphene, have emerged as nano-building blocks to develop high-performance membranes. The atom-level thickness of nanosheets makes a membrane as thin as possible, thereby minimizing the transport resistance and maximizing the permeation flux. Meanwhile, the sieving channels can be precisely manipulated within sub-nanometer size for molecular separation, such as gas separation. For instance, graphene oxide (GO) channels with an interlayer height of about 0.4 nm assembled by external forces exhibited excellent H₂/CO₂ sieving performance compared to commercial membranes. Cross-linking was also employed to fabricate ultrathin (< 20 nm) GO-facilitated transport membranes for efficient CO₂ capture. A borate-crosslinked membrane exhibited a high CO₂ permeance of 650 GPU (gas permeation unit), and a CO₂/CH₄ selectivity of 75, which is currently the best performance reported for GO-based composite membranes. The CO₂-facilitated transport membrane with piperazine as the carrier also exhibited excellent separation performance under simulated flue gas conditions with CO₂ permeance of 1020 GPU and CO₂/N₂ selectivity as high as 680. In addition, metal-organic frameworks (MOFs) with layered structures, if successfully exfoliated, can serve as diverse sources for MOF nanosheets that can be fabricated into high-performance membranes. It is challenging to maintain the structural and morphological integrity of nanosheets. Poly[Zn₂(benzimidazole)₄] (Zn₂(bim)₄) was firstly exfoliated into 1-nm-thick nanosheets and assembled into ultrathin membranes possessing both high permeance and excellent molecular sieving properties for H₂/CO₂ separation. Interestingly, reversed thermo-switchable molecular sieving was also demonstrated in membranes composed of 2D MOF nanosheets. Besides, researchers employed layered double hydroxides (LDHs) to prepare molecular-sieving membranes via in situ growth, and the as-prepared membranes showed a remarkable selectivity of ~80 for H₂-CH₄ mixture. They concluded that the amount of CO₂ in the precursor solution contributed to LDH membranes with various preferred orientations and thicknesses. Apart from these 2D materials, MXenes also show great potential in selective gas permeation. Lamellar stacked MXene membranes with aligned and regular sub-nanometer channels exhibited excellent gas separation performance. Moreover, our ultrathin (20 nm) MXene nanofilms showed outstanding molecular sieving property for the preferential transport of H₂, with H₂ permeance as high as 1584 GPU and H₂/CO₂ selectivity of 27. The originally H₂-selective MXene membranes could be transformed into membranes selectively permeating CO₂ by chemical tuning of the MXene nanochannels. This paper briefly reviews the latest groundbreaking studies in 2D-material membranes for gas separation, with a focus on sub-nanometer 2D channels, exfoliation of 2D nanosheets with structural integrity, and tunable gas transport property. Challenges, in terms of the mass production of 2D nanosheets, scale-up of lab-level membranes and a thorough understanding of the transport mechanism, and the potential of 2D-material membranes for wide implementation are briefly discussed.

Flexible electronic devices have attracted immense attention in recent years. Conventional electronics that are predominantly fabricated with rigid metallic materials demonstrate poor flexibility. Compared to traditional electronic devices, flexible electronic devices with better flexibility can adapt to different working environments. Consequently, they fit perfectly with different systems with minimal rejections. However, such flexible electronic devices need to achieve good extensibility and flexibility without compromising on their electronic properties. Therefore, new challenges and requirements arise while fabricating conductive materials. Manufacturing of flexible metal electrodes for flexible electronic devices include strategies such as reducing the thickness of the electrodes and designing electrodes with unique structures. However, these technologies are complex and expensive. Carbon nanotube (CNT) films exhibit good flexibility, excellent conductivity, good chemical and thermal stability, as well as good optical transparency, making them ideal candidates for flexible electronics. Therefore, the preparation and application of CNT films for the development of next generation flexible electronics have been extensively studied. In this review, we summarize the recent advances in the preparation of CNT films and their application in flexible electronic devices. Initially, the two main kinds of preparation methods for CNT films—dry and wet methods—are introduced. The dry methods for CNT film preparation include the membrane extraction method based on a vertical array of CNTs and the floating catalytic chemical vapor deposition method. Moreover, the wet methods predominantly discussed include vacuum filtration method, impregnation method, electrodeposition method, self-assembly method, and spraying method. Subsequently, the latest research advancements in assembly techniques, their performance and applications in various flexible electronics are discussed. This review primarily introduces the application of CNT films in the fields of flexible sensors, flexible energy devices, flexible transistors, and flexible display screens. The fundamentals of typical flexible sensors, such as strain sensors, pressure sensors, gas sensors, temperature sensors, and humidity sensors are presented. Besides, flexible lithium-ion batteries, flexible nanogenerators, and flexible thermoelectric devices based on CNT films are also investigated. Moreover, other flexible electronic devices, such as flexible transparent conductive film, flexible transistor, and flexible photodetector, based on CNT films are briefly described. Finally, advanced flexible electronics based on CNT films are summarized. The challenges and future prospects of these films are also discussed.

TiO₂ nanotube arrays (NTAs) have high photocatalytic activity; however, their weak visible light absorption limits their solar energy utilization and environmental application. Perovskite (ABO₃)-type oxides with a narrow band gap can absorb visible light in a wide wavelength range and have excellent stability; however, their photocatalytic activity is relatively low. Coupling TiO₂ NTAs with ABO₃ to form heterojunctions is one of the most promising approaches to extend the optical absorption of TiO₂ NTAs into the visible-light range and promote the separation rate of photogenerated electron–hole pairs. However, to date, constructing ABO₃-TiO₂ NTA heterostructured composites has been extremely challenging owing to the different crystallization temperatures of anatase TiO₂ NTAs and ABO₃. In this work, LaCoO₃ nanoparticles were first synthesized using a sol-gel method. The as-prepared LaCoO₃ nanoparticles were then modified on the surface of the TiO₂ NTAs using an electrophoretic deposition technique, and a series of LaCoO₃-TiO₂ NTAs photocatalysts were thus constructed by controlling the deposition time. Results of the scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) demonstrated that the nanoparticles prepared through the sol-gel method were LaCoO₃ with a uniform size and high crystallization. The average diameter of the LaCoO₃ nanoparticles was 100 nm. The binding strength between the LaCoO₃ nanoparticles and the TiO₂ NTAs was strong. The UV-visible absorption spectra (diffuse reflectance spectroscopy; DRS) demonstrated that the absorption band edge of the LaCoO₃-TiO₂ NTAs was gradually red-shifted into the visible light region with the increase in electrophoretic time. The LaCoO₃-TiO₂ NTAs prepared by the electrophoretic deposition technique for 15 min exhibited a strong light absorption in the wide wavelength range from 250 to 700 nm, which was the same as that of the LaCoO₃ nanoparticles loaded on a Ti foil. The results of the photocatalytic degradation of methyl orange (MO) under visible light irradiation demonstrated that the photocatalytic degradation rate of MO over LaCoO₃-TiO₂ NTAs was considerably higher than those of TiO₂ NTAs and LaCoO₃ nanoparticles loaded on a Ti foil. The LaCoO₃-TiO₂ NTAs prepared by the electrophoretic deposition technique for 15 min showed the highest photocatalytic degradation rate of MO, which was a four-fold enhancement compared to that of TiO₂ NTs under the same conditions. The p-n heterojunctions between the LaCoO₃ nanoparticles and the TiO₂ nanotubes were responsible for the enhanced visible light photocatalytic activity. The results of the electrochemical impedance spectroscopy (EIS) and photoluminescence spectroscopy (PL) tests demonstrated that the loading of the LaCoO₃ nanoparticles effectively promoted the separation and transport of photogenerated charges, thereby enhancing the visible light photocatalytic activity of the TiO₂ NTAs.

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.

High-temperature (700–900 ℃) steam electrolysis based on solid oxide electrolysis cells (SOECs) is valuable as an efficient and clean path for large-scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steam methane reforming or coal gasification. The operation parameters, in particular the feeding gas composition and pressure, significantly affect the performance of the electrolysis cell. In this study, a computational fluid dynamics model of an SOEC is built to predict the electrochemical performance of the cell with different sweep gases on the oxygen electrode. Sweep gases with different oxygen partial pressures between 1.01 × 10³ and 1.0 × 10⁵ Pa are fed to the oxygen electrode of the cell, and the influence of the oxygen partial pressure on the chemical equilibrium and kinetic reactions of the SOECs is analyzed. It is shown that the rate of increase of the reversible potential is inversely proportional to the oxygen partial pressure. Regarding the overpotentials caused by the ohmic, activation, and concentration polarization, the results vary with the reversible potential. The Ohmic overpotential is constant under different operating conditions. The activation and concentration overpotentials at the hydrogen electrode are also steady over the entire oxygen partial pressure range. The oxygen partial pressure has the largest effect on the activation and concentration overpotentials on the oxygen electrode side, both of which decrease sharply with increasing oxygen partial pressure. Owing to the combined effects of the reversible potential and polarization overpotentials, the total electrolysis voltage is nonlinear. At low current density, the electrolysis cell shows better performance at low oxygen partial pressure, whereas the performance improves with increasing oxygen partial pressure at high current density. Thus, at low current density, the best sweep gas should be an oxygen-deficient gas such as nitrogen, CO₂, or steam. Steam is the most promising because it is easy to separate the steam from the by-product oxygen in the tail gas, provided that the oxygen electrode is humidity-tolerant. However, at high current density, it is best to use pure oxygen as the sweep gas to reduce the electric energy consumption in the steam electrolysis process. The effects of the oxygen partial pressure on the power density and coefficient of performance of the SOEC are also discussed. At low current density, the electrical power demand is constant, and the efficiency decreases with growing oxygen partial pressure, whereas at high current density, the electrical power demand drops, and the efficiency increases.

Controllable synthesis of MoS₂ with desired number of layers via chemical vapor deposition (CVD) remains challenging. Hence, it is highly desirable to develop a theoretical model that can be used to predict the single- and multilayer growth of MoS₂ quantitatively, and provide guidelines for experimental fabrication. Herein we have established a kinetic Monte Carlo (kMC) model to predict the CVD growth of mono- and bilayer MoS₂. First, we proposed that the growth rates of layer 1 and layer 2 were governed by the distribution of the adatom concentration, and the growth kinetics of compact triangular MoS₂ followed the kink nucleation-propagation mechanism. The adatom concentration was formulated in terms of adatom flux, effective lifetime of adatoms, growth temperature, binding energies, edge energies, and nucleation criterion. The kink nucleation and propagation were determined by energy barriers of the adatom attachments to the zigzag and armchair edges. We then employed an analytic thermodynamic criterion to extract these parameters. Using the calibrated model, we found that the growth rate of layer 2 strongly depended on the size of layer 1 and decreased monotonically with increasing size of layer 1, and might even become prohibited at the maximum size of layer 1. Furthermore, we analyzed the size and morphology evolutions of bilayer MoS₂ at different growth temperatures and adatom fluxes. Throughout the growth processes of bilayer MoS₂, the morphologies of layers 1 and 2 maintained triangular shapes with compact edges, consistent with the kink nucleation-propagation growth mechanism. Our simulations revealed that the growth of bilayer MoS₂ was promoted by increasing the growth temperature or decreasing the adatom flux, which corroborated the experimental observations. The increase in growth temperature led to reduced adatom concentration at the edge of layer 2 in accordance with the adatom concentration far from the edge of layer 2, resulting in a consistent difference in the adatom concentration to promote the growth of bilayer MoS₂. Similarly, the decrease in adatom flux lowered the difference between the adatom concentrations far from the edge and at the edge of layer 1, decelerating the growth of layer 1. The decelerated growth of layer 1 reduced the difference between the adatom concentrations far from the edge and at the edge of layer 2 to zero, permitting the growth of bilayer MoS₂. To guide the experimental synthesis, we constructed a phase diagram to delineate the permitted or prohibited growth of bilayer MoS₂ at different growth temperatures and adatom fluxes. Hence, this work not only unveils the conditions for the growth of mono- and bi-layer MoS₂, but also provides guidelines for controllable synthesis of MoS₂ with the desired number of layers.

This paper reports, for the first time, a gold-silver alloy film based broadband spectral surface plasmon resonance imaging (SPRI) sensor that enables in situ quantitative detection of chemical and biological molecules adsorbed on the partial or entire surface of the alloy film. The use of the gold-silver alloy film as the sensing layer makes the SPRI sensor lower in detection cost and higher in detection sensitivity as compared with the conventional sensor with a pure gold film. The gold-silver alloy films of ~50 nm thicknesses were deposited on glass substrates using a sputtering target made of gold (50%)-silver (50%, w, mass fraction) alloy. Both the SPR spectra and SPR color images for the gold-silver alloy films covered with pure water were measured at different incident angles using the laboratory-made Krestchmann-type multifunctional platform. The two-dimensional (2D) hue profile and the average hue for each SPR color image were obtained by calculation with the hue algorithm. Using the average hue as the sensitivity parameter, the spectral SPRI sensor enables quantitative detection. The spectral range in which the average hue is most sensitive to refractive index (RI) changes of bulk solution and to molecular adsorption was determined to be between 595 and 610 nm. In this narrow spectral range the average hue is linearly dependent on the resonant wavelength and its slope (representing the hue variation induced by per unit change in resonant wavelength) is Δhue/Δλ_R = 7.52 nm^-1, implying that the hue-based RI sensitivity is 7.52 times as high as the wavelength-based RI sensitivity. This implication was experimentally demonstrated in this work. After setting the initial resonant wavelength of the sensor in the hue-sensitive spectral range, the hue-based RI sensitivity of the SPRI sensor was measured to be S = 29879 RIU^-1, which is 8 times higher than that obtained with the gold-film SPR chip under the same conditions (S = 3658 RIU^-1 for the gold-film SPR chip). Nonspecific adsorption of bovine serum albumin (BSA) molecules on the gold-silver alloy film was monitored in real time by the time-resolved spectral SPRI method, and the temporal change in the average hue was obtained. The time required for BSA adsorption to reach equilibrium is determined to be about 15 min. This study illustrates that the gold-silver alloy film based SPRI sensor has the powerful capability of quantitative detection of sub-monomolecular adsorption of proteins.

The preparation of plasmonic metal-based substrates has been a hot research topic during the past decades in the area of surface-enhanced Raman spectroscopy (SERS). The localized surface plasmon resonance effect of plasmonic metal nanostructures enhances the electromagnetic field for SERS analysis, thereby making SERS an extremely sensitive detection technique. However, commonly developed plasmonic metal substrates exhibit poor stability and reproducibility. Since the separation of graphene from graphite, graphene has been widely used in various fields because of its unique physical, chemical, electronic, and optical properties. In the field of SERS, graphene has been used for graphene-enhanced Raman scattering, which makes use of the chemical enhancement mechanism in SERS. In addition, it has capabilities of surface molecular enrichment, quenching fluorescence, surface homogenization, and has strong chemical stability. Due to these characteristics of graphene, SERS substrates based on graphene-metal nanocapsules have attracted the attention of researchers. In this work, a small size gold-graphitic nanocapsules (Au@G) was prepared by chemical vapor deposition (CVD). The material exhibits a core-shell structure consisting of a graphitized carbon layer coated on Au nanoparticles (Au NPs). The Au NP core of the Au@G provides a major enhancement factor for Raman analysis, and the external graphitized carbon shell ensures strong chemical stability of the material. The Au@G exhibits a uniform particle size with diameter ~17 nm. In order to control the size of the Au@G, tetraethyl orthosilicate (TEOS) and tetraethylorthotrimethylammonium bromide were used as the raw material and template, respectively, a 45 nm-thick layer of mesoporous silica was coated on the synthesized Au NPs. The presence of the mesoporous silica capping layer prevented aggregation and particle size growth of the Au NPs during high-temperature CVD. At the same time, we studied the effect of TEOS concentration on the growth of the graphitized carbon layer during CVD. The results revealed that a decrease of the TEOS concentration is conducive for obtaining a high graphitic Au@G, and the concentration of TEOS does not affect the particle size of the Au@G. Raman detection of crystal violet molecules using Au@G demonstrated the latter's good Raman enhancement effect. The Au@G prepared by high-temperature CVD exhibits a clean surface with no impurities. It is an SERS substrate with both physical and chemical enhancement. The unique Raman spectral peaks and small size of Au@G ensure its great potential for use in the fields of molecular detection and cell imaging analysis.

Graphene is one of the most promising materials in nanotechnology and has attracted worldwide attention and research interest owing to its high electrical conductivity, good thermal stability, and excellent mechanical strength. Perfect graphene samples exhibit outstanding electrical and mechanical properties. However, point defects are commonly observed during fabrication which deteriorate the performance of graphene based-devices. The transport properties of graphene with point defects essentially depend on the imperfection of the hexagonal carbon atom network and the scattering of carriers by localized states. Furthermore, an in-depth understanding of the effect of specific point defects on the electronic and transport properties of graphene is crucial for specific applications. In this work, we employed density functional theory calculations and the non-equilibrium Green's function method to systematically elucidate the effects of various point defects on the electrical transport properties of graphene, including Stone-Waals and inverse Stone-Waals defects; and single and double vacancies. The electrical conductance highly depends on the type and concentration of point defects in graphene. Low concentrations of Stone-Waals, inverse Stone-Waals, and single-vacancy defects do not noticeably degrade electron transport. In comparison, DV585 induces a moderate reduction of 25%–34%, and DV55577 and DV5555-6-7777 induce significant suppression of 51%–62% in graphene. As the defect concentration increases, the electrical conductance reduces by a factor of 2–3 compared to the case of graphene monolayers with a low concentration of point defects. These distinct electrical transport behaviors are attributed to the variation of the graphene band structure; the point defects induce localized states near the Fermi level and result in energy splitting at the Dirac point due to the breaking of the intrinsic symmetry of the graphene honeycomb lattice. Double vacancies with larger defect concentrations exhibit more flat bands near the Fermi energy and more localized states in the defective region, resulting in the presence of resonant peaks close to the Fermi energy in the local density of states. This may cause resonant scattering of the carriers and a corresponding reduction of the conductance of graphene. Moreover, the partial charge densities for double vacancies and point defects with larger concentrations exhibit enhanced localization in the defective region that hinder the charge carriers. The electrical conductance shows an exponential decay as the defect concentration and energy splitting increase. These theoretical results provide important insights into the electrical transport properties of realistic graphene monolayers and will assist in the fabrication of high-performance graphene-based devices.

A novel template-free oxalate route was applied to synthesize a series of MnO_x catalysts with different Cu content (MnO_x, Cu1-MnO_x, Cu2-MnO_x, Cu3-MnO_x, Cu4-MnO_x, Cu2-450, and Cu2-550), which were then used in 1, 2, 3, 4-tetrahydroquinoline (THQL) oxidative dehydrogenation aromatization. To obtain insight into the structure-activity relationships of the catalysts, the samples were characterized by thermogravimetry and heat flow analysis, X-ray diffraction (XRD), N₂ physical adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), H₂ temperature programmed reduction (H₂-TPR), and atomic absorption spectroscopy (AAS). The results showed that Cu2-MnO_x possesses the following characteristics: amorphous nature, high specific surface area, increased mesoporous average pore diameter, lower reduction temperature, highest Mn³⁺ and adsorbed oxygen content, and highest Mn³⁺/Mn⁴⁺ ratio among the seven manganese oxide catalysts. Cu2-MnO_x for the oxidative dehydrogenation aromatization of THQL showed conversion (99.1%) and selectivity (97.2%) for quinoline under mild reaction conditions, with cheap air as oxidant and no alkali additive. Cu2-MnO_x was reusable and achieved 95.8% conversion even after five reuse tests. Selectivity decreased slightly with the increase in reuse time, which could be attributed to the leaching of the Cu element. Comparison of structure-activity relationships showed increased catalytic activity when Mn³⁺ and adsorbed oxygen content were highest among these amorphous manganese oxides. Mn⁴⁺ content was related to the formation of quinoline N-oxide by over oxidation. Despite their high Mn³⁺ content and Mn³⁺/Mn⁴⁺ ratio, Cu2-450 and Cu2-550 had reduced surface area, adsorbed oxygen content, and lattice oxygen mobility, which resulted in poor catalytic performance. Although Cu3-MnO_x had the largest BET surface area, highest lattice oxygen mobility, and similar Mn³⁺ and adsorbed oxygen content as Cu2-MnO_x, the smaller average pore diameter of Cu3-MnO_x perhaps caused its conversion and selectivity to be similar to Cu2-MnO_x. The amorphous nature, Mn³⁺ and adsorbed oxygen content, Mn³⁺/Mn⁴⁺ ratio, lattice oxygen mobility, and synergistic effect between CuO and MnO_x were found to play key roles in catalytic performance. The absence of precious metals, the simple catalyst preparation process, the cheap air as the sole oxidant, no ligand and alkali, the mild reaction conditions, along with catalyst reusability and easy isolation of the aromatized products made our catalytic protocol both green and environmentally benign.

Accurate and rapid detection of organic amines in the vapor phase is essential for various applications such as agricultural use, industrial and environmental testing, and food security. Supramolecular gels composed of cholesterol derivative-based low-molecular-mass gelators (LMMGs) have attracted considerable attention owing to their unique character and formation mechanisms. In this study, a ZnS-supramolecular organogel hybrid film for amine vapor sensors was reported. It must be pointed out that the method of preparation of hybrid films considered here is different from that of the ZnS-organogel hybrid films previously reported. Because the sensing performance of nanomaterials strongly depends on their nanostructures, it is expected that nanomaterials synthesized by different methods exhibit different nanostructures and ultimately different sensing properties. The luminescent ZnS nanoparticles were first prepared by the oil-water interface method, before being dispersed in an organic solution containing the LMMG. Finally, the aforementioned solution was casted onto the surface of a glass substrate to fabricate a ZnS-supramolecular organogel fluorescent hybrid film after drying at room temperature. Scanning electron microscopy observations revealed that the surface morphology of the hybrid film was uniform cross-linked nanofibers. Transmission electron microscopy results revealed that the average particle size of the obtained ZnS nanoparticles is about 200 nm. The crystal structure of the ZnS nanoparticles is cubic, as revealed by X-ray diffraction. The photoluminescence emission spectra of the ZnS-supramolecular organogel film were recorded for various quantities of ZnS loading; the maximum emission wavelength of the hybrid films hardly changed, indicating that the dispersity of the ZnS nanoparticles in the hybrids is very well. Because the film network formed by the gelator has a good confinement effect on the ZnS nanoparticles, the hybrid film exhibits stable luminescence performance. Sensing experiments showed that the hybrid films are sensitive to the existence of organic monoamine and diamine vapors, and the sensitivity improved as the dosage of ZnS nanoparticles was increased. The quenching mechanism was discussed by comparing the fluorescence lifetimes of the hybrid films in the presence of air and ethylenediamine (EDA) vapor. It was found that the sensing mechanism is mainly static quenching, with a very small amount of dynamic quenching. The sensing performances of the film for common volatile organic compounds were investigated with a detection limit of 10.13 ppm (1 ppm = 1 × 10^-6, volume fraction) obtained for the EDA vapor. Reversible experiments indicated that the films have a good reversible response in the presence of EDA vapor. It is anticipated that this type of supramolecular organogel hybrid film could find applications in the monitoring of volatile organic amines in the areas of industry and environment.

The E/Z isomerization reaction is found extensively in most organic molecules containing double bond unit. This limits their practical application as luminescent materials partly, especially under photoirradiation. Therefore, it is important to obtain E/Z isomers with stable configuration in the excited state after photoirradiation. It is well known that cyanostilbene and its analogues play an important role in the development of organic opto/electronic materials. The substituted cyano group on C＝C double bonds has strong electron-withdrawing ability and large steric hindrance, which benefits the formation of donor-acceptor (D-A) structures and formation of intramolecular charge transfer. In our previous work, we reported a triphenylamine-cyanostilbene molecule (TPNCF) formed by modifying the cyanostilbene structure with triphenylamine, which maintained a stable E/Z configuration as a film and in high polar solvents. According to solvatochromism mechanisms and the results of theoretical calculations, we proposed that the charge transfer (CT) excited state between the triphenylamine donor and cyanostilbene acceptor groups induced the stable configuration of the E- and Z- isomers under photoirradiation. Under irradiation, the E/Z isomerization process occurring at a higher energy locally excited (LE) state was suppressed by a rapid internal conversion process from the LE to CT state. This work inspired us to provide a universal and effective molecular design strategy by modifying D-A substituents on double bonds that can successfully stabilize E/Z isomers. To further confirm that the CT excited state induced stable E- and Z- isomers in the cyanostilbene structure under photoirradiation, we designed and synthesized a donor-acceptor phenoxazine-cyanostilbene molecule (PZNCF) and successfully characterized its two E/Z isomers. In comparison with the reported TPNCF molecule, the in-situ NMR and UV spectra of E- and Z- isomers of PZNCF demonstrated that the E/Z isomerization rate became slower under photoirradiation, which indicated that the stronger electron-donating group of phenoxazine substituted in the cyanostilbene structure induced a more stable E/Z isomer configuration in its excited state. DFT calculations and photophysical results indicated that a stronger CT state was generated in both E- and Z- isomers of PZNCF. This further confirmed our hypothesized mechanism where the stable E/Z configuration can be obtained under photoirradiation by forming a suitable donor-acceptor structure to suppress the E/Z isomerization reaction in the LE state by a rapid internal crossing process from the LE to CT state. This molecular design strategy is of great significance to organic photochemistry and photoelectronics for molecules with double bond units.

Direct methanol fuel cell (DMFC) is a potential clean energy facility because of abundant resources, easy storage, and high safety of methanol. However, the low activity, poor durability, and high price of the catalysts hamper the development of DMFC. High-index faceted nanocrystals usually show high catalytic activity for the electro-oxidation of small organic molecules due to high densities of low-coordinated surface sites. Surface modification is an alternative approach for improving catalyst performance via ligand effect or electronic effect. Herein, we prepared tetrahexahedral Pd nanocrystals (THH Pd NCs) enclosed by {730} high-index facets via electrochemical square-wave potential deposition, and modified the THH Pd NCs with Ru using cyclic voltammetry (CV). The coverages of Ru (θ_Ru) were controlled by limiting the CV cycles. The electrocatalytic performance of the Ru-modified THH Pd NCs for methanol oxidation was studied using CV in an alkaline methanol solution. We found that Ru modification can greatly reduce the onset and peak potentials of methanol electro-oxidation from -0.33 to -0.39 V and from -0.16 to -0.26 V, respectively. The current densities at -0.3 V during methanol electro-oxidation increased with increasing θ_Ru from 0 to 0.08, and decreased with increasing θ_Ru from 0.08 to 0.27. When θ_Ru was 0.08, the current density on the Ru-modified THH Pd NCs reached 1.5 mA∙cm^-2, which was 10 times higher than that achieved for the THH Pd NCs. To detect the products at molecular level during methanol electro-oxidation, in-situ electrochemical Fourier-transform infrared (FTIR) spectroscopy was applied. The spectra of both THH Pd NCs and Ru-modified THH Pd NCs (θ_Ru = 0.08) showed that both CO₂ and formate were produced. The band intensities of CO₂ and formate on Ru-modified THH Pd NCs (θ_Ru = 0.08) were 1.6- and 1.2-times larger than those of THH Pd NCs, respectively. However, the band intensity of CO_ad during methanol electro-oxidation was almost equal on the two catalysts, implying that the "CO poison path" is not suppressed by Ru modification. These results indicate that a small amount of Ru (θ_Ru = 0.08) modification is beneficial for the electrocatalytic oxidation of methanol by enhancing the "formate path" at low potential. Overall, this study illustrates the influence of Ru modification of THH Pd NCs on its catalytic performance in methanol electro-oxidation, which throws light on the synthesis and application of catalysts with high activities.

The strategy of transition-metal-catalyzed C―H activation has been greatly developed in recent years. Direct transformations of inert C―H bonds undoubtedly provide powerful ways to construct various C―C and C―X (X = heteroatom) bonds, with enhanced atom- and step-economy. Impressive efforts have been devoted to this research all along. However, concerns about reactivity and selectivity remain to be tackled, due to their strong dependence on directing groups and acidic reactive sites. In this regard, more effective catalytic systems are of great importance and therefore in high demand. Bimetallic C―H activation, by virtue of the cooperative effect, has emerged as a promising solution to this issue. The intriguing interactions between two metals with substrates afford exceptional reaction efficiency and selectivity. Intensive interest in both experimental and computational studies has been recently triggered. In this minireview, diverse bimetallic catalytic reactions are summarized into three categories according to the initiator in the C―H activation step, namely, bimetallic catalyses based on palladium, nickel, and other metals. Experimental results as well as density functional theory (DFT) calculations are invoked in the plausible mechanistic considerations. In the first part, collaborative modes based on palladium are described, in which magnesium, chromium, cobalt, and silver are successfully engaged as accessory partners. Most of them stabilize the C―H activation transition states by decreasing the energy, thus facilitating the cleavage of C―H bonds. Notably, some reactions previously reported as examples of monomeric palladium catalysis are now reinvestigated as bimetallic scenarios, in light of computational discussions. In the second part, reactions based on the synergy of nickel, and zinc or aluminum, are generalized, in which zinc or aluminum acts as a Lewis acid to increase the acidity of C―H bonds. It has been shown that the choice of different kinds of Lewis acids and ligands has a great influence on the reaction chemo-, regio-, and stereoselectivity. Gratefully, even enantioselective transformations can be achieved using the cooperation of nickel and aluminum. Moreover, a key reaction intermediate in the bimetallic C―H activation by nickel and aluminum has been isolated, providing guidance for this bimetallic catalytic system in further mechanistic studies and applications. In the last part, synergetic catalysis based on various other metals is presented. Bimetallic regimes of ruthenium/copper, rhodium/bismuth, iridium/aluminum, manganese/zinc, and zirconium/aluminum have been elegantly applied to C―H activation reactions. Multifarious action modes are proposed on account of the mechanistic research.

Micelles, a kind of surfactant aggregate formed in water, may be swollen to a generally limited extent upon addition of a liquid hydrophobic compound. Swollen micelles have attracted considerable research attention because they can enhance the solubility of the said hydrophobic compound. The development of swollen micelles is of significant interest in terms of both scientific and industrial applications, such as drug delivery, oil recovery, and soil remediation. While there have been many studies focusing on micellar solubilization, several questions remain unanswered: the capacity to quantitatively solubilize the drug in drug delivery, the interaction between micelles and non-polar oil when microemulsions are not formed, and the differences and similarities between swollen micelles and microemulsions. Comprehensive understanding of and insight into swollen micelles will be helpful to tailor surfactants for industrial applications. Herein, we reviewed the recent progress in the field of swollen micelles in terms of solubilization capacity, solubilization site, micellar morphology, etc. First, the UV spectrophotometry results demonstrate that the solubilization capacity of micelles is related to their molecular structures and surfactant properties. The solubilization is also dependent on the composition and nature of the hydrophobic compounds, the presence of electrolytes, temperature, etc. Second, the solubilization site may be located in the micellar core, the palisade layer of the micelle, the micelle surface, or the hydrophilic shell of the micelle, depending on the property of the solubilized compounds and the morphology of the micelles. In general, the micellar aggregation number increases with increasing oil concentration; high concentration of oil causes the formation of spherical micelles, while high concentration of oil results in ellipsoidal micelles. Furthermore, the micellar size increased gradually with increasing oil concentrations. Finally, the differences and similarities between swollen micelles and microemulsions were clarified. It is believed that microemulsions can be considered as swollen micelles, but there has been some strong evidence that differentiates swollen micelles and microemulsions. Based on our results, we believe that microemulsions can be considered as swollen micelles, but all micellar solutions cannot be swollen to the extent of microemulsions, unless the specific structural requirements and conditions are satisfied. Overall, understanding the properties of swollen micelles and how they transform to microemulsions not only provide theoretical support for practical applications of surfactants, but can also be used to design new surfactants.

Kerosene is an ideal endothermic hydrocarbon. Its pyrolysis plays a significant role in the thermal protection for high-speed aircraft. Before it reacts, kerosene experiences thermal decomposition in the heat exchanger and produces cracked products. Thus, to use cracked kerosene instead of pure kerosene, knowledge of their ignition properties is needed. In this study, ignition delay times of cracked kerosene/air and kerosene/air were measured in a heated shock tube at temperatures of 657–1333 K, an equivalence ratio of 1.0, and pressures of 1.01 × 10⁵–10.10 × 10⁵ Pa. Ignition delay time was defined as the time interval between the arrival of the reflected shock and the occurrence of the steepest rise of excited-state CH species (CH*) emission at the sidewall measurement location. Pure helium was used as the driver gas for high-temperature measurements in which test times needed to be shorter than 1.5 ms, and tailored mixtures of He/Ar were used when test times could reach up to 15 ms. Arrhenius-type formulas for the relationship between ignition delay time and ignition conditions (temperature and pressure) were obtained by correlating the measured high-temperature data of both fuels. The results reveal that the ignition delay times of both fuels are close, and an increase in the pressure or temperature causes a decrease in the ignition delay time in the high-temperature region (> 1000 K). Both fuels exhibit similar high-temperature ignition delay properties, because they have close pressure exponents (cracked kerosene: τ_ign∝P^-0.85; kerosene:τ_ign∝P^-0.83) and global activation energies (cracked kerosene: E_a = 143.37 kJ·mol^-1; kerosene: E_a = 144.29 kJ·mol^-1). However, in the low-temperature region (< 1000 K), ignition delay characteristics are quite different. For cracked kerosene/air, while the decrease in the temperature still results in an increase in the ignition delay time, the negative temperature coefficient (NTC) of ignition delay does not occur, and the low-temperature ignition data still can be correlated by an Arrhenius-type formula with a much smaller global activation energy compared to that at high temperatures. However, for kerosene/air, this NTC phenomenon was observed, and the Arrhenius-type formula fails to correlate its low-temperature ignition data. At temperatures ranging from 830 to 1000 K, the cracked kerosene ignites faster than the kerosene; at temperatures below 830 K, kerosene ignition delay times become much shorter than those of cracked kerosene. Surrogates for cracked kerosene and kerosene are proposed based on the H/C ratio and average molecular weight in order to simulate ignition delay times for cracked kerosene/air and kerosene/air. The simulation results are in fairly good agreement with current experimental data for the two fuels at high temperatures (> 1000 K). However, in the low-temperature NTC region, the results are in very good agreement with kerosene ignition delay data but disagree with cracked kerosene ignition delay data. The comparison between experimental data and model predictions indicates that refinement of the reaction mechanisms for cracked kerosene and kerosene is needed. These test results are helpful to understand ignition properties of cracked kerosene in developing regenerative cooling technology for high-speed aircraft.

Driven by the wide-scale implementation of intermittent renewable energy generating technologies, such as wind and solar, sodium-ion batteries have recently attracted attention as an inexpensive energy storage system due to the abundance, low cost, and relatively low redox potential of sodium. However, in comparison with lithium-ion batteries, which are known for long cycle life, sodium-ion batteries usually suffer from significant capacity fading during long-term cycling due to the large volume expansion/contraction of the electrode active materials caused by insertion/extraction of the large sodium ion. In recent years, intense effort has been focused on the search for high performance electrode materials and electrolytes to improve the cyclability of sodium-ion batteries, and some progress has been achieved. The incorporation of additives into the electrolyte is a simple and efficient method of improving the cycle stability of sodium-ion batteries. Fluoroethylene carbonate (FEC) is generally considered to be a suitable additive for the formation of the anode solid electrolyte interphase (SEI), due to a relatively low-lying lowest unoccupied molecular orbital (LUMO). However, it is suggested that FEC it will not be oxidized on the cathode since it also has a relatively low highest occupied molecular orbital (HOMO). In this study, we investigated the effect of FEC as an additive on the cycle life of a sodium-ion battery with a P2-Na_xCo_0.7Mn_0.3O₂ (x ≈ 1) layered sodium transition metal oxide as the cathode active material, a sodium metal foil anode, a glass fiber separator, and an electrolyte composed of NaClO₄ and a varying mass content of FEC dissolved in propylene carbonate (PC). We analyzed the effect of the FEC additive on the morphology and chemical composition of the separator and cathode electrode surface using scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS), and studied the evolution of the crystalline structure of the cathode active material during charge and discharge using in situ X-ray diffraction (XRD). We found that an appropriate amount of FEC additive significantly suppressed the decomposition of the PC solvent, and assisted the formation of a NaF-rich protective layer on the cathode surface, which helped to maintain the structural stability of the cathode material, thereby improving the cycle stability of the sodium-ion battery. Density functional theory (DFT) calculations showed that FEC coordinates more readily with the ClO₄^- anion on the cathode surface than does the PC solvent. This drives the formation of the NaF-rich protective layer on the cathode surface. We believe these results could provide inspiration in the design of electrolyte additives for protection of the sodium cathode during cycling, thus improving the cycling performance of sodium-ion batteries.

Recently, ferroelectric materials have attracted considerable research attention. In particular, two dimensional (2D) ferroelectric materials have been considered as most crucial for next-generation circuit designs because of their application as novel electric memory devices. However, a 2D ferroelectric material is very rare. The ferroelectric materials with the form ABP₂X₆ (A = Ag, Cu; B = Bi, In; X = S, Se) are of interest because of their ferroelectric property maintained in their ultrathin structures. Within the ABP₂X₆ monolayer, the P―P bonds form the pillars that hold the top and bottom X planes, while the off-center A―B atoms between the X layers induce a spontaneous ferroelectric polarization. If the two off-center A―B sites are equally aligned, this would lead to the appearance of the paraelectric state. Such intriguing structures must impart novel mechanical properties to the materials. Until now, there has been no report on the mechanical properties of monolayer ABP₂X₆. Based on first-principles calculations, we studied the structural, electronic, mechanical as well as the electromechanical coupling properties of monolayer ABP₂X₆ (A = Ag, Cu; B = Bi, In; X = S, Se). We found that they are all semiconductors with wide bandgaps of 2.73, 2.17, 3.00, and 2.31 eV for CuInP₂Se₆, CuBiP₂Se₆, AgBiP₂S₆, and AgBiP₂Se₆, respectively, which are calculated based on the Heyd-Scuseria-Ernzerhof (HSE) exchange correlation functional model. The conduction band minimum is mainly from p orbitals of X and B atoms, whereas the valence band maximum is due to the hybridization of the p orbital of X atoms and the d orbital of A atoms. Moreover, there are three short and three long A/B―X bonds due to the A―B off-center displacement. Together with the d-p orbital hybridization, the main reason for the distorted ferroelectric structure in ABP₂X₆ monolayers is the Jahn-Teller effect. ABP₂X₆ monolayers are predicted to be a new class of auxetic materials with an out-of-plane negative Poisson's ratio, i.e., the values of the negative Poisson's ratio are in the order AgBiP₂S₆ (−0.805) < AgBiP₂Se₆ (−0.778) < CuBiP₂Se₆ (−0.670) < CuInP₂S₆ (−0.060). This is mainly due to the tensile strain applied in the x/y direction enlarging the angle between P―P bonds and top layer X atoms, thereby enhancing the bucking height of monolayer ABP₂X₆. Moreover, external strain has a significant impact on the A―B off-center displacement, rendering an out-of-plane piezoelectric polarization. The values of e₁₃ for CuInP₂S₆, CuBiP₂Se₆, AgBiP₂S₆, AgBiP₂Se₆ monolayers are calculated to be −3.95 × 10⁻¹², −5.68 × 10⁻¹², −3.94 × 10⁻¹², −2.71 × 10⁻¹² C∙m⁻¹, respectively, which are comparable to the only experimentally confirmed 2D out-of-plane piezoelectric Janus system (piezoelectric coefficient = −3.8 × 10⁻¹² C∙m⁻¹). This unusual auxetic behavior, ferroelectric polarization, and the electromechanical coupling in monolayer ABP₂X₆ could potentially lead to enormous technologically important applications in nanoelectronics, nanomechanics, and piezoelectrics.

The controlled coupling of spin centers is essential in the construction of molecular spin-based quantum information processing architectures. A major challenge is to induce the requisite coupling between two adjacent spins, while protecting them from neighboring spins and other environmental interactions. Owing to their native spin properties, endohedral fullerenes are attractive for use as elements in quantum information processing architectures. N@C₆₀ is an endohedral fullerene molecule with a highly reactive nitrogen atom at the center of the carbon cage. The endohedral nitrogen is atomic and not covalently bound to the cage atoms; therefore, the nitrogen atom is chemically inert toward the outer environment. Owing to its remarkably long electron-spin lifetimes and sharp resonances, N@C₆₀ has exceptional properties for quantum computing. The thermal stability and molecular structure of N@C₆₀ make it a useful embodiment of a quantum bit — a fundamental element for a quantum computer. Several future quantum computer architectures based on N@C₆₀ have been proposed, one of which is a two-dimensional, quantum-bit array on specific substrates. However, a challenging yet important task is to understand the effect of various substrates on the spin properties of the endohedral fullerene, since the interaction between the endohedral fullerene and the substrate may largely affect the spin characters of the endohedral N atom. The fabrication of an endohedral fullerene molecular array on substrates is also a challenge because high-temperature methods such as evaporation will cause decomposition of N@C₆₀. Here we report our investigation on the electron spin resonance (ESR) of N@C₆₀ molecules on various substrates such as Au(111), Si(111), and SiO₂. In this study, N@C₆₀ was prepared using the ion implantation method, and enrichment was performed using a multistep and recycling high-performance liquid chromatography (HPLC) system with a Cosmosil Buckyprep column. N@C₆₀ molecular films on Au(111) substrates were prepared at room temperature. In addition, scanning tunneling microscope (STM) topography of the N@C₆₀/C₆₀ monolayer on Au(111) was obtained at a sample temperature of 5 K in ultra high vacuum (UHV). We found that the ESR signal of the N@C₆₀ molecules decreases rapidly and disappeared approximately 360 min after the deposition of N@C₆₀ on Au(111). In comparison, the ESR signal was maintained for a longer time on the Si(111) and SiO₂ substrates. We propose that coupling between the Au(111) substrate and the endohedral N atoms quenches the ESR signal of the endohedral N atom, while the Si(111) and SiO₂ substrates have a smaller effect on the ESR signal. This result offers useful information for the design of basic quantum computer architectures.

Pyridones represent an important family of heterocycles that exhibit a wide range of biological activities. They are often found in pharmaceutical agents and biomolecules. Several transition-metal-catalyzed transformations have been developed to access this family of heterocycles. Among them, C―H bond activation has recently emerged as a general strategy for the construction of substituted pyridones. In most cases, the core nitrogen-containing heterocycle is assembled via the dehydrogenative annulation of α, β-unsaturated amides and alkynes. Such processes involve a cascade sequence of N―H cleavage, sp² C―H activation, and annulation. Despite this progress, the more readily available α, β-saturated amides are rarely used. Ideally, tethering the direct dehydrogenation of an amide with the above-mentioned C―H annulation cascade would give a more practical synthesis of pyridones. Nevertheless, the dehydrogenation of amides under mild conditions is a synthetic challenge due to their intrinsic weak α-acidity. Recently, we have reported a general protocol for the aerobic dehydrogenation of γ, δ-unsaturated amides, acids, and ketones. A key Ir―allyl intermediate was believed responsible for enhancing the α-acidity of the amides studied, which enables the dehydrogenation step to occur under mild reaction conditions. Herein, we describe a new method for the synthesis of polysubstituted pyridones using γ, δ-unsaturated amides and alkynes. In the presence of [RhCp*Cl₂]₂, the dehydrogenation step occurs via β-C―H bond activation. The resulting π-allyl―Rh intermediate undergoes an accelerated dehydrogenation reaction to afford the doubly unsaturated amide. This in-situ generated dienamide undergoes sp² C―H activation at the β-position and a subsequent alkyne insertion/cyclization reaction to yield the target heterocycle. Regeneration of the Rh catalyst is accomplished using an external oxidant and completes the streamlined double C―H activation and double dehydrogenation catalytic cycle. Various functional groups are well tolerated. The γ-alkenyl moiety not only facilitates the direct dehydrogenation of amides, but also serves as a handle for further derivatization of the as-obtained products. To gain a mechanistic insight into the reaction cascade, a set of control experiments were carried out. The results demonstrate that the dienamide is one of the key reaction intermediates. NMR experiments confirmed that the fast dehydrogenation process occurs during the early stage of the reaction. The alkyne insertion is believed to be the rate-determining step in the reaction cascade, as suggested by competition experiments.

Transition-metal-catalyzed C―H bond activation, which has been widely applied to construct new covalent bonds, has emerged as one of the most effective strategies in synthetic chemistry due to atom economy and simple procedure. In this review, we have summarized the recent reports on the theoretical mechanistic study of transition-metal-catalyzed C―H bond cleavage. Based on these comprehensive theoretical studies, we have systematically discussed the general modes of C―H bond activation, which involves oxidative addition, base-assisted deprotonation, σ-metathesis, Friedel-Crafts-type electrophilic aromatic substitution, α- or β-hydrogen elimination, and hydrogen atom abstraction. From a mechanistic point of view, C―H bond activation by oxidative addition generally involves a zero-valent transition metal catalyst with strong reducibility, which requires a low activation barrier. The concerted metalation-deprotonation (CMD)-type C―H bond cleavage often occurs via a six-membered cyclic transition state using transition metal carboxylate as the catalyst with a directing group, which is a common mechanism for transition metals with high oxidation states. Base-assisted internal electrophilic substitution (BIES)-type C―H bond activation is commonly performed in the presence of cationic transition metal catalysts, in which electron-rich arenes react preferentially compared to electron-deficient arenes. In some other cases, outer-sphere base-assisted deprotonation can also result in C―H activation, which is dependent on the strength of the base used. The stronger the base used, the lower the energy barrier, and thus, the easier it is to protonate. The σ-metathesis pathway, which could occur via a four-membered cyclic transition state, is often considered an alternative for concerted metalation-deprotonation. If the aromatic hydrocarbon is attacked by electrophiles, the C―H bond can be activated by Friedel-Crafts-type electrophilic aromatic substitution. Elimination of α- or β-hydrogen is also frequently proposed for transition-metal-catalyzed C―H functionalization. Hydrogen atom abstraction could achieve C―H bond activation via a free radical process. Moreover, the C―H bonds of hydrocarbons can be considered weak nucleophiles because the electronegativity of carbon is higher than that of hydrogen, and they could be converted to strong nucleophiles (C―M) in the presence of transition metal catalysts via the different pathways mentioned above. It enables further functionalization with electrophiles or nucleophiles to construct complex molecular skeletons. Summarizing the general modes of C―H bond activation will increase our understanding of the associated chemical mechanism and will pave the way for new synthetic strategies. This review aims to offer theoretical guidance for experimental studies and inspire new reaction design by summarizing the modes of transition-metal-catalyzed C―H bond activation.