Glass, an amorphous oxide material with a long history, is widely used in our daily life. Graphene is a novel two-dimensional material formed by carbon atoms. The unique properties of graphene, such as excellent mechanical strength, high electrical and thermal conductivity and optical transparency, serve as complementary components to those of glass. Therefore, the combination of graphene and glass would endow noticeable electrical/thermal conductivity and surface hydrophobicity without sacrificing the transparency of conventional glass. Previously reported routes for integrating graphene with glass mainly used solution-casting of liquid-exfoliated graphene nanoplatelets and transfer-coating of graphene films grown on metals. Compared with the existing methods, the direct growth of graphene on glass could avoid contamination and damage during the integration process, thereby resulting in good graphene quality and scalability, high thickness/ coverage uniformity, much reduced breakage density, and a tight and clean interface with the underlying glass. In this article, we review our recent progress on the direct growth of graphene on various glass by chemical vapor deposition (CVD). With the consideration of the thermo-stabilities of glass and application requirements, three different CVD routes are developed, i.e., high-temperature, atmospheric pressure CVD on solid-state thermostable glass and molten-state glass, as well as low-temperature plasma enhanced CVD on solid-state soda-lime floating glass. We also explore the practical applications of the as-grown graphene glass, where electrochromic windows, defoggers, cell proliferation, and photocatalytic plates were fabricated based on our CVD-grown graphene glass. The high performance of these devices promises practical usage of graphene glass in daily-life applications.
As one of the most promising materials in the field of photovoltaics, organic- inorganic hybrid perovskites have attracted widespread attention in recent years. In addition to their promising applications in the field of photovoltaics, perovskite materials also exhibit outstanding photoluminescence and electroluminescence properties. This paper reviews the latest developments in organic- inorganic hybrid perovskite materials, with particular attention paid to the luminescence. Firstly, a summary of the fundamental issues related to the unique light emitting characteristics and influencing factors of perovskite materials is provided, including the light-emitting mechanism and principles related to spectrum adjustability. The influence of the morphology of perovskite on the photoluminescence properties is discussed. The latest developments and applications of perovskite materials in various devices, including light-emitting diodes, lasers, and lightemitting field effect transistors, are then discussed. Finally, the key issues and challenges of perovskite light emitting materials are addressed and prospects for future perovskite-based applications are discussed.
Photoemission electron microscopy (PEEM)/low energy electron microscopy (LEEM) are surface techniques that can be used to image surface structure, electronic states, and surface chemistry. Important applications of the technique in catalysis, energy, nano science, and material sciences have been seen. In this paper, we briefly introduce the principle of PEEM/LEEM and the recent advances of the technique. Then, some applications of PEEM/LEEM in dynamic studies of surface physics and chemistry of two-dimensional (2D) atomic crystals are highlighted, which include the growth of 2D atomic crystals, the formation of 2D heterostructures, the intercalation of the 2D materials, and chemical reactions confined under the 2D materials. Using surface imaging, micro-region low energy electron diffraction (μ-LEED), and the intensity–voltage (I–V) curves, the kinetics of 2D material growth and reactions at the 2D material/solid interfaces can be deeply understood.
This paper focuses on application of graphdiyne (GDY) in both energy storage and conversion fields, including the most recent theoretical and experimental progress. The unique three-dimensional pore structure formed by stacking of the GDY layer, make it possess the natural advantage which can be applied to lithium storage and hydrogen storage. Because of its lithium storage ability, GDY can be used in energy storage devices, such as lithium ion batteries and lithium ion capacitors. While with the hydrogen storage property, GDY can be used as a hydrogen storage material in fuel cells. By doping method, the performance of GDY for lithium and hydrogen storage can be further improved. Owing to acetylene units composed of sp hybridized carbon atoms and benzene rings composed of sp2 hybridized carbon atoms, GDY possesses multiple conjugated electronic structures. Thus, its band gap can be regulated through many ways accompanied with existence of Dirac cones. This property means that GDY can not only be used as a high-activity non-metal catalyst in place of noble metal catalysts in photocatalysis, but it also plays a promotional role in the hole transport layer and electron transport layer of solar cells. All of the reported results including theoretical and experimental data reviewed here, show the great potential of GDY in energy field applications.
Because of its zero-carbon emission energy, hydrogen energy is considered the cleanest energy. The greatest challenge is to develop a cost-effective strategy for hydrogen generation. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion are promising pathways for sustainable hydrogen production. All of these techniques require highly active noble metal-free hydrogen and oxygen evolution catalysts to make the water splitting process energy efficient and economical. In this review, we highlight recent research efforts toward synthesis and performance optimization of noble metal-free electrocatalysts in our institute over the last 3 years. We focus on (1) hydrogen evolution catalysts, including transition metal phosphide, sulfides, selenides, and carbides; (2) oxygen evolution catalysts, including transition metal phosphide, sulfide, and oxide/hydroxides; and (3) bifunctional catalysts, mainly comprising transition metal phosphides, selenides, sulfides, and so on. Finally, we summarize the challenges and prospective for future development of non-noble metal catalysts for water electrolysis.
Graphitic carbon nitride (g-C3N4) is a new metal-free material. Owing to its multiple unique physicochemical properties, g-C3N4 has promising applications in various research fields, including heterogeneous catalysis, photocatalysis, fuel cells, and gas storage. Compared with bulk g-C3N4 prepared via direct thermal condensation, mesoporous g-C3N4 possesses a higher surface area and abundant accessible mesoporous pores. These features expose many more surface active sites, thereby improving the performance of this material in catalysis as well as in other applications. Thermal condensation is the most convenient strategy to prepare g-C3N4 and, when fabricating mesoporous g-C3N4, one may employ hard-, soft-, or non-templating method. This paper reviews recent advances in the synthesis of mesoporous g-C3N4 using all three routes. Specifically, several crucial issues regarding the hard-templating method are discussed with regard to the synthetic mechanism associated with various precursors and the physicochemical properties of the g-C3N4 products. Novel soft- and non-templating approaches for the preparation of mesoporous g-C3N4 are also addressed and a detailed comparison to the hard-templating method is provided. Finally, future prospects for the development of mesoporous g-C3N4 materials are also assessed.
Quantum dot-sensitized solar cells (QDSCs) have attracted much attention in the past few years because of the advantages of quantum dots (QDs), including low cost, easy fabrication, size-dependence bandgap, and multiple exciton generation (MEG). The properties of QD sensitizers influence the performance of QDSCs, such as their photoelectric characteristics, preparation methods, surface defects, chemical stability, and their sensitization towards TiO2 photoanodes. This review demonstrates the development of QD sensitizers, including narrow bandgap binary QDs, ternary or quaternary alloyed QDs, and Type-Ⅱ core-shell QDs, especially the preparation methods of colloidal QDs. Furthermore, the deposition and sensitization methods of QDs are introduced in detail, particularly bifunctional-assisted self-assembly deposition. Meanwhile, methods to improve electron injection efficiency and reduce charge recombination are also summarized. Finally, a brief introduction is provided to the development of electrolytes and counter electrodes in QDSCs.
Conversion of carbon dioxide (CO2) to value-added chemicals and fuels driven by low-grade renewable electricity is of significant interest since it serves the dual purpose of reducing atmospheric content of CO2 by utilizing it as a feedstock and storing it in the form of high-energy-density fuels. In this regard, there are an increasing number of interesting developments taking place in the popular research focus area of electrochemical reduction of CO2. This review first introduces the general principles of CO2 electroreduction. Next, the latest progress relating to electrocatalytic materials and experimental and theoretical studies of the reaction mechanism has been discussed. Finally, the challenges and prospects for further development of CO2 electroreduction have been presented.
Graphene has potential applications in many fields. In particular, two-dimensional graphene nanochannels assembled from graphene sheets can be used for filtration and separation. In this work, molecular dynamics simulations were performed to investigate the microscopic structural and dynamical properties of water molecules confined in pristine and hydroxyl-modified graphene slit pores with widths of 0.6-1.5 nm. The simulation results indicate that water molecules have layered structure distributions within the graphene nanoscale channels. The special ordered ring structure can be formed for water confined in the subnanometer pores (0.6-0.8 nm). Graphene surfaces are able to induce distinctive molecular interfacial orientations of water molecules. In the graphene slits, the diffusion of water molecules was slower than that in bulk water, and the hydroxyl-modified graphene pores could lead to more reduced water diffusion ability. For the hydroxyl-modified graphene pores, water molecules spontaneously permeated into the 0.6 nm slit pore. According to the simulation results, the dynamic behavior of confined water is associated with the ordered water structures confined within the graphene-based nanochannels. These simulation results will be helpful in understanding the penetration mechanism of water molecules through graphene nanochannels, and will provide a guide for designing graphene-based membrane structures.
Organic-inorganic halide perovskite solar cells (PSCs) have attracted increasing attention because of their desirable properties.A key advance has been the replacement of the liquid electrolytes by solid-state hole-transporting materials (HTMs), which not only improves the power conversion efficiency (PCE) but also enhances the cell stability.HTMs are now an integral part of PSCs.Both organic and inorganic HTMs have found application in PSCs.However, inorganic HTMs are hampered by the limited choice of materials and the relatively low PCE of the solar cells based on them.The development of new organic HTMs is therefore necessary to improve the PCE and stability of PSCs.This has become a focus of various research fields, and new HTMs continue to emerge in large numbers.In this paper, we give an overview of the use of organic HTMs in PSCs. According to their molecular weight, organic HTMs are classified as either molecular or polymeric.We discuss in detail the effects of the functional groups and structures of organic HTMs on the PCE, fill factor, open circuit voltage, and stability of the resulting PSCs, as developed in recent years.The paper also covers the highest occupied molecular orbitals, the hole mobility, and the use of additives in HTMs.Finally, forecasts of the future development of organic HTMs are reviewed.
Mesoporous silica materials have attracted much attention because of their large surface area, uniform pore-size distribution, large pore size, and wide potential applications in the fields of separation, adsorption, and catalysis. The progress in the removal of volatile organic compounds (VOCs, mainly containing hydrocarbons, methanol, formaldehyde, acetone, benzene, toluene, naphthalene, and ethyl acetate) by mesoporous silica materials and supported catalysts in recent years is reviewed. The effect of the structure of mesoporous silica materials on the adsorption of VOCs is discussed. We also discuss the catalytic performance and reaction mechanism for catalytic VOC oxidation over supported catalysts. The recent developments in catalytic combustion of toluene are examined in detail. We found that the surface environment, pore structure, and morphology of mesoporous silica materials are the main factors influencing adsorption of VOC molecules. The application of noble metal catalyst focuses on improving poison resistance and reducing cost. The research on non-noble metal catalysts focuses on developing supported mixed-metal oxide catalysts with high activity. Future developments of mesoporous silica materials and supported catalysts are highlighted. The design of the catalyst can be carried out from two aspects: the silica support and the mesoporous channel. This review will be helpful in choosing an appropriate catalyst for the removal of VOCs with high activity and stability.
Density functional reactivity theory (DFRT) is a recent endeavor to appreciate and quantify molecular reactivity with simple density functionals. Examples of such density functionals recently investigated in the literature included Shannon entropy, Fisher information, and other quantities from information theory. This review presents an overview on the principles of the information-theoretic approach in DFRT, including the extreme physical information principle, minimum information gain principle, and information conservation principle. Three representations of this approach with electron density, shape function, and atoms-in-molecules are also summarized. Moreover, their applications in quantifying steric effect, electrophilicity, nucleophilicity, and regioselectivity are highlighted, so are the recent results in a completely new understanding about the nature and origin of ortho/para and meta group directing phenomena in electrophilic aromatic substitution reactions. A brief outlook of a few possible future developments is discussed at the end.
White organic light-emitting diodes (WOLEDs) are now approaching mainstream display markets, and they are also being aggressively investigated for next-generation lighting applications because of their extraordinary characteristics, such as high efficiency, high luminance, lower power consumption, wide viewing angle, fast switching, ultralight weight, and flexibility. In this paper, we first introduce the various approaches to realize WOLEDs, and then summarize the properties and differences of the four types of WOLEDs from the perspective of the emitting materials. The recent development of fluorescent, phosphorescent, fluorescent/ phosphorescent hybrid, and delayed fluorescence WOLEDs is comprehensively illustrated. By combining with our published works, we systematically review the device structures, design strategies, working mechanisms, physical theories, and electroluminescent processes of the reported WOLEDs. Then, the development of flexible WOLED is presented. Finally, the existing problems and trends of WOLEDs are discussed.
In recent years, significant breakthroughs have been achieved in the development of organicinorganic halide lead perovskite solar cells, with reported power conversion efficiency (PCE) values of up to 22.1%. This value is comparable to the efficiencies obtained using CdTe (22.1%) and CuInGaSn (CIGS) (22.3%) solar cells, and close to the value associated with crystalline silicon solar cells (approximately 25%). However, the limited long-term output efficiency stability and lead toxicity issues associated with organic-inorgan lead halide perovskite cells have limited their commercial applications. This review focuses on these issues and corresponding solutions for halide lead hybrid perovskite solar cells, and discusses advances and developments in Pb-free inorganic perovskite solar cells. We also examine the current body of knowledge regarding perovskite solar cells and discuss critical points and expectations regarding further performance improvements.
Sodium ion batteries (SIBs) have attracted increasing attention for energy storage systems because of abundant and low cost sodium resources. However, the large ionic radius of sodium and its slow electrochemical kinetics are the main obstacles for the development of suitable electrodes for high-performance SIBs. The development of high-performance cathode materials is the key to improving the energy density of SIBs and facilitating their commercialization. Herein, we review the latest advances and progress of cathode materials for SIBs, including transition metal oxides, polyanions, ferrocyanides, organic materials and polymers, and amorphous materials. Additionally, we have summarized our previous works in this area, explore the relationship between structure and electrochemical performance, and discuss effective ways to improve the reversibility, working potential and structural stability of these cathode materials.
Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers, constructed with lightweight elements by covalent bonds. Owing to their low density, high thermal stability, and inherent porosity, COFs have many potential applications in gas adsorption, heterogeneous catalysis, energy storage, etc. This article reviews the latest progress in COFs, including their structural design, synthesis, purification, characterization methods, and applications in gas adsorption, catalysis, and photoelectricity. Finally, the prospects of COFs are also discussed.
Graphitic carbon nitride (g-C3N4) is a promising photocatalyst because of its low cost, high stability, and visible-light-induced photocatalytic activity. Z-scheme photocatalysts based on g-C3N4 (Z-g-C3N4) have attracted considerable attention because of their lower recombination rate of electron-holes and higher catalytic efficiency. In this review, the reaction mechanism of Z-scheme photocatalysis and the recent progress in Z-gC3N4 are introduced and reviewed. The applications of Z-g-C3N4, such as water splitting and CO2 reduction, are presented. The key factors that affect the photocatalytic performance, such as pH and the presence of electron mediators, are discussed. Moreover, the current challenges are described and the future development of Z-gC3N4 is forecast.
As a new type of energy storage device, supercapacitors with high specific capacitance, fast charge and discharge, and long cycle life have attracted significant attention in the energy storage field. Electrode materials are a crucial factor defining the electrochemical performance of supercapacitors. The standard supercapacitor electrode materials used can be classified into three types:carbon-based materials, metal oxides and hydroxide materials, and conductive polymers. This review introduces the principles of supercapacitors and summarizes recent research progress of carbon-based electrode materials, including pure carbon materials, and the binary and ternary complex materials with carbon.
In recent years, TiO2 has been widely investigated as a promising anode material for lithium ion batteries because of its low volume change during the charge/discharge process, environmental benignity, and high safety. However, it suffers from poor electron transport, slow ion diffusion, and low theoretical capacity (335 mAh·g-1), which limit its practical application. In this paper, we review the development history and latest progress of TiO2 nanotubes (TNTs) as anode materials. Three typical synthesis methods of TNTs, namely, hydrothermal method, anodic oxidation, and template method, are analyzed in detail. We explain the formation mechanism, compare the advantages and disadvantages of each method, and identify the factors influencing the formation of TNTs. We also carefully analyze the morphology and crystallography of TNTs and describe how they influence the electrochemical performance. It is pointed out that c-axis oriented, arrayed, unsealed TNTs with a wall thickness less than 5 nm show better electrochemical performance. Various approaches for improving the electrochemical performance of TNTs are summarized, including preparation of threedimensional (3D) structured electrodes, doping, coating, and synthesis of composites. Among these approaches, compositing with materials that have high capacity and high conductivity has proven to be effective, convenient, and controllable. The achievements and the problems associated with each approach are summarized, and the possible research directions and prospects of TNTs as anode materials for Li-ion batteries in the future are discussed.
Lithium ion batteries (LiBs) have been widely utilized, but the limited lithium resource restricts development and application of LiBs in large-scale energy storage. Sodium has similar physicochemical characteristics to that of lithium and is suitable to transfer between two electrodes as a cation in the "rocking chair" mechanism of LiBs. Na-containing compounds have been proposed as the electrodes to store sodium ions and provide channels for diffusion. Polyanion Na3V2(PO4)3 is a Na-super-ionic conductor (NASICON) with specific Na sites in its crystal structure and three-dimensional open channels. Recently, Na3V2(PO4)3 has been demonstrated as potential electrode material with promising properties for energy storage. In this review we systematically summarize the structure of Na3V2(PO4)3, the application and mechanism in a specific energy system, and the recent development of Na3V2(PO4)3 structure for use as electrodes. The potential problems and trends of Na3V2(PO4)3 are also discussed.
Graphene aerogels are obtained from graphene sheets through wet chemical assembly or vaporphase chemical growth. They have a three dimensional graphene architecture that has an interconnected network with a high specific surface area, good electric conductivity and other physicochemical properties and thus has important applications in electrochemical energy storage, adsorption, catalysis and sensing. In this review, we will highlight the assembly strategies and structural designs used to introduce the controlled assembly of the graphene sheets in graphene aerogel materials, such as graphene oxide-, reduced graphene oxide-, CVDgrown graphene and composite graphene aerogels. The current challenges and future development of the grapheme aerogels are also discussed.
Density functional theory dictates that the electron density determines everything in a molecular system's ground state, including its structure and reactivity properties. However, little is known about how to use density functionals to predict molecular reactivity. Density functional reactivity theory is an effort to fill this gap: it is a theoretical and conceptual framework through which electron-related functionals can be used to accurately predict structure and reactivity. Such density functionals include quantities from the information-theoretic approach, such as Shannon entropy and Fisher information, which have shown great potential as reactivity descriptors. In this work, we introduce three closely related quantities: Rényi entropy, Tsallis entropy, and Onicescu information energy. We evaluated these quantities for a number of neutral atoms and molecules, revealing their scaling properties with respect to electronic energy and the total number of electrons. In addition, using the example of second-order Onicescu information energy, we examined how its patterns change with the angle of dihedral rotation of an ethane molecule at both the molecular level and atoms-in-molecules level. Using these quantities as additional reactivity descriptors, researchers can more accurately predict the structure and reactivity of molecular systems.
One of the most appealing ways to resolve the worldwide energy crisis and environmental pollution is by converting solar energy into storable chemical energy as hydrogen through solar water splitting. The redox reactions of photogenerated charge carriers occurring on the surface of photocatalysts during the process of solar water splitting are particularly complex. Owing to the high reaction overpotentials and sluggish desorption kinetics of gas products, surface reaction is the rate-determining step in the solar water splitting process. Therefore, a great deal of attention has been focused on this specific research area. The recent advances and prospects for future directions regarding the importance of surface reactions for solar water splitting are presented. The main strategies to enhance the surface water splitting reaction kinetics are summarized. The roles and classifications of surface cocatalysts, as well as the effects of passivating the surface states and coating surface protective layers, are discussed by integrating the principles of photocatalysis. Prospects for the future development of surface reaction research are also proposed.
Over the past decade, graphene has been the focus of intensive research because of its remarkable physical and chemical properties. Researchers have made many efforts to synthesize graphene and investigate its potential applications. In this article, we first briefly review the fabrication processes and properties of graphene. Then, we discuss the application of graphene/Ag hybrid films as transparent conductive films (TCFs). Next, we introduce our results on this topic. Graphene and Ag nanowires were synthesized by chemical vapor deposition (CVD) and the polyol process, respectively. We successfully fabricated a graphene/Ag hybrid film with a low sheet resistance (Rs) of 26 Ω·□-1. Finally, we describe the main challenges facing graphene hybrid films and their potential applications in a wide range of optoelectronic devices.
Four deep eutectic solvents (DESs) were prepared from tetrabutylammonium chloride: tetrabutylammonium chloride:propionic acid [TBAC:2PA], tetrabutylammonium chloride:ethylene glycol [TBAC:2EG], tetrabutylammonium chloride:polyethylene glycol [TBAC:2PEG], and tetrabutylammonium chloride:phenylacetic acid [TBAC:2PAA]. The density, electrical conductivity, dynamic viscosity, and refractive index of the samples were measured at 288.15-338.15 K under atmospheric pressure. The influence of the temperature on the density, electrical conductivity, dynamic viscosity, and refractive index are discussed. The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy were determined from the measured values using empirical equations. The temperature dependences on the electrical conductivity and dynamic viscosity of the DESs were fitted by the Vogel-Fulcher-Tamman (VFT) equation. The Arrhenius equation is also discussed for the electrical conductivity and dynamic viscosity. The above study will be of great significance for the industrial and engineering applications of DESs.
supramolecular gels, an important type of soft matter, have showed unique advantages in the construction of functional soft materials, such as multiple stimuli responsive, photoelectrical, and biological compatibility materials. Through supramolecular gelation, diverse, uniform nanostructures can be obtained in a large quantity. On the other hand, most gelators are chiral molecules, so supramolecular gel is a medium to realize the expression of the chirality in supramolecular and nano level, especially to realize effectively chirality transfer, amplification, and asymmetric catalysis, and to fabricate various chiral architectures. In this paper, we describe the structural diversity and chirality in supramolecular gels, and discuss the future prospects for supramolecular gels.
The relationship between the bond angle and bond dipole moment is investigated. The atomic dipole moment corrected Hirshfeld (ADCH) charges are used to calculate the bond dipole moment. The electron localization function and its values at the bond critical points are exploited to analyze the bond′s electronic structures. Through analyzing the data of a series of covalent compounds formed by the IVA (IVA = C, Si, Ge), VA (VA = N, P, As), VIA (VIA = O, S, Se) and VIIA (VIIA = F, Cl, Br) group elements, it is found that, owing to the repulsion of bond dipole moments, the bond angles of these molecules become larger as their corresponding bond dipole moments increase if the bonds′ electronic structures are similar. This observation is also true for the ring molecules studied here, although a stress exists within the ring.
Lithium-sulfur (Li-S) batteries are promising electrochemical energy storage systems because of their high theoretical energy density, natural abundance, and environmental benignity. However, several problems such as the insulating nature of sulfur, high solubility of polysulfides, large volume variation of the sulfur cathode, and safety concerns regarding the lithium anode hinder the commercialization of Li-S batteries. Graphene-based materials, with advantages such as high conductivity and good flexibility, have shown effectiveness in realizing Li-S batteries with high energy density and high stability. These materials can be used as the cathode matrix, separator coating layer, and anode protection layer. In this review, the recent progress of graphene-based materials used in Li-S batteries, including graphene, functionalized graphene, heteroatom-doped graphene, and graphene-based composites, has been summarized. And perspectives regarding the development trend of graphene-based materials for Li-S batteries have been discussed.
A Cu3(BTC)2 (copper(Ⅱ) benzene 1, 3, 5-tricarboxylate) metal organic framework (MOF) catalyst was successfully prepared through an electrochemical route and used for selective catalytic reduction of nitrogen oxide (NOx) with NH3 for the first time. After systematically optimizing the reaction conditions such as solvents, voltage, electrolyte concentration, and reaction time, pure Cu3(BTC)2 with high crystallinity was obtained in 97.2% yield. The physicochemical properties of the catalyst were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). TGA results indicated that the framework was stable up to 310℃. The catalytic activity of Cu3(BTC)2 was evaluated using NO conversion as a model reaction. The Cu3(BTC)2 activation temperature significantly affected the catalytic activity. The Cu3(BTC)2 sample activated at 240℃ had the best catalytic activity and gave NO conversion of 90% at 220-280℃. A reaction mechanism was proposed based on the in situ FTIR spectroscopy results.
The electrocatalytic reduction of CO2 to HCOOH is an interesting topic and the efficiency usually depends strongly on the materials of the electrodes. Herein, nanostructured Cu2S on Cu-foam was prepared by electro-deposition method and characterized by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The Cu2S/Cu-foam electrode was used for the first time in the electrocatalytic reduction of CO2 to HCOOH, and acetonitrile (MeCN) with 0.5 mol·L-1 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) was used as the electrolyte. It was demonstrated that the electrolysis system was very efficient for the electrochemical reaction, and faradaic efficiency of HCOOH (FEHCOOH) and reduction current density could reach 85% and 5.3 mA·cm-2, respectively.
A new complex [Eu(4-MOBA)3(terpy)(H2O)]2 (4-MOBA: 4-methoxybenzoate, terpy: 2, 2' :6', 2"-terpyridine) was synthesized. The complex was characterized using Fourier transform infrared (FTIR) spectroscopy, elemental analysis, and powder X-ray diffraction (XRD). The structure of the complex was determined using single-crystal XRD. In the complex, each Eu3+ ion is nine coordinated to one terpy molecule, one water molecule and three carboxylate groups. The carboxylate groups are bonded to the Eu3+ ion in three modes: bidentate, bridging bidentate, and monodentate. Based on thermogravimetry-differential scanning calorimetry/Fourier transform infrared (TG-DSC/FTIR) measurements, we determined the thermal decomposition mechanism. The emission spectra of the complex exhibited characteristic luminescence, suggesting that terpy and 4-methoxybenzoic acid can act as sensitizing chromophores in this system. Also, bacteriostatic activities for the complex to Candida albicans and Escherichia coli are discussed.
Chemical kinetic modeling has become more and more important in the analysis of combustion systems. Considerable progress has been made in the development of combustion models in recent years. This review includes the following contents: electronic structure methods for combustion kinetics, recent developments on the calculation methods of thermodynamic parameters and rate constants in combustion, developments of combustion mechanisms and reduction techniques, molecular simulations with reactive force fields, combustion intermediate measurements, experiments for ignition delay time with shock wave tubes and combustion diagnostics. Due to the extreme complexity of reaction networks, the combustion mechanism is still not clearly understood by researchers. Owing to the strong application background, the combustion kinetics have attracted attention in recent years. The solver for reaction rate of intermediate species during combustion occupies the central point in combustion simulation. The progress in the research on reaction-turbulence interactions, and the combination of combustion kinetics with computational fluid dynamics, will facilitate fuel design and combustion simulation. To build a reliable combustion model for achieving a reasonable flow field structure description of engines is another important aspect.
Bi-based semiconductor photocatalysts are important visible-light-driven photocatalysts. However, the photocatalytic performance of bulk bismuth-containing compounds remains unsatisfactory. Many investigations indicate that morphology control and surface modification are effective methods for improving the photocatalytic activity of these compounds. Herein, we review recent advances in this field, including ultrathin nanoplate fabrication, facet ratio control, hierarchical and hollow architecture construction, functional group and quantum-sized nanoparticle modification, surface defect regulation, and in situ formation of metal bismuth and bismuth compounds. The characteristics and advantages of these modification methods are introduced. In addition, mechanisms for improving light absorption, separation, and utilization of excited carriers are discussed. Trends in the development of Bi-based photocatalysts using morphology control and surface modification, as well as the challenges involved, are also analyzed and summarized.
Graphyne is a rapidly rising star material of carbon allotropes containing only sp and sp2 hybridized carbon atoms forming extended two-dimensional layers. In particular, graphdiyne is an important member of graphyne family. With unique nanotopological pores, two-dimensional layered conjugated frameworks, and excellent semiconducting and optical properties, graphdiyne has displayed distinct superiorities in the fields of energy storage, electrocatalysis, photocatalysis, nonlinear optics, electronics, gas separation, etc. Therefore, the synthesis of high-quality graphdiyne is highly required to fulfill its potentially extraordinary applications. Furthermore, the development of a standardized and systematic set of characterization procedures is an urgent need, and would be based on intrinsic samples. However, there are still obvious barriers to synthesizing this new-born carbon allotrope that can be mainly considered as follows. The selection and stability of monomers is essential for synthesis. The synthesis process in solution also suffers from an annoying problem of the relatively free rotation possible about the alkyne-aryl single bonds, which leads to the coexistence and rapid equilibration of coplanar and twisted structures. Furthermore, the limited reaction conversion and side reactions also lead to a confusion of configuration.
In this review, we primarily focus on the state-of-the-art progress of the synthetic strategies for graphdiyne. First, we give a brief introduction about the structure of graphyne and graphdiyne. We subsequently discuss in detail the recent developments in synthetic methods that can mainly be divided into three aspects: total organic synthesis, on-surface covalent reaction, and polymerization in a solution phase. In particular, much progress in solution polymerization has been achieved since in-situ polymerization on Cu surface was reported in 2010. Liquid/liquid interface, gas/liquid interface, and surface template were also employed for confined reaction, and contribute significantly to the synthesis of a graphdiyne film. Through such strategies, graphdiyne with a well-defined structure and diverse morphologies could be achieved successfully. Finally, the opportunities and challenges for the synthesis of graphdiyne are prospected. A more rational design is desired in terms of monomer modification and reaction regulation.
Hydrogen produced from electrochemical water-splitting driven by renewable resource-derived electricity is considered a promising candidate for clean energy. However, sustainable hydrogen production from water splitting requires highly active catalysts to make the process efficient. Catalysts based on graphene-like two-dimensional (2D) materials present great potential in the hydrogen evolution reaction (HER) and thus gain attention. In this review, which is a combination of our recent works, we highlight research efforts towards electrocatalysts for the HER based on 2D materials including transition metal disulfides, MXenes, and boron monolayers. Finally, we summarize the challenges and prospects for future development of electrocatalysts for the hydrogen evolution reaction.
In response to energy shortages and environmental concerns, global energy consumption is transitioning from a reliance on fossil fuels to multiple, clean and efficient power sources. Energy storage is central to the development of electric vehicles and smart grids, and hence to the emerging nationally strategic industries. Today, lithium-ion batteries (LIBs) are among the most widely used energy storage devices in daily life, but they face a severe challenge to meet the rigorous requirements of energy/power density, cycle life and cost for electric vehicles and smart grids. The search for next-generation energy storage technologies with large energy density, long cycle life, high safety and low cost is vital in the post-LIB era. Consequently, lithium-sulfur and lithium-air batteries with high energy density, and safe, low-cost room-temperature sodium-ion batteries, have attracted increasing interest. In this article, we briefly summarize recent progress in next-generation rechargeable batteries and their key electrode materials, with a particular focus on Li-S, Li-air, and Na-ion batteries. The prospects for the future development of these new energy storage technologies are also discussed.
P25-reduced graphene oxide nanocomposites (RGO-P25) are prepared by using a facile one-step hydrothermal method. Their structure and photoelectrical properties are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The degradation effect of different addition ratios of the RGO-P25 nanocomposite on the photocatalytic degradation of methylene blue (MB) is investigated under UV and visible illumination. Results show that graphene oxide can be reduced during the hydrothermal reaction and thus, a mixed high defect P25 particles and RGO sheet composite is formed by electrostatic attraction. Band gaps of nanocomposites decreased from 3.00 to 2.27 eV with an increase in the amount of the RGO content. The electrical conductivities of the nanocomposites enhanced with an increased RGO amount. Over 80% of the initial methylene blue dye is decomposed by 1% (w, mass fraction) RGO-P25 after 30 min under either visible light or ultraviolet light. Under UV light illumination, 63% (molar fraction) of the N3 dye, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy = 4, 4'-dicarboxy-2, 2'-bipyridyl), is decomposed by the 1% RGO-P25 nanocomposite. Compared with the bare P25 (75% anatase; 25% rutile), the continual addition of RGO enhances the photocatalytic activity and gives rise to the more effective separation of photogenerated electron-hole pairs.
Metal organic frameworks (MOFs) have attracted tremendous attention in electrochemical energy storage and conversion because of their large surface area, high porosity, ordered structure and the tailorability of the structure. In this paper, the unique advantages of synthesizing electrocatalysts from MOFs are introduced. Then, the latest research progress of MOFs derived electrocatalysts in electrochemical energy conversion is mainly summarized. Finally, the application prospects, opportunities and challenges of MOF-based materials are briefly presented to provide an outlook for future research directions.
The metal oxide heterojunction has often been used to improve the gas sensing properties of resistive metal oxide semiconductor gas sensors. Metal oxide heterojunctions have been demonstrated to have many unique properties such as Fermi-level mediated charge transfer effects as well as synergistic behavior of different components. In this short review, we summarize the fundamental types of metal oxide heterojunction materials reported in domestic and foreign research in recent years. Metal oxide heterojunctions are mainly divided into five categories of mixed composite structures, multi-layer films, structure modified with a second phase, 1D nanostructure and core-shell structure. We review the enhanced gas sensing mechanisms of metal oxide heterojunctions. These mechanisms are discussed in detail, including the role of the heterojunction, synergistic effects, the spill-over effect, response-type inversion, separation of charge carriers, and microstructure manipulation. We also analyze the remaining challenges of metal oxide heterojunction gas sensors. Finally, we provide an outlook for future development of metal oxide heterojunction gas sensors. The future research directions of metal oxide heterojunction gas sensors can be developed from the definition of heterojunction interface mechanisms. It is hoped that determining the heterojunction interface mechanisms will provide some reference for the design of needed gas sensors in a bottom-up route.
It is the goal of density functional theory (DFT) researchers to develop the functional formalism of exchange-correlation (XC) with high accuracy and efficiency. Conventional functionals have issues when predicting the properties of the ground and excited states of atomic and molecular systems, and they do not show universal predictions. On the other hand, high-level theory methods such as the couple-cluster (CC) method and many-body perturbation theory (MBPT) based on GW (i.e., the dressed Green's function (G) and the dynamically screened Coulomb interaction (W)) approximation require very expensive computational cost and therefore the size of the systems studied and the practicability are limited. Recently, the optimally tuned range-separated (RS) functional has been developed to partly alleviate the above issues and has attracted great attention because it can achieve a level of accuracy comparable to the high-level method but with low computational cost. In this review, we first provide an overview of the theory in this field and then introduce the optimal tuning concept based on the RS functional. We combine the recent theoretical studies to evaluate their performance in practical calculations. Finally, we give some prospects for the future development and application of the optimally tuned approach.
Singlet exciton fission is the process by which a high-energy singlet exciton splits into two low-energy triplet excitons. Organic solar cells based on singlet fission have the potential to exceed the Shockley-Queisser limit and, in doing so, may improve their efficiency from 30% to 44.4%. Although progress in singlet fission materials and photovoltaic devices has accelerated with recent research, many challenges and debates remain with regard to clarifying the relationship between molecule structures and the rate and efficiency of singlet fission. This review addresses recent advances in singlet fission materials and summarizes the work of our own research group. We begin by introducing the background of singlet fission, following with the general concept, the requirements for singlet fission to proceed, and the applications of transient absorption spectroscopy. Two mechanisms have been proposed to explain singlet fission molecules, intermolecular and intramolecular singlet fission, and these two types of materials are summarized, focusing on dimers, which are novel structures that undergo efficient intramolecular singlet fission. Based on the latest developments in singlet fission, we discuss the possible future advances in, and prospects for the application of, singlet fission materials.
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.
Because of the potential applications of TiO2 in photocatalytic hydrogen production and pollutant degradation, over the past few decades we have witnessed increasing interest in and effort toward developing TiO2-based photocatalysts, and improving the efficiency and exploring the reaction mechanisms at the atomic and molecular levels. Because surface science studies on single crystal surfaces under ultrahigh vacuum (UHV) conditions can provide fundamental insights into these important processes, both the thermo-and photo-chemistry on TiO2, especially on rutile TiO2(110) surfaces, have been extensively investigated with a variety of experimental and theoretical approaches. In this review, commencing with the properties of TiO2, we then focus on charge transport and trapping, and electron transfer dynamics. Next, we summarize recent progress made in the study of elementary photocatalytic chemistry of methanol on mainly rutile TiO2(110), as well as in some studies on rutile TiO2(011) and anataseTiO2(101). These studies have provided fundamental insights into surface photocatalysis and stimulated new investigations in this exciting area. The implications of these studies for the development of new photocatalysis models are also discussed.
ZSM-5 zeolites with different pore structures were synthesized using different templates (tetrapropyl ammonium hydroxide (TPAOH), cetyltrimethylammonium bromide (CTAB) and C18-6-6Br2). The obtained nanosized (NZ), mesoporous (MZ), and nanosheets (NSZ) ZSM-5 samples were compared with conventional microporous ZSM-5 zeolite (CZ). The physicochemical properties of these samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption, and temperature-programmed desorption of ammonia (NH3-TPD). The results showed that the mesopore volumes and surface areas of the four samples increased in the order NSZ > MZ > NZ > CZ, and the ratio of strong/weak acidity increased in the order CZ > MZ > NZ > NSZ. In the methanol to propylene (MTP) reaction, the catalyst porosity played an important role on the product selectivity and catalytic stability. The selectivities for propylene and total olefins improved with increasing mesoporosity; NSZ, with the largest mesopore volume, gave the highest propylene selectivity, i.e., 47.5%, and 78.4% total olefins. Meanwhile, the introduction of mesopores into the ZSM-5 zeolite extended the catalytic lifetime. The NZ sample displayed reliable MTP catalytic activity for 200 h, which was predominately attributed to its optimal combination of acidity and porosity.
Mesoporous TiO2 was prepared by calcinating H2Ti205 at 773.15 K. The sample was characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) analysis. The adsorption behavior and mechanism of mesoporous TiO2 for lysozyme were investigated by isothermal adsorption experiments. The results show that the equilibrium experimental data were correlated with the Langmuir isotherm equation. The adsorption capacity first increased and then decreased with increasing pH value. The capacity showed a maximum value of 72.5 mg·g-1 when the pH value was 7.2. Lysozyme adsorbed on mesoporous TiO2 was extremely stable, and its amount on mesoporous TiO2 maintained 81.6% of its initial value after five adsorption and regeneration cycles. Furthermore, kinetic analysis was conducted using pseudo-first and pseudo-second order models. The adsorption of lysozyme on mesoporous TiO2 was described well by the pseudo-second order rate equation. The rate-determining step of the adsorption was the combined action of film diffusion and intraparticle diffusion. The adsorption thermodynamic analysis suggested ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0, which indicated that the adsorption was a spontaneous and endothermic process with entropy increased.
The crystal facet effect of photocatalysts has aroused increasing attention owing to its importance for the synthesis of novel photocatalysts, understanding photocatalytic mechanisms, and enhancing photocatalytic efficiency. In this paper, the research approaches, recently discovered phenomena, and the application of the facet effect of TiO2 are reviewed. The prospects and challenges of using the crystal facet effect of TiO2 photocatalysts are discussed.
Metal-free carbon catalysts have been receiving increasing attention in the fields of nanomaterials and catalysis. Compared with conventional metal catalysts, there are many advantages for metal-free carbon catalysts, such as simple synthesis, stable structure, large surface area, and diverse applications. Graphene is one layer of carbon atoms and has a periodic structure of aromatic carbon atoms. Graphene oxide is a highly oxidized form of graphene. As a new carbon material, its application in catalysis has emerged over the past 5 years. Graphene-based materials can efficiently catalyze hydrocarbon conversion, organic synthesis, energy conversion, and other heterogeneous catalytic processes. This review highlights the recent progress in the development of metal-free graphene-based catalysts (graphene oxide and graphene) and associated catalytic reactions.
The structural and electronic properties of Pt4 nanoparticles adsorbed on monolayer graphitic carbon nitride (Pt4/g-C3N4), as well as the adsorption behavior of oxygen molecules on the Pt4/g-C3N4 surface have been investigated through first-principles density-functional theory (DFT) calculations with the generalized gradient approximation (GGA). The interaction of the oxygen molecules with the bare g-C3N4 and the Pt4 clusters was also calculated for comparison. Our calculations show that Pt nanoparticles prefer to bond with four edge N atoms on heptazine phase g-C3N4 (HGCN) surfaces, forming two hexagonal rings. For s-triazine phase g-C3N4 (TGCN) surfaces, Pt nanoparticles prefer to sit atop the single vacancy site, forming three bonds with the nearest nitrogen atoms. Stronger hybridization of the Pt nanoparticles with the sp2 dangling bonds of neighboring nitrogen atoms leads to the Pt4 clusters strongly binding on both types of g-C3N4 surface. In addition, the results from Mulliken charge population analyses suggest that there are electrons flowing from the Pt clusters to g-C3N4. According to the comparative analyses of the O2 adsorbed on the Pt4/HGCN, Pt4/TGCN, and pure g-C3N4 systems, the presence of metal clusters promotes greater electron transfer to oxygen molecules and elongates the O―O bond. Meanwhile, its greater adsorbate-substrate distortion and large adsorption energy render the Pt4/HGCN system slightly superior to the Pt4/TGCN system in catalytic performance. The results validate that being supported on g-C3N4 may be a good way to modify the electronic structure of materials and their surface properties improve their catalytic performance.
Hydrothermal processing in conjunction with in situ precipitation were successfully applied to synthesize the magnetic composite catalyst silver bromide/silver phosphate/zinc ferrite (AgBr/Ag3PO4/ZnFe2O4). The phase structure, composition, morphology, and optical property of this material were subsequently assessed by X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. Under visible light illumination, the as-prepared AgBr/Ag3PO4/ZnFe2O4 photocatalyst exhibited superior photocatalytic performance during rhodamine B (RhB) degradation compared with Ag3PO4/ZnFe2O4, AgBr/ZnFe2O4, and P25 TiO2. This new catalyst also showed excellent photocatalytic activity in both acidic and basic solutions. The RhB photodegradation rate was slightly increased at higher temperatures, and the activation energy for this reaction was determined to be 31.9 kJ·mol-1 according to the Arrhenius equation. The high performance of the AgBr/Ag3PO4/ZnFe2O4 catalyst can be attributed to efficient photo-induced charge separation, and the generation of superoxide radicals and holes that are responsible for RhB degradation.
Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.
Chemically modified carbon has attracted significant attention since our first report of its use in lithium/sulfur (Li/S) cells. Compared with traditional carbon materials, chemically modified carbon prevents the dissolution and diffusion of intermediate polysulfides. Therefore, it yields sulfur cathodes with long cycling stability, which has become the focus of current research in the field of Li/S batteries. This review summarizes the use of chemically modified carbon for highly efficient sulfur utilization and the synergistic chemical/physical trapping of sulfur species. The prospects of further developments of Li/S batteries using chemically modified carbon is also discussed.
In response to aggravated fossil resources consuming and greenhouse effect, CO2 reduction has become a globally important scientific issue because this method can be used to produce value-added feedstock for application in alternative energy supply. Photoelectrocatalysis, achieved by combining optical energy and external electrical bias, is a feasible and promising system for CO2 reduction. In particular, applying graphene in tuning photoelectrochemical CO2 reduction has aroused considerable attention because graphene is advantageous for enhancing CO2 adsorption, facilitating electrons transfer, and thus optimizing the performance of graphene-based composite electrodes. In this review, we elaborate the fundamental principle, basic preparation methods, and recent progress in developing a variety of graphene-based composite electrodes for photoelectrochemical reduction of CO2 into solar fuels and chemicals. We also present a perspective on the opportunities and challenges for future research in this booming area and highlight the potential evolution strategies for advancing the research on photoelectrochemical CO2 reduction.
Semiconducting, two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) have attracted significant attention because of their unique properties and promising applications in electronic and optoelectronic devices. However, the controllable tuning of the properties of 2D MoS2 remains a key challenge with regard to its practical application. Among various approaches to addressing this issue, chemical doping is one of the most efficient. This review focuses on three major doping strategies, which are surface charge transfer, in-plane substitution and interlayer intercalation. We discuss the principles, latest progress and limitations of these doping approaches. Finally, we summarize the current challenges and opportunities associated with the chemical doping of 2D MoS2.
Functional materials and devices that can efficiently store and convert energies have attracted a great deal of attention in recent years. The composites of layered double hydroxide and graphene (LDH/G) are important energy materials. They have excellent physical and chemical properties of both components. Furthermore, their performances in energy-related systems can be improved by increasing the electrical conductivity of LDHs by blending graphene and partly preventing the aggregation of graphene sheets using LDH nanostructures. Therefore, LDH/G composites can be used in various energy applications, particularly for developing high-performance supercapacitors and efficient electrocatalysts for electrochemical splitting of water. In this review, we summarize the recent advances on the synthesis of LDH/chemically modified graphene (CMG, e.g., graphene oxide, reduced graphene oxide and their derivatives) composites and their application in electrochemical energy storage and conversion. Furthermore, the challenges and future perspectives in this research field are also outlined.
Graphene and graphene-like two-dimensional (2D) materials exhibit broad prospects for application in emerging electronics owing to their unique structure and excellent properties. However, there are still many challenges facing the achievement of controllable growth, which is the main bottleneck that limits the practical application of these materials. Chemical vapor deposition (CVD) is the most effective method for the controllable growth of high-quality graphene, in which the design of the catalytic substrate catches the most attention because it directly determines the two most significant basal processes--catalyzation and mass transfer. Recently, compared with the selection of the chemical composition of the catalyst, the change of the physical state of the catalyst from a solid phase to liquid phase is expected to lead to a qualitative change and improvement in the CVD of graphene and graphene-like two-dimensional materials. Unlike solid substrates, liquid substrates exhibit a loose atomic arrangement and intense atom movement, which contribute to a smooth and isotropic liquid surface and a fluidic liquid phase that can embed heteroatoms. Therefore, liquid metal shows many unique behaviors during the catalyzation of the growth of graphene, graphene-like two dimensional materials, and their heterostructures, such as strict self-limitation, ultra-fast growth, and smooth stitching of grains. More importantly, the rheological properties of a liquid substrate can even facilitate the self-assembly and transfer of 2D materials grown on it, in which the liquid metal substrate can be regarded as the 'philosopher's stone'. This feature article summarizes the growth, assembly, and transfer behavior of 2D materials on liquid metal catalysts. These primary technology developments will establish a solid foundation for the practical application of 2D materials.
Ordered mesoporous carbon materials (OMCs) have potentially broad applications in many fields, such as adsorption, separation, catalysis, and energy storage/conversion. Compared with the elaborate hardtemplate strategy, the soft-template approach, which is based on the self-assembly between amphiphilic block copolymers and polymerizable precursors (e.g., phenolic resins), is a more effective and efficient method for the synthesis of OMCs. In this review, the mechanism and characteristics for three main soft-template methods, i.e., solvent evaporation-induced self-assembly synthesis, aqueous cooperative self-assembly synthesis and solvent-free synthesis, are discussed and compared. In addition, a few highlights of recent progress, including application of novel carbon precursors, structural modification and functionalization of OMCs, are outlined. Finally, we summarize the crucial issues to be addressed in developing the synthesis methodology of OMCs.
Owing to advantages such as high theoretical specific capacity, designable structure, low cost and environmental friendliness, organic quinone compounds have been proposed as promising electrode materials for rechargeable lithium batteries. In this review, we first introduce the classification, structural characteristics, electrochemical reaction mechanism and performance of quinone-based electrodes. We then summarize the recent progress, existing problems and strategies for improving the electrochemical performance of quinonebased compounds and polymers. Finally, we also discuss the future development of such materials for use in lithium batteries.
With the rapid development of wearable devices, flexible conductive materials, which are one of the most important components of flexible electronics, have continued to attract increasing attention as important materials. Conventional electrodes mainly consist of rigid metallic materials, and consequently lack flexibility. Some of the strategies commonly used to make flexible metal electrodes include reducing the thickness of the electrode and designing electrodes with unique structural features. However, these techniques are generally complicated and expensive. Nanocarbon materials, especially carbon nanotubes and graphene, are highly flexible and exhibit excellent conductivity, superior thermal stability, good chemical stability, and high transmittance, making them good alternative materials for the preparation of flexible conductors. In this review, we have summarized recent advances towards the development of flexible conductors based on different types of nanocarbon materials, including carbon nanotubes arrays, carbon nanotubes films, carbon nanotubes fibers, graphene prepared using exfoliation or chemical vapor deposition techniques and graphene fibers. We have also provided a brief review of flexible conductive materials based on graphene/carbon nanotube composites, as well as a summary of the synthesis, fabrication and performances of these conductors. Finally, we have discussed the future challenges and possible research directions of flexible conductors based on nanocarbon materials.
We report on the in-situ preparation of Na2Ti3O7 nanosheets and their application as high-performance anode material for sodium ion batteries. Nanosheets with interconnected micro-nano architectures are prepared by simply engraving commercial titanium foils. Furthermore, the foils can be used directly as electrodes without redundant conductive additives or binders. The electrode material exhibits excellent electrochemical performance with reversible capacity of 175 mAh·g–1 at 50 mA·g–1 and 120 mAh·g–1 at 2000 mA·g–1 after 3000 cycles (capacity retention of 96.5%). The superior electrochemical performance of Na2Ti3O7 nanosheets results from the short ion/electron diffusion pathway of the two-dimensional architecture and the good conductive capability of the binder-free structure. The anode of the binder-free Na2Ti3O7 nanosheets effectively overcomes poor ion/electron conductivity, the main drawback of Na2Ti3O7 electrodes, and is promising for rechargeable sodium ion batteries.
Nine new D-π-A metal-free sensitizers INI1-INI9 with indolizino [3, 4, 5-ab] isoindole (INI) as electronic donor were investigated using the density functional theory (DFT) and time-dependent DFT calculations. Compared to D5 and D9, some major factors affecting the performance of the cell, including light harvesting, electron injection, dye regeneration, and charge recombination are taken into consideration. Calculations show that these novel INI-based sensitizers have an absorption maximum at 440-500 nm when π conjugated bridge attached at different position of aromatic ring and an excellent charge separation characters. INI2 shows better performance than that of D9 due to the theoretical maximum short-circuit current density of 13.26 mA·cm-2. Fortunately, condensed Fukui function calculation suggested that the INI2 be easiest to obtain due to a largest nucleophilic index at 2 position of INI aromatic ring. Based on the calculations of dyes adsorption on TiO2 cluster, indirect electron injection may be the main path from dye to TiO2 for INI2 and D5. Our calculations indicate that the INI dyes will be promising candidates for fabrication of the high performance dye-sensitized solar cells.
The detection sensitivity of localized surface plasmon resonance (LSPR) microscopic probes is mainly determined by the LSPR property of the modified metal nanoparticle at the end of the probe. In this paper, spherical Au@Ag nanoparticles (NPs) with good size uniformity and a thick Ag shell (≥10 nm) were synthesized using the anion-assisted one-step synthesis method in aqueous solution, and the thickness of the Ag shell can be controlled by simply adjusting the molar ratio of Au to Ag in the solution. We characterized the morphology and composition of Au@Ag NPs with different core-shell ratios by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) line scanning analyses, which confirmed the controllable synthesis of Au@Ag core-shell NPs by this method. Measurement of the dielectric sensitivity of Au@Ag NPs with different core-shell ratios in different refractive index solutions showed that the core-shell nanostructure of 7.5 nm Au@28 nm Ag has the highest figure of merit for detection. Further investigation of the plasmonic properties of a single Au@Ag NP on nonconductive substrates with different refractive indexes confirmed that 7.5 nm Au@28 nm Ag NPs are one of the most suitable candidates for dielectric sensing in LSPR microscopy among the spherical Au@Ag NPs.
Supports have a significant effect on the dispersion and stability of Au nanoparticles because of the support-metal interaction. In the present work, TiOx/SiO2 composite supports were prepared by the surface sol-gel (SSG) method to enhance the binding strength between the metal and the support. The samples were characterized by low-energy ion scattering (LEIS) spectroscopy, X-ray photoelectron spectroscopy (XPS), Xray diffraction (XRD), transmission electron microscopy (TEM), and N2 physisorption (BET). The results showed that the TiOx species in TiOx/SiO2 were highly dispersed on SiO2 with the formation of Ti―O―Si linkages. The catalytic activity and stability for CO oxidation on Au/TiOx/SiO2 were significantly enhanced, because of the better dispersion of Au nanoparticles compared with Au/TiO2.
Metalloporphyrins are a class of metal-organic complexes that exhibit a wide range of interesting properties with prosperous applications in photoelectric conversion devices, catalysis, sensors and medicines. Besides inorganic two-dimensional (2D) materials (e.g., graphene and transitional metal dichalcogenide nanosheets), two-dimensional metal-organic nanosheets have also attracted considerable attention in recent years as interesting materials. Based on the rapid progress of two-dimensional metal-organic and porphyrinoid nanomaterials, this review aims to provide a brief review of the history of two-dimensional metal-organic nanomaterials, followed by a detailed summary of the synthetic methods used to prepare free-standing 2D nanosheets as well as 2D thin film of metalloporphyrins. We have also provided an up-to-date review of the applications of these materials in solar cells, photo- and electric catalysts as well as optical sensors, and a discussion pertaining to the problems associated with the synthesis, properties, and possible applications of metalloporphyrin 2D materials.
The effect of strain on the band structure of the ZnO monolayer has been investigated by firstprinciples calculations based on density functional theory. The results reveal that the band structure of the ZnO monolayer presents different dependences on three types of strain. The band gap linearly and steeply varies under uniaxial zigzag compressive strain and armchair tensile strain, while it shows nonlinear dependence on the other types of strain. Therefore, uniaxial zigzag compressive strain and armchair tensile strain should be the most effective to tune the band gap. This work has significant implications for application of strain to tune the optical and catalytic properties of ZnO nanofilms.
The frequency of oil-spill accidents and industrial wastewater discharges have caused severe water pollution, not only resulting in huge economic losses but also threatening the ecological system. Recently, researchers have developed different types of materials with special wettability (such as superhydrophobicity or superoleophobicity) and used them successfully for oil-water separation. Superhydrophobic and superoleophobic surfaces can generally be obtained by designing the surface geometric micro-topography and chemical composition of solid materials. Endowing porous materials with reverse super-wettability to water and oil using various microfabrication technologies is the key to separate oil-water mixtures. In this review we initially identify the significance of fabricating oil/water-separating materials and achieving effective separations. Then, the typical theoretical principles underlying surface wettability are briefly introduced. According to the difference in surface wettabilities toward water and oil, we classify the current oil-water separating materials into three categories: (ⅰ) superhydrophobic/superoleophilic materials, (ⅱ) superoleophobic/ superhydrophilic materials, and (ⅲ) smart-response materials with switchable wettability. This review summarizes the representative research work for each of these materials, including their fabrication methods, principle and process of oil-water separation, and main characteristics and applications. Finally, existing problems, challenges, and future prospects of this fast-growing field of special wettability porous materials for the separation of oil-water mixtures are discussed.
A series of non-platinic lean NOx trap (LNT) CuO-K2CO3/TiO2 catalysts with different Cu loadings were prepared by sequential impregnation, and they showed relatively good performance for lean NOx storage and reduction. The catalyst containing 8% (w) CuO showed not only the largest NOx storage capacity of 1.559 mmol·g-1 under lean conditions, but also the highest NOx reduction percentage of 99% in cyclic lean/rich atmospheres. Additionally, zero selectivity of NOx to N2O was achieved over this catalyst during NOx reduction. Multiple techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of CO2 (CO2-TPD), extended X-ray absorption fine structure (EXAFS), temperature-programmed reduction of H2 (H2-TPR), and in-situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS), were used for catalyst characterization. The results indicate that highly dispersed CuO is the main active phase for oxidation of NO to NO2 and reduction of NOx to N2. The strong interaction between K2CO3 and CuO was clearly revealed, which favors NOx adsorption and storage. The appearance of negative bands at around 1436 and 1563 cm-1, corresponding to CO2 asymmetric stretching in bicarbonates and -C=O stretching in bidentate carbonates, showed the involvement of carbonates in NOx storage. After using the catalysts for 15 cycles of NOx storage and reduction in alternative lean/rich atmospheres, the CuO species in the catalysts showed little change, indicating high catalytic stability. Based on the results of in-situ DRIFTS and the other characterizations, a model describing the NOx storage processes and the distribution of CuO and K2CO3 species is proposed.
In this work, graphene oxide sheets are cut into graphene quantum dots (GQDs) by acidic oxidation, then GQDs are hydrothermally treated with ammonia (NH3) at 100℃ to form amino-functionalized graphene quantum dots (N-GQDs). Atomic force microscopy (AFM) shows smaller dots in ammonia treated GQDs, and holey graphene structure is directly observed. Fourier transform infrared (FTIR) spectra confirm that NH3 can effectively react with epoxy and carboxyl groups to form hydroxylamine and amide groups, respectively. The absorption and photoluminescence (PL) properties of the samples are determined by ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and steady-state fluorescence spectra. Three PL excitation peaks occurring at around 250, 290, and 350 nm are attributed to C=C related π-π* transition, C-O-C and C=O related n-π* transitions, respectively. After amino functionalization, the C-O-C related n-π* transition is suppressed, and the PL emission spectrum of N-GQDs is less excitation wavelength. The fluorescence quantum yield of the N-GQDs is 9.6%, which is enhanced by 32 times compared with that of the unmodified GQDs (~0.3%). Timeresolved PL spectra are also used to investigate the N-GQDs. The PL lifetimes depend on the emission wavelength and coincide with the PL spectrum, and are different from most fluorescent species. This result reveals the synergy and competition between defect derived photoluminescence and amino passivation of the N-GQDs. Compared with oxygen-related defects, nitrogen-related localized electronic states are expected to have a longer lifetime and enhanced radiative decay rates.
Well-dispersed graphene nanosheets (GNS) were prepared by the 60Co γ-ray irradiation reduction technique. On this basis, the hierarchical graphene nanosheet-supported poly(1, 5-diaminoanthraquinone) (GNS@PDAA) nanocomposites were synthesized by the chemically oxidative polymerization method using camphor sulfonic acid as both the dopant and soft template. The influence of the DAA/GNS mass ratios on the morphology, chemical structure, and supercapacitance performance for GNS@PDAA nanocomposites was investigated. The structure, morphology, and electrochemical properties of the composites were characterized by Fourier infrared spectroscopy (FTIR), Raman spectroscopy (Raman), atomic force microscope (AFM), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), and electrochemical measurements. The results show that for the GNS@PDAA nanocomposite with DAA/GNS mass ratio of 6/1, the PDAA nanoparticles (20-40 nm diameter) are evenly deposited on the surface of GNS, which intercalate a large number of mesopores with 10-30 nmthrough strong π-π stacking and network confinement. As a result, the GNS@PDAA exhibits the highest specific capacitance (398.7 F·g-1 at 0.5 A·g-1), excellent rate capability (71% capacitance retention at 50 A·g-1), and superior cycling stability (only 8.3% capacitance loss after 20000 cycles). Furthermore, based on the GNS@PDAA nanocomposites as both negative and positive electrodes, the as-assembled supercapacitors showed an excellent series/parallel connection effect in aqueous system.
CdTe and Cu(In,Ga)(S,Se)2 (CIGSSe) light absorber materials have dominated the research field of compound semiconductor solar cells. Despite the high power conversion efficiencies and technological advances of CdTe and CIGS photovoltaic technologies, certain issues, like rare earth constituent elements or toxic elements, limit their future upscaled applications. In recent years, Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells have become research hotspots, drawing increased interest. With earth-abundant and environmentallybenign constituent elements, CZTSSe light absorber materials are widely regarded as the next-generation photovoltaic technology that can replace CdTe and CIGS as a promising candidate for terawatt-level power output. In this review, the synthesis, structure, and properties of CZTSSe materials will be discussed. This review will primarily demonstrate the developments and recent advances of different fabrication techniques and deposition methods, such as vacuum-based and solution-based deposition methods, covering their advantages and disadvantages. Recent developments in CZTSSe fabrication methods and CZTSSe nanocrystal preparation approaches will also be reviewed. Finally, some limitations on CZTSSe photovoltaic technology will be analyzed, and directions for improvement will be suggested, helping scientists to make future developments in this field.
A selenium disulfide-impregnated hollow carbon sphere composite was prepared as the cathode material for lithium-ion batteries. The morphology, composition, and structure of the as-synthesized composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer-Emmett- Teller (BET) technique. It was found that uniform monodispersive hollow carbon spheres can be synthesized by the template method combined with chemical polymerization. The diameter of the spheres is about 500 nm and the thickness of their wall is about 30 nm. Furthermore, a selenium disulfide-impregnated hollow carbon sphere composite can be achieved by the melting-diffusion method. The electrochemical performance of the as-synthesized composite as a cathode material for lithium-ion batteries was also investigated. Compared with the pristine bulk SeS2 material, the SeS2@HCS composite exhibits higher initial discharge capacity (956 mAh· g-1 at a current density of 100 mA·g-1), longer cycle life (200 cycles at a current density of 100 mA·g-1), and better rate performance. The results indicate that this composite can be considered as a promising candidate for the cathode material of lithium-ion batteries.
Highly expressed in cancer 1 (HEC1) is a conserved mitotic regulator that is critical for spindle checkpoint control, kinetochore functionality, and cell survival. Overexpression of HEC1 has been detected in a variety of human cancers, and it is linked to poor prognosis of primary breast cancers. Thus, it is important to screen novel inhibitors with high affinity for HEC1. Machine learning (ML) methods were exhibiting good pharmacodynamics, and toxicity. In this work, two ML methods, support vector machines (SVMs) and random forests (RFs), were used to develop a classification method for searching inhibitors and non-inhibitors of HEC1 from the chemical library of structural diversity by screening characteristics of molecular descriptors. Both ML methods achieved promising prediction accuracies, and the RF model showed better performance. We performed virtual screening of HEC1 inhibitors by the RF model from an in-house database to screen potential HEC1 inhibitors. Two novel potential candidates were found. In vitro experiments of the two compounds showed that both had a certain degree of antitumor activity for the MDA-MB-468 and MDA-MB-231 breast cancer cell lines. Our study shows that ML methods are promising to design and virtually screen inhibitors of HEC1.
N-doped graphene has aroused much interest owing to its high activity and stability in oxygen reduction reaction (ORR) catalysis. However, the contribution of different types of N-doped graphene to ORR activity remains in dispute. Based on this issue, this paper conducts a comparative study of the ORR on graphitic N-doped graphene (GNG) and pyridinic N-doped grapheme (PNG). Band structure calculations show that the conductivity of GNG decreases as the nitrogen content increases; while that of PNG first increases to the highest at nitrogen content of 4.2% (atomic fraction), and then decreases. The conductivity of PNG is always higher than GNG when the doped nitrogen content is greater than 1.4%. Additionally, the free energy diagram of ORR shows that protonation of O2 is the potential-determining step among the whole ORR process, and the free energy change of this step on GNG is lower than on PNG, suggesting that GNG has higher ORR activity than PNG if their electron transport ability are the same. When the N content is lower than 2.8%, the conductivity difference between GNG and PNG is almost negligible, thus GNG with a higher capacity of O2 protonation exhibits better ORR activity than PNG. When the N content is greater than 2.8%, in this case, conductivity rather than free energy change will dominate, therefore the ORR on PNG will occur faster than on GNG because of its higher conductivity.
Metallic sulfide fullerenes are compounds with novel structures. Currently, it is an important task to clarify the structures and properties of metallic sulfide fullerenes. Asystematic study is performed on Sc2S@C86 by the density functional theory (DFT) method. The calculated results show that the lowest-energy isomer is IPR-satisfying Sc2S@C86:63751 (the 9th isomer of C86 in the isolated pentagon rule (IPR)-only sequence), sharing the same cage with Sc2C2@C86. The second lowest energy isomer is not an isolated-pentagon-rule (non-IPR) Sc2S@C86:63376. Natural bond orbit (NBO) and theory of atoms in molecules (AIM) analyses show that there are charge transfer and covalent interactions between the encaged cluster and parent cage. The effect of temperature on the concentration is evaluated and the results show that several isomers of Sc2S@C86 may coexist at the high temperature conditions used for producing metallofullerenes. The IR spectra of the two lowest energy isomers are provided to help experimentally identify the structure of Sc2S@C86 in the future.
Microbial fuel cell (MFC) is a novel bioelectrochemical device that uses a biocatalyst to convert chemical energy stored in organic wastewater into electrical energy. However, multiple factors limit the practical applications of MFCs, such as the high cost of electrode production and their low conversion efficiencies of power density and energy. Therefore, improving the catalytic performance of the electrodes and lowering the cost of electrode production have become focuses in MFC research. Because of the excellent electrical conductivity and catalytic properties of graphene-based hybrid materials, the development of these electrode materials for use in MFCs has attracted much attention. This review summarizes recent advances of graphene-based hybrid electrodes in MFCs. The preparation methods and the catalytic performance of graphene-modified electrodes, metal and non-metallic/graphene hybrid electrodes, metal oxide/graphene hybrid electrodes, polymer/graphene hybrid electrodes, and graphene gel electrodes are discussed in detail. The influence of graphene-based hybrid anodes and cathodes on the electricity generation performance of MFCs is analyzed. Finally, the problems facing graphene-based hybrid electrodes for MFCs are summarized, and the application prospects of MFCs are considered.
As a secondary battery, the Li-air battery has the highest theoretical specific energy and has been considered as one of the most promising power sources for electric vehicles. The Li-air battery based on organic electrolyte has become a topic of interest owing to its excellent theoretical energy density, environmental friendliness and low cost. During the past 20 years, much progress has been made in the development of the reaction mechanism, cathode structure, catalyst and electrolyte materials. But there are still many obstacles to overcome before its practical applications. In this paper, we review some of the latest progress in the research on the reaction mechanism, cathode materials, catalysts, electrolytes, as well as the lithium anode. Future research and development prospects are also discussed.
Organic/inorganic perovskites have exhibited great potential as photoelectronic materials, achieving remarkable photoelectric conversion efficiency, currently over 20%. The structural, electronic, and optical properties of organic/inorganic hybrid CH3NH3PbxSn1－xI3 perovskites (x = 0－1) have been investigated by the first-principles theory. Our results indicate that the van der Waals (VDW) interaction plays a crucial role in the structure optimization. Accounting for VDW force correction, both the Pb/Sn―I bond lengths and volumes are decreased. By analyzing the density of states and the Bader charge of CH3NH3+ cations, we find that cations contribute only slightly to the band edge, but play the role of charge donors. There exists a combined covalent and ionic interaction between Pb/Sn and I ions. The valence band maximum (VBM) is mainly contributed by the I 5p orbitals with the overlapping of Pb 6s (Sn 5s) orbitals, while the conduction band minimum (CBM) is dominated by Pb 6p (Sn 5p) orbitals. In the visible light region, with increasing wavelength, the absorption intensity demonstrates a decreasing trend; as the Sn/Pb ratio increases, the absorption intensity shows an increasing trend. CH3NH3SnI3 perovskites demonstrate great potential to absorb light in the visible region.
Mixed halide perovskites of MAPbI3-xBrx and MAPbI3-xClx (MA=CH3NH3) with film thickness of about 300 nm were synthesized through the Br or Cl doping, thanks to the two steps deposition of controlled concentration of the precursor solution and the intramolecular exchange of DMSO molecules intercalated in PbI2 (PbI2(DMSO) complex) with MAX (X=I, Br) or MAX (X=I, Cl), respectively. The doping of Br or Cl in the perovskite film can improve the photovoltaic performance of PSCs with the precursor of MAX contains 5% (in mole fraction, same below) MABr or 15% MACl, respectively, while further increase in the content of MABr or MACl in the precursor did not lead to significant changes in doping amounts, but small white particles or pin-holes were formed in mixed perovskite materials, therefore resulted in adverse effects on the performance of solar cells. The MAPbI3-xBrx perovskite solar cells with 5% MABr in precursor solution showed a power conversion efficiency (PCE) of 13.2%, and the MAPbI3-xClx perovskite solar cells with 15% MACl in precursor solution showed the highest PCE of 13.5%.
F1-ATPase makes extensive interactions with ATP through forming a network of interactions around ATP. These interactions create a steady environment for ATP synthesis/hydrolysis. Thus understanding these interactions between ATP and F1-ATPase is essential for understanding ATP synthesis/hydrolysis mechanism. We performed all-atom molecular dynamics (MD) simulations to elucidate these interactions and attempted to identify key residues which play important roles in stabilizing and positioning ATP. By examining the non-bonded energies between ATP and residues of βTP subunit in F1-ATPase, it is found that residues 158-164, R189, Y345 have significant interactions with ATP. The loop segment (residues 158-164) and R189 surround ATP by a half and they interact with β and γ phosphates through forming a network of hydrogen bonds to constraint the motion of ATP triphosphate. The interaction network seals off the conformation of the catalytic site, creating a steady environment for ATP synthesis/hydrolysis. Additionally, ATP base is positioned by the π-π stacking interaction from Y345. However, ATP base can slide and move paralleling to the aromatic group of Y345. It is deduced that this motion may facilitate ATP hydrolysis.
A series of thermally activated delayed fluorescence (TADF) materials (1-3) based on triphenylamine/diphenyl sulfone were synthesized by Suzuki cross-coupling reactions. The optical, electrochemical, delayed fluorescence, and thermal properties of these materials were characterized by UVVis spectroscopy, time-resolved fluorescence spectroscopic measurements, cyclic voltammetry (CV), theoretical calculations, thermal gravimetric analyses, and differential scanning calorimetry. Materials 1-3 are bipolar compounds based on intramolecular charge transfer (ICT), and they have small energy gaps between the singlet and triplet (ΔEST) of 0.46, 0.39, and 0.29 eV, respectively. The results of fluorescent quantum yields and fluorescent lifetime indicate that these materials can emit delayed fluorescence, and material 3 has the greatest potential as a TADF emitter among materials 1-3. The highest occupied molecular orbital (HOMO) energy levels of materials 1-3 were estimated to be -4.91, -4.89, and -4.89 eV, respectively. From the HOMO energy levels and the optical bandgap (Eg) values, the lowest unoccupied molecular orbital (LUMO) energy levels were estimated to be -1.74, -1.89, and -1.94 eV for materials 1-3, respectively. Thermal gravimetric analysis results reveal that materials 1-3 have high thermal decomposition temperatures (Td), corresponding to 5% weight loss at 436, 387, and 310 ℃, respectively.
Fullerene-derivative [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) plays an important role in terms of electron transport in polymer solar cells. The electronic structure of PCBM is of much importance to investigate. In this study, the near-edge X-ray absorption fine structure spectroscopy and unoccupied orbitals of PCBM were researched with density functional theory. By comparing the calculated sum spectra of nonequivalent carbon atoms, we assigned the main resonances of PCBM. The origin of the shoulder in the right side of the first π* resonance was analyzed, and the results showed that this absorption peak was mainly contributed by the transitions to higher unoccupied orbitals of the unmodified carbons in the C60 cage.
Graphene oxide (GO) composite membranes were fabricated via layer-by-layer (LBL) assembling poly(ethylenimine) (PEI) and a mixture of GO and poly(acrylic acid) (PAA) on a poly(acrylonitrile) (PAN) support membrane. The composite membranes and their application performance were characterized and evaluated. The X-ray powder diffraction (XRD) spectrum shows that GO was successfully synthesized by the modified Hummers method, and it was homogenously dispersed in the composite membranes. Scanning electron microscopy (SEM) shows the successful assembly of multiple polyelectrolyte PEI and a mixture of GO and PAA bilayers on the PAN support membrane. The ultraviolet-visible (UV-Vis) spectrum indicates that the uniformity and continuity of the composite membrane were enhanced with the increasing number of assembled layers. The hydrophilic and selectivity tests reveals that the addition of GO decreased the water contact angle and enhanced the selectivity for monovalent cations of the multilayer polyelectrolyte composite membranes. All these advantages combine to fabricate a high-flux, high selectivity, and anti-fouling composite membrane for separation applications and water softening.
Application of ionic liquid surfactants in chemical synthesis, materials preparation, and environmental pollution control is closely dependent on their self-assembly behavior and aggregate structure in aqueous solution. Thus, the study of the aggregation behavior of ionic liquid surfactants in water is of significant importance. In this review, we focus our attention on the recent progress made in the regulation and control of the self-assembly behavior of ionic liquid surfactants and related microstructure of their aggregates in aqueous solutions by alkyl chain length, cationic structure, anionic type of the ionic liquid surfactants, addition of inorganic salt and organic solvent, and environmental factors such as temperature, solution pH, and light. Some regularities have been summarized for the regulation and control of the self-assembly behavior of ionic liquid surfactants, and the challenges to future development in this field are explained.
A nanocomposite composed of N-doped mesoporous carbon material (NDMPC) and carboxymethylated chitosan (CMCH) was fabricated by mechanical co-mixing and used as an enzyme matrix. A novel glucose/O2 enzymatic biofuel cell was fabricated with a Nafion ion-exchange membrane consisting of a laccase (Lac)-entrapped biocathode and glucose oxidase-incorporated bioanode. Enzyme electrodes were prepared by the dripping coat and air-dried method. The performance of the laccase-based electrode as a biocathode in a fuel cell and an oxygen electro-chemical sensor was characterized by cyclic voltammetry in combination with the rotating disk electrode technique, linear scanning voltammetry (LSV), and chronoamperometry. UV-Vis spectrometry and graphite furnace atomic absorption spectroscopy were used to investigate the configuration of enzyme molecules on the surface of electrode and to evaluate the enzyme loading of the matrix on the electrode interface. The results from the experiments showed that the laccasebased cathode displayed direct electron transfer between the active centre in laccase (T1) and the conductive matrix without any external electron mediators (apparent electron transfer rate 0.013 s-1). A minor overpotential for oxygen reduction (150 mV) was also observed. Through further comparison of the intra-molecule electron relay rate (1000 s-1), substrate turnover frequency (0.023 s-1), and previous enzyme-conductive matrix electron transfer rate, quantitative analysis showed that the latter was the rate-determining step in the whole catalytic cycle of the oxygen reduction reaction. This laccase-based electrode as an oxygen electrochemical sensor for detecting oxygen showed a low detection limit (0.04 μmol·dm-3), high sensitivity (12.1 μA·μmol-1·dm3), and affinity for oxygen (KM = 8.2 μmol·dm-3). This laccase-based cathode also had advantages such as excellent reproducibility, long-term usability, thermal stability, and pH endurance. The results for the fabricated biofuel cell showed an open circuit voltage of 0.38 V and a maximal energy output density of 19.2 μW·cm-2, maintaining greater than 60% of the initial value even after continuous work for 3 weeks under optimal conditions.
Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.
Radiation therapy kills tumor cells via focused high energy radiation, and has become one of the most common and effective clinical treatments for malignant tumors. However, some limitations restrict its clinical efficacy, including a requirement for elevated doses of radiation, side effects due to exposure of healthy tissue, and especially radioresistance of tumor cells. With the development of nanomedicine, multifunctional nanoradiosensitizers offer a new route to improve the efficiency of radiation therapy. In this paper, we summarize the main types of nanoradiosensitizers and their applications in radiation therapy, especially those that have currently entered clinical trials. We also summarize the main approaches to nanomaterials-based radiosensitization, and discuss the factors influencing their application. Finally, the challenges and prospects of multifunctional nanoradiosensitizers are presented.
The structure and thermodynamics of CeCl3 in molten LiCl-KCl-CeCl3 mixtures were studied by molecular dynamics simulation. The relationship formulas of temperature and density, and composition and density were obtained. The first peak for the gCe-Cl(r) radial distribution function was located at 0.259 nm and the corresponding first coordination number of Ce3+ was ~6.9. This inconsistency between molecular dynamics and experimental data could be attributed to the fact that our values were obtained for molten LiCl-KCl-CeCl3 mixtures, in which the interaction between Ce3+ and Cl- was more powerful than that in pure molten CeCl3. Regarding self-diffusion coefficients, the activation energy of Ce3+ was 22.5 kJ·mol-1, which is smaller than that of U3+ (25.8 kJ·mol-1). Furthermore, the pre-exponential factors for Ce3+ decreased from 31.9×10-5 to 21.8×10-5 cm2·s-1 as the molar fraction of Ce3+ increased from 0.005 to 0.05. This means that in the unit volume (ignoring the change of total volume), the diffusion resistance of Ce3+ increased, and the self-diffusion ability decreased, which resulted in a decrease of pre-exponential factors.
A new cyclic byproduct was formed during hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) preparation by direct nitration. Silicone column chromatography with acetone and dichloromethane in various ratios as the eluent was used to separate 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane from the product mixture. A single crystal of 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane was grown from acetone, and characterized using elemental analysis, Fourier-transform infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). Its structure was determined using an X-ray single-crystal diffractometer. The results indicate that the crystal molecular weight is 178.12. It belongs to the monoclinic system with the space group P121/n1, a = 0.58128(13) nm, b = 1.72389(14) nm, c = 0.71072(6) nm, β = 112.056°, V = 0.66006(16) nm3, Z = 4, DC= 1.792 g·cm-3, μ = 0.17 mm-1, and F(000) = 368.0; the final deviation factor R is 0.0397. Differential scanning calorimetrythermogravimetry (DSC-TG) was used to investigate the thermal behavior of the title compound. Sharp peaks were observed at 383.15 K (melting) and 519.05 K (decomposition). The kinetic parameters were obtained using the Kissinger and Flynn-Wall-Ozawa methods and the TG data at different heating rates. The Coats-Redfern method was used to study the thermal decomposition mechanism of 3, 5-dinitro-1-oxygen-3, 5-diazacyclohexane. The results show that the title compound is a low-melting-point compound with good stability; its apparent activation energy and pre-exponential factor, calculated using the Kissinger equation, are 212.32 kJ·mol-1 and 6.20×1020 s-1, respectively. The apparent activation energy, calculated using the Flynn-Wall-Ozawa equation, is 210.39 kJ·mol-1. G(α) = (1-α)-1-1 (n = 2) obtained using Coats-Redfern method is regarded as the most appropriate thermal decomposition kinetic equation.
Anatase titania nanocrystals with different shapes were successfully prepared by a solvothermal method, using titanium butoxide as a precursor, ethanol as a solvent, and lauric acid and dodecyl amine as stabilizing agents. The structure, size, morphology, and shape of the nanocrystals were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, and thermogravimetric-differential thermal analysis (TG-DTA). We discuss how the ratio of lauric acid to dodecyl amine can influence the shape of nanocrystals. XRD results indicate that the phase of titania nanocrystals synthesized under different conditions is pure anatase. The shapes of titania nanocrystals gradually evolve from spheres to rods with increasing dodecyl amine content (at constant total molar content of lauric acid and dodecyl amine). The crystallinity of anatase titania nanocrystals prepared at a molar ratio of 1:1 (lauric acid to dodecyl amine) was better than that of nanocrystals prepared at other molar ratios. The stabilizing agents and nanocrystal core were combined by a bridging coordination ligand, and the content of stabilizing agents in samples was about 5%.
Hierarchical nitrogen-enriched porous carbon containing micropores, mesopores, and macropores were prepared by a nanocasting pathway using a Schiff base precursor and SBA-15 as the hard template. The specific surface area and pore volume of the obtained porous carbon are 752 m2·g-1 and 0.79 cm3·g-1, respectively. The nitrogen content is as high as 7.85% (w). The porous carbon shows a CO2 capacity of 97 cm3·g-1 at ambient pressure and 273 K. The CO2/N2 and CO2/CH4 separation ratios (molar ratios) are accordingly 7.0 and 3.2, and the Henry's low pressure selectivities are 23.3 and 4.2, respectively. CO2 adsorption tests confirmed that the micropores play a dominant role and nitrogen-containing functional groups play a synergistic role. The predicted ideal adsorbed solution theory (IAST) selectivities of the two-component mixed stream are 40 (CO2/N2) and 18 (CO2/CH4) by Toth mode simulation.
A new and optically stable fluorescent derivative (OPBMQ) of 1, 4-bis(phenylethynyl)benzene (BPEB) with 8-hydroxyquinoline (8-HQ) as a capturing unit and cholesterol (Chol) as an auxiliary structure was designed and synthesized. Fluorescence studies demonstrated that the fluorescence emission of the compound in the aqueous phase is characterized by two distinct and independent emissions, of which one originates from 8-HQ and the other from BPEB. Importantly, the emission is highly selective and sensitive to the presence of diethyl chlorophosphate (DCP), a simulant of Sarin. The calculated detection limit (DL) is lower than 1 × 10−9 mol·L−1. Moreover, no significant response was observed when the probe was exposed to simulants of other nerve agents, relevant organophosphorus pesticides, or even their mixtures. More importantly, regardless of whether Milli-Q water, tap water or even sea water was employed as solvent, the presence of the mixture of the interferents studied did not show any significant effect on the detection of DCP. In particular, the sensitive and highly selective detection of DCP was also realized by naked-eye observation, providing a simple and low-cost protocol for the on-site and real-time detection of the chemical. Based on this discovery, a DCP monitoring device was successfully developed.
Two-dimensional (2D) materials possess nanoscale thickness with large aspect ratios on the other two dimensions. The ultrahigh surface-to-volume ratio of 2D materials is the most important property different from their bulk counterparts, and is beneficial for mass and heat transport, and ion diffusion. Among the various 2D materials, carbon-based materials have attracted tremendous attentions since the first explosive research on graphene. Therefore, they provide opportunities for applications in adsorption, catalysis, and electrical energy storage. The porous structure of such carbon materials is a key influence on the properties of these 2D materials. This review focuses on recent developments in synthesis strategies for 2D carbon-based materials, especially the preparation of carbon nanosheets and carbon-inorganic hybrids/composites nanosheets. The main factors influencing the porous structure of the material are discussed for each method. Applications of the materials are introduced, mainly in the fields of adsorption, heterogeneous catalysis, and electrical energy storage. Finally, the leading-edge issues of novel 2D carbon-based materials for the future are discussed.
Membranes with both good permeation and selectivity are highly desired for gas separations. We synthesized a polyimide (PI) asymmetric membrane using the phase-inversion method, and then modified the surface with a mixture of porous fillers and poly(amic acid) (PAA). The porous fillers included the metal organic framework (MOF) of Cu3(BTC)2 (copper benzene-1, 3, 5-tricarboxylate), the zeolite imidazole framework (ZIF) of ZIF-8, and the porous hydrotalcite of MgAl-LDH. A series of asymmetric mixed-matrix membranes (MMMs) were obtained after surface coating and thermal amidation. The MMM structure, CO2, CH4, and N2 permeance, and the ideal gas selectivity were investigated. With the surface modification, the morphology of the surface separation layers of the asymmetric PI/ZIF-8, PI/LDH, and PI/Cu3(BTC)2 MMMs significantly changed, and the gas separation performance changed accordingly. The PI/ZIF-8 asymmetric MMM with 5% (w) ZIF-8 doping exhibited both enhanced ideal gas selectivity and permeance; the CO2/N2 and CO2/CH4 selectivity were as high as 24 and 83, respectively. Thus, this surface modification provides improved MMM gas separation performance.
Self-similar fractals have been extensively investigated because of their importance in mathematics and aesthetics. Chemists have attempted to synthesize various molecular fractal structures through sophisticated design. But because of poor solubility, synthesis of defect-free fractals with large sizes in solution usually proves difficult. Recently, we reported the formation of extended and defect-free Sierpiński triangle fractals by halogen or coordination bonds on surfaces under ultrahigh vacuum conditions. Their growth mechanism has been systematically studied by scanning tunneling microscopy. Using 4, 4′′′-dibromo-1, 1′:3′, 1′′:4′′, 1′′′-quaterphenyl molecules, a series of Sierpiński triangles were successfully prepared on Ag(111) through self-assembly. A slow cooling rate is crucial for growing fractals of higher order. These fractals are only observed below liquid-nitrogen temperature because of the weak interactions in halogen bonds. More stable metal-organic Sierpiński triangles were fabricated by depositing 4, 4″-dicyano-1, 1′:3′, 1″-terphenyl molecules and Fe atoms on Au(111) and annealing at around 100 ℃ for 10 min. The fractals are stabilizedthrough coordination interaction between Fe atoms and N atoms in molecules. Density functional theory calculations revealed their imaging mechanism. Monte Carlo simulations displayed the formation process of surface-supported fractal structures. Three-fold nodes are believed to dominate the structure formation of Sierpiński triangles.
The total interaction energies and two-, three-, and four-body interaction energies of water clusters (H2O)n (n = 8, 10, 16, 20, 22, 24) are obtained from MP2/aug-cc-pVTZ calculations including the basis set superposition error (BSSE) correction. The calculation results show that the two-body interaction energies contribute more than 70% to the total interaction energy, the three-body interaction energies contribute up to 25%, the four-body interaction energies sometimes contribute up to 3%, and other many-body interaction energies always contribute less than 0.5%. It is also found that about 99.4% of the total interaction energies can be reproduced when some special two-, three-, and four-body interactions are considered. These interactions are the two-body interactions where the distance between two water molecules is less than 0.68 nm, the three-body interactions where the nearest water-water distance among three water molecules is less than 0.31 nm, and the four-body interactions where the nearest water-water distance among four water molecules is less than 0.31 nm. Our investigation results suggest that a reliable method, aimed at modeling biosystems, should possess the ability to correctly simulate these special two-, three-, and four-body interactions.
Lithium-sulfur batteries are considered to be rather latest and high-performance storage batteries due to their high theoretical specific capacity (1675 mAh·g-1), high energy density (2600 Wh·kg-1), environmental friendliness, low cost, and safety. These features make them important in the field of mobile electric vehicles and portable devices. However, because of rapid capacity attenuation with poor cycle and rate performances, these batteries are far from ideal for commercial applications. This paper reviews the entire and latest studies in lithium-sulfur batteries. Cathodes, electrolyte, separators, and anodes protection are introduced in detail. The existing lithium-sulfur batteries defects and problems are analyzed. Finally, we provide some insights into the future direction and prospects of lithium batteries.
Melamine and melem molecules are widely used precursors for synthesizing graphitic carbon nitride (g-C3N4), the latter also a hot two-dimensional material with photocatalytic applications. The molecular structures of both are respectively identical to the repeating units of two distinct g-C3N4 phases. In this work, the adsorption and self-assembly of melamine and melem on an Au(111) surface were investigated with low-temperature scanning tunneling microscopy (STM). Particularly, the patterns of hydrogen bonds (HBs) in their assemblies were identified and compared. It was found that melamine can only form one type of HB and two kinds of assembly structures, whereas melem can form three types of HBs and six kinds of assembly structures in total. Moreover, the involved HBs can be transformed by tip manipulation. These findings may provide a new strategy for tuning the functionality of surface self-assemblies by manipulating intermolecular hydrogen bonds. This also paves a route for the in situ synthesis of g-C3N4 on metallic surfaces and subsequent investigations of their physicochemical properties.
The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of-5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of-4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (-0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (-0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (-0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (-0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.
A novel Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst was prepared by hydrothermal posttreatment using dicyandiamide, zinc acetate, ammonium molybdate, cadmium acetate, and sodium sulfide as raw materials. X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), inductively coupled plasma atomic emission (ICP-AES), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The results indicate that heterojunctions are formed across the g-C3N4/Zn-Mo-CdS interface, which promotes interfacial charge transfer and inhibits the recombination of electrons and holes. The activities of as-prepared catalysts were tested through the photocatalytic degradation of Rhodamine B (RhB) under visible light. The results show that the Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst clearly displayed increased activity compared with single g-C3N4 and Zn-Mo-CdS. At an optimal g-C3N4 mass fraction of 20%, the as-prepared heterojunction photocatalyst displayed the highest rate constant under visible light, which was 30 and 10 times of single g-C3N4 and Zn-Mo-CdS, respectively. Not only Zn-Mo-CdS, but also Mo-Ni-CdS and Ni-Sn-CdS can form heterojunctions with g-C3N4 to promote the rate of separation of electrons and holes and improve photocatalytic activity.
Gemini surfactants consist of two amphiphilic moieties covalently connected by a spacer at the level of the head groups.Compared with the corresponding monomeric surfactants, gemini surfactants exhibit higher surface activity, possess unique structural variations, display special aggregate transitions, and form variable aggregate structures.Their aggregation ability and aggregate structures can be effectively adjusted by varying their molecular structures, which results in different intra-or intermolecular interactions.This short review is focused on the behavior of gemini surfactants in aqueous solutions reported in recent years, and summarizes the effects of different molecular structures, including spacers, hydrophobic chains, hydrophilic headgroups, counterions, and functional groups.The mechanisms and trends of the interactions in gemini surfactants are also presented.