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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Underpotential deposition (upd) has been a hotspot in the field of electrochemical research throughout the years owing to its significant theoretical and applied research value. Theoretical research on upd primarily centers around the relations and rules of interaction among deposition substrates, deposition species, and anions (or other organic additives) during upd process. In this paper, the developments in theoretical research in recent years on upd on both the local and international levels are systematically summarized mainly from two viewpoints, namely, thermodynamics and kinetics. With regard to the thermodynamics of upd process, introductory comments and mathematical formulas are summarized from four aspects, i.e., underpotential shift (ΔEupd), electrosorption valency (γ), influence of temperature, and electrochemical adsorption isotherms. The applications and analyses of those related mathematical formulas are also presented in detail. In terms of the kinetics of upd process, nucleation and growth phenomena are mainly presented. We summarize the relevant mathematical models, and additionally introduce research studies on the characteristics of upd kinetics based on these mathematical models. Furthermore, this paper presents an outline of computational chemistry methods and application achievements concerning upd research. Finally, the theoretical research status of upd is presented, giving an overall view of the development trend.
Polyimide (PI) aerogels, which are generally crosslinked using expensive chemical crosslinking agents, are novel porous materials with high strength, high heat resistance, high porosity, and low density. Graphene oxide (GO) is a functional nanofiller that has aroused wide interest in recent years. The reported PI/ GO composites have mostly been in the form of fibers and films. In this study, PI/GO composite aerogels were obtained using chemically modified graphene oxide (m-GO) as the crosslinking agent, instead of traditional ones such as 1,3,5-triaminophenoxybenzene (TAB), by reaction with 4,4'-oxydianiline (ODA) and 3,3',4,4'- biphenyltetracarboxylic dianhydride (BPDA). The chemical modification of GO was achieved by reacting GO with excess ODA using a hydrothermal method. The microstructures of the PI/m-GO aerogels were investigated using scanning electron microscopy (SEM). Nitrogen sorption tests, thermogravimetric analysis, and a hot-wire method were used to investigate the effects of m-GO on the pore properties, thermal stabilities, and thermal conductivities, respectively, of the resulting aerogels. The results show that the PI/m-GO aerogels are highly porous, thermally stable, and heat insulating. Compression tests showed that the PI aerogel prepared using 0.6% (mass fraction, w) m-GO instead of 1.8% (w) TAB as the crosslinking agent had a higher specific Young's modulus [Young's modulus/density (ρ)] and specific yield strength (yield strength/ρ), and less shrinkage.
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.
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.
Density functional theory calculations were performed to study the mechanism and reactivity of methanol oxidation mediated by PtnRum (n+m=3, n≠0) clusters. The potential energy surfaces and pathways of the initial O―H and C―H bond activations were predicted. The results show that the activation of methanol proceeds preferentially along the C―H bond activation pathway. The calculated reactivity order was Pt2Ru>Pt3> PtRu2. Frontier molecular orbital analysis showed that the initial C/O―H bond activation is a proton transfer process. The solvent effect was also investigated. This study will enable a deeper understanding of C/O―H bond activation and provide new ideas for catalyst selection and optimizing conditions for methanol activation.
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.
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.
A visible-light-active graphitic-like carbon nitride (g-C3N4)/BiVO4 nanocomposite photocatalyst was synthesized using a facile ultrasonic dispersion method. The nanocomposite was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and photocurrent response measurements. The photocatalytic activity in the photoreduction of CO2 under visible-light irradiation (λ>420 nm) was determined. The g-C3N4/BiVO4 catalyst containing 40% (w) g-C3N4 showed the highest photocatalytic activity; it was almost twice that of g-C3N4 nanosheets and four times that of BiVO4. The enhanced photocatalytic activity is attributed to the formation of heterostructures at the g-C3N4/BiVO4 interface and appropriate alignment of the energy levels between them, which can facilitate separation of photogenerated electrons and holes.
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.
The effects of sulfate concentration on the open circuit state and anodic polarization behavior of iron in dilute bicarbonate solutions were investigated using immersion tests, electrochemical measurements, and surface analysis techniques. In the absence of sulfate or in the presence of a low concentration of sulfate in dilute bicarbonate solutions, iron was in a passive state, with a corrosion potential of (-0.225±0.005) V. A high electrochemical impedance and low corrosion rate were obtained. No obvious active-passive transition was observed in the anodic polarization curves. In the presence of a high concentration of sulfate in dilute bicarbonate solutions, iron was in an active dissolution state, with a corrosion potential of (-0.790±0.010) V. A low electrochemical impedance, high corrosion rate, and typical active-passive transition in anodic polarization curves were observed and related to the sulfate concentration. In the presence of a high concentration of sulfate, the anodic polarization curves showed current peaks as a result of iron activation by sulfate ions. Sulfate ions of sufficiently high concentration in solutions degraded previously formed oxide layers on iron or transformed oxide layers in bicarbonate solutions. The transition of the open circuit state from passivity to active dissolution occurs at a lower sulfate concentration in a deaerated solution than in an aerated solution.
Graphene oxide (GO) was synthesized using an improved Hummers method. Subsequently, catalysts of manganese oxides (at varying loadings) supported on graphene (MnOx/GR) were prepared by hydrothermal reaction for application in the selective catalytic reduction (SCR) of NOx with NH3 at low temperatures. The structural properties and catalytic performance were evaluated by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). The characterization results indicated that abundant functional groups existed on the surface of the prepared GO that could combine with manganese during preparation of the catalysts. Manganese oxide entities, with different crystallinities (MnO, Mn3O4, or MnO2), were dispersed on the surface of graphene. The results of the catalytic studies showed that the MnOx/GR catalysts prepared with different MnOx loadings all exhibited excellent low-temperature SCR activities. The catalyst with 20%(w) MnOx displayed the best activity, which was attributed to the high content of high-valent manganese and oxygen adsorbed onto the catalyst surface, as well as to the enhancement in redox abilities and the addition of active sites at low temperatures.
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.
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.
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.
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.
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.
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.
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.
We synthesized Ni(OH)2 nanowires/three-dimensional graphene composites using a hydrothermal method, and compared their properties with those of three-dimensional graphene, Ni(OH)2 nanowires, reduced graphene oxide, and Ni(OH)2 nanowires/reduced graphene oxide. The samples were characterized using Xray diffraction, scanning electron microscopy, thermogravimetric analysis, and N2 physisorption measurements. The electrochemical performances were investigated using cyclic voltammetry and galvanostatic chargedischarge methods. The results showed that Ni(OH)2 nanowires of width 20-30 nm were closely combined with graphene and crosslinked to one another to form a three-dimensional structure with a high specific surface area (136 m2·g-1) and mesoporosity (pore diameter 20-50 nm). The mass fraction of Ni(OH)2 nanowires in the Ni(OH)2 nanowires/three-dimensional graphene composite was 88%. The maximum specific capacitance of the Ni(OH)2 nanowires/three-dimensional graphene composite was 1664 F·g-1 in 6 mol·L-1 KOH electrolyte at 1 A·g-1. The specific capacitance decreased by only 7% after 3000 cycles at 1 A·g-1. A comparative study of the specific capacitances and cycling performances of Ni(OH)2 nanowires, Ni(OH)2 nanowires/reduced graphene oxide, three-dimensional graphene, reduced graphene oxide, and Ni(OH)2 nanowires/three-dimensional graphene indicated that three-dimensional graphene with three-dimensional porosity and a larger specific surface area than conventional reduced graphene oxide enabled improved use of the active material and significantly enhanced the electrochemical performance of Ni(OH)2 nanowires.
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.
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.
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.
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.
Molecular dynamics simulation was used to study the effect of the outer-wall on water flux in the inner channel by varying the inter-layer spacing of unconventional double-walled carbon nanotube (DWCNT) under reverse-osmosis conditions. Salt rejection and the water transport behavior inside the DWCNT were also examined. In the simulation, 0.5 mol·L-1 NaCl aqueous solution was used to mimic seawater, and the chiral index of the inner-wall was fixed at (8, 8). A constant force on the salt solution produced pressure. Calculation of the number density profile of ions along the DWCNT axis showed that the water could be separated completely from the NaCl aqueous solution in some types of DWCNTs studied. Analyses of the hydrogen-bond lifetime, potential of mean force, and dipole moment distribution of the water molecules inside the DWCNT showed different permeabilities by water molecules and ions. An increase in the inter-layer spacing improved water flow in the DWCNT, which decreased the salt rejection performance. Finally, it was found that DWCNT with an inter-layer spacing of 0.815 nm gave the optimum balance between water flux and salt rejection. This study provides a molecular insight into the use of DWCNT in desalination, and will enable the design of improved reverse-osmosis membranes with high performance in terms of salt rejection and water permeability.
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.
To address problems such as aging, mutation, and cancer, it is of great importance to understand the damage mechanism of DNA induced by hydroxyl radical. In this study, the abstraction reaction mechanism of hydroxyl radical with guanine-cytosine (GC) base pair in aqueous phase under the polarized continuum model (PCM) has been explored by using density functional theory (DFT). The results indicated that all the abstraction reactions in GC base pair were thermodynamically exothermic, and the stability of dehydrogenation radicals decreased in the order of (H2b-GC)·>(GC-H4b)·>(GC-H6)·>(GC-H5)·~(H8-GC)·. The reaction energy of H2b abstraction pathway was the lowest among all investigated pathways, thus indicating that the reaction conversion of (H2b-GC)· was the highest. In the five hydrogen abstraction pathways, the local energy barriers with respect to the corresponding reactant complexes increased in the following order: H2b
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.
Nitrogen oxides (NOx), which are emitted from stationary sources (such as coal-fired power plant flue gases) and mobile sources (such as motor vehicle exhausts), cause serious atmospheric pollution. As a result, it is very important to control the emissions of NOx. Some studies have suggested that NH3-selective catalytic reduction (NH3-SCR) of NOx is one of the best techniques for this purpose. Ceria-based catalysts are widely used in the NH3-SCR reaction because of their good redox ability, suitable surface acidity, high oxygen storage or release capacity, and rich resource reserves. Investigating the role of ceria component in this reaction is important to understand the nature of the related catalytic process, and provides a valuable scientific reference for the optimization of existing catalysts and the design of novel catalysts. Based on the different roles of ceria in NH3-SCR catalysts, we have performed a systematic review of the latest research progress of ceria-based catalysts in the NH3-SCR reaction for the following aspects: CeO2 used as supports, ceria-based mixed oxides, surface loading components (additives and active species), and ceria-based catalysts with special structures. Finally, we discuss the future directions of this field.
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.
We report a comparative study on the characterization of three trivalent uranium complexes using 12 density functional theory (DFT) methods, i.e., BP86, PBE, B3LYP, B3PW91, BHandHLYP, PBE0, X3LYP, CAM-B3LYP, TPSS, M06L, M06, and M06-2X, representing (meta-)GGA and hybrid (meta-)GGA levels of treatment of molecular systems. The MP2 method was used in single-point calculations to provide an ab initio view of the electronic structure. Three model systems in the experimental work on the activation of CO2 and CS2 by a trivalent uranium complex (Tp*)2U-η1-CH2Ph (Cpd2) were used i.e., (Tp*)2U-η1-CH2Ph (Cpd2), (Tp*)2U-κ2- O2CCH2Ph (Cpd3), and (Tp*)2U-κ2-S2CCH2Ph (Cpd4) (Tp=hydrotris(3, 5-dimethylpyrazolyl)borate). The hybrid functionals, B3LYP and B3PW91, displayed good performance in view of both the geometrical and electronic structures. The MP2 method generated consistent results as DFT methods for Cpd2 and Cpd3, while provided an odd picture of the electronic structure of Cpd4 that may be due to its single determinant feature, leading to its capture of an electronic configuration of Cpd4 different from the one with the DFT methods. The use of a quasi-relativistic 5f-in-core ECP (LPP) treatment for U(III) in the thermodynamic calculations was supported by the calculations with a small-core ECP treatment (SPP) for U. Owing to increasing interests in low-valent actinide molecular systems, this work complements previous comparative studies, which mainly focus on highvalent actinide complexes, and provides timely information on the performance of 12 widely used DFT methods in studying low-valent actinide systems. It is expected to contribute to a more sensible selection of DFT methods in the study of low-valent actinide molecular systems.
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.
Molecular dynamics simulations of oxygen molecules in NaOH and KOH solutions at different temperatures (25-120 ℃) and concentrations (1:100-1:5, molar ratios) were performed in this study. The interactions of oxygen molecules with the surrounding solvent and solute were clarified by considering the solvent-solvent, oxygen-solvent, and oxygen-solute radial distribution functions. The self-diffusion coefficients of the oxygen molecules and the solute were both determined by analyzing the mean-squared displacement (MSD) curves, using Einstein's relationship. It was concluded that at all concentrations, the diffusion coefficient of oxygen in NaOH solution is smaller than that in the corresponding KOH solution. The diffusion coefficients for hydroxide, Na+, and K+ decrease with increasing solute concentration, following similar trends to those of oxygen. The oxygen diffusion coefficient obtained in this study is in good agreement with the reported experimental value, suggesting that MSD is an attractive approach to study the oxygen diffusion behavior in strong alkaline solutions at elevated temperatures, which are experimentally extremely challenging.
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.
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.
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.
Anatase TiO2 shows excellent long-term cycling stability as an anode for sodium-ion batteries. However, the low specific capacity and poor rate capability resulting from its intrinsic low electrical conductivity limit its applications. In this work, TiO2 nanoparticles were coated with reduced graphene oxide (RGO) using a combination of spray-drying and heat treatment. Electrochemical tests showed that the obtained RGO/TiO2 composites had improved electrochemical performances. The reversible capacities of the RGO/TiO2 [4.0% (w)] composites were 183.7 mAh·g-1 (20 mA·g-1), 153.7 mAh·g-1 (100 mA·g-1), and 114.4 mAh·g-1 (600 mA·g-1). Bare TiO2 showed low capacities of 93.6mAh·g-1 (20mA·g-1), 69.6mAh·g-1 (100mA·g-1), and 26.5mAh·g-1 (600 mA·g-1). The 4.0%(w) TiO2/RGO composites exhibited good cycling stability with a charge capacity of 146.7 mAh·g-1 at a current density of 100 mA·g-1 after 350 cycles, compared with 68.8 mAh·g-1 for bare TiO2. RGO modification is a promising method for improving the electrochemical performances of the sodium energystorage materials.
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.
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.
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.
We have to retract this article.
Reason: Some texts of this article are translated from an article published by Brumboiu, I. E.; Anselmo, A. S.; Brena, B.; Dzwilewski, A.; Svensson, K.; Moons, E. Chemical Physics Letters (CPL), 2013, 568－569, 130－134. doi: 10.1016/j.cplett.2013.03.031. Furthermore, some data are also copied from this article.
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.
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.
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.
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.
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.
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.
Carbon aerogels were prepared, using a freeze-drying method, from graphene oxide (GO) and carbon nanotube (CNT) hybrid hydrogels. The resulting aerogels were characterized using scanning electron microscopy and Fourier-transformed infrared spectroscopy. The adsorption of U(VI) on the GO-CNT aerogels was studied as a function of solid dosage, pH value, initial concentration, and contact time. The results showed that GO-CNT aerogels have high uranium(VI) removal capacities, and are promising sorbents.
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.
Highly pure plastic crystal, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (P12TFSI), was synthesized and purified by an easily industrializable recrystallization method. The P12TFSI/LiFSI ionic liquid was obtained by mixing P12TFSI with 30% (molar fraction, x) LiFSI. Electrochemical characterization methods including cyclic voltammetry, constant voltage polarization and charge/discharge at constant current were used to investigate the electrochemical window, stability vs Al corrosion, and battery performance of the ionic liquid.Awide electrochemical window of 5.00 V, non-corrosion of theAl current collector, and 0.92mS·cm-1 of ionic conductivity at room temperature were observed. LiCoO2/Li batteries assembled using this ionic liquid electrolyte showed good charge-discharge characteristics and cycle performance, comparable with those of carbonate-based electrolyte at low rate. The specific capacity of the LiCoO2 remained 175 mAh·g-1 after 20 cycles (95.1% capacity retention) despite cycling at a high voltage up to 4.50 V. These results indicate that the plastic crystal-based ionic liquid P12TFSI/LiFSI could be potentially applied in high-energy density lithium secondary batteries.
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.
The adsorption behavior of cinnamaldehyde on icosahedral Au13 and Pt13 clusters was investigated by density functional theory with the Perdew-Burke-Ernzerh of generalized gradient approximation (GGA-PBE). When analyzing the adsorption energies and geometrical parameters of different adsorption models, the adsorption energy of cis-cinnamaldehyde was higher than that of trans-cinnamaldehyde for the same cluster. On the Au13 cluster, the most stable adsorption was the C＝O and C＝C double bond coadsorption model. While on the Pt13 cluster, the most stable adsorption was the C＝O double bond adsorption model. Comparison between the Au13 and Pt13 clusters showed that the adsorption capacity of cinnamaldehyde on the Pt13 cluster was higher than on the Au13 cluster. Analyzing the electronic structures of the most stable adsorption configurations of cinnamaldehyde on the Au13 and Pt13 clusters showed that electrons transferred from 2s and 2p orbitals of cinnamaldehyde to the metal clusters. Electrons of metal clusters were also back-donated to the anti-bonding orbitals of the cinnamaldehyde molecule. This collaborative process eventually led to the stable adsorption of cinnamaldehyde on the Au13 and Pt13 clusters. In addition, adsorption of cinnamaldehyde on cluster models was more energetically favorable than on flat models.
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.
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.
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.
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.
Ultrafine Au nanowires (AuNWs) were synthesized in high yields by a one-step wet chemical method using oleylamine as the solvent, surfactant, and reductant. The obtained AuNWs were of high purity and had a high aspect ratio, with diameters of ~2 nm and lengths of tens of micrometers. AuNWs of diameter ~9 nm were also obtained in the presence of oleic acid, at an oleic acid:oleylamine volume ratio of 1:1. The formation of AuNWs was studied by changing the reaction temperature and the volume of oleylamine. It is proposed that the growth mechanism of the Au nanostructures involves strong aurophilic interactions from oleylamine-AuCl complexes; the reduced Au atoms agglomerate and attach to preformed particles, and the oleylamine molecular layer acts as a soft template, leading to one-dimensional growth of Au atoms into AuNWs.
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.
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.
Chlorinated phenols (CPs) are the main precursors for forming the persistent organic pollutants dioxins and have strong teratogenicity, carcinogenicity, and mutagenicity. To explore the novel material for the removal or detection of these pollutants, we used density functional theory calculations to investigate the adsorption behaviors and interaction mechanisms of 2-chlorophenol (2-CP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP) on pristine and Co-doped (8,0) single-walled boron nitride nanotubes (denoted by BNNT and Co-BNNT, respectively). The results show that compared with BNNT, Co-BNNT introduces local states near the Fermi levels, and has a smaller band gap. BNNT physisorbs 2-CP, TCP, and PCP molecules, whereas Co-BNNT presents chemisorption towards them. Charge-transfer between Co-BNNT and molecules can be clearly observed and the electronic densities of states of the doped systems change significantly near the Fermi levels after adsorption of molecules. Doping with Co atom significantly increases the electronic transport capability of BNNT and enhances the adsorption reactivity of the tube to CPs. Co-BNNT is expected to be a potential material for removing or detecting CPs pollutants.
Butyl levulinate (BL) is one of the most important biochemicals derived from cellulose, and it is of particular interest in industrial applications. Efficient synthesis of BL from cellulose in bio-butanol (bio-BuOH) medium has been investigated in the presence of acidic SO3H-functionalized ionic liquid (SFIL) catalysts. The results showed that the acid strength of the SFILs, catalyst dosage, reaction temperature, reaction time, and solvent composition significantly affected the conversion of cellulose and the yield of the target products. Using the strongest acidic SFIL 1- (4-sulfobutyl)-3-methylimidazolium hydrosulfate ([C4H8SO3Hmim]HSO4) as the catalyst, 98.4% of cellulose could be converted into 31.1% of BL accompanied with 33.4%, 20.6%, and 23.8% of butyl formate (BF), water soluble products (WSPs), and biofuel (Biof), respectively, under the optimized conditions. This catalytic system was water-tolerant, and the addition of 0.2 mL water did not significantly decrease its ability for conversion of cellulose. Furthermore, this acidic SFIL catalyst could be recycled up to six consecutive times without loss of catalytic activity.
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.
As the most complex element, plutonium and its compounds have long been intensively studied and a large number of remarkable scientific breakthroughs have been reported frequently in the literature. However, modern-day problems concerning plutonium involve predicting its properties under long-term aging in storage environments. Because of its high chemical activity and strong α radioactive decay, plutonium is vulnerable to chemical and physical aging, which can produce macroscopic effects such as surface corrosion, swelling, and degradation of its mechanical properties. Unfortunately, plutonium is one of the most unusual metals and even the most extensively studied plutonium phase diagram, electronic structure and surface structure have been controversial to date. Therefore, developing a predictive aging model for plutonium is a major goal for many laboratories internationally. Such predictions require multi-scale modeling, which until now has not existed. In this paper, progress in theoretical investigations on plutonium, especially first-principles calculations of its electronic structure and atomic-scale simulation of self-radiation damage, is briefly reviewed. Moreover, the feasibility of various density functional theory (DFT) calculations and atomic-scale simulation methods used in plutonium-based solid-state materials studies is discussed. Finally, future directions in this research field are presented.
A spherical Li[Ni1/3Co1/3Mn1/3]O2 cathode material for lithium-ion batteries was synthesized using a combination of modified carbonate co-precipitation and solid-state methods. The as-prepared material was analyzed using X- ray diffractometry (XRD), scanning electron microscopy (SEM), galvanostatic chargedischarge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results indicate that the material synthesized using this new method has a well-ordered layered structure, α-NaFeO2 [space group: R3m(166)], a spherical morphology, and an average particle size of 157 nm. Electrochemical measurements showed that the material has a good rate capability and long-term cycling performance. At a current density of 0.1C (1.0C=180mA·g-1) in the voltage range 2.7-4.3 V, the initial discharge capacity was 156.4 mAh·g-1 and the coulombic efficiency was 81.9%. At 0.5C, 5C, and 20C, the specific capacities of the material were 136.9, 111.3, and 81.3 mAh·g-1, respectively. After 100 cycles at 1C, the material retained 92.9% of its initial capacity; this is higher than those of materials prepared using conventional carbonate co-precipitation (87.0%).
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.
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.
We performed an aberration-corrected scanning transmission electron microscopy(STEM)andenergy-dispersive X-ray spectroscopy(EDS)study of Na0.66Mn0.675Ni0.1625Co0.1625O2,which was prepared via a solidstatereaction for sodium-ion battery applications.Powder X-ray diffraction(XRD)showed that the material hada well-crystallized P2-type layered structure(P63/mmc).Results from further STEM and EDS analyses showedthe presence of reconstructed surface layers of thickness about 1-2 nm,which contained a large amount ofantisite defects and obvious lattice distortions.Detailed chemical analysis showed an inhomogeneous elementaldistribution inside these reconstructed surface layers;they were cobalt rich and nickel deficient.These surfacelayers further evolved into thicker regions of width 5-10 nm,accompanied by a spinel(Fd3m)phase to rocksaltphase(Fm3m)transition.
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.
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.
Surface adsorption of a solution is still a challenging problem in the thermodynamics of surfaces. In this work, a new thermodynamic state function is defined. The equilibrium condition of surface adsorption is that the differential of this state function is equal to zero. Based on this condition, we derived a new equation to describe surface adsorption at equilibrium. No hypothetical dividing surface is needed in this derivation. The new equation is quite different from the Gibbs adsorption equation. We also performed molecular dynamic simulations of aqueous sodium chloride solutions. The simulated results are in good agreement with our theoretical predictions.
A series of novel catalysts derived from Ni-Mg-Al-LDHs (LDHs: layered double hydroxides) were synthesized in-situ on γ-Al2O3 and evaluated in CO2 reforming of CH4 (dry reforming of methane, DRM) reaction system. The catalytic precursors were decomposed and reduced by calcination and an atmospheric plasma technique, respectively. Activity and stability tests showed that the catalytic properties were greatly affected by the pretreatment method. The best catalytic performance was obtained with the catalyst that was directly reduced and decomposed using an atmospheric H2/Ar plasma jet. Compared with the pure LDH precursor, Ni- Mg-Al-LDHs/γ-Al2O3 had much greater mechanical strength, because of the γ-Al2O3 support. This feature extends the long lifetime of catalyst at high temperatures. X-ray diffraction (XRD), transmission electron microscopy (TEM), N2-adsorption-desorption, and thermogravimetry-differential thermal analysis (TG-DTA) results showed that the excellent catalytic performance was based on the small particle size and uniform dispersion of active Ni crystals, as well as the high mechanical strength and large specific surface area of the catalyst.
A variety of primary in situ research techniques applied to underpotential deposition (upd) research, including electrochemical (cyclic voltammetry (CV), chronoamperometry (CHR), and electrochemical impedance spectroscopy (EIS)), interfacial (electrochemical quartz crystal microbalance (EQCM) and electrochemical scanning tunneling microscopy/electrochemical atomic force microscopy (ECSTM/ECAFM)) and X-ray based (X-ray absorption spectroscopy (XAS) and surface X-ray scattering (SXS)) analysis techniques, are summarized in this paper. We summarize and discuss the upd characteristics of many electrochemical systems as determined by these research techniques, and analyze the corresponding relationships and principles between the upd microscopic characteristics and macroscopic test results. Some conclusions of vital importance to upd drawn based on these techniques are explicitly discussed. Also, the merits and demerits of the above-mentioned research techniques are presented and compared. In the matter of application research areas of upd, four main aspects are summarized and analyzed: function materials' electrosynthesis, electroanalysis, electrochemical atomic layer epitaxy (ECALE), and electrochemically active surface area (ECSA) characterization of noble metal (or nano) materials. Meanwhile, the principles involved in the aforementioned applications research related to upd process are briefly explained. Finally, with respect to both research techniques and application research, this paper reveals the current status of upd research and gives a bird's eye view of development trends.
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.
Quenching of a fluorescent probe by amino acid residues can provide valuable information about the structural and conformational dynamics of a biopolymer. Herein, we systematically investigated the ultrafast fluorescence quenching dynamics of Eosin Y in the presence of N-acetyl-tyrosine (AcTyr) in H2O and D2O solutions using both femtosecond transient absorption and time-correlated single-photon counting experiments. We found that the quenching of the fluorescence of Eosin Y by AcTyr in aqueous solution is mainly because of the formation of a ground-state complex between Eosin Y and AcTyr. We also found that the lifetime of the ground-state complex formed between Eosin Y and AcTyr showed a clear kinetic isotope effect, indicating that the quenching of the fluorescence of Eosin Y by AcTyr in aqueous solution is via a proton-coupled electron transfer process.
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.
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.
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.
Hierarchical nanostructured γ-Al2O3 hollow microspheres were synthesized from KAl(SO4)2 and urea precursors by the microwave-assisted hydrothermal (MAH) method at 180 ℃ for 20 min followed by calcination at 600 ℃ for 2 h. The as-prepared sample was used to remove the organic dye Congo red (CR) from aqueous solution. The results showed that the obtained γ-Al2O3 hollow microspheres are about 0.8-1.0 μm in diameter with a shell thickness of approximately 200 nm. The γ-Al2O3 hollow microspheres have a high surface area of 243 m2·g-1 and a hierarchical meso-macroporous structure, which is beneficial for mass transfer in liquid processes. Therefore, the prepared γ-Al2O3 hollow microspheres exhibit faster adsorption and enhanced adsorption performance for CR than particles prepared by the hydrothermal method and commercial γ-Al2O3. The adsorption kinetic data follow the pseudo-second-order equation and the equilibrium data fit well to the Langmuir model. The maximum adsorption capacity (qmax) of the obtained γ-Al2O3 hollow microspheres calculated by the Langmuir model is up to 515.4 mg·g-1 at 25 ℃. The γ-Al2O3 hollow microspheres prepared by the microwave-assisted hydrotherm method show promise as an adsorbent for environmental applications due to their hierarchical porous structure, high surface area, large pore volume, and adsorption capacity.
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.
With the rapid growth of the biodiesel industry, huge amounts of glycerol have been produced as a byproduct.Thus, it is highly desirable to convert low-cost glycerol into highly valuable chemicals, which can both expedite the development of the biodiesel process and save abundant petroleum resources.In this context, one of the most promising approaches is the catalytic hydrogenolysis of glycerol to synthesize 1, 2-propanediol (1, 2-PDO), 1, 3-propanediol (1, 3-PDO), ethylene glycol (EG), and propanols, because these target products have higher selectivity, economic value and potential for industrial application.In this paper, glycerol chemistry will be briefly introduced and then the reaction mechanisms, including dehydration-hydrogenation, dehydrogenation-dehydration-hydrogenation, direct hydrogenolysis, and ionic hydrogenation, will be discussed because of their importance for understanding the catalytic chemistry.Subsequently, the catalytic applications of glycerol hydrogenolysis to obtain 1, 2-PDO, 1, 3-PDO, EG, and propanols will be reviewed in detail based on various catalysts.In the end, we will provide a short summary and an outlook on the future prospects for glycerol hydrogenolysis.
The effects of temperature on the microstructure and physicochemical properties of alkali lignin (AL) in alkaline aqueous solutions were studied at 20-60 ℃. The relationships between temperature and the physicochemical properties of AL, such as the aggregation morphology, molecular surface charge and hydrophobicity, intrinsic viscosity, adsorption characteristics on gas-liquid and liquid- solid interfaces were investigated experimentally using particle charge detection, dynamic light scattering, zeta plus measurements, viscometry, surface tension and dynamic contact angle measurements, quartz crystal microbalance, ultravioletvisible and fluorescence spectroscopies. As the temperature increases, the molecular surface charge density, the intrinsic viscosity, and surface tension of the AL solution decrease significantly. In contrast, the molecular hydrophobicity, intermolecular and intramolecular aggregations, and the amount of AL adsorbed onto liquid-solid interface increase. The AL molecular state changes from extended to compact with increasing temperature. Furthermore, when the temperature increases, the absolute value of the zeta potential first decreases, then increases, and then decreases again. Analysis suggests that the increase in temperature not only reduces the ionization degree of the weak acidic groups in AL, but also weakens the hydrogen bonds between ALmolecules and water molecules. These two factors lead directly to changes in the AL microstructure and physicochemical properties. Based on the results of this study, a mechanism for the microstructural changes in AL with changing temperature was proposed. It was concluded that water would transform from a good solvent to a poor solvent with decreasing temperature. Although AL is often viewed as an anionic surfactant, the regular changes in its physicochemical properties with temperature are more like those of a nonionic surfactant.
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.
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.
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.