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.
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 lithiumstorage 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, 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.
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-g-C3N4 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-g-C3N4 is forecast.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
We performed an aberration-corrected scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) study of Na0.66Mn0.675Ni0.1625Co0.1625O2, which was prepared via a solidstate reaction for sodium-ion battery applications. Powder X-ray diffraction (XRD) showed that the material had a well-crystallized P2-type layered structure (P63/mmc). Results from further STEM and EDS analyses showed the presence of reconstructed surface layers of thickness about 1-2 nm, which contained a large amount of antisite defects and obvious lattice distortions. Detailed chemical analysis showed an inhomogeneous elemental distribution inside these reconstructed surface layers; they were cobalt rich and nickel deficient. These surface layers further evolved into thicker regions of width 5-10 nm, accompanied by a spinel (Fd3m) phase to rocksalt phase (Fm3m) transition.
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.
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.
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.
Graphene/cotton composite fabrics for use as flexible electrodes were prepared using a thermal reduction method. The reducing condition significantly influenced the conductivity of the graphene/cotton fabrics. The conductive graphene/cotton fabrics with hierarchical structures used as flexible electrode substrates facilitate the loading of pseudocapacitor materials, enhancing electron transport and electrolyte ion diffusion. The electrode structure was characterized in detail using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and the standard four-point probe method. After further electrochemical deposition of MnO2 sheets on the composite fabrics, the resulting MnO2/graphene/cotton composite fabrics for use as electrode materials had excellent electrochemical performance and great flexibility. The specific capacitance reached 536 F·g-1 at a scan rate of 5 mV·s-1. The electrochemical test results indicate that it can be further used for flexible energy storage materials.
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.
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.
As a secondary battery, the Li-air battery has the highest theoretical specific energy and has been considered as one of the most promising power sources for electric vehicles. The Li-air battery based on organic electrolyte has become a topic of interest owing to its excellent theoretical energy density, environmental friendliness and low cost. During the past 20 years, much progress has been made in the development of the reaction mechanism, cathode structure, catalyst and electrolyte materials. But there are still many obstacles to overcome before its practical applications. In this paper, we review some of the latest progress in the research on the reaction mechanism, cathode materials, catalysts, electrolytes, as well as the lithium anode. Future research and development prospects are also discussed.
The metal oxide heterojunction has often been used to improve the gas sensing properties of resistive metal oxide semiconductor gas sensors. Metal oxide heterojunctions have been demonstrated to have many unique properties such as Fermi-level mediated charge transfer effects as well as synergistic behavior of different components. In this short review, we summarize the fundamental types of metal oxide heterojunction materials reported in domestic and foreign research in recent years. Metal oxide heterojunctions are mainly divided into five categories of mixed composite structures, multi-layer films, structure modified with a second phase, 1D nanostructure and core-shell structure. We review the enhanced gas sensing mechanisms of metal oxide heterojunctions. These mechanisms are discussed in detail, including the role of the heterojunction, synergistic effects, the spill-over effect, response-type inversion, separation of charge carriers, and microstructure manipulation. We also analyze the remaining challenges of metal oxide heterojunction gas sensors. Finally, we provide an outlook for future development of metal oxide heterojunction gas sensors. The future research directions of metal oxide heterojunction gas sensors can be developed from the definition of heterojunction interface mechanisms. It is hoped that determining the heterojunction interface mechanisms will provide some reference for the design of needed gas sensors in a bottom-up route.
The high temperature oxidative mechanism of a new four-component RP-3 surrogate fuel model was investigated using the ReaxFF MD method. The evolution of the fuel molecules, oxygen, C2H4, and ·CH3, and the underlying reactions, were obtained by systematic analysis of the simulation trajectories with the aid of VARxMD, a unique tool for ReaxFF MD reaction analysis developed by the authors' group. The simulated consumption of fuel and oxygen, as well as the amount of ethylene and methyl radicals, in RP-3 oxidation are of the same magnitude in the ReaxFF MD simulations as that predicted by CHEMKIN under the same temperature and initial pressure conditions. Based on the chemical structures of all the species and the full set of reactions obtained, the detailed mechanisms observed in the simulations broadly agree with the previous literature. The first reactions of the fuel molecules can be categorized into H-abstraction and internal scission, with the latter dominating under various temperature conditions. Observation and statistical analysis of the oxygen reactions reveal that small species of C1-C3 are involved in a relatively large proportion, which may allow the simplification of the reaction mechanism. A reaction network for RP-3 oxidation at high temperature is obtained through the analysis of the reaction mechanisms. This work demonstrates that the ReaxFF MD method, combined with the unique reaction analysis capability of VARxMD, provides useful insights into the mechanism of fuel combustion and should aid the construction of combustion mechanism libraries.
Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.
Chemically modified carbon has attracted significant attention since our first report of its use in lithium/sulfur (Li/S) cells. Compared with traditional carbon materials, chemically modified carbon prevents the dissolution and diffusion of intermediate polysulfides. Therefore, it yields sulfur cathodes with long cycling stability, which has become the focus of current research in the field of Li/S batteries. This review summarizes the use of chemically modified carbon for highly efficient sulfur utilization and the synergistic chemical/physical trapping of sulfur species. The prospects of further developments of Li/S batteries using chemically modified carbon is also discussed.
Three-dimensional direct numerical simulation is conducted to simulate the auto-ignition of the highoctane fuel PRF70 under partially premixed combustion (PPC) engine conditions. A skeletal primary reference fuel (PRF) chemical kinetic mechanism is adopted, including 33 species and 38 elementary reactions. Compression/expansion effects caused by piston motion, the real engine geometry, and the working conditions are considered. The simulation includes two injections, the first being used to form a relatively uniform base mixture and the second to forma stratified mixture and trigger the ignition. It is found that the combustion process in PPC engines is a rather complex combination of homogeneous combustion, rich premixed and diffusioncontrolled combustion. The region between the two injections is near stoichiometry, resulting in the formation of NOx, while abundant CO is retained in the region with equivalence ratio (φ) > 2, which needs to diffuse to meet the oxidizer and burn in a diffusion flame. The marching cube method is used to extract the 3D flame surface and show the temporal evolution of the reaction front. Finally, the joint PDF of the Gaussian curvature (kg) and principle mean curvature (km) and temporal evolution of the probability density function (PDF) in terms of km show that km plays a more important role and becomes negative as time evolves because of the consumption of rich premixed flame in the center.
Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.
Pt-based nanocatalysts are irreplaceable for proton exchange membrane fuel cells (PEMFCs), while the low reserves and high cost of Pt severely impede their commercialization. Tremendous efforts have been devoted to reduce the amount of precious metals and improve their electrocatalytic performance at the same time. Nanocatalysts with a hollow interior possess a large active area, high catalytic activity, good stability, and significantly reduce the amount of noble metal. The synthesis methods for their preparation are various, wherein the galvanic replacement reaction without additional procedure to remove the core, without the functionalization to the template surface and with ease of control, is the main method to prepare hollow structural nanocatalysts. We review the recent developments of hollow Pt-based nanocatalysts synthesized by the galvanic replacement reaction. The further challenges and developments of hollow Pt-based nanocatalysts are also discussed.
Semiconducting, two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2) have attracted significant attention because of their unique properties and promising applications in electronic and optoelectronic devices. However, the controllable tuning of the properties of 2D MoS2 remains a key challenge with regard to its practical application. Among various approaches to addressing this issue, chemical doping is one of the most efficient. This review focuses on three major doping strategies, which are surface charge transfer, in-plane substitution and interlayer intercalation. We discuss the principles, latest progress and limitations of these doping approaches. Finally, we summarize the current challenges and opportunities associated with the chemical doping of 2D MoS2.
In this work, Li1.2Mn0.54Co0.13Ni0.13NaxO2 was prepared via an ion-exchange process combined with a solid- state reaction. Aberration- corrected scanning transmission electron microscopy (STEM), energydispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) were all used to study the surface structure and chemical distribution of the resulting material. Nickel (Ni) was found to be enriched at the surface in regions perpendicular to the lithium diffusion channels (that is, the (200) surfaces) and also exhibited a tendency to diffuse into the lithium (Li) layers, generating a Fm3m rocksalt phase. In contrast, cobalt (Co) segregated along the transition metal (TM) layers of the (001) and (200) surfaces. The results of aging trials demonstrated that Co-enriched layers lead to surface structure instability, as evidenced by the formation of a large number of antisite defects (Li-TM) and rocksalt phase structures at the (001) surface during aging.
The contact resistance effect in the network type carbon nanotube thin film transistors (CNT-TFTs) is studied by using different contact metals. It is shown that palladium (Pd) can form an ohmic type contact with the carbon nanotube thin film, and gold (Au) forms an almost ohmic contact. On-state current and carrier mobility in the devices of these two contacts are high. In contrast, both titanium (Ti) and aluminum (Al) form Schottkytype contacts with the carbon nanotube thin film. The barrier height and the contact resistance of the Al contact are higher than those of the Ti contact. Therefore, the on-state current and carrier mobility are relatively low in the corresponding devices of these two types of contacts. These results indicate that the performance of CNTTFTs can be tuned by the contact metal, which is important for the commercialization of CNT-TFTs.
Polymer light emitting devices incorporating poly(9-vinylcarbazole) (PVK):2,2'-(1,3-phenylene)-bis [5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) as the co-host and the thermally activated delayed fluorescence compound 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) as the emissive dopant exhibited a peak external quantum efficiency of 13%. In addition, 4CzIPN-sensitized (5,6,11,12)-tetraphenyl-naphthacene (Rubrene) devices gave a peak external quantum efficiency of 9.2%, a value that is 5.4 times that of analogous devices without 4CzIPN. Based on transient luminescence measurements, the working mechanism for 4CzIPN sensitization was determined to be Förster energy transfer from 4CzIPN to Rubrene. This work assessed the effects of the Rubrene concentration and the carrier transport balance in the emission layer on the device properties, and the results suggest that the self-aggregation of Rubrene may limit device efficiency.
A durable superhydrophobic coating on polyester fabrics has been fabricated by a simple solutionimmersion method in a solution consisting of a methyl MQ (M: mono-functional silicon-oxygen unit R3SiO1/2, Q: tetra-functional silicon-oxygen unit SiO2) silicone resin and hydrophobic silica nanoparticles. After coating, the microstructured fibers were wrapped by compact hydrophobic nanoparticles that could lower the surface energy of the fibers. Therefore, the obtained fabric exhibited an excellent superhydrophobic property with a water contact angle of 156° and a sliding angle of 5°. It is worth mentioning that the as-prepared fabric was proved to be able to withstand extreme environmental conditions such as mechanical abrasion, acidic and alkaline attack, and UV irradiation. The practical application of the modified fabric for oil-water separation was also demonstrated with a high separation efficiency above 99%. This feasible fabrication method paves the way for using the superhydrophobic fabric on a large scale.
α-MnO2 nanorods, γ-MnO2 nanosheets, and δ-MnO2 nanofilm-assembled microspheres were prepared using a hydrothermal method and evaluated as catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx). They were also structurally characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption-desorption, temperatureprogrammed reduction with hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The γ-MnO2 nanosheets performed the best for the reduction of NOx and selectivity of N2, while the α-MnO2 nanorods performed the worst. Structural analysis indicated that the main factor determining the catalytic activities of the nanomaterials was not the specific surface area but the crystal structure and the exposed active crystals. The γ-MnO2 nanosheets performed best because their exposed (131) planes contained multiple Mn cations in coordinatively unsaturated environments, which formed numerous strongly acidic sites. They also benefited from active oxygen species. The active sites allowed the activation of NH3 and NOx at lower temperatures. Moreover, high concentrations of liquid oxygen and Mn cations at high oxidation states facilitated the redox reactions.
Micro-microporous composite zeolites with binary (or more) structures not only possess the advantages of the two kinds of molecular sieves, but also tailor the pore structure and acid property of the composite samples. These changes induce the formation of special properties of the composites and further present special catalytic performance, which drives many research studies. Based on synthetic methods and micro-structural features, micro-microporous composites can mainly be divided into two types: intergrowth or co-existence composite zeolites. The former has a structural rearrangement that is produced by the stacking of distinct layers and leads to the generation of a new crystal structure. The latter is formed by staggered growth and has a compound interface when two or more zeolites appeared in the same gel system. Compared with the intergrowth zeolites, the co-existence zeolites do not possess the new and perfect crystal structure. This review summarizes the development of micro-microporous composites, focusing on their synthesis and structural characteristics as well as the application of intergrowth and co-existence composite zeolites in the field of catalytic reactions.
Microbial fuel cell (MFC) is a novel bioelectrochemical device that uses a biocatalyst to convert chemical energy stored in organic wastewater into electrical energy. However, multiple factors limit the practical applications of MFCs, such as the high cost of electrode production and their low conversion efficiencies of power density and energy. Therefore, improving the catalytic performance of the electrodes and lowering the cost of electrode production have become focuses in MFC research. Because of the excellent electrical conductivity and catalytic properties of graphene-based hybrid materials, the development of these electrode materials for use in MFCs has attracted much attention. This review summarizes recent advances of graphene-based hybrid electrodes in MFCs. The preparation methods and the catalytic performance of graphene-modified electrodes, metal and non-metallic/graphene hybrid electrodes, metal oxide/graphene hybrid electrodes, polymer/graphene hybrid electrodes, and graphene gel electrodes are discussed in detail. The influence of graphene-based hybrid anodes and cathodes on the electricity generation performance of MFCs is analyzed. Finally, the problems facing graphene-based hybrid electrodes for MFCs are summarized, and the application prospects of MFCs are considered.
A new methanol-tolerant oxygen reduction electrocatalyst, nitrogen-doped hollow carbon microspheres@platinum nanoparticles hybrids (HNCMS@Pt NPs), has been synthesized by a facile template route. In brief, Pt NPs were loaded on the surface of NH2-functionalized SiO2 microspheres (Pt NPs/SiO2). Then, the Pt NPs/SiO2 hybrids were wrapped by polydopamine (PDA) film. After direct carbonization of PDA-wrapped Pt NPs/SiO2 hybrids under a nitrogen atmosphere and further treatment in a hydrofluoric acid solution, Pt NPs embedded within nitrogen-doped hollow carbon microsphere (HNCMS) were obtained and labeled as HNCMS@Pt NPs. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, specific surface area analysis, and X-ray photoelectron spectroscopy were used to characterize the HNCMS@Pt NPs hybrids. The electrochemical properties of the HNCMS@Pt NPs hybrids for oxygen reduction reaction have also been investigated by cyclic voltammetry and linear sweep voltammetry. The results show that the Pt loading mass in the HNCMS@Pt NPs hybrids is up to 11.9% (w, mass fraction). Furthermore, the as-prepared HNCMS@Pt NPs catalyst exhibits good electrocatalytic activity, high stability, and excellent methanol-tolerance toward oxygen reduction reactions, implying potential applications in practical direct methanol fuel cells (DMFCs) as methanol-tolerant cathodic catalysts.
Insulating oxides of SiO2, ZrO2, and Al2O3 were coated using a dipping method on the surface of mesoporous TiO2 nanoparticles for perovskite solar cells. The effects of the insulating oxide coatings on the performance of the perovskite solar cells and the interface charge recombination dynamics were investigated in detail. The efficiency of devices after SiO2 coating improved by 13.7% due to their FF (fill factor) increasing from 67.6% to 72.3%. However, the devices with ZrO2 and Al2O3 coatings exhibited an increase in Voc of up to 50 mV and a decrease in Jsc and FF. Transient absorption spectroscopy on a timescale from nanoseconds to milliseconds was performed to study the interface recombination lifetime between electrons and holes and the changes of the device performances are discussed.
Hydrogen produced from electrochemical water-splitting driven by renewable resource-derived electricity is considered a promising candidate for clean energy. However, sustainable hydrogen production from water splitting requires highly active catalysts to make the process efficient. Catalysts based on graphene-like two-dimensional (2D) materials present great potential in the hydrogen evolution reaction (HER) and thus gain attention. In this review, which is a combination of our recent works, we highlight research efforts towards electrocatalysts for the HER based on 2D materials including transition metal disulfides, MXenes, and boron monolayers. Finally, we summarize the challenges and prospects for future development of electrocatalysts for the hydrogen evolution reaction.
ZIF-8 membranes were prepared on α-alumina substrates in a urea/choline chloride (ChCl) based deep eutectic solvent using an in situ method. The synthesized ZIF-8 membranes were characterized using Xray diffraction (XRD) and scanning electron microscopy (SEM). The effects of the concentration of the reaction solution and the cooling rate on ZIF-8 membrane synthesis were investigated. The results indicate that increasing the concentration of the reaction solution and reducing the cooling rate are beneficial for synthesizing continuous ZIF-8 membranes. A continuous and compact ZIF-8 membrane with a thickness of about 8 μm was obtained on the substrate by optimizing the synthetic conditions. The single gas permeation and binary mixture gas separation performances of the ZIF-8 membrane prepared under the optimized synthetic conditions were determined using the Wicke-Kallenbach technique. For equimolar gas mixtures at room temperature (293 K), the separation factors for H2/CO2, H2/O2, H2/N2, and H2/CH4 were 7.4, 5.2, 9.1, and 13.8, respectively. All the separation factors exceed the corresponding Knudsen diffusion coefficients, indicating that the ZIF-8 membrane displays molecular sieving performance.
Ordered mesoporous carbon materials (OMCs) have potentially broad applications in many fields, such as adsorption, separation, catalysis, and energy storage/conversion. Compared with the elaborate hardtemplate strategy, the soft-template approach, which is based on the self-assembly between amphiphilic block copolymers and polymerizable precursors (e.g., phenolic resins), is a more effective and efficient method for the synthesis of OMCs. In this review, the mechanism and characteristics for three main soft-template methods, i.e., solvent evaporation-induced self-assembly synthesis, aqueous cooperative self-assembly synthesis and solvent-free synthesis, are discussed and compared. In addition, a few highlights of recent progress, including application of novel carbon precursors, structural modification and functionalization of OMCs, are outlined. Finally, we summarize the crucial issues to be addressed in developing the synthesis methodology of OMCs.
With the rapid development of wearable devices, flexible conductive materials, which are one of the most important components of flexible electronics, have continued to attract increasing attention as important materials. Conventional electrodes mainly consist of rigid metallic materials, and consequently lack flexibility. Some of the strategies commonly used to make flexible metal electrodes include reducing the thickness of the electrode and designing electrodes with unique structural features. However, these techniques are generally complicated and expensive. Nanocarbon materials, especially carbon nanotubes and graphene, are highly flexible and exhibit excellent conductivity, superior thermal stability, good chemical stability, and high transmittance, making them good alternative materials for the preparation of flexible conductors. In this review, we have summarized recent advances towards the development of flexible conductors based on different types of nanocarbon materials, including carbon nanotubes arrays, carbon nanotubes films, carbon nanotubes fibers, graphene prepared using exfoliation or chemical vapor deposition techniques and graphene fibers. We have also provided a brief review of flexible conductive materials based on graphene/carbon nanotube composites, as well as a summary of the synthesis, fabrication and performances of these conductors. Finally, we have discussed the future challenges and possible research directions of flexible conductors based on nanocarbon materials.
A highly ordered mesoporous Si/C composite was prepared by magnesiothermic reduction method, using SBA-15 as the precursor at 660 ℃ with subsequent carbon coating. This Si/C composite preserved the ordered honeycomb pore channels of SBA-15 and exhibited a lotus root-like structure with high packing density. A liquid ambient reaction model is proposed to explain the reaction between SBA-15 and magnesium powder at 660 ℃ as well as the mechanism by which the highly ordered mesoporous structure is generated. The phase composition and morphology of this material were analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption- desorption and Raman spectroscopy. The excellent electrochemical performance of the as- prepared material suggests potential applications as an anode material in second-generation Li-ion batteries.
To understand the physical and chemical responses of energetic materials, such as 1,3- dinitrobenzene (DNB, C6H4N2O4), hexanitrohexaazaisowurtzitane (CL20, C6H6N12O12), and CL20/DNB co-crystal, to femtosecond laser ablation (FLA), their molecular reaction dynamics have been investigated using the ReaxFF/ lg force field. The computational results indicate that the temperature and pressure of the CL20/DNB system jump during FLA. In particular, the temperature and pressure gradually reach their maxima following an initial cooling process. N―NO2 bond breaking of the CL20 molecule triggers the reactions for both the CL20 and CL20/ DNB systems. However, the CL20 system prevails the CL20/DNB co-crystal in the decomposition rate simply because coexistence of DNB molecules in the mixture and generated decomposition products containing benzene rings greatly reduce the effective collision probability between CL20 and the products.
Copper nanowires are excellent materials for transparent and flexible conducting electrodes in modern nanoscience and nanotechnology because of their unique optical, electrical, mechanical, and thermal properties. With the distinguishing features of relatively low price and natural abundance, copper is an ideal candidate to substitute for noble metals in technical applications. However, the main hindrances to their practical application are the susceptibility of Cu nanowires to oxidation upon exposure to air or water and the difficulty in reducing Cu ions to metallic Cu. The synthesis of copper nanowires with high monodispersity, stability, and oxidation resistance has become a major research goal. Among the wide variety of methods available to generate copper nanowires, liquid-phase reduction has been widely adopted for the advantages of high yield, simple and straightforward operation, relatively low cost, and fewer constraints on reaction conditions, in addition to solving the above problems. This review begins with an introduction to the research background and significance of copper nanowires. First, we present a brief overview of the research advances, including the synthesis and growth mechanisms, of smooth or rough, single-crystal or twinned copper nanowires. Oxidation and surface modification for oxygen-resistance are then discussed, followed by a brief summary and outlook for research in the field.
Graphene and its derivatives have attracted increasing attention during the last decade as efficient materials for the storage and conversion of energy. In most cases, however, these graphene materials possess large numbers of structural defects such as cavities, heteroatoms and functional groups, making them quite different from the precisely-defined "single carbon layer of graphite" observed for graphene. These materials also differ considerably in terms of their electrochemical properties because of their variable structures, which are strongly influenced by the methods used during their preparation. Structural analyses have indicated that these materials consist of graphene subunits, which are interconnected by organic linkers with properties lying between those of graphene and polymers, which we have defined as "graphenal polymers". The thermal crosslinking reactions of porous polymer networks fabricated from small organic molecules using a bottom-up strategy also result in graphene-like subunits, which are covalently interconnected by polymeric fractions. These materials cover a series of transitional intermediates belonging to the "graphenal polymers" family, where polymers and graphene sit at opposite ends of family spectrum. Moreover, the special structures and properties of these materials make them ideal electrode materials for the storage and conversion of energy via electronic and ionic transport pathways, allowing for a deeper evaluation of the structure-property relationships of different electrode materials.
To understand the principles of the fabrication of nanowire arrays using macroscopic metal-assisted chemical etching (MACE), Si nanowires (SiNWs) are synthesized using Ag-coated Si substrates and Pt electrodes by the macroscopic MACE. Analysis of the SiNWmorphology coupled with the corresponding current density in the MACE process is applied to systematically investigate the effects of the electrical connection, Ag coating, etching conditions, Si substrates, and light irradiation on the formation of SiNWs. It is found that there is a certain relationship between the current density and the SiNWlength. Amode is proposed to fundamentally understand the mechanisms of the preparation of SiNWs using MACE. Associated opportunities are also discussed.
Graphene nanosheets (GNSs) were prepared using oxidation of graphite powder followed by rapid thermal exfoliation under a nitrogen atmosphere. The as-prepared samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The specific surface area was determined using the nitrogen adsorption and desorption method. These analytic techniques revealed that the samples possessed a curled morphology consisting of a thin paper-like structure, which was made of a few graphite layers (approximately four layers) and a large specific surface area (628.5 m2·g-1). The effects of pH, adsorption time, temperature and initial concentration of Pb2+ and Cd2+ on adsorption onto the GNSs were investigated. The maximum adsorption capacities of GNSs for Pb2+ and Cd2+ ions were approximately 460.20 and 72.39 mg·g-1, respectively. These results indicate that the resulting high-quality GNSs can be used as an attractive adsorptive material for removing Pb2+ and Cd2+ from water.
Nanomaterials have excellent properties and have been used widely in chemical engineering, electronics, mechanics, environment, energy, aerospace, and many other fields in recent years. Besides, nanomaterials have attracted increasing attention in the biomedical field. The interactions between nanomaterials and protein molecules are not only significant to the basic science of the biomedical field, but also crucial for the evaluation of biomedical applications and biosafety of nanomaterials. The interfacial interactions between proteins and nanomaterials could induce a series of changes to the structures and functions of proteins, such as the transformation of protein conformations, and the modulation of aggregation states, which would influence the functions of the protein molecules. Interfacial interactions can also influence the physicochemical features of nanomaterials, including morphology, size, hydrophilicity/hydrophobicity, and surface charge density. In this review we explained the molecular level mechanisms for the interactions between nanomaterials and proteins at the interface based on the detection technologies, and discussed the changes in physical and chemical features, structures, and functions. We envision this review could be helpful for the deeper understanding of the complicated interactions between nanomaterials and proteins, and could be beneficial for promoting the healthy, safe, and sustainable development and application of nanomaterials in the biological and medical fields.
Three-dimensional, nanoporous CoFe2O4 catalysts were synthesized, employing a colloidal crystal template method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption were subsequently used to characterize the crystal structures and morphologies of the samples. The catalytic activities of nanoporous CoFe2O4 and CoFe2O4 nanospheres during the thermal decomposition of ammonium perchlorate (AP) were also investigated by differential scanning calorimetry (DSC). The results show that the spinel framework of these materials has an ordered open network of pores averaging 200 nm in diameter. The specific surface area of the nanoporous CoFe2O4 was 55.646 m2·g-1, a value that was higher than that of the nanosphere material. DSC analysis indicates that the catalytic activity of the nanoporous CoFe2O4 is superior to that of the spherical material during the thermal decomposition of AP, and that the nanoporous catalyst makes the peak temperature of high temperature decomposition decrease by 91.46 ℃. The heat release from the AP in the presence of nanoporous CoFe2O4 (1120.88 J·g-1) is 2.3 times that obtained frompureAP. Both the higher specific surface area and greater quantity of active reduction sites on the nanoporous CoFe2O4 relative to the nanosphere material act to reduce the activation energy during the AP decomposition process. Based on the results of this work, a possible catalytic mechanismfor the thermal decomposition of AP over nanoporous CoFe2O4 is proposed, in which gaseous intermediates play an important role.
Nanosheet materials obtained from laminar compounds are new two-dimensional anisotropic nanomaterials that can even reach the sub-nanometer scale. These materials possess unique physical and chemical properties. An example of such a nanosheet materials is graphitic carbon nitride (g-C3N4) nanosheets transformed from bulk g-C3N4. Here, g-C3N4 nanosheets were prepared from bulk g-C3N4 by high-temperature thermal oxidation. The photocatalytic activity of eosin (EY)-sensitized g-C3N4 nanosheets for hydrogen evolution was about 2.6 times higher than that of bulk g-C3N4. The structure of the g-C3N4 nanosheets and process of electron transfer between EY and the g-C3N4 nanosheets were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, fluorescence spectroscopy, and photoelectrochemical measurements. The g-C3N4 nanosheets possessed high specific surface area. The g-C3N4 nanosheets not only effectively absorbed dye molecules, but also enhanced the separation and electron transport efficiencies of photogenerated charges because of their quantum confinement effect. The quantum confinement effect of g-C3N4 nanosheets widened their bandgap, improved electron transfer ability along the in-plane direction, and lengthened the lifetime of photoexcited charge carriers. As a result, the photocatalytic activity of the g-C3N4 nanosheets was improved compared with that of bulk g-C3N4.
Research on the hydrated structure of KCl and NaCl mixed solutions with a concentration range between 0 and 26% was conducted using X-ray diffraction and Raman spectroscopy at 25 ℃. Their reduced structure functions, F(Q), and reduced pair distribution functions, G(r), obtained from X-ray diffraction indicate that compared with Na+, the hydration numbers and shell radii of the hydrated K+ ions are larger. This explains why the solubility of NaCl is higher than that of KCl at 25 ℃. According to the Raman spectroscopy, the tetrahedral hydrogen bonds of water molecules will be destroyed with the increase in KCl concentration and the decrease in NaCl concentration. The extent of the bond destruction has systematic variations; for example, increasing at first and then decreasing. These results show that the destruction of the hydrogen bond structure resulting from Na+ is more serious than from K+. Also, with the appropriate K+ content in the NaCl solution, Na+ will behave as a structure breaker instead of a structure maker, which enhances the destructiveness of the solution structure.
We develop a novel hole extracting buffer layer material, namely PbI2. The structure of the device we fabricate is ITO/PbI2/P3HT:PC61BM/Al (indium tin oxide/lead iodide/poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester/aluminum cathode). The preparation method involves spin-coating and thermal evaporation. We study the effectiveness of using PbI2 in the prototype ITO/P3HT:PC61BM/Al polymer solar cell devices. The concentration, annealing temperature, and annealing time all have an influence on the quality of the PbI2 films. Obviously, higher-quality PbI2 films will lead to better power conversion efficiency. The transmittance, crystallization, and morphology properties of the PbI2 films can be used to describe the quality of the films. We characterize the PbI2 film affording the best performance by UV-Vis spectrophotometry, X-ray powder diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Our results reveal that the performance of the solar cell device is sensitive to the concentration of PbI2, and the best conditions are a concentration of 3 mg·mL-1, annealing temperature of 100 ℃, and annealing time of 30 min. The open circuit voltage (Voc) is 0.45 V, the short circuit current density (Jsc) is 7.9 mA·cm-2, and the fill factor (FF) is 0.46. Compared with the devices without any buffer layer (0.85%), the power conversion efficiency (PCE) using PbI2 as the buffer layer can reach 1.64%.
Mixed halide perovskites of MAPbI3-xBrx and MAPbI3-xClx (MA=CH3NH3) with film thickness of about 300 nm were synthesized through the Br or Cl doping, thanks to the two steps deposition of controlled concentration of the precursor solution and the intramolecular exchange of DMSO molecules intercalated in PbI2 (PbI2(DMSO) complex) with MAX (X=I, Br) or MAX (X=I, Cl), respectively. The doping of Br or Cl in the perovskite film can improve the photovoltaic performance of PSCs with the precursor of MAX contains 5% (in mole fraction, same below) MABr or 15% MACl, respectively, while further increase in the content of MABr or MACl in the precursor did not lead to significant changes in doping amounts, but small white particles or pin-holes were formed in mixed perovskite materials, therefore resulted in adverse effects on the performance of solar cells. The MAPbI3-xBrx perovskite solar cells with 5% MABr in precursor solution showed a power conversion efficiency (PCE) of 13.2%, and the MAPbI3-xClx perovskite solar cells with 15% MACl in precursor solution showed the highest PCE of 13.5%.
The production of 2,3-pentanedione from lactic acid over SiO2-supported alkali metal nitrates under various conditions was investigated. Using nitrate (NO3-) as the anion, the effect of alkali metal cations on Claisen condensation of lactic acid into 2,3-pentanedione was focused on. Among precursors such as LiNO3, NaNO3, KNO3, and CsNO3, CsNO3 displayed the best catalytic performance. Characterization of the fresh and used catalysts by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy revealed that all MNO3 (M = Li, Na, K, Cs) salts were transformed into alkali metal lactates during the reaction. Alkali metal lactates were identified as active species for catalytic Claisen condensation of lactic acid into 2,3-pentanedione. CO2 temperature-programmed desorption (TPD) results of the used catalysts showed that the CsNO3/SiO2 catalyst was the most alkaline. For that reason, the CsNO3/SiO2 catalyst displayed the highest catalytic performance of those examined. The effects of reaction temperature and loading amount of CsNO3 on reaction performance were also discussed. Over the 4.4% (x, molar fraction) CsNO3/SiO2 catalyst, a 54.1% yield of 2,3-pentanedione was achieved at 300 ℃.
Density functional theory (DFT) calculations were performed to gain mechanistic insight into the methanol C―H and O―H bond activations mediated by ruthenium-doped platinum cationic clusters [PtnRum]+ (m + n = 3, n ≥ 1). The charge effect on the reactivity has been elucidated. Calculations show that positive charge is evenly distributed on the three Pt atoms of the [Pt3]+ cluster, while in the Ru-doped clusters, positive charge is mainly distributed on the Ru atom(s). The reactivity of [PtnRum]+ is significantly greater than neutral [PtnRum] during the initial C―H bond cleavage, while only [Pt3]+ exhibits greater reactivity than [Pt3] in the course of O―H bond cleavage. This study may aid in deeper understanding of C―H/O―H bond activations mediated by metal clusters.
The mesoscopic structure of Nafion-[Bmim][TfO] ionic liquid (IL) composite membrane was studied using dissipative particle dynamics (DPD) simulations. The effects of temperature and IL concentration on the mesoscopic structure were investigated. Microphase-separation phenomena were observed. Analyses of the pore size distributions under different conditions indicated that with the increasing IL concentration in composite membrane, the aggregated state was transformed from dispersed IL clusters to coherent IL channels. A chamber structure was formed when the IL concentration was very high. The structure of ionic liquid channels became more complex with increasing temperature and the chamber was transformed into new branches of channels, indicating that the IL channels became more coherent at elevated temperatures. The interfacial distribution probabilities and radial distribution functions indicated that the alkyl chains of ionic liquids were embedded in the Nafion backbone, and changes in the distribution of sulfonic acid groups in the side chains directly affected the distribution of imidazole groups and anions at the microphase interface. In this work, the mesoscopic structures of Nafion-IL composite membrane at the molecular level were explored and valuable insights for developing new high-temperature proton-conducting polyelectrolyte materials were obtained.
The fluorescent dye thioflavin T (ThT) is widely used for the qualitative and quantitative detection of amyloid fibrils. However, many small-molecular inhibitors have been shown to compete with ThT in binding the fibrils and therefore greatly affect the ThT fluorescence. The effect of ThT on the aggregation kinetics of amyloid proteins is not yet fully understood. Here, using amyloid β-protein 40 (Aβ40) as a model system, we show that ThT significantly alters the aggregation kinetics of Aβ40 in a dose-dependent manner, leading to a decrease-increase trend in the lag time that represents the nucleation rate. Specifically, the lag time decreases as a function of ThT concentration at low ranges, but then begins to increase beyond a specific ThT concentration, which itself increases with Aβ40 concentration. By contrast, the elongation rate slowly increases with ThT concentration. As for the secondary structure and morphology of the fibrils, no significant effects of ThT are observed. Isothermal titration calorimetry suggests that the hydrophobic interaction dominates the binding of ThT to Aβ40. Based on these findings, a working mechanism of the dual effects of ThT on Aβ fibrillization is proposed. These results should aid our understanding of the molecular mechanism of ThT binding with Aβ and allow practical improvements in the measurement of the nucleation kinetics of Aβ fibrillization.
The AramcoMech 1.3 mechanism, containing 253 species and 1542 reactions for oxidation of hydrocarbon and oxygenated C1-C2 fuels, is reduced with six direct relation graph (DRG)-related methods. The final skeletal mechanism with 81 species and 497 reactions is achieved from the intersection of the resulting skeletal mechanisms obtained with these DRG-related methods. The maximum error for the ignition delay times with this 81-species mechanism does not increase significantly compared with that obtained for the other skeletal mechanisms. This shows that the intersection of skeletal mechanisms from various mechanism reduction methods can effectively remove the redundant species. Ignition delay times of two-component mixtures with the skeletal mechanism also agree very well with those of the detailed mechanism. The skeletal mechanism has also been validated against the detailed mechanism using many other combustion characters of the involved fuels in different reactors and flames. Results from the element flux analysis demonstrate that the reaction paths for these fuels with the detailed mechanism can be reproduced accurately with the 81-species skeletal mechanism. All the important reaction paths are thus retained in the 81-species mechanism. All these results show that the skeletal mechanism is able to provide the combustion properties of C1-C2 fuels that are in good agreement with those of the detailed mechanism. The 81-species skeletal mechanism can be employed as a reaction base for developing mechanisms of other large hydrocarbon or oxygenated fuels.
The effect of Li+, Zn2+, and Mn2+ ions in aqueous solution on the electrochemical performance of the MnO2 cathode characterized by different crystal structures and morphologies was investigated. The energy storage mechanism of MnO2 in the mixed solution was probed. The results show that in aqueous solution without Mn2+ ions, various MnO2 electrodes exhibit similar electrochemical performance with low capacity and severe attenuation. In an aqueous solution with Zn2+ ions, the capacity of MnO2 electrodes is enhanced, which can be attributed to insertion/extraction of zinc ions. However, the decay of the capacity is drastic. When aqueous solutions containing Mn2+ and Zn2+ ions are used, particle aggregation and crystal structure collapse of MnO2 are effectively prevented owing to the synergistic effect of zinc and manganese ions and the redox reaction process of Mn2+ ions. The negative influence of the ZnSO4·3Zn(OH)2 impurity is also weakened. As a result, the high capacity of MnO2 electrodes resulting from insertion/extraction of zinc ions is maintained (~200 mAh·g-1 at 100 mA·g-1) with excellent cycling stability.
In order to ameliorate the severe capacity fading of LiNi0.5Co0.2Mn0.3O2 cathode materials at elevated temperatures, a Zr-doping strategy was performed via a solid-state method, and the influence of the doping content on the structural and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 was studied. The results indicate that the Li+/Ni2+ cation mixing can be reduced and the electrochemical performance, especially the hightemperature cycling performance, can be improved when the doping content of zirconium is 0.01. After 95 cycles, the capacity retention of Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 is 92.13% at 1C between 3.0 and 4.3 V, which is higher than that of the LiNi0.5Co0.2Mn0.3O2 (87.61%). When cycling at 55 ℃, Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 exhibits a capacity retention of 82.96% after 115 cycles at 1C, while that of the bare sample remains at only 67.63%. Therefore, a small amount of zirconium doping is notably beneficial to the electrochemical performance of LiNi0.5Co0.2Mn0.3O2 at elevated temperatures.
Poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block polyethers are typical nonionic polymeric surfactants, which allow for wide structural design, exhibit temperature-dependent micellization of the copolymers, and function in a variety of solvent systems. It greatly enriched the investigation of their aggregation behaviors in various solutions. In this paper, an overview based on our research work was provided about the basic properties of linear and branched PEO-PPO block polyethers in aqueous solutions. Furthermore, the effects of additives including acid/base, inorganic salts, alcohols, surfactants and polymers on the aggregation behaviors of PEO-PPO polyethers are examined. PEO-PPO block polyethers have good biocompatibility. They can form micelles in aqueous solutions, with a hydrophobic core and a hydrophilic corona around the micelle interior. This micelle structure provides local hydrophobic microenvironments for hydrophobic drugs. Thus, the application of PEO-PPO polyethers in the field of drug delivery is presented; they can be the theoretical dosage support structure in future drug discovery research.
Density functional theory with dispersion correction (DFT-D3) was used to investigate the effects of N-doping on the adsorption of CO2 in carbonaceous materials. The CO2 adsorption energies and equilibrium geometry parameters were studied to compare the effects of various N-containing functional groups. The adsorption energies of single amide-and pyridine-type adsorbents were higher than those of aniline-and pyrroletype adsorbents, as a result of strong electrostatic interactions and/or the formation of weak hydrogen bonds. For pyrrole-type adsorbents, the adsorption energy increased with increasing number of benzene rings, because dispersion became the dominant interaction. These findings indicate that amide-and pyrrole-type adsorbents are the most promising CO2 trappers. The calculation results are consistent with our previous experimental conclusions for N-doped carbonaceous materials and will be useful for screening carbon materials to achieve more efficient CO2 capture.
Rutile is much less active than anatase and brookite for the photocatalytic degradation of organic pollutants in aqueous solution. In this work, we found that addition of a trace amount of CuWO4 greatly accelerated phenol degradation in an aerated aqueous suspension of rutile. The increased rate was not only much higher than those of anatase and brookite, prepared at the same temperature (600 ℃), but also increased continuously with the sintering temperature of rutile from 150 to 800 ℃. These observations indicate that the high intrinsic photocatalytic activity of rutile produced at a high sintering temperature can be exploited by using co-catalyst CuWO4. Furthermore, as the amount of CuWO4 added to the suspension increased, the amount of H2O2 produced in the presence of excess phenol increased and then decreased; the trend was similar to that observed for phenol degradation. The observed positive effect of CuWO4 is mainly caused by solid CuWO4 rather than Cu2+ ions in aqueous solution. A (photo)electrochemical measurement showed that interfacial electron transfer occurred from the irradiated rutile to CuWO4. This would improve the charge-separation efficiency, and consequently increase the rates of O2 reduction and phenol degradation.
A Bi(OH)3 precursor was prepared using a precipitation method using bismuth nitrate as a starting material and ammonia as the precipitation agent. Bi(OH)3 was then calcined at different temperatures and different time. X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry (TG), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UVVis DRS) were used to investigate the phase transformation from Bi(OH)3 to Bi2O3 and the particle size, morphology, and optical properties of Bi2O3 during the phase transformation. It was found that Bi(OH)3 after calcination undergoes the following process: Bi(OH)3 → Bi5O7NO3 → β-Bi2O3/Bi5O7NO3 → β-Bi2O3/Bi5O7NO3/α-Bi2O3 → α-Bi2O3. It was observed that the above phase transformation from Bi(OH)3 to Bi2O3 and the growth of the particle size are interrelated. It was also found that the phase transition from β-Bi2O3 to α-Bi2O3 was faster compared with the phase transition from Bi5O7NO3 to β-Bi2O3. Also, the degradation of Rhodamine B (RhB) was studied to investigate and compare the photocatalytic performance of Bi2O3 with different crystalline phases. The result indicates that Bi5O7NO3 and β-Bi2O3 exhibit excellent photocatalytic performance, while α-Bi2O3 has a low photocatalytic activity.
Rheological properties of aqueous mixtures of the traditional cationic surfactant cetyltrimethylammonium bromide (CTAB) and organic acid 3-methylsalicylic acid (3MS) were studied as a function of concentration and temperature using steady-state and frequency sweep-rheological measurements. Upon being heated, the solutions exhibited three different types of response. Among them, the most interesting response was that light blue dilute solutions formed over the 3MS concentration range of 80 to 100 mmol·kg-1. These samples changed from dilute pale blue solutions to transparent viscoelastic ones as their aggregation state transitioned from vesicles to long worm-like micelles with increasing temperature. Moreover, the threshold temperature of the transition increased with 3MS concentration. The results of rheological temperature scanning and conductivity measurements verified this trend. A qualitative explanation for this transformation is that bound 3MS molecules dissociate from the vesicles and join the bulk aqueous phase at high temperature.
Nitrile-modified 2,5-di-tert-butyl-hydroquinones were synthesized and investigated as redox shuttle overcharge additives for LiFePO4/Li cells. The cyanoethylation reaction was utilized to synthesize the target molecules 2,5-di-tert-butyl-1,4-di(β-cyanoethoxyl)benzene (RS-DCN) and 2,5-di-tert-butyl-1-(β-cyanoethoxyl)- 4-methoxybenzene (RS-MCN) in high efficiency from 2,5-di-tert-butyl-hydroquinone and acrylonitrile. The solubility, cyclic voltammetric measurements, 5 V overcharge test, 100% overcharge test, high rate performance under 100% overcharge conditions, and cycle performance under normal conditions were studied in detail for the electrolyte with the addition of RS-DCN or RS-MCN. The RS-MCN compounds with the asymmetric structure delivered better solubility (with max. 0.3 mol·L-1 in 1.0 mol·L-1 LiPF6/EC+DEC+EMC, 1 : 1 : 1, in vol.), higher overcharge protection life (over 1200 h for the 5 V overcharge test), and excellent rate performance under 100% overcharge conditions (specific discharge capacity reached 153.5 mAh·g-1 at 2.5C). The addition of RS-MCN also improved the cycling performance of the LiFePO4/Li cell under the charge-discharge voltage range of 2.5-3.8 V.
BiOBr/Bi2WO6 with squamous morphology is successfully prepared by a one-step hydrothermal method. BiOBr/Bi2WO6 is shown to be an ideal material for adsorption. The structure of BiOBr/Bi2WO6 is characterized by powder X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, and the morphology is observed with scanning electron microscopy (SEM). The specific surface of BiOBr/Bi2WO6 is tested by a nitrogen adsorption/desorption surface area pore size distribution analyzer. According to the experiments with different concentrations of KBr and the SEM photos of BiOBr and Bi2WO6, the possible morphology formation mechanism of squamous BiOBr/Bi2WO6 is proposed. We design a series of adsorption experiments and test the adsorption properties of the compounds with organic dyes as adsorbent and BiOBr/Bi2WO6 as adsorbent. The results show that BiOBr/Bi2WO6 exhibits a higher adsorption capacity for cationic dyes, especially the adsorption rate of MB, and BiOBr/Bi2WO6 shows a higher adsorption capacity compared with that of activated carbon. Adsorption behavior of BiOBr/Bi2WO6 is consistent with the Freundlich isotherm model and the adsorption process of MB follows a pseudo-second-order kinetic model.
The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of －5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of －4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (－0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (－0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (－0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (－0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.
Proton exchange membrane fuel cells (PEMFCs) are considered as ideal alternative power devices to traditional internal combustion engines for automobile applications because of their high electric power density, high energy conversion efficiency, and low environmental impact as well as low temperatures for start-up and operation. However, PEMFCs normally require a high loading of the expensive precious metal platinum (Pt) as the electrocatalytic material to maintain desirable energy output. Thus, the development of novel catalysts with lower Pt loading, enhanced activity, and improved durability is vital for the scalable commercialization of PEMFC technology. In this regard, core-shell structure has been demonstrated as an effective strategy to minimize the amount of Pt in PEMFCs because of the following two factors:(1) a core-shell architecture with a Pt-rich shell and M-rich (M represents an earth-abundant element) core can greatly improve the utilization of Pt; (2) the activity and stability of Pt on the surface can be greatly enhanced by strain (geometry) and electronic (alloying) effects caused by the M in the core. First, we briefly discuss the structure-performance relationship of typical core-shell structured electrocatalysts for the oxygen reduction reaction (ORR). Then, we review the development of Pt-based core-shell structured catalysts for the ORR. Finally, a perspective on this research topic is provided.
Melamine and melem molecules are widely used precursors for synthesizing graphitic carbon nitride (g-C3N4), the latter also a hot two-dimensional material with photocatalytic applications. The molecular structures of both are respectively identical to the repeating units of two distinct g-C3N4 phases. In this work, the adsorption and self-assembly of melamine and melem on an Au(111) surface were investigated with low-temperature scanning tunneling microscopy (STM). Particularly, the patterns of hydrogen bonds (HBs) in their assemblies were identified and compared. It was found that melamine can only form one type of HB and two kinds of assembly structures, whereas melem can form three types of HBs and six kinds of assembly structures in total. Moreover, the involved HBs can be transformed by tip manipulation. These findings may provide a new strategy for tuning the functionality of surface self-assemblies by manipulating intermolecular hydrogen bonds. This also paves a route for the in situ synthesis of g-C3N4 on metallic surfaces and subsequent investigations of their physicochemical properties.
As the requirements for the performance of high-energy-density materials increase, research to develop new types of high-energy-density materials has become highly heated recently. Octanitrocubane, by virtue of its superior performance, is one of the typical representatives of recently developed high-energy-density materials. However, there have been few studies on the thermal decomposition mechanism of octanitrocubane, even though they are essential to analyze the thermostability and sensitivity of octanitrocubane, as well as to achieve its efficient application. In this study, the initial pyrolysis process of condensed-phase octanitrocubane at high temperature was investigated using ReaxFF reactive molecular dynamics simulation. The results showed that it is the C-C bond of the octanitrocubane cage skeleton structure that breaks first, and then octanitrocubane cage skeleton structure is gradually destroyed, and the small molecules such as NO2 and O occur afterwards. The simulation identified three different damage pathways of the cage skeleton. The main products of octanitrocubane thermal decomposition at high temperature are NO2, O2, CO2, N2, NO3, NO, CNO, and CO, of which N2 and CO2 are the final products. The products that form depend on temperature.
Levo-benzedrine (also known as L-benzedrine or RAT) acts in dopamine receptors of the central nerve cell. In a clinical setting, RAT is used to treat a variety of diseases; however, it can also result in physical dependence and addiction. To investigate the pharmacology and addiction mechanism of RAT as a medication, we have obtained the optimized structure of the dopamine Ⅲ receptor (D3R) complex protein with RAT. On the basis of this structure, by using the method of potential mean force (PMF) with umbrella sampling and the simulated phospholipid bilayer membrane (also known as the POPC bilayer membrane), the molecular dynamics simulation was performed to obtain the trajectories with the changes of free energy on the structure for RAT to move along the molecular channels within D3R. The change of free energy for RAT to transfer toward the outside of the cell along the functioning molecular channel within D3R is 91.4 kJ·mol-1. The change of free energy for RAT to transfer into the POPC bilayer membrane along the protecting molecular channel within D3R is 117.7 kJ·mol-1. These results suggest that RAT is more likely to exert its molecular functions and to increase the release of functioning dopamine molecules by transferring along the functioning molecular channel within D3R, which result in a variety of functional effects by RAT including dependence and addiction. The obtained results show that the pharmacology and addiction mechanism of RAT as a medication are closely related to the molecular dynamics and mechanism for RAT to transfer along molecular channels within dopamine receptors.
5-(Benzyloxy)-isophthalic acid (BIC) derivatives and heptanol (HA) molecules adsorb on a highly oriented pyrolytic graphite (HOPG) surface. The surface forms a 2D network structure through weak hydrogen bond interactions. We used molecular dynamics to simulate this adsorption process and perform quantitative analysis of the characteristic parameters, such as the structure geometry, amount of energy, and the number, length and angle of the hydrogen bonds. We compared these results with the experimental result and performed correlational research on the forming tendency and stability between the hydrogen bonds and the chiral selfassembled structure.
The first-principles plane-wave pseudopotential method within density functional theory formalism is used to investigate the effect of Y atom decoration of graphene on the properties for hydrogen storage. The clustering problem for the Y atoms decorated on graphene is considered, and substitutional boron doping is shown to effectively prevent the clustering of Y atoms on graphene. The geometrical configuration of the modified system is stable and the adsorption properties of H2 are excellent, which can adsorb up to 6 H2 molecules with an average adsorption energy range of -0.539 to -0.655 eV (per H2), as determined by theoretical analyses. This satisfies the theoretical ideal range for hydrogen storage. Moreover, based on the calculation and analysis of the Bader charge, the electronic density of states and the charge density difference of the H2/Y/B/graphene (G) system, it is proved that the Y atom exhibits bonding with graphene by charge transfer and interacts with hydrogen molecules through typical Kubas interactions. The existence of the Y atomalters the charge distribution of the H2 molecules and graphene sheet. Hence, the Y atom becomes a bridge linking the H2 molecules and graphene sheet. Thereby, the adsorption energies of the H2 molecule are adjusted to the reasonable region. The modified system exhibits excellent potential as one of the most suitable candidates for a hydrogen storage medium in the molecular state at near ambient conditions.
Sulfated β-cyclodextrin (β-CD) was prepared by the reaction of β-CD with p-toluenesulfonyl chloride at low temperature in aqueous sodium hydroxide. The product was analyzed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The novel benzil-bridged β-CD (BB β-CD) was acquired by the reaction of benzil with sulfated β-CD at a molar ratio of 1 : 2. UV spectrophotometry was used to study the synthetic mechanism of BB β-CD and benzil and their adsorption onto U(VI). Scanning electron microscopy (SEM) was used to analyze the surface properties of the materials. The adsorption of BB β-CD onto U(VI) was investigated as a function of pH, contact time, temperature, and interfering ions using the batch adsorption technique. It was found that the adsorption equilibrium of BB β-CD was reached faster than that of benzil. The optimum experimental conditions were pH = 4.5 and shaking for 60 min, achieving the maximum adsorption capacity of 12.16 mg·g-1 and a U(VI) removal ratio of 91.2%. Kinetic studies revealed that the adsorption reached equilibrium within 60 min for U(VI) and followed a pseudo-second-order rate equation. The isothermal data correlated with the Langmuir model better than with the Freundlich model. The thermodynamic data indicated the spontaneous and endothermic nature of the process.