The stable and reliable red phosphor with high-photon energy emission (620-650 nm) is critical for the fabrication of the phosphor-converted white light-emitting diode (WLED) with low correlated color temperature and high color rendering index. Mn 4+-activated phosphor is an emerging kind of red-emitting phosphor for WLED. Herein, the energy levels transition and photoluminescence characteristics of the Mn 4+ ion were introduced; then, the preparation, crystal structure and luminescent properties of as-far reported seven kinds of Mn 4+-doped oxyfluoride red phosphors (such as Na2WO2F4:Mn 4+) containing d 0, d 10 or s 0 cations were reviewed. Currently, only in quite rare case of oxyfluoride, Mn 4+ was found to exhibit strong R-line emission, with local coordination remaining as either [MnF6] or [MnO6]. The studies on the chemical stability and quantum efficiency of Mn 4+-doped oxyfluoride phosphors are still insufficient. Finally, we prospected the future development of Mn 4+-doped oxyfluoride phosphor.
Chromogenic materials are capable of optical change reversibly in response to physical stimuli (e.g., electric field, temperature, illumination, and atmosphere). Among them, electrochromic materials are expected to be widely used in smart windows, screen displays, multi-functional energy storage devices and other fields due to their characteristics such as large adjustment range, fast response rate, high coloring efficiency and good cycle stability. However, compared with semi-solid-state electrochromic devices that are difficult to package and organic electrochromic materials that are prone to denaturation and failure, inorganic all-solid-state electrochromic materials and devices have better comprehensive application. This paper focuses on the typical inorganic all-solid-state electrochromic materials and devices, presents a brief review on the current preparation methods of each structure layer of electrochromic devices and compares its advantages and disadvantages, introduces in detail the main alternative electrochromic materials and its key performance evaluation index, and explains the principle of several representative electrochromic devices, proposes to use transparent flexible electrodes with both high light transmittance, low surface resistance and excellent bending fold to replace the traditional rigid substrate in order to realize multi-field responsible device application development. Finally, the application prospect of inorganic all-solid-state electrochromic devices is prospected from the perspective of performance bottleneck, process difficulty and industrialization opportunity, which provides reference for the industrialization process of electrochromic devices.
High-entropy ceramics, a novel class of single-phase ceramic solid solutions consisting of near-equimolar multielement species, are recently attracting tremendous attentions. Especially, the transition metal non-oxide high-entropy ceramics, such as transition metal carbide and boride high-entropy ceramics, have been proposed for potential applications in aerospace, nuclear energy, high-speed machining and many other extreme environments, owing to their excellent physical and chemical properties including super-high hardness, low thermal conductivity, good oxidation resistance and corrosion/erosion resistance. Recently, the research of high-entropy ceramics is only focused on composition design, fabrication methods, single-phase stability and mechanical properties, but the design criterion and theoretical analysis are rarely reported. Based on the researches of high-entropy alloy, the fabrication, characterization and theoretical study of several transition metal non-oxide high-entropy ceramics are summarized, along with some related results of high-entropy film. The prospects for the future developments of high-entropy ceramics are also discussed.
Two-dimensional materials have attracted broad interest because of their wide variety of properties. They can be used as photocatalysts and electrocatalysts due to their extremely high specific surface area, and have great potential application in the field of environment and renewable energy. This review focuses on the structure and properties of common two-dimensional materials such as 2D carbides and nitrides (MXenes), g-C3N4 and black phosphorus (BP). Furthermore, the latest research on the modification of two-dimensional materials in the area of photocatalysis and electrocatalysis are discussed and commented. Finally, research prospects for two-dimensional materials in the future are predicted.
In recent years, the development of new energy vehicles industry is accelerating. Lithium nickel cobalt manganese/aluminum oxide ternary cathode materials (NCM/NCA), especially with the nickel content ≥50%, has aroused great interest in both academia and industry. This is mainly due to the fact that the aggregative parameters of performance and cost of NCM/NCA are superior to those of traditional cathode materials, such as LiCoO2 and LiFePO4. However, the application of NCM/NCA is affected by a number of drawbacks, including poor safety and insufficient cycle stability and so on, which are mainly attributed to its crystal and surface structure. Researchers have carried out various efforts to solve these problems and further improve the performance of NCM/NCA. Some remarkable results have been achieved in the past few years. In this review, the latest research progress on coating and doping of Ni-rich ternary cathode materials is summarized from the view on the mechanism of structural and electrochemical improvement of NCM/NCA. Finally, the perspective for the development of NCM/NCA cathode materials is also prospected.
Membrane-based gas separation is one of the critical technologies in filtration and separation industry, since it is more efficient, energy-saving and environmentally friendly compared with traditional separation technologies. Novel inorganic two-dimensional materials (2DMs) for gas separation are expected to achieve both high selectivity and high permeability, breaking through the trade-off between selectivity and permeability of commercial polymer membranes. This review begins with a brief explanation of gas separation mechanisms for membranes. Afterwards, special attention will be given to the recent advances in novel inorganic 2DMs including graphene and their derivatives, TMDs and MXene, about their design, fabrication and application in gas separation. The gas separation characteristics of different materials, their challenges and directions for future research are summarized. Moreover, the application of other novel inorganic 2DMs, such as LDH, h-BN and mica nanosheets in gas separation technology is also discussed. Finally, the perspectives and challenges for future research of novel inorganic 2DMs in gas separation field are outlined.
Graphene, as a representative of two-dimensional (2D) materials, has excellent intrinsic properties such as high specific surface area and conductivity, but its macroscopic bulk behaves poorly owing to severe face-to-face restacking and hand-in-hand contact resistance. Three-dimensional (3D) design of 2D materials can deliver the excellent nanoscaled properties to the macroscopic world, to realize the high surface area, conductivity, interconnected pores, and good mechanics of the bulks. It is necessary and highlighted to develop the porous monolith of 2D materials for applications as electrodes, adsorbents, elastomers, etc. The blowing route has the advantages of low cost and simple processing, which has been accentually developed to produce the foams of 2D materials for several years. This article introduces the principle of the blowing method, summarizing the recent examples of blown foams of graphene, boron nitride nanosheet, and others. The scientific front about foams of 2D materials is discussed, and the broad applications of the new materials are prospected in energy, environment, etc.
Anode material is an important component for Li-ion battery. The current anode materials are mainly based on graphite, which possesses low theoretical specific capacity of 372 mAh/g, and thus hinder the further development of Li-ion battery. Among the newly developed anode materials, metal oxides have recently attracted intense attention due to their high theoretical specific capacity, low cost and environmental friendliness. However, metal oxides own poor electrical conductivity and large volume changes during cycling. Nanosizing can overcome these disadvantages while maintaining the advantages for metal oxide based anode materials, and thus becomes a research hot spot. Herein, we review the recent research advances of the nanostructured metal oxides as anode materials, mainly focusing on the microstructure design and performance optimization of representative metal oxides and their composites. In addition, some suggestions are presented for further explorations in relative fields.
Hydrolysis is a unique method for hydrogen generation at ambient condition. Widespread attentions have been paid to materials for hydrogen generation via hydrolysis due to several advantages: high theoretical hydrogen capacity, moderate storage and operation condition, safety, etc. In this paper, recent progress and development in this area were reviewed. Three types of materials including borohydride (NaBH4, NH3·BH3), metal (Mg, Al), and metal hydride (MgH2) were introduced. Several issues about them were discussed specifically: mechanism, main problems, designments of catalysts and materials, etc. Based on these discussions, we compared the different materials mentioned above, commented their current performances and practical difficulties. At last, prospects in this field were presented.
Solid-state cooling technology based on the electrocaloric (EC) effect is attracting increasing attention as an important alternative for traditional cooling systems because of its advantages of high efficiency, environmental friendliness, light weight, low cost, and easy miniaturization. Ferroelectric materials are suitable candidates for EC refrigeration due to their large polarization and entropy change through applying or removing an external electric field. Recently, study on the EC effect of lead-free bulk ceramics has become one of hot topics on ferroelectric community due to the requirements of sustainable development. In this review, we firstly introduce the significant history events in EC research and the basic principles of EC refrigeration. Then, design strategy for achieving a large EC temperature change near room temperature and a wide using range is summarized. Subsequently, we systematically review the research status of EC effect in BaTiO3-based, Bi0.5Na0.5TiO3-based and K0.5Na0.5NbO3-based lead-free bulk ceramics and discuss their advantages as well as challenges. Finally, we propose some prospects for the future work on EC effect in lead-free bulk ceramics.
During charge and discharge of lithium-ion battery, the concentration gradient produced by lithium- ion diffusion process and deformation caused by lithiation expansion of the active material result in diffusion-induced stress. Excessive diffusion-induced stress can cause various mechanical failure modes such as cracking of active particles, separation between active particles, fracture of active layers, and delamination between active layers and current collectors, which eventually leads to a series of failure phenomena such as capacity attenuation, impedance rise and cycle life loss of the battery. Therefore, the diffusion-induced stress and the derived failure mechanism of lithium-ion battery become one of the research hotspots in the field of lithium-ion batteries, which has important theoretical and practical value. In this paper, research progress of the failure mechanism of lithium-ion battery caused by diffusion-induced stress in recent years is reviewed from different levels of the active particle, the active electrode, the half-cell, the cell unit, and the cell. The generation mechanism and research methods of diffusion-induced stress are introduced. The influence of diffusion-induced stress on the mechanical and electrochemical properties of the battery is analyzed, and the influencing factors of the diffusion-induced stress are summarized. Finally, the future research directions and development trends are prospected.
Boron nitride aerogel is a kind of new nanomaterials with three-dimensional porous network structure, which takes solid as the framework and gas as the dispersion medium. It has high specific surface area, high porosity, low density and other excellent properties. In addition, compared with graphene aerogels, it exhibits better insulation, oxidation resistance, thermal stability and chemical stability. These outstanding properties make it promising application in the fields of gas adsorption, catalysis, sewage purification, thermal insulation/conduction. This article systematically reviewed the preparation methods of boron nitride aerogels including the hard template method, soft template method, low-dimensional boron nitride assembly method, and template-free method in the light of domestic and foreign research status. Moreover, the important applications of boron nitride aerogels in key fields are summarized, and the future development direction is prospected.
With continuous development of electronics, the requirements for power supply systems are increasing. Supercapacitors (SCs), which have high energy density and excellent power output performance, are ideal power supplies for new generation of miniaturized, intelligent and wearable electronic devices. Thus, developing SCs with fast charge-discharge speed and high stability is a key research topic in the field of energy storage. As the most important part of SCs, electrode materials are critical to its performance. Due to the excellent performances of high-ordered pore structure, large specific surface area, diverse morphologies and dimensions, and adjustable conductivity, conductive metal-organic frameworks (MOFs) materials have shown great potential as promising SCs electrode materials, and have attracted wide attention. This review introduces the structure, conductive mechanism and preparation methods of conductive MOFs following a short introduction of SCs, describes its design strategy as SCs electrode materials, reviews the research progress of conductive MOFs in the field of SCs, and prospects its future application.
The third generation SiC fibers have near-stoichiometric composition and polycrystallinity with high density. Compared with the first and second generations, they have obvious improvements in heat-resistance, creep-resistance and radiation-resistance. Accordingly, they have more advantages and broader prospects in engineering applications, especially in the nuclear field. In this paper, the fabrication and performance characteristics of the third generation SiC fibers are introduced and compared. The applications of the third generation SiC fibers in the field of nuclear energy are reviewed, and the development prospects are prospected.
As smart electronic products are increasingly applied in our daily life, there is not only an increasing demand for high-performance photovoltaic power generation devices, but also strong need for in-situ energy storage functions in these devices. The integration of energy generating components and energy storage components into one device has become an attractive challenging technology. The basic idea is that by integration design and engineering the assembly of the photoelectric conversion layer and the energy storage layer into one in-situ energy conversion and storage system could not only offer multiple functions, such as self-powered ability, weak light buffer and portability, but reduce sunlight fluctuation effect on energy output. This review summarizes the research progress in novel in-situ integrative photovoltaic-storage tandem cells, classified by silicon solar cell, sensitized solar cell and perovskite solar cell. Evaluation of methodology, operational principle, construction feature, and performance parameter are also discussed and critically reviewed, and the further development of in-situ integrative photovoltaic-storage tandem cell is also prospected.
Semiconductor photocatalytic water splitting has been considered as a potential strategy to overcome global energy shortage and environmental pollution. In recent years, phosphorene (BP) attracted great attention in photocatalytic water splitting due to its adjustable band gap, high hole mobility and wide absorption spectrum. This review summarizes the recent significant advances on designing high-performance BP-based photocatalysts for water splitting. The synthetic methods and modification strategies (e.g., surface modification and heterostructure design) of BP-based photocatalysts are described. Furthermore, in order to elucidate the structure-activity relationship of BP-based photocatalysts, the charge transfer mechanism is illustrated. Finally, the ongoing challenges and opportunities for the future development of BP-based photocatalysts in the exciting research area are highlighted.
Metal organic frameworks (MOFs) materials have received extensive attention in capture and separation of CO2. Herein, molecular dynamic simulation (MD) and grand canonical Monte Carlo (GCMC) simulation were used to investigate the process of negative gas adsorption to DUT-49, an MOF, and the effect of structural transition on the CO2/N2 adsorption and separation behavior. Results showed that DUT-49 underwent stable structural deformation at 20-60 MPa, with a transition between open pore (DUT-49-op) and closed pore (DUT-49-cp). Its adsorption capacity decreased with the increase of temperature. DUT-49-cp owned a contractive framework, exhibiting a considerably decreasing adsorption capacity due to reduction of effective adsorption sites. In addition, its selectivity decreased significantly compared with that of DUT-49-op, and decreased with increase of temperature, which is not conducive to gas separation. The present study provides a scientific basis for the development of adsorbent materials.
The mechanism of Fe-N/C catalysts in oxygen reduction reactions is critical to the development of efficient, sustainable non-noble metal catalysts in polymer electrolyte membrane fuel cells, but it is still in controversy. In order to understand the relationship between composition and the nanostructure of material and the electrochemical activity, this study developed a type of Fe-N/C catalyst with high electrochemical activity, which contained Fe-Nx active sites and Fe/Fe3C nanocrystals encapsulated with nitrogen-doped carbon nanotubes. Despite being free of precious metals, the as-prepared catalyst displays high oxygen reduction reactions (ORR) activity in alkaline medium with the half-wave potential of 0.86 V(vs RHE), the mass activity of 18.84 A/g at 0.77 V(vs RHE), and the maximum current density of -4.3 mA·cm -2. Meanwhile, the electron transfer number is 3.7 at 0.2 V(vs RHE), revealing that the 4-electron ORR reaction exists in the catalyst. The excellent electrochemical activity is attributed to the graphene-encapsulated metallic Fe/Fe3C nanocrystals which improves the conductivity after the growth of N-doped carbon nanotubes, and the relatively high proportion of Fe-Nx active sites distributed on the surface of Fe/Fe3C nanoparticles. This study provides a certain reference and basis for the further study of non-noble metal catalyst and their wide application in commercial production.
Photocatalysis technology possesses great potential in the field of oxidation of nitrogen oxides due to the low energy costs and little secondary pollution. Bismuth carbonate (Bi2O2CO3, BOC)/polypyrrole (PPy) was prepared at room temperature to remove NO under visible light irradiation. After being decorated with PPy, the NO removal efficiency of BOC is enhanced from 9.4% to 20.4% while the generation of NO2 is reduced from 2% to approximately zero, which are attributed to the oxygen vacancy formed at the interface between BOC and PPy via interfacial hydrogen bonding. Photocurrent and electrochemical impedance spectra indicate that oxygen vacancies promote the separation and migration of photo-induced electrons and holes over BOC, hence improve its photocatalytic activity. Furthermore, the presence of oxygen vacancy promotes the formation of more •O2 -, and then improve the NO oxidation activity and safety of BOC together with •OH.
Lanthanum-substituted LaxSr2-3x/2Fe1.5Ni0.1Mo0.4O6-δ (LaxSFNM, x=0, 0.1, 0.2, 0.3, 0.4) oxides were synthesized by the solid-state reaction method, and investigated as potential anodes for Solid Oxide Fuel Cells(SOFC). X-ray diffraction patterns of as-synthesized powders confirm the formation of the cubic perovskite structure. Reduction in H2 promotes the segregation of nano-scale metallic Fe-Ni alloy particles on the grain surfaces. Scanning electron microscopy observations indicate that increasing La 3+ dopants results in a decrease in the density of the exsolved nanoparticulates. Based upon impedance measurements on symmetrical fuel cells, the anode polarization resistance decreases with the La 3+ dopant increasing, and attains a minimal value of 0.16 W?cm 2 for La0.3SFNM at 750 ℃, followed by a slight increase to 0.17 W?cm 2 for La0.4SFNM. The highest catalytic activity of La0.3SFNM toward electro- oxidation of hydrogen fuels could be ascribed to the synergy between the exsolved Fe-Ni alloy nanoparticulates and the supporting LaxSFNM oxides. Thin La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte fuel cells with La0.3SFNM anodes and SmBa0.5Sr0.5Co2O6 cathodes exhibit the highest power densities, e.g., 1.26, 0.90 and 0.52 W?cm -2 at 750, 650 and 550 ℃, respectively. These results demonstrate La0.3SFNM oxide as a promising high performance SOFC anode.
A lightweight, environmentally-friendly thermal insulation coating was experimentally applied to the carbon fiber to reinforce epoxy resin composites. The coating is mainly composed of bonding layer, barrier layer and reflective layer, and prepared by using titanium dioxide, silica, aluminum oxide and hollow glass microspheres as function fillers. The addition of waterborne polyurethane with a thermal expansion coefficient of 120×10 -6 K -1 as a film-forming material, is to solve the problem of cracking caused by the mismatch of the thermal expansion coefficients of the coating and the substrate material. The results show that after being applied the coating, can solidify within 24 h at room temperature. When the thicknesses of the bonding layer, the heat barrier layer and the reflective layer were 80, 120, and 90 μm, the thermal insulation coating has the best performance with reflectance of the coating higher than 0.95, the thermal conductivity at 0.048 W·m -1·K -1 and the temperature difference as high as 20.1 ℃. After being subjected to thermal shock at 190 ℃ for 6 times, and the maximum weight loss rate of the coating was 3.7%, indicating the coating highly stable. When kept at 160 ℃ for 4 h, its surface turned yellow without falling off, and its nano filler particles still remained stable.
Zinc-manganese (Zn/MnO2) batteries with outstanding advantages of high operation safety, high environmental benignity and high cost performance, is suitable for the application of large-scale energy storage battery. However, the uncontrolled growth of zinc dendrites on the metal zinc anode during charge-discharge cycling causes serious problems such as quick capacity decrease and short circuit failure. In this study, the aqueous electrolyte was converted into a composite quasi-gel electrolyte by adding hydrophilic nano-silica (SiO2) and sodium alginate (SA), which effectively inhibits the dendrite growth of the surface of the zinc negative electrode and the capacity degradation of the Zn-MnO2 battery. Galvanostatic charge-discharge tests showed that the Zn/MnO2 battery with composite gel electrolyte achieves a capacity retention of 78% after 1800 cycles, while the capacity of Zn/MnO2 battery using ordinary electrolyte almost fails after 1000 cycles. The three-dimensional network structure of the gel electrolyte can improve the distribution uniformity of zinc ion in electrolyte, reduce the capacity decay rate and failure risk of the batteries.
Lithium metal anode, due to its highest theoretical specific capacity (3860 mAh·g -1) and lowest electrochemical potential (-3.04 V (vs SHE)), has become the first choice of the next generation of electrochemical energy storage devices. It is known as the “holy grail” of the battery industry. However, the disadvantage of lithium metal battery is particularly obvious: during the charge and discharge process, lithium metal battery is easy to deposit unevenly on the anode electrode, resulting in lithium dendrite which causes the continuous rupture and formation of solid electrolyte interface (SEI) film. The unstable SEI film, intensifying the formation of lithium dendrites and then piercing the separator, causes a decline for the battery cycle performance and the safety hazard. Therefore, it is particularly important to take corresponding measures to make lithium metal uniformly deposited on the anode. In this study, the uniform lithiophilic copper oxide nanosheet array formed on the surface of commercial copper mesh through oxidation of alkaline solvent and calcination of air. The 3D structure of copper mesh can effectively reduce the current density, and the lithiophilic nanosheet array can effectively reduce the overpotential of lithium deposition simultaneously. This lithiophilic 3D copper-based current collector makes lithium deposited uniformly and effectively, and inhibits the formation of lithium dendrites. In the half-cell test at a current density of 3 mA·cm -2 the battery circulated stably for 230 cycles with Coulombic efficiency remaining above 99%. The lithium iron phosphate (LFP) full battery with the as-prepared material as current collector worked stably for more than 300 cycles at 1C(0.17 mA·mg -1) and present a capacity retention of ~95%. This study provides a new design strategy of 3D current collector for stable lithium metal batteries.
Carbon nanospheres enriched with α-MoC1-x nanocrystalline (α-MoC1-x/CNS) were synthesized by self-assembly and applied as a mediator for the surface of commercial polypropylene (PP) separator. Compared with pristin PP separator, the cycling stability and rate performance of the lithium-sulfur batteries with the modified α-MoC1-x/CNS-PP separator are significantly improved and the battery with α-MoC1-x/CNS-PP separator exhibits an initial discharge capacity of 1129.7 mAh/g at 0.5C and retains 855.5 mAh/g after 100 cycles with above 98% Coulombic efficiency. Remarkably, the capacity loss rate is only 7.7% after 48 h static storage. Combined with the morphology and XPS analysis of α-MoC1-x/CNS, it is found that the designed α-MoC1-x/CNS-PP separator prevents the migration of lithium polysulfide to the anode during the process of charge and discharge in lithium sulfur batteries. Formations of Mo-S bonds, thiosulfate and polythionate are attributed to the contact between lithium polysulfide and α-MoC1-x/CNS, which further restrains active material in cathode region and improves the performance of lithium- sulfur batteries consequently.
Porous bioceramic scaffolds, which possess attractive biocompatibility, ability to guide tissue regeneration and porous surface morphologies and channels beneficial to ingrowth of new born tissues, have seized increasing attentions and been widely applied in the field of hard tissue restoration. Whereas, the weak osteoinductive activity, monotonous biological function and poor mechanical property have restrained the therapeutic efficacy and wider application of bioceramic scaffolds. In view of this, we intended to introduce the existing modification methods of bioceramic scaffolds, including the surface modification with functional coating, construction of surface micro-/nano- structures, functional element doping and enhancement of mechanical property, along with the state of the research progresses in the improvement of biocompatibility, bone defect restoration, drug delivery, tumor therapy, and antibacterial capacity of multifunctional bioceramic scaffolds. In addition, potential research directions and applications of functionally modified bioceramic scaffolds are prospected to provide references for the related exploration afterwards.
Dynamic mechanical analysis (DMA) has the advantage of high sensitivity, excellent cooling system, flexible rotation testing part, multiple deformation mode, and continuous frequency and temperature scanning mode. DMA is able to characterize the strain response under alternating stress, creep, stress relaxation, and thermomechanical properties, which has application in the investigation of plastic, thermoset, composite, high elastomer, coating, alloy and ceramic. This paper briefly introduced the fundamental and method about DMA, the application of DMA in the investigation of ferroelectric-paraelectric phase transformation, low frequency relaxation, ferroelectric fatigue, and ferroelectric composite damping. In the measurement of relaxation behavior of PZT ceramics and single crystals, and BaTiO3 ceramics, DMA tended to be more sensitive than dielectric characterization especially in the low frequency range. DMA has been one of the critical instruments for ferroelecric investigation.
Ethylene is the main factor of postharvest spoilage of fruits and vegetables. Therefore, how to reduce or remove the ethylene released during the storage of fruits and vegetables is a problem to be solved. In this study, a series of nickel foam supported TiO2/WO3 were prepared by Sol-Gel method. The samples were characterized by different methods. The photocatalytic degradation activity of ethylene under ultraviolet light irradiation was investigated. The results show that TiO2/WO3 film is successfully supported on the nickel foam, and there formed heterojunction between TiO2 and WO3, which efficiently enhanced the separation and transfer rates of photogenerated electron and hole. The narrowed band-gap also leads to a red shift of optical absorbance and high photoactivity. The photocatalytic activity and stability of TiO2/WO3 were excellent under UV light irradiation. When the mass percentage of WO3 is 6% of TiO2, the photocatalytic ethylene degradation of the TiO2/WO3 composite film reaches maximum, and the degradation rate constant is almost 9.8 times as that of TiO2. The mechanism of photocatalytic degradation of ethylene by TiO2/WO3 supported on nickel foam under ultraviolet light irradiation was also discussed.
To investigate the modification mechanism of mixed heterogeneous on photocatalysis, a series of Nd3+-doped BiVO4 photo-catalysts with different Nd3+ contents were synthesized through a facile hydrothermal reaction. The samples exhibit Nd3+ content-dependent phase transition from monoclinic to tetragonal phase, as demonstrated by XRD and Raman analyses. SEM images show that the phase transition is accompanied by obvious morphology variation. Less than 1at% Nd3+-doped monocline BiVO4 is composed of irregular particles, while more than 7at% Nd3+ doping results in tetragonal phase BiVO4 of sphere-like or kernel with groove surface. When Nd3+content is in the range of 1at%-7at%, the micron cuboid bars appear in the samples. More importantly, monoclinic and tetragonal phase is concomitant in the product and a heterogeneous junction with staggered band structure is formed. The Rhodamine B degradation efficiencies of all Nd3+-doped samples are higher than those of undoped samples due to the regular morphology after doping. The formed heterogeneous junction inhibits photo-generated electrons and holes recombination of Nd3+-doped BiVO4, inducing 99.4% catalytic efficiency in 4at% Nd3+-doped sample. The novel morphology and the intrinsic mechanism of photocatalysis enhancement upon Nd3+-doped BiVO4 are obtained from the synthesis strategy and the energy band structure.
Ceramic fiber has the advantages of low density, high strength, high temperature resistance and good mechanical vibration resistance. It is the critical high temperature thermal insulation materials especially in thermal protection fields such as aerospace vehicles, nuclear power plants and chemo-metallurgical industry, etc. The traditional ceramic fiber with large diameter (> 5 μm), high brittleness and high thermal conductivity has been greatly restricted in high temperature thermal insulation fields. In recent years, more and more attention has been paid to the preparation of micro-nano ceramic fibers by decreasing the diameter of fiber, which is not only beneficial to improve the mechanical properties of the fibers, but also to enhance their high temperature thermal insulation properties. Further, by finely regulating the composition and structure of the micro-nano ceramic fibers that intrinsically affecting the heat transfer (heat conduction of gas, heat conduction of solid and radiative heat transfer) mechanism in micro-nano ceramic fibers, the high temperature thermal insulation performance can be effectively improved, which is the current focus of the micro-nano ceramic fibers in high temperature thermal insulation fields. The thermal insulation mechanism of the micro-nano ceramic fibers was firstly introduced. Then, based on the research at home and abroad, this review divides the current micro-nano ceramic fibers into three categories according to the difference of their composition and structure, namely fibers aerogels, hollow/porous fibers and composite fibers. The latest research progress on composition and structure optimization of micro-nano ceramic fibers for high temperature thermal insulation is reviewed, and the future development tendency is prospected.
Metal-organic frameworks (MOF) as piezoelectrical materials used in mechano-catalytic degradation of organic dye are rarely investigated. In this work, NH2-UiO-66 was synthesized by the solvothermal method and applied in mechano-catalytic degradation of Rhodamine B under ultrasonic vibration. The results show that NH2- UiO-66 behaves a high mechano-catalytic decomposition efficiency of 80% for Rhodamine B within 5 h vibration and possesses a good stability. The piezoelectrically induced electric charges on the surfaces of NH2-UiO-66 via the piezoelectric effect could induce hydroxyl radicals as strong oxidants to decompose Rhodamine B. The piezoelectrical effect of MOFs is potential in utilizing vibration energy for dye wastewater treatment.
CoFe2O4 nanofibers with fishbone-like structure were prepared by a electrospinning method followed with high temperature calcination, using polyvinylpyrrolidone (PVP), iron nitrate nonahydrate (Fe(NO3)3·9H2O) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) as raw materials. Results show that the crystallinity and grain size of nanofibers become larger with increasing calcination temperature. Meanwhile, the surface morphology of CoFe2O4 nanofibers changes from smooth to rough and porous. The morphology of CoFe2O4 nanofibers exhibits a fishbone-like structure with calcination temperature exceeding 800 ℃. The diameter of the fiber is gradually decreased with the increase of calcination temperature, and the average diameter of CoFe2O4 nanofibers calcined at 900 ℃ reaches 80.3 nm. By vibration sample magnetometer (VSM) test, the saturation magnetization (Ms) of CoFe2O4 nanofibers increases with the increase of calcination temperature, and the Ms of CoFe2O4 nanofibers calcined at 900 ℃ is 87.13 A·m2/kg. In a result of vector network analyzer (VNA) analysis, the microwave absorption performance is significantly different with calcination temperature changing. Among them the fibers calcined at 800 ℃ have the highest wave absorption ability. The microwave absorption mechanism of CoFe2O4 nanofibers mainly includes hysteresis loss and eddy current loss. The morphology of porous and fishbone-like generated by calcination can increase the reflection loss, for the reason that this morphology is beneficial for microwave reflection multiple times on the fiber surface.
Ultralong hydroxyapatite nanowires (UHANWs) exhibit great potential in constructing different kinds of biomaterials such as the highly flexible biomedical paper and elastic porous scaffolds for various biomedical applications. Moreover, strontium (Sr), a trace element in human body, plays an important role in bone metabolism. In this study, Sr-doped UHANWs (Sr-UHANWs) with various Sr/(Sr+Ca) molar ratios have been successfully prepared by the one-step oleate precursor solvothermal method. The effects of the Sr/(Sr+Ca) molar ratio on the morphology and crystal phase of the Sr-UHANWs were investigated. The as-prepared Sr-UHANWs exhibit high flexibility and ultralong 1D nanostructure. Moreover, the energy dispersive spectroscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy of the as-prepared samples reveal that Sr element has been successfully incorporated in UHANWs. The preparation method developed in this work may be suitable for the synthesis of Sr-UHANWs with Sr/(Sr+Ca) molar ratios ranging from 0 to 100 %, which may enlarge the biomedical applications of UHANWs such as bone and teeth defect repair.
Hollow carbon spheres (HCS) with controllable diameter and shell thickness using a simple encapsulation pyrolysis synchronous deposition method is reported. This method changed the polystyrene spheres (PS), a widely used sacrifice hard template, into carbon by a pyrolysis and synchronous deposition process in the hermetical silica shell, without any cross-linking agent and catalyst, simplifying synthesis, and lowering costs. The obtained HCS exhibited uniform spherical morphology with tailorable particle size (190-1600 nm) and well controlled hollow voids. Moreover, HCS samples with precisely tuned thickness (4.5-13.5 nm) were obtained only by changing the silica precursor amount. The resultant HCS showed promising potential for applications in cefalexin adsorption with capacity of 291 mg·g -1. Therefore, this synthetic strategy may offer an efficient production route to commercial applications for HCS.
Ni-Co-S/CA composite aerogels were prepared by hydrothermal method using bacterial cellulose-derived carbon aerogels (CA) as support. The microstructure and properties of the composites were adjusted via adding trace vanadium. The characterization results show that the main phase of Ni-Co-S is NiCo2S4 with the secondary phase of NiS2. With the increment of the nickel-cobalt salt concentration, the load amount increases, and the peak current density of electrocatalysis firstly upgraded and then degraded. After being doped with a small amount of vanadium at lower nickel-cobalt salt concentration, Ni-Co-S transforms from spherical particles with high crystallinity to square particles with low crystallinity, and its electrocatalytic activity and stability are improved. Under the preparative conditions of 0.01 mol/L total concentration of nickel-cobalt salt and 3mol% vanadium salt, the as-obtained electrode exhibits the optimal catalytic performance for methanol oxidation. Compared with the sample without V doping, its peak current density (78.1 mA/cm 2) enhanced by 45.7% at least. The Ni-Co-S/CA composite aerogel electrodes with the advantages of light weight and high porosity, is expected to be applied in portable direct methanol fuel cell.
To explore the interface engineering on the carrier recombination in two-dimensional (2D) van der Waals (vdW) heterostructures, we developed a theoretical model to address the size-dependent interlayer and Auger recombination rates in MoS2/WSe2 in terms of interface bond relaxation method and Fermi's golden rule. It is found that the Auger recombination lifetime in MoS2/WSe2 increases with increasing thickness due to the weakening of Coulomb interaction between holes and electrons, as well as the Auger recombination rate is much smaller than that of MoS2 and WSe2 units. However, when the thin h-BN layer is introduced into the MoS2/WSe2, the interlayer and Auger recombination rates show opposite trends as the h-BN thickness increases. When the thickness of h-BN reaches 9.1 nm under the condition of 1L MoS2/h-BN/1L WSe2, the Auger recombination rate approaches 5.3 ns -1. These results indicate that the relevant recombination processes can be tuned by interface and dimension. Therefore, our results provide a useful guidance for the optimal design of 2D transition metal dichalcogenides-based optoelectronic nanodevices.
La0.3Y0.7Ni3.4-xMnxAl0.1(x=0-0.5) hydrogen storage alloys were prepared by vacuum arc melting followed by homogenized annealing. Effect of Mn element on the microstructure, hydrogen storage behavior and electrochemical properties were systematically investigated via different methods. The results show that the microstructure of the annealed alloys closely relates to the Mn content. Higher Mn content facilitates the formation of Ce2Ni7 type phase until single phase structure of Ce2Ni7- type forms in the alloys with x≥0.3. With the increment of Mn content, the unit cell parameters (a, c) and unit cell volume (V) of Ce2Ni7- type phase increase, resulting in the hydrogen absorption platform pressure of the alloys decreasing from 0.079 MPa to 0.017 MPa and the hydrogen storage capacities reaching 1.268wt%-1.367wt%. The electrochemical properties are significantly improved with the addition of Mn. La0.3Y0.7Ni3.25Mn0.15Al0.1 alloy exhibits the highest discharge capacity (390.4 mAh·g -1). The capacity retention S100 of the alloys with x=0.15 and 0.5 are 86.03% and 88.01%, respectively, presenting good cycle stability. Meanwhile, high rate discharge ability (HRD900) of the as-prepared alloys is 71.53%-87.73%. It is shown that electrochemical reaction kinetics of the alloy electrodes is controlled by both the electron transfer at the electrode/ solution interface and the diffusion of hydrogen atoms in the alloy bulk.