In recent years, ternary layered carbide/nitride MAX phases and their derived two-dimensional nanolaminates MXenes have attracted extensive attention. The crystal structure of MAX phase is composed of Mn+1Xn unit interleaved with layers of A element. MAX phases combine good properties of metal and ceramic, which makes them promising candidates for high temperature structural materials, friction and wear devices, nuclear structural materials, etc. When etching the A-layer atoms of the MAX phase, the two-dimensional nanolaminates with the composition of Mn+1XnTx (Tx is surface termination), i.e. MXene, is obtained. MXenes have wide range of composition, and tunable physical and chemical properties, which endow them great potential in the applications of energy storage devices, electromagnetic shielding materials, and electronic devices, etc. In this paper, the research progress of MAX phase and MXene was introduced in terms of composition and structure, synthesis methods, and properties and application. Furthermore, the research prospects of this large family of materials were discussed.
Ceramic matrix composites (CMCs) are promising candidates for application in aeroengine, aerospace aircraft thermal protection systems, nuclear power system, and other fields. At present, CMCs are developing from structural bearing materials to multi-functional composites. MAX phases are a group of layered ternary ceramics with excellent plastic deformation capacity, high electrical conductivity, good irradiation resistance and ablation resistance. Besides strengthening and toughening CMCs, the introducing MAX phases into CMCs can effectively improve the anti-irradiation, anti-ablation and electromagnetic interference shielding performance, meeting requirements of multi-functional CMCs. This paper reviewed the progress on MAX phases modified CMCs, design mechanism and application prospect.
With the development of wearable flexible electronic technology, the demand for flexible sensor with high sensitivity and wide sensing range is gradually increasing. The application of suitable conductive materials with high electrical conductivity and high flexibility as sensitive materials for sensors is the key to obtain high performance sensors. In recent years, MXene materials have become very promising sensitive materials due to their good conductivity, high flexibility, good hydrophilicity, and controllable synthesis. The types of MXene-based flexible force sensors, microstructure design of sensitive materials, sensing performance, and sensing mechanism analysis have been expound and summarized in this paper.
Phase diagrams, also known as equilibrium phase diagrams, serve as a road map for materials design. However, preparation process of coatings (such as Physical Vapor Deposition, PVD) is generally far from equilibrium and results in metastable phases. Thus, the CALPHAD (Calculation of Phase Diagrams) approach faces a challenge in calculating the metastable phase diagrams for PVD coating materials. Here we summarized the development of the modeling methodology for the metastable phase diagrams, where the model with critical surface diffusion distance established in recent years were highlighted. The CALPHAD approach, first-principles calculations coupled with high-throughput magnetron sputtering experiments were used to model the atomic surface diffusion, while only one key combinatorial experiment was performed to obtain the basic data for the computation, and the calculated metastable phase diagrams were confirmed by further experiments. Therefore, the database of the stable and metastable phase diagrams can be established, which will be used to guide the design of the ceramic coating materials by the relationship of composition, processing, microstructure, and performance. This model can also help to achieve the goal to shorten the time and reduce the costs of materials research and development.
In recent years, hexagonal boron nitride (h-BN) two-dimensional (2D) atomic crystal has attracted considerable attention due to its unique structure, novel property and potential applications. The synthesis of high quality h-BN determines how far we can go for property research and practical applications. However, the sizes of h-BN domains obtained by mechanical exfoliation were limited to several micrometers. Transition metal substrates are usually used in the CVD growth of 2D h-BN layers, and thus a transfer process is required for fabricating h-BN-based electronic devices. Therefore, it is strongly desirable to directly synthesize 2D h-BN on dielectric substrates. In this article, we review recent process on the direct growth of h-BN by CVD, MOVPE, PVD on different dielectric substrates, including silicon-based substrates, sapphire, quartz, etc. Several approaches, such as, increasing substrate temperature, oxide-assisted nucleation, and surface nitridation were adopted to directly grow h-BN on dielectric substrates. Besides, we also summarized the main applications of 2D h-BN grown on dielectric substrates.
Silver nanowire transparent conductive film is one of the new indium-free electrode materials. It has attracted increasing attention from academia and industry due to its superior optoelectronic properties and excellent flexibility. It has been employed in a wide variety of applications in displays, touch panels, solar cells, smart heaters, electromagnetic interference shielding, and so on. However, silver nanowire transparent conductive film has a serious stability issue in service, for example, break or spheroidization above 300 ℃ under fulfidation, accelerating the degradation under ultraviolet light, pores for mation or even breakdown due to electromigration. In this review, the degradation phenomena is thoroughly introduced, the degradation mechanisms is analyzed, and the remedy strategy of degradation is discussed.
Due to its unique physical and chemical property, diamond is widely used in many fields such as detectors and optoelectronic devices. Many scholars’ attention is drew into single crystal diamond because of its potential to significantly increase the functionality of these devices. Presently, single crystal diamonds grown heteroepitaxially on iridium (Ir) substrates reach the largest size and an excellent growth quality. In this paper, substrates with different structures for nucleation and growth processes of epitaxial diamond are introduced. The mechanisms of diamond nucleation by Bias Enhanced Nucleation (BEN) method and growth undergoing an Epitaxial Lateral Overgrowth (ELO) process are described, including technique of Patterned Nucleation and Growth(PNG). Limitations of current study are pointed out, and the future development of heteroepitaxial theory and experiment are also forecasted in this paper.
Co-doping of silicon in zinc gallate spinel persistent luminescent phosphor was adopted to enhance the afterglow properties. Firstly, a series of silicon-chromium co-doping zinc gallate spinel samples were prepared by high temperature solid state reaction method. Phosphor with chemical formula of Zn1+xGa2-2xSixO4:Cr 3+ (x = 0, 0.1, 0.15, 0.2, 0.5, 1) was obtained with the raw materials of ZnO, Ga2O3, SiO2, and Cr2O3. The experimental results show that the introduction of suitable concentration of silicon improves the afterglow performance effectively. The strongest afterglow intensity was obtained for sample with x = 0.2, which is 3 times higher than ZnGa2O4:Cr 3+, and the afterglow duration is up to 24 h. Through further trap distribution analysis, it is shown that the introduction of silicon in the ZnGa2O4 host can regulate the distribution of trap depths. Particularly, besides the antisite defects, the co-doping of silicon can induce the formation of aliovalent substitution defects and interstitial defects, as well as tune the band gap value, thereby achieving the purpose of improving the afterglow performance.
The structure and electrical properties of Ce 3+-doped intergrowth bismuth layer-structured piezoelectric ceramics Na0.5Bi8.5-xCexTi7O27 (NBT-BIT-xCe, 0≤x≤0.1) prepared by conventional solid-state reaction process were systematically studied. In this study, all the ceramic samples were found to possess a single bismuth layer structure, and with the increase of x content, there is an increasing trend towards the lattice distortion of the sample, while the average grain size decreased. As demonstrated by dielectric spectrum and DSC method, two dielectric anomalies of the samples occur, which corresponds to ferroelectric phase transitions of the ceramics. And Ce 3+doping significantly reduces concentration of oxygen vacancy and dielectric loss in materials, improving piezoelectric constant (d33) of ceramic samples. The resultant ceramics with x=0.06 reached the optimal performance, possessing a d33 up to 27.5 pC/N with the Curie temperature of 658.2 ℃ and tanδ=0.39%.
The electrocaloric (EC) effect is strongly related to interaction of polarization and temperature changes, showing great potential in high-efficient solid state refrigeration. This work focuses on the Pb0.3CaxSr0.7-xTiO3 (PCST(x), x = 0.00, 0.05, 0.10, 0.15) ceramics in which the influence of Ca content on dielectric and ferroelectric property under electric field was studied, and the EC temperature change was calculated through indirect method. Substitution of Ca largely modifies the diffused phase transition behaviors of PCST ceramics, which the diffusion exponent of PCST(0.05) increases with electric field up, indicating a promising wide temperature range of large electrocaloric effect. Thus, the largest adiabatic temperature change (1.71 K) is obtained near the room temperature in PCST(0.05) by indirect method. With an electric field of 8 kV/mm, PCST(0.05) ceramic shows good EC effect in a wide temperature range that the adiabatic temperature change is larger than 1 K from 5 ℃ to 70 ℃.
As a new solid-state lighting source, the white light-emitting diodes (WLEDs) have a greatly promising application in the field of lighting and display. They have superior advantages of high luminous efficacy, fast response speed and long service life, etc. compared with the existing light sources (incandescent lamps, fluorescent lamps, etc.). At present the WLEDs are commonly fabricated by combination of a blue LED chip and YAG: Ce 3+ yellow-emitting phosphor, and combination of a ultraviolet-near ultraviolet excitation chip and red-green-blue (RGB) emitting color phosphors, compared with the above two phosphors, the single-phase phosphors containing white emission have the advantages of a higher luminous efficacy, color rendering. Meanwhile, the single-phase phosphors may effectively solve the reabsorption problem existing in RGB phosphors. There have been a large number of reports on the research of single-phase phosphors, involving a variety of material systems. According to the principle of luminescence, it can be simply divided into three groups: single ion doped system, multi-ion doped system and other systems which do not rely on rare earth ion to light. This paper reviews the research progress of single-matrix WLEDs phosphors, and points out the problems in their development, and forecasts the future development trend.
Visible laser has been widely used in data storage, optical communication, laser display, laser medical treatment, laser printing, and scientific research. With the development of commercial blue light LD, the direct pumping of rare-earth ions doped laser crystals have attracted a lot of interests. Currently, visible ions mainly concentrat on Pr 3+, Dy 3+, Tb 3+, and Sm 3+. Trivalent praseodymium (Pr 3+) is a famous rare-earth ion with extensive laser transitions in visible region such as blue, green, red and orange light. However, there is still a region in yellow emission which is not covered by Pr 3+. Dy 3+ and Tb 3+ have attracted much attention because of their yellow laser transitions. In addition, Sm 3+ and Eu 3+ are also typical visible rare-earth ions. In this paper, we mainly reviewed properties of rare-earth ions doped laser crystals for visible lasers, especially Pr 3+, Dy 3+, Tb 3+ and Sm 3+-doped YAlO3 (YAP), SrAl12O19 (SRA) crystals. A design criterion for Pr 3+ doped oxide materials was summarized. The crystal growth, structure, thermal properties, polarization spectroscopic and laser characteristics were analyzed in detail.
Graphene, which has two-dimensional carbon single atomic layer, attracts great attention due to its superb mechanical, electrical and thermal properties. In addition to its excellent mechanical properties, a large surface area (about 2600 m 2?g -1) makes it an ideal reinforcement for copper-based composites. However, graphene owns a low density (2.2 g?cm -3), while the density of copper is about 8.9 g?cm -3. The traditional powder metallurgy process is difficult to solve the problem of uniform dispersion of graphene in the copper matrix and the poor bonding strength between graphene and copper due to the huge density difference between copper and graphene. With the in-depth exploration in the issue of graphene/copper interface in recent years, some novel preparation processes and strengthening mechanisms were proposed and demonstrated. This review systematically introduces and compares the recently-developed preparation processes of graphene-reinforced copper composites, also summarizes the mechanism of mechanical enhancement in graphene-reinforced copper matrix composites.
Silicon has the highest theoretical lithium insertion specific capacity, more than ten times the theoretical specific capacity of graphite electrode material, and low delithiation potential, with abundant resources and good rate characteristics, high-energy-density lithium-ion battery silicon-based materials have become hot spots in application fields such as electric vehicles and renewable energy storage systems. However, it will cause powdering and structural collapse of the silicon electrode material due to its large volume expansion effect in the process of delithiation and lithium insertion. In addition, the solid electrolyte interface (SEI) layer on the surface of silicon is repeatedly formed in the electrolyte, which increases the polarization and reduces the coulomb efficiency, eventually leading to deterioration of electrochemical performance. In order to solve the above problems and realize the commercial application of silicon electrodes. This paper systematically summarizes the work to solve the volume effect in charge and discharge process through the selection and structural design of silicon-based materials, and deeply analyzes and discusses the preparation methods, electrochemical properties and corresponding mechanisms of representative silicon-based composite materials, focusing on silicon-carbon composites and SiOx (0<x≤2) based anode materials. Finally, the problems of silicon-based anode materials are analyzed and their prospects are prospected.
Thermoelectric materials are a kind of energy conversion materials, which are extensively used in power generation or refrigeration. The key parameter that measure the performance of thermoelectric materials is the figure of merit ZT value, which requires material excellent electrical transport performance and low thermal conductivity. Standard first principles calculations on thermoelectric materials focus on small samples of materials, which is difficult to conclude general rules and propose new candidates. The Materials Genome Initiative speeds up the discovery and design of materials based on big data and high-throughput computational methods, which is promising in novel material screening. In thermoelectrics, first principles high-throughput calculations play an increasingly important role in the predicting and designing new materials. However, there are some drawbacks in the current high-throughput efforts for thermoelectric material screening, such as the demand of efficient high-throughput algorithms for transport properties, suitable tools for analyzing big data, etc. Solving these challenges strongly determines the efficiency and accuracy of high-throughput applications in thermoelectrics. This review summarizes several high-throughput theoretical methods and cases study on electrical and thermal transport properties in thermoelectric materials, and prospects the future trend of the combination of high-throughput and thermoelectric material research.
High-throughput experiments aimed to promptly obtain the relationship among composition-phase-structure-performance with fewer experiments and screen out optimal material systems with optimized compositions. Up to now, high-throughput experiments are successfully applied in superconducting materials, fluorescent materials and giant magnetoresistance materials. Thermoelectric materials are functional materials that can realize the direct conversion between thermal energy and electrical energy and can be potentially applied in the fields of thermoelectric power generation and waste heat utilization. However, traditional preparation and characterization methods for thermoelectric materials have disadvantages of time consuming and low efficiency. Therefore, it is of great theoretical and practical significance to introduce methods and concepts of high-throughput experiments into development and optimization of new thermoelectric materials. In this paper, we summarize and discuss the existing high-throughput experimental preparation and characterization techniques with great application prospects in thermoelectric materials, including high-throughput sample preparation, composition-structure, and electro-thermal transport properties characterization, and then analyze the advantages and limitations of these high-throughput techniques. We hope to provide a reference for future high-throughput optimization and screening of thermoelectric materials.
With rapid development of sustainable energies and energy conversion technologies, application prospect of thermoelectric (TE) materials in power generation and cooling has received increasing attention. The requirement of improving TE materials with high figure of merit becomes much more important. How to obtain the low lattice thermal conductivity is one of the main concerns in TE materials. In this review, the influences of specific heat, phonon group velocity and relaxation time on the lattice thermal conductivity are discussed, respectively. Several typical features of TE materials with intrinsic low lattice thermal conductivity are introduced, such as strong anharmonicity, weak chemical bonds and complex primitive cells. Introducing multiscale phonon scatterings to reduce the lattice thermal conductivity of known TE materials is also presented and discussed, including but not limited to point defect scattering, dislocation scattering, boundary scattering, resonance scattering and electron-phonon scattering. In addition, some theoretical models of the minimum lattice thermal conductivity are analyzed, which has certain theoretical significance for rapid screening of TE materials with low lattice thermal conductivity. Finally, the efficient ways to obtain the low lattice thermal conductivity for TE property optimization are proposed.
Thermoelectric power generation via Seebeck effect features an unique advantage in converting large amount of distributed and low-grade waste heat into electricity. Thermoelectric materials have become a hot topic of research in the field of new energy materials, guided by the high figure of merit ZT. Although various mid-temperature thermoelectric materials were discovered, the industrial application of these materials, especially in power generation applications, progressed very slowly. The staggering interface technology associated with thermoelectric device restricted the advance of thermoelectric conversion technology. In this review, the bottleneck issues of utilizing Bi2Te3-based devices for power generation were used as an example to illustrate the critical interface technologies. The key issues at designing electrode contact interfaces were summarized, including low contact resistance, high bonding strength, and superior thermal chemical stability at high temperature. The recent progress on the metallization and interfacial barrier layer for typical materials of Bi2Te3, PbTe and CoSb3 were also reviewed.
Here we report a novel surface modified bamboo charcoal/TiO2 (SMBC/TiO2) nanocomposites with high adsorption and photocatalytic property. SMBC were prepared by a wet oxidization method of cheap natural bamboo charcoal (BC) with good absorbent and chemical stabilities. After modification, high density of carboxyl groups were generated on the surface of BC, thus SMBC particles can be easily dispersed in water and have stronger interactions with TiO2 nanoparticles, which ensure SMBC uniformly coated on TiO2. And SMBC/TiO2 nanocomposties have much higher specific surface area than BC/TiO2, which could offer higher adsorption capacity. The saturated adsorption capacity of SMBC/TiO2 is approximately 1.6 times, 12.1 times as great as BC/TiO2 and pure TiO2, respectively. The synergetic effect of adsorption and catalysis endow SMBC/TiO2 composites much higher photocatalytic activity than BC/TiO2 and pure TiO2 for MB degradation, and the rate constant for MB photocatalytic degradation of SMBC/TiO2 was almost 7 times and 6 times as large as BC/TiO2 and pure TiO2, respectively.
Sphere-like hierarchical Y zeolite was synthesized by a “steam-assisted conversion (SAC)” procedure. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, solid-state nuclear magnetic resonance (NMR) spectra, and Fourier transform infrared (IR) spectroscopy. Results observed by SEM displayed that the as-synthesized Y zeolite was sphere-like polycrystalline aggregates composed of primary crystals with size of about 50-300 nm. These results exhibited that some polycrystalline aggregates were hollow Y zeolite spheres. Combined with characterization results of FT-IR, 29Si NMR, SEM, and TEM, a mechanism illustrating formation of the hollow Y zeolite polycrystalline spheres was proposed.
Two dimensional (2D) materials have attracted wide attention due to their ultrathin atomic structure, large specific surface area and quantum confinement effect which are remarkably different from their bulk counterparts. Anisotropic materials are unique among reported 2D materials. Their orientation-dependent physical and chemical properties make it possible to selectively improve the performance of materials. As representative examples, Re-based transition metal dichalcogenides (Re-TMDs) have tunable bandgaps in visible spectrum, extremely weak interlayer coupling, and anisotropic properties in optics and electronics, which make them attractive in the application areas of electronics and optoelectronics. In this riviev, the unique crystal structures and intrinsic properties of the Re-based TMDs semiconductors are introduced firstly, and then the synthetic method is introduced, followed by discussion on the unique physical characterizations and optimized means. Finally, prospects and suggestions are put forward for the preparation and research of ReX2.
With the development of nuclear energy, the long-lived radionuclides are inevitably released into the natural environment during the mine process, fuel manufacture, nuclear power usable and spent fuel management, which are dangerous to human health and environmental pollution. Thereby the efficient elimination of radionuclides is an important parameter which affects the development of nuclear power. In recent years, the metal-organic frameworks (MOFs) have attracted worldwide attention in the adsorption of radionuclides from large volume of aqueous solutions, because of their high chemical stability, abundant functional groups and changeable porous structures. In this review, we mainly summarized the recent works of MOFs in the efficient removal of radionuclides, and to understand the interaction mechanism from batch adsorption experiments, model analysis, advanced spectroscopy analysis, and theoretical calculation. The adsorption capacities of MOFs with other materials were also summarized, and the future research opportunities and challenges are given in the perspective.
The technique for Materials Genetic Initiative (MGI) is the key tool for realizing the demand-oriented design of new materials assisted by the artificial intelligence (AI). Accordingly, the development and application of innovative intelligence algorithms are particularly important. Based on the generalization and analyses of the existing nature-inspired algorithms, this work aims at outlining the suggestion to build the nature-inspired algorithms library (NIAL). The potential route in which inspirations are obtained from varieties of disciplines, was used to produce new algorithms in high-throughput ways is introduced. The general procedure for building algorithm library is elaborated, while its advantages and characteristics are anatomized. Finally, the potential of NIAL in new materials development has been envisioned to enhance the standard for the application of AI including MGI.
All-inorganic cesium lead halide CsPbX3 (X = Cl, Br, I) perovskite materials emerged as a rising star in the area of optoelectronics since 2015, due to its excellent photoelectric properties and environmental stability. Substantial progresses were made in the application of many electronic and optoelectronic devices, which attracted wide attention from the scientific community. This paper mainly reviews the latest research progress of cesium lead halide perovskite based planar heterojunction LED, where the structure and working principle of LED devices are briefly introduced. In addition, the classification and summarization of some optimization strategies for improving luminescence performance and working stability of LED devices are emphatically suggested, and the development trend of stable and efficient inorganic perovskite based planar heterojunction LED is finally prospected.
As the continuous development of the photovoltaic industry and the flat panel display devices, the demand for transparent electrodes is increasing rapidly. The most commonly used transparent conductive material, ITO, was criticized for its brittleness, which limited its application in the up-and-coming market. Cu nanowire transparent electrodes acts as promising candidate for the new generation of transparent electrodes due to their superior conductivity, low cost, easy accessibility and high flexibility. The synthesis of Cu nanowires and their application in transparent electrodes has drawn lots of attention. Progresses have been made in recent years. A comprehensive elaboration of the controllable synthesis of Cu nanowires through liquid synthesis methods and the mechanism behind them, the fabrication and post-treatment methods of Cu nanowire electrodes, the application of Cu nanowire electrodes in photovoltaic devices, transparent heaters and flexible devices are given. The trends of Cu nanowire electrodes is proposed.
Micro/meso-porous SiOC ceramics with high surface area and narrow pore size distribution were prepared by the low temperature phase separation method (namely water vapor assisted pyrolysis) followed by etching in hydrofluoric acid (HF) solution. The cross-linked body was made from hydrogen-containing polysiloxane (PHMS), tetramethyl-tetravinylcycletetrasiloxane (D4vi) and Pt-complex by thermal cross-linking. Phase compositions, chemical bonds, microstructures, and specific surface area of the prepared SiOC ceramic were investigated by XRD, FT-IR, SEM, and BET, etc. Water vapor can promote the precursor to produce Si-O-Si bonds, SiO2-rich clusters, and SiO2 nanocrystals in SiOC ceramics. All of these species act as pore-forming substrate and can be etched away by HF. Water vapor injection and pyrolysis temperature have important effects on phase compositions, microstructures and specific surface area of SiOC porous ceramics, which have a maximum specific surface area of 1845.5 m2/g and pore size distribution of 2.0-10 nm at pyrolysis temperature of 1300℃.
Avoiding the use of templates and employing natural minerals as raw materials could promote the cost-efficient preparation of mesoporous materials. This work demonstrated a template-free route to process natural halloysite into mesoporous silica with high specific surface area (SSA) up to 767 m2/g and pore size of about 5 nm. The halloysite was successively calcined, alkali-treated and acid-treated. The transformation of calcined halloysite into crystalline sodium aluminosilicate (zeolite LTA) by longtime alkali-treating, was found to be the key for obtaining high-SSA mesoporous silica in the final acid treatment. The optimized mesoporous silica showed a monolayer adsorption capacity as high as 741 mg/g for methylene blue, suggesting its great potential in adsorption applications.
Thermoelectric (TE) power generation technology is highly expected for various applications such as special power supply, green energy, energy harvesting from the environment and harvesting of industrial waste heat. Over the past years, the record of zT values of TE materials has been continuously updated, which would bode well for widespread practical applications of TE technology. However, the TE device as the core technology for the TE application lags behind the development of TE materials. Especially, the large-scale application of TE power generation technology is facing bottlenecks and new challenges. This reviewpresents an overview of the recent progress on TE device design and integration with particular attentions on device optimization design, electrode fabrication, interface engineering, and service behavior. The future challenges and development strategies for large-scale application ofthermoelectric power generation are also discussed.
PbNb2O6-xmol%Nb2O5 (PN-x=0, 5, 10, 15, 20) Piezoelectric ceramics were prepared by solid-state reaction method. The effects of excess Nb2O5 on the sintering and electrical properties of PbNb2O6 ceramics were investigated. The sintering and electrical properties were evidently improved after the addition of Nb2O5 into PN in the condition set for a high Tc and high coupling anisotropy. The improvement may originate from NbO6 octahedral distortion by excess Nb2O5, which prevents phase transition from rhombohedral to tetragonal during the sintering process. With excess addition of Nb2O5, the piezoelectric coefficient (d33) and relative density of PN ceramics increased and reached up to 69 pC/N and 93.1%, respectively, at 5mol% addition of Nb2O5.
A self-designed traveling zone melting method was employed to fabricate perovskite CsPbBr3 crystals, which is helpful for impurities removing and moisture excluding. A large-size CsPbBr3 crystal with a dimension of ϕ 25 mm× 60 mm is successfully obtained. The as-grown crystal shows orange color and displays an excellent transmittance of 78.6% in the range of 600 nm - 2000 nm wavelength. It is revealed by DSC analysis that there is phase transition at 88.1℃ and 131.25℃, respectively. The band gap Eg of the crystal is calculated to be 2.25 eV. The above results prove that the traveling zone melting method is indeed a potential approach for large size and high quality CsPbBr3 crystal preparation.
A facile strategy for anatase titanium dioxide (TiO2) nanoparticle preparation was proposed via a non-aqueous precipitation method. With the aid of glacial acetic acid, tetrabutyl titanate underwent non-hydrolytic reaction in solvent ethanol. Glacial acetic acid increased polarity of Ti-O and C-O bonds of tetrabutyl titanate, and promoted non-hydrolytic de-etherization poly condensation reaction to form Ti-O-Ti bond in the solvent. After refluxing at 80℃ for 24 h, the Ti-O-Ti bond was rearranged to form anatase TiO2 nanoparticles with the particle size of 5 nm-20 nm and specific surface area of 169.4 m2/g, which exhibited good dispersion and excellent photocatalytic activity. The degradation rate against methyl orange under ultraviolet radiation for 2 h reached 99.81%, showing promising prospect in wastewater treatment process.
SiOx anodes of lithium ion batteries have attracted considerable attention in recent years, due to their cycle stability, large capacity, and feasibility on composition manipulation. Many previous works have focused on clarifying the influences of oxygen contents on SiOx based anodes. However, the size effect is still far from understanding. Herein, the size effect on electrochemical properties of SiOx with thin-film type anodes in different thickness was investigated. It is found that the SiOx electrodes prepared by sputtering is of a Si/O ratio of 0.7 and exhibits the highest initial Coulombic efficiency (ICE) of 71.68% and the highest capacity retention of 92.01% when the film thickness being 450 nm, compared with those in other thickness. The best performance under such intriguing thickness-performance relationship is attributed to the low charge transfer resistance, formation of the reduced SEI layer and good electrode integrity upon cycling, as evidenced by SEM images and EIS collected during cycling. These results indicate that as anodes of LIBs, the SiOx anodes with controlled size can greatly improve the electrochemical performance.
The stable high-capacity anode has been an urgent demand for high energy density lithium-ion batteries (LIBs). Herein, a simple and effective strategy to synthesize high-performance reduced graphene oxide (rGO) in-situ wrapped MnTiO3 nanoparticles (MnTiO3@rGO) by Sol-Gel method is designed. The MnTiO3 nanoparticles are uniformly dispersed and wrapped by few-layer graphene. Due to high conductivity of rGO, MnTiO3@rGO nanoparticles show excellent rate performance, with a specific capacity of 286 mAh·g-1 being displayed at the higher rate of 5.0 A·g-1. Moreover, benefited from porous structure and flexible rGO shell, the MnTiO3@rGO anode delivers a remarkable long-term cycling stability. The specific capacity maintains 441 mAh·g-1 after 500 cycles at 0.5 A·g-1, only losing 8.4%. Therefore, the results demonstrate that the facile synthetic strategy is highly desirable for improving the conductivity and stability of metal oxide anodes.
Li-O2 batteries are regarded as a promising energy storage system for their extremely high energy density. MnO2-based materials are recognized as efficient and low-cost catalyst for a Li-O2 battery positive electrode material. In this work, α-MnO2 nanowires were successfully synthesized by a hydrothermal method and their electrocatalytic performance were investigated in Li-O2 batteries. X-ray diffraction and field emission scanning electron microscope confirms the formation of α-MnO2. The Li-O2 battery which consists of α-MnO2 nanowires shows a high discharge capacity up to 12000 mAh•g-1 at a restrict voltage of 2.0 V with the current density of 100 mA•g-1. When restricting the discharge capacity at 500 mAh•g-1, it can operate over 40 cycles and exhibit good cycle stability. These results indicate that the α-MnO2 nanowires can be used as positive electrode catalysts for Li-O2 batteries.
Two special CeO2-ZrO2 composites with combined compositions were prepared by a simple sequential precipitation method. The effect of the combination styles on properties of the supported Pd-only three-way catalysts was investigated by means of X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption, H2-temperature programmed reduction (H2-TPR), and oxygen storage capacity measurement (OSC). The results reveal that the structural and textural properties are modified for the two catalysts with compositional heterogeneity. Combined configuration facilitates the formation of Ce3+ and lattice defects, resulting in improved oxygen mobility, due to strong interaction between the noble metal and the support as well as the synergistic function inside the support. Consequently, the corresponding catalysts show amplified operation windows for the conversions of CO, C3H8 and NO before and after aging, indicating promising application in purification of automobile exhaust gases.
Multiferroic KBiFe2O5 was successfully prepared by a facile hydrothermal method. Its phase purity and morphology were investigated by powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The visible-light absorption was confirmed by UV-Vis diffuse reaction spectroscopy (UV-Vis DRS). Effect of pH value on visible-light-driven photocatalytic properties of KBiFe2O5 was evaluated by degrading rhodamine B (RhB) and methyl orange (MO). It can be found that lower pH value contributed to smaller average particle size. The D50 of the sample at pH 7 is about 10 times larger than that at pH 2. Acid condition is beneficial to the dispersion of KBiFe2O5 nanoparticles, which leads to an enhanced photocatalytic performance. Photocatalytic activity of KBiFe2O5 is significantly improved by decreasing pH value of the solution, which is attributed to the promoted dispersion of catalyst particles in the suspension and the enhanced adsorption of dye molecules on the catalyst surface.
Spindle-like Y4.67(SiO4)3O apatite crystallites composed of numerous nanoparticles with a mean diameter of about 50 nm were synthesized via a facile hydrothermal method at 503 K for 12 h. To the best of our knowedge, the thermal properties of the spindle-like Y4.67(SiO4)3O apatite crystallites was firstly reported. Their phase composition, microstructure, formation mechanism were investigated. Results show that hydrothermal temperature greatly influences the crystal phase composition and the crystal morphology. In addition, the obtained Y4.67(SiO4)3O ceramics possess low thermal conductivity and a relatively high thermal expansion coefficient, which make them a promising candidate material for environmental/thermal barrier coatings.
Strength of Engineered Stress Profile glass has been proved narrowly distributed owing to its particular exchanged ion profile. In order to predict the K+ concentration profile, Finite-Difference Time-Domain method was introduced to simulate the diffusion processes. Simulation procedures were conducted based on detected diffusion coefficients, surface concentrations, and ion profile subjected to single step ion exchange. The calculated results show a reasonable agreement with the experimental measurements (Energy Dispersive Spectroscopy). According to the simulation results, the relation between K+ profile and strength performance were interpreted.
With unique electronic effect, TiO2 nanoparticles can be used as photocatalysts to reduce or eliminate the organic pollutants only under irradiation of sunlight. It is, therefore, highly desirable to improve its dispersion and solubility to broaden its application in different fields especially in environmental conservation. Here provides a case of two-step method to prepare yellow transparent water-soluble TiO2-ionic liquids hybrid nanomaterial. In this hybrid system, organic sulfonate groups as canopy provide “self-solvent” for the dispersion of the TiO2 nanoparticles. This dispersion experiment results indicated that the water-soluble organic canopy in the TiO2-ionic liquids hybrid nanomaterial offered good solubility in water and the TiO2-ionic liquids hybrid nanomaterials used in-home decoration could be easily wiped away on the surface of furniture. Data from photocatalytic degradation efficiency for decomposing formaldehyde demonstrated that the hybrid nanofluids possessed excellent photocatalytic performance. The water-soluble TiO2-ionic liquids hybrid nanomaterials could be a promising candidate for environmental conservation in the future.
In this study, a CQDs/BiPO4 nanocomposite with enhanced visible-light absorption and charge separation was fabricated via a one-step hydrothermal reaction. The photocatalytic activity of the CQDs/BiPO4 nanocomposite was evaluated by degradation of rhodamine B (RhB). The result showed that the CQDs/BiPO4 composite exhibited superior photocatalytic performance to pure BiPO4 under simulated solar light, as well as under visible light irradiation. Its enhanced photocatalytic performance could be ascribed to the excellent light harvesting properties, which increased utilization rate of solar energy, electron transfer efficiency and reservoir ability of the nanocompsites, facilitating the charge separation efficiency of the composite.