Introduction Mixing hydrogen into natural gas pipelines is one of the critical technologies for achieving large-scale and long-distance hydrogen transmission, which can be directly used for power generation or combined cooling, heating, and power supply through solid oxide fuel cells (SOFC), without the hydrogen separation and purification, enabling efficient energy conversion and utilization. Ni-YSZ metal-ceramic composite anodes are widely used in SOFC single cells, which have a superior performance under hydrogen and reformed hydrogen-rich fuel systems. However, carbon deposition susceptibly occurs under carbon-hydrogen fuels, and metal-nickel agglomeration migrates under high fuel utilization operating modes. Sr(Ti1-xFex)O3-δ (STF) is one of the potential alternative anodes with superior structural stability and mixed ionic-electronic conductivity, as well as great resistance to redox cycling, fuel impurities and hydrocarbon fuels. It was indicated that the introduction of transition metal (i.e., Co, Ni, Ru, etc.) doping into the B-site of STF perovskite oxides, which in-situ exsolved metal nanoparticles from substrate in reducing atmosphere, exhibiting a superior anodic catalytic activity. In this paper, A-deficient Sr0.95Ti0.4-xFe0.6CoxO3-δ (x=0.03, 0.05, 0.07) was prepared as a SOFC anode. In addition, the material structure evolution, porous anode conductivity, electrochemical performance and stability of single-cell under methane fuels with different hydrogen doping ratios were also investigated. Methods Sr0.95Ti0.4-xFe0.6CoxO3-δ (x=0.03, 0.05, 0.07) powder was prepared via a high-temperature solid-state reaction with SrCO3, TiO2, Fe2O3 and Co(NO3)2·6H2O. The precursors were mixed and ball-milled in ethanol for 48 h, dried and calcined at 1100 ℃ for 10 h. Subsequently, the perovskite electrode powders were obtained (i.e., denoted as STFC-3, STFC-5, STFC-7), Respectively. The electrode slurry with the powder and a binder in a mass ratio of 1.0:1.5 was prepared by a three-roll mill. The La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte pellets with a thickness of 300 μm and a diameter of 15.5 mm were prepared via tape casting and high-temperature sintering. La0.4Ce0.6O2-δ (LDC) was screen-printed on the LSGM electrolyte and calcined at 1 350 ℃ for 4 h, to prevent the potential reaction between STFC and LSGM. Afterwords, the STFC, La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O1.95 (LSCF-GDC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrode were screen-printed as anode and cathode, respectively, and then were co-fired at 1 075 ℃ for 3 h. The effective area of the cathode was 0.5 cm2. Finally, 1 mm×1 mm silver grids were printed on the cathode and anode of the single cell, as a current-collector, calcined at 600 ℃ for 1 h. The structural evolution of the materials obtained before and after reducing in humidified hydrogen (~4% H2O, in volume) at 800 ℃ for 3 h was characterized by a model Bruker D2 Advance X-ray diffracometer (XRD) and a model Escalab 250X-ray photoelectron spectrometer (XPS). The microscopic morphology of the electrode powder after reduction was characterized by a model JSM-IT500HR scanning electron microscope (SEM). The conductivity of the screen-printed STFC porous electrodes was tested in air and humidified hydrogen (~4% H2O, in volume) atmospheres through the van der Pauw method. The stability and electrochemical performance (i.e., the discharge curves and electrochemical AC impedance spectra (EIS, 0.1 Hz~1.0 MHz, 50 mV)of single cells under different hydrogen blended methane fuels were investigated by a model P4000A electrochemical workstation (Princeton). Results and discussion The peak power density (Pmax) and limiting current density (jmax) of the single cell at 800 ℃ enhance with the increase of the volume ratio of H2. Taking STFC-3 cell as an example, the Pmax of the single cell is 0.506, 0.467, 0.414, 0.338 W/cm2 at different hydrogen ratios of 80%, 60%, 40%, and 20% (in volume), respectively. According to the EIS spectra and DRT results, the polarization resistances (Rp) of the STFC anode single cell gradually increase with the increase of CH4 ratio, which mainly corresponds to the change of middle frequency P4 (~10 Hz) and low frequency P5 (1~10-1 Hz) responses, possibly due to the complexity of catalytic oxidation and slow reaction kinetics of CH4. The STFC-3 single cell is operated at 0.14 A/cm2 with humidified 10 H2-40 CH4 (~4% H2O, in volume). The STFC-3 cell can stably operate for 140 h without an obvious voltage decay, showing a superior long-term stability. The SEM images indicate that the interface contacts between the electrolyte, the barrier layer and the STFC anode is dense, without having anode structure changes. Moreover, little carbon deposition appears on the surface of the anode, indicating a decent coking-resistance property of STFC anode in hydrogen blended natural gas. It has significant guidance in response to the demand for high-performance and stability of SOFC with hydrogen and compressed natural gas. Conclusions The Co-Fe alloy nano particles were exsolved on the surface of STFC perovskite oxide after humidified hydrogen reduction, and the exsolution enhanced with increasing Co doping content. At 800 ℃, the conductivity of STFC-3 porous electrode under hydrogen atmosphere reached 3 S/cm, with a single cell maximum output power density of 0.457 W/cm2 in methane fuel doping with 20% (in volume) hydrogen. The continuous operation at 0.14 A/cm2 for ~140 h indicated good durability and coking resistant property.

Introduction Solid oxide fuel cells (SOFCs) are an efficient all solid-state power generation device and an important choice for achieving the energy goals. The existing shortcomings like low high-temperature strength, structural reliability, and short service life of SOFCs restrict the commercialization of SOFCs. The core component of SOFC, i.e., the positive-electrolyte-negative (PEN) multilayer composite ceramic electrode plate that works in a redox environment for a long time and bears the cyclic thermal stress caused by multiple starts and stops of the SOFC stack should have a good mechanical strength. The common anode material for SOFC is nickel oxide-yttria-stabilized zirconia (NiO-YSZ) porous ceramic. The NiO-YSZ anode has some problems such as alternating high and low temperature redox, carbon deposition, impurity poisoning, and Ni particle growth during operation, thus leading to the deterioration of the mechanical properties of the anode. It is thus of great significance to evaluate the mechanical properties of the NiO-YSZ anode for SOFCs and evolute the degradation over service time. However, the excessive clamping force can lead to the fragmentation of the entire specimen due to the thin thickness of NiO-YSZ anode and the brittleness of the material. It is difficult for conventional tensile tests to achieve the evaluation of the mechanical strength of the NiO-YSZ anode and PEN components. The small punch test (SPT) is a testing technique that uses micro-sized specimens to obtain the mechanical strength of materials without the need to clamp the specimens. This paper focused on the homogeneous NiO-YSZ anode material of planar SOFC and conducted multiple sets of SPTs. In addition, a method was also proposed to evaluate the mechanical strength of anode NiO-YSZ ceramic component of planar SOFCs using SPT. Methods The initial experimental material was planar anode-supported SOFC multilayer PEN plate, which did not yet put into service and prepared by a tape-casting method. The anode, electrolyte, and cathode materials were NiO-YSZ, YSZ, and LSM (strontium-doped lanthanum manganate)-YSZ, respectively. The plate-shaped PEN was cut into circular specimens with a radius of R=5 mm. The cathode, barrier layer, and electrolyte layer of the specimen were removed by mechanical polishing. The initial thickness t0 of the NiO-YSZ specimen was ultimately controlled to be (0.380±0.010) mm. The SPT adopted a self-developed testing machine with a self-designed SPT clamp. The experiment was controlled by displacement loading at a constant loading rate of 0.02 mm/min. The specimen underwent deformation until failure under the stamping of the punch and loading ball. The load and displacement data were collected by sensors and the load-displacement curve was drawn. The surface and fracture morphology of the specimen were observed by scanning electron microscopy (SEM). The mechanical properties of NiO-YSZ anode (i.e., elastic modulus, characteristic strength, and Weibull modulus) were obtained via the experimental results and mechanical modeling based on an inverse finite element method and the Weibull failure probability model. Results and discussion The load-displacement curve of SPT of NiO-YSZ has three characteristic stages and three load characteristic values P1, P2, and Pm. Based on the fracture observation by SEM, different loading stages correspond to the process of crack initiation and propagation in NiO-YSZ sample, and P1 is determined as a fracture load of the specimen. The elastic modulus of NiO-YSZ anode is determined to be 40 GPa through a reverse finite element method, and the maximum tensile stress of the specimen occurs at the center of the lower surface when the displacement reaches its maximum value (i.e.,149.16 MPa). The corresponding mechanical model was developed, and a formula for calculating the tensile strengths of NiO-YSZ anode specimens was proposed. Under the same conditions, the maximum tensile stress of the theoretically calculated for the specimen is 152.29 MPa, which is only 2.1% different from the numerical simulation result. The reason for the deviation ise due to the simplification of the contact process during theoretical modeling, while the finite element method can more closely simulate the deformation between the loading ball and the specimen during the experimental process to obtain a more accurate numerical solution. The ultimate tensile strengths of 22 NiO-YSZ specimens were calculated through the theoretical formulas. The ultimate tensile strength exhibits a certain degree of dispersion due to the inherent properties of brittle ceramic materials. Therefore, the Weibull failure probability model was used to statistically analyze the results, and the characteristic strength of ultimate tensile strength of NiO-YSZ anode material is 160.88 MPa, with the Weibull modulus of 7.61. This achieves the evaluation of strength, reliability and uniformity of NiO-YSZ anode material. Conclusions The load-displacement curve of SPT of NiO-YSZ anode had three load characteristic values P1, P2, and Pm. Based on the SEM observation, different experimental stages corresponded to the crack initiation and propagation stages of the specimen. After the load reaches P1, some cracks appeared at the center of the lower surface of the specimen, and P1 was determined as a material fracture load. A mechanical theoretical model for the SPT of ceramic materials was proposed. The Weibull statistical results of the tensile strength of NiO-YSZ anode were obtained by four different methods, and a formula for calculating the tensile strength of NiO-YSZ ceramic specimens suitable for SPT was obtained. The mechanical strength of NiO-YSZ anode material had a dispersibility, and the elastic modulus of the research object NiO-YSZ anode material was determined to be 40 GPa through the reverse finite element method. A method for evaluating the mechanical strength of SOFC electrode ceramic components based on SPT was proposed. The statistical analysis was conducted on 22 sets of experimental results, yielding a characteristic tensile strength of 160.90 MPa with a Weibull modulus (m) of 7.61 for this material.

Introduction There exists a poor contact between the current collector and the electrode due to the warping of planar solid oxide fuel cells and the uneven compressive forces of the stack. In the operation of solid oxide fuel cells (SOFCs), the poor contact between the current collector and the electrode can result in a contact resistance, thereby severely deteriorating the electrical performance of SOFCs. To optimize the current collection performance of SOFCs, it is necessary to conduct the experimental research and numerical simulation on the impact of current collector on the performance of planar SOFCs. Methods The fuel cell samples were provided by Xuzhou Huatsing Jingkun Energy Co., Ltd., China. The long anode-supported SOFC samples were prepared with cathode segmented to four insulted areas of 2.0 cm×2.1 cm. Each region was covered with different areas of silver mesh to constitute differential contact resistances. This ensured the consistency in the sample cell preparation and cell installation process, aside from the variations in the current collection. To enhance fuel sealing, the anode-side test fixture was made from a single metal plate, while the cathode-side fixture consisted of four metal blocks and three insulating mica sheets. A model RD2-12-10 electric heating furnace (Zhongyang Co., China) was used to heat at a rate of 1 ℃/min to 720 ℃, and then the temperature was maintained. The current-voltage characteristics of the SOFC were measured by a model Kikusui PLZ664WA DC electronic load. The voltage signals from various regions were measured by a model JC-9600B/8 multi-channel voltmeter (Jiangsu Jiechuang Technology Co., Ltd., China). The electrochemical impedance spectroscopic tests were conducted by a model Zennium electrochemical workstation (Zahner Co., Germany) with a frequency range from 0.1 Hz to 100 kHz. The microstructure of the samples was measured using a model FESEM SU-8220 field emission scanning electron microscope (Hitachi Co., Ltd., Japan). An one-dimensional numerical model was constructed via the FORTRAN language, following the double-layer theory and the conductivity data were adopted in the model. The current distribution along the flow channel of the SOFC was simulated, and the simulated data were compared with the experimental results. Results and discussion The cathode conductivity is different at different temperatures. At 220 ℃, the cathode conductivity reaches a minimum value of 1 125 S/m. As 500 ℃, the conductivity rapidly increases to 6 066 S/m. The conductivity tends to stabilize, reaching 6 192 S/m at 720 ℃. In the electrochemical impedance spectroscopic tests, the hydrogen flow rate is 100 mL/min, and the airflow rate is 450 mL/min. Under open-circuit conditions, the real-axis impedance of the 25% silver mesh-covered area is greater than that of other areas. The real part of the impedance for regions 1 to 4 is 1.22, 0.44, 0.38 Ω-cm2, and 0.39 Ω-cm2, respectively. The voltage-current characteristics were measured under various operating conditions. When the hydrogen inlet flow rate is 50 mL/min, the area-specific polarization resistance for regions 1 to 4 is 2.22, 0.95, 0.77 Ω-cm2, and 0.64 Ω-cm2, with corresponding current densities of 0.19, 0.42, 0.56 A/cm2, and 0.72 A/cm2. When the hydrogen inlet flow rate increases to 150 mL/min, the corresponding area specific resistances (ASRs) are 2.07, 0.87, 0.60 Ω-cm2, and 0.53 Ω cm2, while the current densities are 0.21, 0.51, 0.75 A/cm, and 0.84 A/cm, respectively. The results simulated by a model reveal that a poor current collection can lead to a reduction in overall current output and uneven current density distribution. The results show that at an average output voltage of 0.57 V or an average current density of 0.5 A/cm2, the simulated values for regions 4 and 3 closely match the experimental results. However, region 2 exhibits some deviation, while region 1 shows the most significant discrepancy. In addition, the simulated results also demonstrate the distribution of electrode voltage and current density along the airflow direction in the fuel cell. Conclusions The cathode of industrial-sized finished SOFC was fabricated with a 50% (in mass) La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and 50% (in mass) Ce0.9Gd0.1O2-δ (GDC) composite. The experimental results showed that the electrical conductivity of the fabricated cathode was 6 192 S/m at 720 ℃. The electrical conductivity of the anode support layer made from a NiO/YSZ mixture was approximately 0.65×106 S/m at room temperature. The long anode-supported SOFC samples were prepared, with cathode segmented to four insulted areas of 2.0 cm×2.1 cm. Each region was covered with different areas of silver mesh to constitute differential contact resistances. The electrochemical impedance spectroscopic tests and current-voltage characteristic curve scans were carried out in each localized region. The experimental results indicated that the real impedance spectrum of the 25% silver mesh coverage area under open circuit conditions was greater than that of other regions. At the same output voltage, the current density decreased monotonically with the decrease of the silver mesh area. The electronic conductivities of the cathode and anode of the same type of SOFCs were measured. The tested parameters were substituted into a numerical model to simulate the current and voltage distributions along the flow channel direction. The simulated results showed that there existed an accumulative parallel current in the area not covered by the silver mesh. The total output current decreased and the current density distribution was uneven, affecting the electrode polarization process and deteriorating the output performance of SOFCs.

Introduction Lithium-sulfur batteries are one of the most promising secondary rechargeable batteries due to their high energy density, environmental friendliness, abundant reserves and low price. However, lithium-sulfur batteries have some problems such as poor electrical conductivity at the cathode, structural damage caused by volume expansion during charging and discharging, and shuttle effect caused by polysulfide dissolution, seriously restricting the development of lithium-sulfur batteries. One of the effective methods to solve the problems above is to prepare sulfur-carbon composite cathode materials by using carbon materials as sulfur carriers. Among them, porous carbon can increase the loading of monolithic sulfur, improve the electrical conductivity of the cathode material, inhibit the dissolution of soluble lithium polysulfide, and alleviate the volume expansion. It cannot inhibit the dissolution of soluble lithium polysulfide effectively for a long time due to the weak interaction between the no npolar and polar soluble lithium polysulfide of the carbon material. Pyridine nitrogen has the maximum binding energy with soluble lithium polysulfide (Li2Sx, 4≤x≤8), which has the most obvious inhibition effect on the shuttle effect. The nitrogen in C3N4 is as high as 55.1%, and it is mainly pyridine nitrogen. The preparation method is simple and low cost. Therefore, C3N4 modified bituminous mesoporous carbon composites were proposed as sulfur carriers for lithium-sulfur composite batteries. The morphology and structure of the composites, the effect of the composites on the adsorption-catalyzed conversion of soluble lithium polysulfide (Li2Sx, 4≤x≤8), and the electrochemical performance of lithium-sulfur batteries were investigated. Methods 5% mass fraction silane coupling agent (KH550) aqueous solution was used to surface treat SiO2 nanopowder(Jinan Zhiding Welding Materials Co., Ltd., China) and then porous carbon materials were prepared with treated SiO2 powder with asphalt powder. The porous carbon material was compounded with urea (Sinopharm Chemical Reagent Co., Ltd., China) and a sublimation sulfur powder (Shanghai McLean Biochemical Technology Co., Ltd., China)as amelted sulfur ina ratio of 40:60 to obtain the active material of cathode material. Al foil was used as acollector, and the electrode material was obtained via mixing the active material, carbon black and polyvinylidene fluoride (PVDF) in aratio of 8:1:1. The CR2025 coin-type cells were assembled in a glove box in Ar gas (<1 ppm of O2) with cathodes, separator, Li foil as an anode, and electrolyte. The phase composition and structure were characterized by X-ray diffraction. The surface composition of materials was determined by X-ray photoelectron spectroscopy. The surface morphology was characterized by scanning electron microscopy and transmission electron microscopy. The specific surface area was measured by specific surface area analysis based on the BET. The sulfur content was analyzed by thermo gravimetric analysis. The sample structure was determined by a model Sentera R200-L Raman spectroscope. The constant current charging and discharging tests were performed. The CV and EIS were determined by a model CHI660E electrochemical workstation. Results and discussion A porous carbon composite with C3N4 (i.e., AC/C3N4)has more reaction sites, greater adsorption, higher electrical conductivity and faster redox kinetics, compared with C3N4. This is mainly because AC/C3N4 has a large specific surface area and porosity, which is conducive to the capture of polysulfides. Also, this composite increases the contact area of the electrolyte, which is conducive to the penetration of electrolytes, accelerates the transfer of Li+ and electrons, thereby promoting the redox kinetics of polysulfides. Moreover, this composite provides more reaction sites for electrochemical reactions, enabling the redox reaction to proceed quickly and improving the utilization rate of sulfur. In the calcination process, urea pyrolysis forms C3N4 and adheres to the surface of porous carbon. AC/C3N4/S contains rich pyridine nitrogen, which can effectively anchor polysulfides. This composite has a great adsorption capacity for soluble lithium polysulfide (Li2Sx, 4≤x≤8) and can effectively inhibit the dissolution of lithium polysulfide (Li2Sx, 4≤x≤8), thus reducing the shuttle effect. The results of symmetric cell kinetic test and deposition kinetic test showed that AC/C3N4 has more catalytic active sites and a higher electronic conductivity, thus accelerating the catalytic conversion of polysulfides and promoting the nucleation and growth of Li2S. The first discharge capacities of the three samples, i.e., C3N4/S, AC/S, and AC/C3N4/S, are 705, 1 084 mA·h/g, and 1 248 mA·h/g, respectively, at a current density of 0.2 C. The voltage differences between the charging and discharging platforms of the three samples are 0.30, 0.21 V, and 0.19 V. Compared with C3N4/S, the polarization voltage of AC/C3N4/S is significantly reduced. The average discharge specific capacity of AC/C3N4/S is 986, 815, 736, 640, 520 mA·h/g and 859 mA·h/g at current densities of 0.2, 0.5, 1.0, 2.0, 4.0 C, and 0.2 C, indicating that AC/C3N4/S has abetter rate performance. This is attributed to the catalytic and adsorption effects of C3N4 on lithium polysulfide, which can accelerate the electrochemical reaction rate and inhibit the dissolution of soluble lithium polysulfide (Li2Sx, 4≤x≤8), resulting in an improved rate performance. The results of CV tests and EIS tests indicated that the difference between the oxidation and reduction peaks of AC/C3N4/S is smaller than that of AC/S. The charge transfer resistance of AC/C3N4/S is smaller than that of C3N4/S. This is because C3N4 has a catalytic effect on soluble lithium polysulfide (Li2Sx, 4≤x≤8), reducing the polarization, enhancing the electrochemical reaction kinetics, accelerating the charge transfer, and reducing the transfer impedance. Conclusions C3N4 was composited with asphalt porous carbon material to obtain a AC/C3N4 composite material, which was used as a sulfur carrier for lithium sulfur batteries. The AC/C3N4/S composite material hada large specific surface area and porosity, promoting the redox kinetics of polysulfides and providing a buffer space for the volume expansion of sulfur during charging and discharging processes. Meanwhile, polar C3N4 adhered to the surface and pores of porous carbon, effectively improving the material adsorption and catalysis of soluble lithium polysulfide (Li2Sx, 4≤x≤8), reducing shuttle effect and loss of active substances, improving sulfur utilization rate, and ensuring a long-term stability. The first discharge capacity of the AC/C3N4/S was 1 248 mA·h/g at a current density of 0.2 C, and the capacity still remained 862 mA·h/g after 100 cycling. The average discharge specific capacity of AC/C3N4/S was 986, 815, 736, 640, 520 mA·h/g and 859 mA·h/g at current densities of 0.2, 0.5, 1.0, 2.0, 4.0 C, and 0.2 C, indicating that AC/C3N4/S had abetter rate performance.

Introduction Sodium batteries become a novel energy storage device due to their higher safety factor and superior comprehensive performance. The existing electrode materials such as NaxCoO2, NaxTiO2, NaTi2(PO4)3, etc. are investigated for sodium batteries. However, these electrodes have a disadvantage of poor ion/electronic conductivity, restricting their widespread application. Na2Ti3O7 is an ideal alternative titanium-based negative electrode material for sodium batteries due to its Ti3+/Ti4+ variability and suitable redox pairs, as well as its low voltage plateau. Embedding carbon in Na2Ti3O7 electrode for sodium ion batteries can improve their conductivity and electrochemical performance, especially for the large-scale energy storage applications with different energy density and volume requirements. In this paper, Na2Ti3O7/C composite anode material for sodium ion battery was prepared by a special template method, and its electrochemical characteristics were investigated. Methods Na2Ti3O7/C composite anode material for sodium ion battery was synthesized with natural spirulina as a biological template. Spirulina was added into Na2Ti3O7 precursor solution, heated and stirred in a magnetic stirrer for 1 h, and then put them in a hydrothermal reactor (with a polytetrafluoroethylene inner tank capacity of 100 mL) at 180 ℃ for 18 h. In addition, Na2Ti3O7 precursor solution was also placed into a tank to hydrothermal reaction under the same condition for comparing with the template method. The final products were calcined in an air furnace (with a heating rate of 1 ℃/min from room temperature to 850 ℃) at 850 ℃ for 5 h to form the perfect crystals and remove the spirulina templates. A CR2032-typed buckle battery was assembled in a glove box (GRS-1200, Wuhan Grace New Energy Co., Ltd., China) filled in argon gas and with the synthesized Na2Ti3O7/C or Na2Ti3O7 electrodes as anodes, high purity sodium tablets as counter electrodes. The microstructure of the product was characterized by a model Quanta 200 environmental scanning electron microscopy (ESEM) (FEI Ltd., Netherlands), and the components were analyzed by an EDAX spectrometer in the ESEM microscope. The crystal structure was determined by a model X’Pert PRO X-ray diffracto meter (XRD, PANalytical B.V. Ltd., Netherlands). The 2θ range of XRD is 5° to 70°. Their electrochemical properties were analyzed by a model CT2001A programmatical-controllable Land battery testing system (Hubei Lanbo New Energy Equipment Co., Ltd., China). The test parameters involved the charge-discharge capacities at a constant current (i.e., 0.5 C=125 mA/g), cycle stability and coulomb efficiency, and discharge capacities after 20 cycles at different rates (i.e., 0.1, 0.2, 0.3, 0.4 C, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0 C, and 5.0 C). The alternating aurrent (AC) impedance was analyzed via a model CS350 electrochemical workstation (Wuhan Kesite Instrument Co., Ltd., China). The test parameters are the total impedance (R1) of electrode and electrolyte in series, electrode contact resistance (R2), sodium ion charge transfer resistance (R3) and semi-infinite diffusion Warburg impedance of Na+ in electrolyte (Ws). Results and discussion The ESEM results show that Na2Ti3O7/C material prepared with the spirulina biological template has a good network strip structure, with a small amount of carbon residue (the mass fraction of carbon of 1.29%). The Na2Ti3O7 materials by a hydrothermal method are nano-particles with the diameters of approximately 10-30 nm. Their XRD patterns of both materials are consistent with the standard spectra of Na2Ti3O7 (JCPDS 31-1329), indicating a perfect crystal structure. The initial charge-discharge capacity of Na2Ti3O7/C electrode material prepared with spirulina template is 109.3 mA·h/g and 117.6 mA·h/g, respectively. The initial charge-discharge capacity is 89.3 mA·h/g and 86.3 mA·h/g of Na2Ti3O7 electrode material by the hydrothermal method, respectively. After 250 cycles, the average retention rate of the charge-discharge specific capacity of Na2Ti3O7/C material is 70%, which is better than that of Na2Ti3O7 material (i.e., 35%), showing a better cyclic stability and a higher Coulomb efficiency. Based on the results of the specific discharge capacities at different rates, the discharge attenuation of both the materials are faster at a lower current, while they are relatively stable at a higher current, which provides a good power support for high-power hybrid electric vehicles. At the same rate, the stability of Na2Ti3O7/C electrode material is better than that of Na2Ti3O7 electrode material. The electrochemical impedance spectra shows that R1, R2, R3 and Ws resistances of Na2Ti3O7/C material are smaller than those of Na2Ti3O7 material. Conclusions The specific capacity decay rate of Na2Ti3O7/C electrode obtained by the spirulina template method was slower than that of Na2Ti3O7 electrode obtained by the hydrothermal method after charge-discharge cycles. This was due to the nano-network strip structure prepared by natural spirulina as a template. Na2Ti3O7/C electrode reduced the detachment resistance of sodium ions on the electrode surface and the diffusion resistance in the electrolyte, increased the contact area between the electrolyte and the electrode surface, thereby proved a good channel for the detachment of sodium ions, thus effectively improving the electrochemical performance of electrode materials. Moreover, the residual carbon in calcination improved its conductivity of Na2Ti3O7 electrode material, and enhanced its electrochemical performance, thus providing a basic support for the development and application of novel sodium batteries.

Introduction Mirabilite as a phase change energy storage material becomes a research hotspot because of its high latent heat, low material cost, and high thermal conductivity. However, the problems of supercooling, phase delamination, and easy leakage in the phase transition cycle seriously restrict its application. Some work indicate that stereotype-phase change materials can effectively solve these problems. In this paper, crosslinked carbon nanotubes (CL-CNTs) were prepared via the Friedel-Craft alkylation and high-temperature carbonization. The CL-CNTs shaped Na2SO4·10H2O based phase change materials were prepared via melting, and their properties were investigated. Methods Pyrene (1×10-3 mol), 1, 2-dichloroethane (20 mL), and FeCl3 (3×10-3 mol) were added into 100 mL beakers. After FeCl3 was dissolved, methyl acetal (3×10-3 mol) was added and stirred magnetically at room temperature for 5 h. At the end of the reaction, the solution was filtered, and the solid obtained was alternately rinsed with methanol, distilled water, methylene chloride, and acetone. The cleaned solid material was extracted with methanol Soxhlet for 48 h and then dried in vacuum for 7 h. The yellow powder was heated to 650 ℃ in a tube furnace with a nitrogen atmosphere for 4 h. Finally, it was cooled to room temperature and carbonized to obtain a black powder. 4.0% NaCl, 1.0% borax, and 0.1% sodium metaphosphate were added into a mixture of Na2SO4·10H2O and Na2CO3·10H2O (9:1) to prepare a phase change energy storage material of mirabilite. Afterwards, CL-CNTs were added into the phase change material with a mass fraction of 0, 1%, 2%, 3%, 4%, and 5%, respectively, and the phase change material was prepared by a melting intercalation method. These samples were ultrasonically treated for 24 h in the molten state and then stirred in a mixer for 2 h, which were labeled as PCMs-0, PCMs-1, PCMs-2, PCMs-3, PCMs-4, and PCMs-5, respectively. Results and discussion Most CL-CNTs prepared show a tubular structure, and a few carbon spheres grow on the carbon nanotubes. Hydrophilic CL-CNTs were prepared with hydroxyl and benzene ring groups on the CL-CNTs. Na2SO4·10H2O shaped phase change materials were prepared via melting intercalation at different mass fractions of carbon nanotubes (i.e., 1%, 2%, 3%, 4%, and 5%).The samples at >4% CL-CNTs show a superior stereotyped state. According to the analysis by SEM, a uniform mixture of PCMs-4 phase change material and the crystalline particles of the mirabilite phase change material exist around the carbon nanotubes, indicating that CL-CNTs shaped Na2SO4·10H2O phase change material can be prepared. The thermal conductivity of PCMs-4 is greater than that of PCMs-0, and the thermal conductivity increases with the increase of temperature at 0-20 ℃ and at 30-50 ℃. At 20 ℃, the thermal conductivity has the maximum value. At 20-30 ℃, the thermal conductivity of PCMs-0 and PCMs-4 decreases due to the heat absorption during the solid-liquid phase change of hydrated salt. Based on the DSC data of PCMs-0 and PCMs-4 before and after 500 phase transition cycles, PCMs-4 has better cyclic stability than PCMs-0. The enthalpy loss rate of melting and crystallization before and after phase transition cycles of PCMs-0 is 18% and 25%, respectively, indicating that a phase stratification occurs as phase transition cycle increases. The latent heat release of phase change decreases, and the Na2SO4·10H2O-based hydrate salt gradually fails. The melting enthalpy loss rate of sample PCMs-4 before and after the phase transformation cycle is 2%, and the crystallization enthalpy loss rate is 2.3%, indicating that, the potential heat of phase transformation is not significantly reduced as the number of phase transformation cycle is increased. It is indicated that adding CL-CNTs to PCMs-4 can effectively reduce the phase stratification and improve the cycle stability of mirabilite phase change materials. Conclusions The shaped Na2SO4·10H2O based phase change materials were prepared, thus effectively solving the problems of supercooling and phase stratification of materials. The sample PCMs-4 had a good shape. The thermal conductivity reached a maximum value of 1.008 W·m-1·K-1 at 20 ℃. There was still a high melting latent heat of 230.1 J/g and solidification latent heat of 205.2 J/g after the phase transformation cycle, indicating that the latent heat of phase transformation was not reduced as the number of phase transformation cycle was increased.

It is necessary to explore efficient and environmentally friendly energy storage devices due to the rapid consumption of fossil fuels and increasing environmental pollution. Among various energy storage devices, supercapacitors have some advantages of high power density, short charging and discharging time, good cycle stability, safety and reliability. The related studies focused on transition metal oxides and sulfides. However, their conductivity and cycle stability are rather poor. Compared with transition metal oxides and sulfides, transition metal selenides as an advanced multifunctional material dominate the field of energy storage and conversion by virtue of their high theoretical capacity, good electrical conductivity, and good cycling stability. Also, the coexistence of different metal cations with multiple valence leaps enables multiple redox reactions and enriches structural defects, and the coupling between the bimetals favors the regulation of the electronic structure and improved electrical conductivity, resulting in better electrochemical activity than monometallic selenides. Transition metal selenide electrodes for electrochemical studies are usually prepared with polymer binders by conventional slurry coating methods, which increases the dead volume of the active transition metal selenide surface and decreases the contact with the electrolyte. Therefore, transition metal selenides can be designed and prepared on a conductive substrate with an ideal porous network to obtain better charge storage performance. In this paper, NiMo precursor was firstly synthesized on a nickel foam substrate by a hydrothermal method, and then NiSe/Mo15Se19 electrode materials were prepared via in-situ selenation reaction of this precursor with Se powder. In addition, the effect of NiMo ratio on their electrochemical properties was also investigated.

Introduction The all-inorganic wide-band gap CsPbI2Br perovskite (1.92 eV) trades off stability and light absorption performance, showing a great application potential in tandem solar cells and flexible solar cells. However, its power conversion efficiency (PCE) and stability still need to be further improved. Usually, the CsPbI2Br perovskite films derived from solution process will inevitably generate various defects at interfaces or grain boundaries as non-radiative recombination centers for photogenerated carriers, and they are sensitive to water molecules to degrade, thus reducing the photovoltaic performance and stability of the devices. It was reported that the interface modification of functional cations (i.e., alkali metal ions, organic amine ions, etc.) and anions (i.e., halogen ions, acetic acid ions, etc.) had a positive effect on improving the efficiency and stability of perovskite solar cells (PSCs). In this paper, a modifier tetrabutylammonium hexafluorophosphate (TBAPF6) with both defect passivation and hydrophobic functions was used to modify the interface of CsPbI2Br/Carbon for the improvement of the PCE and stability of hole-free carbon-based CsPbI2Br PSCs with an architecture of indium tin oxide (ITO)/SnO2/CsPbI2Br/TBAPF6/Carbon. TBAPF6 as an ionic liquid with the Lewis base properties was used as a dopant or an interfacial modifier of perovskite films, which was conducive to passivating the defects of devices. The surface modification of CsPbI2Br perovskite films was carried out at different concentrations of TBAPF6, and its effect on the film quality of CsPbI2Br perovskite and the photovoltaic performance and environmental the stability (including wet and thermal stability) of CsPbI2Br PSCs devices was investigated. Methods Lead iodide (PbI2, 99.999%, in mass fraction, the same below, Advanced Election Technology Co., Ltd.), lead bromide (PbBr2, 99.999%, Advanced Election Technology Co., Ltd.), cesium iodide (CsI, 99.999%, Advanced Election Technology Co., Ltd.), tetrabutylammonium hexafluorophosphate (TBAPF6, 98%, Aladdin Co.), dimethyl sulfoxide (DMSO, analytical reagent, Sigma-Aldrich Co.), tin (IV) oxide colloid (SnO2, Alfa Co.), isopropanol (99.5%, Aladdin Co.), ITO-etched glass (square resistance 7-9 -/square, Advanced Election Technology Co., Ltd.), and conductive carbon paste (Huamin New Material Technology Co., Ltd.). 1.0 mol/L CsPbI2Br perovskite precursor was prepared via dissolving CsI, PbBr2, and PbI2 at a molar ratio of 1.0:0.5:0.5 in DMSO. The ITO-etched glass substrates were cleaned with ethanol, acetone, isopropanol, and ethanol under ultrasonication for 15 min and dried in an oven, and then treated with UV ozone for 25 min. The SnO2 colloid precursor was spin-coated onto ITO glass substrates at 3 000 r/min for 30 s and then put on a hot plate in ambient air at 150 ℃ for 30 min. After 10 min for UV ozone, 44 μL perovskite precursor solution was deposited on the SnO2 layer through a spin-coating process at 1 000 r/min for 10 s and then 3 000 r/min for 30 s in anitrogen-filled glove box. After the spin-coating process, the obtained films were placed on a hot plate at 40 ℃ for 3 min and then annealed at 150 ℃ for 5 min. Afterwards, 45 μL TBAPF6 solution in isopropanol (IPA) with different concentrations (i.e., 0, 0.5, 1.0 and 2.0 mg/mL) was spin-coated on the CsPbI2Br films at 4 000 r/min for 30 s and then annealed at 120 ℃ for 10 min, respectively. Finally, the carbon electrode was deposited on top of the device by a doctor-blading method and then the prepared device was completed after annealing at 120 ℃ for 20 min. The morphology of the absorber layers was observed by a model JSEM-5610LV field-emission scanning electron microscope (SEM, JEOL Co., Japan). The X-ray diffraction (XRD) pattern was recorded by a model AXS X-ray diffractometer (Bruker Co., Germany) with Cu Kα radiation (λ=1.54 -). The current density-voltage (J-V) curves of devices were obtained by a model Keithley 2400 source meter under an illumination of AM 1.5G (100 mW/cm2) with cell area controlled at 0.09 cm2 by a black metal mask. The ultraviolet photoelectron spectra (UPS) were determined by a model ESCALAB 250XI ultraviolet photoelectron spectroscope (Thermo Co., USA) and a model PHI 5 000 Versa Probe III (ULVAC-PHI. Inc., Japan), and the test light source energy was 21.22 eV. The UV-Vis absorption spectra were recorded by a model UV-3600plus spectrophotometer (Shimadzu Co., Japan) in a wavelength range from 300 to 800 nm at room temperature. The steady-state photoluminescence (PL) was obtained by a model FLS1000 UltraFast fluorescence spectrometer (Edinburgh Co., UK) with an excitation wavelength of 450 nm at room temperature. The time-resolved photolumine-scene (TRPL) spectra were obtained on a model Delta Flex fluorescence spectrometer (HORIBA Scientific Co., Japan) using a time-dependent single photon counting method. The electrochemical impedance spectroswpy (EIS) were carried out with a model PP211&CHI1030B electrochemical workstation under illumination with a bias at 0 V in a frequency range of 1 Hz-2 MHz. Results and discussion Based on density functional theory, the Gauss View and Gaussian were used to conduct molecular modeling and electrostatic potential simulation analysis for TBAPF6. The cation is a quaternary ammonium ion (TBA+) containing 4 butyl groups, and the anion is 6 fluorophosphate ion (PF6-). TBAPF6 has the Lewis base properties, in which nitrogen has some uncoordinated lone pair electrons, which can effectively passivate the uncoordinated Pb2+ through electrostatic action. TBA+ can interact with negatively charged defects such as Cs+ vacancies through ionic and hydrogen bonds. Since anion PF6- is negatively charged, positively charged defects (such as halogen vacancies) are passivated by electrostatic action, and fluorine atoms on the anion also play a hydrophobic role to a certain extent. The effect of TBAPF6 interface modifier on the surface morphology of CsPbI2Br perovskite films was analyzed by SEM. The surface morphology of the pristine sample is uneven and rugged. Clearly, there are many pinholes on the surface of the film and cannelures between the grains possibly due to the corrosion of water molecules on the grain boundaries. These characteristics are the main causes of leakage current. Compared with the pristine film, the surface morphology of TBAPF6-modified film is more smooth, uniform and dense. There are few pinholes on the surface and no cannelures between grains. Therefore, TBAPF6 modification can effectively improve the surface morphology of CsPbI2Br perovskite films to prevent the erosion of water molecules in air, and the dense microstructure is conducive to improving the photovoltaic performance and stability of the devices. The phase composition of CsPbI2Br perovskite films treated at different concentrations of TBAPF6 was analyzed by XRD. Clearly, all the samples have characteristic diffraction peaks with 2θ of 14.5° and 29.6°, corresponding to the planes (100) and (200) of perovskite phase. The characteristic peak intensity increases significantly with the increase of TBAPF6 concentration. When the concentration increases upto 1.0 mg/mL, the characteristic diffraction peak intensity reaches the maximum value. However, the characteristic peak intensity decreases when the concentration of TBAPF6 further increases. The pristine device has a PCE of 9.93%, with an open circuit voltage (Voc) of 1.16 V, a short circuit current density (Jsc) of 14.02 mA/cm2, and a fill factor (FF) of 60%. As TBAPF6 concentration increases from 0 to 1.0 mg/mL, the device with an architecture of ITO/SnO2/CsPbI2Br/TBAPF6/carbon exhibits the maximum PCE of 12.04%, with Voc of 1.24 V, Jsc of 14.60 mA/cm2, and FF of 67%. To test the repeatability, 30 devices based on different concentrations of TBAPF6 were set up. The overall PCE distribution of the modified device is significantly greater than that of the pristine device. The PCE distribution of the modified device at 0.5 mg/mL is mainly in a range of 11.0%-11.5%, and some can reach more than 11.5%. The PCE of 1.0 mg/mL modified device increases, mainly distributes 12%, which is the optimum overall distribution of PCE (i.e., 12.04%). The PCE of 2.0 mg/mL modified device is mainly distributed in a range of 11.0%-11.8%, which decreases slightly. Compared with the optimized device, the PCE of the pristine device is mainly distributed in a range of 7%-10%. Therefore, 1.0 mg/mL TBAPF6 is an optimal concentration of the interface modifier. The optical band gap (Eg) of the pristine and 1.0 mg/mL TBAPF6-modified CsPbI2Br perovskite films is 1.92 eV and 1.91 eV, respectively. The Fermi level (Ef) of the pristine and modified samples can be calculated as -5.23 eV and -5.25 eV, respectively, which drops from -5.23 eV to -5.25 eV before and after modification, and is closer to the valency band, indicating that CsPbI2Br perovskite film changes from N-type to P-type semiconductor. The valence maximum (Ev) moves up by 0.05 eV, which reduces the energy level shift of the CsPbI2Br/carbon electrode interface, thus effectively reducing Voc loss and promoting the hole transfer between perovskite and carbon electrode. At last, in the humidity environment of 35%-40%, 80% of the initial efficiency of the optimal 1.0 mg/mL TBAPF6 modified device is maintained after 16 h, and in air at 85 ℃ after 72 h, 70.2% of the initial efficiency is maintained, indicating that the moisture and thermal stability are greatly improved, compared with the pristine device. Conclusions The results showed that TBAPF6 interface modification agent could effectively passivate the surface defects of CsPbI2Br perovskite films, reduce the non-radiative recombination of carriers, improve the energy level arrangement of CsPbI2Br/carbon electrode interface, and promote the carrier transport. It played a hydrophobic role. Thus, the PCE and stability of all inorganic hole-free carbon-based CsPbI2Br PSCs were improved. The microstructure of TBAPF6 modified CsPbI2Br films was more smooth and dense with a higher crystallinity. The Eg decreased slightly, and the light absorption capacity increased. The Ef was closer to the valence band, indicating the transition from N-type to P-type semiconductor. The upward movement of Ev was conducive to the hole transfer at the CsPbI2Br/carbon electrode interface. The steady-state photoluminescence intensity was more intense, indicating a longer average carrier lifetime. The decrease of dark current and the increase of recombination resistance indicated that the defects of the modified device were effectively passivated, and the probability of carrier non-radiative recombination was reduced. The molecular modeling and electrostatic potential simulation showed that PF6- of TBAPF6 passivated the positively charged halogen vacancies through electrostatic action, while TBA+ passivated the negatively charged Cs+ vacancies through ionic and hydrogen bonding. Some functional groups with long alkyl chains and fluorine atoms effectively prevented the intrusion of water molecules in air, thus improving the wet stability of the devices. The optimal 1.0 mg/mL TBAPF6 modified device exhibited a champion PCE of 12.04%, with Voc of 1.24 V, Jsc of 14.60 mA/cm2, and FF of 67%, demonstrating the superior moisture and thermal stability, compared with the pristine device.

Introduction Graphite carbon nitride (g-C3N4) composite manganese cobalt based prussian blue (MnCoPBA/g-C3N4) catalyst was prepared by a self-assembly method, a coprecipitation method and a high-temperature annealing method. The catalyst prepared was used to analyze the catalytic degradation of rhodamine B (RhB) in the SR Photo Fenton like system. The MnCoPBA/g-C3N4 catalyst has a degradation efficiency of 96% for RhB within 10 minutes and exhibits a good cyclic stability. The catalyst also has a good catalytic degradation performance for RhB at pH values of 1-9, indicating a superior applicability in acidic, neutral, and weakly alkaline environments. Methods Catalytic performance test is an important indicator for evaluating MnCoPBA/g-C3N4 catalysts. A certain amount of MnCoPBA/g-C3N4 (0.05-0.20 g/L) catalyst was added into 100 mL of RhB (5-20 mg/L) solution. The suspension was stirred magnetically for 30 min to achieve adsorption-desorption equilibrium. Subsequently, 3 mL of suspension was taken and centrifuged to add the supernatant to a colorimetric dish. The data were recorded using a UV spectrophotometer. Subsequently, in a xenon lamp (350 W, >420 nm), a certain amount of PMS (5-60 mg/L) was added and 3 mL of suspension was treated by centrifugal force every 5 minutes to obtain the supernatant. The data were recorded in a UV spectrophotometer until the solution become colorless and the UV absorption spectrum data unchanged. The cyclic stability of catalysts is an important indicator for evaluating their practical application. To reduce the possible experimental errors caused by catalyst loss in the cyclic experiment, the cyclic experiment was designed as a parallel experiment, where each cyclic experiment was conducted independently. Sampling was no longer conducted during the n-1st cycle before the n-th cycle experiment, and sampling was conducted again during the n-th cycle experiment. The experimental operation was the same as the catalytic experiment. The waste liquid was collected and centrifuged, and the product was washed and dried with deionized water and ethanol. The UV spectrophotometer was used to test the data and collect records. Results and discussion Based on the analysis of the results, a possible catalytic degradation mechanism for the Photo-Fenton like system was proposed. The photocatalytic excitation of g-C3N4 semiconductor material in the Photo-Fenton like system generates photo- generated electrons and hole pairs, which are captured by metal ions in MnCoPBA and undergo a reduction reaction, achieving an effective separation of photo-generated carriers in the photocatalytic system and overcoming the defect of high photo-generated carrier recombination efficiency in g-C3N4 photocatalytic system. Simultaneously achieving a closed loop cycle of Fe(III)/Fe(II), Mn(III)/Mn(II) and Co(III)/Co(II) ions in the Fenton like system is obtained. An energy support for the Fenton like system is provided. The rate limiting step is broken through, and the defect of ion deficiency in the Fenton like system is overcome. Also, photo-generated electrons can directly activate PMS to generate SO4·-, triggering chain reactions to produce ·OH, and reacting with O2 to form ·O2-. Various strong oxidizing radicals efficiently degrade RhB, thus improving the catalytic degradation performance. Conclusions MnCoPBA/g-C3N4 catalyst was prepared by a coprecipitation method combined with a high-temperature calcination method. The effect of catalytic condition on the catalytic degradation performance of RhB was investigated. The results indicated that when MnCoPBA/g-C3N4-2.5 had the optimal catalytic degradation efficiency for RhB under the optimum condition (i.e., the catalyst dosage of 0.1 g/L, RhB concentration of 10 mg/L, PMS dosage of 0.15 g/L, and pH values of 1-9). The catalytic degradation mechanism indicated that Mn and Co metal ions in MnCoPBA acted as mediators for photocatalytic and the Fenton like connections, capturing photo-generated electrons to slow down the rate of photo generated electron hole recombination. Also, the reduced metal ions could promote the Fenton like reaction to decompose PMS, producing the more intense oxidizing free radicals and accelerating the catalytic degradation of RhB. The catalytic degradation efficiency of RhB was 90% within 2 min, and 96% within 10 min. In addition, the catalyst also exhibited a good cycling stability.

Introduction Photocatalytic oxidation degradation of cyanide is an effective technology to treat cyanide wastewater. TiO2/SiO2 is a common catalyst. A preliminary research indicates that the pore structure of SiO2 has a certain influence on the degradation of cyanide and the removal of zinc and copper. If TiO2 particles are only loaded on the surface of mesoporous SiO2, the contact between the surface of SiO2 and the target substance in wastewater is reduced, thus affecting its adsorption performance. In this study, a macroporous SiO2 was prepared, and TiO2 particles were loaded on the surface and in three-dimensional interconnected channels of SiO2, thus increasing the adsorption sites on the surface of SiO2 and improving the adsorption performance of target pollutants, and enhancing its efficiency of treating cyanide in wastewater. Methods Gravity self-assembled polystyrene microspheres (PS) were used as hard templates, impregnated in silica sol for 8.0 h, dried in an oven at 60 ℃, and roasted in a Muffle furnace at 550 ℃ for 10 h to obtain macroporous SiO2. SiO2/TiO2 precursors were prepared by a sol-gel method and roasted at 500 ℃ for 90 min. SiO2/TiO2 composites with a three-dimensional interconnected macroporous structure were prepared. The wastewater and materials were placed and mixed in a beaker in a certain proportion. After stirring magnetically for a period of time, a small air pump was used to pump air into the bottom of the beaker at room temperature, and a high-pressure mercury lamp was used as the light source for photocatalytic oxidation of the wastewater. The effects of TiO2 particle loading mass, catalyst dosage, catalytic time, adsorption time on the treatment of cyanide wastewater were investigated. N2 adsorption-desorption, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR) and other characterization techniques were used to determine the structural characteristics of the material and its adsorption-catalytic degradation mechanism. Results and discussion PS presents a monodisperse, independent and spherical structure with a particle size of 1.65 μm. PS templates are arranged in an orderly manner, independent of each other but closely connected, and they do not show a large continuous structure. SiO2 is a three-dimensional ordered macroporous structure with a pore size of 1.2 μm, which is smaller than the diameter of microspheres, indicating that the skeleton structure shrinks during the roasting process. SiO2 particle is broken mainly because of mechanical grinding. The long distance of the channels is orderly, the large holes are uniform and interconnected through small holes. The sizes of the small holes are 170-220 nm, the holes are formed due to the accumulation of microspheres. TiO2 particles are fragmented and loaded on the concave surface of SiO2. The particle size of TiO2 is uneven, and smaller than the pore size of SiO2. TiO2 particles are evenly dispersed on the surface of SiO2 or in the physical structure of the cavity, which eliminates the agglomeration of TiO2. N2 adsorption-desorption test shows that the SiO2/TiO2 material has a large pore structure, and the specific surface area is increased by 5 times, compared with TiO2 nanoparticles. The thermogravimetric curve shows that the materials have less weight loss at 250-800 ℃. The X-ray diffraction pattern of the material shows that the diffraction peak intensity of SiO2 loading with TiO2 particles decreases. The experimental results show that the degradation efficiency of total cyanide and the removal efficiencies of copper, iron and zinc are 98.79%, 99.10%, 100.00% and 92.26%, respectively, under the optimum conditions (i.e., 10% of TiO2 particle loading mass, 0.35 g of the material mass when treating 100 mL cyanide wastewater, 1.0 h of dark adsorption and 4.0 h of illumination time). The material was regenerated in a sulfuric acid solution by ultrasonic treatment. Under the same experimental conditions, the total cyanide degradation efficiency is reduced by 4.95% after three catalytic cycles, indicating that the material has strong stability and reusability. The XRD results before and after adsorption-catalysis show that ZnO, CuSCN, Cu2Fe(CN)6 and Fe2O3 are adsorbed on the surface of the material. The FTIR results show that a characteristic peak of C≡N appears on the surface of the material after 1-h adsorption and a characteristic peak of NO3- appears after 4-h catalysis. The EDS of the material after 1-h adsorption shows that cyanide is adsorbed on the surface of the material, and metal ions are uniformly distributed on the surface of the material. The EDS of the material after 4-h illumination shows that the metal content is higher than that after 1-h adsorption, and the distribution of Si and Ti is uniformly crossed. The results of free radical quenching experiment show that electron capture by oxygen is the main factor to improve the catalytic effect. Conclusions Macroporous SiO2/TiO2 materials were prepared by PS self-assembly template, impregnation, roasting and loading, which were used to treat cyanide wastewater. Under optimal experimental conditions, the degradation efficiency of total cyanide and the removal efficiencies of copper, iron and zinc were 98.79%, 99.10%, 100.00% and 92.26%, respectively. The three-dimensional ordered pore structure of macroporous SiO2 made TiO2 particles evenly dispersing on its surface and inside the cross-linked pore. The mechanism indicated that the cyanide was degraded into non-toxic nitrogen oxides and carbon oxides, and the metals were removed by precipitation.

Introduction Hydrogen peroxide (H2O2) is an important chemical that can be utilized as oxidant and fuel. Photocatalytic technology based on semiconductors can produce H2O2 from water and oxygen with sustainable solar energy as a sole energy input, which is a promising approach for industrial application. Nevertheless, the photoactivity of the common catalysts (i.e., graphitic carbon nitride, metal oxide, metal-organic frameworks, etc.) is low due to the poor utilization of solar light, easy recombination of electron-hole pairs, small quantity of reactive sites and weak redox ability. Developing efficient photocatalytic systems thus becomes an urgent target. Metal sulfides can be classified to single metal sulfide (i.e., CdS, In2S3, etc.), bimetallic sulfide (i.e., ZnIn2S4、CdIn2S4, etc.) and trimetallic sulfide (i.e., Cu2ZnSnS4). Sulfides exhibits the suitable band structures that can harness visible light and possess the proper redox capability. Meanwhile, the high structural symmetry enables them ultrafast charge carries transportation. The band structure of the semiconductor is a prerequisite both for optical absorption and redox ability. For photocatalytic H2O2 production, oxygen reduction reaction (ORR) and water oxidation reaction (WOR) channels can synergistically achieve the maximum activity. The ORR requires a potential that is more negative than -0.33 V vs. normal hydrogen electrode (NHE). The WOR needs a potential that is more positive than +1.78 V vs. NHE. The larger bandgap can induce the limited photon absorption. Thus, modulating the band structure of the metal sulfide through changing the metals ratio is an effective strategy to boost the photoactivity. Methods InxSn5-xS8 samples were prepared through a hydrothermal approach. A certain amount of InCl3·4H2O and SnCl4·5H2O were dissolved into deionized water and then added L-Cysteine into the solution. Thereafter, the suspension was treated by a hydrothermal method at 180 ℃ for 24 h. In2S3 and SnS2 were prepared by the same procedure without the addition of SnCl4·5H2O or InCl3·4H2O. The XRD patterns were characterized by X'Pert3MRD. The Raman spectra were obtained by LabRAM HR Evolution with 532 nm laser. The morphology structure was detected by a modelGemini SEM 500 scanning electron microscope and a modelJEM-2100 transmission electron microscope. The specific surface area and pore size were analyzed by a model ASAP2460BET instrument. The XPS spectra were obtained by an X-ray photoemission spectroscope with Al Kα excitation. The ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) was determined by an ultraviolet-visible absorbance spectroscope. The photoluminescence (PL) and time-resolved photoluminescence (TR-PL) spectra were collected on Horiba Fluorologat 375 nm. The transient photocurrent, electrochemical impedance spectra and Mott-Schottky plots were measured on a modelDH7000 electrochemical workstation. Photocatalytic H2O2 production was evaluated in a sealed three-neck round bottom flask with the mixture of deionized water and isopropanol under visible light illumination (λ≥420 nm). After purging with oxygen for 30 min, the reaction system was placed under Xenon lamp and then extracted the suspension at certain time interval. The concentration of H2O2 was estimated by iodometry methods. The reaction pathway was investigated by scavengers experiment and changing the gases. Results and discussion The as-prepared In4SnS8 nanomaterials have a typical cubic structure with the flower-like morphology that is composed of ultrathin 2D nanosheets with the thicknesses of 5-10 nm. Apristine In2S3 presents a 3D solid sphere with the diameters of 4-7 μm, and SnS2 has a plate-like structure with a lateral size of ~1 μm. The hierarchical structure of In4SnS8 endow it with the maximum specific surface area of 648.056 m2/g, benefiting for the surface photoreaction. Nevertheless, pure In2S3 and SnS2 possess the small specific surface area of 70.631 m2/g and 30.411 m2/g. According the UV-Vis DRS, the bandgap of In2S3, In9SnS16, In4SnS8, In3Sn2S8, In2Sn3S8 and SnS2 is 2.03, 1.98, 2.16, 1.87, 1.80 and 1.78 eV, respectively. According to Mott-Schottky (MS) plots, their conductive band (CB) potential is calculated to be -0.24、-0.26、-0.39、-0.24、-0.22 and -0.31 eV, respectively. Their corresponding valance band (VB) is thus 1.79、1.72、1.77、1.63、1.58 and 1.47 eV, respectively. CB and VB both for In4SnS8 can meet the requirement of ORR and WOR channels for H2O2 evolution. While other photocatalysts can only undergo the single pathway of direct two-electron reduction reaction. Under visible light illumination, In4SnS8 nanomaterials have the maximum photoactivity with a H2O2 production rate of 1.936 μmol·L-1·min-1, which is 5.2- and 71.7- fold greater than that of pristine In2S3 and SnS2. They also present a good stability after 4 cycles experiments. The photo-reactivity of In9SnS16, In3Sn2S8 and In2Sn3S8 dramatically decreases in N2 atmosphere, indicating that ORR is a dominant pathway in the three systems above. For In2S3 and In4SnS8, the concentration of H2O2 is decreased by 30%-50% in N2, implying that WOR pathway is also responsible for H2O2 evolution. The trapping agent experiment demonstrates that 2e- WOR, direct one-step two-electron ORR and indirect sequential two-step single-electron ORR all exist in In4SnS8 system. Among all the photocatalysts, In4SnS8 exhibits the maximum photocurrent of 0.25 mA-cm-2, the minimum interfacial electron transfer resistance, the lowest photoluminescence signal and the shortest charge carrier lifetime, indicating that the electron-hole pairs in In4SnS8 can efficiently separate and migrate to the surface, then boost the photo-reactivity. Conclusions A series of InxSn5-xS8 materials were prepared through a hydrothermal process. In4SnS8 nanomaterials exhibited the superior photocatalytic performance and its visible-light-driven H2O2 production rate was 1.936 μmol·L-1·min-1, which was 5.2- and 71.7- fold greater than that of pristine In2S3 and SnS2. The band structure analysis demonstratedthat the bandgap and band position of InxSn5-xS8 could be controlled by In/Sn molar ratio. In4SnS8 had the proper bandgap of 2.16 eV and its CB and VB lied at -0.39 and 1.77 eV, thus satisfying the potential of two independent pathways for H2O2 generation, i.e., oxygen reduction reaction and water oxidation reaction. In addition, the hierarchical nanoflower-like structure of bimetallic In4SnS8 nanomaterials could also provide the more reactive sites, which were responsible for the improved photocatalytic performance.

Introduction Photocatalysis is one of the most potential techniques to solve energy crisis and environmental pollution problems, and how to obtain photocatalysts with a greater catalytic efficiency is always a research hotspot in the photocatalysis. The heterogeneous photocatalyst is proved as a promising efficient strategy to address this issue. The heterojunction photocatalysts can be utilized to expedite the separation of photo-induced electron-hole pairs. In particular, Z-scheme heterojunctions exhibit the dual advantages of suppression of recombination of electron-hole pairs, reserving a high redox ability for both semiconductors. The visible-light-driven photocatalysts Bi2WO6 and g-C3N4 exhibit a poor photocatalytic activity because of their fast recombination of photo-generated carriers. It is advisable to choose the g-C3N4 and Bi2WO6 to form an all-solid-state Z-scheme photocatalytic system to obtain the higher photocatalytic performance. It is reported that carbon materials often put up a low work function when they modify the electronic and optical properties of hybrids. In this paper, a novel amorphous carbon/g-C3N4/Bi2WO6 (C/C3N4/Bi2WO6) Z-scheme heterojunction with a visible light response was synthesized. The performance of C/C3N4/Bi2WO6 was measured by photo-degrading TC under the visible light (i.e., ≥420 nm). The as-synthesized composites played an enhanced visible-light photoactivity than the pure g-C3N4 and Bi2WO6. Furthermore, the possible mechanism of the enhanced performance of the C/C3N4/Bi2WO6 composite was discussed. Methods All reagents with analytical grade were used without further purification. First, the C/C3N4 sample was prepared by a milling/roasting method. When a mass ratio of glucose to urea was 0.1%, the as-fabricated C/C3N4 composite exhibited an optimum photocatalytic performance. The C/C3N4/Bi2WO6 nanocomposites were prepared through a facile hydrothermal method. The obtained products were denoted as C/C3N4/Bi2WO6-1, C/C3N4/Bi2WO6-2, C/C3N4/Bi2WO6-3 and C/C3N4/Bi2WO6-4, when the mass ratios of C/C3N4:Bi2WO6 were 1.0:0.1, 1.0:0.4, 1.0:0.7 and 1:1, respectively. For the comparison, a pure Bi2WO6 sample was synthesized through the same procedur without introducing C/C3N4. The crystal structure was detected by X-ray diffraction with Cu Kα radiation (λ=0.154 06 nm). The morphology and microstructures of the synthesized samples were investigated on high-resolution transmission electron microscopy (HRTEM). The ultraviolate-visible (UV-Vis) diffuse reflectance spectra (DRS) were taken on UV-Vis-near infrared (NIR) spectrophotometry with BaSO4 as a reference. The chemical composition and chemical state of C/C3N4/Bi2WO6 were analyzed by X-ray photoelectron spectroscopy (XPS) with Al Kα excitation source. The photocurrent response under simulated solar light irradiation was recorded with an electrochemical workstation in a sandwich-type configuration, a Pt slice as a counter electrode, a saturated calomel electrode (SCE) as ae reference, and 0.1 mol/L Na2SO4 solution as electrolyte. A 300 W xenon arc lamp equipped with a simulated solar light filter calibrated to 100 mW/cm2, which was measured with a radiometer, employed as a light source. Electrochemical impedance spectroscopy (EIS) Nyquist plots were obtained at 0.6 V with a small alternating current amplitude of 5 mV in a frequency range of 0.1 Hz-105 Hz. The photocatalytic activity of the C/C3N4/Bi2WO6 sample was determined by degrading the simulated pollutant tetracycline (TC). In the experimental setup, a 300W Xe lamp was employed as a light source and a 420 nm cut-off filter was used to provide only visible-light irradiation. The photocatalyst of 100 mg was added to 100 mL of TC solution (1×10-4 mol/L). Before being irradiated, the suspensions were magnetically stirred in the dark for 3 h to reach the adsorption-desorption equilibrium between photocatalysts and TC. The solution was exposed to visible light irradiation under magnetic stirring. The aliquot of 3 mL was collected from the suspension and centrifuged immediately for every 10 min. The degradation of TC was monitored by checking the absorbance at 357 nm using an UV-Vis spectrometer. Results and discussion The degradation ratios of TC are 25% and 50% after irradiation for 240 min by visible-light in the presence of g-C3N4 and Bi2WO6, respectively. Furthermore, it is clear that the C/C3N4 composite exhibits a higher photocatalytic activity in the degradation of TC than the g-C3N4 sample. All the C/C3N4/Bi2WO6 photocatalysts exhibit better photocatalytic performance than the C/C3N4 composite and Bi2WO6 under the same experimental condition. Specifically, the photocatalytic activities of C/C3N4/Bi2WO6 nanocomposites gradually improve as Bi2WO6 ratio increases, and the photocatalytic performance is optimal when the mass ratio of C/C3N4:Bi2WO6 is 1.0:0.7. The photocatalytic activities decrease when Bi2WO6 ratio continues to increase. Hence, the as-prepared C/C3N4/Bi2WO6-3 nanocomposite has the optimum photocatalytic performance, and the maximum degradation efficiency of 97.1% is attained after the irradiation for 240 min. The improved photocatalytic performance of C/C3N4/Bi2WO6 composites is ascribed to the formed amorphous carbon-mediated Z-scheme heterojunction. When the heterojunction C/C3N4/Bi2WO6 is exposed to visible light (λ>420 nm), the electrons generated from CB of Bi2WO6 can transfer to the VB of g-C3N4 via the amorphous carbon mediator due to the good electrical conductivity of amorphous carbon, and then annihilate with the holes induces from the VB of g-C3N4, the photo-induced carriers can be effectively separated. Conclusion We constructed Z-scheme C/C3N4/Bi2WO6 heterojunction photocatalyst with enhanced photocatalytic activities in degradation of TC. When the mass ratio of C/C3N4:Bi2WO6 was 1.0:0.7, the as-fabricated C/C3N4/Bi2WO6 heterojunction exhibited an optimum photocatalytic performance. The mechanism illuminated that the efficient separation of charge carriers generated by the amorphous carbon-mediated Z-scheme mechanism mainly contributed to the improved photocatalytic performance of C/C3N4/Bi2WO6 heterojunction. We anticipated that the results of this work could favor the application of solar energy in water pollution.

Introduction Dyeing wastewater is one of environmental pollutions, having a serious threat to the environment and human-being health. Therefore, the purification of dyeing wastewater becomes a challenge. Among various methods for treating dyeing wastewater, photocatalysis is developed as an efficient environmental pollution control technology due to its mild reaction conditions, sustainable driving energy sources, and no secondary pollution after the reaction. Zinc tungstate (ZnWO4) as a semiconductor photocatalyst material with stable physical and chemical properties has a promising application potential in photocatalytic removal of environmental pollutants. However, ZnWO4 has a wide bandgap and a low migration efficiency of carriers, resulting in unsatisfactory photocatalytic intrinsic activity. Therefore, researchers attempted to optimize the photocatalytic performance of ZnWO4 via regulating its morphology, size and crystallinity. Sonochemical method is a highly concerned method for synthesizing nanomaterials. Under ultrasonic cavitation conditions, the physical and chemical environment of the reaction system will undergo significant changes, i.e., the instantaneous generation of high temperature, high pressure, and strong shock waves, which are beneficial for strengthening the fracture of chemical bonds and the generation of new chemical bonds, thereby regulating the morphology and structure of material. In this work, ZnWO4 with oxygen defects nanomaterials were prepared by a sonochemistry-assisted hydrothermal method, and the influence of sonochemical treatment time on the photocatalytic activity of ZnWO4 was investigated as methylene blue was used as a target pollutant. Methods ZnWO4 with oxygen defects nanomaterials were prepared by a sonochemistry-assisted hydrothermal method. In the preparation, 0.297 g Zn(NO3)3·6H2O was dissolved in 8 mL distilled water under constant stirring, to obtain solution A. Also, 7 mL distilled water containing 0.392 g Na2WO4·2H2O was added in dropwise to solution A and mixed by stirring for 30 min. Afterwards, LC-UP-400 ultrasonic signal connected Φ10 luffing rod (selecting ultrasonic power was 50%, ultrasonic treatment for 2 s, and stay for 2 s) was used to irradiate the white suspension for 1h, and then the suspensions were put into Teflon-lined autoclave, sealed and maintained at 140 ℃ for 20 h. After cooling to room temperature, the product was washed with distilled water and ethanol for several times. The final products were obtained after drying at 60 ℃ for 12 h. The samples of ZnWO4 nanomaterials treated at different ultrasonic treatment time (X min) were named as ZnWO4-X. Results and discussion The photocatalytic activity of as-prepared samples was evaluated by MB photocatalytic removal in 10 mg/L of MB dyeing wastewater. Herein, MB dyeing wastewater under light illumination without the addition of photocatalysts as a blank test for comparison, having an unsatisfactory photoreduction effect. After 40 min of illumination, ZnWO4 has a weak photocatalytic activity for MB photodegradation, i.e., 52% of MB is photocatalytically degradated by pure ZnWO4. However, the induction of oxygen vacancy defects results in an enhanced photocatalytic performance for MB removal over ZnWO4-5 min. The optimized ZnWO4-5 min displays a superior photocatalytic activity for MB removal, which can remove 95.0% of MB after 40 min of illumination. The kinetic of MB photodegradation was further analyzed by plotting the -ln(c/c0) as a function of irradiation time. The calculated rate constant k of ZnWO4-5min is 0.067 min-1, which is 4.5 times greater than that of ZnWO4. The reusability of ZnWO4-5min was investigated by performing 5 consecutive cycles for MB photodegradation. The results show that the photoreduction efficiency maintains at a high level (i.e., >90%) after five cycling experiments, indicating the superior stability and huge potential value of ZnWO4-5 min for the treatment of dyeing wastewater. The oxygen vacancy defects induced by ultrasound cause the lattice contraction within ZnWO4, which is beneficial for optimizing electronic structure, exposing more catalytic active sites, broadening the photocatalytic response range, and improving the migration efficiency of photogenerated carriers, thereby significantly enhancing the photocatalytic degradation performance of ZnWO4 in dyeing wastewater. Conclusions ZnWO4 with oxygen defects nanomaterials were prepared by a sonochemistry-assisted hydrothermal method, and the influence of sonochemical treatment time on the photocatalytic activity of ZnWO4 was investigated when MB was used as a target pollutant. The results showed that sonochemical treatment could induce the formation of oxygen vacancy defects in ZnWO4 nanoparticles, thereby optimizing electronic structure, exposing more active sites, broadening the light response range and improving the transfer efficiency of photogenerated carriers, thus enhancing the photocatalytic degradation performance of ZnWO4 for dyeing wastewater. The optimized ZnWO4-5 min displayed a superior photocatalytic activity for MB removal, which removed 95.0% of MB after 40 min of illumination. The calculated rate constant k of ZnWO4-5 min was 0.067 min-1, which was 4.5 times greater than that of ZnWO4. Furthermore, ZnWO4-5min displayed a superior photocatalytic stability, and the photoreduction efficiency maintained at a high level (>90%) after five cycling experiments. This indicated that sonochemically-induced oxygen vacancy defects be an effective method to improve the photocatalytic performance of ZnWO4. This work can provide some ideas for the preparation of high-performance semiconductor photocatalytic materials for the treatment of dyeing wastewater.

Introduction Antimony mainly exists in the oxidation states of Sb(III) and Sb(V), where Sb(V) is the predominant species and exists as Sb(OH)6- in oxidic environments. The environmental contamination of Sb has received much attention due to the toxicity and adverse effect on the hematic, gastrointestinal, and respiratory systems of human-beings. Treatment of antimony-contaminated water is a prominent topic. Adsorption is considered as one of the most attractive and practical approaches for Sb remediation in aqueous media because of its operation simplicity, cost-effectiveness, high efficiency, and less sludge production. Magnetite (Fe3O4) as one of the most promising magnetic materials is extensively investigated. However, some previous studies showed that the removal capacity and reactivity for pollutants of the iron-based magnetic nanoparticles are size dependent. A high surface free energy results in a greater aggregation for nanoparticles. The formation of aggregates can decrease the surface area of the magnetic nanoparticles, thereby restricting the treatment performance for contaminants. Recent technologies are developed using some porous materials as mechanical supports to enhance the dispersibility of magnetic nanoparticles. Herein, acid-treatment sepiolite was prepared as support materials, and acid-sepiolite supported magnetite nanocomposite powder was obtained for Sb(V) adsorption. In addition, the effects of initial pH value, reaction time, initial mass concentration of Sb(V), adsorbent dosage, and coexisting ions (SO42-, Ca2+, Mg2+, Fe3+, and humic acid) on the adsorption of Sb(V) were also investigated. Methods For acid-treatment of sepiolite, all chemical reagents used were of analytical grade. Acid-treatment sepiolite was firstly prepared, i.e., 1.0 g of sepiolite was added into 100 mL of 1.2 mol/L HCl solution and reacted at 60 ℃. After 12 h of stirring, the suspension was centrifuged, and washed with deionized water until the pH value was 7.0. Finally, the precipitate was collected and dried at 50 ℃. For preparation of acid-sepiolite supported magnetite nanocomposite powder, the acid-sepiolite supported magnetite nanocomposite powder was prepared by a microwave-assisted reflux method. In the synthesis process, 1 mmol (0.27 g) of FeCl3·6H2O and 0.5 mmol (0.10 g) of FeCl2·4H2O were dissolved in 20 mL of ethylene glycol, and then 0.25 g of acid-treatment of sepiolite was dispersed in the solution under ultrasonication to form solution A. Afterwards, 0.16 g (4 mmol) of NaOH was dissolved in 3 mL of deionized water to form solution B. Solution B was introduced into solution A in a 100 mL round-bottomed flask. Subsequently, the round-bottomed flask with the reactants was equipped on the microwave reactor, and irradiated for 20 min at 80% of the full power (640 W). After cooling to room temperature, the precipitates were collected and washed with alcohol for several times, and finally dried in a vacuum oven at 60 ℃ for overnight. A stock solution containing Sb(V) (600.0 mg/L) was prepared via dissolving K[Sb(OH)6] with deionized water, and a series of solutions used were prepared via diluting the stock to the desired concentrations-actual concentrations measured by inductive coupled plasma-atomic emission spectroscopy (ICP-AES). In a typical adsorption run, 50 mg of adsorbent was added into 50 mL of solution containing 60.0 mg/L Sb(V) with constantly stirred at 180 r/min at 25 ℃. The initial pH of the solution was adjusted with HCl and/or NaOH solutions before the addition of adsorbent. The effect of pH value, contact time, adsorbent dosage, and initial concentration of Sb, coexisting anions (Ca2+, Fe3+, Mg2+, SO42-, and humic acid) on the Sb adsorption were investigated in the same procedures. After adsorption, the residual level of Sb in solution was determined by ICP-AES. Results and discussion After the microwave irradiation, the prepared Acid-Sep-Fe3O4 composite powder maintains a nanorod-like structure of sepiolite, and massive magnetite nanoparticles appear on the surface of the powder. The corresponding energy dispersive X-ray spectroscopy and X-ray diffraction patterns indicate the preparation of Acid-Sep-Fe3O4 composite powder. The BET surface area and total pore volume of the composite powder are 269.00 m2/g and 0.96 cm3/g, respectively. Moreover, the magnetic saturation of the powder is 10.4 emu/g. The obtained composite powder has high surface area and good magnetic nature, which are beneficial for Sb(V) adsorption and adsorbent recovery. The Sb(V) adsorption by nanocomposite powder is dependent on the pH value with the maximum adsorption under acidic conditions and decreases with the increase of pH value. The adsorption percentage of Sb(V) increases with the increase of adsorbent dosage, and over 85% of Sb(V) is removed at the adsorbent dosage of 50 mg/50 mL. The prepared powder has a great adsorption rate to Sb(V) due to its high specific surface area. 81.4% of Sb(V) is adsorbed after 240 min of agitation. Moreover, the maximum removal capacity of the powder toward Sb(V) is 92.3 mg/g, which is greater than that of the nanoscale magnetite (79.2 mg/g), acid-treatment sepiolite (42.3 mg/g), and raw sepiolite (35.6 mg/g). The results indicate that the adsorption capacity of magnetite toward Sb(V) is enhanced after the support of acid-treatment sepiolite. The presence of SO42-, Ca2+, Mg2+, and humic acid has a negligible effect on the adsorption of Sb(V), while the Sb(V) sorption process is enhanced with the addition of Fe3+, due to the formation of Fe precipitates. The adsorption behavior of nanocomposite powder toward Sb(V) fits the pseudo-second-order kinetic model and the Langmuir model. The XPS analysis reveal that the adsorption of composite powder toward Sb(V) mainly occurs via electrostatic interaction followed by chemical reactions. Conclusions Acid-treatment sepiolite supported Fe3O4 nanocomposite powder was prepared via acid-treatment of sepiolite and microwave-assisted reflux method with a natural nanorod-like sepiolite. The prepared composite powder exhibited a superior adsorption capacity toward Sb(V) with the maximum adsorption capacity of 92.3 mg/g, which was greater than that of the unsupported Fe3O4 nanoparticles (i.e., 79.2 mg/g), acid-treatment sepiolite (i.e., 42.3 mg/g), and raw sepiolite (i.e., 35.6 mg/g). The adsorption behavior of Sb(V) followed the pseudo-second-order kinetic model and Langmuir model. The Sb(V) adsorption by magnetic nanocomposites mainly occurred via electrostatic interaction followed by chemical reactions. The prepared acid-treatment sepiolite supported Fe3O4 nanocomposite powder could be used as an ideal adsorbent for Sb(V) due to the facile fabrication, efficient adsorption performance and easy magnetic separation.

Introduction 1-3 type piezoelectric composites are widely used to fabricate high-sensitivity and broadband ultrasonic transducers due to the advantages like a low dielectric constant, a low acoustic impedance, and a high electromechanical coupling coefficient. However, some conventional manufacturing methods such as the cut-and-fill method, the arrangement-casting process, and the injection molding method have challenges to emanate from geometric complexity and structural integrity. Stereolithography technology based on the mask projection approach is an alternative method for manufacturing piezoelectric ceramics with a rapid prototyping and a high precision. Lead-free barium titanate BaTiO3 (BTO) ceramics are widely investigated for piezoelectric sensors and dielectric capacitors applications because of their high dielectric constant, good piezoelectric coefficient, and favorable electromechanical coupling coefficient. In this work, digital light processing (DLP) technology was used to manufacture barium titanate based 1-3 type piezoelectric composites. The influence of piezoelectric phase volume fraction (i.e., 20%-45%) on the micrograph, acoustic impedance and electrical properties of BTO 1-3 composites was investigated. Methods The printed ceramic slurries with 84% (in mass fraction) BTO content, including BTO powders (d50=500 nm), dispersant, and liquid photopolymers, were mixed by a model ZYMC-180V homogenizer (ZYE) at 2 000 r/min for 90 s. The printed models were built by a software named Computer-Aided Design (CAD) and sliced to a thickness of 7 μm. The piezoelectric pillars (150 μm) with a support were printed layer by layer to form the physical models (i.e., Soon solid, TC-Ⅱ). The printed samples were washed in alcohol by aultrasonic cleaner to remove the residual slurry. Afterwards, the green bodies were treated by a two-step heating treatment, i.e., a debonding process and a sintering process, to obtain the piezoelectric phase structures. Two-time vacuum treatments below -100 kPa were introduced to remove air bubbles in epoxy resin (EPO-TEK301) that filled in the kerfs between piezoelectric pillars (width of 120 μm, height of 330 μm). The samples filled with epoxy resin were heat treated at 60 ℃ for 12 h and then coated with gold electrodes. The BTO 1-3 composites were polarized in an electric field of 4 kV/mm in silicone oil. The microstructures of samples were characterized by a model TM4 000 Plus scanning electron microscope (Hitachi Co., Lted., Japan). The dielectric constant εr, dielectric loss δ, and frequency impedance spectrum were measured by a model 6500B precision impedance analyzer (Wayne Kerr Co., Ltd., UK). Piezoelectric constant d33 was determined by a model ZJ-3A piezo-d33 meter (Institute of Acoustics, Chinese Academy of Sciences, China). The ferroelectric hysteresis loop was measured by a model 2000E ferroelectric analyzer (aixACCT Co., Germany). Results and discussion The uniform piezoelectric pillars with a width of (150±10) μm are printed through optimizing the slurry formula, and the minimum distance between pillars is approximately 100 μm. The bending deformation of BTO pillars is negligible, and the lateral shrinkage rate is 20%. The forming mechanism of DLP technology results in a clear lamination of the piezoelectric pillar along the printing direction. The shrinkage of ceramics and the growth of grains fill the gap between interlayers, thus reducing the lamination after sintering. There are no residual bubbles in the epoxy resin after vacuum treatment. The density and acoustic impedance of the piezoelectric composites increase with the growth of the piezoelectric phase volume proportion. Compared with the acoustic impedance of BTO ceramics (i.e., Z=31.64 MRayl, 1Rayl=1 Pa·s/m=10-6 MRayl), the acoustic impedance of composites (45%, in volume fraction) is decreased by 67%. The piezoelectric constant d33 and electromechanical coupling coefficient kt enhance with the piezoelectric phase volume proportion of the composites, meeting their maximum values of 74 pC/N and 0.48, respectively. Compared with the BTO ceramics (kt=0.37), the electromechanical coupling coefficient is improved by 30%. According to the frequency impedance spectra of piezoelectric composites, 1-3 type composites have a pure thickness vibration mode. The dielectric constant εr increases linearly with increasing the piezoelectric phase volume fraction, reaching its maximum of 1 167. The dielectric loss tanδ is lower than 3%, which can enhance the receiving sensitivity of ultrasound transducers. The residual polarization intensity increases with the increase of volume fraction of the piezoelectric phase. The residual polarization intensity of the piezoelectric composite with a volume fraction of 45% reaches a maximum of 1.77 μC/cm2 at 4 kV/mm. Conclusions 1-3 type barium titanate/epoxy resin piezoelectric composites were fabricated by the DLP technology. The effect of volume fraction of piezoelectric phases on the electrical performances of composites was investigated. The electrical properties such as piezoelectric constant d33, electromechanical coupling coefficient kt, and dielectric constant εr were optimized as the volume fraction of the piezoelectric phase (≤45%) was increased. The polymer phase could effectively reduced the acoustic impedance of piezoelectric materials, thus obtaining an acoustic matching between the piezoelectric materials and tissues or water. Compared to pure barium titanate ceramics, 1-3 type composites as a material of ultrasound transducers could effectively suppress the lateral vibration of the material and enhance the thickness vibration mode, which could improve the pulse echo response. The DLP technology with a high resolution provides an effective and low-cost method for fabricating the piezoelectric composites.

Introduction Ga2O3 is an ultra-wide bandgap semiconductor, which has a direct bandgap of 4.9 eV. Also, it has the superior thermodynamic and chemical stability, making it suitable for the development of deep ultraviolet optoelectronic devices. Ga2O3 exhibits the superior photosensitive and resistive properties, which has a promising application in sensor-memory integrated optoelectronic devices. In this paper, the crystal structure, composition, and morphology of the Ga2O3 thin film grown via pulsed laser deposition (PLD) was discussed, and then an optoelectronic device with Pt/Ga2O3/NSTO/In structure was designed and constructed. The physical mechanism of the Ga2O3-based device was investigated. The device process was optimized to achieve both high sensitivity ultraviolet photo-response and stable resistive switching characteristics. This work can provide theoretical guidance and technical support for the development of novel Ga2O3-based multifunctional optoelectronic devices. Methods Ga2O3 thin films were grown on (100) Nd: SrTiO3 (NSTO) substrates by the PLD method. The target material used was a pure Ga2O3 ceramic target prepared by a solid-state method. Before thin film deposition, the ceramic target was pre-ablated for 3 min to remove surface contaminants. The film deposition was performed at pulse laser energy of 300 mJ, O2 partial pressure of 3.0 Pa, and substrate temperature of 650 ℃. The target rotation speed was 5 r/min, the substrate rotation speed was 10 r/min, the pulse laser frequency was 5 Hz, and the deposition time was 30 min. Based on the deposited Ga2O3 thin films, a device with metal/Ga2O3/electrode sandwich structure was further constructed. At room temperature, Pt metal dot electrodes were fabricated on the surface of Ga2O3 thin films by a DC magnetron sputtering method as a top electrode of the device, and then weld the metal indium (In) directly onto the back of the NSTO substrate as a bottom contact electrode. The above Pt metal electrode preparation process was run at DC source power of 100 W, working pressure of 1.5 Pa, Ar flow rate of 10 mL/min, substrate rotation of 10 r/min, and sputtering time of 60 s. The structure of Ga2O3 thin films was characterized by a model D8 Discover type high-resolution four circle single crystal X-ray diffractometer. The elemental composition of Ga2O3 thin film material was analyzed by a model Escalab 250Xi X-ray photoelectron spectroscope. The surface and cross-sectional morphology of the films was characterized by a model Sigma 500 field emission scanning electron microscope. A semiconductor electrical performance testing system was constructed by a model Keithley 2635 digital source meter, probe station, and electromagnetic shielding dark box, to examine the I-V scanning loop, multi-level resistive state, retention, and fatigue resistance characteristics of the device. A 255 nm LED light source was driven by a digital signal generator to test the time-dependent UV photoresponse characteristics. A Omni-λ 3027 setup consisting of monochromator, 150 W xenon lamp light source, chopper, collimating light converter, and phase-locked amplifier, was utilized to measure the dark current, spectral response, UV-visible suppression ratio, and detectivity of the photodetector. Results and discussion The deposited β-Ga2O3 film with small particles and a flat and dense surface exhibits (004) plane preferential orientation. The Pt/Ga2O3/NSTO/In device with both fast self-driven ultraviolet photoresponse and stable resistive switching characteristics was fabricated. Under illumination, the photocurrent of the device rapidly increases to its maximum value and then gradually decreases to a steady state possibly due to the reduction in the Schottky junction built-in electric field caused by the injection of photogenerated carriers into the barrier region. The self-driven photoresponse is attributed to the efficient separation of photo-generated carriers by a built-in electric field formed at the Pt/Ga2O3 interface. On the other side, the device exhibits a stable bipolar resistive switching behavior. Alternating -5 V and +3 V pulse voltages with a 10 ms pulse width results in a resistive switching ratio of nearly 104. A rapid switching between multi-level resistance states occurs at different pulse voltages. The intrinsic oxygen vacancy defect in Ga2O3 thin film as the trap center dominates the capture/release process of charge carriers, thereby maintaining the resistance state. Changing the pulse voltage can control the amount of electron injection, thus affecting the height of the interface barrier, which can explain the multi-level resistive characteristics of the device. The resistance state shows a good retention, and there is no significant degradation within 104 s, showing the nonvolatile characteristics. In addition, the device also exhibits stable and fast switching characteristics after multiple repeats, indicating potential applications in memory devices. The mechanism of resistive switching effect can be attributed to the interface type resistance mechanism. The variation of the Schottky barrier caused by external electrical injection and the carrier trapping/detrapping process caused by the oxygen vacancy defect trap center jointly determine the resistive switching effect. Conclusions The fabricated device had a fast UV photoresponse (-r/-d=60 ms/120 ms) with a peak responsivity of 13.4 mA/W and 1.49×1011 Jones (-=250 nm) at 0 V bias. According to the analysis, the Schottky contact formed at the Pt/Ga2O3 interface resulted in a fast self-driven photoresponse at 0 V bias. In addition, the fabricated device also exhibited a stable bipolar resistive switching behavior with a high/low resistance ratio of 104. The fast switching between multiple resistance state was achieved with the superior anti-fatigue and retention characteristics at different pulse voltages. The external electric field and oxygen-vacancy trap centers was considered as the main origin of resistive switching effect in Ga2O3-based optoelectronic device.

Introduction Machinery and equipment are prone to equipment failure and even safety accidents caused by insufficient lubrication under severe working conditions. Adding additives with some superior performance in lubricant is an effective approach to improve the lubricant performance, reduce the friction and wear, and extend the service life of machinery. Lubricants are widely used in machinery and equipment as an important method of anti-wear and friction reduction. Silicate minerals are harmless to the environment and the humanbeing. A low roughness, high hardness friction reaction film can be formed by silicate minerals as lubricant additives during the lubrication process, which can effectively reduce wear. Organic molybdenum as a commonly used lubricant additive has superior antioxidant properties, and can decompose when pressure, temperature and other conditions meet the requirements, and then lead to a chemical reaction and form the protective film containing molybdenum elements, thus preventing the surface oxidation reactions to improve the tribological properties of the lubricant. In this paper, the friction and wear reduction properties of composite lubricant additives of montmorillonite (MMT) and organomolybdenum were investigated to obtain superior lubrication, thereby improving the operational stability and safety of machinery and equipment under severe operating conditions. Methods The lubrication performance of three molybdenum-based lubricants, i.e., MoDDP (C28H60O4P2S4Mo), MoDTC (C34H72Mo2N2O2S6) and RS-568, was evaluated by a four-ball friction and wear tester to determine the organic molybdenum type and the optimal mass fraction of organic molybdenum in the composite lubricant additives. Tribological tests were then carried out on lubricant samples at different concentrations of MMT to determine the optimal mass fraction of MMT in the composite additives. After the preparation of the composite additive, the lubricating properties of the MMT/MoDDP composite additives were examined, and the friction reduction and anti-wear mechanism of the composite additive was investigated by energy dispersive spectroscopy, X-ray photoelectron spectroscopyand Raman spectroscopy. Results and discussion The results show that among the organic molybdenum additives, molybdenum dialkyldithiophosphate (MoDDP) exhibits the optimum lubricant properties. The friction coefficient and wear spot diameter firstly decrease and then increase with the increase in the mass fraction of MMT and MoDDP in the oil, and the optimal mass fractions of MMT and MoDDP are 3.0% and 1.5%, respectively. Compared with the base oil, the friction coefficient is reduced by 41.0% and the wear spot diameteris decreased by 48.9% for oil sample at 1.5% MoDDP, and the friction coefficient is reduced by 40.6% and the wear spot diameter is decreased by 48.2% for the oil sample at 3.0% MMT. Compared with the oil samples at 3.0% MMT, the friction coefficient and the wear spot diameter was reduced by 26.3% and 7.9%, respectively, for the oil sample with the composite additives. Compared with the oil samples at 1.5% MoDDP, the friction coefficient and the wear spot diameter are reduced by 26.6% and 6.6%, respectively, for the oil sample with the composite additives. The 3.0% MMT/1.5% MoDDP composite lubricant additives can further improve the friction reduction and anti-wear performance of the lubricant. Compared with the base oil, the friction coefficient and wear spot diameter are reduced by 56.3% and 52.3%, respectively, for the oil sample with the composite additives . During the friction process, a SiO2 physical adsorption film was deposited on the friction surface due to the adsorption property of MMT additives. Under the action of shear force, the layered MMT particles are subjected to shear, resulting in an interlayer slip, which can reduce the friction between the contact surfaces. The fractured MMT particles are mechanically filled in the surface wear area to improve the carrying capacity of the oil film. Moreover, a layered MoS2 film with a low shear strength and a high melting point can be generated due to the chemical reaction of the MoDDP additive. Also, the MoO2, FeS2, Fe2O3 metal compound reaction film can be generated to prevent the direct contact of the friction interfaces. Although the single additive has a great lubrication effect, the MMT and MoDDP composite additives show a better lubrication performance and synergistic effects in the friction process. The composite metal compound layer and the physical adsorption film can be generated during friction to form the high load-bearing capacity of the lubricant film, thus increasing the strength and stability of the lubricant film, and it was able to continuously and effectively reduce friction and wear. The friction tests also verify that MoDDP and MMT have a positive synergistic effect in the friction process. During the lubrication process, chemical reaction films with MoS2, MoO2, FeS2, and Fe2O3 and SiO2 physical adsorption films were generated, thus effectively reducing thefriction and wear. Conclusions The 3.0% (in mass fraction) MMT/1.5% (in mass fraction) MoDDP composite additives exhibited the better lubricating properties, compared with a single additive. It was indicated that the MMT/MoDDP composite lubricant underwent a chemical reaction during the friction process, which produced molybdenum sulfides and oxides containing molybdenum (MoS2, MoO2) and iron sulfides and oxides containing FeS2, Fe2O3, as well as physically adsorbent films containing SiO2. The compound lubrication film could effectively reduce the friction of the interface.

Introduction With the increasing demand for turbine engine performance, turbine blade structure becomes increasingly complex. The investment of precision casting ceramic core is a serious challenge. The existing solubility is the most important issue restricting the application of alumina-based ceramic cores. Increasing the porosity can enhance the substrate material and the interaction of chemical solutions. The main research direction is to improve the corrosion performance of alumina-based ceramic core. However, the increase of porosity will cause the core strength to plummet, affecting the performance of alumina-based ceramic core. To meet the requirements of investment casting，the organic-inorganic hybrid fiber can improve the porosity and strength of alumna-based ceramic core system. The synergic strengthening mechanism of hybrid fiber modified aluminum ceramic cores pore-system was investigated. Methods Capacitive corundum powder, fused mullite, and quartz glass powder were used as matrix material, mineralizer, and firing aid, respectively. Meanwhile, organic short-cut fiber as a pore-making agent, inorganic short-cut alumina fiber as reinforcement, coupling agent solution, and hydroxypropyl methylcellulose modified fiber were used to prepare alumina ceramic cores with different hybrid fiber ratios via hot pressing injection. According to aviation industry standard HB 5353.1-3—2004, the key performance parameters of each core sample were obtained. A scanning electron microscope was used to observe the pore characteristics, fracture morphology, and fiber distribution of the core, and analyze the fiber fracture mode. The synergic strengthening mechanism and the pore strength of the hybrid fiber-modified alumina-based ceramic core were investigated. Results and discussion The introduction of hybrid fibers changes the pore characteristics of the alumina-based ceramic core, and irregularly connected pores and nearly circular closed pores appear in the ceramic core. The fracture mode of the alumina-based ceramic core changes from "transcrystalline fracture" of like-metal to "intergranular fracture" as the proportion of hybrid fibers decreases. The addition of hybrid fiber reduces the sintering shrinkage rate of the alumina-based ceramic core, the shrinkage rate of the sample NA67 is only 0.2%. For the comparison, the rate is reduced by 77.8% for the sample NA60 without alumina fibers, which may be since an appropriate amount of alumina fiber can effectively increase the center separation of sintered particles, hinder the migration and diffusion of substances, offset the sintering shrinkage stress, and inhibit the sintering shrinkage of the core. The mass-burn loss of alumina-based ceramic core is 19.5% as the proportion of hybrid fibers decreases. As the mass loss mainly comes from the oxidation burn loss of plasticizer and nylon fiber, the alumina fiber has an impact on the migration of crystal water in the sintering process, so the mass-burn loss rate fluctuates slightly. The number of large pores in the aluminum ceramic core increases, the number of small pores decreases, and the apparent pores in the ceramic core firstly increase and then become stable with the decrease in the proportion of hybrid fibers. Small-aperture pores are mainly composed of closed pores lost by chopped organic nylon fiber (Nsf) fiber, while large-aperture pores are mainly connected pores formed by chopped inorganic alumina fiber (Asf) crossing closed pores when the hybrid fiber ratio is less than 6:7. The apparent porosity of the core tends to be stable at 43.31% because the intersected Asf fibers are clustered among the sintered particles. The effect of Asf fibers on the increase of the distance between the sintered particles becomes slight, the number and size of connected pores in the ceramic core almost unchange, and the apparent porosity tends to be stable. The bending strength of the alumina-based ceramic core increases firstly and then decreases as the proportion of hybrid fiber decreases. This is because the appropriate amount of Asf fiber effectively increases the fiber-matrix interface bonding area. When the core is subjected to external loads, Asf fiber consumes the more crack propagation energy through the behavior of debonding, fracture, and pull-out, and the bending strength of cores increases significantly. The excessive Asf fiber is unevenly dispersed in the matrix material, dividing the matrix, reducing the interface bonding area between the agglomerated fiber and the core matrix, weakening the strengthening effect of the fiber on the core, and leading to a slight decline in the bending strength of the core. Conclusions The shrinkage rate of the alumina-based ceramic core decreased after firing as the hybrid Nsf/Asf fiber ratio decreased. The Asf fibers interspersed in the core matrix effectively hindered the diffusion and migration of sintered particles and reduced the core densification. The shrinkage rate of the sample NA67 after firing was 0.2% when the hybrid fiber ratio was 6:7, which was 77.8% lower than that of the sample NA60 without hybrid fiber, showing a good dimensional stability. The increase of apparent porosity of hybrid fiber reinforced alumina-based ceramic core was mainly due to the loss of residual closed porosity by oxidation of Nsf fiber at a high temperature and the formation of connected porosity by Asf fiber interpenetrating matrix. The number of connected pores, the volume proportion of open pores and the apparent porosity increased, while the volume density decreased as the hybrid fiber proportion decreased. An appropriate amount of Asf fiber consumed the crack propagation energy through the mechanism of de-bonding, pulling out, and breaking, and improved the bending strength of alumina-based ceramic core, effectively making up for the strength loss caused by in-situ burning of Nsf. The bending strength of the alumina-based ceramic core reached a maximum value of 20.1 MPa when the hybrid fiber ratio was 6:7. However, the agglomeration and cross of Asf fibers could form some penetrating cracks in the core matrix and cut the matrix, affecting the strengthening effect of the fibers when the proportion of hybrid fibers further decreased.

Introduction Ordinary concrete rapidly loses its bearing capacity under impact, while the addition of steel fibers effectively enhances the overall integrity and matrix toughness of concrete, thus meeting the concrete performance requirements of high strength, high durability, and high toughness in practical engineering. The existing work on the strengthening and toughening mechanism and failure mechanism of steel fiber reinforced concrete is mainly based on the macroscopic experiments. It is thus difficult to reflect the randomness and non-uniformity of concrete. In this paper, the dynamic response of steel fiber reinforced concrete beam specimens at a low-speed impact was investigated by a drop hammer testing machine to comprehensively reveal the internal damage and failure process of concrete and the toughening mechanism of steel fibers. A three-dimensional microscopic model of steel fiber reinforced concrete beams was proposed, and the mechanical properties and crack development of steel fiber reinforced concrete beams under dynamic impact were analyzed. In addition, the effects of steel fiber volume fraction and impact velocity on the impact resistance and failure morphology of steel fiber reinforced concrete beams were also discussed. Methods Steel fiber reinforced concrete beams with different steel fiber volume fractions (i.e., 0%, 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%) were prepared based on the experimental mix proportion. The effect of steel fiber volume fraction on the impact performance of steel fiber reinforced concrete beams was analyzed via dynamic three-point bending performance in a model INSTRON-9530 drop hammer impact testing machine. A steel fiber model was randomly proposed based on the Monte Carlo method, and a spring element was used to simulate the bond slip between steel fibers and concrete matrix. Based on its bond slip relationship, a three-dimensional fine calculation model for steel fiber concrete was established. The dynamic response and failure forms of steel fiber concrete were simulated at different volume fractions (i.e., 0%, 0.5%, 1.0%, 1.5%, 2.0%) and different impact rates (i.e., 1, 2, 3, 4, 5, 10, 20 m/s), respectively, The effects of steel fiber content and impact rate on the impact resistance and failure morphology of steel fiber reinforced concrete beams were analyzed. Results and discussion The drop hammer impact test is widely used to test the dynamic bending performance of concrete beams, but the hammer impact force measured by a hammer force sensor is not an actual impact force due to its inclusion of structural inertia force. In the low-speed impact test of steel fiber reinforced concrete beams, this study integrated some force sensors with roller bearings to accurately obtain the support reaction force of the beam during the impact process and reduce the influence of inertial force, thereby revealing the true dynamic response of the tested specimens. The key to improving the mechanical properties of fiber reinforced materials lies in the micro bridging effect of fibers on the concrete matrix. Steel fiber exhibit a large number and random distribution in the concrete matrix, making it difficult to quantitatively evaluate the fiber reinforcement effect at an impact load. This study used the Monte Carlo method to propose a fiber microscopic model and determine the range based on the unique three-dimensional position and direction information of each fiber. The numerical analysis methods were used to more intuitively clarify the deformation and damage situation of steel fibers and concrete matrix during the impact process to obtain the accurate energy quantification evaluation. The key to improving the mechanical properties of steel fiber reinforced concrete lies in the bond slip between steel fibers and concrete matrix. Simulating the bond slip between concrete matrix and steel fibers accurately becomes a key to simulating steel fiber reinforced concrete. In this paper, spring elements were used to simulate steel fibers. The stiffness of the spring element adopts a "two-stage" model. The simulation data by the model are in reasonable agreement with the experimental results. Conclusions The simulation data of three-dimensional steel fiber reinforced concrete beams based on bonded slip spring elements were in reasonable agreement with the experimental results. The bearing capacity and energy dissipation capacity of steel fiber reinforced concrete beams increased with the increase of steel fiber volume fraction when the fiber volume fraction was small. The peak impact force of the concrete beam was increased by 16.71% at the optimal dosage of steel fiber of 1.5%. However, the energy dissipation capacity and impact resistance of steel fiber reinforced concrete beams decreased as the volume fraction of steel fibers further increased. The bearing capacity of steel fiber reinforced concrete beams was positively correlated to the rate when the impact rate was in the range of 1 m/s to 20 m/s. The peak impact force of steel fiber reinforced concrete beams increased, but the reinforcement effect of steel fiber on the steel fiber reinforced concrete gradually weakened as the rate continues to increased. The reinforcement effect of steel fiber was slight when the rate increased to 20 m/s. Therefore, for steel fibers with a length of 12.5 mm and an aspect ratio of 20, their enhancement effect on the dynamic mechanical properties of concrete beams was more significant in a low-speed impact range of less than 10 m/s.

Bi2Te3 based alloys have attracted considerable attention in low-temperature thermoelectric materials due to their superior electrical transport properties and low thermal conductivity. However, the conversion efficiency of thermoelectric power generation or refrigeration devices made of Bi2Te3-based alloys is still low. It is thus crucial to further improve the thermoelectric figure of merit zT of Bi2Te3 based materials. There are some correlations between lattice thermal conductivity and electrical performance parameter. Reducing the lattice thermal conductivity by phonon engineering becomes an important method to increase zT without deteriorating the electrical performance. This review summarized the main research progress in recent years to optimize the thermoelectric properties of Bi2Te3 based materials by phonon engineering, such as nano-modification, superlattice structure, nanocomposing, doping and adding dislocation arrays. The effect of the optimization method on the specific heat capacity, phonon group velocity and phonon mean free path was discussed. The specific heat capacity, phonon group velocity or phonon mean free path of Bi2Te3 based materials can be significantly reduced by the optimization methods. As a result, the lattice thermal conductivity of Bi2Te3 based materials is significantly reduced, leading to a significant increase in the thermoelectric properties. Nano-modification: The interface density is increased via low dimensionalization and grain refinement, resulting in an enhanced scattering of low-frequency phonons, reduced phonon mean free path and phonon group velocity, significantly reducing the lattice thermal conductivity. Nowadays, the grain size and morphology of Bi2Te3-based alloys can be precisely controlled by mechanical milling, MBE method, hydrothermal method, chemical vapour deposition and wet chemical method. Bi2Te3 nanostructures with a ultra-low grain size can be prepared. However, heat conduction cannot be completely prevented even at rather small sizes due to the incomplete suppression of low-frequency phonons. Therefore, it is difficult to improve zT by a single low-dimensionalisation and grain refinement method. The specific surface area can be increased either by combining the phases of different nanostructures to form a heterogeneous interface or by introducing special nanostructures such as twins and nanopores, which can strongly scatter the low-frequency phonons caused by lattice mismatch and lattice vibration, and further reduce the lattice thermal conductivity. Bi2Te3-based superlattice structure: Furthermore, in the microscopic and mesoscopic scales, the superlattice structure generated by artificially controlling the ordered arrangement of atomic layers of Bi2Te3-based materials is considered as the optimum candidate material to achieve the ‘phonon glass-electron crystal’ thermoelectric material standard. Especifically, the quantum well structure in the thin film superlattice produces an intense boundary scattering effect and a quantum confinement effect on phonons, resulting in a decrease in the mean free path and group velocity of phonons, greatly reducing the thermal conductivity of Bi2Te3-based thermoelectric materials. The bulk superlattice structure of the Bi2Te3-based alloy relies on its complex crystal structure and acousto-optic coupling effect, causing a low cut-off frequency of phonon mode and an intense phonon resonance scattering, and resulting in a low intrinsic thermal conductivity. In addition, the low phonon group velocity caused by chemical bond softening and lattice anharmonicity is also a reason for the low intrinsic thermal conductivity of the bulk superlattice structure of Bi2Te3-based alloy. Nanocomposites, doping modification and dislocation arrays: Nanocomposite and doping modification are the main approaches to improve the thermoelectric properties of Bi2Te3-based materials. In the nanocomposite process, the nanoparticles dispersed in the thermoelectric material do not enter the matrix lattice, but attach onto the surface of the matrix grain, forming a heterogeneous interface with the matrix. Also, introducing nanoparticles increases the grain boundary density, resulting in a further scattering of low frequency phonons. Doping modification is achieved by doping elements entering the Bi2Te3 lattice, replacing Bi site (or Te site) or entering the van der Waals gap for interstitial doping. This process can introduce multiple scattering centers such as grain boundaries, point defects, in-situ precipitates and dislocations into Bi2Te3-based alloy, enhancing a multi-scale scattering of phonons and effectively reducing the mean free path of phonons. Combined with the preparation process such as sintering, the dislocation array is increased, which leads to a higher scattering intensity of intermediate frequency phonons, further reducing the lattice thermal conductivity. Summary and prospects The phonon specific heat capacity, phonon group velocity and mean free path of the Bi2Te3-based alloy could be effectively controlled by phonon engineering including nano-modification, superlattice structure, nanocomposite, doping and introduction of the dislocation array to achieve a sufficiently low lattice thermal conductivity. The electrical transport properties were optimized by the carrier engineering and energy band engineering techniques, and the synergistic regulation of the electrical and thermal transport properties was realized. As a result, the thermoelectric properties of Bi2Te3-based alloys were significantly improved. This provided a scientific and technical support for the application of thermoelectric devices. However, a lot of work remained in improving the thermoelectric properties of Bi2Te3 materials by phonon, carrier and energy band engineering. Nevertheless, the large-scale commercialization of Bi2Te3-based alloys as thermoelectric materials still attracts much attention. Also, interdisciplinary research in thermoelectricity and other disciplines becomes popular. The future research and large-scale application of Bi2Te3 thermoelectric materials are expected.

Thermoelectric (TE) materials as one of clean energy materials can realize the direct conversion between heat and electricity. Flexible TE films have attracted recent attention because they can be used to fabricate flexible TE generators (f-TEGs) to replace batteries that need to be charged or replaced frequently to power rapidly developing wearable electronic devices. Bi2Te3-based films exhibit the optimum TE performance at room temperature (RT), but Bi2Te3-based films are easy to oxidize, and Te is expensive, rare, and toxic, so suitable alternatives need to be explored. Silver selenide (Ag2Se) is a narrow bandgap semiconductor and has a superior TE performance at RT. Furthermore, compared with element Te, element Se is less toxic and more abundant. However, the TE properties of Ag2Se are still lower than that of Bi2Te3. This review summarized the mechanism of improving the TE properties and flexibility of Ag2Se by functional unit order strategy, and provided a route to enhance the TE properties and flexibility of Ag2Se. Typical strategies for improving the zT values of Ag2Se-based films include the introduction of secondary phase, defect engineering, stoichiometry manipulation, etc.. However, charge carrier and phonon transport in TE material are strongly coupled with each other, seriously restricting the improvement of TE performance. The functional unit order is an effective strategy to optimize the performance of materials. Functional units with different roles constructed orderly in materials can enhance a synergistic effect between functional units and thus improve the performance. For Ag2Se-based flexible TE films, the effect of functional unit ordering and the synergetic effect between functional units on the electronic, phonon transport, and flexibility were discussed. The S-doped Ag2Se film shows a power factor ~954 μW·m-1·K-2 at 300 K and superior flexibility (94.4% of the original electrical conductivity was preserved after bending for 2 000 times around a rod with a radius of 4 mm). The S-doped Ag2Se film consists of a special “core-shell” microstructure, namely, the “core” is an S-doped Ag2Se phase and the “shell” (thickness of 15 nm) is Se-doped Ag2S and amorphous S mixed phase. The formation of the “core-shell” microstructure is mainly due to the different affinities between Ag and Se and Ag and S. The “core” acts as TE functional units because of the well-preserved conductive paths formed by well-crystallized S-doped Ag2Se grains, thus maintaining a high electrical conductivity of the film. The “shell” acts as a flexible functional unit to enhance the flexibility of the film mainly due to the inherently flexible amorphous S phase and the ductile Se-doped Ag2S. Moreover, the thermal conductivity of the film is low because of the strengthened phonon scattering resulting from the hetero-interfaces and the intrinsically low thermal conductivity of the amorphous S phase and the Se-doped Ag2S nanograins. The Ag2Se/PVP composite film has a high power factor of ~1 910 μW·m-1·K-2 and a superior flexibility at 300 K. Most Ag2Se grains with coherent interfaces in the Ag2Se/PVP composite film indicate that the Ag2Se TE functional unit is constructed, leading to a high electrical conductivity. The formation of the unique microstructure is related to the special sintering mechanism and the effect of PVP. The superior flexibility (i.e., 98% of the original electrical conductivity is preserved after bending for 1 000 times around a rod with a radius of 4 mm) is due to the good adhesion and viscosity of PVP acting as a flexible functional unit. The composite film has a pretty low thermal conductivity because of PVP with an extremely low intrinsic thermal conductivity and it contains numerous nano-sized- to micron-sized-pores and Ag2Se/PVP hetero-interfaces. The Ag2Se/Se/PPy composite film has an exceptionally high power factor of ~2 240 μW·m-1·K-2 and excellent flexibility at 300 K. The Ag2Se/Se/PPy composite film has a superior crystallinity of Ag2Se grains and continuous grain boundaries without defects, indicating that the Ag2Se TE functional unit is constructed, leading to a high electrical conductivity. There exist energy-filtering effects at the heterointerfaces of Ag2Se/Se and Ag2Se/PPy in the film, leading to a high Seebeck coefficient. The formation of the unique microstructure is related to the special sintering mechanism. The superior flexibility (i.e., 92.5% of the original electrical conductivity is preserved after bending for 1 500 times around a rod with a radius of 4 mm) is due to the good adhesion and viscosity of PPy acting as a flexible functional unit. Moreover, the nano-sized to submicron-sized pores, and the Ag2Se/PPy and Ag2Se/Se heterointerfaces in the composite film can scatter short- to long-wavelength phonons because PPy has an intrinsic low thermal conductivity, the composite film has a low thermal conductivity. Summary and prospects The functional unit order is an effective strategy to optimize the performance of materials. For Ag2Se-based TE films, the TE functional units ordering (such as coherent adjacent Ag2Se grains, good crystalline qualities, continuous grain boundaries, and core-shell nanostructure) and flexible functional units were constructed in Ag2Se-based films. The effective regulation of electron and phonon transport and flexibility was realized due to the synergistic effect between different functional units, thus increasing the electrical conductivity, reducing the thermal conductivity, and improving the flexibility. The more work are needed to verify whether the relevant strategies are universal.

Conventional metal materials affect the development of microwave integrated circuits, while the use of microwave electric materials can achieve the miniaturization and high-performance requirements. With the continuous exploration of modern microwave communication technology, microwave devices will face some opportunities and challenges like multi-frequency, and multi-mode capabilities. Tunable microwave devices are also an essential core of phased array radar and modern mobile technology, with the broad application prospects. BaxSr1-xTiO3 (BST) film material is considered as one of the most materials for tunable microwave devices due to its high dielectric tunability and low dielectric loss with a high figure of merit (FOM). However, BST thin film material still has some problems in applications, such as the synergistic optimization of tunability and dielectric loss, as well as temperature stability. To optimize the performance of films, the dielectric properties are adjusted through the improved preparation processes, annealing modification, controlled composition ratio, and doping modification as well. These optimization measures provide some opportunities for the design and preparation of microwave devices based on the BST films. To investigate the dielectric properties of BST thin film, high-annealing in the preparation process can repair defects and improve grain growth, while controlling growth atmosphere can optimize the surface roughness and grain boundary characteristics of the film. Selecting appropriate substrates or inserting buffer to control stress can optimize the film structure and improve the dielectric performance. In addition, the Ba/Sr/Ti molar ratio regulation has a significant impact on the ferro-dielectric properties (i.e., the Curie temperature) of the film. The use of oxide molecular beam epitaxy (MBE) can achieve a better stoichiometric control and a low defect density. Doping regulation can change the lattice parameters and ion interactions of BST films. Some methods such as acceptor doping donor doping, and multicomponent doping are used. For instance, the FOM of La/Fe co-doped Ba0.65Sr0.35TiO3 films prepared by a solid-phase reaction is increase by 5 times, compared to pure BST. The super lattice structures prepared by alternate doping and the multilayer films prepared by different material combinations indicate better comprehensive dielectric properties. The BST thin film materials have nonlinear characteristics, in which the dielectric constant changes with the applied electric field, and these dielectric properties play an important role as parameter indicators in microwaveable devices. It is indicated that the oxide bottom electrode is of great significance to improve the performance of BST thin film variable capacitors in high-frequency applications. The BST film capacitors with SrMoO3 (SMO) oxide was designed as a bottom electrode instead of conventional precious metal electrode materials, which avoids an acoustic resonance at high frequencies. Using the BST tunable filters instead of conventional filters composed of multiple filters is more in line with the needs of miniaturized and integrated devices in radar and communication fields. However, current research is limited due to the high insertion losses in practical devices, and reducing the insertion losses remains an important issue for BST-based microwave devices. Some phase shifters made using BST films were reported, demonstrating a large phase shift range and a high figure-of-merit, and achieving continuous tunable phase shift capability at different frequency ranges. Film phase shifters are applied in antenna arrays and end-fire arrays, realizing radiation directionality steering and linear beam scanning, thus promoting the development of radar and antenna systems. The power oscillators using BST films and single-chip AlGaN/GaN high electron mobility transistors voltage controlled oscillator were reported, showing the potential of BST films in the field of microwave oscillators. Summary and prospects The dielectric properties were reduced via optimizing film growth conditions. However, some related problems were not solved, i.e., decoupling the physical mechanism of dielectric tunability and dielectric loss, and the optimization of high-frequency film dielectric performance testing and extraction. In terms of microwave devices, more efforts need to be made in microwave device design, simulation, preparation, and testing. In summary, to commercialize ferroelectric thin film-based tunable microwave devices, we need to clarify the physical mechanisms of thin film dielectric properties, optimize the growth conditions preparation processes (i.e., synergistic optimization of dielectric tunability and dielectric loss), and obtain high-quality films, thus laying a foundation for the application prospects of tunable microwave devices.

Solid-state lithium-ion batteries (SSLBs) are one of the most promising next-generation batteries due to their excellent safety, higher energy density and longer cycle life. Solid-state electrolytes (SSEs) with a high ionic conductivity, a wide electrochemical window, and good mechanical properties are the importance of the high-performance SSLBs. The organic polymer SSEs have some advantages of flexibility and good mechanical property, that makes them almost have no serious interfacial problems. However, the low ionic conductivity is a major drawback for most polymer SSEs. Inorganic SSEs show a high ionic conductivity, a good electrochemical stability, and a high thermal stability, but their main disadvantages are a weak mechanical property (i.e., brittle and fragile), a poor air stability and an inferior compatibility with metal lithium anode. Compared to inorganic and organic polymer SSEs, composite solid-state electrolytes (CSSEs) integrating the merits of organic polymers and inorganic electrolytes exhibit a good electrochemical performance and an excellent interface compatibility, which have attracted extensive attention in the SSEs research. This review detailly summarized the research progress on CSSEs in lithium batteries. The CSSEs are usually composed of inorganic fillers, organic polymers and lithium salts. The inorganic fillers are classified into inert and active fillers. The inert fillers, such as SiO2, Al2O3 and TiO2, do not transport Li+ themselves, but can promote the ionic properties of polymer matrices. The active fillers conduct Li+ themselves including oxides (i.e., perovskite-type, garnet-type, NASICON-type), sulfides, and halides, etc.. Lithium salts used for the investigation of CSSEs include LiPF6, LiBF4 and LiN(CF3SO2)2(LiTFSI), etc.. The first CSSE with an inert filler was prepared via introducing an Al2O3 into a matrix, thus improving the mechanical property of LiClO4/PEO CSSEs at 100 ℃. SiO2 and TiO2 were a commonly used inert ceramic filler for the fabrication of CSSEs. The content, particle size and shape of metal oxide inert fillers affect the performance of CSSEs. The layered nano-sized claylike montmorillonite (MMT) as a passive filler was doped into polyvinylidene fluoride (PVDF)-hexafluoropropylene (HFP) polymer to prepare a ultraviolet (UV)-crosslinked MMT/PVDF-HFP membrane, having a room-temperature ionic conductivity of 1.6×10-3 S/cm. Carbon materials were also served as inert fillers to prepare CSSEs. The CSSEs with active fillers were synthesized via adding active fillers to polymers. Li0.5La0.5TiO3 (LLTO) is a typical perovskite-type active filler. The reduction of Ti ions in LLTO with lithium was prevented as combining LLZO with polymers, and the LLZO CSSEs exhibited a wide electrochemical window and a good stability. For instance, a PVDF polymer CSSEs with LLTO nanowires delivers a room temperature ion conductivity of 5.8×10-4 S/cm, an electrochemical window of 5.2 V, and a mechanical strength of 10 MPa. The cell of Li|PVDF/LLTO-15%/Li+|LiFePO4 (LFP) has a superior Coulomb efficiency of approaching 100% after 200 cycles. The garnet-type active filler Li7La3Zr2O12 (LLZO) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) were divided into zero-dimensional nanoparticles, one-dimensional nanowires and nanotubes, two-dimensional nanosheets, and three-dimensional structures according to the geometric structures. For instance, a LLZTO/PEO CSSEs was prepared by dispersing a zero-dimensional LLZTO powder into acetonitrile solution of PEO/LiTFSI. The room-temperature ion conductivity and electrochemical stability window of LLZTO/PEO CSSEs are 4.76×10-4 S/cm and 4.75 V, respectively. The multi-mixing CSSE membrane consisting of LLZTO, PEO, PVDF-HFP, and LiTFSI has a high ionic conductivity of 1.05×10-4 S/cm at 35 ℃, an electrochemical window of 5.2 V, and a high Li+ transference number of 0.52 at 60 ℃. A three-dimensional PVDF/LLZO/LiClO4 CSSEs was obtained by adding 3D coral-like LLZO nanofiller into PVDF/LiClO4. This CSSE membrane structured 3D interconnected framework has an enhanced ionic conductivity of 1.51×10-4 S/cm at room temperature. The assembled battery delivers a capacity retention of 95.2% after 200 cycles at 1 C. The NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP) ceramics as active fillers were added into PEO and PVDF-HFP polymers. A PVDF-HFP/LiTFSI CSSE containing 50% (in mass fraction) LAGP displays the maximum ionic conductivity of 9.2×10-4 to 9.6×10-4 S/cm at room temperature. After 50 cycles, the cell with PVDF-HFP/50% LAGP/LiTFSI CSSE remains 141.3 mA-h/g and a capacity retention rate of 89.5%. Besides, sulfide fillers were investigated. However, sulfides are instability in air because it intrinsically tends to react with moisture to generate toxic H2S gas. The CSSEs prepared with sulfide fillers improve asulfide stability and offer a high ion conductivity. For instance, adding sulfide active filler Li10GeP2S12 (LGPS) to PEO polymer can prepare a PEO/LGPS/LiTFSI CSSE membrane with a stability in air. The CSSE has an ionic conductivity of 1.18×10-4 S/cm at room temperature. After 150 cycles at 0.5 C, the cells using PEO/LGPS/LiTFSI as a membrane demonstrates superior capacity retention and rate performance. To meet high-voltage cathodes and lithium metal, CSSEs with bi-layered or multi-layered structures maximize the synergistic effect of each layer without or withless sacrificing their properties, particularly for adjustable interphase. A bi-layer structure used Li6.4La3Zr2Al0.2O12/PEO/LiTFSI and I2/PEO/LiTFSI CSSE layers to contact with cathode and anode, respectively. After 500 cycles at 0.2 C, the LFP||Li cell maintains a specific capacity of 146.20 mA-h/g. A sandwich structure CSSE with PAN/PVDF-80% (in mass) LLTO/PEO was prepared by a casting method, having an ionic conductivity of 2.81×10-4 S/cm and an electrochemical window of 4.92 V. The assembled battery delivers the Coulomb efficiency of 99.2% and a capacity retention rate of 88% at 0.5 C after 500 cycles. The mechanism of ion transport in CSSEs has not yet clarified due to itscomplexity. The current well-known ion transport pathways in CSSEs include polymer matrix, inorganic active fillers and interfacial regions between polymer matrix and active fillers. Among them, the ion-transport pathway at the interfaces is relatively complex, and more efforts are needed to reveal the mechanism. Summary and prospects CSSEs have attracted great attention for the development of SSLBs because they can improve ionic conductivity and enhance the mechanical strength and stability of the SSEs by incorporating inorganic fillers into polymer electrolytes. Recent research progress on the CSSEs were summarized. The main components of the key materials of CSSEs, i.e., inert and active fillers in the polymer matrix, were classified and summarized. The advanced structures of CSSEs to withstand lithium metal reduction and high-voltage positive electrode oxidation were explored. In addition, the possible mechanism of ion conductivity in CSSEs wasalso discussed. Although CSSEs were used in battery applications, they still had some challenges in ion conductivity, lithium-ion transport mechanism, and interface compatibility. Some key issues need to be considered for the future studies, i.e., further increasing in the room-temperature ionic conductivity of CSSEs, understanding of ion conduction mechanism in different types of CSSEs, and optimizing the interphase between the solid electrolytes and the electrodes.

With the rapid growth of population and the development of industry, the lack of clean water resources becomes increasingly prominent. For the shortage of clean water resources, China as a country rich in seawater resources vigorously promotes seawater desalination technology, which has gradually developed into a strategic industry. Compared with the existing desalination technologies such as multi-effect distillation, multi-stage flash evaporation, reverse osmosis membrane, electrodialysis and so on, the desalination technology based on the principle of solar photothermal conversion has unparalleled advantages, i.e., environmental-friendly, high efficiency and low cost. Solar-driven steam generation (SSG) could be widely applied in seawater desalination, sewage treatment and other fields, which is of great significance in acquiring pure water and solving the problem of water resource shortage. Ultra-high solar steam conversion efficiency could be achieved by increasing photothermal conversion efficiency, water transfer rate and heat management of the SSG system. In recent years, the evaporation models underwent a gradual transition from using photothermal particles dispersed in volume water to interface water evaporation with porous insulation layer or 1D or 2D water transport channels to the hydrophilic gel evaporation structure. It is reported that TiN hyperbranched nanowires have a better solar light absorption and a higher specific surface area to evaporate water rather than TiN nanoparticles and nanotubes. Its solar water evaporation rate and solar thermal conversion efficiency are 1.525 2 kg·m-2·h-1 and 94.01%, respectively, under 1 kW·m-2 simulated solar irradiation. Zhu et al. demonstrated that a carbon foam with a three-dimensional interconnected porous structure enables a sufficient diffusion of vapor with a convective flow and realizes an evaporation rate of 10.9 kg·m-2·h-1. Solar-driven steam-electricity system expands the functionary of SSG, providing an innovative pattern for the electricity supply for tiny electronic devices, flexible wearable devices and remote area. Solar-driven steam-electricity system is mainly divided into integrating electricity generation module and self-powered electricity generation module. In SSG and PV cell integration modules, Xu et al. experimentally demonstrated that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W·m-2 and purify water at 0.80 kg·m-2·h-1 under 1-sun illumination. Deng et al. realized that the evaporation rate of the prepared TEC in seawater electrolyte is 1.1 kg·m-2·h-1, and the solar vapor conversion efficiency of the TEC is 60% with a peak output power of 0.5 mW·m-2. In self-powered electricity generation modules, Guo et al. presented a device prototype for enhanced power generation from ambient humidity, the device to ambient humidity can produce voltages of 0.78 V and a current of 7.5 μA, both of which can be sustained for more than 10 d. In this review, we summarized recent research work on the solar-driven steam-electricity system, and analyzef the advantages and disadvantages of different electricity generation modules. Summary and prospects Selection of solar absorbers: Three categories of solar-absorbing materials including carbon materials (such as carbon nanotubes, carbon nanoparticles, and graphene), plasmonic metals (such as Al, Au, Ag, Cu) and ceramic nanomaterials (such as transition metal nitrides and carbides) and semiconducting nanomaterials (such as TiO2-x, MoS2) were developed. The present research focuses on the preparation of high-light-absorption photothermal absorbers with a low-cost and a superior chemical stability. 1) Structural design of solar steam generation system: The solar-vapor conversion efficiency (η) can be calculated by (1) where Qs is the incident light power (1 kW·m-2); Qe is the water evaporation power; Hv is the evaporation heat of water (~2 260 kJ·kg-1); m is the evaporated water mass; t is time. Based on Eq. (1), the solar steam conversion efficiency is directly proportional to water evaporation enthalpy and water evaporation rate. It is proved that the latent heat of water vaporization in a porous nanostructure is lower than the standard value. However, it is still unclear how to obtain a low water evaporation enthalpy by regulating the porous structure of the solar photothermal materials. It is crucial to obtain hierarchical nanostructures and evaluate its water vaporization latent heat. In order to increase the specific surface area of solar photothermal materials, porous foams and gels are designed and prepared, but the preparation of these artificially hierarchical materials is a time-consuming and costly process. It is thus imperative to explore naturally hierarchical plants that are low-cost and easy to obtain. 2) Efficiency and mechanism of VOCs photodegradation in water: Solar-driven steam generation is utilized to produce fresh water by removing salts, heavy metals, micro-organisms, and most organic pollutants in raw water. However, it also accelerates the volatility of the volatile organic compounds (VOCs) and enrich them in the distilled water if the water source is contaminated by VOCs because of their similar boiling point with water, which poses a serious threat to the atmospheric environment and human-being health. VOCs such as alcohols, aldehydes, ketones, olefins, and aromatic compounds tend to migrate and accumulate in different environmental media such as soil, water, and air. The World Health Organization and China's sanitary standards for drinking water quality both have established limit values for VOCs. Consequently, it is crucial to efficiently remove VOC during the solar-driven interfacial evaporation. 3) The relative merits of different electricity generation systems: Solar-driven steam-electricity system is mainly divided into integrating electricity generation system and self-powered electricity generation system. The integrating electricity generation module integrates a solar water evaporation module and an electricity generation module by rationally connecting the solar water evaporation module with photovoltaic device harvesting light energy, thermoelectric module recovering heat energy from water vapor, membrane structure utilizing salt concentration gradients and triboelectric nanogenerator based on steam condensation process. The electricity generation capacity of an integrated electricity generation system typically depends on the electrical output performance of the power generation module itself. Though the integrated electricity generation system can be commercially produced and has a stable performance, it has some problems such as complex structure, high cost and non-adaptability of different modules, which limit its practical application. The self-powered electricity generation system does not connect solar water evaporation module with other auxiliary equipment for electricity generation. It generates electricity directly by a hydrovoltaic effect, and its evaporation-electricity generation performance mainly depends on the microstructure of the photothermal material, such as the size of micro-/nano-pore channels and the zeta potential. The currently reported output currents range from nanoamps to microamps, and exploring current output in the milliamp range is a further research direction.

Aqueous rechargeable batteries have great prospects in the field of large-scale energy storage due to their high safety, low cost, and environmental friendliness. As a key component of batteries, electrode materials play important roles on their electrochemical performance. Vanadium oxides, manganese oxides, Prussian blue analogues, and organic materials are often used as active materials in aqueous batteries. Among these materials, vanadium oxides possess a variety of compounds, high theoretical specific capacity, and superior cycling performance. However, their redox potential is relatively low, restricting the operating voltage of aqueous batteries. Moreover, these materials are toxic, which are not conducive in the large-scale applications. Compared with vanadium oxides, Prussian blue analogues have a higher redox potential and a stable structure, but they have some disadvantage of low theoretical specific capacity, resulting in the low energy density of batteries. In contrast, organic materials possess abundant sources, facile structure regulation, and superior sustainability. However, their poor conductivity and low compaction density make it difficult to prepare high-loading electrodes. Compared with the materials above, manganese oxides have the advantages of diverse crystal structures, high theoretical specific capacity, high redox potential, non-toxicity, and low cost, which are beneficial for constructing high-performance aqueous batteries. Therefore, manganese oxides are considered as a promising electrode material in aqueous batteries. Recent efforts are made in the design of manganese oxides-based aqueous batteries, but the corresponding comprehensive review on this topic is still sparse. This review firstly analyzed the crystal structure types and characteristics of manganese oxides. According to the connection mode between MnO6 units, the crystal structure of manganese oxides can be divided into one-dimensional tunneled structure (i.e., α-MnO2, β-MnO2, γ-MnO2, R-MnO2, Todorokite-MnO2), two-dimensional layered structure (i.e., δ-MnO2), and three-dimensional spinel structure (i.e., l-MnO2, Mn3O4, LiMn2O4, ZnMn2O4). The characteristics of corresponding crystal structure were summarized. Manganese oxides exhibited unique physical and chemical properties, endowing their wide application as electrode materials in aqueous batteries. The reaction mechanisms of manganese oxides are rather complex in aqueous batteries, especially for aqueous zinc-ion batteries, which were summarized according to the acidity of electrolytes. In alkaline Zn-MnO2 batteries, MnO2 is firstly converted into MnOOH, and then Mn(OH)2 is formed. As the acidity of the electrolyte decreases, manganese oxides exhibit different electrochemical reactions, mainly including ion insertion-extraction, conversion, and dissolution-deposition (Mn2+/MnO2). The different electrochemical reaction mechanisms of manganese oxides provide plentiful energy storage chemistry for the design of aqueous battery systems. However, there are also irreversible side reactions and structural distortions in manganese oxides during the cycling process, which hinder their further development. The application of manganese oxides in aqueous batteries is briefly elaborated, including alkaline-metal-ions (such as Li+, Na+), multivalent-metal-ions (such as Zn2+, Mg2+, Al3+), and non-metallic-ions (such as H+, NH4+) batteries. To address the poor conductivity, unstable structure, as well as manganese dissolution of manganese oxides, nanostructure design, hetero-element doping, defect engineering, and composite construction with other conductive materials are adopted to regulate the electronic structure and alleviate the Jahn-Teller distortion. As a result, the rate capability and cycling stability of manganese oxides-based aqueous batteries are significantly improved. Summary and Prospects Although significant progress has been achieved in the design of manganese oxides for the electrodes of aqueous batteries, great challenges still remain in the scientific researches and practical application. The reaction mechanisms of manganese oxides are relatively complex, compared with those of other electrode materials. The reaction processes are also different for the same crystal structure. It is thus necessary to conduct the systematic and comprehensive investigation. The detailed structure evolution of manganese oxides could be revealed during electrochemical reaction process through some advanced in-situ characterization techniques (i.e., electrochemical quartz crystal microbalance, cryo-electron microscopy, X-ray photon-electron spectroscopy). The poor structure stability and manganese dissolution of manganese oxides result in the capacity attenuation upon cycling. The precise structure optimization strategies are urgently needed to suppress the Jahn-Teller distortion and enhance structural stability, such as interface interaction regulation through introducing carbon materials and other functional materials into the composites, valence state adjustment of manganese elements through anionic doping. Furthermore, the development of novel electrolyte systems also plays a crucial role in the improvement of electrochemical performances for manganese oxides-based aqueous batteries. High-concentrated electrolytes, molecular-crowding electrolytes, hydrated-eutectic electrolytes, and organic/inorganic hybrid electrolytes could reduce free water content and water molecule activity, regulate the solvation structure, which would be beneficial for suppressing manganese dissolution and promoting reaction kinetics. In addition, the diverse reactions of manganese oxides could be also utilized by adjusting the pH value of the electrolytes, thus developing the electrochemical energy storage devices with a high voltage, high capacity, and high rate capability. The electrochemical performance of manganese oxide electrodes with a high mass loading could be improved by the synergistic effect of material structure design and electrolyte optimization. Finally, some controllable methods of manganese oxides in a largescale could be further developed for the industrial application of aqueous batteries.

Gas sensor can monitor the composition and content of trace toxic and harmful gases in environment. As the core of gas sensor technology, the performance of the sensor is closely related to the properties of the gas sensing materials. Recent work focused on development of novel sensitive materials with a large specific surface area, a high carrier mobility, a high catalytic activity, a wide measurement range and a good long-term stability to build high-performance gas sensors. Among them, halide perovskite materials are a potential option for gas-sensitive materials due to their advantages (i.e., high room temperature carrier migration rate, sensitive surface properties, directly adjustable band gap and simple preparation). The toxic and harmful gas detection applications were analyzed and its sensing mechanism was clarified based on the advantages of halide perovskite in gas sensors. It is necessary to summarize the existing halide perovskite gas sensing materials. This review represented halide perovskite sensitive materials, discussed their working mechanisms in gas sensors, and summarized the application of halide perovskite gas sensors in NOx, NH3, H2S and volatile organic compounds (VOCs). Halide perovskite gas sensors can be used for detection NOx gas. Especially, MA- or Cs-based halide perovskite gas sensors with a bipolar charge transfer can achieve a high response/recovery speed at low operating temperatures and quickly and accurately detect NO2 and NO gas. Some recent work indicate that the Cs-based halide perovskite materials have better stabilities rather than the MA-based halide perovskite materials, so the as-prepared Cs-based halide perovskite gas sensors have better repeatability than the MA-based halide perovskite gas sensors. NH3 detection is another important application of halide perovskite gas sensor. This is because NH3 pollution seriously threatens human health and safety, and affects the sustainable development of ecological environment. Also, NH3 is also a metabolite of the human body and widely exists in exhaled gas, which can be used as a marker for a variety of diseases for non-destructive diagnosis in clinical medicine. The perovskite film color changing, resistance changing, and reversible weak bond action are mainly used to achieve ammonia detection. Moreover, the detection of ammonia is also extended from MA- or Cs-based halide perovskite to PEA-based halide perovskite. The material dimensions also extend from three dimensions to two dimensions, and ammonia can be efficiently detected at room temperature. H2S is an important chemical raw material, and a highly toxic and dangerous gas. In recent years, H2S poisoning accidents occur frequently. There is a coincidence in the fact that the halide perovskite sensitive materials with high performance, low cost and small size are an ideal option for H2S gas sensors and H2S gas alarms. The FAPbBr3-based sensor has an extremely high H2S response sensitivity (at room temperature), and works well under both dark and half-light conditions, especially in half-light condition. The assembled gas sensor can be used to detect oxidizing and reducing gases and a variety of VOCs due to the bipolar nature of halide perovskite. VOCs are extremely volatile and accompanied by a pungent odor, and their emission can seriously pollute the environment and threaten human-being health. To meet different needs, A/B bit substitution and halogen or pseudohalogen doping were used to achieve the superior device sensing performance. Summary and prospects As a recent research hotspot, halide perovskite sensitive materials with the advantages (i.e., strong stability, good selectivity and low working temperature) are one of the effective options of gas sensitive materials. Halide perovskite sensitive materials are also developed from the simple original MAPbI3 system to different systems. The corresponding applications of gas sensors were also enriched to detect oxidizing gases, reducing gases, and a variety of VOCs. This review summarized the recent research progress on halide perovskite gas sensors to provide a reference for halide perovskite gas sensors used in related fields. In the future research, we proposed 1) to further explore more perovskite (i.e., double perovskite materials such as MA2AgBiI6, Cs2AgBiI6, Cu2AgBiI6, and perovskite-like materials such as AgBiI4, CuBiI4, etc.) materials, and expand their application in the detection of toxic, harmful gases and VOCs gases; 2) to grow more perovskite single crystal sensitive materials instead of halide perovskite polycrystalline sensitive materials, and develop more perovskite single crystal sensors with superior photoelectric properties and sensing properties; and 3) to use halide perovskite gas sensors with high precision, miniaturization, a low power consumption and low cost in medical detection (i.e., human metabolites, neurotransmitters and various disease-related substances), thus achieving a deep cross-integration of medical and industrial fields.

The catalytic conversion of greenhouse gases, such as carbon dioxide and methane, into high-value-added chemicals/fuels (i.e., formic acid, methanol, ethylene, etc.) is recognized as a cost-effective tactic for achieving the "dual-carbon" purpose. It provides an alternative to fossil fuels, and also offers novel approaches to environmental dilemmas such as global warming. Catalysts with an extensive specific surface area and plentiful surface active sites are capable of absorbing and aligning reactant molecules, including CO2 and methane, in an orientated manner. This reduces the energy required to activate the reaction, thereby enhancing the efficiency and selectivity of CO2 reduction and methane activation reactions. Developing novel catalysts with low cost, high catalytic activity, good long-term stability, and high product selectivity becomes popular to improve the efficiency of energy catalytic conversion. Perovskite composite oxides are a promising nanomaterial with superior redox performance, high stability, facile structural regulation, and rich active sites, offering some advantages for developed catalysts. For the advantageous properties of perovskite composite oxides in catalytic reactions, it is crucial to comprehensively investigate the catalytic mechanism of these oxides in CO2 reduction and methane activation, promote the development of high-performance perovskite composite oxide catalysts, and accelerate global efforts towards achieving carbon peak and carbon neutrality. Therefore, there is an urgent need to summarize the research progress on perovskite composite oxides for CO2 reduction and methane activation. This review represented the thermocatalytic, photocatalytic, electrocatalytic, and synergistic catalysis applications of perovskite composite oxides, with summarizing their catalytic performance in CO2 reduction and methane activation. Perovskite composite oxide catalysts have a potential in facilitating thermally catalyzed CO2 reduction and methane activation reactions. In particular, some rare-earth-based perovskite composite oxide catalysts serve a crucial function in this regard. The morphology, compositional structure, and surface adsorption properties of perovskite composite oxide catalysts are modulated via optimizing the preparation method and doping/substitution of metal elements. This leads to an increase in the oxygen vacancies and active sites of the catalysts, thereby improving their catalytic performance in thermocatalytic reactions. Compared to the photocatalytic and electrocatalytic materials, thermaocatalytic material yields a faster reaction rate, but the catalyst is susceptible to coking and carbon deposition at elevated temperatures. In addition, perovskite composite oxide catalysts demonstrate the superior effectiveness in the processes of photocatalytic reduction of CO2 and activation of methane. The energy band structure of the perovskite composite oxide photocatalyst are adjusted via doping with transition and rare-earth metals, optimizing morphology, regulating oxygen vacancy, loading cocatalysts, and constructing heterogeneous structures, etc.. This can broaden the light absorption range, reduce the reaction activation energy, promote the photogenerated carrier separation, inhibite the electron-hole pair recombination, and improve the reactant adsorption on the photocatalyst surface. This leads to the improved production rate, yield, and selectivity of the product. Photocatalysis offers environmentally friendly and controllable processes, yet it is limited due to its low reaction rate and selectivity for product formation. Also, perovskite composite oxide catalysts demonstrate a significant potential for electrocatalytic CO2 reduction and methane activation reactions. Perovskite composite oxides constitute a commendable class of electrocatalytic cathode materials showcasing exceptional ionic conductivity and redox properties. Scientists further enhance the conductivity of the materials by elemental doping at A/B sites and constructing oxygen vacancy to facilitate electron transfer, thereby improving the electrocatalytic performance of perovskite composite oxides. The electrocatalytic reaction offers some advantages like efficiency, cleanliness, and high product selectivity. Nonetheless, the reaction performance is extensively impacted underits reaction conditions (i.e., electrodes, electrolyte solution, etc.). In recent years, the combination of two or more catalytic technologies through synergistic catalysis has attracted much attention alongside the progress of catalytic research. Synergistic catalysis incorporates the benefits of individual catalytic technologies, while overcoming their inherent drawbacks, leading to the more effective and stable catalytic reactions. Synergistic catalytic techniques also allow catalysts that are not suitable for an individual catalytic reaction to be applied to a synergistic catalytic reaction under appropriate imposed conditions. Currently, perovskite composite oxide catalysts are still in their infancy for synergistic catalysis reactions, and researchers have not thoroughly examined the reaction conditions, basic principles, and interactions of various catalytic methods involved in synergistic catalysis reactions yet. The further exploration is required to generate more stable and efficient catalysts for synergistic catalysis reactions. Summary and prospects Perovskite composite oxides have some advantages of adjustable structure, excellent stability, and high catalytic activity, which make them a promising catalyst. They have undergone a significant growth since the initial simple CaTiO3, with dozens of varieties now available and in widespread use in energy conversion, chemical production, and environmental protection. This review represented recent research progress on catalytic CO2 reduction and methane activation by perovskite composite oxide catalysts. The objective was to offer a reference for research on perovskite composite oxide catalysts for catalytic energy conversion and related fields. In future research, we proposed the following perspectives: 1) new methods (e.g., high-pressure, high-temperature synthesis techniques and in-situ dipole source electrostatic field modulation strategies, etc.) and novelprocesses (e.g., supercritical fluid deposition and atomic layer deposition, etc.) are necessary to produce perovskite composite oxide catalysts with improved structural stability and diversity to enhance their performance; 2) The catalytic principles and reaction pathways of perovskite composite oxide catalysts are further investigated via theoretical calculations (e.g. first-principles calculations, molecular thermodynamics, and kinetic simulations, etc.) as well as characterization techniques (e.g. In-situ Fourier IR spectroscopy and in-situ electron paramagnetic/spin resonance, etc.) to provide a theoretical guidance for the design of perovskite composite oxide catalysts for a novel system; 3) The benefits of perovskite composite oxides should be maximized to extend their application in photothermocatalytic, photoelectrocatalytic, thermoelectrocatalytic, and photoelectrothermal synergistic catalytic as well.

WO3, a typical transition metal oxide, has attracted great attentions in photocatalysis due to its abundant reserves, environmentally friendly, good physicochemical stability, visible-light response and proper band edge positions, etc.. Nevertheless, several drawbacks such as the low utilization of solar energy, high charge carrier recombination rate, weak reduction ability and limited reactive sites lead to a poor photoactivity, thus restricting the industrial application. Various modification strategies are explored and utilized to promote the photocatalytic activity. It is thus necessary to review recent development on WO3-based photocatalysts that might provide a general guidance for designing high-efficient WO3 catalyst systems. Morphology control can tailor WO3 nanomaterials to expose a highly active crystal plane, which is beneficial for reactivity. Low-dimensional nanomaterials possess the larger surface area and large quantity of unsaturated coordination sites, then accelerates the surface reaction. The charge carrier migration efficiency can be increased in a small size of catalysts due to the limited transportation distance. However, the preparation of low-dimensional WO3 with a precise structure and a stable crystal plane is an obstacle. Oxygen vacancy in WO3 materials can capture the photoinduced electrons and hence suppress the recombination of electron-hole pairs. Moreover, the creation of oxygen affects the band structure that can broaden the light absorption and enhance the redox ability. Nevertheless, excessive oxygen vacancy may induce the structural instability. Thus, the precise control of oxygen vacancy in WO3 is the key point. Metal or non-metal doping can induce the lattice distortion and then affect the physicochemical properties of semiconductor. Doping element acts as an electron acceptor that contributes to the ultrafast charge separation. Also, the introduction of impurity energy level favors the reduction of energy band. The more comprehensive understanding of the reactive sites in doping catalysts still needs further exploitation. Loading co-catalyst in WO3 benefits for charge carrier separation and migration. Metal co-catalyst can increase the solar energy utilization resulting from its localized surface plasmon resonance effect. The current common co-catalysts focus on noble metal that is high cost. The pursuit of abundant reserves materials is highly desired for commercial application. The construction of II-type, Z-type and S-type WO3-based heterojunctions is an effective strategy for solving the problems of single materials. The charge carriers in II-type heterojunction tend to transfer from agreatability of positions to the low positions, which are beneficial for spatial separation of electron-hole pairs, but the redox ability weakens. The unique merit in Z-scheme and S-scheme heterojunction is an intense redox ability maintained in separate components, thus triggering the unique photoreaction. Summary and prospects WO3, as a typical oxidation photocatalysts, had some advantages such as visible light harnessing, suitable band edge position, good physicochemical stability, cost benefit and environmental friendliness. It was widely utilized in various photocatalytic areas like pollutant removal, water splitting, CO2 photoreduction and nitrogen fixation. This review summarized the developed modification strategy for improving the photocatalytic performance of WO3 nanomaterials in recent years, i.e., morphology regulation, oxygen vacancy regulation, element doping, cocatalyst loading, and construction of heterojunctions. Through these modification approaches, the band structure could be modulated and then increase the solar energy utilization. The spatial separation of electron-hole pairs could be thus accelerated. And electrons and holes with an intense redox ability could participate into the catalytic reactions. Besides, the surface structure and interfacial structure could be regulated, exposing themore unsaturated coordination sites and thereby accelerating the surface reaction. Despite the tremendous progress, further improvements are still urgently required to satisfy the industrial application. The cost-effective and large-scale preparation of WO3 nanomaterials with uniform size and unique structure is always a challenge. The understanding of the actual reactive sites in WO3 is important for getting insights into the structure-reactivity correlations. The synchrotron radiation and in-situ spectroscopy, the structural configurations for catalysts and the formation of intermediates during photoreaction could be monitored by some advanced characterizations like environmental transmission electron microscope, and aberration scanning transmission electron microscope. Combining the simulation with the related experiments could favor the in-depth understanding the mechanism during photocatalysis including reactant adsorption, diffusion and surface reaction, along with the charge carrier kinetics composed of light excitation, carrier migration and reaction barrier. These key points are crucial for designing high-efficient photocatalytic systems.

Attapulgite is a rod like silicate clay minerals with a 2:1 type chain layered nanostructure, and the length of rod crystal is 0.5-5.0 μm. It is a non-renewable natural nanomaterial. The layered crystal structure of the attapulgite chain endows it with special physical and chemical properties, including adsorption, colloidal, and cation exchange properties. Attapulgite is widely used in agriculture, environmental protection, chemical industry, and other fields due to its superior properties. The breakthrough in key common technologies for the dissociation of crystal beams in palygorskite rods enables the expansion of palygorskite from conventional applications to high-tech applications. Attapulgite as a non-toxic natural mineral material has good biocompatibility, abundant reserves, and low price. It has an enormous application potential in the field of high value-added biopharmaceuticals. This review summarized recent research work on the application, the structure and properties of attapulgite. The first part summarized the research progress of the application of attapulgite in the field of biological antibacterial, elaborated on the possible antibacterial mechanisms of attapulgite composite antibacterial materials, compared the preparation methods and antibacterial properties of different attapulgite based composite antibacterial materials, and gave that one of the research hotspots for attapulgite based composite antibacterial materials is to explore a simple and green preparation method. The second part summarized the application of attapulgite in the field of feed additives, represented the preparation of three different attapulgite based feed additives and their respective advantages and disadvantages, and pointed out that the relevant products are used in production practice, and listed some typical production process diagrams of the products. The third part represented the application of palygorskite in drug carriers. Attapulgite based drug carriers are mainly in the form of hydrogels and nanofibers. At present, there is no research on the application of attapulgite based drug carriers in vivo. The main reason is that the safety of palygorskite in vivo is unknown, and it is also stable, making it difficult to enter the blood and urinary circulation system as a drug carrier. However, the prepared attapulgite sustained-release tablets can be discharged through the digestive system and have great application prospects. The fourth part represented the application of attapulgite in composite scaffold materials. Although attapulgite based composite scaffold materials have a good osteogenic induction in vitro, their osteogenic induction in vivo is still unclear, and the mechanism of osteogenic induction in vitro is still unclear. The fifth part summarized the application of attapulgite in wound healing. Attapulgite based wound dressings have a good usability. Mixed dimensional attapulgite seems to have better usage effects and is expected to become a novel generation of hemostatic materials. Summary and prospects 1) In the future, it is necessary to accelerate the technological research on the full dispersion of attapulgite single crystals. Also, there is still a room for progress in the surface modification technology of attapulgite based composite antibacterial materials. The more attention should be paid to green and simple physical modification technologies, which can improve the production efficiency, and reduce the environmental pollution and costs. 2) Further research should be conducted on the application of palygorskite as a drug carrier on the body surface and digestive system, and pathways and methods suitable should be found to enable palygorskite to undergo harmless degradation in the blood and urinary systems. 3) It is necessary to accelerate the research on surface modification technologies of palygorskite, and make palygorskite based wound dressings into a form similar to gauze, which can to some extent reduce the risk of its entry into the blood system. 4) The practical application of attapulgite in the field of biomedicine is still relatively limited. In the future, we should accelerate the clinical research of attapulgite in the field of biomedicine, while still expanding the research of attapulgite in the field of biomedicine practice. For instance, we could use attapulgite to adsorb the metabolite of cholesterol-bile acid-to treat hypertension and hyperlipidemia. The adsorption of palygorskite is used to regulate the intestinal flora and interfere with the occurrence of type 2 diabetes. It is possible for the treatment of tumors to utilize the stability and biocompatibility of attapulgite to prepare high-performance drug loaded microspheres for embolization. The antibacterial and biocompatibility of attapulgite are also utilized to prepare alternative products for orthopedics and dentistry. This review provided a reference for the application research of attapulgite in the field of biomedicine.