Reduction of carbon dioxide with water under concentrated sunlight using photocatalyst combined with Fe-based catalyst

The reduction of CO₂ with water into valuable organic compounds under concentrated sunlight was investigated for the first time over a hybrid catalyst, in which a Pt-loaded K₂Ti₆O₁₃ photocatalyst was combined with a Fe-based catalyst supported on a dealuminated Y-type zeolite (Fe-Cu-K/DAY). In this reaction system, the Pt/K₂Ti₆O₁₃ catalyst decomposes water to produce H₂ and the Fe-Cu-K/DAY catalyst reduces CO₂ with the resulting H₂ into organic compounds. When only the Pt/K₂Ti₆O₁₃ photocatalyst was used, organic compounds such as CH₄, HCOOH, and HCHO were formed together with H₂, indicating that CO₂ can also be directly reduced over Pt/K₂Ti₆O₁₃. On the contrary, when the hybrid catalyst was used, CH₃OH and C₂H₅OH were produced in addition to the above products, depending on the reaction temperature and catalyst composition. The reaction temperature significantly increased by concentrating the solar irradiation, reaching 600 K and increasing the product yields. It is suggested that such a high reaction temperature facilitates both the photoreduction and hydrogenation of CO₂ over Pt/K₂Ti₆O₁₃ and Fe-Cu-K/DAY, respectively.     

Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

A new smooth potassium dititanate film was prepared by sol-gel method and characterized by thermogravimetry (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible diffuse reflectance and Raman spectroscopy. The gaseous photocatalytic activity of smooth K₂Ti₂O₅ films was studied using contact angle analysis from the photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayers (SAMs) formed on K₂Ti₂O₅ films. The photocurrent response of the film was determined by an electrochemical method. It was shown that the films were smooth, compact, and transparent when formed on glass. Compared with TiO₂ film, the K₂Ti₂O₅ film showed wide absorption in the ultraviolet and visible region. It was found that the monolayers on K₂Ti₂O₅ decomposed much faster than those on TiO₂ under UV irradiation of 254 nm in air. The film also exhibited a stronger photoresponse and a more stable anodic photocurrent. The K₂Ti₂O₅ film efficiently decomposes the alkylsiloxane monolayers under UV irradiation in air and it was found to be a good photocatalyst for gaseous organic pollutant treatment.     

纳/微复合结构TiO2负载催化剂的加氢脱硫性能

以传统固相烧结法制备的不稳定的层状K₂Ti₂O₅为前驱体, 直接将钛酸钾晶须进行离子交换得到具有纳微复合结构的TiO₂载体, 等体积浸渍法制备出MoO₃/TiO₂催化剂, 运用SEM、XRD、BET、TEM等技术手段对载体和催化剂进行表征, 并考察了该TiO₂复合结构负载催化剂的加氢脱硫催化活性。SEM和XRD分析显示:该纳微米复合结构是由纳米颗粒与微米晶须构成的特殊结构, 拥有不同形貌和尺寸的TiO₂却具有相同的锐钛矿相。与单独TiO₂纳米粒子和TiO₂晶须相比, TiO₂复合结构负载催化剂表现出更佳的脱硫催化能力, 在温度310℃、压力2.1 MPa、体积空速6 h^-1、氢/油体积比600条件下, 催化剂表现出优异的DBT脱硫性能。     

Facile ultrasonic-assisted synthesis of micro–nanosheet structure Bi4Ti3O12/g-C3N4 composites with enhanced photocatalytic activity on organic pollutants

The Bi₄Ti₃O₁₂/g-C₃N₄ composites with microsheet and nanosheet structure were prepared through facile ultrasonic-assisted method. The SEM and TEM results suggested that the nanosheets g-C₃N₄ were stacked on the surface of regular Bi₄Ti₃O₁₂ sheets. Comparing with pure Bi₄Ti₃O₁₂ and g-C₃N₄, the Bi₄Ti₃O₁₂/g-C₃N₄ composites showed significant enhancement in photocatalytic efficiency for the degradation of RhB in solution. With the mass ratio of g-C₃N₄ increasing to 10 wt%, the Bi₄Ti₃O₁₂/g-C₃N₄-10% presented the best photocatalytic activity. Its photocatalysis reaction constant was approximately 2 times higher than the single component Bi₄Ti₃O₁₂ or g-C₃N₄. Meanwhile, good stability and durability for the Bi₄Ti₃O₁₂/g-C₃N₄-10% were confirmed by the recycling experiment and FT-IR analysis. The possible mechanism for the improvements was the matched band positions and the effective separation of photo-excited electrons (e^-) and holes (h⁺). Furthermore, based on the results of active species trapping, photo-generated holes (h⁺) and superoxide radical (·O₂^-) could be the main radicals in reaction.     

Selective oxidation of toluene on V2O5/TiO2/SiO2 catalysts modified with Te, Al, Mg, and K2SO4

The effect of the modification of vanadia catalysts supported on TiO₂/SiO₂ by the oxides of Al, Mg and Te, and K₂SO₄on the selective oxidation of toluene in the vapor phase has been studied. The catalysts were prepared by successive impregnation and characterized by BET surface measurements, XRD, XPS, and TPR. Addition of the second component decreased specific activity in all cases, except Al, mainly due to the decrease of surface area. Intrinsic activity was increased with addition of Te and Al, and decreased by that of Mg, while K₂SO₄ had little effect. These differences could be explained by the observed changes in either vanadium surface dispersion or reducibility. Selectivity to benzaldehyde increased markedly with addition of Te or K₂SO₄, that caused the formation of new oxide phases, V₃Ti₆O₁₇ and TiV₂O₆, in which vanadium is in a partially reduced state.     

Control of Composition and Structure in Laminated Silicon Nitride/Boron Nitride Composites

Based on a biomimetic design, Si₃N₄/BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si₃N₄ matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si₃N₄ or Al₂O₃. The results showed that the addition of SiC whiskers in the Si₃N₄ matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m^1/2), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al₂O₃ or 10 wt% Si₃N₄ to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si₃N₄/BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si₃N₄/BN composites were present as the first-level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull-out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers.     

Effects of processing conditions on the mechanical performance of maleic anhydride compatibilized in-situ composites of polypropylene with liquid crystalline polymer

Maleic anhydride compatibilized blends of isotactic polypropylene (PP) and thermotropic liquid crystaline polymer (LCP) were prepared either by the direct injection molding (one-step process), or by twin-screw extrusion blending, after which specimens were injection molded (two-step process). The morphology and mechanical properties of these injection molded in situ LCP composites were studied by means of scanning electron microscopy (SEM), Izod impact testing, static tensile, and dynamic mechanical measurements. SEM observations showed that fine and elongated LCP fibrils are formed in the maleic anhydride compatibilized in situ composites fabricated by means of the one-step process. The tensile strength and modulus of these composites were considerably close to those predicted from the rule of mixtures. Furthermore, the impact behavior of LCP fibril reinforced composites was similar to that of the glass fiber reinforced polymer composites. On the other hand, the maleic anhydride compatibilized blends prepared from the two-step process showed lower mechanical performance, which was attributed to the poorer processing behavior leading to the degradation of PP. The effects of the processing steps, temperatures, and compatibilizer addition on the mechanical properties of the PP/LCP blends are discussed.     

Fracture Behavior of SiC-Whisker-Reinforced Barium Aluminosilicate Glass-Ceramic Matrix Composites

Barium aluminosilicate (BAS) glass-ceramic composites reinforced with various volume percents (0, 10, 20, 30, 40 vol%) of SiC whiskers were fabricated by hot pressing. The microstructure, the whisker/matrix interface structure, the phase constitution, and the mechanical properties of the composites were systematically studied by means of SEM, TEM, and XRD techniques as well as by indentation crack microfracture and single-edge-notched-beam bend testing. It was demonstrated that the incorporation of SiC whiskers could significantly increase the flexural strength and fracture toughness of BAS glass-ceramic matrices. The addition of active Al₂O₃ to the BAS matrix reduced the amount of SiO₂ in the matrix, forming needlelike mullite, which further improved the mechanical properties.     

Mechanical properties of Al2O3 + ZrO2 + nano-SiCp ceramic composites

The mechanical properties of Al₂O₃ matrix composites reinforced by ZrO₂(2 mol% Y₂O₃) and nanometre scale SiC dispersions have been investigated. It is shown that the Al₂O₃ matrix is simultaneously strengthened and toughened by both ZrO₂(2 mol% Y₂O₃) and nano-SiC particles. The maximum flexural strength and fracture toughness of the composites are 945 MPa and 7.3 MPam^1/2, respectively. The reinforcing effect of both t-m phase transformation of ZrO₂ (2 mol% Y₂O₃) and nano-SiC particles appears to be synergetic.     

Toughening of Silicon Nitride Matrix Composites by the Addition of Both Silicon Carbide Whiskers and Silicon Carbide Particles

Si₃N₄ matrix composites reinforced by SiC whiskers, SiC particles, or both were fabricated using the hot-pressing technique. The mechanical properties of the composites containing various amounts of these SiC reinforcing materials and different sizes of SiC particles were investigated. Fracture toughness of the composites was significantly improved by introducing SiC whiskers and particles together, compared with that obtained by adding SiC whiskers or SiC particles alone. On increasing the size of the added SiC particles, the fracture toughness of the composites reinforced by both whiskers and particles was increased. Their fracture toughness also showed a strong dependence on the amount of SiC particles (average size 40 μm) and was a maximum at the particle content of 10 vol%. The maximum fracture toughness of these composites was 10.5 MPa·m^1/2 and the flexural strength was 550 MPa after addition of 20 vol% of SiC whiskers and 10 vol% of SiC particles having an average particle size of 40 μm. These mechanical properties were almost constant from room temperature to temperatures around 1000°C. Fracture surface observations revealed that the reinforcing mechanisms acting in these composites were crack deflection and crack branching by SiC particles and pullout of SiC whiskers.     

钛酸锂/石墨烯复合负极材料的制备及电化学性能

以Li₂CO₃、锐钛矿TiO₂和石墨烯为原料，采用固相球磨及喷雾干燥相结合的方法制备钛酸锂和钛酸锂/石墨烯复合负极材料。用X射线衍射（XRD）、拉曼光谱、扫描电子显微镜（SEM）表征了样品的晶体结构及形貌。通过恒流充放电测试样品的电化学性能，考察不同石墨烯添加量对钛酸锂材料电化学性能的影响。当石墨烯添加量质量分数为1%时，钛酸锂/石墨烯复合负极材料（LTO-G-2）具有优异的倍率性能及循环稳定性。在0.2C、0.5C、1C、3C、5C和10C倍率下的充电比容量为172.9mA·h/g、165.7mA·h/g、163.5mA·h/g、157.4mA·h/g、154.0mA·h/g和143.5mA·h/g。5C倍率下经历200次循环，容量保持率为94.8%。循环伏安测试(CV)表明LTO-G-2样品的极化程度是最小的。交流阻抗测试（EIS）结果显示LTO-G-2的电荷转移阻抗（69.6Ω）小于纯的钛酸锂的电荷转移阻抗（140.5Ω）。     

Fiber reinforcement and fracture resistance of PC/PBT/LCP ternary in situ composite

The microstructures, mechanical properties, and fracture toughness of LCP (Vectra B950) reinforced PC/PBT blend with a 60/40 weight ratio have been studied. LCP of varying concentrations were investigated as rigid fillers in matrices of multiphase polymer blends. In this study, differences in microstructures and morphology between samples of two thicknesses (4 mm thick and 6 mm thick) and two geometries (dumbbell and rectangular) were compared using scanning electron microscopy (SEM). Given identical processing conditions, fibrous LCP structures were evident in the 4-mm-thick injection molded, dumbbell-shaped samples, whereas the 6-mm-thick rectangular samples displayed spherical dispersion of LCP aggregates that embrittled the preblended ductile matrix. Tensile properties of the dumbbell specimens showed superior strengthening and stiffening whereby the tensile strength increased twofold and the modulus increased fourfold. Plane strain fracture toughness was slightly enhanced as the LCP content increased because of the fiber strengthening effect but the overall fracture performance of the in situ composites was relatively poor compared with PC/PBT. Experimental results were compared with those predicted in composite theory. Simplified micromechanics equations were developed to describe the tensile moduli of injection molded LCP reinforced blends that exhibited a strong skin-core morphology.     

Electromagnetic properties of ferroelectric-ferrite ceramic composites

The NiFe₂O₄ and Pb(Zr_0.52Ti_0.48)O₃ ceramic composites are prepared by conventional solid state reaction method. The microstructural and morphological properties of the composites are studied by X-ray diffraction analysis and scanning electron microscopy. Results indicate that the ferrite and piezoelectric phases can co-exist in the composites. The relationship between the dielectric constant and frequency (40 Hz–40 MHz) as well as temperature is also investigated. It is noted that the transition temperature of the composites is about 380 °C. A double electric hysteresis loop is observed in our composites. The magnetic properties are relatively weak according to the magnetic hysteresis loop. With increase in the content of the ferrite phase, the permeability increases. The electromagnetic properties of the as-prepared composites are tunable according to the content of the NiFe₂O₄ phase.     

Hot isostatic pressing of SiC/Si3N4 composite with rare earth oxide additions

SiC/Si₃N₄ composites with rare earth oxide additions have been prepared by glass encapsulated hot isostatic pressing at 1850 °C and 200 MPa pressure. Mechanical properties and microstructures of the sintered samples have been studied. It is shown that different molar ratios of La₂O₃ to Y₂O₃ and the total amount of La₂O₃ and Y₂O₃ additions can affect the mechanical properties significantly. With 3 wt% La₂O₃ + Y₂O₃ additions, lower La₂O₃/Y₂O₃ molar ratio exhibits higher bending strength and median fracture toughness, but relatively lower Vickers hardness. For addition of 6 wt% La₂O₃ + Y₂O₃, the higher bending strength, Vickers hardness and fracture toughness correspond to a certain La₂O₃/Y₂O₃ molar ratio of 1.5, 1.0 and 0.5, respectively. SEM observation shows that the SiC matrix composite with fine grain size and homogeneous microstructure can be obtained.     

Oxidative coupling of methane over oxide catalysts with layered structure

The catalytic properties of complex oxides with a layered structure Bi₂GeO₅, Bi₂SiO₅, Bi₄Ti₃O₁₂, Bi₂CaSrCu₃O₈+x and YBa₂Cu₃O₆+δ in oxidative coupling of methane (OCM) have been studied. Bi₂EO₅ metastable compounds have been found to possess the high activity and C₂-selectivity 53–70%. It has been assumed that the intergrowth boundaries for the Bi₂EO₅ decomposition products, on which active catalytic sites may be located, play a specific role on the catalytic performance of the oxides. Bi₄Ti₃O₁₂ and Bi₂CaSrCu₃O₈+x have close catalytic activity values but Bi₂CaSrCu₃O₈+x as well as YBa₂Cu₃O₆+δ are not selective in OCM reaction.     

The reaction sequence and dielectric properties of BaSm2Ti4O12 ceramics

To establish the correct reaction sequence of BaO–Sm₂O₃–4TiO₂, phases present in different calcining temperatures are identified by X-ray diffraction patterns. When different calcining temperatures are used, the source phase BaO (BaCO₃) consumes below 850°C, the source phases TiO₂ and Sm₂O₃ consume at 1000 and 1150°C; the intermediate phases BaTiO₃, BaTi₄O₉, and Sm₂Ti₂O₇ consume at 1050, 1200, and 1250°C, respectively. The BaSm₂Ti₄O₁₂ phase starts to reveal at the 1100°C-calcined powder. The integrating intensity of BaSm₂Ti₄O₁₂ phase increases with the raising of calcining temperatures, accompanying with the decrease of integrating intensities of the source and intermediate phases. As the sintering temperature increases, the densities, quality values, and dielectric constants of BaSm₂Ti₄O₁₂ ceramics increase and saturate at 1325^oC. The BaSm₂Ti₄O₁₂ ceramics sintered at 1325°C have the properties of Q^*f=5180,_r=81.8, and τ_f=−19.2 ppm/°C.     

γ-Al2O3/TiO2混合纳米粒子改性PVDF超滤膜

为提高聚偏氟乙烯（PVDF）膜的亲水性和强度,将纳米二氧化钛（TiO2）溶胶和纳米氧化铝（γ-Al2O3）按不同比例与聚偏氟乙烯共混,采用相转化法制得共混超滤膜。考察了不同比例的混合纳米粒子对PVDF超滤膜的纯水通量、截留率、力学性能等的影响。并利用扫描电子显微镜（SEM）观察了膜的表面和内部微观结构,红外光谱分析（FTIR）和X射线衍射仪（XRD）考察纳米粒子在PVDF基体中的存在状态,通过对复合膜进行拉力测试研究混合纳米粒子对膜力学性能的影响,并使用接触角测量仪测定膜表面和水之间的接触角来定量分析比较膜表面的亲水性。结果表明,γ-Al2O3/TiO2混合比为1∶2时,膜的性能达到最优,孔隙率为74%,水通量为120 L/（m2.h）,截留率为93%,拉力最大负荷为35 N,拉伸应变为22%。     

Microwave assisted sintering of CaCu3Ti4O12

CaCu₃Ti₄O₁₂ electroceramic was prepared by a microwave assisted solid-state reaction technique from CaCO₃, CuO and TiO₂ powders. Processing involved the preparation of raw material, mixing and milling, calcination, pellet forming and sintering processes. Conventional furnace and microwave assisted sintering processes were employed in order to improve phase structures, morphology and dielectric properties of CaCu₃Ti₄O₁₂ ceramics. Surface and fracture FESEM analysis showed that the microwave assisted sintered CaCu₃Ti₄O₁₂ produced better densification and more uniform grain size compared to the conventional sintered sample.     

Liquid crystalline polymer (LCP) reinforced polyethylene blend blown film: Effects of counter-rotating die on fiber orientation and film properties

Polyethylene blends (LLDPE:HDPE ≈ 2:1 by wt) used in NASA's balloon film applications can be effectively reinforced by addition of a small amount of liquid crystalline polymer (LCP). Cast and blown PE films containing ≈ 10% LCP show an appreciable enhancement in tensile modulus ≈400% over that of the neat PE matrix. Anisotropy in these in-situ composites was reduced by controlling LCP molecular orientation via a counter-rotating (C/R) annular die. LCP/PE blend blown films with nearly isotropic properties are obtained. Based on microscopy studies, LCP domains were generally present as fibrils with diameters of ≈ 1 to 3 µM and lengths of ≈ 100 to 300 µM. Films, produced using a C/R die, had fibrillated LCP phases and variable orientation through the film thickness. This paper describes the influence of some key process variables including temperature profile, number of extrusion cycles, degree of mixing, adapter geometry, and die counter-rotation on LCP/PE blend film morphology and mechanical properties. The structure of LCP/PE blend blown films was also evaluated using scanning electron microscope (SEM) and wide angle X-ray scattering (WAXS) techniques.     

多孔Al2O3/SiC、MoSi2/SiC复合材料的制备及吸波性能

以Si、Al₂O₃、MoSi₂微粉和生物竹材为原料,采用包埋烧结法分别制备出SiC多孔材料、Al₂O₃/SiC、MoSi₂/SiC复合材料。采用XRD、SEM及波导法测试其物相组成、显微结构及吸波性能。结果表明：MoSi₂/SiC复合材料的厚度为2 mm时有明显的吸波特性,有效吸收带宽在X波段的9.65~12.4 GHz频率范围内达2.75 GHz,且最低反射损耗为-38.27 dB。Al₂O₃/SiC复合材料孔道内的Al₂O₃与SiC晶须交缠,形成大量电偶极矩,产生介电损耗;MoSi₂/SiC复合材料除介电损耗外还存在电阻损耗,使得复合材料电磁损耗增加,是较有前途的结构功能吸波材料。