CuAlO2 thermoelectric compacts by SPS and thermoelectric performance improvement by orientation control

We fabricated CuO/Al₂O₃ green compacts from plate-like Al₂O₃ and granular CuO powders by multi-press forming and investigated the alumina orientation using Lotgering's method. The results showed that Al₂O₃ particles preferentially aligned perpendicular to the pressure direction and the orientation degree increased as the forming pressure was increased. We proposed a model describing the movement of the alumina particles to explain the pressure effect on their orientation. The orientation calculation was in good agreement with those by Lotgering's method. Furthermore, we prepared the CuAlO₂ compacts by regular or spark plasma sintering (SPS). However, the compacts sintered by SPS exhibited higher orientation degree and density than those produced by regular sintering. The electrical conductivity values of the orientation-controlled compacts sintered by SPS reached 770 S m⁻¹ at 928 K, which was close to that of CuAlO₂ single crystal. The power factor of the CuAlO₂ compacts with highest orientation degree is as high as 5.95 × 10⁻⁵ W m⁻¹ K⁻¹ at 928 K. Therefore, we can conclude that orientation control is an effective method to enhance the thermoelectric performance of compact polycrystalline CuAlO₂ bulks.     

Morphology and orientation of MoS2 clusters on Al2O3 and TiO2 supports and their effect on catalytic performance

The catalytic performance of MoS₂-based hydrotreating catalysts strongly depends on their morphology and orientation on the support. The effects of the morphology and orientation of MoS₂ clusters on supports, typically Al₂O₃ and TiO₂, on the catalytic performance are reviewed here, focusing on recently reported epitaxial relationships at the interface between MoS₂ clusters and the support.     

Effect of Sn doping on the electrochemical performance of NaTi2(PO4)3/C composite

In this paper, NaTi_2-xSn_x(PO₄)₃/C (x?=?0.0, 0.2, 0.3, and 0.4) composites were fabricated via facile sol-gel method, and employed as anodes for aqueous lithium ion batteries. Effect of Sn doping with various content on electrochemical properties of NaTi₂(PO₄)₃/C was investigated systematically. Sn doping on Ti site has no obvious effect on the lattice structure and morphology of NaTi₂(PO₄)₃/C. Among all samples, NaTi_1.7Sn_0.3(PO₄)₃/C (NC-Sn-3) demonstrates the best electrochemical properties. NC-Sn-3 exhibits the outstanding rate performance, delivering a discharge capacity of 103.3, 95.2, and 87.4?mAh?g^?1 at 0.5, 7, and 20?°C, respectively, 1.7, 30.5, and 56.2?mAh?g^?1 larger than those of pristine NaTi₂(PO₄)₃/C. In addition, NC-Sn-3 shows excellent cycling performance with the capacity retention of 80.6% after 1000 cycles at 5?°C. This work reveals that Sn doped NaTi₂(PO₄)₃/C with outstanding electrochemical properties are potential anode for aqueous lithium ion batteries.     

Catalytic reduction of NO by C3H6 over Rh/TiO2 catalysts: Effect of W-cation doping of TiO2 on morphological characteristics and catalytic performance

The effect of W⁶⁺-cation doping of TiO₂ on its physicochemical characteristics has been examined and related to the catalytic performance of dispersed rhodium crystallites for the selective catalytic reduction (SCR) of NO by propylene in the presence of excess oxygen. It was found that doping of TiO₂ with small amounts of W⁶⁺ cations results in materials with increased surface areas and anatase-to-rutile contents, in a manner which depends on dopant concentration and calcination temperature. The acidity of the doped supports, measured by adsorption of ammonia, increases with increasing W⁶⁺-cation concentration and goes through a maximum for dopant contents of ca. 0.45 at.% W⁶⁺. The catalytic performance of supported rhodium for the SCR of NO by propylene is significantly improved over the doped carriers and varies with W⁶⁺-content in a way which is qualitatively similar to that of acidity. Results are explained evoking the beneficial effect of acidity on adsorption and partial oxidation of propylene, which results in faster regeneration of the catalytically active Rh⁰ sites, and the dopant-induced modifications of the electronic structure of rhodium crystallites which result in higher dissociation rates of adsorbed NO. Under the experimental conditions employed, the conversion of NO over the 0.5%Rh/TiO₂(0.45% W⁶⁺) catalyst is significantly improved and reaches 52%, compared to 38% over the undoped one. A further increase of conversion to 65% is achieved with increasing Rh loading to 1.5 wt.%. Measurements of the specific reaction rates show that the turnover frequency (TOF) of the reaction is only affected by electronic-type modifications and not by the geometric properties of the active sites.     

Photocatalytic performance of ZnGa2O4 for degradation of methylene blue and its improvement by doping with Cd

ZnGa₂O₄ powder catalysts, synthesized by a sol–gel process, exhibit high photocatalytic activity for methylene blue (MB) degradation. The pH value at the point of zero charge (pH_pzc) was determined to be 5.9 by a titrations method and MB conversion increased with the increase of the pH value. The valence and conduction band positions were determined at 3.35 V and − 1.45 V (Normal Hydrogen Electrode, NHE), respectively, indicating high photocatalytic ability. Improved photocatalytic efficiency was achieved by substituting cadmium for zinc in the ZnGa₂O₄. The improvement can be attributed to high UV absorption efficiency and high separation of photogenerated electron-hole pairs.     

Transition from mobility-activated small polaron to carrier density-activated conduction of sol-gel-derived highly-oriented CuAlO2 thin film and enhanced thermoelectric properties

CuAlO₂ is a technologically important material having diverse applications, including superior thermoelectric properties. Its unique crystallographic structure manifests an anisotropic environment for the charge carriers and phonons, which is considered to be the reason for the enhancement of the thermopower. To exploit this novel property, a controlled sol-gel deposition technique is adopted to realize highly c-axis-oriented growth of CuAlO₂ thin film on Si and glass substrates. Thermoelectric measurements are performed in such a way that the carriers are confined along the a-b plane of the nanocrystal, which is parallel to the substrate. This allows a two-dimensional confinement of the charge carriers, leading to enhanced thermoelectric properties. Additionally, the temperature-dependent electrical characterizations depict two different charge-transport regimes with a cross-over at 360 K. The low-temperature region corresponds to the mobility-activated small-polaron conduction and the high-temperature region belongs to the semiconductor-type carrier-density-activated conduction. Calculation of polaron activation energy from low-temperature regime indicates considerable influence of band carriers (hole) on the polaronic levels, due to which the above-mentioned transition is manifested. Calculations of activation and Fermi energy from high-temperature regime reveal a deep acceptor level and shallow Fermi level, which is typical of a non-degenerate semiconductor with acceptors not fully ionized at room temperature.     

Electrical Properties of Sr0.7Ba0.3TiO3 Ceramics Doped with Nb2O5, 3Li2O · 2SiO2, and Bi2O3

The electrical properties of Sr_0.5Ba_0.3TiO₃ in the presence of Nb₂O₅ as a donor, 3Li₂O · 2SiO₂ as a sintering agent, and Bi₂O₃ as a dopant have been studied. When the compositions of the ceramics were 1 mol Sr_0.7Ba_0.3TiO₃+ 0.5 mol% Nb₂O₅+ 2 mol% 3Li₂O · 2SiO₂+ 0.2 mol% Bi₂O₃, the ceramics were sintered at 1100°C and exhibited the following characteristics: apparent dielectric constant ɛ, 25000; loss factor tan δ, 2%; insulating resistivity ρ_j, 10¹⁰Ω· cm; variation of dielectric constant with temperature Δɛ/ɛ (−25° to +85°C), +10%, −14%. ɛ and tan δ show only small changes with frequency. The study shows this ceramic can be used in multilayer technology.     

Tubular V-free and V-doped TiO2 derived from H2Ti12O25 hollow spheres: Vapour-thermal synthesis,morphology evolution,and photocatalytic performance

Vanadium (V)-free and V-doped H₂Ti₁₂O₂₅ hollow spheres (HTOHSs) were first synthesised via vapour-thermal method at 290?°C using common chemicals and solvents, over super-critical temperature (243?°C) of ethanol (vapour source). Then, they were annealed at 600?°C under different processing conditions to obtain titanium dioxide (TiO₂) photocatalysts. All catalysts were characterised by means of XRD, SEM, TEM, XPS, UV–vis DRS, FT-IR, N₂ adsorbtion-desorbtion and fluorescence lifetime. Results indicated that after the treatment in air, V-free HTOHSs were transformed into open-ended hollow tubes with uniform length of ~5?µm and diameter of ~1?µm, and walls of hollow tubes consisted of aggregated nanosheets. Furthermore, HTOHS crystallised into anatase TiO₂ (white) phase. The treatment in N₂ atmosphere led to the breaking of longer tubes into shorter ones. In contrast, after the treatment in N₂ atmosphere or by reduction using NaBH₄ as a reductant, V-doped HTOHS resulted in the formation of anatase TiO₂ (black) samples and consisted of fewer tubes and more deformed spheres. In this study, fluorescence lifetime (τ) of photo-generated carriers corresponded well with the ratio of oxygen vacancy, indicating that oxygen vacancy dominates the lifetime even though it is very sensitive to many factors. The evolution of structure and morphology and photocatalytic mechanism were analysed and discussed.     

Reduction of SO2 by CO to elemental sulfur over Co3O4–TiO2 catalysts

Mixed oxides of Co₃O₄–TiO₂ have shown the highest catalytic activity for the reduction of SO₂ by CO among catalysts that have been developed so far. Almost zero conversion was observed with cobalt alone, whereas a high conversion was obtained with TiO₂ especially at high temperatures. There existed a strong synergistic promotional effect in the conversion of SO₂ when cobalt was mixed with TiO₂. The synergistic effect observed with mixed oxides is caused by simultaneous contributions from two different reaction routes via COS intermediate mechanism and modified redox mechanism. The synergistic effect that is caused by the COS mechanism has a smaller amount of contribution in the conversion increase and remains almost constant with an increase in the reaction temperature. A larger portion of the synergistic effect is contributed from the modified redox mechanism especially at low temperatures, but the effect disappears at temperatures above 450°C. It is found that the introduction of cobalt into TiO₂ produces COS by the reaction between sulfided CoS₂ and CO even at low temperatures. The COS intermediate can react with SO₂ to produce an additional sulfur via the COS intermediate mechanism, and also behaves as a strong reductant to keep oxygen vacancies on the TiO₂ in a high concentration for the production of sulfur via modified redox mechanism.     

新型Sr2V2O7:Eu3+荧光材料的制备及表征

以高纯度的SrCO3、NH4VO3、Eu2O3和Yb2O3等为主要原料,采用高温固相法合成荧光粉。X-粉末衍射及荧光光谱证实合成了一种在可见光范围内有广泛吸收的发黄光的钒酸盐体系荧光粉。其中Eu3+的最佳掺杂摩尔浓度比为0.09,最佳煅烧温度为1223K。     

Hydrothermal synthesis of graphene wrapped Fe-doped TiO2 nanospheres with high photocatalysis performance

In this study, graphene wrapped Fe-doped TiO₂ (G-TiO₂-Fe) spheres were prepared through a simple hydrothermal process. The structural, optical and photocatalytic properties of synthesized composite were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), Raman Microprobe (Raman), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectrophotometer (DRS). The G-TiO₂-Fe composite showed a significant red-shift in light response edge as compared with TiO₂. Meanwhile, the band gap exhibited an obvious decline from 3.24 to 2.99 eV. The photocatalytic capacity of G-TiO₂-Fe was further evaluated by methylene blue (MB) degradation experiments, and the results indicated that the optimized G-TiO₂-Fe exhibited a remarkable increase in photocatalytic activity. The superior photocatalytic performance of the novel material could be ascribed to the synthetic effects of doped Fe and wrapped graphene shells. The unique geometrical configuration and constructive component which modified the TiO₂ electronic structure will largely improve the electron transporting efficiency and restrain the electron-hole recombination.     

Mn和Zr共掺杂钛酸锶钡/氧化镁复合陶瓷材料的微结构和介电性能

通过固相反应法制备Mn、Zr共掺杂钛酸锶钡/氧化镁陶瓷粉体,经干压成型后在空气气氛中于1450℃烧结4h,通过扫描电子显微镜和X射线衍射研究了ZrO2和MnO2共掺杂的Ba0.6Sr0.4TiO3/MgO复合陶瓷材料的微结构和介电性能。结果表明:ZrO2可以显著降低材料的介电常数和介电损耗,有效提高了陶瓷材料的温度稳定性;随ZrO2添加量的增加,体系的晶胞参数略有增加,MgO在钛酸锶钡中以独立相的形式存在;制备出的BST铁电陶瓷材料的25℃相对介电常数较低(εr<110),介质损耗小于1.0×10–3(在频率为10kHz时),温度系数小于6.012×10–3,可调性大于20%(8.0kV/mm),适用于制作移相器。     

Effect of Praseodymium and Uranium Addition on the Jc of Ba2 YCu3O7

Ba₂YCu₃O₇ ceramics doped with either Pr or U at 0.000 17 to 1.7 wt% levels have been prepared. For each sample J _c (magn) has been measured with a vibrating sample magnetometer. No improvement in J _c was found for either dopant and it is concluded that neither provides the clusters necessary to produce suitable pinning sites.     

Electrochemical synthesis of polyacetylene tetrachloroferrate [CH(FeCl4)y]x and tetrachloroaluminate [CH(AlCl4)y]x

Polyacetylene can be electrochemically oxidized in LiClFeCl₃ nitromethane and LiClAlCl₃ nitromethane solutions to give a highly conducting (500 ohm⁻¹ cm⁻¹) polymer exhibiting p-type conductivity. The limiting composition obtainable in the electrolysis can be expressed by the following formula: [CH(MCl₄)_0.05]_x where M = FeAl.     

Promoting effect of calcium on reduction of NO by C3H6 over V2O5/ZrO2 catalysts

The reduction of nitrogen monoxide by propene on V₂O₅/ZrO₂ doped with or without calcium has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Considerable promoting effect of calcium doping on the reduction of nitrogen monoxide by propene was observed on the V₂O₅/ZrO₂ catalysts. For the reaction of a mixture of NO+C₃H₆, carbonyl and carboxylate species were observed above 373 K, although nitrate species formed at room temperature on V₂O₅/ZrO₂ doped with calcium. No bands due to a compound including both carbon and nitrogen atoms were observed. Thus, the redox mechanism, i.e. propene reduces the catalyst and nitrogen monoxide oxidizes the catalyst, is confirmed on V₂O₅/ZrO₂ catalysts doped with or without calcium. The analysis of the V=O band in the region of 1100–900 cm⁻¹ indicates that this promotion is mainly due to new V=O species formed by the addition of calcium onto the catalyst. This species is easily reproduced in comparison with the other V=O species on the surface in the reoxidation process of the catalyst.     

Comparison of dispersants performance on the suspension Lu2O3:Eu stability and high-density compacts on their basis

The conditions for obtaining a stable Lu₂O₃:Eu³⁺ suspension of spherical particles with a diameter of 100 nm using three dispersants possessing an electrosteric stabilizing effect (Dolapix CE 64, Darvan 821 A, Darvan C-N) have been studied. It has been shown that in colloidal processing of ceramics the packing density and microstructure of green bodies can be controlled by regulating the interactions between ceramic particles in the suspension. The influence of the molecular weight and concentration of the dispersant on the stability of Lu₂O₃:Eu³⁺ suspensions containing 5-10 vol.% of the solid loading has been considered. It has been determined that use of Dolapix CE 64 with a concentration of 1 mass.% in the alkaline pH range allows to obtain suspensions with high stability and low viscosity (∼1.7 сP). Such suspensions were used to produce compacts with a maximum relative density of ∼52% and uniform density distribution by the pressure slip casting method. The obtained compacts were densified into translucent Lu₂O₃:Eu³⁺ ceramics by the vacuum sintering method.     

Synthesis of highly efficient,structurally improved Li4SiO4 sorbents for high-temperature CO2 capture

Li₄SiO₄ sorbents for high-temperature CO₂ removal have drawn extensive attention owing to their potential application in carbon capture and storage (CCS). The major challenge in the application lies in the poor CO₂ capture performance under realistic conditions of low CO₂ concentrations, owing to the dense structure and poor porosity. In this work, Li₄SiO₄ sorbents were prepared with porous micromorphologies and large contact areas using a variety of organometallic Li-precursors, achieving fast CO₂ sorption kinetics, high capacity and excellent cyclic stability at a low CO₂ concentration (15?vol%). It was found that a high conversion of ~?74% was maintained for pure Li₄SiO₄ even after 100 sorption/desorption cycles. Moreover, by doping with Na₂CO₃ to reduce the CO₂ diffusion resistance, the conversion of the sorbent was further enhanced to 93.2%. The enhancement mechanism of alkali carbonate have been proven here to be ascribed to the formation of the eutectic melt of Li/Na carbonates, the existence and function of which has been confirmed in this study.     

Enhancement of the visible light photocatalytic performance of C-doped TiO2 by loading with V2O5

V₂O₅ was loaded on the surface of C-doped TiO₂ (C-TiO₂) by incipient wetness impregnation in order to enhance the visible light photocatalytic performance. The physicochemical properties of the C-TiO₂/V₂O₅ composite were characterized by XRD, Raman, TEM, XPS, UV–vis diffuse reflectance spectra, and PL in detail. The result indicated that a heterojunction between C-TiO₂ and V₂O₅ was formed and the separation of excited electron–hole pairs on C-TiO₂/V₂O₅ is greatly promoted. Thus, this composite photocatalyst exhibited enhanced visible light photocatalytic activity in degradation of gas-phase toluene compared with the pristine C-TiO₂.     

The negative and positive structural effects of Ga doping in the electrochemical performance of LiCoO2

The electrochemical performance of LiGa_yCo_1−yO₂ electrodes_,y = 0.005 and 0.1, was studied. Charge/discharge curves in galvanostatic condition were obtained for a series of voltages ranging from 4.35 to 4.7 V. Samples were previously characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray absorption spectroscopy (XAS) and conductivity measurements. Comparison of data obtained for LiGa_yCo_1−yO₂ and the pristine oxide LiCoO₂ is provided. Ga doping at 0.5 mol% drastically reduces the electrode capacity fading when charges at 4.35 or 4.5 V are applied, while Ga doping at 10 mol% spoils the Ga-doped oxides electrochemical response, even at a cut-off limit of 4.35 V. These positive and negative effects were attributed to changes in both the electronic conductivity and local structure of LiCoO₂, induced by substitution of Co for Ga and cationic disorder. For y = 0.005, a slight distortion in the LiCoO₂ local structure occurs, and formation of states in the band gap that the raise oxide electronic conductivity is observed, explaining the electrochemical improvement in LiGa_yCo_1−yO₂. In contrast, hybridization with oxygen occurs when y = 0.1, opening LiCoO₂ band gap and making LiGa_yCo_1−yO₂ an insulator and a cationic disorder material that leads to poor electrochemical performance. Finally, XAS results show that Ga doping does not change the LiCoO₂ charge transfer mechanisms, where oxygen is reduced during lithium extraction.