Synthesis of mullite nanofibres by electrospinning of solutions containing different proportions of polyvinyl butyral

In this paper, the synthesis of continuous mullite (3Al₂O₃·2SiO₂) nanofibres by combination of the sol–gel and electrospinning technique is reported. To find out the optimum viscosity of the electrospinning solution for obtaining the high quality mullite nanofibers, solutions containing different amounts of polyvinyl butyral (PVB, 0–8 wt%) and the precursor sol were prepared for the electrospinning process. The precursor sol was made by using proper amounts of aluminium isopropoxide (AIP), hydrated aluminium nitrate (AN) and tetraethylorthosilicate (TEOS). Crystal phase, microstructure and thermal decomposition behaviour of the electrospun mullite nanofibres were investigated by conventional methods of analysis. The optimal amount of PVB in the electrospinning polymeric solutions was found to be between 4 and 6 wt% and the mullite nanofibres obtained as such were pure, smooth and uniform with diameter sizes of 85–130 nm after calcination at 1200 °C.     

Influence of sintering temperature on dielectric properties and crystal structure of corundum-structured Mg4Ta2O9 ceramics at microwave frequencies

Microwave dielectric properties of corundum-structured Mg₄Ta₂O₉ ceramics were investigated as a function of sintering temperatures by an aqueous sol–gel process. Crystal structure and microstructure were examined by X-ray diffraction (XRD) technique and field emission scanning electron microscopy (FE-SEM). Sintering characteristics and microwave dielectric properties of Mg₄Ta₂O₉ ceramics were studied as a function of sintering temperature from 1250 °C to 1450 °C. With increasing sintering temperature, the density, ε_r and Qf values increased, saturating at 1300 °C with excellent microwave properties of ε_r=11.9, Qf=195,000 GHz and τ_f=?47 ppm/°C. Evaluation of dielectric properties of Mg₄Ta₂O₉ ceramics were also analyzed by means of first principle calculation method and ionic polarizability theory.     

Effects of sintering temperature on mechanical properties of 3D mullite fiber (ALF FB3) reinforced mullite composites

A new method to weaken the interfacial bonding and increase the strength of 3D mullite fiber reinforced mullite matrix (Mu_f/Mu) composites is proposed and tested in this paper. Firstly, Mu_f/Mu composites were fabricated through sol–gel process with varied sintering temperature. Then, the effects of sintering temperature on mechanical properties of the composites were tested. As sintering temperature was raised from 1000 °C to 1300 °C, the three-point flexural strength of the composites firstly decreased from 66.17 MPa to 41.83 MPa, and then increased to 63.17 MPa. In order to explain the relationship between composite strength and sintering temperature, morphology and structure of the mullite fibers and mullite matrix after the same heat-treatment as in the fabrication conditions of the composites were also investigated. Finally, it is concluded that this strength variation results from the combined effects of matrix densification, interfacial bonding and fiber degradation under different sintering temperatures.     

Ag/CeO2-ZnO催化剂上甲醇部分氧化制氢气研究

研究了用于甲醇部分氧化制氢气反应的Ag/CeO2-ZnO催化剂的制备条件以及反应条件对催化剂性能的影响.Ag/CeO2-ZnO催化剂中银含量、焙烧温度、反应温度以及反应气的比例等对催化剂性能具有很大的影响.Ag/CeO2-ZnO催化剂的制备条件以及反应条件控制在一定范围内时,Ag/CeO2-ZnO催化剂对甲醇部分氧化制氢气具有很高的催化活性与选择性.     

银掺杂对二氧化钛晶型转变的影响

采用溶胶-凝胶法制备了银掺杂的TiO2粉末,用XRD分析了掺银TiO2胶体经不同温度热处理后的晶型转变。结果表明:与未掺银的TiO2粉末相比,掺银TiO2从锐钛矿相向金红石相转变的起始温度较高,而且锐钛矿-金红石相变的温区范围变窄,晶型转变过程较快。     

“Deactivation of copper electrode” in electrochemical reduction of CO2

Metallic Cu electrode can electrochemically reduce CO₂ to CH₄, C₂H₄ and alcohols with high yields as revealed by the present authors. Many workers reported that formation of CH₄ and C₂H₄ rapidly diminishes during electrolysis of CO₂ reduction. This paper shows that such deactivation of Cu electrode is reproduced with electrolyte solutions prepared from reagents used by these workers. Deactivated Cu electrodes recovered the electrocatalytic activity for CO₂ reduction by anodic polarization at −0.05 V versus she in agreement with the previous reports. Features of the deactivation depend greatly on the individual chemical reagents. Purification of the electrolyte solution by preelectrolysis with a Pt black electrode effectively prevents the deactivation of Cu electrode. Anode stripping voltammetry of Cu electrodes, which were deactivated during electrolysis of CO₂ reduction, showed anodic oxidation peaks at ca. −0.1 or −0.56 V versus she. The severer the deactivation of the Cu electrode was, the higher electric charge of the anodic peak was observed. It is presumed that some impurity heavy metal, originally contained in the electrolyte, is deposited on the Cu electrode during the CO₂ reduction, poisoning the electrocatalytic activity. On the basis of the potential of the anodic peaks, Fe²⁺ and Zn²⁺ are assumed to be the major contaminants, which cause the deactivation of the Cu electrode. Deliberate addition of Fe²⁺ or Zn²⁺ to the electrolyte solutions purified by preelectrolysis exactly reproduced the deactivation of a Cu electrode in CO₂ reduction. The amount of the deposited Fe or Zn on the electrode was below the monolayer coverage. Electrothermal atomic absorption spectrometry (etaas) showed that Fe originally contained in the electrolyte solution is effectively removed by the preelectrolysis of the solution. Mechanistic difference is discussed between Fe and Zn in the deterioration of the electrocatalytic property of Cu electrode in the CO₂ reduction. The concentration of the impurity substances originally contained in the chemical reagents as Fe or Zn is estimated to be far below the standard of the impurity levels guaranteed by the manufacturers. Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO₂ reduction. It was concluded that the deactivation of Cu electrode in CO₂ reduction is not caused by adsorption of the products or the intermediates produced in CO₂ reduction.     

Silver nanostructured catalyst for modification of dielectrics surface

The preparation of nano-size Ag particles and their application for forming nanostructured catalysts on various surfaces are described. Silver colloid solutions were prepared by reduction of Ag(I) salt by tin(II) and characterized by electron microscopy, X-ray diffraction and light absorption spectra. Depending on the colloid preparation conditions metal particles of 5-100 nm size were obtained. According to XRD data, the colloid particles contain Ag and SnO₂ phases and no metallic Sn. The Ag nanoparticles were found to be efficient electrocatalysts for anodic oxidation of formaldehyde in alkaline solutions. The catalytic activity of a glassy carbon electrode with Ag surface coverage of 0.3-1 μg cm⁻² is similar or even exceeds that of the metallic electrode. The silver particles were used for the initiation of the electroless copper deposition process on dielectrics; for that 1-2 μg cm⁻² Ag is needed.     

Cu基分子筛催化剂抗中毒性能的研究进展

以SAPO-34、SSZ-13和ZSM-5载体为主线,综述了近年来国内外Cu基分子筛的中毒失活机理,以及在制备方法、Cu物种种类和含量、分子筛载体改性对催化剂抗失活性能提升的研究进展,并展望了该领域未来可能的发展方向和研究热点。     

Synthesis and characterization studies of NiO nanorods for enhancing solar cell efficiency using photon upconversion materials

We report the effect of calcination on the structural and optical properties of nanocrystalline NiO nanoparticles were successfully synthesized by virtue of a single source precursor method at mild reaction conditions between nickel nitrate and sodium hydroxide. Composition, structure and morphology of the products were analyzed and characterized by X-ray powder diffraction (XRD). The ultra-violet visible (UV–vis) absorption peaks of NiO exhibited a large blue shift and the luminescent spectra had a strong and broad emission band centered at 328 nm. The intense band gap was also observed, with some spectral tuning, to give a range of absorption energies from 2.60 to 3.41 eV. The various functional groups present in the NiO nanorods were identified by FTIR analysis. High resolution transmission electron microscopy (HRTEM) and the chemical composition of the samples the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS) in detail. The electrochemical response of NiO proved that the nano-nickel has a high level of functionality due to its small size and higher electrochemical activity without any modifications. The above studies demonstrate the potential for the utilization of NiO nanoparticles as a promising material for opto-electronics applications.     

银基析氧催化剂的研究进展

近年来基于阳极析氧催化的电解水制氢技术引起了广泛关注,安全、高效的阳极析氧催化剂是实现该技术的核心。银基析氧催化剂具有操作条件温和、析氧过电位低及结构易于调变的特性,是一种颇具发展前景的新型阳极析氧催化剂。本文综述了Ag基析氧催化剂的制备及其在电解水制氢方面的应用,着重介绍了Ag基析氧催化剂的两种调控改性方法,包括原位调控方法和后制备调控方法,其中原位调控方法主要有电解质溶液的匹配、电解质(浓度、酸碱度、温度)的调变和工作电极的修饰,后制备调控方法主要有金属氧化物复合、石墨烯复合和银氧化物纳米晶的调控。将原位调控和后制备调控相结合,可为制备具有较低过电势、较高催化活性的新型Ag基阳极析氧催化剂提供方法指导和为后续研究提供依据。