Sol-Gel Synthesis of Potassium Titanyl Phosphate: Solution Chemistry and Gelation

The solution chemistry and aggregation mechanisms involved in sol-gel synthesis of potassium titanyl phosphate (KTP) are studied in detail. The chemistry of the metal precursors are shown to be critical for the formation of the desired KTP phase. The precursor solution as well as some preparation intermediates were studied by several spectroscopic methods to determine the structure of the organometallic species present in these solutions. The structural evolution taking place in the solution after hydrolysis was studied using photon correlation spectroscopy and small angle X-ray scattering techniques. The influence on the gelation of several preparation parameters such as, the precursors chemistry, the mixing order of the metal alkoxides, the solvent/KTP ratio and the water/KTP molar ratio was also examined.     

Synthesis and Characterisation of Aluminium-Zirconium Based Organic-Inorganic Materials via Sol-Gel Route

Monolithic and transparent hybrid Al-Zr gels were obtained by the reaction of homogeneous mixtures of metal alkoxides: (Al(OBu^s)₃ + Zr(OPr)₄) with Butan-1,3-diol at room temperature, without solvent, catalyst, or water. The products have been characterized by IR spectroscopy, DTA and TGA. The results show that the diol has reacted with the mixture of alkoxides leading to the monolithic transparent gels in which both organic-inorganic (–Al–O–R–O–Zr–) and inorganic (–Al–O–Zr–O–) bridges are formed.Xerogels obtained after the drying of gels were pyrolysed at different temperatures in air. The structure and morphology of the obtained materials were studied by X-ray powder diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method. At 1200°C, the materials were composed of Al₂O₃, t-ZrO₂ and m-ZrO₂.     

Ultraviolet-Laser-Induced Crystallization of Sol-Gel Derived Inorganic Oxide Films

Structural changes stimulated by ultraviolet (UV) laser irradiations of sol-gel derived inorganic oxide films were investigated. Dried gel films of TiO₂, Nb₂O₅, Ta₂O₅, SrTiO₃ and Pb(Zr _x Ti_1–x )O₃ (PZT) were found to be crystallized by the laser irradiation. On the other hand, the photo-induced change in gel films of BaTiO₃, LiNbO₃ and LiTaO₃ was not observed although the laser beams were absorbed in the films. These sol-gel films were thermally crystallized at almost the same temperature around 600–700°C except TiO₂. Thus, the UV-laser-induced crystallization is not directly ascribed to a simple thermal effect with the irradiation. Photochemical properties of the cations are assumed to be important for the change in sol-gel films.     

Ti-Si复氧化物载体对金催化剂上丙烯环氧化的影响

 以TiCl4和SiCl4为原料,采用水解和非水水解溶胶-凝胶两种方法制备了一系列不同Ti含量的Ti-Si复氧化物载体,继而用沉积-沉淀法制得载金催化剂. 采用X射线衍射、紫外-可见漫反射光谱、 N2吸附和高分辨透射电镜对催化剂进行了表征,并考察了催化剂在氢气和氧气存在下的丙烯气相环氧化催化性能. 研究表明,钛含量在6%～14%范围内时,两种方法制得的Ti-Si复氧化物均为无定形结构,但采用非水水解溶胶-凝胶法制得的载体比表面积较高. 以非水水解溶胶-凝胶法制备的钛含量10%的Ti-Si复氧化物为载体得到的载金催化剂表现出较高的活性和选择性,反应60 min时,丙烯转化率为5.7%, 240 min后降为3.3%, 环氧丙烷的选择性稳定于95%左右. 还考察了非水水解溶胶-凝胶的陈化时间和金沉积-沉淀溶液的pH值等对反应结果的影响.     

Sol-Gel Synthesis of Nanocrystalline PZT Using a Novel System

A simple system has been developed for the preparation of lead zirconate titanate, Pb(Zr _x Ti_{1 – x} )O₃ powders by sol-gel process. To achieve stable and homogeneous precursor solutions, chelating ligands such as acetic acid and acetylacetone have been used for the chemical modification of titanium and zirconium starting precursors. Phase-pure PZT powders were obtained, through a pyrochlore-free pathway, from the amorphous xerogel after heat treatment at 600°C. The formation of the crystalline phase, compositional homogeneity, sinterability, dielectric and piezoelectric characteristics of PZT are reported.     

以一氧化二氮或氧气为氧化剂的丙烯环氧化催化反应

丙烯环氧化制环氧丙烷是催化领域的最关键的挑战之一. 本文对作者等近年来开展的以一氧化二氮为氧化剂的铁催化体系和以氧气为氧化剂的铜催化体系的研究进展进行了综述. 在这两类催化体系中,碱金属离子(特别是K )的修饰作用均是获得较高环氧丙烷选择性的关键. 碱金属离子通过调变催化剂中铁或铜物种的分散度、配位环境和酸碱性等,实现了对反应途径的调控,使反应朝着有利于环氧丙烷生成的方向进行. 活性金属组分(铁或铜)与氧化剂(一氧化二氮或氧气)间的特定的组合对丙烯环氧化反应的发生也起着重要作用. 推测在两类催化体系中,氧化剂均在具有特定结构和价态的铁或铜活性位上活化,产生导致丙烯环氧化反应发生的亲电性活性氧物种.     

The Effect of Nanoscaled Metal Oxide Sols on the Structure and Properties of Glycidoxypropyltrimethoxysilane Derived Sols and Gels

Glycidoxypropyltrimethoxysilane (GPTS) is frequently used as precursor for the preparation of sol-gel derived nanoscaled hybrid polymers. The influence of nanoscaled metal oxide sols of silica, boehmite, zirconia and ceria on reactions of GPTS in ethanolic hydrolysates and in corresponding gels (epoxide ring-opening, condensation degree) was examined by liquid- and solid-state ¹³C and ²⁹Si NMR with regard to a better correlation between structure and material properties. Generally, a higher condensation degree of RSi(O_0.5)₃ units of GPTS is found after addition of metal oxide sols compared to GPTS without additives. The metal oxide sols (10 mole% series) cause an epoxide ring-opening up to 20% in GPTS hydrolysates after 24 h. A nearly complete ring opening was found in the boehmite and silica containing hybrid gels whereas gels containing ceria and other types of silica only show a low degree of ring-opening. The results show an accelerated ring-opening with increasing content of AlO/OH-species in silica sols. ¹³C NMR studies reveal that the epoxide ring-opening does not completely lead to polyether structures but to considerable amounts (up to 40%) of ethylether groups which can influence the material properties (hardness).     

Ultraviolet-Laser-Induced Crystallization of Sol-Gel Derived Indium Oxide Films

Modification of sol-gel derived indium oxide thin films using ultraviolet lasers was investigated. Irradiation by an ArF excimer (6.4 eV) and the fourth harmonic generation of a Nd : YAG laser (4.7 eV) was found to be effective in crystallization with a loss of hydroxyl groups and a decrease in the sheet resistance of the sol-gel films. Transparent crystalline indium oxide films were successfully obtained by 6.4 eV laser irradiation at fluences below 20 mJ/(cm2·shot), whereas degradation of the films was induced by a relatively high-fluence beam.     

Preparation and Characterization of Molybdenum Oxide Thin Films by Sol-Gel Process

This paper presents a new sol-gel process to prepare molybdenum oxide thin films. A molybdenum acetylacetonate sol was prepared by employing the system CH₃COCH₂COCH₃/MoO₃/C₆H₅CH₃/HOCH₂CH₂OCH₃. A molybdenum acetylacetonate gel was prepared by addition of aqueous NH₃. Thermal gravimetry (TG) and differential thermal analyses (DTA) of the gel suggested that crystallization of MoO₃ occurs in a 140 K temperature range around 508°C. MoO₃ films were prepared on fused silica, Si (111) and Al₂O₃ (012) substrates by annealing spin coating films of the sol in oxygen environment at 508°C. X-ray diffraction (XRD) showed that all films crystallize in -MoO₃ structure, and crystallites on fused silica substrate are arbitrarily oriented while those on Si (111) and Al₂O₃(012) substrates oriented in the (010) direction. SEM investigations showed that MoO₃ grains of all films are randomly distributed, with a longitudinal dimension of about 1–5 m and the film thickness is about 1 m.     

Preparation of Metal Oxide Nanotubes Using Gelators as Structure-Directing Agents

Summary: Cationic gelators, capable of gelling alcohols, were developed as structure-directing agents for preparing metal oxides. The sol-gel polymerization of metal alkoxides using the gelators as templates afforded metal oxide nanotubes. The unique structure of metal oxides was created by transferring the shape of fibrous aggregates of gelator. The electrostatic interaction between cationic gelator and anionic metal oxide precursor plays an important role for acting as templates.     

Electrocatalytic Synthesis of Propylene Carbonate from CO_2 and Propylene Oxide

The electrocatalytic synthesis of propylene carbonate(PC) from CO2 and propylene oxide(PO) was studied under mild conditions(PCO2=1.01×105 Pa, t=25 ℃). Influences of solvents, supporting electrolytes, the passed charge, the nature of electrodes and the current density(j) on the yield of PC were investigated to optimize the electrolytic conditions, with the maximal yield to be 46.2%, the selectivity of propylene carbonate is 100%. The reduction of propylene oxide in the absence and presence of CO2 was examin...     

Stress and Moisture-Sorption in Ozone-Annealed Films of Zirconium Oxide Obtained from Sol-Gel

The stress development in zirconium oxide films prepared by sol-gel and annealed under ozone-enriched oxygen has been investigated. The organic compounds are mostly oxidized at 200°C with ozone and the stress rises up to higher values than the stress in films annealed with pure oxygen between 200 to 400°C. During exposure to humid air of films annealed at 150°C under pure or ozone-enriched oxygen chemical transformations of organic compounds have been observed. The moisture-induced stress change during film exposure to the ambient air also has been investigated. The competition between hydration of ZrO₂, H-bound formation, surface ionization and capillary condensation mechanisms is discussed.     

Synthesis of Molybdenum Oxide by Thermal Decomposition of Molybdenum Acetylacetonate Sol-Gel

Synthesis of monophasic ultrafine molybdenum oxide at low temperatures by thermal decomposition of molybdenum acetylacetonate sol-gel is reported. The sol-gel is obtained through a solvent extraction technique from the organic solvent with the reduction in oxidation state of molybdenum. The thermal behaviour of the sol-gel is studied from the thermal analysis traces. The structural changes accompanying the thermal decomposition of the gel and the formation of monophasic molybdenum oxide is also reported with the help of X-ray diffraction and scanning electron microscopy techniques. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Treatment of Sol-Gel Derived Nickel Oxide Xerogels

Very fine nickel hydroxide and oxide xerogel powders were prepared using a new sol-gel synthesis procedure in which nickel ethoxide was produced through the reaction of nickel chloride, as a precursor, with sodium ethoxide in dehydrated ethanol, followed by the hydrolysis of nickel ethoxide with ammonia and drying the resulting hydrogel under subcritical pressures to form the xerogel. The effects of thermal treatment on the surface area, pore volume, crystallinity and particle structure of the resulting xerogels were investigated and found to have significant effects on all of these properties. Overall, the xerogel remained amorphous as Ni(OH)₂ space up to 200°C, with little change in the surface area and pore volume. At 250°C, the Ni(OH)₂ began to decompose and form crystalline NiO with the uniformity of the crystals increasing with an increase in temperature. The surface area and pore volume decreased sharply when increasingthe temperature beyond 250°C; this was the temperature where maximums of about 270 m²/g and 0.33 cm³/g were exhibited by this composite amorphous Ni(OH)₂ and crystalline NiO xerogel powders. At the higher calcination temperatures, very uniform NiO crystals with average crystallite sizes of 1.7 nm and 14.5 nm were obtained at 400 and 600°C, respectively.     

Sol-Gel Technology as Reflected in Journal of Sol-Gel Science and Technology

Journal of Sol-Gel Science and Technology started as unique journal devoted to sol-gel science and technology in 1993. First, papers so far published in the Journal were intoduced. It was shown that the titles of invited papers and special issues show the broadening of the sol-gel area. Second, the change of the research tendency was conjectured from the four proceedings volumes. It was shown that the increase of importance of a particular class of materials and appearance of emergent materials are reflected in the title of the paper.     

KI与无机铵盐催化CO2与环氧丙烷合成碳酸丙烯酯

以无毒、合成简单、廉价的无机铵盐(氨基甲酸铵、碳酸氢铵、碳酸铵等)为助催化剂,研究其对卤化钾(KCl、KBr、KI)催化CO2与环氧丙烷合成碳酸丙烯酯(PC)的影响.结果表明,卤化钾与无机铵盐显示出很好的协同催化效应.其中以氨基甲酸铵为助催化剂,KI为主催化剂时,催化合成PC的效果最好.同时考察了催化剂用量、反应温度、CO2初始压力、PC的预加入量、反应时间等因素对反应的影响.在优化条件下,PC收率大于99%.     

Green Synthesis of ZnO Nanoparticles Using Plant Extract as a Template

Plant-based nanoparticles (NPs) have found great interest among various scientist in the present era and used in various sector including medicine, agriculture, and food industry. The various chemical constituents of plants aid in the bioreduction of metal ions to a nanoscale. Among the various NPs synthesized, zinc oxide (ZnO) NPs hold a premier position. ZnO NPs have use in textile, cosmetic, diagnostics, optoelectronics, photocatalysis, diodes, and many other areas. NPs synthesized through green synthesis have a potentially greater role in treating clinical pathogens. Present investigations show a simple eco-friendly method for the synthesis of ZnO NPs from the husk of sunflower seeds. Sunflower is an economically important crop, for the formation of edible oil. The husk is considered to be a waste, product in oil industry, however, the biomolecules present in sunflower husk can be used to produce ZnO NPs. Present investigations reveal formation of ZnO NPs and investigations of their structure through scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Their optical properties have been studied by ultraviolet–visible spectrophotometer (UV–Vis) and fluorophotometer. ZnO NPs have also been investigated for their potential phytoremedial properties.     

Low Temperature Synthesis of Nano-Sized Lithium Manganese Oxide Powder by the Sol-Gel Process Using PVA

Lithium manganese oxide (LiMn₂O₄) powder with spinel structure has been synthesized by a sol-gel method using an aqueous solution of metal nitrates containing polyvinyl alcohol (PVA). The role of PVA and the calcination conditions for the formation of LiMn₂O₄ have been studied. Homogeneity and reactivity of the precursor powder are enhanced with an increase in the amount of PVA in the starting solution. When the amount of PVA is low, an impurity phase-Mn₂O₃ is formed at low temperature. On the other hand, when the vinyl alcohol monomer unit of PVA to metal ion ratio is 2 : 1 in the starting solution, only spinel phase is formed at 180°C and organic-free LiMn₂O₄ powder is obtained at as low as 400°C. Nanosized LiMn₂O₄ particles with a narrow size distribution have been successfully prepared by this technique. This method with proper amount of PVA results in much lower calcination temperature and shorter calcination time for producing the single spinel phase in comparison with the conventional solid state reaction and other solution techniques.     

SiO2-Iron Oxide Composites Obtained by Sol-Gel Method

Composite SiO₂-iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO₂ sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods.     

温和条件下电催化CO2与环氧丙烷合成碳酸丙烯酯

 在常温常压下研究了CO2的电化学活化及其与环氧丙烷反应合成碳酸丙烯酯,考察了支持电解质对碳酸丙烯酯产率的影响. 结果表明,含有Br-的支持电解质对合成碳酸丙烯酯起到明显的催化效果. 在实验研究基础上,对反应机理进行了初步推测,认为Mg2+起到路易斯酸的作用并与环氧丙烷的氧原子配位,同时Br-作为亲核试剂进攻环氧丙烷的 C-O 键使其断裂开环,形成的中间物与CO2还原产生的活化物质结合形成碳酸丙烯酯.