Preparation and Characterization of Bismuth Doped TiO2 Thin Films

A series of Bismuth-doped titanium oxide (Bi-doped TiO₂) thin films on glass substrates have been prepared by sol-gel dip coating process. The prepared catalysts were characterized by XRD and XPS. The photocatlytic activity of the thin film catalysts was evaluated through the photodegradation of aqueous methyl orange under UV illumination. The experiments demonstrated that the Bi-doped TiO₂ prepared was anatase phase. The doped bismuth was in the 3⁺ oxidation state. The presence of Bi significantly enhanced the photocatalytic activity of TiO₂ films. At calcination temperature of 500°C, with doping concentration of 2 wt %, Bi-doped TiO₂ thin film showed the highest photocatalyic activity.     

Preparation and properties of highly conductive La1−x M x MnO3−y thin film showing magnetic effect from sol-gel process

The sol-gel synthesis of Sr-doped-LaMnO₃ thin film was investigated. The optimum condition was obtained when strontium, lanthanum and manganese nitrates were used as raw materials and diethylene or propylene glycol was used as solvent. An alumina plate was used as a substrate. The film thickness was about 0.2 m for one dip coating. The conductivity of Sr-substituted-LaMnO₃ increased with increasing Sr content and showed ferromagnetic properties. The conduction mechanism was a hopping conduction due to the small polaron. The metal-semiconductor transition at around room temperature was considered to be caused by the Jahn-Teller effect.     

二氧化钛纳米晶薄膜的吸收光谱和激发发射光谱

由TiO₂反胶束溶胶制备一系列TiO₂纳米晶薄膜，对膜的吸收光谱和激发发射光谱研究表明制备的膜存在有二种模式的跃迁，直接跃迁和间接跃迁。由于厚膜中存在较强的表面相互作用，厚膜的直接跃迁禁带宽与薄膜相比发生了红移。在不同陈化时间，浸渍相同次数制得的膜具有相同的直接跃迁禁带宽。除浸渍一次的膜不存在间接跃迁外，所有的膜具有相同的间接跃迁禁带宽。所有的膜具有几乎相同的发射光谱模式。     

Aqueous Titanate Sols from Ti Alkoxide-α-Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols

Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with -hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO₂) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH₃ (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH₃ (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions.     

Epitaxial Growth of Sr x Ba1 − x Nb2O6 Thin Films Prepared from Sol-Gel Process

In this study, we prepared Sr _x Ba_{1 – x} Nb₂O₆ (x = 0.3, 0.5 and 0.7) thin film on 0.75 wt% La doped SrTiO₃ (100) and (110) single crystal substrates. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)₅ as raw materials, and acetic acid and diethlene glycol monomethyl ether as solvents. The substrates were coated with the solution by spin coating method. As-coated thin films were heated from 973 to 1273 K in air. The grains of the thin film on La doped SrTiO₃ (100) were pillar shaped and arranged in right angle to each other. On the other hand, the grains of these thin films on La doped SrTiO₃ were pillar shape and arranged in one direction. The crystallographic relationship of the thin film between Sr _x Ba_{1 – x} Nb₂O₆ and substrate that the 130 and 310 direction of the thin film on the substrate were oriented with c-axis in parallel to the substrate surface. On the other hand, (hk0) phase diffractions of Sr _x Ba_{1 – x} Nb₂O₆ thin film on the substrate (110) were investigated in the XRD theta-2theta measurement. It is expected that the Sr _x Ba_{1 – x} Nb₂O₆ (x = 0.3, 0.5 and 0.7) were highly oriented or epitaxial growing on La doped SrTiO₃ (110) single crystal substrate.     

Epitaxially Grown LaSrCoO3 Thin Films on Various Substrates by the Sol-Gel Method

LaSrCoO₃ thin films have been prepared on various substrates by the sol-gel method using inorganic salts as starting materials. The crystallinity and in-plane alignment of the films were analyzed by X-ray diffraction -2 scans and scans (pole-figure analysis), respectively. Highly (h00)/(00l)-oriented LaSrCoO₃ films with crack-free surfaces were obtained by annealing at 800°C on SrTiO₃(100), while films grown on MgO(100) and Si(100) exhibited poor crystallinity. According to the X-ray diffraction -2 scan, crystallinity of the product films was found to depend on lattice-misfit values between the films and the substrates used. On the contrary, the lattice-misfit values were less effective to the epitaxy of the LSCO film. Epitaxial film grown on SrTiO₃ annealed at 800°C was found by reciprocal-space mapping (-2 scan) analysis to consist of the pseudocubic phase.     

Ni控制掺杂TiO2薄膜的光电化学及光催化活性

采用溶胶-凝胶法通过分步控制工艺制备了镍离子不同掺杂方式的TiO₂薄膜。通过甲基橙的光催化降解动力学来表征其光催化活性。结果表明：镍离子非均匀掺杂在掺杂量0.5%时可以明显增强TiO₂的光催化活性，而均匀掺杂提高TiO₂的光催化活性较小。光电化学表征结果显示：镍离子非均匀掺杂TiO₂薄膜的瞬时光电流信号较强，说明其光生载流子易于生成且分离效果较好；循环伏安曲线表明，光照时Ni非均匀掺杂的TiO₂薄膜改变了体系的氧化还原电位，说明了薄膜内建电场的建立。基于半导体的P-N结原理探讨了镍离子非均匀掺杂TiO₂薄膜的光催化活性机理。     

Preparation and Formation Mechanism of Porous TiO2 Films Using PEG and Alcohol Solvent as Double-Templates

Porous nanocrystalline TiO₂ anatase thin films have been synthesized on glass substrates via a sol-gel dip-coating method. The coating sol was obtained by suppressed hydrolysis of Ti(OC₄H₉)₄ through the addition of complexing molecules as stabilizers in an alcohol solution containing polyethylene glycol (PEG). Chemical changes taking place during the sol-gel process were discussed based on IR spectra analysis. A model concerning the pore formation was established to explain the role of PEG and solvent with core-shell configuration as double-templates. The structural characteristics of porous TiO₂ films were found to greatly depend on the concentration and molecular weight of PEG, the types of stabilizing agents and solvents. The pore size of the films was tunable in the range of 10–500 nm and their surface area varied from 51 to 72 m²·g^–1.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

Studies on photocatalytic activity of Ag/TiO2 films

Ag/TiO₂ photocatalytic films were produced by hybrid sol-gel method. The photocatalytic degradation of methyl orange (MO) in aqueous solution under 365 nm irradiation on TiO₂ and Ag/TiO₂ thin films was investigated. The state and amount of Ag species within the film and the enhancement mechanism of photocatalytic activity of Ag/TiO₂ were discussed. With a loading molar ratio of Ag/Ti = 0.135 in TiO₂ film, the maximum catalytic efficiency was observed. __________ Translated from Journal of Beijing Normal University (Natural Sciences), 2005, 41(6) (in Chinese)