| Several nanostructured photocatalysts were prepared by sol-solvothermal, microemulsion-mediated solvothermal, and self-propagating combustion methods. The products were characterized by X-ray diffraction (XRD), nitrogen adsorption, UV-VIS diffuse reflectance spectroscopy, micro-Raman spectroscopy, Fourier transform infrared absorption spectroscopy (FT-IR), thermal analysis (TGA/DSC), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR). Their photocatalytic activities were evaluated by degradation of organic pollutants in gas-solid or liquid-solid systems.; The first part of the thesis describes the preparation of nanocrystalline TiO2 by using a titanium oxo cluster precursor in a sol-gel process. The photocatalytic activity of the resulting nanocrystalline TiO 2 was evaluated by the degradation of acetone in air. This nanocrystalline TiO2 showed better activity than TiO2 prepared by using a titanium tetraisopropoxide precursor and the commercial photocatalyst P25. The high activity of the nanocrystalline TiO2 was attributed to more surface hydroxyl groups, larger surface area and pore volume.; A sol-solvothermal route was also developed to prepare nanocrystalline TiO2 photocatalysts with mesoporous structure at a low temperature. The samples obtained from nitric acid, deionized water, and ammonia media were denoted as HT-1, HT-2 and HT-3, respectively. The characterization results showed that mesoporous structures of the prepared samples consisted of the interparticle porosity and was better formed in acidic medium. The photocatalytic activities of the samples were tested by self-photosensitized degradation of an azo dye Mordant Yellow 10 (MY) in an aqueous solution under visible light irradiation. All three samples showed much higher photocatalytic activity than the commercial P25, and the sequence of their activities was HT-1 > HT-2 > HT-3 > P25.; A macroporous nanocrystalline YFeO3 was finally prepared by a self-propagating combustion method using yttrium nitrate and iron nitrate as precursors and glycine as a fuel. The phase structure of the product could be selectively controlled to be hexagonal or orthorhombic by simply adjusting the ratio of glycine to nitrate. Photocatalytic activity for the degradation of methylene blue in water under visible light irradiation showed that the orthorhombic YFeO3 was superior to the hexagonal form. More adsorbed oxygen and ferromagnetism of the orthorhombic sample might explain its high activity. (Abstract shortened by UMI.)... |
