Preparation And Characterization Of New Photocatalytic Materaials

Environmental pollution and the lack of energy sources are the most serious problems of recent environmental problems in the world. A large number of investigations had been focused on how to solve these two problems. Among various oxide semiconductor photocatalysts, titania appears to be a promising and important prospect for use in environmental purification due to its strong oxidizing power, photoinduced hydrophilicity, nontoxicity and long-term photostability. However, the fast recombination rate of photogenerated electron/hole pairs hiders the commercialization of this technology. On the other hand, because of its large band gap, TiO₂ is effective only under ultraviolet irradiation (λ < 380 nm). However, sunlight is comprised of less than 3-4% ultraviolet light. Therefore, to prepare highly active photocatalytic materials, this thesis focuses on the following works.In order to resolve the problems that TiO₂ powder was hard to be applied. Ag-TiO₂ multiphase nanocrystal composite thin films were prepared on quartz substrates by the liquid phase deposition (LPD) method. The grain growth of anatase was depressed upon Ag+ doping. However, silver ions not only promoted (or catalyzed) the formation of brookite phase but also reduced the phase transformation temperature of anatase to rutile. With increasing AgNO₃ concentration, the transmittance and band gap of the composite thin films decreased; however, the intensity of surface plasmon absorption (SPA) peaks increased and their peak position shifted to a longer wavelength range. When AgNO₃ concentration was higher than 0.03 M, the prepared samples consisted of anatase, brookite, rutile and metal silver nanocrystal particles, and their grain size ranges were 5-30 nm. The photocatalytic activity of the Ag-TiO₂ multiphase nanocrystal composite thin films prepared by this method exceeded that of pure TiO₂ thin films by a factor of more than 6.3 when AgNO₃ concentration was kept in the range of 0.03-0.05 M. This was attributed to the fact that there were many hetero-junctions, such as anatase/rutile, anatase/brookite, Ag/anatase, Ag/rutile and so on, existed in the Ag-TiO₂ multiphase nanocomposite films.Highly photoactive anatase TiO₂ nanocrystal photocatalyst was prepared using Ti(SO₄)₂ and CON₂H₄ as raw materials by a simple hydrothermal method at low temperature. The as-prepared samples were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM) and N₂ adsorption-desorptionmeasurements. The photocatalytic activity of the samples was evaluated using the photocatalytic oxidation of acetone in air at room temperature. It was found that hydrothermal treatment could obviously promote the crystallization of T1O2 at low temperature without heat-treatment. TiO2 powders prepared by this method at 160℃ for 3 h or 180℃ for 2 h showed good photocatalytic activity for photocatalytic oxidation of acetone and the photocatalytic activity of the as-prepared TiO2 powders exceeded that of Degussa P25 by a factor of more than 3 times. This might be attributable to the fact that the prepared TiO2 powders had larger specific surface areas and smaller crystallite size.Bi2WO6 powder photocatalyst was prepared using Bi(NO3)3 and Na2WO4 as precursors by a simple hydrothermal method at 150℃ for 24 h, and then calcined at 300, 400, 500, 600 and 700℃ for 2 h, respectively. The as-prepared samples were characterized with UV-visible diffuse reflectance spectra, fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and N₂ adsorption-desorption measurement. The photocatalytic activity of the samples was evaluated using the photocatalytic oxidation of formaldehyde at room temperature under visible light irradiation. It was found that post-treatment temperature obviously influenced the visible-light photocatalytic activity and physical properties of Bi2WO6 powders. At 500℃, Bi2WO6 powder photocatalyst showed the highest visible-light photocatalytic activity due to the samples with good crystallizati...