Preparation, Characterization And Visible-light-driven Photocatalytic Activity Of Doped Titania Photocatalysts

In recent years, titanium dioxide photocatalysts have been widely investigated for their wide potential application in water and air purification and solar energy conversion since Fujishima and Honda discovered the photocatalytic splitting of water on TiO2 electrodes in 1972. However, due to its large band gap (Eg= 3.2 eV for anatase), the currently used photocatalyst TiO2 can only absorb a small fraction of solar energy, thus restricting its practical applications. In order to use solar energy, it is indispensable to develop a photocatalyst with high photocatalytic activities under visible-light irradiation. Doping is one of the most effectively approaches and it has become a hot research. In this dissertation, valuable explorations have been carried out on the fabrication, characterization and visible-light driven photocatalytic activity of doped titatia photocatalysts. The main points could be summarized as follows:Fe-doped TiO2 nanorods were prepared by an impregnating-calcination method using hydrothermally prepared titanate nanotubes as precursors and ferric nitrate as dopant. Products with different Fe:Ti molar ratios were characterized by Field emission scanning electron microscope, Transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller adsorption analysis, and UV-vis spectroscopy measurements. The photocatalytic activity was evaluated using the photocatalytic oxidation of acetone at room temperature under visible-light irradiation. It was found that Fe-doping greatly enhanced the visible-light photocatalytic activity of mesoporous TiO2 nanorods, and when the atomic ratio of Fe/Ti was in the range of 0.1-1.0%, the photocatalytic activity of Fe-doping TiO2 nanorods was higher than that of P25 and undoped TiO2 nanorods. The visible-light photocatalytic activity of Fe-doped TiO2 nanorods prepared by this method exceeded that of P25 by a factor of more than two times at an optimal atomic ratio of Fe to Ti of 0.5. This is due to the fact that the one-dimensional nanostructure can enhance the transport of charge carrier, and the Fe-doping induce the shift of the absorption edge into the visible light range by narrowing the bandgap and reduce the recombination of photogenerated electron and hole. Furthermore, the electronic structure of Fe-doping TiO2 nanorods was studied by first-principle density functional theory.High visible-light photocatalytic activity of N, S co-doped TiO2 nanosheets with high-energy facets were successfully prepared by a calcination method using tetrabutyl titanate as the precursor and thiourea as the dopant. The content of thiourea influences the grain size and crystallization of the doped TiO2 nanosheets. The N, S co-doped TiO2 nanosheets with high-energy facets show a strong absorption in the visible-light region and a red shift of the band edge. This was ascribed to the fact that the bandgap of N, S co-doped TiO2 nanosheets were narrowed by mixing the N2p and S3p states with O2p states. When the content of the thiourea is optimal, the visible-light photocatalytic activities of N, S co-doped TiO2 nanosheets with high-energy facets exceeded that of Degussa P25 for photocatalytic degradation of p-chlorophenol aqueous solution. Furthermore, the electronic structures of N, S co-doped TiO2 nanosheets were studied using first-principle density functional theory.