Gas-Phase/Solid-Phase Photocatalytic Degradation Of Environmental Contaminants With Nano-TiO₂ Photocatalyst

The paper has reviewed the progress on the research of nanometer semiconductor catalysts. The current development of nano-TiOj photocatalyst has been considered including the preparation of catalyst and the application in degrading environment contaminants. In this thesis, we mainly focus on the study on the gas-phase photocatalytic oxidation of NOx with TiO2 nanometer film and the solid-phase phtotocatalytic degradation of PS film with modified nano-TiO2 catalyst.The porous titanium dioxide nanometer film was prepared on the glass plate with the water glass as binders and sodium fluorosilicate as solidifying agent. The film surface morphology was studied by scanning electron microscope (SEM), and pores distributing of the film was investigated by Barrett-Joyner-Halenda (BJH) method. The gas-phase photocatalytic oxidation of nitric oxides on the TiO2 composite film was carried out in the TiO2 /UV system. After UV-irradiation for 2 h, the photoxidation rate of NOx reached 97.5%. Some important factors affecting the photo-oxidation were also be considered such as the concentration of TiO2, vapour pressure and oxgen. The final product of the photocatalytic oxidation of NOx was detected to be HNO3 by FT-IR. The partial HNO3 was absorbed on the TiO2 surface, causing catalyst deactivation. But when it was washed by water, the catalyst could be reused without the significant loss of catalytic activity.The nano-TiO2 particles were modified by polymer. The photodegradable polystyrene-grafted-Ti02 (PS-G-TiO2) nanocomposite was prepared by embedding the grafted-TiO2 particles into the commercial polystyrene. Solid-phase photocatalytic degradation of the PS-G-TiO2 nanocomposite was carried out in ambient air at room temperature under ultraviolet lamp and sunlight irradiation. The properties of composite films were compared with that of the pure PS films by weight-loss measurement, SEM, gel permeation chromatogram (GPC), X-ray photoelectron spectroscopy (XPS), FT-IR, and UV-Vis spectroscopy etc. methods. The results showed that the photo-induceddegradation of PS-G-TiO2 composite film is significantly higher than that of pure PS film. The weight loss of composite film reached 31.9%, average molecular weight (Mw) of composite film decreased 53.1%, and the number average molecular weight (Mn) decreased 73.2% after 396 h UV-light irradiation. FT-IR analysis and weight loss result indicated that the benzene rings in PS-matrix of composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the composite film is briefly discussed.