Preparation, Characterization And Visible-light Photocatalytic Properties Of Co-doped Titanium Dioxide Photocatalyst

The utilization of solar energy and the integrated control of environmental pollution are two key objects that have to be faced and resolved urgently. Titanium dioxide (TiO₂) photocatalyst is a representative n-type semiconductor oxide. It is widely used in the degradation of the organic pollutants, self-cleaning, sterilization, photoelectric conversion, and so on. Since the bandgap of TiO₂ in the anatase crystalline is comparatively wide (Eg≈3.2 eV), the photocatalytic activities of TiO₂ only effectively work under ultraviolet light irradiation, which accounts for only a small part (3%-5%) of solar energy. Therefore, it has become a crucial issue in the research field of TiO₂ photocatalysis to make the TiO₂ responding to the range of visible radiation wavelengths through adorning or modification and to resolve environmental and energy problems by using the natural resources (solar energy) more effectively.This dissertation places emphasis on the preparation of codoping TiO₂ nanocrystals with visible light response. By means of sol-gel method with other approaches, TiO₂ photocatalyst co-doped with metal or non-metal elements was prepared. The photocatalysts are expected to show an enhancement in the photodegradation efficiency of pollution under visible light.(1) (N, F)-codoped TiO₂ nanocrystals with active visible light response were prepared using a simple sol-gel approach. As compared with other doping methods, this method is lower energy-consuming and easily manipulated, ensuring the uniform dispersal of adorning ion. It is proved by the experimental results proved that the yellow nanocrystal of (N, F)-doped TiO₂ prepared under the molar ratio of Ti:F=1:1.8 and the calcination temperature of 500℃ shows the best photodegradation ability for methylene blue under visible irradiation. X-ray photoelectron spectroscopic measurements (XPS) suggest that the enhanced photocatalytic property is due to the synergetic effect of the nitrogen and fluorine atoms. But the mechanism of the codoping effect is still at the exploratory stage.(2) Pyridine, thiourea and bismuth nitrate were used as precursors of the dopant. TiO₂ photocatalyst codoped with metal and non-metal elements was successfully prepared. The codoping powders were characterized by X-ray diffraction (XRD), UV-vis absorption spectroscopy (UV-vis), XPS measurements and N₂ adsorption-desorption isotherms. And the photocatalytic activity was evaluated by the degradation of indigo carmine under visible light irradiation. The results of the degradation indicate that (Bi, C)-doped TiO₂ prepared with pyridine by employing sol-gel method and high-temperature aging under Ti: pyridine =1:1.8 and the calcination temperature of 500℃ shows the maximum photocatalytic efficiency on the degradation of indigo carmine. (Bi, C)-doped TiO₂ nanocrystals prepared with thiourea shows excellent photocatalytic activities in visible light: 100% of indigo carmine was degraded after 50 min (including the adsorption time in the dark). Further work and characterization are now in progress.In the dissertation, we have fabricated two codoped TiO₂ nanocrystals with metal or nometal ions by sol-gel method. And we investigated the relations between the fabricate process and structure and properties of photodegradation testing. The codoped powders which take advantage of the properties of the two elements and their codoping effect can greatly enhance their photocatalytic properties. Though the codoping mechanism is in discussion, the sol-gel approach provides an appealing pathway to prepare codoped TiO₂ nanocrystals under mild conditions with either two organic species or organic and inorganic species.