The Preparation And Photocatalytic Performance Of Nitrogen-doped Titanium Dioxide

TiO2-based semiconductor photocatalysis technology has been shown to be potentially advantageous for environmental remediation as it may lead to complete mineralization of pollutants at ambient conditions with the use of ultraviolet light as the energy source. However, The large scale application of titanium dioxide as mutual photocatalyst is hampered by the fact that it absorbs only the very small ultraviolet part (3⁴%) of solar light due to its wide band-gap of 3.2eV. An effective approach to shifting the optical response of TiO₂ from the ultraviolet to the visible spectral range is the doping of TiO₂ with nonmetal nitrogen. In this paper, by using ammonia as nitrogen source, nitrogen-doped TiO₂ samples were prepared by the sol-gel and impregnation method or hydrolysis-precipitation method. The photocatalytic degradation of ethylene was used as model reaction to evaluate the visible light and ultraviolet light activity of nitrogen-doped TiO₂ samples prepared under different conditions or by various methods. The structural and photoelectric properties of such photocatalysts were characterized by XRD, BET, DRS, XPS, TEM and EFISPS. The mechanism of the influence induced by nitrogen doping on photocatalytic performance was discussed. Moreover, we invented a new method of preparing nitrogen-doped TiO₂ by using hydrazine as nitrogen source. The results showed: (1)The nitrogen-doped TiO₂(prepared by the sol-gel and impregnation method) calcined at 400℃showed the highest photocatalytic activity under visible light irradiation mainly because a small amount of rutile facilitated the separation of photogenerated charge. Nitrogen doping enhanced the absorption of TiO₂ towards visible light and ultraviolet light, and had little influence on the structure of TiO₂. Nitrogen doping produced impurity midgap levels, involving the enhancement of visible light activity of TiO₂. However, such midgap levels became recombination centers of photogenerated charge, and leaded to the decline of ultraviolet light activity of TiO₂. (2)Compared with that prepared by hydrolysis-precipitation method, nitrogen-doped TiO₂ prepared by the sol-gel and impregnation method demonstrated higher photocatalytic activity due to better structural properties. (3)The nitrogen-doped TiO₂ photocatalyst was prepared by using hydrazine as nitrogen source together with its ignitability. The photocatalyst had small crystalline size, large specific surface area and micropore structure, and showed good photocatalytic performance under visible light. The innovations of this work included: (1) preparing nitrogen-doped TiO2 with high photocatalytic activity by the sol-gel and impregnation method, (2) investigating the photoelectric properties of nitrogen-doped TiO2 by EFISPS, and discussing the mechanism of the influence induced by nitrogen doping on photocatalytic performance, (3)preparing nitrogen-doped TiO2 under short-time high temperature condition using hydrazine as nitrogen source.