The role of nitrogen doping on the development of visible light-induced photocatalytic activity in thin TiO2 films grown on glass by chemical vapour deposition

A brief review of the findings of a range of studies aimed at describing the influence of the N-doping of TiO2 thin films and particles on possible visible light-induced photoactivity is presented. By way of a new approach to the direct growth of N-doped TiO2 thin films, the physical and photochemical effects of the addition of ammonia during atmospheric chemical vapour deposition (CVD) growth of TiO2 are described. It is found that the addition of ammonia to the CVD reactive gas mixture causes a dramatic change in film morphology and a reduction in growth rates. In addition, it is found that although we have clear evidence for the incorporation of β-substitutional N atoms within the growing film, there is no evidence of any appreciable photocatalytic activity of the doped TiO2 films when irradiated with visible light. In fact the degradation in film morphology results in a decrease in conventional UV-induced photoactivity as compared to that for an undoped film. These findings are discussed in terms of the findings of other studies of N-doped TiO2 films that have been reported.