Preparation of anatase, rutile and brookite type anion doped titania photocatalyst nanoparticles and thin films

Anatase, brookite and rutile type nitrogen doped titania nanocrystals (TiO_2-xN_y) which possessed beige color were successfully prepared as single phase using homogeneous precipitation-solvothermal process in TiCl₃-hexamethylenetetramine (C₆H₁₂N ₄) aqueous and alcohol solutions at temperature as low as 190 °C. The phase composition, crystallinity, microstructure, specific surface area, nitrogen doped amount and photocatalytic activity of titania powders were greatly changed depending on pH, temperature and kind of treatment alcohols. TiO_2-xN_y films with various phases and high surface area could be prepared using a novel low temperature process, i.e. a spin-coating of TiO_2-xN_y powder using an organic binder followed by oxygen plasma treatment below 60 °C within a short time period. The nitrogen doped yellowish titania powders and films possessed excellent light absorption up to 565 nm, and showed excellent visible light induced photocatalytic ability under irradiation of visible light of wavelength >510 nm. The relationship between the phase composition, photocatalytic activity and hydrophilic ability of the film was investigated in detail. The effects of film thickness, surface roughness and porosity on the photocatalytic activity were discussed.