Masakazu Komatsu

Synthesis of excellent visible-light responsive TiO2−xNy photocatalyst by a homogeneous precipitation-solvothermal process

Anatase, brookite and rutile type nitrogen-doped titania nanocrystals (TiO2−xNy) which are beige in color were successfully prepared by a ‘Homogeneous Precipitation–Solvothermal Process’ (HPSP) in TiCl3–hexamethylenetetramine (C6H12N4) aqueous and alcohol solutions. The phase composition, crystallinity, microstructure, specific surface area, nitrogen doping amount and photocatalytic activity of titania powders greatly changed depending on pH, temperature and the type of treatment alcohols. The TiO2−xNy powders showed excellent visible-light absorption and photocatalytic activity for nitrogen monoxide destruction under irradiation by both visible-light and UV-light. The beige titania powders prepared in TiCl3–hexamethylenetetramine alcohol solutions at 190 °C for 2 h possessed higher specific surface areas than those in aqueous solution. About 39 and 83% nitrogen monoxide could be continuously removed by the anatase TiO2−xNy photocatalyst under irradiation of visible-light (λ > 510 nm) and UV-light (λ > 290 nm), respectively.

Preparation of nitrogen-doped titania with high visible light induced photocatalytic activity by mechanochemical reaction of titania and hexamethylenetetramine

Nitrogen-doped yellowish rutile titania was prepared by a mechanochemical method. The samples were prepared by high-energy ball milling of a P-25 titania powder with various amounts of hexamethylenetetramine (HMT) under different milling conditions at around room temperature. The effects of the reaction conditions on the phase composition, particle size, specific surface area, amount of nitrogen-doping, microstructure and photocatalysis of nitrogen monoxide destruction were investigated in detail. The high mechanical energy accelerated the transformation of the phase from anatase to rutile, while the presence of HMT decreased the phase transformation. Residual HMT and by-products could be removed by post-milling calcination in air at 400 °C. The nitrogen-doped yellowish titania possessed two absorption edges at around 400 and 550 nm and showed excellent photocatalytic ability for nitrogen monoxide oxidation under visible light irradiation. Irradiation with visible light of wavelength >510 nm allowed nearly 37% nitrogen monoxide to be continuously removed by the nitrogen-doped titania prepared by planetary ball milling of a P-25 titania–10 wt% HMT mixture at 700 rpm for 120 min followed by calcination in air at 400 °C.