Synthesis of nitrogen doped TiO₂ by grinding in gaseous NH₃

TiO₂ was ground in gaseous NH₃ by using a planetary mill to synthesize nitrogen doped TiO₂. Grinding induces phase transformation of TiO₂ from anatase to srilankite, srilankite to rutile in air at room temperature, whereas the phase transformation of TiO₂ is delayed by the grinding in gaseous NH₃. And, product ground under NH₃ has higher surface area than that of under air, and the heated product displays higher specific surface area than that of product without heating. Light-absorption edge of the products is shifted toward visible light wavelength with an increase in grinding period of time. The ground samples exhibit less photocatalytic activity evaluated by the decomposition of NO gas. This may be due to the existence of residual NH₃ and NH₄⁺ formed on TiO₂ surface, which prevents the contact of NO gas with TiO₂ surface. By removing these compositions by thermal treatment at 200 °C for 60 min in air, the photocatalytic activity is improved.