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.