Visible-Light Photoactivity of Nitrogen-Doped TiO₂:  Photo-oxidation of HCO₂H to CO₂ and H₂O

Nitrogen-doped TiO 2 was synthesized by high-temperature exposure of TiO 2 to ammonia. The catalytic efficiency was tested by monitoring the photocatalytic degradation of formate (HCO 2 - ) to CO 2 and H 2 O under visible-light irradiation. The N-doped TiO 2 powders were found to be active for the degradation of formic acid under visible light. However, the catalytic efficiency of the N-doped TiO 2 under UV light alone is less than that of the pure TiO 2 starting material. FTIR evidence indicates that the visible-light-active N-doped TiO 2 has defect sites in the form of Ti−N triple bonds and that the increase of these sites leads to a loss of crystallinity that accounts for the reduced photocatalytic activity under UV irradiation. An optimal synthesis temperature of 550 °C was determined as a balance point between catalyst crystallinity and the presence of defect sites that absorb visible-light photons.