The effect of postnitridation annealing on the surface property and photocatalytic performance of N-doped TiO2 under visible light irradiation

Postnitridation annealing has a remarkable effect on the surface property and photocatalytic performance of N-doped TiO2 for photocatalytic oxidation of ethylene. The activity of N-doped TiO2 under visible light illumination (lambda > 420 nm) can be enhanced fourfold by annealing the sample at 400 degrees C. Characterization results show that the thermal annealing reduces surface oxygen vacancies, removes surface-adsorbed NH3, and facilitates the adsorption of molecular oxygen on catalyst surface. Such a surface reconstruction contributes to the enhanced photocatalytic activity of the N-doped TiO2. The postcalcination also improves the photocatalytic stability of the N-doped TiO2 by stabilizing nitrogen atoms in the TiO2 lattice. A N-doped TiO2 sample without postcalcination suffers from a gradual deactivation, due mainly to the passivation of the catalyst surface by oxidized nitrogen species (e.g., hyponitrite, nitrite ions, and nitrate ions) formed during the photocatalytic degradation of ethylene. (c) 2008 Elsevier Inc. All rights reserved.