Effects of annealing on the microstructures and photoactivity of fluorinated N-doped TiO2

We investigated the effects of annealing in air on fluorinated N-doped TiO2 (F/N-TiO2) photocatalysts prepared by hydrothermal process. The textural properties (specific surface areas) and surface properties (surface defect density, surface Ti-F density) were significantly modified upon annealing. In contrast, due to the shielding effect of surface fluorination, the phase transformation from anatase to rutile as well as removal of N-dopants during annealing was greatly inhibited. The evolution of the chemical nature of doped nitrogen species upon annealing in air was investigated and correlated with the generation and annihilation of oxygen deficiency. The defect density dominated the visible-light absorption and production of active (OH)-O-center dot. The textural properties and the surface characteristics were crucial for UV-light photocatalytic performance, while the visible-light photocatalytic activity was mainly associated with the defect density. The 300 degrees C-annealed F/N-TiO2 sample showed considerable photocatalytic activity under both UV and visible-light irradiation.