Visible-Light-Driven N−F−Codoped TiO2 Photocatalysts. 2. Optical Characterization, Photocatalysis, and Potential Application to Air Purification

N−F−codoped TiO2 (NFT) powders, prepared by spray pyrolysis (SP), were further characterized by ultraviolet−visible (UV−Vis) absorption spectroscopy and photoluminescence (PL) spectra. The UV−Vis spectra indicated that the NFT powders could absorb not only ultraviolet light like pure TiO2 powder but also part of the visible-light spectrum (λ < 550 nm). The PL spectra provided confirmation that four electronic energy states exist between the valence band and conduction band of N−F−codoped TiO2 that were attributed to F center, F+ center, an origin-unidentified energy state, and an impurity energy state formed by doped N atoms. Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalytic properties of these NFT powders. As a result, we found that the photocatalytic activity of the NFT powder prepared at the SP temperature of 1173 K was superior to that of commercial P25 under both UV and Vis irradiation. Moreover, trichloroethylene and toluene were selected as the other two target reactants. Their decompositions on the optimal NFT powder were investigated using a specially designed reactor cell by simulating a commercial blue LED air cleaner. The results indicate that our SP sample has a good potential for application to air purification.