N and N,S-doped TiO2 photocatalysts and their activity in NOx oxidation

Abstract

N-doped and N,S-codoped titania powders were prepared applying simple chemical treatment with various modifiers. The N and S were introduced preserving the crystalline structure, morphology and specific surface area of the initial TiO2. The level of N, S doping varied depending on the modifier two of which were structural isomers. In all samples, N was found interstitially incorporated in the TiO2 lattice. S was recorded in ionic states S6+ and S4+. All modified powders exhibited enhanced visible light absorption and narrower energy band gap in comparison to the initial titania. Except for the N-doped titania, the photocatalytic activity in NOx oxidation under UV light decreased after doping, while the activity under visible light did not increase for all modified samples. This outcome was related to the high level of N and S doping and intense e−–h+ recombination on dopants’ sites. The activity of the photocatalysts in NOx oxidation processes was also connected to the type of non-metal dopant in the lattice of TiO2. The beneficial effect of N-doping was ascribed to the preferential formation of OH species on N-doped surface, whereas the detrimental effect of N,S-codoping was credited to the suppressed OH production on S-doped surface.