Identification of bulk and surface sulfur impurities in TiO2 by synchrotron x-ray absorption near edge structure

Abstract

Synchrotron x-ray absorption near edge structure (XANES) measurements of Ti and S K edges, combined with first principles simulations, are used to characterize S-doped TiO2 prepared by oxidative annealing of TiS2 at various temperatures. Ti-edge XANES and x-ray powder diffraction data indicate that samples annealed above 300°C have an anatase TiO2 crystal structure with no trace of TiS2 domains. S-edge XANES data reveal that the local structure seen by S atoms evolves gradually, from TiS2 to a qualitatively different structure, as the annealing temperature is increased from 200to500°C. For samples annealed at 500°C, the spectrum appears to have features that can be assigned to S on the surface in the form of SO4 and S defects in the bulk (most likely S interstitials) of TiO2.