Identification of bulk and surface sulfur impurities in Ti O2 by synchrotron x-ray absorption near edge structure

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 Ti O2 prepared by oxidative annealing of Ti S2 at various temperatures. Ti-edge XANES and x-ray powder diffraction data indicate that samples annealed above 300 °C have an anatase Ti O2 crystal structure with no trace of Ti S2 domains. S-edge XANES data reveal that the local structure seen by S atoms evolves gradually, from Ti S2 to a qualitatively different structure, as the annealing temperature is increased from 200 to 500 °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 S O4 and S defects in the bulk (most likely S interstitials) of Ti O2

Sulfur doping and its effect on TiO₂ photoactivity

Sulfur-doped TiO2 (S-TiO2 ) was prepared by heat treating thiourea with three types of TiO2 , including commercialP25, C02 and precipitated TiO2 (pTiO2 ). High S content (1.7 %) in S-doped pTiO2 (S-pTiO2 ) was achieved using relativelylow amount of S precursor (S:Ti atomic ratio = 6%). Incorporation of S in TiO2 structure was influenced by polarity of anindividual host and sulfur solution. Water can be used to prepare S-doped P25 (S-P25) but ethanol was suitable to prepareS-doped C02 (S-C02). Hydrophilicity of TiO2 and degraded solution played important role in photocatalytic activity. Thedoping of S either increased or decreased the photocatalytic activity of TiO2 , depending on the total effects arisen afterdoping, including the increase of surface area, the extension of the absorption range, the decrease of hole mobility and theblocking of the active sites by the unknown coating layers on the S-doped particles. In this work, S doping improved onlythe photocatalytic activity of C02 under the sunlight but lessened the activity of P25 and had no effect on pTiO2