Spectroscopic study of the photo-fixation of SO2 on anatase TiO2 thin films
(English)Manuscript (preprint) (Other academic)
Photo-induced SO2 fixation on anatase TiO2 films was studied by in situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The TiO2 films were prepared by reactive DC magnetron sputtering and were subsequently exposed to 50 ppm SO2 gas mixed in synthetic air and irradiated with UV light at substrate temperatures between 298 and 673 K. Simultaneous UV irradiation and SO2 exposure between 373 and 523 K resulted in significant sulfur deposits on crystalline TiO2 films as determined by XPS, whereas amorphous films contained negligible amounts of S. At substrate temperatures above 523 K, the S deposits readily desorbed from TiO2. The oxidation state of sulfur successively changed from S4+ for SO2 adsorbed on crystalline TiO2 films at room temperature without irradiation to S6+ for films exposed to SO2 at elevated temperatures with simultaneous irradiation. In situ FTIR was used to monitor the temporal evolution of the photo-induced surface reaction products formed on the TiO2 surfaces. It is shown that band gap excitation of TiO2 results in photo-induced oxidation of SO2 to form sulfide and sulfate ions, which at elevated temperatures become coordinated to the TiO2 lattice through interactions with O vacancies to form and species. These species makes the surface acidic, which is manifested in weak adherence of stearic acid. The films show good chemical stability as evidenced by sonication experiments. This suggests that photo-induced surface treatment in reactive sulfur gases may be interesting for fabrication of oleophobic and anti-greasing coatings.
TiO2, SO2, photo-reactions, FTIR, XPS
IdentifiersURN: urn:nbn:se:uu:diva-148869OAI: oai:DiVA.org:uu-148869DiVA: diva2:403195