Spectroscopic study of the photofixation of SO2 on anatase TiO2 thin films and their oleophobic properties
2012 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 4, no 2, 672-679 p.Article in journal (Refereed) Published
Photoinduced 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 (S) 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 photoinduced surface reaction products formed on the TiO2 surfaces. It is shown that band gap excitation of TiO2 results in photoinduced oxidation of SO2, which at elevated temperatures become coordinated to the TiO2 lattice through interactions with O vacancies and form sulfite and sulfate surface species. These species makes the surface acidic, which is manifested in nondetectable adherence of stearic acid to the modified surface. The modified films show good chemical stability as evidenced by sonication and repeated recycling of the films. The results suggest a new method to functionalize wide band gap oxide surfaces by means of photoinduced reactions in reactive gases at elevated substrate temperatures. In the case of anatase TiO2 in reactive SO2 gas, we here show that such functionalization yields surfaces with excellent oleophobic properties, as probed by adhesion of stearic acid.
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012. Vol. 4, no 2, 672-679 p.
Materials Chemistry Engineering and Technology Nano Technology
Research subject Chemistry with specialization in Chemical Physics; Engineering Science with specialization in Nanotechnology and Functional Materials; Engineering Science with specialization in Solid State Physics
IdentifiersURN: urn:nbn:se:uu:diva-187492DOI: 10.1021/am201253yISI: 000300644500026PubMedID: 22204641OAI: oai:DiVA.org:uu-187492DiVA: diva2:574876
FunderSwedish Research Council, 2010-3514EU, FP7, Seventh Framework Programme, 267234