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Surface Properties of Reduced and Stoichiometric TiO2 As Probed by SO2 Adsorption
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0003-0296-5247
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 40, p. 24549-24557Article in journal (Refereed) Published
Abstract [en]

The adsorption and photochemical properties of reduced and stoichiometric anatase TiO2 nanoparticles, prepared by annealing in vacuum and air, respectively, at different temperatures up to 500 degrees C and 2 days have been investigated. Combined X-ray diffraction and Raman spectroscopy results suggest that vacuum annealing leads-to a defective, oxygen vacancy rich surface region with an accompanying decrease of the crystalline core. The surface chemical properties of the reduced and calcined TiO2 nanoparticles were studied by means of SO2 adsorption measured by in situ diffuse reflectance Fourier transform spectroscopy. On pristine TiO2 nanoparticles SO2 adsorption leads to a broad absorbance band centered at 1140 cm(-1). In contrast, SO2 does not adsorb on stoichiometric TiO2 obtained after long-term annealing in air at 500 degrees C. However, after the same heat treatment in vacuum, SO2 is shown to bind strongly on well-defined adsorption sites associated with a narrow absorbance band at 1150 cm(-1). The increased adsorption on reduced TiO2 is attributed to formation of subsurface oxygen vacancies and reactive Ti3+ species at the surface that promote SO2 bonding. A surface-sulfite species (HSO3-) was identified as the major adsorbate on both the as-prepared and the vacuum-annealed sample, and a formation mechanism involving reaction with hydrogen from surface hydroxyl groups is proposed. During UV illumination, SO2 is photoadsorbed on TiO2 during SO2 exposure in an inert He gas atmosphere. In contrast to dark SO2 adsorption, this reaction does not involve surface defects, since the concentration of photoadsorbed SO2 did not significantly change on the deeply reduced TiO2 nanoparticles. On the basis of these findings, a new mechanism for the formation of surface-bound SO32- during UV illumination on the stoichiometric surface is proposed, which should be generally applicable for other similar adsorbates and semiconducting oxides.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2019. Vol. 123, no 40, p. 24549-24557
National Category
Materials Chemistry Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-396715DOI: 10.1021/acs.jpcc.9b05805ISI: 000490353900023OAI: oai:DiVA.org:uu-396715DiVA, id: diva2:1368810
Funder
Swedish Research Council, 2015 -04757Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-08Bibliographically approved

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Langhammer, DavidThyr, JakobÖsterlund, Lars

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