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Photochemistry of Carboxylate on TiO2(110) Studied with Synchrotron Radiation Photoelectron Spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
Lund Univ, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
Norwegian Univ Sci & Technol NTNU, Dept Phys, NO-7491 Trondheim, Norway..
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2016 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 44, 11456-11464 p.Article in journal (Refereed) Published
Abstract [en]

We present a dedicated synchrotron radiation photoelectron spectroscopy (SR-PES) study of a photochemical reaction on the surface of rutile TiO2(110). The photoreaction kinetics of carboxylate species (trimethyl acetate, TMA) upon irradiation by UV and soft X-rays were monitored, and we show that it is possible to control the reaction rates from UV light and soft X-rays independently. We directly observe Ti4+ -> Ti3+ conversion upon irradiation, attributed to electron trapping at Ti sites close to surface OH groups formed by deprotonation of the parent molecule, trimethylacetic acid (TMAA). TMA photolysis on two surface preparations with different oxygen vacancy densities shows that the vacancy-related charge quenches the amount of charge that can be trapped at hydroxyls upon irradiation. During the initial stages of reaction the correlation between the amount of photodepleted TMA and the amount of charge trapped in the Ti 3d band gap state is nearly 1:1. A first-order kinetics analysis reveals that the reaction rate decreases with decreasing TMA coverage. There is also a coverage-dependent difference in the electronic structure of TMA moieties, primarily involving the carboxyl anchor group. These changes are consistent with a decreased hole affinity of the adsorbed TMA and hence a decreased reaction rate. This discovery adds to the previously presented picture of a reactivity that is inversely proportional to the number of surface hydroxyls, suggesting that the balance between the amounts of TMA, OH, and trapped charge needs to be considered.

Place, publisher, year, edition, pages
2016. Vol. 32, no 44, 11456-11464 p.
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-310759DOI: 10.1021/acs.langmuir.6b02989ISI: 000387519000013OAI: oai:DiVA.org:uu-310759DiVA: diva2:1058003
Funder
Swedish Energy Agency, 36642-1Carl Tryggers foundation , CTS 12:417The Crafoord Foundation, 20060599
Available from: 2016-12-20 Created: 2016-12-19 Last updated: 2016-12-20Bibliographically approved

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