Photochemical Charge Transfer and Trapping at the Interface between an Organic Adlayer and an Oxide Semiconductor

• Published in: Journal of the American Chemical Society 2003-12, Vol.125 (49), p.14974-14975
• Main Authors: Henderson, Michael A, White, J. Michael, Uetsuka, Hiroshi, Onishi, Hiroshi
• Format: Article
• Language: English
• Subjects: Adsorption and desorption kinetics; evaporation and condensation; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja037764+

Identification of charge transfer and trapping sites on semiconducting oxide surfaces is of fundamental importance in furthering the field of heterogeneous photocatalysts. Using scanning tunneling microscopy, electron energy loss spectroscopy, and photodesorption, we observed both electron trapping and hole transfer events on the (110) surface of TiO2 rutile. UV irradiation of a saturated monolayer of trimethyl acetate (TMA) on TiO2(110) at room temperature resulted in hole transfer to the carboxylate group, followed by (CH3)3C−COO bond cleavage and desorption of CO2 and isobutene/isobutane. Hole transfer to TMA proceeded in the absence of a gas-phase electron scavenger (which is typically O2) because the accompanying photogenerated electrons could be trapped at the surface as Ti3+ cations bound to bridging OH groups. The extent of electron trapping, gauged by electron spectroscopy, correlated directly with the yields of photodesorption fragments resulting from the hole transfer channel. Charge at the Ti3+ sites was titrated in the dark via a reaction between O2 and the Ti3+−OH groups.