Adsorption structure of acetic anhydride on a TiO2(1Â 1Â 0) surface observed by scanning tunneling microscopy

The carboxylic acids are stably adsorbed on TiO2(1 1 0) surfaces at room temperature. To demonstrate the neutralization mechanism proposed by Ashima et al. [H. Ashima, W.-J. Chun, K. Asakura, Surf. Sci. 601 (2007) 1822.] that explains the stable adsorption of carboxylic acids, we studied the full-coverage adsorption structure of acetic anhydride on a TiO2(1 1 0) surface by STM (scanning tunneling microscopy). We directly observed three postulated species on the TiO2(1 1 0) surface; normal acetates (termed acetate A) forming a (2 × 1) ordered structure, a minor acetate species (termed acetate B) which was present between the bridging oxygen and the 5-fold Ti, and the oxygen vacancies. We determined the ratio of these three species. This ratio was in good agreement with the postulated conversion reaction of acetate B to A.