Orientation of acetic acid hydrogen bonded to acetate terminated TiO₂(110)

Acetic acid is a common pollutant for which photocatalytic degradation over titania provides a mitigating strategy. Knowledge of the bonding of acetate/acetic acid to this substrate is needed to aid interpretation of the photocatalytic data. In this work we use ambient pressure near edge X-ray absorption fine structure to measure the coverage and geometry of acetate in the TiO₂(110) contact layer as well as acetic acid in an additional layer. A saturation coverage of 0.5 monolayers in both layers is found up to an acetic acid pressure of 10⁻¹ Torr at 266 K. The geometry of acetate appears to be unchanged by adsorption of an additional layer of acetic acid, with the contact layer involving a majority acetate species bidentate bonded to neighboring Ti_5c sites and a minority acetate species bonded in a perpendicular geometry. Acetic acid has a similar geometry dictated by hydrogen bonding to the contact layer as well as the substrate.