Inferring Protonation States of Hydroxamate Adsorbates on TiO2 Surfaces

Abstract

We explore the protonation states of benzohydroxamic acid adsorbates bound to the {101} facet of TiO2 anatase by using a combination of density functional theory, simulations of UV–vis spectra based on a tight-binding Hamiltonian, and direct comparisons to experimental measurements. We find that the characteristic red-shifted spectrum of nonmethylated, relative to the methylated, hydroxamic acids can only be explained by proposing a monodeprotonated monodentate mode as the main adsorption mode. The reported analysis suggests a simple, yet general, spectroscopic method based on UV–vis absorption measurements and tight-binding calculations for inferring changes of pKa of molecular adsorbates interacting with semiconductor electrode surfaces.