Comprehensive DFT study of hydroxyl coverage on titania surfaces

Titania has broad applications as a catalyst and photocatalyst, and is often used in water-containing environments. Water molecules interacting with titania surfaces–particularly those that are chemisorbed–will affect the interactions of any reactants and products with titania. Here we present results of a comprehensive set of density functional theory calculations of the structure and energetics of chemisorbed water on titania surfaces. With consistent calculation settings that allow direct quantitative comparisons we have examined the anatase (001), (101), and (100), and rutile (001), (101), (110), and (100) surfaces, all with a range of coverages of both associatively and dissociatively chemisorbed water molecules. In addition we have examined the effects of implicit solvation on these surface configurations, as well as the impact of mixed adsorption states. We find that associative adsorption is generally preferred, with the notable exception of rutile (001) surface. Implicit solvation does not significantly change the low-energy configuration of water on titania, but primarily acts to reduce the water adsorption energies. Titania surfaces in both aqueous and (water-containing) vapor environments will generally be fully covered with chemisorbed water that exhibit adsorption energies ranging from ∼−0.4 to −1.0 eV/H₂O.