Hydration Structure of Brookite TiO2 (210)

The interface of TiO2 and water has been heavily researched due to the photocatalytical capabilities of this system. Whereas the majority of existing work has targeted the rutile and anatase phases of TiO2, much less is known about the brookite phase. In this work, we use first-principles molecular dynamics simulations to find the hydration structure of the brookite (210) surface. We find both pure water and an aqueous solution of KCl to order laterally at the sites of surface Ti cations due to electrostatic and chemical considerations, qualitatively in agreement with experimental high-resolution atomic force microscopy measurements. A significant fraction of surface oxygens is hydroxylated for all cases, with up to 40% realized for the aqueous solution at bulk coverage, a result originating in orientational constraints placed on water near the solvated K and Cl ions. Proton transfer is nearly equally frequent between the surface and liquid regions and within the liquid region, but the presence of K and Cl ions makes proton transfer less efficient.