Adsorption of R-OH molecules on TiO2 surfaces at the solid-liquid interface

Abstract

The exploration of TiO2 surface reactivity from first-principles calculations has been almost always limited to the gas phase, even though most of the chemically relevant applications of this interface involve the solid-liquid boundary. The reason for this limitation is the complexity of the solid-liquid interface, which poses a serious challenge to standard ab initio methodologies as density functional theory (DFT). In this work we study the interaction of H2O, CH3OH, H2O2, and HCO2H with anatase (101) and rutile (110) surfaces in aqueous solution, employing a continuum solvation model in a DFT framework in periodic boundary conditions [J. Chem. Phys. 2009, 131, 174108 ]. Different adsorption configurations were analyzed, examining the effect of the first water monolayer explicitly included in the simulation. For water and methanol, molecular adsorption was found to be the most stable in the presence of the solvent, while for hydrogen peroxide the preferred configuration depended on the surface. The explicit inclusion of the first water monolayer turns out to be important since it may play a role in the stabilization of the adsorbates at the interface. In general, the slightly positive adsorption energy values obtained (with respect to water) suggest that CH3OH and H2O2 will poorly adsorb from an aqueous solution at the titania surface. Among the three species investigated other than water, the formic acid was the only one to exhibit a higher affinity for the surface than H2O. © 2011 American Chemical Society.