Theoretical study of the molecular and electronic structure of methanol on a TiO2(110) surface

We present density-functional-theory calculations of the molecular and electronic structure of methanol adsorption on stoichiometric TiO2(110) surface. We have investigated 11 different molecular and dissociated adsorption structures of CH3OH at 1 monolayer coverage. The relative stabilities of different structures depend on the chemisorption-induced charge transfer, the relative strengths of different types of hydrogen bonds, the steric hindrance between methyl groups and the surface stress. We found the intermolecular hydrogen bonding to play an important role in stabilizing the overlayer. We also investigated the occupied and unoccupied surface electronic structure, and the adsorbate-induced surface dipole moment and work-function changes. The electronic structures show that the highest-occupied molecular orbital of CH3OH is near the valance-band maximum, which reflects the character of CH3OH as a hole scavenger on TiO2 surfaces. The unoccupied partially solvated or wet electron states for CH3OH on TiO2 are primarily distributed on H atoms of methyl groups. Despite many different structural motifs, the wet-electron-state energy primarily correlates with the surface dipole moment.