Influence of subsurface defects on the surface reactivity of TiO ₂: Water on anatase (101)

The adsorption of water on a reduced TiO₂ anatase (101) surface is investigated with scanning tunneling microscopy and density functional theory calculations. The presence of subsurface defects, which are prevalent on reduced anatase (101), leads to a higher desorption temperature of adsorbed water, indicating an enhanced binding due to the defects. Theoretical calculations of water adsorption on anatase (101) surfaces containing subsurface oxygen vacancies or titanium interstitials show a strong selectivity for water binding to sites in the vicinity of the subsurface defects. Moreover, the water adsorption energy at these sites is considerably higher than that on the stoichiometric surface, thus giving an explanation for the experimental observations. The calculations also predict facile water dissociation at these sites, confirming the important role of defects in the surface chemistry of TiO₂.