Electron traps and the Stark effect on hydroxylated titania photocatalysts

Electric fields gent rated by photoexcited charge carriers in TiO2 (anatase) produce Stark, effect intensity and wavelength shifts for surface TiO-H stretching vibrations. Deep electron-trapping states affect a single type of TiO-H stretch (Ti(IV)O-H at 3647 cm(-1) --> Ti(III)O-H at 3716 cm(-1)). Shallow electron-trapping states, observed as broad absorption bands above 3000 cm(-1), produce an apparently homogeneous electric field. Intensity changes and corresponding wavelength shifts for v(TiO-H) are proportional to the magnitude and polarity of the electric field. O-2 is shown to reversibly abstract electrons from shallow trapping states. The results suggest that shallow electron traps are not associated with localized structures, but rather are delocalized across the TiO2 surface. This behavior may explain the photon-dependent wettability of TiO2 surfaces.