Infrared spectra of photoinduced species on hydroxylated titania surfaces

We detect transient and persistent diffuse reflectance infrared signals fro m surface intermediates generated by band gap irradiation of polycrystallin e, hydroxylated TiO2 under controlled atmospheres. Irradiation in vacuo or in the presence of CD3OD(ads) leads to a new absorbance at 3716 cm(-1), the decline of a 3647 cm(-1) band, and a reflectivity loss. Overall reflectivi ty, which gauges mobile charge, partially recovers in the dark after a few minutes but fully recovers upon exposure to O-2. The 3716 cm(-1) feature pe rsists for days in a vacuum or dry O-2 but is bleached by the action of (O- 2 + H2O + h nu). It is assigned to a Ti(III)O-H- vibration resulting from e lectron trapping at acidic Ti(IV)OH centers. Irradiation under O-2 yields a new band at 3683 cm(-1), ascribed to surface-bound OH radicals that last i ndefinitely in a vacuum. None of the above events cm occur on thermally gen erated TiO2-gamma specimens subsequently exposed to H2O(g). We infer that ( 1) O-2 is an efficient scavenger of conduction band electrons at the gas-so lid interface, (2) the competition for holes between lattice oxygen photode sorption and OH- oxidation depends on gas pressure and composition, and (3) the trapped carrier buildup eventually results in extended surface reconst ruction involving Ti-OH functionalities, giving rise to restructuring hyste resis.