Enhancing the visible-light photocatalytic activity of TiO2 by heat treatments in reducing environments

Following a series of recent studies that demonstrated enhanced visible-light photocatalytic activities of TiO2 by annealing in reducing atmospheres, a systematic investigation was conducted, in which TiO2 nanoparticles were annealed in various controlled atmospheres with the estimated oxygen partial pressure being varied from ∼10−1 to ∼10−25 atm and presence of other species (Ar, H2, N2, vacuum or hydrocarbon); subsequently, photocatalytic activities were tested. The results suggest that the oxygen partial pressure during annealing is not the dominant controlling factor. Furthermore, the use of vacuum environments or the presence of hydrocarbon species during annealing is effective in enhancing the photocatalytic activity, but the presence of H2 at a partial pressure of 0.05 atm does not show an appreciable beneficial effect. HRTEM suggested that the enhanced photocatalytic activity of vacuum-activated TiO2 may be related to subnanometer-thick disordered surface layers.

► We tested the visible-light photocatalytic activity of 15 heat-treated TiO2.
► The estimated oxygen partial pressure varies from ∼10−1 to ∼10−25 atm.
► The oxygen partial pressure during annealing is not the dominant factor.
► The presence of hydrocarbon species enhances the photocatalytic activity.
► The presence of H2 at a partial pressure of 0.05 atm has little beneficial effect.