Photocatalytic Activity of BulkTiO2Anatase and Rutile Single Crystals Using Infrared Absorption Spectroscopy

A systematic study on the photocatalytic activity of well-defined, macroscopic bulk single-crystal ${\mathrm{TiO}}_{2}$ anatase and rutile samples has been carried out, which allows us to link photoreactions at surfaces of well-defined oxide semiconductors to an important bulk property with regard to photochemistry, the life time of $e\mathrm{\text{\ensuremath{-}}}h$ pairs generated in the bulk of the oxides by photon absorption. The anatase (101) surface shows a substantially higher activity, by an order of magnitude, for CO photo-oxidation to ${\mathrm{CO}}_{2}$ than the rutile (110) surface. This surprisingly large difference in activity tracks the bulk $e\mathrm{\text{\ensuremath{-}}}h$ pair lifetime difference for the two ${\mathrm{TiO}}_{2}$ modifications as determined by contactless transient photoconductance measurements on the corresponding bulk materials.