ABSTRACT
A systematic study on the photocatalytic activity of well-defined, macroscopic bulk single-crystal 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-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 CO(2) than the rutile (110) surface. This surprisingly large difference in activity tracks the bulk e-h pair lifetime difference for the two TiO(2) modifications as determined by contactless transient photoconductance measurements on the corresponding bulk materials.
ABSTRACT
The adsorption of NO on single crystalline rutile TiO(2)(110) surfaces at 100 K and the subsequent formation of N(2)O via NO dimer intermediates was studied by reflection-absorption infrared spectroscopy using a UHV-FTIR system. Analysis of the IR data reveals that the occurrence of s-polarized adsorbate vibrational bands always increases the reflectivity, giving negative bands, whereas p-polarized bands are either positive or negative, depending on the reduction state of the substrate. This sign reversal of optical bands is caused by vacancy doping, which also affects the optical constants governing the complex interplay between reflection and transmission of p-polarized light on a dielectric substrate.
