EFFECTS OF ALTERVALENT CATION DOPING OF TIO2 ON ITS PERFORMANCE AS A PHOTOCATALYST FOR WATER CLEAVAGE

The influence of altervalent cation doping of TiO2 on its performance as a photocatalyst in water cleavage is investigated. It is shown that under illumination in the near-UV region (250-400 nm), platinized anatase TiO2 exhibits H-2 production rates which are significantly higher than those of the rutile form. Photocatalytic efficiency is shown to be independent of the specific surface area of the semiconductor. Incorporation of cations of valence higher than that of the parent cation (W6+, Ta5+, Nb5+) into the crystal matrix of TiO2 results in enhanced rates of water cleavage while the opposite is observed upon doping with cations of lower valence (In3+, Zn2+, Li+). The enhancement or reduction of photocatalytic activity is found to be dependent on the concentration and valence of the doping cations. These results do not correlate with observed alterations in the light-absorption capacity of the doped semiconductor. They are explained in term of alteration of the bulk electronic structure of the semiconductor, which influences its electron-hole generation and separation capacity, under illumination.