Photocatalytic activities of tin(IV) oxide surface-modified titanium(IV) dioxide show a strong sensitivity to the TiO ₂ crystal form

Surface modification of rutile TiO ₂ with extremely small SnO ₂ clusters gives rise to a great increase in its UV light activity for degradation of model organic water pollutants, while the effect is much smaller for anatase TiO ₂. This crystal form sensitivity is rationalized in terms of the difference in the electronic modification of TiO ₂ through the interfacial Sn-O-Ti bonds. The increase in the density of states near the conduction band minimum of rutile by hybridization with the SnO ₂ cluster levels intensifies the light absorption, but this is not seen with modified anatase. The electronic transition from the valence band to the conduction band causes the bulk-to-surface interfacial electron transfer to enhance charge separation. Further, electrons relaxed to the conduction minimum are smoothly transferred to O ₂ due to the action of the SnO ₂ species as an electron transfer promoter.