Is sulfur-doped TiO2 an effective visible light photocatalyst for remediation?

Doping titania with main group elements increases the visible light absorbance by introducing a localized band of orbitals within the band gap, but the effect of such dopants on the oxidizing power of the catalysts remains ambiguous. Three aromatic organic probe molecules - 4-methoxyresorcinol, quinoline, and 1-(p-anisyl)neopentanol - have been used to evaluate the oxidative chemistry of S-doped TiO2 and test the efficacy of the catalyst with visible irradiation. With visible irradiation, a phenol is degraded efficiently, apparently through absorption by a CT band. For the other two probes, the most straightforward interpretation is that visible irradiation does not produce hydroxyl-type chemistry, but can accomplish single-electron transfers in favorable cases. The utility of sulfur-doped TiO2 as a photocatalyst over undoped titania depends entirely whether the requirement for visible-light functionality, even if at low efficiency, outweighs a modest drop in the efficiency of catalysis using UV light. (C) 2009 Elsevier B.V. All rights reserved.