Photosensitization of TiO2 by MxOy and MxSy nanoparticles for heterogeneous photocatalysis applications

Currently, TiO2 is the most popular semi-conductor used in heterogeneous photocatalysis processes. Upon irradiation, conduction band electrons and valence band holes will be created in the relevant semi-conductor. These electrons and holes react with dissolved oxygen and/or adsorbed hydroxyl ions on the semi-conductor surface. That reaction will then initiate redox in the aqueous medium, resulting in the oxidization of organic pollutants. However, the rapid recombination that occurs in relation to photoproduced electrons and holes in TiO2 significantly diminishes the efficiency of the photocatalytic reaction. In 1995, to enhance the photocatalytic efficiency of semi-conductors, Serpone et al. proposed an interparticle electron transfer process by coupling two semi-conductors with different redox energy levels to increase the charge separation for the corresponding conduction and valence bonds. In the past decade, a certain number of studies related to the photocatalytic activity of TiO2 coupled with other semi-conductors such as for example CdS, SnO2, WO3, Bi2S3, Cu2O and CdSe. The main focus of this paper is to review the recent progress of the photocatalytic efficiency of coupled semi-conductors, comparing their efficiency with that of TiO2 alone. (c) 2007 Elsevier B.V. All rights reserved.