Photocatalysts, titanium oxide semiconductor properties

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

The most common photocatalytic processes, in terms of both mechanistic analysis and practical use, involve insoluble semiconductor metal oxides or sulfides, which upon irradiation undergo dual interfacial electron transfer between the excited semiconductor surface and adsorbed donor (D) and/or acceptor (A) molecules (Scheme 6.291). Titanium dioxide (Ti02) is a particularly popular photocatalyst due to its good redox properties (see also Special Topic 6.29), high stability, low toxicity and low price. 

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