New synthetic routes in heterogeneous photocatalysis

Heterogeneous photocatalysis is a sustainable technology mainly employed for water and air cleaning purposes. However, in the last two decades a lot of attention has been given to photocatalysis as an alternative route to be used in place of traditional industrial processes. The sustainability of photocatalysis mainly comes from the exploitation of renewable sources, such as solar light, and the possibility to avoid unsafe reagents/solvents and severe temperatures and pressures. In this chapter we give a critical presentation of some case studies concerning the use of heterogeneous photocatalysts, such as modified and bare TiO₂, ZnO, ZnS, WO₃, titanium silicalite, V₂O₅, polyoxometalates, CdS, CdSe, Bi₂O₃, PbBi₂Nb₂O₉, PbBiO₂Br and SrBi₂Nb₂O₉, in organic synthetic paths. Given the huge number of studies, a selection has been made among reactions of synthetic significance and/or of industrial interest, such as for instance (poly)aromatic partial oxidation, hydration and oxidation of propene, reduction and alkylation reactions. Special attention was paid to selectivity issues, the influence of catalyst features on selectivity and the possible use of green organic solvents when water-insoluble species have to be converted.