Photocatalysts and catalytic supports
Air treatment by photocatalytic processes

The photocatalysts used (mainly TiO ₂ , ZnO, Fe ₂ O ₃ , CdS, ZnS) are semiconductors with a medium-energy electronic band gap (1 to 3 eV) between the valence and conduction bands. Several semiconducting oxides or sulfides enable photocatalytic acceleration of a wide range of reactions of environmental interest. One of the most important factors in catalyst selection is the position of the band gap on the redox potential scale; this is shown in table 5 for the main catalysts used.