Titanium Dioxide Photocatalysts for Environmental Applications Metal-Doping with Cerium Ions for Visible Light Activation and Efficiency Improvement

The photocatalytic mechanism with titanium dioxide (TiO2) as a catalyst is initiated by the absorption of photons with energy equal to or greater than the bandgap of TiO2 (~ 3.1 eV for the anatase phase), producing electron-hole pairs in the semiconductor particle, as shown schematically in Fig. 13.1. Electrons are promoted to the conduction band, while positive holes are formed in the valence band. Excited-state electrons and holes can recombine and dissipate the input energy as heat, get trapped in metastable surface states or react with electron donors and electron acceptors adsorbed at the semiconductor surface or within the surrounding electrical double layer of the charged particles. Holes can react with adsorbed water to produce hydroxyl radicals with high redox oxidizing potential (Dong et al. 2015, Gopinath et al. 2020).