The role of Cerium, Europium and Erbium doped TiO2 photocatalysts in water treatment: A mini-review

Heterogeneous photocatalysis is a promising environmentally friendly strategy for removing contaminants of emerging concern from water, with titanium dioxide being the most studied and exploited photocatalyst, thanks to its good optical and electrical properties. However, one of the main drawbacks linked to its use is the limited absorption of sunlight; several strategies have been explored to enhance the absorption in visible light region and, among them, the doping with elements belonging to the lanthanoid series is particularly attractive. This review focuses on these systems analysing the cases of Cerium, Europium and Erbium doped TiO2 and giving an overview on the structural, optical and electronic characteristics of these materials. Synthesis procedures, inserted dopant percentages, structural and optical properties and the main operating conditions adopted in the photodegradation studies are considered. Particular attention is devoted to unravel the effect induced by the introduction of lanthanoids on the energy gap, on the recombination rate of photogenerated electron-hole pairs and on the inhibition of phase transition from anatase to rutile.