Photocatalytic removal of perfluoroalkyl substances from water and wastewater: Mechanism, kinetics and controlling factors

This review focuses on heterogeneous photocatalysis of perfluoroalkyl substances (PFAS) which are of worldwide concern as emerging persistent organic contaminants. Heterogeneous photocatalysis is an effective and advanced technology for PFAS removal from water with relatively high efficacy. During photocatalysis, various short chain perfluorocarboxylic acids (PFCA) are produced as intermediates and the efficacy is related to the photo-generated hole (h⁺) and photo-generated electron (e⁻). PFAS photodegradation in water under UV irradiation is most effective by using In₂O₃ as the catalyst, followed by Ga₂O₃ and TiO₂. Significantly, modifying the chemical composition or morphology of the catalyst can improve its efficacy for PFAS removal. In₂O₃ porous nanoplates were found to have the best performance of 100% PFAS decomposition under UV light with rate constant (k_t) and half-time (τ_1/2) of 0.158 min⁻¹ and 4.4 min, respectively. Catalysts perform well in acidic solution and increasing temperature to a certain extent. The photocatalytic performance is reduced when treating wastewater due to the presence of dissolved organic matter (DOM), with the catalysts following the order: needle-like Ga₂O₃ > In₂O₃ > TiO₂. Future studies should focus on the development of novel photocatalysts, and their immobilization and application for PFAS removal in wastewater.