Photocatalysis of aqueous PFOA by common catalysts of In2O3, Ga2O3, TiO2, CeO2 and CdS: influence factors and mechanistic insights.

Gallium oxide (Ga2O3), titanium dioxide (TiO2), cerium dioxide (CeO2), indium oxide (In2O3) and cadmium sulfide (CdS) were commonly used under UV light as photocatalysis system for the pollutants' degradation. In this study, these five catalysts were applied for the photodegradation of perfluorooctanoic acid (PFOA), a well-known perfluoroalkyl substance (PFAS). As a result, the PFOA photodegradation performance was sequenced as: Ga2O3 > TiO2 > CeO2 > In2O3 > CdS. To further explain the photocatalysis mechanism, the effects of initial pH, photon energy and band gap were evaluated. The initial pH of 3 ± 0.2 hinders the catalytic reaction of CdS, resulting in low degradation of PFOA, while it has no significant effect on Ga2O3, TiO2, CeO2 and In2O3. In addition, quantum yield was sequenced as TiO2 > CeO2 > Ga2O3 > In2O3, which may not be the main factor determining the degradation effect. Notably, the band gap energy from large to narrow was as: Ga2O3 > TiO2 > CeO2 > In2O3 > CdS, which exactly matched their degradation performance.