Photocatalytic reductive defluorination of perfluorooctanoic acid in water under visible light irradiation: The role of electron donor

The development of efficient technology for perfluorooctanoic acid (PFOA) treatment has prompted much concern in water environmental fields, due to its global distribution and threats to ecosystems. In this study, a new method for reductive defluorination of PFOA under visible light (VL) was established by using Pt-Bi2O4 as photocatalysts and KI as electron donors. The defluorination process in water was found to undergo photocatalytic reductive pathway, in which the photo-generated e− played the dominated role. The Pt served as co-catalyst to trap photo-generated e−, while KI could trap photo-generated h+ to suppress the undesired e−-h+ recombination, which cooperatively promote the defluorination efficiency. Along with PFOA reduction, very limited amount of short-chain perfluorocarboxylic acids intermediates were generated, all of which were capable to be further degraded to inorganic ions, and total recovery of fluorine could reach 99% after 6 h of irradiation. The system also possesses high photostability, since the photocatalyst surface maintained clean during the degradation. Finally, a decomposition pathway of stepwise removal of CF2 unit was proposed in detail. As a proof-of-concept, the VL/Pt-Bi2O4/KI system not only shows potential for sustainable and 'green' removal of PFOA in water, but also may find applications in water treatment of various refractory organic pollutants using solar energy.