Photocatalytic removal of perfluorooctanoic acid pollutant from water via reverse fluorination strategy.

Solar-driven photocatalytic strategies can degrade representative perfluorooctanoic acid (PFOA) in water through a stepwise decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) mechanism; however, this process often leaves short-chain PFCAs in water as persistent degradation byproducts. The health risks of these degradation products are comparable to or even greater than those of the parent compound. Herein, we report that a heterojunction BiOIO3-P25 TiO2 photocatalyst, by incorporating the reactivity of long-lived triplet excited state of the BiOIO3 moiety in conventional photocatalysis, can repurpose part of the generated F- to drive inverted fluorination of the shorter-chain PFCAs generated in situ during PFOA degradation. The process yields volatile perfluoroalkanes (PFAs), which can be subjected to downstream thermocatalytic treatment. Under simulated sunlight without adding any chemicals, PFOA is degraded in water by this approach, achieving ∼71% defluorination to F-, ∼23% release of volatile PFAs that could subsequently be thermocatalytic degraded, and less than 2% residual short-chain PFCAs.