MOF-mediated cascade photoreactions under nanoconfinement for defluorination of per- and polyfluoroalkyl substances

Abstract

Heterogeneous catalytic degradation of per- and polyfluoroalkyl substances (PFAS) through cleavage of the strong C-F bonds offers a robust and sustainable approach for mitigating their global threat to ecosystems and human health. However, current reduction or oxidation methods generally achieve only partial degradation of PFAS, producing chain-shortened intermediates that are often more recalcitrant and thus resulting in limited defluorination efficiency. In this study, we developed a nanoconfined photocatalytic system by encapsulating MIL-125-NH2(Ti) within a graphene aerogel (GA) matrix. Mechanistic investigations reveal that the MIL-125-NH2(Ti)/GA composite could generate both reductive hydrated electrons (eaq–) and oxidative hydroxyl radicals (HO•) under UV irradiation, enabling integrated cascade reduction-oxidation reactions in a single system. Interestingly, the nanoconfinement effect of GA improves the adsorption affinity towards PFAS with various chain lengths by more than 30% and lowers the C-F bond energy by a maximum of 10.8%. These kinetic and thermodynamic advantages collectively resulted in high defluorination ratios, i.e., 90.2% for perfluorooctanoic acid (PFOA), 65.3% for perfluorohexanoic acid (PFHxA), and 51.8% for perfluorobutanoic acid (PFBA) within 12 h, which are typically unattainable in conventional heterogeneous catalytic systems. Our findings open avenues for advanced heterogeneous systems to address the global PFAS challenge. Here, authors report a nanoconfinement strategy to encapsulate a MOF photocatalyst within a graphene aerogel matrix. This not only allows cascade reduction-oxidation reactions but also provides kinetic and thermodynamic advantages for efficient defluorination of various PFASs.