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

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-NH 2 (Ti) within a graphene aerogel (GA) matrix. Mechanistic investigations reveal that the MIL-125-NH 2 (Ti)/GA composite could generate both reductive hydrated electrons (e aq – ) 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.