Photocatalytic Degradation and Defluorination of GenX in Lake Water: Elucidating the Enhanced Role of Natural Organic Matter

The widespread water contamination of hexafluoropropylene oxide dimer acid (HFPO–DA, GenX), a replacement for perfluorooctanoic acid (PFOA), necessitates the development of effective destructive treatment technologies. This study investigates the photocatalytic degradation of GenX in environmentally relevant water matrices using a titanium-based metal–organic framework (MOF), MIL-125-NH 2 . Contrary to commonly reported inhibitory effects of natural organic matter (NOM) in photocatalytic treatment processes, natural lake water significantly enhanced GenX degradation and defluorination compared to ultrapure water. To elucidate the promotional effect of lake water, NOM and representative model compounds of its redox-active moieties (glucose, phenol, and p -benzoquinone) were introduced for systematic investigation. The observed differences in GenX degradation behaviors suggest that electron-donating NOM moieties can enhance degradation and defluorination efficiency by suppressing electron–hole recombination and increasing the availability of photogenerated electrons for GenX breakdown. The degradation products of GenX were identified, and plausible degradation pathways were also evidenced by density functional theory (DFT) calculations. In addition, neutral pH conditions enable both effective GenX degradation and MOF structural stability. Overall, this study provides mechanistic insight into how redox-active NOM moieties influence PFAS degradation in heterogeneous photocatalytic systems under environmentally relevant conditions.