Coal gasification fine slag activates dual oxidants for PFOA degradation: Synergy of reactive species and C-F cleavage mechanisms.

Perfluorooctanoic acid (PFOA) is highly recalcitrant, necessitating degradation strategies that go beyond phase-transfer adsorption. Here, we constructed a synergistic "waste-treating-waste" system that uses coal gasification fine slag (CGFS) to dually activate peroxymonosulfate (PMS) and H2O2. Under optimal conditions, the CGFS/PMS/H2O2 system removed 75.34% of PFOA within 4 h via radical (SO4•- and O2•-) and non-radical (1O2 and electron transfer) pathways. Combining LC-MS and DFT calculations, we identified the electron-rich carboxyl terminus of PFOA as the primary nucleophilic site for single-electron oxidation. DFT calculations revealed that SO4•--driven Kolbe decarboxylation was barrierless and exergonic, whereas O2•--mediated decarboxylation (+3.49 eV) and direct C-F bond cleavage (>3.0 eV) were endothermic in the homogeneous phase. Nevertheless, LC-MS confirmed that all three pathways operated concurrently, which we attributed to the heterogeneous CGFS interface. Localized O2•- pools and substrate pre-polarization lower activation energies, unlocking theoretically constrained routes. The CGFS/PMS/H2O2 system effectively removed C6-C10 perfluorocarboxylic acids from real water samples, reducing toxicity and improving biodegradability after treatment. This study provides in-depth mechanistic insight and a practical, environmentally friendly approach for PFOA remediation.