Effect of temperature on oxidative transformation of perfluorooctanoic acid (PFOA) by persulfate activation in water

Perfluorooctanoic acid (PFOA) is an emerging environmental pollutant attracting significant attention due to its global distribution, high persistence, and bioaccumulation properties. In this study, the degradation of aqueous PFOA at different temperatures was examined using heat-activated persulfate. Using this approach, 93.5% of PFOA was degraded after 30 h at 85 °C with 43.6% of F ^- yield, and the shorter chain length compounds (PFHpA (C ₆F ₁₃COOH), PFHxA (C ₅F ₁₁COOH), PFPeA (C ₄F ₉COOH), and PFBA (C ₃F ₇COOH)) were observed as degradation intermediates. The sequential degradation mechanism of losing one CF ₂ unit from PFOA and its intermediates on a step-by-step basis were observed. Controlled temperature kinetics studies yielded an activation energy of approximately 60 kJ/mol for the degradation of PFOA by heat-activated persulfate. However, at elevated temperatures, excess persulfate is needed for efficient PFOA degradation, presumably due to more intensive SO4- scavenging. Lower reaction pH was generally found to inhibit PFOA degradation, presumably due to the more prevalent radical-to-radical interactions.