Synergistic enhancement by formic acid in the oxidation system for perfluorooctanoic acid defluorination: efficiency and mechanism

Perfluorooctanoic acid (PFOA), a persistent organic pollutant with high oxidative resistance, presents significant challenges for efficient defluorination. This study demonstrates a novel approach to enhance PFOA defluorination efficiency in a UV-activated persulfate (PS) system by introducing formic acid (FA). Results showed that the UV/PS system alone achieved merely 27% PFOA defluorination in 24 h, whereas adding 2 mM FA significantly enhanced defluorination efficiency to 89%. Quenching experiments and electron paramagnetic resonance (EPR) analyses identified carbon dioxide radical anions (CO2•−) as the dominant active radicals driving PFOA reduction. The oxidative radicals (SO4•− and •OH) derived from PS activation react with FA to generate CO2•−, thereby facilitating efficient PFOA degradation. PS and FA concentrations, solution pH, and the presence of common anions (SO42−, HCO3−, NO3−, and NO2−) were systematically evaluated for their impact on PFOA defluorination. This study presents a simple yet effective method for PFOA defluorination, offering new insights into the defluorination of perfluorinated compounds.