Due to the potential hazard of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) has become a typical alternative since 2009. However, GenX has recently been reported to have equal or even greater toxicity and bioaccumulation than PFOA. Considering the suitability of alternatives, it is quite essential to study and compare the degradation degree between PFOA and GenX in water. Therefore, in the present study, a comprehensive degradation comparison between them via electrooxidation with a titanium suboxide membrane anode was conducted. The degradation rate decreased throughout for PFOA, while it first increased and then decreased for GenX when the permeate flux increased from 17.3 L to 100.3 L m-2·h-1. The different responses of PFOA and GenX to flux might be attributed to their different solubilities. In addition, the higher kobs of PFOA demonstrated that it had a better degradability than GenX by 2.4-fold in a mixed solution. The fluorinated byproduct perfluoropropanoic acid (PFPrA) was detected as a GenX intermediate, suggesting that ether bridge splitting was needed for GenX electrooxidation. This study provides a reference for assessing the degradability of GenX and PFOA and indicates that it is worth reconsidering whether GenX is a suitable alternative for PFOA from the point of view of environmental protection.
Keywords: Degradation pathway; Electrooxidation; Hexafluoropropylene oxide dimer acid; Perfluorooctanoic acid; Titanium suboxide anode.
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