Hexafluoropropylene oxide dimer acid (HFPO-DA), commonly referred to as GenX, is a replacement compound for the straight-chain perfluoroalkyl substance (PFAS), perfluorooctanoic acid (PFOA). It has been recently detected worldwide in different waters, and is known to have environmental persistence and toxicity. In this study, we investigated the degradation kinetics of GenX in water by the vacuum ultraviolet (VUV) photolysis at 185 nm under anoxic condition by nitrogen purging to effectively produce hydrated electrons (eaq-) by removing dissolved oxygen. The VUV irradiation of water results in the in-situ generation of hydroxyl radicals (.OH), hydrogen atoms (.H), and eaq-. The production of .OH and eaq- during the VUV photoreaction was confirmed using electron paramagnetic resonance (EPR) spectroscopy (Fig. 1). The contributions of these three reactive species at various pH values were compared using nitrite (NO2-), nitrate (NO3-) ions, and tert-butanol (t-BuOH) as the radical scavengers. The radical scavenging results indicated that the degradation of GenX is mainly contributed by eaq-, especially at pH 6, achieving 67% degradation within 3 hr reaction time (Fig. 2). Finally, the transformation products of GenX during the VUV photolysis were identified using LC-QTOF/MS, and the resulting degradation pathways were proposed.

Degradation of hexafluoropropylene oxide dimer acid (GenX) in water using the vacuum ultraviolet (VUV) photolysis process under anoxic condition

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