GenX degradation mechanism using 2-hydroxyphenyl acetic acid and cetyl trimethyl ammonium bromide under UV-LED irradiation through micelle formation.

This study investigated the removal of hexafluoropropylene oxide dimer acid (GenX) using 2-hydroxyphenyl acetic acid (2-HPA) as a hydrated electron (e) producer under UV-LED (265 nm) irradiation in the presence of cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant. The addition of CTAB above the critical micelle concentration of 0.62 mM at pH 7 resulted in an enhancement of GenX removal due to the formation of a micelle structure. The generation of hydrated electron (e) by 2-HPA was confirmed through ESR analysis. At pH 7, 3.0 mM CTAB led to 86% GenX removal and 40% defluorination after 6 h. While the removal of GenX remained consistent at pH 5, 7, and 9, it declined at pH 11. GenX removal efficiency was affected by the presence of anionic e scavengers such as NO and NO, with NO showing higher inhibition than NO. Identification by LC-MS/MS revealed PFPrA and TFA as the main transformation products (TPs), while seven additional TPs (TP 64, TP 146, TP 162, TP 186, TP 228, TP 282, and TP 312) were newly identified by non-target screening. The degradation pathway of GenX involves ether bond cleavage, decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) chain shortening, and α-carbon H/F exchange, as determined through identified TPs and theoretical calculations. ECOSAR simulation indicated that most TPs exhibit lower ecotoxicity compared to GenX. This study firstly utilized UV-LED (265 nm) as a light source for degrading GenX by the reaction took in the micelle without high pH or anoxic conditions, as typically required in advanced reduction processes.