Enhanced photoreductive degradation of perfluorooctanesulfonate by UV irradiation in the presence of ethylenediaminetetraacetic acid

Abstract

Perfluorooctanesulfonate (PFOS) is a persistent organic pollutant (POP) that is globally distributed. Hydrated electrons (eaq−) are known to effectively initiate the decomposition of PFOS. In this study, we explore an alternative photolytic approach employing aquated electrons, eaq− in the presence of ethylenediaminetetraacetic acid (EDTA) in order to enhance the photo-induced degradation of PFOS. EDTA, in this case, serves primarily as a hydroxyl radical scavenger, which inhibits the recombination of eaq− with ·OH resulting in an increased average photolytic lifetime for eaq−. The net effect is to enhance the degradation of PFOS. UV/EDTA irradiation is shown to increase the overall decomposition percentages of PFOS. The empirical pseudo first-order rate constant for the loss of PFOS is 0.113 h−1. In addition, we used laser flash photolysis kinetics to show that the eaq− is the dominant species responsible for the decomposition of PFOS. EDTA also allows for the photolytically-produced hydrated electrons to be used in the presence of air over a wide range of pH. Furthermore, perfluoroalkyl sulfonates with longer chain lengths have higher overall decomposition percentages and increased defluorination percentages. The observed kinetic enhancements appear to be due primarily to the impact of the amine and methylene groups of EDTA with respect of hydroxyl radical scavenging.