Hydrated-electron-based short chain perfluorosulfonic acid decomposition in VUV/sulfite system

Perfluorosulfonic acids (PFSAs) have attracted increasing attention due to their global distribution, high chemical stability and persistence. As a powerful reductant, hydrated electron (e aq) shows extraordinary reactivity towards halogenated organic substances like PFSAs. In this study, e aq-based photo-decomposition of perfluorohexane sulfonate (PFHxS) in a VUV/sulfite system was investigated. The kobs of PFHxS decomposition in the studied system was 0.0049± 0.0005 min , which was 24.5-fold faster than that in a sole VUV system. It was demonstrated that e aq was the main reactive species responsible for PFHxS decomposition. PFHxS decomposition kinetics were accelerated at higher initial solution pH and sulfite dosage, but were restrained when higher initial PFHxS concentration was introduced. Co-existence of chloride showed slight enhancement of PFHxS decomposition, whereas nitrate and bicarbonate suppressed PFHxS decomposition. Accompanying PFHxS decomposition, short chain perfluorocarboxylic acids (PFCAs) were detected as main intermediate products. PFHxS decomposition started with C-S bond fracture, followed by perfluoroalkyl radical hydrolysis reactions and perfluorohexanoic acid (PFHxA) formation. Afterwards, PFHxA was defluorinated by stepwise loss of CF2 units to generate other short chain PFCAs.