Photodegradation in the absence of externally added chemicals could be an attractive solution for the removal of perfluorooctane sulfonate (PFOS) in aqueous environment, but the low decomposition rate presents a severe challenge and the underlying mechanisms are unclear. In this study, we demonstrated that PFOS could be effectively degraded in a catalyst-free aqueous solution via a reduction route. Under appropriate pH and temperature conditions, a rapid PFOS photodegradation, with a pseudo-first-order decomposition rate constant of 0.91 h−1, was achieved. In addition, hydrated electrons were considered to be the major photo-generated reductive species responsible for PFOS photodegradation in this system. Its production and reduction ability could be significantly affected by the environmental conditions such as pH, temperature and presence of oxidative species. This study gives insights into the PFOS photodegradation process and may provide useful information for developing catalyst-free photodegradation systems for decomposing PFOS and other persistent water contaminants.

Decomposition of perfluorooctanoic acid (C7F15COOH, PFOA) has been gaining increasing interests because it is a ubiquitous environmental contaminant and resistant to the most conventional treatment processes. In this work, the rapid and complete mineralization of PFOA and simultaneous defluorination were achieved by γ-ray irradiation with a 60Co source. The degradation rate of PFOA by γ-ray irradiation would be high, and a pseudo-first-order kinetic rate constant of 0.67 h−1 could be achieved in the N2 satured condition at pH 13.0. The experimental results and quantum chemical calculation confirmed that two radicals, i.e., hydroxyl radical (·OH) and aqueous electrons (eaq−), were responsible for the degradation of PFOA, while only either eaq− or ·OH might not be able to accomplish complete mineralization of PFOA. The synergistic effects of ·OH and eaq− involved in the cleavage of C-C and C-F bonds, and therefore complete mineralization of PFOA were achieved. The intermediate products were identified and the degradation pathway was also proposed. The results of this study may offer a useful, high-efficient approach for complete mineralizing fluorochemicals and other persistent pollutants.

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