Effect of pH and Coexisting Species on the Photochemical Decomposition of Perfluorooctanoic Acid by Iron (III) Sulphate

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Perfluorinated compounds including perfluorooctanoic acid (PFOA), which have been detected globally in the environment and in wildlife, have recently received a great deal of attention as environmental contaminants because they are ubiquitous in the environment. In this study, the effect of pH and coexisting ions on the decomposition of PFOA was evaluated under a combined treatment of ferric ion and ultraviolet radiation. The defluorination ratio at pH 2.0 after 72 hr was 101% of the initial PFOA concentration (48 μM). The defluorination rate constant of PFOA during the initial 4 hr at pH 2.0 was 56 × 10-3 hr-1. Furthermore, SO42- ions might have interfered with the complexation of PFOA with Fe3+. Moreover, hydroxyl radical was detected in the sample solution of pH 2.0, 3.0, and 3.5 using electron spin resonance spectroscopy. The hydroxyl radical oxidized Fe2+ to Fe3+, which was reduced by the PFOA decomposition. The strongest absorbance at 250 nm was observed at the sample solution at pH 2.0. Consequently, the photochemical decomposition for PFOA was more efficient at pH 2.0 due to the strong UV absorbance and the influence of the hydroxyl radical.