Factors influencing aqueous perfluorooctanoic acid (PFOA) photodecomposition by VUV irradiation in the presence of ferric ions

• PFOA can be completely defluorinated in relatively long time (72 h).
• OH radical shows profound impact on the reoxidation of Fe2+ to Fe3+.
• Persulfate inhibits the defluorination of PFOA in studied system.
• The environmental matric effect is firstly demonstrated.

In this study, four photochemical reaction parameters, including the reaction atmosphere, extra inorganic oxidant, inorganic anion and organic matter, were investigated in an aqueous environment to determine their effects on perfluorooctanoic acid (PFOA) photodecomposition. The photochemical defluorination of PFOA was conducted by vacuum ultraviolet light (VUV) using ferric ions as the catalyst. Both direct photolysis and photocatalysis were involved in the reaction. PFOA was completely decomposed by VUV irradiation with and without ferric ions within 72 or 144 h, respectively. There was no significant evidence indicating that the type of atmosphere (oxygen, nitrogen, or air) had any effect on the decomposition results. However, OH radicals generated during the photolysis process profoundly affected the decomposition of PFOA. The introduction of persulfate inhibited the mineralization of PFOA in the VUV/Fe3+ system. Inorganic anions hindered the defluorination of PFOA in the following order: HCO3− > SO42− > NO3− ∼ Cl− > ClO4−. The adverse effects of organic matter, including volatile organic compounds and dissolved natural organic compounds, were also examined. This study is beneficial to the understanding of the photodecomposition of other similar perfluorinated compounds (PFCs).