Photochemical defluorination of aqueous perfluorooctanoic acid (PFOA) by VUV/Fe3+ system

• Defluorination of PFOA in VUV/Fe3+ system was firstly demonstrated.
• Ferric ion could effectively catalyze the activation of PFOA under VUV radiation.
• Both direct and catalytic photolysis were main mechanism of PFOA defluorination.

Perfluorooctanoic acid (PFOA), which is a typical perfluorinated acid, is bioaccumulative and extremely resistant to environmental degradation processes. In this study, a combined process using vacuum ultraviolet light (λ = 185 nm) and trivalent iron ions (VUV/Fe3+) was used to defluorinate aqueous PFOA. PFOA could be efficiently defluorinated under acidic condition (pH = 3–4), with a molar ratio of PFOA/Fe3+ between 1.8:1 and 1.2:1. Moreover, the decomposition mechanism of PFOA was also investigated. In addition to fluoride ions, other intermediates produced during PFOA decomposition were identified and quantified using HPLC/MS/MS, including six shorter-chain perfluorinated carboxylic acids (PFCAs) with C7, C6, C5, C4, C3 and C2. Our results indicated that direct light degradation played a major role in PFOA defluorination under VUV radiation (λ = 185 nm), while the defluorination of PFOA was simultaneously photocatalytically decomposed and defluorinated in the presence of ferric ion (λ = 254 nm). Additional Fe3+ enhanced the defluorination of PFOA and intermediates under VUV radiation.

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