Ferric ion mediated photochemical decomposition of perfluorooctanoic acid (PFOA) by 254 nm UV light

The great enhancement of ferric ion on the photochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) under 254 nm UV light was reported. In the presence of 10 mu M ferric ion, 47.3% of initial PFOA (48 mu M) was decomposed and the defluorination ratio reached 15.4% within 4 h reaction time. While the degradation and defluorination ratio greatly increased to 80.2% and 47.8%, respectively,when ferric ion concentration increased to 80 mu M, and the corresponding half-life was shortened to 103 min. Though the decomposition rate was significantly lowered under nitrogen atmosphere, PFOA was efficiently decomposed too. Other metal ions like Cu2+ and Zn2+ also slightly improved the photochemical decomposition of PFOA under irradiation of 254nm UV light. Besides fluoride ion, other intermediates during PFOA decomposition including formic acid and five shorter-chain perfluorinated carboxylic acids (PFCAs) with C7, C6, C5, C4 and C3. respectively, were identified and quantified by ICor LC/MS. The mixture of PFOA and ferric ion had strong absorption around 280nm. It is proposed that PFOA coordinates with ferric ion to form a complex, and its excitation by 254 nm UV light leads to the decomposition of PFOA in a stepwise way. (C) 2008 Elsevier B.V. All rights reserved.