Study On Degradation Characteristics And Mechanism Of Perfluorooctanoic Acid And Perfluorooctane Sulfonate By Electron Beam Irradiation

This paper makes a study about a series of PFOA and PFOS degradation by electron beam irradiation.Perfluorooctane sulfonate?PFOS?and perfluorooctanoate?PFOA?are among the perfluorinated compounds?PFCs?that have received a great deal of concern in recent years.Because of their extraordinary stability,hydrophobicity,and excellent surfactant performance,many PFCs have been widely applied to industrial and domestic production for over sixty years.PFOA and PFOS have been found almost ubiquitously in various environmental media including waters,air,sediments,wildlife even human.Moreover,toxic and bioaccumulative effects of contaminants also have been confirmed by extensive studies.These results suggest that they are toxic pollutants that can accumulate in human body,and might pose a risk to human health.However,PFCs are chemically inert due to the unique properties of fluorine and relatively strong carbon-fluorine bond?C-F,116 kcal/mol?making them resistant to conventional advanced oxidation processes.In order to find an effectual way to remove PFOA and PFOS,this paper makes a deep research on the degradation of PFOA and PFOS by electron beam irradiation technologies.The degradation characteristics of PFOA and PFOS irradiated by electron beam were studied in aqueous solutions.The degradation of PFOA and PFOS followed the pseudo-first-order kinetics.The degradation of PFOA and PFOS increased with the increasing p H value.The fluoride release results obtained during PFOA and PFOS degradation at different pH values.The released fluoride ions concentration also increased with the increasing p H.These results might be attributed to hydrogen radical would be inverted into hydrated electron in alkaline condition and the loss of hydrated electron in acidic condition.Thus,the solutions in alkaline conditions may be helpful to the degradation of PFOA and PFOS.The addition of hydrogen peroxide is not good for the remove of PFOA and PFOS.However,the excess hydrogen peroxide may decreased the quantity of hydroxyl radicals and hydrated electron,which could inhibit the degradation of PFOA and PFOS.In order to investigate which active species played the leading role in the degradation of PFOA and PFOS,the aqueous solutions?20 mg/L?was saturated by the aqueous solutions?20 mg/L?was saturated by N₂,O₂ and 0.1 mol/L tert-butanol with N₂.The relatively higher degradation rates and concentrations of fluoride ions occurred in N₂ saturated solution contains 0.1mol/L tert-butanol.The result indicates that hydrated electron and hydrogen radical play a critical role on the electron beam degradation of PFOA and PFOS.In order to investigate the optimal degradation condition of PFOA and PFOS by electron beam irradiation,the aqueous solutions?20 mg/L?were saturated by N₂ and adjusted initial p H to 13.At absorbed doses 500kGy,the degradation rates of PFOA and PFOS in nitrogen atmosphere were 95.7%and 85.9%at p H 13,and the concentration of fluoride ions rapidly increased to324.6?mol/L and 416.9?mol/L,respectively.PFOA,PFOS and their degradation products in the aqueous solutions were identified using HPLC-MS/MS method,observed that short-chain perfluorinated compounds and hydrogen substitution product appeared after irradiation.Based on these results mentioned above,the possible mechanism for degradation of PFOA and PFOS by electron beam irradiation was proposed.The hydrated electrons attack PFOA and PFOS,which induce the fluoride elimination and react with H₂O.The electrophilic radicals are attack by hydrated electrons,then may undergo an intramolecular defluorination and react further with H₂O.The unstable products also further removed CF₂·unit and transformed to short-chain.Other short-chain perfluorinated compounds were formed successively by similar reaction,and finally complete degradation.In conclusion,these results suggested that PFOA and PFOS could be efficiently decomposed by electron beam irradiation in an anoxic alkaline solution.The findings in this study may bring an efficient and environmentally friendly technique for PFCs degradation.