Reductive Degradation Of Perfluorooctane Sulfonate Catalyzed By Vitamin B₁₂

Perfluorinated acids?PFAs?are the new emerging persistent organic pollutants subsequent to polychlorinated biphenyls and dioxins,and there are some potential health risks because of the pollution of drinking water sources,such as groundwater.Perfluorooctane Sulfonate?C8,PFOS?,a typical representative of PFAs,its available removal technologies are generally characterized by harsh reaction conditions,high treatment costs.Therefore,there is an urgent need to develop a PFOS degradation technology that is economical and effective with mild reaction conditions.In this study,the degradation of PFOS using VB₁₂ catalyst synthesized by soil microorganisms and titanium?III?citrate,nano-zero-iron and nano-zero-valent copper electron donors under mild regulation was investigated.At the same time,steady state degradation products were analyzed by HPLC-MS/MS and HPLC-QTOF.And combined with isotope labeling technology(¹³C₄-PFOS),the pathway and mechanism of PFOS degradation were also explored in detail.The experimental results of VB₁₂ catalyzed titanium?III?citrate reduction degradation of PFOS show that:1)The higher reaction temperature and the longer reaction time of the system,the higher defluorination rate and degradation rate of PFOS.2)Steady-state degradation products include PFTA,PFDoA,PFDA,PFNA,PFOA,PFHpA,PFHxA,PFHpS,PFHxS and 1H-perfluoropentane,1H-perfluorohexane,1H-perfluoroheptane,1H-perfluorodecane,1H-perfluorodecane,1H-perfluoroundecane and 1H-perfluorotridecane.3)Degradation pathway of PFOS:?i?The C-S bond of¹³C₄-PFOS breaks to generate C₈F₁₇·radicals and then hydrolyzes to form PFOA,or the C₈F₁₇·radicals connects the four-CF₂-groups and hydrolyzes to form PFDoA.?ii?The C-C bond between the carbon of No.6 and No.7 of PFOS is broken,and four-CF₂-groups are connected to generate C₆F_13·radicals,and then combined with SO₃^-to generate PFHxS,or the C₆F_13·radical is hydrolyzed to generate PFHxA;the C-C bond between the carbon of No.5 and No.6 of PFOS is broken,and four-CF₂-groups are connected to generate C₆F_13·radicals,and then combined with SO₃^-to generate PFHpS,or the C₆F_13·radical is hydrolyzed to generate PFHpA.?iii?The sulfonic acid group of the intermediate product PFHxS is removed to generate C₆F₁₃·radicals,and four-CF₂-groups are connected and then hydrolyzed to form PFDA,Or the C₆F₁₃·radicals are continuously linked to four-CF₂-groups and hydrolyzed to form PFTA.PFNA is generated by the hypothetical degradation product PFPeS according to this rule.It is assumed that the degradation product PFPeS reacts according to this rule to generate PFNA.?iv?The short chain perfluoroalkane is produced by H substitution after PFOS removal of the sulfonic group,and the long chain perfluoroalkane is generated by the corresponding short chain perfluoroalkane connecting four-CF₂-groups.The results of VB₁₂ catalyzes nCu⁰ to degrade PFOS show that the VB₁₂/nCu⁰system can not effectively remove PFOS.VB₁₂2 catalyzed nFe⁰ reduction degradation PFOS results show that:1)When the temperature is 70°C,the concentration of VB₁₂ is 200umol/L,and the dosage of nFe⁰is 2.0 g/L,the defluorination rate and degradation rate of PFOS are 17.03%and 53.75%,respectively.And the reaction process conforms to the first-order reaction kinetics.2)Steady-state degradation products include PFTA,PFDoA,PFUdA,PFOA,PFHxA,PFHpS,PFHxS.3)Degradation pathway of PFOS:?i?The formation of PFOA,PFDoA,PFHpS,PFHxS etc.is similar to the VB₁₂/Ti?III?system.?ii?After the sulfonic acid group is removed from the PFHpS,four-CF₂-groups are connected and hydrolyzed to form PFUdA.?iii?PFTA is generated by the cleavage of the C-S bond by PFHxS,followed by two successive additions of four-CF₂-groups.