Reductive Degradation Of Perfluorooctane Sulfonate Catalyzed By Transition Metal Coenzyme In A Bionic System

Perfluorooctane sulfonate（PFOS）was considered as persistent organic pollutant.Many people have paid close attention to the pollution of PFOS due to the detection in various environmental and organisms.In this study,PFOS was degraded by a mild method which uses vitamin B12(VB₁₂)as catalyst and Ti（III）-citrate as bulk reductant.Meanwhile,degradation products were analyzed and the effects of reaction parameters were investigated as well as the decomposition mechanisms were proposed.The results show that PFOS（200mol/L）was degraded and the fluoride concentration of the solution increased from 6.67mol/L（initial）to 64.91mol/L（4d）,along with the formation of other fluorine degradation products.The qualitative analysis was performed by HPLC-MS/MS.Perfluorobutyric acid（PFBA,C4）,perfluoroheptanoic acid（PFHpA,C7）,perfluorooctanoic acid（PFOA,C8）,perfluorononanoic acid（PFNA,C9）,perfluorodecanoic acid（PFDA,C10）,Tricosafluorododecanoic acid（PFDoA,C12）,Perfluorobutanesulfonic acid（PFBS,C4）and perfluoroheptanesulfonic acid（PFHpS,C7）was detected.In addition,due to the dissolution interference of HPLC-MS/MS system,perfluoropentanoic acid（PFPeA,C5）,perfluor-ohexanoic acid（PFHx A,C6）,Perfluoroundecanoic acid（PFUdA,C11）PFCAs and perfluorohexanesulfonic acid（PFHx S,C6）regard as suspected degradation products beacause of the peak area of PFSAs was detected but did not reach the standard of detection.The reaction time,concentration of VB₁₂ and Ti（III）-citrate and temperature had influence for the reductive degradation of PFOS.During the 12 d experiment,the removal rate of PFOS increased continuously,and the concentration of fluorine ion in solution was increased and then decreased with the increase of reaction time.The peak concentration of fluorine ion of 64.92μmol/L decreased to 37.02μmol/L at the end of the experiment.Probably it’s because of the formation of more long-chain PFCAs（>C8）in the later period of the experiment（>4d）.The initial concentration of VB₁₂ significantly affected the reductive degradation of PFOS.The concentration of fluorine ion in solution was firstly increased and then decreased when the concentration was between 100⁴00μmol/L.When the initial concentration of VB₁₂ was 300μmol/L,the concentration of fluorine ion reached 38.42μmol/L.With the increase of concentration of Ti（III）-citrate（18⁵0mmol/L）,the defluorination effect of PFOS increased.When the initial concentration of Ti（III）-citrate was 50mmol/L,the concentration of fluorine ion reached 200.00μmol/L.With the increase of concentration of temperature（25⁷5℃）,the defluorination effect of PFOS increased.The concentration of fluorine ion at 75℃ is 8.75,17.20 and 18.22 times greater than it was at 25,35,55℃,respectively.Decomposition mechanisms were proposed by isotope(¹³C)labeling technique.The study found that the ¹³C4-PFOA was obtained by the removal of sulfonic acid group and hydrolysis of [1,2,3,4-¹³C4]-PFOS（MPFOS）.The¹³C4-PFHpS was obtained with the removal of the eighth carbon atoms by MPFOS.¹³C₂-PFHpA was generated by the combination of remaining carbon chain and carboxylic acid group after the breaking of chemical bond between MPFOS number 2 and number 3 carbon atom.The ¹³C₂-PFBA was generated after the breaking of chemical bonds between number 2,3,5,6 carbon atom of MPFOS.The ¹³C₂-PFOA was generated after the breaking of chemical bond between number 2 carbon atom and number 3 carbon atom of MPFOS.In addition,no standard degradation products such as m/z 448.8may be MPFOS lose 3F was found.