全氟辛烷磺酸的紫外光降解及降解机理

Ultraviolet Light Degradation of Perfluorooctane Sulphonate and Degradation Mechanism

为优化全氟辛烷磺酸(PFOS)的紫外光降解条件及探明其降解机理,研究了PFOS在暗反应(Dark)、暗反应/碘化钾体系(Dark/KI)、紫外(UV)、紫外/碘化钾体系(UV/KI)、真空紫外(VUV)及真空紫外/碘化钾体系(VUV/KI)6种反应条件下的降解效果;在VUV/KI体系下,以单因素分析法研究了PFOS初始浓度、pH、KI添加量对PFOS降解效果的影响;通过中间产物分析提出PFOS在紫外光下的降解机理与路径.结果表明:①在Dark、Dark/KI体系下,PFOS均不会降解;在UV、UV/KI、VUV体系下,PFOS降解率均低于30%;在VUV/KI体系下,初始浓度为200μg/L、KI添加量为2 mmol/L,PFOS的8 h降解率可达70%.②降低PFOS的初始浓度、提高pH、增加KI添加量均有助于PFOS的降解.③轨道阱液质联用仪共鉴定出全氟辛酸(PFOA)、全氟丁酸(PFBA)、五氟乙烷磺酸(PFEtS)、五氟丙酸甲酯(MPFA)、三氟乙酸甲酯(MTFA)和三氟乙酸(TFA)等6种中间产物,PFOS的降解过程包括脱磺酸基团以及脱碳碳键反应.研究显示,水合电子是PFOS紫外光降解过程中的主要活性因子,VUV/KI反应体系可有效去除PFOS,降解路径及降解机理的分析可为其他全氟化合物的紫外光降解提供参考.

In order to optimize the UV degradation conditions of perfluorooctane sulphonate(PFOS)and understand the degradation mechanism,this article studied the removal of PFOS under 6 reaction conditions:dark reaction(Dark),dark/potassium iodide system(Dark/KI),ultraviolet(UV),ultraviolet/Potassium iodide system(UV/KI),vacuum ultraviolet(VUV)and vacuum ultraviolet/potassium iodide system(VUV/KI).Under the VUV/KI system,a single factor analysis method was used to study the effect of initial concentration,pH and KI addition on the degradation effect of PFOS.Through the analysis and identification of intermediate products,the degradation mechanism and degradation pathways of PFOS under ultraviolet light were proposed.The results showed that PFOS didn't degrade in Dark and Dark/KI systems,the degradation rate of PFOS in the UV,UV/KI,and VUV systems was less than 30%.The degradation rate of PFOS reached 70%in the VUV/KI system with initial concentration of 200μg/L PFOS and 2 mmol/L KI in 8-hour.Decreasing the initial concentration of PFOS,increasing the pH value and the amount of KI were all helpful to the degradation of PFOS.Based on the Orbitrap LC/MS analysis,6 kinds of intermediate products were identified:perfluorooctanoic acid(PFOA),perfluorobutyric acid(PFBA),pentafluoroethane sulfonic acid(PFEtS),methyl pentafluoropropionate(MPFA),methyl trifluoroacetate(MTFA)and trifluoroacetic acid(TFA).The degradation process of PFOS includes desulfonation and cleavage of C-C bonds.This study shows that hydrated electrons are the main active species in the degradation of PFOS by ultraviolet light,and the VUV/KI light reaction system can effectively remove PFOS.The analysis of degradation pathways and degradation mechanisms can provide references for the UV degradation of other perfluorinated compounds.