电活化过硫酸盐降解全氟辛酸及其中间产物的探究分析

全氟化合物（PFCs）是一种新兴的持久性有机污染物，具有环境持久性、高毒性和难降解性，因此急需研发高效的降解方法.本文采用电化学恒电位电解法活化过硫酸盐，利用得到的具有强氧化性的SO₄^·-有效降解全氟辛酸（PFOA），考察了恒定电位值、过硫酸钠的初始浓度、溶液初始pH值和共存离子对电活化过硫酸盐降解PFOA的影响.同时，结合超高效液相色谱-三重串联四级杆质谱联用仪（UPLC-MS/MS）和气相色谱与质谱联用仪（GC-MS），对其降解的液相和气相中间产物进行探究.结果表明，在控制阴极电位为-1.8 V，初始过硫酸钠溶液浓度为200 mmol·L^-1，初始溶液pH=3.29，恒电位电解4 h后，PFOA去除率约达到60%.当体系中有NO₃^-、异丙醇和过硫酸钠共存时，PFOA降解效率明显提高（91%，4 h），当有ClO₄^-存在时PFOA去除率约达到76.8%，但HCO₃^-和Cl^-的存在会出现抑制效果.通过对降解中间产物（短链PFCAs和加氢产物）和TOC去除率（62.5%，24 h）的监测分析，进而推断其可能的降解机理为SO₄^·-介导的Kolbe脱羧过程和羧酸逐步被加氢还原的过程.

Electrochemical activated persulfate to degrade perfluorooctanoic acid and the analysis of intermediate products

Developing efficient methods to degrade perfluorochemicals (PFCs), an emerging class of highly recalcitrant contaminants, are urgently needed in recent years, due to their persistence, high toxicity, and resistance to most regular treatment procedures. Herein, the electrochemical degradation of perfluorooctanoic acid (PFOA) has been achieved by the electrochemical activation of persulfate. The generated sulfate radicals (SO₄^·-) greatly improve the efficiency of electro-degradation of PFOA. The effects of constant potential, initial concentration of sodium persulfate, initial pH value and coexisting ions of solution on the electrochemical degradation of PFOA are discussed in detail. The intermediate products of liquid phase and gas phase are monitored by UPLC-MS/MS and GC-MS. The results show that the degradation of PFOA could reach ~60% at the initial concentration of 200 mmol·L^-1 Na₂S₂O₈ solution (pH=3.29, E=-1.8 V for 4 h). The presence of NO₃^- (100 mmol·L^-1)+isopropanol (1.8 mmol·L^-1) or ClO₄^- alone (100 mmol·L^-1) would prompt the degradation of PFOA, reaching 91% or 76.8%, respectively. While the presence of HCO₃^- and Cl^- alone (100 mmol·L^-1) would inhibit the degradation of PFOA. By analyzing the intermediate products (short-chain PFCAs and hydrogenated products) and the removal efficiency of TOC (62.5%, 24 h) comprehensively, a possible degradation pathway is proposed, including the typical Kolb e decarboxylation (with CF₂-unzipping cycle) and the hydrogenation reduction process.