Temple University, Civil and Environmental Engineering Department, NSF Water and Environmental Technology (WET) Center, 1947 N 12thStreet, Philadelphia, PA, 19122, USA.
Chemosphere. 2020 Mar;243:125349. doi: 10.1016/j.chemosphere.2019.125349. Epub 2019 Nov 13.
This study investigates electrooxidation of short (C3-C6) and long (C7-C-18) chain perfluorocarboxylic acids (PFCAs) including perfluorooctane sulfonate (PFOA) using Si/BDD electrode. The effect of operational parameters (supporting electrolyte type, applied current density, and initial pH) were explored for PFOA removal. At the optimized conditions, 74% TOC removal and 37% defluorination ratio were gained for 10 mg L of PFOA solution which evidences that the shorter chain PFCAs were formed. The PFOA degradation pathway followed one direct electron transfer from PFOA molecule to anode surface. Then two different degradation pathways were proposed. The first proposed degradation mechanism involved the reaction of perfluoroheptyl radical and hydroxyl radical, the release of HF and hydrolysis. The second mechanism involved the reaction between perfluoroheptyl radical and O, formation of CFO and perfluorohexyl radical with releasing COF. The removal of short- (C3-C6) and long-chain PFCAs (C7-C18) was also characterized. More than 95% of removal efficiency was gained for all long-chain PFCAs, excluding C7. The removal ratios of short-chain PFCAs (C3-C6) were 39%, 41%, 66% and 70% for C3, C4, C5 and C6, respectively. Contrary to long-chain PFCAs, chain-length dependence for short-chain PFCAs were observed. Defluorination ratio of short-chain PFCAs was only 45% signifying that defluorination partially occurred. Water matrix did not significantly affect the degradation of short-chain PFCAs in deionized water (DI), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCAs was noticeably affected by water matrix with the order of DI water > WWTP effluent > river water.
本研究采用 Si/BDD 电极，考察了短链（C3-C6）和长链（C7-C-18）全氟羧酸（PFCAs），包括全氟辛烷磺酸（PFOA）的电化学氧化。探讨了操作参数（支持电解质类型、施加电流密度和初始 pH 值）对 PFOA 去除的影响。在优化条件下，对于 10mg/L 的 PFOA 溶液，TOC 去除率达到 74%，脱氟率达到 37%，这表明形成了较短链的 PFCAs。PFOA 的降解途径是 PFOA 分子向阳极表面直接传递一个电子。然后提出了两种不同的降解途径。第一种提出的降解机制涉及过氟庚基自由基与羟基自由基的反应、HF 的释放和水解。第二种机制涉及过氟庚基自由基与 O 的反应、CFO 和过氟己基自由基的形成以及 COF 的释放。还对短链（C3-C6）和长链 PFCAs（C7-C18）的去除进行了表征。对于所有长链 PFCAs，除 C7 外，去除率均超过 95%。短链 PFCAs（C3-C6）的去除率分别为 C3、C4、C5 和 C6 的 39%、41%、66%和 70%。与长链 PFCAs 不同，短链 PFCAs 存在链长依赖性。短链 PFCAs 的脱氟率仅为 45%，表明脱氟部分发生。水基质对去离子水（DI）、河水和污水处理厂（WWTP）二级出水的短链 PFCAs 降解没有显著影响。相比之下，长链 PFCAs 的脱氟率明显受到水基质的影响，顺序为 DI 水＞WWTP 出水＞河水。
