Electrooxidation of short and long chain perfluorocarboxylic acids using boron doped diamond electrodes

摘要

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-1 of PFOA solution which evidences that the shorter chain PFCA5 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-2, formation of C7F15O center dot and perfluorohexyl radical with releasing COF2. 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 PFCA5, 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 PFCA5, 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 PFCA5 in deionized water (Dl), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCA5 was noticeably affected by water matrix with the order of DI water INWTP effluent river water. Published by Elsevier Ltd.