[Selection of electrochemical anodic materials for PFOA degradation and its mechanism]

Perfluorooctanoate (PFOA) is environmentally stable and endocrine-disrupting. It was resistant to conventional biodegradation and advanced oxidation processes. Electrochemical oxidation method was adopted to degrade PFOA. The anodes, including BDD, Pt, Ti, Ti/RuO2, Ti/RuO2-IrO2, Ti/In2O3, Ti/SnO2-Sb2O5,-IrO2, Ti/SnO2-Sb2O5,-RhO2, Ti/SnO2-Sb2O5, Ti/ SnO2-Sb2O5,-CeO2 and Ti/SnO2-Sb2O5-Bi2O3, were selected as the candidate materials. The oxygen evolution potential (OEP) were determined by linear sweep voltammetry (LSV). The degradation ratios and the defluorination ratios were used to evaluate the oxidation ability of anodic materials. Ultrasonic electrochemical oxidation indirectly demonstrated that direct electron transfer was the initial step for PFOA decomposition. The anodes of Ti/SnO,-Sb20 ,-Bi2,03, Ti/SnO-Sb ,O,-CeO,, Ti/SnO2-Sb20, and BDD effectively degraded PFOA, and the decomposition ratios were 89. 8% , 89. 8% , 93. 3% and 98. 0% , respectively. The removal ratios of PFOA on Ti/ SnO2-Sb2O5,-RhO2, Ti/SnO2-Sb2O5-IrO2, and Ti/In2O3 anodes were low, and the values were 2. 1%, 2.3% , 12. 5% and 3.1%, respectively. However, Ti, Ti/RuO2 and Ti/RuO2-IrO2, had no effect on PFOA. PFOA molecule transferred electrons to the anode, decarboxylated, and followed the CF2, unzipping cycle. The intermediate products detected were C6F13 COO- , C5F11COO-, C4F9COO- and C3F7,COO-.