Electrochemical degradation of perfluorooctanoic acid (PFOA) by Yb-doped Ti/SnO2-Sb/PbO2 anodes and determination of the optimal conditions

Model aqueous solutions of perfluorooctanoic acid (PFOA, 100 mg L-1) were electro-oxidized in a homemade container. The electrocatalytic behavior and anodic performance of Ti/SnO2-Sb/Yb-PbO2, Ti/SnO2-Sb-PbO2 and Ti/SnO2-Sb-Yb anodes in sodium electrolytes were compared. The SnO2-Sb/Yb-PbO2 anode demonstrated better electrocatalytic performance compared with the SnO2-Sb-PbO2 and SnO2-Sb-Yb electrodes in terms of both degradation and defluorination. Then a systematic experimental study was designed as follows to analyze the influencing factors: initial concentration of PFOA (10 mg L-1 to 200 mg L-1), current density (1 mA cm(-2) to 40 mA cm(-2)), initial pH value (3 to 11) and electrode distance (5 mm to 20 mm). After a 150 min electrolysis, the optimum reaction conditions were obtained and the degradation and defluorination ratios reached 95.11 +/- 3.9% and 75.7 +/- 2.8%, respectively. Under the optimum conditions, the degradation of PFOA followed pseudo-first-order kinetics (0.0193 min(-1)) and the degradation half-life was 35.9 min. The produced F- was measured using a fluoride ion selective electrode, whereas the intermediate PFCAs with short-chain lengths were measured using HPLC-MS. A detailed degradation pathway was proposed in this study by analyzing the intermediates and the recovery of fluoride.