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

Abstract

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.