Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2 anodes

Abstract

Electrochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous solution was investigated over Ti/SnO(2)-Sb, Ti/SnO(2)-Sb/PbO(2), and Ti/SnO(2)-Sb/MnO(2) anodes. The degradation of PFOA followed pseudo-first-order kinetics. The degradation ratios on Ti/SnO(2)-Sb, Ti/SnO(2)-Sb/PbO(2), and Ti/SnO(2)-Sb/MnO(2) anodes achieved 90.3%, 91.1%, and 31.7%, respectively, after 90 min electrolysis at an initial 100 mg/L PFOA concentration at a constant current density of 10 mA/cm(2) with a 10 mmol/L NaClO(4) supporting electrolyte solution. The defluorination rates of PFOA on these three anodes were 72.9%, 77.4%, 45.6%, respectively. The main influencing factors on electrochemical decomposition of PFOA over Ti/SnO(2)-Sb anode were evaluated, including current density (5-40 mA/cm(2)), initial pH value (3-11), plate distance (0.5-2.0 cm), and initial concentration (5-500 mg/L). The results indicated that PFOA (100 mL of 100 mg/L) degradation ratio and defluorination ratio achieved 98.8% and 73.9%, respectively, at the optimal conditions after 90 min electrolysis. Under this optimal condition, the degradation rate constant and the degradation half-life were 0.064 min(-1) and 10.8 min, respectively. The intermediate products including short-chain perfluorinated carboxylic acids (PFCAs, C(2) ≈ C(6)) and perfluorocarbons (C(2) ≈ C(7)) were detected by electrospray ionization (ESI) mass spectrum. A possible electrochemical degradation mechanism of PFOA including electron transfer, Kolbe decarboxylation, radical reaction, decomposition, and hydrolysis was proposed. The electrochemical technique could be employed to degrade PFOA from contaminated wastewater as well as to reduce the toxicity of PFOA.