Degradation of a persistent organic pollutant perfluorooctane sulphonate with Ti/SnO2–Sb2O5/PbO2-PTFE anode

Abstract PbO2-poly tetra fluoro ethylene (PTFE) coating anode was prepared through electrodeposition method, which involved the use of scanning electron microscope, linear sweep voltammetry, contact angle, and accelerated life test. Degradation of perfluorooctane sulfonate (PFOS) with Ti/PbO2 and Ti/SnO2–Sb2O5/PbO2-PTFE anodes was performed. Operating parameters, including initial concentration of PFOS, current density, and initial pH value were evaluated. Experimental results indicated that Ti/SnO2–Sb2O5/PbO2-PTFE had longer lifespan (46.5 h) than Ti/PbO2 anode (3.5 h). The hydrophobic property of PbO2 was substantially improved after the addition of PTFE. Hydrophilic Ti/PbO2 with the contact angle of 45.4° was transformed into hydrophobic Ti/SnO2–Sb2O5/PbO2-PTFE with a contact angle of 130.9°. The electrochemical performance was also enhanced after PTFE particles were added into PbO2 electrodeposition coating. The oxygen evolution potential was increased by 0.32 V, and removal ratios of PFOS had increased from 53.5% to 89% after addition of PTFE. When initial PFOS concentration varied from 100 mg/L to 300 mg/L, PFOS removal ratios increased with the initial concentration. High current density favored the high PFOS removal ratio and the defluorination ratio. Low pH profited the degradation of PFOS. However, alkaline atmosphere had detrimental effect to the PFOS desulfonation. Intermediate products of PFOS degradation were identified with liquid chromatography system coupled with a triple-stage quadruple mass spectrometer. Moreover, mechanisms of PFOS degradation were proposed.