Effects of chloride on electrochemical degradation of perfluorooctanesulfonate by Magnéli phase Ti4O7 and boron doped diamond anodes

Abstract

This study examined the degradation of perfluorooctanesulfonate (PFOS) in an electrochemical system using Magnéli phase titanium suboxide (Ti4O7) as the anode. In particular, the influence of chloride on the treatment process was examined. Tests were also conducted with boron doped diamond (BDD) electrodes for comparison. Experimental data demonstrated that PFOS was effectively degraded by electrochemical oxidation on both BDD and Magnéli phase Ti4O7 anodes. It appeared that PFOS degradation occurred via direct electron transfer (DET) in combination with attack by hydroxyl radicals adsorbed on the anode surface (HO•ads) that were formed by anodic oxidation of water. The presence of Cl− inhibited the degradation of the PFOS on Ti4O7 electrode by suppressing the oxidation of water, but accelerated PFOS degradation on BDD electrode, where the oxidation of Cl− via DET occurred. Formation of chlorate and perchlorate was slower on Ti4O7 than on the BDD anode. The mechanisms governing the behavior of PFOS and chloride reactions on BDD and Ti4O7 anodes were explored by experiments in combination with density functional theory (DFT) computations.