Nonradical oxidation from electrochemical activation of peroxydisulfate at Ti/Pt anode: Efficiency, mechanism and influencing factors

Electrochemical activation of peroxydisulfate (PDS) at Ti/Pt anode was systematically investigated for the first time in this work. The synergistic effect produced from the combination of electrolysis and the addition of PDS demonstrates that PDS can be activated at Ti/Pt anode. The selective oxidation towards carbamazepine (CBZ), sulfamethoxazole (SMX), propranolol (PPL), benzoic acid (BA) rather than atrazine (ATZ) and nitrobenzene (NB) was observed in electrochemical activation of PDS process. Moreover, addition of excess methanol or tert-butanol had negligible impact on CBZ (model compound) degradation, demonstrating that neither sulfate radical (SO₄[rad]⁻) nor hydroxyl radical (HO[rad]) was produced in electrochemical activation of PDS process. Direct oxidation (PDS oxidation alone and electrolysis) and nonradical oxidation were responsible for the degradation of contaminants. The results of linear sweep voltammetry (LSV) and chronoamperometry suggest that electric discharge may integrate PDS molecule with anode surface into a unique transition state structure, which is responsible for the nonradical oxidation in electrochemical activation of PDS process. Adjustment of the solution pH from 1.0 to 7.0 had negligible effect on CBZ degradation. Increase of either PDS concentration or current density facilitated the degradation of CBZ. The presence of chloride ion (Cl⁻) significantly enhanced CBZ degradation, while addition of bicarbonate (HCO₃⁻), phosphate (PO₄³⁻) and humic acid (HA) all inhibited CBZ degradation with the order of HA >> HCO₃⁻ > PO₄³⁻. The degradation products of CBZ and chlorinated products were also identified. Electrochemical activation of PDS at Ti/Pt anode may serve as a novel technology for selective oxidation of organic contaminants in water and soil.