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Enhanced Perfluorooctanoic Acid Degradation by Electrochemical Activation of Sulfate Solution on B/N Codoped Diamond

Liu, Yanming, Fan, Xinfei, Quan, Xie, Fan, Yaofang, Chen, Shuo, Zhao, Xueyang
Environmental science & technology 2019 v.53 no.9 pp. 5195-5201
carboxylic acids, cost effectiveness, electrochemistry, electrodes, electrolytes, hydroxyl radicals, mineralization, nitrates, oxidation, perchlorates, perfluorooctanoic acid, persistent organic pollutants, sulfates, total organic carbon
Electrochemical oxidation based on SO₄•– and •OH generated from sulfate electrolyte is a cost-effective method for degradation of persistent organic pollutants (POPs). However, sulfate activation remains a great challenge due to lack of active and robust electrodes. Herein, a B/N codoped diamond (BND) electrode is designed for electrochemical degradation of POPs via sulfate activation. It is efficient and stable for perfluorooctanoic acid (PFOA) oxidation with first-order kinetic constants of 2.4 h–¹ and total organic carbon removal efficiency of 77.4% (3 h) at relatively low current density of 4 mA cm–². The good activity of BND mainly originates from a B and N codoping effect. The PFOA oxidation rate at sulfate electrolyte is significantly enhanced (2.3–3.4 times) compared with those at nitrate and perchlorate electrolytes. At sulfate, PFOA oxidation rate decreases slightly in the presence of •OH quencher while it declines significantly with SO₄•– and •OH quenchers, indicate both SO₄•– and •OH contribute to PFOA oxidation but SO₄•– contribution is more significant. On the basis of intermediates analysis, a proposed mechanism for PFOA degradation is that PFOA is oxidized to shorter chain perfluorocarboxylic acids gradually by SO₄•– and •OH until it is mineralized.