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

Electrochemical oxidation based on SO4 center dot- and (OH)-O-center dot 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)-O-center dot quencher while it declines significantly with SO4 center dot- and (OH)-O-center dot quenchers, indicate both SO4 center dot- and (OH)-O-center dot contribute to PFOA oxidation but SO4 center dot- 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 center dot- and (OH)-O-center dot until it is mineralized.