Mechanism of highly efficient electrochemical degradation of antibiotic sulfadiazine using a layer-by-layer GNPs/PbO2 electrode

A PbO 2 electrode integrating electrocatalytic and adsorptive functions was successfully fabricated by embedding layer-by-layer graphene nanoplatelets (GNPs) into β-PbO 2 active layer (GNPs/PbO 2 ) and employed as anode for high-efficient removal of sulfadiazine (SDZ). In electrochemical degradation experiments, SDZ was quickly enriched on the surface of GNPs/PbO 2 film via adsorption and then oxidized by ⋅OH in-site. In terms of the electrocatalytic performance and adsorption of electrode, the optimal electrodeposition time for each β-PbO 2 outer layer was 4 min (GNPs/PbO 2 -4). Compared with conventional PbO 2 electrode, the layer-by-layer GNPs resulted in the smaller crystal size and denser surface of PbO 2 electrode, thus facilitating the generation of active oxygen species. At the same time, the specific surface area, oxygen evolution potential (OEP) of the anode were enhanced and the charge-transfer resistance was reduced. For GNPs/PbO 2 -4 anode, the optimal conditions of electrochemical oxidation of SDZ were identified as initial pH 9, 50 mg/L of SDZ and 20 mA/cm 2 of current density using response surface methodology (RSM), 98.15% of SDZ could be removed in this case. The contribution of radical oxidation and non-radical oxidation to SDZ removal was about 79% and 21%, respectively. Moreover, the reaction pathways of SDZ on the GNPs/PbO 2 -4 electrode involving hydroxylation, radical reaction and ring cleavage were speculated. Finally, the continuous SDZ degradation and accelerated service lifetime test suggested that the GNPs/PbO 2 -4 electrode was shown to be stable and repeatable, and the Pb 2+ concentration was measured to ensure the safety of the treated solution. Consequently, the above findings provide an innovative way to design and prepare an effective and stable PbO 2 electrode for electrochemical degradation of antibiotic wastewater.