Electrochemical oxidation of ceftazidime with graphite/CNT-Ce/PbO₂-Ce anode: Parameter optimization, toxicity analysis and degradation pathway

In this work, the electrochemical degradation of antibiotic ceftazidime has been studied using a novel rare earth metal Ce and carbon nanotubes codoped PbO2 electrode. A competitively high oxygen evolution potential (2.4 V) and enhanced catalytic surface area were obtained, evidence by LSV and CV electrochemical characterization. The G/CNT-Ce/PbO2-Ce electrode possessed a more compact structure and a smaller grain size than the other PbO2 and Ce-PbO2 electrodes, exhibiting a prolonged service lifetime, evidence by accelerated lifespan test and recycling degradation experiment. As electrolysis time reached 120 min, the removal efficiency of ceftazidime and TOC arrived at 100.0% and 54.2% respectively in 0.05 M Na2SO4 solution containing 50 mg.L-1 ceftazidime. The effect of applied current density, pH value, initial ceftazidime concentration and chloride contents on the degradation performance were systematically evaluated. The results demonstrated that electrochemical oxidation of ceftazidime over the G/CNT-Ce/PbO2-Ce electrode was highly effective, and the mineralization rate was greatly improved, compared with pristine PbO2 electrode. Considering the toxicity was increased after 30 min electrolysis, the intermediates were quantitatively investigated through HPLC-MS, GC-MS and IC technology. According to the identified products, a reaction mechanism has been proposed and pyridine and aminothiazole were detected with concentration from approximately 1 to 3 mg,L-1, which were regarded as toxic byproducts during electrooxidation. Further electrocatalyzing by ring cleavage reaction and complete mineralization to CO2, NO3- and NH4+ was proposed, which demonstrated the G/CNT-Ce/PbO2-Ce electrode exhibited high efficiency for ceftazidime removal in mild conditions. (C) 2020 Elsevier Ltd. All rights reserved.