Highly efficient stepwise electrochemical degradation of antibiotics in water by in situ formed Cu(OH)₂ nanowires

Abstract

The extensive use of antibiotics has been a rapidly growing concern worldwide due to their environmental and health impacts. Electrooxidation is considered a promising route towards antibiotics removal but currently hindered by high overpotential, involvement of noble metals, and strict requirement. We report herein an electrocatalytic system using in situ formed Cu(OH)₂ nanowires as the electrocatalyst to facilitate the electrooxidation of three common antibiotics (ampicillin, tetracycline, and chloramphenicol). Such Cu(OH)₂ nanowires can be formed by Cu(II) species present in wastewater. In our study, the stepwise and potential-dependent electrooxidation process of antibiotics is suggested by voltammetric methods, and low overpotential values (ampicillin: 251 mV, tetracycline: 382 mV, and chloramphenicol: 394 mV) are demonstrated. In situ UV–vis spectroelectrochemical investigations indicate that the Cu(OH)ᵧˣ⁻ species on the surface of Cu(OH)₂ nanowires acts as the active site via the formation of Cu(III)-antibiotics intermediate, which can be regenerated upon the formation and dissociation of Cu(II)-antibiotic complex. Long-term electrooxidation shows the high stability and efficiency of electrochemical removal of antibiotics, and the electron transfer numbers are estimated to be 1.23 (˜1) for ampicillin electrooxidation, 4.78 (˜5) for tetracycline, and 7.93 (˜8) for chloramphenicol at 800 mV (vs. Ag/AgCl). UPLC-QTOF-MS results show that the active structural fragments of antibiotics responsible for targeting bacteria are destroyed by electrooxidation and the subsequent activity test using E. coli confirms the deactivation of antibiotics. The electrooxidation of all antibiotics shows similar reaction rate with much lower voltage requirements, suggesting its high energy efficiency.