Insights into the degradation of norfloxacin antibiotics on boron-doped diamond anode: Kinetics, pathways and mechanisms

Background

The massive production and irrationally overuse of antibiotics have resulted into the increase and accumulation of antibiotics in the aquatic system. The efficient decomposition of emerging antibiotic pollutants needed to be emphatically discussed considering their persistence and ecological risks.

Method

The electrochemical elimination of norfloxacin (NOR) is systematically investigated on BDD anode. The quenching and capturing experiments manifest the predominant radical species. Probable attack locations of reactive radicals are predicted via DFT calculations while evaluating the toxicity evolution of the intermediates during the degradation process by quantitative structure-activity relationship model.

Significant findings

The optimal degradation conditions are determined as the initial NOR concentration 50 mg L⁻¹, current density 30 mA cm⁻², 0.05 M Na₂SO₄ supporting electrolyte, and initial pH 5. The NOR removal rate reach 91.0% with apparent rate constants 0.396 h⁻¹ after 360 min electrolysis. The ^•OH and SO₄^•− reactive radicals contribute to the NOR degradation. Possible degradation pathways of NOR mainly include defluorination, decarboxylation, piperazine ring cleavage, and quinolone group transformation, ultimately achieving complete mineralization. The toxicity evolution of the intermediates suggests a low ecotoxicological risk of the anodic oxidation of NOR on BDD anode.