Synthesis of a trivalent copper complex for efficient degradation of antibiotic ofloxacin

Copper-based catalysts have been widely used in heterogeneous advanced oxidation processes (AOPs) to degrade emerging contaminants, with trivalent copper species (Cu(III)) often identified as crucial intermediates. However, the current understanding of the reactivity and potential oxidation mechanism associated with such reactive species remains quite limited. In the present study, a stable Cu(III) complex was synthesized, and its reactivity towards a typical fluoroquinolone antibiotic, ofloxacin (OFX), was comprehensively investigated. The results revealed that Cu(III) itself functioned as the primary oxidizing agent instead of secondary hydroxyl radicals generated during OFX decomposition, which exhibited high reactivity over a wide pH range (3.0–9.0) with molar ratio of Cu(III) to OFX between 1:2 and 3:1. Interestingly, prevalent constituents of natural water, including (bi)carbonate (0–10 mM), chloride (0–10 mM), nitrate (0–10 mM) and humic acid (0–30 mg/L), displayed minimal influence on the oxidation efficiency of Cu(III). Piperazine moiety was identified as the primary reaction site, and three different pathways including tertiary amine oxidation, hydroxylation, and N-demethylation process were proposed. The detailed oxidation mechanisms were further illustrated by density functional theory (DFT) calculations. This study contributes to the theoretical foundation for investigating the mechanism of Cu(III)-mediated oxidation of antibiotics.