Enhanced photocatalytic degradation of ciprofloxacin over Bi₂O₃/(BiO)₂CO₃ heterojunctions: Efficiency, kinetics, pathways, mechanisms and toxicity evaluation

In this study, the degradation of antibiotic ciprofloxacin (CIP) over Bi₂O₃/(BiO)₂CO₃ heterojunctions under simulated solar light irradiation (SSL-Bi₂O₃/(BiO)₂CO₃) was examined for the first time. The results showed that the Bi₂O₃/(BiO)₂CO₃ heterojunctions dramatically improved CIP decay efficiency. The effect of parameters showed that the CIP decay was optimized with the Bi₂O₃/(BiO)₂CO₃ dosage of 0.5 g/L and a wide pH range of 4.0–8.3, based on which, a kinetic model was derived to predict the remaining CIP concentration. It was found that the presence of anions like SO₄²⁻, NO₃⁻ and HCO₃⁻ decelerated the CIP decay, while the co-existence of Cl⁻ accelerated the CIP decay. Six degradation intermediates were identified by ultra-performance liquid chromatography coupled with mass analyzer (UPLC/MS) and ion chromatographic (IC) analysis, and the decay pathways and degradation mechanism of CIP were proposed by combining the experiment data with theoretical calculation of frontier electron densities. Hydroxyl radical's reaction, photo-hole (h⁺) oxidation and reductive defluorination were found to involve in the CIP decay. The efficient alleviation on total organic carbon (TOC) and toxicity indicated that the complete mineralization and de-toxicity are possible by this system with sufficient reaction time.