Degradation of ciprofloxacin by UV and UV/H2O2 via multiple-wavelength ultraviolet light-emitting diodes: Effectiveness, intermediates and antibacterial activity

•Ciprofloxacin is degraded by UV and UV/H2O2 via multiple wavelengths UV-LEDs.•280 nm UV-LED/H2O2 has the highest efficiency for ciprofloxacin degradation.•UV irradiation only induces transformations of peripheral functional groups.•UV/H2O2 induces consecutive oxidation of core quinolone functional group.•Incomplete degradation of ciprofloxacin reduced its antibacterial activity.

Although the efficiency and mechanism of the degradation of quinolone antibiotics by 254 nm UV radiation or UV/H2O2 have been well elucidated, the same is not true for other UV wavelengths. The degradation of ciprofloxacin (CIP), a representative quinolone, was explored by UV and UV/H2O2 using 255, 265, 280, 310 and 365 nm ultraviolet light-emitting diodes (UV-LEDs). The results of LC/MS2 indicated that treatment at 280 nm UV/H2O2 had the highest removal efficiency ([CIP] = 30 μM, apparent rate constants reached 0.0759 min−1, half-time at 9.1 min) among these five wavelengths. Both the qualitative and quantitative analyses demonstrated that the intermediate abundance and distribution at 280 nm UV/H2O2 were drastically altered in comparison to traditional 254 nm UV irradiation or photocatalysis. In the 280 nm UV-LED irradiation experiment, the primary intermediate was C17H19N3O4 (m/z 330.1), which was generated by the substitution of the fluorine by a hydroxyl. In the 280 nm UV-LED/H2O2 experiment, the dominant intermediate was C17H18FN3O4 (m/z 348.1), in which a hydroxyl was added at the CC bond of the cyclohexene moiety. The further oxidation of C17H18FN3O4 was proposed to involve a consecutive oxidation pathway, following the order of CIP, C17H18FN3O4, C17H18FN3O5, C16H18FN3O4 and C15H18FN3O3, which eventually destroyed the quinolone structure. Notably, the microbial analysis also proved that 280 nm UV-LED/H2O2 degraded the moieties those are responsible for antibacterial activity. Based on these results, it was concluded that 280 nm UV-LED/H2O2 can be used as a novel effective technology to improve the removal efficiency of quinolones in wastewater treatment.

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