Rapid degradation of ciprofloxacin over BiOCl: Insight into the molecular structure transformation and antibacterial activity elimination

Abstract Currently, the widespread usage of antibiotics brings great challenge to sustainable water environment due to the production of drug-resistant bacteria, the rapid and effective removal of antibiotics attracts more and more attention. Herein, a BiOCl microsphere prepared by a facile hydrolysis method via controlling the EG-H2O ratio was found to have unexpected photocatalytic activity for ciprofloxacin (CIP) removal. The photodegradation rate of CIP over optimal BiOCl-20 reached 92.9% in only 3 min of simulated sunlight irradiation, and the mineralization rate was 30.8% after 60 min reaction. The antibacterial tests of CIP solution under different irradiation minutes were evaluated using Escherichia coli (E. coli) as the model bacteria. The results indicated that CIP photodegradation intermediates had also certain antimicrobial potency, which could be eliminated almost completely after 3 min irradiation, although there still had some incompletely mineralized intermediates. In view of these results, the macroscopic degradation behavior of CIP over BiOCl-20 as well as the microscopic existence state and reaction behavior of the intermediates should be clarified. A ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for determination of CIP and its intermediates. Ten primary intermediates were separated and identified, and their corresponding molecular structures were elucidated. Three main photodegradation pathways were deduced, and the correlation between molecular structure transformation and antibacterial activity of CIP was established. Because of the destruction of piperazine ring and defluorination of quinolone ring, the antibacterial activity of the treated CIP solution was weakened or even eliminated. Finally, a possible photodegradation mechanism was proposed, the OVs, O2−, h+ and OH played significant roles in the CIP photodegradation. This work does have great perspective for BiOCl potential application in CIP wastewater treatment.