Degradation of quinolone antibiotics by freeze activated periodate: effect of the number of fluorine substituents and DFT calculations

The detection rate and concentration of fluoroquinolone antibiotics in wastewater have experienced an upward trend in recent years, primarily attributed to their extensive utilization. The effects of fluorine substituents on the degradation of fluoroquinolone and the associated mechanism remain uncertain. This study aimed to assess the efficacy of freeze-activated periodate (Freezing/PI) in the degradation of three different fluoroquinolones with varying quantities of fluorine. Additionally, the study analyzed the underlying mechanism using density functional theory (DFT) calculations. The results showed that under the optimal experimental conditions (IO4-=0.05mM, pH=3.0, freezing temperature=-25 ℃), the degradation rate of fluoroquinolone antibiotics reached 90.1% after 45minutes of Freezing/PI process. Fluoroquinolone is primarily oxidized by non-free radical pathway, while co-existing substances such as HCO3- and humic acid inhibited the degradation of fluoroquinolone. The primary reaction pathway for the degradation of fluoroquinolone involves the cleavage and detachment of the piperazine ring. The reaction rates of the fluorine substituents at the C-7 and C-9 positions of lomefloxacin and flerofloxacin on the piperazine ring were found to be higher than that of ciprofloxacin. This can be attributed to the presence of synergistic electron conjugation. The objective of this experiment was to analyze additional influencing factors of the Freezing/PI process. The impact of the quantity of fluorine substituents on the reaction and the degradation of fluoroquinolone by free radical pathway were elucidated using DFT. This analysis offers insights into the potential application of the process in low-temperature environments and the management of fluorinated organic compounds.