Degradation of fluoroquinolone antibiotic levofloxacin by UV-induced ferric ion photolysis in aqueous medium: The role of pH and chelation

Abstract

The increased use of fluoroquinolone antibiotic levofloxacin (LVX) contributes to its significant presence as a pollutant in water and soil environments and the consequent need for developing efficient water processing methods for its degradation and removal. The understanding of coordination and photo-chemistry of LVX in the presence of ferric ions enables potential improvements of iron-based advanced oxidation processes (AOPs) for wastewater treatment. Herein, the pH-dependence of LVX chelation with ferric ions was investigated by UV–Vis and fluorescence spectroscopy at pH 2, pH 5, and pH 7. The results obtained for examined pHs showed pH 5 as optimal for forming LVX-Fe³⁺ complex. The formation of LVX-Fe³⁺ complex makes coordinated LVX more susceptible to oxidation. Photosensitivity of LVX and LVX/Fe³⁺ system to UV irradiation was examined at acidic pHs, using UV–Vis spectroscopy and HPLC analysis. In acidic aqueous solutions, LVX remains unchanged after UV irradiation, while the presence of ferric ions promotes its UV-induced photodegradation. The investigated UV/Fe(III)-based AOP for degradation of LVX showed the best performance at pH 5 in the presence of Fe³⁺ ions in excess due to LVX-Fe³⁺ complex formation and sufficient amount of Fe³⁺–OH⁻ species available for photolysis and production of OH^• radical.