Heterogeneous Photocatalysis of Fluoroquinolone Antibiotics: Scavenger Study and Determination of Residual Antibacterial Activity

The increasing presence of antibiotics in water bodies poses a significant environmental threat due to their persistence and potential to induce antibiotic resistance. TiO₂ photocatalysis under UVC (254 nm) irradiation was used to study the degradation of a mixture of fluoroquinolone antibiotics (moxifloxacin (MOX), levofloxacin (LEVO), and ciprofloxacin (CIP) in aqueous solution. Complete degradation of fluoroquinolone antibiotics (25 mg/L correspondingly) was achieved in 180 min of photocatalytic oxidation and COD removal of 72% at pH 6. Photocatalytic reactions approximately followed a second order kinetics, and the rate constants (k) were 0.0015, 0.0009, and 0.0011 L/mg/min for MOX, LEVO, and CIP, correspondingly. Additionally, the TiO₂ showed a durability (recyclability up to 5 cycles) with a 52% degradation rate loss. The involvement of hydroxyl radicals as primary reactive species was confirmed by scavenging experiments using isopropanol. Furthermore, the antibacterial activity of the treated solutions was assessed against Escherichia coli and Pseudomonas fluorescens using an agar diffusion test. Results indicated that 180 min of irradiation effectively eliminated the antibacterial activity. Hence, the photocatalytic method shows the ability to effectively degrade fluoroquinolone antibiotics and their antibacterial properties, and it produces encouraging outcomes as a potential use for antibiotic removal in wastewater.