Degradation of ciprofloxacin using photo, sono, and sonophotocatalytic oxidation with visible light and low-frequency ultrasound: Degradation kinetics and pathways

This study investigates the degradation of an antibiotic ciprofloxacin (CPX) by the photocatalytic, sonocatalytic and sonophotocatalytic oxidation inside a novel multi-frequency reactor under low ultrasonic frequencies and visible light using N-doped TiO2 (N-TiO2) nanoparticles as the catalysts. The synthesized nanoparticles were characterized by XRD, FTIR, TEM, BET and UV-Vis reflectance spectroscopy. The average particle size of these nanoparticles was in the range of 12-18 nm. The effects of different operational parameters affecting the CPX degradation during these processes were studied. Maximum CPX degradation of 54.5%, 41.2%, and 44% was observed for photocatalysis, sonocatalysis and sonophotocatalysis under their individual optimum conditions after 210, 90, and 90 min respectively. The application of these doped catalysts improved the photocatalytic and sonocatalytic oxidation of CPX due to the improved visible light activity and extra nuclei for cavitation respectively. Further, a synergistic effect was observed by the simultaneous application of light and ultrasound in sonophotocatalytic oxidation in comparison to individual processes with a synergy index of 1.22. During the Sonophotocatalysis process, the simultaneous application of ultrasound and visible light was found more effective in comparison to their sequential or intermittent application. The degradation products in all three oxidation processes were identified, and potential degradation pathways are proposed. In addition, effect of real wastewater matrix on the process performance was also investigated.