Visible light degradation of macrolide antibiotic azithromycin by novel ZrO2/Ag@TiO2 nanorod composite: Transformation pathways and toxicity evaluation

Macrolide antibiotics are one of the major groups of emerging pharmaceutical contaminants that have been detected in aquatic systems. Photocatalytic degradation under UV light is useful for mineralization of various pharmaceutical pollutants but very limited studies are available for degradation of azithromycin (AZY) using visible light. In the present study, a novel ZrO2/Ag@TiO2 nanorod ternary nanocomposite was prepared by a simple hydrothermal and photodeposition method for efficient degradation of AZY under visible light. The composite was detailed characterized by XRD, XPS and TEM analyses, which revealed the formation of cubic ZrO2 and Ag nanoparticles on TiO2 nanorods (TNR). More than 90% of azithromycin (20 mg/L) was degraded after 8 h of visible light irradiation. The plausible transformation pathway for azithromycin was proposed based on the LC/MS-IT-TOF analysis. The phytotoxicity evaluation of the azithromycin and its degraded products was assessed on Vigna radiata. The germination index (GI) of azithromycin was found to be 12.3% before degradation while it increased to 81.05% after 8 h of degradation, indicating this photodegradation process achieved nearly complete detoxification. Furthermore, the toxicity of the degradation products was determined on the basis of Escherichia coli colony forming unit assay which confirmed high detoxification efficiency. Thus, this work demonstrated an efficient strategy for visible light degradation and detoxification of azithromycin, which provided new insight on macrolide antibiotic photodegradation and would be promising for antibiotic wastewater treatment. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.