Enhanced visible-light photocatalysis of a senary mixture of antibiotics using a low-dose of TiO2-ZnO nanocomposite.

Antibiotics discharged from wastewater treatment plants continue to pose severe environmental and public health risks by promoting antibiotic resistance. While photocatalysis has shown promising degradation of antibiotics, most studies have evaluated single antibiotics at high catalyst doses, limiting the feasibility of practical application. In this study, a TiO2-ZnO nanocomposite (TZ-NC) was synthesized via a modified sol-gel method. A low dose of this TZ-NC was applied to degrade a senary antibiotic mixture comprising erythromycin, azithromycin, linezolid, enrofloxacin, oxacillin, and sulfamethazine under both UV and visible irradiation. Characterization by XRD, FTIR, TEM, and UV-Vis spectroscopy confirmed the formation of a mixed oxide system with improved charge separation and reduced band gap, thereby enabling visible-light activity. Multi-component adsorption experiments revealed selective interactions of TZ-NC with macrolides and fluoroquinolone through electrostatic interactions. Photolysis under UV and visible irradiation resulted in minimal degradation. Under both irradiation conditions, the TZ-NC achieved near-complete degradation (∼99 %) for the antibiotic mixture with initial concentration of 0.6 mg/L. Degradation followed a pseudo-first-order model, and the observed rate coefficients were marginally higher under visible light. A three-way ANOVA confirmed significant effects of light source, antibiotic concentration, and antibiotic type on degradation efficiency. The degradation pathways were elucidated based on LC-HRMS analysis. These findings highlight TZ-NC as an efficient, scalable, and sustainable solution for antibiotic degradation, emphasizing its potential for real-world wastewater treatment applications.