Studies on photocatalytic removal of antibiotics, ciprofloxacin and sulfamethoxazole, by Fe3O4-ZnO-Chitosan/Alginate nanocomposite in aqueous systems

Abstract

An ultraviolet-light-induced antibiotic degradation system based on nano-ZnO and Fe3O4 and chitosan/alginate nanocomposite bead assembly has been developed using a facile green-synthesis approach. In this study Camellia sinensis extract was used as reducing agent to facilitate the formation of the nanoparticles. The Fe3O4-ZnO-CS/SA nanocomposite was employed to degrade ciprofloxacin (CIP) and sulfamethoxazole (SMX) under UV-C light irradiation, and 94.77% and 93.31% degradation was achieved respectively within 180 min with the optimized conditions [pH of 4.0, antibiotic concentration of 10 mg/L, and Fe3O4-ZnO-CS/SA nanocomposite weight of 10 g and 15 g for CIP and SMX respectively]. For both the antibiotics, the pseudo-first-order model fitted well with the reaction kinetics data, while the Langmuir isotherm model showed a better fit compared to the Freundlich and Temkin models. Analyzing various characterization data reaction mechanism for CIP and SMX degradation was proposed. In addition, possible degradation pathways of CIP and SMX were proposed based on the intermediates detected by HR-LCMS analysis. Furthermore, the trapping experiments showed that superoxide (1O2) and hydroxyl (OH) radicals play major role in the photodegradation of CIP and SMX. The effects of ionic strength, natural organics and various natural water systems on degradation efficacy was investigated. The degraded products were found to show less toxicity to a model organism, a fresh water alga, compared to the parent compounds. This work provides a simple strategy to integrate CS/SA with nano-ZnO and Fe3O4 to construct effective nanocomposite photocatalyst for the degradation of different classes of antibiotics.