Synthesis and Characterization of ZnO/Chitosan Nanocomposites for Photocatalytic Degradation of Tetracycline in Water Media

Antibiotic contamination of water, particularly tetracycline (TC), poses significant environmental risks and requires sustainable treatment solutions. This study reports a green and cost-effective synthesis of a ZnO/chitosan nanocomposite (ZnO/CS) for photocatalytic TC removal. ZnO nanoparticles were synthesized using lime juice as a natural stabilizing agent and subsequently incorporated into a chitosan matrix. The physicochemical properties of the composite were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area analysis. The results confirmed the successful formation of hexagonal wurtzite ZnO and strong interfacial interactions between ZnO nanoparticles and the –NH2/–OH functional groups of chitosan. The incorporation of chitosan significantly increased the specific surface area from 10.7 to 21.7 m2 g−1 and reduced the band gap from 3.18 to 3.03 eV, thereby improving visible-light absorption. The photocatalytic performance was evaluated under varying pH, initial TC concentration, and catalyst dosage, with optimal conditions identified at pH 6, 20 mg/L TC, and 1 g/L catalyst. Under these conditions, the ZnO/CS nanocomposite achieved 94.1% TC degradation within 120 min under visible-light irradiation. Scavenger experiments revealed that •OH and •O2− radicals are the dominant reactive species, and a possible degradation mechanism was proposed. These findings demonstrate the potential of the green-synthesized ZnO/CS nanocomposite for antibiotic removal from aqueous environments.