Facile ultrasound-assisted synthesis of heterogeneous g-C3N4/ZnO nanocomposite for tetracycline adsorption from aqueous solution

Tetracycline (TC) pollution is a global threat to aquatic and terrestrial biodiversity due to its widespread use in aquaculture, livestock, and human disease prevention, which require the development of effective remediation strategies. In this study, a g-C3N4/ZnO nanocomposite was synthesized by a facile ultrasound-assisted method, characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller specific surface area, and further used for the adsorption of TC from aqueous solutions. Isothermal, kinetic, and thermodynamic studies were also carried out to evaluate the adsorption mechanisms and the process feasibility. According to TEM measurements, the particle size ranged from 10 to 30 nm. The adsorption performance was evaluated under different conditions. The results showed that the removal efficiency significantly improved in an alkaline medium (pH = 10) reaching 50 %. Furthermore, the adsorption process followed pseudo-second-order (PSO) kinetics, indicating a chemisorption mechanism. The intraparticle diffusion model and the Elovich models also provided satisfactory fits (R-2 > 0.93). In addition, the Langmuir model fitted the equilibrium data well, suggesting monolayer adsorption with maximum capacities ranging from 106.38 to 131.58 mg g- (298-318 K). The Freundlich model also showed a good fit, whereas the Temkin model indicated a strong interaction between TC and the g-C3N4/ZnO. Delta G< 0, Delta H< 0 and Delta S> 0 showed a spontaneous and exothermic adsorption. The results obtained demonstrate the promising performance of the proposed g-C3N4/ZnO nanocomposite in removing TC from aqueous solutions and suggest that it can be scaled up as an effective approach for providing clean, antibiotic-free water.