This study's goal is to treat a tetracycline (TC) antibiotic containing water with a graphitic carbon nitride (g-C₃N₄) based composite zinc oxide (ZnO)-barium titanate (BaTiO₃) nanoparticles (g-C₃N₄-ZnO-BaTiO₃) prepared from the extract of Olea Europaea leaves as an initiator under the ultrasound method. The FTIR, XRD, XPS, SEM, and TEM analyses were used for g-C₃N₄-ZnO-BaTiO₃ nanocomposite. Response surface methodology-Box-Behnken design (RSM-BBD) was used to design the experiment and optimize the process parameters. TC adsorption ability of the g-C₃N₄-ZnO-BaTiO₃ was evaluated and optimized by varying the pH, contact time, and initial TC solution concentration. RSM results demonstrated that g-C₃N₄-ZnO-BaTiO₃ nanocomposite effectively improves the adsorption performance of g-C₃N₄-ZnO-BaTiO₃ with optimal adsorption capacity of 209.19 mg g⁻¹ at pH = 4.59 and for 180 min of contact time, and 60 mg L^–1 of TC concentration. The whole adsorption process applies to the pseudo-second-order kinetics and the Freundlich isotherm model describes the best adsorption behavior of g-C₃N₄-ZnO-BaTiO₃. Various characterization methods and zeta potential show the mechanism of adsorption of g-C₃N₄-ZnO-BaTiO₃ toward TC, involving hydrogen bonds, electrostatic action, and π-π interactions. The quantum chemical calculations based on electrostatic potential maps, HOMO–LUMO distributions, and energy gaps showed that TC forms a stable cluster with g-C₃N₄-ZnO-BaTiO₃, indicating its favorable adsorption. This indicates that the g-C₃N₄-ZnO-BaTiO₃ nanocomposite is an admirable adsorbent to remove antibiotics from water.