Efficient removal of antibiotics from wastewater by a low-cost olive leaf biosorbent: Thermodynamics, kinetics and quantum chemical studies

In this study, the feasibility of olive leaf powder (OLP), an agricultural waste material, is investigated as an effective, cost-effective, and green biosorbent material for the efficient removal of the antibiotics amoxicillin (AMX) and cefixime (CFX) from water bodies. The surface characteristics of OLP, confirmed through FTIR and SEM, indicated the presence of an abundance of functional groups, such as -OH, -C=O, etc., which are the predominant sites for the adsorption of the antibiotics. The adsorption kinetics were found to follow the pseudo-second-order model, while the equilibrium isotherm best fit the Langmuir equation, with maximum adsorption capacities of 99.01 mg/g for AMX and 34.72 mg/g for CFX, respectively. Thermodynamic calculations confirmed the spontaneity of the adsorption process, as ΔH < 0, ΔG < 0, with the activation energy (E a ) being < 40 kJ/mol, indicative of site-specific physisorption. Quantum chemical computations employing density functional theory (DFT) also supported the findings, where the energy gap between the HOMO-LUMO orbitals, as well as the electronic density, further validated the stability of the molecules and the physical nature of the binding process. In addition, the OLP material showed good reusability after four cycles, with a high removal efficiency. This study therefore suggests that OLP is a technically viable and eco-friendly option for the treatment of pharmaceutical wastewater. Graphical Abstract