Mechanistic understanding of ivermectin and diclofenac removal from Pinus elliottii biochar modified by niobium deposition

Abstract This study investigated the effect of niobium (Nb) surface modification of biochar via magnetron sputtering on the adsorption of ivermectin and diclofenac potassium, using an integrated approach combining equilibrium experiments and statistical physics-based adsorption models. The biochar was obtained by pyrolysis and then coated with Nb for 30 min at 150 W DC power. We analyzed adsorption equilibrium data using advanced isotherm models to evaluate the process’s steric and energetic parameters. The results indicated predominantly physisorption, with adsorption energies of 17–19 kJ mol − 1 for ivermectin and approximately 11 kJ mol − 1 for diclofenac. Steric parameters exceeded 1 for both drugs, suggesting multi-molecular adsorption, while modeling indicated the formation of two layers on the material’s surface. For ivermectin, maximum adsorption capacities ranged from 81 to 111 mg g − 1 . Furthermore, increasing temperature enhanced ivermectin’s affinity for the modified biochar, whereas diclofenac showed the opposite behavior, highlighting distinct adsorption responses between the two contaminants. Based on the modeling parameters and the adsorbent’s physicochemical characteristics, the results suggest that ivermectin adsorption may involve dipole–dipole interactions, hydrogen bonding, and π–π interactions, while diclofenac adsorption may involve electrostatic interactions, hydrogen bonding, and π–π interactions. These results show that Nb surface modification distinctly influences the adsorption behavior of the two drugs and highlight the potential of magnetron sputtering as a surface-engineering strategy for developing biochars with differential affinity for pharmaceutical contaminants.