Facile synthesis of ZnONP/carbon-coated-eggshell nanocomposite: fast and efficient adsorbents for amoxicillin sequestration

This article reports the synthesis and characterization of a novel eggshell/carbon/ZnO nanoparticles composite (ECZ) for efficient adsorption of amoxicillin (AMX) from aqueous solution. Systematic batch adsorption tests were conducted to compare and assess the AMX removal efficiency of ECZ with raw eggshell biochar (ESB). The most significant operating parameters, including solution pH, contact time, adsorbent dosage, temperature, and initial AMX concentration, were optimized. Maximum adsorption efficiency occurred at pH 5, and equilibrium was achieved in 80 min. ECZ composite possessed a significantly enhanced adsorption capacity of 37.91 mg g⁻¹ at 313 K, which is nearly double that of ESB (18.73 mg g⁻¹), illustrating the synergistic effect of ZnO nanoparticles and carbon modification. Equilibrium adsorption analysis according to Freundlich and Langmuir models determined that AMX adsorption on ECZ represented the Freundlich isotherm model, depicting multilayer adsorption over a heterogeneous surface, while ESB exhibited Langmuir representation, signifying monolayer coverage. The kinetic model ratified that pseudo-first-order representation efficiently captured the process of adsorption in both samples. Thermodynamic values (ΔG°, ΔH°, and ΔS°) determined in the temperature interval 298–313 K indicated that the adsorption process was spontaneous, endothermic, and entropy-stimulated with increased randomness at the solid–solution interface. In general, the ECZ composite is an excellent choice as a low-cost, effective, and eco-friendly adsorbent for the removal of pharmaceutical pollutants such as amoxicillin from wastewater, ensuring environmental protection and water purification.