Kinetic, isotherm, and thermodynamic study of Cu(II) ions removal from groundwater using acid-activated carbon based on coconut tree waste (<i>Cocos nucifera</i> L.)

This work focuses on determining the potential of activated carbon synthesised from coconut stem biomass (CSAC) as an effective adsorbent activated with hydrochloric acid (HCl) in adsorbing copper ions (Cu) from contaminated groundwater.Heavy metal pollution, particularly copper, poses serious environmental threats, and low-cost agricultural waste-derived adsorbents offer a sustainable solution for remediation.CSAC was synthesised via chemical activation with 0.1 M HCl and characterised using SEM, SEM-EDX, FTIR, and BET analysis.The surface area increased significantly from 82.465 to 230.096 m/g post-activation.To evaluate the adsorption behaviour, batch experiments were performed under varying conditions of initial Cu concentrations (25-150 mg/L), adsorbent dosage (2-3.5 g), pH (3-10), contact time (0-180 min), and temperature (298-338 K).Atomic absorption spectroscopy (AAS) was used to analyse the residual content of Cu ions after the adsorption process.The kinetic analysis revealed that the adsorption process conformed to the pseudo-firstorder model, with a high correlation coefficient (R = 0.9782), indicating that physisorption primarily governed the mechanism.The Freundlich isotherm best describes the equilibrium data (R = 0.9993), implying multilayer adsorption on a heterogeneous adsorbent surface.Furthermore, thermodynamic evaluations demonstrated that the process occurred spontaneously (G < 0), was endothermic (H = +22.19kj/mol), and involved an increase in system disorder, as reflected by a positive entropy change (S = +0.0711kj/molK).Although conducted at a laboratory scale, the study shows significant potential for practical application in industrial wastewater treatment.The novelty of this research lies in utilizing HCl-activated coconut stem carbon as a cost-efficient and high-performance material for Cu(II) removal, addressing a gap in the use of underexplored agricultural waste materials.As future research, exploring multi-contaminant scenarios and assessing regeneration and costefficiency will be critical to confirming the viability of CSAC in real-world industrial settings.