Arginine-modified surface coffee grounds activated carbon for Pb\(^{2+}\) adsorption: Kinetic, isotherm and thermodynamic studies

This research focuses on enhancing the value of coffee waste by converting it into activated carbon for removing Pb²⁺ ions from contaminated water. Coffee grounds were activated with KOH and carbonized at 600°C for 4 h to produce activated carbon (CGAC), then modified with arginine via hydrothermal treatment at 120°C for 48 h to create Arg-CGAC. The adsorbents' chemical and physical properties were analyzed using SEM, FT-IR, BET, and pHpzc methods. Batch experiments revealed that Arg-CGAC exhibited superior Pb2+ adsorption (223.10 mg∙g‒1) compared to CGAC (119.23 mg∙g‒1) under optimal conditions. Isotherm analysis showed stronger adsorbate-adsorbent interactions and a more endothermic adsorption for Arg-CGAC. Arg-CGAC demonstrated both physisorption and weak chemisorption, while CGAC primarily exhibited physisorption. Increasing temperatures made ΔG° values more negative, indicating more favorable adsorption for Arg-CGAC. Desorption tests showed a 98% yield over four cycles, but efficiency declined after the 7th cycle, stabilizing at 55% to 60%, suggesting good initial performance despite some regeneration limitations.