Cross-linked chitosan-argan nutshell bio-composite beads: Optimization using Box-Behnken design and adsorption mechanism for Pb (II) and Cd (II) removal

Abstract

Industrial heavy metal contamination in water poses a significant threat to both the environment and human health, necessitating the development of affordable and effective remediation solutions. This study introduces a novel chitosan–argan nutshell bio-composite bead cross-linked in situ with glutaraldehyde (CS/ANS@GA), which exhibits enhanced mechanical stability and serves as an eco-friendly adsorbent for the efficient removal of Pb (II) and Cd(II). The bio-composite beads were thoroughly characterized using swelling tests, XRD, FTIR, and SEM-EDX, confirming their semi-crystalline structure and functionalities, as well as their high porosity and accessible adsorption active sites. Response surface methodology was employed to optimize the effects of pH, adsorbent dose, and contact time to achieve high removal efficiencies of Pb (II) and Cd (II). The synthesized beads exhibited Sips isotherm behavior, indicating a heterogeneous surface with maximum adsorption capacities of 433 mg g⁻¹ (Pb) and 391 mg.g⁻¹ (Cd). Thermodynamic analysis revealed an endothermic and spontaneous process, while Avrami kinetics suggested a complex adsorption mechanism involving pore diffusion, electrostatic interactions, and hydrogen bonding. Remarkably, the CS/ANS@GA beads maintained an efficiency of over 90 % after three adsorption–desorption cycles. These results highlight the potential of CS/ANS@GA beads as a sustainable, high-performance material for removing heavy metals from water.