Facile synthesis, characterization, and adsorption properties of Cd (II) from aqueous solution using β-cyclodextrin polymer impregnated in functionalized chitosan beads as a novel adsorbent

This study explores the adsorption capacity of carboxymethyl-β-cyclodextrin (CMβ-CD) functionalized chitosan (CS) impregnated with water-insoluble epichlorohydrin cross-linked β-cyclodextrin polymer (β-CDP) to yield CS-β-CDP-CMβ-CD composite beads for the removal of toxic Cd (II) ions from aqueous solutions. Characterization of the adsorbent was performed with XPS, FTIR, NMR, BET and SEM. The synergistic effect was expected and found at removing Cd (II) with a sorption capacity exceeding 378 mg g−1 (approximately 3.37 mmol g−1), which is higher than any other existing technology. The removal of Cd (II) was found maximum at pH 6.5. The rate reduction can be expressed by pseudo-second-order reaction kinetics. Thermodynamic parameters such as the enthalpy (ΔH0), entropy (ΔS0), and free energy change (ΔG0) suggest the endothermic adsorption of Cd (II) in solution. The activation energy was calculated to be 65.62 kJ mol−1 indicating a chemisorption process. The regeneration and reusability of the adsorbent were found suitable for in situ application of this technology for Cd remediation. The Langmuir isotherm model, which is effective for analyzing equilibrium data, indicated both monolayer adsorption and chemisorption. The intraparticle diffusion model indicated both film diffusion and intraparticle diffusion as the rate limiting steps. Thus, the synthesized CS-β-CDP-CMβ-CD beads showed good adsorption selectivity for Cd (II) having excellent regeneration and reusability.