Synthesis of chitosan/MCM-48 and β-cyclodextrin/MCM-48 composites as bio-adsorbents for environmental removal of Cd2+ ions; kinetic and equilibrium studies

Abstract Chitosan/MCM-48 (CH/MCM) and β-cyclodextrin/MCM-48 (CD/MCM) composites were synthesized as promising and eco-friendly bio-adsorbents for Cd2+ ions from water. The composites showed novel porous structures and complex functional groups making them of high adsorption capacities. The adsorption behaviors of CH/MCM and CD/MCM are highly controlled by the tested pH values realizing their best capacities at pH 7. The kinetic evaluation indicated the excellent agreement between the uptake of Cd2+ by CH/MCM and CD/MCM with the pseudo-first-order model achieving equilibrium intervals of 480 min and 600 min, respectively. Based on the values of Chi-squared (X2) and the correlation coefficient, the composites displayed adsorption properties related to the Freundlich hypothesis with a multilayer form. Additionally, the Gaussian energies of them are 2.23 KJ/mol (CH/MCM) and 2.46 KJ/mol (CD/MCM) reflecting physical uptake of Cd2+ by the studied composites. The thermodynamic investigation implied spontaneous uptake of Cd2+ by the composites with endothermic reactions. The prepared CH/MCM and CD/MCM are of 122.4 mg/g and 152.2 mg/g theoretical qmax, respectively which are higher values than the reported results for several studied adsorbents. Moreover, the synthetic CH/MCM and CD/MCM showed high reusability as adsorbents for Cd2+ to be applied effectively six times.