Rapid removal of heavy metal cations by novel nanocomposite hydrogels based on wheat bran and clinoptilolite: Kinetics, thermodynamics, and isotherms

Novel nanocomposite hydrogels based on wheat bran-g-poly(methacrylic acid) and nano-sized clinoptilolite have been successfully utilized for the removal of Pb(II), Cu(II), Cd(II), and Ni(II) cations from their aqueous solution. The experimental results were investigated using Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich isotherm models. The pseudo-first-order, pseudo-second-order and interparticle diffusion kinetic models were studied in order to analyze the kinetic data. The kinetic data indicated that the rate of cation adsorption on nanocomposite hydrogels was fast that more than 80 % of the equilibrium adsorption capacity occurs within 15 min. The maximum monolayer adsorption capacity of the nanocomposite hydrogel, as obtained from the Langmuir adsorption isotherm, was found to be 166.7, 243.9, 175.4, and 166.6 mg g−1 for Pb(II), Cu(II), Cd(II), and Ni(II), respectively. Thermodynamic parameters such as free energy (ΔG 0), enthalpy (ΔH 0), and entropy (ΔS 0) change were determined; the sorption process was found to be endothermic. The results of five times sequential adsorption–desorption cycle showed high adsorption efficiency and a good degree of desorption.