Enhanced removal of methyl orange from aqueous solutions by poly HEMA-chitosan-MWCNT nano-composite

A nanocomposite of multi-walled carbon nanotube (MWCNT) functionalized (f) with chitosan (CS) and poly-2-hydroxyethyl methacrylate (pHEMA) was prepared and characterized. The adsorption of methyl orange (MO) on pHEMA-CS-f-MWCNT composites from an aqueous solution was investigated with respect to the contact time, dosage, pH, temperature and initial MO concentration. Pseudo first-order and pseudo second-order kinetics, as well as intra-particle diffusion were adopted to evaluate the experimental data. Our pseudo second-order model, with a correlation coefficient greater than 0.9986, was found to most accurately describe the adsorption kinetics. Additionally, we used Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherms to describe equilibrium adsorption in the nanocomposite system. The best agreement was achieved with the Langmuir model with a correlation coefficient of 0.9991. The standard enthalpy change (ΔH⁰), the standard free energy change (ΔG⁰) and the standard entropy (ΔS⁰) were also calculated. The thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic.