Chitosan-montmorillonite hydrogel beads for effective dye adsorption

Abstract

In this study, several different chitosan beads with incorporated montmorillonite were prepared. The materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Scanning Electron Microscopy and nitrogen sorptometry. The adsorption capacity of the materials studied was analyzed based on the use of FeCl3 as a chitosan solvent, montmorillonite's presence, and organic modification of the clay mineral surface. The chitosan beads were employed to remove methyl green from aqueous solutions. Several parameters influencing adsorption were investigated to optimize the process. The highest adsorption capacities after 24 h were obtained for the adsorbents dose of 5 mg, methyl green initial concentration of 500 mg g−1 and pH 6.0. The presence of iron(III) oxide resulted in improved adsorption ability. However, the composite beads with montmorillonite proved to be better adsorbents than those without the clay mineral. The effect of organic functional groups did not show an analogous correlation for all the adsorbents studied. The maximum experimental adsorption capacity was 303.21 mg g−1 for the composite chitosan beads with organically-functionalized montmorillonite prepared in acetic acid. The adsorbents without clay mineral fit the Langmuir model, while the Freundlich isotherm model described the adsorption data for the chitosan-montmorillonite beads. All the materials followed the pseudo-second-order kinetic model. The intraparticle-diffusion model played an essential part in the adsorption mechanism. The materials demonstrated higher efficiency of methyl green removal from real water samples and increased stability than pure chitosan beads. They can be successfully reused several times, increasing their potential application for dye removal.