Study of adsorption of cationic dye on magnetic kappa-carrageenan/PVA nanocomposite hydrogels

Abstract

In this study, magnetic nanocomposite hydrogels were synthesized by incorporation of kappa-carrageenan, polyvinyl alcohol (PVA), and magnetic Fe3O4 nanoparticles. Magnetite nanoparticles were prepared in the presence of a mixture of kappa-carrageenan/PVA (CaraPVA) via in situ co-precipitation method. For preparation of hydrogels, the synthesized magnetite-polymers were crosslinked with freezing–thawing technique and subsequently with K+ solution. The structure of magnetic hydrogels was characterized by transmittance electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The adsorption of cationic dye crystal violet (CV) from aqueous solution by magnetic hydrogels was investigated via a batch adsorption system on the subject of contact time, pH of the initial dye solution, temperature, ion strength, and initial dye concentration. The results showed that while the removal of dye decreased by the incorporation of magnetite particles, removal efficiency was improved by increasing the ratio of kappa-carrageenan. Dye adsorption capacity of hydrogels decreased with increasing the ion strength of dye solution. The effect of pH of the initial dye solution revealed that while the adsorption capacity of hydrogels was not significantly changed in the pH range 2–10, removal efficiency was reduced at highly basic media. According to thermodynamic parameters, the adsorption of CV on magnetic hydrogels occurred spontaneously. The equilibrium adsorption data were analyzed with non-linear Langmuir and Freundlich models. It was found that the equilibrium process was followed the Langmuir model well.