Hybrid nanocomposite of kappa-carrageenan and magnetite as adsorbent material for water purification

A novel polysaccharide based hydrogel; kappa-carrageenan grafted with N-hydroxyethylacrylamide (κC-g-PHEAA) was synthesized via microwave assisted free radical polymerization process. A hybrid nanocomposite has also been made by incorporation of Fe₃O₄ nanoparticles into the κC-g-PHEAA network. The materials were characterized by FTIR, TGA, XRD, SEM, BET and VSM techniques. The nanocomposite exhibited super-paramagnetic behavior. The κC-g-PHEAA and κC-g-PHEAA/Fe₃O₄ presented significant adsorption capacity towards cationic dyes, methylene blue (MB) and rhodamine 6G (R6G); and metal ions, Cu(II) and Hg(II) from aqueous solution. The magnetite nanoparticles enhance the adsorption characteristics of the hydrogel and enables easy separation of the adsorbent with an external magnetic field. Adsorption process is observed to follow both Langmuir and Freundlich isotherm models for R6G and Freundlich isotherm model for MB, Cu(II) and Hg(II). The adsorption was found to be a pseudo first order process for MB and pseudo second order process for R6G, Cu(II) and Hg(II). Thermodynamic studies have shown the adsorption of dyes and metal ions to be spontaneous and endothermic in nature. The desorption studies revealed the efficient recovery of adsorbate species. The study indicates that the synthesized adsorbents have potential applications for the removal of dyes and metal ions from wastewater.