We synthesized novel magnetic nanocomposite hydrogels of κ-carrageenan by incorporating magnetic laponite RD. The magnetite nanoparticles were embedded in laponite RD through in situ method. The structure of nanocomposites were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer techniques. The swelling of hydrogel nanocomposites was studied and decrease in water absorbency was found by introducing magnetic laponite RD. The results indicated that the water absorbency was independent on pH of swelling media. The magnetic nanocomposites were examined as adsorbents for the removal of crystal violet (CV) from aqueous solutions. The removal of CV was investigated through batch method on the subject of contact time, initial pH of dye solution, ion strength, and initial concentration of CV. The effect of pH revealed that the adsorption process was independent of pH. Compared to the neat κ-carrageenan hydrogel (78 mg/g), the nanocomposites showed high adsorption capacity for CV due to the introduced magnetic laponite RD (164 mg/g). The adsorption isotherm data were modeled by Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The correlation of adsorption isotherm data by mentioned models was affected by the content of magnetic laponite RD. Based on Dubinin–Radushkevich isotherm models, the adsorption process was associated with physical adsorption mechanism. Investigation of thermodynamic parameters revealed that the adsorption of CV on nanocomposites was occurred spontaneously.
