Unusual dye adsorption behavior of κ-carrageenan coated superparamagnetic nanoparticles

κ-Carrageenan coated magnetic iron oxide nanoparticles (NPs) were synthesized and tested as adsorbents for the magnetically assisted removal of methylene blue (MB) from aqueous solutions, a cationic dye commonly present in wastes from the textile industry. The resulting composite NPs were superparamagnetic and contained ca. 12 wt% carrageenan. The MB uptake ability was found to vary with the pH solution and was larger in alkaline conditions. Both pseudo-first-order and pseudo-second-order equations predicted well the kinetics with the maximum adsorption achieved very fast, within 5 min. The MB adsorption has shown an unusual Z-type isotherm which suggests the generation of new adsorbing sites with increasing MB initial concentration. Under the experimental conditions used (23 °C, pH 9) the materials presented here displayed MB adsorption capacity (185.3 mg/g) higher than other magnetic sorbents previously reported. Thus κ-carrageenan coated magnetic NPs are very promising eco-friendly materials for removing MB from wastewater using magnetic separation.