Magnetic bioadsorbents based on chitosan with different molecular weights were prepared. To stabilize under acidic condition the synthesized magnetic chitosan was crosslinked with κ-carrageenan. The characterization of magnetic bioadsorbents revealed that the size of magnetic nanoparticles is affected by the chitosan molecular weight. Magnetic nanoparticles with larger sizes were obtained with the high molecular weight of chitosan. The removal of eriochrome black-T (EBT) by the magnetic bioadsorbents was investigated. The equilibrium adsorption isotherm data of EBT on bioadsorbents were found to be well explained through Langmuir isotherm model, from which the maximum adsorption capacities were found to be 280, 235, and 199 mg/g for bioadsorbents prepared with low, medium, and high molecular weights of chitosan, respectively. A remarkable reduction in adsorption capacities of bioadsorbents was observed as the pH of dye solution was increased. The reduction in the dye adsorption under basic media suggested using a mild condition (pH = 9) to recycle and reuse the bioadsorbents. Cyclic experiments indicated that current bioadsorbents can be effectively reused to remove anionic EBT from aqueous solutions. The removal efficiencies remained >93% even after five adsorption-desorption cycles, which suggest the present bioadsorbents as a great candidate in the wastewater treatment.
