Kinetics, thermodynamics, equilibrium isotherms, and reusability studies of cationic dye adsorption by magnetic alginate/oxidized multiwalled carbon nanotubes composites

Magnetic beads (AO-gamma-Fe2O3) of alginate (A) impregnated with citrate coated maghemite nanoparticles (gamma-Fe2O3) and oxidized multiwalled carbon nanotubes (OMWCNTs) were synthesized and used as adsorbent for the removal of methylene blue from water. The XRD analysis revealed that the diameter of gamma-Fe2O3 is 10.24 nm. The mass saturation magnetization of AO-gamma-Fe2O3 and gamma-Fe2O3 were found to be 27.16 and 42.63 emu. g(-1), respectively. The adsorption studies revealed that the data of MB isotherm were well fitted to the Freundlich model. The Langmuir isotherm model exhibited a maximum adsorption capacity of 905.5 mg.g(-1). The adsorption was very dependent on initial concentration, adsorbent dose, and temperature. The beads exhibited high adsorption stability in large domain of pH (4-10). The thermodynamic parameters determined at 283, 293, 303, and 313 K revealed that the adsorption occurring was spontaneous and endothermic in nature. Adsorption kinetic data followed the intraparticle diffusion model. The AO-gamma-Fe2O3 beads were used for six cycles without significant adsorptive performance loss. Therefore, the eco-friendly prepared AO-gamma-Fe2O3 beads were considered as highly recyclable and efficient adsorbent for methylene blue as they can be easily separated from water after treatment. (C) 2018 Elsevier B.V. All rights reserved.