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

Magnetic beads (AO-γ-FeO) of alginate (A) impregnated with citrate coated maghemite nanoparticles (γ-FeO) 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 γ-FeO is 10.24 nm. The mass saturation magnetization of AO-γ-FeO and γ-FeO were found to be 27.16 and 42.63 emu·g, 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. 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-γ-FeO beads were used for six cycles without significant adsorptive performance loss. Therefore, the eco-friendly prepared AO-γ-FeO beads were considered as highly recyclable and efficient adsorbent for methylene blue as they can be easily separated from water after treatment.