Efficiency, Kinetics and Thermodynamics of Toluidine Blue Dye Removal from Aqueous Solution Using MWCNTs Decorated with NiFe2O4

NiFe2O4/Carbon nanotube composite materials have been prepared using in-situ chemical precipitation of metal hydroxides in the presence of multi-walled carbon nanotubes (MWCNTs) and followed by hydrothermal processing. The obtained composite powders were characterized using XRD and TEM. The adsorption efficiency of NiFe2O4/carbon nanotubes for toluidine blue at various temperatures was examined. The amount adsorbed increased with the NiFe2O4/CNTs dosage. The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined. The results revealed that Langmuir isotherm fitted the experimental results well. Kinetic analyses were conducted using pseudo first-order, second-order and the intraparticle diffusion models. The regression results showed that the adsorption kinetics were more accurately represented by a pseudo second-order model. Changes in the free energy of adsorption (G(0)), enthalpy (H-0) and entropy (S-0), as well as the activation energy (E-a) were determined. H-0 and S-0 were 15.99 kJ/mol and 98 J/mol K, respectively. The activation energy was 8.2 kJ/mol. H-0, G(0) and E-a values reflected that the adsorption of toluidine blue onto NiFe2O4/CNTs was by physisorption.