Adsorption characteristics of montmorillonite clay modified with iron oxide with respect to methylene blue in aqueous media

Montmorillonite clay modified with iron oxide (MtMIO) was prepared for use as an adsorbent of methylene blue dye. Structural characterization of MtMIO was performed by field-emission scanning electron microscopy, energy-dispersive spectroscopy, surface area measurements, zeta potential analysis and Fourier transform infrared spectroscopy. Batch experiments were carried out under different conditions of initial dye concentration, contact time and temperature to investigate the adsorption of methylene blue onto MtMIO. Adsorption isotherms were experimentally determined and the Freundlich and Langmuir models were used to fit the data, better results being obtained for the latter with a maximum adsorption capacity of 71.12 mg g− 1 at 333 K. Thermodynamic parameters, such as standard enthalpy, standard entropy and standard free energy changes were determined, indicating an endothermic and non-spontaneous process. Also, pseudo-first-order and pseudo-second-order kinetic models were applied, and the experimental data fitted the pseudo-second order model. The activation energy of + 19.32 kJ mol− 1 was determined using the Arrhenius equation.