Removal of Congo Red by Magnetic MnFe₂O₄ Nanosheets Prepared via a Facile Combustion Process

Magnetic MnFe₂O₄ nanosheets were prepared via the facile combustion process, the morphology, chemical composition, microstructure and magnetic properties of them were investigated by SEM, EDX, XRD, TEM, SAED and VSM. The as-prepared magnetic MnFe₂O₄ nanosheets calcined at 400 °C for 2 h with absolute alcohol of 30 mL were characterized with average diameter of about 55 nm, the thickness of around 20 nm, the specific magnetization of 44.0 Am²/kg and the specific surface area of 49.6 m²/g. The removal behavior of Congo red (CR) from aqueous solutions onto MnFe₂O₄ nanosheets was investigated by UV spectroscopy at room temperature; the adsorption kinetics data related to the adsorption of CR from aqueous solutions were in good agreement with the pseudo-second-order kinetic model in the initial concentrations of 80-400 mg/L. By comparison of the Langmuir, Freundlich and Temkin models for adsorption isotherms of CR, the Temkin model (correlation coefficient R² = 0.998) could be used to evaluate the adsorption isotherm of CR onto the magnetic MnFe₂O₄ nanosheets at room temperature, which suggested that the adsorption of CR onto the magnetic MnFe₂O₄ nanosheets was a hybrid of monolayer and multilayer absorbing mechanism.