Selective adsorption of amaranth dye on Fe3O4/MgO nanoparticles

This research work is concerned with investigation of removal amaranth food stuff dye on magnetic Fe3O4/MgO nanoparticles synthesized by facile sol-gel route. The crystalline feature and the nanostructure of the magnetic nanoparticles were investigated by X-ray diffraction (XRD), N2-adsorption-desorption isotherm, field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM). FESEM and HRTEM analysis illustrate the existence of MgO nanoparticles with rod-like structure of average size about 14 nm in diameter and 22 nm in length. However, N2 adsorption-desorption isotherm reveals the existence of mesoporous nanoparticles with ink-bottle pore shape. It is obvious to notice a change in sample crystallography from cubic MgO to hexagonal Mg(OH)2 crystals after adsorption of amaranth dye which reveal the full hydration of the magnetic nanoparticles. The influence of reaction parameters affecting dye uptake including contact time, catalyst dosage, initial dye concentration and temperature were investigated for proper choosing the optimization parameters of the removal process. Different types of adsorption isotherms equations were performed for the better fit to get a clear picture on the mechanism of the adsorption process. The kinetics of the adsorption process was analyzed using different models to indicate the rate determine step. Thermodynamic parameters such as free energy, entropy, and enthalpy were estimated. The intra-particle diffusion was identified to be the rate-limiting step in addition to the film diffusion. The experimental results have pointed out that the adsorption equilibrium data are fitted well to the Langmuir isotherm rather than Freundlich isotherm reflecting favor formation of monolayer of this dye on MgO surface. The adsorption isotherm indicates that the adsorption capacities are 37.98 mg/g. The value of enthalpy change is17.03 kJ/mol indicating that the removal process is endothermic. The adsorption process follows pseudo-second order rate equation and the negative values of standard free energy (ΔG°) suggested that the adsorption process is spontaneous. The existence of magnetic Fe3O4 facilitates the recovery of solid catalyst after adsorption process. Overall; this research work promotes the possible use of Fe3O4/MgO as an effective magnetic adsorbent for removal of dye from aqueous solution and recovery the catalyst to be used for several cycles.