Mesoporous MgO nanoparticles as a potential sorbent for removal of fast orange and bromophenol blue dyes

Abstract

The removal of fast orange 3R and bromophenol blue dyes was successfully performed on mesoporous MgO nanoparticles. MgO nanoparticles were prepared by sol–gel route using CTAB as template agent. The crystalline, texture and the morphology feature of the prepared nanoparticles were investigated using X-ray diffraction, adsorption–desorption isotherm, scanning electron microscope, transmission electron microscope and high resolution transmission electron microscope. The results showed that the formation of nanorods of average size about 24 nm in diameter and 38 nm in length. Adsorption of both dyes changed crystallography of catalyst from cubic MgO to hexagonal Mg(OH)2. This research work investigated the factors affecting dye uptake such as contact time, catalyst dosage, initial dye concentration and temperature. Different types of adsorption isotherms and kinetic models were performed to get a clear picture on the mechanism and the kinetic of the adsorption process. Thermodynamic parameters such as free energy, entropy and enthalpy were estimated. The experimental results showed that the adsorption equilibrium data are fitted well to the Langmuir and Freundlich isotherms. The adsorption isotherms indicated that the adsorption capacities are 30 and 40 mg g−1 for fast orange and bromophenol blue, respectively. The adsorption processes follow pseudo-second-order rate equation. Enthalpy change (ΔH°) for fast orange and bromophenol blue dye is +37.8 and +7.3 kJ mol−1, respectively, indicating that the removal processes are endothermic. The negative values of free energy (ΔG°) suggested that the adsorption processes are spontaneous.