Hierarchical core-shell structured Fe3O4@NiSiO3 magnetic microspheres: preparation, characterization, and adsorption of methylene blue from aqueous solution

Hierarchical core-shell structured Fe3O4@NiSiO3 magnetic microspheres have been synthesized using a modified Stober sol-gel process and solvothermal methods. The prepared composites were investigated by SEM-EDS, TEM, XRD, FTIR, SQUID magnetometry, and nitrogen adsorption/desorption measurements. The microspheres possess high porosity and magnetic properties, which allow the Fe3O4@NiSiO3 microspheres to exhibit efficient adsorption capacity and convenient separation. The adsorption isotherm and adsorption kinetics for the adsorption of methylene blue (MB) on the Fe3O4@NiSiO3 microspheres were analyzed. The adsorption isotherm is well fitted by the Langmuir isotherm model, which is valid for monolayer adsorption of MB on the surface of Fe3O4@NiSiO3 magnetic microspheres. The pseudo-second-order model accurately describes the adsorption kinetics process for the adsorption of MB on the Fe3O4@NiSiO3 microspheres, suggesting a chemical adsorption process. MB removal of the Fe3O4@NiSiO3 magnetic microspheres can reach 87% after the fifth adsorption, indicating good regeneration capacity and reusability.