Adsorption of heavy metal ions by hierarchically structured magnetite-carbonaceous spheres

Magnetically driven separation technology has received considerable attention in recent decade for its great potential application. In this work, hierarchically structured magnetite-carbonaceous microspheres (Fe3O4-C MSs) have been synthesized for the adsorption of heavy metal ions from aqueous solution. Each sphere contains numerous unique rattle-type structured magnetic particles, realizing the integration of rattle-type building unit into microspheres. The as-prepared composites with high BET surface area, hierarchical as well as mesoporous structures, exhibit an excellent adsorption capacity for heavy metal ions and a convenient separation procedure with the help of an external magnet. It was found that the maximum adsorption capacity of the composite toward Pb2+ was ∼126 mg g−1, displaying a high efficiency for the removal of heavy metal ions. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Pb2+ removal was found to follow pseudo-second-order rate equation. The as-prepared composite of Fe3O4-C MSs as well as Pb2+-adsorbed composite were carefully examined by scanning electron microscopy (SEM), Zeta potential measurements, Fourier transform infrared spectroscopy (FT-IR), nitrogen sorption measurements, and X-ray photoelectron spectroscopy (XPS). Based on the characterization results, a possible mechanism of Pb2+ removal with the composite of Fe3O4-C MSs was proposed.