Hierarchically structured manganese oxide-coated magnetic nanocomposites for the efficient removal of heavy metal ions from aqueous systems

In this study, hierarchical MnO₂-coated magnetic nanocomposite (Fe₃O₄/MnO₂) was synthesized by a mild hydrothermal process, and its application for removing heavy metal ions from contaminated water systems was examined. Structural characterization showed that the Fe₃O₄ nanoparticle core was coated with amorphous MnO₂ shell with flowerlike morphology. The as-prepared nanocomposite had a large surface area and high magnetic saturation value, which ensured its good sorption ability and convenience of separation. Fe₃O ₄/MnO₂ exhibited a greatly improved removal capacity toward four different heavy metals (Cd(II), Cu(II), Pb(II), and Zn(II)) compared to unmodified Fe₃O₄ nanoparticles. The adsorption property of Fe₃O₄/MnO₂ was studied with Cd(II) in more detail. The sorption equilibrium data were well fitted to the Langmuir model, and the maximum adsorption capacity toward Cd(II) was 53.2 mg g ^-1. Fe₃O₄/MnO₂ retained over 80% of its adsorption capacity under various solution conditions that are typically encountered in natural waters. This nanocomposite was easily recovered and reused through consecutive adsorption-desorption experiments with the assistance of an external magnetic field. Overall, the findings propose that Fe ₃O₄/MnO₂ could be used as an effective recyclable adsorbent for heavy metal ions.