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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. Fe₃O₄/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 …