Redox‐Mediated Synthesis of a Fe3O4–MnO2 Nanocomposite for Dye Adsorption and Pseudocapacitance

A logically chosen redox reaction of submerged Fe⁰ in an aqueous KMnO₄ solution has been reported. The template‐free reaction conditions produced gram amounts of a hierarchical flowerlike Fe₃O₄–MnO₂ nanocomposite. More precisely, freshly prepared Fe⁰ nanoparticles were prepared from air‐free hot water under submerged conditions using a door magnet. The black Fe⁰ particles were oxidized in water quantitatively by KMnO₄ in the solution phase and the nanocomposite was prepared. The material has been used as a dye adsorbent and the representative cationic dye uptake, recovery, and recycling of the dye becomes easy owing to the ferromagnetic properties and surface negative charge of the material. The nanocomposite also showed a higher specific capacitance (327 F g^?1 at 10 mV s^?1) than the reported values of pure MnO₂ and Fe₃O₄. The material exhibited a high energy density as well as a high power density, and remained stable even after a large number of charge–discharge cycles.