Facile synthesis and enhanced electromagnetic microwave absorption performance for porous core-shell Fe₃O₄@MnO₂composite microspheres with lightweight feature

Functional composite microspheres with porous Fe₃O₄cores and hierarchical MnO₂shells have been synthesized successfully via a two-step hydrothermal method. X-ray diffraction was employed to determine the crystal forms of samples. The morphologies and microstructures of Fe₃O₄nanoparticles and Fe₃O₄@MnO₂composite microspheres were observed by the scanning electron microscope and transmission electron microscope. It can be seen that hierarchically structured MnO₂shells have coated Fe₃O₄nanoparticles, and the shell thickness is about 140–160 nm. The BET specific surface area and porosity were estimated by the N₂absorption-desorption isotherms and the magnetic properties were measured by the vibrating sample magnetometer. As-synthesized Fe₃O₄@MnO₂composite microspheres have a BET specific surface area of 167 m²/g, and the pore width is mainly distributed in the mesoporous range, especially from 2.0 nm to 12.0 nm. Investigations of microwave absorbing properties manifest that Fe₃O₄@MnO₂composite microspheres with loading 10% weight fraction possess the strongest RL peak of −42.6 dB (5.7 GHz) at the matching thickness 4.0 mm, and Fe₃O₄@MnO₂composite microspheres with loading 20% weight fraction have a broader absorbing bandwidth (10.2–15.0 GHz and 15.5–17.3 GHz) at the matching thickness 1.5 mm. Achieving the advantages of intensive absorption, wide effective absorbing bandwidth band and intrinsic lightweight feature, porous core-shell Fe₃O₄@MnO₂composite microspheres are believed to be more promising in the application of microwave absorption.