Facile synthesis and enhanced electromagnetic microwave absorption performance for porous core-shell Fe3O4@MnO2 composite microspheres with lightweight feature

Functional composite microspheres with porous Fe 3 O 4 cores and hierarchical MnO 2 shells 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 Fe 3 O 4 nanoparticles and Fe 3 O 4 @MnO 2 composite microspheres were observed by the scanning electron microscope and transmission electron microscope. It can be seen that hierarchically structured MnO 2 shells have coated Fe 3 O 4 nanoparticles, and the shell thickness is about 140–160 nm. The BET specific surface area and porosity were estimated by the N 2 absorption-desorption isotherms and the magnetic properties were measured by the vibrating sample magnetometer . As-synthesized Fe 3 O 4 @MnO 2 composite microspheres have a BET specific surface area of 167 m 2 /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 Fe 3 O 4 @MnO 2 composite 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 Fe 3 O 4 @MnO 2 composite 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 Fe 3 O 4 @MnO 2 composite microspheres are believed to be more promising in the application of microwave absorption.