Hierarchical magnetic-dielectric synergistic Co/CoO/RGO microspheres with excellent microwave absorption performance covering the whole X band

Based on the rational component regulation and micro-nano structure design, hierarchical dielectric-magnetic microspheres become the ideal functional materials in the microwave absorption field. Herein, unique three-dimension (3D) Co/CoO/reduced graphene oxide (RGO) (denoted as CCOR) microspheres with the hierarchi-cal structure are prepared by a simple solvothermal method and annealing treatment. Due to the plentiful growth sites on the surface of graphene oxide, Co/CoO nanoparticles (NPs) homogeneously anchor on the RGO. Meanwhile, larger size Co/CoO particles connect 2D RGO nanosheets to form the hierarchical CCOR micro-spheres, which introduce abundant heterojunctions and interfaces. The electromagnetic parameters have been effectively adjusted by tuning the synergistic effect between the magnetic Co/CoO particles and highly conductive RGO nanosheets. The obtained CCOR composites exhibit excellent microwave absorption perfor-mance with the maximum reflection loss (RLmax) of-50.1 dB. The effective absorption bandwidth reaches 6.56 GHz covering the whole X-band frequency. The outstanding microwave absorption performance of CCOR mi-crospheres stems from the followings: i) well micro-nano structure design provides abundant heterojunction interfaces, resulting in the enhanced interfacial polarization; ii) the magnetic-dielectric synergistic loss ability from rational Co/CoO and RGO component design, facilitating the microwave energy dissipation; iii) the Co/CoO particles induce multi-scale magnetic coupling effect and strengthen the magnetic response capability. Thus, as-synthesized Co/CoO/RGO microspheres demonstrate the huge potential for application of stealth in X band as microwave absorption materials.