Paramagnetic CoS2@MoS2 core-shell composites coated by reduced graphene oxide as broadband and tunable high-performance microwave absorbers

Nowadays, developing microwave absorbers with tunable and high-efficiency electromagnetic absorbing performance is still facing many challenges, in spite of their wide applications in civilian and military roles. Here, flower-like CoS2@MoS2 core-shell microspheres coated by reduced graphene oxide (rGO) is designed and synthesized by a facile hydrothermal method. The formation of typical flower-like core-shell microspheres is attributed to the combined effect of CoS2 microsphere and MoS2 nanosheet during hydrothermal reaction process. Further, with the addition of graphene oxide, the wrinkled rGO nanosheet is successfully coated on the surface of flower-like CoS2@MoS2 core-shell microspheres, forming a specific three-dimensional (3D) structure. The microstructure, morphology and chemical composition of the as-synthesized composites are characterized by XRD, Raman, XPS, SEM and TEM. Magnetic measurement shows that CoS2@MoS2 microspheres exhibit paramagnetic behavior. The electromagnetic properties of CoS2@MoS2/rGO composites are measured by a vector network analyzer, where the unique flower-like core-shell structure and multiple interfaces, particular surface defects as well as the specific electric properties of CoS2, MoS2 and rGO lead to the impressive microwave absorption properties. The effect of filler loading ratio on microwave absorption performance of the wax-based absorbers is analyzed in detail. It is noted that the sample with 20 wt% loading of CoS2@MoS2/rGO exhibits optimal reflection loss (RL) characteristics, where the minimum RL is -58 dB with a broad effective bandwidth of 6.24 GHz from 11.76 to 18 GHz at 2.4 mm. Apparently, the as-synthesized CoS2@MoS2/rGO composites can be acted as a lightweight and broadband microwave absorber with low filler loading. This work offers a new strategy to design high-performance and tunable microwave absorbers with individual microstructure and morphology using a facile, low-cost and environmental-friendly synthesis route.