Self-assembly of ternary hollow microspheres with strong wideband microwave absorption and controllable microwave absorption properties

In this study, we report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Co nanoparticles (Air@rGO€Co). The microspheres showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to microwaves. The minimum reflection loss (RL(min)) value of S(1.5) reaches −68.1 dB at 13.8 GHz with a thickness of 2.2 mm, and the absorption bandwidth (lower than −10 dB) is 7.1 GHz covering from 10.9 GHz to 18.0 GHz. More interestingly, we can easily controll the microwave absorbing properties of the microspheres by changing the ratio of the two components in the composites. The excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss play an important role in improving microwave absorption property. Our study provides a good potential method for preparation of lightweight microwave absorbing materials.