Fabrication of ultralight nitrogen-doped reduced graphene oxide/nickel ferrite composite foams with three-dimensional porous network structure as ultrathin and high-performance microwave absorbers

The development of lightweight and high-performance microwave absorbers is still a challenge in the field of electromagnetic absorption. Graphene foam with three-dimensional (3D) network structure and low bulk density has been considered as an ideal candidate for microwave absorption. In this work, nitrogen-doped reduced graphene oxide/nickel ferrite composite foams were prepared by the solvothermal and hydrothermal two-step method. The as-prepared composite foams had very low bulk density (7.8 ∼ 10.0 mg·cm-3) and a unique 3D porous network structure. Furthermore, results revealed that the microwave absorption performance of attained composite foams could be improved by adjusting the calcination temperature. Significantly, the obtained composite foam exhibited the best microwave absorption performance when calcined at 650.0 °C for 2.0 h. The minimum reflection loss was as large as -60.6 dB at an ultrathin matching thickness of only 1.55 mm, and the effective absorption bandwidth could reach 5.5 GHz with a thin thickness of 1.62 mm. In addition, the possible microwave attenuation mechanisms of attained composite foams were proposed. It was believed that our results could be helpful for developing graphene-based 3D magnetic composites as lightweight and high-performance microwave absorbers.