Graphene-based magnetic composite foam with hierarchically porous structure for efficient microwave absorption

In the design of microwave absorbing materials, synergistically optimizing the relationship between impedance matching and attenuation constant remains a great challenge. In this work, a hierarchically porous graphene/ iron trioxide magnetic composite foam (GMF) is successfully constructed by an electrostatic assembly of metal -organic frameworks (MOF) in reduced graphene oxide skeletons and subsequent annealing treatment. As a unique template, the in-situ pyrolysis of MOF facilitates the transition from flake-like MOF to anisotropic porous magnetic nanosheet (Fe2O3), promoting the composites to break Snoek's limitation. The combination between magnetic nanosheets and conductive graphene skeletons can further optimize the impedance gradient and attenuation constant of those foams. More importantly, the successful construction of hierarchically porous magnetic foam from micro-to nano-sized pores effectively induces the generation of huge multiple scattering and defect polarization. As a result, more incident electromagnetic waves thus are allowed to enter the materials and dissipate as much as possible after entering the foam, endowing the composite foam with an excellent absorption capacity (-60.13 dB) and bandwidth (6.23 GHz).