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 (Fe 2 O 3 ), 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). A hierarchically porous magnetic foam from micro-to nano-sized pores is constructed by in situ pyrolysis of iorn-based MOF on porous graphene foam. The formation of anisotropic porous magnetic nanosheets improve the magnetic loss, promoting the construction of hierarchically impedance gradient structures. By regulating annealing time and temperature, the optimal RL min reaches −60.13 dB with EAB max of 6.23 GHz. • Hierarchically porous magnetic foam from micro-to nano-sized pores is fabricated. • The pyrolysis of MOF promotes the formation of anisotropic porous magnetic sheet. • The magnetic sheet on GN facilitates the formation of hierarchical impedance. • Hierarchical impedance structure actuates the entrance and dissipation of EMW. • Optimization of impedance improves the absorption capacity and bandwidth.