Hollow spherical NiFe-MOF derivative and N-doped rGO composites towards the tunable wideband electromagnetic wave absorption: Experimental and theoretical study

N-doped rGO (N-rGO) based nano materials are considered to be competent candidates for absorbing electro-magnetic waves (EMWs), owing to the low filler loading and abundant relaxation polarization losses. With a unique multistage porous structure, NiFe@N-C/rGO, derived from the composite of NiFe-MOF anchoring on GO nanosheeets, was successfully constructed by a facile solvothermal method and high-temperature annealing technique. Adjusting the ratio of GO is an effective strategy to optimize the EMWs absorption performance to a large extent. At a filler loading of 20 wt%, when the content of graphene is 30 mg, the corresponding product NiFe@N-C/rGO-30 is found to have a minimum reflection loss (RLmin) of-72.28 dB at 10.82 GHz, and an effective absorption bandwidth (EAB, RL <=-10 dB) is 5.25 GHz (12.43-17.68 GHz) under the matching thickness of 2.46 mm, its EAB dramatically reached 7.14 GHz (9.74-16.88 GHz) when the graphene content was increased to 90 mg at 2.04 mm matching thickness, which covers most of the X and Ku radar frequency band. Combined with the analysis of the electronic and surface structures of NiFe@N-C/rGO composites, the formation energy and dipole moment were calculated to reveal the mechanism of EMWs absorption within them. The results show that the N-doped structure is more stable than the vacancy modification, where the pyridinic-N is the source of dipole relaxation polarization under high-frequency electromagnetic field. The combination of experimental and theoretical research reveals the inherent mechanism of EMWs attenuation in as-prepared composites, paving an inspirational route for controllable high performance absorbing materials.