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 electromagnetic 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.