Solvothermal synthesis of nitrogen-doped graphene decorated by superparamagnetic Fe3O4 nanoparticles and their applications as enhanced synergistic microwave absorbers

Fe3O4 nanocrystals anchored on nitrogen-doped graphene nanosheets were fabricated by solvothermal method as synergistic microwave absorbers. Electron microscopy investigations show that the Fe3O4 nanocrystals are uniformly dispersed on the nitrogen-doped graphene nanosheets without aggregation. The Fe3O4 nanocrystals cannot be separated from nitrogen-doped graphene even under powerful ultrasound treatment, suggesting that the Fe3O4 nanocrystals are chemically bonded on the surface of nitrogen-doped graphene. Taking the advantage of synergistic effect between Fe3O4 nanocrystals with magnetic loss and nitrogen-doped graphene with dielectric loss, the Fe3O4/nitrogen-doped graphene hybrids show enhanced microwave absorption capabilities with highly efficient performance. A maximum reflection loss of -65.3 dB can be achieved at 6.8 GHz with a matching thickness of 3.4 mm for the hybrids with 20 mg original graphene oxide, and the effective absorption bandwidth with reflection loss values less than -10 dB covers 12-16 GHz with the absorber thickness of only 2.0 mm. Moreover, the frequency of microwave absorption peak in the hybrids can be tuned by changing the amount of nitrogen-doped graphene or the thickness of the hybrids. These results indicate that the Fe3O4/nitrogendoped graphene hybrids are ideal candidates to be used as synergistic microwave absorbers with anti oxidation, light weight, high-efficient performance and broad frequency bandwidth. (C) 2017 Elsevier Ltd. All rights reserved.