Synthesis of porous nitrogen-doped graphene decorated by γ-Fe2O3 nanorings for enhancing microwave absorbing performance

Excellent wave absorbers are key materials for reducing electromagnetic radiation pollution. In this work, novel gamma-Fe2O3 nanoring/porous nitrogen-doped graphene (gamma-Fe2O3 NR/PNG) composites with varying mass ratios were successfully synthesized as lightweight absorbers using a two-step solvothermal method in combination with a partial reduction process. The diameter of the uniform gamma-Fe2O3 NRs is approximately 150 nm with a shell thickness of approximately 50 nm. The uniform gamma-Fe2O3 NRs are dispersed onto PNG sheets. Compared with pure gamma-Fe2O3 NRs and PNG, all gamma-Fe2O3 NR/PNG composites exhibit better microwave absorbing performance, among which a gamma-Fe2O3 NR/PNG composite with a 4:1 mass ratio of gamma-Fe2O3 NR:PNG shows the best absorption over a broad bandwidth for its special nanoring and porous structure and excellent impedance matching. The minimum reflection loss (RLmin) reaches -40.18 dB at 7.80 GHz with a thickness of 2.5 mm; the absorption bandwidth (RL < -10 dB) is 3.41 GHz. Moreover, the composite also reveals a good absorption for microwaves in the low frequency range. At 3.38 GHz, RLmin reaches -32.69 dB with a thickness of 5.5 mm. This work provides guidance for designing absorbers that are lightweight, wideband with strong absorption.