Preparation and characterization of microwave absorbing composite materials with GSs or FeCo/GS composites

[Display omitted] •It is found that adding GSs or FeCo/GSs composite into the sample SiC/NR can greatly increase RL and the absorbing peak shifts to low-frequency with increasing the adding amount.•The optimum adding amount of GSs is 2%. The sample GS-200-2% possesses the lowest RL value of −31.27 dB at 7.6 GHz.•The optimum adding amount of FeCo/GSs composite is 3%. The sample AGS-450-3% possesses the lowest RL value of −20.67 dB at 7.8 GHz. This study mainly explored the synthesis method of graphene sheets (GSs) and FeCo/graphene sheet (FeCo/GS) composites and evaluated the microwave absorbing characteristics of composite materials containing GSs or FeCo/GS composites. First, graphite oxide (GO) was synthesized by the modified Hummers method. The synthesized GO was further used to synthesize GSs and FeCo/GS composites. Afterward, GSs or FeCo/GS composites were mixed with silicon carbide (SiC) and natural rubber (NR) to prepare microwave absorbing materials with thicknesses of 2 mm. Finally, identification and characterization of these samples were performed by XRD, FE-SEM, TEM, TGA, ESCA, RS, AFM and VNA. GSs were synthesized successfully at a low annealing temperature of 200 °C, and their thicknesses were between 0.848 nm and 2.115 nm, which corresponds to 2–6 stacked layers of graphene. FeCo/GS composites were also synthesized successfully at three different annealing temperatures. The nanoparticles of metals and metal oxides were well-dispersed on the surfaces of and the spaces between GSs. It was found that adding GSs or FeCo/GS composites into the SiC/NR sample can greatly increase reflection loss (RL) and that the absorbing peak shifts to lower frequencies as the concentration of added particles increases. The optimum concentration of added GSs was 2 wt.%. The GS-200-2% sample possessed the lowest RL value of −31.27 dB at 7.6 GHz. The optimum concentration of added FeCo/GS composites was 3 wt.%. The AGS-450-3% sample possessed the lowest RL value of −20.67 dB at 7.8 GHz.