Strong contribution of: In situ grown nanowires to enhance the thermostabilities and microwave absorption properties of porous graphene foams under different atmospheres

Free-standing and high-performance electromagnetic (EM) absorbing materials of three-dimensional (3D) hierarchical graphene foams (GFs) decorated with in situ grown Si₃N₄ nanowires (Si₃N_4nws) and SiC nanowires (SiC_nws) were prepared using a one-step carbothermal reduction process under flowing N₂ and Ar, respectively. The as-obtained Si₃N_4nws consist of single crystalline Si₃N₄ cores ∼200 nm in diameter and amorphous SiO_x layers ∼2 nm in thickness, and the SiC_nws are composed of single crystalline SiC cores about 200 nm in diameter and amorphous SiO_x sheaths with an average thickness of 25 nm. By incorporating Si₃N_4nws and SiC_nws into GFs, the thermostability and EM absorption of the composites were simultaneously improved effectively. The Si₃N_4nws-GFs and SiC_nws-GFs were thermostable in an air atmosphere beyond ∼640 °C with above 98% and 94% weight retention, respectively. Compared with those of pure GFs, the Si₃N_4nws-GFs exhibit a stronger EM microwave absorption performance with a minimum reflection loss (RL) value of -48.7 dB at 6.4 GHz with a thickness of 2.36 mm, and the minimum RL value of the SiC_nws-GFs could be as low as -67.8 dB at 5.9 GHz with 2.6 mm thickness. The multiscale Si₃N_4nws-GFs and SiC_nws-GFs in the present study are very promising as absorber materials with strong EM wave absorption performance in critical environments.