Crystalline–Amorphous Permalloy@Iron Oxide Core–Shell Nanoparticles Decorated on Graphene as High-Efficiency, Lightweight, and Hydrophobic Microwave Absorbents

The exploration of high-efficiency microwave absorption materials with lightweight and hydrophobic features is highly expected to reduce or eliminate the electromagnetic pollution. Graphene-based nanocomposites are universally acknowledged as promising candidates for absorbing microwaves due to their remarkable dielectric properties and lightweight characteristic. However, the hydrophilicity of graphene may reduce their stability and restrict the applications in moist environment. Herein, a well-designed heterostructure composed of crystalline permalloy core and amorphous iron oxide shell was uniformly adhered on oleylamine-modified graphene nanosheets by a one-pot thermal decomposition method. Compared with the recognized hydrophilic graphene-based hybrid materials, the permalloy@iron oxide/graphene nanocomposites show excellent hydrophobic and water-resistant features with a water contact angle of 136.5°. Besides, the nanocomposites show high-efficiency microwave absorption performance, benefiting from the tunneling effect, polarization, interface interaction, impedance matching condition, and synergistic effect between core-shell permalloy@iron oxide nanoparticles and graphene nanosheets. A broad effective absorption bandwidth with reflection loss (RL) value exceeding -10 dB can be obtained from 4.25 to 18 GHz, covering about 86% measured frequency range when the absorber thickness is 2.0-5.0 mm. Also, the microwave absorption performance of nanocomposites can be tuned by changing the amount of graphene. More importantly, a greatly improved microwave absorption effectiveness of -71.1 dB can be achieved for the nanocomposites in comparison with the bare permalloy@iron oxide nanoparticles (-5.6 dB) and oleylamine-modified GO nanosheets (-3.56 dB). The lightweight and hydrophobic permalloy@iron oxide/graphene nanocomposites with high-efficiency microwave absorption performance are highly promising to improve the environmental adaptability of electric devices, especially in the wet environment.