Three-dimensional conductive network constructed by in-situ preparation of sea urchin-like NiFeO in expanded graphite for efficient microwave absorption.

Expanded graphite (EG) is a modified conductive lamellar carbon that has been widely studied in the field of electromagnetic wave absorption due to its low density, good electrical conductivity, and unique structure. However, its application is limited because the interlayer gap cannot match microwave wavelength, and its single composition has less microwave loss. In this study, sea urchin-like NiFeO/EG composites are prepared in situ between expanded graphite layers by microwave treatment. The sea urchin-like NiFeO grows between the expanded graphite to form a three-dimensional conductive network structure, which enhances conductive loss of composites and further increases the interlayer distance of EG. The extended interlayer distance promotes multiple reflections and scattering of electromagnetic waves in composites and improves dielectric properties. In addition, EG with a large specific surface area provides many active sites, further promoting interface and dipole polarization. Benefiting from synergistic effect of NiFeO and EG, magnetic loss and dielectric loss of NiFeO/EG composites have been improved and impedance matching is further enhanced. The results indicate that the minimal reflection loss of NiFeO/EG-4 reaches -53.47 dB at 2.69 mm, and the effective absorption bandwidth reaches 2.97 GHz. In addition, based on the computer simulation technology results, NiFeO/EG can attenuate microwave energy under experimental conditions. This work provides a strategy for synthesizing carbon matrix composites with adjustable dielectric parameters and electromagnetic wave properties.