Carbon-based composites have shown excellent electromagnetic wave-absorption properties. In this work, an extremely facile and green method was developed to prepare Fe@Fe3C/C nanocomposites by carbonizing the bulrush impregnated with Fe­(NO3)3 solutions. The core–shell Fe@Fe3C was generated from carbothermal reductions and interfacial reactions. The minimum reflection loss exceeded −50 dB with absorbers thickness almost no more than 2.00 mm. The widest absorption bandwidth was up to 4.57 GHz with a thickness only 1.43 mm. Meanwhile, the absorption performance with RL < −10 dB could be observed in a bandwidth of about 15 GHz as absorbers thickness varied from 1.00 to 5.00 mm. The excellent wave-absorbing properties could be attributed to the synergistic effect of dielectric loss and magnetic loss of Fe@Fe3C/C nanocomposites. Also, the optimized impedance matching and high attenuation abilities of absorbers contributed to the absorption performance. This work provides a new way of recycling the abundant natural herbage waste to be used in electromagnetic applications.

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The study on novel physical properties of structural ceramics or ceramic composites could make them more conducive to be function‐ and structure‐integrated materials. Herein, titanium nitride‐alumina (TiN–Al2O3) duplex ceramics were prepared and the dielectric spectra of the ceramics were studied from 10 MHz to 1 GHz. Negative permittivity appeared when TiN content exceeded 40 wt% due to the induced plasmonic state of massive delocalized electrons in connected TiN grain networks. Meanwhile, alternating current conduction behaviors of the duplex ceramics were discussed with percolation theory. Furthermore, the analysis of reactance by equivalent circuit models indicated that negative permittivity ceramics exhibited inductive character. This work realized negative dielectric behaviors in TiN–Al2O3 duplex ceramics and would promote the study of electromagnetic functionalization in wave shielding or attenuation for structural ceramics.

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High-performance microwave absorbents play a key role in the information technology field. Here, excellent microwave absorption properties were achieved via embedded Fe@Fe3C core-shell nanoparticles in polyvinyl alcohol-derived porous carbon matrix. The results indicate that the microwave absorption performance will be greatly enhanced due to the interface between the nanoparticles and matrix, as well as the core-shell and the porous structure, with an increase in energy consumption capacity via dipole polarization, interface loss, and multiple reflection/scattering. The maximum reflection loss (RLmax) reaches -56.88 dB at 11.3 GHz with the thickness of 2.11 mm, and the effective absorption bandwidth (EAB, RL<-10 dB) can get up to 5.2 GHz (from 12.9 to 18 GHz) with the thickness of 1.64 mm. Moreover, due to the low density of the porous carbon matrix, the total weight of the absorbents can be greatly reduced, which provides an efficient method for lightweight and high-performance microwave absorption materials design.