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Biomass carbon composites have the shining points of lightweight, economy, harmlessness, and large specific surface area, casting on them great development prospects in terms of excellent wave absorbing properties. Herein, a facile route to fabricate magnetic porous with a special spongy structure for its great contribution to microwave absorption is reported. It is endowed with a strong absorption capacity and a wide absorption band. The 3D spongy structure and uniform distribution of magnetic Co particles can promote defect polarization, interface polarization, and dipole polarization, which are conducive to scattering and reflection of electromagnetic waves (EMW) in the absorbing body. The magnetic Co particles can enhance the magnetic loss on the one hand and harmonize the impedance matching on the other hand. The minimum reflection loss can reach −54.7 dB. The effective absorption bandwidth at 2.1 mm can reach 7.61 GHz, almost covering the X and Ku bands. This proposed strategy provides more possibilities for the application of biomass microwave absorbers with lightweight and broadband properties. [ABSTRACT FROM AUTHOR]

Cobalt ferrite (CoFe2O4), with good chemical stability and magnetic loss, can be used to prepare composites with a unique structure and high absorption. In this study, CoFe2O4@mesoporous carbon hollow spheres (MCHS) with a core-shell structure were prepared by introducing CoFe2O4 magnetic particles into hollow mesoporous carbon through a simple in situ method. Then, the microwave absorption performance of the CoFe2O4@MCHS composites was investigated. Magnetic and dielectric losses can be effectively coordinated by constructing the porous structure and adjusting the ratio of MCHS and CoFe2O4. Results show that the impedance matching and absorption properties of the CoFe2O4@MCHS composites can be altered by tweaking the mass ratio of MCHS and CoFe2O4. The minimum reflection loss of the CoFe2O4@MCHS composites reaches -29.7 dB at 5.8 GHz. In addition, the effective absorption bandwidth is 3.7 GHz, with the thickness being 2.5 mm. The boosted microwave absorption can be ascribed to the porous core-shell structure and introduction of magnetic particles. The coordination between the microporous morphology and the core-shell structure is conducive to improving the attenuation coefficient and achieving good impedance matching. The porous core-shell structure provides large solid-void and CoFe2O4−C interfaces to induce interfacial polarization and extend the electromagnetic waves' multiple scattering and reflection. Furthermore, natural resonance, exchange resonance, and eddy current loss work together for the magnetic loss. This method provides a practical solution to prepare core-shell structure microwave absorbents. [ABSTRACT FROM AUTHOR]