Mesoporous Fe/C and Core–Shell Fe–Fe3C@C composites as efficient microwave absorbents

• Mesoporous Fe/C and core–shell Fe–Fe3C@C absorbents were designed and synthesized.
• Fe/C and Fe–Fe3C@C absorbents process high surface area of 467.3 and 259.5 m2/g.
• The bandwidth reaches 3.36 and 5.04 GHz when the matching thickness is 2 and 1.5 mm.

Mesoporous Fe/C and core–shell Fe–Fe3C@C composites were successfully prepared through the in-situ polymerization of Fe3+/phenolic resin coupled with F127 and the subsequent high-temperature carbonization. The experiments involved the preparation of an iron-containing carbon precursor and the heat-treatment process. Two composites with different morphology and structure could be obtained by changing the content of Fe(NO3)3·9H2O in the precursor. The crystalline phase, structure and microwave absorption of the two composites were investigated. Fe particles were uniformly embedded into the mesoporous networks to form mesoporous Fe/C composite with high surface area of 467.3 m2/g and low density of 1.92 g/cm3. The Fe–Fe3C particles encapsulated by graphitized carbon layers formed the core–shell structure with surface area and density of 259.5 m2/g and 2.67 g/cm3. Fe/C and Fe–Fe3C@C composites exhibited excellent electromagnetic absorbing ability, the effective absorption bandwidth reached 3.36 and 5.04 GHz with the matching thicknesses of 2 and 1.5 mm correspondingly. This originated mainly from the effective impedance match and multiple interfacial polarizations. Furthermore, the increase of Fe3+ not only promoted the graphitization degree of carbon shell, but also increased the complex permittivity and permeability of core–shell structure, thus improved the impedance matching. Owing to high surface area, low density and excellent microwave absorbability, the mesoporous Fe/C and core–shell Fe–Fe3C@C composites are promising candidates as lightweight and high-efficiency microwave absorbents.

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