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Metal–organic framework (MOF)-derived materials have gained popularity as microwave absorbing materials due to their electromagnetic dissipation advantages. In this study, a special type of MOF (ZIF-L) was used as a precursor; tannic acid was introduced for chemical etching. The resulting material obtained by in situ carbonization was a hollow structure of N-doped carbon embedded by Co nanoparticles (CoHNC), which retained the original pumpkin seed shape but had a hierarchical porous structure on the inside. By adjustment of the amount of cobalt nitrate and the carbonation temperature, the electromagnetic parameters could be altered, improving impedance matching and enabling different microwave absorption properties to be obtained. At 16.96 GHz, the material exhibits an optimal reflection loss of −45.5 dB, an effective bandwidth of 3.04 GHz, and a matching thickness of only 1.4 mm with a material filler of 30 wt %. The microwave loss mechanism is formed by the dual loss mechanism with dielectric loss as the main loss and magnetic loss as the auxiliary one. Therefore, the synthesis of the CoHNC composite through simple etching provides a useful idea for optimizing microwave absorbing materials. [ABSTRACT FROM AUTHOR]

Transition metal composites doped with heteroatomic nitrogen and having a hierarchical porous structure are considered to be an effective way to improve the electromagnetic wave absorption ability of carbon-based absorbent materials. In this work, a mixture of melamine, glucose, and nickel nitrate was used as a precursor to synthesize a multi-interface carbon nanotube network with tubular morphology by one-step catalytic pyrolysis. The absorption mechanism was further discussed in detail. The composite materials have a better complementary loss mechanism and good matching impedance capability by combining carbon and magnetic Ni nanoparticles. Notably, 6.4Ni/CNTs-900 exhibits a strong reflection loss (RL) of −49.3 dB at 8.88 GHz with a low filling content of 15% and an effective bandwidth (EAB, RL < −10 dB) of 2.96 GHz. The excellent microwave absorption properties of these materials can be attributed to the multiple scattering, interface polarization, dipole polarization, and conductivity loss induced by the unique structure of the multi-interface carbon nanotube network. This work provides a method for managing electromagnetic radiation pollution, which has great potential for efficient microwave absorption. [ABSTRACT FROM AUTHOR]