Hollow nitrogen-doped carbon nanofibers filled with MnO₂ nanoparticles/nanosheets as high-performance microwave absorbing materials

The nitrogen-doped carbon nanofiber absorber (MnO₂@HNCFs) filled with MnO₂ nanoparticles/nanosheets is constructed through layer-by-layer coating assisted by vacuum carbonization and etching. The MnO₂ nanoparticles/nanosheets filled in the hollow carbon fibers make the material exhibit a hierarchical porous structure, and reduce the density of the material as well. MnO₂@HNCFs show excellent microwave absorbing properties, with a minimum reflection loss (RL_min) of −48.87 dB@14.9 GHz at a low loading of 10%, and the thickness is 2.5 mm. The corresponding effective absorption bandwidth (EAB) is 6.2 GHz, covering the entire Ku-band. When the thickness is adjusted to 2.8 mm, the EAB is up to 7.8 GHz and the RL_min is −32.17 dB. The EAB is 5.7 GHz at 3.4 mm, covering the X-band, and the RL_min is −30.62 dB. Through the comparison of the absorbing properties of materials, it is proved that the construction of porous structures can effectively enhance the absorbing properties, which provides a solid argument for the claim that multiple reflection can enhance the electromagnetic wave loss. This work is of great significance to the construction of porous structure microwave absorbing materials, and provides a new idea for the design of lightweight microwave absorbing materials.