Corncob-Derived Two-Dimensional N-Doped Carbon Sheets as the Ultrabroadband Microwave-Absorbing Material

Biomass-derived carbon is a microwave-absorbing material that has shown considerable potential for diverse applications due to advantages such as the wide range of sources and the natural multilevel structure. However, the primary issues related to pure carbon materials are their weak absorption intensity and narrow absorption band. In this study, two-dimensional N-doped carbon sheets were prepared by using corncob as the biomass precursor and melamine as the nitrogen source. After nitrogen doping, the samples attained high loss capability in the low-frequency region and enhanced impedance matching in the high-frequency region due to the combined effects of the structure, morphology, and composition on the electromagnetic parameters. Therefore, the absorption performance of the full frequency band was significantly enhanced, which was conducive to broadband absorption. The optimal sample attained a minimum RL of −57.27 dB at 14.64 GHz when the sample thickness was 2.6 mm. In addition, the effective bandwidth was up to 8.26 GHz (9.74–18.00 GHz) when the thickness was 2.9 mm. The strong absorption and broad effective bandwidth indicate that the N-doped carbon sheet can be used as a potential microwave absorber.