Efficient microwave absorption induced by hierarchical pores of reed-derived ultralight carbon materials

[Display omitted] •Ultralight carbon absorbers with tunable pores were synthesized from waste reed.•The prepared carbon had efficient microwave absorption at a low loading of 10 wt.%.•The RLmin value of -63.9 dB and the widest bandwidth of 7.6 GHz were revealed.•The wave absorption properties were related to the hierarchical pores of carbon. Manipulation on pore structure is an effective approach to reinforce electromagnetic wave absorption function of carbon-based materials. Herein, ultralight carbon materials with hierarchical pores are facilely synthesized from the waste reed through one-step calcination process. Through regulating the porous structure and complex permittivity of pure carbon, it can be found that the strongest microwave absorption peaks appear in different frequency range and shift from a high frequency of 17.2 GHz to a low frequency of 5.1 GHz. The unique cellular structure with hollow microchannels contributes to the conduction loss and multiple scattering, while the formation of abundant nanopores enhances the polarization loss, resulting in excellent microwave absorption performance. Under a low filler loading of 10 wt.%, the remarkable reflection loss reaches -63.9 dB at 10.8 GHz, and the effective absorption bandwidth as wide as 7.6 GHz. Moreover, by controlling the thickness (1.8-5.5 mm), the absorption bandwidth less than -20 dB ranges from 4.6 GHz to 18 GHz. This work offers the relevance of porous structure and wave absorption properties of pure carbon materials and provides a feasible strategy to design absorbers with efficient microwave absorption performance.