Pore-regulation in 2D biochar-based flakes towards wideband microwave absorption.

• Porous biochar from waste bamboo is used for electromagnetic wave absorption. • Porous structure improves electromagnetic wave absorption performance. • The good hydrophobicity of porous biochar helps in practical applications. The rational use of agroforestry waste and the development of highly efficient electromagnetic wave absorbing materials have attracted a lot of attention. Carbon based electromagnetic wave absorbing materials derived from agroforestry waste have the advantages of low density, stable physicochemical properties, and therefore they became a research hotspot. However, the good conductivity, high permittivity of pure carbon materials are prone to electromagnetic mismatch, which limits their further applications. In this paper, a series of 2D biochar-based flakes with different pore sizes were prepared by pyrolysis of cellulose from bamboo wood, followed by chemical etching, using waste bamboo as an example. The increase of the etching time directly affected the pore size of the material, which affected its dielectric properties. It was shown that the pores of biochar-based flakes (PGC-6) with macroporous structure obtained by 6 h of etching provided an ideal impedance match an enhanced polarization effect, which made it an excellent electromagnetic wave absorber. The lowest RL value of PGC-6 is −15.8 dB, while the absorption bandwidth achieves 3.8 GHz at 1.70 mm. This study provides a viable pathway for the reuse of agroforestry waste. [ABSTRACT FROM AUTHOR]