A clean bamboo-based carbon-iron multi-interface complex for electromagnetic radiation attenuation and thermal insulation

Civilian electromagnetic wave (EMW) absorbers are urgently needed to solve the excessive electromagnetic (EM) radiation energy pollution. Biomass, such as wood and bamboo, has a wide range of sources, is porous, and is suitable for forming functional composites. However, the diverse composition and microstructure directly affect the EM and thermal properties of conversion composites, and the corresponding influencing mechanisms are unclear. Here, a series of iron-containing biochar-based composites (CFBs) were synthesized by in-situ pyrolysis of impregnated flattened bamboo sliced veneers with Fe(acac)₃ dimethylformamide (DMF) solutions. The components and microstructures were pre-regulated through moisture-heat coupling softening, flattening and slicing treatments. Excellent EMW absorption performance with a $\left|{RL}_{\min }\right|$ value as large as 33.03 dB was obtained for CFB-0.8 at a fixed thickness of 1.15 mm, along with the widest effective frequency bandwidth as large as 4.08 GHz. Besides, In addition, CFB-0.8 has stable Joule heating performance (0.9V, 79.7 °C), and its in-plane thermal conductivity is 31.4 times that of flattened bamboo (0.62 W m⁻¹ K⁻¹). These are attributed to the rich heterojunction interfaces, electromagnetic attenuation caused by structures (porous structure scattering, nanoscale effects), deep absorption mechanisms caused by defects (lattice defects, electric field concentration, non-uniform carbonization structures), and thermal conversion. This work provides theoretical and experimental data for developing EMW absorption materials and new ideas for the high-value utilization of biomass materials and the continuation of their carbon fixation life.