Regulating lignin content to obtain excellent bamboo-derived electromagnetic wave absorber with thermal stability

Biochar decorated with inorganic magnetic materials has both conductivity and magnetism, and has application prospects in many fields. Synthesis of magnetic biochar composites by in-situ pyrolysis of inorganic precursor (metallic cations or oxide) doping biomass-based composites has been widely reported. However, the chemical composition of biomass is complex and changeable, which is an important and easily neglected factor that affects the inorganic material loading characteristics. Here, we took bamboo as an example biomass material, regulated the chemical components by delignification, and then prepared a series of magnetic biochar by in-situ decoration of inorganic material (Fe3O4) followed by high-temperature pyrolysis phase transition. The lignin content is found to directly affect the absorption efficiency of Fe2+/Fe3+ cations, and then affect the loading amount of magnetic phase as well as the graphitization degree of biochar after carbonization. The formed Fe3C/biochar composites from delignified bamboo with cellulose, hemicellulose and lignin content of 53.8, 39.2 and 7.0 respectively (termed as A4), exhibit excellent EMW absorption capacities with the lowest RLmin value of -45.60 dB and a broad maximal f(e) regions of 5.5 GHz when the thickness is under 2.00 mm. In addition, due to the excellent thermal stability of A4, the EMW absorption performance is maintained at temperature as high as 85C. Our work reveals the adsorption mechanism of cations onto biomass materials and puts forward a top-down method for designing inorganic decorated biochar with excellent EMW absorption behavior and thermal stability.