Dimensionality-driven sustainable biocarbon-based microwave absorbers: From bio-waste to functional materials

In the quest for a sustainable economy and an electromagnetic pollution-free environment, microwave absorbers have garnered significant interest. Researchers are diligently investigating the use of precursors derived from bio-waste materials, such as agricultural waste, sewage sludge, and animal waste, to promote a greener future. The electromagnetic wave (EMW) absorption characteristics of biocarbon are intricately linked to its morphology, dimensionality, microstructure, and composition, which are influenced by the biocarbon precursor, carbonization technique, and temperature. Herein, we summarized the recent advances in the synthesis approaches of microwave absorption materials. Then, based on EMW absorption theory, the microwave absorption of pure and biocarbon-based composite absorbers has been discussed in detail. Since biocarbon keeps its natural morphology after carbonization we classified the biocarbon-based absorbers into three categories: 1) 1D microstructures, 2) 2D flaky microstructures, and 3) 3D porous microstructures. In addition, the effect of surface modifications and doping of these microstructures with different dielectric/magnetic compounds have been analyzed. By comparative analysis of reported literature on these microstructures, 3D porous biocarbon microstructures and their composites emerge as the most promising candidates as low-cost and efficient EMW absorbers. Finally, we discussed the prospect of low-cost, low-density, highly efficient microwave absorbers obtained from waste-derived biocarbon.