Salt/microwave co-assisted graphitization of wheat straw lignocelluloses towards porous carbon low-frequency electromagnetic absorbent.

The critical risks to human health and the significant interference of electromagnetic (EM) radiation with electronic equipment highlight the limitations of conventional EM absorbers in providing high attenuation, low density and sustainable material sourcing. Biomass-derived carbon is attractive yet fundamentally constrained by low graphitisation and insufficient loss pathways. Herein, we introduce a salt-microwave synergistic transformation that achieves concurrent pore construction and graphitisation, outperforming existing biochar engineering routes. Microwave activation preconfigures a defect-rich, interconnected porous framework, while salts function as ionically dynamic media that accelerate carbon mobility and direct the formation of ordered graphitic domains. The cooperative regulation constructs a hierarchical dissipation system in which engineered porosity enhances wave trapping, salt-induced graphitisation boosts conductive loss and abundant heterogeneous interfaces strengthen the polarisation loss, collectively yielding well-balanced impedance matching. The optimised porous carbon-based absorber delivers superior minimum reflection loss of -57.31 dB and effective absorption bandwidth of 3.82 GHz, thereby verifying its application potential. Overall, this study establishes a general strategy for converting low-value biomass into high-performance EM functional carbon materials and elucidates the mechanisms of salt-microwave co-assisted graphitisation for porous carbon to achieve enhanced EM attenuation properties.