A “Cure-in-the-Cause” Strategy: Transforming Waste Cork into Labyrinthine Porous Carbon with Exceptional Microwave Absorption Performance via DES-Mediated Component Redistribution

Biomass-derived carbon materials are promising for electromagnetic wave (EMW) absorption. However, the inherent structural rigidity of raw biomass severely restricts the microstructural tunability of its carbonized derivatives, limiting their scalable fabrication and high-performance EMW absorption applications. To address this issue, a “cure-in-the-cause” strategy is proposed based on deep eutectic solvent (DES)-mediated redistribution of cork components, with no external additives required. Notably, DES plays a vital role in pore structure regulation by selectively dissolving lignin and part of the suberin from raw cork. The subsequent regeneration of these dissolved components on the cork surface induces controllable shrinkage and deformation of the cork cell lumens, thereby not only constructing a labyrinthine porous structure but also achieving precise modulation of the material’s microstructure. After carbonization, the labyrinthine porous structure is well retained, forming a porous carbon framework with tunable pore size, graphitization degree, and nitrogen doping. Benefiting from the well-regulated microstructure, the obtained sample C-R-DLC 1000 exhibits superior EMW absorption performance at a thickness of 1.44 mm, with a minimum reflection loss of −77.5 dB and an effective absorption bandwidth of 4.32 GHz (13.12–17.44 GHz), which nearly covers the entire Ku-band. This facile, low-cost “cure-in-the-cause” strategy provides a viable route for the high-value transformation of waste biomass into advanced EMW absorbers and offers a universal pathway strategy for microstructure engineering of biomass-derived functional materials.