Green synthesis of carbon nanosheets from corn straw for high-performance electromagnetic wave absorption

The escalating electromagnetic pollution from electronic devices necessitates the development of high-performance and eco-friendly electromagnetic wave (EMW) absorbing materials. Herein, we report a facile and sustainable strategy for synthesizing ultra-thin carbon nanosheets derived from corn straw via potassium oxalate activation and subsequent carbonization. The as-prepared carbon nanosheets exhibit a unique hierarchical porous structure with a thickness of <10 nm, an ultrahigh specific surface area of 1649.7 m²/g, and a large pore volume of 0.97 cm³/g. By optimizing the pyrolysis temperature, the material achieves exceptional EMW absorption performance: a minimum reflection loss (RL_min) of −70.8 dB at 10.0 GHz with a thickness of 2.6 mm, and a broad effective absorption bandwidth (EAB) of 5.3 GHz (12.7–18.0 GHz) at 1.9 mm. Remarkably, when the thickness is varied from 1.0 mm to 5.0 mm, the cumulative EAB expands to 14.0 GHz (4.0–18.0 GHz), with RL_min values below −20 dB across 13.6 GHz (4.4–18.0 GHz). The superior performance stems from synergistic effects of impedance matching, multiple scattering/reflection, conductive loss, and polarization loss. This work not only advances biomass-derived carbon materials for next-generation EMW absorption applications but also provides a green and cost-effective pathway for repurposing agricultural waste, addressing both environmental and technological challenges.