Biomass-Derived Porous Carbon Materials for Tunable Microwave Absorption with Excellent Low-Frequency Performance

Biomass-derived porous carbon (BPC) is promising for sustainable and cost-efficient microwave absorption (MA), but its absorption frequencies are primarily concentrated in the mid- and high-frequency ranges (8–18 GHz), posing challenges for low-frequency applications crucial to 5G and radar technologies. Herein, we report a novel strategy to tune the BPC absorption frequency effectively. The absorption frequency is shifted from the Ku-band (12–18 GHz) to the C-band (4–8 GHz) by engineering nitrogen (N) concentration in corn-cob-pith-derived carbon materials through appropriate thermal treatment. Furthermore, the low-frequency absorption performance is enhanced by the porous structure activated by KOH. As a result, the optimized sample achieves superior low-frequency absorption in humid and corrosive environments, with a minimum reflection loss (RLmin) of −53.92 dB at 7.84 GHz (C-band) at 3.03 mm thickness and an ultrawide maximum effective absorption bandwidth (EABmax) of 6.56 GHz at 2.0 mm. Moreover, another high-frequency absorption sample can also be obtained by tuning the thermal treatment and KOH activation parameters, which exhibits an RLmin of −47.31 dB at 15.84 GHz (Ku-band) at 2.59 mm and an EABmax of 8.08 GHz at 3.0 mm. This research presents an innovative approach to design and fabricate high-performance BPC microwave absorbers for both low-frequency and high-frequency applications.