Molten Salt Preparation of Rice Husk Biocarbon for Lightweight and Efficient Microwave Absorption

Electromagnetic (EM) pollution poses a threat to human health and electronic devices. Thus, there is a urgent need to develop low-cost microwave absorbing materials featured by lightweight and high efficiency. Herein, porous biocarbons are facilely obtained via heating rice husk in Li₂CO₃ melt within 750–850 °C. Impact of temperature on the pore and structural properties of biocarbons are investigated. ORH800, prepared at 800 °C, displays the optimal microwave absorption performance likely because of its high dielectric-loss capacity and decent impedance matching. The minimum reflection loss (RL_min) is -64.4 dB at frequency of 5.65 GHz in C band (4–8 GHz). The maximum effective absorption bandwidth (EAB) is 3.6 GHz at thickness of 2.1 mm. Carbonization and activation of biomass in Li₂CO₃ melt can generate mesopores, defective carbon structures and polar groups for biocarbons, contributing to the excellent microwave absorption performance of ORH800.