Gong and coworkers selected the almond shells and ferric nitrate to prepare the composites. The FexOy@Biochar was prepared with the heat treatment of almond shells in different concentrations of iron nitrate solution at 600, 800 and 1000 °C, respectively. "The composite material was examined and found to have good microwave absorption properties and multi-loss synergistic effects". "Therefore, almond wood porous biomass carbon exhibits strong microwave absorbing properties" . "At high temperatures, carbon reduces iron nitrate to form a mixture of iron oxide, ferroferric oxide, and iron". In the Table , provided by Gong et al., we can find the iron-containing substances produced by the reaction at temperatures above 500 °C. For the temperature range 500-600 °C, the solid residues are of Fe(NO3)3, Fe2O3, Fe3O4. For 600-800 °C, the residues contain Fe2O3, Fe3O4, Fe. Iron (Fe) is the residue for the range 800-1000 °C.