Biomass-derived fire-retardant porous carbon towards efficient electromagnetic wave absorption and shielding

Biomass-derived carbon materials show great potential in electromagnetic wave (EMW) absorption and shielding. However, their flammability presents a challenge for practical applications. Herein, we present a novel strategy for preparing biomass-derived fire-retardant porous carbon materials with enhanced EMW absorption and shielding performance. We obtained two carbon materials through phosphorylation and alkali etching of natural balsa wood: phosphorylated carbonized wood (PCW) and hierarchical porous phosphorylated carbonized wood (HP-PCW). Phosphorylation lowered the carbonization temperature, imparting excellent flame retardancy and improved impedance matching. Alkali etching, on the other hand, adjusts the graphitization degree of the material without altering the carbonization temperature. As a result, we successfully achieved outstanding EMW absorption and shielding performance at a relatively low annealing temperature of 660 °C. Specifically, PCW demonstrated a remarkable minimum reflection loss of −59.8 dB, with an effective absorption bandwidth covering the entire X-band (8.2–12.4 GHz) across a wide thickness range. HP-PCW demonstrated an EMW shielding effectiveness of 52 dB within the X-band. These carbon materials exhibit features such as lightweight (0.12–0.15 g/cm³), robust thickness sensitivity (5.7–7.3 mm), and fire-retardancy (120 s unburned in the flame), providing valuable insight into the potential large-scale engineering application of EMW compatible materials.