Carbon-Coated Octahedral Fe₃O₄/Fe₂O₃ Nanocomposites for Enhanced Electromagnetic Wave Absorption

The application of heterostructures and complex morphology has been favored by researchers of electromagnetic wave-absorbing materials. Herein, Fe3O4/Fe2O3/C composites with carbon-coated octahedral structures were prepared and obtained using a polymer self-assembly-guided nonhomogeneous structure engineering strategy to form hierarchical polyhedral structures (200–400 nm in size). The electrostatic attraction of anionic polyacrylamide (APAM) is used to chelate Fe3+. Due to the synergistic effect of intermolecular forces, APAM can be used as a “bridge” to connect multiple micellar particles, and this bridging and entanglement effect facilitates the formation of octahedral Fe3O4/Fe2O3. Compared with nanoparticles, the octahedral structure easily forms a conductive network, and the presence of sharp corners can effectively promote the concentration of charge, promote polarization loss, and extend the reflection and scattering path. Through the high-temperature reduction of APAM, the conversion of part of Fe2O3 to Fe3O4 is realized, which effectively improves the electromagnetic parameters and thus optimizes the impedance matching. Meanwhile, the synergistic effect between the magnetic loss (ferromagnetic resonance) of Fe3O4 and the dielectric loss (interfacial polarization, dipole polarization, and conduction loss) of Fe3O4/Fe2O3/C enhances the absorption of electromagnetic waves. Unsurprisingly, the synthesized Fe3O4/Fe2O3/C composites exhibit excellent EMW absorption performance, with a reflection loss of up to −34.7 dB at 30% paraffin filler ratio and an effective absorption bandwidth (EAB) of 8.64 GHz at 1–3 mm.