Carbon-Coated OctahedralFe₃O₄/Fe₂O₃ Nanocompositesfor Enhanced ElectromagneticWave 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.