This paper demonstrates a facile and low-cost carbothermal reduction preparation of monodisperse Fe3O4/C core-shell nanosheets (NSs) for greatly improved microwave absorption. In this protocol, the redox reaction between sheet-like hematite (α-Fe2O3) precursors and acetone under inert atmosphere and elevated temperature generates Fe3O4/C core-shell NSs with the morphology inheriting from α-Fe2O3. Thus, Fe3O4/C core-shell NSs of different sizes ( a) and Fe3O4/C core-shell nanopolyhedrons are obtained by using different precursors. Benefited from the high crystallinity of the Fe3O4 core and the thin carbon layer, the resultant NSs exhibit high specific saturation magnetization larger than 82.51 emu·g-1. Simultaneously, the coercivity enhances with the increase of a, suggesting a strong shape anisotropy effect. Furthermore, because of the anisotropy structure and the complementary behavior between Fe3O4 and C, the as-obtained Fe3O4/C core-shell NSs exhibit strong natural magnetic resonance at a high frequency, enhanced interfacial polarization, and improved impedance matching, ensuring the enhancement of the microwave absorption. The 250 nm NSs-paraffin composites exhibit reflection loss (RL) lower than -20 dB (corresponding to 99% absorption) in a large frequency ( f) range of 2.08-16.40 GHz with a minimum RL of -43.95 dB at f = 3.92 GHz when the thickness is tuned from 7.0 to 1.4 mm, indicating that the Fe3O4/C core-shell NSs are a good candidate to manufacture high-performance microwave absorbers. Moreover, the as-developed carbothermal reduction method could be applied for the fabrication of other composites based on ferrites and carbon.
Keywords: Fe3O4/C composites; carbothermal reduction; core−shell structures; magnetic properties; microwave absorption; nanosheets.