Oxygen-vacancy-rich Fe3O4/carbon nanosheets enabling high-attenuation and broadband microwave absorption through the integration of interfacial polarization and charge-separation polarization

Metal-oxide/carbon composites with remarkable dielectric-magnetic properties are promising as microwave absorption materials, but achieving high-attenuation and broadband microwave absorption properties still remains challenging. Herein, we develop a one-step carbonization of the ferric gluconate precursor to manufacture two-dimensional oxygen-vacancy-rich Fe3O4/carbon nanosheets (Fe3O4/C) for high-attenuation microwave absorption. The key to the synthesis is employing the Fe3+-gluconate complex as the precursor, which has the ability to release small molecules within the viscosity foaming window to spontaneously obtain a 3D self-foamed material. Followed by high-temperature annealing, the as-obtained Fe3O4/C hybrid composite features large lamellar (>20 μm) carbon nanosheets with abundant yolk–shell heterostructures and highly dispersed and high-loaded (∼44%) oxygen-vacancy-rich Fe3O4 nanocrystals. The unique 2D structure could facilitate multiple scattering absorption and interconnect into a 3D conductivity-loss network. Meanwhile, the abundant yolk–shell heterostructures could trigger extra interfacial polarization. And density functional theory calculation results demonstrate that oxygen vacancies endow magnetic Fe3O4 nanocrystals with charge-separation induced polarizations. Consequently, Fe3O4/C exhibit superior microwave absorption capability with an impressive reflection loss (RL) of −65.4 dB and an ultra-broad effective absorption bandwidth of 6.24 GHz. The spontaneous foaming strategy in this work could provide feasible technological approaches for the practical fabrication of microwave absorption materials.