The construction of carbon-coated Fe3O4 yolk-shell nanocomposites based on volume shrinkage from the release of oxygen anions for wide-band electromagnetic wave absorption.

The demand for microwave absorbing materials with strong absorption capability and wide absorption band is increasing due to serious electromagnetic interference issues and defense stealth technology needs. Here the carbon-coated Fe3O4 (Fe3O4@C) yolk-shell composites were successfully synthesized in a large scale for the application of microwave absorption through an in-situ reduction process from carbon-coated γ-Fe2O3 precursor. The results show that the Fe3O4 nanoparticles are uniformly coated with a thin carbon layer about 10nm in thickness and a clear void about 1 nm in width between Fe3O4 core and carbon shell are formed due to the volume shrinkage during the reduction treatment. The obtained yolk-shell composites exhibit excellent microwave absorption properties. The absorption bandwidth with RL values exceeding -10dB is up to 5.4GHz for the absorber with a thickness of 2.2mm. The optimal RL can reach up to -45.8dB at 10.6GHz for the composite with a thickness of 3.0mm. The outstanding microwave absorption properties may be attributed to the multiple interfacial polarization, good impedance match and multiple reflections and scattering owing to the unique yolk-shell structures.