The synergistic effects of carbon coating and micropore structure on the microwave absorption properties of Co/CoO nanoparticles

Abstract

25 nm carbon-coated microporous Co/CoO nanoparticles (NPs) were synthesized by integrating chemical de-alloying and chemical vapor deposition (CVD) methods. The NPs possess micropores of 0.8–1.5 nm and display a homogeneous carbon shell of about 4 nm in thickness with a low graphitization degree. The saturation magnetization (M_S) and coercivity (H_C) of the NPs were 70.3 emu g⁻¹ and 398.4 Oe, respectively. The microporous Co/CoO/C NPs exhibited enhanced microwave absorption performance with a minimum reflection coefficient (RC) of −78.4 dB and a wide absorption bandwidth of 8.1 GHz (RC ≤ −10 dB), larger than those of the nonporous counterparts of −68.3 dB and 5.8 GHz. The minimum RC values of the microporous Co/CoO/C NPs at different thicknesses were much smaller than the nonporous counterparts. The high microwave absorption mechanism of the microporous Co/CoO/C nanocomposite can be interpreted in terms of the interfacial polarization relaxation of the core/shell and micropore structures, the effective permittivity modification of the air in the micropores and the polarization relaxation of the defects in the low-graphitization carbon shell and the porous Co NPs. Our study demonstrates that the microporous Co/CoO/C nanocomposite is an efficient microwave absorber with high absorption intensity and wide absorption bandwidth.