Facile synthesis of CoFe2O4@SiO2 nanoparticles anchored on reduced graphene oxide for highly efficient electromagnetic wave absorption

Abstract

In this study, a ternary composite material composed of CoFe₂O₄@SiO₂ nanospheres and reduced graphene oxide (RGO) was successfully synthesized through a facile route. The composites exhibited a layered "sandwich" structure, where CoFe₂O₄@SiO₂ nanospheres were anchored onto the surface of RGO nanosheets. The microstructure and electromagnetic wave absorption properties of the synthesized CoFe₂O₄@SiO₂/RGO were systematically investigated. Results revealed that the composites possessed excellent electromagnetic wave absorption performance, with a minimum reflection loss (RL) of -27.7 dB at 13.02 GHz for a thickness of 1.8 mm. Furthermore, the composites exhibited a broad absorption bandwidth of up to 14.52 GHz (3.48-18 GHz) with reflection losses less than -10 dB over a thickness range of 1.5 to 5.0 mm, covering the S-Ku band. The enhanced absorption performance could be attributed to the optimized impedance matching and synergistic electromagnetic loss mechanisms. The CoFe₂O₄@SiO₂/RGO composites demonstrated balanced dielectric and magnetic loss, enabled by the effective interaction of electromagnetic parameters. These results indicate that the developed composites provide a promising candidate for high-performance microwave absorbing materials with lightweight, strong absorption, and broad bandwidth characteristics, potentially applicable in military stealth technology, electromagnetic compatibility enhancement, and ecological protection.

Fig. 1. Schematic illustration of the preparation of CoFe₂O₄@SiO₂/RGO.

Fig. 2. TEM images of (a) CoFe₂O₄, (b) CoFe₂O₄/RGO, (c) CoFe₂O₄@SiO₂ and (d) CoFe₂O₄@SiO₂/RGO composites.

Fig. 3. SEM images of (a) CoFe₂O₄, (b) CoFe₂O₄/RGO, (c) CoFe₂O₄@SiO₂ and (d) CoFe₂O₄@SiO₂/RGO composites and (e–h) the corresponding EDS spectra.

Fig. 4. (a) XRD spectra of RGO, CoFe₂O₄, CoFe₂O₄/RGO, CoFe₂O₄@SiO₂ and CoFe₂O₄@SiO₂/RGO nanocomposites and (b) Raman spectra of GO, RGO, CoFe₂O₄/RGO and CoFe₂O₄@SiO₂/RGO nanocomposites.

Fig. 5. VSM measurement results of CoFe₂O₄, CoFe₂O₄/RGO, CoFe₂O₄@SiO₂, CoFe₂O₄@SiO₂/RGO nanocomposites.

Fig. 6. Frequency dependence of (a) the real part of complex permittivity ε′, (b) the imaginary part of complex permittivity ε′′, (c) the real part of complex permeability μ′, (d) the imaginary part of complex permeability μ′′, (e) dielectric loss tan δ_ε and (f) magnetic loss tan δ_μ of CoFe₂O₄, CoFe₂O₄/RGO, CoFe₂O₄@SiO₂ and CoFe₂O₄@SiO₂/RGO nanocomposites.

Fig. 7. (a) Typical Cole–Cole semicircles, (b) C₀ (representing eddy current loss) versus frequency of CoFe₂O₄, CoFe₂O₄/RGO, CoFe₂O₄@SiO₂ and CoFe₂O₄@SiO₂/RGO nanocomposites, and (c) attenuation constant of CoFe₂O₄, CoFe₂O₄/RGO, CoFe₂O₄@SiO₂ and CoFe₂O₄@SiO₂/RGO nanocomposites.

Fig. 8. Reflection loss curves of (a) CoFe₂O₄, (b) CoFe₂O₄/RGO, (c) CoFe₂O₄@SiO₂ and (d) CoFe₂O₄@SiO₂/RGO composites with a thickness in the range of 1.5–5.0 mm, and (e–h) the corresponding three dimensional presentation.

Fig. 9. (a) Frequency dependence of the RL with different thicknesses, (b) the simulations of the absorber thickness (t_m) versus peak frequency (f_m) under quarter-wave thickness criterion, and (c) the relationship between the impedance matching characteristics (Z = |Z_in/Z₀|) and the EMW frequency of CoFe₂O₄@SiO₂/RGO composite.

Fig. 10. Schematic of the EMWs absorbing mechanisms in CoFe₂O₄@SiO₂/RGO composites.