Mesoporous CoFe alloy@SiO2 nanocapsules with controllable Co/Fe atomic ratio for highly efficient tunable electromagnetic wave absorption

Exploring new types of electromagnetic wave absorption materials with lightweight, strong and tunable wideband absorption are highly desirable but remains a significant challenge. Herein, hybrid composites consisting of mesoporous CoFe nanoparticles embedded within SiO2 nanocapsules have been rationally synthesized. By controlling the experimental conditions, the CoxFe3-x@SiO2 nanocapsules with different Fe/Co atomic ratio can be obtained. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images indicate that the as-prepared FeCo nanoparticles with relative porous structure are well embedded in the SiO2 shell to form the unique nanocapsule structure. Duo to the increasement in the Co content, these nanocapsules exhibit a higher coercivity and result in the high resonance frequency. The effect of Fe/Co molar ratio on the complex permittivity, complex permeability and reflection loss (RL) in the frequency range of 2–16 GHz has been studied. The results demonstrate that the frequency of absorption peak and the width of effective absorption band can be effectively controlled by adjusting the content of Co atom in CoxFe3-x@SiO2 nanocapsules. It indicates that, at the thickness of 2 mm, a minimum reflection loss of −19.93 dB at 13.37 GHz can be gained and an effective absorption bandwidth (RL < −10.0 dB) of 4.29 GHz can be achieved. It is expected that these novel nanocapsules can be good candidates for using as new types of microwave absorption materials with lightweight.