Yolk-shell structured Co@SiO2@Void@C nanocomposite with tunable cavity prepared by etching of SiO2 as high-efficiency microwave absorber.

Nowadays, high-performance microwave absorption materials with light weight, strong absorbing intensity and wide absorption bandwidth are urgently demanded to solve the electromagnetic pollution issues. In this work, the yolk-shell structured Co@SiO2@Void@C nanocomposites with tunable cavity are obtained by etching SiO2 in the Co@SiO2@C nanoparticles. They exhibit better microwave absorption properties than the unetched counterpart. When the etching time is 6 h, the Co@SiO2@Void@C nanocomposite shows high absorption efficiency with a minimum reflection loss (RL) value of -44.5 dB at 8.8 GHz. Notably, its effective absorption bandwidth (RL < -10 dB) is as wide as 8.0 GHz (9.7-17.7 GHz) at a thin thickness of only 1.7 mm. The excellent microwave absorbing performances are attributed to the abundant heterointerfaces, well-controlled cavity, synergistic effects between magnetic and dielectric loss, and optimal impedance matching. Owing to the characteristics of strong absorbing capacity, ultrabroad absorption bandwidth and thin matching thickness, the yolk-shell structured Co@SiO2@Void@C nanocomposites are promising candidates as highly effective microwave absorbers.