Construction of air/SiO2@Fe/C yolk-shell nanospheres for boosted low frequency electromagnetic wave absorption

Using air/SiO₂@Fe/C yolk-shell nanospheres (NSs) absorbers as a carrier, this research studies the coupling relationship between low-frequency electromagnetic wave (EMW) absorption performance and construction of materials with dual-sized pores and dual-component. Endured via synergistic process of pyrolysis and etching, the sizes of large cavities (~ 200 nm) and mesopores (~ 10 nm) were finely tuned at near-atomic scales. In addition, plenty of polarization attenuation structures (e.g., cavities/carbon, cavities/silica, iron/carbon and defects) were also generated. Results revealed that construction of multi-scale pores has slender contribution on the peak reflection loss (RL_min) values, while EMW absorption in the low-frequency range was obviously enhanced. The resulted H12 sample presented a resonance reductions at 6.72 GHz with the RL_min value of -22.4 dB, which shifted ~9.8 GHz towards lower frequencies compared to H0 (-20 dB, 16.52 GHz). This case can be elucidated via the resonance mechanism of cavity, where the air/SiO₂@Fe/C yolk-shell NSs function as dielectric resonators. This work offers a novel way to design the micro/nano-scale pores in carbon-based EMW-absorbing materials, and a promising approach to develop materials designed for low-frequency EMW absorption.