Enhanced interfacial polarization through the conversion of Co@C into Co@Co1−xS@C nanocapsules utilizing a facile sulfidation process

Abstract

The design and development of efficient Co-based electromagnetic (EM) absorbents with double-shell structures have received relatively less attention in the literature. The construction of multiple heterointerfaces gives rise to a unique morphology that holds significant potential in expanding the absorbing frequency range. Co@Co1−xS@C nanocapsules (NCs) with Co as the cores, Co1−xSx and C as the middle and outside shells separately, were successfully prepared using a facile two step process: synthesizing Co@C core–shell NCs by arc-discharge method and subsequently converting them into Co@Co1−xS@C NCs through chemical sulfidation reaction. The experimental results indicate that the thickness of the carbon shell exhibits a decreasing trend (from 1 ± 0.1 nm to 0.6 ± 0.02 nm) following the post-sulfidation process, lasting for approximately two hours. The defect density of the carbon shell also declines from 1.88 × 1011 cm−2 to 1.14 × 1011 cm−2. The reduction in thickness of the carbon shell and the formation of new Co1-xS not only enable efficient manipulation of impedance matching between the dielectric shells and magnetic cores but also facilitate the construction of multiple interfacial polarizations. The study provides evidence that the multi-interfacial Co@Co1−xS@C nanocomposite serves as an effective EM absorbent achieving a minimum reflection loss (RL) up to –78.6 dB at a thickness of merely 1.52 mm within the frequency range of 2~18 GHz.