Facile, Large-Scale, and Expeditious Synthesis of Hollow Co and Co@Fe Nanostructures: Application for Electromagnetic Wave Absorption

Hollow metal materials have drawn a lot of attention owing to their excellent performance for wide potential applications. Here we have successfully synthesized hollow Co nanostructure with controllable structures and compositions, including hollow Co nanospheres, hollow Co nanochains, and hollow Co@Fe nanospheres. Uniform Fe nanospheres and nanochains are first synthesized; then, Fe@Co nanospheres are achieved by electroless plating cobalt on iron surfaces. Hollow Co nanostructures are obtained easily by galvanic cell reaction between Co shells and Fe cores in hydrochloric acid at room temperature. Furthermore, hollow Co@Fe nanospheres form after plating iron on the as-synthesized hollow Co nanospheres, which acted as templates. Electromagnetic (EM) wave absorption properties of hollow Co nanostructures are investigated. Hollow Co nanochains, when blended with 40 wt % in paraffin-based filler, exhibit better EM wave absorption (−42.5 dB) than the hollow Co nanospheres (−30.4 dB) with same ratio of filler. On the contrary, because the filler content is 60 wt %, the reflection loss of hollow Co nanochains degrades to −14.0 dB, which is much worse compared with hollow Co nanospheres (−41.7 dB). Moreover, hollow Co@Fe nanospheres (with 60 wt % filler) show excellent EM wave absorption properties with minimum RL of −47.3 dB and effective bandwidth of 4.8 GHz compared with hollow Co nanospheres. The method of electroless plating followed by galvanic cell reaction to synthesize hollow nanostructures is simple, robust, and widely applicable for some metals or composites with various potential.