Combinatorial Structural Engineering of Multichannel Hierarchical Hollow Microspheres Assembled from Centripetal Fe/C Nanosheets to Achieve Effective Integration of Sound Absorption and Microwave Absorption

Electromagnetic radiation and noise pollution are two of the four major environmental pollution sources. Although various materials with excellent microwave absorption performances or sound absorption properties have been manufactured, it is still a great challenge to design materials with both microwave absorption and sound absorption abilities due to different energy consumption mechanisms. Herein, a combination strategy based on structural engineering was proposed to develop bi-functional hierarchical Fe/C hollow microspheres composed of centripetal Fe/C nanosheets. Both of the interconnected channels created by multiple gaps among the adjacent Fe/C nanosheets and the hollow structure have positive effects on the absorbing performances by promoting the penetration of microwaves and acoustic waves and prolonging action time between microwave energy and acoustic energy with materials. In addition, a polymer-protection strategy and a high-temperature reduction process were applied to keep this unique morphology and further improve the performances of the composite. As a result, the optimized hierarchical Fe/C–500 hollow composite exhibits a wide effective absorption bandwidth of 7.52 GHz (10.48–18.00 GHz) at only 1.75 mm. Furthermore, the Fe/C–500 composite can effectively absorb sound wave in the frequency of 1209–3307 Hz, basically including part of the low frequency range (