Enhanced Microwave Absorption Performance from Abundant Polarization Sites of ZnO Nanocrystals Embedded into CNTs via Confined Space Synthesis
Dielectric composites constructed by carbon and metal oxides have been becoming a hot topic, however, the strategy to strengthen the coupling of components still needs to be optimized to enhance dielectric loss. Here, ultra-fine ZnO derived from ZIF-8 are uniformly distributed and tightly embedded in multi-wall carbon nanotubes (C-ZnO@CNTs) via a novel confined space synthesis. Due to the presence of polypyrrole coating, ZnO nanocrystals can be formed in the space of the original polyhedron and inserted into CNTs, promoting the generation of polarized CNTs and providing abundant polarization centers on CNTs. The composites exhibited a superior microwave absorption capacity with a reflection loss values up to −48.2 dB at 6.0 GHz, and the effective bandwidth can reach 14.9 GHz by adjusting the thickness. By the geometric phase analysis, the strain driven by the tight-coupling between ZnO-CNTs is confirmed to be existed in the interfaces, boosting the instinct electromagnetic properties. The improved dielectric loss is caused by the strong interfacial polarization among ZnO-ZnO or ZnO-CNTs and the conductive loss among intertwined CNTs network, revealing by electron holography. Therefore, the overall electrical properties can be improved by the polarized C-ZnO@CNTs with high electron conductivity. The confined space strategy may have a promising potential to synthesize new composites of polarized carbon materials tightly coupled with metal oxides nanocrystals.