Multi-dimensional ZnO@MWCNTs assembly derived from MOF-5 heterojunction as highly efficient microwave absorber

Metal-organic framework (MOF) derivatives have been arousing great attention in microwave absorption (MA) applications because of the adaptable morphological and component variance. However, it is still a huge challenge to construct multi-dimensional assembly with special heterostructure based on MOF and conductive carbon materials for excellent MA performance. Here, we successfully synthesized the cube-like assembly of multi-walled carbon nanotubes (MWCNTs) and ZnO (ZnO@MWCNTs) with unique multi-dimensional architecture via controlling the pyrolysis time of MOF-5 wrapped by MWCNTs. The ZnO@MWCNTs-4h are composed of zero-dimensional ZnO nanoparticles, one-dimensional MWCNTs, and three-dimensional micro-scale porous carbon framework. These various dimensional components confined within the cube space lead to the strong reflection loss (RL) at different frequencies, thus resulting in exceptional MA performance. The ZnO@MWCNTs-4h can reach a RL peak of −34.4 dB at only 1.5 mm thickness. More importantly, the maximum RL can achieve −47.4 dB at 2.7 mm with a mass loading as low as 20%. The optimized MA performance can be ascribed to high-density polarized sites, tightly interwoven MWCNTs conductive network, and strong multiple scattering that all induced by the multi-dimensional structures and components. Therefore, novel ZnO@MWCNTs composites are promising as a lightweight and highly efficient microwave absorber.