Non-magnetic hollow ZnO/C fabricated by a novel ZnO self-sacrificial template hollow engineering for efficient microwave absorption

The derivatives of metal–organic frameworks have been proven to be ideal candidates for microwave absorption due to their ability to form diverse microstructures of metals/heteroatom doped-carbon composites. In this study, we synthesized three types of zinc oxide (ZnO)@ZIF-8 with varying ZIF-8 shell thicknesses using ZnO colloidal spheres as sacrificial templates. Subsequently, we investigated the microwave absorption properties of a series of non-magnetic ZnO/N-doped carbon nanospheres pyrolyzed by ZnO@ZIF-8 at different temperatures. Remarkably, the non-magnetic samples (30 wt% filler loading) with a hollow structure pyrolyzed at 800 °C exhibited a broad effective absorption band exceeding 6 GHz. The excellent microwave absorbing performance of the samples pyrolyzed at 800 °C can be attributed to the reduction of the ZnO core to Zn⁰, anchoring it in the graphitized N-carbon layer, and the formation of an inner hollow cavity that enhances impedance matching. Therefore, this research not only provides an array of excellent dielectric-type microwave absorbing materials but also presents a novel strategy for developing lightweight and high-performance non-magnetic carbon-based microwave absorbing materials.