ZIF-Derived Co Nanoparticles Embedded in Pumpkin Seedlike, Hollow N-Doped Carbon Structures for Efficient Microwave Absorption

Metal-organic framework (MOF)-derived materials have gained popularity as microwave absorbing materials due to their electromagnetic dissipation advantages. In this study, a special type of MOF (ZIF-L) was used as a precursor; tannic acid was introduced for chemical etching. The resulting material obtained by in situ carbonization was a hollow structure of N-doped carbon embedded by Co nanoparticles (CoHNC), which retained the original pumpkin seed shape but had a hierarchical porous structure on the inside. By adjustment of the amount of cobalt nitrate and the carbonation temperature, the electromagnetic parameters could be altered, improving impedance matching and enabling different microwave absorption properties to be obtained. At 16.96 GHz, the material exhibits an optimal reflection loss of -45.5 dB, an effective bandwidth of 3.04 GHz, and a matching thickness of only 1.4 mm with a material filler of 30 wt %. The microwave loss mechanism is formed by the dual loss mechanism with dielectric loss as the main loss and magnetic loss as the auxiliary one. Therefore, the synthesis of the CoHNC composite through simple etching provides a useful idea for optimizing microwave absorbing materials.