Co/C broad band electromagnetic wave absorption composite derived from preferred precursor ZIF-67: preparation and performance

Abstract

A simple sacrificial template method was used to prepare Co/C composite with cobalt nanoparticles embedded in nitrogen-doped polyporous graphite carbon as an efficient electromagnetic wave (EMW) absorbent. Effects of solvent polarity, ratio of Co2+ to 2-methylimidazole and pH value of reaction system on precursor metal–organic skeleton ZIF-67 were systematically studied by a single variable method, and then the optimal preparation process was obtained. Thermal decomposition time and temperature of precursor ZIF-67 are the keys to the formations of ferromagnetic metal cobalt particles and carbon matrix. Therefore, effects of calcined temperature in inert atmosphere on the carbon content, graphitization degree, magnetic properties and microwave-absorbing performances of Co/C composite prepared were studied, and then nitrogen-doped porous composite Co/C composed of a highly dispersed core–shell Co@graphite nanoparticles coated by amorphous carbon skeleton was successfully prepared by optimizing pyrolysis technology. Composite Co/C-900 obtained by ZIF-67 calcinated at 900 °C exhibits excellent EMW absorption performances at low filling amount; its maximum reflective loss (RLmax) reaches − 34.41 dB at 17.49 GHz with the test thickness of 2.0 mm only, and most importantly, when the test thickness is 2.5 mm, its effective absorption bandwidth (RL < − 10 dB) reaches 7.37 GHz (10.18–17.5 GHz), spanning the X and Ku bands. The synergistic effects of the self-loss (dielectric loss and magnetic dissipation) and structural attenuation (multiple scattering and interface polarization) of Co/C-900 obtained greatly improve its impedance matching with free space and attenuation coefficients to EMW, significantly widening its effective bandwidth. As a new high-performance EMW absorbent with thin thickness, light weight, strong absorption capacity and wide bandwidth, the Co/C composite optimized by precursor preparation and calcination process should have a broad application prospect.