Optimizing the size-dependent dielectric properties of metal–organic framework-derived Co/C composites for highly efficient microwave absorption

Abstract

Precise control of the dielectric properties of metal–organic framework-derived carbon-based composites is required to extend the effective absorption bandwidth. Herein, ZIF-67 particles with different sizes have been prepared by changing the content and solvent, and they have been converted into Co/C composite particles at different pyrolysis temperatures. The electromagnetic properties of Co/C particles with different filling ratios have been investigated. The results showed that a higher pyrolysis temperature, larger filling ratio and smaller particle size have a positive effect on the increase of complex permittivity especially at low frequencies. The filling ratio and particle size should have an effect on inter-particle conduction loss by affecting electrical conduction networks, while the pyrolysis temperature decides conduction loss, as well as dipole polarization within individual particles. When the balance between dielectric loss and impedance matching is achieved, an extended effective absorption bandwidth in both Ku and X bands can be obtained. With a filling ratio of only 30 wt%, the effective absorption bandwidth of samples with a size of ∼1000 nm and ∼400 nm covered the whole Ku and X bands, respectively. This research offers a facile route to obtain excellent light weight microwave absorbing materials for practical application and deeper insights into the regulation of dielectric properties to achieve an extended effective absorption bandwidth.