Abstract:

In order to solve the potential preparation problem of carbon fibers, a biomass-derived method was proposed to obtain carbon fiber-based microwave absorbers, where cotton fibers was used as the raw material, Co²⁺ served as the metal source, and 2-methylimidazole as ligand. The cotton fiber/ZIF-67 were acquired by coordination and self-assembly of Co²⁺and 2-methylimidazole. Cobalt/carbon fibers were successfully prepared by controlled high-temperature pyrolysis in the inert atmosphere. It is proved that the increased pyrolysis temperature can improve the crystallinity of cobalt nanoparticles and the coercivity and saturation magnetization are enhanced simultaneously, displaying the typical ferromagnetic properties. Raman spectra indicate that the high pyrolysis temperature is conductive to the transformation from amorphous carbon to microcrystalline graphite,which induce the increased degree of graphitization degree of carbon components. The calculated results of reflection loss show that the cobalt/carbon fiber pyrolyzed at 800 ℃ provides the best microwave absorbing performance, where the bandwidth coverage reached 5.44 GHz (9.36-14.80 GHz) with a thickness of 2 mm. The appropriate impedance matching and synergistic enhancement of dielectric loss and magnetic loss are considered to be responsible for the intensified microwave absorption. Additionally, the cross-linked carbon fibers create the suitable attenuation space for electromagnetic waves, which promotes the quick attenuation of electromagnetic energy in the conductive carbon fiber network. It is believed that the research provides reference for the rational design and development of novel carbon fiber-based microwave absorbing materials.

Key words: biomass, ZIF-67, cobalt/carbon fiber, aspect ratio, microwave absorbing material