An Efficient Co/C Microwave Absorber with Tunable Co Nanoparticles Derived from a ZnCo Bimetallic Zeolitic Imidazolate Framework

A facile strategy is developed to modulate the content, particle size, and dispersity of magnetic metal nanoparticles (NPs) in porous carbon composite derived from Co/Zn bimetallic zeolitic imidazolate framework (ZIF). By adjusting the Co/Zn mole ratio in ZIF structure, porous carbon embedded with controllable Co NPs is synthesized through pyrolysis of CoZn-based ZIF during which Zn is selectively evaporated away at 900 degrees C. The Co/C composite derived from ZIF with Co/Zn ratio of 1/1 (Co50/C composite) displays well-dispersed Co NPs uniformly embedded in porous carbon. Meanwhile, the impedance matching of the composite is significantly improved due to the appropriate amount of Co NPs. Benefiting from the synergistic effect between Co NPs with magnetic loss and carbon with dielectric loss, the Co50/C composite exhibits excellent microwave absorbing properties with strong absorption, thin thickness, and lightweight, which is superior to previous metal-organic framework-derived absorbers. When the filler loading of Co50/C composite in paraffin matrix is only 20 wt%, a minimum reflection loss of -51.6 dB is achieved at a very thin layer thickness of 1.6 mm.