Structure controllable of cobalt/nitrogen-doped carbonaceous materials derived from zeolitic imidazolate frameworks with improved microwave absorption performance

Cobalt/nitrogen-doped carbonaceous particles were synthesized by the calcination of zeolitic imidazolate frameworks (Co-ZIF-67) at different heating rates. Their morphology, composition, and electromagnetic properties were measured. It was found that the structure and morphology of the derivatives were easily controlled by adjusting the heating rate. At a low heating rate, the derivatives retained their original shape, and smaller Co nanoparticles were formed. Consequently, more carbon nanotubes were formed, and the degree of graphitization improved, building a 3D conductive network. At a much higher heating rate, most of the carbon skeleton was destroyed; however, the smaller fragments endowed the samples with more conductive pathways because of the percolation and tunnel effects, increasing the dielectric loss. At a filler loading of 30%, the nanocomposites prepared at a heating rate of 1 degrees C/min exhibited the optimal reflection loss, -70.76 dB, at a thickness of 3.46 mm and an effective absorption bandwidth of 12.4 GHz.