Achievement of excellent microwave absorption on the Co/C-based composite from coal hydrogasification residue

Coal hydrogasification semi-coke (CHSC for short) is a coal-based solid waste with high content of carbon and well-developed porous structures. With CHSC as the carbonaceous matrix, Co/carbon-based composite micro-wave absorption (MA) materials were prepared by a liquid-phase impregnation and then an in-situ carbothermal reduction. And the MA performance of these composites were further optimized by altering the Co content. At the proper carbothermal temperature of 700 degrees C and concentration of Co(NO3)2 solution of 0.69 M, the composite CoSC700-20 demonstrated the optimal MA performance with the lowest reflection loss value of-40.2 dB and the maximum absorption bandwidth up to 5.0 GHz at a coating thickness of 2 mm. Both the graphitized carbon and porous structure inherited form CHSC serve important roles in this exceptional MA performance, as they are essential to the formation of uniformly dispersed conductive network and the estabilishments of multiple re-flections and scattering of microwaves. The high dispersion of Co particles on CHSC surface not only enhances the polarization losses but also facilitates impedance matching. This study will provide inspirations for either the low-cost construction of carbon-based MA materials or the facile recycling of carbon and the cobalt-based catalyst in the residue of coal catalytic hydrogasification.