Polymer-bubbling for one-step synthesis of three-dimensional cobalt/carbon foams against electromagnetic pollution

Constructing three-dimensional (3D) foam-like structure in magnetic metal/carbon composites is regarded as a promising pathway to reinforce their electromagnetic (EM) functions. Herein, a nitrate-assisted polymer-bubbling strategy is reported for the synthesis of Co/carbon foams, which is simply accomplished by direct pyrolyzing the mixture of polyvinylpyrrolidone (PVP) and cobalt nitrate hexahydrate (Co(NO3)2∙6H2O). Co(NO3)2∙6H2O not only plays as the source of Co nanoparticles, but also accounts for the formation of 3D microstructure through releasing gas. By manipulating the weight ratio of Co(NO3)2∙6H2O to PVP, the chemical composition, microstructure, and EM properties of these composites can be easily regulated. When the weight ratio reaches 1.5, the resultant composite displays good microwave absorption performance, whose reflection loss intensity and effective absorption bandwidth are superior to those of many common Co/C composites. EM analysis reveals that such architecture is greatly helpful to establish cross-linked conductive networks in the wax matrix, resulting in powerful dielectric loss under low absorber loading. Meanwhile, 3D microstructure is also beneficial for multiple reflections that equal to extend the transmission path of incident EM waves. Simple synthesis strategy and desirable properties of these magnetic carbon foams may render them as the low-cost substitute of 3D graphene for the application against EM pollution.