Co Nanoparticles Embedded in N-Doped Carbon Nanotubes for Broadband Microwave Absorption

Herein, an efficient one-dimensional (1D) N-doped Co/C nanotube absorber was designed by a cobalt source and solvent ratio comodulation strategy. First, we explored the influences of different cobalt sources (CoCl2, Co(OAc)2, Co(NO3)2, and CoSO4) on the morphology and microwave absorption (MA) property, which showed that CoCl2 facilitated the formation of nanotubes with a relatively uniform diameter and length. Notably, the Co/C nanotubes displayed an ultrawide effective absorption bandwidth (EAB) of 6.885 GHz at 2.2 mm when the filling ratio was only 8 wt %. Then, by adjusting the solvent ratio of isopropanol (IPA) and water, Co/C showed a strong absorption of −44.51 dB with an EAB of 5.44 GHz at 2.35 mm. The outstanding MA performance is ascribed to the synergistic effect of dielectric and magnetic components, which is conducive to optimizing the impedance matching, thus broadening the EAB. In addition, the 1D nanostructure is good for constructing three-dimensional (3D) conductive networks and enhancing conductive loss. Since Co nanoparticles are wrapped in carbon nanotubes (CNTs), the confinement effect can effectively prevent the agglomeration of ferromagnetic nanoparticles, adjusting the MA performance. It is worth mentioning that the maximum Radar cross section (RCS) value of Co/C can be reduced by 28.8 dB m2. Furthermore, the RCS values are all lower than −10 dB m2 from −90 to 90° and the minimum RCS value can reach −46.8 dB m2. This work provides a strategy for designing lightweight MA absorbers with strong RL and ultrawide EAB.