Co Nanoparticles\nEmbedded in N‑Doped Carbon\nNanotubes for Broadband Microwave Absorption

Abstract

Herein, an efficient one-dimensional (1D) N-doped Co/C\nnanotube\nabsorber was designed by a cobalt source and solvent ratio comodulation\nstrategy. First, we explored the influences of different cobalt sources\n(CoCl₂, Co(OAc)₂, Co(NO₃)₂, and CoSO₄) on the morphology and microwave absorption\n(MA) property, which showed that CoCl₂ facilitated the\nformation of nanotubes with a relatively uniform diameter and length.\nNotably, the Co/C nanotubes displayed an ultrawide effective absorption\nbandwidth (EAB) of 6.885 GHz at 2.2 mm when the filling ratio was\nonly 8 wt %. Then, by adjusting the solvent ratio of isopropanol (IPA)\nand water, Co/C showed a strong absorption of −44.51 dB with\nan EAB of 5.44 GHz at 2.35 mm. The outstanding MA performance is ascribed\nto the synergistic effect of dielectric and magnetic components, which\nis conducive to optimizing the impedance matching, thus broadening\nthe EAB. In addition, the 1D nanostructure is good for constructing\nthree-dimensional (3D) conductive networks and enhancing conductive\nloss. Since Co nanoparticles are wrapped in carbon nanotubes (CNTs),\nthe confinement effect can effectively prevent the agglomeration of\nferromagnetic nanoparticles, adjusting the MA performance. It is worth\nmentioning that the maximum Radar cross section (RCS) value of Co/C\ncan be reduced by 28.8 dB m². Furthermore, the RCS values\nare all lower than −10 dB m² from −90 to\n90° and the minimum RCS value can reach −46.8 dB m². This work provides a strategy for designing lightweight\nMA absorbers with strong RL and ultrawide EAB.