Nitrogen-doped carbon nanotubes-locally-grown three-dimensional CeO2/C/Co foam enabling fabulous hydrophobicity, thermal insulation, and highly efficient microwave absorption

Self-assembly of graphene nanosheets and conversion of biomass materials are two popular strategies in the field of microwave absorption for the development of three-dimensional (3D) foam structures. However, the complexity of their synthetic routes, which involve time-consuming and costly procedures, presents challenges in bridging the gaps between scientific research and practical application. In this study, we employ a nitrate-assisted polymer-bubbling strategy for the synthesis of 3D foamy composites. Solid-state hybrids consisting of metal (i.e., Ce and Co) nitrates and polyvinylpyrrolidone (PVP) serve as the precursors in a one-step annealing treatment. Intriguingly, in the presence of both Ce³⁺ and Co²⁺ within these precursors, the nitrogen-doped carbon nanotubes (NCNTs), with metallic Co nanoparticles encapsulated at their tips, are locally grown on the surface of the resultant pyrolyzed products. By augmenting the feeding amount of Co²⁺ quantitatively, not only are the loading amount and length of NCNTs synchronously reduced, but also there exist disparities in the EM parameters for pyrolyzed products, resulting in their distinguishable EM absorption performances. When the feeding amount of Co²⁺ is moderate, the sample, denoted as CeO₂/C/Co@NCNT-2, demonstrates admirable EM absorption characteristics, including an exceptional minimum RL intensity of − 56.2 dB (2.3 mm) and a spectacular maximum EAB value of 7.3 GHz (2.7 mm), which are owed to the positive interference cancellation phenomenon, favorable multiple-reflection behavior of incident EM waves, and the collaborative contributions of dielectric-magnetic dual losses. Additionally, it also showcases charming characteristics in the aspects of waterproof functionality and thermal insulation.