In situ metal-catalyzed scale modulation to implement electromagnetic response for ultra-wideband microwave absorbers

Carbon nanotubes (CNTs), as a typical one-dimensional nanomaterial, attract considerable attention in the field of microwave absorption due to their unique hollow structure and intrinsic conductivity properties. However, the unclear correlation between heteroatom modification/scale modulation of CNTs and their electromagnetic response mechanisms hinders the precise modulation of attenuation and impedance in CNTs-based microwave absorbers. In this work, we formulate a functional modulation strategy for CNTs based on the catalytic variations of diverse metal sources. A functionalized architecture featuring three-dimensional dielectric-magnetic coupling networks is constructed on carbon matrices through the in-situ catalytic growth of CNTs using Fe/Ni/Co metal catalysts. Through an activity regulation strategy for transition metal nanoparticles (NPs), we precisely tailor hierarchical CNTs morphologies, enabling controlled electromagnetic properties. Density functional theory calculations further reveal the unique cooperative electromagnetic nano-unit of the Co catalytic system, which endows the interface with efficient dynamic charge reconstruction, thereby realizing multi-band spatial polarization response. Additionally, the relatively ordered structure of hollow CNTs and magnetic Co NPs cleverly regulate the dielectric imbalances among the components. Benefiting from these comprehensive characteristics, the Co/CNTs/CM microspheres exhibit "ultra-broadband" absorption covering 8.2 GHz at a mere 2.0 mm, along with preeminent absorption capabilities at low frequencies across multiple thicknesses. The investigation reveals the foundational link between different metal catalysts and CNTs growth, providing valuable support for developing “ultra-broadband” microwave-absorbing materials.