Hollow SiO2/Co/CNTs hybrid with magnetic-dielectric synergistic effect for high-performance microwave absorption

The development of high-performance microwave absorbing materials with strong absorption, broad bandwidth, and lightweight characteristics remains a critical challenge. In this study, a hierarchical core–shell hybrid structure (HSM S @Co@CNTs) composed of hollow silica microspheres (HSM S ) as the core, a cobalt layer as the magnetic shell, and radially aligned carbon nanotubes (CNTs) grown on the surface is successfully fabricated via a combination of electroless plating and chemical vapor deposition (CVD). By optimizing the CVD parameters, CNTs with controlled morphologies and graphitization degrees are obtained, enabling the construction of a continuous conductive network that effectively regulates the complex permittivity and improves impedance matching. The cobalt shell contributes natural resonance, exchange resonance, and eddy current loss, while the abundant heterointerfaces (CNT/Co and Co/SiO₂) induce significant interfacial polarization. Furthermore, the hollow structure promotes multiple internal reflections and scattering of electromagnetic waves. Benefiting from the synergistic dielectric–magnetic loss mechanisms and multiscale structural design, the optimized HSM S @Co@CNTs composites exhibit excellent microwave absorption performance. Specifically, the sample prepared at 700 °C achieves a minimum reflection loss of −55.7 dB at 2.5 mm with an effective absorption bandwidth of 3 GHz, and a maximum bandwidth of 4 GHz at 1.9 mm; the sample prepared at 650 °C shows a minimum reflection loss of −55.2 dB at 1.7 mm with an effective absorption bandwidth of 3.5 GHz. Radar cross section simulations further confirm the superior electromagnetic wave attenuation capability. This work provides a promising strategy for designing lightweight, high-efficiency microwave absorbing materials through synergistic dielectric–magnetic integration and hollow core–shell engineering.