3D Network-structured Fly Ash Microbeads@Carbon Nanotubes Composites for Electromagnetic Wave Absorption

With rapid development of 5G communication and miniaturization of electronic devices, development of lightweight, broadband and high-efficiency electromagnetic wave absorbing materials has emerged as a critical solution to challenges posed by electromagnetic pollution and information leakage. However, traditional absorbing materials face significant limitations, such as high density, narrow absorption bandwidth and poor environmental compatibility, while the resource utilization of industrial solid waste provides an innovative path for the design of high-performance absorbing materials with both economic and ecological benefits. Here, magnetic fly ash (MFA) microbeads were derived from solid waste of coal-fired power plants through magnetic separation. Additionally, magnetic fly ash microbeads@carbon nanotubes (MFA@CNTs) composite wave-absorbing materials with a three-dimensional interpenetrating network structure were successfully prepared by chemical vapor deposition (CVD) using in situ-loaded Fe-based nanoparticles on surface of the MFA microbeads as catalysts. Microstructural characterization showed that the bamboo-like CNTs grown on surface of the MFA microbeads formed a porous structure by inter tubular winding and bridging with silicate framework. The composite material achieves a minimum reflection loss (RLmin) of -44.52 dB at 8.8 GHz (with a thickness of 2.99 mm) and an effective absorption bandwidth (EAB, RL3O4) in the MFA microbeads interacts with conductive network of the CNTs, thereby establishing a magneto-electrical coupling effect to optimize the impedance matching. (2) The defective structure of bamboo-like CNTs induces multiple polarized relaxation (including interfacial and dipole polarizations), significantly enhancing the dielectric loss. (3) The 3D porous network extends the propagation path of electromagnetic wave, thereby promoting multiple reflection and scattering loss. This study not only provides a new paradigm for high-value utilization of industrial solid waste, but also lays a theoretical and technical foundation for the design of lightweight and broadband wave-absorbing materials.