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

doi:10.15541/jim20250177

Abstract

Abstract:

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 (RL_min) of -44.52 dB at 8.8 GHz (with a thickness of 2.99 mm) and an effective absorption bandwidth (EAB, RL<-10 dB) covering 4.72 GHz (with a thickness of 1.7 mm). The performance enhancement mechanism can be attributed to the following aspects. (1) The magnetic component (Fe₃O₄) 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.

Key words: fly ash microbeads@carbon nanotube, 3D network structure, electromagnetic wave absorption

CLC Number:

TB333

ZHANG Xiaomin, TONG Liangyu, GAO Hongjie, CHEN Xu, YAN Huhu, GAO Yang. 3D Network-structured Fly Ash Microbeads@Carbon Nanotubes Composites for Electromagnetic Wave Absorption[J]. Journal of Inorganic Materials, 2026, 41(2): 208-216.

Figures/Tables 11

Fig. 1 Schematic diagram of preparation process of MFA@CNTs microspheres

Fig. 2 Microscopic morphologic structures of MFA and MFA@CNTs microspheres (a-c) SEM images of (a) MFA, (b) MFA@CNTs and (c) CNTs on the surface of MFA@CNTs; (d) TEM image of CNTs; (e, f) EDS elemental mappings of (e) C and (f) Fe in MFA@CNTs as shown in Fig. (b)

Fig. 3 (a) XRD patterns of MFA and MFA@CNTs microspheres; (b) Raman spectrum of MFA@CNTs microspheres

Fig. 4 XPS spectra of MFA@CNTs microspheres (a) Total XPS spectrum; (b) C1s XPS spectrum; (c) Fe2p XPS spectrum

Fig. 5 Reflective loss diagrams of MFA and MFA@CNTs microspheres (a) RL, (b) 3D mapping RL and (c) 2D mapping RL of MFA; (d) RL, (e) 3D mapping RL and (f) 2D mapping RL of MFA@CNTs. Colorful figures are available on website

Fig. 6 Electromagnetic parameters of MFA and MFA@CNTs microspheres (a) Real part (ε′) and imaginary part (ε″) of relative permittivity; (b) Real part (μ′) and imaginary part (μ″) of relative permeability; (c) Dielectric loss tangent (tanδε); (d) Magnetic loss tangent (tanδµ); (e, f) Cole-Cole curves of (e) MFA and (f) MFA@CNTs

Fig. 7 Impedance matching and attenuation coefficients of MFA and MFA@CNTs microspheres (a, b) Impedance matching of (a) MFA and (b) MFA@CNTs; (c) Attenuation coefficients

Table 1 Comparison of microwave absorption performance[15,17,22,25,35 -37]

Microwave absorption material^*	RL/dB	EAB/GHz	d_EAB^**/mm	f/ GHz	Ref.
CNTs/PyCHMs	-56.0	4	3.0	12.2	[15]
Fe/C	-21.0	6.3	2.5	12.8	[17]
TiC/Fe@NCNHs	-41.62	4.85	1.4	17.66	[22]
ZnFe₂O₄@PHCMS	-51.43	3.52	4.8	7.2	[25]
Ni@CNT	-44.4	4.3	1.5	13.5	[35]
CoFe₂O₄@CNTs	-34.6	7.1	2.5	13.4	[36]
FeCo/Cu/CNTs	-48.1	5.76	1.8	15.2	[37]
MFA@CNTs	-44.52	4.72	1.7	8.8	This work

Fig. 8 Schematic of electromagnetic wave absorption mechanism of MFA@CNTs microspheres

Fig. S1 EDS mapping images of MFA

Fig. S2 Total EDS distribution spectrum of MFA@CNTs

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