MOFs-derived flower-like cobalt@carbon multiscale hierarchical composites with effective microwave absorption in the low frequency range

Abstract

The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields. In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials. In the present work, layer-structured Co-metal-organic frameworks (Co-MOFs) precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method. After annealed at 500°C under Ar atmosphere, a novel multiscale hierarchical composite (Co@C/CF) was obtained with the support of carbon fibers, keeping the flower-like structure. Scanning electron microscope, transmission electron microscope, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy were performed to analyze the microstructure and composition of the hierarchical structure, and the microwave absorption performance of the Co@C/CF composites were investigated. The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio. The optimized Co@C/CF flower-like composites achieved the best reflection loss of −55.7 dB in the low frequency band of 6–8 GHz at the thickness of 2.8 mm, with the corresponding effective absorption bandwidth (EAB) of 2.1 GHz. The EAB of 3.24 GHz was achieved in the high frequency range of 12–16 GHz when the thickness was 1.5 mm. The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure. The flower-like structure not only balanced the impedance of the fibers themselves, but also extended the propagation path of the microwave and then increased the multiple reflection losses. This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.

1. Introduction

To enhance the survivability of military combat aircraft on the battlefield [1] and to accommodate the evolving service environment, the use of integrated structure materials with excellent microwave absorption performance is the development trend of aircraft stealth materials to replace the traditional coated microwave absorption materials [2]. In recent years, the design of aircraft skins has incorporated carbon-based materials such as honeycomb, foam, and carbon fibers [3]. These matrices have been designed as the novel Wave Absorbing-Structural Integration Composites (WASICs) to simultaneously realize both load bearing and stealth performance [4]. Carbon fiber is a one-dimensional tubular structure with high temperature resistance, low cost, high electrical conductivity, and excellent mechanical properties [5]. It has become the most promising reinforcing material in the field of composites due to these characteristics [6]. Some special structural composites originated from in-situ loaded carbon fibers were investigated previously, for example, core–shell, hollow, and polyhedral structural composites. These structures increased the specific surface area of the composites, inducing multiple reflective behaviors of electromagnetic waves, and were effective in enhancing microwave absorption [7]. Zhou et al. [8] in-situ grew CoFe2O4 nanoparticles on cocoon-derived carbon fibers and the reflection loss of the composite could reach the minimum value of −53.3 dB with a thickness of 2.63 mm. J. Qiu and T.T. Qiu [9] synthesized a wave-absorbing material with a “dendritic” structure by depositing magnetite particles and carbon tubes on the surface of hollow porous carbon fibers. The carbon material was hybridized and modified by the magnetic particles, and the synergized effect between the multicomponents in the composite led to the minimum reflection loss of −50.9 dB. Thus, the in-situ decoration of carbon-based materials by wave-absorbing materials, aimed at constructing integrated specialized structures, has emerged as an effective solution to obtain structural-stealthy materials with high performance.

In recent years, metal-organic frameworks (MOFs) derived materials have attracted significant attention due to their tunable porosity, high surface area, and versatile chemical compositions. MOFs can serve as sacrificial templates to fabricate metal/carbon composites with controlled morphologies and enhanced electromagnetic properties. In this study, we report a facile method to construct flower-like Co@C hierarchical structures on carbon fibers via in-situ growth of Co-MOFs followed by thermal annealing. The resulting composites exhibit excellent microwave absorption performance, particularly in the low frequency range, demonstrating the potential of MOF-derived hierarchical structures for advanced stealth applications.