COV Fe/Fe = COF's ?
Covalent organic framework-derived hollow core-shell Fe/Fe3O4@porous carbon composites with corrosion resistance for lightweight and efficient microwave absorption
Author links open overlay panelXiaojieZhuaYanyanDongaFeiPanaZhenXianga
ZhichengLiuaBaiwenDengaXiangZhangaZhongShibWeiLua
https://doi.org/10.1016/j.coco.2021.100731
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Abstract
The functionalization of covalent organic frameworks (COFs) has recently captured great attention due to their designable structures and high specific surface area. However, their application in the field of microwave absorption is still scarce. In this work, hollow core-shell Fe/Fe3O4@porous carbon composites were successfully synthesized by calcining Fe3O4@COF composites. The composite obtained after heat treatment inherits the characteristics of porous and high specific surface area of the COF material, and the hollow core-shell porous structure facilitates multiple reflections and scattering of electromagnetic waves, the increase of active center sites, and the improvement of impedance matching. The results demonstrate that the composite exhibits efficient electromagnetic absorption performance at ultra-thin matching thickness (d = 1.8 mm): the minimum RL value is -50.05 dB and the effective absorption bandwidth is 5.20 GHz. Meanwhile, the absorption band with RL < -10 dB covers almost the whole C, X and Ku bands with varied thicknesses (1.50 ~ 5.00 mm). In addition, owing to the protective effect of the COF-derived carbon shell, the material exhibits improved stability of composition, structure and properties in harsh environments. This work may further develop the functionalization of COF materials, and facilitate the development of stable core-shell materials with improved electromagnetic wave absorption properties.
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Introduction
With the rapid development and extensive usage of wireless communication equipment, electromagnetic wave pollution has significantly impacted on industrial production and people's daily life [[1], [2], [3]]. Therefore, researchers have made great efforts to design and synthesize materials with specific compositions and structures [[4], [5], [6]].
Recently, porous materials such as porous zeolite material, activated carbon, and MOFs have attracted growing attention in the field of microwave absorption with their low relative density and high surface area [7,8]. As an emerging porous material, COFs have the large specific surface area, tunable pore channels, and designability of composition. Moreover, COFs have good stability with robust covalent bonds and only contain light elements (e.g., H, B, C, N, and O), which makes it possible to endow materials with a lightweight characteristic. Since the pioneering work of Yaghi in 2005 [9], COFs have been extensively developed in many fields, such as gas storage, sensing, and catalysis [10]. Nevertheless, to the best of our knowledge, there have been rare reports on the microwave absorbing performance of COFs or COF derivatives.
According to previous reported investigations, it is quite difficult for a single system of absorbers to achieve the characteristics of thin thickness, lightweight, wide absorption bandwidth and strong absorption simultaneously [[11], [12], [13], [14]]. This research improves impedance matching and achieves a double-loss synergistic effect by introducing Fe3O4 as the magnetic core. It is noteworthy that the COF-derived composites pyrolyzed at 700 °C achieve both the strong absorption intensity (−50.05 dB) and the wide effective absorption bandwidth (5.20 GHz) at a thin thickness of 1.8 mm when the filling rate is 30%. The results show that COF-derived materials can serve as promising candidates for lightweight and high-efficiency microwave absorption materials, which can be used to broaden the functional application of COFs.