构造煤中类碳纳米管结构的发现及其形成机制探讨

Discovery of Carbon Nanotube-Like Structures in Tectonically Deformed Coals and Discussion of Their Formation Mechanisms

  • 摘要: 【目的】碳纳米管因独特的结构与性能备受关注,但人工合成常需高温(700~2 300 ℃)、稳定碳源与催化剂等严苛条件,自然界中鲜有发现。煤作为富碳介质,在其变质‑变形过程中可形成多种有序碳结构,为探索天然碳纳米管的生成提供了理想载体。【方法】选取平顶山、淮北典型构造煤为主要研究对象,经脱矿与氯仿萃取处理后,采用高分辨率透射电镜(HRTEM)进行观测,意外发现煤中富含的纤维管状结构,结合X射线衍射(XRD)与拉曼光谱系统表征其结构,并初步探讨其形成机制。【结果】在中煤级构造煤中首次发现类碳纳米管结构,该结构多呈中空、管壁平行的线状或卷曲状,以2~18层多壁为主,直径范围为0.4~6.0 nm,单层碳间距约0.4 nm。拉曼光谱中G峰(1 595、1 599 cm-1)与D峰(1 354、1 364 cm-1)的分布与石墨高度一致;XRD分析显示d002晶面间距为0.343~0.348 nm,进一步证实其具有类石墨晶体结构。同时发现,有机溶剂萃取可有效富集并增强该类结构的观测性。【结论】(1) 分析认为强构造应力(尤其是剪切应力)通过力化学作用、元素迁移与摩擦热的协同效应,显著降低了煤中芳香层有序化与卷曲的能量壁垒,从而在远低于传统合成温度的条件下,驱动有机碳形成类碳纳米管结构。(2) 该发现不仅丰富了天然碳材料体系,更重要的是提出了一种不依赖极端热‑催化条件的“构造力-化学”形成路径,为发展基于应力调控的碳纳米管绿色仿生制备技术提供了关键理论与新途径。(3) 未来研究的关键在于定量揭示煤基类碳纳米管结构形成的“力化学”作用过程及动力学机制。

     

    Abstract: 【Objective】 Carbon nanotubes have attracted extensive attention due to their unique structures and properties, yet their artificial synthesis usually requires harsh conditions such as high temperatures (700~2 300 ℃), stable carbon sources and catalysts, leading to their rare occurrence in nature. As a carbon-rich medium, coal can form a variety of ordered carbon structures during its metamorphic-deformational processes, which serves as an ideal carrier for exploring the formation of natural carbon nanotubes. 【Method】 In this study, typical tectonically deformed coals from Pingdingshan and Huaibei were selected as the mainresearch objects. After demineralization and chloroform extraction treatments, high-resolution transmission electron microscopy (HRTEM) was employed for observation, and in-situ carbon nanotube-like structures were unexpectedly discovered. Furthermore, X-ray diffraction (XRD) and Raman spectroscopy were combined to systematically characterize the structures of these formations. 【Results】 For the first time, in-situ carbon nanotube-like structures were discovered in medium-rank tectonically deformed coal. Most of these structures are hollow with parallel tube walls, presenting a linear or curled morphology, and are mainly multi-walled with 2~18 layers, with a diameter range of 0.4~6.0 nm and an interlayer spacing of single carbon layers of approximately 0.4 nm. The distribution of G bands (1 595, 1 599 cm-1) and D bands (1 354, 1 364 cm-1) in the Raman spectra is highly consistent with that of graphite; XRD analysis showed that the d002 interplanar spacing is 0.343~0.348 nm, which further confirms its graphite-like crystal structure. The study also found that organic solvent extraction can effectively enrich such structures and enhance their observability. 【Conclusions】(1)Analysis suggests that intense tectonic stress, especially shear stress, through the synergistic effects of mechanochemical effects, element migration and frictional heat, significantly reduces the energy barrier for the ordering and curling of aromatic layers in coal. Thus, it drives the formation of carbon nanotube-like structures from organic carbon under temperatures far lower than those required for traditional synthetic methods. (2) This discovery not only enriches the system of natural carbon materials, but more importantly, proposes a “Tectonic Stress-Chemistry” formation pathway that is independent of extreme thermo-catalytic conditions. It provides a key theoretical basis and a new approach for the development of green bionic preparation technology of carbon nanotubes based on stress regulation. (3) The key to future research lies in quantitatively uncovering the mechanochemistry action process and the dynamic mechanism underlying the formation of coal-based carbon nanotube-like structures.

     

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