构造煤中类碳纳米管结构的发现及其形成机制探讨OA

[Objective]Carbon nanotubes(CNTs)have attracted wide attention due to their unique structures and per-formance.However,their artificial synthesis requires stringent conditions,including high temperatures(700 ℃ to 2 300 ℃),stable carbon sources,and catalysts.Furthermore,these structures are rarely discovered in nature.As a carbon-rich medium,coals can form a variety of ordered carbon structures during their metamorphic and deformational pro-cesses,serving as an ideal carrier for exploring the formation mechanisms of natural CNTs.[Methods]Typical tectonic-ally deformed coals from the Pingdingshan and Huaibei mining areas were investigated in this study.After demineraliza-tion and chloroform extraction,coal samples were observed under the high-resolution transmission electron microscope(HRTEM),revealing the presence of abundant fibrous tubular structures in coals unexpectedly.These structures were systematically characterized using X-ray diffraction(XRD)and laser Raman spectroscopy(LRS),and their formation mechanisms were preliminarily explored.[Results]This study revealed the presence of quasi-CNT structures in medium-rank tectonically deformed coals for the first time.These structures were largely characterized by a hollow structure and parallel tube walls,presenting a linear or curled morphology.They were dominated by multi-walled structures com-posed of 2-18 carbon layers,with a diameter range of 0.4-6.0 nm and an interlayer spacing of approximately 0.4 nm.The laser Raman spectra of the quasi-CNT structures showed G peaks at 1 595 cm-1 and 1 599 cm-1 and D peaks at 1 354 cm-1 and 1 364 cm-1,which are highly consistent with those of graphite.The XRD analysis indicates that the quasi-CNT structures had an intershell spacing(d002)range of 0.343-0.348 nm,further confirming the presence of graphite-like crystal structures.Additionally,organic solvent extraction was found to enable the effective enrichment of quasi-CNT structures and enhance their observability.[Conclusions]The analysis suggests that intense tectonic stress,espe-cially shear stress,can significantly reduce the energy barriers against the ordering and curling of aromatic layers in coals through the synergistic effects of mechanochemistry,element migration,and frictional heat.Consequently,the tec-tonic stress drives organic carbon to form quasi-CNT structures under temperatures far below those required by tradi-tional synthetic methods.The discovery of quasi-CNT structures in tectonically deformed coals enriches the system of natural carbon materials.More importantly,the discovery facilitates the introduction of another formation pathway of quasi-CNT structures,i.e.,a tectonic stress-driven chemical process,which is independent of extreme thermo-catalytic conditions.This pathway provides a critical theoretical basis and a novel approach for developing green bionic prepara-tion technology of CNTs based on stress adjustment.The key to future research lies in quantitatively revealing the mechanochemical process and dynamic mechanisms for the formation of coal-based quasi-CNT structures.