Yick Tim, Gangoli Varun Shenoy, Orbaek White Alvin
Energy Safety Research Institute, Swansea University, Bay Campus, Swansea SA1 8EN, UK.
Department of Chemical Engineering, Faculty of Science and Engineering, Swansea University, Bay Campus, Fabian Way, Swansea SA1 8EN, UK.
Nanomaterials (Basel). 2023 Jul 26;13(15):2172. doi: 10.3390/nano13152172.
This research endeavours to study the growth of ultralong carbon nanotubes (UL-CNTs) from methane using diverse catalysts, namely FeCl, bi-metallic Fe-Cu, Fe-Ni, and Fe-Co chlorides. Aqueous catalyst solutions were evenly dispersed on silica substrates and grown at 950 °C in the presence of hydrogen via a horizontal chemical vapour deposition (CVD) furnace. The samples underwent characterisation by Raman spectroscopy, scanning electron microscopy (SEM), and optical microscopy to identify the quality of CNTs and enumerate individual UL-CNTs. Our findings revealed that FeCl, as a mono-metallic catalyst, generated the longest UL-CNTs, which measured 1.32 cm, followed by Fe-Cu (0.85 cm), Fe-Co (0.7 cm), and Fe-Ni (0.6 cm), respectively. The G/D ratio (graphene to defects) from the Raman spectroscopy was the highest with the FeCl catalyst (3.09), followed by Fe-Cu (2.79), Fe-Co catalyst (2.13), and Fe-Ni (2.52). It indicates that the mono-iron-based catalyst also produces the highest purity CNTs. Moreover, this study scrutinises the vapour-liquid-solid (VLS) model for CNT growth and the impact of carbide formation as a precursor to CNT growth. Our research findings indicate that forming iron carbide (FeC) is a crucial transition phase for amorphous carbon transformation to CNTs. Notably, the iron catalyst generated the longest and densest CNTs relative to other iron-based bi-metallic catalysts, which is consistent with the temperature of carbide formation in the mono-metallic system. From correlations made using the phase diagram with carbon, we conclude that CNT growth is favoured because of increased carbon solubility within the mono-metallic catalyst compared to the bi-metallic catalysts.
本研究致力于使用多种催化剂，即氯化铁（FeCl）、双金属铁 - 铜（Fe - Cu）、铁 - 镍（Fe - Ni）和铁 - 钴（Fe - Co）氯化物，研究由甲烷生长超长碳纳米管（UL - CNTs）的情况。将催化剂水溶液均匀分散在二氧化硅基底上，并在氢气存在下于950℃通过卧式化学气相沉积（CVD）炉进行生长。通过拉曼光谱、扫描电子显微镜（SEM）和光学显微镜对样品进行表征，以确定碳纳米管的质量并计数单个超长碳纳米管。我们的研究结果表明，作为单金属催化剂的氯化铁生成的超长碳纳米管最长，长度为1.32厘米，其次是铁 - 铜（0.85厘米）、铁 - 钴（0.7厘米）和铁 - 镍（0.6厘米）。拉曼光谱的G/D比（石墨烯与缺陷之比）在氯化铁催化剂下最高（3.09），其次是铁 - 铜（2.79）、铁 - 钴催化剂（2.13）和铁 - 镍（2.52）。这表明单铁基催化剂也能产生纯度最高的碳纳米管。此外，本研究详细考察了碳纳米管生长的气 - 液 - 固（VLS）模型以及碳化物形成作为碳纳米管生长前驱体的影响。我们的研究结果表明，形成碳化铁（FeC）是无定形碳转变为碳纳米管的关键过渡阶段。值得注意的是，相对于其他铁基双金属催化剂，铁催化剂生成的碳纳米管最长且最密集，这与单金属体系中碳化物形成的温度一致。通过与碳的相图进行关联，我们得出结论，与双金属催化剂相比，单金属催化剂中碳溶解度的增加有利于碳纳米管的生长。
