Observation of local changes of "carbon-to-metal ratio" in the growth mechanism of carbon nanostructures grown from FePd-based and Fe3C catalysts by pyrolysis of ferrocene and dichlorocyclooctadiene-palladium mixtures: the crucial role of Cl
Observation of local changes of "carbon-to-metal ratio" in the growth mechanism of carbon nanostructures grown from FePd-based and Fe3C catalysts by pyrolysis of ferrocene and dichlorocyclooctadiene-palladium mixtures: the crucial role of Cl
复制标题
通过二茂铁和二氯环辛二烯-钯混合物热解，FePd 基和 Fe3C 催化剂生长碳纳米结构生长机制中“碳金属比”局部变化的观察：Cl 的关键作用
DOI：
10.1039/c7ra01207a
复制
发表时间：
2017
期刊：
影响因子：
3.9
通讯作者：
Wang Shanling
中科院分区：
文献类型：
--
作者：
Boi Filippo S.;Zhang Xiaotian;Ivaturi Sameera;He Yi;Wang Shanling
碳纳米材料领域的主要挑战之一是了解其生长机制动态。最近的报告显示了将 FePd 基合金封装在碳基纳米结构内的初步稳态化学气相沉积 (CVD) 实验。然而，人们对它们的生长机制动态知之甚少。在这里，我们研究了通过稳态CVD和粘性边界层化学气相合成（CVS）实验，涉及二茂铁/二氯环辛二烯-钯混合物和二茂铁/二氯苯混合物的热解，从FePd基和Fe3C催化剂颗粒生长的碳纳米结构的生长机制中可能存在“碳与金属比”的局部变化。在第一种情况下，我们证明了观察到一种不寻常的生长机制，其中在相同的碳结构中存在从球形细长碳洋葱状（CNOs 状）形态（低碳金属比条件）到碳纤维状形态（高碳金属比条件）的直接转变。我们将这种转变归因于热解过程中 Cl 自由基浓度的变化，这意味着局部“碳金属比”参数的变化。然后将所报道的机理与通过二茂铁/二氯苯混合物的 CVD 获得的 Fe3C 填充的 CNT 的机理以及文献中报道的其他过渡金属催化剂体系的机理进行详细比较。相反，当热解二茂铁/二氯环辛二烯-钯前体和粗糙表面之间产生粘性边界层时，发现填充有大量 FePd3 和 Fe3C 晶体的径向 CNT 结构是主要反应产物。径向结构核心内存在填充的 CNO（由粘性边界层中颗粒的均匀成核引起）表明局部“碳金属比”的波动也存在于此类机制中。通过SEM、TEM、STEM、HRTEM、ED和X射线衍射对所得碳结构的形貌、截面和结构特性进行了详细分析。
One of the major challenges in the field of carbon nanomaterials consists of understanding their growth mechanism dynamics. Recent reports have shown preliminary steady state chemical vapour deposition (CVD) experiments for the encapsulation of FePd-based alloys inside carbon-based nanostructures. However, very little is known about their growth mechanism dynamics. Here we investigate the possible presence of local changes of “carbon-to-metal ratio” in the growth mechanism of carbon nanostructures grown from FePd-based and Fe3C catalyst-particles by steady state CVD and viscous-boundary-layer chemical vapour synthesis (CVS) experiments involving the pyrolysis of ferrocene/dichlorocyclooctadiene-palladium mixtures and of ferrocene/dichlorobenzene mixtures. In the first case, we demonstrate the observation of an unusual growth mechanism in which a direct transition from a spherically elongated carbon-onion-like (CNOs-like) morphology (low carbon-to-metal ratio condition) to a carbon fiber-like morphology (high carbon-to-metal ratio condition) is present within the same carbon structure. We attribute such transitions to the variation of the Cl-radicals concentration during the pyrolysis process, which implies a variation in the local “carbon to metal ratio” parameter. The reported mechanism is then compared in detail with that of Fe3C filled CNTs obtained by CVD of ferrocene/dichlorobenzene mixtures and with those reported in the literature for other transition metal catalyst systems. In contrast, when a viscous boundary layer is created between the pyrolysed ferrocene/dichlorocyclooctadiene-palladium precursors and a rough surface, radial CNT structures filled with large quantities of both FePd3 and Fe3C crystals are found as major reaction products. The presence of filled-CNOs within the radial structures-core (resulting from the homogeneous nucleation of particles in the viscous boundary layer) suggests that fluctuations in the local “carbon-to-metal ratio” are also present in this type of mechanism. The morphological, cross-sectional and structural properties of the obtained carbon structures are analyzed in detail by SEM, TEM, STEM, HRTEM, ED and X-ray diffraction.