School of Chemistry,Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
ACS Nano. 2012 Mar 27;6(3):2000-7. doi: 10.1021/nn300400z. Epub 2012 Mar 1.
Graphitized carbon nanofibers (GNFs) act as efficient templates for the growth of gold nanoparticles (AuNPs) adsorbed on the interior (and exterior) of the tubular nanostructures. Encapsulated AuNPs are stabilized by interactions with the step-edges of the individual graphitic nanocones, of which GNFs are composed, and their size is limited to approximately 6 nm, while AuNPs adsorbed on the atomically flat graphitic surfaces of the GNF exterior continue their growth to 13 nm and beyond under the same heat treatment conditions. The corrugated structure of the GNF interior imposes a significant barrier for the migration of AuNPs, so that their growth mechanism is restricted to Ostwald ripening. Conversely, nanoparticles adsorbed on smooth GNF exterior surfaces are more likely to migrate and coalesce into larger nanoparticles, as revealed by in situ transmission electron microscopy imaging. The presence of alkyl thiol surfactant within the GNF channels changes the dynamics of the AuNP transformations, as surfactant molecules adsorbed on the surface of the AuNPs diminished the stabilization effect of the step-edges, thus allowing nanoparticles to grow until their diameters reach the internal diameter of the host nanofiber. Nanoparticles thermally evolved within the GNF channel exhibit alignment, perpendicular to the GNF axis due to interactions with the step-edges and parallel to the axis because of graphitic facets of the nanocones. Despite their small size, AuNPs in GNF possess high stability and remain unchanged at temperatures up to 300 °C in ambient atmosphere. Nanoparticles immobilized at the step-edges within GNF are shown to act as effective catalysts promoting the transformation of dimethylphenylsilane to bis(dimethylphenyl)disiloxane with a greater than 10-fold enhancement of selectivity as compared to free-standing or surface-adsorbed nanoparticles.
石墨化碳纳米纤维 (GNF) 作为高效模板，可用于生长吸附在管状纳米结构内部（和外部）的金纳米粒子 (AuNP)。被包裹的 AuNP 通过与组成 GNF 的各个石墨纳米锥的阶梯边缘相互作用而稳定，其尺寸限制在约 6nm 左右，而吸附在 GNF 外表面原子级平坦石墨表面上的 AuNP 在相同的热处理条件下继续生长至 13nm 及以上。GNF 内部的波纹结构对 AuNP 的迁移施加了显著的阻碍，因此其生长机制仅限于奥斯特瓦尔德熟化。相反，吸附在光滑的 GNF 外表面上的纳米颗粒更容易迁移并聚合并形成更大的纳米颗粒，这一点通过原位透射电子显微镜成像得到了揭示。烷基硫醇表面活性剂存在于 GNF 通道内改变了 AuNP 转变的动力学，因为吸附在 AuNP 表面上的表面活性剂分子削弱了阶梯边缘的稳定作用，从而允许纳米颗粒生长，直到其直径达到宿主纳米纤维的内径。在 GNF 通道内热演变的纳米颗粒由于与阶梯边缘的相互作用而垂直于 GNF 轴排列，并由于纳米锥的石墨面而平行于轴排列。尽管 AuNP 尺寸较小，但它们在环境气氛中高达 300°C 的温度下仍保持高稳定性且不变。研究表明，固定在 GNF 内阶梯边缘上的纳米颗粒可作为有效催化剂，促进二甲基苯基硅烷向双（二甲基苯基）二硅氧烷的转化，与游离或表面吸附的纳米颗粒相比，选择性提高了 10 倍以上。
