School of Chemistry, University of Nottingham , University Park, Nottingham NG7 2RD, United Kingdom.
Central Facility of Electron Microscopy, Electron Microscopy Group of Materials Science , Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
J Am Chem Soc. 2016 Jul 6;138(26):8175-83. doi: 10.1021/jacs.6b03633. Epub 2016 Jun 23.
In organic synthesis, the composition and structure of products are predetermined by the reaction conditions; however, the synthesis of well-defined inorganic nanostructures often presents a significant challenge yielding nonstoichiometric or polymorphic products. In this study, confinement in the nanoscale cavities of single-walled carbon nanotubes (SWNTs) provides a new approach for multistep inorganic synthesis where sequential chemical transformations take place within the same nanotube. In the first step, SWNTs donate electrons to reactant iodine molecules (I2), transforming them to iodide anions (I(-)). These then react with metal hexacarbonyls (M(CO)6, M = Mo or W) in the next step, yielding anionic nanoclusters M6I14, the size and composition of which are strictly dictated by the nanotube cavity, as demonstrated by aberration-corrected high resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy. Atoms in the nanoclusters M6I14 are arranged in a perfect octahedral geometry and can engage in further chemical reactions within the nanotube, either reacting with each other leading to a new polymeric phase of molybdenum iodide [Mo6I12]n or with hydrogen sulfide gas giving rise to nanoribbons of molybdenum/tungsten disulfide [MS2]n in the third step of the synthesis. Electron microscopy measurements demonstrate that the products of the multistep inorganic transformations are precisely controlled by the SWNT nanoreactor with complementary Raman spectroscopy revealing the remarkable property of SWNTs to act as a reservoir of electrons during the chemical transformation. The electron transfer from the host nanotube to the reacting guest molecules is essential for stabilizing the anionic metal iodide nanoclusters and for their further transformation to metal disulfide nanoribbons synthesized in the nanotubes in high yield.
在有机合成中，产物的组成和结构由反应条件决定；然而，制备具有明确组成和结构的无机纳米结构通常具有很大的挑战性，因为这往往会导致非化学计量比或多晶型产物的生成。在这项研究中，单壁碳纳米管（SWNTs）的纳米级空腔限制提供了一种新的多步无机合成方法，其中在同一纳米管内发生连续的化学转化。在第一步中，SWNTs 将电子捐赠给反应物碘分子（I2），将其转化为碘阴离子（I(-)）。然后，这些碘阴离子在下一个步骤中与金属六羰基化合物（M(CO)6，M = Mo 或 W）反应，生成阴离子纳米团簇M6I14，其大小和组成严格由纳米管空腔决定，这一点通过像差校正高分辨率透射电子显微镜、扫描透射电子显微镜和能量色散 X 射线光谱得到了证实。纳米团簇M6I14中的原子排列成完美的八面体几何形状，并且可以在纳米管内进一步进行化学反应，要么彼此反应生成新的钼碘聚合相[Mo6I12]n，要么与硫化氢气体反应生成钼/钨二硫化物纳米带[MS2]n，这是合成的第三步。电子显微镜测量表明，多步无机转化的产物被 SWNT 纳米反应器精确控制，互补的拉曼光谱揭示了 SWNTs 的显著特性，即在化学转化过程中充当电子储库。从主体纳米管到反应客体分子的电子转移对于稳定阴离子金属碘化物纳米团簇以及进一步将其转化为在纳米管中高产率合成的金属二硫化物纳米带是必不可少的。
