Dept. of Materials Science, National University of Tainan, 33, Sec. 2, Shu-Lin St., Tainan 70005, Taiwan.
Nanoscale. 2012 Aug 7;4(15):4757-64. doi: 10.1039/c2nr30854a.
A sulphate-activated mechanism is proposed to describe the growth of bamboo-like carbon nanotubes (CNTs) over copper catalysts using chemical vapour deposition with helium-diluted ethylene. Sulphate-assisted copper catalysts afford a high-yield growth of bamboo-like CNTs at a mild temperature, 800 °C; however, non-sulphate-assisted copper catalysts, e.g., copper acetate and copper nitrate prepared catalysts, were inert to CNT growth and only gave amorphous carbons (a-C) surrounding copper nanoparticles under the same conditions. Nevertheless, the addition of sulphate ions in the preparation step for the two inert catalysts can activate their abilities for CNT growth with remarkable yields. Furthermore, Raman spectra analysis demonstrates a linear dependence between the concentration of sulphate ions in copper catalysts and the ratio of CNT-a-C in the as-grown carbon soot. The sulphate-activated effect on CNT growth over copper catalysts could be related to a three-way interaction of sulphate ions, copper nanoparticles and support. In situ TEM images of an as-grown CNT irradiated by electron beams without the inlet of carbon sources reveal a new pathway of carbon diffusion through the bulk of copper nanoparticles and an enlarged inner-wall thickness of the on-site CNT. This carbon diffusion model over copper catalysts can provide new insights into the CNT growth mechanism over non-magnetic metal catalysts.
提出了一种硫酸盐激活机制，用于描述氦稀释乙烯化学气相沉积法在铜催化剂上生长竹状碳纳米管（CNT）。硫酸盐辅助铜催化剂在 800°C 的温和温度下提供了竹状 CNT 的高产生长；然而，非硫酸盐辅助铜催化剂，例如醋酸铜和硝酸铜制备的催化剂，对 CNT 生长惰性，仅在相同条件下在铜纳米颗粒周围得到无定形碳（a-C）。然而，在两种惰性催化剂的制备步骤中添加硫酸盐离子可以激活它们的 CNT 生长能力，产率显著。此外，拉曼光谱分析表明，铜催化剂中硫酸盐离子的浓度与生长碳黑中 CNT-a-C 的比值之间存在线性关系。硫酸盐对铜催化剂上 CNT 生长的激活作用可能与硫酸盐离子、铜纳米颗粒和载体之间的三向相互作用有关。在没有碳源入口的情况下，用电子束辐照生长的 CNT 的原位 TEM 图像揭示了碳通过铜纳米颗粒体扩散的新途径和原位 CNT 的内壁厚度增大。这种铜催化剂上的碳扩散模型可以为非磁性金属催化剂上的 CNT 生长机制提供新的见解。
