Department of Chemistry, Bar Ilan Institute for Nanotechnology and Advanced materials (BINA), Bar Ilan University, Ramat Gan, 52900, Israel.
Nanoscale. 2019 Jan 23;11(4):1929-1936. doi: 10.1039/c8nr08197b.
Many catalyst materials have been tried to synthesize ultra-long carbon nanotubes (CNTs) by extending catalyst lifetime and delaying growth termination. We propose a time-controlled, variable composition iron-molybdenum catalyst system, where the diffusion of molybdenum (as a thin layer reservoir) is mediated by the alumina underlayer, to reach and to slowly alloy with the Fe catalyst on the surface during the thermal process. This technique enhanced both the catalytic activity and the catalytic lifetime to grow CNT carpets with heights up 5 mm, compared to a maximum of approximately 1.5 mm for a regular sample (without Mo reservoir). Moreover, the CNT height increased with the thickness of the Mo thin layer reservoir for thicknesses from 10 nm to 30 nm. We discuss this new growth mechanism using high resolution transmission microscopy (HRTEM) images of cross-section lamellas and Rutherford Back Scattering (RBS) analysis to show the increasing alloying of Mo with Fe. Overall, the proposed technique of mediated diffusion of Mo to the surface with subsequent progressive alloying with the Fe catalyst, besides enhancing CNT height, could allow the one-step synthesis of CNT carpets with regions of different heights based on patterning these regions with different thicknesses of the Mo reservoir during sample preparation.
许多催化剂材料已被尝试用于通过延长催化剂寿命和延迟生长终止来合成超长碳纳米管 (CNT)。我们提出了一种时间控制的、可变组成的铁-钼催化剂体系，其中钼（作为薄储层）的扩散通过氧化铝底层来介导，以在热过程中到达并与表面上的 Fe 催化剂缓慢合金。与常规样品（无 Mo 储层）最多约 1.5 毫米相比，这种技术提高了催化活性和催化寿命，可生长高达 5 毫米的 CNT 地毯。此外，对于厚度从 10nm 到 30nm 的 Mo 薄层储层，CNT 高度随 Mo 薄层储层的厚度增加而增加。我们使用横截面薄片的高分辨率透射显微镜 (HRTEM) 图像和卢瑟福背散射 (RBS) 分析来讨论这种新的生长机制，以显示 Mo 与 Fe 的合金化程度增加。总的来说，Mo 向表面的受控扩散以及随后与 Fe 催化剂的逐步合金化的提议技术，除了提高 CNT 高度之外，还可以允许基于在样品制备过程中用不同厚度的 Mo 储层对这些区域进行图案化，来一步合成具有不同高度区域的 CNT 地毯。
