Abstract
The initial development of carbon nanotube synthesis revolved heavily around the use of 3d valence transition metals such as Fe, Ni, and Co. More recently, noble metals (e.g. Au) and poor metals (e.g. In, Pb) have been shown to also yield carbon nanotubes. In addition, various ceramics and semiconductors can serve as catalytic particles suitable for tube formation and in some cases hybrid metal/metal oxide systems are possible. All-carbon systems for carbon nanotube growth without any catalytic particles have also been demonstrated. These different growth systems are briefly examined in this article and serve to highlight the breadth of avenues available for carbon nanotube synthesis.
Highlights
The current excitement in carbon nanotubes (CNTs) was triggered by Sumio Iijima’s Nature publication in 1991 [1]
Iijima analysed the deposit on the cathode and found macroscopic amounts of multi-walled carbon nanotubes (MWNTs) and facetted graphitic particles
The roots of the graphitic walls do not terminate on the metal particle but rather on the oxide support as shown in Figure 5 [43]. This highlights the diversity with which carbon nanotubes can grow, in that some base growth modes show the CNT is rooted at the metal catalyst particle [44] much like tip growth grown CNT [45] or in other cases from the oxide support [42,43]
Summary
The current excitement in carbon nanotubes (CNTs) was triggered by Sumio Iijima’s Nature publication in 1991 [1]. The roots of the graphitic walls do not terminate on the metal particle but rather on the oxide support as shown in Figure 5 [43] This highlights the diversity with which carbon nanotubes can grow, in that some base growth modes show the CNT is rooted at the metal catalyst particle [44] much like tip growth grown CNT [45] or in other cases from the oxide support [42,43]. Ex situ studies are necessarily limited in that they cannot unequivocally testify to Figure 7 Schematic representation of the carbothermal reduction of silica to silicon carbide and carbon nanostructure formation: (a) SiO2 is reduced to SiC via a carbothermal reaction, (b) SiC nanoparticles coalesce, (c) carbon caps form on the surface of the SiC particles through precipitation and/or SiC decomposition.
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