Tailoring (n,m) Structure of Single-Walled Carbon Nanotubes by Modifying Reaction Conditions and the Nature of the Support of CoMo Catalysts

Abstract

The (n,m) population distribution of single-walled carbon nanotubes obtained on supported CoMo catalysts has been determined by photoluminescence and optical absorption. It has been found that the (n,m) distribution can be controlled by varying the gaseous feed composition, the reaction temperature, and the type of catalyst support used. When using CO as a feed over CoMo/SiO2 catalysts, increasing the synthesis temperature results in an increase in nanotube diameter, without a change in the chiral angle. By contrast, by changing the support from SiO2 to MgO, nanotubes with similar diameter but different chiral angles are obtained. Finally, keeping the same reaction conditions but varying the composition of the gaseous feed results in different (n,m) distribution. The clearly different distributions obtained when varying catalysts support and/or reaction conditions demonstrate that the (n,m) distribution is a result of differences in the growth kinetics, which in turn depends on the nanotube cap-metal cluster interaction.

Effect of Catalyst Pretreatment on Chirality-Selective Growth of Single-Walled Carbon Nanotubes

“…This is in line with previous literature. 17,39,41,42 Several suggestions have previously been made to explain (n, m) dependence on carbon source. For instance, selective cap formation from particular intermediate carbon species provided by a particular precursor onto a particularly faceted catalyst nanoparticle has been suggested, 41 and theoretical calculations have shown that different intermediate carbon species (from different precursor gases) can influence resulting chirality.…”

Understanding the “Activation” of the Nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98-y(EtOH)y] for Low Temperature Growth of Carbon Nanotubes

“…Current CVD growth generally produces a mixture of diameters and chiralities unsuitable for applications, such as electronics, that require defined structures. However, limited control over CNT morphology has been reported by tuning CVD growth conditions, such as gaseous composition, substrate, and growth temperature [4][5][6]. Of particular interest are the reports of narrowed chirality and diameter distributions at lower growth temperatures [6,7].…”

“…Considering the problems in controlling the composition and size of binary metal oxide nanoparticles [12] single molecular precursors would be considered an ideal solution: given the unique composition and hence size of the final nanoparticle. Recently, Li et al used the molecular nanocluster Na 15 [Na 3 ,{Co(H 2 O) 4 (12,6), (14,4), and (16,0) CNTs in efficiencies of 92, 97, and 80% respectively [13][14][15]. They propose the high chiral selectivity arises from two key factors: 1) the excellent matching between the (n,m) nanotube chirality and the Miller (plane) indices of the l-phase W 6 Co 7 alloy, and 2) the stability of the high melting point alloy that maintains its well-defined structure under CVD conditions.…”

Scalable Method for the Reductive Dissolution, Purification, and Separation of Single-Walled Carbon Nanotubes

“…Despite recent progress in selective synthesis, current techniques still produce heterogeneous samples containing SWNTs of varying geometry and electronic character, as well as other carbonaceous contaminants. [6][7] Post-production separation of metallic and semiconducting SWNTs follows various strategies based on physical (dielectrophoresis, 8 …”