Large-scale production of single-walled carbon nanotubes by the electric-arc technique

Abstract

Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications 1 . High yields (70-90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets 2 . The electric-arc technique used to generate fullerenes and multiwalled nanotubes is cheaper and easier to implement, but previously has led to only low yields of SWNTs 3,4 . Here we show that this technique can generate large quantities of SWNTs with similar characteristics to those obtained by laser ablation. This suggests that the (still unknown) growth mechanism for SWNTs must be independent of the details of the technique used to make them. The ready availability of large amounts of SWNTs, meanwhile, should make them much more accessible for further study.In our electric arc-discharge apparatus 5 , the arc is generated between two electrodes in a reactor under a helium atmosphere (660 mbar). The cathode was a graphite rod (16 mm diameter, 40 mm long) and the anode was also a graphite rod (6 mm diameter, 100 mm long) in which a hole (3.5 mm diameter, 40 mm deep) had been drilled and filled with a mixture of a metallic catalyst and graphite powder. The arc discharge was created by a current of 100 A; a voltage drop of 30 V between the electrodes was maintained by continuously translating the anode to keep a constant distance (ϳ3 mm) between it and the cathode. Typical synthesis times were ϳ2 min. As the catalyst we used mixtures such as Ni-Co, Co-Y or Ni-Y in various atomic percentages; these are known to yield a series of interesting carbon nanostructures 6 . The mixture used by Guo et al. 7 during their laser ablation process (Co and Ni, both at 0.6 at.%) did not produce a good yield of nanotubes in our case. However, we found that a mixture of 1 at.% Y and 4.2 at.% Ni gave the best results. In this case we observed (in a total carbon mass of 2 g): (1) large quantities of rubbery soot condensed on the chamber walls; (2) web-like structures between the cathode and the reactor walls (no webs when either Y or Ni were absent); (3) a cylindrical deposit at the cathode's end; and (4) a small 'collar' (ϳ20% of the total mass) around the cathode deposit, as a black, very light and porous but free-standing material.Within all these products it was possible to observe by scanning electron microscopy (SEM; using a JEOL JSM 6300F instrument) filament-like structures that are more or less dense, depending on where in the reactor they were deposited. The 'collar' deposit was densest; the soot was the least dense. A characteristic SEM image of the collar deposit (Fig. 1) shows large amounts of entangled carbon filaments, homogeneously distributed over large areas (here at least a few square millimetres) and with diameters ranging from 10 to 20 nm. The average length between two entanglement points is several micrometres; we could not identify any filament ends. From several SEM images we estimate the yield of these filaments (with respect to the total volume of the solid material...

Chemistry of Single-Walled Carbon Nanotubes

“…[13][14][15][16][17][18] The SWNTs thus formed have diameters on the order of a nanometer when prepared by current techniques. [19][20][21] Typically, the as-prepared SWNT soot (AP-SWNTs) from the electric arc procedure contains metal particles, metal clusters coated with carbon, amorphous carbon, and in some cases fullerenes, with a 30 wt % abundance of carbon nanotube ropes (Figure 1). …”

A Simple Road for the Transformation of Few-Layer Graphene into MWNTs

“…42 Formation of ferrocene nanorods, attributed to π−π stacking of ferrocene molecules, on the surface of graphene sheets has been observed experimentally. 43 We performed a combination of molecular mechanics and molecular dynamics calculations for an increasing number of Fc-CHO molecules deposited on the nanoribbon obtained by unzipping a (8,8) CNT (see Table SI Crucial for templating the folding of graphene sheets by Fc-CHO is the presence of iron inside the MWNTs, as detected by TEM (SI-13, Supporting Information). It confirms that incorporation of Fc-CHO occurs and strongly vouches for their templating activity and supports the idea that this is the starting mechanism in the formation of the MWNT.…”

Photophysics of Individual Single-Walled Carbon Nanotubes

“…14 In arc discharge, the carbon source is composed of two rod-shaped graphite electrodes that are separated by about a millimeter (Figure 1-3a). 2 SWNT synthesis is achieved by drilling holes into the anode, which is subsequently filled with a powdered mix of graphite and metal catalyst (e.g., Fe, Ni, or Co).…”

“…14 In 1996, Smalley and co-workers developed laser ablation as a second technique to produce nanotubes (Figure 1-3b). 12 The process is carried out inside a quartz tube heated to 1200 ºC.…”