Single-Walled Carbon Nanotubes

Droplets bounce off this nanotube surface. The contact angle with water is more than 165°.

 

The fascinating electrical and mechanical properties of single-walled carbon nanotubes (SWNT) have opened a great number of potential application for these unique materials. However, the high costs of the current production method and the difficulty in making them available for large-scale manufacturing can slow down the process of bringing this technology to commercial production.

To develop a cost-effective operation for the manufacture of SWNT a drastic change in the production scale is necessary.Following the original arc-discharge method, other synthesis methods have been investigated, including laser ablation, plasma discharge, and catalytic decomposition of carbon-containing gaseous. The catalytic method for production of nanotubes has been known for a long time, but this method typically results in production of multi-wall nanotubes (MWNT).

SWNT pillars prepared by nano-sphere lithography over a silicon wafer substrate. This surface is superhydrophobic.

 

At the University of Oklahoma we pointed out that the catalytic decomposition method was suitable for scaling up and for achieving a "controlled production" of SWNT. By this we implied the ability to control the selectivity towards SWNT by changing catalyst parameters and operating conditions, all combined with the ability to obtain a reliable quantitative measurement of the amount of SWNT produced.

For the last eight years we have been performing research on the development and optimization of a cost effective method that we named CoMoCAT process. Our expertise in heterogeneous catalysis allowed us to tailor the material in such a way that selectivity and yield are maximized. The method employed involves disproportionation of CO at moderate pressure and temperature, which results in a scalable, cost-effective process.

Spectrofluorimetry result

 

Characterization on carbon nanotubes reveals distributions resolved at the level of individual (n,m) structures. Two structures, (6,5) and (7,5) together dominate the semiconducting nanotube distribution obtained by the CoMoCat process and comprise more than half of the population. Moreover, SEM and AFM analyses of parallel arrays of well aligned single-walled carbon nanotubes show that tubes are hundreds of microns long and are produced by decomposition of hydrocarbons on patterned metal lines evaporated over a quartz substrate.


SEM and AFM images of parallel arrays of well aligned single-walled carbon nanotubes.

What's new?

Role of water on the surface-guided growth of horizontally aligned
single-walled carbon nanotubes on quartz

The role of water in carbon feed on the surface-guided growth of horizontally aligned single-walled carbon
nanotubes (HA-SWCNTs) was investigated. It is shown that the amount of water can be optimized to favor HA-SWCNT growth, which is proposed to be due to selective etching of carbon deposits at carbon–metal interface. Without water, nanotube–nanotube interaction and carbon accumulation at the interface are disproportionately large compared to the rate of nanotube growth, leading to catalyst deactivation. With excess water, suppression of nanotube growth occurs, resulting in reduced carbon yield on the surface.
Intermediate carbon/water feed ratios achieve cleaner growth with high efficiency.

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