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Potential applications for carbon nanotubes--tiny straws of pure carbon just billionths of a meter wide--are wide ranging. But manufacturing them is a complicated process that is expensive and often tedious because of the number of steps required to remove impurities. A report published in the current issue of Science describes a simple approach to improving a common synthetic approach: just water it down. The resulting nanotubes were more than 99.98 percent pure without requiring additional refinement.
Many current production schemes for single-walled carbon nanotubes (SWNTs) utilize catalyst particles to speed up the reaction, but they can become incorporated into the tubes, decreasing their usefulness. Kenji Hata of the National Institute of Advanced Industrial Science and his colleagues studied a manufacturing process that uses a solid catalytic surface. Under typical operating conditions, it became ineffective after about a minute. But when the team added just 100 parts per billion of water to the mixture used to make the carbon tubes, they found that a veritable forest of nanotubes grew up from the catalyst (see image). Once the nanotubes were removed, the catalyst could be reused.
The authors report that their approach can be applied to a variety of nanotube synthesis schemes, and will make them more affordable and feasible on a larger scale. In the report, they posit that eventually, "highly pure SWNTs could be grown into scaled-up macroscopic organized structures with defined shape, be it a three-dimensional complex structure or a two-dimensional flexible sheet."