Carbon Nanotubes Get a New and Simple Bulk Sorting Process

Recently researchers at the Lawrence Berkeley National Laboratory, Stanford University, and the University of California Davis devised methods for sorting single-walled carbon nanotubes (SWNTs) so that semi-conducting and non-conducting SWNTs are separated. One obvious application is artificial skin.

This has long been a bottleneck in using SWNTs for electronics applications and it seems that dam has broken because now researchers at the London Centre for Nanotechnology at Imperial College London, UK, have also developed a simple separation solution for SWNTs.

Previous methods for separating nanotubes have been fantastically expensive—billions of pounds per kilo, as Milo Shaffer, head of the London Centre, notes in an interview with Chemistry World.

In contrast, the method that the London researchers developed should allow for bulk separation at an industrial scale. But cautious optimism seems called for at this point.

“There are many different methodologies in the literature that can achieve separation but the work here has the additional benefit of being potentially scalable,” says Karl Coleman, a nanotechnologist at the University of Durham, UK, who was also quoted in the article. “There is still plenty to be done as, in the grand scheme of things, the work still discusses milligrams and it remains to be seen whether you can use this methodology for kilograms.”

This line of research began after researchers at the University College London, UK observed that Buckminster fullerenes dissolved in ammonia. The two labs then collaborated on finding a separation method for SWNTs by seeing what would happen when they mixed SWNTs with sodium-ammonia solution.

This mixture results in what is described as an ammonia solution of sodium “nanotubide”. The next step is to remove the ammonia from the mixture, which leaves behind a dry powder of the nanotubide salt. When dry dimethylformamide is added to this nanotubide salt, a portion of immediately dissolves. The portion that dissolves is the part that contains the metallic SWNTs.

What this presents is the possibility of developing a large-scale separation method that relies just on the different electronic characteristics of the SWNTs and eliminates the need for centrifugation. This method could find itself fairly quickly adopted into commercial usage—Chemistry World also reports that Shaffer’s team has already licensed the technology to the industrial gas company, Linde.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

Dexter Johnson
Madrid, Spain
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY