Research yields ‘designer’ carbon nanotubes

Researchers at Rice University say fluorine could prove to be a key in unlocking the potential of carbon nanotubes and other carbon nanostructures.

Researchers at Rice University say fluorine – the most reactive element in nature – could prove to be a key in unlocking the potential of carbon nanotubes and other carbon nanostructures.

Rice chemists are presenting research at this week’s annual meeting of the American Chemical Society in Orlando, Florida, that describes their work in the fluorination of polyfullerenes, groupings of C-60 molecules that have been joined together in polymer chains and planes. Polyfullerenes are reportedly much more stable than organic polymers and the addition of fluorine to the polyfullerenes could make it easier for chemists to use them in subsequent chemical reactions.

The Rice research is a collaboration with scientists at the Russian Academy of Science’s Institute for High-pressure Physics near Moscow. The Russian researchers – Dr. V. A. Davydov and co-workers – created the polymeric fullerenes using a process involving temperatures up to 500º Celsius, and pressures up to 60,000 atmospheres. At Rice, researchers – Faculty Fellow Valery Khabashesku and Graduate Student Zhenning Gu – fluorinate the polyfullerenes, using techniques pioneered over the past three years in the fluorination of carbon nanotubes.

‘Compared to other methods of forming derivatives of carbon nanostructures, fluorination leads to reactions that are more general in nature and more easily extrapolated to a macro or production scale,’ said John Margrave, Butcher Professor of Chemistry.

Since their discovery in 1991, scientists have speculated that carbon nanotubes could be used for everything from biological probes small enough to penetrate a living cell to wires in computer chips that are 100 times smaller than anything available with today’s technology.

But carbon nanotubes are also inert and chemically stable, which has made it difficult for chemists to create nanotube derivatives – tubes decorated with extra molecules that act as chemical ‘handles’ for further manipulation.

Most processes that laboratory researchers have used to create nanotube derivatives are said to be impractical on a macro scale because they involve the use of extremely high temperatures, high pressures or other techniques that are difficult to reproduce in a production setting.

Fluorine, which is often shunned by chemists because of its highly reactive nature, has proven to be very useful as an alternative means of creating nanotube derivatives, precisely for that reason. The addition of fluorine opens the door to subsequent chemical reactions, giving chemists the ability to attach other types of molecules to nanotubes.

So far, Margrave and his colleagues have used this process to create dozens of ‘designer’ nanotube derivatives. These include hydrotubes, which contain hydrogen in an activated form; hexyl nanotubes, methoxy nanotubes, amido nanotubes, and other varieties containing organic side chains; polymers similar to nylon; and hydrogen-bonded nylon analogs. Unlike pure carbon nanotubes, all these derivatives are soluble in traditional organic solvents.

Potential applications for the nanotube derivatives are still being identified, but hydrotubes, which contain hydrogen in an activated form, might find a use as an ultra efficient fuel, and silicate-coated nanotubes could be used in nanoscale electronic devices.