Carbon nanotube structures changed by 'attack' from within

A team of researchers involving scientists from The University of Nottingham has shown for the first time that chemical reactions at the nano-level which change the structure of carbon nanotubes can be sparked by an ‘attack’ from within.

The discovery challenges previous scientific thinking that the internal surface of the hollow nanostructures is chemically unreactive, largely restricting their use to that of an inert container or a ‘nano-reactor’ inside which other chemical reactions can take place.

Their research, published in the journal Nature Chemistry, shows that carbon nanotubes that have had their structures changed are exciting new materials that could be useful in the development of new technologies for gas storage devices, chemical sensors and parts of electronic devices such as transistors.

Dr Andrei Khlobystov, of the University’s School of Chemistry, who led the work at Nottingham, said: “It has universally been accepted for some time now that the internal surface of carbon nanotubes — or the concave side — is chemically unreactive, and indeed we have been successfully using carbon nanotubes as nano-reactors.

“However, in the course of this new research we made the serendipitous discovery that in the presence of catalytically active transition metals inside the nanotube cavity, the nanotube itself can be involved in unexpected chemical reactions.”

In this latest research, the scientists found that an individual atom of Rhenium metal (Re) sets off a chemical reaction leading to the transformation of the inner wall of the nanotube. Initially, the attack by the Rhenium creates a small defect in the nanotube wall which then gradually develops into a nano-sized protrusion by ‘eating’ additional carbon atoms.

The protrusion then rapidly increases in size and seals itself off, forming a unique carbon structure dubbed a NanoBud, so called because the protrusion on the carbon nanotube resembles a bud on a stem.

Previously, NanoBuds were believed to be formed outside the nanotube through reactions on the outer surface with carbon molecules called fullerenes.

The new study demonstrates for the first time that they can be formed from within, provided that a transition metal atom with suitable catalytic activity is present within the nanotube.