Does water dope carbon nanotubes?

Robert A. Bell, Mike C. Payne and Arash A. Mostofi, Does water dope carbon nanotubes?, J. Chem. Phys. 141, 164703 (2014)

Carbon nanotubes (CNTs) possess remarkable electronic and physical properties, and many applications have been proposed since their discovery. For any application to be practical, however, these properties must be robust to their local environmental conditions. One technologically-important impurity is water, which may be found not only in the surrounding atmosphere, but also as a result of purification processes that are done in solution. Experimental studies show that water does have an effect on CNT conductivity, yet observations have been contradictory, with both increases and decreases in conductivity observed. A disagreement exists over the effect, and indeed the existence, of charge transfer between water and CNTs.

Using large-scale density functional theory calculations, we show that the interaction between water and CNTs is remarkably long ranged, such that it could not be accurately represented in previous calculations in the literature employing smaller system sizes. The dominant effect is due to the classical electrostatic interaction of the water molecule dipole with the electronic charge density of the CNT. This accounts for the vast majority of the redistribution of charge in the CNT, which had previously been misinterpreted as charge transfer. So, with regard to the question posed at the start, water does not dope carbon nanotubes.

This work is part of Rob Bell’s PhD.