Ab initio study of hydrogen chemisorption in nitrogen-doped carbon nanotubes

The electronic structure of single walled nitrogen-doped carbon nanotubes is calculated by first principles using density functional theory within the supercell approach with periodic boundary conditions. The effect of the adsorption of hydrogen atoms on different sites, relative to the position of the nitrogen atom, is explicitly taken into account. Both non-chiral and chiral geometries are analyzed. The obtained band structure shows that the non-chiral (6,0) nanotube is a semimetal under all different doping and adsorption configurations treated. The non-chiral (10,0) nanotube behaves mostly as a semiconductor, with the band gap width modulated by nitrogen doping and the relative position of the adsorbed hydrogen atom. The increase of substitutional N doping from one to three atoms per cell turns a (6,5) single-walled carbon nanotube from a semiconductor into a semimetal at zero temperature. Optical absorption related to carrier transitions between the calculated states is investigated from the imaginary part of the dielectric function, constructed with the use of the calculated Kohn-Sham states. The importance of the variation of the relative position of the adsorbed hydrogen atom on the chemical and physical properties investigated is particularly highlighted.

Aqueous nanosilica dispersants for carbon nanotube

Nanosilicas can disperse single-wall carbon nanotube (SWCNT) in aqueous solution efficiently; SWCNTs are stably dispersed in aqueous media for more than 6 months. The SWCNT dispersing solution with nanosilica can produce highly conductive transparent films which satisfy the requirements for application to touch panels. Even multiwall carbon nanotube can be dispersed easily in aqueous solution. The highly stable dispersion of SWCNTs in the presence of nanosilica is associated with charge transfer interaction which generates effective charges on the SWCNT particles, giving rise to electrostatic repulsion between the SWCNTs in the aqueous solution. Adhesion of charged nanosilicas on SWCNTs in the aqueous solution and a marked depression of the S11 peak of optical absorption spectrum of the SWCNT with nanosilicas suggest charge transfer interaction of nanosilicas with SWCNT. Thus-formed isolated SWCNTs are fixed on the flexible three-dimensional silica jelly structure in the aqueous solution, leading to the uniform and stable dispersion of SWCNTs.