Dissociation Chemistry of Gas Molecules on Carbon Nanotubes—Applications to Chemical Sensing

It is well known in the literature that carbon nanotubes (CNTs) interact weakly with many gas molecules like ${\rm H}_{2}{\rm O}$, ${\rm O}_{2}$, CO, ${\rm NH}_{3}$, ${\rm H}_{2}$ , and ${\rm NO}_{2}$, to name a few. Exposure to ${\rm NO}_{2}$ , ${\rm O}_{2}$, and ${\rm NH}_{3}$ significantly affects the electrical conductance of a single wall nanotube (SWNT). These can be explained using a simple charge transfer picture, which results in the observed changes in the hole conduction of the tubes. It is also known that pure SWNTs only weakly interact with these molecules. We have recently investigated (Andzelm , 2006) how common defects in CNTs [Stone–Wales (SW), monovacancy, and interstitial] influence the chemisorption of ${\rm NH}_{3}$. This paper is a continuation of our previous work. Here, we further investigate, via Density Functional Theory (DFT) calculations, the effects of SW defects on the adsorption/dissociation of ${\rm O}_{2}$ and ${\rm H}_{2}{\rm O}$. We also study the diffusion of adsorbed oxygen atoms on the nanotube surface in the vicinity of the SW defect, as well as the dissociation of ${\rm NH}_{3}$ in the presence of adsorbed oxygen atoms.