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 likeH₂ O,O₂, CO,NH₃,H₂, andNO₂, to name a few. Exposure toNO₂,O₂, andNH₃significantly 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 ofNH₃. 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 ofO₂andH₂ 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 ofNH₃in the presence of adsorbed oxygen atoms.