Ammonia adsorption on single-walled C nanotubes was studied by means of infra-red spectroscopy at both cryogenic levels (about 94K) and ambient (about 300K). At 94K, vacuum-annealed single-wall C nanotubes showed no detectable NH3 up-take. However, the NH3 adsorption was found to be sensitive to the functionalities and defects on the nanotube surfaces. Ammonia adsorption was detected on HNO3-treated nanotubes, characterized by significant functionalities and defects, prior to vacuum annealing. Ammonia desorbed from those nanotubes above 140K, indicating a weak adsorbate-nanotube interaction (approximately 30kJ/mol). Exposure of annealed samples to ambient air, which possibly regenerated functionalities and defects on nanotube surfaces, partially restored the NH3 up-take capacity. No NH3 adsorption on single-wall C nanotubes was observed by infra-red spectroscopy at room temperature with up to 80Torr dosing pressure. This suggested an influence of functionalities and/or defect densities upon the sensitivity of single-wall C nanotube chemical gas sensors. The present theoretical studies of NH3 adsorption on pristine and defective tubes, as well as oxidized tubes, supported these findings.

Sensitivity of Ammonia Interaction with Single-Walled Carbon Nanotube Bundles to the Presence of Defect Sites and Functionalities. X.Feng, S.Irle, H.Witek, K.Morokuma, R.Vidic, E.Borguet: Journal of the American Chemical Society, 2005, 127[30], 10533-8