Sensitivity of Ammonia Interaction with Single-Walled Carbon Nanotube Bundles to the Presence of Defect Sites and Functionalities

by Xue Feng et al. Journal of the American Chemical Society, 8 Jul 2005 (web release) Ammonia adsorption on single-walled carbon nanotubes (SWNTs) was studied by means of infrared spectroscopy at both cryogenic (~94 K) and room (~300 K) temperatures. At 94 K, vacuum-annealed SWNTs showed no detectable ammonia uptake. However, the ammonia adsorption was found to be sensitive to the functionalities and defects on the nanotube surfaces. NH3 adsorption was detected on HNO3-treated nanotubes, characterized by significant functionalities and defects, prior to vacuum annealing. NH3 desorbed from those nanotubes above 140 K, indicating a weak adsorbate-nanotube interaction (~30 kJ/mol). Exposure of annealed samples to ambient air, which possibly regenerated functionalities and defects on nanotube surfaces, restored partially the ammonia uptake capacity. No ammonia adsorption on SWNTs was observed by infrared spectroscopy at room temperature with up to 80 Torr dosing pressure. This work suggests the influence of functionalities and/or defect densities on the sensitivity of SWNT chemical gas sensors. Our theoretical studies on NH3 adsorption on pristine and defective tubes, as well as oxidized tubes, corroborate these findings. Read more