Feng Xue, Irle Stephan, Witek Henryk, Morokuma Keiji, Vidic Radisav, Borguet Eric
Chemistry Department, Temple University, Philadelphia, Pennsylvania 19122, USA.
J Am Chem Soc. 2005 Aug 3;127(30):10533-8. doi: 10.1021/ja042998u.
Ammonia adsorption on single-walled carbon nanotubes (SWNTs) was studied by means of infrared spectroscopy at both cryogenic (approximately 94 K) and room (approximately 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 (approximately 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.
通过红外光谱法，在低温（约94 K）和室温（约300 K）下研究了单壁碳纳米管（SWNTs）对氨的吸附。在94 K时，真空退火的单壁碳纳米管未检测到氨的吸收。然而，发现氨吸附对纳米管表面的官能团和缺陷敏感。在真空退火之前，在经硝酸处理的具有大量官能团和缺陷的纳米管上检测到了氨的吸附。氨在140 K以上从这些纳米管上解吸，表明吸附质与纳米管之间的相互作用较弱（约30 kJ/mol）。将退火后的样品暴露于环境空气中，这可能会使纳米管表面的官能团和缺陷再生，从而部分恢复氨的吸收能力。在室温下，当进样压力高达80 Torr时，通过红外光谱未观察到单壁碳纳米管对氨的吸附。这项工作表明了官能团和/或缺陷密度对单壁碳纳米管化学气体传感器灵敏度的影响。我们对氨在原始、有缺陷以及氧化的纳米管上吸附的理论研究证实了这些发现。
