APPLICATION OF SINGLE WALLED CARBON NANOTUBES IN ENVIRONMENTAL ENGINEERING: ADSORPTION AND DESORPTION OF ENVIRONMENTALLY RELEVANT SPECIES STUDIED BY INFRARED SPECTROSCOPY AND TEMPERATURE PROGRAMMED DESORPTION

摘要

This study evaluated the environmental applications of carbon nanotubes through the adsorption and desorption of representative environmentally relevant adsorbates; ammonia, hydrogen sulfide and acetone under ultra high vacuum (UHV) and high pressure conditions. The results showed that functionalities/defects sites on nanotube surfaces play an important role on the interaction between molecules and carbon nanotubes. The oxygen containing functional groups on single-walled carbon nanotubes (SWNTs) are studied by Fourier Transform Infrared (FTIR) spectroscopy under vacuum. Vacuum heating to ~ 1300 K removes most of the functionalities in the samples. The similarities in the infrared spectra of the Rice Tubes after a 1400 K treatment with spectra for HiPco nanotubes suggest the observation of intrinsic SWNT IR bands.Ammonia adsorption on single walled carbon nanotubes (SWNTs) was studied in order to investigate the environmental application of nanotubes, mainly possible uses as sensors. 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 desorbed from those nanotubes above 140 K, indicating a weak adsorbate-nanotube interaction (~30 kJ/mol). This work suggests the influence of functionalities and/or defect densities on the sensitivity of SWNT chemical gas sensors. Both physisorption and chemisorption of acetone on nanotubes were observed. It was found that H2S adsorbed on nanotube surfaces at cryogenic temperature but not at room temperature. The low desorption temperature suggests only physisorption of H2S on nanotubes.In this study, low concentration of functionalities on carbon material surfaces was detected by fluorescent labeling technique. Florescent labeling indicated the presence of COOH and CHO groups on the ACF 25 fiber surface. Neither the infrared spectrum nor the X-ray photoelectron spectrum showed evidence of the existence of those low concentration groups. The key findings of this work make it possible that applying scientific information obtained from studies under ideal conditions to industrial sorbents/sensors under realistic process conditions. Nanotube surfaces can be modified chemically to enhance their affinities for certain kinds of gas molecules.