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INVESTIGATION OF ADSORPTION, REACTION AND CONFINEMENT OF MOLECULES IN SINGLE WALL CARBON NANOTUBES

by Byl, Oleg

Abstract (Summary)
Adsorption of simple molecules (CF4, Xe, CO2, NO and H2O) inside single wall carbon nanotubes has been investigated by means of infrared spectroscopy. It was demonstrated that confinement has a profound effect of the IR spectra of the internally adsorbed species. The spectral changes relate to the enhanced binding of the adsorbates to the nanotube interior walls and to the spatial limitations that prohibit formation of bulk-like structures. It was found that CF4 exhibits a 15 cm-1 redshift in its í3 symmetric stretching mode when adsorbed on the exterior surface of closed SWNTs. Adsorption on the nanotube is accompanied by adsorption in the interior in the case of opened SWNTs and the í3 mode is redshifted 35 cm-1. In addition it was shown that confined CF4 does not exhibit LO-TO splitting observed in the bulk phase. Physisorption of NO inside of carbon nanotubes results in cis-(NO)2 dimer formation for almost all adsorbed NO, indicating that confinement shifts the equilibrium according to Le Chatelier's Principle. In all cases Xe was used as a displacing agent to verify the internal adsorption. It was shown that Xe preferentially adsorbs inside nanotube displacing high coverage CF4 molecules. The externally bound adsorbates do not form a full monolayer and therefore Xe adsorbs non-competitively on empty external sites. Confinement of H2O in the nanotube interior leads to appearance of a sharp mode at 3507 cm-1 that is indicative of a weaker hydrogen bond relative to hydrogen bonding in bulk ice. Molecular simulations show that the confined water forms stacked ring structures with bulk-like intra-ring and weaker inter-ring hydrogen bonds. The spectroscopy studies of adsorption in nanotubes were accompanied by nitrogen volumetric adsorption studies of bulk nanotubes. It was demonstrated that n-nonane can be utilized as a nanotube interior blocking agent. The oxidation of SWNTs by ozone, followed by heating to remove oxidized carbon atoms as carbon oxides occurs preferentially on the outer surface of bulk samples of nanotubes. The high surface reactivity of O3 at the outer surface of a bulk nanotube sample causes this effect. It was found that CF4 exhibits a 15 cm-1 redshift in its í3 symmetric stretching mode when adsorbed on the exterior surface of closed SWNTs. Adsorption on the nanotube is accompanied by adsorption in the interior in the case of opened SWNTs and the í3 mode is redshifted 35 cm-1. In addition it was shown that confined CF4 does not exhibit LO-TO splitting observed in the bulk phase. Physisorption of NO inside of carbon nanotubes results in cis-(NO)2 dimer formation for almost all adsorbed NO, indicating that confinement shifts the equilibrium according to Le Chatelier's Principle. In all cases Xe was used as a displacing agent to verify the internal adsorption. It was shown that Xe preferentially adsorbs inside nanotube displacing high coverage CF4 molecules. The externally bound adsorbates do not form a full monolayer and therefore Xe adsorbs noncompetitively on empty external sites.
Bibliographical Information:

Advisor:Prof. J. T. Yates. Jr.; Prof. D. H. Waldeck; Prof. C. S. Wilcox; Prof. J. K. Johnson

School:University of Pittsburgh

School Location:USA - Pennsylvania

Source Type:Master's Thesis

Keywords:chemistry

ISBN:

Date of Publication:03/17/2006

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