The aim of this project was to investigate methods for purification and modification of Single Wall and Multi Wall Carbon Nanotubes. Covalent and noncovalent approaches to functionalization were studied. The dispersibility, structure and electronic properties of modified tubes were characterized by Raman, UV-vis-NIR and XPS. Fluorescence, NMR and TEM were further employed to characterize the interaction between nanotubes and non-covalent modifiers. The effects of five different purification methods on the dispersibility, and degree of carboxylic acid functionality of SWCNTs, along with the level of defects on the tube side walls, and the resulting electronic properties of SWCNTs have been investigated. It was found that all oxidation treatments successfully removed metallic oxides and amorphous carbon impurities, while different oxidation treatments introduced different levels of oxidized sites on the SWCNTs. Heat treatment after oxidation eliminated some of the carboxylic groups introduced by oxidation. SWCNTs covalently functionalized by aromatic diazonium salts containing nitro, carboxylate and fluoro groups on the aromatic ring were prepared. Heating of these tubes in vacuum at 350_C for 5 h partially reversed the effects of functionalization. However, due to the low degree of functionalization achieved in the preliminary studies, the dispersibility/solubility of functionalized tubes did not greatly improve. The interaction in stable suspensions of CNTs with positively or negatively charged pyrene derivatives via noncovalent functionalization, was extensively studied. 1-pyrene methylamine hydrochloride gave most stable dispersions. 1H and 2H NMR spectroscopy of MWCNTs/1-pyrene methylamine hydrochloride dispersion in DMF-d7 showed that the broadened signals are associated with weakly or unbound pyrene, while strongly bound pyrene is not observable in solution-state NMR. The strong pyrene attachment on MWCNTs by π-π stacking can be reversed by dialysis and/or extensive washing. Biological molecules such as polypeptides and amino acids also dispersed MWCNTs into solvents by noncovalent modification. It is found that polytryptophan demonstrated the greatest ability to disperse MWCNTs. Digestion with chymotrypsin enabled polytryptophan binding to be reversed. A combination of tube cutting and non-covalent functionalization by pyrenes or peptides enables tubes to be suspended/dissolved in solvents such as DMF and ethanol, and significantly allows tubes to be manipulated for practical device applications.
| Identifer | oai:union.ndltd.org:ADTP/187551 |
| Date | January 2008 |
| Creators | Liu, Rongmei, Chemistry, Faculty of Science, UNSW |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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