Investigating the structural and electronic properties of carbon nanotubes upon chemical functionalization and purification.

摘要

Carbon nanotubes are widely known at a fundamental research point of view for their unique structural, electronic and mechanical properties in many fields, including biological, electronics and materials. However, before they can reach their full potential in practical and affordable applications, issues such as purity, solubility and homogeneity of nanotube type need to be resolved. Presently, there are several methods known for the purification of nanotubes, which includes solution-phase ozonolysis, contributed previously by our group. As a result of purification, ends and defect sites on the nanotube framework are functionalized with oxygenated groups, which further facilitate addition of many moieties. One of the objectives of this work was to better understand the effects of purification and functionalization of carbon nanotubes on their structural and electronic properties. This knowledge is lacking and would be useful for applications, e.g. in gas storage. A fundamental study was carried out with lanthanide ions coordinated to acid purified carbon nanotubes, which indicated that hydrogen bonding plays a critical role in the spatial arrangement of the oxidized nanotubes. Attempts were also made to coordinate Jacobsen's catalyst to oxygenated functionalities localized on purified single-walled carbon nanotubes, for catalyst support. Specifically, to further understand pore structure and spatial arrangement upon purification, adsorption analysis on ozone purified tubes was performed. NEXAFS spectroscopy was also developed as a means of probing sidewall functionalization of the ozone purified nanotubes. In addition, to solve issues of solubility and homogeneity, silylation of relatively pure as-prepared single-walled carbon nanotubes was carried out, which provided for increased solubility and reactive selectivity towards semiconducting tubes of specific diameter range. Analysis of carbon nanotube alignment is also critical for optimization of electronic applications. We have demonstrated the use of NEXAFS spectroscopy, to not only investigate alignment across different nanotube samples, but also to simultaneously monitor purity, in terms of presence of oxygenated groups. Another system which was also investigated by NEXAFS spectroscopy was the boron nitride nanotube system, where its structural integrity was monitored. Techniques such as SEM, TEM, AFM, NMR, IR, UV-Vis, XPS and Raman were used in analyzing nanotube samples.