Fluorescence Labeling of Surface Species as an Efficient Tool for Detection, Identification and Quantification of Oxygen Containing Functionalities on Carbon Materials

Abstract

1. Fluorescence labeling and quantification of oxygen-containing functionalities on the surfaces of single walled and multi-walled carbon nanotubes. Nearly all applications of nanotubes (CNTs), from nanoelectronics to composites, require knowledge of the type and concentration of functionalities on the surface of the material. None of the methods conventionally used to characterize CNTs, such as Raman spectroscopy, IR spectroscopy, UV-VIS-NIR spectroscopy, and X-ray photoelectron spectroscopy, provide selectivity in identification together with sensitivity in quantification. Fluorescence labeling of surface species (FLOSS) to identify and quantify oxygen containing functionalities on single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) provides a solution that is reported in this dissertation. The high selectivity of covalent attachment combined with the sensitivity of the fluorescence measurements, allowed us reliably determine concentrations of aldehyde (together with ketone), alcohol, and carboxylic functional groups on as-produced and acid treated SWCNTs. The detection limit is as low as ~ 0.5 % at (1 in every 200 carbon atoms).(You never established the lower limit clearly) 2. Purification of carbon nanotubes by dynamic oxidation in air. The outstanding mechanical and electronic properties of carbon nanotubes make them promising materials for use in different areas of nanotechnology. However, the presence of impurities in as-produced nanotubes has been a major obstacle toward their industrial scale applications. Amorphous and graphitic carbon, and catalytic metal particles are the major impurities in raw carbon nanotubes. Isothermal oxidation of as-produced carbon nanotubes, followed by acid treatment, is the most commonly used purification strategy. The thermal oxidation step eliminates carbonaceous impurities and the acid treatment decreases the metal content. Unfortunately, most of the existing oxidation procedures either do not destroy all carbonaceous impurities or partially destroy carbon nanotubes as well. In the dissertation, a novel purification protocol via dynamic oxidation of as-produced single-walled carbon nanotubes (SWCNT) is reported. In the new procedure, carbon nanotubes are exposed to a wide range of temperatures during the heating ramp. The results of the purification of arc-produced and laser vaporization grown SWCNT using dynamic oxidation are presented. Purity analysis of dynamically oxidized samples by UV-VIS-NIR and Raman spectroscopy, as well as transmission electron microscopy, explicitly demonstrate that dynamic oxidation enables obtaining undamaged carbon nanotubes almost free of carbonaceous impurities. 3. Surfactant- free method of solubilization of non-functionalized single-walled carbon nanotubes in common solvents. One of the major factors that hamper the extensive use of carbon nanotubes (CNTs) in large-scale applications are related to the poor purity of CNTs, and the weak dispersibility of CNTs in the most common solvents. The presence of substantial impurities (sometimes up to 80% wt.) in as-produced CNTs almost obliterates the unique properties of the material. Furthermore, the difficulties with solubilization of CNTs slow down the processability of the material in potential applications. A new one-step method of making pure single-walled carbon nanotubes (SWCNTs) via the sequence of sonication cycles is described in the dissertation. Hours long stable solutions of SWCNTs in acetone, methanol and isopropanol of concentrations as high as ~ 15 mg/L were prepared using the procedure. The results of UV-VIS-NIR, Raman and Transmission Electron Microscopy suggest that SWCNTs were not destroyed or damaged by purification and solubilization processes. A possible physico-chemical explanation of the solublization mechanism is discussed.