Chemistry of nanostructured carbon: I. Fluorination, cutting and derivatization of single-wall carbon nanotubes; II. Fluorination and characterization of polymeric carbon 60
Margrave, John L.
Doctor of Philosophy
Purified HiPco SWNTs have been fluorinated with elemental fluorine under various conditions to control the stoichiometry of the resultant Fluorotubes. The partially fluorinated SWNTs with stoichiometry CFx (x ≤ 0.3), which were originally microns in length and extensively bundled, when pyrolyzed in an argon atmosphere to high temperatures (>800°C) are cut into short pieces (mostly <50 nm). The "cut" nanotubes have been characterized with Raman, ATR-IR, EDAX and AFM. The reactivities of the "cut" SWNTs have been explored through re-fluornation, acidification (reflux in dilute nitric acid) and hexylation (with hexyl lithium). The reactions of ozone with SWNTs on both gas-solid interface and on gas-solution interface have been studied. Ozone was found to oxidize the nanotube on both ends and sidewall forming functional groups such as epoxy groups and carboxylic acid groups. Intermittent ozone treatment of individually dispersed SWNTs in aqueous surfactant solution was found to effectively "cut" the nanotubes into short pieces. The effects of pH, surfactant types, and other factors on the reactions were investigated in situ with Raman and UV-vis-NIR spectroscopy. In an acidic environment, the reactions can develop to such an extent that the nanotubes were gradually "etched" away as CO 2. The process of using diluted gaseous HCl to treat the softly oxidized HiPco SWNT raw materials at high temperature to remove the metal impurities (especially carbon shell encapsulated Fe nanoparticles) has been studied by EDAX, Raman, UV-vis-NIR and ESEM. Refluxing of pristine HiPco SWNTs in dilute HNO3 (1--2 M) was found to remove most of the Fe catalyst from the SWNTs with less loss of SWNT mass and, as well, can add carbonyl, carboxylic, and hydroxyl group to the ends and sidewall of carbon nanotubes. The process and the products have been studied with TGA, ATR-IR, microscopic Raman, and TGA/MS. The solubility of the treated SWNTs in alcohol solvents such as ethanol was found greatly improved. The pristine HiPco SWNTs have been fluorinated and/or hexylated and the products suspended in organic solvents such as THF or chloroform to extract derivatized giant fullerene species formed as byproduct in the HiPco process. The hexylated giant fullerenes were also pyrolyzed in argon atmosphere to study the chemical desorption of the hexyl-functionalities. Such recovered pristine giant fullerenes were also studied with IR, Raman spectroscopy and were compared with SWNTs. The transformation of SWNTs under high pressure and high temperature (HPHT) treatment was studied by characterizing the treated SWNTs samples with Raman and X-ray diffraction (XRD). The characterization provided evidence for covalent interlinking between SWNTs through sp 3 C-C bond formation under HPHT treatment. The "depolymerization" of the interlinked SWNTs with ultrasonication was also studied. The fluorination of the 1D and 2D structures of polycrystalline polymeric C60 synthesized from the fullerene monomer (C60) under high temperature-high pressure (HPHT) conditions has been studied. The fluorinated C60 polymers have been characterized with IR, Raman, XRD, VTP-MS, SEM, and EDAX to determine their structures and stoichiometries. The polymeric C60 and their fluorinated derivatives were dissolved/suspended in organic solvents and the UV absorption spectra of thus formed solutions/suspensions were studied.
Inorganic chemistry; Physical chemistry; Engineering; Materials science