Science of single-wall carbon nanotubes: Purification, characterization and chemistry

[摘要] Characterization of raw nanotube materials produced by different methods is demonstrated. Depending on the production methods, tubes of different diameters can be produced. Purification of single wall carbon nanotubes produced by laser-oven and HiPco process is also discussed. Metal catalyzed oxidation at low temperature has been shown to selectively remove non-SWNT carbon and permit extraction of metals with concentrated HCl. These multi-stage purification methods have been investigated and the sample purity is documented by EDAX, ESEM, TGA, Raman and UV-vis-Nir spectroscopy. Covalent attachment of functional groups and molecules, including fluorine, methyl, n-butyl and n-hexyl groups, to the sidewalls of single wall carbon nanotubes has been achieved. Further fluorination study is done to investigate the effect of HF which is used as catalysts. Parallel fluorination experiments are performed on both laser-oven-grown and HiPco SWNTs. Larger diameter tubes, i.e. laser-oven-grown SWNTs, require higher fluorination temperatures. A limiting stoichiometry of C2F can be reach for Fluorotubes. Quantitative measurement of the alkylation was done by thermal gravimetric analysis. A mechanism involving electron transfer and effects of reaction temperature, solvents and steric effects of the alkyl groups are discussed. Prolonged exposure of small diameter SWNT ropes (diameters < 5 nm) to hot fuming sulfuric acid has been shown to grow super-ropes with approximately 10,000 tubes in cross-section from rope sizes of approximately 10 tubes. This represents the largest rope sizes ever seen. Examination of the spectral properties of the SWNTs indicates that the roping occurs without changing the chemical state of the nanotubes. Acid intercalation of single wall carbon nanotubes is examined. Several super acids and strong acids are used to study the charge transfer and protonation effects on SWNTs. The degree of charge transfer is clearly correlated with the ability of acid to intercalate into the nanotube packs. A molecular mechanics calculation is used to optimize the proposed Fluorotube structures. This is the first theoretical work on the modeling of Fluorotubes. Results show that fluorine would like to add along the circumference of the tubes instead of going down the tube axis. The (1,4) isomer has the lower total steric energy (TSE) between the two proposed Fluorotube structures, but the energy difference is small. Scanning tunneling microscopy has been used for atomic scale imaging of the fluorotubes. Significant band features are seen on fluorotubes, not on pristine carbon nanotubes. Butylated tubes have also been investigated by STM imaging. Instead of bands, relatively large, distinct features with spacings of about 50 A are observed. Both theoretical and experimental results indicated the (1,4) isomer with bands around the tubes should be the preferred structure.

[发布机构] Rice University

[效力级别] Engineering