[show abstract][hide abstract] ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
[show abstract][hide abstract] ABSTRACT: Translating the unique characteristics of individual single-walled carbon nanotubes into macroscopic materials such as fibres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of fluid-phase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5 wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquid-crystal phases that can be readily processed into fibres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.
[show abstract][hide abstract] ABSTRACT: An ultrafine aerosol consisting of airborne single-walled carbon nanotubes (SWCNTs) was produced by nebulizing functionalized SWCNTs in methanol. Prior to atomization, purified SWCNTs were functionalized with aryl sulfonate groups via a Birch reaction. The functionalized SWCNTs were then dispersed in methanol and nebulized using a TSI-3076 constant output atomizer. Atomic force microscopy of a mica plate placed in the flow revealed both individual and bundled SWCNTs. We anticipate that this method for producing ultrafine mists of SWCNTs will enable respiratory toxicity studies of inhaled ultrafine SWCNT particulate.
[show abstract][hide abstract] ABSTRACT: Electron beam irradiation with moderate fluences of approximately 1016–1017 electrons per cm2 is used for controllable, bulk-scale cutting of single-walled carbon nanotubes (SWCNTs). The effectiveness of high energy electron irradiation in cutting SWCNTs is dependent on the nature of the sidewall. While pristine nanotubes are very stable under irradiation conditions, ozonated SWCNTs combined with a moderate fluence of electrons resulted in bulk-scale cutting of nanotubes. The length distribution of the cut SWCNTs could be controlled by adjusting the irradiation fluence. The average length of the cut nanotubes was 65 nm with 85% of the nanotubes shorter than 100 nm.
[show abstract][hide abstract] ABSTRACT: The carboxylate residues of the open ends of aryl-tert-butyl and arylsulfonic acid side-walled functionalized single walled carbon nanotubes (SWNTs) have been investigated for the complexation conditions of the iron-molybdenum cluster [H(x)PMo(12)O(40)CH(4)Mo(72)Fe(30)(O(2)CMe)(15)O(254)(H(2)O)(98)] ("FeMoC"). A range of alternative donor groups for the attachment of FeMoC have been investigated for piranha etched SWNTs, dodecyl side-walled functionalized SWNTs (DD-SWNTs) and ultra-short SWNTs (US-SWNTs), including include pyridines, thiols and phosphines, using coupling reactions to either the carboxylate or hydroxide residues of the SWNTs' open ends. The functionalized SWNTs have been characterized by XPS, uptake of Fe(3+) and, where appropriate, MAS (31)P NMR. The efficacy of binding is dependent on the presence and identity of the ligand moiety. TEM and AFM of the SWNT-FeMoC conjugates show the presence of a 2-3 nm spherical feature on the tip of individual SWNTs.
[show abstract][hide abstract] ABSTRACT: Methods for cutting single-walled carbon nanotubes (SWNTs) to controlled lengths for material, biological and electronic applications are being developed. The research aims at establishing scalable cutting processes for preparing high quality short SWNTs with high yield, systematic procedure for evaluating the cutting results, and effective, scalable methods for length sorting of cut SWNTs. Caro's acid has been studied and chosen as the finishing cutting reagent. High temperature fluorination plus Caro's acid have been developed as our primary cutting method. Electron beam irradiation of ozonated SWNTs has shown promising cutting result. A standard procedure has been developed to individualize SWNT samples and to determine the length distribution. Preliminary results have indicated that phase separation technique could be a scalable, efficient means for length sorting of SWNTs. Ultra-short SWNTs (US-SWNTs) were produced by oxidation in oleum using fuming nitric acid.
[show abstract][hide abstract] ABSTRACT: Single-walled carbon nanotubes (SWNTs) show great promise for use in a wide range of applications. One of the most promising avenues for attaining these applications is the dispersion of SWNTs at high concentrations in superacids, and their processing into macroscopic articles such as fibres or films. Fibres spun from SWNT/superacid dispersions indicate that the morphology of the starting SWNT material is reflected in the final morphology of the as-spun fibre. Here, we describe a method (termed disentanglement) of dispersing SWNTs in superacids and treating them using a high-shear, rotor/stator homogenizer, followed by coagulation to recover the solid SWNT material for use in fibre spinning. Several lines of experimental evidence (rheology and optical microscopy of the SWNTs in solution, scanning electron microscopy (SEM) of the coagulated material, and SEM of fibres spun from the coagulated material) show that this treatment radically improves the degree of alignment in the SWNTs' morphology, which in turn improves the dispersibility and processability. Raman microscopy and thermogravimetric analysis (TGA) before and after homogenization show that the treatment does not damage the SWNTs. Although this technique is particularly useful as a pre-processing step for fibre spinning of neat SWNT fibres, it is also useful for neat SWNT films, SWNT/polymer composites, and surfactant- or polymer-stabilized SWNT dispersions.
Proceedings of the Institution of Mechanical Engineers Part N Journal of Nanoengineering and Nanosystems 01/2008; 222(3):101-109.
[show abstract][hide abstract] ABSTRACT: Pristine, individualized single-walled carbon nanotubes (SWCNTs) have been noncovalently captured within PEG-terminated block copolymer amphiphiles. Two cross-linkable amphiphiles were evaluated: polyethylene glycol-polyacrylic acid-polystyrene (PEG-PAA-PS) and polyethylene glycol-polybutadiene (PEG-PB). The resulting self-assembled PEG-PAA-PS structures, called PEG-eggs, are freely soluble in water and stable in physiological media. SWCNTs in PEG-eggs retain their intrinsic near-infrared fluorescence, resist exchange with serum proteins, and are non-cytotoxic to mouse macrophage and human renal cells based on in vitro viability assays.
[show abstract][hide abstract] ABSTRACT: The ability to accurately measure the length of nanotubes is important to understanding nanotube growth and cutting processes. To date, there have been few methods available to obtain a statistically significant length measurement of any nanotube sample due to difficulties in obtaining a complete suspension of individual nanotubes and the tedious nature of measuring 1000+ nanotubes. Here we describe a relatively simple method that functionalizes single-walled carbon nanotubes to achieve a high propensity of individual nanotubes in chloroform as high as 92%. This suspension can be dispersed on mica substrates for AFM analysis. Nanotube lengths and heights can be determined using the Nanotube Length Analysis module of SIMAGIS yielding an accurate measure of length and height distribution of a large population of the nanotube sample.
Journal of Nanoscience and Nanotechnology 09/2007; 7(8):2917-21. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on a new high-resolution optical spectroscopy, coherent phonon measurement, for determining the chiral index of carbon nanotubes. Using femtosecond pump-probe spectroscopy, we demonstrate the real-time observation of lattice vibrations in individualized single-walled carbon nanotubes in an aqueous surfactant solution. Almost all available radial breathing modes in the Fourier transform spectrum from coherent phonon oscillations are well-resolved with less ambiguity in comparison to continuous-wave resonant Raman scattering.
Journal- Korean Physical Society 08/2007; 51. · 0.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Pristine carbon nanotubes (CNTs) dissolve as polycarbocations in superacids through direct protonation. The solvating power of a superacid is determined by the stability of the conjugate base anion that competes with the CNTs for the dissociated proton. We have demonstrated that this equilibrium can be controlled in a predictable fashion, thus rendering the solvating power of a superacid system tunable. In this article, we show that the solvating power of chlorosulfonic acid can be changed in a desired fashion by forming binary mixtures in different proportions with a non-superacid such as methane sulfonic acid. Thus, the successive extraction of carbon nanotubes with binary acid mixtures of increasing solvating power leads to the differentiation of CNTs by their molecular geometry. We show that solvation by direct protonation is sensitive to the geometric strain at the carbon atom and, hence, to the nanotube diameter. In this respect, the direct protonation method is distinct from surfactant-based or electrical-field-based methods that distinguish metallic CNTs from semiconducting types mainly on the existence of finite density of states or not at the Fermi level. We have employed solid-state Raman spectroscopic analysis of the CNT radial breathing modes and UV−vis absorption spectroscopy and a systematic mapping method to support our conclusions. We believe the concept demonstrated in this paper holds the potential to be developed into a chemical tool kit useful in the scaleable separation of CNTs by their (n, m) types, thus paving the way for molecular carbon nanotechnology.
Journal of Physical Chemistry C - J PHYS CHEM C. 07/2007; 111(48).
[show abstract][hide abstract] ABSTRACT: Single-walled carbon nanotubes (SWNTs) may be grown from designed seeds containing an SWNT and the catalyst required for continued growth. Dodecyl side-walled functionalized SWNTs (DD-SWNTs) are end-functionalized with 4-hydroxypyridine via dicyclohexylcarbodiimide coupling to allow covalent coordination of an inorganic cluster pro-catalyst (FeMoC). DD-SWNT-py-FeMoC on spin-on glass was exposed to H2/CH4 at 800 °C, resulting in 3-fold growth in the length of 40% of the seed SWNTs. Only 1% of the procatalyst alone nucleate SWNTs under the same conditions, suggesting effective separation of the nucleation and growth processes.
Journal of Physical Chemistry C - J PHYS CHEM C. 06/2007; 111(48).
[show abstract][hide abstract] ABSTRACT: We describe a fast, reproducible method to accurately measure the length of single-walled carbon nanotubes (SWNTs). The method is based on measuring the viscosity of a macroscopic sample of dilute suspended SWNTs. The average length is determined from the difference between the zero-shear viscosity of the suspension and that of the solvent. Using the relationship between viscosity and length, the average length of HiPco SWNTs is found to range from 400 to 700 nm, in agreement with atomic force microscopy (AFM) measurements. Compared to AFM, length determination by viscosity is faster and appears more reproducible.
[show abstract][hide abstract] ABSTRACT: We report on a one-pot, highly selective chemistry to remove residual catalysts from single-walled carbon nanotubes (SWNTs). The impurities, initially present at approximately 35 wt % and mostly as carbon-coated iron nanoparticles, can be driven below 5 wt % with nearly no loss of SWNTs. The carbon-coated iron impurities are dissolved simply by reacting with an aqueous mixture of H2O2 and HCl at 40-70 degrees C for 4-8 h. This purification combines two known reactions involving H2O2 and HCl, respectively; however, by combining these two typically inefficient reactions into a one-pot reaction, the new process is surprisingly selective toward the removal of the metal impurities. This high selectivity derives from the proximity effect of the iron-catalyzed Fenton chemistry. At pH approximately 1-3, iron is dissolved upon exposure, avoiding the otherwise aggressive iron-catalyzed digestion of SWNTs by H2O2. This extremely simple and selective chemistry offers a "green" and scalable process to purify carbon nanotube materials.
The Journal of Physical Chemistry B 03/2007; 111(6):1249-52. · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: Continued growth is a way of growing nanotubes targeted to produce continuous and chirality-controlled single-walled carbon nanotube (SWNT) materials. This growth method strongly depends on efficient preparation of open-ended SWNT substrates. Nanoscopically flat open-ended SWNT substrates have been prepared by cutting the SWNT spun fiber with a focused ion beam cutting technique and followed by etching schemes for cleaning amorphous carbon and opening the ends of the SWNTs. The open ends were effectively characterized through selective etch back of open SWNT ends by carbon dioxide gas at 950 degrees C. High density continued growth was demonstrated from these nanoscopically flat open-ended substrates.
[show abstract][hide abstract] ABSTRACT: The Raman response of the radial breathing mode in single-wall carbon nanotubes was analyzed for excitation with 10 different laser lines. The line shape was fitted with 14 Voigtian oscillators which could be correlated to tubes of different helicity. The strongest lines were observed between 172 and 199 cm−1. For an assignment frequencies evaluated from a density functional calculation and scattering intensities for the resonance transitions were used. The 5 strongest lines observed are consistent with scattering from tubes with 11 different helicities. From the evaluation of the scattering intensities the nearest-neighbor integral between two carbon atoms on the curved sheet was found to be 2.6 ± 0.5 eV.