HiPco Single-walled Carbon Nanotubes Research Articles

Diameter-Selective Fractionation of HiPco Single-Walled Carbon Nanotubes in Repeated Functionalization Reactions

The functionalization reaction of the diamine-terminated oligomeric poly(ethylene glycol) with a purified HiPco single-walled carbon nanotube sample was repeated multiple times to yield the corresponding number of soluble fractions and the final insoluble residue. According to results from the characterization with various instrumental techniques, these soluble fractions and the final residue all have different nanotube diameter distributions from that found in the starting sample. A general conclusion is that the functionalization and solubilization are selective toward smaller diameter nanotubes, regardless of their being semiconducting or metallic. Mechanistic implications, especially with respect to the post-production separation in terms of the nanotube metallicity, are discussed.

Growth of Single-Walled Carbon Nanotubes on a Nanorough Surface

We compare the growth of single-walled carbon nanotubes (SWNTs) on rough and smooth surfaces. Individual raw HiPco (high-pressure CO) SWNTs are deposited onto porous oxide nanoparticles on a silicon or quartz substrate. The HiPco SWNTs are shown to retain their original catalyst particles that are carbon coated as a result of arrested growth due to bundle formation in the HiPco reactor. Overcoated catalysts are activated with O2 oxidation and SWNTs grown at 900 °C in the presence of CO and H2. The typical length of the SWNTs is more than 10 μm when grown on nanorough surfaces such as fumed silica. This is much longer than the original HiPco SWNTs where the average length is approximately 0.5 μm. They are also much longer than SWNTs grown from the same source material with the same growth conditions on a flat silicon oxide surface. These results support the general impression that extensive interaction of both the nanotube and the catalyst particle with an adjacent surface greatly retards growth.

Effects of ozonolysis and subsequent growth of quantum dots on the electrical properties of freestanding single-walled carbon nanotube films

A significant challenge exists in probing the transport behavior of chemically modified single-walled carbon nanotubes (SWNTs). Thin films of SWNTs offer one facile approach to integration of these materials into electronics and sensing applications. Data on bulk resistivities of ‘bucky paper’ films created from HiPco SWNTs that were initially ozonized and subsequently decorated with CdTe quantum dots have been collected via 4-point probe measurements. Both the oxidation process and addition of CdTe nanocrystals result in increased bulk resistivities, presumably due to the introduction of additional scattering centers in tube sidewalls as well as charge traps in the CdTe functionalized tubes.

Phases of ethane adsorbed on purified HiPco single-walled carbon nanotubes

We have used adsorption isotherms to study ethane films on bundles of purified HiPco single-walled carbon nanotubes (SWNTs). We infer the existence of a possible phase transition in this system from a sudden change in the temperature dependence of the coverage interval corresponding to a feature present in the isotherms. The possible phase transition occurs near monolayer completion, at approximately $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We also measured isotherms at low fractional coverages and relatively high temperatures $(220--240\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ in order to determine the binding energy of ethane on the SWNT bundles. We obtained a value of $308\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ for this quantity; this is 1.76 times larger than the binding energy of ethane on graphite. We used isotherm results obtained at all measured temperatures and coverages to determine the coverage dependence of the isosteric heat of adsorption for this system.

Intermediate-frequency Raman modes for the lower optical transitions of semiconducting single-walled carbon nanotubes

A new class of intermediate-frequency modes (IFMs) associated with the ${E}_{22}^{S}$ and ${E}_{11}^{S}$ optical transitions of bundled HiPco single-walled carbon nanotubes (SWNTs) have been investigated via tunable laser (700\char21{}$985\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$) resonance Raman spectroscopy. ``Steplike'' dispersive behavior was observed for these IFMs, along with associated clusters of radial breathing mode (RBM) overtones at higher frequencies. While the excitation profiles of both RBM and RBM overtones follow a classical behavior predicted by resonance Raman theory, significant differences are observed for the IFM excitation profiles. The observed IFM maxima were found to obey a resonance behavior based on a combination of the ${E}_{22}^{S}$ and${E}_{11}^{S}$ transition energies, scaled by the inverse diameter of the respective nanotube. Only IFMs for the $\mathrm{mod}(n\ensuremath{-}m,3)=2$ nanotubes are visible, with intensities found to obey the family-based chiral angle dependence similar to previously reported electron-phonon interaction patterns observed for the RBM.

Simple Length Determination of Single-Walled Carbon Nanotubes by Viscosity Measurements in Dilute Suspensions

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.

Single-Wall Carbon Nanotubes Bearing Covalently Linked Phthalocyanines − Photoinduced Electron Transfer

HiPco single-walled carbon nanotubes (SWNTs) have been sidewall-functionalized with phthalocyanine addends following two different approaches: a straightforward Prato reaction with N-octylglycine and a formyl-containing phthalocyanine, and a stepwise approach that involves a former Prato cycloaddition to the double bonds of SWNTs using p-formyl benzoic acid followed by esterification of the derivatized nanotubes with an appropriate phthalocyanine molecule. The two materials obtained by these routes comprise different carbon/Pc-addenda ratios, as evidenced by Raman, TGA, and photophysical studies. The occurrence of electron transfer from photoexcited phthalocyanines to the nanotube framework in these ZnPc-SWNT ensembles is observed in transient absorption experiments, which confirm the absorption of the one-electron oxidized ZnPc cation and the concomitant bleaching of the van Hove singularities typical from SWNTs. Charge-separation (i.e., 2.0 x 1010 s(-1)) and charge-recombination (i.e., 1.5 x 106 s(-1)) dynamics reveal a notable stabilization of the radical ion pair product in dimethylformamide.

Aqueous Dispersion, Surface Thiolation, and Direct Self-Assembly of Carbon Nanotubes on Gold

We report the efficient aqueous dispersion of pristine HiPco single-walled carbon nanotubes (SWNTs) with ionic liquid (IL)-based surfactants 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), the thiolation of nanotube sidewalls with 2, and the controlled self-assembly of positively charged SWNT-1,2 composites on gold. Optical absorption spectra and resonance Raman (RR) data of obtained aqueous SWNT-1,2 dispersions are consistent with debundled and noncovalently functionalized nanotubes whose electronic properties have not been disturbed. Additionally, the dispersion of pristine nanotube material with surfactants 1 and 2 leads to a high degree of purification from carbonaceous particles. The chiralities of the 14 smallest semiconducting HiPco SWNTs in resonance with Raman excitation at 1064 nm (1.165 eV) were determined in SWNT-2 aqueous dispersion using UV-vis-NIR and RR spectra. X-ray photoelectron spectroscopy (XPS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopy of SWNT-2 submonolayers on gold verified the encapsulation of individualized SWNTs with IL surfactants, the cleavage of S-S disulfide bonds formed in aqueous SWNT-2 suspensions, and the direct chemisorption of the SWNT-2 composite on bare gold via the Au-S bond. Aqueous dispersions of SWNTs with IL-based surfactants add biofunctionality to carbon nanotubes by imparting the positive surface charge necessary for interactions with cell membranes. Our technique, which purifies pristine nanotube material and produces water-soluble, positively charged nanotubes with pendent surface-active thiol groups, may also be translated to other carbon nanotubes and carbon nanostructures. Self-assembled, positively charged submonolayers of SWNTs can be further used for applications in cell biology and sensor technology.

The purification of HiPco SWCNTs with liquid bromine at room temperature

A new procedure to purify HiPco single-walled carbon nanotubes (SWCNTs) from iron catalyst impurity is introduced. The protocol, which uses liquid bromine at room temperature (RT) as an oxidant, improves nanotube purity from iron by a factor of approximately 10, while maintaining good nanotube integrity as demonstrated by near infrared (NIR) luminescence and absorbance measurements. When HiPco SWCNTs are dissolved in RT Br 2(l) (free of O 2 and H 2O), the metallic iron impurity is quickly oxidized to its bromide salt and easily removed by aqueous washing or by washing with dilute acid. The iron content (by ICP-AE) for the purified SWCNT material was 2.8–3.6% by weight (for three different samples) for a single purification step, but could be lowered to 1.6–1.8% with an additional purification cycle. Characterization of the resulting purified SWCNT material has been achieved by TEM imaging, XPS, ICP-AE analysis, Raman spectroscopy, electronic absorption spectroscopy, and by NIR photoluminescence measurements. Finally, the new Br 2(l) purification procedure has been compared to and contrasted with other established purification procedures for HiPco SWCNTs and found to be a highly desirable alternative.

Nondestructive Formation of Supramolecular Nanohybrids of Single-Walled Carbon Nanotubes with Flexible Porphyrinic Polypeptides

Strategies for single-walled carbon nanotube (SWNT) separation are critical to developing nanotubes as useful nanoscale building blocks. Herein, diameter-selective dispersion of HiPco single-walled carbon nanotubes has been accomplished through noncovalent complexation of the nondestructive nanotubes with a flexible porphyrinic polypeptide bearing 16 porphyrin units [P(H2P)16] in DMF at 298 K. Supramolecular formation occurs through wrapping of peptidic backbone in P(H2P)16 and π−π interaction between porphyrins and nanotubes to extract the large-diameter nanotubes (ca. 1.3 nm) as revealed by ultraviolet−visible-near-infrared and Raman spectroscopy as well as high-resolution transmission electron micropscopy. The photoexcitation of the supramolecular complex affords the long-lived charge-separated state.

Optical enzymatic detection of glucose based on hydrogen peroxide-sensitive HiPco carbon nanotubes

We recently observed that surfactant sodium dodecyl sulfate (SDS)-encased HiPco single-walled carbon nanotubes (SWNTs) respond optically to hydrogen peroxide (H2O2) in the near-infrared region. In this report, we demonstrate that SDS-encased SWNTs immobilized with glucose oxidase (GOx) can be used to optically detect an enzymatic reaction of glucose based on their H2O2 sensitivity as well as pH sensitivity. Only the enzymatic product H2O2 induces the SWNT near-infrared spectral changes in buffer solutions (pH = 6.0), but both H2O2 and gluconic acid products do this in unbuffered solutions. The SWNT optical response to glucose possesses sensitivity and selectivity similar to an electrochemical method using carbon nanotube nanoelectrode arrays. Our results suggest possible carbon nanotube-based optical tools for molecular recognition applications.

Determination of the Concentration of Single-Walled Carbon Nanotubes in Aqueous Dispersions Using UV−Visible Absorption Spectroscopy

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV-visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV-visible absorbance spectra of SWNTs-surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the pi-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV-visible measurements.

The identification of dispersive and non‐dispersive intermediate frequency modes of HiPco single walled carbon nanotubes by in situ Raman spectroelectrochemistry

AbstractThe intermediate frequency modes (IFM) of HiPco single walled carbon nanotubes (SWCNT) were analyzed by in situ Raman spectroelectrochemistry. We demonstrate that dispersive and non‐dispersive IFM features show a different dependence on electrochemical charging. While during p ‐doping the dispersive IFM features exhibit much stronger shift than non‐dispersive IFM ones, during n ‐doping an opposite effect was observed. Therefore we propose the application of the Raman spectroelectrochemical method for the identification of dispersive and non‐dispersive features using only one laser energy excitation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Estimation of the (n,m) Concentration Distribution of Single-Walled Carbon Nanotubes from Photoabsorption Spectra

Deconvolution of the absorption spectrum of single-walled carbon nanotubes (SWNTs) into distinct (n,m) contributions is complicated because transition energies are closely spaced. The algorithm presented in this work attempts to simplify the problem by grouping nanotubes with similar transition energies and assigning weights to their spectral contributions. Voigt line shapes were used to fit absorption spectra of sodium dodecyl sulfate suspended HiPco SWNT and CoMoCat SWNT. Line widths for the metallic (93.42 meV) and two semiconducting regions (57.96 and 29.86 meV) were obtained from the absorption spectra of DNA-wrapped SWNT fractionated by ion-exchange chromatography. The method is used to describe the reaction kinetics of certain HiPco SWNTs upon reaction with 4-chlorobenzene diazonium and 4-hydroxybenzene diazonium salts. The code for deconvolution has been provided as open source in the Supporting Information for future modifications.

Bundling and Diameter Selectivity in HiPco SWNTs Poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene) Composites

Temperature-dependent (TD) Raman measurements at laser excitation 514.5 nm were performed at different concentrations. The spectral profile of the radial breathing modes were investigated up to a polymer concentration of 1 g/L and were found to be dominated by approximately 1.2-1.4 nm diameter tubes at room temperature. Upon heating above the glass transition of the polymer (60 degrees C) the smaller tubes around approximately 0.9 nm increased significantly in relative intensity. This suggests that below the glass transition of the polymer (60 degrees C) RBMs within the composite are damped and spectral changes cannot be interpreted as diameter selective solubilization. The observed RBM damping at room temperature only occurred up to a concentration of approximately 1.2 x 10(-4) g/L and below this no damping was observed. Photoluminescence intensity (PL) measurements were taken for a range of PmPV concentrations, in which HiPco single walled carbon nanotubes (SWNTs) at 100%, 10%, 1%, 0.1%, 0.01%, and 0% mass fractions were added. Fitting of the concentration dependence to a dynamic absorption/desorption model indicates that the polymer interacts with nanotube bundles until a critical concentration of approximately 1.2 x 10(-4) g/L is reached, below which the nanotubes are isolated. The polymer and or solvent has a significant effect on the debundling and aggregation within these systems. Aggregation and/or interaction with the polymer at higher concentrations can effect the RBM profile in the composite at ambient temperatures, providing an incomplete representation of the selection of diameters present within composites at a particular wavelength.

Supramolecular Hybrids of [60]Fullerene and Single‐Wall Carbon Nanotubes.

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Microwave absorbing properties of hydrogen plasma in single wall carbon nanotubes

The complex permittivity of hydrogen plasma in single wall carbon nanotubes (SWNTs), which were grown by iron-catalyzed high-pressure disproportionation (HiPco), is deduced using double-fluid theory and phenomenological model. We calculate the absorptional attenuations of microwave in HiPco SWNTs in the range of 300 MHz–30 GHz under different conditions. The experimental phenomenon of strong microwave absorption (around 2.45 GHz) by hydrogen plasma in HiPco SWNTs can be explained numerically. The influences of the liberal electron density and electronic effective collision frequency on microwave absorption are presented theoretically.

Supramolecular Hybrids of [60]Fullerene and Single‐Wall Carbon Nanotubes

Noncovalent interactions between purified HiPCO single-wall carbon nanotubes (SWNT) and a [60]fullerene-pyrene dyad, synthesized through a regioselective double-cyclopropanation process, produce stable suspensions in which the tubes are very well dispersed, as evidenced by microscopy characterization. Cyclic voltammetry experiments and photophysical characterization of the suspensions in organic solvents are all indicative of sizeable interactions of the pyrene moiety with the SWNT and, therefore, of the prevalence in solution of [60]fullerene-pyreneSWNT hybrids.

The feature of the Breit-Wigner-Fano Raman line in DNA-wrapped single-wall carbon nanotubes

Breit-Wigner-Fano (BWF) Raman line in DNA-wrapped single-wall carbon nanotubes (SWNTs) was investigated. For as-produced HiPco SWNT bundles, the asymmetric profile of BWF line is clearly observed with an excitation energy of 2.33eV. The asymmetric feature almost disappears in isolated HiPco SWNTs by DNA wrapping in aqueous solution. Such a significant change provides evidence that the asymmetric feature of BWF line is attributed to the bundling effect of SWNTs. In addition, the asymmetric feature of BWF line strongly appears even when the DNA-wrapped SWNTs are exposed to air. This means that the rebundling in the DNA-wrapped SWNTs can occur due to drying.

The Fourier Raman spectra of HiPCO single-wall carbon nanotubes under high pressure

The Raman spectra of single-wall carbon semiconducting nanotubes of the HiPCO type were investigated upon excitation at 1.06 µm at pressures up to 3 GPa. A method of purification of the initial material from iron is proposed and the diffraction patterns of purified nanotubes are considered. The diameters and chiralities of the nanotubes manifesting themselves in the spectra are determined. Pressure dependences of the frequencies are obtained and the Gruneisen parameters and their relationship with interatomic interactions in nanotubes are discussed.