HiPco Single-walled Carbon Nanotubes Research Articles

Comparative Study of Methane Adsorption on Single-Walled Carbon Nanotubes

We present the combined results of ab initio and molecular mechanical calculations, computer simulations, and adsorption isotherms investigations of CH(4) adsorbed on HiPco single-walled carbon nanotubes. Isotherms and adsorption energies obtained in our model and simulations are in good agreement with ours and others experimental results. The theoretical analysis conducted for various homogeneous bundles of close-ended and open-ended tubes confirm not only the adsorption in at least two different stages but also the role played by each of the different adsorption sites on the nanotube bundles. The study of different site and nanotube sizes allows us to establish the presence of open tubes in the as-produced HiPco bundles, without regarding the role that adsorption in large interstitial channels may play. Our results also show that predicted scenarios, for the mechanism and the preferential adsorption sites depend on the size of the nanotubes and those of the bundles.

Monitoring the Dispersion Process of SWNTs in Aqueous Solutions by UV-Vis and Raman Spectroscopies

The current bottleneck to carbon nanotubes (CNT) application in composite materials field consists in the difficulty of dispersing them in solvents. As a result of strong van der Waals interactions, as produced CNTs are tightly bundled in ropes of several tubes, rendering the carbon-powder insoluble in aqueous and organic liquids and thus unprocessable. The interest in applications that require water-soluble CNTs is growing and much attention is being directed to the study of surfactant aqueous solutions. In a typical dispersion procedure, after the surfactant has been adsorbed on the nanotube surface by hydrophobic or pi-pi interactions, ultrasonication helps nanotubes debundling, providing a mechanical energy able to overcome van der Waals interactions in CNT bundles. The electrostatic repulsion between surfactant polar heads that remain in solution allows the colloidal stability. In this work the dispersibility of HiPCO Single Walled Carbon Nanotubes (SWNT) in different surfactant solutions has been evaluated by using UV-vis and Raman spectroscopies. UV absorbance as well as intensity of SWNTs characteristic Raman bands have been studied as a function of sonication time for each type of surfactant. Moreover the surface morphology of SWNTs films obtained by solutions drying has been observed by using Scanning Electron and Atomic Force Microscopies.

Magnetic field and electromagnetic wave properties of carbon monoxide with high-pressure disproportionation single-walled carbon nanotubes

A double-fluid theory is used to find the electromagnetic wave absorption of carbon monoxide with iron-catalyzed high-pressure disproportionation (HiPco)-grown single-walled carbon nanotubes (SWNTs). The electromagnetic wave absorption of carbon monoxide with HiPco SWNTs is obtained and is studied numerically. The absorption is then deduced and their functional dependence on the number density, collision frequency, cyclotron frequency, and angle of propagation is studied. The double-fluid theory predicts that there is an electromagnetic frequency dependency on the energy absorption properties of the system under investigation. The calculation results show that effects of magnetic field strength and the angle of microwave propagation on the absorption coefficient as well as the frequency band of resonant absorption are very significant.

Charging Nanowalls: Adjusting the Carbon Nanotube Isoelectric Point via Surface Functionalization

Controlling the point of zero charge (PZC) of carbon nanotubes is important for depositing finely dispersed metal nanoparticles from precursors in solution for fabricating chemical and biological sensor and catalyst surfaces. HiPco single-walled carbon nanotubes (p-SWNTs) were functionalized with carboxylic acid (COOH-SWNT), nitroso (NO-SWNT), and maleic anhydride (MA-SWNT) groups. The presence of attached moieties on the carbon nanotube surface was verified using X-ray photoelectron (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopies. PZC measurements (in parentheses) were in the descending order: NO-SWNTs (7.5) > p-SWNTs (3.5) > MA-SWNTs (2.0) > COOH-SWNTs (1.2). The trend in measured PZC values correlated with the electron withdrawing character of the attached moieties, consistent with Hammett σ constants. Variations in the electron withdrawing character of the moieties led to SWNTs with differing semiconducting character, as observed in the UV−vis-NIR E11 semiconducting region and R...

Preparation and Selected Properties of an Improved Composite of the Electrophoretically Deposited Single-Wall Carbon Nanotubes, Electrochemically Coated with a C60-Pd and Polybithiophene Mixed Polymer Film

An improved carbon nanotube conducting composite material for electrochemical capacitors has been devised and tested. It was prepared by electrophoretic deposition of a film of noncovalently surface modified with 1-pyrenebutyric acid HiPCO single-wall carbon nanotubes (pyr-SWCNTs), which were then electrochemically coated, under multiscan cyclic voltammetry (CV) conditions, with a mixed film of the fullerene-palladium (C60-Pd) polymer and the polybithiophene (PBT) polymer. Both the electrophoretic deposition of pyr-SWCNTs and electrochemical polymerization of (C60-Pd)-PBT was in situ monitored by piezoelectric microgravimetry (PM) with the use of an electrochemical quartz crystal microbalance (EQCM). Atomic force microscopy imaging of the film revealed that pyr-SWCNTs formed tangles of pyr-SWCNTs bundles surrounded by globular clusters of (C60-Pd)-PBT. X-ray photoelectron spectroscopy provided information on the mole ratio of BT/C60/Pd ≈ 1:2:4 indicating that, most likely, the C60-Pd and PBT polymers are ...

Combined electron microscopy and spectroscopy characterization of as-received, acid purified, and oxidized HiPCO single-wall carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) are very important materials due to their combination of unique structure, dimension, strength, chemical stability, and electronic properties. Nevertheless, SWCNTs from commercial sources usually contain several impurities, which are usually removed by a purification process that includes reflux in acids and strong oxidation. This strong chemical procedure may alter the nanotube properties and it is thus important to control the extent of functionalization and oxidation during the purification procedure. In this report, we provide a comprehensive study of the structure and physical composition of SWCNTs during each step of the purification process. Techniques such as Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and Infrared spectroscopy were used to track the SWCNTs structure, in terms of length and diameter distribution, and surface chemical modifications during each purification stage .

Continuous and Scalable Fabrication of Transparent Conducting Carbon Nanotube Films

We report an industrially scalable, fast, and simple process for the large scale fabrication of optically transparent and electrically conducting thin films of single-walled carbon nanotubes (SWNT). Purified, pristine HiPco SWNTs were dispersed in water at high concentrations with the help of surfactants, rod-coated into uniform thin films, and doped by various acids. We show how to combine different surfactants to make uniform dispersions with high concentration of SWNTs and optimal rheological behavior for coating and drying, including preventing dewetting and film rupture that has plagued earlier attempts. Doping by fuming sulfuric acid yielded the films with best performance (sheet resistance of 100 and 300 Omega/sq for respective transparency of 70% and 90%). We use a figure of merit (FOM) plot for an immediate evaluation and comparison of the performance and microstructure of CNT films produced by different methods. Further scientific engineering will pave the way to the deployment of CNT films in commercial applications.

Quantitative Analyses of Microwave-Treated HiPco Carbon Nanotubes Using Absorption and Raman Spectroscopy

As-produced samples of HiPco single-walled carbon nanotubes were subject to microwave radiation treatment, a process which has been reported to selectively destroy metallic nanotubes, leaving samples of predominantly semiconducting nanotubes. Raman measurements of samples exposed for differing durations demonstrate the preferential degradation of metallic nanotubes. UV−vis−NIR absorption spectroscopy demonstrates however that metallic tubes of different diameters degrade at different rates and that prolonged exposure results in the degradation of semiconducting nanotubes. The reaction process was monitored as a function of exposure time through variations in the graphitic band and the radial breathing modes of the Raman spectrum at 633 nm excitation wavelength leading to the determination of the reaction rates and optimum time period for the maximum destruction of metallic tubes. A batch of SWNTs treated under these optimum conditions was produced, and suspensions in 1% aqueous sodium dodecyl benzene sulfonate (SDBS) were prepared. The concentration dependence of the Raman scattering and UV−vis−NIR absorption demonstrated the debundling of the semiconducting bundles to isolated tubes. Extinction coefficients of the bundles and isolated tubes were determined using the Beer−Lambert law. The critical debundling point or dispersion limit was found to be 0.16 ± 0.03 mg/mL compared to the untreated sample which was 0.07 ± 0.03 mg/mL.

Conductive, Capacitive, and Viscoelastic Properties of a New Composite of the C60−Pd Conducting Polymer and Single-Wall Carbon Nanotubes

Thin films of a new composite of an electroactive fullerene-based (C60-Pd) polymer and HiPCO single-wall carbon nanotubes, which were noncovalently modified by 1-pyrenebutiric acid (pyr-SWCNTs), were electrochemically prepared under multiscan cyclic voltammetry conditions. With respect to blank polymer, superior conductive, capacitive, and viscoelasitic properties of the composite were demonstrated. Composition of pyr-SWCNTs was determined by thermogravimetric analyses, which showed one molecule of 1-pyrenebutiric acid per approximately 20 carbon atoms of SWCNT. Atomic force microscopy imaging revealed that pyr-SWCNTs form tangles of pyr-SWCNTs bundles surrounded by globular clusters of the C60-Pd polymer. Peaks characteristic of both pyr-SWCNTs (radial breathing modes at approximately 200 to 300 cm(-1)) and C60-Pd polymer in the Raman spectra recorded for the composite confirmed the presence of pyr-SWCNTs in the composite film. The mass of the deposited film was in situ measured by piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance (EQCM). Then, curves of the current, resonant frequency change, and dynamic resistance change versus the potential in different potential ranges were simultaneously recorded in a blank acetonitrile solution of tetrabutylammonium perchlorate. Specific capacitance, determined at -1.20 V for the composite as 90 F g(-1), was twice as high as that for the polymer. Electrochemical impedance spectroscopy was used to determine impedance parameters of both the C60-Pd polymer and C60-Pd/pyr-SWCNTs composite film. This data analysis indicated increased capacitance and decreased resistance for the new composite film.

Layer-by-Layer Assembly of Nanotube-Polymer Thin Films with High Electrical Conductivity and Transparency

AbstractLayer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (˜ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 °C. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications.

Effect of Solvent Solubility Parameters on the Dispersion of Single-Walled Carbon Nanotubes

A systematic study of the effect of a series of organic solvents on the dispersion of as-produced HiPco single-walled carbon nanotubes (SWNTs) has been conducted. UV−vis−NIR absorption spectroscopy coupled with an integrating sphere was employed to differentiate absorbance and scattering. For each solvent, a concentration-dependent study of the absorbance in the normal chamber and in the integrating sphere enabled the calculation of the total extinction coefficient and absorption coefficient. A correlation between the extinction/absorption coefficient and the Hildebrand and Hansen solvent parameters was established, indicating that polar interactions and hydrogen bonding dominate.

Spectroscopic Evidence of Carbon Nanotubes’ Metallic Character Loss Induced by Covalent Functionalization via Nitric Acid Purification

A detailed characterization of covalently functionalized HiPco single-walled carbon nanotubes (SWNTs) has been carried out using several physicochemical methods (thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman scattering). The chemical process, finally leading to SWNT−ester derivatives, starts from nitric acid purification of pristine SWNTs. Besides the efficiency of the functionalization, we show that a loss of metallic character of the carbon nanotubes is initiated by the nitric acid treatment of pristine SWNTs and is maintained in the final SWNT ester derivatives. A higher reactivity of the metallic tubes is also demonstrated.

Covalent Functionalization of Single-Walled Carbon Nanotubes Alters Their Densities Allowing Electronic and Other Types of Separation

We show that covalently attached functional groups can alter the densities of individual single-walled carbon nanotubes (SWNTs) in a predictable and highly controllable manner. A volume-additivity model based on molecular group contributions can be used to estimate the density difference between 4-hydroxyphenyl-functionalized and nonfunctionalized HiPco SWNTs as approximately 98.3 kg/m3, compared with 97.9 kg/m3 measured by density-gradient centrifugation. Conversely, the estimated density difference between the (6,5) (0.75 nm diameter) and (9,8) (1.17 nm diameter) SWNTs is smaller at 23.4 kg/m3. We conclude that covalent functionalization can provide an effective handle to separate particular SWNTs from a typical diameter distribution. We show that SWNT mixtures in which metallic SWNTs have been selectively reacted produce two distinct density fractions corresponding to functionalized metallic and pure semiconducting SWNTs. The results were confirmed by Raman spectroscopy, where the high-density fraction...

Improved Bath Sonication Method for Dispersion of Individual Single-Walled Carbon Nanotubes Using New Triphenylene-Based Surfactant

We developed a new surfactant for the dispersion of single-walled carbon nanotubes (SWNTs). The surfactant is an amphiphilic compound with a π-conjugative triphenylene skeleton. SWNTs were individually dispersed by the aid of the surfactant using a common low-power bath sonicator. Well-dispersed HiPco SWNTs in D2O solution were obtained using the surfactant by the repetition of surfactant addition and sonication, followed by overnight sonication. Spectroscopic measurements of the dispersed solution revealed that the SWNTs were dispersed sufficiently to show clear photoluminescence (PL) without ultracentrifugation. Moreover, this method was applied to the dispersion of SWNTs using a typical surfactant, sodium dodecylbenzene sulfate (SDBS). The observed clear PL from SWNTs in the solution obtained without ultracentrifugation suggested that gradual surfactant addition and sonication, followed by overnight sonication, strongly contributed to the efficient dispersion of SWNTs in water.

Debundling of Single-Walled Carbon Nanotubes by a Nanoball-Penetrating Method

Water-based FePt nanoparticles (NPs) have been used to disperse acid-treated HiPCO single-walled carbon nanotubes (SWNTs) in TMAOH solution under mild experimental conditions. The result shows that seriously aggregated SWNTs with bundle sizes from 20 to ∼30 nm can be exfoliated into individually dispersed tubes in water while their intrinsic chemical properties and long lengths are kept intact. A novel nanoball-penetrating method is proposed, and the dispersion and exfoliation mechanism is discussed to explain the debundling results. Electrostatic interaction between (CH3)4N+ and carboxyl groups on SWNTs decreasing the van der Waals force of the bundles, deep penetration of FePt NPs into the gaps of SWNT ropes, and repulsive interaction between negatively charged SWNTs and FePt NPs all contribute to the final efficient exfoliation. More than 50% of SWNTs can be debundled into individually dispersed nanotubes under optimum conditions. Raman scattering spectroscopy used to characterize the properties of SWN...

Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

The second-order Raman modes in the range of $380--650\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ were investigated for individually dispersed and aggregated HiPco single-walled carbon nanotubes (SWNTs) using a $700--985\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ tunable laser source. For individually dispersed SWNTs, this Raman region displays relatively weak response from both intermediate frequency modes (IFMs) and the overtones of the radial breathing mode (RBM), with the latter dominating. In contrast, for aggregated SWNTs, the IFMs dominate and gain significant intensity relative to the RBM fundamental. Utilizing the correlation between RBM overtone and RBM fundamental intensity ratio as a function of laser energy, we derived Huang-Rhys factors for several $(n,m)$ nanotube species in both individually dispersed and aggregated states. These values were further used to obtain the corresponding absolute values of the exciton-phonon interaction matrix element for these nanotube species. It is demonstrated that the chiral-angle dependence of exciton-phonon coupling parameters is similar for dispersed and bundled samples. However, we find that bundling results in a decrease in the exciton-phonon coupling for the RBM, while the IFMs display the opposite behavior. These findings are particularly relevant for further clarifying the factors that govern Raman intensities and provide a tool for the selective characterization of various $\mathrm{mod}(n\ensuremath{-}m,3)=2$ $(n,m)$-SWNTs as a function of their aggregation state.

Diameter-Selective Solubilization of Carbon Nanotubes by Lipid Micelles

The one-step dispersion of HiPco single-walled carbon nanotubes in aqueous media with the use of a synthetic lyso-phosphatidylcholine was studied. Solubilization occurs through wrapping of lipid molecules around the circumference of the tubes, yielding lipid monolayers on the graphitic sidewalls as evidenced by atomic force microscopy imaging and dynamic light scattering measurements. Raman spectroscopy showed that the dispersion and centrifugation process leads to an effective enrichment of the stable aqueous suspension in carbon nanostructures with smaller diameters.

Investigation of Sodium Dodecyl Benzene Sulfonate Assisted Dispersion and Debundling of Single-Wall Carbon Nanotubes

The dispersion limit of HiPco single-wall carbon nanotubes (SWCNT) in 1% by weight sodium dodecyl benzene sulfonate (SDBS) assisted dispersions in water is reported. The starting concentration of the tubes in water surfactant solution was 5 mg/mL which was diluted sequentially by a factor of 2 down to 1.2 × 10-3 mg/mL. Sonication and centrifugation were performed to obtain a homogeneous dispersion of HiPco SWCNTs in water surfactant solution. Concentration-dependent absorption and Raman spectroscopic studies were used to analyze the SWCNTs behavior in water-based solution, and atomic force microscopy (AFM) was employed to examine the aggregation state of the nanotubes over the concentration range. Both spectroscopic techniques demonstrate a clear concentration below which the nanotube bundles become significantly dispersed in the solution. The concentration limit at which debundling starts was found to be 0.07 ± 0.03 mg/mL. The dispersion behavior and optical parameters determined are compared with those ...

Preferential functionalisation of carbon nanotubes probed by Raman spectroscopy

We have chemically grafted methoxypheny functions on HiPco single-walled carbon nanotubes through a radical procedure. To characterise the efficiency of this functionalisation, the materials have been examined via Raman spectroscopy at five laser excitation energies (1.96, 2.33, 2.41, 2.54 and 2.71 eV). This work concentrates mostly on the radial breathing mode band between 150 and 300 cm −1. Clear evidence is put forward showing that those tubes which are preferentially functionalised are the smaller-diameter semiconducting tubes and the metallic tubes.

Dispersibility and stability improvement of unfunctionalized nanotubes in amide solvents by polymer wrapping

Improvement on the stability and loading of unfunctionalized single wall carbon nanotubes (SWNTs) in amide solvents is necessary to enhance the performances of SWNT-polymer composites used for optical applications (e.g., as non-linear saturable absorbers). We show that polyvinylpyrrolidone (PVP) can not only increase the stability of ultrasonically dispersed HiPco SWNTs in pure N-methyl-2-pyrrolidone (NMP), but also improve the photoluminescence emission signals from SWNTs even after 1 month of incubation. Compared to two non-ionic surfactants (Igepal DM-970 and Pluronic F-98), we find that PVP-aided SWNT dispersions in NMP can improve the SWNT loading by at least four times. Unlike surfactant-aided dispersions, the PVP-aided dispersions remain completely stable by close visual inspection even after 6 months of incubation.