Pure Single-walled Carbon Nanotubes Research Articles

The synthesis of covalent bonded single-walled carbon nanotube/polyvinylimidazole composites by in situ polymerization and their physical characterization

Single-walled carbon nanotube (SWCNT) polyvinylimidazole (PVI) composites have been prepared by in situ emulsion polymerization. Dispersion of raw SWCNTs in the PVI matrix was improved by surface modification of the SWCNTs using nitric acid treatment and air oxidation. The carbonyl-terminated SWCNTs were covalently bonded to PVI by in situ polymerization and the SWCNT/PVI composite was thus obtained. The morphological and structural characterizations of the surface-functionalized SWCNTs and SWCNT/PVI composites were carried out by Fourier transform infrared spectroscopy, X-ray diffraction, conductivity measurements, scanning, and transmission electron microscopy. Thermograms of the materials were determined by the differential scanning calorimetry technique. The characterization results indicate that PVI was covalently bonded to SWCNTs and a new material was then obtained. The functionalized SWCNTs showed homogenous dispersion in the composites, whereas purified SWCNT resulted in poor dispersion and nanotube agglomeration. SWCNT/PVI composites exhibited chemical stability enhancement in many common solvents. I–V curves of the samples exhibit an ohmic character. Conductivity values for pure SWCNTs, pure PVI and SWCNT/PVI composite were measured to be 3.47, 2.11 × 10−9, and 2.3 × 10−3 S/m, respectively. Because of resonance, a large dielectric constant is obtained for SWCNT/PVI composite, which is not observed for ordinary materials. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Carbon monoxide adsorption on transition element-doped single wall carbon nanotube

The present work focuses on the carbon monoxide (CO) gas adsorption on transition element doped (8, 0) zig-zag single wall carbon nanotube (SWCNT) and pure SWCNT. Density functional theory studies show that Sc, Ti and V doped SWCNTs adsorb CO molecules effectively compared to pure SWCNT. The binding energy of Sc, Ti and V doped SWCNT is 1.31, 1.81 and 0.95 eV, respectively, which is much higher than pure SWCNT. The band structures and density of states of these transition elements show dramatic changes in their structures on doping CO molecules. The band gap of pure SWCNT is 0.7 eV while on doping transition elements and on absorbing CO molecules, it reduces up to 0.35 eV. This study shows that the transition element doped SWCNTs can be used as a good CO molecule absorber at room temperature.

Diameter-selective purification of carbon nanotubes by microwave-assisted acid processing

Narrowly diameter-distributed single-walled carbon nanotubes (SWCNTs) were purely achieved by a facile technique combining microwave irradiation with mixed acid-assisted dispersion. Using this process, besides removal of conventional impurities, both small SWCNTs with highly chemical reactivity and the outer layers of large double-walled carbon nanotubes with more topological defects were preferentially eliminated, retaining only pure SWCNTs of which the diameter distribution was significantly narrowed. The chemical structure of resulting materials was carried by Raman spectroscopy, and electron microscopies. Results revealed that the technique employed is of great efficacy not only for purifying carbon nanotubes, but also especially for narrowing carbon nanotubes. The dual effects of purifying and diameter distribution narrowing make this method promising for achieving high purity single-walled CNTs of specific types. The purification mechanism of the present technique was discussed in detail.

Magnetic and binding properties of Co-doped single-walled carbon nanotubes: a first principles study

An attempt has been made to analyze the magnetic-spin quenching property of Co, as a representative of transition metals, in Co-doped single-walled carbon nanotubes (SWCNTs) as well as the binding property of CO with the side walls of the Co-doped SWCNTs by means of hybrid density functional theory (DFT) calculations. Four different types of SWCNTs are considered: semi-conducting (5,0) zigzag, metallic (5,2) and semi conducting (5,3) chirals, and metallic (5,5) armchair. The results show that while the spin states of Co in the whole of the present Co-doped SWCNTs were preserved, the combined effects of adsorbate (CO) and substrate (Co-doped SWCNT) were strong enough to favor the low-spin states, and to quench the spins in the Co-doped SWCNTs (5,0) and (5,2). The doped Co atom converts the endothermic reactions of CO molecules on the outer surfaces of the pure SWCNTs into exothermic reactions. The nature of charge transfer between the d-orbitals of Co, and the π* orbital of the nearby C of CO is clarified. Natural bond orbital (NBO) analysis reveals that the electronic configuration of the doped Co metal represents a qualitative change with respect to that of the free-metal. The binding of CO precursor is mostly dominated by the metal E(i)Co..CO pairwise additive contributions, and the role of the SWCNTs is not restricted to supporting the metal. The spin quenched SWCNTs are characterized in terms of isodensity contours of frontier orbitals. Molecular electrostatic potentials (MEPs) indicate that SWCNTs can act as effective gas sensors for nucleophiles. The results show that Co-doped SWCNTs can be useful in spintronics applications and sensor technology.

Bulk Purification and Deposition Methods for Selective Enrichment in High Aspect Ratio Single-Walled Carbon Nanotubes

Aqueous batch processing methods for the concurrent purification of single-walled carbon nanotube (SWNT) soot and enrichment in high aspect ratio nanotubes are essential to their use in a wide variety of electronic, structural, and mechanical applications. This manuscript presents a new route to the bulk purification and enrichment of unbundled SWNTs having average lengths in excess of 2 μm. Iterative centrifugation cycles at low centripetal force not only removed amorphous C and catalyst nanoparticles but also allowed the enhanced buoyancy of surfactant encapsulated, unbundled, high aspect ratio SWNTs to be used to isolate them in the supernatant. UV-vis-NIR and Raman spectroscopy were used to verify the removal of residual impurities from as-produced (AP-grade) arc discharge soot and the simultaneous enrichment in unbundled, undamaged, high aspect ratio SWNTs. The laminar flow deposition process (LFD) used to form two-dimensional networks of SWNTs prevented bundle formation during network growth. Additionally, it further enhanced the quality of deposits by taking advantage of the inverse relationship between the translational diffusion coefficient and length for suspended nanoparticles. This resulted in preferential deposition of pristine, unbundled, high aspect ratio SWNTs over residual impurities, as observed by Raman spectroscopy and atomic force microscopy (AFM).

Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter.

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8–1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.

Purification of Single-Wall Carbon Nanotubes by Controlling the Adsorbability onto Agarose Gels Using Deoxycholate

One of the key challenges to the industrialization of single-wall carbon nanotubes (SWCNTs) is the commercial-scale production of highly purified SWCNTs separated into metallic and semiconducting species. In the present study, the purification of SWCNTs, i.e., the removal of amorphous carbon or bundled SWCNTs, was performed by quantifying and controlling their adsorbability onto agarose gel. The quantification of the adsorbability was achieved by assuming the Langmuir isotherm, and control over the adsorbability was exerted using 0.05–1% sodium deoxycholate (DOC). The results show that the adsorbability depends on the concentration of DOC. At a low DOC concentration (approximately 0.05%), impurities such as amorphous carbon or bundled SWCNTs were preferentially adsorbed onto the gels, whereas, at an intermediate DOC concentration (ca. 0.25%), high-purity SWCNTs were mainly adsorbed onto the gels. Thus, the impurities, which are difficult to remove by conventional methods, could be separated from unpurified SWCNTs by controlling the adsorbability, leading to the extraction of high-purity SWCNTs. In the purification, diameter-selective separation of SWCNTs was also observed. The purification method using a gel column can be conducted simply and continuously, so that it can be applied for the high-throughput production of high-purity SWCNTs.

Mo–Co catalyst nanoparticles: Comparative study between TiN and Si surfaces for single-walled carbon nanotube growth

Highly pure single-walled carbon nanotubes (SWNT) were synthesized by alcohol catalytic chemical vapor deposition on silicon substrates partially covered by a thin layer of TiN. The TiN coating selectively prevented the growth of carbon nanotubes. Field emission scanning electron microscopy and Raman spectroscopy revealed the formation of high purity vertically aligned SWNT in the Si region. X-ray Photoelectron Spectroscopy and Atomic Force Microscopy indicated that Co nanoparticles are present on the Si regions, and not on the TiN regions. This clearly explains the obtained experimental results: the SWNT only grow where the Co is presented as nanoparticles, i.e. on the Si regions.

Carbon Nanotubes Doped with Nitrogen, Pyridine-like Nitrogen Defects, and Transition Metal Atoms

Dopants and defects can be introduced as well as the intercalation of metals into single wall carbon nanotubes (SWCNTs) to modify their electronic and magnetic properties, thus significantly widening their application areas. Through spinpolarized density functional theory (DFT) calculations, we have systemically studied the following: (i) (10,0) and (5,5) SWCNT doped with nitrogen (), (ii) (10,0) and (5,5) SWCNT with pyridine-like defects (3NV-), and (iii) chemical functionalization of (10,0) and (5,5) 3NV- with 12 different transition metals (TMs) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, and Pt). Attention was done in searching for the most stable configurations, deformation, calculating the formation energies, and exploring the effects of the doping concentration of nitrogen and pyridine-like nitrogenated defects on the electronic properties of the nanotubes. Also, calculating the corresponding binding energies and effects of chemical functionalization of TMs on the electronic and magnetic properties of the nanotubes has been made. We found out that the electronic properties of SWCNT can be effectively modified in various ways, which are strongly dependent not only on the concentration of the adsorbed nitrogen but also to the configuration of the adsorbed nitrogen impurities, the pyridine-like nitrogenated defects, and the TMs absorbed; due to the strong interaction between the d orbitals of TMs and the p orbitals of N atoms, the binding strengths of TMs with the two 3NV- are significantly enhanced when compared to the pure SWCNTs.

Binder-free composite electrodes using carbon nanotube networks as a host matrix for activated carbon microparticles

In this research, networks of single-walled carbon nanotubes (SWNTs) were used to host activated carbon (aC) microparticles to fabricate freestanding composite electrodes without the use of polymer binders. The aC-SWNT composite electrodes with up to 50 wt. % aC showed specific surface areas approaching 1000 m2/g and electrical conductivities >36 S/cm. The composite electrodes possessed the properties of both pure SWNT electrodes (e.g. low ohmic drop and rapid ion diffusion) and activated carbon particles (e.g. high specific capacitance). With an interconnected mesoporous microstructure and high electrical conductivity, the CNT networks provide an attractive alternative to polymer binders for forming freestanding electrodes for electrical energy storage devices. Here we show that micron-sized particles can be supported in this framework to utilize the performance enhancement and robustness provided by CNTs. Symmetric electrochemical capacitors fabricated with the electrodes in 6 M potassium hydroxide (KOH) aqueous electrolyte maintained specific capacitances of more than 45 F/g after 30,000 constant-current charge–discharge cycles with a current of 3.6 mA/cm2.

Production and Characterization of Boron-Doped Single Wall Carbon Nanotubes

We have synthesized boron-doped single wall carbon nanotubes in a high vacuum chemical vapor deposition (CVD) system using a new boron precursor. Transmission electron microscopy was used in order to confirm the presence of single wall carbon nanotubes and field emission scanning electron microscopy to allow a qualitative characterization of the produced tubes. To estimate the doping level, we compared the Raman spectra with pure single wall carbon nanotubes and we found an upshifted G band as an evidence of doping. X-ray photoelectron spectroscopy analysis and ab initio electronic structure calculations reveals the presence of substitutional boron atoms incorporated on the tubes. We have also developed a simple method to determine quantitatively in which temperature range the carbon nanotubes are produced more efficiently by high vacuum CVD.

Functionalization of single-walled carbon nanotubes and their binding to cancer cells

BackgroundSingle-walled carbon nanotubes (SWCNTs) have novel properties including their nanoscale size and ease of cellular uptake. This makes them useful for drug delivery, and their photo-thermal effects make them potentially useful in a wide range of applications, particularly the treatment of solid tumors. The poor solubility of SWCNTs has, however, been an issue that may potentially limit the utility of SWCNTs for cancer treatment. Functionalization of the surface of the tubes may be an approach to overcome this problem.MethodsSWCNTs were refluxed in HNO3/H2SO4 (1:3) at 120°C for 120 minutes. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and near infrared (NIR) light exposure were used to assess the functionalization process. The attachment of a carbohydrate-binding protein (lectin) labeled with fluorescein isothiocyanate to the functionalized SWCNTs enabled evaluation of the functionalization step via confocal microscopy. The lectin from Helix pomatia, (Helix pomatia agglutinin [HPA]), can detect changes in protein glycosylation associated with aggressive metastatic cancer. The interaction between the lectin HPA alone and HPA conjugated to the functionalized SWCNTs with human breast cancer cells (MCF-7) was measured using a quartz crystal microbalance biosensor.ResultsFollowing the functionalization process, TEM images showed a layer had formed on the surface of the SWCNTs. In the FTIR experiment, results illustrated the presence of the −COOH group on the functionalized SWCNTs. Contact angle measurements showed that upon functionalization the hydrophilicity of the SWCNTs increased. The temperature increase in the liquid (supernatant) surrounding the functionalized SWCNTs following exposure to light in the NIR (808 nm) was greater than for non-functionalized SWCNTs. The biosensor work showed that HPA binds with high affinity (nanomolar range) to human breast cancer cells; HPA-binding properties to MCF-7 cells were retained following conjugation to the functionalized SWCNTs.ConclusionTreating pure SWCNTs with HNO3/H2SO4 (1:3) at 120°C for 120 minutes is an effective method for functionalization of SWCNTs. HPA linked to SWCNTs is a suitable candidate for the delivery of the functionalized SWCNTs to cancer cells.

Evaluation of the Effect of PEGylated Single-Walled Carbon Nanotubes on Viability and Proliferation of Jurkat Cells.

Among the numerous nanosized drug delivery systems currently under investigation, carbon nanotubes (CNTs), regardless of being single or multiple-walled, offer several advantages and are considered as promising candidates for drug targeting. Despite the valuable potentials of CNTs in drug delivery, their toxicity still remains an important issue. After the PEGylation of single-walled CNTs (SWCNTs) with phospholipid-PEG (Pl-PEG) conjugates to prepare water-dispersible nanostructures, the present study was designed to evaluate whether the functionalization with Pl-PEG derivatives could alter the cytotoxic response of cells in culture, affect their viability and proliferation. In-vitro cytotoxicity screens were performed on cultured Jurkat cells. The SWCNTs samples used in this exposure were pristine SWCNTs, Pl-PEG 2000/5000-SWCNTs at various concentrations. Jurkat cells were first incubated for 3 h at 37°C with test materials and seeded in 6-well culture plates at a given concentration. The plates were then incubated for 24, 48 and 72 h at 37°C in a 5% CO2 humidified incubator. Cell Viability and proliferation assay were performed using trypan blue exclusion test and the cell cycle kinetic status of Jurkat cells was analyzed by flow cytometry. Cell morphology was finally studied using double staining technique and a fluorescence microscope. We found that, regardless of the duration of exposure, functionalized SWCNTs were substantially less toxic, compared to pure SWCNTs and that the molecular weight of Pl-PEGs played an important role at higher concentrations. In conclusion, our noncovalent protocol seemed to be effective for increasing SWCNTs biocompatibility.

Free-standing single-walled carbon nanotube–CdSe quantum dots hybrid ultrathin films for flexible optoelectronic conversion devices

In this work, we described a facile route for the fabrication of free-standing single-walled carbon nanotubes (SWCNT)-CdSe quantum dots (QDs) hybrid ultrathin films and investigated their optoelectronic conversion properties. A free-standing SWCNT film with thickness of ∼36 nm was firstly prepared via vacuum filtration. The film was then immersed into the pre-synthesized oleic acid-capped CdSe QDs (average diameter of 3.5 nm) solution, where CdSe QDs anchored spontaneously onto the surface of SWCNT film to produce SWCNT-CdSe QDs hybrid film. By using pure SWCNT films in different thicknesses as bottom and top electrodes, a flexible all-carbon electrode optoelectronic conversion device with sandwich structure of SWCNT film (thickness of ∼200 nm)/SWCNT-CdSe QDs hybrid film (thickness of ∼36 nm)/SWCNT film (thickness of ∼36 nm) was constructed to generate optoelectronic conversion under illumination of solar-simulated light. Our results demonstrated that the all-carbon electrode structure was effective for charge separation and a sensitive and stable photocurrent signal could be produced in such a device. In addition, our SWCNT-CdSe QDs hybrid film exhibited high flexibility and durability. No clear change in the resistance of the film was detected under bending in various bending angles.

Electrostatically controlled isolation of debundled single-walled carbon nanotubes from nanoplatelet dispersant

Individually dispersed single-walled carbon nanotubes (SWCNTs) were isolated and stabilized from electrostatically tethered nanoplatelets in aqueous solution, following nanoplatelet-assisted exfoliation. SWCNT isolation was achieved by precipitating nanoplatelets with cations and by concurrent usage of appropriate surfactants to stabilize SWCNTs. It was found that the precipitation of nanoplatelets induced by monovalent cations was due to the ionic screening effect, whereas ion exchange was the main cause for nanoplatelet aggregation when divalent cations were used. When the above processes are optimized, isolation of pure SWCNTs with yield greater than 90% can be achieved. Effects of ion valency, ion size, reaction time, concentration of SWCNTs and surfactant type for the separation process are discussed. The structure and composition of the exfoliated SWCNTs were characterized using various microscopy and spectroscopy tools. The above exfoliation and separation approach does not noticeably affect the electronic state of the SWCNTs, and is thus highly attractive for applications where optimal SWCNT properties are desired.

Unweaving the rainbow: a review of the relationship between single-walled carbon nanotube molecular structures and their chemical reactivity

Single-walled carbon nanotubes (SWNTs) are a fundamental family of distinct molecules, each bearing the possibility of different reactivities due to their intrinsically distinct chemical properties. SWNT syntheses generate a heterogeneous mixture of species with varying electronic character, lengths, diameters and helicities, (n,m), as well as other amorphous, graphitic and metal catalyst impurities. In recent years, selective syntheses and post-synthetic separation strategies have advanced, driven by the requirement for pure SWNTs displaying particular features. Covalent surface modifications are widely-used to adapt SWNTs for specific applications with modified solubility, compatibility and specific functionalities. In many cases, such reactions have been found to be selective, illuminating the fundamentally distinct chemistry of each (n,m) species. This differential reactivity has found immediate utility in facilitating the sorting of nanotubes according to specific diameter, electronic properties and, most importantly, helicity. In this tutorial review, we discuss a wide range of selective reactions, the mechanisms that are thought to govern selectivity, and the challenges of separating, characterising and regenerating the modified SWNTs.

Analytical Solution of Joule-Heating Equation for Metallic Single-Walled Carbon Nanotube Interconnects

In this paper, we address a closed-form analytical solution of the Joule-heating equation for metallic single-walled carbon nanotubes (SWCNTs). Temperature-dependent thermal conductivity κ has been considered on the basis of second-order three-phonon Umklapp, mass difference, and boundary scattering phenomena. It is found that κ , in case of pure SWCNT, leads to a low rising in the temperature profile along the via length. However, in an impure SWCNT, κ reduces due to the presence of mass difference scattering, which significantly elevates the temperature. With an increase in impurity, there is a significant shift of the hot spot location toward the higher temperature end point contact. Our analytical model, as presented in this study, agrees well with the numerical solution and can be treated as a method for obtaining an accurate analysis of the temperature profile along the CNT-based interconnects.

Self-Supporting Electrode Based-on SWNT Paper for Supercapacitors

Self-supporting film of single-walled carbon nanotubes (SWNTs), also known as SWNT paper, is held together by Van der Waals force without any chemical binders. Prepared by vacuum filtration method, SWNT paper was then decorated wirh polypyrrole (PPy) through pulsed potentio amperometric polymerization. The results indicated that the SWNT paper had a typical network structure, after polymerizing PPy, cauliflower-like structure was observed on the surface of SWNT ropes. The composite thin film has good cyclic voltammetry (CV) property and the specific capacitance wass ca.420Fg-1, which was much larger than that of pure SWNT paper.

Pulmonary and systemic responses of highly pure and well-dispersed single-wall carbon nanotubes after intratracheal instillation in rats

The present study was conducted to assess the pulmonary and systemic responses in rats after intratracheal instillation of highly pure, well-dispersed, and well-characterized SWCNTs. Exposure to SWCNTs up to 2 mg/kg did not produce mortality, changes in clinical signs, or body weights during the observation period. Dose-dependent changes were observed in the lung weight, BALF inflammatory cells, and biochemical parameters such as LDH value, protein content, IL-1β and IL-6 activity, and histopathology. In the 0.04 mg/kg SWCNT-exposed group, almost no changes were observed during the observation period. In the 0.2 mg/kg SWCNT-exposed group, pulmonary inflammatory responses were observed after instillation. In the 1 mg/kg and 2 mg/kg SWCNT-exposed group, acute lung inflammation and subsequent granuloma accompanied by increased lung weights were observed. Furthermore, the histopathological findings in the lungs of rats exposed to SWCNTs showed inflammatory responses related with the vital reaction to the foreign substance that was instilled intratracheally, and there were no fibrosis, atypical lesion, or tumor-related findings even at the highest dose (2 mg/kg) of SWCNT-exposed groups up to 6 months after instillation. For all groups, histopathological changes due to the instillation exposure of SWCNTs were observed only in the lungs and lung-associated lymph nodes and not in the other tissues examined (i.e. the liver, kidney, spleen, and cerebrum).

Purity-enhanced bulk synthesis of thin single-wall carbon nanotubes using iron–coppercatalysts

We report high purity and high yield synthesis of single-wall carbon nanotubes (SWCNTs)of narrow diameter from iron–copper bimetal catalysts. The SWCNTs with diameter of0.8–1.2 nm are synthesized using the zeolite-supported alcohol chemical vapour depositionmethod. Single metal and bimetal catalysts are systematically investigated to achieve boththe enhancement of SWCNT yield and the suppression of the undesired formation ofgraphitic impurities. The relative yield and purity of SWCNTs are quantified using opticalabsorption spectroscopy with an ultracentrifuge-based purification technique. For thesingle metal catalyst, iron shows the highest catalytic activity compared withthe other metals such as cobalt, nickel, molybdenum, copper, and platinum. Ithas been found that the addition of copper to iron results in the suppression ofcarbonaceous impurity formation without decreasing the SWCNT yield. Thepurity-enhanced SWCNT shows fairly low sheet resistance due to the improvement ofinter-nanotube contacts. This scalable design of SWCNT synthesis with enhancedpurity is therefore a promising tool for shaping future high performance devices.