Pure Single-walled Carbon Nanotubes Research Articles

High yield synthesis and characterization of the structural and magnetic properties of crystalline ErCl3 nanowires in single-walled carbon nanotube templates

Crystalline ErCl3 nanowires have been fabricated in single-walled carbon nanotubes (SWCNTs) with high yield (∼90%), and the structural and magnetic properties of the resulting ErCl3 nanowires encapsulated in SWCNTs (ErCl3@SWCNTs) characterized. Encapsulation under high temperature and vacuum using high quality SWCNTs results in a high filling-ratio of ErCl3 nanowires in the SWCNTs. The high filling-ratio of ErCl3 nanowires and the use of highly pure SWCNTs with only a small amount of residual Fe catalyst nanoparticles enabled us to observe the magnetic properties of ErCl3@SWCNTs. Structure determination based on simulated annealing calculations and high-resolution transmission electron microscope (HRTEM) image simulations revealed that the structure of the ErCl3 nanowires is unusual with respect to the coordination environment of the Eu3+ ions. This work opens up new possibilities to fabricate various metal complex nanowires with high yield and may also be of more general importance in understanding and exploring magnetic properties in low-dimensional magnetic systems.

High-Yield Single-Walled Carbon Nanotubes Synthesized on the Small-Pore (C10) Co-MCM-41 Catalyst

High-quality single-walled carbon nanotubes (SWNT) with high yield were produced by using small-pore Co-MCM-41 catalyst, templated by a C10 surfactant and containing 3 wt % Co. A complete incorporation of Co ions in the silica matrix without formation of surface Co oxides and the contact time of the reaction, in the catalyst synthesis and the SWNT production, respectively, were the most critical factors to be considered. By controlling the reduction temperature and contact time in the reaction, the carbon yield could reach 34 wt % or higher with a selectivity of 96 wt % to SWNT. The metal content after purification of SWNT by base-acid treatments was 0.7 wt %, and the surface area was as high as 1800 m 2 /g. The metal surface occlusion effect by amorphous silica might play a key role in the stabilization of the completely reduced Co metallic clusters in the SWNT synthesis procedure, using small-pore C10 Co-MCM-41.

Role of thermal treatment on the structural behavior of the arc SWCNTs in the purification system process

The role of thermal oxidation before acid treatment and post high-temperature vacuum annealing of single walled carbon nanotube (SWCNTs) was studied by scanning electron microscopy, high-resolution transmission electron microscopy, thermogravimetric analyses and Raman spectroscopy. An efficient procedure is developed for the purification of SWCNTs with minimal damage to the walls and minimal modification in the length of the tubes. SWCNTs are employed in this study, are synthesized by arc-discharge method containing impurity of amorphous carbon, carbon shells, graphitic particles, metallic nanoparticles and metallic nanoparticles encapsulated inside the amorphous carbon or graphite.

Theoretical study of the interactions of carbon monoxide with Rh-decorated (8,0) single-walled carbon nanotubes

Recent laboratory studies have shown that metal nanoparticles-decorated single-walled carbon nanotubes (SWCNTs) can be used to detect carbon monoxide (CO) gases at room temperature, which is known not able to be adsorbed on pure SWCNTs. In this paper, we investigated the Rh-decorated (8,0) SWCNT and its interaction with CO gases by using density functional theory (DFT) methods. Upon Rh atom adsorption, the conductivity of the (8,0) SWCNT and the atomic charges of some carbon atoms around Rh atom are enhanced dramatically. The Rh-adsorption may be thought of as providing “activated” carbon-sites of adsorbing foreign species. Both the Rh-site and the “activated” C-sites are considered as reactivity sites for the adsorption of CO gases. The binding energy is larger for CO-adsorption on the Rh-site than on the “activated” C-sites. Since the interaction between CO gases and the Rh-site is very strong, the Rh-decorated SWCNT is not reusable for CO gases detecting due to the large binding energy. On the other hand, the CO gases can also be adsorbed on the “activated” C-site with the binding energy of about −0.80 eV and 0.12 electrons transfer. The electronic properties have changed dramatically upon the CO gases. These calculation results are useful not only to explain the sensing mechanisms but also to evaluate the potential for SWCNTs-based sensing materials at room temperature.

PURITY MEASUREMENT OF SINGLE-WALLED CARBON NANOTUBES BY UV-VIS-NIR ABSORPTION SPECTROSCOPY AND THERMOGRAVIMETRIC ANALYSIS

We measured the content of single-walled carbon nanotubes (SWCNTs) in SWCNT soot within 3.7% error using UV-VIS-NIR absorption spectroscopy. We also propose a better overall evaluation method by combining thermogravimetic analysis with UV-VIS-NIR absorption spectroscopy to analyze the purity of SWCNT providing the accurate assessment of the amounts of noncarbonaceous impurity, carbonaceous impurity, and SWCNT each with respect to a highly purified reference.

Characterization of single-walled carbon nanotube mats and their performance as electromechanical actuators

Carbon nanotube mats (buckypapers) were prepared from three commercial grades of single-walled carbon nanotubes (SWCNTs) and by two processing variants (i.e. filtration of centrifuged and uncentrifuged dispersions). Material properties such as Young’s modulus, tensile strength, electrical conductivity, electrical capacitance, specific surface area and morphology were investigated and put in relation to the in-plane actuation performance in an aqueous electrolyte (1 M NaCl). A dynamic mechanical analyzer was adapted for actuation strain measurements on the samples under various tensile prestress levels. High SWCNT purity and dispersibility were found to be crucial for preparing dense and strong cohesive mats with good actuation performance.

Purification of Single-Walled Carbon Nanotubes by a Highly Efficient and Nondestructive Approach

Single-walled carbon-nanotubes (SWCNTs) in their as-grown state contain a large quantity of impurities such as catalytic particles and encapsulating graphitic shells. Previous purification approaches usually depended upon severe oxidation. But such oxidation in either a gas phase or a liquid phase induces structural destruction and a big loss of the SWCNT material. In this study, a new method is reported that involves transformation of catalytic iron particles to iron oxide at a low temperature of 400 °C, removal of graphitic shells by reaction with the encapsulated iron oxide at a high temperature of 800–900 °C, and final elimination of iron oxide particles by HCl. Experimental results, based on transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and near-infrared spectroscopy, show that catalytic particles and encapsulating graphitic shells can be removed. More importantly, this highly efficient purification induces little damage to the graphitic structure of SWCNTs. These ...

Separation of Single-Walled Carbon Nanotubes by Use of Ionic Liquid-Aided Capillary Electrophoresis

This paper presents a simple, highly efficient method for analyzing single-walled carbon nanotube (SWNT) bundles based on (1) ultrasound-assisted solubilization/dispersion of SWNTs in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, (2) encapsulation of the nanotubes in sodium dodecyl sulfate micelles, and (3) analysis by capillary electrophoresis. The process by which SWNTs disperse in the ionic liquid was studied by Raman spectroscopy. No degradation of SWNTs was observed under mild sonication conditions. The shape and position changes observed in the Raman spectral bands for the nanotubes are ascribed to debundling and interaction with the ionic liquid. Separation of solubilized SWNTs was accomplished by using a 50 mM formic acid solution at pH 2.0 as background electrolyte and a potential of -10 kV. Under these conditions, separation was completed within only 4 min. Eighteen peaks for SWNTs were identified in the analysis of commercial SWNT bundles. The two types of bundles studied exhibited distinct, highly characteristic electrophoretic profiles which could be used to control SWNTs purity.

Carbon Nanotube−Polymer Nanocomposite Infrared Sensor

The infrared photoresponse in the electrical conductivity of single-walled carbon nanotubes (SWNTs) is dramatically enhanced by embedding SWNTs in an electrically and thermally insulating polymer matrix. The conductivity change in a 5 wt % SWNT-polycarbonate nanocomposite is significant (4.26%) and sharp upon infrared illumination in the air at room temperature. While the thermal effect predominates in the infrared photoresponse of a pure SWNT film, the photoeffect predominates in the infrared photoresponse of SWNT-polycarbonate nanocomposites.

Highly Stabilized Conductivity of Metallic Single Wall Carbon Nanotube Thin Films

The extremely stable conductivity against molecular physisorptions was revealed in thin films of high-purity metallic single wall carbon nanotubes (SWCNTs). The stability of the metallic SWCNTs results from their constant electronic density of state near the Fermi level. In the case of a mixture of metallic and semiconducting SWCNTs, the existence of semiconducting SWCNTs in the films makes the sheet resistance more sensitive to the adsorption of molecules mainly due to carrier doping. In the practical use for the transparent electrode, stability of the resistance is important and pure metallic SWCNTs have great advantages for such kind of applications.

Purification of single-wall carbon nanotubes by using high-pressure micro reactor

In DC arc discharge method, a large amount of single-wall carbon nanotubes (SWNTs) can be produced. However, as-grown soot contains a lot of impurities such as metallic particles used as catalyst and amorphous carbon. It is necessary to purify as-grown soot to obtain pure SWNTs for many applications. Catalytic metal particles in soot are covered by thick amorphous carbon layer. We follow the H 2O 2 oxidation process to remove out amorphous carbon using iron particle as a catalyst to activate the reaction. Moreover, it is allowed to react at a high temperature by using high-pressure micro reactor. It is observed that the reaction of Fe/H 2O 2 couple is accelerated by raising the reaction temperature resulting to hydroxyl radical generation which is key factor for the removal of amorphous carbon.

A parametric study of the synthesis and purification of single-walled carbon nanotubes using the high-pressure carbon monoxide process

Single-walled carbon nanotubes (SWCNTs) were synthesized using the high-pressure carbon monoxide disproportionation process. The SWCNT diameter, diameter distribution and yield can be varied depending on the process parameters. Important parameters are the temperature, the pressure, the CO gas flow rate and the nozzle injection velocity and geometry for the injection of reactant gas into the reaction zone. Carbon nanotubes as small as 1.0 nm in diameter have been produced. The purity and yield of the deposited material were increased with increasing CO gas flow by means of rapid heating of the gas mixture and using an optimum injection profile. Highly pure SWCNTs were produced at 1250 K, pressures between 5 and 10 bar and gas in the turbulent flow regime in the cold line of 2000–2500 sccm CO. The raw materials were purified by oxidation in high vacuum at 523 K in wet Ar/20 vol. % O2 to remove SWCNT carbon-like impurities and to oxidize the iron catalyst nanoparticles. The iron oxides were removed by chemical treatment in concentrated HCl/C2H5OH mixture solution. The SWCNTs were analyzed by scanning electron microscopy, high-resolution transmission electron microscopy, atomic absorption spectroscopy and optical absorption spectroscopy to determine the purity, the diameter and diameter distribution, the chemical composition and the catalyst morphology, as well as the optical properties of deposited SWCNTs in dependence on the synthesis parameters.

Electrochemical Determination of Zn 2+ ion us- ing Diphenylamine/Single Walled Carbon Nanotube/Cetyltrimethylammonium Bromide Modified Glassy Carbon Electrode

Diphenylamine encapsulated inside a composite film of single walled carbon nano tube (SWCNT) and cationic cetyltrimethylammonium bromide (CTAB) on the surface of Glassy Carbon (GC) electrode can be converted into diphenylbenzidine on application of a potential of +0.600 V versus Ag-AgCl reference electrode for 60 seconds. This modified electrode, in tris buffer solution (pH 7.0), shows reversible cyclic voltammogram due to diphenylbenzidine / diphenylbenzidine violet redox couple. This cyclic voltammogram is observed in pure CTAB film but not observed inside the film of pure SWCNT, polyvinyl pyrollidone or TX-100. In the SWCNT + CTAB film the redox potential is ca. +0.430 V. The oxidation and reduction currents of the modified electrode decreases with the increase in the concentration of Zn 2+ ion in the electrolytic solution. The relative decrease is found to be 0.60 to 0.65. The ions such as Na + , K + , Ca 2+ and Mg 2+ , do not affect the redox currents. Diphenylbenzidine / SWCNT / CTAB modified GC electrode can determine Zn 2+ ion concentration in the range 20 × 10 -6 mol L -1 to 200 × 10 -6 mol L -1 while diphenylbenzidine/CTAB modified GC electrode can determine between 0.2 × 10 -6 mol L -1 to 2 × 10 -6 mol L -1 . A mechanism for the electrochemical inactivation of the electrode by Zn 2+ ions has been proposed.

Purification of single-walled carbon nanotubes using a fixed bed reactor packed with zirconia beads

Single-walled carbon nanotube (SWCNT) soot produced by arc discharge was purified through gas and liquid phase oxidations. In the gas-phase oxidation, zirconia beads with different diameters of 1, 5, and 10 mm were packed together with raw SWCNT soot inside a vertical quartz tube to enhance air flow uniformity and an exposed surface area of the raw soot during thermal oxidation in air. A decrease of the bead sizes led to such a stronger oxidation of carbonaceous impurities that ∼10 wt.% higher weight loss was then achieved with the 1 mm beads than without them. A subsequent HNO 3 treatment and the second thermal oxidation were engaged to improve further the purity of SWCNTs. Thermogravimetric (TG) analysis, scanning electron microscopy, high resolution transmission electron microscopy, and Raman spectroscopy were used to characterize the samples. The derivative TG (DTG) curves were deconvoluted to quantitatively determine the SWCNT purity of the samples. Our final purified samples showed a yield of ∼26%, a metal impurity of ∼7% and a SWCNT purity of ∼83% as calculated from the deconvoluted DTG curves.

A Synthesis of High Purity Single-Walled Carbon Nanotubes from Small Diameters of Cobalt Nanoparticles by Using Oxygen-Assisted Chemical Vapor Deposition Process

A successful combination of “oxygen-assisted chemical vapor deposition (CVD) process” and Co catalyst nanoparticles to grow highly pure single walled carbon nanotubes (SWNTs) was demonstrated. Recently, it was reported that addition of small amounts of oxygen during CVD process dramatically increased the purity and yield of carbon nanotubes. However, this strategy could not be applied for discrete Fe nanoparticle catalysts from which appropriate yields of SWNTs could be grown directly on solid substrates, and fabricated into field effect transistors (FETs) quite efficiently. The main reason for this failure is due to the carbothermal reduction which results in SiO2 nanotrench formation. We found that the oxygen-assisted CVD process could be successfully applied for the growth of highly pure SWNTs by switching the catalyst from Fe to Co nanoparticles. The topological morphologies and p-type transistor electrical transport properties of the grown SWNTs were examined by using atomic force microscope (AFM), Raman, and from FET devices fabricated by photolithography.

Flexible transparent conducting single-wall carbon nanotube film with network bridging method

We fabricated random network films of highly pure single-wall carbon nanotubes (SWCNTs) on flexible polyethylene terephthalate substrate by dip- and spray-coatings and their combination method for application to flexible transparent conducting films (TCFs). The dip-coating treatment was a more efficient method for fabricating the SWCNT-TCFs of high electrical conductivity without drastic drop in the optical transmittance, compared to the spray-coating one. This should be primarily due to more loose contact in intertube and interbundle junctions of the spray-coated SWCNT networks. Although the electrical conductivity of the SWCNT-TCFs was dramatically enhanced as increasing the number of dipping times, the dip-coating treatment with a large number of dipping times considerably reduced the transmittance without corresponding improvement in the electrical conductivity, indicating the patch-wise coating of the SWCNTs. On the other hand, the combination of the spray- and dip-coatings gave a supplementary effect for formation of a highly transparent film of better electrical conductivity. For SWCNT-TCF coated with 100 dipping times, an additional spray-coating dramatically decreased the sheet resistance from 1300 to 340 Ω/square, which is accompanied by slight reduction of the transmittance from 88 to 80%. Therefore, the post spray-coating can efficiently bridge the patch-wise SWCNT networks produced by the successive dip-coating.

Fabrication of carbon nanotube based transparent conductive thin films using layer-by-layer technology

This paper presents a simple and convenient process for the fabrication of carbon nanotube based optically transparent and electrically conductive thin films. Single-walled carbon nanotubes (SWNTs) are chemically treated to introduce negatively charged carboxylic groups on their surfaces, so that a stable SWNT aqueous dispersion can be obtained without any surfactant. The substrate surface is modified by a layer-by-layer nanoassembly technique, in which a positively charged hydrophilic polymer molecular layer is formed on the top of the substrate. This helps the SWNT dispersion to be cast onto the substrate using convenient wet coating techniques and increases the bonding force between the thin films and the substrates. Using the developed process, large sizes of conductive pure SWNT thin films that are uniform and highly transparent have been fabricated.

Purification of Single-Walled Carbon Nanotubes

The discovery of carbon nanotubes (CNTs) created much excitement and stimulated extensive research into the properties of nanometer-scale cylindrical networks. From then on, various methods for the synthesis and characterization of aligned CNTs-both single-walled (SWCNTs) and multi-walled (MWCNTs) by different methods have been hotly pursued. Unfortunately, most methods currently in use produce raw multi component solid products, only a small fraction of which contains carbon nanotubes. The balance of the material is composed of residual catalyst particles (some of which are encased in concentric graphitic shells), fullerenes, other graphitic materials and amorphous carbon. These impurities cause a serious impediment for their detailed characterization and applications. If the carbon nanotube is ever to fulfill its promise as an engineering material, large, high quality aliquots will be required. A number of purification methods involving elimination processes such as physical separation, gas phase and liquid phase oxidation in combination with chemical treatments have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of skepticism on the method of assay. In this article, a review is given on the past and recent advances in purification of SWCNTs.

Purification-induced sidewall functionalization of magnetically pure single-walled carbonnanotubes

In this contribution we present systematic studies on the purification and subsequentfunctionalization of magnetically pure single-walled carbon nanotubes. We show through acombination of burning treatments and microwave digester treatments in aqua regia thatsingle-walled carbon nanotubes can be purified without incurring any damage,with 90 wt% of catalyst material being removed. It is also shown that multiplemicrowave digester treatments lead to incremental functionalization of the nanotubes.The obtained functional groups are easily removed by annealing the sample invacuum.

Residue catalyst support removal and purification of carbon nanotubes by NaOH leaching and froth flotation

The synthesis of single-walled carbon nanotubes (SWNTs) by the catalytic decomposition of gaseous carbon-containing molecules has been considered to be the most promising process for large-scale production with a relatively low cost. However, the as-prepared SWNTs from this process always contain significant amounts of impurities such as metallic catalysts, catalyst support, and other unwanted forms of carbon. For a variety of potential applications, the purification of SWNTs is considered to be an important step. In this research, NaOH solution was utilized to dissolve the silica support, a major impurity, from the SWNTs produced by the CO disproportionation over a CoMo/SiO 2 catalyst. Subsequently, froth flotation was used to further recover and concentrate the total carbon after the NaOH pretreatment. To achieve a high purity of total carbon by the proposed purification techniques, the effects of operating parameters were investigated in order to minimize the entrainment of undissolved silica with the froth. At the optimum operating conditions: 3 h of sonication time, 30 mg/l of surfactant dosage, 1.0 g/l of pulp density, 100 ml/min of air flow rate, and 22 cm of froth height, the purity of total carbon was found to increase to 30% after the first step of NaOH treatment and to 78% after the second step of froth flotation as compared to the initial carbon content of only 4% of the as-prepared SWNTs. From the temperature-programmed oxidation (TPO) results, the Raman spectra and the scanning electron microscope (SEM) images, the physical and chemical structures of SWNTs are not damaged by NaOH treatment and froth flotation.