Production Of Single-walled Carbon Nanotubes Research Articles

Synthesis of single-walled carbon nanotubes using induction thermal plasma technology with different catalysts: thermodynamic and experimental studies

The effects of the type and quantity of three catalyst mixtures (i.e. Ni-Y2O3, Ni-Co-Y2O3, and Ni-Mo-Y2O3) on single-walled carbon nanotubes (SWCNT) synthesis by induction thermal plasma process have been examined in order to evaluate their individual influences on SWCNT production. Thermodynamic calculations, in gas and particularly in liquid solution phases, have also been performed to better understand the effects of the catalysts on the production of SWCNT. Characterization of the synthesized SWCNT by different techniques including Raman spectroscopy, high resolution scanning electron microscopy (HRSEM) imaging and thermogravimetric analysis (TGA) clearly indicated that the best quality of SWCNT was achieved using Ni-Co-Y2O3 catalyst mixture in the feedstock.

Constructing Ag nanoparticles–single wall carbon hybrid nanostructure to improve field emission properties

The overall process of field emission can be dominated by the contact resistance between the single wall carbon nanotubes (SWCNTs) and the substrate. In order to reduce the contact resistance, we present a wet chemical process of constructing Ag–SWCNTs hybrid nanostructure. Constructing Ag–SWCNTs emitters could improve the electrical contact by increasing the contact area between SWCNTs and substrate. Contact resistance is greatly reduced compared to that of pristine SWCNTs. Field emission properties of Ag–SWCNTs hybrid emitters including current density and emitting image are remarkably improved. Field emission properties based on the modified Fowler–Nordheim (F–N) equation are discussed. Our studies show that this method can enhance the field emission properties of the SWCNTs by improving the contact resistance and is a promising way for mass production of SWCNTs for field emission display.

Synthesis of single-walled carbon nanotubes from heavy oil residue

Single-walled carbon nanotubes (SWNTs) were synthesized by a chemical vapor deposition (CVD) method using heavy oil residue as carbon source. Different kinds of metals as catalysts including transition metals (Fe, Co and Ni) and nonmagnetic metals (Au and Pt) are used in the growth of SWNTs. The morphology and structure of the synthesized SWNTs products were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and atomic force microscopy. It was found that diameters of the as-grown SWNTs strongly depend on the type of catalysts. Compared with the case of nonmagnetic catalysts, SWNTs synthesized from transition metal catalysts have a narrow diameter distribution. Our findings indicate that oil residue is cheaper and suitable industrial carbon source for the SWNT growth with high quality.

Controllable growth of single-walled carbon nanotubes by ethanol-ferrocene aerosol method

Aerosol-assisted chemical vapor deposition (AACVD), a method for producing single-walled carbon nanotubes (SWCNTs) with the use of ethanol and ferrocene as the sources of carbon and a catalyst introduced into a reactor by means of an ultrasound nebulizer, is described. The influence of different parameters such as temperature, growth time, and catalyst precursor concentration on the diameter and chirality of SWCNTs is studied by optical absorption spectroscopy. The suggested technique makes the production of small-diameter SWCNTs (0.75–1.43 nm) with sufficiently stable chirality distribution close to the achiral structures.

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.

Preparation of Single-Walled Carbon Nanotubes from Starch by Arc Discharge

Single-walled carbon nanotubes (SWNTs) have been successfully prepared from starch by arc discharge technique. The SWNTs products were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The growth mechanism of the SWNTs was discussed in terms of the starch. The results demonstrate that starch is one of the suitable precursor for making SWNTs by arc discharge method.

Purification of Single-Wall carbon nanotubes by heat treatment and supercritical extraction

Arc discharge is the most practical method for the synthesis of single wall carbon nanotubes (SWCNT). However, the production of SWCNT by this technique has low selectivity and yield, requiring further purification steps. This work is a study of purification of SWCNT by heat treatment in an inert atmosphere followed by supercritical fluid extraction. The raw arc discharge material was first heat-treated at 1250 °C under argon. The nanotubes were further submitted to an extraction process using supercritical CO2 as solvent. A surfactant (tributylphosphate, TBP) and a chelating agent (hexafluoroacetylacetone, HFA) were used together to eliminate metallic impurities from the remaining arc discharge catalysts. Analysis of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) showed an efficient removal of iron and cobalt (>80%). The purified nanotubes were further analyzed by TGA and Raman spectroscopy.

Pulsed KrF-laser synthesis of single-wall-carbon-nanotubes: effects of catalyst content and furnace temperature on their nanostructure and photoluminescence properties

In this article, we report on the use of a pulsed KrF-laser (248 nm, 20 ns) for the synthesis of single wall carbon nanotubes (SWCNTs) from the ablation of a graphite target loaded with Co/Ni catalyst, under various growth conditions. By varying the Co/Ni catalyst load of the graphite target, from 0 to 2.4 at.%, the laser synthesized SWCNTs, under a furnace temperature (Tf) of 1,100 °C, were found to be decorated by C60 buckyballs, of which the density decreases as the catalyst content is increased. The effect of the catalyst content of the laser-ablated graphite target on the produced carbon nanostructures (C60 vs. SWCNTs) was systematically investigated by means of various characterization techniques, including Raman spectroscopy, thermogravimetry, and SEM/HR-TEM microscopies. A [Co/Ni] ≥ 1.2 at.% was identified as the optimal concentration for the production of SWCNTs without any detectable presence of C60 buckyballs. Thus, under the optimal growth conditions (i.e., [Co/Ni] = 1.2 at.% and Tf = 1,100 °C), the produced SWCNTs were found to be characterized by a very narrow diameter distribution (centered on 1.2 nm) with lengths in excess of 10 μm. By increasing Tf from 900 to 1,150 °C, the diameter of the SWCNTs can be varied from ~0.9 to ~1.3 nm. This nanotube diameter variation was evidenced by Raman and UV–Vis absorption measurements, and its effect on the photoluminescence of the SWCNTs is presented and discussed.

Additive‐Free Dispersion of Single‐Walled Carbon Nanotubes and Its Application for Transparent Conductive Films

AbstractA good dispersion of single‐walled carbon nanotubes (SWCNTs) in liquid media is a prerequisite to fulfill many of their applications. This contribution reports an efficient approach to additive‐free dispersion of SWCNTs with the aid of functionalized carbonaceous byproducts (CBs, e.g., amorphous carbon, carbon nanoparticles, and carbonaceous fragments) in SWCNT products. SWCNT bundles are treated by oleum intercalation and nitric acid oxidation in sequence, which leads to the selective functionalization of the CBs while the structure and properties of the SWCNTs are well preserved. These functionalized CBs can improve the subsequent dispersion of SWCNTs and the majority of SWCNTs in the suspension are present in small bundles or individually. Moreover, SWCNT transparent conductive films (TCFs) are fabricated by using these suspensions. The SWCNT TCFs obtained can achieve a low sheet resistance of 76 and 133 Ω sq−1, with optical transmittance of 82% and 90% at 550 nm, respectively.

Purification of single-walled carbon nanotubes

We present a study of purification of single-walled carbon nanotubes (SWCNTs) using different oxidation temperatures and chemical treatments. We have developed a simple two annealing-steps procedure resulting in high nanotube purity with minimal sample loss. The process involves annealing the SWCNTs at 300 °C for 2 h with subsequent reflux in 6 M HCl at 130 °C, followed by further annealing at 350 °C for 1 h with reflux in 6 M HCl at 130 °C. The process results in effective removal of carbon impurities and metal particles which are associated with SWCNTs production. The process is less time consuming (complete in 4.5 h) than conventional acid purification methods which require over 5 h, and less destructive than conventional methods with a yield of 26%. SWCNT purity was assessed using Raman spectroscopy, thermogravimetry and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.

Millimeter-Tall Single-Walled Carbon Nanotubes Rapidly Grown with and without Water

Millimeter-tall vertically aligned single-walled carbon nanotubes (SWCNTs) were grown in 10-15 min by chemical vapor deposition from C(2)H(2)/Ar with or without water addition using Fe catalyst supported on an Al-Si-O underlayer. Using combinatorial catalyst libraries coupled with the real-time monitoring of SWCNT growth, the catalyst and chemical vapor deposition conditions were systematically examined, and millimeter-tall SWCNTs were obtained even without water addition. The key for millimeter-scale growth of SWCNTs is to limit the C(2)H(2) supply to below a certain partial pressure to retain an active catalyst. Water prolongs the catalyst lifetime under excess C(2)H(2) supply, whereas it deactivates small catalyst particles and degrades the quality of SWCNTs at the same time. We also observed a gradual increase in the diameter of SWCNTs with growth because of the coarsening of catalyst particles and found that water had no effect on this phenomenon. We demonstrate millimeter-tall SWCNTs grown by simply using C(2)H(2)/Ar gas without water addition, which revealed the mysterious role of water, and we show a practical route for the large-scale production of SWCNTs.

Synthesis and characterization of carbon nanotubes via ultrasonic spray pyrolysis method on zeolite

Ultrasonic spray pyrolysis method for the synthesis of carbon nanotubes (CNTs) has been investigated with zeolite supporting material. Single wall carbon nanotubes (SWCNTs) were obtained at 850 °C in nitrogen environment. Such deposition system makes it possible to grow CNTs without reducing agent at atmospheric pressure in a simple setup. Iron and cobalt acetate were used as catalyst and ethanol as carbon source for the synthesis of CNTs. Results show that nature of zeolite and cobalt concentration play important roles for SWCNTs production. Interestingly, we notice that in catalyst particles of sharp shape, nucleation of a nanotubes cap occurs dominantly in the forward direction.

Synthesis of SWNTs from charcoal by arc-discharging

With charcoal as carbon source and FeS (20wt%) as catalyst, single-wall carbon nanotubes (SWNTs) were successfully produced by dc arc-discharge method. The analysis by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy clearly demonstrated that the SWNTs developed from charcoal achieved a high purity with diameter about 1.2 nm, and FTIR measurement showed the inner structural transformation of carbon source, in which functional groups and grapheme sheets were decomposed and then ordered into nanotubes. By this easy-get and relatively low cost material, the experimenal results clearly indicate that charcoal has the opportunity of reducing the cost of SWNTs production.

In situ optical emission study on the role of C2 in the synthesis of single-walled carbon nanotubes

In situ optical emission spectroscopy was used to study the temporal and spatial behavior of laser induced plasmas in the laser-furnace synthesis of single-walled carbon nanotubes (SWCNTs). A graphite composite target located within a sealed quartz tube with a chemical stoichiometric composition of 95:4:1 at. wt % of carbon, yttrium, and nickel, respectively, was ablated by a Q-switched Nd:YAG laser delivering colinear, focused laser pulses of 1064 and 532 nm temporarily separated by 20 ns. The ablation process was done at a furnace temperature of 1273 K in a flow of argon gas at either 150 or 200 SCCM (SCCM denotes cubic centimeter per minute at STP). The pressure was varied (100, 400, and 600 Torr) for each gas flow setting. The temporal and spatial behavior of the emission intensity associated with C2 Swan bands (d Π3g−a Π3u) was investigated and found to be influenced by the pressure and flow rate of the argon gas. At conditions optimal to SWCNT production, a sharp drop in C2 intensity followed by a rise in C2 intensity was observed. The temporal and spatial behavior of the electron density was determined by the Stark broadening profile of the CII emission peak at 283.7 nm and was found to decrease with the adiabatic expansion of the plume. We propose that the sharp drop in C2 intensity and the rise in electron density and electron temperature observed in this study are due to the accompanying rapid nucleation and growth of SWCNTs.

A molecular level model for the nucleation of a single-wall carbon nanotube cap over a transition metal catalytic particle

Recent in-situ video rate TEM studies have revealed that the base growth of single-wall carbon nanotubes (SWCNT) in thermal chemical vapour deposition (CVD) is accompanied by a considerable deformation of the Ni catalyst nanoparticle and the creation of a subsurface carbon layer. In this paper we argue that these effects may be produced by the adsorption – on the catalyst nanoparticle – of cyclopentadienyl ions formed in gas phase during C 2H 2 pyrolysis. These ions can, at the same time, facilitate the nucleation of a SWCNT cap by the provision of “ready made” pentagons. To this end we have performed semi-empirical quantum mechanical calculations with the ZINDO method. The results support the above proposed mechanism. We also suggest that this mechanism could also explain the increased rate of SWCNT production in plasma enhanced CVD, where these ions are expected to be present in higher concentrations during C 2H 2 pyrolysis.

Nanoengineering NixFe1−x Catalysts for Gas-Phase, Selective Synthesis of Semiconducting Single-Walled Carbon Nanotubes

The inhomogeneity of as-grown single-walled carbon nanotubes (SWCNTs), in terms of chiral structure, is a major obstacle to integration of these novel materials in advanced electronics. While separation methods have circumvented this problem, current synthesis approaches must be refined for large-scale production of SWCNTs with uniform properties. In addition, it is highly desirable to alter the initial chirality distribution which constrains fundamental study and applications. Here, we demonstrate that semiconducting SWCNTs are selectively produced in the gas phase by engineering catalysts at the nanoscale with precise size and composition. The semiconducting content in as-grown mixtures of SWCNTs is assessed by UV-visible-NIR absorbance and micro-Raman spectroscopy and reaches a maximum purity of 90% for samples catalyzed by Ni(0.27)Fe(0.73) nanoparticles (2.0 nm mean diameter). Electrical studies are performed on thin film transistors (TFTs) fabricated from as-grown SWCNTs and reveal high on/off current ratios of 10(3).

Density functional theory and tight binding-based dynamical studies of carbon metal systems of relevance to carbon nanotube growth

Density functional theory (DFT) and tight binding (TB) models have been used to study systems containing single-walled carbon nanotubes (SWNTs) and metal clusters that are of relevance to SWNT growth and regrowth. In particular, TB-based Monte Carlo (TBMC) simulations at 1000 or 1500 K show that Ni atoms that are initially on the surface of the SWNT or that are clustered near the SWNT end diffuse to the nanotube end so that virtually none of the Ni atoms are located inside the nanotube. This occurs, in part, due to the lowering of the Ni atom energies when they retract from the SWNT to the interior of the cluster. Aggregation of the atoms at the SWNT end does not change the chirality within the simulation time, which supports the application of SWNT regrowth (seeded growth) as a potential route for chirality-controlled SWNT production. DFT-based geometry optimisation and direct dynamics at 2000 K show that Cr and Mo atoms in Cr5Co50 and Mo5Co50 clusters prefer to be distributed in the interior of the clusters. Extension of these calculations should deepen our understanding of the role of the various alloy components in SWNT growth.

Influence of the anode filling carbon granulometry on plasma features in the electric arc process applied to carbon nanotubes synthesis

This paper is a part of a comprehensive study aiming to understand the relationships between the conditions of the electric arc plasma process applied to the single walled carbon nanotubes (SWCNTs) synthesis and the features of the resulting carbon products. The parameters for this work were the type of hybridization (either sp2 (graphite) or sp3 (diamond)) and the grain size of the carbon source (the anode).The physical properties of the plasma were determined by in situ optical emission spectroscopy. Atomic neutral nickel Ni I and carbon C I lines at 349.3 nm and 909.4 nm, respectively, were selected to quantify the radial concentration distribution of these species in the plasma. The Swan band C2(0,0) at 516.5 nm was used to determine the radial temperature and the C2 column density distributions at the centre of the plasma. Carbon materials formed were analysed using high-resolution transmission electron microscopy.A significant improvement of both yield and purity of the SWCNTs formed was found when the way the anode was prepared corresponded to the highest apparent density of the packed powder. This improvement was correlated with reproducible plasma characteristics, typically an axial temperature in the range 5500–6500 K, a temperature gradient lower than 2800 K mm−1 and a high carbon concentration (∼1025 m−3) associated with a C I/Ni I concentration ratio higher than 108. However, anodes prepared in such a way that their apparent density was lower—which corresponds to standard conditions commonly used for the regular electric arc production of SWCNTs—consistently resulted in the formation of the usual heterogeneous carbon product, including tubular and non-tubular nano-morphologies. These results were correlated with fluctuating, non-reproducible plasma characteristics, typically a high axial temperature (>7000 K), a rapid cooling within the first 0.5 mm away from the discharge axis (>3000 K) and a low carbon concentration (<1021 m−3). The relationships between the synthesis conditions, the resulting plasma features, and the characteristics of the carbon products obtained are finally fully explained, the results from the literature are understood, and the conditions of the plasma for the optimization of the SWCNT synthesis are revealed.

Oxidative stress and inflammatory response in dermal toxicity of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNT) represent a novel material with unique electronic and mechanical properties. The extremely small size (∼1 nm diameter) renders their chemical and physical properties unique. A variety of different techniques are available for the production of SWCNT; however, the most common is via the disproportionation of gaseous carbon molecules supported on catalytic iron particles (high-pressure CO conversion, HiPCO). The physical nature of SWCNT may lead to dermal penetration following deposition on exposed skin. This dermal deposition provides a route of exposure which is important to consider when evaluating SWCNT toxicity. The dermal effects of SWCNT are largely unknown. We hypothesize that SWCNT may be toxic to the skin. We further hypothesize that SWCNT toxicity may be dependent upon the metal (particularly iron) content of SWCNT via the metal's ability to interact with the skin, initiate oxidative stress, and induce redox-sensitive transcription factors thereby affecting/leading to inflammation. To test this hypothesis, the effects of SWCNT were assessed both in vitro and in vivo using EpiDerm FT engineered skin, murine epidermal cells (JB6 P+), and immune-competent hairless SKH-1 mice. Engineered skin exposed to SWCNT showed increased epidermal thickness and accumulation and activation of dermal fibroblasts which resulted in increased collagen as well as release of pro-inflammatory cytokines. Exposure of JB6 P+ cells to unpurified SWCNT (30% iron) resulted in the production of ESR detectable hydroxyl radicals and caused a significant dose-dependent activation of AP-1. No significant changes in AP-1 activation were detected when partially purified SWCNT (0.23% iron) were introduced to the cells. However, NFκB was activated in a dose-dependent fashion by exposure to both unpurified and partially purified SWCNT. Topical exposure of SKH-1 mice (5 days, with daily doses of 40 μg/mouse, 80 μg/mouse, or 160 μg/mouse) to unpurified SWCNT caused oxidative stress, depletion of glutathione, oxidation of protein thiols and carbonyls, elevated myeloperoxidase activity, an increase of dermal cell numbers, and skin thickening resulting from the accumulation of polymorphonuclear leukocytes (PMNs) and mast cells. Altogether, these data indicated that topical exposure to unpurified SWCNT, induced free radical generation, oxidative stress, and inflammation, thus causing dermal toxicity.

Centrifugal Length Separation of Carbon Nanotubes

Separation of single-wall carbon nanotubes (SWCNTs) by length via centrifugation in a high density medium, and the characterization of both the separated fractions and the centrifugation process are presented. Significant quantities of the separated SWCNTs ranging in average length from <50 nm to approximately 2 microm were produced, with the distribution width being coupled to the rate of the separation. Less rapid separation is shown to produce narrower distributions; these length fractions, produced using sodium deoxycholate dispersed SWCNTs, were characterized by UV-visible-near-infrared absorption and fluorescence spectroscopy, dynamic light scattering, Raman scattering, and atomic force microscopy. Several parameters of the separation were additionally explored: SWCNT concentration, added salt concentration, liquid density, rotor speed, surfactant concentration, and the processing temperature. The centrifugation technique is shown to support 10 mg per day scale processing and is applicable to all of the major SWCNT production methods. The cost per unit of the centrifugation-based separation is also demonstrated to be significantly less than size exclusion chromatography-based separations.