Production Of Single-walled Carbon Nanotubes Research Articles

Influence of carbon structure on carbon nanotube formation and carbon arc plasma

Carbon electrodes with different grain size (1–26 nm) and doped with Fe (ca. 1 at.%) catalyst were tested in the process of production of single-walled carbon nanotubes (SWCNTs) in Ar-H 2 arc plasma. We have found that the use of the carbon material with smaller microcrystals comparing to the well-graphitized electrodes drastically increased the yield of SWCNTs, while plasma parameters (temperature, C 2 radical content and carbon vapor pressure) remained on similar levels. We have also shown that carbon black can be used for production of SWCNTs with high quality and yield by Ar-H 2 arc discharge.

Parametric study of synthesis conditions in plasma-enhanced CVD of high-quality single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWCNTs) have been synthesized from H 2–CH 4 mixtures on a MgO-supported bimetallic Mo/Co catalyst using microwave plasma-enhanced chemical vapor deposition (PECVD). Reaction parameters including temperature, H 2:CH 4 ratio, plasma power, and synthesis time have been examined to assess their influence on SWCNT synthesis. Raman spectroscopy and high-resolution field emission scanning electron microscopy reveal that the quality, selectivity, density and predominant diameter of SWCNTs depend on the varied synthesis parameters. Results of this study can be used to optimize SWCNT synthesis conditions and products and to improve understanding of the growth of SWCNTs by PECVD.

Spectroscopic study during single-wall carbon nanotubes production by Ar, H 2, and H 2–Ar DC arc discharge

A new method to produce a macroscopic oriented web (30 cm in length) of single-wall carbon nanotubes (SWNTs) has been developed in our laboratory. In order to understand the growth mechanism of SWNTs, the optical emission spectra during SWNTs production in pure Ar, H 2 gas, and H 2–Ar mixture gas were investigated. In pure Ar gas, Fe spectra are strongly appeared, in which SWNTs could not be formed, but in pure H 2 gas, Fe spectra almost disappeared in which small amount of SWNTs were formed. In the case of H 2–Ar gas, Fe and C 2 species were commonly identified, in which SWNTs were highly produced. H 2–Ar gas provides the optimum condition for high production and high quality of SWNTs. Spectroscopic study during carbon nanotubes production by DC arc discharge provides the useful method to under the growth mechanism of nanotubes.

Gas‐Phase Production of Single‐Walled Carbon Nanotubes from Carbon Monoxide: A Review of the HiPco Process

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic synthesis of single-walled carbon nanotubes from coal gas by chemical vapor deposition method

Single-walled carbon nanotubes (SWNTs) have been successfully prepared from coal gas by catalytic chemical vapor deposition technique with ferrocene as catalyst. The SWNTs products were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The growth mechanism of the SWNTs derived from coal gas was discussed in terms of the catalyst property and the coal gas composition. The results demonstrate that coal gas is one of the suitable starting carbon sources for making SWNTs by catalytic decomposition method.

Large‐Scale Synthesis of High‐Quality Single‐Walled Carbon Nanotubes by Catalytic Decomposition of Ethylene.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Generation of single-walled carbon nanotubes from alcohol and generation mechanism by molecular dynamics simulations.

Recent advances in high-purity and high-yield catalytic chemical vapor deposition (CVD) generation of single-walled carbon nanotubes (SWNTs) from alcohol are comprehensively presented and discussed on the basis of results obtained from both experimental and numerical investigations. We have uniquely adopted alcohol as a carbon feedstock, and this has resulted in high-quality, low-temperature synthesis of SWNTs. This technique can produce SWNTs even at a very low temperature of 550 degrees C, which is about 300 degrees C lower than the conventional CVD methods in which methane or acetylene is typically used. We demonstrate the excellence of the proposed alcohol catalytic CVD method for high-yield production of SWNTs when Fe-Co on USY-zeolite powder was used as a catalyst. At optimum CVD conditions, a SWNT yield of more than 40 wt % was achieved over the weight of the catalytic powder within the reaction time of 120 min. In addition to the advantages for mass production, this method is also suitable for the direct synthesis of high-quality SWNTs on Si and quartz substrates when combined with the newly developed liquid-based "dip-coat" technique to mount catalytic metals on the surface of substrates. This method allows easy and costless loading of catalytic metals without the need for any support or underlayer materials that were usually required in previous studies for the generation of a sufficient quantity of SWNTs on an Si surface. Finally, the result of molecular dynamics simulation for the SWNT growth process is presented to obtain a fundamental insight into the initial growth mechanism on the catalytic particles.

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process.

The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

Large-Scale Synthesis of High-Quality Single-Walled Carbon Nanotubes by Catalytic Decomposition of Ethylene

High-quality single-walled carbon nanotubes (SWNTs) have been synthesized over Fe−Mo/MgO catalyst by catalytic decomposition of ethylene at 800 °C. The produced carbon material primarily consists of a SWNT bundle with few defects and a very small amount of amorphous carbon coating. The diameter of an individual SWNT is in the range of 0.7−2.8 nm. The as-synthesized SWNTs have a high yield of over 550% relative to the weight of Fe−Mo metal in the Fe−Mo/MgO catalyst. Our results show that ethylene can be a very ideal carbon source for the synthesis of SWNTs. We suggest that catalytic decomposition of ethylene over Fe−Mo/MgO catalyst can promise a large-scale production of high-quality SWNTs.

Large scale synthesis of single-walled carbon nanotubes by an arc-discharge method at controlled temperatures

Large amounts of single-wall carbon nanotubes(SWNTs) deposited on all the wall of the chamber have been obtained in helium and nitrogen mixed atmosphere using Co-Ni alloy catalyst with a modified arc furnace which can control the temperature during arcing process. Additionally, there are many weblike deposition products located between the cathode and anode. By twostep purification:the as-grown SWNT was heated in air at 500℃ for 30min, then soaked in 37% hydrochloric acid for 72h and filtered with deionized water. Microanalysis was carried out by Transmission electron microscopy(TEM), high-resolution TEM and Raman spectroscopy. The results obtained indicate that the purified SWNTs have high purity (higher than 95%) and uniform diameter (from 1.24 to 1.38nm).This experiment indicates that the temperature strongly affects the production of SWNT; the production and purity of SWNT increase with temperature. When the temperature is 600℃, the purity is about 70% and the production of SWNT is 12g/h.

Synthesis of single-walled carbon nanotubes by a fluidized-bed method

Single walled carbon nanotubes (SWNTs) have been successfully synthesized using a fluidized-bed method that involves fluidization of a catalyst/support at high temperatures by a hydrocarbon flow. When nickel-nitrate coated silica–gel particles and methane were used, SWNTs were found to grow densely on the entire surface of the support particles at 760 °C, as revealed by Raman spectrometry and SEM analysis. This approach offers multiple advantages over the common fixed bed process, such as uniform gas-solid mixture and avoidance of catalyst particle sintering, and shows promise for the large-scale, potentially continuous, production of SWNTs, at high yield.

Synthesis and characterization of single-wall carbon nanotubes by hot-filament assisted chemical vapor deposition

We report a simplified production method for single-wall carbon nanotubes (SWNTs) by hot-filament assisted chemical vapor deposition (HFCVD) using pure alcohol vapor (ethanol, methanol and 2-propanol) as a carbon source. Under the optimized conditions, high-purity SWNTs are synthesized for the first time in large quantities. Raman spectra of the synthesized SWNTs show similar G/D ratios and the peak distribution of radial breathing mode to those obtained by the conventional CVD method with an electric furnace. The efficiency of the SWNTs synthesis has been increased by the hot-filament-induced pyrolysis of carbon sources, which promises an easy scale-up of the production of SWNTs at a low cost.

Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide.

The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

Production of high quality single-walled carbon nanotubes in a nano-agglomerated fluidized bed reactor

ABSTRACTSSingle-walled carbon nanotubes (SWNTs) have attracted much attention due to their unique structural, mechanical, chemical, and electrical properties. Catalytic chemical vapor deposition (CCVD) through decomposition of hydrocarbons is one of the most challenging synthesis methods to produce SWNTs in large scale. In this paper, high quality SWNTs prepared in a nano-agglomerated fluidized bed reactor (NAFBR) was reported. The reactor is a vertical quartz tube with the inner diameter of about 50 mm. Catalysts nanoparticles used for the production of SWNTs were prepared with Fe metal nanoparticles carried on the surface of MgO. About 150g catalysts powders were loaded on the gas distribution grid. The reaction temperature was controlled at not less than 1123 K. The carrier gas of argon was used to maintain turbulent fluidization of the catalysts powders in FBR. The hydrogen gas was used to reduce the catalysts and to synergize the growth of SWNTs with methane. The powder products were spherical agglomerates of SWNTs bundles tangling with the catalysts particles. By optimizing the process parameters of CCVD, the products of SWNTs with the diameter about 0.9 ∼ 1.8 nm were prepared, without any multi-walled carbon nanotubes (MWNTs) or amorphous carbon. The microstructure of SWNTs products were characterized by the methods of high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectra, etc. The NAFBR is a commercially viable (effective and continuous production at a low cost) process for the production of SWNTs.

Oxidation of Fe Nanoparticles Embedded in Single-Walled Carbon Nanotubes by Exposure to a Bright Flash of White Light

Single-walled carbon nanotubes (SWNTs), upon exposure to the flash from a regular 35 mm camera, were found to ignite and produce small amounts of a bright orange solid. X-ray powder diffraction analysis revealed this solid to be composed mostly of Fe2O3, along with trace amounts of Fe3O4, originating from the Fe catalyst used in SWNT production. Upon TEM investigation, this material was further found to be composed of two different oxide morphologies, including nanoparticles entrapped within SWNT bundles and larger aggregates of fused grains.

Reduced diameter distribution of single-wall carbon nanotubes by selective oxidation

We report an easy way to narrow the diameter distribution of single-walled carbon nanotubes (SWNT) by oxidization treatments. Both a chemical treatment in 2 M HNO 3 as well as oxidation in a reduced O 2 atmosphere lead to a selective burning of the narrower SWNT in bulk samples and to a diameter distribution which is smaller by a factor of two. This is a first important step towards a selective production of SWNT with a defined diameter on a bulk scale.

Gas-phase synthesis of SWNT by an atmospheric pressure plasma jet

We present here a new method for producing single wall carbon nanotubes (SWNT) based on the atomization of a gaseous mixture (composed of argon, ferrocene and ethylene) in an atmospheric plasma jet. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy were performed to study the samples obtained. They contain SWNT with diameters and structure comparable to those produced by laser ablation and arc discharge techniques. Since this method is continuous and easily scalable, we feel it has potential for large-scale commercial production of SWNT.

CVD synthesis and purification of single-walled carbon nanotubes on aerogel-supported catalyst

Single-walled carbon nanotubes (SWNTs) were synthesized by disproportionation of carbon monoxide on an aerogel-supported Fe/Mo catalyst. A simple acidic treatment followed by an oxidation process produced a high purity (>99%) of SWNTs. The nanotubes obtained are bundled SWNTs and free of amorphous-carbon coating. Several factors that affect the yield and the quality of the SWNTs were also studied. This method shows great promise for large-scale production of SWNTs.

A scalable CVD synthesis of high-purity single-walled carbon nanotubes with porous MgO as support material

The choice of support and catalyst materials has been proved to be critical to scalable chemical vapor deposition (CVD) synthesis of carbon nanotubes. In our study, we found that porous MgO prepared by thermal decomposition of its salts was an eminent support material for CVD growth of single-walled carbon nanotubes (SWNTs). Compared with other kinds of supports such as SiO2, ZrO2, Al2O3 and CaO etc., the quality of as-grown SWNTs on MgO supports was stable; the effects of reaction conditions such as furnace temperature, flow rate of the gas and the types of catalysts and supports on the properties of as-prepared SWNT products were thoroughly investigated and characterized by micro-Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry (TG) techniques. The results indicated that the yields of SWNTs on MgO supports could be up to about 120% with the addition of a small amount of assistant catalyst Mo salt. The obtained purity of the as-grown products was higher than 90% after treatment with 4 M HCl. The obvious advantages of using MgO supports include efficient and stable growth of SWNTs, scalable synthesis of SWNTs at low cost, and easy removal of the support in mild acid, causing little harm to the products.

Relationship between the Structure/Composition of Co–Mo Catalysts and Their Ability to Produce Single-Walled Carbon Nanotubes by CO Disproportionation

A series of analytical techniques have been employed to fully characterize the structure and chemical state of Co–Mo/SiO2 catalysts used for the production of single-walled carbon nanotubes (SWNT) by CO disproportionation at 700–850°C. The state of Co and Mo on a series of silica-supported catalysts was investigated using extended X-ray absorption fine structure, X-ray absorption near-edge spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and diffuse reflectance Fourier transform infrared spectroscopy of adsorbed NO after two sequential pretreatments and after the production of SWNT under pure CO. It was found that the selectivity of the Co–Mo catalysts toward SWNT strongly depends on the stabilization of Co species in a nonmetallic state before exposure to CO, which results from an interaction with Mo. The extent of this interaction is a function of the Co:Mo ratio and has different forms during the different stages of the catalyst life. From the detailed characterization conducted over the catalyst series it is concluded that after calcination, Mo is in the form of a well-dispersed Mo(6+) oxide while Co is either interacting with Mo in a superficial Co molybdatelike structure (at low Co:Mo ratios) or as a noninteracting Co3O4 phase (at high Co:Mo ratios). After a subsequent treatment in hydrogen, the noninteracting phase is reduced to metallic Co, while the Co molybdate-like species remain as well-dispersed Co2+ ions. During the production of SWNT under pure CO, the Mo oxide species are converted into Mo carbide. This conversion disrupts the interaction between Co and Mo and results in the release of metallic Co in the form of extremely small clusters, which are responsible for the production of SWNT. By contrast, large Co clusters that are formed from the noninteracting Co phase produce the nonselective forms of carbon (mult iwalled nanotubes, filaments, graphite, etc.).