Synthesis Of Single-walled Carbon Nanotubes Research Articles

Preparation of Single-Walled Carbon Nanotubes from Fullerene Waste Soot

Single-walled carbon nanotubes (SWCNTs) were successfully prepared from fullerene waste soot (FWS) by the arc discharge method in a helium atmosphere. The yield of the as-prepared SWCNTs reached as high as 6 g/h, indicating a great potential for further large scale production. FWS-based SWCNTs were systematically examined using scanning electron microscopy, transmission electron microscope, high-resolution transmission electron microscopy, and Raman spectroscopy. The results show that the as-obtained SWCNTs have an extraordinary crystalline integrity with a diameter of 1.2–2.2 nm. Compared with the SWCNTs synthesized from graphite under the same experimental conditions, it was found that FWS as feedstock for synthesis of SWCNTs was more efficient due to its higher reactivity in the electric arc discharge environment. The possible mechanism involved in the formation process of SWCNTs from FWS is proposed and discussed in terms of its turbostratic structure with pentagonal defects and the process parameters...

Synthesis of Graphene and Carbon Nanotubes Hybrid Nanostructures and Their Electrical Properties

The gapless semimetallic nature of graphene-based nanoelectronics is a major hurdle for the advancement of graphene-based field-effect transistors. Here graphene-carbon nanotubes hybrid nanostructures (Gr-CNTs HNSs) were formed by synthesizing single-walled carbon nanotubes (SWCNTs) with a bandgap on monolayer graphene by thermal chemical vapor deposition. We systematically established optimum conditions for the synthesis of Gr-CNTs HNSs by adjusting catalytic layer formation. The structural features of Gr-CNTs HNSs were investigated by scanning electron icroscopy and Raman spectroscopy. The surface morphologies and chemical states of the catlytic films used to optimize Gr-CNTs HNSs synthesis were explored by atomic force microscopy and X-ray photoelectron spectroscopy. In this process, graphene played a role as a barrier to prevent Fe nanoparticles from interdiffusing into Al2O3 layer. Based on these studies, we determined the catalytic structure (Fe/Graphene/Al2O3/SiO2) optimal for growing high-density SWCNTs on monolayer graphene. Electrical transport measurements revealed that Gr-CNTs HNSs exhibited p-type semiconducting behavior with combined properties of graphene and CNTs.

Counter-current ammonia injection flow during synthesis of single-walled carbon nanotubes by induction thermal plasma

Mass production of single-walled carbon nanotubes (SWCNTs) has been enabled through introduction of solid feedstock into the Ar–He thermal plasma generated by radio-frequency induction torch. The non-reactive nature of Ar–He plasma and solid carbon results in formation of pristine SWCNT final product soot which is insoluble in many solvents and is poorly incorporated in polymers matrix. To better understand the effects of reactive synthesis environment on the SWCNTs material, ammonia (NH3) was counter-currently injected into the main plasma stream with different nozzles and at different positions in the reactor. Raman analysis showed that the quality of SWCNTs was evidently altered upon the ammonia injection. Elemental analysis of nitrogen on the SWCNT samples revealed a maximum of 10-fold increase after NH3 injection. TEM imaging showed the presence of onion-like and planar carbon nanostructures in the SWCNT sample obtained after the highest NH3 injection rate (15vol%). A long-term dispersibility enhancement was observed for the NH3-treatd SWCNT sample in dimethylformamide and isopropanol. Finally, to clarify possible reactions and species at equilibrium state and to better understand the importance of nozzle in the NH3 injection process on the thermo-flow field of the induction thermal plasma reactor, the synthesis system was simulated through a thermodynamic calculation and computational fluid dynamic (CFD) method, respectively.

Narrow-chirality distributed single-walled carbon nanotube synthesis by remote plasma enhanced ethanol deposition on cobalt incorporated MCM-41 catalyst

We demonstrated the synthesis of single-walled carbon nanotubes (SWCNTs) with narrow chiral distribution on cobalt incorporated MCM-41 catalyst using ethanol as carbon feedstock by remote plasma enhanced chemical vapor deposition. The use of remote plasma enables the decomposition of the nontoxic ethanol to occur away from the site of SWCNT growth. This allows separate manipulation of carbon radical generation and SWCNT growth. A series of syntheses were carried out at plasma power from 0 to 250W and growth temperature from 625 to 875°C. Results have revealed that the plasma power and growth temperature affect carbon radical generation and recombination, as well as the reduction and nucleation of cobalt species. In addition, the remote ethanol plasma etching does not damage the grown SWCNTs. The chirality of resulting SWCNTs shows minor changes under different plasma power. On the other hand, the diameter of SWCNTs can be adjusted (from 0.7 to 1nm) by changing the growth temperature. At the optimum condition of 200W plasma power and 775°C growth temperature, (7,5) and (8,4) nanotubes account for more than 50% of all semiconducting nanotube species. These results demonstrate the potential of utilizing plasma process in chiral selective growth of SWCNTs.

Synthesis of nitrogen-doped single-walled carbon nanotubes and monitoring of doping by Raman spectroscopy

Nitrogen-doped single-walled carbon nanotubes (CNx-SWNTs) with tunable dopant concentrations were synthesized by chemical vapor deposition (CVD), and their structure and elemental composition were characterized by using transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS). By comparing the Raman spectra of pristine and doped nanotubes, we observed the doping-induced Raman G band phonon stiffening and 2D band phonon softening, both of which reflect doping-induced renormalization of the electron and phonon energies in the nanotubes and behave as expected in accord with the n-type doping effect. On the basis of first principles calculations of the distribution of delocalized carrier density in both the pristine and doped nanotubes, we show how the n-type doping occurs when nitrogen heteroatoms are substitutionally incorporated into the honeycomb tube-shell carbon lattice.

Synthesis of high quality single-walled carbon nanotubes via a catalytic layer reinforced by self-assembled monolayers

This work reports the synthesis of high quality single-walled carbon nanotubes (SWCNT) using a catalytic layer reinforced by self-assembled monolayers (SAM). Amine-SAM was introduced on a SiO2/Si substrate and then an iron nanoparticles solution was dropped on the substrate by spin-coating. This catalytic template was used to grow carbon nanotubes by chemical vapor deposition and the synthesized SWCNT were observed to be prominent, based on the size distribution. Highly dense SWCNT with a diameter of about 1.1-1.2 nm were produced at 800-850 °C. Moreover, the diameter distribution of the SWCNT was more selective at a growth temperature of 900 °C. These findings provide important insights for a SAM support layer that can play the role as a restriction for the agglomeration of iron catalyst and is promising for the synthesis of high quality SWCNT.

A Fundamental Limitation of Small Diameter Single-Walled Carbon Nanotube Synthesis-A Scaling Rule of the Carbon Nanotube Yield with Catalyst Volume.

Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT forests continuously spanning a wide range of diameters (1.9–3.2 nm), and have revealed an additional fundamental growth limiting process where the mass of the individual SWCNT is determined by the individual catalyst volume. Calculation of the conversion rate of carbon atoms into CNTs per Fe atom is 2 × 102 atoms per second. This rate limiting process provides an important understanding where the larger diameter SWCNT would grow faster, and thus be more suited for mass production.

Highly selective synthesis of single-walled carbon nanotubes from methane in a coupled Downer-turbulent fluidized-bed reactor

For the synthesis of single-walled carbon nanotubes (SWCNTs) from CH4 over a Fe/MgO catalyst, we proposed a coupled Downer-turbulent fluidized-bed (TFB) reactor to enhance the selectivity and yield (or production rate) of SWCNTs. By controlling a very short catalyst residence time (1–3 s) in the Downer, only part of Fe oxides can be reduced to form Fe nano particles (NPs) available for the growth of SWCNTs. The percentage of unreduced Fe oxides increased and the yield of SWCNTs decreased accordingly with the increase of catalyst feeding rate in Downer. SWCNTs were preferentially grown on the catalyst surface and inhibited the sintering of the Fe crystallites which would be formed thereafter in the downstream TFB, evidenced by TEM, Raman and TGA. The coupled Downer-turbulent fluidized-bed reactor technology allowed higher selectivity and higher production rate of SWCNTs as compared to TFB alone.

Synthesis of single-walled carbon nanotubes over Co–Mo/Al2O3 catalyst by the catalytic chemical vapor deposition of methane

A series of alumina-supported Co–Mo samples prepared by the wet impregnation method have been used as catalysts for the synthesis of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD) using CH4 at 900 °C. The mass ratio of the bimetallic catalyst with a composition of Co:Mo:Al2O3 has been demonstrated to play an important role in the formation of the single-walled carbon nanotubes obtained. In addition, the selection of solvent to disperse the Co–Mo/Al2O3 catalysts has a significant effect on the resulting quality of the carbon nanotubes produced.

Characterization of Metal Nanocatalyst State and Morphology during Simulated Single-Walled Carbon Nanotube Growth

The catalyst nanoparticle structure has been proposed as a potential template to guide nanotube growth toward desired chiralities during chemical vapor deposition synthesis of single-walled carbon nanotubes. However, exploitation of such an effect depends on understanding the state of the nanocatalyst throughout the various stages of nanotube growth for different reaction conditions. Here we show that during nucleation there is a high carbon transport activity through the nanoparticle, but eventually a nickel–carbon core is stabilized. The nickel–carbon stoichiometry of the nanoparticle at such a state is found to correspond to known carbide compositions, with such composition varying with nanoparticle size. The Ni–C core adopts layered structures that resemble those found along the [100] and [001] directions in Ni2C (Pbcn or Pnnm) and Ni3C (P6322). The calculated self-diffusion coefficients of nickel atoms are consistent with viscous-solid nanoparticles, where atomic mobility changes are observed during growth according to variations in the nanoparticle carbon content.

Controlling the crystalline quality of carbon nanotubes with processing parameters from chemical vapor deposition synthesis

Carbon nanotubes (CNTs) were synthesized by direct spinning from chemical vapor deposition (CVD) reactions and their assembly for continuous fibers was fabricated through post-processing devices. The complicated processing parameters that include a precursor solution composition, reaction temperature, flow rate of a carrier gas, and injection rate of the precursor solution were precisely controlled to synthesize CNTs during the reaction process. The effects of the processing factors were analyzed with respect to the formation of CNTs and the crystallinity in the CNT structure. The CNT fibers were characterized by a scanning electron microscope, high-resolution transmission electron microscopy, and Raman spectroscopy. The type and crystalline quality of the CNT fibers were characterized by a Raman radial breathing mode and its relative intensities of the G and D bands. A high reaction temperature, high H2 flow rate, and low injection rate of solution precursor were important factors to improve the crystalline quality of the CNT fibers. Low concentrations of iron catalysts in the reaction were favorable for the synthesis of single-walled carbon nanotubes (SWCNTs) that have high electric conductivity, superior specific strength, and high crystallinity. The CNT fibers could be tunable to meet a particular application by varying the reaction conditions.

Effect of adding W to Fe catalyst on the synthesis of SWCNTs by arc discharge

Combining iron (Fe) and tungsten (W) as a bimetallic catalyst, we synthesized high-yield single-wall carbon nanotubes (SWCNTs) of narrow diameter distribution by a hydrogen–argon arc discharge method. Raman spectra indicate that the diameters of SWCNTs prepared using the Fe–W catalysts are about 0.5nm smaller than those using Fe catalyst alone. The transmission electron microscopy and X-ray diffraction studies show that the SWCNTs prepared by the bimetallic catalyst coexist with few graphite flakes and other amorphous carbon. At the W content of 2–4at%, tungsten cannot be found in the SWCNT samples. Thus by using a simple two-step purification process, high-purity SWCNT samples can be obtained. We have demonstrated the growth mechanism for the high melting metal (such as W, Mo)–Fe catalyst synthesis of SWCNTs by the arc discharge method.

Synthesis of dark brown single-walled carbon nanotubes and their characterization by HSQC-NMR

We report here a simple and effective approach to the covalent attachment of single-walled carbon nanotubes (SWCNTs) and azo compounds. The functionalized SWCNTs prepared (through a radical mechanism) have been used for a diazonium coupling reaction. The results showed that the chemical method used has improved the processability and solubility of the carbon nanotubes. The dark brown SWCNTs obtained which can produce a yellow colour in organic solvents were characterized by different spectroscopic analyses. Heteronuclear single quantum coherence spectra (13C-1H HSQC) have been used to detect the carbon nanotube allylic protons. The morphology of the main product has been shown by scanning electron microscopy (SEM). Dark brown SWCNTs have been prepared through a covalent attachment of diazo compound to the surfaces of functionalized single-walled carbon nanotubes. The structure of the products have been assigned by HSQC-NMR spectroscopy.

CoSO4/SiO2 catalyst for selective synthesis of (9, 8) single-walled carbon nanotubes: Effect of catalyst calcination

A sulfate-promoted CoSO4/SiO2 catalyst is developed for chirally selective synthesis of large-diameter single-walled carbon nanotubes needed for electronic applications. The catalyst shows tunable nanotube chiral selectivity by changing catalyst calcination temperature. After calcination in air at 400°C, it has excellent single chiral selectivity toward large-diameter (9,8) nanotubes at 1.17nm. The selectivity shifts to small-diameter nanotubes, when it is calcined at 800°C. Catalyst characterizations by hydrogen temperature-programed reduction, X-ray absorption spectroscopy at the cobalt K-edge and sulfur K-edge suggest that the presence of chelating bidentate SO42- bonded with cobalt on the silica surface may limit the aggregation of cobalt and/or form cobalt–sulfur compounds during nanotube growth, leading to the selectivity toward the (9,8) nanotubes. Furthermore, the removal of sulfur at higher calcination temperatures may form surface cobalt oxides and silicates that shift the chiral selectivity toward small-diameter nanotubes.

Thermodynamic and Energetic Effects on the Diameter and Defect Density in Single-Walled Carbon Nanotube Synthesis

Single-walled carbon nanotube (SWCNT) ensembles are characterized by their defect density and diameter distribution. Here, SWCNTs are grown using chemical vapor deposition with acetylene as the carbon source and cobalt as the catalyst and analyzed ex situ, without any modification or processing, using Raman spectroscopy. The defect density shows an activated temperature dependence (activation energy ∼0.8 eV or ∼80 kJ/mol) with fewer defects at high growth temperatures for a wide range of experimental parameters. This is consistent with a single activated mechanism, such as the catalytic healing of defects, possibly a single simple defect. Consistent with previous reports, we see that low growth temperatures produce smaller diameter SWCNTs than high growth temperatures. Elementary thermodynamic considerations of the strain energy in the lattice constrain the SWCNT diameter distribution and its temperature dependence and appear consistent with our observations. A “phase diagram” for SWCNT growth is construc...

Rigid versus Flexible Ligands on Carbon Nanotubes for the Enhanced Sensitivity of Cobalt Ions

Carbon nanotubes have shown great promise in the fabrication of ultracompact and highly sensitive chemical and biological sensors. Additional chemical functionalization schemes can controllably improve selectivity of the carbon nanotube-based sensors; however, the exact transduction mechanism is still under debate. In this article we detail the synthesis and selective response of single-walled carbon nanotubes (SWNTs) functionalized with polyazomethine (PAM) polymer toward the application of a specific trace metal ion detector. The response of the polymer system was compared to shape persistent macrocycle (MAC) comprised of identical ion coordination ligands. While ion detection with rigid MAC/SWNT chemiresistor was comparable to bare SWNT, flexible PAM offers significant SWNT signal amplification, allowing for picomolar detection of Co2+ ions with both selectivity and a fast response. We hypothesized that rearrangement of the flexible PAM on the SWNT network is a sensing mechanism which allows for ultrasensitive detection of metal ions. The electron transfer and polymer rearrangement on the SWNT were studied by a combination of optical spectroscopy and electrical measurements—ultimately allowing for a better understanding of fundamental mechanisms that prompt device response.

Characterization of carbon atomistic pathways during single-walled carbon nanotube growth on supported metal nanoparticles

One of the outstanding questions about synthesis of single-walled carbon nanotubes is what is the role and mechanism of carbon diffusion during chemical vapor deposition synthesis. Examination of individual trajectories of all carbon atoms in reactive molecular dynamics simulated growth of single-walled carbon nanotubes on supported nanoparticles identifies carbon atoms involved in surface diffusion, bulk diffusion, and potential carbide formation. We show that transitions between induction, nucleation, and growth are denoted by saturation of the nanoparticle and by changes in the catalytic regime. It is found that nucleation and dissolution may occur simultaneously, with pre-saturation nucleation driven by the low-energy barrier for surface diffusion. It is concluded that for carbon-philic catalysts, induction and nucleation periods are usually governed by bulk diffusion, while the growth period is dominated by surface diffusion. Surface diffusion control during growth is in agreement with successful nanotube growth on metals such as copper and gold, which do not dissolve carbon. In the range studied, C solubility decreases with particle size, and the Ni/C ratios found coincide with stoichiometries of known Ni carbides.

Diameter-Controlled Synthesis of Single-Walled Carbon Nanotubes

With the technological progress in the synthesis of multi-walled carbon nanotubes and single-walled carbon nanotubes, more attention was attracted to the synthesis of carbon nanotubes with diameter distribution, ideal length, different chirality and certain orientation. In recent decade, all these factors have been investigated and a number of progresses have been made for the application of carbon nanotubes. The latest researches on the growth of diameter-controlled single-walled carbon nanotubes are reviewed and discussed. The existing problems and challenges of the synthesis processes have been addressed in the future directions.

Hydrothermal synthesis of single-walled carbon nanotube–TiO2 hybrid and its photocatalytic activity

A single-walled carbon nanotube (SWCNT)–TiO2 hybrid was prepared hydrothermally by direct growth of TiO2 nanoparticles on the surface of functionalized SWCNTs to develop highly efficient photocatalysts. The SWCNT–TiO2 hybrid was characterized by X-ray diffraction, electron microscopy, N2-adsorption analysis, FT-IR, Raman, and UV–vis spectroscopy. The photocatalytic activity of the SWCNT–TiO2 hybrid was examined by the photocatalytic degradation of pirimicarb. Although the SWCNT–TiO2 hybrid exhibits no visible-light-induced activity, the photocatalytic degradation efficiency of pirimicarb over TiO2 can be increased significantly with the introduction of SWCNTs (2–3 times) because SWCNTs can act as electron conductors that hinder the recombination of photo-generated electrons and holes. Compared with a multi-walled carbon nanotube–TiO2 hybrid, it can be found that the electronic configurations of carbon nanotubes significantly affect the photocatalytic activity of carbon nanotube–TiO2 hybrid. Metal-typed SWCNTs act more as an electrical conductor than a photosensitizer, which efficiently suppress charge recombination, improve interfacial charge transfer, and improve the photoactivity.

Synthesis of coal-derived single-walled carbon nanotube from coal by varying the ratio of Zr/Ni as bimetallic catalyst

In this paper coal, source has been used in place of graphite for synthesis of single-walled carbon nanotubes (SWCNTs) with new Zr/Ni bimetallic catalyst. Using coal as starting material to produce the high-value-added SWCNTs is an economically competent route. SWCNTs have been synthesized by the electric arc discharge method using the so-called heterogeneous annealed coal anode filled with Zr and Ni catalyst. SWCNTs have been synthesized using annealed coal rod. The SWCNTs bundles synthesized generally have diameters of 4–10 nm. Most of those produced with Zr/Ni as the catalyst has a diameter ranging from 2.0 to 1.0 nm. The as-synthesized SWCNTs have been characterized employing XRD, HRTEM, EDX, Raman spectroscopy, and FTIR. It has been found that the change of the ratio of Zr and Ni concentration (wt%) in the catalyst affects the yield of SWCNTs. However, the purity of SWCNTs is very sensitive to the concentration of Zr. An optimal range of Zr/Ni compositions for synthesis of SWCNTs with relatively high purity and yield is obtained at specific concentration of 3:1.