High-quality Multi-walled Carbon Nanotubes Research Articles

低電流水中アーク放電法によるカーボンナノチューブの合成

As described in this paper, we report the first successful trial of a facile carbon nanotube synthesis method yielding high-quality multi-walled carbon nanotubes (MWNTs) using low current arc discharge in water. The low current arc (10 A, 20 V) discharge system obviated nearly all complex and expensive machinery that is usually required. Using this method, the low current underwater arc discharge process produced carbon nanotubes simply, easily, and inexpensively.

Integration and characterization of aligned carbon nanotubes on metal/silicon substrates and effects of water

We report here a facile way to grow aligned multi-walled carbon nanotubes (MWCNTs) on various metal (e.g. gold, tungsten, vanadium and copper)/silicon electrically conductive substrates by aerosol-assisted chemical vapor deposition (AACVD). Without using any buffer layers, integration of high quality MWCNTs to the conductive substrates has been achieved by introducing appropriate amount of water vapor into the growth system. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) determination indicate tidy morphology and narrow diameter distribution of the nanotubes as well as promising growth rate suitable for industrial applications. Raman spectra analysis illustrates that the structural order and purity of the nanotubes are significantly improved in the presence of water vapor. The growth mechanism of the nanotubes has been discussed. It is believed that water vapor plays a key role in the catalyst-substrate interaction and nucleation of the carbon nanotubes on the conductive substrates. This synthesis approach is expected to be extended to other catalyst-conductive substrate systems and provide some new insight in the direct integration of carbon nanotubes onto conductive substrates, which promises great potential for applications in electrical interconnects, contacts for field emitters, and other electronic nanodevices.

High-Quality Multiwalled Carbon Nanotubes from Catalytic Decomposition of Carboneous Materials in Gas−Solid Fluidized Beds

The effects of reaction temperature (873-1223 K), carbon sources (CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6 ), and the amount of catalyst (2.5-20 g) on the physical properties (tube diameter, conversion, volume expansion, intensity ratio of the D- and G-band peaks (I D /I G )) of multiwalled carbon nanotubes (MWCNTs) in a gas-solid fluidized bed reactor (with an inner diameter (id) of 0.056 m and a height of 1.0 m) have been determined. The MWCNTs synthesized by the catalytic decomposition of methane produce the smallest tube diameter and the highest intensity ratio (I D /I G ) among the carbon sources (acetylene, ethylene, and ethane). Although the tube diameter of MWCNTs that have been synthesized from the decomposition of methane and ethane at 1073 K are similar, the volume expansion of the carbon nanotubes (CNTs) agglomerate from ethane is higher than that from methane. Both the tube diameter and the I D /I G ratio of the MWCNTs synthesized from the decomposition of methane decrease as the reaction temperature increases (in the temperature range of 1073-1223 K). The amount of catalyst does not affect the mean tube diameter of the synthesized CNTs; however, CNTs with a bamboo structure are synthesized when the carbon decomposition rate is higher than the CNT growth rate.

Large-scale production of high-quality multi-walled carbon nanotubes: Role of precursor gas and of Fe-catalyst support

The crucial role of precursor gas (PG) and of catalyst support (CS) in the growth of multi-walled C nanotubes (MWCNTs) by iron-catalysed chemical vapour deposition (CVD) is evidenced. This is accomplished by comparing structural and morphological properties of MWCNTs synthesised by the use of different PGs (ethane and isobutane) and CSs (silica and alumina). The results of analyses, carried out on catalysts and C deposits by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermo-gravimetry (TG) and X-ray diffraction (XRD), demonstrate that Al 2O 3-supported catalysts are more efficient than SiO 2-supported ones in decomposing hydrocarbons. The use of i-C 4H 10 as PG allows reducing Fe-encapsulation and improving yield ( Y C) and selectivity, so as the large-scale production ( Y C > 900 wt.%) of high-quality nanotubes can be operated even at moderate reaction temperature (600 °C) after proper calibration of Fe-load (29 wt.%) and catalyst reduction temperature (500 °C).

Application of multi-walled carbon nanotubes as efficient support to NiMo hydrotreating catalyst

The feasibility of multi-walled carbon nanotubes (MWCNTs) as support to NiMo catalysts for hydrotreating of gas oil derived from Athabasca bitumen was tested in a trickle bed reactor at industrial conditions. High quality MWCNTs were prepared by CVD method using ferrocene as catalyst and toluene as carbon source. The produced MWCNTs were characterized by XRD, TEM, TGA and Raman spectroscopy in order to reveal the morphological and structural characteristics. Using functionalized MWCNTs as support, NiMo catalysts were prepared with varying Ni and Mo content by pore filling impregnation method. The calcined NiMo/MWCNTs catalysts were characterized by ICP-MS, N2 adsorption, XRD and TPR and the sulfide form of the catalysts was examined by DRIFT spectroscopy of adsorbed CO. The XRD patterns confirm the enhanced dispersion of MoO3 particles when increasing the Ni content from 0 to 4.5 wt.% over 12 wt.% Mo/MWCNTs. The TPR profiles indicate the two step reduction characteristics of Mo6+ to Mo in lower oxidation state such as Mo4+ and Mo0. The promoted and unpromoted MoS2 sites were clearly differentiated with the help of DRIFT of adsorbed CO over sulfided catalysts. The number of Ni promoted MoS2 (NiMoS phase) sites is increased significantly with increasing Ni addition up to 3 wt.% over 12 wt.% Mo/MWCNTs. The HDN and HDS activities of sulfided NiMo/MWCNTs using bitumen derived light gas oil were carried out at different temperatures under industrial condition. The HDN and HDS activities of the catalysts increased with increasing Ni content up to 3 wt.% and Mo content up to 12 wt.%. Based on weight of the catalyst, the HDN and HDS activities of 3 wt% Ni–12 wt.% Mo/MWCNTs are significantly higher than those over conventional Al2O3-based catalyst under the experimental conditions studied. The introduction of 2.5 wt.% P to MWCNTs-based catalyst found to show a fall in hydrotreating activity.

Laser direct writing carbon nanotube arrays on transparent substrates

The authors report the synthesis of multiwalled carbon nanotubes on transparent substrates by utilizing a diode laser to locally heat the catalysts to high temperature. Well-aligned bamboo-shaped multiwalled carbon nanotubes can be synthesized on glass substrate covered with a carbon black layer. If the carbon black was substituted by the commercial graphite inner coating, randomly oriented but high quality multiwalled carbon nanotubes were obtained with excellent field emission performance. This approach facilitates the fabrication of multiwalled carbon nanotube field emitters for field emission flat panel displays without limitations on the geometry size and temperature requirement of the substrate.

Synthesis of carbon nanotubes and nanofibers by decomposition of acetylene over a SMAD palladium catalyst

AbstractFilament‐like Carbon Nanostructures were synthesized by decomposition of acetylene over an alumina supported palladium catalyst prepared by the SMAD method. The structure of carbon products was analyzed by transmission electron microscopy. Between 500 and 700 °C the predominant structures were carbon nanofibers. Between 750 and 800 °C an important mass and volume increase of carbon products was observed. For this temperature range most of the Carbon was in the form of high quality multiwall carbon nanotubes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Morphology of Multi-Walled Carbon Nanotubes Affected by the Thermal Stability of the Catalyst System

High-quality multi-walled carbon nanotubes (MWCNTs) were efficiently synthesized on the CaCO3 supported Fe−Co catalyst with catalytic chemical vapor deposition method using acetylene as carbon source. The relationship between the catalyst structure and the carbon nanotube growth was systematically studied by using multiple techniques including SEM, TEM, TGA, Raman spectroscopy, and XRD. It was found that the MWCNT product demonstrates two groups in the outer diameter distribution, which is associated with the partial decomposition of CaCO3. This thermal decomposition was found to have as a result the coexistence of two catalytic systems throughout the entire synthesis process: Fe−Co/CaCO3 and Fe−Co/CaO. It was also found that the smaller diameter nanotubes grow on the Fe−Co/CaO system, while Fe−Co/CaCO3 produces larger diameter tubes.

Chemical vapor deposition of multi-walled carbon nanotubes from nickel/yttria-stabilized zirconia catalysts

Multi-walled carbon nanotubes (MWNT) were produced by chemical vapor deposition using yttria-stabilized zirconia/nickel (YSZ/Ni) catalysts. The catalysts were obtained by a liquid mixture technique that resulted in fine dispersed nanoparticles of NiO supported in the YSZ matrix. High quality MWNT having smooth walls, few defects, and low amounts of by-products such as amorphous carbon were obtained, even from catalysts with large Ni concentrations (>50 wt. %). By adjusting the experimental parameters, such as flux of the carbon precursor (ethylene) and Ni concentration, both the MWNT morphology and the process yield could be controlled. The resulting YSZ/Ni/MWNT composites can be interesting due to their mixed ionic-electronic transport properties, which could be useful in electrochemical applications.

One‐Step Water‐Assisted Synthesis of High‐Quality Carbon Nanotubes Directly from Graphite.

AbstractFor Abstract see ChemInform Abstract in Full Text.

One-step water-assisted synthesis of high-quality carbon nanotubes directly from graphite.

At 1 atm pressure, high-quality multiwall carbon nanotubes were synthesized directly from graphite in the absence of catalyst by a one-step water-assisted method.

High-yield synthesis of multi-walled carbon nanotubes by arc discharge in liquid nitrogen

Synthesis of multi-walled carbon nanotubes (MWNTs) by arc discharge in liquid nitrogen is reported. As liquid nitrogen substituted both vacuum and cooling systems, high-quality MWNTs were produced at a low cost. The content of the MWNTs can be as high as 70% of the reaction product. Auger-spectroscopy analysis revealed that no nitrogen is incorporated in the MWNTs. This method can be an economical route for the mass production of highly crystalline MWNTs.

Formation of carbon nanotubes in water by the electric-arc technique

A simplified arc discharge apparatus was used for growing carbon nanotubes, required only water (solution) in a glass container with no need for vacuum, water-cooled chamber. Carbon nanotubes with highest purity (20%) and highest yield (7 mg/min) were obtained when using salt solution as the medium. Resonance Raman spectrum of multi-walled carbon nanotubes (MWNTs) presented in as-grown materials was measured and RBM peaks originating from very thin core nanotubes were observed. The results show that high-quality MWNTs can be effectively prepared in water-arcing process.

Carbon nanotube films grown by laser-assisted chemical vapor deposition

Films of pure high-quality multiwall carbon nanotubes are grown by laser-assisted thermal chemical vapor deposition in a cold wall reactor. A CO2 laser is used to locally heat a substrate on which nanotubes are grown, employing the catalytic activity of iron nanoparticles. Two kinds of experiments are reported: In a two-step mode, catalytic iron particles and solid carbon are deposited separately, leading to the formation of homogeneous films of nonaligned pure multiwall nanotubes (MWNTs). The role of gas phase heating was investigated by the addition of a sensitizing molecule that absorbs the laser radiation. It is found that large-volume gas phase heating is not needed for the synthesis of high-quality nanotube films. Focused laser radiation allows growth of locally defined nanotube films. In a second set of experiments, iron and carbon are deposited simultaneously. Films of vertically aligned MWNTs of extremely high packing density were produced in this mode under very lean hydrocarbon supply conditions.

Metal-free production of high-quality multi-wall carbon nanotubes, in which the innermost nanotubes have a diameter of 0.4 nm

The production of high-purity multi-wall carbon nanotubes (MWNTs) without metal catalysts was produced using radio-frequency plasma. The MWNTs had diameters of about 5 nm, with the innermost tubes having a diameter of 0.4 nm, the smallest value possible for a single-wall carbon nanotube. Two types of aggregates were obtained, depending on the conditions of formation: moss-like aggregates (diameter: about 1μm) and long bundles (length: 10μm, diameter: 100 nm). The MWNTs in the moss-like aggregate, referred to as acute MWNTs, had tips with a cone angle of 19.2°.

Thin film metallic catalyst coatings for the growth of multiwalled carbon nanotubes by pyrolysis of xylene

Thin film metallic coatings applied to alumina and silicon substrates are investigated for their use as a catalyst to help grow high-quality multiwall carbon nanotubes (MWNTs). Substrate coatings examined include Fe, Tb:Fe, Ni, Cu, and Ni:Fe, with xylene used as the hydrocarbon source. Coating the substrate with Tb 90Fe 10 and Ni 80Fe 20 facilitated dense and uniform growth of MWNTs without graphitic particles; Ni and Fe substrate coatings produced graphitic particles in addition to the MWNTs, while Tb and Cu were found to be completely inactive with no MWNT growth. Many of the MWNTs grown over Ni:Fe have a helical appearance, while the MWNTs grown over Tb 90Fe 10 did not contain catalyst particles

Characterization of Carbon Nanotubes Grown by Chemical Vapor Deposition

Since the superior properties of multi-wall carbon nanotubes (MWCNT) could improve numerous devices such as electronics and sensors, many efforts have been made in investigating the growth mechanism of MWCNT to synthesize high quality MWCNT. Chemical vapor deposition (CVD) is widely used for MWCNT synthesis, and scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) are useful methods for analyzing the structure, morphology and composition of MWCNT.Temperature and pressure are two important growth parameters for fabricating carbon nanotubes. in MWCNT growth by CVD, the plasma assisted method is normally used for low temperature growth. However, a high temperature environment is required for thermal CVD. A systematic study of temperature and pressure-dependence is very helpful to understanding MWCNT growth. Transition metal particles are commonly used as catalysts in carbon nanotube growth. It is also interesting to know the how temperature and pressure affect the interface of carbon species and catalyst particles.

Structure analysis of purified multiwalled carbon nanotubes

High quality multiwalled carbon nanotubes (MWNTs) prepared by hydrogen DC arc discharge were purified by infrared irradiation in air at about 500°C. The morphology and nanostructure of the purified MWNTs were investigated by using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. Each MWNT was highly graphitized and most of the MWNTs had approximate 1.0 nm inner diameter. The radial breathing modes corresponding to the innermost nanotubes were observed in the micro-Raman spectra of the purified MWNTs. The dependence on the incident laser power of Raman-allowed mode, E 2g, and new Raman peak at about 1840 cm −1 was also studied.

アーク放電によるカーボンナノチューブの大量作製

Two kinds of methods for mass production of carbon nanotubes by DC arc discharge are described. One is conventional arc method to prepare multi-walled carbon nanotubes (MWNTs), but newly designed that the cathode graphite rod was automatically fed to get continuous arc discharge. By evaporating in the atmosphere of rarefied pure hydrogen gas, high-quality MWNTs were obtained in the cathode deposit. The second is newly developd arc plasma jet method to produce single-wall carbon nanotubes (SWNTs). High yield of SWNTs was obtained in the cottony carbon soot within the chamber. Prepared MWNTs and SWNTs were characterized by SEM, TEM and Raman spectroscopy. Several breathing modes of MWNTs were obtained at 206-388cm-1.

Optical Emission Spectra during Carbon Nanotube Production by Arc Discharge in H2, CH4 or He Gas

Optical emission spectra during carbon nanotube production by DC arc discharge in H2, CH4 or He gas were investigated. Emission spectra for C(I) (neutral carbon) atoms and C2 dimers were commonly observed in the three gases. The existence of H atoms and CH molecules was verified by in situ observation during the evaporation in H2 or CH4 gas, because strong H and CH spectra were identified. It was concluded that H atoms were conducive for production of high-quality multiwalled carbon nanotubes by means of forming hydrocarbon species, but were not conducive for production of C60 and C70.