Bamboo-shaped Carbon Nanotubes Research Articles

Synthesis of carbon nanotubes and carbon onions by CVD using a Ni/Y catalyst supported on copper

Bamboo-shaped carbon nanotubes and carbon onions have been synthesized, respectively, by CVD using a novel Ni/Y/Cu catalyst at different reduction and reaction temperature (500–700 °C). Characterization of the as-prepared catalyst and carbon nanoproducts are investigated by X-ray diffractometer (XRD), transmission electron microscopes (TEM) and X-ray energy dispersive spectrometer (EDS). The results show that yttria doped in nickel catalyst plays a key role in keeping the activity of the catalyst by resisting or postponing the interaction between copper and nickel. Along with the temperature increasing, the morphologies of the carbon products will be changed: carbon nanotubes at 500 °C, carbon onions at 600 and 700 °C. The growth mechanisms of CNTs and carbon onions are discussed in details.

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.

Electrochemical Double-Layer Capacitors Based on Activated Bamboo-Shaped Carbon Nanotubes

Bamboo-shaped carbon nanotubes (BCNTs) have been synthesized by chemical vapor deposition method. The activated BCNTs after simple ball milling and KOH etching are used as polarizable electrodes in electric double layer capacitor (EDLC). Our results show that the specific capacity of BCNTs can be improved by the activation treatment.

TEM studies of the initial stage growth and morphologies of bamboo-shaped carbon nanotubes synthesized by CVD

The initial stage growth of bamboo-shaped carbon nanotubes (CNTs) synthesized by catalytic decomposition of methane is investigated. A special experimental procedure has been developed to stop the process after short durations (0 s to 3 min). It has found that during the early stages (60 s), carbon cluster-encapsulated nanoparticles are formed. With prolonging synthesis time (3 min), some CNTs coexisted with carbon cluster-encapsulated nanoparticles are formed. HRTEM observations show that these CNTs display multi-walled and bamboo structure and the encapsulated catalytic particles are quasi-cone morphologies. At the same time, the catalytic particles only encapsulated with carbon clusters present quasi-sphere structures. For growth up to 60 min, two kinds of bamboo mode structures are observed: conical, and cylindrical, which are developed by quasi-cone and quasi-sphere catalytic particles, respectively. Moreover, the early stage growth mode of the CNTs is predominantly of the base growth mode according to TEM observations.

Electrochemical properties of bamboo-shaped multiwalled carbon nanotubes generated by solid state pyrolysis

We report herein on an electrochemical study of bamboo-shaped multiwalled carbon nanotubes (BMWCNTs) that were synthesized by a simple and efficient solid state pyrolysis method. Cyclic voltammetry was used to evaluate the electrochemical behavior of BWCNTs in 0.1 M KCl containing 5 mM of K 4Fe(CN) 6. The electron transfer rates of as-synthesized bamboo-shaped multiwalled carbon nanotubes and commercial hollow multiwalled CNTs were evaluated and compared. Among the studied electrodes, BMWCNTs showed a faster electron transfer rate, as compared with the other electrodes. The higher electron transfer kinetics can be attributed to the surface oxide functional groups. IR, Raman, XPS, and electrochemical studies showed that the as-synthesized carbon nanotubes exhibit some functional groups on BMWCNTs. This phenomenon can be attributed to the larger amount of exposed edge planes in the as-prepared BMWCNTs, as compared with the ordinary multiwalled carbon nanotubes. The capacitive properties of BMWCNTs electrodes were studied in 1 M KNO 3 using cyclic voltammetry with the scan rates ranging from 25 to 500 mV/s. The specific capacitance of the BMWCNTs electrodes were 11.5 and 6.7 F/g with scan rates of 25 and 500 mV/s, respectively.

Bamboo-shaped carbon nanotubes produced by catalytic decomposition of methane over nickel nanoparticles supported on aluminum

Bamboo-shaped carbon nanotubes (CNTs) and herringbone nanofibers were catalytically synthesized by a decomposition of methane over Ni/Al catalyst under N 2 at the low temperature (500–600 °C). Transmission electron microscopy (TEM) was used to investigate the bamboo-shaped CNTs and the nanofibers. High-resolution TEM analysis revealed that two species of bamboo-shaped tubes with different morphologies and structures, categorized according to the shape and participation of the encapsulated catalytic nanoparticles, coexist in one sample. It is found that the morphology and structure of the catalytic particles play very important roles during carbon nanomaterial growth. The growth mechanisms for the bamboo-shaped CNTs and nanofibers are proposed in detail, especially the formation process of compartments of the bamboo-shaped CNTs.

SINGLE WALL BAMBOO SHAPED CARBON NANOTUBE: A MOLECULAR DYNAMICS AND ELECTRONIC STUDY

Thermal stability and molecular electronic properties of a single walled, bamboo shaped carbon nanotube has been investigated. Molecular dynamics method is applied to investigate thermal stability, and electronic properties are calculated at the Extended Huckel level. Although bamboo shaped carbon nanotubes observed in experimental literature are multi-walled, it is shown that the suggested structural model in this work, which is single-walled, is also both thermodynamically and energetically stable. Bamboo shape of the model investigated is due to periodical coronene-like spacers. The resultant structure is compartmented, having geometrical aberrations in the vicinity of spacers. There is no degradation in the average coordination number. The geometrical aberrations in the vicinity of spacers is due to curvature induced by the pentagons of the resultant geometry.

Lateral force microscopy of bamboo-shaped multiwalled carbon nanotubes

Morphologies of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) grown on Fe catalyst deposited onto SiO2/Ti substrates by thermal chemical vapor deposition were investigated by means of atomic force microscopy (AFM) and lateral force microscopy (LFM). For the structural speciality, the bamboo structures were more distinctly observed by LFM. 2005 Elsevier B.V. All rights reserved. PACS: 68.37.Ps; 81.05.Tp; 81.07.De; 81.40.Pq

Generation of Hydrophilic, Bamboo-Shaped Multiwalled Carbon Nanotubes by Solid-State Pyrolysis and Its Electrochemical Studies

A simple, efficient, and novel method was developed for the direct preparation of hydrophilic, bamboo-shaped carbon nanotubes by the pyrolysis of ruthenium(III) acetylacetonate in a Swagelock cell is reported. The obtained product exhibits mostly bamboo-shaped, straight, periodic twisted, multiwalled carbon nanotubes possessing diameters of 50-80 nm and lengths of around 10 microm. The pyrolyzed product was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), micro-Raman, and cyclic voltammetric techniques. HRTEM studies showed that the walls of bamboo-shaped carbon nanotubes consisted of oblique grapheme planes with respect to the tube axis. The interlayer spacing between two graphitic layers was found to be 0.342 nm. XPS measurements have suggested that as-prepared carbon nanotubes consist the surface functional groups on the surface of carbon nanotubes. The electrochemical properties of synthesized carbon nanotubes have been evaluated. Thermogravimetric analysis (TGA), IR, and cyclic voltammetric studies showed the presence of oxygen functionalities. Raman studies revealed the presence of disorder in the graphitic carbon and the presence of exposed edge plane defects in the generated carbon nanotubes for influencing the surface behavior and electrochemical properties. The electrochemical behavior of electrodes made of bamboo-shaped carbon nanotubes served for an oxygen reduction reaction.

Synthesis, characterizations and applications of some nanomaterials (TiO2 and SiC nanostructured films, organized CNT structures, ZnO structures and CNT-blood platelet clusters)

TiO2 nanostructured films have been synthesized by the hydrolysis of Ti[OCH(CH3)2]4 as the precursor. These films have been utilized for the dissociation of phenol contaminant in water. Free-standing nanostructured film of silicon carbide (SiC) has been synthesized, employing a simple and new route of spray pyrolysis technique utilizing a slurry of Si in hexane. Another study is done on organized carbon nanotube (CNT) structures. These are made in the form of hollow cylinders (50 mm length, 4 mm diameter and 1.5 mm wall thickness). These CNT-based cylinders are made of conventional CNT and bamboo-shaped CNT. The filtrations of heavy hydrocarbons andE. coli bacteria from water have been carried out. In addition to this, ZnO nanostructures have also been studied. Another study concerns CNT-blood platelet clusters.

Hydrogen storage capacity of different carbon nanostructures in ambient conditions

The hydrogen storage capacity of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) in ambient conditions was studied by means of the volumetric method, and compared with those of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). The BS-MWNTs, whose herringbonelike structure was characterized by the transmission electron microscopy, showed the greatest hydrogen storage capacity with about 0.4wt% at atmospheric pressure. The SWNTs showed a comparable hydrogen storage capacity, whereas the MWNTs were insensitive to the pressure change. Our work indicates that the herringbone carbon nanotube structure is more capable of hydrogen storage than the herringbone graphite nanofiber structure.

Mechanical cutting of bamboo-shaped multiwalled carbon nanotubes by an atomic force microscope tip

Mechanical cutting of the bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) was achieved by using an atomic force microscope (AFM) tip. Nip- and pen cap-like shapes were observed in the BS-MWNT cut sections. By close inspection of the cut sections, we were able to identify the mechanism of the mechanical cutting in BS-MWNTs.

Influence of acid treatments of carbon nanotube precursors on Ni/CNT in the synthesis of carbon nanotubes

The Ni/CNT catalyst was fabricated by directly dipping carbon nanotube precursors refluxed in 4 M of nitric acid into Ni electroless plating bath, and used to synthesize new carbon nanotubes. The experimental results indicate that the duration of acid-treatment of carbon nanotubes precursors exerts a great influence on the catalysis of Ni/CNT in the synthesis of carbon nanotubes and hence the structures of the new carbon nanotubes. When the carbon nanotubes precursors were refluxed for 0.5 h in 4 M of nitric acid, bamboo-shaped carbon nanotubes (BSCNT) or Y junction carbon nanotubes in the carbon products were obtained. As the duration of acid-treatment of carbon nanotubes precursors increased to 6 h, the as-prepared Ni/CNT displayed higher activity, and the carbon nanotube products were high pure without any Y junction structure or any separation layers in hollow.

Formation of Carbon Nanotubes and Cubic and Spherical Nanocages

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes and cubic and spherical carbon nanocages, have been prepared by an ethanol thermal reduction process. Scanning electron microscopy studies showed that carbon nanotubes predominated. Transmission electron microscopy investigations indicated that as-synthesized sample contained mostly bamboo-shaped carbon nanotubes, with some carbon cubic and spherical nanocages. Detailed examination of high-resolution transmission electron micrography showed that the walls of bamboo-shaped carbon nanotubes consisted of oblique graphene planes with respect to the tube axis, whose interlayer spacing was about 0.335 nm. The experimental results suggest that the growth mechanism of the bamboo-shaped carbon nanotubes follows the base growth model and the appearance of cubic and spherical carbon nanocages arises from the graphitic sheets bending in an attempt to eliminate the highly energetic dangling bonds present at the edge of the growing structure....

Structural study of nitrogen-doping effects in bamboo-shaped multiwalled carbon nanotubes

We have investigated nitrogen doping effects on the structure and crystallinity of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) by means of x-ray photoemission spectroscopy (XPS) and transmission electron microscopy. By controlling the NH3/C2H2 flow ratio during the chemical vapor deposition, the nitrogen concentrations of 0.4% to 2.4% were obtained. According to the XPS measurements, the increasing nitrogen concentration gave rise to an increase of the N-sp3 C bonds as well as the deterioration of the crystallinity of the BS-MWNTs. Besides, the N-sp3 C bonds were found to prevail over the N-sp2 C bonds above 5% nitrogen concentration. At higher nitrogen concentrations, the BS-MWNTs showed shorter compartment distances, presumably due to the suppressed surface diffusion of carbon on the catalyst particles.

Large-Scale Synthesis of Carbon Nanotubes by an Ethanol Thermal Reduction Process

The bamboo-shaped carbon nanotubes were synthesized on a large scale through an ethanol thermal reduction process, in which ethanol was used as the carbon source and magnesium was used as the reductant. The toxic or corrosive reagents have been completely avoided. Furthermore, Y-junction carbon nanotubes obtained from our experiment can be used as the building blocks of nanoelectronics. Because of the simplicity and high yield of this route, it may potentially be applied on the scale of industrial production.

Atomic force microscopy of bamboo-shaped multiwalled carbon nanotube structures

Atomic force microscopy (AFM) was employed for the morphology measurements of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) grown by thermal chemical vapor deposition on Fe catalyst deposited SiO 2/Ti substrates. Greater diameters and compartment distances of the bamboo structures were observed for the BS-MWNTs grown at 950 °C than for those grown at 850 °C.

The formation and characterization of palladium nanowires in growing carbon nanotubes using microwave plasma-enhanced chemical vapor deposition

Multi-wall carbon nanotubes were synthesized on electroplated palladium nanoclusters using a microwave plasma-enhanced chemical vapor deposition system in a mixture of methane and hydrogen as precursors. During the synthesis, Pd was melted to fill up the growing multi-wall carbon nanotubes. A growth mechanism was proposed to describe the Pd filling phenomenon. The multi-wall carbon nanotubes could be burned in oxygen plasma and the filled Pd nanowires could thus be collected. The surface morphology of electroplated Pd clusters and the nanostructure of multi-wall carbon nanotubes with filled Pd nanowires were examined by scanning electron microscopy and transmission electron microscopy, respectively. Raman spectra were used to study the first- and second-order signals of multi-wall carbon nanotubes. Bamboo-shaped carbon nanotubes free of filled Pd were observed under a pure methane atmosphere.

The effect of laser power on the formation of carbon nanotubes prepared in CO 2 continuous wave laser ablation at room temperature

Single-walled carbon nanotubes (SWNTs) were prepared by continuous wave CO 2 laser ablation without applying additional heat to the target. Transmission electron microscope and Raman spectrum were used to investigate the effect of laser power on the growth and diameter distribution of the tubes. The average diameter of single wall carbon nanotubes produced by CO 2 laser increases with increasing laser power. We have presented the radial breathing mode of Raman spectrum of SWNTs prepared by using CO 2 continuous laser vaporization in laser power from 500 to 850 W, and the Raman spectrum are also compared with those of single-walled carbon nanotubes produced by pulsed CO 2 laser ablation of previous reports. SWNTs and bamboo-shaped carbon nanotubes were observed from web-like carbon soot in a lower laser power of 500 W. Experiment confirmed that laser power play a crucial role in SWNTs formation and diameter distribution.

Growth-temperature induced metal–insulator transition in bamboo-shaped multiwalled carbon nanotubes

Temperature-dependent resistivity measurements were carried out on bamboo-shaped multiwalled carbon nanotubes (CNT) grown on cobalt-catalyst-deposited A1 2O 3/Ti substrates by a thermal chemical vapor deposition. The resistivity decreased with increasing growth temperature, and a reduced activation energy analysis showed that the CNT moved from the critical regime to the metallic regime with increasing growth temperature. The improved electrical conductivity with increasing growth temperature is attributed to the improved crystallinity and the increased diameters of the CNT.