Bamboo-shaped Multiwalled Carbon Nanotubes Research Articles

Direct curvature measurement of the compartments in bamboo-shaped multi-walled carbon nanotubes via scanning probe microscopy

Bamboo-shaped multi-walled carbon nanotubes (BS-MWCNTs) have compartmented structures inherently obtained during their catalytic growth, and the curvature of the compartmented structure is known to be determined by the morphology of the metal catalysts. In this study, the inside curvature of the BS-MWCNTs was directly measured through scanning probe microscopy (SPM). The surface of the compartment structures of BS-MWCNTs has discontinuous graphene layers and different frictional force levels depending on the curvature direction. That of the inside curvature can be directly observed through tribological analysis by adding and subtracting the lateral force microscopy images obtained on opposite sides along the axial direction of the BS-MWCNT (diameter of 500 nm). This tells us the direction of the inside curvature of the BS-MWCNT, which was also confirmed by identifying the growth direction of the BS-MWCNTs via scanning electron microscopy. Our demonstration implies that SPM can give the same insight into the structural characterization of nanomaterials that is relatively inexpensive and more user-friendly than currently used methods.

Electrochemical Study of Tartrazine Using a Carbon Paste Electrode Modified with Nanostructured Materials

Tartrazine (Trz) is one of the most widely used azoic dyes in the alimentary industry; it is added to a great variety of products, for this reason it is necessary to develop analytic methods and materials which allow its detection and quantification. For this purpose ultraviolet-visible spectrophotometry (UV-Vis), high performance liquid chromatography (HPLC), capillary electrophoresis and potentiometric and voltammetric sensors have been used. Potentiometric and voltammetric sensors have many advantages such as simplicity; rapid analysis and cost, besides most recently developed sensors are environmentally friendly and avoid the use of mercury which is toxic. In this regard, carbonaceous electrodes such as carbon paste electrodes have been employed due to its low cost, they are easy to manufacture and can be modified with a great diversity of materials an methods. Nanostructured materials such as bamboo-shaped multiwalled carbon nanotubes (BS-MWCNT) and Pt nanoparticles (Pt/NPs) allow great electrochemical activity and in this work are proposed to modify a CPE in order to detect and quantify Tartrazine samples. The electrochemical experiments were performed in a potentiostat/galvanostat AUTOLAB30, using NOVA 2.1 software, a typical three-electrode electrochemical cell was used. A Pt wire was employed as counter electrode; Ag/AgCl (3M NaCl) in a Luggin capillary as reference electrode, the working electrode was a CPE prepared by mixing graphite powder and mineral oil in a proportion 1:1, the CPE was modified by adding an aliquot of 5mL of BS-MWCNT dispersion and by adding an aliquot of 5mL of Pt/NPs and BS-MWCNT. Cyclic voltammograms obtained in 0.5M NaCl + 2.0x10-5 M Trz (adjusted to a pH=4.0) are shown in Figure 1. In the case of CPE, a peak due to Trz oxidation appears at 0.77V, the oxidation peak is positively shifted (0.15V) when BS-MWCNT are added and now appears at 0.92V, even though the oxidation potential is greater on BS-MWCNT the associated current is also greater. When the experiment is performed on BS-MWCNT + Pt/NPs the oxidation peak appears at 0.99V, the associated current in this last case is greater than in the previous cases, a great current leads to an improvement of some analytical parameters such as sensibility, which may help to detect and quantify Trz more accurately. S Food and Drug Administration Center for Food Safety and Applied Nutrition. (2003) U. S Department of Health and Human Services.López-de-Alba, P. L., López-Martínez, L., De-León-Rodríguez, L. M. Simultaneous Determination of Synthetic Dyes Tartrazine, Allura Red and Sunset Yellow by Differential Pulse Polarography and Partial Least Squares. A Multivariate Calibration Method. (2002). 14(3):197-205.Ramírez-Silva, T., Palomar-Pardavé, M. E. Gónzalez, I., Rojas-Hernández, A. (1995). Carbon Paste Electrodes with Electrolytic Binder: Influence of the Preparation Method. Electroanalysis. 7:184-188.Yu, L., Shi, M., Yue, X., Qu, L. (2016). Detection of Allura Red Based on the Composite of Poly (diallylmethylammonium chloride) Functionalized Graphene and Nickel Nanoparticles Modified Electrode. Sensors and Actuators B: Chemical. 225:398-404. Figure 1

Exponential decrease of scission length and low tensile strength of bamboo-shaped multi-walled carbon nanotubes under ultrasonication

We report here scission of bamboo-shaped multi-walled carbon nanotubes (BS-MWCNTs) under ultrasonication. As the applied sonication energy increases, mean length of BS-MWCNTs decreases. When sonication energy increases over 500 J/mL, the length of BS-MWCNTs no longer decreases; the limited scission length (L0) is about 1.7 μm for BS-MWCNTs with diameter between 50 and 100 nm. From the L0 of BS-MWCNTs, their tensile strength (σ∗) is calculated and found to be smaller than that of multi-walled carbon nanotubes (MWCNTs). In addition, exponential decrease of the length of BS-MWCNTs with increasing sonication energy is observed, which is distinguished from typical power law dependence of sonication-induced scission of MWCNTs. These exclusive characteristics in the scission of BS-MWCNTs under ultrasonication are regarded to result from weak binding at discontinuous graphene sheets obtained from forming compartment structures of BS-MWCNTs during growth.

Bulk production of bamboo-shaped multi-walled carbon nanotubes via catalytic decomposition of methane over tri-metallic Ni–Co–Fe catalyst

In this work, bamboo-shaped, multi-walled carbon nanotubes were synthesized via methane decomposition over a Ni–Co–Fe tri-metallic catalyst at 1000 °C. The nitrogen absorption (BET), X-ray diffraction (XRD), and particle size analysis results of the catalyst were used to demonstrate the surface area, size distribution, and crystallinity of the sample. The scanning electron microscopy (SEM) micrographs of the nanocarbons deposited via methane decomposition indicated that highly uniform carbon nanotubes were grown on the surface of the tri-metallic catalyst. The transmission electron microscopy (TEM) images showed that the carbon nanotubes were multi-walled and bamboo-shaped with a diameter of ~20 nm. Raman spectra revealed the graphitization degree of the CNTs with an I D /I G of 1.84, indicative of the crystallinity of CNTs with structural defects. The thermal analysis shows the high oxidation stability of the multi-walled carbon nanotubes.

Formation of bamboo-shaped carbon nanotubes on carbon black in a fluidized bed

For the first time, bamboo-shaped multiwalled carbon nanotubes, having diameter of the order of 50 nm, have been grown on carbon black in a fluidized bed in bulk amount. The activation energy for the synthesis of the product was found out to be around 33 kJ/mol in the temperature range of 700−900 °C. The carbon nanotubes were separated from the carbon black by preferential oxidation of the later, the temperature of which was determined by thermogravimetry. The transmission electron microscopy revealed different features of the nanotubes such as “Y” junction, bend, and catalyst filling inside the nanotubes. Small angle neutron scattering was performed on the nanotubes synthesized at different temperatures. The data were fitted into a suitable model in order to find out the average diameter, which decreases with increase in synthesis temperature. The Monte Carlo simulation predicts the same behavior. Based on the above observations, a possible growth mechanism has been predicted. The oscillation in carbon saturation value inside the catalyst in the fluidized bed has been indicated as the responsible factor for the bamboo-shaped structure.

Oxygen reduction characteristics of bamboo-shaped, multi-walled carbon nanotubes without nitrogen in acid media

The oxygen reduction characteristics of bamboo-shaped, multi-walled carbon nanotubes (BCNTs) were compared with those of hollow-shaped, multi-walled carbon nanotubes (HCNTs). Structural and compositional differences between HCNTs and BCNTs were assessed using TEM, BET, TDS, Raman, TG-DTA and XPS measurements. A rotating disk electrode was used to study the influence of their structure on the activity of the oxygen reduction reaction (ORR). It was found that BCNTs showed higher catalytic activity in the ORR compared with HCNTs regardless of whether the BCNTs were untreated or acid-treated. The onset potential for the ORR was 0.66 V (vs. RHE) for acid-treated BCNTs, 0.32 V higher than that of acid-treated HCNTs. In addition, it was confirmed that the reduction current normalized by the BET surface area at a potential of −0.1 V (vs. RHE) was approximately 2.2 times higher for acid-treated BCNTs. Collectively, the results indicate that a disordered surface with pentagonal defects, rounded compartments, and edge plane sites contribute to the superior ORR characteristics of BCNTs.

Multi-Walled Carbon Nanotubes Fabricated by Electrospinning of Acrylonitrile/Nylon Solution and Subsequent Carbonization

The poly(acrylonitrile) (PAN) nanofiber web interpenetrated nylon-6 nanofiber supporters were prepared by electrospinning of an acrylonitrile (AN)/nylon-6 solution. It was realized that the average diameters of PAN and nylon-6 nanofiber were 20 and 100 nm, respectively, and that the PAN nanofibers constructed spider-mat networks which were supported by the robust nylon-6 nanofiber pillars. After stabilization and carbonization above 600 degrees C, both hollow-shaped and bamboo-shaped multi-walled carbon nanotubes (MWCNTs) were formed with the diameter range from 5 to 20 nm. The morphology and structure of MWCNTs had been further investigated by the combination techniques of transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffraction (XRD) and elemental analyzer (EA).

Field emission properties of Fe70Pt30 catalysed multiwalled carbon nanotubes

Multi-walled carbon nanotubes were grown on nanocrystalline Fe70Pt30 film using low-pressure chemical vapour deposition (LPCVD) method. The growth time was varied between 5 min to 30 min. SEM micrograph of this film revealed that the size of nanoparticles varied from 5 nm to 10 nm. The diameter of the carbon nanotubes varied from 20 nm to 50 nm as verified by TEM. HRTEM image confirmed that the carbon nanotubes are bamboo-shaped multiwalled carbon nanotubes (MWNTs). Field emission characteristics of MWNTs at various growth times (5 min, 15 min and 30 min) with working distances (50 µm, 100 µm and 150 µm) were also studied. The carbon nanotubes grown for 30 min with working distance 150 µm exhibited the lowest turn-on field of 2.45 V/µm. The turn-on field increases from 2.45 V/µm to 6.21 V/µm as the growth time decreases from 30 min to 5 min whereas for lower working distances (100 µm and 50 µm), the turn-on field increases from 4.74 V/µm to 6.74 V/µm and from 8.79 V/µm to 14.49 V/µm respectively. The turn-on field (E to) and field enhancement factor (β) were studied as a function working distance (d) and growth time respectively to see the effect of these parameters on field emission properties. The field enhancement factor (β) was also studied as a function of radius of apex curvature (r) . It was found the field enhancement factor (β) decreases with the increase in radius of apex curvature (r) and growth time whereas the value of field enhancement factor (β) increases as working distance (d) increases. On the basis of the dependence of β on radius of apex curvature (r) a relationship of β ∝ r −1/2 is fitted.

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 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.

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.

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.

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.

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.

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.

Metallic conductivity in bamboo-shaped multiwalled carbon nanotubes

Temperature-dependent resistivity measurements were carried out on bamboo-shaped multiwalled carbon nanotubes (MWNTs) grown by thermal chemical vapor deposition. They were deposited on Al 2O 3/Ti and SiO 2/Ti substrates using cobalt and iron catalysts, respectively. As a result, a metallic conductivity, i.e. resistivities with a positive temperature slope, was observed for the MWNTs grown on the SiO 2/Ti substrates. The different temperature behaviors of the resistivity for the MWNTs grown on different substrates are discussed in view of the substrate morphology and crystallinity.