Synthesis and characterization of electrocatalytic conjugates of tetraamino cobalt (II) phthalocyanine and single wall carbon nanotubes

In this paper we report on the synthesis and characterization of electrocatalytic conjugates of tetraamino cobalt (II) phthalocyanine and single walled carbon nanotubes (CoTAPc–SWCNT-linked) for use as electrode surface modifiers. FTIR, UV–vis and Raman spectroscopies were used to ascertain the chemical linkage between CoTAPc and SWCNT while cyclic voltammetry and rotating disk electrode voltammetry were used to assess the electrocatalytic efficiency of the linked product towards the oxidation of 2-mercaptoethanol. The CoTAPc–SWCNT-linked-GCE demonstrated very good catalytic efficiency relative to CoTAPc–SWCNT-mixed-GCE, CoTAPc-GCE and f-SWCNTs-GCE (functionalised SWCNT). CoTAPc–SWCNT-linked-GCE gave a sensitivity of 0.2 μA/μM and a limit of detection (LOD) of 1.2 × 10⁻⁷ M for 2-mercaptoethanol (2-ME) at pH 4.     

In-situ studies of electron field emission of single carbon nanotubes inside the TEM

Electron field emission characteristics of individual multi-walled carbon nanotubes (MWCNTs) were investigated in situ inside the transmission electron microscope (TEM). For a single MWCNT it was found that while field-emission can hardly occur from the side of the nanotube, a curved nanotube may result in finite side emission and the best emission geometry is the top emission geometry. Current-voltage (I-V) measurements made at different vacuum conditions and voltage sweeps emphasize the importance of the adsorbates on the electron field emission of MWCNTs. For a contaminated MWCNT, although the field emission current was reduced, the stability of its emission was improved. A current of up to several tens of μA was observed for a single MWCNT, but it was found that long time emission usually results in drastic structure damage that may lead to sudden emission failure.     

Raman characterization of single wall carbon nanotubes prepared by the solar energy route

A Raman scattering characterization is reported that confirms the preparation of single wall carbon nanotubes (SWNT) by the solar energy route. The results are presented for samples synthesized with various catalysts—mixtures of Ni and Co (Y, La)—and compared to those obtained from electric arc discharge or laser ablation. In the light of the calculations of the vibrational spectra of SWNT by Eklund et al. (Carbon, 1995, 33, 959) it is shown that both the diameter and structure of the nanotubes depend strongly on the synthesis conditions. For the first time the presence of nanotubes with “zigzag” or “chiral” helical pitches for some of the samples are shown as well as a large distribution of tube diameters.     

Thermionic emission of amorphous diamond and field emission of carbon nanotubes

Thermal-field emission characteristics from nano-tips of amorphous diamond and carbon nanotubes at various temperatures are reported in this study. Amorphous diamond emitted more than 13 times more electrons at a temperature of 300 °C than at room temperature. In contrast, CNTs exhibited no increase of emitted current upon heating to 300 °C. The thermally agitated emission of amorphous diamond is attributed to the presence of defect bands. The formation of these defect bands raises the Fermi level into the upper part of the band gap, and thus reduces the energy barrier that the electrons must tunnel through. From defect bands within the band gap, the conduction band electrons were significantly increased due to electron tunnels from defect bands. The enhanced thermal-field emission originating from defect bands was observed in this study. This thermally agitated behavior of field emission for amorphous diamond was highly reproducible as observed in this research.     

Liquid crystal behavior of single wall carbon nanotubes

Single wall carbon nanotubes are dispersed in water with the water-soluble polymer polyvinylpyrrolidone and the surfactant sodium dodecylbenzene sulfonate, and then deposited by evaporative deposition onto degeneratively-doped silicon wafer substrates. These deposits were examined by scanning electron microscopy, which revealed highly-ordered arrays of large single wall carbon nanotube bundles. Various solution concentrations were prepared and deposition conditions were varied to determine their affect on the single wall carbon nanotube arrays. These observations were related to existing lyotropic liquid crystal theory and theories explaining the behavior of carbon nanotubes in solution, which allowed for further development and interpretation of the phase diagram which describes the behavior of single wall carbon nanotubes in lyotropic liquid crystal systems, and how competing liquid crystal systems in the same solution directly affect the ordering of the single wall carbon nanotube arrays.     

Synthesis of PEGylated single wall carbon nanotubes by a photoinitiated graft from polymerization

A considerable amount of research has been devoted to carbon nanotubes because of their unique electrical, mechanical, optical, and chemical properties. Here, in this report, we introduce a novel, simple ultraviolet initiated “graft from” polymerization method to synthesize PEGylated carbon nanotubes. This grafting procedure significantly enhanced nanotube aqueous dispersibility and long term stability in solution. Mass of grafted polymer chains was easily modulated by adjusting polymerization reaction time, and nanomaterials containing up to 80% polymer by weight were synthesized. Nanotube morphology was characterized by SEM, TEM before and after the functionalization. In addition, the covalent bonding of polymer chains to the nanotubes structure was elucidated by Raman, ATR‐FTIR, and XPS spectroscopy. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Application of carbon nanotubes to field emission displays

Large-area field emission displays were fabricated with single-wall carbon nanotube emitters. A carbon nanotube paste was prepared and screen-printed to form an electron emission layer on a glass-based substrate. Carbon nanotube-based field emission displays fabricated by thick film processing were successfully integrated to demonstrate moving color images. They revealed excellent field emission characteristics of a threshold electric field of approximately 2 V/μm. We have also investigated triode-type field emission display structures to achieve high-gray scale and high brightness. In the triode structure, it was observed that electron emission from carbon nanotube emitters was controlled by modulation of gate voltages.     

Quantum-mechanical simulations of field emission from carbon nanotubes

We present simulations of field emission from 2-nm long open (5,5), closed (5,5) and open (10,0) carbon nanotubes. Besides usual effects associated with the field-emission process, the total-energy distributions of the field-emitted electrons present peaks that are shifted by the electric field. Their sharpness and the evolution of their amplitude when changing the electric field depend on the semiconducting or metallic character of the nanotube.     

Raman spectroscopy on isolated single wall carbon nanotubes

A review is presented on the resonance Raman spectra from one isolated single wall carbon nanotube. The reasons why it is possible to observe the spectrum from only one nanotube are given and the important structural information that is provided by single nanotube spectroscopy is discussed. Emphasis is given to the new physics revealed by the various phonon features found in the single nanotube spectra and their connection to spectra observed for single wall nanotube bundles. The implications of this work on single wall carbon nanotube research generally are also indicated.     

Hydrogen adsorption studies on single wall carbon nanotubes

Hydrogen adsorption data on as-grown and heat-treated single walled carbon nanotubes (SWNTs) obtained by a volumetric procedure using a Quantachrome Autosorb-1 equipment are presented. The amounts of hydrogen adsorbed at atmospheric pressure reach approximately 0.01 wt.% at 298 K and 1 wt.% at 77 K. The isosteric heat of adsorption has been calculated for both samples from H₂ equilibrium adsorption data at three temperatures, having initial values of 7.42 and 7.75 kJ mol⁻¹. Studies in porous structure by N₂ adsorption and density measurements in helium pycnometer are reported.     

Oriented and exfoliated single wall carbon nanotubes in polyacrylonitrile

Polyacrylonitrile (PAN)/single wall carbon nanotubes (SWNT) fibers were gel spun at 0, 0.5, and 1 wt% SWNT content to a draw ratio of 51. Structure, morphology, and mechanical and dynamic mechanical properties of these fibers have been studied. PAN/SWNT composite exhibited much higher electron beam radiation resistance than PAN. As a result, PAN lattice images could be easily observed in the composite fiber by high resolution transmission electron microscopy. The PAN/SWNT composite fiber also exhibited higher solvent resistance than the control PAN fiber. UV-vis spectroscopy of highly drawn fiber exhibited van Hove transitions, suggesting SWNT exfoliation upon drawing. SWNT exfoliation was also confirmed by high resolution transmission electron microscopy (HRTEM). At 1 wt% SWNT loading, fiber storage modulus (at 1 Hz) increased by 13.9, 6.6, and 0.2 GPa at −75, 25, and 150 °C, respectively. This suggests that the load transfer ability and hence interfacial strength is increasing with decreasing temperature, even below the polymer's γ transition temperature.     

Characterization of single wall carbon nanotubes by nonane preadsorption

The preferential blocking of the interior adsorption sites of single walled carbon nanotubes (SWNTs) by n-nonane is demonstrated. Following adsorption of n-nonane and evacuation for 24 h at 323 K, it was found that interior sites with diameters less than ∼14 Å remained filled with n-nonane, blocking the physical adsorption of N₂ on these sites at 77.3 K. We demonstrate that “nonane blocking” is a very useful technique for nanotube porosity characterization.     

Preparation and field emission properties of Er-decorated multiwalled carbon nanotubes

The field emission of multiwalled carbon nanotubes (MWCNTs) was improved after decorating their external surface with erbium (Er)-nanoparticles. The decoration was performed by liquid-phase reduction using ethylene glycol as the reducing agent. The oxidation of MWCNTs and the attachment of Er-nanoparticles on the surface of MWCNTs were confirmed by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Raman spectroscopy also revealed the oxidation and functionalization of the nanotubes. Thermogravimetric analysis showed that the decomposition temperature of the MWCNTs decreased gradually as a result of the oxidation process and sequential decoration with uniformly sized Er-nanoparticles (2-3 nm). This means that some of the defects formed by oxidation and decoration with Er-nanoparticles reduced the ignition temperature of the MWCNTs. After decoration with Er-nanoparticles, the MWCNTs showed a significantly better emission current density (3.45 mA/cm² at 3.98 V/μm) and turn-on field (1.8 V/μm) than the pristine MWCNTs.     

Shadow mask field emission display with carbon nanotubes emitters

Printable carbon nanotubes field emission displays with shadow mask (Shadow Mask CNT-FED) is suggested. A layer of insulator is screen printed on the upper surface of shadow mask, and address electrodes are fabricated on it. MgO film is deposited on shadow mask by electron beam evaporation. Secondary emission electrons escape from MgO film under the bombardment of primary electrons. In the simulation, 93% of the landing electrons are found to be secondary emission electrons. The modulating amplitude of the voltage on the address electrodes is low (∼ 250 V) because of the low-energy secondary emission electrons. The comparable results are also got from the experiments. The modulating amplitude of the voltage is found to increase with the thickness of the insulator. The optimized thickness (40 ∼ 50 μm) and the fabrication process of the insulator are suggested in this research report.     

Synthesis, characterization and cytotoxicity of phosphoryl choline-grafted water-soluble carbon nanotubes

Carbon nanotubes (CNTs) were rendered water-soluble by grafting on phosphoryl choline (PC). The modified CNTs were characterized utilizing Fourier transform infrared spectra, X-ray photoelectron spectra, thermogravimetric analysis, nuclear magnetic resonance, transmission electron microscopy, ultraviolet/visible absorbance spectra and dynamic laser light-scattering. The results show that the target products are easily dispersed in water and remain dispersed for at least three months. This study showed that both CNTs and CNT-PC induce no cytotoxicity on clonal pheochromocytoma cells (PC12) and human colon carcinoma cell lines (Caco-2). The grafted PC group confers water solubility and keeps the cell-compatibility of CNTs.     

Synthesis and characterization of double-walled carbon nanotubes from multi-walled carbon nanotubes by hydrogen-arc discharge

Double-walled carbon nanotubes (DWNTs) were synthesized in a large scale by a hydrogen arc discharge method using graphite powders or multi-walled carbon nanotubes/carbon nanofibers (MWNTs/CNFs) as carbon feedstock. The yield of DWNTs reached about 4 g/h. We found that the DWNT product synthesized from MWNTs/CNFs has higher purity than that from graphite powders. The results from high-resolution transmission electron microscopy observations revealed that more than 80% of the carbon nanotubes were DWNTs and the rest were single-walled carbon nanotubes (SWNTs), and their outer and inner diameters ranged from 1.75 to 4.87 nm and 1.06 to 3.93 nm, respectively. It was observed that the ends of the isolated DWNTs were uncapped and it was also found that cobalt as the dominant composition of the catalyst played a vital role in the growth of DWNTs by this method. In addition, the pore structures of the DWNTs obtained were investigated by cryogenic nitrogen adsorption measurements.     

Synthesis of carbon nanotubes on single crystal diamond

Vertically aligned multiwalled carbon nanotubes (MWCNTs) have been synthesised on Ni coated single crystal diamond substrates using a glow-discharge technique. A mixture of gases including CH₄, H₂ and N₂ has been used for growth. The effect of the CH₄/H₂ gas mixture and growth temperature on the structure and yield of the MWCNTs has been studied. Atomic force microscopy is used to characterise the annealed Ni film prior to growth. Scanning electron microscope studies have also been carried out to observe the yield, height and diameter of MWCNTs produced under various experimental conditions. Raman spectroscopy has been performed to provide quantitive information on the crystallinity of our as-grown MWCNTs. It has been shown that highly adherent, vertically aligned MWCNTs can be grown on type Ib diamond (100) substrates with an interface free from metal catalyst.     

Investigation of ionomers as dispersants for single wall carbon nanotubes

A novel conjugated ionomer was prepared from a diamine and a bis(pyrylium salt). Single-walled carbon nanotubes (SWNT) were dispersed in solutions of the ionomer in N,N-dimethylacetamide resulting in homogenous suspensions or quasi-solutions. These suspensions were used to cast unoriented thin films. In addition, the ionomer/SWNT solutions were used to aid in the dispersal of SWNTs in a soluble, low color polyimide. The use of the ionomer as a dispersant enabled the nanotubes to be dispersed at loading levels up to 1 wt% in a polyimide solution without visual agglomeration. SWNTs were well dispersed in the thin films as evidenced by visual inspection, optical microscopy, and high resolution scanning electron microscopy. The films were further characterized for their electrical and mechanical properties.