Correlation of the chemical properties of carbon nanotubes with their atomic and electronic structures

The nature of chemical bonding in carbon nanoclusters is investigated by the PM3 semiempirical quantum-chemical method. The influence of the atomic structure on the electronic characteristics and chemical properties of nanoclusters is analyzed. A σ-π model is proposed for the chemical bonding in nanotubes. It is shown that, in the framework of the proposed model, nanotubes are objects characterized by a small contribution of π states to the valence band top.     

Effect of electrochemical treatment on structural properties of conical carbon nanotubes

Interaction of multiwalled conical carbon nanotubes (CNTs) with hydrogen during their electrochemical treatment was studied by galvanostatic measurements and Raman spectroscopy. The structural changes occurring in the conical walls of the CNTs in consequence of the hydrogenation were investigated by using X-ray diffraction (XRD). The results obtained show that hydrogen sorption by conical CNTs is reversible. XRD studies revealed that the electrochemical hydrogenation leads to a change in the diffraction peak profile (2θ=26^°) and its position corresponding to the interplanar distance in conical CNTs. The results indicate structural changes occurring in the conical walls of the CNTs during hydrogenation. We assume that these structural changes can be caused by the hydrogen intercalation into the interplanar spaces of conical CNTs. Thus, the charge/discharge and structure data can be explained by the existence in this system of physically adsorbed molecular hydrogen and chemically bound atomic hydrogen.     

Synthesis,characterization, and electrochemical properties of imidazole derivatives functionalized single‐walled carbon nanotubes

The imidazole derivatives functionalized single‐walled carbon nanotubes (SWNTs) were synthesized by a diazonium‐based reaction. We have designed and synthesized two imidazole derivatives to modify SWNTs. The resulting products were characterized by Fourier transform infrared (FT‐IR) spectroscopy, Raman spectroscopy, ultraviolet visible (UV/Vis) spectroscopy, thermo gravimetric analysis (TGA), energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Electrochemical measurements via a cyclic voltammetry method revealed that the weak intramolecular electronic interactions presented between the attached imidazole derivatives groups and the nanotubes. Copyright © 2008 John Wiley & Sons, Ltd.     

Controllable one-step synthesis of magnetite/carbon nanotubes composite and its electrochemical properties

Magnetite nanocrystals are deposited on carbon nanotubes by a reflux method in diethylene glycol. The morphological characterization proves that magnetite nanocrystals are decorated on the external surfaces of carbon nanotubes. The crystal size of magnetite nanocrystals can be readily tuned by adjusting the content of sodium acetate, but the content of sodium acetate has little effect on the amount of magnetite. The magnetite/carbon nanotubes composites exhibit an initial capacity as high as 840 mAh g⁻¹ and an excellent cycling performance for lithium storage. The reversible capacity, as high as 390 mAh g⁻¹, can be maintained after 75 charge/discharge cycles. The research has potential implications for the application of magnetite/carbon nanotubes composites as anode materials of lithium ion batteries.     

Optimum degree of functionalization for carbon nanotubes

Covalent functionalizations, especially oxidization and derivative functionalization, significantly improve the surface characteristics of carbon nanotubes, but also bring undesired devastation of sidewalls. This paper presents a theoretic model to investigate double-edge effects of covalent functionalization on carbon nanotubes for the polymer composite application. An optimal degree of functionalization is proposed and calculated based on the trade-off of required load-transfer and induced devastation of nanotube sidewalls. The negative effect on elastic modulus is also calculated. For oxidization-based functionalization of originally defect-free nanotubes, the calculation results indicate that about 10% functionalization degree is suggested to be optimum for the balance of efficient load-transfer and conspicuous devastation from the highly covalent functionalization. The original defects in nanotube surface also reduce the optimum functionalization degree and the reduction is dependent on the original defect concentration. The computational results indicate that nanotube diameter and percentages in the polymer composites show considerably effect on the optimum functionalization degree. Carbon nanotubes with smaller diameter show lower optimum functionalization degree. Increasing percentage of carbon nanotubes in the polymer composites also leads to lower optimum functionalization degree.     

Preparation of graphene/polyaniline-modified carbon nanotubes and their electrochemical properties in microbial fuel cell

Using chemical vapor deposition methods to prepare carbon nanotubes growing in situ on a carbon felt, graphene and polyaniline were applied to the carbon felt for modifying carbon nanotubes. Microbial fuel cell was constructed with graphene/polyaniline-modified carbon nanotubes as anode, graphite as cathode, and glucose solution as substrate. The effects of electrodes, substrate concentration, and temperature on the properties of microbial fuel cell have been studied. At 38 °C using glucose solution of 1450 mg L^?1 and external resistance of 2500 Ω, the optimum output voltage of 687 mV and removal rate of 83% for chemical oxygen demand were obtained in the microbial fuel cell. The prepared nanomaterials are stable and reusable.     

Mechanical properties of carbon nanotubes

A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young’s moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young’s modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 29 July 1999     

Superconducting properties of carbon nanotubes

Metallic single wall carbon nanotubes have attracted much interest as 1D quantum wires combining a low carrier density and a high mobility. It was believed for a long time that low temperature transport was exclusively dominated by the existence of unscreened Coulomb interactions leading to an insulating behavior at low temperature. However experiments have also shown evidence of superconductivity in carbon nanotubes. We distinguish two fundamentally different physical situations. When carbon nanotubes are connected to superconducting electrodes, they exhibit proximity induced superconductivity with supercurrents which strongly depend on the transmission of the electrodes. On the other hand intrinsic superconductivity was also observed in suspended ropes of carbon nanotubes and recently in doped individual tubes. These experiments indicate the presence of attractive interactions in carbon nanotubes which overcome Coulomb repulsion at low temperature, and enables investigation of superconductivity in a 1D limit never explored before. To cite this article: M. Ferrier et al., C. R. Physique 10 (2009).     

Longitudinal unzipping of carbon nanotubes and their electrochemical performance in supercapacitors

The capacitive properties of graphene nanoribbons (GNRs) with different reduction levels were investigated. GNRs have been synthesized through thermal reduction of oxidized GNRs in the temperature range 100–400 °C. Oxidized GNRs were synthesized by longitudinal unzipping of multi-walled carbon nanotubes (MWCNTs) by means of chemical treatments. Scanning electron microscopy and transmission electron microscopy observations showed, that the efficient tube unzipping yielded improved effective surface area without any tube annihilation by the unzipping process of MWCNTs. Electrochemical studies indicated that through unzipping of MWCNTs, specific capacitance increased from 8 to 28 F g⁻¹ at discharge current density of 0.5 A g⁻¹, confirming increased active surface area and increased defect density in the MWCNTs surface. Unzipping of MWCNTs resulted in decreased rate capability of the electrode because of low electrical conductivity due to oxidization during the unzipping process. Thermal reduction of unzipped sample affected both specific capacitance and rate capability of electrodes. The highest specific capacitance of 62 F g⁻¹ at discharge current density of 0.5 A g⁻¹ was obtained for the sample unzipped and thermally annealed at about 150 °C. The amount of oxygen-containing groups was shown to be an important factor influencing the performance of the GNRs. These results make unzipped MWCNTs promising electrode materials for supercapacitor applications.     

Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes

Thorn-like, organometallic-functionalized carbon nanotubes were successfully developed via a novel microwave hydrothermal route. The organometallic complex with methyl orange and iron (III) chloride served as reactive seed template, resulting in the oriented polymerization of pyrrole on the modified carbon nanotubes without the assistance of other oxidants. Morphological and structural characterizations of the carbon nanotube/methyl orange-iron (III) chloride and polypyrrole/carbon nanotube composites were examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), infrared spectroscopy and X-ray diffraction (XRD). The electrochemical property of the polypyrrole/carbon nanotube composite was elucidated by cyclic voltammetry and galvanostatic charge-discharge. A specific capacitance of 304 F g⁻¹ was obtained within the potential range of −0.5-0.5 V in 1 M KCl solution.     

Efficient and facile one pot carboxylation of multiwalled carbon nanotubes by using oxidation with ozone under mild conditions

In this study, oxidation of carbon nanotubes with ozone in the presence of hydrogen peroxide was investigated. The reaction was performed under clean and mild conditions and oxidized products with high concentration of oxygenated groups were yielded. The reaction products were characterized with attenuated total reflectance (ATR), Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffractometry (XRD), back titration, X-ray photoelectron spectroscopy (XPS) and the dispersion behavior of the oxidized multiwalled carbon nanotubes (MWCNTs) was also studied. The results confirmed the presence of high concentrations of oxidative groups on the carbon nanotubes (CNTs) treated by the method of the present work.     

Purification and magnetic properties of carbon nanotubes

Received: 5 January 1998     

Formation mechanism of carbon nanotubes in the gas-phase synthesis from colloidal solutions of nanoparticles

Single- and multi-wall carbon nanotubes have been synthesized by the gas-phase catalytic reaction of colloidal solutions of metal nanoparticles using a vertical flow reactor. The reverse micelle solution of the Co–Mo nanoparticles with the mean diameter of 11 nm dissolved in toluene was injected directly into the reactor maintained at 1200 °C. The nanoparticles and the solvent act as the catalyst and carbon source, respectively. When the concentration of the thiophene additive is low (1 wt.%), the formation of SWNT bundles preferentially occurred. The SWNT bundles were present together with the relatively small metal nanoparticles with the diameter of 0.5–5.5 nm. It is likely that the original nanoparticles with the diameter of 11 nm break into smaller ones, 1–2 nm diameters, which is suitable for the SWNT growth. The synactic effect of Co and Mo was also observed.     

Field emission properties and synthesis of carbon nanotubes grown by rf plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition (PECVD) method was employed to grow the Fe-catalyzed carbon nanotubes (CNTs). The grown CNTs with a uniform diameter in the range of about 10-20 nm and the typical lengths beyond 1 μm resulted in a very high aspect ratio. The Raman and TEM results showed that the grown CNTs contained a large amount of carbonaceous particles and crystal defects, such as pentagon-heptagon pair defects. XPS measurement indicated that the CNTs had CH covalent bonds. Field emission characteristics exhibited the low turn-on threshold field of 2.75 V/μm and the maximum emission current density of 7.75 mA/cm² at 6.5 V/μm. The growth mechanism of CNTs and the effects of hydrogen plasma on their structure were discussed.     

Electronic properties of oxidized carbon nanotubes

The effect of oxygenation on the electronic properties of semiconducting carbon nanotubes is studied from first principles. The O2 is found to bind to a single-walled nanotube with an adsorption energy of about 0.25 eV and to dope semiconducting nanotubes with hole carriers. Weak hybridization between carbon and oxygen is predicted for the valence-band edge states. The calculated density of states shows that weak coupling leads to conducting states near the band gap. The oxygen-induced gap closing for large-diameter semiconducting tubes is discussed as well. The influence of oxygen on the magnetic property is also addressed through a spin-polarized calculation and compared to experiment.     

Electronic properties of double-layer carbon nanotubes

The electronic spectra for double-wall zigzag and armchair nanotubes are found. The influence of nanotube curvatures on the electronic spectra is also calculated. Our finding that the outer shell is hole doped by the inner shell is in the difference between Fermi levels of individual shells which originate from the different hybridization of π orbital. The shift and rotation of the inner nanotube with respect to the outer nanotube are investigated. We found stable semimetal characteristics of the armchair DWNTs in regard of the shift and rotation of the inner nanotube. We predict the shift of k_F towards the bigger wave vectors with decreasing of the radius of the armchair nanotube.     

Unusual high degree of unperturbed environment in the interior of single-wall carbon nanotubes

Double wall carbon nanotubes were prepared by vacuum annealing of single wall carbon nanotubes filled with C60. Strong evidence is provided for a highly defect free and unperturbed environment in the interior of the tubes. This is concluded from unusual narrow Raman lines for the radial breathing mode of the inner tubes. Lorentzian linewidths scale down to 0.35 cm(-1) which is almost 10 times smaller than linewidths reported so far for this mode. A splitting is observed for the majority of the Raman lines. It is considered to originate from tube-tube interaction between one inner tube and several different outer tubes. The highest RBM frequency detected is 484 cm(-1) corresponding to a tube diameter of only 0.50 nm. Labeling of the Raman lines with the folding vector is provided for all inner tubes. This labeling is supported by density functional calculations.     

Synthesis, integration, and electrical properties of individual single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWNTs) are synthesized by chemical vapor deposition (CVD) of methane on silicon-dioxide substrates at controlled locations using patterned catalytic islands. With the synthesized nanotube chips, microfabrication techniques are used to reliably contact individual SWNTs and obtain low contact resistance. The combined chemical synthesis and microfabrication approaches enable systematic characterization of electron transport properties of a large number of individual SWNTs. Results of electrical properties of representative semiconducting and metallic SWNTs are presented. The lowest two-terminal resistance for individual metallic SWNTs (≈5 μm long) is ≈16.5 kΩ measured at 4.2 K. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 14 July 1999