Comparative measures of single-wall carbon nanotube dispersion

Model composites of DNA-wrapped single-wall carbon nanotubes in poly(acrylic acid) are used to evaluate metrics of nanotube dispersion. By varying the pH of the precursor solutions, we introduce a controlled deviation from ideal behavior. On the basis of small-angle neutron scattering, changes in near-infrared fluorescence intensity are strongly correlated with dispersion, while optical absorption spectroscopy and resonant Raman scattering are less definitive. Our results represent the first systematic comparison of currently accepted measures of nanotube dispersion.     

Phosphoryl choline-grafted water-soluble carbon nanotube

Water-soluble property is the precondition of biomedical evaluation and application of carbon nanotube （CNT）. Novel water- soluble CNT was synthesized in this letter by grafting phosphoryl choline （PC） onto multi-wall CNTs. Utilizing FTIR, XPS, TGA and TEM, the title CNTs were characterized and it was found that the target products could facilely dissolve in water. 2007 Tao Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

Electrochemistry at chemically assembled single-wall carbon nanotube arrays

Single-wall carbon nanotubes (SWNTs) chemically assembled on gold substrates were employed as electrodes to investigate the charge transfer process between SWNTs and the underlying substrates. Cyclic voltammetry (CV) indicates that the assembled SWNTs allow electron communication between a gold electrode and the redox couple in solution, though the SWNTs are linked directly onto the insulating monolayer of 11-amino-n-undecanethiol (AUT) on the Au substrate. An electron transfer (ET) mechanism, which contains an electron tunneling process across the AUT monolayer, is proposed to explain the CV behavior of Au/AUT/SWNT electrodes. Electrochemical measurements show that the apparent electron tunneling resistance, which depends on the surface density of assembled SWNTs, has apparent effects similar to those of solution resistance on CV behavior . The theory of solution resistance is used to describe the apparent tunneling resistance. The experimental results of the dependence of ET parameter psi on the potential scan rate upsilon are in good agreement with the theoretical predictions. Kinetic studies of the chemical assembly of SWNTs by atomic force microscopic (AFM), electrochemical, and Raman spectroscopic methods reveal that two distinct assembly kinetics exist: a relatively fast step that is dominated by the surface reaction, and a successive slow step that is governed by bundle formation.     

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.     

Spontaneous dissolution of a single-wall carbon nanotube salt

Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.     

Flexible transparent conducting single-wall carbon nanotube film with network bridging method

Hollow ZrO(2) microspheres with mesoporous shells have been synthesized by a novel hydrothermal reaction of zirconium oxychloride in the presence of urea, hydrochloric acid, and ethanol. The morphology and shell thickness of the hollow microspheres can be controlled by varying synthesis conditions. After calcination at high temperature, the morphologies of the hollow microspheres are essentially preserved. Pt catalyst supported on the hollow calcined ZrO(2) microspheres exhibits more excellent catalytic performance in CO oxidation than those on ZrO(2) powders derived from conventional precipitation methods.     

Raman studies of solutions of single-wall carbon nanotube salts

Polyelectrolyte solutions of Na-doped single-wall carbon nanotube (SWNT) salts are studied by Raman spectroscopy. Their Raman signature is first compared to undoped SWNT suspensions and dry alkali-doped SWNT powders, and the results indicate that the nanotube solutions consist of heavily doped (charged) SWNT. Raman signature of doping is then used to monitor in situ the oxidation reaction of the nanotube salt solutions upon exposure to air and to an acceptor molecule (benzoquinone). The results indicate a direct charge-transfer reaction from the acceptor molecule to the SWNT, leading to their gradual charge neutralization and eventual precipitation in solution. The results are consistent with a simple redox titration process occurring at the thermodynamical equilibrium.     

Carbon nanotube salts. Arylation of single-wall carbon nanotubes

[reaction: see text] Carbon nanotube salts prepared by treating single-wall carbon nanotubes (SWNTs) with lithium in liquid ammonia react readily with aryl iodides to give SWNTs functionalized by aryl groups.     

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS

The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.     

Water-soluble full-length single-wall carbon nanotube polyelectrolytes: preparation and characterization

HiPco single-wall carbon nanotubes (SWNTs) have been noncovalently modified with ionic pyrene and naphthalene derivatives to prepare water-soluble SWNT polyelectrolytes (SWNT-PEs), which are analogous to polyanions and polycations. The modified nanotubes have been characterized with UV-vis-NIR, fluorescence, Raman and X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The nanotube-adsorbate interactions consist of pi-pi stacking interactions between the aromatic core of the adsorbate and the nanotube surface and specific contributions because of the substituents. The interaction between nanotubes and adsorbates also involves charge transfer from adsorbates to SWNTs, and with naphthalene sulfonates the role of a free amino group was important. The ionic surface charge density of the modified SWNTs is constant and probably controlled by electrostatic repulsion between like charges. The linear ionic charge density of the modified SWNTs is similar to that of common highly charged polyelectrolytes.     

Electrochemical and conductivity measurements of single-wall carbon nanotube network electrodes

The electrochemical response of two-dimensional networks of pristine single-wall carbon nanotubes (SWNTs) has been investigated. SWNTs were grown by catalyzed chemical vapor deposition on an insulating SiO2 substrate, and then electrically contacted by lithographically defined Au electrodes. Subsequent insulation of the contact electrodes enabled the electrochemical properties of the SWNT network to be isolated and directly studied for the first time. The electrochemical activity of the SWNT network was found to be strongly dependent on the applied potential. For the same SWNT electrode, the limiting current for the oxidation of 5 mM Fe(phen)32+ was found to be much greater than expected based on the signal for the reduction of 5 mM Ru(NH3)63+. Simultaneous conductance and electrochemical measurements demonstrated decreasing conductance as the potential was scanned negative (versus Ag/AgCl) with the minimum conductance at around the reduction potential for Ru(NH3)63+. These results are consistent with the presence of both metallic and semiconducting SWNTs in the SWNT network electrode. Moreover, these results show that through appropriate choice of mediator and electrode potential, metallic SWNTs can be electrochemically addressed independently of semiconducting SWNTs.     

Elemental analysis of a single-wall carbon nanotube candidate reference material

A material containing single-wall carbon nanotubes (SWCNTs) with other carbon species, catalyst residues, and trace element contaminants has been prepared by the National Institute of Standards and Technology for characterization and distribution as Standard Reference Material SRM 2483 Carbon Nanotube Soot. Neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP–MS) were selected to characterize the elemental composition. Catalyst residues at percentage mass fraction level were determined with independent NAA procedures and a number of trace elements, including selected rare earth elements, were determined with NAA and ICP–MS procedures. The results of the investigated materials agreed well among the NAA and ICP–MS procedures and good agreement of measured values with certified values was found in selected SRMs included in the analyses. Based on this work mass fraction values for catalyst and trace elements were assigned to the candidate SRM.     

用羟基磷灰石和单壁碳纳米管制备葡萄糖传感器的研究

在滴涂法制得单壁碳纳米管(SWNTs)修饰电极的基础上,采用电化学方法沉积纳米羟基磷灰石(HA)涂层,进而利用分子组装技术将葡萄糖氧化酶(GOD)固定到该电极上,制得的修饰电极的循环伏安测量结果表明,GOD发生了直接的电子传递.GOD-HA-SWNTs/GC修饰电极对不同浓度的葡萄糖呈现两个良好的线性响应范围,有望开发...     

Titanium coverage on a single-wall carbon nanotube: molecular dynamics simulations

The minimum energy structures of Ti covered (8,0) single-wall carbon nanotube (SWNT) have been investigated theoretically. Using available experimental data and the results of density functional theory calculations, we first parametrized a reliable empirical many-body potential energy function (PEF) for the CTi binary system. The PEF used in the calculations includes two- and three-body atomic interactions. Then performing molecular dynamics simulations at 1 and 300 K, we obtained the minimum-energy configurations for Ti covered (8,0)-SWNT. The configurations reported here include low and high coverage of Ti on nanotubes. We have found that one layer of Ti did not distort the nanotube significantly, whereas two-layer coverage showed an interesting feature: the second layer of Ti pushed the first layer inside the wall of nanotube, but the general shape of the nanotube was not affected so much.     

A water-soluble carbon nanotube network conjugated by nanoparticles with defined nanometre gaps

Cage-shaped proteins with an affinity for carbonaceous materials were constructed and used to assemble a nanostructure in which single-walled carbon nanotubes are surrounded by cobalt oxide nanoparticles with nanometre gaps. By changing the size of proteins and materials incorporated inside the cavity, similar structures with distinctively different properties can be fabricated.     

Molecular beam-controlled nucleation and growth of vertically aligned single-wall carbon nanotube arrays

The main obstacle to widespread application of single-wall carbon nanotubes is the lack of reproducible synthesis methods of pure material. We describe a new growth method for single-wall carbon nanotubes that uses molecular beams of precursor gases that impinge on a heated substrate coated with a catalyst thin film. In this growth environment the gas and the substrate temperature are decoupled and carbon nanotube growth occurs by surface reactions without contribution from homogeneous gas-phase reactions. This controlled reaction environment revealed that SWCNT growth is a complex multicomponent reaction in which not just C, but also H, and O play a critical role. These experiments identified acetylene as a prolific direct building block for carbon network formation that is an order of magnitude more efficient than other small-molecule precursors. The molecular jet experiments show that with optimal catalyst particle size the incidence rate of acetylene molecules plays a critical role in the formation of single-wall carbon nanotubes and dense vertically aligned arrays in which they are the dominant component. The threshold for vertically aligned growth, the growth rate, the diameter, and the number of walls of the carbon nanotubes are systematically correlated with the acetylene incidence rate and the substrate temperature.     

Synthesis of gold nanorod/single-wall carbon nanotube heterojunctions directly on surfaces

This contribution describes the synthesis of gold nanorod (Au NR)/single-wall carbon nanotube (SWCNT) heterojunctions assembled directly on Si/SiOx substrates. SWCNTs are attached to amine-functionalized Si/SiOx substrates, and Au monolayer-protected clusters (MPCs) are adsorbed to the surface of SWCNTs through hydrophobic interactions. Seed-mediated reduction of HAuCl4 with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB) onto the Au MPCs leads to the growth of larger Au nanostructures directly on the SWCNTs. Au NRs account for 19% of the nanostructures, some of which are attached directly to the sidewall and some at the ends of the SWCNTs. Raman spectroscopic measurements of SWCNTs before and after growth of the Au nanostructures reveal that the presence of Au leads to an approximately 50-fold enhancement of the Raman scattering signal. Combining 1D nanostructures of different materials (Au and carbon in this example) is of fundamental interest and may find use in nanoelectronics, chemical sensing, electrochemical, and spectroscopy applications.     

Brownian dynamics simulations of single-wall carbon nanotube separation by type using dielectrophoresis

We theoretically investigate the separation of individualized metallic and semiconducting single-wall carbon nanotubes (SWNTs) in a dielectrophoretic (DEP) flow device. The SWNT motion is simulated by a Brownian dynamics (BD) algorithm, which includes the translational and rotational effects of hydrodynamic, Brownian, dielectrophoretic, and electrophoretic forces. The device geometry is chosen to be a coaxial cylinder because it yields effective flow throughput, the DEP and flow fields are orthogonal to each other, and all the fields can be described analytically everywhere. We construct a flow-DEP phase map showing different regimes, depending on the relative magnitudes of the forces in play. The BD code is combined with an optimization algorithm that searches for the conditions that maximize the separation performance. The optimization results show that a 99% sorting performance can be achieved with typical SWNT parameters by operating in a region of the phase map where the metallic SWNTs completely orient with the field, whereas the semiconducting SWNTs partially flow-align.