Sidewalls Of Single-walled Carbon Nanotubes Research Articles

Effect of Different Functional Groups on the Free Radical Scavenging Capability of Single-Walled Carbon Nanotubes

The effect of different functional groups on the free radical scavenging capability of single-walled carbon nanotubes (SWCNT) is investigated using density functional theory calculations. The reaction mechanism that is considered in this study is the radical adduct formation. The reactions of a •OH radical with eight different functionalized SWCNTs (armchair and zigzag) were studied. All of them were found to be exothermic and exergonic. Different sites of reaction were considered, and the increase on reactivity with respect to pristine tubes was found to be site-dependent. The presence of functional groups on the sidewalls of SWCNTs is predicted to increase their OH radicals scavenging activity. To enhance this property, the best functional groups are −CH2−OH for the armchair (3,3) SWCNT and −CONH−CH3 for the zigzag (5,0) fragment. The major conclusion from this work is that functionalized SWCNTs, in addition to be soluble in different media, are also very good free radical scavengers, being the armchair...

Temperature Dependent Raman Spectra of Carbon Nanobuds

Carbon nanobuds (CNBs) represent an emerging nanostructure, in which fullerene molecules are covalently bonded to the outer surface of single-walled carbon nanotubes (SWNTs). The Raman spectra of CNBs were systematically investigated and compared to those of SWNTs. The spectra were recorded using a 514 nm laser and evaluating the temperature-dependent Raman frequency shift in CNBs in the range 27−475 °C. The temperature coefficient of the G-mode frequency of the CNBs was much larger than that of the SWNTs. Consequently, the CNBs have lower thermal stability, which is attributed to the fact that the fullerenes are covalently bonded to the sidewall of SWNTs. At the same time, we observed that the radical breathing modes (RBMs) of CNBs downshift ∼2−6 cm−1 compared to the RBMs of SWNTs, and this shift can be attributed to the smaller van der Waals (VDWs) interactions between the CNBs. Using a 750 nm laser, a broad G− band, which is an intrinsic character of metallic properties, was clearly observed. This char...

Electronic Properties of Propylamine‐Functionalized Single‐Walled Carbon Nanotubes

We present resonant Raman measurements on single-walled carbon nanotubes (SWCNT) functionalized with propylamine groups at different degrees. Direct nucleophilic addition based on in situ generated primary amides is used for attaching n-propylamine to the sidewalls of SWCNTs. The influence of the amino functionalities on the electronic structure of the nanotubes is investigated. From the Raman resonance profiles of the radial breathing modes (RBMs), the chiral indices of the corresponding tubes are assigned. We observe significant redshifts of the transition energies and a broadening of the resonance windows due to chemical modification of SWCNTs. Similar redshifts are derived from the analysis of the NIR/Vis transmission spectrum. The relative Raman intensities of the functionalized samples and the evaluation of their transmission spectra indicate a diameter dependence of the reactivity as it has been observed for other moieties. By analyzing the defect induced D mode we observe a considerable degree of functionalization accompanied by an almost unharmed tube structure, which ensures that the observed effects are mainly driven by changes of the electronic structure.

Reductive Retrofunctionalization of Single‐Walled Carbon Nanotubes

As if nothing had happened: A detailed mechanistic investigation of the nucleophilic addition of organolithium reagents onto single-walled carbon nanotubes (SWCNTs) revealed that the initial functionalization step is part of an equilibrium. Consequently, the functionalization of the sidewalls of SWCNTs is reversible, and the introduced substituents can be detached easily by reduction.

Selective Formation and Efficient Photocurrent Generation of [70]Fullerene–Single‐Walled Carbon Nanotube Composites

For the first time nanocarbon composites with C70 molecules aligned on the sidewall of single-walled carbon nanotubes (SWNTs) are demonstrated. The C70–SWNT photoelectrochemical devices exhibit efficient photocurrent generation properties that result from selective formation of a single composite film consisting of a SWNT network covered with C70 molecules and high electron mobility through the C70–SWNT network.

Selection of single-walled carbon nanotubes according to both their diameter and chirality via nanotweezers

Diameter- and chirality-dependent interactions between aromatic molecule-based nanotweezers and single-walled carbon nanotubes (SWNTs) are revealed by density functional theory calculations. We found that the threshold diameter of selected SWNTs is determined by the end-to-end distance of the nanotweezer. Large-diameter SWNTs are preferred by a nanotweezer with an obtuse folding angle, whereas small-diameter SWNTs are favored by a nanotweezer with an acute folding angle. The adsorption can be further stabilized by the orientational alignment of the hexagonal rings of the nanotweezer and the SWNT sidewall. Therefore, by taking advantage of the supramolecular recognition ability of the aromatic molecule-based nanotweezer, SWNTs can be enriched with both controllable diameter and chirality. Open image in new window

A Novel Diameter‐Selective Functionalization of SWCNTs with Lithium Alkynylides

AbstractCovalent functionalization by addition to the sidewalls ofsingle‐walled carbon nanotubes (SWCNTs) is one of the most important methods for the derivatization of carbon nanotubes. The nucleophilic addition of organometallic reagents (carbon‐ and nitrogen‐based carbanions) has recently become a widely used tool for the introduction of functional moieties onto the surface of this new carbon allotrope. The extension of this concept by the successful nucleophilic addition of in situ generated lithium acetylides to the SWCNT scaffold is presented herein. The chemically derivatized SWCNTs have been characterized in detail by TGA/MS, Raman, UV/Vis/NIR and fluorescence spectroscopy. On the basis of a detailed examination of the signals in the radial breathing‐mode region of the Raman spectra, the preferred functionalization of smaller‐diameter tubes has been clearly demonstrated.

Hydrogen Sensing and Sensitivity of Palladium-Decorated Single-Walled Carbon Nanotubes with Defects

Individual single-walled carbon nanotubes (SWCNTs) become sensitive to H(2) gas when their surfaces are decorated with Pd metal, and previous reports measure typical chemoresistive increases to be approximately 2-fold. Here, thousand-fold increases in resistance are demonstrated in the specific case where a Pd cluster decorates a SWCNT sidewall defect site. Measurements on single SWCNTs, performed both before and after defect incorporation, prove that defects have extraordinary consequences on the chemoresistive response, especially in the case of SWCNTs with metallic band structure. Undecorated defects do not contribute to H(2) chemosensitivity, indicating that this amplification is due to a specific but complex interdependence between a defect site's electronic transmission and the chemistry of the defect-Pd-H(2) system. Dosage experiments suggest a primary role is played by spillover of atomic H onto the defect site.

Atomistic Oxidation Mechanism of a Carbon Nanotube in Nitric Acid

Motivated by recent experiments, we investigate how NO3-SWNT interactions become energetically favorable with varying oxidation state of a single-walled carbon nanotube (SWNT) using first-principles calculations. Chemisorption becomes less endothermic with respect to physisorption when the SWNT oxidation state is elevated. Importantly, the dissociative incorporation of an oxygen atom into the SWNT sidewall becomes highly favorable when the SWNT oxidation state is elevated from electron density depletion in the vicinity, as caused experimentally using electrochemical potential. The elevation of the SWNT oxidation state through accumulating local charge transfer from the surrounding molecules does not have the same effect. Our investigation reveals the crucial effects of the SWNT oxidation state in understanding the molecule-SWNT interaction.

Electron Transfer Kinetics at Single-Walled Carbon Nanotube Electrodes using Scanning Electrochemical Microscopy

An important open question on the electrochemistry of single-walled carbon nanotube (SWNT) electrodes concerns the sites at which electron transfer (ET) occurs. This issue is addressed herein for the case of a simple outer sphere redox couple, (ferrocenymethyl)trimethylammonium (FcTMA+). Using relatively sparse networks (<1% surface coverage) of electrically connected SWNTs, coupled to a scanning electrochemical microscopy (SECM) substrate generation−tip collection setup, we show that high rates of mass transport can be generated to SWNTs, allowing kinetic effects to be observed in the voltammetric waveshape. By developing a numerical model that faithfully represents all aspects of the experimental geometry, highly accurate kinetic data can be obtained. Assuming that all SWNTs are active, a minimum average ET rate constant k0SWNT > 1.0 ± 0.6 cm s−1 is assigned, which is of similar size to other electrode materials and suggests that the sidewall of SWNTs has considerable ET activity.

Functionalization of Single‐Walled Carbon Nanotubes with Cubic Prussian Blue and Its Application for Amperometric Sensing

AbstractIn this work, we synthesized electroactive cubic Prussian blue (PB) modified single‐walled carbon nanotubes (SWNTs) nanocomposites using the mixture solution of ferric‐(III) chloride and potassium ferricyanide under ambient conditions. The successful fabrication of the PB‐SWNTs nanocomposites was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and cyclic voltammetry (CV). PB nanocrystallites are observed to be finely attached on the SWNTs sidewalls in which the SWNTs not only act as a carrier of PB nanocrystallites but also as Fe(III)‐reducer. The electrochemical properties of PB‐SWNTs nanocomposites were also investigated. Using the electrodeposition technique, a thin film of PB‐SWNTs/chitosan nanocomposites was prepared onto glassy carbon electrode (GCE) for the construction of a H2O2 sensor. PB‐SWNTs/chitosan nanocomposites film shows enhanced electrocatalytic activity towards the reduction of H2O2 and the amperometric responses show a linear dependence on the concentration of H2O2 in a range of 0.5–27.5 mM and a low detection limit of 10 nM at the signal‐to‐noise ratio of 3. The time required to reach the 95% steady state response was less than 2 s. CV studies demonstrate that the modified electrode has outstanding stability. In addition, a glucose biosensor is further developed through the simple one‐step electrodeposition method. The observed wide concentration range, high stability and high reproducibility of the PB‐SWNTs/chitosan nanocomposites film make them promising for the reliable and durable detection of H2O2 and glucose.

The adsorption of methanol at the defective site of single-walled carbon nanotube

The adsorption of methanol on the perfect and defective single-walled carbon nanotubes (SWCNTs) has been investigated using effective cluster models in conjunction with density functional theory. It has been found that methanol is adsorbed very weakly on the sidewall of perfect SWCNT, which is in agreement with experiment observation. In contrast, it is quite interesting to find that methanol is not only strongly chemisorbed at the zigzag edge site of defective SWCNT, but also the O–H bond of methanol is completely dissociated. This suggests that the zigzag edge of SWCNT can be the active site for adsorption and activation of methanol. However, the adsorption of methanol at the armchair edge of SWCNT is rather weak, hence suggesting the crucial effect of local edge carbon atoms arrangement on the adsorption behavior of methanol on carbon nanotubes.

Multidomain Peptides as Single-Walled Carbon Nanotube Surfactants in Cell Culture

We present a series of short, multidomain peptides as biocompatible solubilizing agents of single-walled carbon nanotubes (SWCNTs). These peptides are organized into an ABA block motif, where the A block is composed of charged amino acids, such as glutamic acid, and the B block is composed of alternating hydrophilic and hydrophobic residues. The hydrophobic amino acid residues interact with SWCNT sidewalls, while the hydrophilic residues interact primarily with water in an aqueous solution. When many peptides assemble along the length of the nanotube, it becomes effectively encapsulated within a peptide nanofiber. This noncovalent interaction between the peptide and the nanotube solubilizes SWCNTs while keeping the electronic structure of the nanotube intact, thereby preserving the optical and electrical properties that make SWCNTs promising for use in biological applications. To assess the toxicity of these peptide coatings, they were added to cultures of NIH 3T3 mouse fibroblasts and the effect on cell viability was measured. Toxicity was found to be far lower than for ionic surfactants typically used for SWCNT suspension and similar to Pluronics. The near-IR fluorescence intensity of SWCNTs in peptide suspensions was comparable to that in Pluronics. Five surfactants were tested for their effect on the proliferation of NIH 3T3 cells with and without SWCNTs. Although some differences were observed among surfactants, in no case did the presence of SWCNTs make a statistically significant difference. Based on their ability to solubilize SWCNTs, the fluorescence of the suspended tubes, their minimal impact on cell viability, and their potential for easy chemical modification, multidomain peptides have been found to have excellent potential as a biocompatible surfactant for suspension of SWCNTs.

An XANES study on the modification of single-walled carbon nanotubes by nitric acid

X-ray absorption near-edge structure (XANES) spectroscopy has been applied to identify the modification process of single-walled carbon nanotubes (SWCNTs) treated by nitric acid. The carboxyl groups created by the nitric acid treatment have been found to be formed on both the carbonaceous fragments and the side walls of SWCNTs. The carbonaceous fragments could be removed by a following washing treatment with sodium hydroxide. XANES spectra indicate that carbonaceous fragments are the result of the synthesis process and/or of the nitric acid treatment. Tube walls of SWCNTs are weakly oxidized by the nitric acid treatment although, after removing carbonaceous fragments, a direct oxidation process of SWCNTs is observed. Experimental data address the removal of carbonaceous fragments on SWCNTs as an efficient method for side-wall modification of a SWCNT.

Antioxidant Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) and ultrashort SWCNTs (US-SWCNTs) were functionalized with derivatives of the phenolic antioxidant, butylated hydroxytoluene (BHT). By using the oxygen radical absorbance capacity (ORAC) assay, the oxygen radical scavenging ability of the SWCNT antioxidants is nearly 40 times greater than that of the radioprotective dendritic fullerene, DF-1. In addition, ORAC results revealed two divergent trends in the antioxidant potential of SWCNTs, depending on the type of functionalization employed. When existing pendant sites on US-SWCNTs were further functionalized by either covalent or noncovalent interactions of the existing pendant sites with a BHT derivative, the amount of BHT-derivative loading proportionately increased the overall antioxidant activity. If, however, functionalization occurred via covalent functionalization of a BHT-derivative directly to the SWCNT sidewall, the amount of BHT-derivative loading was inversely proportional to the overall antioxidant activity. Therefore, increasing the number of pendant sites on the SWCNT sidewalls by covalent functionalization led to a concomitant reduction in ORAC activity, suggesting that the nanotube itself is a better radical scavenger than the BHT-derivatized SWCNT. Cytotoxicity assays showed that both nonfunctionalized and BHT-derivatized SWCNTs have little or no deleterious effect on cell viability. Therefore, SWCNTs may be attractive agents for antioxidant materials and medical therapeutics research.

Wrapping of Self-Organized Fluorescent Nanofibers with a Silica Wall

Amphiphilic compounds 1 and 2, composed of an aromatic pyrene core and an amphiphilic three-branched unit, were synthesized and investigated for their self-organizing process in solution by UV-vis, fluorescence spectra, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and fluorescence microscopes. While 2 formed spherical objects in a mixed solvent of methanol and water, 1 assembled into long, flexible, and fluorescent fibers through pi-pi stacking of pyrene cores and hydrogen bonding among amide groups. The fluorescence spectra and morphologies strongly depended on the concentration and solution temperature. The fibrous assemblies were wrapped with an ultrathin silica wall by the acidic sol-gel polymerization of tetraethoxysilane (TEOS). A transmission electron microscopy (TEM) image after the sol-gel polymerization showed discrete fibrous structures with a uniform diameter of 3.5 nm and several micrometers in length. The thickness of the silica wall and the inner diameter of one fiber were estimated to be 0.5 nm and 2.5 nm, respectively. The observed inner diameter of the fiber was almost compatible with the width of the cylindrical assembly made of 1. The pyrene unit in 1 can interact with the sidewall of single-walled carbon nanotubes (SWNTs) through pi-pi interaction, and the adsorption of 1 onto the surface of SWNTs could disrupt the formation of bundles. The accumulation of oligomeric silica species at the hydrophilic surface created organic-inorganic nanoscopic fibers containing electronic conductive SWNTs.

Anisotropic Electronic Conductivity in Layer‐By‐Layer Composite Film Composed of Water‐Soluble Conjugated Polymers and SWNTs

AbstractThis paper reports the anisotropic electrical properties of a layer‐by‐layer (LBL) film composed of water‐soluble conjugated polymers and single‐walled carbon nanotubes (SWNTs). The water‐soluble poly (p‐phenylene ethynylene)s (PPEs) are capable of a strong π‐π interaction with the sidewall of SWNTs and results in a very stable PPE‐SO3/SWNTs composite in aqueous solution. Aligned LBL films were prepared by self‐assembly using the anionic PPE/SWNTs and cationic PPE on various substrates. The polarized Raman spectra exhibited the cos2α polarization dependence of the G‐band intensity between the polarization direction and the SWNTs alignment direction. The electric conductivity within the LBL films can be controlled by the deposition direction in the LBL formation.magnified image

Evidence of sidewall covalent functionalization of single-walled carbon nanotubes and its advantages for composite processing

Single-walled carbon nanotubes (SWCNTs) were functionalized in a three-step procedure. The first step is a radical reaction creating a covalent bond between the carbon nanotube surface and grafted p-methoxyphenyl functional groups. In a second step, a deprotection of the methoxy functions generates free alcohol groups and in the final step an esterification is done in order to install a double bond for further polymerization. Evidence that functionalization has actually occurred on the SWCNT sidewalls is furnished through investigations involving several complementary techniques (visual dispersion tests, transmission electron microscopy, thermal gravimetric analysis and adsorption volumetry). We show that surface properties of SWCNTs are changed throughout the chemical treatments and that the obtained level of functionalization is low. Incorporation of functionalized SWCNTs in a polymer (poly(methyl methacrylate)) matrix was done through an in situ polymerization process. Observations of the obtained composites using scanning and transmission electron microscopy illustrate that interactions between the SWCNT surface and the polymer matrix are improved.

STUDY ON CLUSTER FORMATION OF POLY 2-HYDROXYETHYL METHACRYLATE FUNCTIONALIZED SINGLE-WALLED CARBON NANOTUBES

Cluster-like network structures of single-walled carbon nanotubes (SWNTs) were synthesized by chemical grafting poly 2-hydroxyethyl methacrylate (polyHEMA) to the sidewalls of SWNTs. Acid chloride-functionalized tubes were coupled with commercially available HEMA monomer, which was in turn polymerized using a radical initiator. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to identify the surface changes on the nanocomposites. Microscopic observations of the nanotube complexes by field emission scanning electron microscopy (FE-SEM) show that the tubes were dispersed and formed cluster-like network, branched structures with less bundling, thus, strongly suggesting a firm coating of the polymer on nanotube walls. The coating was further confirmed by transmission electron microscopy. The thermal properties of the nanotube complex as studied by thermal gravimetric analysis (TGA) revealed that coating enhanced stability of the complex, when compared to that of bulk polyHEMA and pristine SWNTs. The nanotube complexes showed excellent suspension stability when dispersed in organic solvent.

Optical detection of DNA hybridization using absorption spectra of single-walled carbon nanotubes

Abstract Single-walled carbon nanotubes (SWCNTs) exhibit sharp absorption peak distributions in the UV–vis–nIR range when they are individually dispersed in aqueous solution medium. In this paper, we developed SWCNT-based molecular probes by conjugating single-stranded DNA (ssDNA) with SWCNT. The DNA hybridization event was investigated using the absorption spectra of the ssDNA–SWCNT probes. The results showed that DNA hybridization on the sidewall of SWCNT resulted in systematic red shifts of the absorption spectra of semiconducting nanotubes. However, metallic species did not show any shift in the absorption spectra. The work demonstrated that ssDNA–SWCNTs probes might be used to detect specific kinds of DNA oligonucleotides as optical nano-biosensors.