Preferential growth of single-walled carbon nanotubes on silica spheres by chemical vapor deposition

The preferential growth of single-walled carbon nanotubes (SWNTs) on silica spheres with various diameters was realized for the first time by chemical vapor deposition (CVD) of methane. SWNTs tend to wrap the silica spheres to form a new superstructure of uniform SWNT nanoclaws when the diameters of the silica spheres are larger than 400 nm. The SWNTs obtained on silica spheres have highly graphitic tubular walls as characterized by Raman spectroscopy and HRTEM. This is a new method to obtain tunable uniform elastic deformation of SWNTs, which may act as the model for the study about the effect of delocalized bending on the properties of SWNTs. In addition, the combination of SWNTs with monodispersed silica spheres could conveniently integrate SWNTs into photonic crystals.     

A route for bulk separation of semiconducting from metallic single-wall carbon nanotubes

Substantial separation of single-wall carbon nanotubes (SWNTs) according to type (metallic versus semiconducting) has been achieved for HiPco and laser-ablated SWNTs. We presently argue that stable dispersions of SWNTs with octadecylamine (ODA) in tetrahydrofuran (THF) originate from the physisorption and organization of ODA along the SWNT sidewalls in addition to the originally proposed zwitterion model. Furthermore, the reported affinity of amine groups for semiconducting SWNTs, as opposed to their metallic counterparts, contributes additional stability to the physisorbed ODA. This provides a venue for the selective precipitation of metallic SWNTs upon increasing dispersion concentration, as indicated by Raman investigations.     

Studies of bromine modified single-walled carbon nanotubes using photoelectron spectroscopy and density-functional theory

Many applications based on single-walled carbon nanotubes (SWNTs) require chemical modification of carbon nanotube to optimize the functionalities of the device. In this contribution we discuss the properties of SWNTs immersed in a hydrobromic acid (HBr) solution. Changes of atomic and electronic structures of bromine modified SWNTs were investigated using photoelectron spectroscopy (PES). Spectra of SWNTs before and after immersion in the HBr solution exhibit different features. To understand the mechanism of interaction between SWNTs and bromine, we performed density-functional theory calculations to reveal the structural changes, adsorption energy and chemical bonding information of SWNTs interacting with bromine. In addition, based on the Gelius model, from the molecular orbitals (MOs), we calculated ultraviolet photoelectron spectra (UPS) of SWNTs with and without functionalizing and compared them with the experiment. The present study is a first step in the understanding of the functionalization mechanism of carbon nanotubes.     

Optically sensing additional sonication effects on dispersed HiPco nanotubes in aerated water

Ultrasonication is a necessary process to make single-walled carbon nanotubes (SWNTs) soluble in aqueous solution with surfactants such as sodium dodecyl sulfate (SDS). However, an understanding of the sonication effects on the electronic and optical properties of SWNTs in aqueous solution is still lacking. Here, we have observed that sonication-induced pH changes suppress the optical transitions of the first interband transition pair (S11) in the density of states of semiconducting SWNTs while other possible intermediates induced by sonication contribute less significantly to the observed spectral changes without the involvement of sonication-induced pH decrease. The suppressed S11 peaks can be restored by adding basic solution, suggesting that the lattice structure of SWNTs is undisrupted by the sonication used here. The absorbance of S11 peaks shows a nearly linear relationship with sonication-induced pH changes in the narrow pH range of 5.2 and 6.1. The results indicate that SDS-encased SWNTs may be used as an indicator for sonolysis-related applications.     

Mechanism of horizontally aligned growth of single-wall carbon nanotubes on R-plane sapphire

As a promising one-dimensional material for building nanodevices, single-wall carbon nanotubes (SWNTs) should be organized into a rational architecture on the substrate surface. In this study, horizontally aligned SWNTs with two alignment modes were synthesized on the same R-plane sapphire wafer by chemical vapor deposition with cationized ferritins as catalysts. In the middle part of the wafer, SWNTs were aligned on the R-plane sapphire in the direction [1101]. At the edge of the wafer, SWNTs were aligned in the tangential direction to the wafer edge. The comparison of these two groups of SWNTs suggests the competition between the two alignment modes and indicates that atomic steps in high density have superior influence on the SWNTs' alignment to the crystal structure on the surface of the sapphire substrate. A "raised-head" growth mechanism model is proposed to explain why catalysts can stay active during the horizontally aligned growth of relatively long SWNTs with the strong interaction between SWNTs and the sapphire substrate.     

Molecular dynamics study of the catalyst particle size dependence on carbon nanotube growth

The molecular dynamics method, based on an empirical potential energy surface, was used to study the effect of catalyst particle size on the growth mechanism and structure of single-walled carbon nanotubes (SWNTs). The temperature for nanotube nucleation (800-1100 K), which occurs on the surface of the cluster, is similar to that used in catalyst chemical vapor deposition experiments, and the growth mechanism, which is described within the vapor-liquid-solid model, is the same for all cluster sizes studied here (iron clusters containing between 10 and 200 atoms were simulated). Large catalyst particles, which contain at least 20 iron atoms, nucleate SWNTs that have a far better tubular structure than SWNTs nucleated from smaller clusters. In addition, the SWNTs that grow from the larger clusters have diameters that are similar to the cluster diameter, whereas the smaller clusters, which have diameters less than 0.5 nm, nucleate nanotubes that are approximately 0.6-0.7 nm in diameter. This is in agreement with the experimental observations that SWNT diameters are similar to the catalyst particle diameter, and that the narrowest free-standing SWNT is 0.6-0.7 nm.     

FeCo/MgO催化生长体相单壁碳纳米管的直径调控

单壁碳纳米管的直径可控生长是碳纳米管生长与应用领域的重要问题。直径在0.9–1.2 nm范围内的碳纳米管非常适合应用于近红外荧光生物成像领域和量子器件单光子光源之中。本文使用FeCo/MgO催化剂生长出了直径在这一范围内的体相单壁碳纳米管,并研究了催化剂制备和CVD生长条件对碳纳米管直径的影响。催化剂前驱体的制备是获得小尺寸催化剂颗粒的关键步骤。在浸渍过程中,使用难水解的金属硫酸盐作为前驱体、降低浸渍pH以及加入络合剂分子都会抑制溶液干燥过程中金属盐的水解,从而控制催化剂的尺寸,使其适合于生长出直径可控的单壁碳纳米管。在CVD生长过程中,使用乙醇作为碳源、使用较低的碳氢比例也有利于小直径碳纳米管的生长。     

Cobalt-filled apoferritin for suspended single-walled carbon nanotube growth with narrow diameter distribution

Cobalt-filled apoferritin (Co-ferritin) was, for the first time, used as a wet catalyst for the synthesis of single-walled carbon nanotubes (SWNTs) with narrow diameter distribution. Co-ferritins were spin-coated and converted to cobalt nanoparticles by calcination. Using chemical vapor deposition, suspended networks of SWNTs were formed on pillar-structured substrates. The suspended SWNTs show narrow tube diameter distribution with a relatively good graphite structure. By virtue of the low diffusion coefficient of cobalt, Co-ferritin might be more useful for narrow diameter SWNTs growth than ferritins, which encase iron particles.     

Atomic Force Microscopic and Electrochemical Investigations of an Electrostatically Fabricated Single‐Wall Carbon Nanotubes Modified Electrode

Single‐wall carbon nanotubes (SWNTs) sub‐monolayer film has been prepared by simply electrostatically adsorbing nanotubes onto a 2‐aminoethanethiol self‐assembled monolayer (SAM) on a gold bead electrode. Tapping‐mode atomic force microscopy (TM‐AFM) is used to characterize the SWNT film, which exhibits that the orientation of SWNTs on the SAM is horizontal and the surface coverage is quite low. The SWNTs modified electrode shows nearly ideal electrochemical response to Fe(CN) /Fe(CN) redox probe. The electrode with such a low SWNTs coverage, however, shows good electrocatalytic behavior to cytochrome c.     

Simultaneous determination of nitrophenol isomers at the single-wall carbon nanotube compound conducting polymer film modified electrode

One of the challenging areas of electrochemistry and electroanalytical chemistry is the simultaneous determination of isomers at the same electrode. Con- ventional electrode only possesses a single function of electron transfer; therefore, it is difficult…     

Fluorescence derivatization of single-walled carbon nanotubes for analysis by means of conventional CE-LIF

Single-walled carbon nanotubes (SWNTs) are now widely used in many fields, and while many analytical methods for SWNTs have been reported, there are few practical analytical methods that combine the necessary levels of selectivity and sensitivity. We have developed a highly sensitive separation method for fluorescence-derivatized SWNTs by means of conventional CE with laser-induced fluorescence. First, SWNTs were dispersed using a triphenylene derivative into the water, and the excess dispersant was removed by nitric acid treatment. The dispersed SWNTs were then derivatized with a fluorescence reagent, 4-aminofluorescein. Finally, the derivatized SWNTs were analyzed using a conventional apparatus CE-LIF detection. The SWNTs migrated within 20 min. The detection sensitivity of SWNTs was improved by about 170 times with LIF detection as compared with UV detection. We anticipate that the derivatized SWNTs can also be detected with high sensitivity using LC.     

单壁碳纳米管与卤代烷的亲电加成反应

主要考察了以路易斯酸为催化剂,几种卤代烷烃为反应试剂的单壁碳纳米管侧壁的亲电加成反应,并通过傅立叶红外光谱、热失重分析和拉曼光谱验证了实验所得产物。此反应的目的是在单壁碳纳米管的侧壁连上烷基基团以提高其溶解性和分散性,并可使其更好地与聚烯烃相结合从而提高复合材料的性能,因而具有较高的研究和应用价值。     

Dispersant Effects on Single-Walled Carbon Nanotube Antibacterial Activity

There is significant interest in understanding whether nanomaterials with outstanding mechanical or electrical properties also possess antibacterial properties. However, assessment of antibacterial activity is a complex problem at the interface of chemistry and microbiology. Results can be affected by many factors including nanomaterial size, surface chemistry, concentration, and the dispersion media. The difficulty of dispersing nanomaterials such as single-walled carbon nanotubes (SWNTs) has resulted in many studies being conducted in the presence of dispersion aides which may themselves contribute to bacterial stress. The recent discovery that a standard microbial growth media, tryptic soy broth (TSB), is an effective SWNT dispersant provides a new opportunity to investigate the potential antibacterial activity of SWNTs using dispersants that range from antibacterial to growth-supporting. The five dispersants chosen for this work were Sodium dodecyl sulfate (SDS), pluronic, lysozyme, DNA, and tryptic soy broth. Staphylococcus aureus and Salmonella enterica were used as the model Gram-positive and Gram-negative bacteria. Activity was measured in terms of colony forming unit (CFU) and optical density measurements. None of the systems exhibited activity against Salmonella. SDS was fatal to Staph. aureus regardless of the presence of SWNTs. The activity of pluronic and lysozyme against Staph. aureus was enhanced by the presence of SWNTs. In contrast, the DNA and TSB dispersions did not have any activity regardless of the presence of SWNTs. These results highlight that the purported antibacterial activity of SWNTs may only be effective against bacteria that are sensitized by the dispersant and suggests the need for additional research on the mechanisms by which SWNT-dispersant interactions can result in antibacterial activity.     

Doping polyaniline with pristine carbon nanotubes into electroactive nanocomposite in neutral and alkaline media

This study describes a facile but effective route to synthesis of electroactive polyaniline (PANI) in the neutral and alkaline media simply with pristine single-walled carbon nanotubes (SWNTs) as the dopant. Cyclic voltammetry (CV) studies reveal that the SWNT/PANI nanocomposite processes a good electrochemical activity in the neutral and alkaline media. Control experiments with PANI mixed with heat-treated SWNTs imply that the electrochemical properties of the SWNT/PANI nanocomposite in the neutral and alkaline media do not result from the presence of carboxylic groups at SWNTs themselves, and in turn show that the pristine SWNTs can be potentially used as a new and effective dopant to preserve the electrochemical property of PANI in the neutral and alkaline media. This property of the SWNT/PANI nanocomposite is reasonably envisaged to be promising for electrochemical investigations and electroanalytical applications, especially for the development of electrochemical sensors, biosensors and biofuel cells.     

Stable luminescence from individual carbon nanotubes in acidic, basic, and biological environments

Aqueous surfactant suspensions of single walled carbon nanotubes (SWNTs) are very sensitive to environmental conditions. For example, the photoluminescence of semiconducting SWNTs varies significantly with concentration, pH, or salinity. In most cases, these factors restrict the range of applicability of SWNT suspensions. Here, we report a simple strategy to obtain stable and highly luminescent individualized SWNTs at pH values ranging from 1 to 11, as well as in highly saline buffers. This strategy relies on combining SWNTs previously suspended in sodium dodecylbenzene sulfonate (SDBS) with biocompatible poly(vinyl pyrrolidone) (PVP), which can be polymerized in situ to entrap the SWNT-SDBS micelles. We present a model that accounts for the photoluminescence stability of these suspensions based on PVP morphological changes at different pH values. Moreover, we demonstrate the effectiveness of these highly stable suspensions by imaging individual luminescent SWNTs on the surface of live human embryonic kidney cells (HEK cells).     

Effect of electron-donating and electron-withdrawing groups on peptide/single-walled carbon nanotube interactions

Nano-1, a designed peptide, has been demonstrated to efficiently disperse individual single-walled carbon nanotubes (SWNTs) by folding into an amphiphilic alpha-helix wherein the phenylalanine (Phe) residues on the hydrophobic face of the helix interact via pi-stacking with the aromatic surface of the SWNT. In this study, the ability of electron-donating (hydroxyl) and electron-withdrawing (nitro) groups on the phenyl ring of Phe to affect the interactions between the peptide and SWNTs is examined by substituting the Phe residues in the nano-1 sequence with tyrosine and p-nitro-phenylalanine, respectively. Atomic force microscopy measurements and optical absorption spectroscopy revealed that the ability to disperse individual SWNTs increases with increasing electron density of the aromatic residue on the hydrophobic face of the amphiphilic helical peptides. Scanning tunneling spectroscopy (STS) and Raman analyses were used to examine the effect of noncovalent protein functionalization on the electronic properties of SWNTs. Small shifts in the Raman G band peak for the peptide/SWNT composites, as well as weak features that appear near the Fermi energy (Ef) in the STS dI/dV spectra of the peptide-coated SWNTs, are suggestive of a weak charge-transfer interaction between the peptides and the SWNTs.     

Single-walled carbon nanotubes template the one-dimensional ordering of a polythiophene derivative

We have used a mechanochemical high-speed vibration milling (HSVM) technique to solubilize single-walled carbon nanotubes (SWNTs) in organic solvents through the formation of complexes between the SWNTs and a polythiophene (PT) derivative. This HSVM approach is superior to the conventional sonication method used to solubilize SWNTs in organic solvents. Moreover, we found that in these supramolecular complexes the PT chains were ordered one-dimensionally on the SWNT surfaces in organic solvents. [structure: see text].     

Selective dispersion of single-walled carbon nanotubes with specific chiral indices by poly(N-decyl-2,7-carbazole)

Physico-chemical methods to sort single-walled carbon nanotubes (SWNTs) by chiral index are presently lacking but are required for in-depth experimental analysis and also for potential future applications of specific species. Here we report the unexpected selectivity of poly(N-decyl-2,7-carbazole) to almost exclusively disperse semiconducting SWNTs with differences of their chiral indices (n - m) ≥ 2 in toluene. The observed selectivity complements perfectly the dispersing features of the fluorene analogue poly(9,9-dialkyl-2,7-fluorene), which disperses semiconducting SWNTs with (n - m) ≤ 2 in toluene. The dispersed samples are further purified by density gradient centrifugation and analyzed by photoluminescence excitation spectroscopy. All-atom molecular modeling with decamer model compounds of the polymers and (10,2) and (7,6) SWNTs suggests differences in the π-π stacking interaction as origin of the selectivity. We observe energetically favored complexes between the (10,2) SWNT and the carbazole decamer and between the (7,6) SWNT and the fluorene decamer, respectively. These findings demonstrate that subtle structural changes of polymers lead to selective solvation of different families of carbon nanotubes. Furthermore, chemical screening of closely related polymers may pave the way toward simple, low-cost, and index-specific isolation of SWNTs.     

Electrochemical study of single wall carbon nanotubes/graphene/ferritin composite for biofuel cell applications

A single wall carbon nanotubes (SWNTs)/graphene/ferritin/GOx layer on a glassy carbon electrode (GCE) acting as a biofuel cell anode was fabricated using a SWNTs/graphene/ferritin composite as an electron transfer mediator from the enzyme to the electrode. In the presence of glucose, the SWNTs/graphene/ferritin/GOx composite showed a higher current response than SWNTs/graphene/GOx composite and the electrocatalytic oxidation of glucose on the anode increased linearly with increasing concentration of glucose. The highly distributed SWNTs/graphene/ferritin composite acts as a platform for enzyme immobilization resulted in an enhanced electrocatalytic activity towards glucose. The SWNTs/graphene/ferritin composite showed an enhanced electron transfer from enzyme to the electrode; therefore, SWNTs/graphene/ferritin/GOx composite can be used as an anode in biofuel cells.