Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.     

Single-walled carbon nanotubes based chemicapacitive sensors

Carboxylated single-walled carbon nanotubes (SWNTs) based chemicapacitive gas sensors were fabricated by AC dielectrophoretically aligning SWNTs across microfabricated gold electrodes with controlled density/device resistance. Two different sensing configurations (i.e., horizontal/in-plane and vertical/out-of-plane) were utilized to compare their sensing performance. Upon exposure to water vapor at room temperature, the response (R = [(C--C0)/C0] x 100%) increased with an increase in water vapor concentration similar to that of resistance response. In horizontal configuration, the response was increased with an increase in device resistance which might be attributed to preferentially alignment of semiconducting SWNTs during initial phase of alignment. However, the response was independent of device resistance in vertical/out-of-plane configuration which indicated that the sensing mechanism is based on the change of dielectric constant of gate and atmosphere.     

Structural dependence of excitonic optical transitions and band-gap energies in carbon nanotubes

The optical transitions of semiconducting carbon nanotubes have been ascribed to excitons. Here we use two-photon excitation spectroscopy to measure exciton binding energies, as well as band-gap energies, in a range of individual species of semiconducting SWNTs. Exciton binding energies are large and vary inversely with nanotube diameter, as predicted by theory. Band-gap energies are significantly blue-shifted from values predicted by tight-binding calculations.     

Excited excitonic states in single-walled carbon nanotubes

Polarized photoluminescence excitation spectroscopy on individual SWNTs reveals not only the longitudinal and transverse E 11, E 22, and E 12 ground-state excitons but also excited excitonic states including the continuum. When heated, SWNTs are known to undergo a bandgap shift transition (BST), which effectively changes the nanotube dielectric environment. Here, we show that the entire spectrum of excitonic resonances blue shifts under this transition, with excited states showing larger shifts, approaching 100 meV for a 1 nm diameter nanotube. The excitonic binding energy, Coulomb self-energy correction, and dielectric shift under the BST are estimated. Analysis of this blue shift reveals the dominant effect of dielectric screening on SWNT excitonic states.     

Single-walled carbon nanotubes modified by ionic liquid as antiwear additives of thermoplastics

Pristine single-walled carbon nanotubes (CNTs) were dispersed in the room-temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium tetrafluoroborate ([OMIM]BF₄) by grinding and ultrasounds. Excess IL was removed to obtain single-walled carbon nanotubes modified by [OMIM]BF₄ (mCNTs). mCNTs were added in a 1 wt.% to polystyrene (PS), polymethylmethacrylate (PMMA) and polycarbonate (PC) to obtain PS + mCNT, PMMA + mCNT and PC + mCNT. The dry tribological performance of the new nanocomposites was studied against AISI 316L stainless steel pins and compared with that of the neat polymers and with the nanocomposites containing pristine carbon nanotubes without IL (PS + CNT; PMMA + CNT and PC + CNT). The maximum wear rate and friction coefficient reduction is obtained for PS + mCNT. Results are discussed upon the basis of optical, SEM and TEM microscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

Single-walled carbon nanotubes nanocomposite microacoustic organic vapor sensors

We have developed highly sensitive microacoustic vapor sensors based on surface acoustic waves (SAWs) configured as oscillators using a two-port resonator 315, 433 and 915 MHz device. A nanocomposite film of single-walled carbon nanotubes (SWCNTs) embedded in a cadmium arachidate (CdA) amphiphilic organic matrix was prepared by Langmuir–Blodgett technique with a different SWCNTs weight filler content onto SAW transducers as nanosensing interface for vapor detection, at room temperature. The structural properties and surface morphology of the nanocomposite have been examined by X-ray diffraction, transmission and scanning electron microscopy, respectively. The sensing properties of SWCNTs nanocomposite LB films consisting of tangled nanotubules have been also investigated by using Quartz Crystal Microbalance 10 MHz AT-cut quartz resonators. The measured acoustic sensing characteristics indicate that the room-temperature SAW sensitivity to polar and nonpolar tested organic molecules (ethanol, ethylacetate, toluene) of the SWCNTs-in-CdA nanocomposite increases with the filler content of SWCNTs incorporated in the nanocomposite; also the SWCNTs-in-CdA nanocomposite vapor sensitivity results significantly enhanced with respect to traditional organic molecular cavities materials with a linearity in the frequency change response for a given nanocomposite weight composition and a very low sub-ppm limit of detection.     

Einstein relation in carbon nanotubes and quantum wires of nonlinear optical and optoelectronic materials

We study the Einstein relation for the diffusivity-to-mobility ratio (DMR) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical and optoelectronic materials. The respective DMR in QWs exhibits increasing quantum steps with increasing electron statistics. In CNTs, the DMR exhibits periodic oscillations with increasing carrier degeneracy and the nature is radically different as compared with the corresponding DMR of QWs since they emphasize the different signatures of the two entirely different one dimensional nanostructured systems. In addition, we have suggested an experimental method of determining the DMR for CNTs and QWs having arbitrary dispersion laws.     

Transient grating measurements of excitonic dynamics in single-walled carbon nanotubes: The dark excitonic bottleneck

Transient grating measurements affirm the excitonic model for single-walled carbon nanotubes (SWNT) by identifying the dark exciton (D) as the population relaxation bottleneck in semiconducting-SWNT (S-SWNT). The data allow the reconstruction of the kinetics of excitonic cascade and cooling, from band continuum to vibrational cooling in the ground electronic state. In S-SWNT, the intraband relaxation occurs in 40 fs, localization into the 2g exciton occurs in 50 fs, followed by the excitonic cascade: 2g --> 1u --> D --> 1g with time constants of 175 fs, 3 ps, 300 ps, respectively. Fluorescence from the 1u state is quenched by efficient population transfer to 1D dark exciton. In metallic tubes, cooling is completed on the time scale of 1 ps.     

Field-enhanced photocurrent spectroscopy of excitonic states in single-wall carbon nanotubes

Excitonic and free-carrier transitions in single-wall carbon nanotubes are distinguished using field-enhanced photocurrent spectroscopy. Electric field dissociation allows for the detection of bound-exciton states that otherwise would not contribute to the photocurrent. Excitonic states associated with both the ground-state semiconductor and the ground-state metallic nanotube transitions are resolved. The observation of a metallic excitonic state corroborates recent predictions of a symmetry gap existing in metallic nanotubes.     

Single-walled carbon nanotubes induces oxidative stress in rat lung epithelial cells

Single-walled carbon nanotubes (SWCNT) show unique properties find applications in micro devices; electronics to biological systems specially drug delivery and gene therapy. However the manufacture and extensive use of nanotubes raises concern about its safe use and human health. Very few studies have been carried out on toxicity of carbon nanotubes in experimental animals and humans, thus resulted in limiting their use. The extensive toxicological studies using in vitro and in vivo models are necessary and are required to establish safe manufacturing guidelines and also the use of SWCNT. These studies also help the chemists to prepare derivative of SWCNT with less or no toxicity. The present study was undertaken to determine the toxicity exhibited by SWCNT in rat lung epithelial cells as a model system. Lung epithelial cells (LE cells) were cultured with or without SWCNT and reactive oxygen species (ROS) produced were measured by change in fluorescence using dichloro fluorescein (DCF). The results show increased ROS on exposure to SWCNT in a dose and time dependent manner. The decrease in glutathione content suggested the depletion and loss of protective mechanism against ROS in SWCNT treated cells. Use of rotenone, the inhibitor of mitochondrial function have no effect on ROS levels suggested that mitochondria is not involved in SWCNT induced ROS production. Studies carried out on the effect of SWCNT on superoxide dismutase (SOD-1 and SOD-2) levels in LE cells, indicates that these enzyme levels decreased by 24 hours. The increased ROS induced by SWCNT on LE cells decreased by treating the cells with 1 mM of glutathione, N-Acetyl Cysteine, and Vitamin C. These results further prove that SWCNT induces oxidative stress in LE cells and shows loss of antioxidants.     

Single-walled carbon nanotubes modified carbon ionic liquid electrode for sensitive electrochemical detection of rutin

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10^− 7 to 8.0 × 10^− 4 mol/L with the detection limit as 7.0 × 10^− 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.     

Single-walled carbon nanotubes under the influence of dynamic coordination and supramolecular chemistry

A dynamic coordinative-directed solubilization of single-walled carbon nanotubes (SWNTs) in aqueous solutions has been achieved through a combination of a Zn(II) metalloporphyrin complex and a cis-protected Pd(II) complex, which are believed to form charged acyclic and/or cyclic adducts on or around the side walls of SWNTs. The solubilization of SWNTs in aqueous solution only occurs when these acyclic and/or cyclic complexes are allowed to enter simultaneously into a self-assembly process with SWNTs under mild conditions. The aqueous solubility properties that these dynamic complexes confer upon SWNTs are believed to involve noncovalent bonding interactions between the two entities. They have been probed in solution using ultraviolet and visible absorption spectroscopy and in thin films using high-resolution transmission electron microscopy. The supramolecular electronic effects that the individual components of their acyclic and/or cyclic complexes impart upon a single semiconducting SWNT have been probed within a nanotube field-effect transistor device.     

Enhanced electrical conduction in aluminum wires coated with carbon nanotubes

Electrophoretic deposition was used to create SWCNT nanosized coatings on commercial aluminum wires. Electrical measurements showed an increase in the conductivity of about 160%. Due to the semiconductor nature of a fraction of the deposited SWCNTs, the high conductivity of the coated wires did not substantially decrease with increasing temperature (up to 600 K). Instead, increasing temperature and current were observed to affect the arrangement of the CNTs on the substrate, such that a web-like structure of SWCNTs was induced and resulted in further resistivity decrease.     

Single-walled MoTe(2) nanotubes

The structural, electronic, and mechanical properties of single-walled MoTe(2) nanotubes are investigated using density functional theory. All large-diameter MoTe(2) nanotubes are found to be narrow-gap semiconductors, whereas small-diameter nanotubes are found to be less stable compared to large-diameter nanotubes. Notably, the armchair MoTe(2) nanotubes exhibit an indirect band gap, whereas the zigzag nanotubes exhibit a direct band gap. The band gap decreases with decreasing diameter of the tube or if the tube is under compression or elongation in the axial direction. Young's modulus of MoTe(2) nanotubes is calculated and is found to be dependent on the diameter and chirality of the tubes. The armchair nanotubes are stiffer than the zigzag nanotubes with the same diameter. Compared to the homologous MoTe(2) nanotubes, the MoTe(2) nanotubes are softer due to less strain-energy cost in forming the nanotube structures.     

Single-walled carbon nanotube electronics

Single-walled carbon nanotubes (SWNTs) have emerged as a very promising new class of electronic materials. The fabrication and electronic properties of devices based on individual SWNTs are reviewed. Both metallic and semiconducting SWNTs are found to possess electrical characteristics that compare favorably to the best electronic materials available. Manufacturability issues, however, remain a major challenge     

Single-walled carbon nanotube diameter

Two different single-walled carbon nanotube (SWNT) growth modes (cap growth mode and circumference growth mode) are shown to exist. General SWNT diameter windows are derivable from catalyst particle size considerations. In addition, an almost complete picture of nanotube diameter dependencies for the cap growth mode is drawn from experiment. The nanotube diameter always scales linear with temperature, but the degree of dependence varies with the catalyst element. The nanotube diameter scales logarithmically with the gas pressure and catalyst composition. Very few or exactly one atom of a catalyst additive is sufficient to induce SWNT diameter changes. The experimental data allow the conclusion that the observed nanotube diameter is based on materials properties of sp2-bonded carbon/graphene sheets, on individual properties of the catalyst elements, and on additional kinetic components from temperature and pressure changes. Indications are found for a specific and maybe decisive role of adsorbate atoms at the surface of a catalyst particle on the nanotube diameter and therefore on the process of nanotube nucleation and growth.     

Single-walled carbon nanotubes in the intact organism: near-IR imaging and biocompatibility studies in Drosophila

The ability of near-infrared fluorescence imaging to detect single-walled carbon nanotubes (SWNTs) in organisms and biological tissues has been explored using Drosophila melanogaster (fruit flies). Drosophila larvae were raised on food containing approximately 10 ppm of disaggregated SWNTs. Their viability and growth were not reduced by nanotube ingestion. Near-IR nanotube fluorescence was imaged from intact living larvae, and individual nanotubes in dissected tissue specimens were imaged, structurally identified, and counted to estimate a biodistribution.     

Single-walled carbon nanotube network ultramicroelectrodes

Ultramicroelectrodes (UMEs) fabricated from networks of chemical vapor deposited single-walled carbon nanotubes (SWNTs) on insulating silicon oxide surfaces are shown to offer superior qualities over solid UMEs of the same size and dimensions. Disk shaped UMEs, comprising two-dimensional "metallic" networks of SWNTs, have been fabricated lithographically, with a surface coverage of <1% of the underlying insulating surface. The electrodes are long lasting and give highly reproducible responses (either for repeat runs with the same electrode or when comparing several electrodes with the same size). For redox concentrations 相似文献   

Ultra-thin double-walled carbon nanotubes: A novel nanocontainer for preparing atomic wires

Double-walled carbon nanotubes (DWCNTs) with high graphitization have been synthesized by hydrogen arc discharge. The obtained DWCNTs have a narrow distribution of diameters of both the inner and outer tubes, and more than half of the DWCNTs have inner diameters in the range 0.6–1.0 nm. Field electron emission from a DWCNT cathode to an anode has been measured, and the emission current density of DWCNTs reached 1 A/cm² at an applied field of about 4.3 V/μm. After high-temperature treatment of DWCNTs, long linear carbon chains (C-chains) can be grown inside the ultra-thin DWCNTs to form a novel C-chain@DWCNT nanostructure, showing that these ultra-thin DWCNTs are an appropriate nanocontainer for preparing truly one-dimensional nanostructures with one-atom-diameter.