Binding tendency with oligonucleotides and cell toxicity of cetyltrimethyl ammonium bromide-coated single-walled carbon nanotubes

Functionalized carbon nanotubes （CNTs） were made for the delivery of genes and drugs and CNT-based biosensors. The basis of CNTs is for binding with biomolecules in biomedical applications. The binding tendency with small interfering RNA oligonucleotides and cytotoxicity of cetyltrimethyl ammonium bromide （CTAB）-coated single-walled carbon nanotubes （SWNTs） were studied. The field emission scanning electron microscopy and transmission electron microscopy results show that a SWNT suspension in CTAB solution was well-dispersed and stable. CTAB is the cross-linker between SWNTs and oligonucleotides. The CTAB-coated SWNTs have less cytotoxicity to human umbilical vein endothelial cells than single SWNTs and the cytotoxicity of CTAB-coated SWNTs depended on the concentration of CTAB-coated SWNTs.

Enhanced hydrogen evolution reaction over molybdenum carbide nanoparticles confined inside single-walled carbon nanotubes

Carbon nanotubes(CNTs) have shown as unique nanoreactors to tune the catalytic activity of confined nano-catalysts. Here we report that the catalytic performance of molybdenum carbide nanoparticles(MoC_x NPs) for the hydrogen evolution reaction(HER) process can be enhanced by encapsulation within single-walled carbon nanotubes(SWNTs) with a diameter of 1–2 nm. The catalyst with MoC_x NPs located on the interior surface of SWNTs(MoCx@SWNTs) exhibits a lower onset over-potential and a smaller Tafel slope than the one with MoC_x NPs attached on the exterior surface(MoCx/SWNTs). This is likely attributed to the much smaller particle size and the more reduced states of the confined MoC_x NPs, as well as the larger specific surface area of MoCx@SWNTs compared with Mo Cx/SWNTs. In addition, the electronic structure of the confined MoC_x NPs might be modified by the confinement effects of SWNTs, and hence the adsorption free energy of H atoms on the confined MoC_x NPs, which could also contribute to their higher performance. These results suggest that the SWNTs can be further explored for constructing novel catalysts with beneficial catalytic performance.

Effect of Single-walled Carbon Nanotubes on Cellulose Phenylcarbamate Chiral Stationary Phases

Single-walled carbon nanotubes（SWNTs） have a high adsorption ability and nanoscale interactions. Cellulose trisphenylcarbamates possess high enantioseparation ability in high-performance liquid chromatography（HPLC）. Single-walled carbon nanotubes mixed with cellulose trisphenylcarbamate are coated on the silica gel as chiral stationary phases and higher enantioseparation factors are obtained. After a single-walled carbon nanotube is linked to the 6-pesition of cellulose 2,3-bisphenylcarbamate, its enantioseparation resolution increases compared to that of the cellulose trisphenylcarbamate. It is the first time that SWNTs have been applied to enantioseparation. The results indicate that the single-walled carbon nanotubes are good promoters of chiral recognition. This method can be used to improve the enantioseparation efficiency of the polysaccharide chiral stationary phases.

Semiconducting single-walled carbon nanotubes synthesized by S-doping

An approach was presented for synthesis of semiconducting single-walled carbon nanotubes(SWNTs) by sulfur(S) doping with the method of graphite arc discharge. Raman spectroscopy, UV-vis-NIR absorption spectroscopy and electronic properties measurements indicated the semconducting properties of the SWNTs samples. Simulant calculation indicated that S doping could induce convertion of metallic SWNTs into semiconducting ones. This strategy may pave a way for the direct synthesis of pure semiconducting SWNTs.

ANALYSIS OF MATERIAL MECHANICAL PROPERTIES FOR SINGLE-WALLED CARBON NANOTUBES

Abstract The carbon-carbon bond between two nearest-neighboring atoms is mod- eled as a beam and the single-walled carbon nanotubes are treated as the space frame structures in order to analyze the mechanical properties of carbon nanotubes. Based on the theory of Tersof- Brenner force feld, the energy relationships between the carbon-carbon bond and the beam model are obtained, and the stifness parameters of the beam are determined. By applying the present model, the Young’s moduli of the single-walled carbon nanotubes with diferent tube diameters are determined. And the present results are compared with available data.

Synthesis and evaluation of carbon nanotubes composite adsorbent for CO2 capture： a comparative study of CO2 adsorption capacity of single-walled and multi-walled carbon nanotubes

As a preliminary investigation towards obtaining carbon nanotube composite adsorbent for CO2 capture, in this study CO2 adsorption performance of three commercial carbon nanotubes （CNTs） one single-walled carbon nanotubes （SWCNTs）, and two （2） different multi-walled carbon nanotubes （referred to as A-MWCNTs and B-MWCNTs） were evaluated and compared. The purpose of this study was to compare the different types of CNTs and select the best to serve as the solid anchor in the development of a hydrophobic composite adsorbent material for CO2 capture. The N2 physi- sorption of the CNTs was conducted to determine their surface area, pore volume and pore size. In addition, morphology and purity of the CNTs were checked with Transmission Electron Microscopy and Raman Spectroscopy, respectively. The CO2 adsorption capacity of the CNTs was evaluated using Thermo-gravimetric analysis （TGA） at 1.1 bar, at operating temperature ranged from 25 to 55 ~C and at different CO2 feed flow rates, in order to evaluate the effects of these variables on the CO2 adsorption capacity. The results of CO2 adsorption with the TGA show that CO2 adsorption capacity for both SWCNTs and MWCNTs was the highest at 25 ~C. Changing the CO2 flowrates had no significant effect on the adsorption capacity of MWCNTs, but decreasing the CO2 flow rate resulted in the enhancement of the CO2 adsorption capacity of SWCNTs. Overall, it was found that the SWCNTs displayed the highest CO2 adsorption capacity （29.97 gCO2/kg ad- sorbent） when compared to the MWCNTs （12.09 gCO2/kg adsorbent）, indicating a 150% increase in adsorption capacity over MWCNTs.

Production of single-walled carbon nanotubes from methane over Co-Mo/MgO nanocatalyst:A comparative study of fixed and fluidized bed reactors

In this study,the performances of fixed and fluidized bed reactors in the production of single-walled carbon nanotubes（SWNTs）have been investigated.In both reactors,single-walled carbon nanotubes were grown by catalytic chemical vapor decomposition（CCVD）of methane over Co-Mo/MgO nanocatalyst under two different operating conditions.The synthesized samples were characterized by TEM,TGA and Raman spectroscopy.It is found that the performance of a fluidized bed in the synthesis of carbon nanotubes is much better than that of a fixed bed.The quality of carbon nanotubes obtained from the fluidized bed was significantly higher than that from the fixed bed and the former one with the ID/IG ratio of 0.11 while the latter one with the ID/IG ratio of 0.71.Also,the yield of SWNTs in the fluidized bed was 92 wt%,while it was 78 wt%in the fixed bed.These advantages of fluidized bed reactors for the synthesis of carbon nanotubes can be attributed to more available space for the growth of carbon nanotubes and more uniform temperature and concentration profiles.

Molecular Simulation of Hydrogen Adsorption Density in Single-Walled Carbon Nanotubes and Multilayer Adsorption Mechanism

The adsorption of hydrogen onto single-walled carbon nanotubes (SWCNTs) was studied by molecular dynamics (MD) sim'lation. It was found that the hydrogen molecules distribute regularly inside and outside of the tube. Density distribution was computed for H2 molecule. Theoretical analysis of the result showed the multilayer adsorption mechanism of SWCNTs. The storage of H2 in SWCNTs is computed, which provides essential theoretical reference for further study of hydrogen adsorption in SWCNTs.

Synthesis of nitrogen-doped single-walled carbon nanotubes and monitoring of doping by Raman spectroscopy

Nitrogen-doped single-walled carbon nanotubes （CNx-SWNTs） with tunable dopant concentrations were synthesized by chemical vapor deposition （CVD）, and their structure and elemental composition were characterized by using transmission electron microscopy （TEM） in combination with electron energy loss spectroscopy （EELS）. By comparing the Raman spectra of pristine and doped nanotubes, we observed the doping-induced Raman G band phonon stiffening and 2D band phonon softening, both of which reflect doping-induced renormalization of the electron and phonon energies in the nan- otubes and behave as expected in accord with the n-type doping effect. On the basis of first principles calculations of the distribution of delocalized carrier density in both the pristine and doped nanotubes, we show how the n-type doping occurs when nitrogen heteroatoms are substitutionally incorporated into the honeycomb tube-shell carbon lattice.

Effects of single-walled carbon nanotubes on growth and physiological characteristics of Microcystis aeruginosa

In order to explore a novel and potential method using carbon nanotubes （CNTs） for controlling blue-green algal blooms efficiently in future, effects of single-walled carbon nanotubes （SWCNTs） on Microcystis aeruginosa growth control were investigated under lab cultured conditions. Related physiological changes were tested involving several important enzyme of antioxidant defense system （superoxide dismutase （SOD）, peroxidase （POD）, catalase （CAT）, malondiadehyde （MDA）, photosynthetic pigments, protein, soluble sugar and extracellular microcystin toxins （MC-LR））. Algal cell density was significantly inhibited by SWCNTs at high concentration （〉5.00 mg/L）, and the inhibition rate was dose-dependent. For treatment with 100 mg/L SWCNTs, the inhibitory rates even reached above 90%. 96 h IC50 was determined as 22 mg/L. Antioxidant enzyme activities were dramatically dropped with increasing lipid peroxidation at higher SWCNTs concentration, indicating intracellular generation of reactive oxygen species （ROS） and oxidative stress damage in algae. Reduction of photosynthetic pigments, soluble sugar and protein contents suggested that SWCNTs may severely ruin algal photosynthesis system, destroy the metabolism-related structure of cell, and thus lead to negative physiological status in M. aeruginosa. Besides, SWCNTs can effectively decrease the amount of extracellular microcystins in culture medium.

High-speed countercurrent chromatography for purification of single-walled carbon nanotubes

A new chromatographic purification of single-walled carbon nanotubes using high-speed countercurrent chromatography is reported. The purification was accomplished on the basis of experiment that dispersed the single-walled carbon nanotubes with sodium dodecyl sulfate, and the result mixture was separated using the two phase system composed of n-butanol/water = 1/1 （v/v）. The sizes of SWNTs separated were observed by scanning electron microscopy. The results demonstrated that the high-speed countercurrent chromatography possessed a good efficency for purification of single-walled carbon nanotubes.

Size-dependent sinusoidal beam model for dynamic instability of single-walled carbon nanotubes

In this study, a model for dynamic instability of embedded single-walled car- bon nanotubes （SWCNTs） is presented. SWCNTs are modeled by the sinusoidal shear deformation beam theory （SSDBT）. The modified couple stress theory （MCST） is con- sidered in order to capture the size effects. The surrounding elastic medium is described by a visco-Pasternak foundation model, which accounts for normal, transverse shear, and damping loads. The motion equations are derived based on Hamilton＇s principle. The differential quadrature method （DQM） in conjunction with the Bolotin method is used in order to calculate the dynamic instability region （DIR） of SWCNTs. The effects of differ- ent parameters, such as nonlocal parameter, visco-Pasternak foundation, mode numbers, and geometrical parameters, are shown on the dynamic instability of SWCNTs. The re- sults depict that increasing the nonlocal parameter shifts the DIR to right. The results presented in this paper would be helpful in design and manufacturing of nano-electromechanical system （NEMS） and micro-electro-mechanical system （MEMS）.

Density Functional Theory Study of MoO_3 Molecule Encapsulated inside Single-walled Carbon Nanotubes

The binding energies, geometric structures and electronic properties of molybde- num trioxide （MOO3） molecule encapsulated inside （8, 0）, （9, 0）, （10, 0） and （14, 0） single-walled carbon nanotubes （SWNTs） have been investigated using density functional theory （DFT） method. Due to curvature effect, the calculated binding energy values are different, the variation of which indicated that the stability of MoO3/SWNT systems increases with increasing the radius of SWNTs. At the same time, owing to the presence of MoO3 molecule, the band gap of MoO3/SWNTs systems decreases. The analysis of density of states （DOS） reveals hybridization between C-2p and Mo-4d and between C-2p and O-2p orbitals near the Fermi level, which results in electron transfer from SWNTs to MoO3 molecule. The present computations suggest that electronic properties of SWNTs can be modified by doping MoO3 molecule.

Development of a microcomposite with single-walled carbon nanotubes and Nd_2O_3 for determination of paracetamol in pharmaceutical dosage by adsorptive voltammetry

This study presents for the first time a new composite of carbon paste(CP), single-walled carbon nanotubes(SWCNTs) and Nd2 O3(NdOX). This versatile composite(NdOX-SWCNT/CPE) was applied to the oxidation of paracetamol(PCM). The newly formed surface was characterized by scanning electron microscopy(SEM), electrochemical impedance spectroscopy(EIS) and cyclic voltammetry(CV). The results showed greater conductivity and a higher surface area for the composite than those of the carbon paste alone. Moreover, the anodic peak currents for PCM increased from 1.6 to 3.6 m A with CPE and NdOXSWCNT/CPE, indicating an increase of nearly 51.0% for the anodic peak current. On the other hand, the anodic peak potentials shifted from 0.67 to 0.57 V. The detection limits were 0.05 mmol/L with NdOXSWCNT/CPE and 0.50 mmol/L with SWCNT/CPE. The relative standard deviations(RSDs) were 1.5%(n=7). The accuracy and interference of the methods were evaluated with a urine chemistry control spiked with known quantities of PCM, uric acid, dopamine, ascorbic acid, caffeine, acetylsalicylic acid,tartrazine, sunset yellow, allure red, rutin, morin and metal ions. Finally, the novelty and usefulness of the composite were evaluated to quantify PCM in pharmaceutical dosage forms such as tablets, powders and syrups for children.

Analysis of Single-Walled Carbon Nanotubes Using a Chemical Bond Element Model

A three dimensional nano-scale finite element model （FEM）, called the chemical bond element model, is proposed for the simulation of mechanical properties of single-walled carbon nanotubes （SWCNTs） based upon molecular mechanics method. Chemical bonds between carbon atoms are modeled by chemical bond elements. The constants of a sub-stiffness matrix are determined by using a linkage between molecular mechanics and continuum mechanics. In order to evaluate the correctness and performance of the proposed model, simulation was done to determine the influence of nanotube wall thickness, radius and length on the elastic modulus （Young＇s modulus and shear modulus） of SWCNTs. The simulation results show that the choice of wall thickness significantly affects the Young＇s modulus and shear modulus. The force field constants is also very important, because the elastic modulus is sensitive to force field constants and the elastic properties of SWCNT are related to the radii of the tubes. The contribution of length to elastic modulus is insignificant and can be ignored. In comparison with the Young＇s modulus and shear modulus reported in the literature, the presented results agree very well with the corresponding theoretical results and many experimental measurements. Furthermore, if the force constants are properly chosen, the present method could be conveniently used to predict the mechanical behavior of other single-walled nanotubes such as boron nitride nanotubes. The results demonstrate the value of the proposed model as a valuable tool in the study of mechanical behaviors of carbon nanotubes and in the analysis of nanotube-based equipments.

Optimization Conditions for Single-Walled Carbon Nanotubes Dispersion

The sonication-driven dispersion of single-walled carbon nanotubes (SWCNTs) in aqueous surfactant solution has been monitored by UV-vis-NIR spectroscopy and scanning electron microscopy. Dispersion of SWCNTs experiments reveal that the maximum concentration of dispersed SWCNTs corresponds to the maximum UV-vis-NIR absorbance of the solution. With higher surfactant concentration the dispersion rate of SWCNTs increases and low temperature sonication is required to achieve maximum dispersion. Dispersion of higher SWCNT concentrations requires longer sonication time. For effective dispersion the optimal concentration of surfactant is 1.5 wt%, the concentration of SWCNTs that can be homogeneously dispersed in aqueous solution is about 0.4 mg/ml.

Controlling the Diameter of Single-Walled Carbon Nanotubes by Improving the Dispersion of the Uniform Catalyst Nanoparticles on Substrate

To have uniform nanoparticles individually dispersed on substrate before single-walled carbon nanotubes(SWNTs)growth at high temperature is the key for controlling the diameter of the SWNTs.In this letter,a facile approach to control the diameter and distribution of the SWNTs by improving the dispersion of the uniform Fe/Mo nanoparticles on silicon wafers with silica layer chemically modified by 1,1,1,3,3,3-hexamethyldisilazane under different conditions is reported.It is found that the dispersion of the catalyst nanoparticles on Si wafer surface can be improved greatly from hydrophilic to hydrophobic,and the diameter and distribution of the SWNTs depend strongly on the dispersion of the catalyst on the substrate surface.Well dispersion of the catalyst results in relatively smaller diameter and narrower distribution of the SWNTs due to the decrease of aggregation and enhancement of dispersion of the catalyst nanoparticles before growth.It is also found that the diameter of the superlong aligned SWNTs is smaller with more narrow distribution than that of random nanotubes.

Research on the Relationship between Density of States and Conducting Properties of Single-walled Carbon Nanotubes

The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The distinctive properties of the DOS, the normalized differential conductivity and the current us bias for SWNTs are deduced and analyzed theoretically. The singularities in the DOS (or in the normalized differential conductivity) predict that the jump structure of current (or conductance)-bias of SWNTs exists. All conclusions from the theoretical analysis are in well agreement with the experimental results of SWNT's electronic structure and electronic transport. In other words, the simple theoretical model in this paper can be applied to understand a range of spectroscopic and other measurement data related to the DOS of SWNTs.

High-energy pulse generation using Yb-doped Q-switched fiber laser based on single-walled carbon nanotubes

An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs,and the highest single pulse energy of 40.6 nJ respectively.

Transverse Vibration Analysis of Single-Walled Carbon Nanotubes Embedded in an Elastic Medium Using Bernoulli-Fourier Method

Based on the Timoshenko beam theory and Bernoulli-Fourier method, a single-elastic beam model is developed for transverse vibrations of single-walled carbon nanotubes under additional axial load, which includes the effects of the elastic medium around them. Explicit expressions are derived for the natural frequencies and transversal responses of simply supported single-walled carbon nanotubes. The influence of addition axial load and the properties of elastic medium on the vibrations are discussed. The results showed that the effects of addition axial load on the lower natural frequencies of single-walled carbon nanotubes are sensitive to the lower vibration modes and the stiff elastic medium. The lower natural frequencies depend on the axial load;they become smaller with increasing axial load and vary with the vibration modes. In addition, except for the first mode, the effects of the axial load on the stiff elastic medium are considerably greater than those on the flexible one. However, the constants of the elastic medium have little effect on the first mode. The critical axial buckling stress and strain for simply-supported single-walled carbon nanotubes are also obtained.