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 carbon nanotubes(SWCNTs) is presented. SWCNTs are modeled by the sinusoidal shear deformation beam theory(SSDBT). The modified couple stress theory(MCST) is considered 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 different parameters, such as nonlocal parameter, visco-Pasternak foundation, mode numbers,and geometrical parameters, are shown on the dynamic instability of SWCNTs. The results 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).

Purification of Single-walled Carbon Nanotubes Grown by a Chemical Vapour Deposition(CVD) Method

A procedure for purification of single walled carbon nanotubes(SWNTs) grown by the chemical vapour deposition(CVD) of carbon monooxide has been developed. Based on the result from TGA/DTA of as prepared sample, the oxidation temperature was determined. The process included sonication, oxidation and acid washing steps. The purity and yield after purification were determined and estimated by TEM. Moreover, for the first time, a loop structure for CVD SWNTs has been observed.

A study of single-walled carbon nanotubes modified by organics of the phthalocyanine category

Organics of the phthalocyanine category have very good nonlinear optical properties. The single-walled carbon nanotubes were modified by using the phenoxy phthalocyanine. Characterization analysis was made by means of the transmission electron microscope (TEM), ultraviolet visible absorptive spectra, fluorescent spectra and Raman spectra. Under the TEM, it was observed that the composite looked like sugarcoated haws. By comparing the ultraviolet visible absorptive spectra before and after absorption, it was disclosed that the spectral intensity and the intensity of the peaks in the fluorescent spectra dropped remarkably. This shows that the single-walled carbon nanotubes have absorbed a large number of phenoxy phthalocyanines. Raman analysis revealed that in the Raman spectra, the position of the main peaks of the single-walled carbon nanotubes after absorption moved in the direction of long waves. The analysis suggests that the movement of the Raman spectra results from the change in the state of the single-walled carbon nanotubes before and after absorption.

Instability of single-walled carbon nanotubes conveying Jeffrey fluid

We report instability of the single-walled carbon nanotubes(SWCNT) filled with non-Newtonian Jeffrey fluid.Our objective is to get the influences of relaxation time and retardation time of the Jeffrey fluid on the vibration frequency and the decaying rate of the amplitude of carbon nanotubes.An elastic Euler-Bernoulli beam model is used to describe vibrations and structural instability of the carbon nanotubes.A new vibration equation of an SWCNT conveying Jeffrey fluid is first derived by employing Euler-Bernoulli beam equation and Cauchy momentum equation taking constitutive relation of Jeffrey fluid into account.The complex vibrating frequencies of the SWCNT are computed by solving a cubic eigenvalue problem based upon differential quadrature method(DQM).It is interesting to find from computational results that retardation time has significant influences on the vibration frequency and the decaying rate of the amplitude.Especially,the vibration frequency decreases and critical velocity increases with the retardation time.That is to say,longer retardation time makes the SWCNT more stable.

Theoretical Study on the Reaction Mechanism between Dichlorocarbene and Armchair Single-walled Carbon Nanotubes

The reaction mechanism between CCl2 and armchair single-walled carbon nanotu- bes (ASWCNTs) (3,3) and (4,4) has been studied by semiempirical AM1 and ab initio methods. The activation barriers of CCl2 adding to ASWCNT (3,3) and (4,4) are computed and compared. The lower barrier of CCl2 forms cycloaddition isomer on (3,3) maybe because the strain energy of (3,3) is larger than that of (4,4). Our theoretical results are consistent with the experimental results.

Alignment of Nanoscale Single-Walled Carbon Nanotubes Strands

Depositing single-walled carbon nanotubes(SWNTs) with controllable density, pattern and orientation on electrodes presents a challenge in today's research. Here, we report a novel solvent evaporation method to align SWNTs in patterns having nanoscale width and micronscale length. SWNTs suspension has been introduced dropwise onto photoresist resin microchannels; and the capillary force can stretch and align SWNTs into strands with nanoscale width in the microchannels. Then these narrow and long aligned SWNTs patterns were successfully transferred to a pair of gold electrodes with different gaps to fabricate carbon nanotube field-effect transistor(CNTFET). Moreover, the electrical performance of the CNTFET show that the SWNTs strands can bridge different gaps and fabricate good electrical performance CNTFET with ON/OFF ratio around 106. This result suggests a promising and simple strategy for assembling well-aligned SWNTs into CNTFET device with good electrical performance.

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.

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.

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.

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.

A semi-analytical approach for calculating the equilibrium structure and radial breathing mode frequency of single-walled carbon nanotubes

A semi-analytical model for determining the equilibrium configuration and the radial breathing mode(RBM)frequency of single-wall carbon nanotubes(CNTs) is presented. By taking advantage of the symmetry characteristics,a CNT structure is represented by five independent variables. A line search optimization procedure is employed to determine the equilibrium values of these variables by minimizing the potential energy. With the equilibrium configuration obtained, the semi-analytical model enables an efficient calculation of the RBM frequency of the CNTs. The radius and radial breathing mode frequency results obtained from the semi-analytical approach are compared with those from molecular dynamics(MD) and ab initio calculations.The results demonstrate that the semi-analytical approach offers an efficient and accurate way to determine the equilibrium structure and radial breathing mode frequency of CNTs.

Large magnetic moment at sheared ends of single-walled carbon nanotubes

In this work we report that after single-walled carbon nanotubes(SWNTs) are sheared with a pair of titanium scissors,the magnetization becomes larger than that of the corresponding pristine ones. The magnetization increases proportionally with the number of SWNTs with sheared ends, suggesting that there exist magnetic moments at the sheared ends of SWNTs.By using the coefficient of this linear relation, the average magnetic moment is estimated to be 41.5 ± 9.8 μB(Bohr magneton) per carbon atom in the edge state at temperature of 300.0 K, suggesting that ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of the carbon atoms at sheared ends play important roles in determining the unexpectedly high magnetic moments, which may have great potential applications.

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.

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.

PARAMETRIC STUDY FOR THE PREPARATION OF ALIGNED SINGLE-WALLED CARBON NANOTUBES BY ANODE-ARC DISCHARGE METHOD

Well aligned quasi-straight single-walled carbon nanotubes (SWCNTs) and straight SWCNTs bundle have been prepared in large scale by anode-arc vaporization of gr aphite with metallic catalysts. Various parameters such as the catalyst preparat ion, the kinds and pressure of the buffer gases, the quantity of anode-arc curre nt intensity, and the method of purification have been examined. The influence o f these parameters on the deposited carbon yield is reported, together with obse rvations of the produced material. Improvement in synthetic techniques has resul ted in the optimal conditions for the production of large quantities of high qua lity SWCNTs in our semi-continuous synthesis method. The formation of carbon nan otubes (CNTs) was studied briefly in this paper. Owing to the magnetic pinching effect of arc current, the CNTs arrange in parallel lines along the arc current direction.

Adsorption of Folic Acid on the Single-walled Carbon Nanotubes: AIM and NBO Analyses via DFT

In the present work,the behavior of folic acid（FA） molecule adsorbed onto single-walled carbon nanotube（SWCNT） was examined using the DFT-B3LYP/6-31G* level.In order to obtain information about the binding features of SWCNT as adsorbent with FA molecule,several studies,including the structural and electronic parameters and also the Atoms in Molecules（AIM） analysis,were performed.It was observed that the FA molecule via hydrogen bond prefers to adsorb on SWCNT with adsorption energy of about-18.70 kcal/mol.The molecular orbitals（HOMO and LUMO）,natural bond orbital（NBO） analysis,and density of states（DOS） plot indicated that a charge about 0.032 | e | is transferred from the FA molecule to the nanotube.After solvation energy calculations,it was found that the presence of a polar solvent causes an increase in FA adsorption on the single-walled carbon nanotube.Topological features such as electron energy density（Hc） and Laplacian of the electron density(2ρc) demonstrate partial covalent nature for H（116）…O（10） interaction in the FA/SWCNT complex.According to the calculated results,the single-walled carbon nanotubes are expected to be a potential efficient adsorbent for the adsorption of folic acid drug and also can be used as a suitable drug delivery vehicle within biological systems.

Modulating the Electronic Structures of Single-walled Carbon Nanotubes by Filling with Electron Acceptors and the Effect on Their Reactivity with Aryl Diazonium Salts

The electronic structures of single-walled carbon nanotubes(SWCNTs)were modulated by filling with tetracyanoquinodimethane(TCNQ),a strong electron acceptor.The structures of TCNQ-filled SWCNTs were checked by X-ray diffraction analysis,high-resolution transmission electron microscopy and Raman spectroscopy.Optical absorption spectroscopy demonstrated an enhanced reactivity between aryl diazonium and semiconducting SWCNTs.

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.

A molecular mechanics approach for analyzing tensile nonlinear deformation behavior of single-walled carbon nanotubes

在这篇论文，由捕获原子信息并且反映非线性的潜在的功能管理的行为，一条分析分子的力学途径被建议。为围单人赛的碳 nanotubes 的一种组成的关系(SWCNT 的) 被建立描述 SWCNT 的非线性的压力紧张曲线并且在张力的变丑期间预言有弹性的性质和 SWCNT 的碎紧张。基于虚拟内部契约(VIB ) ，模型由 P. 张等建议了的分析。也为比较被介绍。结果显示建议分子的力学途径是确实为分析 SWCNT 的机械行为的一个可接受的分析方法。

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

The binding energies, geometric structures and electronic properties of molybdenum 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.