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.

Printable Aligned Single-Walled Carbon Nanotube Film with Outstanding Thermal Conductivity and Electromagnetic Interference Shielding Performance

Ultrathin,lightweight,and flexible aligned single-walled carbon nanotube(SWCNT)films are fabricated by a facile,environmentally friendly,and scalable printing methodology.The aligned pattern and outstanding intrinsic properties render“metal-like”thermal conductivity of the SWCNT films,as well as excellent mechanical strength,flexibility,and hydrophobicity.Further,the aligned cellular microstructure promotes the electromagnetic interference(EMI)shielding ability of the SWCNTs,leading to excellent shielding effectiveness(SE)of~39 to 90 dB despite a density of only~0.6 g cm^(−3) at thicknesses of merely 1.5-24μm,respectively.An ultrahigh thickness-specific SE of 25693 dB mm^(−1) and an unprecedented normalized specific SE of 428222 dB cm^(2)g^(−1) are accomplished by the freestanding SWCNT films,significantly surpassing previously reported shielding materials.In addition to an EMI SE greater than 54 dB in an ultra-broadband frequency range of around 400 GHz,the films demonstrate excellent EMI shielding stability and reliability when subjected to mechanical deformation,chemical(acid/alkali/organic solvent)corrosion,and high-/low-temperature environments.The novel printed SWCNT films offer significant potential for practical applications in the aerospace,defense,precision components,and smart wearable electronics industries.

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.

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.

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.

Electron field emission from single-walled carbon nanotube nonwoven

Field emission from single-walled carbon nanotube （SWNT） nonwoven has been investigated under high vacuum with different vacuum gaps, A low turn-on electric field of 1.05 V/μm is required to reach an emission current density of 10μA/cm^2. An emission current density of 10 mA/cm^2 is obtained at an operating electric field of 1.88V/μm. No current saturation is found even at an emission current of 5 mA. With the vacuum gap increasing from 1 to 10 mm, the turn-on field decreases monotonically from 1.21 to 0.68 V/μm, while the field amplification is augmented. The good field-emission behaviour is ascribed to the combined effects of the intrinsic field emission of SWNT and the waved topography of the nonwoven.

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.

Broad Microwave Dielectric Property of Single-walled Carbon Nanotube Composites

Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes （SWNT） embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompa- nied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.

Electrooxidation of Nitric Oxide at a Glass Carbon Electrode Modified with Functionalized Single-walled Carbon Nanotube

The electrocatalytic oxidation of nitric oxide（NO） at a glass carbon electrode（GC） modified with functionalized single-walled carbon nanotubes（SWCNTs） was investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）.It was found that the SWCNT modified electrode could speed greatly up the electron transfer rate compared with the bare GC electrode.After the SWCNT was treated with alkali or mixed acids,the reaction rate and activation energy of NO electrooxidation were changed to different extent.Chemical modification of the SWCNT surface is one of the most powerful methods to change the sensitivity of NO electrooxidation reaction.The modified electrode with SWCNT obtained by the firstly alkali treatment and then the mixed acids treatment was the best one for NO electrooxidation,the result of CV was also confirmed by that of EIS.The anodic processes of NO were recognized more clearly by exploring the reaction mechanism of NO electrooxidation at the SWCNT modified electrode.

Thermal properties of single-walled carbon nanotube crystal

In this work, the thermal properties of a single-walled carbon nanotube （SWCNT） crystal are studied. The thermal conductivity of the SWCNT crystal is found to have a linear dependence on temperature in the temperature range from 1.9 K to 100.0 K. In addition, a peak （658 W/mK） is found at a temperature of about 100.0 K. The thermal conductivity decreases gradually to a value of 480 W/mK and keeps almost a constant in the temperature range from 100.0 K to 300.0 K. Meanwhile, the specific heat shows an obvious linear relationship with temperature in the temperature range from 1.9 K to 300.0 K. We discuss the possible mechanisms for these unique thermal properties of the single-walled carbon nanotube crystal.

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.

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.

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.

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）.

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.