Zigzag Single-walled Carbon Nanotubes Research Articles

Optimization of Hydrogen Storage Capacity by Physical Adsorption on Open-ended Single-walled Carbon Nanotube as Diameter Function

In this paper, we perform combination methods of semi-empirical research, a theoretical approach, and force-matching to determine the optimum adsorption capacity on an open-ended single-walled carbon nanotube (SWCNT) as a diameter function. Using a semi-empirical study, we can determine the value of monolayer coverage and isosteric heat of adsorption from available thermodynamic data. By completing the semi-empirical study, we carried out quantum mechanical calculations to determine the adsorption energy on the interior and exterior of SWCNTs. Furthermore, monolayer coverage, specific surface area, and maximum adsorption capacity as the main quantity in the adsorption process was estimated using the combination method of force-matching and a classical Lennard-Jones potential model. Hydrogen physisorption was investigated on zig-zag SWCNTs at conditions for a pressure range of 0.1 to 10 MPa at 233 K and 298.15 K temperature. The adsorption of all data can be explained with the Toth model. The results shows the SWCNT exterior physisorption energy range between 1.35 to 1.62 kcal/mol. The interior range from 1.22 to 2.43 kcal/mol. With a wide degree of temperature and pressure variations, we obtained an optimum SWCNT diameter of 8-12 A . At the optimum diameter maximum adsorption capacity, we achieved 1.75 wt% at 233 K and an operating pressure of 10 MPa.

Commensurate Phases of Kr Adsorbed on Single-Walled Carbon Nanotubes

In this paper, we show that Krypton atoms form a commensurate solid (CS) phase with a fractional coverage of one krypton atom per every four carbons on zigzag carbon nanotubes. This is a unique phase, different from the $$\sqrt{3} \times \sqrt{3}$$ R30 $$^\circ $$ CS monolayer formed on graphite, which has a lower coverage of one krypton atom per every six carbons. Our prediction disagrees with experiments that observe in nanotubes the same solid structure found on graphite. In order to address this discrepancy, we simulated adsorption of Kr on zigzag and armchair single-walled carbon nanotubes with radii ranging from 4.7 to 28.83 A. Our simulations confirm that the CS of coverage 1/4 forms on medium-sized zigzag nanotubes. We also found the 1/6-coverage solid on graphene, which represents the infinite-radius limit of a nanotube. Our findings are key to experiments of adsorption on nanotubes where the interpretation and justification of the results are based on the monolayer coverage, such as mass or conductance isotherms measurements.

A New, Simple and Versatile Strategy for the Synthesis of Short Segments of Zigzag-Type Carbon Nanotubes.

Short segments of zigzag single-walled carbon nanotubes (SWCNTs) were obtained from a calixarene scaffold by using a completely new, simple and expedited strategy that allowed fine-tuning of their diameters. This new approach also allows for functionalised short segments of zigzag SWCNTs to be obtained; a prerequisite towards their lengthening. These new SWCNT short segments/calixarene composites show interesting behaviour in solution. DFT analysis of these new compounds also suggests interesting photophysical behaviour. Along with the synthesis of various SWCNTs segments, this approach also constitutes a powerful tool for the construction of new, radially oriented π systems.

(4 + 2) and (2 + 2) Cycloadditions of Benzyne to C60 and Zig-Zag Single-Walled Carbon Nanotubes: The Effect of the Curvature

Addition of benzyne to carbon nanostructures can proceed via (4 + 2) (1,4-addition) or (2 + 2) (1,2-addition) cycloadditions depending on the species under consideration. In this work, we analyze by means of density functional theory (DFT) calculations the reaction mechanisms for the (4 + 2) and (2 + 2) cycloadditions of benzyne to nanostructures of different curvature, namely, C60 and a series of zigzag single-walled carbon nanotubes. Our DFT calculations reveal that, except for the concerted (4 + 2) cycloaddition of benzyne to zigzag single-walled carbon nanotubes, all cycloadditions studied are stepwise processes with the initial formation of a biradical singly bonded intermediate. From this intermediate, the rotation of the benzyne moiety determines the course of the reaction. The Gibbs energy profiles lead to the following conclusions: (i) except for the 1,4-addition of benzyne to a six-membered ring of C60, all 1,2- and 1,4-additions studied are exothermic processes; (ii) for C60 the (2 + 2) benzyne...

Effects of B, N, P and B/N, B/P pair into zigzag single-walled carbon nanotubes: A first-principle study

Single atom (B, N or P) doping zigzag single-walled carbon nanotubes (SWCNTs) evolve from semiconducting to metallic by using density functional theory. The energy gaps of (8,0) tubes significantly narrow as a result of B/N and B/P pair co-doping. Especially, B/P pair co-doping makes the bottom of conduction band move to the Fermi level direction, and the top of valence band barely shift. With the increasing concentration of B/P pair, the bottom of conduction movement becomes stronger and the energy gaps decrease. Moreover, B or N-rich doping significantly changes the semiconducting character of pure B/N pairs co-doped models.

Curvature, vacancy size and chirality effects of mono- to octa-vacancies in zigzag single-walled carbon nanotubes

Defect modes with the smallest Ef were inclined to be along the armchair chain of (n,0) tubes.

Nonlinear Vibration Analysis of Single-Walled Carbon Nanotube With Shell Model Based on the Nonlocal Elasticity Theory

In this paper, nonlinear vibration of a single-walled carbon nanotube (SWCNT) with simply supported ends is investigated based on von Karman's geometric nonlinearity and nonlocal shell theory. The SWCNT is designated as an individual shell, and the Donnell's formulations of a cylindrical shell are used to obtain the governing equations. The Galerkin's procedure is used to discretized partial differential equations (PDEs) into the ordinary differential equations (ODEs) of motion, and the method of averaging is applied to obtain an analytical solution of the nonlinear vibration of (10,0), (20,0), and (30,0) zigzag SWCNTs. The effects of the nonlocal parameters, nonlinear parameters, different aspect ratios, and different circumferential wave numbers are investigated. The results of the classical and the nonlocal models are compared with different nonlocal elasticity constants (e0a). It is shown that the nonlocal parameter predicts different resonant frequencies in comparison to the local models. The softening and/or hardening nonlinear behaviors of the CNTs may change against the nonlocal parameters. Hence, considering the geometrical nonlinearity and the nonlocal elasticity effects, the dynamical models of the SWCNTs predict their vibration behaviors accurately and should not be ignored during theoretical modeling.

Improvement of electronic properties of carboxylated zigzag single wall carbon nanotubes by interaction with benzene derivatives

In this article, we reported the structural and conductive properties of benzene derivatives/carboxylated zigzag SWCNTs. It was noticed that the carboxylated carbon nanotubes were appropriate adsorbents for benzene derivatives. We presented novel density of states and band structures for modified SWCNTs by both carboxylic group and benzene derivatives. The result showed that nitrobenzene/COOH-SWCNT comprising superb electronic properties can be effectually applied for electronic devices and solar cells, instead of aniline/SWCNT combined system.

Stabilities and mechanical and electronic properties on BN doped zigzag single-wall carbon nanotubes

Abstract Electronic structures of undoped and BN doped zigzag (8,0) single-walled carbon nanotube (SWCNT) were investigated using density functional theoretical calculations. Their stabilities due to BN doping and spin states were considered and those with the shortest B–N distance and singlet spin is the most stable. The BN substitution also causes the reduction of the band gap energy. While the BN doping reduces the band gap energy from 0.606 to 0.183 eV, it has no effect on the Young׳s modulus value. The band gap energy of SWCNTs can be varied upon applying stress. At high stress ratio, SWCNT could become metallic.

Young’s Modulus Variation of Carbon Nanotubes Due to Defects Associated with Atomic Reconstruction of Random Vacancies

This paper studies the effect of three different types of defects on the Young’s modulus of zigzag and armchair single-walled carbon nanotubes. The defects are randomly introduced into the structure with a maximum distribution density of 2%. The defects include monovacancies, before and after reconstruction of dangling bonds, resulting finally to the Stone-Wales defect. As the length of model effects computation time significantly, finite element models are created in pristine and very short tube lengths to investigate the effect of model length on the results obtained. The investigation shows that the introduction of defects generally weakens the elastic strength of tubes but to rather different degrees. However, the structure is capable of restoring its elastic strength by rearranging its atoms in form of the Stone-Wales defect. The use of shorter nanotube models on the other hand can lead to accurate results if appropriate cylindrical boundary conditions are defined.

Influence of uniaxial strain on the linear optical spectra in the metallic single-walled carbon nanotubes

The linear absorption spectra of metallic zigzag single-walled carbon nanotubes (SWNTs) have been theoretically studied under the uniaxial strain by using the standard formulas of Orr and Ward. Due to the trigonal warping effect, the linear absorption spectra of M11 and M22 transitions are dominated by two major peaks, which come from the split Mii− and Mii+ excitons with different band index q. As the uniaxial strain is applied, it is interesting to find that the split peaks will overlap at one point of the uniaxial strain, and the splitting is zero at this point. Hence, we can also describe this variation tendency as the size of splitting, which first decreases to zero and then increases with increasing the uniaxial strain, based on which a supplemented tool is offered to detect the deformation degree of a metallic SWNT under uniaxial strain. In addition, the linear absorption spectra of the bands that nearest to the Fermi level have also been calculated, displaying an increase with the increase of the uniaxial strain, which can offer some useful information for the THz applications. The results obtained here are expected to be confirmed by the future experiment.

Structural, Vibrational and Electronic Properties of Defective Single-Walled Carbon Nanotubes Functionalised with Carboxyl Groups: Theoretical Studies.

Covalent sidewall functionalisation of defective zigzag single-walled carbon nanotubes [SWCNTs(10,0)] with COOH groups is investigated by using DFT. Four types of point defects are considered: vacancy (V), divacancy [V2 (5-8-5), V2 (555-777)], adatom (AA) and Stone-Wales (SW). The energetic, structural, electronic and vibrational properties of these systems are analysed. Decreasing reactivity is observed in the following order: AA>V>V2 (555-777)>V2 (5-8-5)>SW. These studies also demonstrate that the position in which a carboxyl group is attached to a defective SWCNT is of primary importance. Saturation of two-coordinate carbon atoms in systems with the vacancy V-7 and with the adatom AA-1(2) is 3.5-4 times more energetically favourable than saturation of three-coordinate carbon atoms for all studied systems. Vibrational analysis for these two systems shows significant redshifts of the ν(CO) stretching vibration of 96 and 123 cm-1 compared to that for carboxylated pristine systems. Detailed electronic-structure analysis of the most stable carboxylated systems is also presented.

Growing Zigzag (16,0) Carbon Nanotubes with Structure-Defined Catalysts.

The growth of zigzag single-walled carbon nanotubes (SWNTs) is most challenging among all types of SWNTs, with the highest reported selectivity of ∼7%. Here we realized the dominant growth of (16,0) tubes at the abundance near ∼80% by using intermetallic W6Co7 catalysts containing plenty of (1 1 6) planes together with optimizing the growth conditions. These (1 1 6) planes may act as the structure templates for (16,0) SWNTs due to the geometrical match between the open end of the (16,0) tube and the atomic arrangements of the (1 1 6) planes in W6Co7. Using catalysts with designed structure as solid state template at suitable kinetic conditions offers a strategy for selective growth of zigzag SWNTs.

Adsorption of gases from SF6 decomposition on aluminum-doped SWCNTs: a density functional theory study

Adsorption of gases produced by SF6 decomposition (i.e., SO2, H2S, SOF2, SO2F2, and CF4) by aluminum-doped zigzag (8, 0) single-walled carbon nanotubes (Al-SWCNTs) was investigated based on first-principles density functional theory (DFT). Different binding sites were considered to determine the most stable structures. Furthermore, adsorption energy, density of state, band structure, frontier molecular orbital, and population were analyzed to interpret the mechanism of gas adsorption on the surface of Al-SWCNTs. The calculation results predicted that the Al atom acted as an active site to adsorb the SF6 decomposition products in the adsorption process. SO2, H2S, and CF4 molecules were adsorbed on the sidewall of Al-SWCNTs by physisorption, whereas SOF2 and SO2F2 were molecularly chemisorbed. Conductivity of Al-SWCNTs was increased when the gas molecules of SO2, H2S, and SO2F2 were adsorbed. Conversely, SOF2 adsorption slightly decreased the conductivity of the adsorption system. Al-SWCNTs were insensitive to CF4. The different responses in conductivity of Al-SWCNTs for different gas molecule adsorptions present a potential selective and sensitive gas detection sensor.

CO2 Adsorption on Charged Carbon Nanotube Arrays: A Possible Functional Material for Electric Swing Adsorption

The adsorption and orientational ordering of carbon dioxide molecules on parallel bundles of charged as well as uncharged carbon nanotubes were investigated at 300 K using grand canonical Monte Carlo and molecular dynamics. Zigzag and armchair single-walled carbon nanotubes of radius ∼1.5 nm and different intertube distances between 0 and 2 nm were used. A fixed charge of 0.01–0.04e was placed on each carbon to investigate the effect of charge. Adding a positive charge to the carbon nanotubes causes a significant increase in adsorption (up to 35% at a pressure of 1.88 bar), while the gas adsorption decreases by up to 15% on negatively charged carbon nanotubes. The increase or decrease of adsorption upon charging is attributed to the change in potential energy for the interaction between the individual carbon dioxide molecule and the nanotube. The higher adsorption on positively charged nanotubes leads to thicker adsorbed layers and a lower orientational order of the adsorbed molecules.

Generation of Temperature Dependent Transversely Isotropic Properties for Zigzag and Armchair Single-Walled Carbon Nanotubes

Finite element analysis has been carried out to obtain temperature dependent transversely isotropic properties of the single-walled carbon nanotubes (SWCNTs). Finite element models of SWCNTs are generated by specifying the C-C bond rigidities. The five independent transversely isotropic properties for different chiralities are evaluated using the stress fields of thick-walled cylinders and the elastic deformations of SWCNTs subjected to pure extension, internal pressure and pure torsion loads. Empirical relations are provided for the five independent elastic constants useful to armchair and zigzag SWCNTs.

Hydrogen Adsorption and Associated Electronic and Magnetic Properties of Rh-Decorated (8,0) Carbon Nanotubes Using Density Functional Theory

A systematic spin-polarized density functional theory (DFT) study of hydrogen interaction with pristine and Rh-decorated zigzag (8,0) single-walled carbon nanotubes (SWCNTs) was performed. The most stable decoration site for Rh atoms as well as atomic and molecular hydrogen adsorption inside and outside the SWCNT was studied. Hydrogen adsorption energy in Rh-decorated SWCNTs was improved compared to that of pristine nanotubes. In addition, Rh-decorated SWCNT systems present a magnetic moment. Density of states and work function (WF) were computed to study the bonding evolution and electronic structure. When hydrogen is considered on Rh-SWCNT and pristine SWCNT, the WF increased while band gap decreased compared to that of pristine SWCNT.

The Impact of Generalized Stacking Fault Energy on the Mechanical Properties of Shuffle Dislocation in Zigzag Single-Walled Carbon Nanotubes

The calculation of generalized stacking fault energy for covalent materials exists several relaxation methods. And the modification factor of the restoring force should be different for different relaxation. In order to study the impact of generalized stacking fault energy on the mechanical properties of dislocations, the dislocation energy, Peierls barrier and Peierls stress of shuffle dislocation in zigzag single-walled carbon nanotube (SWCNT) under different modification factors are studied by the improved Peierls-Nabarro (P-N) theory. It is found that the misfit energies decreased, and the strain and total energies increased with increasing of the modification factor Δ. With the modification factor Δ of the restoring force changes from -0.2 to 0.5, the dislocation energy changes from 17.4eV to 19.3eV. The Peierls barriers Ep and σp Peierls stresses increased first and then decreased and the results are not as same as we thought. The impact of generalized stacking fault energy on mechanical properties of dislocations is not so simple as we thought and need to be further studied.

Structural, energetic and electrical properties of encapsulation of penicillamine drug into the CNTs based on vdW-DF perspective

First-principles van der Waals density functional (vdW-DF) calculation using GGA/PBE functional and DZP basis set implemented in the SIESTA package was carried out to investigation the encapsulation of penicillamine drug into the both armchair and zigzag single wall carbon nanotubes (SWCNTs). The results reveal that the drug encapsulated inside the CNT cavity is weakly bounded. The obtained results of binding energies indicated that incorporation of drug is favored inside the zigzag SWCNTs compared with armchair counterparts. We address here the role of vdW interaction for penicillamine drug when inclusion in the CNTs. It worth mentioning that encapsulation of vdW forces can be effects on the binding properties. The electronic structures and Mulliken charge population are analysed for the energetically most favorable complexes which shows that encapsulated penicillamine changes slightly the electronic properties of SWCNTs and trivial charges are transferred from drug to CNTs during encapsulation process.Global reactivity descriptor values such as electronegativity (χ), global hardness (η), global softness (S), electronic chemical potential (μ), and electrophilicity index (ω) were calculated. We anticipated that these findings supply the new way and value information for help in the experimental study and future applications.

Nonlinear vibration properties of a zigzag single-walled carbon nanotube embedded in a polymer matrix

In the current study, the nonlinear vibration properties of an embedded zigzag single-walled carbon nanotube (SWCNT) are investigated. Winkler-type model is used to simulate the interaction of the zigzag SWCNTs with a surrounding elastic medium. The relation between deflection amplitudes and resonant frequencies of the SWCNT is derived through harmonic balance method. The equivalent Young\'s modulus and shear modulus for zigzag SWCNT are derived using an energy-equivalent model. The amplitude – frequency curves for large-amplitude vibrations are graphically illustrated. The simulation results show that the chirality of zigzag carbon nanotube as well as surrounding elastic medium play more important roles in the nonlinear vibration of the single-walled carbon nanotubes.