Armchair CNTs Research Articles

Understanding the synergistic catalysis effect on the dual-metal-N4 embedding single-walled carbon nanotubes from first principles

Developing high-efficiency electrocatalysts for the oxygen evolution reaction (OER) remains a crucial bottleneck on the way to the water splitting for producing clean fuel (H2). Compared with single atom catalysis (SACs), dual-atom catalysts (DACs) have attracted great interest due to higher OER catalytic efficiency. In this work, the OER properties of dual-metal-N4 embedding armchair single-walled carbon nanotubes (D-MN4/CNTs) were systematic studied by density functional theory (DFT) simulations. Our results indicate that CoN4 embedding armchair CNTs exhibit higher OER activity than the corresponding planar structure, especially for CoN4 embedding in armchair CNT (4, 4) (CNT4). For MN4-CoN4 co-embedding CNTs, the TiN4-CoN4/CNTs have good OER synergistic effect with the lowest overpotential. Besides, the diameter of CNTs have a significant impact on the OER efficiency. The lowest reaction overpotential 0.47 V were obtained in TiN4-CoN4/CNT4 with a 5.69 Å tube diameter. Interestingly, compressive stress will further enhance the synergistic effect between two metal atoms in the OER reaction. The OER overpotential of CoN4-TiN4 embedding armchair CNT4 can reduce to 0.40 V under the −4 % uniaxial compression strain. These works were expected to better understand the synergistic mechanisms and design high-efficiency dual-atom OER electrocatalysts.

Bending characteristics of carbon nanotubes: Micropolar elasticity models and molecular dynamics simulations

The present paper aims at evaluating non-classical continuum parameters for each class of armchair and zigzag single-walled CNTs focusing on the scale effect in their flexural behavior observed in molecular dynamics (MD) simulations. Through a non-linear optimization approach, the bending rigidities obtained from atomistic simulations are compared to those derived from non-classical continua. For MD simulations, a novel method ensuring pure bending is introduced and for continuum modeling, micropolar, constrained micropolar, and modified couple stress theories are employed. The results reveal that adopted non-classical theories, notably micropolar theory, provide reasonable outcomes with an obvious failure of classical Cauchy theory.

Induced magnetization in armchair and Zig-zag CNTs on adsorbing transition metals

In this paper, we investigated the effect of adsorption of transition metal on electronic properties of metallic and semiconducting (CNTs). It was found that magnetization can be induced in metallic and semiconducting CNTs by adsorbing transition metals on them. Density of states (DOS) and bandstructure results suggest ferromagnetic (FM) and half metal ferromagnetic (HMF) characteristics in transition metal adsorbed metallic and semiconducting CNTs. Metallic (6, 0) CNT shows induced ferromagnetism on adsorbing Ag, Co, Cr, Ti, Mo, and shows HMF characteristic on adsorbing Zr. Semiconducting (8, 0) CNT shows induced HMF characteristic on adsorbing Ag, Co, Cr, Ti, Mo, and shows ferromagnetic characteristic on adsorbing Zr. Induced magnetism in CNTs can find application in magnetic sensors, magnetic forced microscopy, biomedical cell transportation and 1-D magnetoresistive spintronic devices.

Stitching up the Belt[n]arenes

A synthetic strategy reported recently in the Journal of the American Chemical Society by Wang and coworkers, who used laser irradiation in the final key step of the synthesis, has led to the formation of highly strained belt[8]arene derivatives. This breakthrough could open doors to more controlled and precise syntheses of zigzag carbon nanotubes.

Numerical prediction of elastic properties for carbon nanotubes reinforced composites using a multi-scale method

The main aim of this research was to investigate longitudinal elastic and effective modulus of composites reinforced with zigzag and armchair single-walled (CNT) and multi-walled carbon nanotubes (MWCNT) with different volume fractions and aspect ratios via finite element simulation. A three-phased volume element was adopted for the modeling of nanocomposite behavior and nonlinear spring elements were used to model interphase part joints and the effective force between nanotubes and resin were determined based on Lennard-Jones potential. After the evaluation and validation of the model, elastic modulus and Poisson’s ratio of composites reinforced with zigzag and armchair CNTs with different volume fractions and aspect ratios were extracted. It was found that by increasing volume fraction and aspect ratio, elastic modulus of representative volume element of composite was increased and its Poisson’s ratio was decreased. At similar aspect ratio and volume fraction, the elastic modulus of composites reinforced with armchair CNTs and Poisson’s ratio of those reinforced with zigzag CNTs were higher. Also, results showed that elastic modulus of composite was independent from elastic modulus of interphase.

Advanced molecular structural mechanics model for carbon nanotubes incorporating the 2nd generation REBO potential

Molecular mechanics models like the molecular structural mechanics (MSM) model have been proven to be a valuable tool for the investigation of carbon nanotubes. This class of models is based on a chemical force field representing the bonds present in the structure. Up to now, the underlying chemical force field applied in the MSM model is usually based on harmonic potentials. This simple approach comes with major drawbacks limiting the abilities of the MSM approach. In order to overcome these limitations, the present work integrates the 2nd generation reactive bond order potential (REBO), which is a sophisticated chemical force field, into the MSM approach. The development of this advanced MSM model is given in detail. As a demonstration of its capabilities, the elastic properties of different armchair and zig-zag CNTs are investigated numerically. It was found, that the results for the elastic properties differ significantly with the choice of the underlying chemical force field. The arising differences are discussed and reasons for the occurring behavior are given. The developed advanced MSM approach on the basis of the REBO potential strongly enhances the capabilities of the MSM approach while maintaining its excellent accessibility and applicability together with a low computational effort.

Some properties of solid helium and helium nanoclusters using the effective HFD-like interaction potential: Adsorption and desorption inside carbon nanotube

We have calculated the zero equation of state of solid helium using a two-body Hartree–Fock dispersion (HFD)-like potential from molecular dynamics (MD) simulation. To take many-body forces into account, our simple and accurate empirical expression is used with the HFD-like potential without requiring an expensive three-body calculation. This potential model also includes the quantum effects for helium at low temperatures. The results indicate that our effective HFD-like potential improves the prediction of the classical two-body results to get better agreement with experiment than many other two-body and three-body potentials of helium reported in the literature. We have also simulated the adsorption and desorption processes of the (He)55, (He)147, (He)309, (He)561, and (He)923 icosahedral nanoclusters confined into the different armchair and zigzag CNTs from 0 to 50 K using our effective model. We have observed an interesting phenomenon at 0 K for helium. The nanoclusters adsorb to the inner CNT wall as a melting process. But, the heavier noble gas clusters (such as Ne and Xe) show the different behavior than the He clusters. They form a multilayered solid structure into the CNT at zero temperature and adsorb into the inner wall of the CNT at higher temperatures. Our results for He clusters show that the absolute value of the adsorption energy increases as the size of the nanocluster increases. The desorption process begins at a certain temperature and represents itself by a jump in the configurational energy values. We have also investigated the structural and dynamical properties of the confined helium nanoclusters during the adsorption and desorption processes at different temperatures.

Phosphate functionalized (4,4)-armchair CNTs as novel drug delivery systems for alendronate and etidronate anti-osteoporosis drugs

The ability of (4,4)-armchair CNT and its three phosphate functionalized forms (CNT-nH2PO4, n=1–3) were evaluated as novel drug delivery systems (DDSs) for the two commercially well-known anti-osteoporosis drugs namely alendronate (AL) and etidronate (ET). For this purpose, the DFT calculations were accomplished at both B3LYP and B3PW91 levels using 6–31g(d) basis set. The binding energy was increased by increasing number of H2PO4 moieties attached on the CNT with the most negative binding energy was measured for the carrier containing three phosphate groups. The dipole moments of all phosphate containing CNTs were much greater (∼2.2–4.4D) than that of pristine CNT (∼0D). The contour maps proved that when the CNT was functionalized by H2PO4 groups, the symmetric distribution of electric charge was vanished with the charge distribution was the highest asymmetric for the CNT-2H2PO4 while it was the lowest asymmetric for CNT-3H2PO4 leading to the greatest dipole moment for the CNT-2H2PO4 (4.177D) while the smallest dipole moment for the CNT-3H2PO4 (1.614D). Among all compounds, those containing the CNT-3H2PO4 exhibited the smallest band gap energy, chemical potential and hardness but the greatest electronegativity and electrophilicity index which were all suitable and effective for the attachment of drugs onto the bone surface (having partial positive charge due to the presence of Ca2+ as CaCO3) and therefore inhibiting the osteoporosis. Consequently, it was established that the drug-CNT-3H2PO4 was the most appropriate drug-carrier compound for both of the AL and ET drugs and it could be used as the most effective drug vehicle. The attachment of AL, ET drugs as well as the AL-CNT-3H2PO4 and ET-CNT-3H2PO4 drug-carrier systems to the bone tissue was modelled by optimization of the structures of these compounds bonded to the hydroxyapatite (HA)-17water (w). It was found that among these four systems, the AL-CNT-3H2PO4 could be suggested as the most suitable DDS for application in the treatment of osteoporosis.

Raman intensity and vibrational modes of armchair CNTs

Raman intensity changes and frequency patterns have been studied using the various armchair (n,n) to understand the variations of bond polarizability, in regard to changing diameters, lengths, and the number of atoms in the (n,n). The Raman intensity trends of the (n,n) are validated by those of Cn isomers. For frequency trends, similar frequency patterns and frequency inward shifts for the (n,n) are characterized. Also, VDOS trends of the (n,n) expressing Raman modes are interpreted. The decomposition of vibrational modes in the (n,n) into radial, longitudinal, and tangential mode is beneficially used to recognize the distinct characteristics of vibrational modes.

Investigation of geometrical effects in the carbon allotropes manipulation based on AFM: multiscale approach

Carbon allotropes are used as nanocarriers for drug and cell delivery. To obtain an accurate result in the nanoscale, it is important to use a precise model. In this paper, a multiscale approach is presented to investigate the manipulation process of carbon allotropes based on atomic force microscopy (AFM). For this purpose, the AFM setup is separated into two parts with different sizes as macro field (MF) and nano field (NF). Using Kirchhoff’s plate model, the cantilever (the main part of MF) is modeled. The molecular dynamics method is applied to model the NF part, and then the MF and NF are coupled with the multiscale algorithm. With this model, by considering the effect of size and shape, the manipulation of carbon allotropes is carried out. The manipulations of armchair CNTs and fullerenes are performed to study the diameter changing effects. The result shows that the manipulation and friction force increases by increasing the diameter. The result of the indentation depth for the armchair CNTs indicates that decreasing the diameter causes the indentation depth to reduce. Moreover, the manipulations of four kinds of carbon allotropes with the same number of atoms have been studied to investigate the geometrical effects. The shapes of these nanoparticles change from sphere to cylinder. The results illustrate that the manipulation and the friction force decrease as the nanoparticle shape varies from sphere to cylinder. The Von-Mises results demonstrate that by changing the nanoparticle shape from the spherical to the cylindrical form, the stress increases, although the manipulation force reduces.

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.

Energy consistent modified molecular structural mechanics model for the determination of the elastic properties of single wall carbon nanotubes

A new, modified molecular structural mechanics model for the determination of the elastic properties of carbon nanotubes is presented. It is designed specifically to overcome drawbacks in existing molecular structural mechanics models, which are not consistent with their underlying chemical force fields in terms of energy. As a result, modifications are motivated, developed and implemented in order to create a new, energy consistent molecular structural mechanics model. Hence, the new model leads to a better prediction of the material parameters for single wall carbon nanotubes, while the simple applicability of the approach is maintained. The results calculated for the elastic constants (Young's modulus, Poisson ratio) of armchair and zig-zag CNTs are given and discussed. Both elastic constants were found to be dependent on the chirality as well as on the carbon nanotube diameter. An asymptotic value of approximately 800 GPa was obtained for the Young's modulus and a value of approximately 0.28 for the Poisson ratio.

Structural and electronic properties of endohedral doped SWCNTs: A DFT study

The structural and electronic properties of semiconductors (Si and Ge) and metal (Au and Tl) atoms doped armchair (n, n) and zigzag (n, 0); n=4–6, single wall carbon nanotubes (SWCNTs) have been studied using an ab-initio method. We have considered a linear chain of dopant atoms inside CNTs of different diameters but of same length. We have studied variation of B.E./atom, ionization potential, electron affinity and HOMO–LUMO gap of doped armchair and zigzag CNTs with diameter and dopant type. For armchair undoped CNTs, the B.E./atom increases with the increase in diameter of the tubes. For Si, Ge and Tl doped CNTs, B.E./atom is maximum for (6, 6) CNT whereas for Au doped CNTs, it is maximum for (5, 5) CNTs. For pure CNTs, IP decreases slightly with increasing diameter whereas EA increases with diameter. The study of HOMO–LUMO gap shows that on doping metallic character of the armchair CNTs increases whereas for zigzag CNTs semiconducting character increases. In case of zigzag tubes only Si doped (5, 0), (6, 0) and Ge doped (6, 0) CNTs are stable. The IP and EA for doped zigzag CNTs remain almost independent of tube diameter and dopant type whereas for doped armchair CNTs, maximum IP and EA are observed for (5, 5) tube for all dopants.

Numerical modeling of eigenmodes and eigenfrequencies of hetero-junction carbon nanotubes with pentagon–heptagon pair defects

This study examines the vibrational behavior of numerous hetero-junctions and their fundamental CNTs under different boundary conditions. The natural frequencies of homogeneous CNTs (zigzag and armchair) were obtained analytically and through a finite element method and compared with each other. In addition, the computational results of hetero-junctions were obtained and also compared with their constituent homogeneous CNTs. It has been shown that the natural frequency of straight hetero-junction CNTs lies within the range of the values of their fundamental CNTs in the case that the wider tube fixed. In addition, it was also concluded that the eigen-values of straight hetero-junctions and their fundamental CNTs increase by increasing the chiral number of CNTs. Finally, it was also shown that the armchair CNTs are more stable in their vibration due to higher natural frequencies than zigzag configurations.

Investigations on the Antiretroviral Activity of Carbon Nanotubes Using Computational Molecular Approach

Carbon nanotubes are the interesting class of materials with wide range of applications. They have excellent physical, chemical and electrical properties. Numerous reports were made on the antiviral activities of carbon nanotubes. However the mechanism of antiviral action is still in infancy. Herein we report, our recent novel findings on the molecular interactions of carbon nanotubes with the three key target proteins of HIV using computational chemistry approach. Armchair, chiral and zigzag CNTs were modeled and used as ligands for the interaction studies. The structure of the key proteins involved in HIV mediated infection namely HIV- Vpr, Nef and Gag proteins were collected from the PDB database. The docking studies were performed to quantify the interaction of the CNT with the three different disease targets. Results showed that the carbon nanotubes had high binding affinity to these proteins which confirms the antagonistic molecular interaction of carbon nanotubes to the disease targets. The modeled armchair carbon nanotubes had the binding affinities of -12.4 Kcal/mole, -20 Kcal/mole and -11.7 Kcal/mole with the Vpr, Nef and Gag proteins of HIV. Chiral CNTs also had the maximum affinity of -16.4 Kcal/mole to Nef. The binding affinity of chiral CNTs to Vpr and Gag was found to be -10.9 Kcal/mole and -10.3 Kcal/mole respectively. The zigzag CNTs had the binding affinity of -11.1 Kcal/mole with Vpr, -18.3 Kcal/mole with Nef and -10.9 with Gag respectively. The strong molecular interactions suggest the efficacy of CNTs for targeting the HIV mediated retroviral infections.

Effect of Tubular Chiralities and Diameters of Single Carbon Nanotubes on Gas Sensing Behavior: A DFT Analysis

Using density functional theory, the adsorption of CO, CO2, NO and CO2 gas molecules on different chiralities and diameters of single carbon nanotubes is investigated in terms of energetic, electronic properties and surface reactivity. We found that the adsorption of CO and CO2 gas molecules is dependent on the chiralities and diameters of CNTs and it is vice versa for NO and NO2 gas molecules. Also, the electronic character of CNTs is not affected by the adsorption of CO and CO2 gas molecules while it is strongly affected by NO and NO2 gas molecules. In addition, it is found that the dipole moments of zig-zag CNTs are always higher than the arm-chair CNTs. Therefore, we conclude that the zig-zag carbon nanotubes are more preferred as gas sensors than the arm-chair carbon nanotubes, especially for detecting NO and NO2 gas molecules.

Structural and electronic properties of armchair (7, 7) carbon nanotubes using DFT

The density functional theory full-potential linearized augmented plane wave method with the Generalized Gradient Approximation (PBE-GGA & WC-GGA) and Local Density Approximation for the exchange–correlation potential were applied to calculate the structural and electronic properties of armchair (7, 7) carbon nanotubes. Structural properties such as lattice constants, bulk modules, Young’s modulus, compressibility, bond lengths, muffin-tin radius and effective atomic charge were calculated. According to PBE-GGA, CC bond lengths are equal to 1.429Å and Young’s modulus is equal to 0.930tetra Pascal being in good agreement with other studies. Band structure, density of states and electronic charge density were calculated. CNTs (7, 7) show a metallic behavior and the electron charge densities of CNTs (7, 7) confirm a covalent bond between two carbon atoms. Moreover, the effects of armchair CNTs chirality on the band gaps and Young’s modulus are illustrated which confirm the calculations.

Emergent properties and trends of a new class of carbon nanocomposites: graphene nanoribbons encapsulated in a carbon nanotube

Using density functional theory calculations, we show that recently synthesized carbon nanocomposites of graphene nanoribbons encapsulated in a carbon nanotube (GNR@CNT) possess rich emergent electronic and magnetic properties that offer new functionality and tunability and display systematic trends that are sensitive to the matchup of constitutive GNRs and CNTs. The encapsulation of H-passivated GNRs in metallic armchair CNTs always leads to a metallic complex while those in semiconducting zigzag CNTs can be either metallic or semiconducting depending on the chirality of GNRs. In particular, the complex of armchair GNRs in a zigzag CNT exhibits an oscillating electronic band gap with changing GNR width and a well-separated spatial distribution of electrons and holes localized in the CNT and GNR components, respectively. When bare large zigzag GNRs are encapsulated in an armchair CNT, the resulting complex shows strong structural stability and enhanced magnetism and, most interestingly, such GNR@CNT configurations can be tuned to be metallic or semiconducting depending on relative bond position and magnetic order. These results offer key insights for understanding and predicting emergent properties of GNR@CNT, which establish a roadmap for guiding design and synthesis of specific nanocomposite configurations with tailor-made properties for nanoelectronic, photovoltaic and spintronic applications.

Boron-Vacancy Pairing and Its Effect on the Electronic Properties of Carbon Nanotubes

We examined the effect of B-V pairing on the electrical conductivity and electronic properties of CNTs, compared to isolated V and substitutional B cases. Using DFT calculations we first looked at the interaction of a mobile V with substitutional B in armchair CNTs with different tube diameters. NEGF-DFT calculations were then performed to determine the electronic structure and electrical conductivity of (5, 5) CNTs with an V, Bs, or Bs-V. Our study unequivocally demonstrates that upon B-V pairing vacancy-related features mostly disappear in the tube conductance, which turns out to be due to the passivation of V dangling bonds.

Prediction of nonlocal scale parameter for carbon nanotubes

Based on the theory of nonlocal elasticity, a nonlocal shell model accounting for the small scale effect is developed for the bending characteristics of CNTs subjected to the concentrated load. With this nonlocal shell model, explicit expressions are derived for the bending solutions. To extract the proper values of nonlocal scale parameter, we have made molecular dynamics (MD) simulations for various radii and lengths of armchair and zigzag CNTs, the results of which are matched with those of nonlocal continuum model. It is found that the present nonlocal elastic shell model with its appropriate values of nonlocal scale parameter has the capability to predict the bending behavior of CNTs, which is comparable with the results of MD simulations. Moreover, exact closed form solutions for the nonlocal scale parameter for zigzag and armchair CNTs are obtained. The results show that nonlocal scale parameter is independent of the length of CNTs, and dependent on the radius of CNTs.