Armchair Single-walled Carbon Nanotubes Research Articles

STRUCTURAL AND ELECTRONIC PROPERTIES OF FINITE-LENGTH SINGLE-WALLED CARBON AND SILICON CARBIDE NANOTUBES: DFT STUDY

This paper presents a systematical analysis of the structure and electronic properties of armchair single-walled carbon nanotubes (SWCNTs) as well as single-walled silicon carbide nanotubes ( SiCNTs ) by using density functional theory. The geometries of all species were optimized at the B3LYP level of theory using the SVP basis set. The different behavior of C – C bonds "parallel" and "perpendicular" to the nanotube axis has been found. The HOMO–LUMO energy gap, ionization potential, electron affinity, electronegativity and hardness of studied tubes were compared. The influence of both SWCNTs and SiCNTs lengths on their electronic properties has been analyzed.

Prediction of Elastic Mechanical Behavior and Stability of Single-Walled Carbon Nanotubes Using Bar Elements

A computationally effective structural mechanics approach based on the exclusive use of bar elements is developed in order to test its efficiency to predict the elastic longitudinal, torsional, and radial mechanical properties of zigzag, chiral, and armchair single-walled carbon nanotubes (SWCNTs). In addition, the proposed method is used for the investigation of the stability of SWCNTs under compressive and radial loads. The proposed model uses three-dimensional, two-noded, linear bar finite elements of three degrees-of-freedom per node to represent the force field appearing between carbon atoms due to the basic interatomic interactions. The numerical results, which are compared with corresponding data given in the open literature, demonstrate the convergence and stability of the method in predicting the elastic properties and critical forces that cause the instability of the tubes. The effect of chirality, length, and radius of carbon nanotubes on numerical predictions is thoroughly and clearly demonstrated.

Adsorption of Chlorobenzene onto (5,5) Armchair Single-Walled Carbon Nanotube and Graphene Sheet: Toxicity versus Adsorption Strength

Adsorption of the homologues series of chlorobenzenes (CBs) onto the surface of the (5,5) armchair single-walled carbon nanotube (SWCNT) and graphene (Graph) sheet has been investigated using density functional theory-based calculations, and the concomitant interaction between the CBs and SWCNT/Graph has also been characterized with the help of the Bader’s theory of atoms in molecules. Results reveal that interaction of CBs with the SWCNT and Graph enhances with the increase in the chlorine content. The adsorption of CBs on Graph is more favorable when compared with SWCNT. Evidence shows that the planar surface of the graphene facilitates the direct through-space interaction of the chlorine atoms of CBs with the aromatic surface. The π character of CBs governs the interaction process in the case of SWCNT. Findings from this study clearly demonstrate the importance of geometry (curved or planar) of the nanomaterial in the adsorption of aromatic pollutants. In addition, the inter-relationship between the electrophilicity index (a powerful conceptual DFT descriptor of toxicity of CBs) and the interaction energy (adsorption capacity) has also been derived.

First-Principles Study on Chemical Bonding Characteristics between Cr and Single-Walled Silicon Nanotubes

The adsorption energy and structural properties of Cr doped armchair (5, 5) single-walled silicon or Carbon nanotubes are investigated in detail by the first-principles theory. It is found that Cr atom above on hole position is most energetically favorable for SWSiNTs, which means that Cr atom is prone to absorb on Silicon nanotubes than Carbon nanotubes. Structural analyses suggest that Cr adsorption in silicon nanotubes induces the dehybridization of mixed sp2-sp3hybrid orbital and the subsequent formation of sp3-like orbital. That enhances the adsorption energy of silicon nanotubes.

Study of H2 physical adsorption in single-walled carbon nanotube array

The potential energies of a single H2 inside and outside an armchair single-walled carbon nanotube (SWCNT) are calculated by the electronic density functional theory (DFT), and influences of the SWCNT tube diameter on the potential energy minimum and equilibrium position are studied. Hydrogen storage capacity of the armchair SWCNTs in the rhombic arrays is estimated by using grand canonical Monte Carlo (GCMC) simulations in a pressure range from 10 to 100 bar and at temperatures of 77 K, 150 K, 220 K, 298 K, and 318 K, respectively; influences of the SWCNT diameter and VDW distance on the hydrogen storage capacity, and the isosteric heats of the H2-armchair SWCNTs arrays at several discrete temperatures and pressures are also investigated. The present main discoveries include (i) variation pattern of the H2 adsorption saturation pressure with the tube diameter and temperature; (ii) existence of extremum of the hydrogen storage capacity as a function of the VDW distance and tube diameter; (iii) diametrically opposite change of H2 storage capacity with the tube diameter in different pressure domains; (iv) layered distribution of the H2 adsorbed inside the tube. A theoretical mode is suggested to explain self-consistently all of these discoveries by combining the potential field information with the arguments of liquid state theories, and further verified by snapshots of representative configuration. The present discoveries, particularly, the theoretical mode explaining them, may serve to provide some guidance in improving the hydrogen storage capacity by doping the CNT and optimization of parameters.

Chirality dependence of quantum thermal transport in carbon nanotubes at low temperatures: A first-principles study

We study the transport properties of single-walled carbon nanotubes (SWCNTs) using the nonequilibrium Green's function method based on first-principles calculations. We compared three SWCNTs with different chiralities (3, 3), (5, 0), and (4, 2), and found that the thermal conductance varies significantly with the chirality, especially at low temperatures. Such differences are attributed to the dependence on the chirality of the frequency of the lowest optical mode and phonon-phonon interaction with the semi-infinite leads. To obtain accurate low-vibrational frequencies, a force constant correction based on the Lagrange undetermined multiplier method was employed. The phonon-phonon interaction was analyzed in terms of the projection of the phonon coupling with the semi-infinite leads onto the normal modes of the center region. Our result indicates that high optical mode frequency and weak phonon coupling on the armchair (3, 3) SWCNT are the origin of the long quantized plateau found in the experimental thermal conductance.

Effect of chirality, length and diameter of carbon nanotubes on the adsorption of 20 amino acids: a molecular dynamics simulation study

We carried out molecular dynamics simulations to study the adsorption of all the 20 amino acids (AAs; aromatic, polar and non-polar) on the surface of chiral, zigzag and armchair single-walled carbon nanotubes. The adsorption was occurring in all systems. In the aromatic AAs, the π–π stacking and the semi-hydrogen bond formation cause a strong interaction with the carbon nanotubes (CNTs). We also investigated the chirality, length and diameter dependencies on adsorption energies. We found that all AAs have more tendency to adsorption on the chiral and zigzag CNTs over the armchair. The results show that increasing both the diameter and the length causes the enhancement of the adsorption energy. But, the effect of the length is more than of the diameter. For example, the adsorption energy of Trp on the surface of CNT (4,1), with 2 nm length, is 20.4 kcal/mol. When the length of CNT becomes twice, the adsorption energy increases by 24 ± 0.3%. But by doubling the diameter, the adsorption energy increased only by 9.8 ± 0.25%.

Comparative Theoretical Study on the Positional Preference for Functionalization of Two OH and SH Groups with (5,5) Armchair SWCNT

Covalent sidewall functionalization of (5,5) armchair single-walled carbon nanotube by OH and SH groups has been investigated using density functional theory. Two possibilities for each of 1,2- (adjacent), 1,3- (alternate), and 1,4-additions were considered. Strong intramolecular O–H···O hydrogen bond plays an important role in determining the positions for attachment of two OH groups with SWCNTs and reaction feasibility. The reactions of OH addition(s) are considerably more exothermic than the reactions of SH addition(s). The addition of two OH or SH functional groups prefers to attach at adjacent (1–2 and 1–1′) and 1,4-positions (1–4 and 3–6) rather than at alternate carbon sites (1–3 and 2–6). Owing to the strong intramolecular hydrogen bond, 1,2-addition (1-2-OH) is slightly more favored (by 2.4 kcal/mol) than 1,4-addition (1-4-OH), while 1,4-addition of two SH groups (1-4-SH) is more feasible (by 10 kcal/mol) than 1,2-addition (1-2-SH). Interestingly, the addition reactions of two SH groups at altern...

Edge states in horseshoe-shape carbon nanotubes transformed by hydrogen adsorption

We have investigated hydrogenated single-wall armchair ($n$,$n$) carbon nanotubes (CNTs) with $4\ensuremath{\le}n\ensuremath{\le}12$ by using density functional theory calculations. Hydrogen adsorption may transform the CNTs into a horseshoe shape. Nonmagnetic edge-localized electron states have been identified in CNTs of horseshoe shape in this work. The $\ensuremath{\sigma}$-bond-like orbital overlaps across the edge-localized electrons, which sustain the horseshoe shape of the CNTs and hinder spontaneous unravelling into a graphene nanoribbon, cause the horseshoe-shape CNTs to become nonmagnetic metal. The bonding energy between the hydrogenated edges increases with the CNT diameter, approaching a limit of $\ensuremath{\sim}$1 eV.

Size effects on water adsorbed on hydrophobic probes at the nanometric scale

Molecular dynamics simulations of liquid water at ambient conditions, adsorbed at the external walls of (n,n) single-walled armchair carbon nanotubes have been performed for n = 5, 9, 12. The comparison with the case of water adsorbed on graphene has also been included. The analysis of Helmholtz free energies reveals qualitatively different ranges of thermodynamical stability, eventually starting at a given threshold surface density. We observed that, in the framework of the force field considered here, water does not wet graphene nor (12,12) tubes, but it can coat thinner tubes such as (9,9) and (5,5), which indicates that the width of the carbon nanotube plays a role on wetting. On the other hand, density profiles, orientational distributions of water, and hydrogen-bond populations indicate significant changes of structure of water for the different surfaces. Further, we computed self-diffusion of water and spectral densities of water and carbon molecules, which again revealed different qualitative behavior of interfacial water depending on the size of the nanotube. The crossover size corresponds to tube diameters of around 1 nm.

Adsorption model of atomic hydrogen on the surfaces of carbon nanotubes

A model for the adsorption of atomic hydrogen on the surfaces of single-walled zig-zag and armchair carbon nanotubes is constructed on the basis of the single-impurity periodic Anderson model. Features of the bands caused by the adsorption of hydrogen atoms in the structure of carbon nanotubes are studied. A reduction in the forbidden gap as a result of adsorption is revealed, and its dependence on the diameter of the semiconducting nanotubes is established. It is concluded that the model can be used to study the adsorption of other monovalent atoms on the surfaces of carbon particles.

Formation of helicity in an armchair single-walled carbon nanotube during tensile loading

In previous molecular dynamics (MD) simulations of deformation behavior of carbon nanotubes (CNTs), displacement rates ranging from 5.0×10−3 to 8.0×10−4nm/step were used. In this work, a slower displacement rate (1.4×10−5nm/step) was used to investigate deformation behavior of CNTs under tensile loading. Interesting findings were obtained. For the armchair CNT, during loading shear deformation occurred to the lattices before rupture, causing bond-breaking and re-bonding to the original carbon rings, and leading to the formation of a helix to the armchair, which is equivalent to introducing a screw dislocation into the CNT with a Burgers vector equal to the spacing between the carbon rings. The helix spiraled and propagated along the CNT. For the zigzag CNT, observable necking was formed locally before rupture, but no helix was formed. The necking in the zigzag was found to be recoverable after the external strain was released.

Mechanical Properties Investigation of Single-Walled Carbon Nanotube Using Finite Element Method

This paper presents a three dimensional finite element model for armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs). The influences of diameter, chirality and length on the elastic moduli (Young’s modulus and shear modulus) of SWCNTs are investigated. The formulation presented is based on the assumption of viewing the construction of SWCNTs as a geometric frame-like structure. The interatomic interactions of bond length, bond angle, bond torsion and non-bonded interactions are equivalent to corresponding structure features straightforwardly. The models of SWCNTs are developed according to the atomistic structure network of nanotubes. The interatomic interactions of C- C atoms are simulated via appropriate straight spring and torsional spring elements. The computational results indicate that both diameter and chirality have a significant effect on the Young’s and shear moduli of SWCNTs, while the elastic moduli are not very sensitive to the variation of length. It is also shown that with a similar radius, armchair SWCNT has a slight higher value of Young’s modulus than zigzag and chiral SWCNTs. While zigzag SWCNT has a slight higher value of shear modulus than armchair and chiral SWCNTs.

Temperature and Chirality Dependent Mechanical Properties of Single-Walled Carbon Nanotube

Presented herein is an investigation into the stretching and fracture behavior of single-walled carbon nanotubes (SWCNT) subjected to axial tensile load at various temperatures. This study is carried out using molecular dynamics (MD) simulation at temperatures ranging from 200 K to 2200 K. The authors find that single-walled carbon nanotubes exhibit obvious temperature and chirality dependent properties. The values of tensile strain and tensile strength of zigzag (12, 0) and armchair (7, 7) SWCNTs with similar radii decrease with increase in temperature, but decline slightly on different slopes. The stress-strain curves of zigzag and armchair SWCNTs vary significantly when the temperature is more than 1200 K. Our studies suggest temperature and chirality play an important role in determining the tensile strength and tensile strain of SWCNT.

Structure and electronic properties of a Mn nanowire encapsulated in carbon nanotubes

Abstract First-principles calculations using density functional theory are performed studying the stability and the electronic structure of an one-dimensional chain of Mn atoms as a nanowire encapsulated in a single-walled (5,5) armchair carbon nanotube. The results show a ferromagnetic ground state for a dimerized nanowire where the interatomic Mn–Mn distance is 2.65 A and the interdimer separation is 3.40 A. The average Mn moment is 4.35 μ B . A charge transfer from the nanotube to the nanowire is observed. A polarized spin channel is identified for conduction electrons in the filled nanotube.

A DFT Computation for Comparison of NQR of O<sub>2</sub>, N<sub>2</sub> and CO over the Surface of Single-Walled Carbon Nanotubes

In this study we assumed Single-Walled Carbon Nano Tubes (SWCNTs) as ideal candidates for various applications of gas sensors due to their amazing physical adsorption properties. The adsorption behavior of selected nitrogen, oxygen and CO molecules on the surface of the Single-Walled Carbon Nano Tubes (SWCNTs) was studied by the Density Functional Theory (DFT) (B3LYP/6-311G*) using the Gaussian 98 software. We studied the Nuclear Quadrupole Resonance (NQR) of the armchair (4, 4) SWCNTs with the optimal diameter of 5.6 Å and the length of 9.8 Å. For the first time, DFT calculations were performed to calculate oxygen and nitrogen the interaction of quadrupole moment with Electric Field Gradient (EFG) in NQR in the representative considered model of the (N2-CNTs), (O2-CNTs) and (CO-CNTs). The evaluated NQR parameters reveal that the EFG tensors of Oxygen-17, Nitrogen-14 and Carbon-13 are influenced and show particular trends from gas molecules in the SWCNTs due to the contribution of N-N, O-O and C-O gas molecules of SWCNTs.

Low velocity impact of a nanoparticle on nanobeams by using a nonlocal elasticity model and explicit finite element modeling

In this paper, analytical solutions of low velocity transverse impact of a nanoparticle (mass) on a nanobeam are presented using the nonlocal theories to bring out the effect of the nonlocal behavior on dynamic deflections. Impact of a mass on simply supported and clamped nanobeams are investigated by using nonlocal Timoshenko beam theory. In order to obtain an analytical result for this problem, an approximate method has been developed wherein the applied impulse is replaced by a suitable boundary condition. The dynamic deflections predicted by the classical theory are always smaller than those predicted by the nonlocal theory due to the nonlocal effects. Based on molecular mechanics, an improved 3D finite element (FE) model for armchair and zigzag single-walled carbon nanotubes (SWNTs) has been developed. Numerical examples for estimating Young's modulus of nanotubes are presented to illustrate the accuracy of this simulation technique. Based on this model, the maximum dynamic deflections of single-walled carbon nanotubes with different boundary conditions, geometries as well as chiralities are obtained and then compared with theory investigation. The simulation results demonstrated good agreement with analytical results. Furthermore, the mass and the velocity of the nanoparticle (striker) have significant effects on the dynamic behavior of nanobeams.

Theoretical investigation of CO2 and NO2 adsorption onto Co-, Rh- and Ir-doped (5,5) single-walled carbon nanotubes

Density functional theory calculations were employed for investigation of three transition metals (TMs), i.e. Co, Rh and Ir binding to armchair (5,5) single-walled carbon nanotubes (SWCNTs) and adsorption of CO2 and NO2 onto TM-doped SWCNTs. It was found that the binding abilities of TMs to the SWCNT are in order: Ir > Rh > Co. The adsorption abilities of CO2 and NO2 gases individually on the pristine and TM-doped SWCNTs were found as orders: Co-doped > Ir-doped > Rh-doped ≫ pristine SWCNTs and Ir-doped > Co-doped > Rh-doped ≫ pristine SWCNTs for adsorptions of CO2 and NO2, respectively. The Ir-doped SWCNT was found to be the best NO2 storage. Either the Ir-doped SWCNT or Co-doped SWCNT or Rh-doped SWCNT can also be used as the NO2 storage.

Electronic and mechanical properties of single-walled carbon nanotubes interacting with epoxy: A DFT study

Carbon nanotubes exhibit extremely high stiffness and strength, and are regarded as perfect reinforcing fibers for developing a new class of nanocomposites. The use of quantum mechanical calculations is more accurate than other atomistic methods for studying the interface and mechanical properties on the nanoscale for such materials. Ab initio calculations based on density functional theory (DFT) are employed to investigate the interaction properties of epoxy on typical zigzag and armchair single-walled carbon nanotubes (SWCNTs). The interaction energies for epoxy monomers with different orientations on SWCNTs are investigated. The results indicate that epoxy is weakly bound to the outer surface of the considered nanotubes and that the obtained interaction energy values are typical for physisorption. In addition, the influence of different defects (Stone–Wale, one- and two-atom vacancies) and functional groups (–NH2 and –OH) on the interaction properties between the epoxy and the respective SWCNTs has been investigated. Our results indicate that the interaction energy between the SWCNT and the epoxy decreased as the number of defects increased. In addition, the strongest interaction was observed for the SWCNT functionalized with the –OH group. Therefore, DFT calculations were performed to investigate the effect of the –OH functional group on the mechanical properties of SWCNTs interacting with epoxy.

Multidrug resistance protein P-gp interaction with nanoparticles (fullerenes and carbon nanotube) to assess their drug delivery potential: a theoretical molecular docking study

P-glycoprotein (P-gp)-mediated efflux system plays an important role to maintain chemical balance in mammalian cells for endogenous and exogenous chemical compounds. However, despite the extensive characterisation of P-gp potential interaction with drug-like molecules, the interaction of carbon nanoparticles with this type of protein molecule is poorly understood. Thus, carbon nanoparticles were analysed, such as buckminsterfullerenes (C20, C60, C70), capped armchair single-walled carbon nanotube (SWCNT or C168), and P-gp interactions using different molecular docking techniques, such as gradient optimisation algorithm (ADVina), Lamarckian genetic algorithm (FastDock), and shape-based approach (PatchDock) to estimate the binding affinities between these structures. The theoretical results represented in this work show that fullerenes might be P-gp binders because of low levels of Gibbs free energy of binding (ΔG) and potential of mean force (PMF) values. Furthermore, the SWCNT binding is energetically unfavourable, leading to a total decrease in binding affinity by elevation of the residual area (Ares), which also affects the π-π stacking mechanisms. Further, the obtained data could potentially call experimental studies using carbon nanostructures, such as SWCNT for development of drug delivery vehicles, to administer and assess drug-like chemical compounds to the target cells since organisms probably did not develop molecular sensing elements to detect these types of carbon molecules.