Single-walled Carbon Nanotubes System Research Articles

Stochastic Analysis for the Embedded Single-Walled Carbon Nanotube Under Random Vibrations

It is inevitable that carbon nanotubes (CNTs) are subjected to random vibrations due to environmental noise, which may impair their mechanical properties. The nonlinear dynamics associated with single-walled carbon nanotubes (SWCNTs) under random noise has been investigated in this work. First, based on the nonlocal theory and the Euler–Bernoulli beam model with fixed supports at both ends, the governed equations and boundary conditions are established according to Hamilton’s principle. Second, the Galerkin method is used to approximate the differential equations of motion and the stochastic averaging method (SAM) is applied to predict the approximate response of the original system. Subsequently, a detailed parametric study is conducted to analyze the nonlinear random vibration response of the SWCNT with nonlocal effects, and the effectiveness of the proposed method is verified by comparing the analytical results with those from the Runge–Kutta method. Finally, by solving the backward Kolmogorov (BK) equation and the generalized Pontryagin (GP) equation simultaneously, the conditional reliability function (CRF) and mean first-passage time (MFPT) for determining the reliability of SWCNT systems are obtained.

Modeling and simulation of carbon nanotube amino-acid sensor: A first-principles study

In this study, we have investigated a single-walled carbon nanotube (SWCNT) based device to detect the essential amino acids, Glutamine and Tryptophan, by analyzing changes in various properties of the device. The models were simulated using density functional theory in combination with non-equilibrium Green’s function formalism. Furthermore, interaction energy plots are obtained and a molecular dynamics study is done to investigate the interactions of the molecules with the SWCNT surface. The results show significant changes in the current and conductance due to the alteration in the geometry and aromaticity of the SWCNT system. The results also show suppressed density of states (DOS), leading to an increase in the electron density. Molecular dynamics study shows that the energy of the system remains conserved up to some small fluctuations, maintaining the stability of the system during the interaction. Thus, amino acid detection is reported using CNTs indicating reliable applications in medical diagnosis.

Atomistic Study of Several Peptides Covering Single‐walled Carbon Nanotube by Noncovalent Adsorption

Single-walled Carbon Nanotubes (SWNTs) have shown outstanding physicochemical, mechanical, electronic, and optical properties that enable a broad range of biomedical applications, including drug delivery (carrier for anti-cancer drugs), imaging (carrier for contrast agents), tissue engineering (bone, nerve, and cardiac), gene delivery, and biosensors. However, their carbon hexagonal-lattice nanostructure causes a sizeable surface-to-volume ratio with a potent van der Waals surface that leads to limiting characteristics for bioapplications (e.g., low solubility, agglomeration, and potential toxicity). In this perspective, the biomolecule-adsorption strategy that exhibits advantageous characteristics over covalent functionalization could not only help overcome these SWNT limitations but also preserve its pristine sp2 hybridization wall by noncovalently binding amphiphilic peptides. The objective of this computational study is to investigate the fundamental interactions and properties of ten different segments (lower than 40 amino acids) on (16,0) SWNT system using Molecular Dynamics (MD) simulations that are essential and effective factors on SWNT applications, particularly for drug delivery. This proposed coverage of natural-sequence peptides can potentially be easier recognized by biological processes as well as increase dispersibility and decrease toxicity of SWNT.

Lie symmetry analysis, invariant subspace method and q-homotopy analysis method for solving fractional system of single-walled carbon nanotube

In this paper, we investigate the time fractional system of fluid-conveying single-walled carbon nanotube (SWCNT), the generalization of SWCNT system which plays important roles in many applied fields. The corresponding Lie symmetries admitted by this fractional system in Riemann–Liouville sense are obtained and symmetry reductions are performed. In addition, based on the above symmetries, the conservation laws are derived using new Noether theorem. Furthermore, analytical solution and numerical series solution to the initial value problem of time fractional SWCNT system in Caputo sense are constructed by applying invariant subspace method and q-homotopy analysis method, respectively.

Molecular dynamics studies for enhancing the anticancer drug efficacy: Toward designing a new carbon nanotube-based paclitaxel delivery system

The promising outcomes for biological applications of single-walled carbon nanotubes (SWCNTs) including biomolecules carriers have been reported before. Therefore, the investigation of the interactions of these nano-vectors with drug molecules can provide fundamental knowledge to design appropriate SWCNT-based carriers for drug delivery purposes. The current study addressed the underlying mechanism of a widely-used anticancer drug, paclitaxel (PTX), loading on the pristine SWCNT as well as that functionalized with (-OH), (-COOH), and PW3 peptide (a biologically compatible peptide as a novel candidate for nano-carrier surface modification). The effect of the functional group of nano-carrier on the drug binding was also investigated by all-atom molecular dynamics (MD) simulations. The binding free energy calculations based on the MM-PBSA approach indicated the exothermic and spontaneous adsorption of PTX molecules onto the pristine and modified SWCNTs. The π − π stacking interactions between three separate phenyl rings of PTX and SWCNT sidewall can explain the proper drug adsorption. Moreover, remarkable differences were identified in the arrangements of the aromatic rings toward the surface of nanotubes in the four studied complexes. According to the qualitatively and quantitatively analyses, the PTX drug delivery system exhibited especial effectiveness due to the stronger interactions with the nano-carrier and more water solubility upon coupling with the PW3-functionalized SWCNT at 310 K which could be well explained by microscopic structural evaluations. For the peptide-modified SWCNT system, PTX molecules still prefer to bind the sidewall of the nano-vector rather than the peptides.

Electrical doping in single walled carbon nanotube systems: A new technique

First report on electrically doped semiconducting carbon nanotube is presented using Extended Huckel Theory in combination with Non-equilibrium Green’s function formalism. The results show increase in current with the increasing electrical doping concentration. Electrical doping induces high charge concentration at small applied voltages and is far more superior because of its fault free approach overcoming the limitations of conventional doping. Furthermore, the device density of states confirms the sufficient number of peaks in the valence and conduction bands. The obtained results were compared with other theoretical results in the field in the form of a table. The results are very beneficial for the designing of high-performance CNT devices and enhancing their potential applications in the electronics industry.

Natural Frequency of Rotating Single-Walled Carbon Nanotubes with Considering Gyroscopic Effect

This paper investigates the bending vibration of rotating single-walled carbon nanotubes (SWCNTs) based on nonlocal theory. To this end, the rotating SWCNTs system modeled as a beam with a circular cross section and the Euler-Bernoulli beam theory (EBT) is applied with added effects such as rotary inertia, gyroscopic effect and rotor mass unbalance. Using nonlocal theory, two coupled sixth order partial differential equations that govern the vibration of rotating SWCNTs are derived. To obtain the natural frequency and dynamic response of the nanorotor system, the equation of motion for the rotating SWCNTs are solved. It is found that there are two frequencies in the frequency spectrum. The positive rootintroduced as forward whirling mode, while the negative root represents backward whirling mode. The detailed mathematical derivations are presented while the emphasis is placed on investigating the effect of the several parameters such as, tube radius, angular velocity and small scale parameter on the vibration behavior of rotating nanotubes. It is explicitly shown that the vibration of a spinning nanotube is significantly influenced by these effects. To validate the accuracy and efficiency of this work, the results obtained herein are compared with the existing theoretical and experimental results and good agreement is observed. To the knowledge of authors, the vibration of rotating SWCNTs considering gyroscopic effect has not investigated analytically yet and then the results generated herein can be served as a benchmark for future works.

First principles study on hydrogen storage in yttrium doped graphyne: Role of acetylene linkage in enhancing hydrogen storage

Through Density Functional Theory Simulations we predict that a Ytrrium atom attached on graphyne surface can adsorb up to a maximum of 9 molecular hydrogens (H2), with a uniform binding energy of ∼0.3 eV/H2 and an average desorption temperature of around 400 K (ideal for fuel cell applications), leading to 10 wt% of hydrogen, substantially higher than the requirement by DoE. The higher hydrogen wt% in Y doped graphyne compared to Y doped Single Walled Carbon Nanotubes (SWNT) and graphene is due to the presence of sp hybridized C atoms (in the acetylene linkage) supplying additional in-plane px-py orbitals leading to π (π*) bonding (antibonding) states. Charge transfer from metal to carbon nanostructure results in a redistribution of s, p, d orbitals of the metal leading to a non - spin polarized ground state in Y doped graphyne, due to the presence of the acetylene linkage, whereas Y doped SWNT and graphene remain magnetic like the isolated metal atom. In the non-magnetic graphyne + Y system, the net charge transfer from Y to successive H2 molecules is less than in magnetic Y + graphene and Y + SWNT systems, enabling Y + graphyne to store a larger number of H2 molecules. Furthermore, our ab initio MD simulations show that the system is stable even at room temperature and there is no dissociation of H2 molecules, enabling the system to achieve 100% desorption. So Y doped graphyne is found to be a promising hydrogen storage device with high wt%, 100% recyclability and desirable desorption temperature.

(Invited) Development and Utilization of an in Vitro Single Walled Carbon Nanotube System to Quantify Extracellular Nitric Oxide Concentration

Nitric oxide (NO) is an important biological signaling factor, but due to its fast degradation rate quantification is difficult. Single walled carbon nanotube sensors for NO are unique in their ability to quantify NO concentrations in vitro over extended time periods without genetically altering the cells of interest. Since nanotubes are so small they are readily taken up by cells. To investigate just the extracellular concentration of nitric oxide, avoiding detection of the intracellular concentration, we developed a system to look at extracellular nitric oxide concentrations for in vitro samples. This new system allows for seeding adherent cells in desired patterns without altering the nanotube sensors, therefore allowing spatial and temporal detection of NO in regions between cell islands or associated with multiple cell types. The system is robust enough to allow for other nanotube sensors to be used with alternate cell types, creating a technique to quantify multiple analytes that are excreted from cells in a temporal and spatial fashion.

Ruthenium decorated single walled carbon nanotube for molecular hydrogen storage: A first-principle study

Molecular hydrogen storage on Ruthenium (Ru) decorated single-walled carbon nanotube (SWCNT) has been studied by using spin-polarized density functional theory (DFT). When a Ru atom is adsorbed on SWCNT, the Bader analysis reveals that Ru transfers a charge of 0.44e− to SWCNT. Accordingly, Ru acts as adsorption center for H2 molecules; thus, it can hold up to four H2 molecules with an adsorption energy (Eads) of −0.93 eV/H2. A uniform addition of Ru atoms on SWCNT shows that this nanomaterial can adsorb up to five Ru without clustering. Each Ru atom of 5Ru-decorated SWCNT system can bind up to four H2 molecules involving an Eads of −0.83 eV/H2. After H2 molecules adsorption, Ru atoms shifted from a near hollow site to a bridge site. Moreover, Ru-decorated systems reduce their magnetic moment when the number of H2 molecules increase from 2 μB to 0 μB.

Numerical Analysis of the Structural Stability of Ideal (Defect-Free) and Structurally and Morphologically Degenerated Homogeneous, Linearly- and Angle-Adjoined Nanotubes and Cylindrical Fullerenes Under Axial Loading Using Finite Element Method

We report on the structural stability of ideal (defect-free) and structurally and morphologically degenerate carbon nanotubes and nanotube junction systems under axial loading based on the finite element method. We estimated the values for critical buckling load for uncapped and capped single-walled carbon nanotubes (SWCNTs) and linear and angle-adjoined SWCNT heterojunctions in ideal and structurally degenerate systems containing single-, double-, triple-, pinhole- and pentagon–heptagon (i.e., 5–7) structural defects and also containing a substitutional nitrogen (N) atom inclusion under compressive loading. Absolute atomic vacancy (defect) concentration in studied SWCNTs models was assumed to be nil for ideal systems, and was up to 3.0 at.% for structurally and morphologically degenerate systems. It was found that all types of structural defects and the morphological N-defect had reduced the load carrying capacity and mechanical strength in all SWCNT systems studied. The SWCNT models containing physically large vacant sites, such as triple- and pinhole-defects, displayed significantly lower critical load values compared to the systems that contained only a single-, double- or triple-vacancies. In addition, we found that capped SWCNTs performed marginally better in critical load carrying capacity compared to uncapped SWCNT systems. Furthermore, majority of the investigated structures displayed reduced load in SWCNTs with narrower tube widths, proportional to the size and the type of the defect investigated. The effects of chirality, such as zigzag- versus armchair-type, on the structural stability of the investigated SWCNT models were also investigated.

(Invited) Nanotube Excitonic Emitter at the Subwavelength Scale

It is slightly embarrassing to accept the fact that after a decade of very intensive research on optics of single-wall carbon nanotubes (SWCNT) still there is no complete understanding of fundamental physics behind it. For example, our knowledge of excitonic effects in SWCNTs is limited, nailed at two extremes – sophisticated and often highly idealized numerical simulations of very small systems or rudimentary empirical models of more realistic systems, not even always yielding analytical results. In this talk, one question arising in the physics of nanotube excitons is addressed: what is the shape of the excitation for a finite size SWCNT object? Since a whole SWCNT is sub-diffraction scale object, one may expect something similar to Hertz dipole, modified for a semiconductor material (as opposed to metal). To the best of our knowledge, such a solution was not known, thus a theory shedding light on the distribution of current of a nanotube excitonic emitter has been developed. While in our earlier work we considered localization of a free excitonic wave (aka binding) on a single charged impurity[1], in this talk we assume localization effects due to SWCNT end reflections. Unlike many of earlier excitonic works we take this into account via a self-consistent response of the whole nanotube antenna. Unexpectedly, even for a charge neutral SWCNT system, plasmonic resonances were found to develop on top of the excitonic spectral response[2]. We demonstrate that these plasmonic features are robust and should be detectable in near-field experiments. [1] BO. Tayo, SV. Rotkin, “Charge impurity as a localization center for singlet excitons in single-wall nanotubes”, Phys. Rev. B 86, 125431 (2012). [2] B. Sofka, SV. Rotkin, “Nanotube exciton-antenna polaritons”, in preparation. This research is supported by the NSF ECCS-1509786. Fig. 1. Spectral current density distribution for an excitonic SWCNT emitter: 1d-current density is plotted vs. axial coordinate of a 50 nm long nanotube and vs. the frequency of excitation (in energy units). Figure 1

Understanding the co-loading and releasing of doxorubicin and paclitaxel using chitosan functionalized single-walled carbon nanotubes by molecular dynamics simulations.

Two widely used anticancer drugs, doxorubicin (DOX) and paclitaxel (PTX), possess distinct physical properties and chemotherapy specificity. In order to investigate their interaction mechanism with single-walled carbon nanotubes (SWCNTs), co-loading and releasing from the SWCNTs, all-atom molecular dynamics (MD) simulations were firstly carried out for different SWCNT systems, followed by binding free energy calculation with MM-PBSA. The results indicate that the co-loading of DOX and PTX onto the pristine SWCNT is exothermic and spontaneous. The DOX molecules predominantly interact with the SWCNT via π-π stacking through the conjugated aromatic rings, while the separated aromatic rings of PTX also primarily interact with the SWCNT through π-π stacking yet supplemented by an X-π (X = C-H, N-H and C[double bond, length as m-dash]O) interaction. Moreover, the strongest binding of DOX and PTX with the pristine SWCNT shows similar strength (ΔG: -32.0 vs. -33.8 kcal mol-1). For the chitosan functionalized SWCNT (f-SWCNT), the DOX and PTX molecules still prefer binding to the sidewall of the CNT rather than binding with the polymer, and the non-covalent functionalization of the SWCNT with chitosan decreases the binding of DOX and PTX with the sidewall of the f-SWCNT as compared with the DOX/PTX-SWCNT system (ΔG: -24.0 and -21.9 kcal mol-1). The protonation of chitosan and drug molecules further weakens the interaction between DOX/PTX and the f-SWCNT, and shows a consequent displacement of the drug molecules, triggering the release of the drugs. The variation of binding strength of the three systems (DOX/PTX-SWCNT, DOX/PTX-f-SWCNT, and DOXH+/PTXH+-f-SWCNT) was also discussed in terms of the histogram or frequency of the distance from the drugs to the SWCNT. In addition, the encapsulation of two DOX molecules by the f-SWCNT is considerably stronger than the binding of the other six drug molecules to the sidewall, indicating that the encapsulation of anticancer drugs may also play a very important role and should be considered in the drug delivery.

A Computational Study of a Single-Walled Carbon-Nanotube-Based Ultrafast High-Capacity Aluminum Battery.

Exploring suitable electrode materials is a fundamental step toward developing Al batteries with enhanced performance. In this work, we explore using density functional theory calculations the feasibility of single-walled carbon nanotubes (SWNTs) as a cathode material for Al batteries. Carbon nanotubes with hollow structures and large surface area are able to overcome the difficulty of activating the opening of interlayer spaces as observed in graphite electrode during the first intercalation cycle. Our results show that AlCl4 binds strongly with the SWNT to result in an energetically and thermally stable AlCl4 -adsorbed SWNT system. Diffusion calculations show that the SWNT system allows ultrafast diffusion of AlCl4 with a more favorable inner surface diffusion than outer surface diffusion. Our charge-density difference and Bader atomic charge analysis confirm the oxidation of SWNT upon adsorption of AlCl4 , which shows a similar behavior to the previously studied graphite cathode. The average open-circuit voltage and AlCl4 storage capacity increases with increasing SWNT diameter and can be as high as 1.96 V and 275 mA h g-1 in (25,25) SWNT relative to graphite (70 mA h g-1 ). All of these properties show that SWNTs are a potential cathode material for high-performance Al batteries and should be explored further.

Low-Dimensional Carbon Allotropes: Ground- and Excited-State Charge Transfer with NIR-Absorbing Heptamethine Cyanine

Summary At the focal point of our studies are mutual interactions between an anionic heptamethine cyanine and individualized single-walled carbon nanotubes (SWCNTs) or exfoliated nanographene (NG). Here, we report the distinct near-infrared absorption of the heptamethine cyanine, which assists in visualizing the electronic interactions in the ground state with ease and precision. In statistical Raman assays, we conclude from downshifted 2D- and G-modes for SWCNTs, as well as upshifted 2D- and downshifted G-modes for NG, that these electronic interactions result in stable n-doping of SWCNTs and NG. Key to this shift of charge density is the electron-donating character of the heptamethine cyanine. In the excited state, a complete but metastable transfer of charges is accompanied by a radical-ion-pair state that lives for several nanoseconds. Such a time domain has not yet been realized, for example, in NG to date.

Computational comparative study of substitutional, endo and exo BN Co-Doped single walled carbon nanotube system

In this report we investigate the effect of doping on electronic properties of a zig-zag (4, 0) semi-conducting single walled two probe carbon nanotube system by using substitutional, endo and exo doping in the configuration. We choose atoms of elements Boron (B) and Nitrogen (N) because of their similar atomic radii to that of carbon. The Atomistic Tool Kit software (Version 13.8.1) and its graphical interface Virtual Nanolab is used in device mode for simulations. The calculations were carried out by using Huckel Parameters and the comparative study of current-voltage characteristics and conductance of the proposed models were done under low bias conditions. The results show that substitution doping has increased the conductance of the model than endo and exo. However, when the concentration of BN dopants is increased from two atom to four atom the endo doping model shows better performance than other two models. Hence the study is very beneficial for designing various CNT devices for commercial applications including amplifiers and oscillators.

Intrinsic current–voltage characteristics of metal-carbon nanotube networks: A first-principles study

The interconnections involving metal atoms in single-walled carbon nanotube (SWNT) networks are crucial for building nanoscaled devices. The influence of the metal-(η6-SWNT) interconnects in the electrical conductivity of SWNT film have been reported in recent experiments [X. Tian et al. Nano lett. 2014,14,3930]. Using non-equilibrium Green's function with density function theory, we performed theoretical calculations on the electron transport properties of (Cr, Li, Au)-SWNT systems. We revealed the roles of transition metal Cr, alkalis metal Li and inert metal Au in improving the electrical conductance of metal-SWNT systems. Our calculated results show that transport properties along the inter-tube direction are strongly dependent on the connecting metal atoms varying over many orders of magnitudes. Gold atoms fail to enhance the electrical conductance of SWNT systems. Meanwhile, negative differential resistances are demonstrated in semiconducting inter-tube models, which would have potential applications in the electronic device. Our results provide a promising way to optimize the performance of SWNT based networks.

Photoinduced Absorption within Single-Walled Carbon Nanotube Systems

We study the photoabsorption properties of photoactive bulk polymer/fullerene/nanotube heterojunctions in the near-infrared region. By combining pump–probe spectroscopy and linear response time-dependent density functional theory within the random phase approximation (TDDFT-RPA) we elucidate the excited state dynamics of the E11 transition within (6,5) and (7,5) single-walled carbon nanotubes (SWNTs) and combined with poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in P3HT/PCBM/SWNT blended samples. We find the presence of a photoinduced absorption (PA) peak is related mainly to the width of the photobleach (PB) peak and the charge carrier density of the SWNT system. For mixed SWNT samples, the PB peak is too broad to observe the PA peak, whereas within P3HT/PCBM/SWNT blended samples P3HT acts as a hole acceptor, narrowing the PB peak by exciton delocalization, which reveals a PA peak. Our results suggest that the PA peak originates from a widening of the band gap in the presence of excited electrons and holes. These results have important implications for the development of new organic photovoltaic heterojunctions including SWNTs.

Static Analysis of Magnetic Field Affected Double Single Walled Carbon Nanotube System

In this study, a model to obtain the transverse displacement of double single walled carbon nanotube system (DSWNTS) with the application of longitudinal magnetic field has been developed. Here, two magnetically sensitive single walled carbon nanotubes are coupled by an elastic medium. The governing equation for transverse displacement of the system is modeled with the help of a modified couple stress theory. Total minimum potential energy principle is employed using variational formulation to develop the governing equations. This model is then applied to a cantilever beam problem and results are presented. Numerical results reveal that DSWNTS with larger length of CNTs would deflect more. Lesser deflection of DSWNTS is observed as the magnetic field increases. This system gives same transverse displacement for different values of size effect within the range of applied magnetic field. This mathematical model can be used for further dynamic analysis of other numerical or experimental models.

Biocompatible polymers coated on carboxylated nanotubes functionalized with betulinic acid for effective drug delivery.

Chemically functionalized carbon nanotubes are highly suitable and promising materials for potential biomedical applications like drug delivery due to their distinct physico-chemical characteristics and unique architecture. However, they are often associated with problems like insoluble in physiological environment and cytotoxicity issue due to impurities and catalyst residues contained in the nanotubes. On the other hand, surface coating agents play an essential role in preventing the nanoparticles from excessive agglomeration as well as providing good water dispersibility by replacing the hydrophobic surfaces of nanoparticles with hydrophilic moieties. Therefore, we have prepared four types of biopolymer-coated single walled carbon nanotubes systems functionalized with anticancer drug, betulinic acid in the presence of Tween 20, Tween 80, polyethylene glycol and chitosan as a comparative study. The Fourier transform infrared spectroscopy studies confirm the bonding of the coating molecules with the SWBA and these results were further supported by Raman spectroscopy. All chemically coated samples were found to release the drug in a slow, sustained and prolonged fashion compared to the uncoated ones, with the best fit to pseudo-second order kinetic model. The cytotoxic effects of the synthesized samples were evaluated in mouse embryonic fibroblast cells (3T3) at 24, 48 and 72h. The in vitro results reveal that the cytotoxicity of the samples were dependent upon the drug release profiles as well as the chemical components of the surface coating agents. In general, the initial burst, drug release pattern and cytotoxicity could be well-controlled by carefully selecting the desired materials to suit different therapeutic applications.