Neon atoms oscillating inside carbon and boron nitride nanotubes: a fully atomistic molecular dynamics investigation

In the present work, based on extensive fully atomistic molecular dynamics simulations, we discuss the dynamics of neon atoms oscillating inside (5,5) single-walled carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs). Our results show that sustained high-frequency oscillatory regimes are possible for a large range of temperatures. Our results also show that the general features of the oscillations are quite similar to those observed in CNT and BNNT, in contrast with some speculations in previous works in the literature about the importance of broken symmetry and chirality exhibited by BNNTs.     

Can trans-polyacetylene be formed on single-walled carbon-doped boron nitride nanotubes?

Recently, the grafting of polymer chains onto nanotubes has attracted increasing attention as it can potentially be used to enhance the solubility of nanotubes and in the development of novel nanotube-based devices. In this article, based on density functional theory (DFT) calculations, we report the formation of trans-polyacetylene on single-walled carbon-doped boron nitride nanotubes (BNNTs) through their adsorption of a series of C(2)H(2) molecules. The results show that, rather than through [2 + 2] cycloaddition, an individualmolecule would preferentially attach to a carbon-doped BNNT via "carbon attack" (i.e., a carbon in the C(2)H(2) attacks a site on the BNNT). The adsorption energy gradually decreases with increasing tube diameter. The free radical of the carbon-doped BNNT is almost completely transferred to the carbon atom at the end of the adsorbed C(2)H(2) molecule. When another C(2)H(2) molecule approaches the carbon-doped BNNT, it is most energetically favorable for this C(2)H(2) molecule to be adsorbed at the end of the previously adsorbed C(2)H(2) molecule, and so on with extra C(2)H(2) molecules, leading to the formation of polyacetylene on the nanotube. The spin of the whole system is always localized at the tip of the polyacetylene formed, which initiates the adsorption of the incoming species. The present results imply that carbon-doped BNNT is an effective "metal-free" initiator for the formation of polyacetylene.     

Predicting doxorubicin drug delivery by single-walled carbon nanotube through cell membrane in the absence and presence of nicotine molecules: a molecular dynamics simulation study

Abstract

In order to study the interaction of the anticancer agent Doxorubicin with the single-walled carbon nanotubes with different diameters as drug delivery systems, the molecular dynamics (MD) simulations have been used. Also, for design and development of intracellular Doxorubicin drug delivery systems, a series of steered MD simulations are applied to explore the possibility of encapsulated Doxorubicin–carbon nanotube penetration through a lipid bilayer in presence and absence of Nicotine molecules at different pulling rates. Our simulation results showed that in spite of the adsorption of drug molecules on the outer sidewall of the nanotubes, the spontaneous localization of one Doxorubicin molecule into the cavity of the nanovectors with larger diameters is observed. It is found that the presence of Nicotine molecules in extracellular medium increases the required force for pulling nanotube-encapsulated drug as well as the required time for penetration process, especially at higher velocity. Also, the entering process of the Nicotine molecules into the carbon nanotube causes that the encapsulated drug molecule is fully released in the hydrophobic phase of the lipid bilayer.

Communicated by Ramaswamy H. Sarma     

Hydrogen adsorption capacities of multi-walled boron nitride nanotubes and nanotube arrays: a grand canonical Monte Carlo study

Hydrogen adsorption in multi-walled boron nitride nanotubes and their arrays was studied using grand canonical Monte Carlo simulation. The results show that hydrogen storage increases with tube diameter and the distance between the tubes in multi-walled boron nitride nanotube arrays. Also, triple-walled boron nitride nanotubes present the lowest level of hydrogen physisorption, double-walled boron nitride nanotubes adsorb hydrogen better when the diameter of the inner tube diameter is sufficiently large, and single-walled boron nitride nanotubes adsorb hydrogen well when the tube diameter is small enough. Boron nitride nanotube arrays adsorb hydrogen, but the percentage of adsorbed hydrogen (by weight) in boron nitride nanotube arrays is rather similar to that found in multi-walled boron nitride nanotubes. Also, when the Langmuir and Langmuir-Freundlich equations were fitted to the simulated data, it was found that multi-layer adsorptivity occurs more prominently as the number of walls and the tube diameter increase. However, in single-walled boron nitride nanotubes with a small diameter, the dominant mechanism is monolayer adsorptivity.     

Molecular insight into adsorption affinities of Carmustine drug on boron and nitrogen doped functionalized single-walled carbon nanotubes using density functional theory including dispersion correction calculations and molecular dynamics simulation

Abstract

We report a quantum mechanics calculation and molecular dynamics simulation study of Carmustine drug (BNU) adsorption on the surface of nitrogen (N) and boron (B) doped-functionalized single-walled carbon nanotubes. The stability of the optimized complexes is determined on the basis of relative adsorption energy (ΔE_ads). The ΔE_ads results claim that drug molecule tends to adsorb on the nitrogen and boron doped functionalized tubes with the energy values in the range of ?61.177 to ?95.806?kJ/mol. Based on the obtained results, it is observed that N-doping compared with B-doping has improved more effectively drug absorption on the surface of functionalized nanotube. The results of Atoms in Molecule calculations indicate that drug adsorbs molecularly via hydrogen bonds interactions on the surface doped-functionalized carbon nanotubes. Moreover, molecular dynamics simulation is performed to investigate the dynamics behavior of the drug molecules on the nitrogen-doped functionalized carbon nanotube (f-NNT) and functionalized carbon nanotube (f-CNT). The higher average calculated electrostatic and van der Waals energies as well as higher number of intermolecular hydrogen bonds in BNU-f-NNT in comparison with BNU-f-CNT model suggest the more effectual interaction between drug molecules and nitrogen-doped functionalized carbon nanotube.

Communicated by Ramaswamy H. Sarma     

Molecular dynamics simulation of doxorubicin adsorption on a bundle of functionalized CNT

In this study, molecular dynamics simulation is used to investigate the adsorption of an anticancer drug, doxorubicin, on bundles of functionalized single-walled carbon nanotubes (SWNTs) in an aqueous solution. Carboxylic group has been selected as the functional group. Molecular dynamics (MD) simulations are performed for both separated systems containing a SWNT bundle and a functionalized carbon nanotube bundle, and results are compared with existing experimental data. MD results show that doxorubicin can be adsorbed on CNTs using different methods such as entrapment within CNT bundle, attachment to the side wall of the CNT, and adsorption on the CNT inner cavity. For functionalized CNT, the adsorption of drugs on the functional groups is essential for predicting the enhancement of drug loading on the functionalized nanotubes. Furthermore, the adsorption behavior of doxorubicin on CNTs is fitted with Langmuir and Freundlich isotherm models. The results show that Langmuir model can predict the adsorption behavior of doxorubicin on CNTs more accurately than Freundlich model does. As predicted by this isotherm model, the adsorption process of doxorubicin on CNTs is relatively difficult, but it can be improved by increasing the functional groups on the CNTs surface.     

DFT and MD study of adsorption sensitivity of aluminium phosphide nanotube towards some air pollutant gas molecules

To investigate the adsorption behaviour of CS₂, CO₂, SO₂, H₂Se and H₂S gas molecules on the external surface of (6, 0) single-walled aluminium phosphide nanotube (AlPNT), the density functional theory (DFT) calculations at the B3LYP level of theory are performed. The partial densities of states (PDOS) for the SO₂ molecule, the S and O atoms of SO₂ molecule before and after adsorption on the surface of AlPNT have been plotted. The vibrational frequencies and physical properties such as chemical potential, chemical hardness, dipole moment and chemical electrophilicity of all studied complexes have been systematically investigated. The electron density and the Laplacian of the electron density for bond critical points have been examined by the AIM theory. Also the molecular dynamics (MD) simulations of two complexes with the minimum and maximum negative interaction energies that is: AlPNT/CO₂ and AlPNT/SO₂ complexes, respectively, have been considered.     

Molecular dynamics simulation of single-walled carbon nanotubes inside liquid crystals

Molecular dynamic simulations of systems of single-walled carbon nanotubes (CNTs) in liquid crystalline solvents were performed, in order to investigate the effect of the molecular structure and phase of the liquid crystal (LC) on the interactions between the CNTs. Three different LC molecules (5CB, 8CB and 5CF) were considered in our study. Our results with 5CB and 8CB suggest that increasing the chain length of the hydrophobic part of the LC molecule by three carbon atoms is insufficient to decrease the tendency for the CNTs to aggregate in the LCs. Additionally, varying the phase of the LC is also insufficient to decrease the aggregation tendency of the CNTs. However, simulations with 5CF (which has fluorine atoms in the head group of the LC molecule) suggest that this LC solvent can decrease the tendency of the CNTs to aggregate. This study is relevant to assist experimentalists with the development of high-quality dispersions of large concentrations of CNTs in the LCs.     

Accurate prediction of emission energies with TD-DFT methods for platinum and iridium OLED materials

Journal of Molecular Modeling - In this work we use the ab initio calculations to study the intercalation of lithium (Li) atoms in the channels of the single-wall boron nitride nanotube (BNNT)...     

Boron nitride nanotube based nanosensor for acetone adsorption: a DFT simulation

We have investigated the adsorption properties of acetone on zigzag single-walled BNNTs using density functional theory (DFT) calculations. The results obtained show that acetone is strongly bound to the outer surface of a (5,0) BNNT on the top site directly above the boron atom, with a binding energy of ?96.16 kJ?mol^?1 and a B–O binding distance of 1.654 Å. Our first-principles calculations also predict that the ability of zigzag BNNTs to adsorb acetone is significantly stronger than the corresponding ability of zigzag CNTs. A comparative investigation of BNNTs with different diameters indicated that the ability of the side walls of the tubes to adsorb acetone decreases significantly for nanotubes with larger diameters. Furthermore, the stability of the most stable acetone/BNNT complex was tested using ab initio molecular dynamics simulation at room temperature.

Molecular dynamics simulation study for diffusion of Na+ ion in water-filled carbon nanotubes at 25°C

We present results of molecular dynamics simulations for diffusion of Na⁺ ion in water-filled carbon nanotubes (CNTs) at 25°C using the extended simple point charge water potential. Simulation results indicate the general trend that the diffusion coefficients of Na⁺ ion and water molecule in CNTs decrease with an increase in water density and are larger than those in the bulk solution. The average potential energies of ion–water and water–water, the radial distribution functions, the hydration numbers and the residence times of the hydrated water molecules are discussed. The classical solventberg picture describes Na⁺ ion in water adequately for systems with the small values of diffusion coefficients.     

Theoretical study on the encapsulation of Pd3-based transition metal clusters inside boron nitride nanotubes

Chemical functionalization of the boron nitride nanotube (BNNT) allows a wider flexibility in engineering its electronic and magnetic properties as well as chemical reactivity, thus making it have potential applications in many fields. In the present work, the encapsulation of 13 different Pd₃M (M?=?Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Pt, and Au) clusters inside the (10, 0) BNNT has been studied by performing comprehensive density functional theory (DFT) calculations. Particular attention is paid to searching for the stable configurations, calculating the corresponding binding energies, and evaluating the effects of the encapsulation of Pd₃M cluster on the electronic and magnetic properties of BNNT. The results indicate that all the studied Pd₃M clusters can be stably encapsulated inside the (10, 0) BNNT, with binding energies ranging from ?0.96 (for Pd₃Sc) to ?5.31 eV (for Pd₃V). Moreover, due to a certain amount of charge transfer from Pd₃M clusters to BNNT, certain impurity states are induced within the band gap of pristine BNNT, leading to the reduction of the band gap in various ways. Most Pd₃M@BNNT nanocomposites exhibit nonzero magnetic moments, which mainly originate from the contribution of the Pd₃M clusters. In particular, the adsorption of O₂ molecule on BNNT is greatly enhanced due to Pd₃M encapsulation. The elongation of O-O bonds of the adsorbed O₂ molecules indicates that Pd₃M@BNNT could be used to fabricate the oxidative catalysis.     

Effect of the Si,Al and B doping on the sensing behaviour of carbon nanotubes toward ethylene oxide: a computational study

ABSTRACT

Exo– and endo–adsorption of ethylene oxide (EO) on pristine (9,0) (zigzag) carbon nanotube (CNT) and its doped forms with silicon (Si–CNT), aluminum (Al–CNT) and boron (B–CNT) were investigated using density functional theory (DFT) at M06–2X/6–311++G** level. The natural bond orbital (NBO) and the quantum theory of atoms in molecules (QTAIM) analyses were also performed by using the same level of theory. The effect of the doping on sensing behaviour of the CNT toward EO molecule was investigated through intermolecular interactions studies by calculation of total and partial density of states (DOS, PDOS). The enhanced sensitivity of doped–CNTs towards EO molecule associated with adsorption energies (E_ads) and the changes in geometric and electronic structures was examined and the global chemical reactivity parameters were calculated and comprehensively analysed. The thermodynamic property changes were calculated and compared. The results indicated that the EO adsorption on the pristine and doped CNTs was an exothermic spontaneous process. Moreover, based on the calculated E_g change (ΔE_g) and E_ads values, Al–CNT with superior sensitivity for sensing of EO molecule, indicates promising perspectives for its use in fabrication of new EO gas–sensing devices.     

Monte Carlo simulation of intercalated carbon nanotubes

Monte Carlo simulations of the single- and double-walled carbon nanotubes (CNT) intercalated with different metals have been carried out. The interrelation between the length of a CNT, the number and type of metal atoms has also been established. This research is aimed at studying intercalated systems based on CNTs and d-metals such as Fe and Co. Factors influencing the stability of these composites have been determined theoretically by the Monte Carlo method with the Tersoff potential. The modeling of CNTs intercalated with metals by the Monte Carlo method has proved that there is a correlation between the length of a CNT and the number of endo-atoms of specific type. Thus, in the case of a metallic CNT (9,0) with length 17 bands (3.60 nm), in contrast to Co atoms, Fe atoms are extruded out of the CNT if the number of atoms in the CNT is not less than eight. Thus, this paper shows that a CNT of a certain size can be intercalated with no more than eight Fe atoms. The systems investigated are stabilized by coordination of 3d-atoms close to the CNT wall with a radius-vector of (0.18–0.20) nm. Another characteristic feature is that, within the temperature range of (400–700) K, small systems exhibit ground-state stabilization which is not characteristic of the higher ones. The behavior of Fe and Co endo-atoms between the walls of a double-walled carbon nanotube (DW CNT) is explained by a dominating van der Waals interaction between the Co atoms themselves, which is not true for the Fe atoms.     

First-principles simulations of the chemical functionalization of (5,5) boron nitride nanotubes

We perform density functional theory studies to investigate structural and electronic properties of the (5,5) boron nitride nanotubes (BNNTs) with surfaces and ends functionalized by thiol (SH) and hydroxyl (OH) groups. The exchange-correlation energies are treated according to the functional of Hamprecht-Cohen-Tozer-Handy within the generalized gradient approximation (HCTH-GGA). We use the base function with double polarization DNP. To determine the (5,5) BNNT-SH and (5,5) BNNT-OH relaxed structures the minimum energy criterion is applied considering six different geometries depending upon the SH and OH functional groups orientation: (C1) The adsorbed functional group is oriented toward the N atom, (C2) the functional group is oriented toward the B atom, (C3) the functional group is at the central hexagon of the BNNT surface. The (C4) fourth and (C5) fifth configurations are formed by allowing bonds (of S or O) with B or N atoms at one end of the nanotube. (C6) The sixth geometry is obtained by placing the functional group at the center of one end of the BNNT. The (5,5) BNNT-SH system, in vacuum, suffers a semiconductor to metal transition while the (5,5) BNNT-OH system retains the semiconductor behavior. When structures are solvated in water these systems behave as semiconductors. The polarity increases as a consequence of the functional group-nanotube interactions no matter if they are in vacuum or in solvation situation, which indicates the possible solubility and dispersion. According to the work function the best option to construct a device is with the BNNT-OH system.     

Sensing behavior of Al-rich AlN nanotube toward hydrogen cyanide

In order to explore a sensor for detection of toxic hydrogen cyanide (HCN) molecules, interaction of pristine and defected Al-rich aluminum nitride nanotubes (AlNNT) with a HCN molecule has been investigated using density functional theory calculations in terms of energetic, geometric, and electronic properties. It has been found that unlike the pristine AlNNT, the Al-rich AlNNT can effectively interact with the HCN molecule so that its conductivity changes upon the exposure to this molecule. The adsorption energies of HCN on the pristine and defected AlNNTs have been calculated to be in the range of ?0.16 to ?0.62 eV and ?1.75 to ?2.21 eV, respectively. We believe that creating Al-rich defects may be a good strategy for improving the sensitivity of these tubes toward HCN molecules, which cannot be trapped and detected by the pristine AlNNT.     

Cytotoxicity of doxrubicin loaded single-walled carbon nanotubes

Carbon nanotube (CNTs) is a new alternative for efficient drug delivery and it has a great potential to change drug delivery system profile in pharmaceutical industry. One of the important advantage of CNTs is their needle-like, cylindrical shape. This shape provides a high surface area for multiple connections and adsorption onto for millions of therapeutic molecules. CNTs can be internalized by cells via endocytosis, passive diffusion and phagocytosis and release the drug with different effects like pH and temperature. The acidic nature of cancer cells and the susceptibility of CNTs to release the drug in the acidic environment have made it a promising area of research in cancer drug delivery. In this research, we investigated cell viability, cytotoxicity and drug delivery in breast cancer cell line by designing non-covalent single walled carbon nanotubes (SWNT)–doxorubicin (DOX) supramolecular complex that can be developed for cancer therapy. Applied high concentrations of DOX loaded SWNTs changed the actin structure of the cells and prevented the proliferation of the cells. It was showed that doxorubicin loaded SWNTs were more effective than free doxorubicin at relatively small concentrations. Once we applied same procedure for short and long (short: 1–1.3 µm; long: 2.5–4 µm) SWNTs and compared the results, more disrupted cell structure and reduction in cell proliferation were observed for long CNTs. DOX is bounded more to nanotubes in basic medium, less bound in acidic environment. Cancer cells were also examined for concentration at which they were effective by applying DOX and it was seen that 3.68 µM doxorubicin kills more than 55% of the cells.     

On the vibrational behavior of single- and double-walled carbon nanotubes under the physical adsorption of biomolecules in the aqueous environment: a molecular dynamics study

The adsorption of biomolecules on the walls of carbon nanotubes (CNTs) in an aqueous environment is of great importance in the field of nanobiotechnology. In this study, molecular dynamics (MD) simulations were performed to understand the mechanical vibrational behavior of single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) under the physical adsorption of four important biomolecules (L-alanine, guanine, thymine, and uracil) in vacuum and an aqueous environment. It was observed that the natural frequencies of these CNTs in vacuum reduce under the physical adsorption of biomolecules. In the aqueous environment, the natural frequency of each pure CNT decreased as compared to its natural frequency in vacuum. It was also found that the frequency shift for functionalized CNTs as compared to pure CNTs in the aqueous environment was dependent on the radius and the number of walls of the CNT, and could be positive or negative.     

Methane storage in homogeneous armchair open-ended single-walled boron nitride nanotube triangular arrays: a grand canonical Monte Carlo simulation study

The physisorption of methane in homogeneous armchair open-ended SWBNNT triangular arrays was evaluated using grand canonical ensemble Monte Carlo simulation for tubes 11.08, 13.85, 16.62, and 19.41 ? [(8,8), (10,10), (12,12), and (14,14), respectively] in diameter, at temperatures of 273, 298, 323, and 373 K, and at fugacities of 0.5-9.0 Mpa. The intermolecular forces were modeled using the Lennard-Jones potential model. The absolute, excess, and delivery adsorption isotherms of methane were calculated for the various boron nitride nanotube arrays. The specific surface areas and the isosteric heats of adsorption, Q(st), were also studied, different isotherm models were fitted to the simulated adsorption data, and the model parameters were correlated. According to the results, it is possible to reach 108% and 140% of the US Department of Energy's target for CH(4) storage (180 v/v at 298 K and 35 bar) using the SWBNNT array with nanotubes 16.62 and 19.41 ? in diameter, respectively, as adsorbent. The results show that for a van der Waals gap of 3.4 ?, there is no interstitial adsorption except for arrays containing nanotubes with diameters of >15.8 ?. Multilayer adsorption starts to occur in arrays containing nanotubes with diameters of >16.62 ?, and the minimum pressure required for multilayer adsorption is 1.0 MPa. A brief comparison of the methane adsorption capacities of single-walled carbon and boron nitride nanotube arrays was also performed.     

Molecular simulation of carbon nanotubes as sorptive materials: sorption effects towards retene,perylene and cholesterol to 100 degrees Celsius and above

New water purification technologies are being developed as the world’s water sources are increasingly being polluted and experience a dramatic consumption with the increasing world population. In this context, the emerging era of nanotechnology has introduced a series of innovations and materials with promising potential as sorptive materials for water decontamination. The application of nanomaterials for the purification of ground/surface water introduces nevertheless a series of important challenges, such as health and safety, cost, process-efficiency and chemical sorption properties. In this study, we consider the latter class and present a study of the sorptive properties of carbon nanotubes (CNTs) as potential water decontaminating materials. Molecular dynamics simulations are used and three molecular candidates of the water contaminants, cholesterol, perylene and retene were selected for interaction study with CNTs at different diameters. The results show that CNTs form densely packed clusters with retene, perylene and cholesterol, binding each strongly to their tubular surfaces, as well as in their hollow tubular spaces. Cholesterol and perylene bind more strongly than retene, accounting for the calculated binding energies in vacuo, however the planar geometries of polycyclics may in general favour binding to CNTs over semi-polar molecules and can require further studies. Our studies show furthermore that the CNTs retain the adsorbed molecules also at 100 degrees Celsius, and require therefore additional steps of separation for eventual recycling and reusing the nanomaterials for additional decontamination. This study is important in providing data for initiating studies and developments of water purification approaches based on using CNTs.