Polyoxometalate ionic liquid between graphene oxide surfaces as a new membrane in the desalination process: a molecular dynamics study.

In this study, the performance of the positioning of polyoxometalate ionic liquid ([Keggin][emim]3 IL) between graphene oxide (GO) plates with different concentrations (nIL-GO (n = 1-4)) were examined in the desalination process at different external pressures using molecular dynamics (MD) simulations. The use of Keggin anions with charged GO layers was also investigated in the desalination process. The potential of the mean force, average number of hydrogen bonds, self-diffusion coefficient, and angle distribution function were calculated and discussed. The results showed that although the presence of polyoxometalate ILs between the GO plates decreases water flux, they efficiently increase salt rejection. The positioning of one IL increases salt rejection to two times at lower pressure and increases it up to four times at higher pressure. Moreover, the positioning of four ILs results in almost complete salt rejection at all pressures. The use of only Keggin anions between the charged GO plates (n[Keggin]-GO+3n) presents more water flux and a smaller salt rejection rate than the nIL-GO systems. However, the n[Keggin]-GO+3n systems show a nearly complete salt rejection at high concentrations of Keggin anions. These systems also have a smaller risk of the contamination of the desalinated water by the probable escape of cations from the nanostructure to the desalinated water at very high pressures.

Structure, dynamics, and morphology of nanostructured water confined between parallel graphene surfaces and in carbon nanotubes by applying magnetic and electric fields.

Water molecules experience certain changes in their properties when they feel an external magnetic or electric field. These changes are significant in different applications, such as biological and biotechnological processes, nano-pumping, and water treatment. In this work, we have performed molecular dynamics (MD) simulations to investigate the different thermodynamics, structure, and dynamics of water molecules confined between two parallel surfaces and also confined in carbon nanotubes (CNTs). We have also applied different electric and magnetic fields in different directions to the confined molecules. In the graphene system, no polygonal shape was formed in either low or high electric fields, whereas rhombic and pentagonal shapes were formed in low and high magnetic fields. In the CNT system, applying electric fields in all three dimensions made the pentagonal shape disappear and the confined water molecules formed a ring shape when the electric field was applied in the axial direction. Applying the electric field perpendicular to the graphene surfaces increases the self-diffusion of the confined molecules, whereas applying the electric and magnetic fields along the CNT axis decreases the self-diffusion of the confined water molecules. In the graphene system, applying the electric field perpendicular to the graphene surfaces decreases the average number of hydrogen bonds (〈HB〉) whereas the magnetic field has little effect on the 〈HB〉. In the CNT system, applying Ex also leads to a smaller number of HBs. Also, applying the magnetic field along the x-direction (along the CNT direction) leads to a greater number of HBs than the other fields.

Molecular dynamics simulation of anticancer drug delivery from carbon nanotube using metal nanowires.

In this study, we have investigated delivery of cisplatin as the anticancer drug molecules in different carbon nanotubes (CNTs) in the gas phase using molecular dynamics simulation. We examined the shape and composition of the releasing agent by using the different nanowires and nanoclusters. We also investigated the doping effect on the drug delivery process using N-, Si, B-, and Fe-doped CNTs. Different thermodynamics, structural, and dynamical properties have been studied by using the pure and different doped CNTs in this study. Our results show that the doping of the CNT has significant effect on the rate of the drug releasing process regardless of the composition of the releasing agent. © 2019 Wiley Periodicals, Inc.

Molecular dynamics simulation of liquid water and ice nanoclusters using a new effective HFD-like model.

We have determined a new two-body interaction potential of water by the inversion of viscosity collision integrals of water vapor and fitted to achieve the Hartree-fock dispersion-like (HFD-like) potential function. The calculated two-body potential generates the thermal conductivity, viscosity, and self-diffusion coefficient of water vapor in an excellent accordance with experimental data at wide temperature ranges. We have also used a new many-body potential as a function of temperature and density with the HFD-like pair-potential of water to improve the two-body properties better than the SPC, SPC/E, TIP3P, and TIP4P models. We have also used the new corrected potential to simulate the configurational energy and the melting temperatures of the (H2 O)500 , (H2 O)864 , (H2 O)2048 , and (H2 O)6912 ice nanoclusters in good agreement with the previous simulation data using the TIP4P model. The extrapolated melting point at the bulk limit is also in better agreement with the experimental bulk data. The self-diffusion coefficients for the ice nanoclusters also simulated at different temperatures. © 2017 Wiley Periodicals, Inc.

Pt-Co nanocluster in hollow carbon nanospheres.

Recently, it has been reported that small Pt/Co bimetallic nanoclusters into hollow carbon spheres (HCS) show outstanding catalytic performances in deriving biomass fuels due to the small particle size and the homogeneous alloying. Thus, the knowledge about the thermal evolution and stability of the nanoclusters into the HCS has a great importance. We have simulated the heating process beyond the melting point for the bare and encapsulated Pt/Co clusters into the HCS with the different sizes of 55, 147, and 309. The different thermodynamic and structural properties of the nanoclusters have also been investigated in this work. Our results show that the nanoclusters are more stable into the HCS than the bare clusters. The melting points of the supported clusters are also higher than the unsupported clusters. The confined nanoclusters have also lower excess energy values than the bare clusters which means that the encapsulation of Pt/Co nanoclusters into the HCS is favorable. The structural investigations show that a core-shell structure cannot be observed for the different supported and unsupported clusters and the initial mixed structure of the different nanoclusters remains also at the melting points. To more investigate this claim, the radial chemical distribution function (RCDF) and radial distribution function (RDF) of the bare and encapsulated clusters have also been calculated and discussed. © 2018 Wiley Periodicals, Inc.

Delivery of Cisplatin Anti-Cancer Drug from Carbon, Boron Nitride, and Silicon Carbide Nanotubes Forced by Ag-Nanowire: A Comprehensive Molecular Dynamics Study.

In this work, liberation of cisplatin molecules from interior of a nanotube due to entrance of an Ag-nanowire inside it was simulated by classical molecular dynamics method. The aim of this simulation was investigation on the effects of diameter, chirality, and composition of the nanotube, as well as the influence of temperature on this process. For this purpose, single walled carbon, boron nitride, and silicon carbide nanotube were considered. In order for a more concise comparison of the results, a new parameter namely efficiency of drug release, was introduced. The results demonstrated that the efficiency of drug release is sensitive to its adsorption on outer surface of the nanotube. Moreover, this efficiency is also sensitive to the nanotube composition and its diameter. For the effect of nanotube composition, the results indicated that silicon carbide nanotube has the least efficiency for drug release, due to its strong drug-nanotube. Also, the most important acting forces on drug delivery are van der Waals interactions. Finally, the kinetic of drug release is fast and is not related to the structural parameters of the nanotube and temperature, significantly.

Competition between stability of icosahedral and cuboctahedral morphologies in bimetallic nanoalloys.

In this study, we investigated the heating process for pure (Rh55 and Cu55), single dopant (Rh1Cu54 and Rh54Cu), core@shell (Rh13@Cu42 and Cu13@Rh42), and alloy (Rh13Cu42, Rh42Cu13) nanoclusters in two structures (cuboctahedral and icosahedral) from 0 to 2000 K using molecular dynamics (MD) simulations. Our aim was to investigate the effects of composition and chemical arrangement on the kinetic and thermodynamic stability of Rh-Cu bimetallic nanoalloys. Our results indicated that Cu55, Ir55, Rh1Cu54, Rh54Cu, and Cu13@Rh42 in the cuboctahedral and icosahedral structures and Rh42Cu13 in the icosahedral structure did not experience any transformation with the exception of melting. It was also observed that the cuboctahedral Rh42Cu13 shows a solid-solid transformation to the icosahedral structure before the melting point. It is also observed that Rh13@Cu42 and Rh13Cu42 nanoclusters in both structures exhibit a transition to a pseudo-spherical structure before the melting point. Our results also illustrated that the Rh and Cu atoms tend to lie in the inner and outer shells of the nanoclusters, respectively. We have also discussed the changes in the melting points of the doped nanoclusters in the different arrangements.

Phase transition in crown-jewel structured Au-Ir nanoalloys with different shapes: a molecular dynamics study.

We have studied the melting process for crown-jewel structured Ir55, Ir54Au, Ir43Au12, Ir25Au30, Ir13Au42, and Au55 nanoclusters in the icosahedral, Ir55, Ir54Au, Ir43Au12, Ir19Au36, Ir13Au42, and Au55 nanoclusters in the cuboctahedral, and Ir54, Ir53Au, Ir47Au7, Ir17Au37, Ir7Au47, and Au54 nanoclusters in the decahedral morphologies. We have investigated the different thermodynamic, structural, and dynamical properties for the different nanoclusters in the different structures. Our thermodynamic results indicated that as the concentration of Au atoms in the nanoclusters increases, the absolute value of internal energy, and so the melting points, of the nanoclusters decrease. It is also shown that the Au atoms decrease the melting temperature of the pure cuboctahedral cluster more than that of the other structures. We have also found that the Au atoms were located in favorable positions at the surface sites of nanoalloys. Also, the doping of the Ir nanocluster by Au atoms makes the cluster more stable. It is also found that nanoclusters with different morphologies have almost the same stability. Our structural results indicated that after the melting process, the Au atoms generally tend to lie in the outer shell of the cluster, but the Ir atoms generally tend to lie in the core of the cluster (see the Ir13Au42 and Ir7Au47 nanoclusters, for example). We have also found the interesting result that the Ir7Au47 nanocluster shows a solid-solid transition from a decahedral structure to an icosahedral structure before melting. The Ir43Au12 nanocluster also shows a transformation from a cuboctahedral structure to an icosahedral-like structure before melting. Our dynamical results showed that doping of the Ir55 cluster with an Au atom sharply increases the self-diffusion coefficient in the initial state in the solid phase, especially in icosahedral and cuboctahedral structures. It is also shown that the Ir13Au42 cluster in icosahedral and cuboctahedral and the Ir7Au47 and Ir17Au37 clusters in decahedral morphologies have smaller values of self-diffusion coefficients than other clusters after the melting point and that this could be due to the formation of core-shell structures.

A molecular dynamics study of the effect of the substrate on the thermodynamic properties of bound Pt-Cu bimetallic nanoclusters.

In this work confinement of the Pt708Cu707 bimetallic nanocluster in single-walled carbon, boron nitride, and silicon carbide nanotubes was investigated using molecular dynamics simulation. The results of the calculations showed that at 50% composition, a eutectic-like behavior is seen during the melting-freezing process. Also, the Pt708Cu707 bimetallic nanocluster tends to have a core-shell like structure with a Pt-rich core and a Cu-rich shell, except for boron nitride nanotubes in which the nanocluster exhibits a completely different pattern on the tube wall. The Pt-Cu nanoclusters confined in boron nitride nanotubes are extremely extended on the tube wall in such a way that most of the nanotube-nanocluster interface is covered by a monolayer metal coating which can promise unique physical and chemical properties for these types of nanocomposites. Also, extension of the nanocluster on the substrate surface reduces its melting point.

Investigation of thermodynamic, dynamic, and structural properties of H2 adsorption on a Ag-Au nanoalloy with a carbon nanotube support.

We have performed MD simulations to investigate H(2) adsorption on Ag-Au nanoclusters with the different Au mole fractions supported on the carbon nanotubes with the different diameters. Our thermodynamic results shown that the saturation value of coverage and the enthalpy of adsorption increases as the mole fraction of Au is increased. Our structural results showed that the presence of the H(2) gas exerts a significant effect on the nanocluster surface atoms and tends to stabilize the surface atoms on the nanocluster. Also, the structural changes are irreversible in such a way that by gradually decreasing the pressure to zero, the nanocluster geometry is not reversed to its initial structure in vacuum conditions. We have also shown that the nanoclusters have smaller values of the self-diffusion coefficients in presence of H(2) molecules than those values in the initial state (vacuum), which is due to the increasing of the interface structure between the nanocluster and the nanotube.

Investigation of thermal evolution of copper nanoclusters encapsulated in carbon nanotubes: a molecular dynamics study.

We have studied the heating and cooling processes of CuN nanoclusters encapsulated in CNTs with different diameters and chiralities in the range of 100-1700 K. We have investigated all of the possible effects: the effects of the nanocluster size, CNT diameter, and CNT chirality on the thermodynamic, structural, and dynamic properties during the melting process. Our thermodynamic results showed that the melting temperatures of the confined nanoparticles tend to increase with the nanoparticle size. Our energy results also showed that the melting temperature of the nanocluster decreases upon decreasing the CNT diameter, which is due to the greater nanocluster-CNT wall interactions in the smaller nanotube which make the cluster to expand more easily on the interface. The results also showed that the encapsulation of the nanocluster in the zigzag CNT has lower energy values than the armchair one, which is due to the greater interaction of the nanocluster and the zigzag CNT wall. We have also recognized a hysteresis in the course of the cooling process, which can be due to the fact that the nanoclusters and the nanotube make a coherent interface structure with more stability. Using the radial distribution function, it has been shown that the structural change with temperature is irreversible. Our dynamical results indicated that the bigger nanocluster has slower dynamics than the smaller cluster. It is also shown that the nanocluster on the smaller and zigzag CNTs has slower dynamics than the bigger and armchair tubes.

Investigation of small inhibitor effects on methane hydrate formation in a carbon nanotube using molecular dynamics simulation.

In this work, we simulated water molecules in fixed and rigid (15,0) CNTs and the confined water molecules formed a hexagonal ice nanotube in the CNT. After the addition of methane molecules in the nanotube, the hexagonal structure of confined water molecules disappeared and were replaced by almost all the guest methane molecules. The replaced molecules formed a row of water molecules in the middle of the hollow space of the CNT. We also added five small inhibitors with different concentrations (0.8 mol% and 3.8 mol%) to methane clathrates in CNT: benzene, 1-ethyl-3-methylimidazolium chloride ionic liquid ([emim+][Cl-] IL), methanol, NaCl, and tetrahydrofuran (THF). We investigated the thermodynamic and kinetic inhibition behaviors of the different inhibitors on the methane clathrate formation in the CNT using the radial distribution function (RDF), hydrogen bonding (HB), and angle distribution function (ADF). Our results showed that the [emim+][Cl-] IL is the best inhibitor from both aspects. It was also shown that the effect of THF and benzene is better than that of NaCl and methanol. Furthermore, our results showed that the THF inhibitors tended to aggregate in the CNT, but the benzene and IL molecules were distributed along the CNT and can affect the inhibitor behavior of THF in the CNT. We have also examined the effect of CNT chirality using the armchair (9,9) CNT, the effect of CNT size using the (17,0) CNT, and the effect of CNT flexibility using the (15,0) CNT by the DREIDING force field. Our results showed that the IL has stronger thermodynamic and kinetic inhibition effects in the armchair (9,9) and the flexible (15,0) CNT than the other systems, respectively.

Investigation of thermodynamics, and structural, dynamical, and electrical properties of polyoxometalate ionic liquid confined into carbon nanotubes during the melting process using molecular dynamics simulation.

Understanding the properties of ionic liquids confined into nano-pores is required to use ionic liquids for many applications such as electrolytes for energy storage in capacitors and solar cells. Recently, polyoxometalate ionic liquids have attracted much attention for their potential applications in electrochemistry, catalysis, and nanotechnology. In this work, we have performed MD simulations on 1-ethyl-3-methylimidazolium Keggin ([emim]3[PW12O40]) confined into armchair (20,20) CNTs to study the thermal properties and melting process. Changes in the simulated results of configurational energy of confined polyoxometallate IL indicated that the melting range of the confined polyoxometalate IL is about 650-750 K. Heat capacity at constant volume of the confined IL is about 2 (cal K-1 mol-1) which shows sharp changes around the melting range. The average number of hydrogen bonds (〈HB〉) of the confined IL is about 2.8 which also presents sharp changes around the melting range. The ion conductivity and self-diffusion coefficient of [emim]3[PW12O40] IL also present a sharp maximum of 25 (S m-1) and 6 × 10-10 (m2 s-1) at the melting point. Our results did not show a significant hysteresis in the melting process and therefore, the process is reversible. Our simulation also indicated that the confinement of the polyoxometallate IL into the CNT increases its thermal stability and melting point. Our simulations also indicated that the type of CNT configuration has a small effect on the melting point of the confined polyoxometallate IL.

Phase transitions in nanostructured water confined in carbon nanotubes by external electric and magnetic fields: a molecular dynamics investigation.

Applying electric and magnetic fields on water molecules confined in carbon nanotubes (CNTs) has important applications in cell biology and nanotechnology-based fields. In this work, molecular dynamics (MD) simulations were carried out to examine the probable phase transitions in confined water molecules confined in (14,0) CNTs at 300 K by applying different electric and magnetic fields in the axial direction. We have also studied some thermodynamics and structural properties of the confined water molecules in the different fields. Our results showed that the confined water molecules experience. Some phase (shape) transitions from the pentagonal to twisted pentagonal, spiral and circle-like shapes by increasing the electric field from 104 (V m-1) to 107 (V m-1). Also, applying the magnetic field with different intensities has small effects on the pentagonal shape of confined water molecules but applying the highest magnetic field (300 T) makes the pentagonal shape more ordered. These phase transitions have not been reported before. Our results also indicated that the ring-like shapes obtained in the presence of the electric field form more hydrogen bonds (HBs) than the other structures. The phase transitions of confined water molecules have been also proved by radial distribution function (RDF) and angle distribution function (ADF) analyses.

Melting Behavior of Bimetallic and Trimetallic Nanoparticles: A Review of MD Simulation Studies.

In recent years, bimetallic and trimetallic nanoparticles (NPs) have become attractive materials for many researchers especially in the field of catalysis due to their interesting physical and chemical properties. These unique properties arise mainly from simultaneous effects of two different metal atoms in their structure. In this review, recent theoretical studies on these NPs using molecular dynamics simulation are presented. Since investigation of thermodynamic stabilities of metallic NPs is a critical factor in their construction for catalytic applications, our focus in this review is on the thermal stability of bimetallic and trimetallic NPs. The melting behavior of these materials with different atomic arrangements including core-shell, three-shell, crown-jewel, ordered and disordered alloy, and Janus materials are discussed. Other factors including stress, strain, atomic radius, thermal expansion coefficient, cohesive energy, surface energy, size, composition, and morphology are described in detail, because these properties lead to complexity in the melting behavior of bimetallic and trimetallic NPs.

Investigation of the thermal properties of phase change materials encapsulated in capped carbon nanotubes using molecular dynamics simulations.

Due to the high demand for clean, economic, and recyclable energy, phase change materials (PCMs) have received significant attention in recent years. To improve the performance of PCMs, they are confined in micro- and nano-capsules composed of organic or inorganic materials. In this study, encapsulated phase change material (EPCM) systems were constructed with paraffin molecules as the core material and capped carbon nanotubes (CNTs) as the shell. We investigated the effects of different parameters including CNT diameter, length, and chirality and the length of the alkane molecule chain. We also investigated metal nanocluster-enhanced PCM systems via the addition of Cu, Ag, and Al clusters to the EPCM systems. Different thermodynamic, dynamic, and structural properties including configurational energy, melting range, mean square displacement, self-diffusion coefficient, radial distribution function (RDF), and average end-to-end distance of the confined molecules were examined. We also investigated the effect of metal doping in CNT on the different properties of the confined PCM. The results indicated that a longer CNT has a lower melting point than the normal CNT system. It was also observed that the bigger (30,0) CNT, (14,14) armchair CNT, and icosane systems have higher melting ranges than the normal (25,0) system. The metal cluster systems also have a lower starting melting point than the normal system. Furthermore, it was found that the Al cluster system has the lowest starting melting point among the studied systems.

Investigation of solvation of iron nanoclusters in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate using molecular dynamics simulations: Effect of cluster size at different temperatures.

The systems composed of metal nanoclusters in ionic liquids are relevant for applications in lubrication, electrochemical devices, catalysis, and chemical processes. The mechanism of solvation and interactions of these systems are not understood at present. In this work, we have simulated iron nanoclusters with different sizes in ionic liquid 1-butyl-1,1,1-trimethylammonium methane sulfonate [N1114][C1SO3] at two temperatures (300 and 500K) and at atmospheric pressure. We have investigated the effects of cluster size and the temperature on some of the thermodynamics, structural and dynamical properties of the systems. Our results also show that the absolute value of solvation energy increases as the nanocluster size increases. Also the absolute solvation energy increases as the temperature increases. It is also shown that the effect of the cluster size is much more than the effect of the temperature. Our structural investigations indicate at least two shells (a double layer) around the nanocluster and the anions are closer to the cluster surface than the cations. The self-diffusion coefficients of cations, anions, and iron clusters have been also presented and discussed in this work.

Au@void@AgAu Yolk-Shell Nanoparticles with Dominant Strain Effects: A Molecular Dynamics Simulation.

Au@void@AgAu yolk-shell nanoparticles with different morphologies were studied by classical molecular dynamics simulation. The results indicated that all of simulated yolk-shell nanoclusters with ∼3.8 nm size and different morphologies are unstable at room temperature, and collapse of the shell atoms into the void space completely fills it and creates more stable Au@AgAu core-shell structures. Also, it was observed that thermodynamic stabilities of the created core-shell structures strongly depend on the morphology of nanocluster, for which competition between strain and surface energy effects plays the key role in this phenomenon. Within this competition, strain effect is dominant and helps the stability of the created core-shell structure. Herein, the icosahedral nanocluster with the lowest strain effect exhibits the highest thermodynamic stability. By comparing the simulation results with experimental data, it was concluded that the essential factor that controls the stability of these nanoparticles is their size.

Molecular Dynamics Simulation of Argon, Krypton, and Xenon Using Two-Body and Three-Body Intermolecular Potentials.

We have performed the molecular dynamics simulation to obtain energy and pressure of argon, krypton, and xenon at different temperatures using a HFD-like potential which has been obtained with an inversion of viscosity data at zero pressure. The contribution of three-body dispersion resulting from third-order triple-dipole interactions has been computed using an accurate simple relation between two-body and three-body interactions developed by Marcelli and Sadus. Our results indicate that this simple three-body potential which was originally used in conjunction with the BFW potential is also valid when used with the HFD-like potential. This appears to support the conjecture that the relationship is independent of the two-body potential. The energy and pressure obtained are in good overall agreement with the experiment, especially for argon. A comparison of our simulated results with HMSA and ODS integral equations and a molecular simulation have been also included.