Predicting whether aromatic molecules would prefer to enter a carbon nanotube: A density functional theory study

The interaction of a carbon nanotube (CNT) with various aromatic molecules, such as aniline, benzophenone, and diphenylamine, was studied using density functional theory able to compute intermolecular weak interactions (B3LYP-D3). CNTs of varying lengths were used, such as 4-CNT, 6-CNT, and 8-CNT (the numbers denoting relative lengths), with the lengths being chosen appropriately to save computation times. All aromatic molecules were found to exhibit strong intermolecular binding energies with the inner surface of the CNT, rather than the outer surface. Hydrogen bonding between two aromatic molecules that include N and O atoms is shown to further stabilize the intermolecular adsorption process. Therefore, when benzophenone and diphenylamine were simultaneously allowed to interact with a CNT, the aromatic molecules were expected to preferably enter the CNT. Furthermore, additional calculations of the intermolecular adsorption energy for aniline adsorbed on a graphene surface showed that the concavity of graphene-like carbon sheet is in proportion to the intermolecular binding energy between the graphene-like carbon sheet and the aromatic molecule.     

A first principle study of adsorption of two proximate nitrogen atoms on graphene

Different possible configurations of two nitrogen‐adatoms on graphene are studied using density functional theory. Adsorption of single nitrogen atom on the bridge site of graphene is accompanied by distortion of the sheet. Electronically, this case amounts to p‐type doping. Two N atoms adsorbed on the graphene sheet can share a bond in two ways. They acquire positions either just above two adjacent carbon atoms or they form a bridge across opposite bonds of a hexagon in the sheet. Both these configurations also induce structural distortion of the sheet. Another stable configuration consists of two N atoms bonded as an N₂ molecule physisorbed on the graphene sheet. It is also possible to adsorb two N atoms on opposite sides of the graphene sheet, bonded to the same two C atoms. Moreover, two N atoms can be individually adsorbed on alternate bridge sites of neighboring hexagons experiencing a repulsion, the energy for which arises from the additional distortion of the graphene sheet. The densities of states near the Fermi level are found to be dependent on the adsorption configurations of two nitrogen atoms on graphene. Thus the electronic properties of graphene can be controlled by the selective adsorption of two nitrogen atoms. © 2014 Wiley Periodicals, Inc.     

A theoretical study of the cohesion of noble gases on graphite

The interactions of the noble gases with a graphene sheet are investigated theoretically. The short range repulsive interaction between the noble gas and each carbon atom is described using Hartree-Fock atomic densities and a local density functional theory with the exchange functional corrected for the finite range of the interaction by introducing a Rae-type correction depending on the effective number of electrons. The long range interactions are introduced as the sum of the Axilrod-Teller triple-dipole interaction plus the dipole-dipole and dipole-quadrupole dispersive attractions damped according to the theory of Jacobi and Csanak. The energy arising from the interactions between the permanent quadrupoles on the carbon atoms with the dipole they induce on the noble gas is negligible, being nonzero only on account of the atomistic structure of graphene. The mobile and delocalized nature of the graphene pi electrons causes the effective number of electrons to be around 500 rather than that of 12 appropriate for a system of entirely localized interactions with individual carbon atoms. Inclusion of the Axilrod-Teller term is required to obtain reliable predictions for the binding energies and equilibrium geometries. Absorption of a noble gas atom is predicted to occur at the site above the center of a six membered ring although this is preferred over two other sites by only about 5 meV. The methods presented for generating all the potentials can be applied to derive the interactions between any ion and carbon atom in the wall of a single-walled nanotube. Knowledge of these interactions is required to study the alkali halide nanocrystals encapsulated in single-walled carbon nanotubes of current interest.     

On the Addition of Aryl Radicals to Graphene: The Importance of Nonbonded Interactions

Dispersion‐corrected density functional theory is utilized to study the addition of aryl radicals to perfect and defective graphene. Although the perfect sheet shows a low reactivity against aryl diazonium salts, the agglomeration of these groups and the addition onto defect sites improves the feasibility of the reaction by increasing binding energies per aryl group up to 27 kcal mol^?1. It is found that if a single phenyl radical interacts with graphene, the covalent and noncovalent additions have similar binding energies, but in the particular case of the nitrophenyl group, the adsorption is stronger than the chemisorption. The single vacancy shows the largest reactivity, increasing the binding energy per aryl group by about 80 kcal mol^?1. The zigzag edge ranks second, enhancing the reactivity 5.4 times with respect to the perfect sheet. The less reactive defect site is the Stone–Wales type, but even in this case the addition of an isolated aryl radical is exergonic. The arylation process is favored if the groups are attached nearby and on different sublattices. This is particularly true for the ortho and para positions. However, the enhancement of the binding energies decreases quickly if the distance between the two aryl radicals is increased, thereby making the addition on the perfect sheet difficult. A bandgap of 1–2 eV can be opened on functionalization of the graphene sheets with aryl radicals, but for certain configurations the sheet can maintain its semimetallic character even if there is one aryl radical per eight carbon atoms. At the highest level of functionalization achieved, that is, one aryl group per five carbon atoms, the bandgap is 1.9 eV. Regarding the effect of using aryl groups with different substituents, it is found that they all induce the same bandgap and thus the presence of NO₂, H, or Br is not relevant for the alteration of the electronic properties. Finally, it is observed that the presence of tetrafluoroborate can induce metallic character in graphene.     

Graphene and carbon nanotube composite electrodes for supercapacitors with ultra-high energy density

We describe a graphene and single-walled carbon nanotube (SWCNT) composite film prepared by a blending process for use as electrodes in high energy density supercapacitors. Specific capacitances of 290.6 F g(-1) and 201.0 F g(-1) have been obtained for a single electrode in aqueous and organic electrolytes, respectively, using a more practical two-electrode testing system. In the organic electrolyte the energy density reached 62.8 Wh kg(-1) and the power density reached 58.5 kW kg(-1). The addition of single-walled carbon nanotubes raised the energy density by 23% and power density by 31% more than the graphene electrodes. The graphene/CNT electrodes exhibited an ultra-high energy density of 155.6 Wh kg(-1) in ionic liquid at room temperature. In addition, the specific capacitance increased by 29% after 1000 cycles in ionic liquid, indicating their excellent cyclicity. The SWCNTs acted as a conductive additive, spacer, and binder in the graphene/CNT supercapacitors. This work suggests that our graphene/CNT supercapacitors can be comparable to NiMH batteries in performance and are promising for applications in hybrid vehicles and electric vehicles.     

Self assembled graphene/carbon nanotube/polystyrene hybrid nanocomposite by in situ microemulsion polymerization

Self-assembled graphene/carbon nanotube (CNT)/polystyrene hybrid nanocomposites were prepared by water-based in situ microemulsion polymerization. The resulting nanocomposites were used as filler in a host polystyrene matrix to form composite films. An admixture of the two types of carbon fillers provided better improvement in the thermal and mechanical properties compared to the neat polymer. The sheet resistance decreased progressively due to the formation of an extended conjugation network with the CNT bridging the gap between the graphene sheets coated with polymer nanoparticles. The details of the analysis are presented.     

Investigation of Simultaneous Cation-Π and Π–Π Stacking Interactions on Graphene and Some Bent Graphenes as Curved Surfaces of Carbon Nanohorns

Computational quantum chemistry methods are used to study simultaneous cation-π and π–π stacking interactions with a graphene sheet and on the inner and outer faces of some bent graphenes as curved surfaces of carbon nanohorns (CNHs). Structural parameters and energy data of ternary benzene–graphene–Na⁺ and benzene-bent graphene–Na⁺ complexes are studied. Also, effects of charge transfer and aromaticity are estimated to determine how changes in the structure influences the above interactions. The results indicate that the graphene curvature leads to structural changes affecting simultaneous interactions of the Na+ cation and benzene with bent graphenes. Also, the results show that although π–π stacking is a weak interaction, it can manipulate the order of binding energies in complexes involving both mentioned interactions and affect drug delivery abilities of these systems.     

Theoretical study on singlet oxygen adsorption onto surface of graphene-like aromatic hydrocarbon molecules

Recently, graphene sheet is one of interesting systems to realize novel electronic properties. Especially, interaction between graphene and adsorbed oxygen molecule is very important to control electronic condition. In this paper, we employed some aromatic hydrocarbons as simple systems of graphene sheet and ab initio MO calculations were carried out to investigate inter-molecular interaction. It is found that not triplet but singlet O₂ molecule have potential of chemisorption onto graphene surface. From the calculated potential energy surface (PES) for distance between benzene and O₂ molecules, meta-stable structure is found at about 1.5 Å with potential barrier. In the optimized structure of its meta-stable state, structural strain can be relaxed through bending of planer benzene ring. Its energy is estimated at 70.10 kcal/mol for benzene. We also estimated the strain effects for naphthalene and pyrene molecules as larger case of graphene and they were 80.85 and 72.45 kcal/mol, respectively.     

Predicting Glass Transition Temperature of Polyethylene/Graphene Nanocomposites by Molecular Dynamic Simulation

The glass transition temperature of polyethylene/graphene nanocomposites was investigated by molecular dynamic simulation. The specific volumes of three systems(polyethylene, polyethylene with a small graphene sheet and two small graphene sheets) were examined as a function of temperature. We found that the glass transition temperature decreases with increasing graphene. Then the van der Waals energy changes obviously with increasing graphene and the torsion energy also plays an important role in the glass transition of polymer. The radial distribution functions of the inter-molecular carbon atoms suggest the interaction between PE and graphene weakens with increasing graphene. These indicate that graphene can prompt the motion of chain segments of polymer and decrease the glass transition temperature (T_g) of polymer.     

A comprehensive study on the impact of RGO/MWCNT hybrid filler reinforced polychloroprene rubber multifunctional nanocomposites

Flexible dielectric chloroprene rubber (CR) nanocomposites reinforced by one-dimensional carbon nanotube (CNT)/two dimensional reduced graphene oxide hybrids have been prepared using two-roll mill mixing technique. Non-covalent π-π interaction between multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) nanosheets and the secondary interaction between fillers and chloroprene rubber matrix are responsible for generating the effective load transfer between RGO/MWCNTs and CR. The prepared RGO-MWCNT hybrid nanocomposites with high dielectric constant (≈650), low dielectric loss (≈0.42) and high energy storage efficiency (78.6%) values are practically good enough to use as a low cost polymeric dielectric layer in transistors. Furthermore, the prepared nanocomposites showed excellent electromagnetic effectiveness; a maximum shielding efficiency of 11.87 dB @ 3.5 GHz was achieved at 4 phr of MWCNT loading. This excellent electromechanical performance can be ascribed to the synergistic effect of RGO-MWCNT hybrid suggesting that this novel hybrid nanocomposite serves as an attractive candidate in modern electronics and electric power systems.     

Comprehensive study of threonine adsorption on carbon nanotube: A dispersion complemented density functional theory‐based treatment

The interaction mechanism of threonine (Thr) on the sidewall of (8, 8) single‐walled carbon nanotubes (CNTs) was investigated by density functional tight‐binding method. All the functional groups of Thr were used to interact with the surface of CNT. The structural parameters were analyzed to identify the noncovalent interactions, and the binding energy and strain energy were used to indicate the binding properties. We found that the CH/π interactions play more important roles than NH/π and OH/π interactions in stabilizing the complex structures. Furtherly, the charge transfer properties, density of states (DOS) and partial density of states, and highest occupied molecular orbitals and lowest unoccupied molecular orbitals were also studied to illustrate the adsorbed interactions. The results show that the DOS structure of CNT could be modified by the adsorption of Thr, and, therefore, the conductivity of CNT will be improved by introducing proper amino acids. Our data should be helpful for the design of biocompatible molecules for CNT modification. © 2015 Wiley Periodicals, Inc.     

Dynamic behaviors on zadaxin getting into carbon nanotubes

The dynamic behaviors of drug zadaxin getting into carbon nanotubes (CNTs) in different water surroundings were investigated by molecular dynamics simulation. It was found that the diameter (1.9 nm) of (14, 14) CNT is the critical size for inserting zadaxin into CNT at the present conditions. In addition, the length of CNTs is another factor for inserting. A certain length is needed. It implies that interactions of zadaxin with both the CNT and the water molecules are competitive in the insertion process. The CNT-zadaxin attractive interaction is found to be the main driving force with the lower density of water molecules in the surroundings, while the zadaxin-water interaction becomes dominant with the higher density. The study of the authors suggests that biomolecules-CNT systems can be further exploited for the potential applications to drugs, vaccines, and gene delivery.     

Density functional and molecular docking studies towards investigating the role of single-wall carbon nanotubes as nanocarrier for loading and delivery of pyrazinamide antitubercular drug onto pncA protein

The potential biomedical application of carbon nanotubes (CNTs) pertinent to drug delivery is highly manifested considering the remarkable electronic and structural properties exhibited by CNT. To simulate the interaction of nanomaterials with biomolecular systems, we have performed density functional calculations on the interaction of pyrazinamide (PZA) drug with functionalized single-wall CNT (fSWCNT) as a function of nanotube chirality and length using two different approaches of covalent functionalization, followed by docking simulation of fSWCNT with pncA protein. The functionalization of pristine SWCNT facilitates in enhancing the reactivity of the nanotubes and formation of such type of nanotube-drug conjugate is thermodynamically feasible. Docking studies predict the plausible binding mechanism and suggests that PZA loaded fSWCNT facilitates in the target specific binding of PZA within the protein following a lock and key mechanism. Interestingly, no major structural deformation in the protein was observed after binding with CNT and the interaction between ligand and receptor is mainly hydrophobic in nature. We anticipate that these findings may provide new routes towards the drug delivery mechanism by CNTs with long term practical implications in tuberculosis chemotherapy.     

Curvature‐dependent adsorption of water inside and outside armchair carbon nanotubes

The curvature dependence of the physisorption properties of a water molecule inside and outside an armchair carbon nanotube (CNT) is investigated by an incremental density‐fitting local coupled cluster treatment with single and double excitations and perturbative triples (DF‐LCCSD(T)) study. Our results show that a water molecule outside and inside (n, n) CNTs (n = 4, 5, 6, 7, 8, 10) is stabilized by electron correlation. The adsorption energy of water inside CNTs decreases quickly with the decrease of curvature (increase of radius) and the configuration with the oxygen pointing toward the CNT wall is the most stable one. However, when the water molecule is adsorbed outside the CNT, the adsorption energy varies only slightly with the curvature and the configuration with hydrogens pointing toward the CNT wall is the most stable one. We also use the DF‐LCCSD(T) results to parameterize Lennard‐Jones (LJ) force fields for the interaction of water both with the inner and outer sides of CNTs and with graphene representing the zero curvature limit. It is not possible to reproduce all DF‐LCCSD(T) results for water inside and outside CNTs of different curvature by a single set of LJ parameters, but two sets have to be used instead. Each of the two resulting sets can reproduce three out of four minima of the effective potential curves reasonably well. These LJ models are then used to calculate the water adsorption energies of larger CNTs, approaching the graphene limit, thus bridging the gap between CNTs of increasing radius and flat graphene sheets. © 2016 Wiley Periodicals, Inc.     

Density-functional calculations of icosahedral M13 (M = Pt and Au) clusters on graphene sheets and flakes

Density-functional calculations were done to examine the interface between graphene and a Pt₁₃ or Au₁₃ cluster. Introducing a carbon vacancy into a graphene sheet enhanced the interaction between graphene and the metal clusters. Five- or seven-member rings introduced into the graphene also increased the stability of the interface. The CO and H chemisorption energies on the metal clusters on graphene were calculated to clarify support-dependent reactivity.     

运用功能化修饰的碳纳米管针尖测量配体-受体的作用力

电弧法自制碳纳米管原子力显微镜针尖,对其末端进行功能化修饰,然后测量配体-受体之间的作用力。运用没有功能化修饰的碳纳米管针尖与修饰有亲和素分子的基底进行接触测量时,没有粘滞力出现;而运用末端修饰生物素分子的碳纳米管针尖测量时,有粘滞力产生。功能化的碳纳米管针尖直接测得的粘滞力均大约200pN,此值符合一对配体生物素和受体亲和素之间的作用力。这一结果很难用传统的针尖获得,功能化修饰的碳纳米管针尖能够克服传统针尖在力测量中的局限,在生物学和化学领域有着广泛的应用前景。     

碳纳米管与咪唑类离子液体相互作用机制的理论研究

离子液体(IL)与碳纳米管(CNT)形成的复合体系在许多重要领域有潜在的应用价值,然而人们对于其微观结构的理解尚不清晰,对IL与CNT相互作用机理的认识还存有争议.本文以(8,0)CNT与1-丁基-3-甲基咪唑六氟化磷IL为例研究了CNT与IL的相互作用,分别探讨了1-丁基-3-甲基咪唑阳离子([BMIM+])、六氟化...     

In search for structure of active site in iron-based oxygen reduction electrocatalysts

Calculations to elucidate the structure of Fe-based electrocatalysts were performed. Lowest energy configurations for incorporation of nitrogen in bulk of graphene sheet as well as on edge were determined. Substitution of nitrogen in bulk graphene is endothermic, while on the edge it can be either exothermic, if hydrogen is present, or endothermic. Energies of various configurations for the incorporation of iron on the edge of the nitrided graphene sheet were also examined. In the absence of hydrogen, iron prefers to bond with nitrogen and a carbon atom. In the presence of hydrogen, however, iron was found to prefer bonding to two nitrogen atoms on the graphene edge.     

New insights into the interaction of hydrogen atoms with boron-substituted carbon

Boron substitution in carbon materials has been comprehensively investigated using the density functional theory method. It was found that there is a correlation between the stability of the graphene sheet, the distribution of pi electrons, the electrostatic potential, and the capability for hydrogen-atom adsorption. Boron substitution destabilizes the graphene structure, increases the density of the electron wave around the substitutional boron atoms, and lowers the electrostatic potential, thus improving the hydrogen adsorption energy on carbon. However, this improvement is only ca. 10-20% instead of a factor of 4 or 5. Our calculations also show that two substitutional boron atoms provide consistent and reliable results, but one substitutional boron results in contradictory conclusions. This is a warning to other computational chemists who work on boron substitution that the conclusion from one substitutional boron might not be reliable.