Inside Carbon Nanotubes Research Articles

Activation of Nanoflows for Fuel Cells

Propagation of Rayleigh traveling waves from a gas on a nanotube surface activates a macroscopic flow of the gas (or gases) that depends critically on the atomic mass of the gas. Our molecular dynamics simulations show that the surface waves are capable of actuating significant macroscopic flows of atomic and molecular hydrogen, helium, and a mixture of both gases both inside and outside carbon nanotubes (CNT). In addition, our simulations predict a new “nanoseparation” effect when a nanotube is filled with a mixture of two gases with different masses or placed inside a volume filled with a mixture of several gases with different masses. The mass selectivity of the nanopumping can be used to develop a highly selective filter for various gases. Gas flow rates, pumping, and separation efficiencies were calculated at various wave frequencies and phase velocities of the surface waves. The nanopumping effect was analyzed for its applicability to actuate nanofluids into fuel cells through carbon nanotubes.

Investigation of the Effect of Bending on the Polymerization of Fullerenes Inside Carbon Nanotubes

The process of bending empty carbon nanotubes (10,10) and the tube filled by fullerenes C60 was investigated. The polymerization of fullerenes and the chemical interaction between the fullerenes and the tube wall is observed in the tube filled with fullerenes in the bending of 270 degrees. It was found that the minimum angle of the bending, which is required for the polymerization, is equal to 16 degrees. The inside of the nanotube is transformed into a wave-like. We used two methods: the empirical and the quantum–mechanical methods. The simulation until the polymerization of fullerenes is carried out by the empirical method and the polymerization process are modeled by the tight binding method.

Pt-NP–MWNT nanohybrid as a robust and low-cost counter electrode material for dye-sensitized solar cells

Pt-NPs hybridized inside and outside multi-walled carbon nanotubes (MWNTs) were successfully synthesized using a liquid plasma system with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide under atmospheric pressure. The Pt-NPs with a size of 3–4 nm were stably and uniformly hybridized on both inner and outer surfaces of the MWNTs. The nanohybrid materials were applied to the counter electrode of dye-sensitized solar cells (DSCs). Electrochemical impedance measurement of DSCs revealed that the charge-transfer resistance of a MWNT–Pt nanohybrid-coated electrode was less than that of Pt-sputtered and MWNT-coated electrodes. Due to the low charge-transfer resistance, the DSC exhibited fairly improved energy conversion efficiency compared to the DSCs equipped with Pt-sputtered and MWNT-coated counter electrodes.

Assemblies of energetic 3,3′-diamino-4,4′-azofurazan on single-walled carbon nanotubes

The structure, adsorption energy, and initial dissociation reaction of the energetic 3,3′-diamino-4,4′-azofurazan (DAAzF) assembled inside or outside single-walled carbon nanotubes (i.e. CNT(6,6), CNT(8,8), and CNT(10,10)) were calculated by using an ONIOM approach. It was found that the geometrical changes in the furazan rings were obvious for the DAAZF assembled into CNT(6,6) with respect to that of the isolated DAAzF. As for the other assemblies, the DAAzF showed very similar geometrical parameters of the furazan rings as the isolated DAAzF. Only the furazan rings rotated slightly. It was also found that the DAAZF@CNT(6,6) had a positive adsorption energy. However, the DAAZF/CNT(6,6), DAAZF/CNT(8,8), DAAZF/CNT(10,10), DAAZF@CNT(8,8), DAAZF@CNT(10,10) were found to have the negative adsorption energy, which indicates that these adsorption processes are exothermic and thermodynamically favorable. The total energy of DAAzF@CNT(6,6) was higher than that of DAAZF/CNT(6,6) but the DAAZF@CNT(8,8) and DAAZF@CNT(10,10) had a lower energy than the DAAzF/CNT(8,8) and DAAzF@CNT(10,10), respectively. It is suggested that the DAAzF might spontaneously assemble inside the two CNTs of larger diameters. The calculated potential energy curves showed that that the CN bond thermal decomposition of the DAAzF was not significantly affected when DAAzF was assembled outside the three CNTs or inside the CNT(8,8) and CNT(10,10). However, the thermal decomposition of DAAzF could be promoted when it was assembled within the CNT(6,6). Our theoretical results would be very valuable for the design of the energetic nanocomposites based on CNTs and the azofurazan explosives.

Delivery of Gold Nanoparticles Inside Carbon Nanotubes by Oligonucleotides

Delivery of gold nanoparticles with 2nm or so in diameter inside multiwall carbon nanotubes (MCNTs) by oligonucleotides was performed under the condition of 400k and 3bar for 20 min. The Au-oligo-CNT complexes were first purified via 1% agarose gel electrophoresis and then analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X–ray spectroscopy (EDX). The results showed that the excess of oligonucleotides, Au nanopartilces and the Au-oligo hybrids attached to the outside walls of CNTs could be removed away by agarose gel electrophoresis. HR-TEM and EDX results demonstrated that 2% or so Au-oligo hybrids were successfully delivered inside MCNTs. In contrast, few Au nanopartilces were observed to locate inside CNTs under identical experimental conditions. This is the very first confirmation that oligonucleotides can be used to deliver Au nanoparticles inside MCNTs. The van der Waals attraction between CNT and Au-oligo hybrids is likely the main driving force for this phenomenon. This phenomenon has potential applications in future nanotechnology such as molecular electronics, biochemical sensors, nano-devices, gene storage and delivery systems.

Laser-induced damage and destruction of HiPCO nanotubes in different gas environments

We have studied the thermal and chemical stability of HiPCO-produced single-walled carbon nanotube bundles to high laser power in air and argon. The samples were exposed to 110 kW/cm2 during 8 h with a 1.96 eV laser and the temperature was monitored via downshift of G+-Raman peak. The structural changes in the carbon nanotubes (CNTs) caused by laser heating were monitored by recording their Raman spectra at ambient T (reference conditions) to ensure unaltered resonance conditions. The initial temperature was estimated to be 550 °C and 870 °C in air and argon, respectively. The Raman signal intensity from the CNTs radial breathing mode (RBM) increased rapidly at the beginning of the laser heating both under air and argon due to desorption of impurities for all but the smallest diameter CNTs. The temperature dropped by 30% under argon and 60% under air due to destruction of the absorbers – CNTs in resonance with incident radiation. The final RBM spectra exhibited intensity loss only for the smallest diameter CNTs in argon atmosphere and for all but the largest diameter CNTs in air. Our results demonstrate the importance of (i) impurity desorption from exterior and interior of CNTs; (ii) different temperature thresholds for the CNT destruction due to oxidation and overheating; (iii) the role of photon absorbers on the thermal stability of the sample. The small diameter CNTs are more easily destroyed than large diameter ones. The metallic nanotubes also tend to have lower thermal stability.

Origin of Giant Ionic Currents in Carbon Nanotube Channels

Fluid flow inside carbon nanotubes is remarkable: transport of water and gases is nearly frictionless, and the small channel size results in selective transport of ions. Very recently, devices have been fabricated in which one narrow single-walled carbon nanotube spans a barrier separating electrolyte reservoirs. Ion current through these devices is about 2 orders of magnitude larger than predicted from the bulk resistivity of the electrolyte. Electroosmosis can drive these large excess currents if the tube both is charged and transports anions or cations preferentially. By building a nanofluidic field-effect transistor with a gate electrode embedded in the fluid barrier, we show that the tube carries a negative charge and the excess current is carried by cations. The magnitude of the excess current and its control by a gate electrode are correctly predicted by the Poisson-Nernst-Planck-Stokes equations.

Photoluminescence Study of Encapsulated Dye Inside Single-Walled Carbon Nanotubes Dispersed in Solvents

Photo-luminescent dye, 1-(2-amino-phenyl) naphthalene-2-ylamine (APNA) molecules were synthesized and encapsulated inside single-walled carbon nanotubes (APNA@SWNTs) in vacuum. Here we measured X-ray diffraction (XRD) pattern and attenuated total reflectance (ATR) spectrum to confirm the encapsulation of APNA molecules inside SWNTs. Strong photoluminescence (PL) spectrum was observed around 400 nm at an excitation of 326 nm. We employed the PL intensity of the dye to reveal suspension stability of SWNTs in solvents. The intensity of PL spectrum increased as a function of SWNTs suspension stability, i.e., the PL intensity was proportional to suspension stability of SWNTs in various solvents.

Water Boiling Inside Carbon Nanotubes: Toward Efficient Drug Release

We show using molecular dynamics simulation that spatial confinement of water inside carbon nanotubes (CNTs) substantially increases its boiling temperature and that a small temperature growth above the boiling point dramatically raises the inside pressure. Capillary theory successfully predicts the boiling point elevation down to 2 nm, below which large deviations between the theory and atomistic simulation take place. Water behaves qualitatively different inside narrow CNTs, exhibiting transition into an unusual phase, where pressure is gas-like and grows linearly with temperature, while the diffusion constant is temperature-independent. Precise control over boiling by CNT diameter, together with the rapid growth of inside pressure above the boiling point, suggests a novel drug delivery protocol. Polar drug molecules are packaged inside CNTs; the latter are delivered into living tissues and heated by laser. Solvent boiling facilitates drug release.

Adsorption and Dissociation of Ammonia Borane Outside and Inside Single-Walled Carbon Nanotubes: A Density Functional Theory Study

Amonia borane (AB) has been identified as a potential candidate high-capacity hydrogen storage material. This work probes the adsorption and dissociation of AB inside and outside single-walled carbon nanotubes (SWCNTs) within the framework of density functional theory. The dissociation barriers of AB have been calculated and compared with that of the isolated AB molecule. On the basis of the present calculations, no notable improvement results from SWCNT confinement; on the contrary, the dissociation barrier slightly increases with respect to isolated AB.

Adsorption and dissociation of ammonia borane outside and inside single-walled carbon nanotubes

Ammonia borane (AB) has been identified as a potential candidate highcapacity hydrogen storage material. This work probes the adsorption and dissociation of AB inside and outside single-walled carbon nanotubes (SWCNTs) within the framework of density functional theory. The dissociation barriers of AB have been calculated and compared with that of the isolated AB molecule. On the basis of the present calculations, no notable improvement results from SWCNT confinement; on the contrary,the dissociation barrier slightly increases with respect to isolated AB.

Energetic Molecules Encapsulated Inside Carbon Nanotubes and between Graphene Layers: DFT Calculations

Insensitive energetic materials are desirable for propellants because of the reduced risks involved with their use. The ability to control the decomposition pathways for such materials is also of interest since it leads to optimal performance and controlled energy release. With these goals in mind, molecular structure and total energy calculations are used to investigate the confinement of energetic molecules inside carbon nanostructures. The molecules considered were FOX-7 (1,1-diamino-2,2-dinitroethylene), RDX (hexahydro-1,3,5-trinitro-striazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), DHT (3,6-di(hydrazino)-1,2,4,5-tetrazine), DiAT (3,6-diazido-1,2,4,5-tetrazine), DAAT (3,3′-azo-bis(6-amino-1,2,4,5-tetrazine)), and five different N-oxides of DAAT (DAATOn, with n = 1–5). Each of the eleven molecules is encapsulated inside a carbon nanotube (CNT) in order to determine if it is stabilized from such confinement. The calculations predict that each molecule could be stabilized by 32–53 kcal/...

Structural and Electronic Properties of Bismuth and Lead Nanowires Inside Carbon Nanotubes

Structural and electronic properties of very thin bismuth and lead nanowires encapsulated inside zigzag carbon nanotubes are investigated by density-functional calculations. As is expected, these properties are found to be heavily dependent on the configuration of the nanowire and the diameter of the nanotube, but the inclusion of spin–orbit interaction in the calculation significantly modifies the energy bands of the hybrid system, opens subband spacing, and induces semiconductor–metal transition. These results should be observed by the scanning tunneling spectroscope and could serve as a reference for deriving a variety of configurations of bismuth and lead nanowires by choosing proper carbon nanotubes.

The Dissociation of Nitramide and Methylnitramine When Confined Inside Armchair Single-Walled Carbon Nanotubes

Chemical reactivity and molecular structure of energetic materials may be significantly changed when they are confined inside carbon nanotubes (CNTs). The ONIOM calculations were carried out to investigate the molecular structures and the N-N bond decomposition of nitramide (NA) and methylnitramine (MNA) confined inside armchair single-walled CNTs with different diameter. Results showed that confinement in CNT(6, 6) and CNT(7, 7) had no evident influence on the structure of NA and MNA. However, the structures of NA and MNA within CNT(5, 5) were altered significantly with respect to the structures of the isolated NA and MNA. Compared with NA, MNA showed stronger interaction with these CNTs studied. By analyzing the potential energy curve along the N-N bond, we found that the energy barriers of the N-N bond decomposition for the NA and MNA are decreased by 11.6 and 10.8 kcal/mol, respectively, due to the confinement of CNT(5, 5). Confinement in CNT(6, 6) resulted in a slight decrease in the activation energy. Confinement in CNT(7, 7) did not affect the thermal decomposition of NA and MNA. We conclude that the N-N bond dissociation of NA and MNA can be promoted by confinement in a CNT with small diameter.

Chemically reactive species remain alive inside carbon nanotubes: a density functional theory study

The behavior of alkyl guest radicals inside carbon nanotube hosts with different diameters is analyzed using density functional theory (DFT) calculations. Here the inner alkyl radicals are assumed to be formed by decomposition of their precursors, which had been incorporated into the tubes. DFT calculations show that inner alkyl radicals prefer to exist separately from the nanotube wall (separate form) rather than forming an inner covalent bond with the wall (bound form). Keeping a radical apart from the inner wall is more likely for a more bulky radical inside a smaller diameter tube. A key to the preference for the separate forms over the bound forms is that the bound forms gain a weak attraction due to the formation of a bond with the inner wall. The weak attraction, ascribed to the inertness of the inner surface, is counteracted by destabilization due to deformations of a tube and radical induced by guest-host coupling. The energy balance argument illuminates that the inertness of the inner wall makes an alkyl radical species remain alive inside a tube and retain its reactivity. These findings can help us to understand experimental results where chemical reactions inside a tube proceed after guests are activated.

Tuning the energy barrier of water exchange reactions on Al(iii) by interaction with the single-walled carbon nanotubes

The limiting dissociative (D) and interchange dissociative (I(d)) water exchange pathways on Al(III) inside and outside single-walled carbon nanotubes (SWCNTs) were modelled using ONIOM calculations with density functional theory, and the influence of SWCNTs on both D and I(d) pathways was examined. The interchange dissociative water exchange pathway was revealed, in which the zigzag SWCNTs (13,0), (14,0) and (15,0) with the same length were modelled for interaction. The results indicate that the confinement effect of SWCNTs on the energy barriers is strong when the reaction takes place inside SWCNTs with small diameter relative to reaction complexes, and varies heavily along with the change of diameters of SWCNTs. The results also indicate that SWCNTs act as trans-activating ligand to effectively lower the energy barriers of both D and I(d) pathways outside SWCNTs. The interaction between aluminium-water complexes and SWCNTs can effectively lower the energy barriers in general and may accelerate the reaction rates, which has great importance for the influence of carbon nanotubes on dissolution and transformation rates of minerals such as aluminium (hydr)oxide.

Small scale effects on the stability of carbon nano-peapods under radial pressure

In this paper, a nonlocal elasticity formulation is presented for analyzing the instability of nano-peapods by modeling the nanotube as a shell. Using the nonlocal elasticity theory, the small scale characteristics of Carbon Nano-Peapods (CNPs) are taken into account. While the classical elastic shell model overestimates the critical pressure for the onset of structural instability of carbon nanotubes, the obtained results show that the nonlocal elastic shell model for nano-peapods can potentially provide better predictions. According to the results, it is concluded that the presence of C 60 inside (10,10) Carbon Nanotubes (CNTs) significantly increases the stability resistance of the single CNT.

Selective Deposition of Gold Nanoparticles on or Inside Carbon Nanotubes and Their Catalytic Activity for Preferential Oxidation of CO

AbstractGold nanoparticles have been deposited on three kinds of carbon nanotubes (CNTs), including nitrogen‐doped CNTs, by three different methods, namely, impregnation, organometallic decomposition, and deposition–precipitation. The choice of the gold precursor, the support, and the preparation procedure is critical for the control of the size and location (on or inside the nanotubes) of the gold nanoparticles. These catalysts were tested for the selective oxidation of CO in a hydrogen‐rich atmosphere. We have shown that the use of nitrogen‐doped CNTs as a support permits one to reach much higher activity and selectivity at low temperaturethan with the other CNT supports. This catalyst also shows a good stability under reaction conditions without detectable sintering.

Molecular Origin of Fast Water Transport in Carbon Nanotube Membranes: Superlubricity versus Curvature Dependent Friction

In this paper, we study the interfacial friction of water at graphitic interfaces with various topologies, water between planar graphene sheets, inside and outside carbon nanotubes, with the goal to disentangle confinement and curvature effects on friction. We show that the friction coefficient exhibits a strong curvature dependence; while friction is independent of confinement for the graphene slab, it decreases with carbon nanotube radius for water inside, but increases for water outside. As a paradigm the friction coefficient is found to vanish below a threshold diameter for armchair nanotubes. Using a statistical description of the interfacial friction, we highlight here a structural origin of this curvature dependence, mainly associated with a curvature-induced incommensurability between the water and carbon structures. These results support the recent experiments reporting fast transport of water in nanometric carbon nanotube membranes.

Heat-Driven Release of a Drug Molecule from Carbon Nanotubes: A Molecular Dynamics Study

Hydrophobicity and the ability to absorb light that penetrates through living tissues make carbon nanotubes (CNTs) promising intracellular drug delivery agents. Following insertion of a drug molecule into a CNT, the latter is delivered into a tissue, is heated by near-infrared radiation, and releases the drug. To assess the feasibility of this scheme, we investigate the rates of energy transfer between CNT, water, and the drug molecule and study the temperature and concentration dependence of the diffusion coefficient of the drug molecule inside CNTs. We use ciprofloxacin (CIP) as a sample drug: direct penetration of CIP through cell membranes is problematic due to its high polarity. The simulations show that a heated CNT rapidly deposits its energy to CIP and water. All estimated time scales for the vibrational energy exchange between CNT, CIP, and water are less than 10 ps at 298 K. As the system temperature grows from 278 to 363 K, the diffusion coefficient of the confined CIP increases 5-7 times, depending on CIP concentration. The diffusion coefficient slightly drops with increasing CIP concentration. This effect is more pronounced at higher temperatures. The simulations support the idea that optical heating of CNTs can assist in releasing encapsulated drugs.