Inside Single-walled Carbon Nanotubes Research Articles

Polymorphic Structures of Iodine and Their Phase Transition in Confined Nanospace

Atomic chains and crystal of iodine were successfully generated in a controlled manner inside single-walled carbon nanotubes (SWNTs). The structure is strongly dependent on the diameter of SWNTs; the single, double, and triple helical structures became quite stable when the diameter of SWNTs matches the certain size. More than three chains of iodine are not very stable, and they often crystallize inside the carbon nanotube when the diameter is larger than 1.45 nm. The crystallization or phase transition in a confined nanospace is thus directly observed, and there is indeed a critical size of the hollow nanospace for the stable formation of the atomic chains of iodine.

Unusual Hydrogen Bonding in Water-Filled Carbon Nanotubes

We present the first experimental vibrational spectroscopy study providing direct evidence of a water phase inside single-walled carbon nanotubes that exhibits an unusual form of hydrogen-bonding due to confinement. Water adopts a stacked-ring structure inside nanotubes, forming intra- and inter-ring hydrogen bonds. The intra-ring hydrogen bonds are bulk-like while the inter-ring hydrogen bonds are relatively weak, having a distorted geometry that gives rise to a distinct OH stretching mode. The experimentally observed infrared mode at 3507 cm(-1) is assigned to vibrations of the inter-ring OH-groups based on detailed atomic-level modeling. The direct observation of unusual hydrogen bonding in nanotubes has potential implications for water in other highly confined systems, such as biological channels and nanoporous media.

Energetics and electronic structure of acetylene molecules encapsulated inside a carbon nanotube: A density functional theory study

Abstract We study the energetics of a single acetylene (C2H2) molecule inside single-walled carbon nanotubes (SWCNT) using first principles total energy calculations. We have found that energetically it is not favorable for the acetylene molecule to be encapsulated in the smallest nanotubes: our results suggest an energetic preference for acetylene to be enclosed in nanotubes wider than the (5,5) tube. This result is similar to the case of the adsorption of poly-acetylene on SWCNT. We have also studied the local density of states for the molecule-nanotube system, and found little effect of the acetylene molecule on the nanotube LDOS close to the Fermi Level.

Highly Stabilized β‐Carotene in Carbon Nanotubes

Encapsulation of β-carotene inside single-walled carbon nanotubes (SWCNTs) greatly improves the stability of β-carotene. The Figure shows a schematic illustration of β-carotene inside a SWCNT. The surrounding tube wall protects β-carotene from reacting with radical species and suppresses its isomerization. This protection counters the degradation of π-conjugated molecules, which is a bottleneck impeding their application in photonic devices.

Electrochemistry of fullerene peapod modified electrodes

Redox processes of C 60@SWNT and C 70@SWNT modified electrodes corresponding to electron transfer reactions of C 60 and C 70 inside single-wall carbon nanotubes have been firstly observed. Three pairs of reversible electro-reduction waves have been obtained in acetonitrile containing tetrabutylammonium cation as supporting electrolyte. The influencing factors on electrochemistry of fullerene peapod modified electrodes have been investigated. The results suggest that voltammetric behavior of C 60@SWNT or C 70@SWNT is dependent on the nature of the supporting electrolyte and the solvent system.

Polymerizing Peas in a Pod

CHEMISTRY When materials are introduced into the narrow interior of a carbon nanotube, the confinement can alter their properties; for example, by stabilizing crystal forms that are unstable in the bulk. Britz et al. show that confinement can also affect the reactivity of fullerene epoxide (C60O) molecules that are lined up inside single-walled carbon nanotubes like peas in a pod, in a fashion similar to what has already been observed for fullerene (C60). When the C60O-containing nanotubes are heated for three days at 260°C, the C60O molecules form linear (C60O) n chains connected via C-O-C bonds. In contrast, when heated under bulk conditions, C60O forms a tangled, branched, three- dimensional polymer. — JFU Chem. Commun. 10.1039/b414247k (2005).

Recombination and Exchange Reactions of Hydrogen and Dihydrogen Molecular Condensation in Single-Walled Carbon Nanotubes

The hydrogen recombination reaction, H + H → H2, and the hydrogen exchange reaction, H + H2→ H2 + H, taking place inside single-walled carbon nanotubes have been studied by using quantum mechanics molecular dynamics simulations. Two types of hydrogen exchange reactions have been found. The fast reaction lasts in less than 5 fs, and the slow one lasts for about 40 fs with a clear intermediate state manifested. The collisional reaction for two H atoms to form a H2 molecule usually takes place in a time interval of 25 fs. We also describe the detailed process of the reaction of individual H atoms to form H2 molecules and, with an increase of the density of H2 molecules confined in the tubes, H2 molecular condensation to form clusters and finally to form condensed H2 molecular lattices.

THE EQUILIBRIUM CONSTANTS FOR MOLECULAR HYDROGEN ADSORPTION IN CARBON NANOTUBES BASED ON ITERATIVELY DETERMINED NANO-CONFINED BOUND STATES

A model for H 2 inside single-walled carbon nanotubes is outlined. ARPACK (the Arnoldi package), a robust iterative matrix-vector eigenvalue software library, is used to determine the allowed quantum states of H 2 inside various carbon nanotubes. This information is used to construct the equilibrium constants for H 2 adsorption as a function of temperature for a variety of CNTs.

Fullerene Coalescence in Nanopeapods: A Path to Novel Tubular Carbon

A fascinating structural transformation occurring inside single-walled carbon nanotubes (SWNTs) is the fullerene coalescence, which is responsible for forming stable zeppelinlike carbon molecules. We report in situ transmission electron microscope (TEM) observations revealing sequences of fullerene coalescence induced by electron irradiation on pristine nanotube peapods, together with extensive theoretical investigations of the microscopic mechanism underlying this process. TEM images indicate that the merging of fullerenes results in stable but corrugated tubules (5 to 7 Angstrom in diameter) confined within SWNTs. These observations have been confirmed using a combination of theoretical approaches based on molecular dynamics, empirical potentials, tight-binding methods, Monte Carlo techniques, and first principles calculations. We have fully elucidated the coalescence mechanism of fullerenes inside SWNTs under electron irradiation and thermal annealing. The process occurs via the polymerization Of C-60 molecules followed by surface reconstruction, which can be triggered either by the formation of vacancies (created under electron irradiation) or by surface-energy minimization activated by thermal annealing. These novel tubular forms of carbon contain hexagons, pentagons, heptagons, and octagons. The stability, electronic properties, and electron conductance of the novel tubules are strongly affected by the final geometry of the coalesced fullerene complex. The possibility of forming highly conducting and semiconducting tubular structures suggests new avenues in designing carbon nanowires with specific electronic characteristics.

Adsorption of CF4 on the internal and external surfaces of opened single-walled carbon nanotubes: a vibrational spectroscopy study.

Infrared spectroscopy has been used to make the first experimental discrimination between molecules bound by physisorption on the exterior surface of carbon single-walled nanotubes (SWNTs) and molecules bound in the interior. In addition, the selective displacement of the internally bound molecules has been observed as a second adsorbate is added. SWNTs were opened by oxidative treatment with O(3) at room temperature, followed by heating in a vacuum to 873 K. It was found that, at 133 K and 0.033 Torr, CF(4) adsorbs on closed SWNTs, exhibiting its nu(3) asymmetric stretching mode at 1267 cm(-1) (red shift relative to the gas phase, 15 cm(-1)). Adsorption on the nanotube exterior is accompanied by adsorption in the interior in the case of opened SWNTs. Internally bound CF(4) exhibits its nu(3) mode at 1247 cm(-1) (red shift relative to the gas phase, 35 cm(-1)). It was shown that, at 133 K, Xe preferentially displaces internally bound CF(4) species, and this counterintuitive observation was confirmed by molecular simulations. The confinement of CF(4) inside (10,10) single-walled carbon nanotubes does not result in the production of lattice modes that are observed in large 3D ensembles of CF(4).

C70Molecular Stumbling inside Single-Walled Carbon Nanotubes

We report the structural study of C 70 -one-dimensional (1D) crystal formed inside single-walled carbon nanotubes (SWNTs). X-ray diffraction measurements were performed between 100 K and 999 K on C...

Layering Behavior and Axial Phase Equilibria of Pure Water and Water + Carbon Dioxide Inside Single Wall Carbon Nanotubes

We have studied the phase equilibrium and layering behavior of the liquid phase in water and water + CO2 systems inside single wall carbon nanotubes. The system containing pure water was examined at temperatures between 274 and 500 K. At low temperatures and close to the wall of the nanotube, the formation of layers enclosing the liquid phase was observed. Upon addition of CO2, gas−liquid equilibrium was observed, resulting in an enhanced layering effect in the liquid phase.