Encapsulation of Carbon Chain Molecules in Single-Walled Carbon Nanotubes

One-dimensional carbon chains encapsulated in hollandite

One-dimensional carbon chains are highly reactive allotropes that are stabilized inside the protective environment of carbon nanotubes. Here we show that carbon chains can be encapsulated in metal oxides containing open structural channels, exemplified by hollandite α-MnO2. The α-MnO2 channels stabilize cumulene chains due to their structural commensurability, whereas the triple bonds in polyyne chains exhibit excessive steric repulsion to the oxide ions bordering the channel. Cumulene exhibits an interaction energy of only 0.065 eV per carbon atom, obtained by first-principles calculations, which is significantly more favorable than for encapsulation in a similarly sized carbon nanotube. Encapsulation of carbon chains is associated with lateral expansion of the α-MnO2 channel and polarization of the manganese and oxygen charge densities adjacent to the chains. Accordingly, the interaction energy is governed by a balance between van der Waals attraction and steric repulsion between the materials.

Molecular Dynamics Study on Dynamical Features of Reorganization Process for Nanocapsule Formed with Gear-Shaped Amphiphile Molecules

We have analyzed the dynamical feature of a hexameric structure of nanocube (1₆) from a gear-shaped amphiphile molecule (1) upon addition of solvophobic spherical adamantane molecule (G), by means of molecular dynamics (MD) simulation, to elucidate the conversion mechanism from the hexameric nanocube G@1₆ to a tetrameric G@1₄ tetrahedron. The adamantane molecule (G) in the nanocube G@1₆ is located around the triple π stacking, although G in the G@1₄ tetrahedron is at the central position of the capsule. Our MD simulation shows that the nanocube G@1₆ is more fluctuated than the G@1₄ tetrahedron. We have also found that a demethylated nanocube G@2₆ is converted to a tetrameric G@2₃ tetrahedron due to the solvophobic effect for the adamantane molecule.

Stabilities and electronic properties of nanowires made of single atomic sulfur chains encapsulated in zigzag carbon nanotubes

Theoretical investigations are carried out on the recently synthesized one-dimensional nanowires made of atomic sulfur chains encapsulated in carbon nanotubes (called S@CNTs). Special attention is paid to stability, electronic property and transport properties of these combined nanowires. It is found that the encapsulation is exothermic when S@CNTs are built from the tubes with diameter larger than 6.4 Å. Thus the experimental results are energetically favorable since the diameters of the CNTs are about 6 Å in the obtained S@CNTs. The combined nanowires can be stabilized by van der Waals interaction between sulfur chain and tube as indicated from radial distribution function and reduced density gradient descriptions. All S@CNTs studied in this work exhibit metallic property with the partially filled bands. However, the conducting component and the pathway of charge carriers are various. For instance, only the sulfur chain is the conducting pathway for S@CNT(8, 0), while both the sulfur chain and tube are the conducting pathways for S@CNT(9, 0). This interesting feature was understood based on the band structures and crystal orbital analysis. The electronic transport properties of the systems are performed by investigating and analyzing the transmission spectra, current-voltage (I-V) curves and transmission eigenstate, which confirm that the sulfur chains can improve the electronic transport of CNTs. Moreover, the electrostatic interaction resulted from the charge transfer between the two components of S@CNTs should be favorable to the stability of the combined nanowires.

Exploring the effect of confinement on water clusters in carbon nanotubes

Using armchair-type single-walled carbon nanotubes (SWCNTs) of different sizes as model compounds for lignite, the effect of water molecule confinement on the water-holding capacity of lignite pores was investigated. Results indicated that the water-holding capacity of pores with diameters of <10 nm was eight times larger than that of pores with diameters of 100 nm. The configuration of the cluster of water molecules in each SWCNT and the binding energy between each SWCNT and the water molecules within it were calculated by means of density functional theory using a hybrid functional: M06-2X/6-311+G**, 6-31G*. The results prove that the configurations of the water molecules in the SWCNTs are very different to their configuration in the unconfined state. In vacuum, the cluster of three water molecules adopted a trimer configuration, while they presented a linear configuration in the 6.78 Å SWCNT. Similarly, in vacuum, the cluster of five water molecules formed a five-membered ring, while they favored a linear configuration in the 6.78 Å SWCNT, a zigzag configuration in the 8.14 Å SWCNT, and a trimer + 1 + 1 configuration (i.e., a trimer plus two isolated water molecules) in the 9.49 Å, 10.85 Å, and 13.75 Å SWCNTs. There was found to be a degree of competition between the coupling energy of the water molecules with the SWCNT and the hydrogen bonding among the water molecules. When the diameter of the SWCNT was >1 nm, the hydrogen bonding among the water molecules dominated, while the coupling energy of the water molecules with the SWCNT amounted to only 30-40% of the total interaction energy of the water molecules. Graphical Abstract Computed equilibrium structures of five water molecules confined in SWCNTs with diameters of 6.78 Å, 8.14 Å, 9.49 Å, 10.85 Å, and 13.75 Å, and in vacuum.

Importance of the alignment of polar π conjugated molecules inside carbon nanotubes in determining second-order non-linear optical properties

Dispersion-corrected DFT calculations found energetically preferred alignments of certain p,p′-dimethylaminonitrostilbene (DANS) molecules inside an carbon nanotube, and their importance in determining second-order non-linear optical properties.

Controlling luminescent silicon nanoparticle emission produced by nanosecond pulsed laser ablation: role of interface defect states and crystallinity phase

In this study, we provide a systematic study on the origin of green and blue emission from luminescent silicon nanoparticles (Si-NPs) synthesized in water using a nanosecond pulsed laser ablation methodology.

Confinement and controlling the effective compressive stiffness of carbyne

Carbyne is a one-dimensional chain of carbon atoms, consisting of repeating sp-hybridized groups, thereby representing a minimalist molecular rod or chain. While exhibiting exemplary mechanical properties in tension (a 1D modulus on the order of 313 nN and a strength on the order of 11 nN), its use as a structural component at the molecular scale is limited due to its relative weakness in compression and the immediate onset of buckling under load. To circumvent this effect, here, we probe the effect of confinement to enhance the mechanical behavior of carbyne chains in compression. Through full atomistic molecular dynamics, we characterize the mechanical properties of a free (unconfined chain) and explore the effect of confinement radius (R), free chain length (L) and temperature (T) on the effective compressive stiffness of carbyne chains and demonstrate that the stiffness can be tuned over an order of magnitude (from approximately 0.54 kcal mol(-1) Å(2) to 46 kcal mol(-1) Å(2)) by geometric control. Confinement may inherently stabilize the chains, potentially providing a platform for the synthesis of extraordinarily long chains (tens of nanometers) with variable compressive response.

Conformational analysis of single perfluoroalkyl chains by single-molecule real-time transmission electron microscopic imaging

Whereas a statistical average of molecular ensembles has been the conventional source of information on molecular structures, atomic resolution movies of single organic molecules obtained by single-molecule real-time transmission electron microscopy have recently emerged as a new tool to study the time evolution of the structures of individual molecules. The present work describes a proof-of-principle study of the determination of the conformation of each C-C bond in single perfluoroalkyl fullerene molecules encapsulated in a single-walled carbon nanotube (CNT) as well as those attached to the outer surface of a carbon nanohorn (CNH). Analysis of 82 individual molecules in CNTs under a 120 kV electron beam indicated that 6% of the CF2-CF2 bonds and about 20% of the CH2-CH2 bonds in the corresponding hydrocarbon analogue are in the gauche conformation. This comparison qualitatively matches the known conformational data based on time- and molecular-average as determined for ensembles. The transmission electron microscopy images also showed that the molecules entered the CNTs predominantly in one orientation. The molecules attached on a CNH surface moved more freely and exhibited more diverse conformation than those in a CNT, suggesting the potential applicability of this method for the determination of the dynamic shape of flexible molecules and of detailed conformations. We observed little sign of any decomposition of the specimen molecules, at least up to 10(7) e·nm(-2) (electrons/nm(2)) at 120 kV acceleration voltage. Decomposition of CNHs under irradiation with a 300 kV electron beam was suppressed by cooling to 77 K, suggesting that the decomposition is a chemical process. Several lines of evidence suggest that the graphitic substrate and the attached molecules are very cold.

High-Pressure Phase Favored by a Symmetry-Recognized Nanoconfinement Effect

Recently, a high-pressure phase (B2) of KI has been experimentally observed in the inner space of single-walled carbon nanotubes. Our first-principles calculations indicate that in a confined nanospace, relative stabilities of the high-pressure B2 phase and the low-pressure B1 phase of KI are not necessarily determined by their external pressures. As a result of crystal symmetry differences, different phases are preferred at different K/I ratios. Such a symmetry-recognized confinement effect opens a new avenue for nanomaterials synthesis.