Open-ended Single-walled Carbon Nanotubes Research Articles

Synthesis and stockpile of polyynes in paraffin as well as extraction for preparing single-walled carbon nanowires (LLCCs@SWCNTs)

The polyynes are extremely unstable and reactive, and their long-term storage is still a challenge. We first used paraffin as an organic solvent in a submerged electric arc for preparing polyynes, placed them in solid paraffin at room temperature, and assessed their storage stability. One month late, we extracted the polyynes from paraffin, and separated the extracted polyynes by HPLC for obtaining single isolated polyynes. The polyynes extracted from solid paraffin were also purified and filled into open-ended single-walled carbon nanotubes (SWCNTs) to obtain polyynes@SWCNTs samples, which were heated to prepare single-walled carbon nanowires (SWCNWs, LLCCs@SWCNTs), made of long linear carbon chains (LLCCs) inserted inside SWCNTs. The 4L band at 7250 cm−1 was observed in the normal Raman spectra of SWCNWs for the first time. This work solves the problem of long-term storage of polyynes, and opened new avenues for exploring physical properties and applications of polyynes, LLCCs and SWCNWs.

Smallest carbon nanowires made easy: Long linear carbon chains confined inside single-walled carbon nanotubes

The carbon nanowires are defined as long linear carbon chains (LLCCs) or carbynes confined inside carbon nanotubes (CNTs). LLCCs were synthesized previously inside multi-walled CNTs (LLCCs@MWCNTs) and double-walled CNTs (LLCCs@DWCNTs). In this work, a feasible, efficient, controllable and scalable method was developed to mass-produce the smallest carbon nanowires (LLCCs@SWCNTs) consisting of LLCCs encapsulated inside single-walled CNTs (SWCNTs) with diameters of 0.70–0.95 nm. The polyynes were inserted into the open-ended SWCNTs, and then polyynes@SWCNTs were heated at 700 °C in argon gas. A combination of Raman spectra studies and high-resolution transmission electron microscopy observations demonstrated the formation of LLCCs@SWCNTs nanostructure. Density functional theory calculations and reactive molecular dynamics simulations indicated that the polyynes could fuse and grow to LLCCs inside the hollow space of SWCNTs. This work opened new avenues for exploring various physical properties of both LLCCs (carbyne) and LLCCs@SWCNTs, as well as their potential applications in nanoelectronics, nanomechanics and composite nanomaterials.

Adsorption simulation of open-ended single-walled carbon nanotubes for various gases

In order to study the adsorption capacity of open-ended single-walled carbon nanotubes for various gases, the grand canonical Monte Carlo method is used to simulate the adsorption capacities of methane, nitrogen, water, carbon dioxide, and carbon monoxide in different types of open-ended single-walled carbon nanotubes at temperatures of 273.15 K and 298.15 K and pressures of 1 Pa–101.325 kPa. Gas adsorption isotherms under various conditions were obtained. The effects of temperature and diameter of open-ended single-walled carbon nanotubes on gas adsorption capacity were discussed. The results showed that the open-ended single-walled carbon nanotubes had a certain adsorption capacity for five kinds of gases under low pressure conditions. For a given temperature, as the diameter of the tube increased, the adsorption capacities of various gases were enhanced. Each gas exhibited different growth gradients; specifically, the growth gradients of methane and nitrogen were relatively small, while the growth gradients of water, carbon dioxide, and carbon monoxide were relatively large. With an increase in the temperature, the adsorption capacities of CH4, N2, H2O, and CO2 exhibited a downward trend, while the adsorption capacity of CO was not affected by temperature, keeping a stable value. The open-ended single-walled carbon nanotube with a diameter of 10.85 Å exhibited a high adsorption capacity for CO, and it could be used as a porous material for storing or separating CO.

Distributive lattice structure on the set of perfect matchings of carbon nanotubes

Carbon nanotubes are composed of carbon atoms linked in hexagonal shapes, with each carbon atom covalently bonded to three other carbon atoms. Carbon nanotubes have diameters as small as 1 nm and lengths up to several centimeters. Carbon nanotubes can be open-ended or closed-ended (fullerenes). Open-ended single-walled carbon nanotubes are also called tubulenes. The resonance graph R(T) of a tubulene T reflects interactions between Kekule structures—i.e. perfect matchings of T. With the orientation of edges the resonance digraph \(\overrightarrow{R}(T)\) of a tubulene is obtained. As the main result we show that \(\overrightarrow{R}(T)\) is isomorphic to the Hasse diagram of the direct sum of some distributive lattices. Similar results were proved in [10, 16], but one can not directly apply them to tubulenes. As a consequence of the main result it is proved that every connected component of R(T) is a median graph. Further we show that the block graph of every connected component H of the resonance graph of a tubulene is a path and that H contains at most two vertices of degree one.

Optimization of Hydrogen Storage Capacity by Physical Adsorption on Open-ended Single-walled Carbon Nanotube as Diameter Function

In this paper, we perform combination methods of semi-empirical research, a theoretical approach, and force-matching to determine the optimum adsorption capacity on an open-ended single-walled carbon nanotube (SWCNT) as a diameter function. Using a semi-empirical study, we can determine the value of monolayer coverage and isosteric heat of adsorption from available thermodynamic data. By completing the semi-empirical study, we carried out quantum mechanical calculations to determine the adsorption energy on the interior and exterior of SWCNTs. Furthermore, monolayer coverage, specific surface area, and maximum adsorption capacity as the main quantity in the adsorption process was estimated using the combination method of force-matching and a classical Lennard-Jones potential model. Hydrogen physisorption was investigated on zig-zag SWCNTs at conditions for a pressure range of 0.1 to 10 MPa at 233 K and 298.15 K temperature. The adsorption of all data can be explained with the Toth model. The results shows the SWCNT exterior physisorption energy range between 1.35 to 1.62 kcal/mol. The interior range from 1.22 to 2.43 kcal/mol. With a wide degree of temperature and pressure variations, we obtained an optimum SWCNT diameter of 8-12 A . At the optimum diameter maximum adsorption capacity, we achieved 1.75 wt% at 233 K and an operating pressure of 10 MPa.

Experimental Information on the Adsorbed Phase of Water Formed in the Inner Pore of Single-Walled Carbon Nanotube Itself.

Thus far, nobody has successfully obtained the accurate information on the properties of the adsorbed phases of gases or vapors formed inside a cylindrical micropore of single-walled carbon nanotube (SWCNT) itself based on the experimental procedure. In this work, we succeeded in analyzing experimentally the properties of adsorbed nitrogen and water confined in the inner pore of SWCNT itself by opening the pore composed of close-ended SWCNT without any changes in the surface state and also by applying the unique method for characterization; both the amounts, as well as properties, of surface functional groups and the bundle structure are the same even after the treatments for introducing an open-ended structure to a close-ended one. As a result, the average pore sizes, as well as characteristic adsorption behavior, on the two types of sample were available from the analysis of respective difference adsorption isotherms of nitrogen measured at 77 K between the adsorbed amounts on the open-ended SWCNT and that on the close-ended one. The evaluated pore sizes well coincide with the results estimated by Raman data. These results strongly support that we could analyze the adsorbed phases formed only in the inner pore of SWCNTs by applying the present method. Furthermore, we could analyze the adsorbed phase of water formed inside the cylindrical micropore of SWCNTs, showing the difference in the densities of adsorbed water depending on the pore sizes from the value of bulk water; the densities of the adsorbed water were evaluated to be 0.62 and 0.71 g mL(-1) for SWCNTs having average pore sizes of 1.3 and 1.7 nm, respectively, which were in harmony with those obtained by the theoretical calculations reported by other researchers. The proposed analysis method makes it possible to recognize the focused states of the adsorbed water formed inside the cylindrical micropore of SWCNT more precisely and correctly. The method proposed will shed light on the discussion related to the detailed nature of various adsorbed gases into SWCNT, to the detailed role of adsorbed species formed inside pore in various phenomena, and to the designing the useful materials based on the gained knowledge.

Binding Energy of Oxygen and Methane Adsorbed on Bundles of Open-ended Single-wall Carbon Nanotubes

Binding Energy of Oxygen and Methane Adsorbed on Bundles of Open-ended Single-wall Carbon Nanotubes

Molecular dynamics properties of varying amounts of the anticancer drug gemcitabine inside an open-ended single-walled carbon nanotube

To investigate the loading of multiple drugs inside single-walled carbon nanotubes (SWCNTs), molecular dynamics simulations were applied to the gemcitabine–SWCNT system with from one to six drug molecules being confined inside the SWCNT cavity. At low drug concentrations (1–4 gemcitabines inside each SWCNT), the π–π stacking of two cytosine rings of adjacent gemcitabine molecules caused them to orientate towards each other and move together inside the SWCNT. In contrast, at high drug concentrations (encapsulated gemcitabines ⩾5), the close contact of gemcitabines promoted electrostatic interactions through hydrogen bonding rather than the π–π stacking interaction from their cytosine rings.

On the stability of single-walled carbon nanotubes and their binding strengths

We have studied the relative stability of hydrogen-terminated single-walled carbon nanotubes (SWNTs) segments, and open-ended SWNT fragments of varying diameter and chirality that are present at the interface of the catalytic metal particles during growth. We have found that hydrogen-terminated SWNTs differ by <1 eV in stability among different chiralities, which presents a challenge for selective and property-controlled growth. In addition, both zigzag and armchair tubes can be the most stable chirality of hydrogen-terminated SWNTs, which is a fundamental obstacle for property-controlled growth utilizing thermodynamic stability. In contrast, the most armchair-like open-ended SWNTs segments are always the most stable ones, followed in sequence by chiral index up to the least stable zigzag segments. We explain the ordering by triple bond stabilization of the carbon dangling bonds at the open ends, which is a fragment stabilization effect that is only manifested when all bonds between two layers are broken. We show convincingly that the bond strength difference between zigzag and armchair tubes is not present when individual bonds are broken or formed.

Ab initio Study of Direct Diffusion Pathway for H+, Li+, Na+, K+ Cations into the (3,3), (4,4), and (5,5) Open-Ended Single-Walled Carbon Nanotubes

To probe the ability of ions to enter and leave a nanotube interior, we calculated the energetic of a direct diffusion pathway for H+, Li+, Na+, K+ cations to move through the (3,3), (4,4) and (5,5) open-ended single-walled carbon nanotubes (SWNTs) with ab initio techniques. For three nanotubes, there is no energy barrier for the Li+ ions to enter the open tubes. In fact, there is a net decrease in the energy of the system, showing that the nanotubes actually act as an attractor for the Li+ ions. Similar results also hold for the H+ and Na+ ions into (4,4) nanotube. These ions can easily diffuse and leave the nanotube from other side. H+ strongly attract with the (3,3) nanotube but cannot diffuse and is trapped. Our results show that the entry of K+ and Na+ ions into (3,3) nanotube is forbidden. In contrast, (4,4) and (5,5) nanotubes for H+ and K+ ions and (5,5) nanotubes for Na+ act as ion channels that conduct these ions. In all NT-H systems and (3,3) NT-Li system, the charge transferred between ion and nanotube and nanotube achieve the positive charge.

Release of encapsulated molecules from carbon nanotubes using a displacing method: a MD simulation study

Using molecular dynamics (MD) simulations, we report a displacing method to release encapsulated molecules out of open-ended single-walled carbon nanotubes (SWNTs). The simulations indicated that encapsulated molecules such as water, DNA and indomethacin (IMT) molecules would be expelled from SWNTs by fillers such as C60 molecules and metal nanowires through a displacement process, which is attributed to the much stronger van der Waals interaction between SWNTs and fillers than that between SWNTs and encapsulated molecules. In order to quantitatively reveal the release process, the center of mass (COM) distances between encapsulated molecules (and fillers) and SWNTs were calculated. Furthermore, investigations of various energies indicated that the release process is spontaneous and the van der Waals force is the main drive for the release process. Moreover, some influencing factors such as nanotube diameter and length are discussed as well. This study provides a new method for the release of drugs/genes in the biomedical field, and provides valuable information for designing novel assembled nanoscale devices.

Theoretical Study of Different Solvents and Temperatures Effects on Single-Walled Carbon Nanotube and Temozolomide Drug: A QM/MM Study

Recently, the majority of the investigation into computational chemistry has been focused on the examination of molecules submerged in various solvents and the interaction of anticancer drug with carbon nanotubes (CNTs). The most likely tendency is toward the interaction between anticancer drug and single-walled carbon nanotubes (SWCNTs). In this investigation, the interaction of Temozolomide, a common form of anticancer drug with open-end of SWCNT, are examined, with MM+, Amber and OPLS force field in molecular mechanic (MM) method. We investigate effects of water, methanol and a mixture of them on interaction of Temozolomide with SWCNT, utilizing these force fields. The interaction of Temozolomide with open-end of SWCNT in gas phase, water and methanol have been processed applying the abinitio calculations. The calculations have been done with the GAUSSIAN 98 program according to Hartree-Fock (HF) theory at the HF/STO-3G level. Gibbs free energy, enthalpy, entropy and dipole moment values are compared in gas phase, water and methanol in this research. Thus, by utilizing a Hartree-Fock method, we studied the effects of different solvents on interaction of Temozolomide with open-end SWCNT within the onsager self-consistent reaction field (SCRF) model, as well as the temperature effects on the stability of the interaction between Temozolomide and single-walled carbon in various solvents.

Encapsulation of Carbon Chain Molecules in Single-Walled Carbon Nanotubes

The vacuum space inside carbon nanotubes offers interesting possibilities for the inclusion, transportation, and functionalization of foreign molecules. Using first-principles density functional calculations, we show that linear carbon-based chain molecules, namely, polyynes (C(m)H(2), m = 4, 6, 10) and the dehydrogenated forms C(10)H and C(10), as well as hexane (C(6)H(14)), can be spontaneously encapsulated in open-ended single-walled carbon nanotubes (SWNTs) with edges that have dangling bonds or that are terminated with hydrogen atoms, as if they were drawn into a vacuum cleaner. The energy gains when C(10)H(2), C(10)H, C(10), C(6)H(2), C(4)H(2), and C(6)H(14) are encapsulated inside a (10,0) zigzag-shaped SWNT are 1.48, 2.04, 2.18, 1.05, 0.55, and 1.48 eV, respectively. When these molecules come inside a much wider (10,10) armchair SWNT along the tube axis, they experience neither an energy gain nor an energy barrier. They experience an energy gain when they approach the tube walls inside. Three hexane molecules can be encapsulated parallel to each other (i.e., nested) inside a (10,10) SWNT, and their energy gain is 1.98 eV. Three hexane molecules can exhibit a rotary motion. One reason for the stability of carbon chain molecules inside SWNTs is the large area of weak wave function overlap. Another reason concerns molecular dependence, that is, the quadrupole-quadrupole interaction in the case of the polyynes and electron charge transfer from the SWNT in the case of the dehydrogenated forms. The very flat potential surface inside an SWNT suggests that friction is quite low, and the space inside SWNTs serves as an ideal environment for the molecular transport of carbon chain molecules. The present theoretical results are certainly consistent with recent experimental results. Moreover, the encapsulation of C(10) makes an SWNT a (purely carbon-made) p-type acceptor. Another interesting possibility associated with the present system is the direction-controlled transport of C(10)H inside an SWNT under an external field. Because C(10)H has an electric dipole moment, it is expected to move under a gradient electric field. Finally, we derive the entropies of linear chain molecules inside and outside an open-ended SWNT to discuss the stability of including linear chain molecules inside an SWNT at finite temperatures.

Hydrogen bond and halogen bond inside the carbon nanotube

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.

Molecular dynamics simulation study of neon adsorption on single-walled carbon nanotubes

Using molecular dynamics (MD) simulations, neon adsorption on an open-ended (10,10) single-walled carbon nanotube (SWCNT) was investigated at supercritical temperatures of neon, i.e. T=50, 70, and 90 K. Adsorption isotherms, heat of adsorption, self-diffusion coefficients, activation energy, and structural properties of neon gas were computed and analyzed in detail. All adsorption isotherms are predicted to be of Langmuir shape type І at this range of temperature. The results show that temperature is in a direct correlation with adsorption capacity, i.e. increase in temperature causes lower adsorption of neon gas by SWCNT. All aforementioned quantities confirm this fact and are in good agreement with previous experimental and theoretical works.

Density functional theory studies of OH-modified open-ended single-wall zigzag carbon nanotubes (SWCNTs)

Functionalized carbon nanotubes (CNTs) are often formed as result of oxidation and cleaning of raw product grown on metal catalyst. Structure and energy of ideal and OH-modified single-wall nanotubes (SWCNTs) of different length (2.8, 7.0 and 13.5 Å) were obtained at the DFT-B3LYP level. From one to nine OH groups were added at the end of the nanotube and a nonadditive dependence of attachment energy on the number of substituents was observed. The energetics of SWCNT end substitution with OH groups was supported by high level MP2 and CCSD(T) determination of reaction energy: R – H + 1 / 2 O 2 → R – OH + Δ E for methane, benzene and anthracene. In addition, a vibrational analysis of the shortest nanotube was carried out and characteristic Raman bands were identified.

Study of neon adsorption on carbon nanocones using molecular dynamics simulation

We have used molecular dynamics simulation to study Ne adsorption on carbon nanocones. Adsorption isotherms were obtained at several temperatures between 22.67 and 49.82 K. Adsorption coverage, isosteric heat, and binding energy were calculated. Adsorption was observed both inside and outside of an individual carbon nanocone. The results indicate that the saturation coverage and saturation pressure depend on temperature. At saturation conditions, the maximum values of interior and exterior coverages are 0.17 and 0.39 neon per carbon, respectively. The results are compared to Ne adsorption on open-ended single-walled carbon nanotubes. It is found that adsorption coverages on carbon nanocones are greater than those on carbon nanotubes. The isosteric heat and binding energy of neon adsorption on nanocones indicate that nanocones and nanotubes have highly desirable characteristics as an adsorbent.

Possibility of driving water molecules along a single-walled carbon nanotube using methane molecules

Molecular dynamics simulation is used to study the transport behavior of water molecules along an open-ended single-walled carbon nanotube (SWCNT) under the driving force of methane molecules. The methane molecules pull the water molecules from the inside of a SWCNT along the axial direction. The transport velocity of water molecules increases with increasing number of methane molecules, but decreases with increasing diameter of the SWCNT.

Field-dependent electron emission patterns from individual SWCNTs simulated with a multi-scale algorithm

The electron distribution of open-ended single-walled carbon nanotubes (CNTs) with chirality indexes (7,0) and (5,5) in field emission conditions was calculated via a multi-scaled algorithm. The field emission images were produced numerically. It was found that the emission patterns change with the applied macroscopic field. Especially, the symmetry of the emission pattern of the (7,0) carbon nanotube is breaking in the lower field but the breaking is less obvious in the higher field. The magnification factor increases with the applied macroscopic field.

“Cloning” of Single-Walled Carbon Nanotubes via Open-End Growth Mechanism

Using the concept of "cloning", we report herein a rational approach to grow single-walled carbon nanotubes (SWNTs) with controlled chirality via an open-end growth mechanism. Specifically, by using open-end SWNTs as "seeds/catalysts" (without metal catalysts), "new/duplicate" SWNTs could be grown and cloned from the parent segments via an open-end growth mechanism. Using this strategy, we have measured more than 600 short seed segments and have found that the yield of cloning is relatively low (around 9%). This yield can be greatly improved up to 40% by growing SWNTs on quartz substrate. Atomic force microscopy and micro resonance Raman spectroscopy characterization indicate that the parent nanotube and the duplicate nanotube have the same structure. These findings provide a potential approach for growing SWNTs with controlled chirality, which are important for the application of SWNTs in nanoelectronics.