A comparative study of argon ion irradiated pristine and fluorinated single-wall carbon nanotubes

Effect of Ar(+) ion irradiation on the structure of pristine and fluorinated single-wall carbon nanotubes (SWCNTs) was examined using transmission electron microscopy (TEM), Raman, and x-ray photoelectron spectroscopy (XPS). The TEM analysis revealed retention of tubular structures in both irradiated samples while Raman spectroscopy and XPS data indicated a partial destruction of nanotubes and formation of oxygen-containing groups on the nanotube surface. From similarity of electronic states of carbon in the irradiated pristine and fluorinated SWCNTs observed by XPS, it was suggested that defluorination of nanotubes proceeded with breaking of C-F bonds.     

Selective extraction of large-diameter single-wall carbon nanotubes with specific chiral indices by poly(9,9-dioctylfluorene-alt-benzothiadiazole)

Semiconducting single-wall carbon nanotubes (SWCNTs) having large diameters (d(t) > 1.3 nm) are successfully extracted in toluene by fluorene-based polymers. In particular, poly(9,9-dioctylfluorene-alt-benzothiadiazole) shows excellent selectivity for (15,4) SWCNTs. Although the importance of structural matching between the fluorene backbone and the tube surface has already been discussed, the present photoluminescence studies reveal that matching the energy levels between fluorene-based polymers and SWCNTs is crucial for selective nanotube extractions.     

Swelling the hydrophobic core of surfactant-suspended single-walled carbon nanotubes: a SANS study

Localized solvent environments form around single-wall carbon nanotubes (SWCNTs) because of the ability of surfactant molecules to solubilize immiscible organic solvents. Although these microenvironments around SWCNTs have already been used for fundamental and applied studies, small-angle neutron scattering (SANS) was used here to assess the size and shape of the solvent domains, their uniformity and distribution on the sidewalls, and the effect of solvent swelling on the aggregation state of the suspension. SANS measurements confirm both the formation of local solvent environments and that no irreversible aggregation of the nanotube suspension occurs after the SDS molecules are swollen in solvent. The results also corroborate prior conclusions based on photoluminescence that the structure formed is dependent of the nature of the solvent-surfactant combination; SWCNTs suspended with SDS and swelled with benzene have a more uniform coating on the sidewall than those swelled with o-dichlorobenzene. These differences can be important to understanding the effect of the local environment on the photoluminescence properties and the interaction of SWCNTs with interfaces.     

Carbon nanotube poroshell silica as a novel stationary phase for fast HPLC analysis of monoclonal antibodies

A new carbon nanotube porous silica poroshell stationary phase was developed. The chromatographic support was coated with ultrashort single-wall carbon nanotubes (SWCNTs) in a noncovalent way. It was demonstrated that the porous amino silica surface of the 300 NH₂ poroshell column stabilized with 1-methyl-2-pyrrolidinone efficiently and stably adsorbed SWCNTs onto the chromatographic support. It was shown that this novel poroshell carbon nanotube (CNT) stationary phase was very useful for the HPLC separation of a series of monoclonal antibodies (mAbs) in a short analysis time (<3 min). The high-performance liquid chromatography (HPLC) method was validated and was successfully tested for the fast quantitative and qualitative control of chemotherapeutic bags fabricated in a hospital pharmacy.     

Comparative study on different carbon nanotube materials in terms of transparent conductive coatings

We compared conductive transparent carbon nanotube coatings on glass substrates made of differently produced single-wall (SWNT), double-wall, and multiwall carbon nanotubes. The airbrushing approach and the vacuum filtration method were utilized for the fabrication of carbon nanotube films. The optoelectronic performance of the carbon nanotube film was found to strongly depend on many effects including the ratio of metallic-to-semiconducting tubes, dispersion, length, diameter, chirality, wall number, structural defects, and the properties of substrates. The electronic transportability and optical properties of the SWNT network can be significantly altered by chemical doping with thionyl chloride. Hall effect measurements revealed that all of these thin carbon nanotube films are of p-type probably due to the acid reflux-based purification and atmospheric impurities. The competition between variable-range hoping and fluctuation-assisted tunneling in the functionized carbon nanotube system could lead to a crossover behavior in the temperature dependence of the network resistance.     

Statistical sampling of carbon nanotube populations by thermogravimetric analysis

Carbon nanotubes are one of the most promising nanomaterials available with applications in electronics devices, sensing, batteries, composites and medicine. Strict control of the carbon nanotube chemistry and properties is necessary as the applications proceed into more specialized areas. Thermogravimetric analysis (TGA) is one analytical method currently utilized for the characterization of carbon nanotubes. Though TGA can provide quantitative measurements of the composition of a sample, many researchers do not ensure the variance of the sample is properly captured. This research demonstrates for four single-wall carbon nanotube (SWCNT) samples how to statistically evaluate the material with TGA to ensure that the variance within the material is represented. SEM results are used to help reach conclusions about purity of the material by providing a visual means for inspection. This data is used to select the SWCNT material with the lowest variability and highest quality, as evaluated by composition and reproducibility.     

Impact of Tube Curvature on the Ground‐State Magnetism of Axially Confined Single‐Walled Carbon Nanotubes of the Zigzag‐Type

The magnetic properties of axially confined, hydrogenated single‐walled carbon nanotubes (SWCNTs) of the (n,0)‐type with n=5–24 are systematically explored by density functional theory. Emphasis is placed on the relation between the ground‐state magnetic moments of SWCNTs and zigzag graphene nanoribbons (ZGNRs). Comparison between the SWCNTs considered here and ZGNRs of equal length gives rise to two basic questions: 1) how does the nanotube curvature affect the antiferromagnetic order known to prevail for ZGNRs, and 2) to what extent do the magnetic moments localized at the SWCNT edges deviate from the zero‐curvature limit of n/3 μ_B? In response to these questions, it is found that systems with n≥7 display preference for antiferromagnetic order at any length investigated, whereas for n=5, 6 the magnetic phase varies with tube length. Furthermore, elementary patterns are identified that describe the progression of the magnitude of the magnetic moment with n for the longest tubes explored in this work. The spin densities of the considered SWCNTs are analyzed as a function of the tube length L, with L ranging from 3 to 11 transpolyene rings for n≥7 and from 3 to 30 rings for n=5 and 6.     

Dramatic reduction of IR vibrational cross sections of molecules encapsulated in carbon nanotubes

Combined temperature-programmed desorption and IR studies suggest that absorption cross sections of IR-active vibrations of molecules "strongly" bound to single-wall carbon nanotubes (SWCNTs) are reduced at least by a factor of 10. Quantum chemical simulations show that IR intensities of endohedrally encapsulated molecules are dramatically reduced, and identify dielectric screening by highly polarizable SWCNT sidewalls as the origin of such "screening". The observed intensity reduction originates from a sizable cancellation of adsorbate dipole moments by mirror charges dynamically induced on the nanotube sidewalls. For exohedrally adsorbed molecules, the dielectric screening is found to be orientation-dependent with a smaller magnitude for adsorption in groove and interstitial sites. The presented results clearly demonstrate and quantify the screening effect of SWCNTs and unequivocally show that IR spectroscopy cannot be applied in a straightforward manner to the study of peapod systems.     

Preparation of micelle-encapsulated single-wall and multi-wall carbon nanotubes with amphiphilic hyperbranched polymer

The hyperbranched polyester (Boltorn^TM H20) was modified by maleic anhydride and then polystyrene (H20-MAh-PSt) to form amphiphilic micelles in water. The single-wall and multi-wall carbon nanotubes (SWCNTs and MWCNTs, respectively) were encapsulated in the formed micelles through non-covalent interactions. The formed structures were confirmed by FTIR, NMR, GPC, and XPS analysis. The dispersion and aggregation behaviors were observed by TEM and UV-vis and Raman spectroscopic analysis. The results showed that the dispersion performance of the obtained micelle-encapsulated carbon nanotubes in water was greatly improved compared to the pure carbon nanotubes. From the TEM observation, the individual SWCNT structure and the uniform polymer coating around the surface of SWCNT were seen after crosslinking. The Raman spectroscopic measurements also demonstrated that for the crosslinked samples, no effect occurred associated with concentration-dependent carbon nanotube aggregation.     

Enthalpy and entropy effects in hydrogen adsorption on carbon nanotubes

Interaction energies and entropies associated with hydrogen adsorption on the inner and outer surfaces of zigzag single-wall carbon nanotubes (SWCNT) of various diameters are analyzed by means of molecular mechanics, density functional theory, and ab initio calculations. For a single molecule the strongest interaction, which is 3.5 greater than that with the planar graphite sheet, is found inside a (8,0) nanotube. Adsorption on the outer surfaces is weaker than that on graphite. Due to the steric considerations, both processes are accompanied by an extremely strong decline in entropy. Absence of specific adsorption sites and weak attractive interaction between hydrogen molecules within carbon nanotubes results in their close packing at low temperatures. Using the calculated geometric and thermodynamic parameters in Langmuir isotherms we predict the adsorption capacity of SWCNTs at room temperature to be smaller than 1 wt % even at 100 bar.     

Direct attachment of well-aligned single-walled carbon nanotube architectures to silicon (100) surfaces: a simple approach for device assembly

A new approach for the attachment of vertically-aligned shortened carbon nanotube architectures to a silicon (100) substrate by chemical anchoring directly to the surface has been demonstrated for the first time. The ordered assembly of single-walled carbon nanotubes (SWCNTs) was accomplished by hydroxylating the silicon surface followed by a condensation reaction with carboxylic acid functionalised SWCNTs. This new nanostructure has been characterised by X-ray photoelectron, Raman and Fourier transform infrared (FTIR) spectroscopy as well as scanning electron and atomic force microscopy. The assembly behaviour of SWCNTs onto the silicon surface shows a fast initial step producing isolated functionalised carbon nanotubes or nanotube bundles anchored to the silicon surface followed by a slower step where the adsorbed nanotubes grow into larger aggregates via van der Waals interactions between adsorbed and solvated nanotubes. The electrochemical and optical properties of the SWCNTs directly attached to silicon have also been investigated. These new nanostructures are excellent electrochemical electrodes. They also fluoresce in the wavelength range 650-800 nm. The successful attachment of the SWCNTs directly to silicon provides a simple, new avenue for fabrication and development of silicon-based nanoelectronic, nano-optoelectronic and sensing devices. Compared to existing techniques, this new approach has several advantages including low operating temperature, low cost and the possibility of further modification.     

单壁碳纳米管受压屈曲行为的数值模拟

The buckling behavior of single-wall carbon nanotubes（SWCNTs）under compression is simulated by using the molecular dynamics method with Tersoff-Brenner potential to describe the interactions between atoms in SWCNT. The results show that the Young's modulus of SWCNTs decreases as the radius of SWCNTs increases,and critical stress and critical strain when the buckling of SWCNTs occurs are related to the slender ratio of SWCNTs. The difference of slender ratio determines two different buckling modes. The global buckling first happens for SWCNTs with the smaller slender ratio,while the local buckling first occurs for those with the larger slender ratio. The critical stress in the global buckling is proportional to the inverse of length of SWCNTs,while the critical stress in the local buckling is inversely proportional to the radius and the square of length of SWCNTs,which shows that the buckling theory of circular cylindrical shell in continuum mechanics can not be directly applied to the buckling of SWCNTs.     

Ordered assembly of protonated porphyrin driven by single-wall carbon nanotubes. J- and H-aggregates to nanorods

Ordered assemblies of protonated porphyrin in the form of J- and H-type aggregates have been achieved on the single-wall carbon nanotube (SWCNTs) surface. This unusual molecular aggregation phenomenon driven by SWCNTs further enables macroscopic assembly in the form of linear bundles.     

Performance of dye-sensitized solar cells with various carbon nanotube counter electrodes

Double-wall carbon nanotubes (DWCNTs), single-wall carbon nanotubes (SWCNTs), and multi-wall carbon nanotubes (MWCNTs) were investigated as an alternative for platinum in counter-electrodes for dye-sensitized solar cells. The counter-electrodes were prepared on fluorine-doped tin oxide glass substrates by the screen printing technique from pastes of carbon nanotubes and organic binder. The solar cells were assembled from carbon nanotubes counter-electrodes and screen printed anodes made from titanium dioxide. The cells produced with DWCNTs, SWCNTs or MWCNTs have overall conversion efficiencies of 8.0%, 7.6% and 7.1%, respectively. Electrochemical impedance spectroscopy measurements revealed that DWCNTs displayed the highest catalytic activity for the reduction of tri-iodide ions. The large surface area and superior chemical stability of the DWCNTs facilitated the electron-transfer kinetics at the interface between counter-electrode and electrolyte and yielded the lowest transfer resistance, thereby improving the photovoltaic activity. A short-term stability test at moderate conditions confirmed the robustness of solar cells based on the use of DWCNTs, SWCNTs or MWCNTs.

The calculations of phonon dispersion relations for single-wall carbon armchair and zigzag nanotubes

A 3D single-wall carbon nanotube can be viewed as a 2D graphite sheet rolled into a 3D cylinder. In the study of dispersion relations of carbon nanotubes, the consistent force parameters for 2D graphite sheets have to be modified to include the curvature effect. The present paper reports a series of calculations of phonon dispersion relations for single-wall carbon armchair, zigzag nanotube in which the curvature effect has been properly treated. The symmetry of crystal vibration mode at the centre of Brillouin zone is analyzed based on our numeric results and the structure symmetry of the nanotubes.     

The use of NH3 to promote the production of large-diameter single-walled carbon nanotubes with a narrow (n,m) distribution

We demonstrate here a simple and effective (n,m)-selective growth of single-walled carbon nanotubes (SWCNTs) in an aerosol floating catalyst chemical vapor deposition (CVD) process by introducing a certain amount of ammonia (NH(3)). Chiralities of carbon nanotubes produced in the presence of 500 ppm NH(3) at 880 °C are narrowly distributed around the major semiconducting (13,12) nanotube with over 90% of SWCNTs having large chiral angles in the range 20°-30°, and nearly 50% in the range 27°-29°. The developed synthesis process enables chiral-selective growth at high temperature for structurally stable carbon nanotubes with large diameters.     

Electronic structures and spectroscopic regularities of phenylene-modified SWCNTs

The equilibrium geometries and electronic structures for a series of single-wall carbon nanotubes (SWCNTs) modified with phenylene were studied using the density functional theory (DFT) at the B3LYP/6-31G(d) level. Of the four configurations of the phenylene-modified SWCNTs, the v-configuration in which the bond is perpendicular to the main axis of the SWCNT is the most thermodynamically stable. The increase in radii of the modified SWCNTs generally leads to a decrease in the energy gaps. The first absorptions in the electronic spectra of the modified SWCNTs compared with those in the electronic spectra of pristine SWCNTs are basically red-shifted. The chemical shifts of bridged carbon atoms connected with phenylene in the v-configuration are shifted downfield relative to those of the pristine SWCNTs. The aromaticity of the rings in SWCNTs is improved owing to the addition of phenylene.     

Enhanced adsorption affinity of anionic perylene-based surfactants towards smaller-diameter SWCNTs

We present evidence from multiple characterization methods, such as emission spectroscopy, zeta potential, and analytical ultracentrifugation, to shed light on the adsorption behavior of synthesized perylene surfactants on single-walled carbon nanotubes (SWCNTs). On comparing dispersions of smaller-diameter SWCNTs prepared by using cobalt-molybdenum catalysis (CoMoCAT) with the larger-diameter SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco), we find that the CoMoCAT-perylene surfactant dispersions are characterized by more negative zeta potentials, and higher anhydrous specific volumes (the latter determined from the sedimentation coefficients by analytical ultracentrifugation), which indicates an increased packing density of the perylene surfactants on nanotubes of smaller diameter. This conclusion is further supported by the subsequent replacement of the perylene derivatives from the nanotube sidewall by sodium dodecyl benzene sulfonate (SDBS), which first occurs on the larger-diameter nanotubes. The enhanced adsorption affinity of the perylene surfactants towards smaller-diameter SWCNTs can be understood in terms of a change in the supramolecular arrangement of the perylene derivatives on the scaffold of the SWCNTs. These findings represent a significant step forward in understanding the noncovalent interaction of π-surfactants with carbon nanotubes, which will enable the design of novel surfactants with enhanced selectivity for certain nanotube species.     

Structural and reactivity properties of finite length cap-ended single-wall carbon nanotubes

The reaction of C2 with growing single-wall carbon nanotubes of different chiralities is investigated using density functional theory. It is found that the energy of the frontier orbitals for (5,5) and (6,6) armchair carbon nanotubes exhibits periodic behavior with an increasing number of carbon atoms in the nanotube. Such periodic behavior induces oscillations in the reaction energy released by adsorption of C2 to the nanotube open edge. In contrast, the energy of the frontier orbitals of the (6,5) chiral tube remains constant as the number of C atoms increases, and the same stability is observed in the adsorption energy. It is suggested that this may be one of the reasons for the low percent of armchair single-wall carbon nanotubes found in the experimental synthesis.