Thermo-physical and impact properties of epoxy nanocomposites reinforced by single-wall carbon nanotubes

The thermo-physical properties and the impact strength of diglycidyl ether of bisphenol F (DGEBF) epoxy nanocomposites reinforced with fluorinated single-wall carbon nanotubes (FSWCNT) are reported. A sonication technique was used to disperse FSWCNT in the glassy epoxy network resulting in nanocomposites having large improvement in modulus with extremely small amount of FSWCNT. The glass transition temperature decreased approximately 30 °C with an addition of 0.2 wt% (0.14 vol%) FSWCNT, without adjusting the amount of the anhydride curing agent. This was because of non-stoichiometry of the epoxy matrix that was caused by the fluorine on the single-wall carbon nanotubes. The correct amount of the anhydride curing agent needed to achieve stoichiometry was experimentally examined by dynamic mechanical analysis (DMA). The storage modulus of the epoxy at room temperature (which is below the glass transition temperature of the nanocomposites) increased up to 0.63 GPa with the addition of only 0.30 wt% (0.21 vol%) of FSWCNT, representing an up to 20% improvement compared with the neat epoxy. The Izod impact strength slightly decreased when the amount of FSWCNT was increased to 0.3 wt%. The excellent improvement in the storage modulus was achieved without sacrificing impact strength.     

Voltammetric determination of bisoprolol fumarate in pharmaceutical formulations and urine using single-wall carbon nanotubes modified glassy carbon electrode

The electrochemistry of bisoprolol fumarate (BF) has been investigated by differential pulse voltammetry at a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE). The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of BF leading to a marked improvement in sensitivity as compared to bare glassy carbon electrode where electrochemical activity for the analyte cannot be observed. The SWNTs-modified GCE exhibited a sharp anodic peak at a potential of ∼950 mV for the oxidation of BF. Under optimum conditions linear calibration curve was obtained over the BF concentration range 0.01-0.1 mM in 0.5 M phosphate buffer solution (pH 7.2) with a correlation coefficient of 0.9789 and detection limit of 8.27 × 10⁻⁷ M. The modified electrode has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has also been validated.     

Iron(III) protoporphyrin IX—single-wall carbon nanotubes modified electrodes for hydrogen peroxide and nitrite detection

Iron(III) protoporphyrin IX (Fe(III)P), adsorbed either on single-walled carbon nanotubes (SWCNT) or on hydroxyl-functionalized SWCNT (SWCNT-OH), was incorporated within a Nafion matrix immobilized on the surface of a graphite electrode. From cyclic voltammetric measurements, performed under different experimental conditions (pH and potential scan rate), it was established that the Fe(III)P/Fe(II)P redox couple involves 1e⁻/1H⁺. The heterogeneous electron transfer process occurred faster when Fe(III)P was adsorbed on SWCNT-OH (11 s⁻¹) than on SWCNT (4.9 s⁻¹). Both the SWCNT-Fe(III)P- and SWCNT-OH-Fe(III)P-modified graphite electrodes exhibit electrocatalytic activity for H₂O₂ and nitrite reduction. The modified electrodes sensitivities were found varying in the following sequences: S_{SWCNT-OH-Fe(III)P} = 2.45 mA/M ≈ S_{SWCNT-Fe(III)P} = 2.95 mA/M > S_Fe(III)P = 1.34 mA/M for H₂O₂, and S_{SWCNT-Fe(III)P} = 3.54 mA/M > S_Fe(III)P = 1.44 mA/M > S_{SWCNT-OH-Fe(III)P} = 0.81 mA/M for NO₂⁻.     

Solid-liquid-solid growth mechanism of single-wall carbon nanotubes

Reasons are presented which suggest that the liquefaction of the catalytic particles is a decisive condition for formation of single wall carbon nanotubes (SWNTs) by physical synthesis techniques. It is argued that the SWNT growth mechanism is a kind of solid-liquid-solid graphitization of amorphous carbon or other imperfect carbon forms catalyzed by molten supersaturated carbon-metal nanoparticles. The assumption of low temperature melting of these nanoparticles in contact with amorphous carbon followed by its precipitation in the form of SWNTs allows to explain qualitatively the experimentally observed SWNT growth rates and temperature dependence of the SWNT yield. Guidelines for increasing SWNT yield are proposed.     

Filling single-wall carbon nanotubes

Single-wall nanotube (SWNT)-based hybrid materials represent a quite recent research field. On the basis of previous works performed on multi-wall carbon nanotubes (MWNTs), the goal is to fill the inner SWNT cavity with various compounds, whose the combination with the surrounding carbon tube is expected to allow peculiar physical phenomena to occur and/or peculiar properties to be obtained. As compared to MWNTs, regular SWNT inner cavity is really nanometric, i.e., in the dimension range where quantum phenomena could occur. However, a major drawback is that filling ∼1-nm wide tubes is less easy (i.e., compared to MWNTs), and the related driving forces not fully understood. Who is working in the field, what and how are the SWNT-based hybrid nano-materials prepared so far, what could possibly be the filling mechanisms, are questions that are discussed in this paper. A review of the existing literature is made, with a focus on C₆₀@SWNTs (peapods), which appear to be the most amazing—and the most promising—SWNT-based hybrid nano-materials to date.     

Structure modification of single-wall carbon nanotubes

Various purification processes were applied to single-wall carbon nanotubes synthesized by metal catalyzed laser ablation. Structure modifications introduced by these processes were investigated by high-resolution transmission electron microscopy and Raman spectroscopy. An apparent structure modification after purification was the increase of bundle size although breaking of nanotubes and a change of nanotube diameter distribution were also observed. More vigorous attacking of single-wall carbon nanotube structure was identified by a strong mixed-acid treatment.     

Third-order optical nonlinearity in single-wall carbon nanotubes

The third-order optical nonlinearity in carbon nanotubes (CNT) exposed to an intensive external electromagnetic field has been investigated. The analysis is based on the quantum kinetic equations for the density matrix of π-electrons in CNT. In the regime of weak driving field, the kinetic equations have been solved by the perturbation method and the third-order nonlinear polarizability of different achiral CNTs has been calculated. The theory elaborated has been used for the evaluation of nonlinear susceptibility of CNT-based composites. Comparison with available experimental data has been presented. In the case of high intensive driving field a nonperturbative numerical simulation of the process has been carried out in the time domain. The axial current density in CNT has been calculated. Excitation of π-plasmons in CNTs has been analyzed.     

Fabrication of the single-wall carbon nanotube compound polymer film electrode and the simultaneous electrochemical behavior of aminophenol isomers

We describe a simple, rapid and selective voltammetry for simultaneous determination of electroactive isomers using nanometer composite electrode. The electrode was constructed by electropolymerization of 4-aminopyridine at single-wall carbon nanotubes modified glassy carbon electrode (SWNTs/POAPE). The configuration and electrochemical properties of SWNTs/POAPE were characterized by scanning electronic micrographs (SEM) and voltammetry. The SWNTs/POAPE showed an excellent electrocatalytic activity to the oxidation of aminophenol isomers and capability of determining three aminophenol isomers simultaneously. The oxidation peak potential difference between m-aminophenol and o-aminophenol was 416 mV, o-aminophenol and p-aminophenol 119 mV, indicating that the o-, m- and p-aminophenol could be identified entirely at the SWNTs/POAPE. The proposed electrode has been applied to the simultaneous voltammetric determination of aminophenol isomers in mixture without previous chemical or physical separations.     

Photoluminescence intensity of single-wall carbon nanotubes

The photoluminescence (PL) intensity of a single-wall carbon nanotube (SWNT) is calculated for each (n, m) by multiplying the photon-absorption, relaxation and photon-emission matrix elements. The intensity depends on chirality and “type I vs type II” for smaller diameter semiconducting SWNTs (less than 1 nm). By comparing the calculated results with the experimental PL intensity of SWNTs prepared by chemical vapor deposition at different temperatures, we find that the abundance of (n, m) nanotubes with smaller diameters should exhibit a strong chirality dependence, which may be related to the stability of their caps.     

Ion-exchange adsorption of copper(II) ions on functionalized single-wall carbon nanotubes immobilized on a glassy carbon electrode

The cation-exchange property of oxidatively treated carbon nanotubes (CNTs) is newly reported. Single-wall carbon nanotubes (SWNTs), which were oxidatively treated, were immobilized on a glassy carbon surface and, on this CNT-modified electrode, Cu(II) ions were spontaneously adsorbed and their redox waves electrochemically measured. It is suggested that the adsorption of the cationic Cu(II) ions occurs by their electrostatic interaction with the negatively charged carboxylic anions on the CNTs after the ion-exchange with protons. The surface coverage of the adsorbed Cu(II) ions depending on the dipping time, the amount of immobilized CNTs, and the Cu(II) concentration was estimated from the electrochemical chronocoulometric measurements. The effect of the ionic strength on the adsorption of the Cu(II) ions was investigated and the adsorption strengths of various alkali metal cations and protons were compared. It is hoped that this new cation-exchange property of CNT-modified electrodes may extend their range of electrochemical applications.     

纳米碳管的制备及其应用

本文综述了纳米碳管的制备及应用,展望了纳米碳管广阔的应用前景。     

Nitrogen-doped carbon nanotubes synthesized with carbon nanotubes as catalyst

Nitrogen-doped carbon (CN_x) nanotubes were synthesized with carbon nanotubes (CNTs) as catalyst by detonation-assisted chemical vapor deposition. CN_x nanotubes exhibited compartmentalized bamboo-like structure. Electron energy loss spectroscopy and elemental mapping studies indicated that the synthesized tubes contained high concentration of nitrogen (ca. 17.3 at.%), inhomogeneously distributed with an enrichment of nitrogen within the compartments. X-ray photoelectron spectroscopy analysis revealed the presence of pyridine-like N and graphitic N incorporated into the graphitic network. The catalytic activity of CNTs for CN_x nanotube growth was ascribed to the nanocurvature and opening edges of CNT tips, which adsorbed C_n/CN species and assembled them into CN_x nanotubes.     

Purification process for single-wall carbon nanotubes

Single-wall carbon nanotubes (SWNTs) have exceptional strength and stiffness and high thermal and electrical conductivity, making them excellent candidates for aerospace structural materials. However, one of the most fundamental challenges is purifying the SWNTs. The purpose of this study was to develop a simple purification process for SWNTs, along with an understanding of the purification process. In addition, uncomplicated analytical methods were sought to screen and compare various purification methods. In this study, we demonstrate an easy method of cleaning SWNTs and evaluating their purity. The cleaning method, which employed oxidative heat treatment followed by acid reflux, was straightforward, inexpensive, and fairly effective. The purification mechanism was determined to be, first, that much of the non-nanotube carbon and iron catalyst was oxidized and, second, that the acid washing removed the iron oxide, leaving relatively pure SWNTs. Also, it was shown that a combination of thermal gravimetric analysis and Raman spectroscopy, both of which take only a few minutes and require little sample preparation, are sufficient as qualitative screening tools to determine the relative purity of SWNTs. Other analytical techniques were used to verify the validity of the screening techniques.     

Structure changes of single-wall carbon nanotubes and single-wall carbon nanohorns caused by heat treatment

Raman spectra and transmission electron microscope images showed that diameter enlargement of HiPco, a kind of single-wall carbon nanotube, accompanied by tube-wall corrugation was caused by heat treatment (HT) at 1000 to 1700 °C. Further enlargement accompanied by straightening of the tube walls and incorporation of carbon fragments within the tubes became obvious after HT at 1800 to 1900 °C. The transformation of some single-wall carbon nanotubes into multi-wall nanotubes was observed after HT at 2000 °C, and most single-wall tubes were transformed into multi-wall ones by HT at 2400 °C. What influence the Fe contained in the HiPco tubes had on these structure changes was unclear; similar changes were observed in single-wall carbon nanohorns that did not contain any metal. This indicates that thermally induced changes in the structure of single-wall carbon nanotubes can occur without a metal catalyst. Heat treatment increased the integrity of the nanotube-papers, and this increase may have been due to tube-tube interconnections created by HT.     

Effect of single-walled carbon nanotubes on thermal and electrical properties of silicon nitride processed using spark plasma sintering

Si₃N₄ nanocomposites reinforced with 1-, 2-, and 6-vol% single-walled carbon nanotubes (SWNTs) were processed using spark plasma sintering (SPS) in order to control the thermal and electrical properties of the ceramic. Only 2-vol% SWNTs additions were used to decrease the room temperature thermal conductivity by 62% over the monolith and 6-vol% SWNTs was used to transform the insulating ceramic into a metallic electrical conductor (92 S m⁻¹). We found that densification of the nanocomposites was inhibited with increasing SWNT concentration however, the phase transformation from α- to β-Si₃N₄ was not. After SPS, we found evidence of SWNT survival in addition to sintering induced defects detected by monitoring SWNT peak intensity ratios using Raman spectroscopy. Our results show that SWNTs can be used to effectively increase electrical conductivity and lower thermal conductivity of Si₃N₄ due to electrical transport enhancement and thermal scattering of phonons by SWNTs using SPS.     

Charge transfer effects in acid treated single-wall carbon nanotubes

Single-wall carbon nanotubes (SWNTs) prepared by the arc discharge method were oxidized using nitric acid. The samples were analyzed by using Raman scattering and Fourier transformed infrared spectroscopy (FTIR). The FTIR results indicate the presence of -COOH acid groups in the treated samples. The up shifts observed in the radial breathing mode frequencies suggest that SWNTs behave as donors after the acid treatment, with charge transfer occurring from the nanotubes to the -COOH groups. Ab initio calculations of SWNTs interacting with -COOH acid groups support the charge transfer process from the nanotubes to the carboxyl groups.     

Enhancement of electrochemiluminesence of lucigenin by ascorbic acid at single-wall carbon nanotube film-modified glassy carbon electrode

The electrochemiluminescent behavior of lucigenin on a single-wall carbon nanotube/DMF film-modified glassy carbon electrode was studied in this paper. Comparing with the bare glassy carbon electrode, the electrochemiluminescent of lucigenin at modified electrode is more stable and without tedious procedure for clean-up the surface of modified electrode. It has been found that ascorbic acid could enhance the electrochemiluminescent intensity of lucigenin greatly at this modified electrode. Based on which, a new sensitive and simple electrochemiluminescent method for determination of ascorbic acid could be developed. The condition for the determination of ascorbic acid was optimized. Under the optimized condition, the enhanced electrochemiluminescent intensity versus ascorbic acid concentration was linear in the range of 1.0 × 10⁻⁸ to 4.0 × 10⁻⁶ mol/L with a detection limit of 2.0 × 10⁻¹⁰ mol/L, and the relative standard derivation for 1.0 × 10⁻⁷ mol/L ascorbic acid was 3.8% (n = 8). The possible mechanism was also discussed.     

Optical absorption matrix elements in single-wall carbon nanotubes

The optical absorption matrix element as a function of one-dimensional (1D) wave vector k, and subband index μ of a single wall carbon nanotube is given analytically for linearly polarized light with polarization parallel to the nanotube axis. For armchair nanotubes, it is found that the optical transitions for non-degenerate A symmetry bands are forbidden over the whole 1D k region and the transitions for all other bands are also forbidden at the k = 0 point. Near the Fermi level, the absorption for all metallic nanotubes is found to be approximately zero. For both metallic and semiconducting nanotubes, it is found that the absorption matrix element has a maximum absolute value at the van Hove singularity (vHS) k point around the Fermi energy for each band. The absorption dependence on diameter and chiral angle is also presented for semiconducting nanotubes. For light polarization perpendicular to the nanotube axis, on the other hand, the absorption for nanotubes is generally weak near a vHS.     

Polyaniline/single-wall carbon nanotube (PANI/SWCNT) composites for high performance supercapacitors

PANI/SWCNT composites were prepared by electrochemical polymerisation of polyaniline onto SWCNTs and their capacitive performance was evaluated by means of cyclic voltammetry and charge-discharge cycling in 1 M H₂SO₄ electrolyte. The PANI/SWCNT composites single electrode showed much higher specific capacitance, specific energy and specific power than pure PANI and SWCNTs. The highest specific capacitance, specific power and specific energy values of 485 F/g, 228 W h/kg and 2250 W/kg were observed for 73 wt.% PANI deposited onto SWCNTs. PANI/SWCNT composites also showed long cyclic stability. Based upon the variations in the surface morphologies and specific capacitance of the composite, a mechanism is proposed to explain enhancement in the capacitive characteristics. The PANI/SWCNT composites have demonstrated the potential as excellent electrode materials for application in high performance supercapacitors.