High-speed countercurrent chromatography for purification of single-walled carbon nanotubes

A new chromatographic purification of single-walled carbon nanotubes using high-speed countercurrent chromatography is reported. The purification was accomplished on the basis of experiment that dispersed the single-walled carbon nanotubes with sodium dodecyl sulfate, and the result mixture was separated using the two phase system composed of n-butanol/water = 1/1 （v/v）. The sizes of SWNTs separated were observed by scanning electron microscopy. The results demonstrated that the high-speed countercurrent chromatography possessed a good efficency for purification of single-walled carbon nanotubes.     

Dispersion and orientation of single-walled carbon nanotubes in a chromonic liquid crystal

A post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale. Here, we demonstrate excellent dispersion, orientation and concomitant-polarised photoluminescence of SWCNTs in a nematic chromonic liquid crystal. The methods to obtain stable suspension are described, and order parameters of the liquid crystal matrix and of the nanotubes are measured independently.     

The Cu-MOF-199/single-walled carbon nanotubes modified electrode for simultaneous determination of hydroquinone and catechol with extended linear ranges and lower detection limits

A novel electrochemical sensor based on Cu-MOF-199 [Cu-MOF-199 = Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylicacid)] and SWCNTs (single-walled carbon nanotubes) was fabricated for the simultaneous determination of hydroquinone (HQ) and catechol (CT). The modification procedure was carried out through casting SWCNTs on the bare glassy carbon electrode (GCE) and followed by the electrodeposition of Cu-MOF-199 on the SWCNTs modified electrode. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were performed to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The composite electrode exhibited an excellent electrocatalytic activity with increased electrochemical signals towards the oxidation of HQ and CT, owing to the synergistic effect of SWCNTs and Cu-MOF-199. Under the optimized condition, the linear response range were from 0.1 to 1453 μmol L⁻¹ (R_HQ = 0.9999) for HQ and 0.1–1150 μmol L⁻¹ (R_CT = 0.9990) for CT. The detection limits for HQ and CT were as low as 0.08 and 0.1 μmol L⁻¹, respectively. Moreover, the modified electrode presented the good reproducibility and the excellent anti-interference performance. The analytical performance of the developed sensor for the simultaneous detection of HQ and CT had been evaluated in practical samples with satisfying results.     

Simultaneous determination of trichloroethylene,perchloroethylene and trichloroacetic acid in human urine using solid-phase microextraction fibre coated with single-walled carbon nanotubes

A reliable and sensitive method for simultaneous determination of perchloroethylene (PCE), trichloroethylene (TCE), and trichloroacetic acid (TCA) in human urine by gas chromatography-mass spectrometry (GC/MS) is described after extraction and preconcentration by a new solid-phase microextraction (SPME) adsorbent. The potential of single-walled carbon nanotubes (SWCNTs) as SPME adsorbent for the pre-concentration of environmental pollutants has been investigated in recent years. This work was carried out to investigate the feasibility of SWCNTs as a headspace SPME adsorbent for the determination of chloroethylenes in human urine. SWCNTs were attached onto a stainless steel wire through an organic binder. Potential factors affecting the extraction efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance. For PCE and TCE, calibration curves were linear (r ^{2 ?}≥?0.994) over the concentration ranges from 15 to 8000?ng?L^?1 and the limit of detection (LOD) at signal-to-noise (S/N) ratio of 3 was 5?ng?L^?1. The analytical procedure also involves derivatization of TCA with dimethyl sulfate, before headspace sampling. For TCA the linear range and LOD were 45-8000 (r ^{2 ?}≥?0.992) and 15?ng L^?1, respectively. In addition, a comparative study between the SWCNT and a commercial carboxen/polydimethylsiloxane (CAR/PDMS) SPME fibre for the determination of chloroethylenes in human urine was carried out. SWCNT fibre showed higher extraction capacity, better thermal stability (over 350°C) and longer life span (over 200 times) than the commercial CAR/PDMS fibre. The developed method was successfully applied to determine chloroethylenes in human urine samples. As the results indicated, the mean concentrations of TCE, PCE and TCA in exposed workers (dry-cleaning industry workers) were significantly greater than that of control group.     

Synthesis of nickel nanoparticles and carbon encapsulated nickel nanoparticles supported on carbon nanotubes

Nickel nanoparticles were prepared and uniformly supported on multi-walled carbon nanotubes (MWCNTs) by reduction route with CNTs as a reducing agent at 600 °C. As-prepared nickel nanoparticles were single crystalline with a face-center-cubic phase and a size distribution ranging from 10 to 50 nm, and they were characterized by transmission electron microscopy (TEM), high-resolution TEM and X-ray diffraction (XRD). These nickel nanoparticles would be coated with graphene layers, when they were exposed to acetylene at 600 °C. The coercivity values of nickel nanoparticles were superior to that of bulk nickel at room temperature.     

Simultaneous determination of copper, nickel, cobalt and zinc using zincon as a metallochromic indicator with partial least squares

The partial least squares (PLS) applied to the simultaneous determination of the divalent ions of copper, nickel, cobalt and zinc based on the formation of their complexes with 2-carboxy-2′-hydroxy-5′-sulfoformazyl benzene (zincon). The absorption spectra were recorded from 515 through 750 nm. The effect of pH on sensitivity and the selectivity was studied in the range 3.0-10.0 and the pH 8.0 was choused according to net analyte signal (NAS) as a function of pH. The concentration range for Cu²⁺, Ni²⁺, Co²⁺and Zn²⁺ in solution calibration sets were 0-2.6, 0-4.6, 0-3.0 and 0-4.92 ppm, respectively. The root mean squares differences (RMSD) for copper, nickel, cobalt and zinc were 0.0181, 0.0488, 0.0309 and 0.0463, respectively.     

Synthesis and characterization of nickel catalysts supported on different carbon materials

Nickel catalysts supported on various carbon materials such as multiwall carbon nanotubes, shortened length carbon nanotubes, graphite and amorphous carbon were synthesized, characterized and tested in cyclohexene hydrogenation reaction. We have found that carbon nanotube supports are superior to graphite and amorphous carbon both in terms of catalytic activity and stability.     

Bare gold nanoparticles mediated surface-enhanced Raman spectroscopic determination and quantification of carboxylated single-walled carbon nanotubes

The paper proposes a simple and portable approach for the surface enhanced Raman scattering (SERS) spectroscopy in situ determination of carboxylated single walled carbon nanotubes (SWNTs) in river water samples. The method is based on the subsequent microfiltration of a bare gold nanoparticles solution and the water sample containing soluble carbon nanotubes by using a home-made filtration device with a small filtration diameter. An acetate cellulose membrane with a pore size of 0.2 μm first traps gold nanoparticles to form the SERS-active substrate and then concentrates the carbon nanotubes. The measured SERS intensity data were closely fit with a Langmuir isotherm. A portable Raman spectrometer was employed to measure SERS spectra, which enables in situ determination of SWNTs in river waters. The limit of detection was 10 μg L⁻¹. The precision, for a 10 mg L⁻¹ concentration of carbon nanotubes, is 1.19% intra-membrane and 10.5% inter-membrane.     

Spectrophotometric and derivative spectrophotometric determination of copper (II) with dithizone in aqueous phase

A Spectrophotometric and derivative Spectrophotometric study of Cu-dithizonate complex in aqueous phase in the presence of Triton X-100, a neutral surfactant, is reported. The system obeys Beer's law between 1.0 × 10^–6–9.0 × 10^–6 mol/l of Cu²⁺; detection limit is 12 ng/ml. The molar absorption coefficient, specific absorptivity and Sandell's sensitivity of the complex are 3.06 × 10⁴ 1 mol^–1 cm^–1, 0.4825 ml g^–1 cm^–1 and 2.1 × 10^–3 g cm^–2, respectively. The conditional stability constant of the 1 2 complex, calculated considering simultaneously existing equilibria, has been found to be 1.73 × 10¹¹ I² mol² (I = 0.07, pH 1.4, temperature = 10 °C). Absorption studies in the derivative mode have been carried out to determine the absorption maximum of the complex and to overcome interference due to the presence of certain metal ions. The method has been validated by determination of copper in beers, wines, human hair, goat liver and fly ash samples.     

Thermal decomposition and electron microscopy studies of single-walled carbon nanotubes

Thermoanalytical and electron microscopic methods were used as characterisation tools for the determination of the composition of single walled carbon nanotube samples. Acid purification method of single-walled carbon nanotubes (SWCN) proved to be effective, resulting in a three fold increase in the percentage of SWNTs present in the purified product as determined by thermogravimetric analysis. In this work we report the thermogravimetric analysis by conventional and high resolution methods of the raw SWNTs and purified SWNTs.     

Covalent functionalization of single-walled carbon nanotubes with polytyrosine: Characterization and analytical applications for the sensitive quantification of polyphenols

This work reports the synthesis and characterization of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr); the critical analysis of the experimental conditions to obtain the efficient dispersion of the modified carbon nanotubes; and the analytical performance of glassy carbon electrodes (GCE) modified with the dispersion (GCE/SWCNT-Polytyr) for the highly sensitive quantification of polyphenols. Under the optimal conditions, the calibration plot for the amperometric response of gallic acid (GA) shows a linear range between 5.0 × 10⁻⁷ and 1.7 × 10⁻⁴ M, with a sensitivity of (518 ± 5) m AM⁻¹ cm⁻², and a detection limit of 8.8 nM. The proposed sensor was successfully used for the determination of total polyphenolic content in tea extracts.     

Preparation of solid-phase microextraction fiber coated with single-walled carbon nanotubes by electrophoretic deposition and its application in extracting phenols from aqueous samples

A novel solid-phase microextraction (SPME) Pt fiber coated with single-walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition (EPD) and applied to the determination of phenols in aqueous samples by direct immersion (DI)-SPME-HPLC-UV. The results revealed that EPD was a simple and reproducible technique for the preparation of SPME fibers coated with SWCNTs without the use of adhesive. The obtained SWCNT coating did not swell in organic solvents nor strip off from substrate, and possessed high mechanical strength due to the strong Van der Waals attractions between the surfaces of the SWCNTs. The prepared SPME fiber was conductive since both SWCNT coating and Pt wire were conductive. Using Pt wire as substrate, the fiber was unbreakable. Owing to the presence of oxygenated groups on SWCNTs and the high surface area of SWCNTs, the SWCNT fiber was similar to or superior to commercial PA fiber in extracting the studied phenols from aqueous sample. A durability of more than 80 analyses was achieved for one unique fiber. Under optimized conditions, the detection limits for the phenols varied between 0.9 and 3.8 ng/mL, the precisions were in the range of 0.7–3.2% (n = 3), and linear ranges were within 10 and 300 ng/mL. The method was successfully applied to the analysis of spiked seawater and tap water samples with the recoveries from 87.5 to 102.0%.     

Covalent immobilization of single-walled carbon nanotubes and single-stranded deoxyribonucleic acid nanocomposites on glassy carbon electrode: Preparation, characterization, and applications

Single-stranded deoxyribonucleic acid (ssDNA)-wrapped single-walled carbon nanotubes (SWNTs) were modified on the surface of glassy carbon electrode (GCE) by covalent modification technique. Field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectrum (XPS), electrochemical impedance spectroscopy (EIS), and cyclic voltammetric (CV) were used to characterize the properties of this modified electrode. The results showed that SWNTs-ssDNA composites were successfully immobilized onto the surface of GCE. Moreover, this modified electrode exhibited high stability, largely active areas, and efficiently electrocatalytic activities. It had been used for the analysis of various biomolecules, such as dopamine (DA), uric acid (UA), and ascorbic acid (AA), and the results were satisfactory.     

Ring formation mechanism of single-walled carbon nanotubes: Energy conservation between curvature elasticity and inter-tube adhesion

Rings of single-walled carbon nanotubes (SWNTs) exist widely during water evaporation from their dispersions at low concentration on such substrates as silica wafer. We examine the phenomenon in terms of energy conservation between the increased significant curvature energy and the inherent inter-tube van der Waals (vdW) attraction potentials. And thereby, the observed multi ring structures for coarse and long SWNT bundles have also gained detailed interpretation. We conclude that carbon nanotubes (CNTs) coil into rings by their own elastic mechanism. The formed rings with different width and diameters originate from appropriate sizes of SWNTs or the bundles. Specially, the associated elasticity may have prospective potentials to reveal other fascinating self-assembling phenomenon on CNTs, for instance, the known liquid crystallinity of them. Besides, we have also analyzed the external factors to the ring formation, both statistically and dynamically.     

On the influence of diameter and length on the properties of armchair single-walled carbon nanotubes: A theoretical chemistry approach

Open-ended fragments of armchair single-walled carbon nanotubes (n, n) with n = 3, 4, 5, and 6, have been modeled, with increasing lengths from 0.6 to 3 nm long. The geometries of all the studied fragments have been fully optimized. The influence of diameter and length on different electronic properties has been analyzed. These properties are electronegativity, ionization potential, electron affinities, and hardness, and all of them have been expressed as functions of the frontier orbitals. The binding energies per C atom have been calculated, using an expression that improves the previously reported ones. Their absolute values were found to steadily increase with tubes length and diameter, which allows extrapolations to obtain BE_/C atom for tubes of infinite length. The extrapolated values are 8.45, 8.65, 8.74, and 8.79 eV for armchair nanotubes with n = 3, 4, 5, and 6, respectively.     

Simultaneous determination of pH, chloride and nickel in electroplating baths using sequential injection analysis

A sequential injection analysis system was developed to quantify pH, chloride and nickel in electrolytic baths, in the ranges 1-5 pH units, and 0.1-1.0 and 0.1-1.6 mol l⁻¹, respectively. To enable pH and chloride determination, potentiometric detection with two ion-selective electrodes in a tubular configuration was used. Nickel concentrations were assessed using colorimetric detection at 660 nm. pH was determined prior to nickel determination and just after sample injection (500 μl) into a 0.025 mol l⁻¹ phosphate buffer carrier stream at pH 6.3 and a 9.10 ml min⁻¹ flow rate. For chloride determination, on-line dialysis through a cellulose membrane was used to enable sample dilution and matrix separation. A 2⁵⁻¹ fractional factorial design based on the carrier solution composition and the levels of the hydrodynamic parameters was used for system optimization. At the optimized settings a sampling rate of 40 samples h⁻¹ was attained, with precision and accuracy statistically indistinguishable from those achieved with conventional procedures.     

Single-walled carbon nanotubes coated fibers for solid-phase microextraction and gas chromatography-mass spectrometric determination of pesticides in Tea samples

Using a single-walled carbon nanotubes (SWCNTs) as stationary phase of solid-phase microextraction (SPME) fibers, a simple, low cost and environmentally friendly method for extraction of 13 pesticides in Tea samples has been developed following gas chromatography-mass spectrometric determination. Potential factors affecting the extraction efficiency were investigated and optimized, including extraction and desorption time, extraction temperature, stirring rate, solution pH and ionic strength. Under optimized conditions, the linearity of the developed method was in the range of 0.125-25 ng/mL with correlation coefficients greater than 0.9928 and the limits of detections (LODs) were 0.027-0.23 ng/mL (S/N = 3). Meanwhile, the relative standard deviations (RSDs) for five successive measurements with single fiber, fiber-to-fiber, day-to-day were 2.3-13.0, 8.2-14.6 and 4.1-12.5%, respectively, indicating good reproducibility of the proposed method. The fiber had high extraction efficiency for studied pesticides in comparison with commercial poly(dimethylsiloxane) (PDMS) and polyacrylate (PA) fibers and could be used for more than 70 times without decrease of efficiency. The developed method was successfully applied for the analysis of real samples including green Tea, oolong Tea, white Tea, and flower Tea, and the recoveries of the pesticides spiked in these samples ranged from 75.1 to 118.4%. Chlorfenapyr and λ-cyhalothrin were found in the Tea samples bought randomly from local market. The results demonstrated that the developed SWCNTs-SPME method was a simple, efficient pretreatment and enrichment procedure for pesticides in complex matrices.     

Simultaneous spectrophotometric determination of cobalt,copper and nickel using 1-（2-thiazolylazo）-2-naphthol by chemometrics methods

The simultaneous determination of cobalt, copper and nickel using 1-（2-thiazolylazo）-2-naphthol （first figure of this article） by spectrophotometric method is a difficult problem in analytical chemistry, due to spectral interferences. By multivariate calibration methods, such as partial least squares （PLS） regression, it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction （OSC） is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 550-750-nm range for 21 different mixtures of cobalt, copper and nickel. Calibration matrices were formed from samples containing 0.05-1.05, 0.05-1.30 and 0.05-0.80 μg·mL^-1 for cobalt, copper and nickel, respectively. The root mean square error of prediction （RMSEP） for cobalt, copper and nickel with OSC and without OSC were 0.007, 0.008, 0.011 and 0.031,0.037, 0.032 μg· mL^-1, respectively. This procedure allows the simultaneous determination of cobalt, copper and nickel in synthetic and real samples and good reliability of the determination was proved.     

偏最小二乘分光光度法同时测定痕量铁、锰、铜、锌、钴和镍

痕量Fe^3 ,Mn^2 ,Cu^2 ,Zn^2 ,Co^2 ,Ni^2 与2－（5－溴－2－吡啶偶氮）－5－二乙氨基苯酚（5－Br-PADAP)和溴化十六烷基三甲基铵（CTMAB）在PH8．3时发生高灵敏显色反应，所形成的三元胶束络合的吸收光谱严重重叠，采用偏最小二乘法（PLS）辅助分光光度法测定了合成试样及饲料中上述6种痕量组分，结果表明，PLS法是化学计量学中一种可适用于基体较复杂的实际试样中痕量组分分光度同时测定的多元计算方法。