Comparison of the stability of multiwalled carbon nanotube dispersions in water

Continuous real-time monitoring of the nanotube concentration in aqueous solution using UV-Vis spectroscopy allows quantitative comparison of the stability of different types of nanotube dispersions. Systematic investigation of the effects of nanotube length and functionalisation for thin multiwalled carbon nanotubes (MWNT) has revealed that shorter MWNT form more stable dispersions than longer nanotubes of the same diameter. MWNT shortened to an average length of approximately 1 microm form stable dispersions in water with concentrations up to 0.013 mg ml(-1) in the absence of surfactants or solubilising functional groups. The introduction of carboxylic or thiol groups on the surface of shortened nanotubes further increases the stability of MWNT dispersions (up to 0.24 mg ml(-1)). The introduction of surfactant or surface charge on MWNT has contrasting effects on functionalised and non-functionalised nanotubes, destabilising and stabilising their dispersions, respectively.     

Clusterization, electrophoretic deposition, and photoelectrochemical properties of fullerene-functionalized carbon nanotube composites

We have successfully developed a new methodology for the self-organization of C(60) molecules on the sidewall of carbon nanotubes for use in photoelectrochemical devices. Novel nanocarbon composites of fullerene (e.g., C(60)) and highly soluble, chemically functionalized single-walled carbon nanotubes (f-SWNT) have been prepared by the rapid injection of a poor solvent (e.g., acetonitrile) into a mixed solution of C(60) and f-SWNT in o-dichlorobenzene. Measurements by using scanning electron microscopy of cast samples revealed that the composites are categorized into three groups; i) f-SWNT bundles covered with layers of C(60) molecules, ii) round, large C(60) clusters (sizes of 500-1000 nm) containing f-SWNT, and iii) typical, round C(60) clusters (sizes of 150-250 nm). The electrophoretic deposition of the composites onto a nanostructured SnO(2) electrode yielded the hierarchical film with a gradient composition depending on the difference in the mobilities of C(60) and f-SWNT during the electrophoretic process. The composite film exhibited an incident photon-to-photocurrent efficiency as high as 18 % at lambda=400 nm under an applied potential of 0.05 V vs. SCE. The photocurrent generation efficiency is the highest value among carbon nanotube-based photoelectrochemical devices in which carbon nanotubes are deposited electrophoretically, electrostatically or covalently onto semiconducting electrodes. The highly aligned structure of C(60) molecules on f-SWNT can rationalize the efficient photocurrent generation. The results obtained here will provide valuable information on the design of carbon nanotube-based molecular devices.     

Processable hybrids of ferrocene-containing poly(phenylacetylene)s and carbon nanotubes: fabrication and properties

A group of ferrocene-containing poly(phenylacetylene)s (PPAs) with different alkyl spacers were synthesized by using organorhodium complexes [Rh(diene)Cl](2) and Rh (+)(nbd)[C(6)H(5)B (-)(C(6)H(5))(3)] as catalysts. With the aid of pi-pi interactions between the walls of carbon nanotubes (CNTs) and the PPA skeleton together with the ferrocene pendants, the polymer (P 1, P2(5) and P2(10)) chains effectively wrapped round the shells of both single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). The "additive effect" of the PPA skeleton and the ferrocene pendants in dispersing the SWNTs and MWNTs resulted in the generation of highly soluble hybrids. The solubilities of P 1-functionalized SWNTs and MWNTs in tetrahydrofuran (THF) are up to 633 mg/L and 967 mg/L, respectively. They are much higher than the solubilities of M 1-modified SWNTs and MWNTs, which are only 167 mg/L and 133 mg/L in THF. The results indicate the existence of a powerful polymer effect on dispersing CNTs. The high solubilities of the hybrids in organic solvents allowed us to fabricate high-quality and large-area films. Meanwhile, the desirable loading of ferrocene-containing PPAs onto the CNTs offered polymer/CNTs hybrids with multiple redox centers and ferrocene-featured electrochemical properties. The P 1/MWNT hybrid exhibits evident optical-limiting properties. At high incident laser fluence, the optical-limiting power of P 1/MWNT is higher than that of C(60), a well-known optical limiter. Thermal analyses indicate that the decomposition temperatures ( T(d), the temperature at which a sample loses its 5% weight) for P1 and P1/MWNT are 342 and 346 degrees C, respectively, much higher than that for PPA (225 degrees C). Thus the attachment of a ferrocene pendant to a PPA backbone, followed by hybridization with CNTs, improved the thermal stability. Upon pyrolysis, both the polymer and the polymer/CNTs hybrid gave rise to superparamagnetic ceramics; the saturation magnetizations ( M(s)) of the ceramics derived from P1 and P1/MWNT are 29.9 and 26.9 emu/g, respectively. The latter datum is in the list of the best results reported for the magnetic nanocomposites obtained by the attachment of magnetic nanoparticles onto CNTs.     

Pt-Ru supported on double-walled carbon nanotubes as high-performance anode catalysts for direct methanol fuel cells

Pt-Ru supported on carbon nanotubes (CNTs) (single-walled nanotubes, double-walled nanotubes (DWNTs), and multi-walled nanotubes) catalysts are prepared by an ethylene glycol reduction method. Pt-Ru nanoparticles with a diameter of 2-3 nm and narrow particle size distributions are uniformly deposited onto the CNTs. A simple and fast filtration method followed by a hot-press film transfer is employed to prepare the anode catalyst layer on a Nafion membrane. The Pt-Ru/DWNTs catalyst shows the highest specific activity for methanol oxidation reaction in rotating disk electrode experiments and the highest performance as an anode catalyst in direct methanol fuel cell (DMFC) single cell tests. The DMFC single cell with Pt-Ru/DWNTs (50 wt %, 0.34 mg Pt-Ru/cm(2)) produces a 68% enhancement of power density, and at the same time, an 83% reduction of Pt-Ru electrode loading when compared to Pt-Ru/C (40 wt %, 2.0 mg Pt-Ru/cm(2)).     

Stabilization effect of single-walled carbon nanotubes on the functioning of photosynthetic reaction centers

The interaction between single-walled carbon nanotubes and photosynthetic reaction centers purified from purple bacterium Rhodobacter sphaeroides R-26 has been investigated. Atomic force microscopy studies provide evidence that reaction center protein can be attached effectively to the nanotubes. The typical diameter of the nanotube is 1-4 nm and 15 +/- 2 nm without and with the reaction centers, respectively. Light-induced absorption change measurements indicate the stabilization of the P+(Q(A)Q(B))- charge pair, which is formed after single saturating light excitation after the attachment to nanotubes. The separation of light-induced charges is followed by slow reorganization of the protein structure. The stabilization effect of light-initiated charges by the carbon nanotubes opens a possible direction of several applications, the most promising being in energy conversion and storage devices.     

Using oxidized carbon nanotubes as matrix for analysis of small molecules by MALDI-TOF MS

Oxidized carbon nanotubes are tested as a matrix for analysis of small molecules by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). Compared with nonoxidized carbon nanotubes, oxidized carbon nanotubes facilitate sample preparation because of their higher solubility in water. The matrix layer of oxidized carbon nanotubes is much more homogeneous and compact than that of nonoxidized carbon nanotubes. The efficiency of desorption/ionization for analytes and the reproducibility of peak intensities within and between sample spots are greatly enhanced on the surface of oxidized carbon nanotubes. The advantage of the oxidized carbon nanotubes in comparison with alpha-cyano-4-hydroxycinnamic acid (CCA) and carbon nanotubes is demonstrated by MALDI-TOF-MS analysis of an amino acid mixture. The matrix is successfully used for analysis of synthetic hydroxypropyl beta-cyclodextrin, suggesting a great potential for monitoring reactions and for product quality control. Reliable quantitative analysis of jatrorrhizine and palmatine with a wide linear range (1-100 ng/mL) and good reproducibility of relative peak areas (RSD less than 10%) is achieved using this matrix. Concentrations of jatrorrhizine (8.65 mg/mL) and palmatine (10.4 mg/mL) in an extract of Coptis chinensis Franch are determined simultaneously using the matrix and a standard addition method.     

Evaluation of carbon nanotubes as a solid-phase extraction adsorbent for the extraction of cephalosporins antibiotics, sulfonamides and phenolic compounds from aqueous solution

The adsorptive potential of carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes) for solid-phase extraction of three groups of highly polar compounds (namely cephalosporins antibiotics, sulfonamides and phenolic compounds) was tested in this article. The analytes were strongly retained by the carbon nanotubes. And acceptable recoveries were obtained with the addition of ammonium acetate into eluents. The effects of solution pH on the recoveries of the antibiotics and phenolic compounds were examined. To check the retention abilities of three groups of compounds on carbon nanotubes, fixed amount of each analyte was added to different volumes (up to 500 mL) of aqueous solution, and then extracted by the sorbents. Comparative studies showed that the carbon nanotubes were much superior to C₁₈ for the extraction of the highly polar analytes. For the cephalosporins antibiotics and sulfonamides, the carbon nanotubes showed stronger retention capability than graphitized carbon blacks, but for some of the phenolic compounds graphitized carbon blacks seemed to be more suitable, indicating different retention mechanisms of these analytes. To further assess the enrichment ability of carbon nanotubes for highly polar compounds, the solid-phase extraction method of multi-walled carbon nanotubes packed cartridge was well developed, and the sulfonamides were used as model compounds. Under the optimal procedures, the detection limits of sulfonamides were in the range of 27-38 ng L⁻¹. The spiked recoveries from several real water samples obtained for sulfathiazole and sulfadiazine ranged from 55% to 79% and 72% to 92%, respectively, while the recoveries of sulfapyridine and sulfamethazine were in the range of 85-102%.     

Diameter-dependent, progressive alkylcarboxylation of single-walled carbon nanotubes

We demonstrate diameter-dependent, progressive alkylcarboxylation of single-walled carbon nanotubes by recycling a modified Billups-Birch reaction. The strong diameter dependence was confirmed by Raman spectroscopy. Alkylcarboxylation made SWNTs soluble in water, allowing the more readily functionalized, smaller diameter nanotubes to be enriched by water extraction.     

Single-wall carbon nanotubes bearing covalently linked phthalocyanines--photoinduced electron transfer

HiPco single-walled carbon nanotubes (SWNTs) have been sidewall-functionalized with phthalocyanine addends following two different approaches: a straightforward Prato reaction with N-octylglycine and a formyl-containing phthalocyanine, and a stepwise approach that involves a former Prato cycloaddition to the double bonds of SWNTs using p-formyl benzoic acid followed by esterification of the derivatized nanotubes with an appropriate phthalocyanine molecule. The two materials obtained by these routes comprise different carbon/Pc-addenda ratios, as evidenced by Raman, TGA, and photophysical studies. The occurrence of electron transfer from photoexcited phthalocyanines to the nanotube framework in these ZnPc-SWNT ensembles is observed in transient absorption experiments, which confirm the absorption of the one-electron oxidized ZnPc cation and the concomitant bleaching of the van Hove singularities typical from SWNTs. Charge-separation (i.e., 2.0 x 1010 s(-1)) and charge-recombination (i.e., 1.5 x 106 s(-1)) dynamics reveal a notable stabilization of the radical ion pair product in dimethylformamide.     

Transparent,Versatile Chemical Vapor Sensor Using Supramolecular Assembly of Block Copolymer and Carbon Nanotubes

Here, a simple and novel approach is reported for developing a new class of transparent chemical vapor sensors with a low power consumption, high sensitivity, good selectivity, and excellent environmental stability by depositing multiwalled carbon nanotubes on prepatterned polymer substrates using supramolecular assembly. The patterned polymer substrates were fabricated from block copolymers, whereas the supramolecular assembly between the carbon nanotubes and block copolymer is utilized for the selective localization of carbon nanotubes at the block copolymer–air interface. The thin film devices made from the block copolymer and carbon nanotubes are highly transparent (transmittance > 90%) and respond to a wide range of solvents of different polarity, both hydrophilic and hydrophobic, with good selectivity and fast response time.

     

Functional macromolecules from single-walled carbon nanotubes: synthesis and photophysical properties of short single-walled carbon nanotubes functionalised with 9,10-diphenylanthracene

9,10-Diphenylanthracene (DPA), a well-studied organic chromophore (Phi(fl) = 0.98) that exhibits electroluminescence, has been covalently bound through 2-(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single-walled carbon nanotubes (sSWNTs) of 1 microm average length, and the resulting DPA-functionalised sSWNT (DPA- sSWNT) macromolecular adducts (4.6 wt % DPA content) characterised by solution (1)H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of DPA fluorescence (steady-state and time-resolved) and of the transient optical spectra of sSWNTs and DPA-sSWNTs show that the covalent linkage boosts the interaction between the DPA and the sSWNT units. DPA-sSWNTs exhibit emission in the near-IR region from 1100-1400 nm with an enhanced quantum yield (Phi = 5.7x10(-3)) compared with sSWNTs (Phi = 3.9x10(-3)).     

Studies on electrochemical properties and scavenge of superoxide anion in aprotic media by using carbon nanotubes powder microelectrode

Multiwall carbon nanotubes (MWCNTs) are filled in the cavity at the tip of a microelectrode to form a carbon nanotubes powder microelectrode (CNTs-PME). CNTs-PME was used to study electrochemical properties of superoxide anion in aprotic media. The reversibility of the oxygen/superoxide anion couple (O(2)/O(2)(.-)) at the different powder microelectrode in different aprotic media was compared by cyclic voltammetry (CV). The result indicated that the nearly reversible redox process of the O(2)/O(2)(.-) couple was obtained at a CNTs-PME. The heterogeneous electron transfer rate constant (k(s)) can be measured by steady-state voltammogram and the result is 4.7 x 10(-3) cm s(-1), suggesting that the electrode reaction is a nearly reversible process as expected. The scavenging activities of bilirubin, alpha-tocopherol (vitamin E), are examined, and the experimental results confirm that alpha-tocopherol is the better scavenger toward O(2)(.-) between them.     

Electrochemical immunoassay platform for high sensitivity protein detection based on redox-modified carbon nanotube labels

We report a highly sensitive immunoassay protocol based on the use of redox-modified multi-walled carbon nanotubes (MWNTs) as electrochemical labels. The MWNTs were coated with methylene blue (MB) at an optically-determined loading of 3.41 × 10(-3) mol g(-1), and were then attached to secondary antibodies (Ab(2)) by adsorption. As a model analyte mouse IgG was collected by primary antibody (Ab(1))-coated magnetic beads. Following binding of the MB-MWNT-Ab(2) conjugates, IgG could be measured by MB reduction. Using differential pulse voltammetry for quantification, IgG was calibrated with a dynamic range of 0.1 pg mL(-1) to 100 pg mL(-1). Given the different possible Ab(1)-MB-MWNT-Ab(2) orientations on the magnetic beads, it was likely that not all the MB communicated with the electrode. A greater quantity of MB could be accessed by using the Fe(CN)(6)(3-/4-) redox couple as a solution phase mediator. This enabled us to lower the dynamic range down to 5 fg mL(-1) to 100 fg mL(-1).     

Carbon nanotube amplification strategies for highly sensitive immunodetection of cancer biomarkers

We describe herein the combination of electrochemical immunosensors using single-wall carbon nanotube (SWNT) forest platforms with multi-label secondary antibody-nanotube bioconjugates for highly sensitive detection of a cancer biomarker in serum and tissue lysates. Greatly amplified sensitivity was attained by using bioconjugates featuring horseradish peroxidase (HRP) labels and secondary antibodies (Ab(2)) linked to carbon nanotubes (CNT) at high HRP/Ab(2) ratio. This approach provided a detection limit of 4 pg mL(-)(1) (100 amol mL(-)(1)), for prostate specific antigen (PSA) in 10 microL of undiluted calf serum, a mass detection limit of 40 fg. Accurate detection of PSA in human serum samples was demonstrated by comparison to standard ELISA assays. PSA was quantitatively measured in prostate tissue samples for which PSA could not be differentiated by the gold standard immunohistochemical staining method. These easily fabricated SWNT immunosensors show excellent promise for clinical screening of cancer biomarkers and point-of-care diagnostics.     

中分子毒素在碳纳米管上的吸附

研究了两种不同形态的碳纳米管(随机生长多壁碳纳米管(MWCNTs)及定向生长多壁碳纳米管(ACNTs))对典型中分子毒素的吸附性能. 并与两种现有商用血液灌流吸附材料(活性炭(AC)及大孔吸附树脂(MR))进行了对比. 结果显示, 碳纳米管(CNTs)具有优异的中分子吸附能力, 其中MWCNTs对典型中分子毒素的吸附量可达47.18 mg·g-1, 为活性炭的10.8倍, 为大孔吸附树脂的5.5倍. 此外, 碳纳米管的吸附非常迅速, 中分子毒素在MWCNTs及ACNTs达到吸附平衡的时间仅为10 min和15 min, 而活性炭及大孔吸附树脂则分别需要60 min及120 min. 碳纳米管优异的吸附性能得益于其独特的微观结构所形成的发达的中孔. 因此, 碳纳米管可望成为高效的吸附材料, 应用于血液灌流中.     

High surface area carbon aerogels as porous substrates for direct growth of carbon nanotubes

Novel carbon composites are fabricated through catalyzed CVD growth of carbon nanotubes directly on the inner surfaces of monolithic carbon aerogel (CA) substrates. Uniform CNT yield is obtained throughout the internal pore volume of CA monoliths with macroscopic dimensions. These composites possess large surface areas (>1000 m(2) g(-1)) and exhibit enhanced electrical conductivity following CNT growth.     

FIA-FT-IR determination of ibuprofen in pharmaceuticals

A method has been developed for the determination of Ibuprofen (2-[4-isobutylphenyl]-propionic acid) in pharmaceuticals by FT-IR, using the carbonyl band which this compound presents at 1710 cm(-1) in carbon tetrachloride solutions. Samples are dissolved in carbon tetrachloride. In this solvent the excipients are not soluble and so the drug can be directly determined without any additional treatment. The use of a simple FIA manifold permits one to carry out this analysis with a low consumption of reagent and the FT-IR provides a continuous monitoring of the spectral base-line which permits an accurate determination of the maximum in the absorbance band. Also, the FIA system permits easy and fast sampling and cleaning of the measurement cell. The method has a dynamic range between 0.5 and 20 mg/ml with a sensitivity of 0.366 +/- 0.004 au . mg(-1) . ml . mm(-1) and a variation coefficient of 0.8% for 5 independent measurements of a real sample containing 200 mg of Ibuprofen per capsule. The developed procedure provides concentration values comparable with those found by UV spectrophotometry in the analysis of real samples but is free from matrix interferences.     

Mediated amperometric immunosensing using single walled carbon nanotube forests

A prototype amperometric immunosensor was evaluated based on the adsorption of antibodies onto perpendicularly oriented assemblies of single wall carbon nanotubes called SWNT forests. The forests were self-assembled from oxidatively shortened SWNTs onto Nafion/iron oxide coated pyrolytic graphite electrodes. The nanotube forests were characterized using atomic force microscopy and resonance Raman spectroscopy. Anti-biotin antibody strongly adsorbed to the SWNT forests. In the presence of a soluble mediator, the detection limit for horseradish peroxidase (HRP) labeled biotin was 2.5 pmol ml(-1) (2.5 nM). Unlabelled biotin was detected in a competitive approach with a detection limit of 16 nmol ml(-1) (16 microM) and a relative standard deviation of 12%. The immunosensor showed low non-specific adsorption of biotin-HRP (approx. 0.1%) when blocked with bovine serum albumin. This immunosensing approach using high surface area, patternable, conductive SWNT assemblies may eventually prove useful for nano-biosensing arrays.     

Hydroboration of C(100) surface,fullerene, and the sidewalls of single-wall carbon nanotubes with borane

Hydroboration of three allotropes of carbon, i.e., diamond (100) surface, [60]fullerene, and single-wall carbon nanotubes (SWNTs), with borane (BH(3)) has been explored by means of quantum chemical calculations. The calculations predicted that the hydroboration of C(60) and the C(100)-2x1 surface occurs readily, whereas the hydroboration of the sidewall of an armchair (5,5) SWNT is thermoneutral with a barrier height of 11.5 kcal/mol. This suggests that sidewall hydroboration, if viable, would be highly reversible on the (5,5) SWNT. The as-hydroborated carbonous materials can be good starting points for further chemical modification and manipulation of these carbonous materials, given the abundant chemistry of organoboranes.     

Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.