Preparation Of Single-walled Carbon Nanotubes Research Articles

Ultrasound-assisted synthesis of PbS quantum dots stabilized by 1,2-benzenedimethanethiol and attachment to single-walled carbon nanotubes

Lead sulfide (PbS) quantum dots stabilized by 1,2-benzenedimethanethiol can be synthesized by mixing Pb(NO3)2 and Na2S solutions in ethanol under ultrasound irradiation. The PbS quantum dots (2.7 and 3.6nm in diameter) are characterized by their absorption and fluorescence spectra in the near infrared region and by other surface analytical techniques. With addition of single-walled carbon nanotubes (SWNT) to the system, this ultrasound-assisted procedure allows attachment of PbS nanoparticles to SWNT surface via π–π stacking, thus providing a simple one-pot method for preparation of SWNT–PbS nanoparticle composite materials. Using the ultrasound-assisted method for synthesizing silica composites containing PbS nanoparticles by a sol–gel process is also described.

Polymer-Coated Single-Walled Carbon Nanotubes for Ethanol and Dichloromethane Discrimination

Sensor response and pattern recognition of polymer-coated single-walled carbon nanotubes (SWNTs) were investigated. Printed circuit board (PCB) with Cu/Au interdigitated electrode was used as sensor platform. SWNTs network was firstly formed on PCB by drop-casting. For polymer-coated SWNTs preparation, poly(methyl methacrylate) (PMMA) and thiophene were employed as polymers to coat on SWNTs by spin coating; PMMA/SWNTs and thiophene/SWNTs. Raman spectra showed no obvious structure changes of SWNTs after polymer coating. Next, gas sensing test was conducted. Pristine SWNTs, PMMA/SWNTs and thiophene/SWNTs were exposed to vapors of ethanol and dichloromethane at room temperature. From normalized sensor response results, it was found that pristine SWNTs and PMMA/SWNTs showed the highest response to ethanol and dichloromethane vapors, respectively. In order to discriminate vapors between ethanol and dichloromethane, pattern recognition technique was utilized. Principal component analysis (PCA) results showed that pattern recognition of ethanol and dichloromethane vapors can be discriminated by using pristine SWNTs and polymer-coated SWNTs sensors.

Surface functionalization of carbon nanomaterials by self‐assembling hydrophobin proteins

Class I fungal hydrophobins are small surface-active proteins that self-assemble to form amphipathic monolayers composed of amyloid-like rodlets. The monolayers are extremely robust and can adsorb onto both hydrophobic and hydrophilic surfaces to reverse their wettability. This adherence is particularly strong for hydrophobic materials. In this report, we show that the class I hydrophobins EAS and HYD3 can self-assemble to form a single-molecule thick coating on a range of nanomaterials, including single-walled carbon nanotubes (SWCNTs), graphene sheets, highly oriented pyrolytic graphite, and mica. Moreover, coating by class I hydrophobin results in a stable, dispersed preparation of SWCNTs in aqueous solutions. No cytotoxicity is detected when hydrophobin or hydrophobin-coated SWCNTs are incubated with Caco-2 cells in vitro. In addition, we are able to specifically introduce covalently linked chemical moieties to the hydrophilic side of the rodlet monolayer. Hence, class I hydrophobins provide a simple and effective strategy for controlling the surfaces of a range of materials at a molecular level and exhibit strong potential for biomedical applications.

Tuning the physical parameters towards optimal polymer-wrapped single-walled carbon nanotubes dispersions

Solubilization of single-walled carbon nanotubes (SWNTs) has been essential for the understanding of their physical properties. Ultrasonication followed by centrifugation has been generally used for the preparation of SWNT dispersion in presence of different surfactants or conjugated polymers. However, the experimental condition and procedure show lab-to-lab dissimilarities. In this study, we report on the preparation and optical characterization of SWNTs dispersed with poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The effects of several processing parameters are investigated, such as sonication time, polymer concentration and centrifugation speed. Optical spectroscopic techniques including absorption and photoluminescence in the near-infrared spectral regions are used for the evaluation of the different SWNT dispersions. The optimal parameters to obtain isolated SWNTs are identified.

Modeling the binding of peptides on carbon nanotubes and their use as protein and DNA carriers

An in-depth study of a novel functionalization of carbon nanotubes for their application as protein and DNA carriers is presented. First, the optimum conditions for the dispersion of single-walled carbon nanotubes (SWCNTs) with amphiphilic polypeptides were obtained, and the SWCNT–polypeptide complexes were characterized by different techniques (UV–Vis-NIR, CD, and AFM). Based on the properties of the SWCNT–polypeptide complexes, a model that characterizes the adsorption of natural proteins onto SWCNT was described for the first time. This model predicts the adsorption of natural proteins on SWCNTs based on the protein structure and composition, and therefore, allows the design of methods for the preparation of SWCNT–protein complexes. Besides, the use of cationic-designed amphiphilic polypeptides to disperse SWCNTs is applied for subsequent and efficient binding of DNA to carbon nanotubes by a bilayer approach. Therefore, in this article, we develop procedures for the use of SWCNTs as protein and DNA carriers. The systems were delivered into cells showing that the efficiency of delivery is affected by the charge of the complexes, which has important implications in the use of SWCNT as platforms for protein and DNA binding and subsequent use as delivery systems.

Preparation of Single-Walled Carbon Nanotubes from Starch by Arc Discharge

Single-walled carbon nanotubes (SWNTs) have been successfully prepared from starch by arc discharge technique. The SWNTs products were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The growth mechanism of the SWNTs was discussed in terms of the starch. The results demonstrate that starch is one of the suitable precursor for making SWNTs by arc discharge method.

A “skeleton/skin” strategy for preparing ultrathin free-standing single-walled carbon nanotube/polyaniline films for high performance supercapacitor electrodes

One of the most critical aspects in the preparation of single-walled carbon nanotubes (SWCNTs)/conducting polymer hybrid electrodes is to improve the energy density without seriously deteriorating their high power capability. Here, we report a “skeleton/skin” strategy for the preparation of free-standing, thin and flexible SWCNT/polyaniline (PANI) hybrid films by a simple in situ electrochemical polymerization method using directly grown SWCNT films with a continuous reticulate structure as template. In situ electrochemical polymerization can achieve effective deposition of PANI onto the surface of SWCNT bundles in the films and control the morphology and microstructure of the SWCNT/PANI hybrid films. In a SWCNT/PANI hybrid film, the directly grown SWCNT film with continuous reticulate architecture acts as the skeleton and PANI layers act as the skin. This unique continuous “skeleton/skin” structure ensures that these hybrid films have much higher conductivity compared to SWCNT/PANI composite films based on post-deposition SWCNT films. Flexible supercapacitors have been fabricated using the SWCNT/PANI hybrid films as both electrodes and charge collectors without metallic current collectors. High energy and power densities (131 W h kg−1 and 62.5 kW kg−1, respectively) have been achieved for the optimized assembly. The high electrical conductivity and flexibility, in combination with continuous porous architecture, suggests that the as-prepared ultrathin free-standing SWCNT/PANI hybrid films have significant potential as promising electrode materials for thin, lightweight and flexible energy storage devices with high performance.

Preparation of Single-Walled Carbon Nanotubes from Starch by Arc Discharge

Single-walled carbon nanotubes (SWNTs) have been successfully prepared from starch by arc discharge technique. The SWNTs products were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The growth mechanism of the SWNTs was discussed in terms of the starch. The results demonstrate that starch is one of the suitable precursor for making SWNTs by arc discharge method.

Zeolite Surface As a Catalyst Support Material for Synthesis of Single-Walled Carbon Nanotubes

Preparation of single-walled carbon nanotubes (SWNTs) has been advanced by controlling several parameters including the catalyst and the catalyst support material. Although zeolite has been frequently used as a catalyst support material for the synthesis of SWNTs, detailed surface properties of previously employed zeolites and thus their role as a catalyst support material have not been sufficiently clarified yet. In this study, a clean b-plane surface of silicalite-1, which is a siliceous MFI-type zeolite, was used as a model substrate for the synthesis of SWNTs. The amount of active cobalt used for SWNT generation was smaller than the initially sputtered amount, and XPS measurements revealed diffusion of cobalt into the zeolite framework. The diffused cobalt was found to interact strongly with the silica framework of zeolite. The diffusion coefficient of cobalt in silicalite-1 zeolite was larger than that in thermally oxidized SiO2 formed on a Si substrate. This difference was ascribed to the microporou...

The role of surface functionalization in the solar light-induced production of reactive oxygen species by single-walled carbon nanotubes in water

Risk assessment of engineered nanomaterials necessitates the need for information on reactivity and persistence of these materials in the environment. To this end, we report on reactivity of single-walled carbon nanotubes (SWCNTs) that: (i) have been functionalized by acid oxidation to contain carboxylic acid groups, (ii) have been further functionalized by esterification with polyethylene oxide groups, or (iii) were unmodified (i.e., unfunctionalized), with all materials used as received from the manufacturer. Aqueous colloidal dispersions of both types of functionalized SWCNTs generated reactive oxygen species (ROS) including singlet oxygen ( 1O 2), superoxide anion ( O 2 - ) , and hydroxyl radicals ( OH) in light within the solar spectrum ( λ = 300–410 nm) under oxic conditions. Under similar experimental conditions (i.e., several days under light near solar intensity) but with a surfactant added as a dispersing agent, aqueous dispersions of unfunctionalized SWCNTs exhibited no measurable ROS production. Defects in the surface caused by functionalization, as well as differences in amorphous carbon and metal impurity content within different SWCNT preparations, may facilitate some ROS production. Adding β-nicotinamide adenine dinucleotide to dispersions of carboxylated SWCNTs resulted in O 2 - generation in the absence of light, suggesting dark reaction electron transfer as a potential mechanism of toxicity.

Preparation of single-walled carbon nanotube (SWNT) gel composites using poly(ionic liquids)

This paper reports a new and practical route for synthesizing nanotube-polymeric ionic liquids gel by non-covalent functionalization of oxidized single-walled carbon nanotube (SWNT) surfaces with imidazolium-based poly(ionic liquids) (PILs), using in situ radical polymerization method. A black and homogeneous precipitate SWNTs was obtained as a gel form, which is well dispersed in aqueous solution without any aggregation. The formation of SWNT gels is explained by the electrostatic attractions or π-bonds between the SWNT surface and the PIL matrix. By anion-exchange reaction of PIL bound to SWNTs, hydrophilic anions in PIL were substituted with hydrophobic anions, resulting in an effective transfer of SWNT-PIL hydrogels to organogels. The result also showed that SWNTs can effectively improve the conductivity along with the thermal stability of nanocomposite gels.

Abstract C142: Safety of single-walled carbon nanotubes for delivery of siRNA

Abstract siRNA is a leading potential new cancer therapy but currently lacks an adequate delivery mechanism. Ensysce has been exploring the use of single-walled carbon nanotubes (SWCNT) as delivery vehicles for siRNA delivery and has previously reported on the in vitro and in vivo efficacy of this platform. This study was conducted to determine what if any toxicities result from the use of SWCNT and identify toxicities that may be directly attributed to this delivery vehicle. For this application, it is not only necessary to determine the maximal load of SWCNT that can be tolerated, the dose limiting toxicities and the fate of the material in the body, but also to carefully prepare the SWCNT suspensions to ensure that contaminating metals, nanotube aggregates and other materials are not present when administered systemically. Ensysce Biosciences has been exploring the safe use of this material and here presents its latest findings from a toxicology study where the total dose of 50 and 100 g of fully suspended and individualized SWCNT were administered to groups of 3 mice. Mice were sacrificed at 12, 24, 48 hr and 1 week following i.v. administration. Blood chemistry and hematology were evaluated at each time point. Urine and feces were collected at 12, and 24 hr. Organs, including spleen, liver, kidney, heart, lung and brain were examined macroscopically and by near IR-fluorescence for the presence of SWCNT. The presence and persistence of SWCNT in the tissues was measured. Data to be presented will include details of the analytical characterization of the SWCNT preparations that were delivered, showing that the tubes were well dispersed and individualized. At both the 24 hr and 1 week timepoints, blood chemistry and hematology showed no evidence of toxicity, as values for all were within the normal ranges. Macroscopic examination of organs indicated that SWCNT were present in liver and spleen at 24 hr. Near IR-fluorescence spectroscopy demonstrated that the nanotube accumulation in the spleen decreased over a 1 week period. Data will be presented showing that a 100 g dose (equivalent to 30 mg in humans) was well tolerated and non-toxic. These studies have led to further work examining limits for use of SWCNT for siRNA delivery, including stability of the siRNA complexes in serum, siRNA loading efficiency and systemic efficacy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C142.

Environmental and Synthesis-Dependent Luminescence Properties of Individual Single-Walled Carbon Nanotubes

Luminescence properties of individual (6,5) single-walled carbon nanotubes (SWNTs) were studied using continuous wave and time-resolved spectroscopy. Nanotubes synthesized by different methods (HiPco and CoMoCat) and dispersed in two different ionic surfactants were examined either in aqueous environments or deposited on surfaces. SWNT preparations leading to the highest luminescence intensities and narrowest spectral widths exhibit the longest luminescence decay times. This highlights the role of the nanotube environment and synthesis methods in the nonradiative relaxation processes of the excitonic recombination. Samples of HiPco nanotubes dispersed in sodium deoxycholate contained the brightest nanotubes in aqueous environments.

Carbon Nanotube Electrodes for Hot‐Wire Electrochemistry

The use and preparation of single-walled carbon nanotubes (SWCNTs) at thin metallic wire electrodes for hot-wire electrochemical studies is described. The nanotubes were deposited on metal substrates such as gold by electrophoresis from a dispersion containing sodium dodecyl sulphate as an anionic surfactant. The formation of a layer of pure SWCNTs is achieved by thermal treatment at 350 degrees C. When heated in situ by a strong ac current, the electrodes can be used for electrochemical studies of nanotubes at increased temperatures. The state and functionality of the electrodes were characterized by Raman spectroscopy, scanning electron microscopy, and cyclic voltammetry with both anionic and cationic redox systems (dopamine, ferrocene carboxylic acid). First time experiments at the heated SWCNT electrodes demonstrated an excellent suitability of these as-prepared electrodes for thermoelectrochemical studies.

Modification of Single Walled Carbon Nanotube Surface Chemistry to Improve Aqueous Solubility and Enhance Cellular Interactions

Single walled carbon nanotubes (SWNTs) continue to demonstrate the potential of nanoscaled materials in a wide range of applications. The ability to modulate the mechanical or electrical properties of a material by varying the SWNT component may result in diverse "application tunable" materials. Similarly, biomaterials used in tissue engineering applications may benefit from these characteristics by varying electrical and mechanical properties to enhance or direct tissue specific regeneration. The interactions between SWNTs and cellular systems need to be optimized to integrate these highly hydrophobic nanoparticles within an aqueous environment while maintaining their unique properties. We assessed solubility, conductance, and cellular interactions between four different SWNT preparations (unrefined, refined, and SWNT with either albumin or human plasma adsorbed). Initial interactions between cells and SWNTs were assessed within a 3D environment using a red blood cell lysis model, with longer-term interactions assessing the effects on PC12 and 3T3 fibroblast function when cultured on SWNT-collagen composite hydrogels. After SWNT purification, the lytic effect on red blood cells (RBCs) is significantly reduced from 11% to 0.7%, indicating manufacturing contaminants play a significant role in undesirable cell interactions. Nanotubes with either human plasma or albumin physisorbed onto the nanotube surface were significantly more hydrophilic than either unrefined or refined preparations and displayed improved RBC interactions. Despite improved dispersion, purification, and adsorption of either plasma or albumin, SWNTs caused a significant reduction in conductance. Although the molecular interactions occurring at the cell membrane remain unclear, these investigations have identified two main factors contributing to membrane failure: manufacturing impurities and to a lesser extend the material's innate hydrophobicity. Although purification is a critical step to remove toxic manufacturing contaminants, care must be taken to ensure improved aqueous dispersion does not compromise desirable mechanical and electrical attributes.

Preparation of single-walled carbon nanotubes-induced poly(p-oxybenzoyl) crystals

Crystallization of oligomers was applied for the preparation of single-walled carbon nanotubes (SWNTs)/poly(p-oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate-like or lozenge-shaped crystals were successfully prepared by direct polymerization of p-hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate-like crystals were ∼200 nm to 3 μm. The crystals consisted of some layers, ∼3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265–1277, 2008

Alteration of deposition pattern and pulmonary response as a result of improved dispersion of aspirated single-walled carbon nanotubes in a mouse model

Nanoparticles have a fundamental dimension of <100 nm. However, on suspension in media, agglomerates of nanoparticles are the more common structure. This is particularly evident in prior intratracheal instillation or aspiration studies of single-walled carbon nanotubes (SWCNT), in which granulomatous lesions encased by epithelioid macrophages were produced by large agglomerates. In this study, we tested the hypothesis of whether exposure to more dispersed SWCNT structures would alter pulmonary distribution and response. A dispersed preparation of single-walled carbon nanotubes (DSWCNT) with a mean diameter of 0.69 microm was given by pharyngeal aspiration to C57BL/6 mice. Electron microscopy demonstrated a highly dispersed, interstitial distribution of DSWCNT deposits by 1 day postexposure. Deposits were generally <1 microm. Macrophage phagocytosis of DSWCNT was rarely observed at any time point. Lung responses were studied by lavage and morphometry at 1 h, 1 day, 7 day, and 1 mo after a single DSWCNT exposure of 10 microg/mouse. Lung sections and lavage cells demonstrated an early, transient neutrophilic and inflammatory phase that rapidly resolved and was similar to that observed with large agglomerates. No granulomatous lesions or epithelioid macrophages were detected. Morphometric measurement of Sirius red staining was used to assess the connective tissue response. The average thickness of connective tissue in alveolar regions was 0.10 +/- 0.02, 0.09 +/- 0.02, 0.10 +/- 0.01, 0.48 +/- 0.04, and 0.88 +/- 0.19 microm for PBS and 1-h, 1-day, 7-day, and 1-mo postexposure groups, respectively. The results demonstrate that dispersed SWCNT are rapidly incorporated into the alveolar interstitium and that they produce an increase in collagen deposition.

Influence of single-walled carbon nanotube films on metabolic activity and adherence of human osteoblasts

The influence of films of differently prepared single-walled carbon nanotubes (SWCNTs) and Ti6Al4V alloy on human osteoblasts was investigated. We focused on a metabolic activity of human osteoblasts as well as on their spreading and adherence ability on tested substrates. It was found that the metabolic activity of osteoblasts cultured on SWCNTs films was decreased of about 15% independently on the SWCNTs preparation technique. This result is comparable with that of osteoblasts cultured on Ti6Al4V alloy. It indicates that SWCNTs films are not toxic for human osteoblasts and could be used for biomedical applications.

Improved Photocurrent in Ru(2,2‘-bipyridine-4,4‘-dicarboxylic acid)2(NCS)2/Di(3-aminopropyl)viologen/Single-Walled Carbon Nanotubes/Indium Tin Oxide System: Suppression of Recombination Reaction by Use of Single-Walled Carbon Nanotubes

This paper reported the use of single-walled carbon nanotubes (SWCNTs) with terminal carboxylic acid groups as an electron-transfer bridge layer for improved photocurrent of viologen/Ru complex-based photoelectrochemical cells. The preparation of SWCNTs on tin-doped indium oxide (ITO) was prepared by spray-coating. The formation of Ru(2,2‘-bipyridine-4,4‘-dicarboxylic acid)2(NCS)2 [(RuL2(NCS)2)]/di(3-aminopropyl)viologen (DPAV)/SWCNTs/ITO was prepared by formation of acid−base complex. RuL2(NCS)2/DAPV/ITO and RuL2(NCS)2/DAPV/SWCNTs/ITO showed photocurrents of 5.6 and 10.3 nA/cm2 under A.M 1.5 condition (I = 100 mW/cm2), respectively. The photocurrents of the RuL2(NCS)2/DAPV/SWCNTs/ITO cells in which Ru complexes were attached to carbon nanotubes by only acid−base complex formation were raised to 83.9% in comparison with RuL2(NCS)2/DAPV/ITO due to retardation of recombination reaction in photoelectrochemical cells.

The effect of composition of the catalysts on the preparation of single-walled carbon nanotubes

The Mo-Co-MgO and W-Co-MgO catalysts were first prepared by the citric acid method. The single-walled carbon nanotubes(SWCNTs) were synthesized by decomposing CH4 in Ar over the Mo-Fe-MgO，Mo-Co-MgO and W-Co-MgO catalysts at 1123 K in the fluidized bed reactor. The effects of composition of the catalysts on the synthesis of SWCNTs were studied by Raman spectroscopy and transmission electron microscopy (TEM). And the mechanism of growth of SWCNTs was discussed. The results show that the citric acid method is effective for to preparing the catalysts and the high-quality SWCNTs were synthesized over the three catalysts. At 1123 K, the growth of SWCNTs over the catalysts may be similar to the liquid micro-area model. The dependence of diameter distribution on the composition of the catalysts was weak. There were some differences in the inner structure of SWCNTs synthesized over the three different catalysts. The carbon yield rates of products were increased by the addition of W and Mo in the catalysts.