Single-walled Carbon Nanotubes Powder Research Articles

A Study on the O2 Plasma Etching Method of Spray-Formed SWCNT Films and Their Utilization as Electrodes for Electrochemical Sensors.

In this study, we analyzed the morphological changes and molecular structure changes on the surface of single-walled carbon nanotube (SWCNT) films during oxygen plasma (O2) etching of SWCNT surfaces formed by the spray method and analyzed their potential use as electrochemical electrodes. For this purpose, a SWCNT film was formed on the surface of a glass substrate using a self-made spray device using SWCNT powder prepared with DCB as a solvent, and SEM, AFM, and XPS analyses were performed as the SWCNT film was O2 plasma etched. SEM images and AFM measurements showed that the SWCNT film started etching after about 30 s under 50 W of O2 plasma irradiation and was completely etched after about 300 s. XPS analysis showed that as the O2 plasma etching of the SWCNT film progressed, the sp2 bonds representing the basic components of graphite decreased, the sp3 bonds representing defects increased, and the C-O, C=O, and COO peaks increased simultaneously. This result indicates that the SWCNT film was etched by the O2 plasma along with the oxygen species. In addition, electrochemical methods were used to verify the damage potential of the remaining SWCNTs after O2 plasma etching, including cyclic voltammetry, Randles plots, and EIS measurements. This resulted in a reversible response based on perfect diffusion control in the cyclic voltammetry, and an ideal linear curve in the Randles plot of the peak current versus square root scan rate curve. EIS measurements also confirmed that the charge transfer resistance of the remaining SWCNTs after O2 plasma etching is almost the same as before etching. These results indicate that the remaining SWCNTs after O2 plasma etching do not lose their unique electrochemical properties and can be utilized as electrodes for biosensors and electrochemical sensors. Our experimental results also indicate that the ionic conductivity enhancement by O2 plasma can be achieved additionally.

Nanocomposite Beta Nb50Ti based SWCNTs by FAST-SPS-FCT

The synthesis of β-type phase NbxTi (x= 50 at%) / SWCNTs (Single Walled Carbon Nanotubes) intermetallic matrix nanocomposite by mechanical alloying to ensure the effective distribution of (SWCNTs) within the matrix. It has been stated by several researchers that during ball-milling of NbxTi (x =50 at%) powder mixtures, Nb-Ti intermetallic compound formation occurs either gradually along milling time of mechanical allowing (MA), or suddenly through amechanically self-propagating reaction (MSPR), which occurs after a ignition time of MA. For this purpose, 0.4and 0.8 at% of SWNTs was added to the powder mixture after the completion of reactionbetween Nb and Ti. The obtained powders Nb50Ti intermetallic compound mixed with SWCNTs powder and then was also ball-milled. Bulk samples were compacted and then sintered by (FAST-SPS-FCT) method (Field Assisted Sintering Technics-Sparck Plasma Sintering- Furnace, Advanced Ceramics for High-Temperature) at the temperature range (1273-1473 °K) with some time that retained the integrity of SWNTs in the intermetallic matrix.Structural and mechanical and vibronic changes of the nanocomposites were investigated by X-ray diffractometery (XRD). Field emission scanning electron microscopy (FESEM) micrographs showed that the offered MA approach caused the SWNTs to be uniformly embedded in the in situ synthesized NbTi intermetallic matrix. Meanwhile better distribution of SWCNTs resulted in higher density of FAST-SPS-FCT bulk nanocomposite as well higher hardness up to 2.75GPa compared to 2.4 of Nb50Ti intermetallic alloy obtained after MA time. The total porosity, compressive strength, and compressive elastic modulus of the FAST-SPS-FCT manufactured material were determined as 7%, 600 MPa, and 120 MPa, respectively. The alloy’s and its intermetallic nanocomposite have Young’s elastic modulus is comparable to that of healthy cancellous bone which makes it applicable in the biomedical field. The in vitro biocomptability will be performed in the near future. The comparable results for the FAST-SPS-FCT nanocomposites were 3%, 650 MPa, and 130 MPa. The alloy’s elastic modulus is comparable to that of healthy cancellous bone. This difference in mechanical properties results from different porosity and phase composition of the bot β-phase NbxTi (x= 50 at%) and NbxTi (x= 50 at%)/SWCNTs intermetallic matrix nanocomposite. More other nanotechnologies applications of the nanocomposite will be focused in the study of the superconducting type I for the ITER Poloidal Field Coils by measuring of Jc (T, B) characteristics.

Binder-free, pre-consolidated single-walled carbon nanotubes for manufacturing thermoset nanocomposites

In this work, we propose a pre-consolidated form of single-walled carbon nanotubes (SWCNT) – SWCNT briquettes – as a binder-free, robust, and safe material for manufacturing electrically and thermally conductive thermoset nanocomposites with universal applicability to all polymer matrices. We prove that the briquettes provide similar performance in nanocomposites compared to reference samples: a pristine powder, a commercial masterbatch and an aerogel based on the same type of SWCNTs. Using comprehensive sets of methods, we observe no significant differences in electrical (∼10−7-1 S/cm depending on SWCNT loading) and thermal (0.210–0.304 W/mK) conductivities for all sample types across a wide range of SWCNT concentrations. Moreover, the percolation thresholds of nanocomposites for SWCNT briquettes were ultra-low and close to that of pre-dispersed masterbatches (0.001–0.003 wt%). Pre-consolidated SWCNT powder is shown to provide the same final functional properties, while being free from common nanotube drawbacks such as the higher price of masterbatch manufacturing or aerosolization and low dispersibility during handling for the SWCNT powder/aerogel. The briquettes not only offer a safe solution for large scale fabrication, cutting away the need for personal and facility level safety measures, but do so at no significant cost increase, can be used with any polymer matrix and associated industrial processing route without any loss of final properties. This makes them universally attractive for all composite industrial production as well as small scale low capital laboratories.

Photothermal Desorption of Toluene from Carbonaceous Substrates Using Light Flash.

Millions of workers are occupationally exposed to volatile organic compounds (VOCs) annually. Current exposure assessment techniques primarily utilize sorbent based preconcentrators to collect VOCs, with analysis performed using chemical or thermal desorption. Chemical desorption typically analyzes 1 µL out of a 1 mL (0.1%) extraction volume providing limited sensitivity. Thermal desorption typically analyzes 100% of the sample which provides maximal sensitivity, but does not allow repeat analysis of the sample and often has greater sensitivity than is needed. In this study we describe a novel photothermal desorption (PTD) technique to bridge the sensitivity gap between chemical desorption and thermal desorption. We used PTD to partially desorb toluene from three carbonaceous substrates; activated carbon powder (AC-p), single-walled carbon nanotube (SWNT) powder (SWNT-p) and SWNT felts (SWNT-f). Sorbents were loaded with 435 ug toluene vapour and irradiated at four light energies. Desorption ranged from <0.007% to 0.86% with a single flash depending on substrate and flash energy. PTD was significantly greater and more consistent in SWNT-f substrates compared to AC-p or SWNT-p at all irradiation energies. We attribute the better performance of SWNT-f to greater utilization of its unique nanomaterials properties: high thermal conductivity along the nanotube axis, and greater interconnection within the felt matrix compared to the powdered form.

Chirality luminescent properties of single-walled carbon nanotubes during redox reactions

The optical measurement of single-walled carbon nanotubes (SWNTs) is a useful approach for understanding chirality characteristics because the excitation and emission wavelengths that produce the maximum emission intensity are unique to the chirality of SWNTs. The emission properties of SWNT chirality are useful in various biological applications and are envisaged to be applicable in nanobiosensors. Therefore, it is necessary to detect even small environmental changes, such as redox reactions, and it is important to identify optimal chirality according to the applications. In this study, we focused on the presence of SWNTs with different chiralities within the same SWNT powder, and we investigated the correlation between the rate of change of the emission intensity due to redox reactions and SWNT chirality. We measured the redox change rate of chirality, which was difficult to detect because of the low emission intensity, by increasing the exposure time during photoluminescence (PL) measurement. 0.5 mg of SWNT powder and 1 mL of double-stranded DNA (dsDNA) stock solution were mixed and sonicated using a probe-type sonicator on ice. The supernatant of the prepared dsDNA-SWNT dispersion was stored after centrifugation. Hydrogen peroxide (H 2 O 2 ; final concentration: 0.03%) was added to this dispersion for oxidation, and then, a catechin aqueous solution (final concentration 1.5 μg/mL) was added to the solution to measure PL. The exposure time was 90 s to obtain sufficient emission intensity. The measurement results showed that the magnitude of the rate of change of the PL intensity due to redox reaction was different for each chirality. Focusing on the (8,6) and (9,4) chiralities, which showed a large rate of change, the PL intensity decreased by 57.4% and 54.6% from the initial state, respectively, when H 2 O 2 was added. Subsequently, these values increased by 1024% and 558% with the addition of a catechin aqueous solution, respectively. Furthermore, from the comparison of the PL detection results and optical response characteristics of each chirality, it was observed that the rate of change of the PL intensity of SWNTs during redox reactions using H 2 O 2 and catechin had the strongest correlation with the SWNT diameter. • The exposure time was increased to 90 s to facilitate comparison of PL intensities between chiralities. • The responsiveness of chirality with small emission intensity was detected, which was difficult to detect in previous studies. • The PL change rate during redox using H 2 O 2 and catechin showed the strongest correlation with the SWNTs diameter. • The larger the diameter of SWNTs, the higher will be the PL change rate during redox reactions.

Detection of Redox Properties of (6,5)-Enriched Single-Walled Carbon Nanotubes Using Potassium Permanganate (KMnO4)

It has been reported that even if single-walled carbon nanotubes (SWNTs) are coated with the same polymer, the redox characteristics change of each chirality may differ. Particularly, the addition of hydrogen peroxide (H2O2) minimally affects the near-infrared (NIR) absorption spectra of the dsDNA-(6,5)-enriched SWNT complex (DNA-SWNT complex). Detecting the redox properties of (6,5) chirality using NIR absorption spectra has been one of the issues to be solved. We hypothesized that an oxidizing agent with high oxidizing power is required to detect the absorption spectra of (6,5) chirality. In this study, we used KMnO4, which contains atoms with a high oxidation number. A dispersion was prepared by mixing 0.5 mg of (6,5)-enriched SWNT powder with 1 mg/mL of DNA solution. After adding H2O2 or KMnO4 to this dispersion and oxidizing it, catechin solutions were added to reduce the dispersion. The absorption peak of the DNA-SWNT complex decreased by 23.9% following the addition of KMnO4 (final concentration: 0.5 µM) and recovered 30.7% following the addition of the catechin solution. We revealed that the changes in the absorption spectra change of (6,5) chirality, which could not be detected by H2O2, can be detected by using KMnO4. We also varied the concentration of KMnO4 and verified whether the adsorption of KMnO4 can be modeled as a Langmuir adsorption isotherm.

Dispersing Carbon Nanotubes in Water with Amphiphiles: Dispersant Adsorption, Kinetics, and Bundle Size Distribution as Defining Factors

Debundling and dispersing single-walled carbon nanotubes (SWNTs) is essential for applications, but the process is not well understood. In this work, aqueous SWNT dispersions were produced by sonicating pristine SWNT powder in the presence of an amphiphilic triblock copolymer (Pluronic F127) as dispersant. Upon centrifugation, one obtains a supernatant with suspended individual tubes and thin bundles and a precipitate with large bundles (and impurities). In the supernatant, that constitutes the final dispersion, we determined the dispersed SWNT concentration by thermogravimetric analysis (TGA) and UV–vis spectroscopy, and the dispersant concentration by 1H NMR. The fraction of dispersant adsorbed at the SWNT surface was obtained by 1H diffusion NMR. Sigmoidal dispersion curves recording the concentration of dispersed SWNTs as a function of supernatant dispersant concentration were obtained at different SWNT loadings and sonication times. As SWNT bundles are debundled into smaller and smaller ones, the ess...

Observation of Adsorption Process of Single Stranded DNA to Single-Walled Carbon Nanotubes Surfaces by Fluorescence Quenching

Single walled carbon nanotubes (SWNTs) are one of the promising nanomaterials for various applications in nanotechnology. In biomedical fields, hybrids of DNA and SWNT (DNA-SWNT hybrids) are expected to be attractive nanodevices for drug delivery and DNA sensors. For preparing DNA-SWNT hybrids, mixture of SWNT and DNA solutions are prepared via sonication. Although DNA-SWNT hybridization techniques have been established, the diverse sonication conditions in every paper may affect structures of DNA-SWNT hybrids. Here we report a method of monitoring adsorption process of DNA to SWNT surfaces using fluorescent labeled single-stranded DNA (Fluor-ssDNA). It is known that fluorescent emission of fluorescent dyes is quenched when the dye is adsorbed on SWNT surfaces. Using this unique quenching phenomenon, we evaluated adsorption process of Fluor-ssDNA on SWNT surfaces. In the experiments, 0.25 mg of SWNT powder, 50 uL of Fluor-ssDNA solution (1.0 mg/mL in tris (hydroxymethyl aminomethane buffer solution, 200mM, pH 7.5)), and 450 uL of the buffer were mixed, and then sonicated under three different sonication conditions as follows: probe type with amplitude 60% of 130 W (P60), probe type with amplitude 20% of 130 W (P20), and bath type with 80 W (B80). In order to monitor the adsorption process, samples were characterized by fluorescent spectroscopy and atomic force microscopy. In the case of P60, fluorescent intensity of Fluor-ssDNA decreased 98% within 2 min. This suggests that most of Fluor-ssDNA rapidly adsorbed on SWNT surfaces. However, AFM images demonstrated that it took more time to form mono-dispersed DNA-SWNT hybrids. In the case of P20 and B80, 30 min was needed for 98% quenching. In addition, reproducibility of the B80 data was much higher than that of P20. This is an advantage of bath type sonicator.

Selective removal of metal impurities from single walled carbon nanotube samples

Large scale production of high quality CNT samples is still challenging. The presence of structural defects and metallic particles in pristine single walled carbon nanotubes (SWNTs) is responsible for the alteration of both their chemical stability and their magnetic and electrical properties. The commonly used purification procedures are based on multi-step treatments that are often too aggressive towards the CNTs, leading to disappointing yields. Here, we propose an alternative process that allows preparing high-quality and high-purity SWNT samples. The proposed process merely consists of heating up SWNT powder under high chlorine partial pressure and high temperature. These thermodynamic conditions favor high chlorine diffusion to metal impurities embedded in carbon shells thus inducing an avalanche process of metal chloride formation and sublimation. The purified samples have been characterized by transmission electron microscopy, thermogravimetric analysis, magnetic measurements and Raman spectroscopy. We show that the developed process combines selective elimination of catalytic impurities and high yields. More importantly, we show that this process preserves the quality of the resulting purified nanotubes.

Gas sensing properties of single-wall carbon nanotubes dispersed with dimethylformamide

Abstract For NO 2 gas sensing, we deposited single-walled carbon nanotubes (SWCNTs) on a pair of interdigitated electrodes (IDEs) by using a simple casting method. In order to achieve well-dispersed SWCNTs, we dispersed the as-grown SWCNT powder into dimethylformamide (DMF). We selected DMF as one of the candidate materials to ravel the entangled SWCNT bundles because the amide group could easily attach to the surface of the nanotubes. The resultant SWCNTs were well separated. However, the SWCNTs dispersed in DMF required a heat treatment to eliminate the DMF molecules adsorbed on the surface of the SWCNTs. Therefore, we heated the SWCNTs on the IDEs to 350 °C for 1, 2, 3, and 5 h, to remove the outer DMF adsorbed layers. The assembled sensors were exposed to NO 2 of 3 and 10 ppm concentrations. We attributed the NO 2 gas sensing to the direct charge transfer from the physically adsorbed molecules to the individual p-type semiconducting SWCNTs.

Aerosolization of Single-Walled Carbon Nanotubes for an Inhalation Study

Single-walled carbon nanotubes (SWCNT) are being produced in increasing quantities because of high interest in applications resulting from their unique properties. Because of potential respiratory exposures during production and handling, inhalation studies are needed to determine potential toxicity. A generation system was designed to produce respirable aerosol at 5 mg/m3 for a 1-wk animal (mouse) exposure. The starting material used in these experiments was as-produced powder from the high pressure carbon monoxide method that was sieved to number 6 mesh (< 2.3 mm). An acoustic feeder system was developed that handled the SWCNT powder without causing compaction of the material. The feed rate was adjustable, allowing output concentrations as high as 25 mg/m3. The powder particles were reduced in size using a mill that produced high shear forces, tearing the agglomerates apart. The resulting aerosol was size-separated using a settling chamber and two cyclones to produce a respirable aerosol. The mass output efficiency of the entire system for producing a respirable aerosol from bulk material was estimated to be about 10%.

A diameter-dependent separation of semiconducting from metallic single-wall carbon nanotubes by using nitronium ions

We have reported the density-functional calculations of NO2 adsorption on single-walled carbon nanotube (SWCNTs) walls. We find that NO2 adsorption is strongly electronic structure- and strain-dependent. The NO2 adsorption on metallic nanotubes (m-SWCNTs) was energetically more favorable than that on semiconducting nanotubes (s-SWCNTs) and furthermore the adsorption became less stable with increasing diameters of nanotubes. The adsorption barrier height shows similar dependence on the electronic structure and diameter to the adsorption energy. On the base of our theoretical model, we have found a method for a diameter-selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) from semiconducting (s-) ones by stirring or sonication SWCNT powder in tetramethylene sulfone (TMS)/chloroform solution with nitronium hexafluoroantimonate (NO2SbF6: NHFA) and nitronium tetrafluoroborate (NO2BF4: NTFB). Positively charged nitronium ions were intercalated into nanotube bundles, where the intercalation was promoted also by the counter ions. Nitronium ions selectively attacked the sidewall of the m-SWCNTs due to the abundant presence of electron density at the Fermi level, thus yielding stronger binding energy compared to the counterpart s-SWCNTs. The s-SWCNTs were left on the filter after filtration, whereas the m-SWCNTs were disintegrated and drained away as amorphous carbons. The effectiveness of removing m-SWCNTs was confirmed by the resonant Raman spectra and absorption spectra.

Behavior of single-walled carbon nanotube-based gas sensors at various temperatures of treatment and operation

The behavior of single-walled carbon nanotube (SWNT)-based gas sensors at various conditions of operation was reported. The sensors were fabricated from SWNT powder by the screen-printing method, followed by an annealing pretreatment in open-air for 2h at various temperatures to enhance the sensor characteristics. It was found that, the annealing at a suitable temperature not only removed the residual solvent and amorphous impurities from the SWNTs, but also opened the nanotube-caps, resulting in enhancement the sensor sensitivity. Subsequently, the sensor annealed at 200°C was employed for detection ammonia (NH3) in 500sccm nitrogen (N2) flowing. After 10min exposing to 5ppm NH3 at room temperature, the resistance of the sensor increased up to 8% in comparison with its initial value. The sensitivity increased as the NH3 concentration increased but was diminished when NH3 concentration reached to 40ppm. The sensor recovery was amended either by increasing the carrier gas flux or by heating in desorption time. By choosing a suitable regime of operation, in which the carrier gas flux, the heating duration and temperature were appropriately controlled, the characteristics of the SWNT-based sensor such as recovery and reproducibility were significantly improved.

SERS, FT-IR and photoluminescence studies on single-walled carbon nanotubes/conducting polymers composites

Surface-enhanced Raman scattering (SERS), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectroscopies were used to investigate composites based on single-walled carbon nanotubes (SWNTs) and different conducting polymers like polyaniline (PANI), poly-paraphenylene vinylene (PPV) and poly 3-hexylthiophene (3-PHT). In the case of SWNTs/PANI, different composites are obtained by adding dispersed SWNTs powder to the polymer solutions and by chemical polymerization of aniline in presence of SWNTs. The difference originates in the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs in fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FT-IR spectra of the composites PANI/SWNTs and PANI/C 60, chemically synthesized. Electrochemical polymerization of aniline in an HCl solution on a SWNT film leads to a covalent functionalization of SWNTs with PANI. In this case, Raman scattering data suggest an additional nanotubes roping with PANI as a binding agent. A post treatment with the NH 4OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. In the case of PPV and 3-PHT, the effect of the concentration of SWNTs on the photoluminescence properties will be described and compared, as probes of interaction.

Effect of Operating Temperature on Characteristics of Single-Walled Carbon Nanotubes Gas Sensor

The effect of operating temperature on characteristics of single-walled carbon nanotubes (SWNT) based gas sensor was investigated. SWNT-based sensor was fabricated from SWNT powder (Iljin Nanotech, Korea) by screen-printing method. SWNT powder (30 mg, AP grade) was dispersed into 0.78 gram a-terpineol (Aldrich) by ultrasonic vibration for 1 hour then stirred manually for 1 hour to increase adhesion. From this condensed solution, a thick film of SWNT was printed onto alumina substrates. The film then was sintered at 300oC for 2 hours to remove residual impurities. Upon exposure to some gases such as nitrogen, ammonia or nitric oxide, resistance of the sensor dramatically changes due to gas adsorption. In our experiments, SWNT-based sensor was employed to detect NH3 gas in N2 ambience. After saturated of N2, the sensor exposes to NH3 with various concentrations (from 5 ppm to 100 ppm, diluted by N2 as carrier gas). This sensor exhibits a fast response, high sensitivity but slow recovery at room temperature. By heating at high temperature and increasing the flow-rate of carrier gas, NH3 gas desorbs easily and recovery of the sensor improved. The heating also influenced the characteristics of sensors such as response and reproducibility. Other special changes in electric property of SWNT-based sensor caused by heating are also discussed.

Single-walled Carbon Nanotubes Are a New Class of Ion Channel Blockers

Here we identify a novel class of biological membrane ion channel blockers called single-walled carbon nanotubes (SWNTs). SWNTs with diameter distributions peaked at approximately 0.9 and 1.3 nm, C60 fullerenes, multi wall nanotubes (MWNTs), and hyperfullerenes (nano-"onions") were synthesized by several techniques and applied to diverse channel types heterologously expressed in mammalian cells. External as-fabricated and purified SWNTs blocked K+ channel subunits in a dose-dependent manner. Blockage was dependent on the shape and dimensions of the nanoparticles used and did not require any electrochemical interaction. SWNTs were more effective than the spherical fullerenes and, for both, diameter was the determining factor. These findings postulate new uses for SWNTs in biological applications and provide unexpected insights into the current view of mechanisms governing the interaction of ion channels with blocking molecules.

Transport phenomena in an anisotropically aligned single-wall carbon nanotube film

Thin films of aligned carbon nanotubes were prepared by a simple mechanical rubbing from a singlewalled carbon nanotube powder, which was synthesized by the catalytic arc discharge. The measured electrical resistivity shows high anisotropy $({\ensuremath{\rho}}_{N}/{\ensuremath{\rho}}_{P})$ ranging from 5 to 15. The annealed samples show a monotonic decrease in the resistivity with increasing temperature. Carbon nanotubes in the mat act as strong Luttinger liquids with g values ranging from 0.18 to 0.26, similar to an isolated nanotube. We propose that the transport is dominantly governed by the formation of metal-metal crossed junctions of nanotubes in the mat.