Separation Of Single-walled Carbon Nanotubes Research Articles

Large-scale single-chirality separation of single-wall carbon nanotubes by simple gel chromatography

Monostructured single-wall carbon nanotubes (SWCNTs) are important in both scientific research and electronic and biomedical applications; however, the bulk separation of SWCNTs into populations of single-chirality nanotubes remains challenging. Here we report a simple and effective method for the large-scale chirality separation of SWCNTs using a single-surfactant multicolumn gel chromatography method utilizing one surfactant and a series of vertically connected gel columns. This method is based on the structure-dependent interaction strength of SWCNTs with an allyl dextran-based gel. Overloading an SWCNT dispersion on the top column results in the adsorption sites of the column becoming fully occupied by the nanotubes that exhibit the strongest interaction with the gel. The unbound nanotubes flow through to the next column, and the nanotubes with the second strongest interaction with the gel are adsorbed in this stage. In this manner, 13 different (n, m) species were separated. Metallic SWCNTs were finally collected as unbound nanotubes because they exhibited the lowest interaction with the gel.

Tunable separation of single-walled carbon nanotubes by dual-surfactant density gradient ultracentrifugation

We present a systematic study of the effects of surfactants in the separation of single-walled carbon nanotubes (SWNTs) by density gradient ultracentrifugation (DGU). Through analysis of the buoyant densities, layer positions, and optical absorbance spectra of SWNT separation using the bile salt sodium deoxycholate (DOC) and the anionic salt sodium dodecyl sulfate (SDS), we clarify the roles and interactions of these two surfactants in yielding different DGU outcomes. The separation mechanism described here can also help in designing new DGU experiments by qualitatively predicting outcomes of different starting recipes, improving the efficacy of DGU and simplifying post-DGU fractionation.

(Invited) Diameter-Based Separation of Single-Walled Carbon Nanotubes with Dipyrene Nanotweezers

not Available.

High-Efficiency Separation of Single-Wall Carbon Nanotubes by Self-Generated Density Gradient Ultracentrifugation

We report an efficient density gradient ultracentrifugation (DGU) method for separation of metallic and semiconducting single-walled carbon nanotubes (SWCNTs) using a self-generated density gradient. A uniform-density SWCNT dispersion (33% v/v in iodixanol) was used to completely fill a centrifuge tube. After ultracentrifugation, separation of the metallic and semiconducting SWCNTs was achieved with a purity comparable to that achieved by DGU using a steplike density gradient. Because the SWCNTs were dispersed within the entire tube during this procedure, a large amount of SWCNTs can be separated at one time.

Diameter-based separation of single-walled carbon nanotubes through selective extraction with dipyrene nanotweezers

We have been developing host–guest methodology for the separation of single-walled carbon nanotubes (SWNTs) according to handedness and diameter with gable-type chiral diporphyrins. The diporphyrins, designated as porphyrin nanotweezers, consist of two porphyrins and rigid spacer in between. As an extension of our strategy, novel nanotweezers having two pyrenes instead of porphyrins have been designed, because pyrene is known to have high affinity toward SWNT surface. The pyrene nanotweezers presented here consist of two 1- or 2-pyrenes and 3,6-carbazolylenes with various N-substituents. For the extraction of SWNTs, the 1- and 2-pyrene nanotweezers show a marked contrast: 1-pyrene nanotweezers selectively extract SWNTs with diameters ranging from 0.84 nm to 0.97 nm, while 2-pyrene nanotweezers are not able to extract SWNTs at all.

Improved selectivity in discriminating handedness and diameter of single-walled carbon nanotubes with N-substituted 3,6-carbazolylene-bridged chiral diporphyrin nanotweezers

Chiral diporphyrin nanotweezers 1 consisting of two chiral porphyrins with N-substituted 3,6-carbazolylene in between have been studied for the separation of single-walled carbon nanotubes (SWNTs). As compared to the analogous nanotweezers 2 without an N-substitutent, nanotweezers 1 with the N-octylcarbazolylene spacer exhibit much higher extraction ability and better selectivity for SWNTs. A narrower diameter range of SWNTs, from 0.88 to 0.92 nm, was selectively extracted with nanotweezers 1. In addition, only (7,6)-SWNTs of 0.90 nm diameter were optically enriched through extraction with 1, while SWNTs extracted with 2 showed lower optical purity of (7,6)-SWNTs. These enhanced extraction and discrimination abilities of 1 can be attributed to the formation of a more stable SWNT complex of 1 than of 2 in methanol.

Understanding the Electrophoretic Separation of Single-Walled Carbon Nanotubes Assisted by Thionine as a Probe

Single-walled carbon nanotubes (SWNTs) dispersed by sodium dodecyl sulfate (SDS) can be simply and effectively separated into semiconducting (s) and metallic (m) fractions by the method of agarose gel electrophoresis, in which s-SWNTs cannot migrate like m-SWNTs and remain unmoved under electric field. The role of SDS is suggested to be crucial for such separation effect. Its mechanism, however, is still unclear and hard to probe. In the present study, by employing thionine (TN), a positively charged dye molecule which may show unique interaction with SDS molecules, we can roughly evaluate the changes of SDS aggregates during the agarose gel electrophoresis. On the basis of the results of the electrophoretic and spectroscopic characterizations, we propose that the unique interaction of s-SWNTs with agarose and the exfoliation of some SDS molecules from SDS-s-SWNT entities lead to the separation of s- and m-SWNTs.

Simultaneous Discrimination of Handedness and Diameter of Single-Walled Carbon Nanotubes (SWNTs) with Chiral Diporphyrin Nanotweezers Leading to Enrichment of a Single Enantiomer of (6,5)-SWNTs

Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT-SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT-SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.

A Comprehensive Review on Separation Methods and Techniques for Single-Walled Carbon Nanotubes.

Structural control of single-walled carbon nanotubes (SWNTs) is attracting enormous interest in view of their applications to nanoelectronics and nanooptics. Actually, more than 200 papers regarding separation of SWNTs have been published since 1998. In this review, they are classified into the following five sections according to the separation methods; electrophoresis, centrifugation, chromatography, selective solubilization and selective reaction. In each method, all literature is summarized in tables showing the separated objects (metallic/semiconducting (M/S), length, diameter, (n, m) structure and/or handedness), the production process of the used SWNTs (CoMoCAT, HiPco, arc discharge and/or laser vaporization) and the employed chemicals, such as detergents and polymers. Changes in annual number of publications related to this subject are also discussed.

Diameter-Selective Metal/Semiconductor Separation of Single-wall Carbon Nanotubes by Agarose Gel

The separation of semiconducting and metallic single-wall carbon nanotubes (SWCNTs) by agarose gel chromatography was investigated. SWCNTs dispersed in sodium dodecyl sulfate (SDS) solution were applied to the top of the gel column. Metallic SWCNTs were eluted with SDS solution. Subsequently, the semiconducting SWCNTs that remained in the gel column were collected with sodium deoxycholate (DOC) solution as the eluant. By the successive addition of DOC solutions with concentrations ranging from 0.05 to 2 wt % and fractional collection at each concentration, we found that smaller-diameter enriched S-SWCNTs were eluted first with the lower concentration DOC solutions and then larger-diameter enriched S-SWCNTs were eluted with the higher DOC concentration solutions. Thus, diameter-selective enrichment of semiconducting SWCNTs was achieved. Diameter-selective enrichment of metallic SWCNTs was also demonstrated by adding a series of SDS solutions with different concentrations. These results demonstrate that agarose gel can be used to simultaneously separate metallic and semiconducting SWCNTs and to perform diameter separation of these SWCNTs.

Separation of single-walled carbon nanotubes from graphite by centrifugation in a surfactant or in polymer solutions

Electric arc single-walled carbon nanotubes (SWCNTs) can be separated from their graphitic impurities by a single centrifugation process in a surfactant or in polymer solutions. The purity of SWCNT dispersions, evaluated from near infrared (NIR) spectroscopy measurements, substantially increased after centrifugation at a moderate speed. The supernatant NIR purity was affected by the surfactant choice, following the sequence: sodium cholate∼Pluronic F68>sodium dodecylbenzene sulfonate>Pluronic F127>sodium dodecyl sulfate. NIR purity was also influenced by the centrifugation speed and the pristine SWCNT concentration in the starting dispersion, but not by the surfactant concentration. SWCNT enrichment was not observed in a pure organic solvent (N,N′-dimethylformamide) under identical centrifugation conditions. X-ray diffraction analysis demonstrated that graphitic impurities were mostly eliminated from SWCNTs during the centrifugation process in a surfactant or in polymer solutions. Thermogravimetric analysis under CO2 showed that metallic impurities were substantially reduced during the centrifugation process.

Effects of NaCl on the Separation of Single-Walled Carbon Nanotubes by Agarose Gel Electrophoresis

Plenty of attention has been paid to obtaining single-walled carbon nanotubes (SWCNT) with single conductive properties so that they can be applied in various fields. Among the separation techniques used for metallic (m-) and semiconducting (s-) single-walled carbon nanotubes, agarose gel electrophoresis (AGE) is thought to be a relatively simple and low-cost method. In this work, we used UV-visible-near infrared (UV-Vis-NIR) absorption spectroscopy to study the effect of NaCl on the separation of SWCNT by AGE. Our results show that the addition of NaCl greatly influences the separation of the SWCNT. At a NaCl concentration of less than 70 mmol . L(-1), the relative content of s-SWCNT increased after separation and at a NaCl concentration of higher than 70 mmol . L(-1), the separation of m-SWCNT and s-SWCNT was restrained as the concentration of NaCl increased. At a NaCl concentration of 160 mmol . L(-1), the separating efficiency of the systemdropped markedly. We suggest that the addition of NaCl may change the adsorption properties of the surfactant towards m-SWCNT and s-SWCNT.

Influence of endohedral water on diameter sorting of single-walled carbon nanotubes by density gradient centrifugation

Separation of single-walled carbon nanotubes (SWNT) by diameter is an important prerequisite for controlled experimental studies and efficient application of these systems. By comparing experimental data with molecular dynamics (MD) simulations, we demonstrate that water filling has a significant, tube-diameter dependent effect on the effective mass density of individual single-walled carbon nanotubes suspended in aqueous surfactant suspensions. We present a model for the effective density of the nanotube-surfactant complex in aqueous solution that permits a comprehensive description of its density across the entire, experimentally relevant range of SWNT diameters. Parameters for this model can be obtained from molecular dynamics simulations and/or experiment and help explain the subtle interplay of surfactant coverage and endohedral water in the separation of a particular diameter species of SWNT by gradient centrifugation.

Selective deposition of semiconducting single-walled carbon nanotubes onto amino-silane modified indium tin-oxide surface for the development of poly(3-hexylthiophene)/carbon-nanotube photovoltaic heterojunctions

A method is described to obtain separation of single-walled carbon nanotubes (SWCNTs) on an indium tin-oxide (ITO) substrate by modifying the conducting surface of ITO with amino-silane functional groups. Scanning electron microscopy confirmed that the amino-silane functionalization of the substrate is a critical parameter for the immobilization of separated nanotubes. In particular spin coating the SWCNT solution onto the amino-silane modified ITO surface results in a lower nanotube density with respect to the reference sample obtained on pure ITO together with the immobilization of semiconducting carbon nanotubes onto the substrate. The possibility of using these SWCNT thin films to obtain polymer/nanotube heterojunctions for the development of organic solar cells is considered.

Density Gradient Ultracentrifugation of Arc Produced Single-Wall Carbon Nanotubes

A great breakthrough in separation of single-wall carbon nanotubes (SWNTs) by a density gradient ultracentrifugation during last years has allowed to obtain fractions of separated metal or semiconductor SWNTs. Another important property of this separation method is the possibility to obtain fractions with the desired positions of absorption peaks. For such fractions a quantum efficiency is significantly increased in case of using them as a non-linear optical material for formation of ultrafast beam modulators. Arc SWNTs demonstrate a saturable absorption in a wide spectral range (from 1.3 μm up to 1.95 μm). The density gradient ultracentrifugation allows to obtain the fractions with a narrow nanotube diameter distribution. This also increases the efficiency of SWNT-based saturable absorbers. In this work the density gradient ultracentrifugation technique has been used and optimized for SWNT separation. The aqueous suspensions of arc nanotubes have been treated. Different combinations and concentrations of surfactants (sodium dodecyl sulphate (SDS) and sodium cholate (SC)) were used for the gradient and the sample layer formation. A gradual shift of the absorption peaks over the layers has been obtained. This shift is very important because it opens a way to adjust the absorption peak position to the exact laser wavelength. The fractions with a prevalence of metallic SWNTs (up to 97%) have been obtained.

Optical Resolution and Diameter-Based Enrichment of Single-Walled Carbon Nanotubes through Simultaneous Recognition of Their Helicity and Diameter with Chiral Monoporphyrin

We have been developing host−guest methodology for separation of single-walled carbon nanotubes (SWNTs) with gable-type diporphyrins, designated as nanotweezers. In our previous works, chiral nanotweezers have been found to discriminate left- and right-handed structures (M and P forms, respectively, defined in our previous papers) as well as (n,m) structures through preferential extraction, giving optically active SWNTs with limited (n,m) forms. Herein, we report that chiral monoporphyrin also serves as a host molecule for separating SWNTs. When methanol was used as a solvent, chiral monoporphyrin extracted SWNTs through simultaneous recognition of their helicity and diameter, providing optically active SWNTs with enrichment of larger diameters. In ethylene glycol, on the other hand, a much larger amount of SWNTs was extracted through complexation with the chiral monoporphyrin, although the selectivity is lower than that in the case of methanol. Since the monoporphyrin can be prepared much more easily than diporphyrins, this finding may open up a practical route for large-scale separation of SWNTs through molecular recognition.

Effective Separation of Carbon Nanotubes and Metal Particles from Pristine Raw Soot by Ultracentrifugation

A quick and effective method for the separation of single-wall carbon nanotubes (SWCNTs) from impurity particles has been demonstrated. High-purity SWCNTs and impurities, such as metal particles and amorphous carbons, were separated by ultracentrifugation from raw soot containing SWCNTs. The purity of each component was evaluated by scanning electron microscopy, thermogravimetric analysis, and Raman spectroscopy. The advantage of this method is that the impurity particles can be collected as residual soot in the ultracentrifugation process without any loss, while the impurity particles are more or less chemically modified or disappeared in previous purification protocols. The present technique can provide suitable samples for the research of both SWCNTs and impurity particles, particularly for nano-risk assessment.

Self-Selective Separation of Single-Walled Carbon Nanotubes via a Hydroxyl Group Reaction

We developed a method of separating metallic single-walled carbon nanotubes (SWNTs) from semiconducting nanotubes (NTs) in suspension using a sodium hydroxide treatment and centrifugation. The semiconducting NTs remained suspended in the solvent while the metallic NTs precipitated out. This self-selective separation occurred because the metallic SWNTs bonded to hydroxyl groups due to strong surface hydrogen-bond interactions. We fabricated thin-film transistors based on random networks of semiconducting SWNTs on a glass substrate and obtained an on/off current ratio of 6.25 × 10 4 .

Centrifugal Length Separation of Carbon Nanotubes

Separation of single-wall carbon nanotubes (SWCNTs) by length via centrifugation in a high density medium, and the characterization of both the separated fractions and the centrifugation process are presented. Significant quantities of the separated SWCNTs ranging in average length from <50 nm to approximately 2 microm were produced, with the distribution width being coupled to the rate of the separation. Less rapid separation is shown to produce narrower distributions; these length fractions, produced using sodium deoxycholate dispersed SWCNTs, were characterized by UV-visible-near-infrared absorption and fluorescence spectroscopy, dynamic light scattering, Raman scattering, and atomic force microscopy. Several parameters of the separation were additionally explored: SWCNT concentration, added salt concentration, liquid density, rotor speed, surfactant concentration, and the processing temperature. The centrifugation technique is shown to support 10 mg per day scale processing and is applicable to all of the major SWCNT production methods. The cost per unit of the centrifugation-based separation is also demonstrated to be significantly less than size exclusion chromatography-based separations.

Reversible separation of single-walled carbon nanotubes in bundles

We show that electrostatic charging of nanotubes and the consequent repulsion can lead to reversible separation of individual single-walled carbon nanotubes in bundles. Low-energy electron beam irradiation leads to this completely reversible phenomenon. A simple semianalytical model is used to explain the observed separation mechanism. The reversibility of the separation process is attributed to discharging and thermal-fluctuation induced motion of the nanotubes in ambient air. Further, the separation impacts the electrical conductance of small nanotube bundled devices.