Separation Of Single-walled Carbon Nanotubes Research Articles

Triton assisted fabrication of uniform semiconducting single-walled carbon nanotube networks for highly sensitive gas sensors

Surfactants are vital for the dispersion and separation of single-walled carbon nanotubes (SWCNTs) when using chromatographic methods. However, excessive surfactant impurities left on the sorted tube surface and in solution may dramatically affect the fabrication and performance of various SWCNT-based thin-film devices. We demonstrated that compared to the widely used anionic surfactants, including sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium deoxycholate, the nonionic Triton surfactant was more effective not only for the enrichment of semiconducting (s-) SWCNTs, but also for preventing the tubes from severe aggregation upon network formation. Simply by spreading and rinsing treatment, a clean and homogenous network of s-SWCNTs was favorably formed between electrode channels, in which intertube contacts or junctions were well built up. The resultant sensor device showed an obviously improved electrical response to H2S with the detection level down to 50ppb even at room temperature, compared to those fabricated from the pristine SWCNTs and s-SWCNTs eluted with anionic surfactants. Our work provides an easy route for the sorting and application of s-SWCNTs at a low cost.

High-Efficiency Single-Chirality Separation of Carbon Nanotubes Using Temperature-Controlled Gel Chromatography

We report the use of temperature-controlled gel chromatography for the high-efficiency single-chirality separation of single-wall carbon nanotubes (SWCNTs). This new method uses temperature to selectively control the interaction between the sodium dodecyl sulfate (SDS)-wrapped SWCNTs and an allyl dextran-based gel. Temperature control enhances the differences in the interactions of various (n, m) SWCNTs with the gel, enabling the separation of high-purity (n, m) single-species in a single-step process. With this technique, we successfully sorted seven (n, m) single-species including (6, 4), (6, 5), (7, 5), (8, 3), (8, 4), (7, 6), and (8, 6) from raw HiPco-SWCNTs at a series of temperatures. Our technique offers the advantages of technical simplicity, low cost, and high yield, representing an important step toward the industrial-scale separation of single-chirality SWCNTs.

Separation of Single-Walled Carbon Nanotubes by 1-Dodecanol-Mediated Size-Exclusion Chromatography

A simple, single-column, high-throughput fractionation procedure based on size-exclusion chromatography of aqueous sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs) is presented. This procedure is found to yield monochiral or near monochiral SWCNT fractions of semiconducting SWCNTs. Unsorted and resulting monochiral suspensions are characterized using optical absorption and photoluminescence spectroscopy.

Chirality‐Dependent Reactivity of Individual Single‐Walled Carbon Nanotubes

Electronic characteristics of a single-walled carbon nanotube (SWCNT) strongly depend on minor variations in its atomic arrangement, specifically chirality. Therefore, precise control over nanotube chirality is highly desired for their application. Theoretically, SWCNTs with different structures have different chemical reactivities, which can be further used for their chirality selection. Here, an approach is developed to examine the relationship between the chirality of SWCNTs and their intrinsic chemical reactivity. By oxidizing individual, high-quality, suspended SWCNTs and using the nanobeam electron diffraction technique, it is shown that the reactivity of SWCNTs to O2 is intricately related to their diameters, metallicity, and chiral angles. In particular, even minor differences in chiral angles lead to big differences in their reactivity, which concords with first-principles calculations. Based on the experimental observations, a chirality-dependent reactivity sequence is constructed for SWCNTs. These findings shed light on effective chiral separation of SWCNTs for their practical application in many fields.

(Invited) Chiral Diporphyrin Nanocalipers: New Host Molecule Next to Nanotweezers for Separation of Single-Walled Carbon Nanotubes

not Available.

Thermodynamic Determination of the Metal/Semiconductor Separation of Carbon Nanotubes Using Hydrogels

The metal/semiconductor separation of single-wall carbon nanotubes (SWCNTs) using hydrogels, such as agarose gel and Sephacryl, together with sodium dodecyl sulfate is one of the most successful techniques necessary for industrial applications. Despite recent improvements in the technique, little is known about the separation mechanism. Here, we show that SWCNTs are reversibly adsorbed onto hydrogels in the presence of sodium dodecyl sulfate. The results enabled us to examine the thermodynamics of the adsorption reaction and thereby elucidate the separation mechanism. The adsorbability of SWCNTs onto the hydrogels was described by the standard Gibbs free energy for the adsorption, as well as the area of the hydrogels allowing the adsorption. We demonstrated, for the first time, that the free energy of adsorption for semiconducting SWCNTs was 0-12 kJ/mol lower than that for metallic SWCNTs in the temperature range of 290-320 K (e.g., ca. -4 kJ/mol for the agarose gel and ca. -9 kJ/mol for Sephacryl at 300 K), which permits metal/semiconductor separation. Importantly, the difference in the free energy was attributed to the difference in the enthalpy of adsorption: the enthalpy of adsorption of metallic SWCNTs was ca. 70 kJ/mol higher than that of semiconducting SWCNTs. Thus, the enthalpy of adsorption was found to be an important parameter in the metal/semiconductor separation of SWCNTs using hydrogels. In addition, the thermodynamic parameters depended on the hydrogel type and the surfactant concentration, which is most likely why under certain conditions hydrogels and surfactants produce different separations, e.g., chirality-selective or diameter-selective separation.

Manipulating Electron Transfer between Single-Walled Carbon Nanotubes and Diazonium Salts for High Purity Separation by Electronic Type

Diazonium salts preferentially react with metallic single-walled carbon nanotubes (SWNT) over semiconducting SWNT, enabling the separation of SWNT by electronic type. Therefore, the reaction selectivity of diazonium salts for metallic SWNT is crucial for high purity separation of both metallic and semiconducting SWNT. Herein, we developed an efficient method of increasing the reaction selectivity by manipulating the redox potential of diazonium salts. The electron affinity of diazonium salts is effectively lowered when the para-substituent of the diazonium salts is an electron-donating group, (i.e., 4-hydroxy and 4-propargyloxy) rather than an electron-withdrawing group (i.e., 4-nitro, 4-carboxy, and 4-cholro). The reduction potential of 4-hydroxyphenyl and 4-propargyloxyphenyl diazonium salt was greater than the oxidation potential of semiconducting SWNT; therefore, the electron transfer reaction between these two reagents was effectively suppressed, leading to a highly selective reaction for metallic SWNT. We confirmed that this highly selective reaction scheme can be used to separate SWNT, and high purity semiconducting SWNT can be obtained via density-induced separation.

Diameter Effect on the Sidewall Functionalization of Single‐Walled Carbon Nanotubes by Addition of Dichlorocarbene

AbstractDichlorocarbene is added to the sidewalls of single‐walled carbon nanotubes (SWNTs) with diameters ranging from 1.2 to 2.2 nm. Small diameter SWNTs are found to react much more easily than large diameter SWNTs. Upon functionalization, the conductance could be largely preserved for almost all SWNTs, while an effective bandgap increase for functionalized metallic SWNTs (m‐SWNTs) and a bandgap reduction for functionalized semiconducting SWNTs (s‐SWNTs) are generally observed. The results suggest that [2 + 1] cycloaddition is an excellent choice of processing, resulting in SWNTs over a large diameter range with electronic properties that are almost unaffected. Furthermore, possible separation of SWNTs according to their diameters could be achieved due to the apparent diameter‐dependent reactivity.

Achieving Diameter-Selective Separation of Single-Walled Carbon Nanotubes by Using Polymer Conformation-Confined Helical Cavity.

A water-soluble poly[(m-phenylenevinylene)-alt-(p-phenylenevinylene)] (PmPV) 2 has been synthesized, which exhibits an unsymmetrical substitution pattern on the para-phenylene unit. With one substituent being hydrophilic while the other being hydrophobic, the polymer chain has a higher tendency to fold in aqueous solution, thereby promoting helical conformation. The polymer is found to selectively disperse the single-walled nanotubes (SWNTs) of small diameters (d = 0.75-0.84 nm), in sharp contrast to PmPV 1 with a symmetrical substitution pattern. The intriguing diameter-based selectivity is believed to be associated with the confined helical conformation, which provides a suitable cavity to host the SWNT of proper sizes. The study thus provides a useful demonstration that the polymer conformation can have a profound impact on the SWNT sorting.

One-pass separation of single-wall carbon nanotubes by gel chromatography with a gradient of surfactant concentration

We have investigated the diameter-selective separation of carbon nanotubes by one-pass gel chromatography with a gradient of surfactant concentration. The formation of surfactant gradient in a column was successfully measured and is explained by a simple diffusion process even in the gel. We found that the diameter of eluted nanotubes is inversely proportional to the surfactant concentration of eluate. The detailed analysis of the movement of the nanotubes in the gel revealed that the separation mechanism was qualitatively explained by a model based on the trapping and de-trapping events of the nanotube–surfactant micelle on the gel surface, where the probability of the trapping and de-trapping events is proportional to the product of the diameter of the nanotubes and the surfactant concentration.

Purification of Single-Wall Carbon Nanotubes by Controlling the Adsorbability onto Agarose Gels Using Deoxycholate

One of the key challenges to the industrialization of single-wall carbon nanotubes (SWCNTs) is the commercial-scale production of highly purified SWCNTs separated into metallic and semiconducting species. In the present study, the purification of SWCNTs, i.e., the removal of amorphous carbon or bundled SWCNTs, was performed by quantifying and controlling their adsorbability onto agarose gel. The quantification of the adsorbability was achieved by assuming the Langmuir isotherm, and control over the adsorbability was exerted using 0.05–1% sodium deoxycholate (DOC). The results show that the adsorbability depends on the concentration of DOC. At a low DOC concentration (approximately 0.05%), impurities such as amorphous carbon or bundled SWCNTs were preferentially adsorbed onto the gels, whereas, at an intermediate DOC concentration (ca. 0.25%), high-purity SWCNTs were mainly adsorbed onto the gels. Thus, the impurities, which are difficult to remove by conventional methods, could be separated from unpurified SWCNTs by controlling the adsorbability, leading to the extraction of high-purity SWCNTs. In the purification, diameter-selective separation of SWCNTs was also observed. The purification method using a gel column can be conducted simply and continuously, so that it can be applied for the high-throughput production of high-purity SWCNTs.

Purification and Separation of Single-Walled Carbon Nanotubes (SWCNTs)

Purification or separation of single-walled carbon nanotubes (SWCNTs) is one of the most fundamental steps before they are used for research and technological applications. Based on the difference of their physical and chemical properties, separation of carbon nanotubes (CNTs) can be categorized into three groups: length separation, metallic and semiconducting tubes separation and chirality separation. In this review, we first briefly review the purification of CNTs and then focus on the different methods for the separation of CNTs.

Facile and Effective Post-Production Separation of Single-Walled Carbon Nanotubes with Paired Aromatic Molecules: A Molecular Tweezers Approach

As-produced single-walled carbon nanotubes (SWNTs) are mostly metallic and semiconducting mixtures. The population of semiconducting SWNTs in the as-produced mixtures is generally much higher than that of their metallic counterparts. Therefore, postproduction separation of metallic and semiconducting SWNTs is important to many potential uses of the nanotubes, especially those demanding higher electrical conductivity yet lower optical absorption. Because planar aromatic species are known to have somewhat different interactions with metallic and semiconducting SWNTs, in this work a molecule with a pair of planar aromatic moieties was specifically designed and synthesized to exaggerate the difference in its noncovalent functionalization and solubilization of the two types of nanotubes. As demonstrated, the molecule exhibited significant selectivity toward semiconducting SWNTs in the solubilization to allow the convenient harvesting of bulk metallic and semiconducting fractions in high purities. The results suggest that molecules with paired aromatic species or essentially molecular tweezers may represent a new class of agents for more effective and also relatively simple postproduction bulk separation of metallic and semiconducting SWNTs.

Effects of Ultrasonic Dispersion on the Separation of Single-Walled Carbon Nanotubes

Recently, gel chromatography has been demonstrated as an effective method for the separation of single-walled carbon nanotubes (SWCNTs) according to their electronic type and structure. The separation of SWCNTs was thought to result from the different affinity forces between the gel and various SWCNTs. Based on this method, we investigated the effect of ultrasonic time on the dispersion and separation of metallic and semiconducting SWCNTs. At a low ultrasonic power, with the increase of ultrasonic time, better monodispersed SWCNTs in sodium dodecylsulfate (SDS) aqueous solution were obtained. The UV-visible-near infrared (UV-Vis-NIR) absorption, Raman and photoluminescence (PL) spectroscopic characterizations confirmed that under the condition of ultrasonication (2 h), higher-purity metallic tubes and semiconducting tubes with different diameter distributions could be obtained. We believe that the control of the ultrasonication time may tune the mono-dispersity and the length of SWCNTs, which would further influence the difference in affinity forces between various SWCNTs and the gel, therefore leading to different separation results.

Preferential extraction of left- or right-handed single-walled carbon nanotubes by use of chiral diporphyrin nanotweezers

Handedness- and diameter-based separation of single-walled carbon nanotubes was achieved through preferential extraction of 76-CoMoCAT with 2,6-pyridylene-bridged chiral diporphyrin nanotweezers.

Scalable Method for the Reductive Dissolution, Purification, and Separation of Single-Walled Carbon Nanotubes

As synthesized, bulk single-walled carbon nanotube (SWNT) samples are typically highly agglomerated and heterogeneous. However, their most promising applications require the isolation of individualized, purified nanotubes, often with specific optoelectronic characteristics. A wide range of dispersion and separation techniques have been developed, but the use of sonication or ultracentrifugation imposes severe limits on scalability and may introduce damage. Here, we demonstrate a new, intrinsically scalable method for SWNT dispersion and separation, using reductive treatment in sodium metal-ammonia solutions, optionally followed by selective dissolution in a polar aprotic organic solvent. In situ small-angle neutron scattering demonstrates the presence of dissolved, unbundled SWNTs in solution, at concentrations reaching at least 2 mg/mL; the ability to isolate individual nanotubes is confirmed by atomic force microscopy. Spectroscopy data suggest that the soluble fraction contains predominately large metallic nanotubes; a potential new mechanism for nanotube separation is proposed. In addition, the G/D ratios observed during the dissolution sequence, as a function of metal:carbon ratio, demonstrate a new purification method for removing carbonaceous impurities from pristine SWNTs, which avoids traditional, damaging, competitive oxidation reactions.

Adsorbability of Single-Wall Carbon Nanotubes onto Agarose Gels Affects the Quality of the Metal/Semiconductor Separation

Although the metal/semiconductor separation of single-wall carbon nanotubes (SWCNTs) using an agarose gel column has been successfully developed, little is known about the mechanism of the separation. In this study, we examined the agarose concentration dependence of the separation using this column. The amount of SWCNTs obtained from the eluate decreased with increasing agarose concentration, indicating that a smaller amount of SWCNTs was adsorbed onto the agarose gels at higher concentrations. To clarify the relation between the adsorbability of SWCNTs and the agarose concentration, various concentrations of SWCNTs were adsorbed onto 2, 4, and 6% agarose gels in a quasi-equilibrium state. The results showed that the concentration of the unadsorbed SWCNTs increased with increasing agarose concentration. By assuming that the adsorption follows the Langmuir isotherm, it was found that the effective gel volume for the adsorption was negatively correlated with the agarose concentration; specifically, the ads...

From metal/semiconductor separation to single‐chirality separation of single‐wall carbon nanotubes using gel

AbstractIn the present work, a review of the metallic (M) and semiconducting (S) separation of single‐wall carbon nanotubes (SWCNTs) using polysaccharide gels is presented. First, the progress of the M/S separation is described, including the following: the discovery of high‐yield separation using agarose gel electrophoresis, the separation of SWCNTs without an electric field, such as through the use of the freeze and squeeze method, the development of continuous separation using column chromatography, and the single‐chirality separation of SWCNTs using a multicolumn with dextran‐based gel. Next, the separation mechanism using gel is discussed, in which separation is achieved by selective adsorption of S‐SWCNTs by gel with a specific combination of surfactant and gel. Lastly, future directions for the separation of SWCNTs and for the use of the separated SWCNTs are discussed.magnified image(© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gel-based separation of single-walled carbon nanotubes for metallic and semiconducting fractions

Common technique for biomaterials recovery in genetics is freeze-squeeze procedure. However, this method found a new application in carbon nanotubes field in a selective separation of metallic and semiconducting nanotubes. None-commercial agarose gel acts as a selective absorbent for semiconducting nanotubes and allows to separate them from metallic type of nanotubes. In this work we point out the great potential of freeze-squeeze technique in the field of separation of nanotubes and prove that the post-separation purification procedure is crucial to perform the quality and quantity estimation of the fractionated samples. Furthermore, the detailed quantitative analysis of the efficiency of this process is shown. Additionally, we emphasize that this technique can be used for high-scale separation of metallic counterparts of single-walled carbon nanotubes due to its simplicity and low cost.

Separation of single-walled carbon nanotubes with aromatic group functionalized polymethacrylates and building blocks contribution to the enrichment

We previously showed that in N,N-dimethylformamide (DMF), poly(9-anthracenylmethyl methacrylate) (PAMMA) and poly(2-naphthylmethacrylate) selectively disperse semiconducting and metallic single-walled carbon nanotubes (SWNTs), respectively. We have also proposed a new noncovalent polymer interaction based on photon induced dipole–dipole interaction to account for the metallicity-based selectivity. In this article, we investigate two other polymethacrylates, that is, poly(benzyl methacrylate) (PBMA) and poly(methylmethacrylate)-co-(9-anthracenylmethyl acrylate) (PMMA-c-PAMA) in the light of our previously proposed photon-induced dipole–dipole interaction. We find that PBMA and PMM-c-PAMMA in DMF show no metallicity selectivity. The different selective behavior of the four polymers in DMF manifests the decisive influence of the side aromatic group in determining their metallicity selectivity. The nonpreferential energy transfer from PMMA-c-PAMA to SWNTs and the nonoverlap of PBMA fluorescence (in the ultraviolet range) with nanotube absorption account for their nonselectivity of specific nanotube species. Further, the parallel relationship between the diameters of extracted tube species and the affinity between polymers and solvents suggests the leading role of the polymeric conformation on the diameter selectivity. A sufficient (i.e., 2 weeks) standing time of the SWNTs solution after sonication, during which the polymers presumably optimize their conformation to the SWNTs, was found to be essential to the enrichment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011