Separation Of Single-walled Carbon Nanotubes Research Articles

Effect of Single-walled Carbon Nanotube (SWCNT) Composition on Polyfluorene-Based SWCNT Dispersion Selectivity.

Applications of single-walled carbon nanotubes (SWCNTs) are hampered by the mixtures of metallic and semiconducting SWCNTs that are present in commercial samples. Separation of SWCNTs according to electronic type is therefore extremely important. Recently, the selective interaction between the conjugated polymer, poly(9,9-di-n-dodecyl-fluorenyl-2,7-diyl) and semiconducting SWCNTs has been reported. However, the mechanism responsible for this selectivity is poorly understood. To determine whether this polymer is only selective for semiconducting SWCNTs, we exposed it to mixtures of metallic and semiconducting SWCNTs in different ratios. We found that the polymer is indeed selective for semiconducting SWCNTs in toluene, but only when the starting ratio is below 67:33 metallic:semiconducting. When the starting ratio is increased to 67:33 or higher, the amount of metallic SWCNTs dispersed dramatically increases. If the solvent is changed to THF, the threshold ratio at which metallic SWCNTs begin to be dispersed is much lower. This indicates that the polymer exhibits a preference for interaction with semiconducting SWCNTs, but is not precluded from interaction with metallic SWCNTs if exposed to a high enough concentration.

Ultra-short-pulse laser ablation and modification of fully sprayed single walled carbon nanotube networks

In this study, we report on femtosecond (470fs) laser pulse ablation and modification of solution processed single-walled carbon nanotube (SWCNT) networks sprayed on oxidized silicon and polyimide substrates. Taking advantage of the small heat affected zone of the femtosecond pulse regime we demonstrate precise and selective laser processes, that advance laser patterning beyond simple galvanic isolation. A thorough investigation regarding the laser pulse-SWCNT film interaction is performed, identifying critical interaction regimes in the single- and multi-pulse operation mode. For the first time we achieve a pronounced debundling of the network, by operating the laser below the ablation threshold, a process that was previously limited to pre-deposition. Furthermore, we investigate the effect of polarized laser pulses on the ablation properties. Making use of linear polarized laser pulses we are able to selectively ablate SWCNTs, which are oriented parallel to the incident laser polarization, resulting in aligned networks with anisotropic conductivity. This feature was previously tied to direct growth of SWCNTs, strongly limiting its implementation. The scaleability of the presented femtosecond laser processes is demonstrated, allowing for the use of low-cost solution processed SWCNT thin-films, while maintaining the advantages of on-chip SWCNT growth such as SWCNT separation and alignment.

Modified mixed chromatography method for separation of single-walled carbon nanotubes based on diameter and conductivity

Single-walled carbon nanotubes (SWCNTs) are popular for their electrical conductivity properties with excellent metallic or semiconducting behavior. Selective separation of SWCNTs can play a significant role in the realization of the potential application of SWCNTs like energy conversion and storage, electronics and biomedical applications. Gel filtration is one of the most well-known and efficient large-scale separation techniques but still complex and lengthy. In this paper, we present a very simple, efficient, and low-cost method with only four column chromatography repetitions for separation of SWCNTs using both sephacryl and agarose gels. Our results demonstrate that the small diameter semiconducting (s-) SWCNTs are adsorbed more strongly to the sephacryl gel column, while large diameter s-SWCNTs adsorbed more strongly to the column with agarose gel. Comparative optical absorption spectra of the separated nanotubes and the reference reveal the effectiveness of the presented method.

Ab Initio Study on Electronic Sorting of Single-Wall Carbon Nanotubes Using Sodium Dodecyl Sulfate

How differently sodium dodecyl sulfate (SDS) surfactants behave on metallic and semiconducting carbon nanotubes (CNTs) is one of the fundamental questions in the science and application of CNTs. In this study, we investigate the adsorption of SDS surfactants onto single-wall CNTs (SWCNTs) using ab initio methods to clarify the mechanism of metal/semiconductor separation of SWCNTs. We found that dodecyl sulfate (DS) ions are more likely to adsorb onto SWCNTs than sodium (Na) ions or SDS molecules, whereas the adsorption energy of SDS molecules becomes stronger as the diameter of the SWCNTs increases, the adsorption energy of DS ions for metallic (5, 5) CNTs is much stronger than those for semiconducting (6, 5) or (10, 3) CNTs, causing a larger aggregation number of DS ions on metallic SWCNTs and a separation of SWCNTs by electronic type. In actual multiple surfactant simulations, for a few DS ions, it is preferred that all DS ions adsorb on metallic (5, 5) CNTs; however, for more than eight DS ions, one or...

High-yield and high-throughput single-chirality enantiomer separation of single-wall carbon nanotubes

Single crystals of single-wall carbon nanotubes are desired for precise analysis of the physical properties of carbon nanotubes, necessitating preparation of single-chirality enantiomers in large quantities. In this work, by investigating the effects of surfactant concentration and temperature on the enantiomer separation, we achieved large-scale single-chirality enantiomer separation for the first time using triple surfactant stepwise elution chromatography with a naturally produced dextran-based gel as the column medium. Through one-round programmed separation, milligram-scale of (11,–5) (equivalent to (5,6)) and (6,5) enantiomers were separated from CoMoCAT carbon nanotube soot. The separation yields estimated from the optical absorbance at 280 nm were 5.6% (11,−5) and 2.6% (6,5) per load of all SWCNTs, which correspond 28% and 13% per load of total (11,–5) and (6,5) enantiomers, respectively. This high yield is mainly attributed to the narrow chirality distribution and high concentrations of (11,–5) and (6,5) in CoMoCAT and the high-resolution selectivity of the triple surfactant system for two enantiomers. The high throughput is sufficient to prepare high-purity (11,–5) and (6,5) bucky papers.

Determination of Enantiomeric Purity of Single-Wall Carbon Nanotubes Using Flavin Mononucleotide.

Although enantiomeric separation of single-wall carbon nanotubes is possible, their enantiomeric purity (EP) remains an issue due to a lack of effective evaluation methods. In this work, we report the EP of (6,5) carbon nanotube enantiomers using flavin mononucleotide (FMN) as an enantiomer-sensitive dispersant. The enantiomers (6,5) and (11,-5) were separated by a gel column chromatography method and dispersed in a FMN aqueous solution. In these solutions, (6,5) and (11,-5) showed E11 optical transitions at different wavelengths due to handedness-dependent interactions with the FMN molecule, which enabled us to estimate each concentration, namely, the EP. We prepared six intermediate-purity enantiomer samples by mixing the (6,5) and (11,-5) enantiomers and measured their circular dichroism (CD) spectra. The CD signal was confirmed to change linearly with the EP. Using this relationship, we can estimate the EP of any mixture of (6,5) and (11,-5) from its CD intensity.

Large-scale separation of single-walled carbon nanotubes by electronic type using click chemistry

Single-walled carbon nanotubes (SWCNTs) can be either metallic or semiconducting, making their separation critical for applications in nanoelectronics, biomedical materials, and solar cells. Herein, we investigate a novel solution-phase separation method based on click chemistry (azide-alkyne Huisgen cycloaddition) and determine its efficiency and scalability. In this method, metallic SWCNTs in metallic/semiconducting SWCNT mixtures are selectively functionalized with alkyne groups by being reacted with 4-propargyloxybenezenediazonium tetrafluoroborate. Subsequently, silica nanoparticles are functionalized with azide groups and reacted with alkyne-bearing metallic SWCNTs in the SWCNT mixture in the presence of a Cu catalyst. As a result, metallic SWCNTs are anchored on silica powder, whereas non-functionalized semiconducting SWCNTs remain in solution. Low-speed centrifugation effectively removes the silica powder with attached metallic SWCNTs, furnishing a solution of highly pure semiconducting SWCNTs, as confirmed by Raman and UV-vis/near-infrared absorption measurements. This novel separation scheme exhibits the advantage of simultaneously separating both metallic and semiconducting SWCNTs from their mixtures, being cost-effective and therefore applicable at an industrial scale.

(Invited) Controlling Carbon Nanotubes By DNA: From Separation to Assembly

In this talk, I will present our latest result on atomic-structure-based separation of single-wall carbon nanotubes (SWCNTs) by DNA, as well as the controlled assembly of SWCNTs via DNA hybridization. In particular, I will describe a quick and easy precipitation based sorting method, a simple pattern underlying many DNA sequences that recognize specific SWCNT structures, and a robust process to wrap SWCNTs by DNA sequences to enable many different applications, including controlled assembly of SWCNTs.

Separation of Semiconducting Carbon Nanotubes for Flexible and Stretchable Electronics Using Polymer Removable Method.

Electronics that are soft, conformal, and stretchable are highly desirable for wearable electronics, prosthetics, and robotics. Among the various available electronic materials, single walled carbon nanotubes (SWNTs) and their network have exhibited high mechanical flexibility and stretchability, along with comparable electrical performance to traditional rigid materials, e.g. polysilicon and metal oxides. Unfortunately, SWNTs produced en masse contain a mixture of semiconducting (s-) and metallic (m-) SWNTs, rendering them unsuitable for electronic applications. Moreover, the poor solubility of SWNTs requires the introduction of insulating surfactants to properly disperse them into individual tubes for device fabrication. Compared to other SWNT dispersion and separation methods, e.g., DNA wrapping, density gradient ultracentrifugation, and gel chromatography, polymer wrapping can selectively disperse s-SWNTs with high selectivity (>99.7%), high concentration (>0.1 mg/mL), and high yield (>20%). In addition, this method only requires simple sonication and centrifuge equipment with short processing time down to 1 h. Despite these advantages, the polymer wrapping method still faces two major issues: (i) The purified s-SWNTs usually retain a substantial amount of polymers on their surface even after thorough rinsing. The low conductivity of the residual polymers impedes the charge transport in SWNT networks. (ii) Conjugated polymers used for SWNT wrapping are expensive. Their prices ($100-1000/g) are comparable or even higher than those of SWNTs ($10-300/g). These utilized conjugated polymers represent a large portion of the overall separation cost. In this Account, we summarize recent progresses in polymer design for selective dispersion and separation of SWNTs. We focus particularly on removable and/or recyclable polymers that enable low-cost and scalable separation methods. First, different separation methods are compared to show the advantages of the polymer wrapping methods. In specific, we compare different characterization methods used for purity evaluation. For s-SWNTs with high purity, i.e., >99%, short-channel (smaller than SWNT length) electrical measurement is more reliable than optical methods. Second, possible sorting mechanism and molecular design strategies are discussed. Polymer parameters such as backbone design and side chain engineering affect the polymer-SWNT interactions, leading to different dispersion concentration and selectivity. To address the above-mentioned limiting factors in both polymer contamination and cost issues, we describe two important polymer removal and cycling approaches: (i) changing polymer wrapping conformation to release SWNTs; (ii) depolymerization of conjugated polymer into small molecular units that have less affinity toward SWNTs. These methods allow the removal and recycling of the wrapping polymers, thus providing low-cost and clean s-SWNTs. Third, we discuss various applications of polymer-sorted s-SWNTs, including flexible/stretchable thin-film transistors, thermoelectric devices, and solar cells. In these applications, polymer-sorted s-SWNTs and their networks have exhibited good processability, attractive mechanical properties, and high electrical performance. An increasing number of studies have shown that the removable polymer approaches can completely remove polymer residues in SWNT networks and lead to enhanced charge carrier mobility, higher conductivity, and better heterojunction interface.

A fundamental investigation of the surfactant-stabilized single-walled carbon nanotube/epoxy resin suspensions by molecular dynamics simulation

The surfactant-assisted stabilization of single-walled carbon nanotubes (SWCNTs) in SWCNT/epoxy resin suspensions were investigated for different surfactant types, concentrations, and temperatures using molecular dynamics simulation. One cationic surfactant, i.e. cetyltrimethylammonium bromide (CTAB), and three anionic surfactants, i.e. sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (NaDDBS), and sodium cholate (SC), as well as a 1:1 mixture of CTAB and SDS were used. Potentials of mean force (PMFs) were generated between two fixed-size (6,6) SWCNTs for all neat (no surfactant) and surfactant-loaded SWCNT/epoxy resin systems at three different surfactant concentrations (0.25, 0.50, and 1.00 wt%) at room (298 K) and elevated temperature (398 K, only for low-surfactant-concentration systems). Overall, two distinct mechanisms of SWCNT stabilization by the surfactants were identified: (1) an increase in the SWCNT aggregation energy barrier due to the wrapping of the SWCNTs by the surfactant molecules, and (2) a constantly positive free energy (repulsion) for all SWCNT separation distances due to the encapsulation of the two approaching SWCNTs. With the second mechanism, there is a delay for the epoxy molecules to be pushed out from the space between the two SWCNTs. With an increase in the surfactant concentration, the first mechanism becomes more prevalent. With an increase in temperature to 398 K, all surfactants migrate to the suspending medium, thereby the second mechanism of SWCNT stabilization dominates. A drop in the SWCNT-surfactant binding energy is observed around 360–370 K, signifying the surfactant migration to the suspending medium. More or less, all surfactants stabilize the SWCNTs in an epoxy resin at one or more surfactant concentrations. However, NaDDBS exhibits a higher SWCNT aggregation barrier at high concentrations and both temperatures (298 K and 398 K), thereby providing a better SWCNT stabilization in the epoxy resin compared to the other surfactants.

Length separation of single-walled carbon nanotubes and its impact on structural and electrical properties of wafer-level fabricated carbon nanotube–field-effect transistors

For an industrial realization of devices based on single-walled carbon nanotube (SWCNTs) such as field-effect transistors (FETs) it becomes increasingly important to consider technological aspects such as intrinsic device structure, integration process controllability as well as yield. From the perspective of a wafer-level integration technology, the influence of SWCNT length on the performance of short-channel CNT–FETs is demonstrated by means of a statistical and comparative study. Therefore, a methodological development of a length separation process based on size-exclusion chromatography was conducted in order to extract well-separated SWCNT dispersions with narrowed length distribution. It could be shown that short SWCNTs adversely affect integrability and reproducibility, underlined by a 25% decline of the integration yield with respect to long SWCNTs. Furthermore, it turns out that the significant changes in electrical performance are directly linked to a SWCNT chain formation in the transistor channel. In particular, CNT–FETs with long SWCNTs outperform reference and short SWCNTs with respect to hole mobility and subthreshold controllability by up to 300% and up to 140%, respectively. As a whole, this study provides a statistical and comparative analysis towards chain-less CNT–FETs fabricated with a wafer-level technology.

Tethered anthracene pair as molecular tweezers for post-production separation of single-walled carbon nanotubes

As-produced single-walled carbon nanotubes (SWNTs) are metallic and semiconducting mixtures. An anthracene mono-derivative with a long alkyl tail and a molecule with a tethered pair of anthracene species (bis-anthracene) in a “molecular tweezers”-like configuration were synthesized and evaluated for the separation of SWNTs. While the mono-derivative was incapable of the noncovalent functionalization–solubilization, the bis-anthracene was found to be very effective. The results suggest that molecular tweezers of a tethered pair of planar aromatic species can be coupled with the selection of a suitable solvent or solvent mixture for effective and efficient post-production separation of metallic and semiconducting SWNTs.

Separation of Single-Walled Carbon Nanotubes by Amine-Functionalized Polydimethylsiloxane

Separation of Single-Walled Carbon Nanotubes by Amine-Functionalized Polydimethylsiloxane

Continuous, Electrokinetic Separation of Single-Walled Carbon Nanotubes Using Selective Covalent Chemistry: Theory and Experiment

Continuous, Electrokinetic Separation of Single-Walled Carbon Nanotubes Using Selective Covalent Chemistry: Theory and Experiment

Effective separation of single-walled carbon nanotubes and their very different electrochemical behaviours.

The electrochemical behaviors of m- and s-SWNTs obtained from as-prepared SWNTs using a novel binaphthyl based separation agent were studied. The s-SWNTs show higher capacitance but lower electrocatalytic activity, while m-SWNTs show the opposite. Their electrochemical properties can be further interconverted through changing the DOS by electron or hole doping.

Single Chirality (6,4) Single-Walled Carbon Nanotubes for Fluorescence Imaging with Silicon Detectors.

Postsynthetic single-walled carbon nanotube (SWCNT) sorting methods such as density gradient ultracentrifugation, gel chromatography, and electrophoresis have all been inspired by established biochemistry separation techniques designed to separate subcellular components. Biochemistry separation techniques have been refined to the degree that parameters such as pH, salt concentration, and temperature are necessary for a successful separation, yet these conditions are only now being applied to SWCNT separation methodologies. Slight changes in pH produce radically different behaviors of SWCNTs inside a density gradient, allowing for the facile separation of ultrahigh purity (6,4) SWCNTs from as-synthesized carbon nanotubes. The (6,4) SWCNTs are novel fluorophores emitting below ≈900 nm and can be easily detected with conventional silicon-based charge-coupled device detectors without the need for specialized InGaAs cameras. The (6,4) SWCNTs are used to demonstrate their potential as a clinically relevant NIR-I fluorescence stain for the immunohistochemical staining of cells and cancer tissue sections displaying high endothelial growth factor receptor levels.

Separation of single-walled carbon nanotubes and their applications on electronic devices

Single-walled carbon nanotubes (SWNTs) possess unique electronic properties which make them promising materials for applications in both nano-electronics and flexible devices. Currently, no effective methods could large-scale synthesize SWNTs with single conductive properties. To obtain SWNTs with single conductive properties, a variety of separation methods have been developed. Among them, liquid phase separation approaches hold the promise for large scale production of the pure semiconducting SWNTs and have attracted intense interests. This paper summarized the mechanism and features of several liquid phase separation methods, including electrophoresis, density gradient centrifugation, chemical functionalization, gel chromatography and extraction. We also demonstrated the applications of the purified SWNTs in electronic devices. Finally, we discussed the challenges and opportunities for the separation of SWNTs.

Competitive Binding in Mixed Surfactant Systems for Single-Walled Carbon Nanotube Separation

The separation of single-walled carbon nanotubes (SWNTs) by chirality is of great interest to enable the next generation of optical and optoelectronic devices. Many separation schemes employ the surfactant sodium dodecyl sulfate (SDS), with or without a bile salt surfactant such as sodium cholate (SC). In this study, we observe and explain the effect of these mixed surfactant systems on the hydrogel-based selective adsorption separation method. We find that sodium cholate outcompetes SDS more effectively on smaller diameter tubes and quantify this difference as the sodium cholate concentration is increased and (6,5) separation is diminished. These changes in separation efficiency with surfactant composition are understood using a theoretical model developed previously and predict that surfactant mixtures alter the charge per unit length of specific (n,m) SWNTs, altering the separation. This understanding of the chiral dependence of the surfactant binding will not only enable a greater understanding of sur...

Solubilization of single-walled carbon nanotubes using a peptide aptamer in water below the critical micelle concentration.

The solubilizing ability of single-walled carbon nanotubes (SWCNTs) in water with several dispersants was investigated. Among the dispersants, including low-molecular-weight surfactants, peptides, DNA, and a water-soluble polymer, the peptide aptamer, A2 (IFRLSWGTYFS), exhibited the highest dispersion capability below the critical micelle concentration at a concentration of 0.02 w/v%. The dispersion of supernatant aqueous solution of SWCNTs containing aptamer A2 was essentially unchanged for several months after high-speed ultracentrifugation and gave rise to an efficient and stable dispersion of the SWCNTs in water. From the results of isothermal titration calorimetry and molecular dynamics simulations, the effective binding capability of A2 was due to π-π interaction between aromatic groups in the peptide aptamer and the side walls of SWCNTs. Interestingly, the peptide aptamer showed the possibility of diameter separation of semiconducting SWCNTs using a uniform density gradient ultracentrifuge. These phenomena are encouraging results toward an effective approach to the dispersion and separation of SWCNTs.

Bolometric Properties of Semiconducting and Metallic Single-Walled Carbon Nanotube Composite Films

Single-walled carbon nanotubes (SWNTs) have shown interesting bolometric properties, making them good candidates for the detection of infrared and terahertz radiation. However, little has been reported on the bolometric characteristics of SWNT as a function of their chirality or the possible influence of composite morphology on these properties. The separation of SWNTs based on chirality allows for almost purely semiconductive or metallic SWNTs to be studied. The current study focuses on the bolometric performance of self-assembled composite films of SWNTs. The dependence of these properties on the chirality of the SWNTs was evaluated. To this end, metallic, semiconducting, and a 1:1 mixture of metallic and semiconductive were studied. Also, a theoretical model based on the Wiedemann–Franz law is used to explain the resistance of the SWNT composite films as a function of temperature. Results show that the composite morphology has a significant impact on bolometer performance, with cracked composite films containing highly aligned SWNT arrays suspended over a silicon substrate showing superior responsivity values due to higher thermal isolation. Uncracked composite films showed superior thermal coefficient of resistance values (α = −6.5%/K), however, the responsivity was lower due to lower thermal isolation.