Sorting Of Single-walled Carbon Nanotubes Research Articles

Size Matters in Conjugated Polymer Chirality-Selective SWCNT Extraction.

Carbon-based nanomaterials have catalyzed breakthroughs across various scientific and engineering disciplines. The key to unlocking a new generation of tailor-made nanomaterials based on single-walled carbon nanotubes (SWCNTs) lies in the precise sorting of raw material into individual chiralities, each possessing unique properties. This can be achieved using conjugated polymer extraction (CPE), but to a very limited extent since the process generates only a few chirality-enriched suspensions. Therefore, it is imperative to comprehend the mechanism of the wrapping of SWCNTs by polymers to unleash CPE's full potential. However, the lack of a diverse palette of chirality-selective polymers with varying macromolecular parameters has hindered a comprehensive understanding of how the nature of the polymer affects the performance and selectivity of SWCNT isolation. To address this gap, multiple batches of such polymers are synthesized to elucidate the impact of molecular weight and dispersity on the purity and concentrations of the generated SWCNT suspensions. The obtained results explain the inconsistent outcomes reported in the literature, greatly improving the application potential of this promising SWCNT sorting approach. Concomitantly, the discovered significant influence of the macromolecular characteristics of conjugated polymers on the SWCNT isolation efficacy sheds considerable insight into the unresolved mechanism of this sorting technique.

Size exclusion chromatography-based length sorting of single-walled carbon nanotubes stably coated with cross-linked polymers

The remarkable stability of gel-coated SWCNT dispersions enables length sorting using size exclusion chromatography. Length-sorted, gel-coated SWCNTs show photoluminescence in near IR and are ready to use for various applications including near IR imaging.

Diameter-Selective Sorting of Single-Walled Carbon Nanotubes Using π-Molecular Tweezers for Energy Materials

Single-walled carbon nanotubes (SWCNTs) have remarkable electrical properties, making them excellent candidate energy materials for applications, such as transistors and thermoelectric devices. However, as-prepared SWCNTs are mixtures of various chiral indices associated with different diameters, and this heterogeneity hinders their practical applications. Therefore, the development of a method for sorting SWCNTs according to the diameter is required. Here, we report one-pot diameter sorting of SWCNTs through noncovalent functionalization with π-molecular tweezers, which act as a structure-selective oligomeric dispersant for SWCNTs. The tweezers are capable of isolating (9,4) SWCNTs and (7,6) SWCNTs with diameters of ∼0.9 nm from as-prepared SWCNTs to a sorting ratio of 90%. This high-diameter selectivity originates from molecular wrapping of the π-molecular tweezers around the SWCNT sidewalls based on π–π and hydrophobic interactions. Our findings are promising not only in terms of developing a suitable SWCNT sorting methodology but also for understanding their molecular-level sorting mechanism.

Synthesis, Sorting, and Applications of Single-Chirality Single-Walled Carbon Nanotubes.

The synthesis of high-quality chirality-pure single-walled carbon nanotubes (SWCNTs) is vital for their applications. It is of high importance to modernize the synthesis processes to decrease the synthesis temperature and improve the quality and yield of SWCNTs. This review is dedicated to the chirality-selective synthesis, sorting of SWCNTs, and applications of chirality-pure SWCNTs. The review begins with a description of growth mechanisms of carbon nanotubes. Then, we discuss the synthesis methods of semiconducting and metallic conductivity-type and single-chirality SWCNTs, such as the epitaxial growth method of SWCNT (“cloning”) using nanocarbon seeds, the growth method using nanocarbon segments obtained by organic synthesis, and the catalyst-mediated chemical vapor deposition synthesis. Then, we discuss the separation methods of SWCNTs by conductivity type, such as electrophoresis (dielectrophoresis), density gradient ultracentrifugation (DGC), low-speed DGC, ultrahigh DGC, chromatography, two-phase separation, selective solubilization, and selective reaction methods and techniques for single-chirality separation of SWCNTs, including density gradient centrifugation, two-phase separation, and chromatography methods. Finally, the applications of separated SWCNTs, such as field-effect transistors (FETs), sensors, light emitters and photodetectors, transparent electrodes, photovoltaics (solar cells), batteries, bioimaging, and other applications, are presented.

Moiré patterns and carbon nanotube sorting

Moiré patterns (MPs), arising from the superposition of two lattices with close periods, are tightly related to the physicochemical properties of bilayer nanostructures. Here, we develop the theory of complex MPs emerging in twisted bilayer graphene and planar nets of double-walled nanotubes at significant relative twist and/or deformation of layers. The proposed theory clarifies the physicochemical regularities arising at sorting of single-walled carbon nanotubes (SWCNTs) by organic molecules, which self-assemble in regular coatings on both the tubes and planar graphene. We introduce and consider an outer tubular virtual lattice that is a parent structure for the deposited coating and due to this fact, its existence is crucial for the coating formation. As we show, such outer lattices exist only for successfully sorted SWCNTs and the superposition between the outer lattice and SWCNT forms a specific long-period MP. We explain known experimental results of SWCNT sorting by molecules of flavin group, poly(9,9-dioctylfluorene-2,7-diyl), and poly [(m-phenylenevinylene)-alt-(p-phenylenevinylene)]. Also, our approach points out other organic molecules and polymers suitable for effective carbon nanotube sorting.

Variations in bile salt surfactant structure allow tuning of the sorting of single-wall carbon nanotubes by aqueous two-phase extraction.

Being some of the most efficient agents to individually solubilize single-wall carbon nanotubes (SWCNTs), bile salt surfactants (BSS) represent the foundation for the surfactant-based structure sorting and spectroscopic characterization of SWCNTs. In this work, we investigate three BSS in their ability to separate different SWCNT chiral structures by aqueous two-phase extraction (ATPE): sodium deoxycholate (DOC), sodium cholate (SC) and sodium chenodeoxycholate (CDOC). The small difference in their chemical structure (just one hydroxyl group) leads to significant differences in their stacking behavior on SWCNT walls with different diameter and chiral structure that, in turn, has direct consequences for the chiral sorting of SWCNTs using these BSS. By performing several series of systematic ATPE experiments, we reveal that, in general, the stacking of DOC and CDOC is more enantioselective than the stacking of SC on the SWCNT walls, while SC has a clear diameter preference for efficiently solubilizing the SWCNTs in comparison to DOC and CDOC. Moreover, combining sodium dodecylsulfate with SC allows for resolving the ATPE sorting transitions of empty and water-filled SWCNTs for a number of SWCNT chiralities. We also show that addition of SC to combinations of DOC and sodium dodecylbenzenesulfonate can enhance separations of particular chiralities.

Aqueous two-phase extraction of single-walled carbon nanotubes using nonionic surfactant Tween 60

<p indent="0mm">Due to its excellent electronic and optical properties, single-walled carbon nanotubes (SWNTs) have attracted extensive attention. Since the property of SWNTs is determined by their structures, applications like high-performance devices require SWNTs with identical structures and uniform properties. Therefore, the sorting of SWNTs is of great significance. Aqueous two-phase (ATP) extraction is an emerging method that can be utilized to realize the structure sorting of SWNTs. ATP extraction is a repeatable and reliable technique that does not require state-of-the-art equipment. It is efficient and easy to scale up. In this article, by adjusting the concentration of sodium deoxycholate (DOC) and nonionic surfactant Tween 60, the diameter sorting of SWNTs and the separation of high purity (6,5) tubes were achieved. The sorting can be carried out at a higher DOC concentration, which could improve the competitive coating between DOC and Tween 60 on the surface of SWNTs, and further improve the sorting efficiency of the co-surfactant system. The comparison of the separation results between the Tween 60-DOC surfactant system and the SDS-DOC surfactant system shows that the introduction of nonionic surfactant Tween 60 is beneficial to the separation of higher purity (6,5) tubes.

The Impacts of Polyisoprene Physical Interactions on Sorting of Single-Wall Carbon Nanotubes.

Conjugated polymer sorting is currently the best method to select large-diameter single-walled carbon nanotubes (SWCNTs) with tunable narrow chirality in the adaption of highly desired electronics applications. The acceleration on conjugated polymers-SWCNTs interaction with long-term stability through different molecular designs; for example, longer alkyl side-chains or conjugation moieties have been extensively developed in recent years. However, the importance of the macromolecules with abundant van der Waals (VDW) interaction in the conjugated-based block copolymer system acting during SWCNTs sorting is not clearly demonstrated. In this work, a conjugated diblock copolymer involving polyisoprene (PI) and highly dense π-interaction of poly (9,9-dioctylfluorene) (PFO) is utilized to investigate the impact of natural rubber PI physical interaction on sorting effectiveness and stability. Through the rational design of diblock copolymer, PFO with ≈1200 isoprene units can remarkably enhance SWCNTs sorting ability and selected few chiralities with a diameter of ≈0.83-1.1nm and highly stable solution for more than 1 year. The introduction of long-chain PI system is attributed not only to form weak VDW force with SWCNTs and strengthen the wrapping of PFO around the semiconducting SWCNTs but also to act as a barrier among nanotubes to prevent reaggregation of sorted SWCNTs.

En route to single-step, two-phase purification of carbon nanotubes facilitated by high-throughput spectroscopy

Chirality purification of single-walled carbon nanotubes (SWCNTs) is desirable for applications in many fields, but general utility is currently hampered by low throughput. We discovered a method to obtain single-chirality SWCNT enrichment by the aqueous two-phase extraction (ATPE) method in a single step. To achieve appropriate resolution, a biphasic system of non-ionic tri-block copolymer surfactant is varied with an ionic surfactant. A nearly-monochiral fraction of SWCNTs can then be harvested from the top phase. We also found, via high-throughput, near-infrared excitation-emission photoluminescence spectroscopy, that the parameter space of ATPE can be mapped to probe the mechanics of the separation process. Finally, we found that optimized conditions can be used for sorting of SWCNTs wrapped with ssDNA as well. Elimination of the need for surfactant exchange and simplicity of the separation process make the approach promising for high-yield generation of purified single-chirality SWCNT preparations.

Enantiomeric Separation of Semiconducting Single-Walled Carbon Nanotubes by Acid Cleavable Chiral Polyfluorene.

Helical wrapping by conjugated polymer has been demonstrated as a powerful tool for the sorting of single-walled carbon nanotubes (SWCNTs) according to their electronic type, chiral index, and even handedness. However, a method of one-step extraction of left-handed (M) and right-handed (P) semiconducting SWCNTs (s-SWCNTs) with subsequent cleavage of the polymer has not yet been published. In this work, we designed and synthesized one pair of acid cleavable polyfluorenes with defined chirality for handedness separation of s-SWCNTs from as-produced nanotubes. Each monomer contains a chiral center on the fluorene backbone in the 9-position, and the amino and carbonyl groups in the 2- and 7-positions maintain the head-to-tail regioselective polymerization resulting in polyimines with strictly all-(R) or all-(S) configuration. The obtained chiral polymers exhibit a strong recognition ability toward left- or right-handed s-SWCNTs from commercially available CoMoCAT SWCNTs with a sorting process requiring only bath sonication and centrifugation. Interestingly, the remaining polymer on each single nanotube, which helps to prevent aggregation, does not interfere with the circular dichroism signals from the nanotube at all. Therefore, we observed all four interband transition peaks (E11, E22, E33, E44) in the circular dichroism (CD) spectra of the still wrapped optically enriched left-handed and right-handed (6,5) SWCNTs in toluene. Binding energies obtained from molecular dynamics simulations were consistent with our experimental results and showed a significant preference for one specific handedness from each chiral polymer. Moreover, the imine bonds along the polymer chains enable the release of the nanotubes upon acid treatment. After s-SWNT separation, the polymer can be decomposed into monomers and be cleanly removed under mild acidic conditions, yielding dispersant-free handedness sorted s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize the chiral polymer. This approach enables high selective isolation of polymer-free s-SWNT enantiomers for their further applications in carbon nanotube (CNT) devices.

Sorting of single-wall carbon nanotubes by aqueous two-phase systems

<p indent=0mm>All intrinsic properties of single-wall carbon nanotubes (SWCNTs) are directly determined by their chirality. Commercially available SWCNTs powder samples are usually mixtures of various chiralities. High-performance carbon nanotube devices, sensing, imaging and other applications require the use of SWCNTs with consistent properties, which imposes requirements on the structural sorting of SWCNTs. As an emerging technology for sorting SWCNTs, the aqueous two-phase (ATP) extraction method exhibits stable and reliable sorting results. It is simple, efficient, and easy to scale up and does not require complicated equipment. This review focused on the aqueous two-phase sorting of surfactant-SWCNTs and DNA-SWCNTs. By explaining the effects of dispersant, salt, pH and other sorting conditions on sorting result, the sorting mechanism of aqueous two-phase extraction of SWCNTs are explained. In the end, the characteristics of the aqueous two-phase extraction of DNA-SWCNTs and surfactant-SWCNTs are compared, followed by the discussion of its possible research directions in the future.

Carbon nanotubes advance next-generation electronics

Abstract Single-walled carbon nanotubes (SWCNTs) are potential candidates for next-generation computing to meet the requirement of device scaling. Here we discuss recent breakthroughs in the CNT-based field-effect transistors (FETs) and highlight key ongoing topics in purification and assembly. A few key challenges that capitalize on the chemical vapor deposition (CVD) of SWCNTs are discussed in which surface science and model systems can enable advances in high-purity synthesis. A full description of the CVD growth and chemical sorting of SWCNTs falls beyond the scope of this opinion, but we focus on the framework of SWCNTs in FETs and draw connections to their requirements for high-quality materials that highlight the underlying mechanisms.

One-step sorting of single-walled carbon nanotubes using aqueous two-phase extraction in the presence of basic salts

We demonstrate a simple one-step approach to separate (6,5) CNTs from raw material by using the aqueous two-phase extraction method. To reach this goal, stable and inexpensive K2CO3, Na2CO3, Li2CO3, and K3PO4 basic salts are used as modulators of the differentiation process. Under the appropriate parameters, near monochiral fractions become available for straightforward harvesting. In parallel, we show that the isolation process is strongly affected not only by pH but by the inherent nature of the introduced chemical species as well. The results of our study also reveal that the commonly used ingredients of the biphasic system make a strong contribution to the course of the separation by having far from neutral pH values themselves.

The Handedness of DNA Assembly around Carbon Nanotubes Is Determined by the Chirality of DNA.

Single-stranded DNA chains enable postsynthesis sorting of single-walled carbon nanotubes (CNTs) according to their diameter and helicity by wrapping helically around CNT surfaces. Both DNA chains and CNTs in these CNT-DNA conjugates are intrinsically chiral. Using a single-stranded DNA chain in both of its chiral realizations, we systematically study cross-chiral interactions between DNA and CNTs by varying the helicity of CNTs within a relatively narrow range of diameters. We find that regardless of the helicity or handedness of the carbon nanotube, the chirality of DNA dictates the handedness of its predominant helical wrap around carbon nanotubes.

Dispersion quality of single-walled carbon nanotubes reveals the recognition sequence of DNA

The specific recognition between DNA and single-walled carbon nanotubes (SWCNTs) has enabled wide applications, especially in the chiral sorting of SWCNTs. However, the molecular recognition mechanism has not been fully understood. In our work, various DNA–SWCNT dispersions were prepared by the ultrasonic dispersion method, and characterized by UV absorption spectroscopy, fluorescence emission spectroscopy, zeta potential measurement, SDBS exchange kinetics and computer simulation. The effect of DNA sequence on the structure and properties of hybrid molecules was analyzed. Data analysis showed that DNA with specific recognition had better dispersion quality of the corresponding SWCNT, which means that higher content of monodispersed SWCNTs was obtained. The high-quality dispersion of the DNA–SWCNT pair was attributed to the stronger binding between DNA and SWCNT, resulting in a tighter conformation of DNA on the SWCNT surface and a larger zeta potential of DNA–SWCNT hybrids. Consequently, DNA–SWCNT dispersions of the recognition pair exhibited better stability against salt and stronger fluorescence emission intensity. However, the correlation between specific recognition and DNA coverage on SWCNT was not observed. This work gives more insight into the recognition mechanism between DNA and SWCNTs.

Separation of Large‐Diameter Metallic and Semiconducting Single‐Walled Carbon Nanotubes by Iterative Temperature‐Assisted Gel‐Column Chromatography for Enhanced Device Applications

It is a challenging and application‐oriented goal to achieve the metal/semiconductor separation of large diameter single‐walled carbon nanotubes (SWCNTs) using a dextran‐based gel chromatograph. Herein, a study of the temperature effect on the metal/semiconductor separation of plasma torch SWCNTs through dextran‐based gel chromatograph is conducted. The temperature governs the interaction between SWCNTs and hydrogel, thus enabling the sorting of SWCNTs by electronic type. In addition, the temperature effect enables the metallic (m‐) and semiconducting (sc‐) fraction to be resolved and eluted using a single cosurfactant system, so that the process can be iterated easily. The fractions containing up to 99% of sc‐SWCNTs and 95% of m‐SWCNTs have been obtained after three times of iteration. The iteration process is not only applicable to sc‐SWCNTs and m‐SWCNTs, but also practicable for the cosurfactant system and circumvents additional preparation steps.

Toward Complete Resolution of DNA/Carbon Nanotube Hybrids by Aqueous Two-Phase Systems.

Sequence-dependent interactions between DNA and single-wall carbon nanotubes (SWCNTs) are shown to provide resolution for the atomic-structure-based sorting of DNA-wrapped SWCNTs. Previous studies have demonstrated that aqueous two-phase (ATP) systems are very effective for sorting DNA-wrapped SWCNTs (DNA-SWCNTs). However, most separations have been carried out with a polyethylene glycol (PEG)/polyacrylamide (PAM) ATP system, which shows severe interfacial trapping for many DNA-SWCNT dispersions, resulting in significant material loss and limiting multistage extraction. Here, we report a study of several new ATP systems for sorting DNA-SWCNTs. We have developed a convenient method to explore these systems without knowledge of the corresponding phase diagram. We further show that the molecular weight of the polymer strongly affects the partition behavior and separation results for DNA-SWCNTs in PEG/dextran (DX) ATP systems. This leads to the identification of the PEG1.5kDa/DX250kDa ATP system as an effective vehicle for the chirality separation of DNA-SWCNTs. Additionally, this ATP system exhibits greatly reduced interfacial trapping, enabling for the first time continuous multistep sorting of four species of SWCNTs from a single dispersion. Enhanced stability of DNA-SWCNTs in the PEG1.5kDa/DX250kDa ATP system also allows us to investigate pH dependent sorting of SWCNTs wrapped by C-rich sequences. Our observations suggest that hydrogen bonding may form between the DNA bases at lower pH, enabling a more ordered wrapping structure on the SWCNTs and improvement in sorting (11,0). Together, these findings reveal that the new ATP system is suitable for searching DNA sequences leading toward more complete resolution of DNA-SWCNTs. A new concept of "resolving sequences", evolved from the old notion of "recognition sequences", is proposed to describe a broader range of behaviors of DNA/SWCNT interactions and sorting.

Thermoelectric properties of sorted semiconducting single-walled carbon nanotube sheets

ABSTRACT Single-walled carbon nanotubes (SWNTs), especially their semiconducting type, are promising thermoelectric (TE) materials due to their high Seebeck coefficient. In this study, the in-plane Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ) of sorted semiconducting SWNT (s-SWNT) free-standing sheets with different s-SWNT purities are measured to determine the figure of merit ZT. We find that the ZT value of the sheets increases with increasing s-SWNT purity, mainly due to an increase in Seebeck coefficient while the thermal conductivity remaining constant, which experimentally proved the superiority of the high purity s-SWNT as TE materials for the first time. In addition, from the comparison between sorted and unsorted SWNT sheets, it is recognized that the difference of ZT between unsorted SWNT and high-purity s-SWNT sheet is not remarkable, which suggests the control of carrier density is necessary to further clarify the superiority of SWNT sorting for TE applications.

Low Molecular Weight Polypyrmidine for Release and Size Controlled Process of Single-Walled Carbon Nanotubes

A process for controlling the size of Single-walled carbon nanotubes (SWCNTs) sorting was achieved by combining various centrifugation speeds with polypyrimidine’s properties of dispersion and release SWCNTs upon acid treatment. At first, the SWCNTs wrapped by polypyrimidine were sperated into different size by centrifugating at various speeds. Then, these size-selected hybrids were treated with H2SO4 (98 %) to release free SWCNTs from hybrids, meanwhile the copolymer was collected for reuse. The purity of the released size-controlled SWCNTs was found to be higher than the commercial SWCNTs. The simple synthetic procedure of the copolymer, the low cost of H2SO4 and low centrifugation speed allow the process of size-controlled SWCNTs sorting to more practical applications and industrial scaling up.

New Methods Towards Designer DNA Sequences for Enantiomeric-Chiral Selective Sorting of Single-Wall Carbon Nanotubes

To date methods in producing structurally defined single-wall carbon nanotubes are inadequate leaving purification or sorting a viable option for obtaining nanotubes of a certain chirality. While several procedures have been developed for structure specific isolation of nanotubes, there are differences in purity, scalability, and economic feasibility. The use of single-stranded DNA sequences has evolved and been refined to select for both nanotube helicity and handedness. These developments through brute force screening of hundreds of sequences show the unique recognition of DNA for nanotube structure. Going a step further DNA recognition combined with a second technique, aqueous two-phase separation, allows for high purity sorting of multiple chiralities. We introduce a few new experimental and computational methods as the next step in discovering new DNA sequences for sorting single-wall carbon nanotubes. Utilizing these new methods followed by experimental verification, novel DNA sequences are discovered for dispersing and sorting single-wall carbon nanotubes.