Single-walled Carbon Nanotubes Species Research Articles

Recent Advances in Structure Separation of Single-Wall Carbon Nanotubes and Their Application in Optics, Electronics, and Optoelectronics.

Structural control of single‐wall carbon nanotubes (SWCNTs) with uniform properties is critical not only for their property modulation and functional design but also for applications in electronics, optics, and optoelectronics. To achieve this goal, various separation techniques have been developed in the past 20 years through which separation of high‐purity semiconducting/metallic SWCNTs, single‐chirality species, and even their enantiomers have been achieved. This progress has promoted the property modulation of SWCNTs and the development of SWCNT‐based optoelectronic devices. Here, the recent advances in the structure separation of SWCNTs are reviewed, from metallic/semiconducting SWCNTs, to single‐chirality species, and to enantiomers by several typical separation techniques and the application of the corresponding sorted SWCNTs. Based on the separation procedure, efficiency, and scalability, as well as, the separable SWCNT species, purity, and quantity, the advantages and disadvantages of various separation techniques are compared. Combined with the requirements of SWCNT application, the challenges, prospects, and development direction of structure separation are further discussed.

Temperature-dependent selective nucleation of single-walled carbon nanotubes from stabilized catalyst nanoparticles

• Enriched (6,5) and (7,5) SWCNTs are respectively synthesized at ambient pressure. • Highly stabilized cobalt nanoparticles are generated from catalyst reduction. • Thermodynamic stability of different tube nuclei accounts for SWCNT selectivity. The utilization of metal nanoparticles supported on oxides substrate as a catalyst for rational single-walled carbon nanotube (SWCNT) growth is hindered by particle coarsening at high synthesis temperature, despite many empirical advances in supported catalyst design. In this study, a newly developed MgO-supported cobalt (Co-MgO) catalyst affords the formation of well-stabilized Co nanoparticles upon reduction, which is attributed to the electronic metal-support interaction and electrostatic stabilization at the Co-MgO interface. The highly stabilized Co nanoparticles led to the predominant growth of (6, 5) SWCNTs at 700 °C by CO disproportionation and the major SWCNT species was found to be (7, 5) SWCNTs at a reaction temperature of 800 °C. The temperature-dependent selective growth of the two SWCNT species was found, by density functional theory calculation, to be strongly correlated with the change of the relative thermodynamic stability of the SWCNT nuclei in the chirality assigning process at different temperatures.

(Invited) Stereoselective Photoluminescent Properties of DNA-Carbon Nanotubes: A Primer for Molecular Perceptron

Single-walled carbon nanotubes (SWCNTs) have emerged to be useful tools in molecular recognition in recent years. Due to their well-defined optical properties, SWCNTs offer unique characteristics that most small-molecule sensors lack. For example, SWCNTs exhibit a near-IR (NIR) photoluminescence which makes them great candidates for sensing biomolecules. Typically, the synthesis of SWCNTs yields over 30 distinct tube chiralities, with two-thirds of the mixture comprising semiconducting and the remaining third consisting of quasi-metallic or true-metallic tubes. To add to the mixture’s structural complexity, each chirality that has the same helicity could also have different handedness – species that are enantiomeric in nature. In our lab at NIST, we have recently developed techniques based on aqueous two-phase extraction (ATPE) to separate enantiomers of SWCNTs wrapped with specific DNA sequences. Most of the sensors that have been developed in this field, whether they are coated and dispersed by surfactants or DNA, take advantage of mixtures of various SWCNT helicities to elicit an optical response from interactions of small molecules. However, the responses obtained from each enantiomeric species of SWCNT is largely ignored, or at best, assumed to be similar. In this presentation, we discuss the differences in photoluminescence responses observed when SWCNTs wrapped with various DNA sequences interact with enantiopure small molecules. With this study, we give proof that specific DNA sequences allow for specific optical responses between the mixtures of diastereomeric DNA-SWCNT nanohybrids and single-chirality enriched DNA-SWCNTs, and enantiomeric amino acids. This study is the first proof-of-concept that small chiral molecules interact with chirality enriched DNA-SWCNTs to different extents and give rise to specific optical signatures that could be exploited for future developments of sensing arrays for complex biological mixtures.

Directed assembly of multiplexed single chirality carbon nanotube devices

Herein, we present the fabrication of multiplexed single-walled carbon nanotube (SWCNT) devices, where selected chiralities were separately immobilized on one chip with single-tube precision. Each chirality was subsequently electrically measured individually. Specifically, (6,5) and (7,5) SWCNT species were isolated via aqueous two-phase polymer systems, after which dielectrophoresis was used to precisely control the placement of each chirality, along with a metallic species, separately on prepatterned electrodes on a single chip.

Colors of Single-Wall Carbon Nanotubes.

Although single-wall carbon nanotubes (SWCNTs) exhibit various colors in suspension, directly synthesized SWCNT films usually appear black. Recently, a unique one-step method for directly fabricating green and brown films has been developed. Such remarkable progress, however, has brought up several new questions. The coloration mechanism, potentially achievable colors, and color controllability of SWCNTs are unknown. Here, a quantitative model is reported that can predict the specific colors of SWCNT films and unambiguously identify the coloration mechanism. Using this model, colors of 466 different SWCNT species are calculated, which reveals a broad spectrum of potentially achievable colors of SWCNTs. The calculated colors are in excellent agreement with existing experimental data. Furthermore, the theory predicts the existence of many brilliantly colored SWCNT films, which are experimentally expected. This study shows that SWCNTs as a form of pure carbon, can display a full spectrum of vivid colors, which is expected to complement the general understanding of carbon materials.

Dye Quenching of Carbon Nanotube Fluorescence Reveals Structure-Selective Coating Coverage.

Many properties and applications of single-wall carbon nanotubes (SWCNTs) depend strongly on the coatings that allow their suspension in aqueous media. We report that SWCNT fluorescence is quenched by reversible physisorption of dye molecules such as methylene blue, and that measurements of that quenching can be used to infer structure-specific exposures of the nanotube surface to the surrounding solution. SWCNTs suspended in single-stranded DNA oligomers show quenching dependent on the combination of nanotube structure and ssDNA base sequence. Several sequences are found to give notably high or low surface coverages for specific SWCNT species. These effects seem correlated with the selective recognitions used for DNA-based structural sorting of nanotubes. One notable example is that dye quenching of fluorescence from SWCNTs coated with the (ATT)4 base sequence is far stronger for one (7,5) enantiomer than for the other, showing that coating coverage is associated with the coating affinity difference reported previously for this system. Equilibrium modeling of quenching data has been used to extract parameters for comparative complexation constants and accessible surface areas. Further insights are obtained from molecular dynamics simulations, which give estimated contact areas between ssDNA and SWCNTs that correlate with experimentally inferred surface exposures and account for the enantiomeric discrimination of (ATT)4.

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

A unique feature of single-wall carbon nanotube (SWCNT) material is its structure diversity: within the same rolled-up graphene sheet structure framework one finds SWCNTs of different electronic bandgaps: metals with zero bandgap, quasi-metals with meV bandgap and semiconductors with ~ 1 eV bandgap. However, making use of SWCNT structure diversity requires a method to obtain SWCNTs of defined structures. In this contribution, we present our current state of DNA-based sorting of SWCNTs. In particular, we show our ability to put any DNA sequence on any SWCNT species, enabling DNA-based assembly of high-density SWCNT devices. In the end, we discuss the design of a device we call Photon Perceptron Array (PPA). PPA is an array of micron-sized spectrometer units that can measure the spectrum of incoming photon in the wavelength range of 200 nm to 2000 nm (and possibly going all the way to THz), with a spatial resolution comparable to the size of a single spectrometer unit. Each spectrometer unit is composed of a set of distinct photodetectors made of SWCNTs of defined atomic structures, placed in parallel with tube-to-tube separations controlled at nanometer precision by DNA origami technology. A high-density array of identical spectrometers can be constructed by placing DNA origami/carbon nanotube complexes in photolithographically-defined locations. PPA may be used for spectral imaging in many fields of science and technology.

(Invited) Determining SWCNT Partition Conditions in Aqueous Two-Polymer Phase Extraction Via Near-Infrared Fluorescence Spectroscopy

Methods for rapidly determining the aqueous surfactant concentration conditions that yield upper or lower phase extraction for specific (n,m) species of single-wall carbon nanotubes (SWCNTs) in aqueous two polymer phase extraction (ATPE) separations are a missing component limiting rapid development and optimization of the ATPE technique. In this talk I will describe the use of near-infrared fluorescence measurements on single-phase dispersions of SWCNT species mixtures to determine these partition coefficient conditions without performing the ATPE separation. This new methodology enables dramatically swifter determination of partitioning conditions for individual (n,m) species and their handed enantiomers, while using dramatically less material and without the ambiguity of mass transfer limitations or interfacial absorption present when conducting the ATPE separation itself. The ability to fully describe the partitioning conditions for each (n,m) and (m,n) is expected for multiple surfactant composition competitions and surfactant variants. Investigation of complicating factors such as temperature effects, polymer compositions, SWCNT properties, and the redox environment are also enabled and will be described.

Near-infrared fluorescence as a method for determining single-wall carbon nanotube extraction conditions in aqueous two polymer phase extraction

Near-infrared fluorescence emission from single-wall carbon nanotubes (SWCNTs) is demonstrated as a measurement technique enabling the determination of aqueous surfactant concentration conditions yielding upper or lower polymer phase extraction in aqueous two-polymer phase extraction (ATPE) separations. From measurements on single-phase dispersions of multiple SWCNT specie mixtures, the fluorescence intensity of a given SWCNT (n,m) species is demonstrated to correlate directly to partitioning in an ATPE separation, as determined by the type of surfactant molecule comprising a preponderance of the adsorbed interfacial layer on that species. This methodology enables rapid quantitative determination of partitioning conditions for individual (n,m) species of SWCNTs without ambiguity of mass transfer limitations or interfacial adsorption present when conducting the ATPE separation itself, while also allowing for ready investigation of complicating factors such as temperature effects or SWCNT enantiomers.

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.

Biomolecular Functionalization of a Nanomaterial To Control Stability and Retention within Live Cells

Noncovalent hybrids of single-stranded DNA and single-walled carbon nanotubes (SWCNTs) have demonstrated applications in biomedical imaging and sensing due to their enhanced biocompatibility and photostable, environmentally responsive near-infrared (NIR) fluorescence. The fundamental properties of such DNA-SWCNTs have been studied to determine the correlative relationships between oligonucleotide sequence and length, SWCNT species, and the physical attributes of the resultant hybrids. However, intracellular environments introduce harsh conditions that can change the physical identities of the hybrid nanomaterials, thus altering their intrinsic optical properties. Here, through visible and NIR fluorescence imaging in addition to confocal Raman microscopy, we show that the oligonucleotide length controls the relative uptake, intracellular optical stability, and retention of DNA-SWCNTs in mammalian cells. Although the absolute NIR fluorescence intensity of DNA-SWCNTs in murine macrophages increases with increasing oligonucleotide length (from 12 to 60 nucleotides), we found that shorter oligonucleotide DNA-SWCNTs undergo a greater magnitude of spectral shift and are more rapidly internalized and expelled from the cell after 24 h. Furthermore, by labeling the DNA with a fluorophore that dequenches upon removal from the SWCNT surface, we found that shorter oligonucleotide strands are displaced from the SWCNT within the cell, altering the physical identity and changing the fate of the internalized nanomaterial. Finally, through a pharmacological inhibition study, we identified the mechanism of SWCNT expulsion from the cells as lysosomal exocytosis. These findings provide a fundamental understanding of the interactions between SWCNTs and live cells as well as evidence suggesting the ability to control the biological fate of the nanomaterials merely by varying the type of DNA wrapping.

Gas sensing mechanism of sulfur chain-encapsulated single-walled carbon nanotubes

Atomic encapsulation inside single-walled carbon nanotubes (SWNT) has drawn notable attention recently due to the unique strength of an extremely confined, stable 1-dimensional structure. However, the charge transport characteristics of these SWNT species, particularly upon specific gas exposure, have not yet been elucidated. Herein, sulfur atoms are encapsulated inside the SWNT, and the electronic properties of sulfur chain-encapsulated SWNT (S@SWNT) are investigated. In addition, the current responses of both pristine and S@SWNT species upon exposure to gas molecules with distinctly opposite natures, oxygen and ammonia, are demonstrated under high vacuum conditions. While the same trends are observed with ammonia purging, oxygen purging induces opposite trends for the two species. Based on the comparison of gas responses between pristine SWNT and S@SWNT, the gas sensing mechanism of S@SWNT is proposed.

(Invited) Methylene Blue Helps to Reveal Selectivity of Carbon Nanotube Affinity to Dispersing Agents

Methylene Blue (MB) is a water-soluble dye which can physically absorb on single-wall carbon nanotube (SWCNT) surface. We discovered the dye can quench SWCNT fluorescence when it is added to a SWCNT dispersions in water. At the same time its own fluorescence is quenched. Analyzing the parameters of both these quenching processes we observed that the attachment of the dye to a SWCNT depends strongly on the quality of the SWCNT coating. As a result the quenching of specific SWCNT species can be used as a specific indicator of the species “protection” and its affinity to a dispersing agent. We have observed that the SWCNT quenching by MB is relatively weak in a case of good ionic surfactants, and such a quenching process does not indicate any specific or unexpected trends. Lowing stability of the protective layer due to lower surfactant concentration or unfavorable pH was causing an increasing quenching. More specific effects were detected with more selective process or SWCNT suspended with single-stranded DNA (ssDNA). Relative quenching of SWCNT species in this case was not constant, and could be used as a measure of adhesion strength or density of the SS-DNA on these species. The process of MB attachment was found to be dynamic, and it be described by an temporal attachment of MB molecules to a SWCNT. A quenching model was developed, resulting in a mathematical description with only two parameters. One of them is the adhesion strength (or binding energy), and another is the available volume (space) near a nanotube surface. The most obvious parameter, the available volume, was increasing in a case of a weaker (sparse or thin) coating of SWCNT surface by ssDNA, that was associated with a lower affinity of such ssDNA type to a SWCVNT species. The volume was becoming much smaller with a good ssDNA-SWCNT affinity, preventing in this way the interaction of the quencher with this SWCNT species. The studied process has appeared to be a simple and reliable tool for quick comparison of the affinity between specific SWCNT and ssDNA in bulk SWCNT solutions. Physical and mathematical models can also help to understand and analyze a wider variety of interactions between SWCNT and suspending agents or wrappers. The attachment of external ionic molecules, such as MB, may also help in development of SWCNT separation methods.

Reductive diazotation of carbon nanotubes: an experimental and theoretical selectivity study.

The reaction of neutral single-walled carbon nanotubes (SWCNTs) with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs - carbon nanotubides - with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.

Novel Strategy for the Investigation on Chirality Selection of Single-Walled Carbon Nanotubes with DNA by Electrochemical Characterization.

There is a correlation between specific bases of DNA molecules and the chirality of single-walled carbon nanotubes (SWNTs), which contributes the recognition ability of DNA toward partner species of chiral SWNTs. A novel strategy of electrochemical characterization is reported here for the investigation on chirality selection of (7,6) and (6,5) SWNTs with various DNA sequences, and it is found that both DNA strand length and sequence composition significantly affected the interaction of chiral SWNTs with DNA. Then (7,6) and (6,5) SWNTs were distinguished from each other with DNA sequences chosen by electrochemical methods, which demonstrated an effective and excellent feasibility for the strategy and presented a new insight into DNA-SWNT applications. This strategy can also be applied to more chiral SWNTs and DNA sequence recognition and may serve as a prescreening method for the recognition and separation of single-chirality SWNTs, which would be a new contribution to the further development of DNA-SWNT hybrids.

“Click” generation of a conjugated polymer library for SWNT dispersion

ABSTRACTNoncovalent functionalization of single‐walled carbon nanotubes (SWNTs) with conjugated polymers enhances SWNT processability and allows for selective dispersion of various SWNT species. Selective dispersions can be obtained by tuning the nature of the polymer, which can involve using various polymer backbones or side‐chains. However, a clear understanding of selectivity determinants is elusive, as the degree of polymerization (DP) has a large effect on SWNT selectivity. Additionally, preparing libraries of conjugated polymers with varying functionality while keeping DP consistent is difficult. Here, we report the utilization of a strained cyclooctyne‐containing conjugated polymer that serves as a versatile scaffold, enabling systematic preparation of a small library of conjugated polymers with different side‐chain functionality, while maintaining a consistent DP. The resulting polymers were used as dispersants for SWNTs, forming supramolecular polymer‐SWNT complexes that were characterized by UV‐Vis‐NIR absorption and Raman spectroscopy. In the series of polymers, we were able to probe the effect of small changes within the side chains, such as the incorporation of a carbonyl group or an aromatic unit, on the quality of the polymer‐SWNT dispersion. The results of these studies provide new insight into the factors that dictate the ability of a polymer to form strong interactions with SWNTs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2053–2058

(Invited) Inner- and Outer-Wall Sorting of Double-Walled Carbon Nanotubes

Double walled carbon nanotubes (DWCNTs) consist of two coaxially aligned single walled carbon nanotubes (SWCNTs) and previous sorting methods only achieved outer-wall electronic type selectivity. Here a separation technique capable of sorting DWCNTs by semiconducting (S) or metallic (M) inner- and outer- wall electronic type is presented. Electronic coupling between the inner- and outer- wall is used to alter the surfactant coating around each of the DWCNT types and aqueous gel permeation is used to separate them. Aqueous methods are used to remove SWCNT species from the raw material and prepare enriched DWCNT fractions. The enriched DWCNT fractions are then transferred into either chlorobenzene or toluene using the copolymer PFO-BPy to yield the four inner@outer combinations of M@M, M@S, S@M and S@S. The high-purity of the resulting fractions is verified by absorption measurements, TEM, AFM, resonance Raman mapping and high-density field effect transistor devices. [1] Han Li, Georgy Gordeev, Soeren Wasserroth, Venkata Sai Kiran Chakravadhanula, Shyam Kumar Chethala Neelakandhan, Frank Hennrich, Ado Jorio, Stephanie Reich, Ralph Krupke, Benjamin Flavel, Nature Nanotechnology (2017) DOI: 10.1038/nnano.2017.207 [2] Katherine Moore, Moritz Pfohl, Daniel Tune, Frank Hennrich, Simone Dehm, Venkata Sai Kiran Chakravadhanula, Christian Kuebel, Ralph Krupke, Benjamin Flavel, ACS Nano (2015) DOI: 10.1021/nn506869h [3] Katherine Moore, Moritz Pfohl, Frank Hennrich, Venkata Sai Kiran Chakravadhanula, Christian Kuebel, Manfred Kappes, Joe Shapter, Ralph Krupke, Benjamin Flavel, ACS Nano (2014) DOI: 10.1021/nn500756a

(Invited) Variance Spectroscopy Studies of Single-Walled Carbon Nanotube Aggregation

Understanding aggregation in samples of dispersed, well-individualized single-walled carbon nanotubes (SWCNTs) is important for many basic studies and applications. We will describe a study that uses the recently developed technique of variance spectroscopy to monitor aggregation kinetics of SWCNTs in aqueous surfactant dispersions. Unlike other techniques used to investigate colloidal dispersions, variance spectroscopy resolves individual subpopulations in mixed samples based on their distinct fluorescence signatures. Following the addition of NaCl coagulant to unsorted SWCNT dispersions, we monitored changes in the independent particle concentrations of six semiconducting (n,m) species. These data were supplemented by time-resolved measurements of fluorescence intensity, which showed pseudo-first order kinetics that was independent of SWCNT structure and was attributed to quenching by energy transfer to metallic SWCNTs. The decreases in particle concentration directly revealed aggregation. They were found to fit reasonably well to a second-order rate law with some dependence on structure at higher salt concentrations. Finally, covariance analysis was applied to the variance data to monitor correlated spectral fluctuations arising from specific heteroaggregates. Those results showed equivalent associations between different semiconducting SWCNT species during salt-induced aggregation.

Low-temperature graphitic formation promoted by confined interphase structures in polyacrylonitrile/carbon nanotube materials

In this work polyacrylonitrile (PAN)/single wall carbon nanotube (SWNT) composites with 50 wt% SWNT loading were studied. A previously studied solvent-based phase separation process was used to enhance PAN-SWNT crystallization conditions and interphase formation within the composites. Two types of SWNT species were used here to produce two composites materials with well-ordered PAN-SWNT interphase structures. All precursor composite films were stabilized and subsequently carbonized at temperatures ranging from 900 to 1500 °C under various carbonization times. Wide-angle X-ray diffraction and electron microscopy were used to analyze the structural change in these precursors during carbonization. It was found that ordered graphitic structures were formed using specific temperature/time conditions as early as 900 °C. This low-temperature graphitic structure can be tracked directly to the PAN interphase structure within the precursors. This paper discusses the linkage between precursor PAN-SWNT interphase formation and subsequent low-temperature graphitic formation.

Inner- and outer-wall sorting of double-walled carbon nanotubes.

Double-walled carbon nanotubes (DWCNTs) consist of two coaxially aligned single-walled carbon nanotubes (SWCNTs), and previous sorting methods only achieved outer-wall electronic-type selectivity. Here, a separation technique capable of sorting DWCNTs by semiconducting (S) or metallic (M) inner- and outer-wall electronic type is presented. Electronic coupling between the inner and outer wall is used to alter the surfactant coating around each of the DWCNT types, and aqueous gel permeation is used to separate them. Aqueous methods are used to remove SWCNT species from the raw material and prepare enriched DWCNT fractions. The enriched DWCNT fractions are then transferred into either chlorobenzene or toluene using the copolymer PFO-BPy to yield the four inner@outer combinations of M@M, M@S, S@M and S@S. The high purity of the resulting fractions is verified by absorption measurements, transmission electron microscopy, atomic force microscopy, resonance Raman mapping and high-density field-effect transistor devices.