Stable Single-walled Carbon Nanotubes Research Articles

The Effects of Lengths of Flavin Surfactant N-10-Alkyl Side Chains on Promoting Dispersion of a High-Purity and Diameter-Selective Single-Walled Nanotube.

Flavin with defined helical self-assembly helps to understand chemical designs for obtaining high-purity semiconducting (s)-single-walled carbon nanotubes (SWNT) in a diameter (dt)-selective manner for high-end applications. In this study, flavins containing 8, 12, 16, and 20 n-alkyl chains were synthesized, and their single/tandem effects on dt-selective s-SWNT dispersibility were investigated at isomolarity. Flavins with n-dodecyl and longer chain lengths (FC12, FC16, and FC20) act as good surfactants for stable SWNT dispersions whereas n-octyl flavin (FC8) exhibits poor dispersibility owing to the lack of SWNT buoyancy. When used with small-dt SWNT, FC8 displays chirality-selective SWNT dispersion. This behavior, along with various flavin helical motifs, prompts the development of criteria for ‘side chain length (lS)’ required for stable and dt-selective SWNT dispersion, which also explains lS-dependent dt-enrichment behavior. Moreover, SWNT dispersions with flavins with dodecyl and longer lS exhibit increased metallic (m)-SWNT, background absorption-contributing carbonaceous impurities (CIs) and preferential selectivity of s-SWNT with slightly larger dt. The increased CIs that affect the SWNT quantum yield were attributed to a solubility parameter. Furthermore, the effects of flavin lS, sonication bath temperature, centrifugal speed, and surfactant concentration on SWNT purity and s-/m-SWNT ratio were investigated. A tandem FC8/FC12 provides fine-tuning of dt-selective SWNT dispersion, wherein the FC8 ratio governs the tendency towards smaller dt. Kinetic and thermodynamic assemblies of tandem flavins result in different sorting behaviors in which wide dt-tunability was demonstrated using kinetic assembly. This study highlights the importance of appropriate side chain length and other extrinsic parameters to obtain dt-selective or high-purity s-SWNT.

Comprehensive Study of the Chemistry behind the Stability of Carboxylic SWCNT Dispersions in the Development of a Transparent Electrode.

Single-walled carbon nanotubes (SWCNTs) are well-known for their excellent electrical conductivity. One promising application for SWCNT-based thin films is as transparent electrodes for uncooled mid-IR detectors (MIR). In this paper, a combination of computational and experimental studies were performed to understand the chemistry behind the stability of carboxylic SWCNTs (SWCNTs-COOH) dispersions in different solvents. A computational study based on the density functional tight-binding (DFTB) method was applied to understand the interactions of COOH-functionalized carbon nanotubes with selected solvents. Attention was focused on understanding how the protonation of COOH groups influences the binding energies between SWCNTs and different solvents. Thin film electrodes were prepared by alternately depositing PEI and SWCNT-COOH on soda lime glass substrates. To prepare a stable SWCNT dispersion, different solvents were tested, such as deionized (DI) water, ethanol and acetone. The SWCNT-COOH dispersion stability was tested in different solvents. Samples were prepared to study the relationship between the number of depositions, transparency in the MIR range (2.5–5 µm) and conductivity, looking for the optimal thickness that would satisfy the application. The MIR transparency of the electrode was reduced by 20% for the thickest SWCNT layers, whereas sheet resistance values were reduced to 150–200 kΩ/sq.

Overcoming Electrochemical Instabilities of Printed Silver Electrodes in All-Printed Ion Gel Gated Carbon Nanotube Thin-Film Transistors.

Silver ink is the most widely used conductive material for printing electrodes in the fabrication of all-printed ion gel gated transistors because of their high conductivity and low cost. However, electrochemical instability of printed silver electrodes is generally one of the biggest issues, whether it is in air where silver gets oxidized or in a moisture environment where electrochemical migration occurs. Notwithstanding, the electrochemical stability of printed silver electrodes in ion gel medium has not been studied so far. In this work, we studied the electrochemical instabilities of printed silver electrodes in fully printed ion gel gated single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) and developed some strategies to overcome these issues. All-printed ion gel-based p-type SWCNT TFTs were employed to investigate the impact of electrochemical instabilities on the electrical behavior of printed SWCNT TFTs. The results have demonstrated that printed silver was unstable at anodic and cathodic polarization because of the corrosion by the ionic liquid. Besides, anodic corrosion of silver source/drain electrodes was shown to be responsible for the electrical failure of printed SWCNT TFTs in both the linear and saturated regime. These issues were completely resolved when preventing printed silver electrodes from coming into direct contact with ion gels. For example, ion gels were partially printed in device channels to avoid contacting the printed silver source and drain electrodes. At the same time, silver side-gate electrodes were replaced by inkjet-printed PEDOT:PSS electrodes to avoid gate electrode-related instabilities. Consequently, all-printed electrochemically stable SWCNT TFTs fabricated were obtained with enhanced performance of higher ION/IOFF ratios (105 to 106), smaller subthreshold slopes (∼70 mV/dec), and smaller hysteresis (ΔV = 0.025 V) at gate voltages from 1.2 to -0.5 V. Additionally, the polarity of all-printed SWCNT TFTs was converted from the p-channel to ambipolar while achieving lower leakage currents.

Structural Recovery of Highly Oxidized Single-Walled Carbon Nanotubes Fabricated by Kneading and Electrochemical Applications

Harsh oxidation of 1 nm single-walled carbon nanotubes (SWCNTs) can lead to fatal defect structures, which can jeopardize their mechanical and electrical performances. Here, we show the structural recovery of highly oxidized SWCNTs (Ox-SWCNTs), which were rapidly (within 1 h) oxidized by kneading without forming failure-causing defects inspired by flour dough. The rational oxidation of SWCNTs by kneading debundled the SWCNTs and led to obtaining thermodynamically stable SWCNT solutions in water or even in alcohol without dispersant molecules. Importantly, the structure of the Ox-SWCNTs could be recovered by chemical, thermal, photothermal, or solvothermal reduction, enhancing the electrical conductivity of the Ox-SWCNT films from ∼100 to ∼1000 S cm–1. These Ox-SWCNTs and chemically reduced Ox-SWCNTs showed high performance in supercapacitors and Li-ion batteries as electrochemical conductors, respectively.

Novel single-walled carbon nanotubes periodically embedded with four- and eight-membered rings

Based on experimental results, we obtain five types of single-walled carbon nanotube (SWNT) clusters with different chirality indices and diameters using density functional theory (DFT). We then obtain the corresponding SWNTs by using periodic boundary conditions. Studies of the stability and electronic properties show that the stability of the novel SWNTs is independent of the chirality index and relates only to the tube diameter; larger diameters correspond to more stable SWNTs. The electronic properties all show metallic characteristics independent of the chirality indices and tube diameters, thereby promoting the application of metallic-type SWNTs.

Polypyrimidine/SWCNTS composite comprising Pt nanoparticles: Possible electrocatalyst for fuel cell

The poly(9,9-dioctyl fluorine-alt-2-amino-4,6-pyrimidine) (oligomer) is used as an effective dispersant for single walled carbon nanotubes (SWCNTs) and generates stable SWCNTs hybrid after elimination of the excess polymer. The covered polymers immobilized Pt nanoparticles onto the surface of single-walled carbon nanotubes (SWCNTs) by coordination between Pt and polymer and the amount of the loaded Pt on the hybrid was calculated to be 38.5 wt %. The average diameter of the Pt nanoparticles on the SWCNTs were about ∼4–5 nm and have a moderate electrochemically active surface area of 40.5 m2/g. These studies strongly imply the possible application of novel pyrimidine/carbon materials as catalyst supports in the electrodes of fuel cells.

On the Stability and Abundance of Single Walled Carbon Nanotubes.

Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.

A new designed π conjugated molecule for stable single walled carbon nanotube dispersion in aqueous medium

A molecule with a π conjugated backbone built from aromatic thiophene and dialkoxyphenylene units and substituted imidazolium groups (TPO) is designed to obtain ultra-stable single walled carbon nanotube (SWCNT) dispersion in aqueous medium. The proposed mechanism of non-covalent interaction is accompanied by individualization of SWCNT and comprises of dominant nondisruptive π–π and cation–π interaction between them and the TPO conjugated oligomer. The individualization of SWCNT and dispersibility and stability of the ultra-stable suspensions were estimated using high resolution transmission electron microscopy, UV–Visible–NIR absorption spectroscopy, Raman spectroscopy, photoluminescence and zeta potential measurement. Nuclear magnetic resonance data provides direct evidence toward possible cation–π interaction.

Enhanced solubilization of large-diameter single-walled carbon nanotubes with amino-functionalized dipyrene nanotweezers

Pyrene-based nanotweezers 1 consisting of two pyrenes and amino-substituted carbazole in between have been successfully synthesized via Suzuki–Miyaura coupling reaction. The supramolecular complex formation of nanotweezers 1 with single-walled carbon nanotubes (SWNTs) was studied, and it was found that nanotweezers 1 exhibited much higher the SWNTs extraction ability as compared to the analogous dipyrene nanotweezers 2 and 3 with soluble alkyl-substituents. This enhanced extraction ability of 1 can be attributed to the formation of more stable SWNT complexes in methanol. On the basis of photoluminescence excitation and UV–Vis-NIR absorption of 76-CoMoCAT SWNTs before and after the extraction, nanotweezers 1 were found to show high selectivity towards (8,4)-, (7,6)-, (9,4)-, and (8,6)-SWNTs with diameter ranging from 0.84 to 0.97 nm.

New hybrid materials with porphyrin-ferrocene and porphyrin-pyrene covalently linked to single-walled carbon nanotubes

Novel porphyrin derivatives bearing additional pyrene or ferrocene units as light harvesting antenna systems were synthesized and fully characterized. Following a covalent functionalization approach for single-walled carbon nanotubes (SWCNTs), stable SWCNT suspensions in common organic solvents were produced. Subsequently, the resulting porphyrin-pyrene and porphyrin-ferrocene dyads were incorporated onto the nanotubes' backbone yielding donor–donor–acceptor hybrids. The resulting hybrid materials were soluble in common organic solvents and were characterized using micro-Raman, ATR-IR, UV-Vis and photoluminescence spectroscopy, transmission electron microscopy, thermogravimetric analysis and electrochemistry. Photoluminescence quenching of the porphyrin emission in both hybrid materials was detected thus suggesting the potentiality of these materials in photoelectrochemical cells.

Cellulose Nanocrystal-Assisted Dispersion of Luminescent Single-Walled Carbon Nanotubes for Layer-by-Layer Assembled Hybrid Thin Films

Highly stable single-walled carbon nanotube (SWNT) dispersions are obtained after ultrasonication in cellulose nanocrystal (CN) aqueous colloidal suspensions. Mild dispersion conditions were applied to preserve the SWNT length in order to facilitate the identification of hybrid objects. This led to a moderate dispersion of 24% of the SWNTs. Under these conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments succeeded in demonstrating the formation of hybrid particles in which CNs are aligned along the nanotube axis by a self-assembly process. These SWNT/CN dispersions are used to create multilayered thin films with the layer-by-layer method using polyallylamine hydrochloride as a polyelectrolyte. Homogeneous films from one to eight bilayers are obtained with an average bilayer thickness of 17 nm. The presence of SWNTs in each bilayer is attested to by characteristic Raman signals. It should be noted that these films exhibit a near-infrared luminescence signal due to isolated and well-separated nanotubes. Furthermore, scanning electron microscopy (SEM) suggests that the SWNT network is percolating through the film.

Effect of Surfactant Structure on Carbon Nanotube Sidewall Adsorption

AbstractOne conventional and two related gemini surfactants have been used for the preparation of stable single‐walled carbon nanotube (SWNT) aqueous dispersions. The surfactants investigated are able to disperse SWNTs at surfactant/carbon nanotube weight ratios far lower than widely used conventional surfactants. The gemini surfactants investigated demonstrated the ability to solubilize a larger amount of SWNTs with respect to the related single‐tailed surfactant at concentrations far lower than their critical micellar concentrations. Their selectivity towards semiconducting SWNTs with large diameters was inferred from radial breathing mode Raman data.

Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.

Ultrahigh Density Alignment of Carbon Nanotube Arrays by Dielectrophoresis

We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on-off ratio. Ultrahigh density alignment reported here will have important implications in fabricating high-quality devices for digital and analog electronics.

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

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

Single-walled carbon nanotubes modified carbon ionic liquid electrode for sensitive electrochemical detection of rutin

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10 − 7 to 8.0 × 10 − 4 mol/L with the detection limit as 7.0 × 10 − 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.

Dispersion of pristine single-walled carbon nanotubes using pyrene-capped polystyrene and its application for preparation of polystyrene matrix composites

A pyrene-capped polystyrene (PyPS) is synthesized by an anionic polymerization method and acts as dispersant for dispersion of pristine single-walled carbon nanotubes (SWCNTs). Through a well-known π-stacking interaction confirmed qualitatively by proton nuclear magnetic resonance and fluoroscopic analyses, PyPS is strongly but noncovalently adsorbed onto the nanotube surface, affording highly uniform and stable SWCNT dispersion in chloroform with the nanotube content as high as 250±30mgL−1. Since no direct chemical reaction takes place on the nanotubes, their intrinsic electronic structure is maintained, thus ensuring them as functional fillers for application in conductive polymer composites. The so-obtained dispersion is subsequently used to prepare polystyrene matrix composites. A solution-based process adopted here preserves the good nanotube dispersing state in dispersion into the composites. Hence, the resultant composites show good optical transmittance and a low electrical percolation threshold of 0.095wt.% SWCNTs. In comparison, the composites with absence of PyPS prepared by the same process have a relatively high percolation threshold of 0.28wt.% SWCNTs.

Retracted article: The Adsorption of L-Phenylalanine on Oxidized Single-Walled Carbon Nanotubes

A simple and green approach was proceeded to obtain a stable single-walled carbon nanotubes (SWNTs)/L-phenylalanine (Phe) solution. The oxidized SWNTs (OSWNT) were used in this work. The scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HRTEM), Raman spectrometer, Fourier transform-infrared resonance (FT-IR), Ultraviolet-visible (UV-vis) spectroscopy, Thermogravimetric analysis (TGA) and High performance liquid chromatography (HPLC) were joined together to investigate the interaction between OSWNT and Phe. The OSWNT became soluble in the water and formed a stable solution since the Phe was adsorbed. The absorbed amount of Phe on the OSWNT is around 33 wt%. Adsorption of the Phe was mainly carried out on the OSWNT with smaller diameters. The Phe molecules were absorbed on the OSWNT by conjunct interaction of the pi-pi stacking, hydrogen bond and part of covalent bond.

Improved Optical Enrichment of SWNTs through Extraction with Chiral Nanotweezers of 2,6-Pyridylene-Bridged Diporphyrins

Chiral single-walled carbon nanotubes (SWNTs) have left- and right-handed helical structures (M and P, respectively, according to the IUPAC nomenclature). In this report, optically active SWNTs were obtained through preferential extraction of (M)- or (P)-SWNTs with 2,6-pyridylene-bridged chiral diporphyrins 1. In the circular dichroism (CD) spectra, the SWNTs extracted with 1 exhibit much larger intensity than those extracted with 1,3-phenylene-bridged chiral diporphyrins 2, indicating an improved chiral discrimination ability of 1. In particular, (6,5)-SWNTs display the most intensified CD signals among the SWNTs extracted with 1. In addition, the SWNT extraction ability of 1 has been shown to be considerably enhanced in comparison to 2. These improved discrimination and extraction abilities of 1 are attributed to the formation of its more stable SWNT complex. Computer-calculated energy minimized structures for 1:(6,5)-SWNT complexes show that (R)- and (S)-1 form complexes preferentially with (M)- and (P)-(6,5)-SWNTs, respectively. These calculations also predict that the 1:(6,5)-SWNT complex is approximately 1.6 kcal mol-1 more stable than the corresponding complex of 2, accounting for the improved abilities of 1 in the chiral discrimination and extraction.

Fabrication of carbon nanotube based transparent conductive thin films using layer-by-layer technology

This paper presents a simple and convenient process for the fabrication of carbon nanotube based optically transparent and electrically conductive thin films. Single-walled carbon nanotubes (SWNTs) are chemically treated to introduce negatively charged carboxylic groups on their surfaces, so that a stable SWNT aqueous dispersion can be obtained without any surfactant. The substrate surface is modified by a layer-by-layer nanoassembly technique, in which a positively charged hydrophilic polymer molecular layer is formed on the top of the substrate. This helps the SWNT dispersion to be cast onto the substrate using convenient wet coating techniques and increases the bonding force between the thin films and the substrates. Using the developed process, large sizes of conductive pure SWNT thin films that are uniform and highly transparent have been fabricated.