Ionic Dopant‐Encapsulating Single‐Walled Carbon Nanotube Films with Metal‐Like Electrical Conductivity

Heavy doping is inevitable for utilizing single‐walled carbon nanotubes for wiring. However, the electrical conductivity of their films is currently as low as one tenth of the films made from typical metal pastes. Herein we report on metal‐comparable electrical conductivity from single‐walled carbon nanotube network films. We use ionic liquids and crown ether complexes for p‐type and n‐type doping, respectively. The encapsulation of counterions into carbon nanotubes promotes the conductivities in the range of 7000 S cm^?1, approximately ten times larger than those of undoped films.     

Sorting Semiconducting Single‐Walled Carbon Nanotubes by Water‐Soluble Polyfluorene Assisted Electrophoresis and Its Application in Field‐effect Transistors

We report a considerably promising method based on agarose gel electrophoresis (AGE) to separate single‐walled carbon nanotubes by adding a water‐soluble polyfluorene (w‐PFO) as surfactant into the agarose gel. In this effective method, the AGE/w‐PFO gel network will trap more semiconducting single‐walled carbon nanotubes (SWNTs) with the assistance of w‐PFO, for the strong interaction between w‐PFO and semiconducting species. The optical absorbance, photoluminescence emission and resonant Raman scattering characterization were used to verify the separation effect. The purity of separated semiconducting species is as high as (98±1)%. The demonstrated field effect transistors give the on/off ratio and mobility about 27000 and 10.2 cm²·V^?1·s^?1, respectively.     

Experimental and Computational Investigations of the Properties of Fluorinated Single‐Walled Carbon Nanotubes

Fluorination of single‐walled carbon nanotubes by reaction with elemental fluorine at elevated temperatures provides fluorinated single‐walled carbon nanotubes (F‐SWNT), which have the highest degree of functionalization (up to F/C=1/2) of any derivatized carbon‐nanotube material reported to date. Also, F‐SWNTs have received more scrutiny than any other functionalized carbon nanotubes. This Minireview covers experimental and computational investigations of F‐SWNTs with a focus on the nature and the strength of the C–F linkage.     

Surfactant‐Dependent Charge Transfer between Polyoxometalates and Single‐Walled Carbon Nanotubes: A Fluorescence Spectroscopic Study

Hybridizations of redox‐active polyoxometalates (POMs) with single‐walled carbon nanotubes (SWNTs) have been widely investigated for their diverse applications. For the purpose of constructing high‐quality electronic devices, controlling charge transfer within POM/SWNT hybrids is an inevitable issue. As determined by means of fluorescence spectroscopy, electron transfer between SWNTs and a common POM dopant, phosphomolybdic acid (PMo₁₂), can be tuned simply by an alteration of nanotube surfactant type from anionic to nonionic. The mechanism is attributed to the influence of surfactant type on the stabilization of the electron donor–acceptor hybrid and effect of surfactant–nanotube interactions. These results will be important to control charge‐transport behavior in nanohybrids consisting of carbon nanotubes.     

Hydrophobic End‐Modulated Amino‐Acid‐Based Neutral Hydrogelators: Structure‐Specific Inclusion of Carbon Nanomaterials

Hydrophobic end‐modulated l ‐phenylalanine‐containing triethylene glycol monomethyl ether tagged neutral hydrogelators ( 1 – 4 ) are developed. Investigations determine the gelators’ structure‐dependent inclusion of carbon nanomaterials (CNMs) in the self‐assembled fibrillar network (SAFIN). The gelators ( 1 , 3 , and 4 ) can immobilize water and aqueous buffer (pH 3–7) with a minimum gelator concentration of 10–15 mg mL^?1. The hydrophobic parts of the gelators are varied from a long chain (C‐16) to an extended aromatic pyrenyl moiety, and their abilities to integrate 1 D and 2 D allotropes of carbon (i.e., single‐walled carbon nanotubes (SWNTs) and graphene oxide (GO), respectively) within the gel are investigated. Gelator 1 , containing a long alkyl chain (C‐16), can include SWNTs, whereas the pyrene‐containing 4 can include both SWNTs and GO. Gelator 3 fails to incorporate SWNTs or GO owing to its slow rate of gelation and possibly a mismatch between the aggregated structure and CNMs. The involvement of various forces in self‐aggregated gelation and physicochemical changes occurring through CNM inclusion are examined by spectroscopic and microscopic techniques. The distinctive pattern of self‐assembly of gelators 1 and 4 through J‐ and H‐type aggregation might facilitate the structure‐specific CNM inclusion. Inclusion of SWNTs/GO within the hydrogel matrix results in a reinforcement in mechanical stiffness of the composites compared with that of the native hydrogels.     

Separation of Semiconducting Single‐Walled Carbon Nanotubes by Using a Long‐Alkyl‐Chain Benzenediazonium Compound

We designed and synthesized 4‐dodecyloxybenzenediazonium tetrafluoroborate ( 1 ), which preferentially reacts with metallic single‐walled carbon nanotubes (SWNTs) by kinetic control. We first determined the suitable experimental conditions for the preferential reaction of 1 with individually dissolved SWNTs by monitoring the decrease in absorbance for the metallic SWNT in the range of 400–650 nm in the absorption spectrum of the SWNTs. The reacted SWNTs were thoroughly rinsed with THF to obtain THF‐insoluble SWNTs. The Raman spectrum of the THF‐insoluble SWNTs showed a strong peak near 180 cm^?1, which corresponds to a semiconducting breathing band. The metallic breathing bands (≈220 cm^?1) and Breit–Wingner–Fano (BWF) modes (1520 cm^?1) corresponding to the metallic SWNTs were much weaker than those of the pristine SWNTs. We also confirmed that metallic peaks in the range of 400–650 nm in the absorption spectrum of THF‐insoluble SWNTs that were individually dissolved in an aqueous micelle of sodium cholate were almost nondetectable. All the results indicate that the THF‐insoluble SWNTs are semiconducting.     

Direct Bioelectrocatalysis of PQQ‐Dependent Glucose Dehydrogenase

The direct bioelectrocatalysis was demonstrated for pyrroloquinoline quinone‐dependent glucose dehydrogenase (PQQ‐dependent GDH) covalently attached to single‐walled carbon nanotubes (SWNTs). The homogeneous ink‐like SWNT suspension was used for both creating the SWNT network on the microelectrode carbon surface and for enzyme immobilization. Functionalization of the SWNT surface by forming active ester groups was found to considerably enhance SWNT solubility in water with a range from 0.1 to 1.0 mg/mL. The PQQ‐dependent GDH immobilized on the surface of the SWNTs exhibited fast heterogeneous electron transfer with a rate constant of 3.6 s^?1. Moreover, the immobilized PQQ‐dependent GDH retained its enzymatic activity for glucose oxidation. A fusion of PQQ‐dependent GDH with SWNTs has a great potential for the development of low‐cost and reagentless glucose sensors and biofuel cells.     

Spectroscopic Characteristics of Differently Produced Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X‐ray absorption near edge structure, along with X‐ray photoemission by following the total valence bands and C 1s core‐level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp² hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence‐band X‐ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.     

Synthesis of soluble single‐walled carbon nanotubes with poly (1,3‐cyclohexadiene): Grafting poly(1,3‐cyclohexadienyl)lithium onto a solid surface

The first‐ever grafting of poly(1,3‐cyclohexadiene) (PCHD) onto single‐walled carbon nanotubes (SWNTs) was accomplished by reaction with poly(1,3‐cyclohexadienyl)lithium. The rate of this reaction was especially slow due to the heterogeneous nature of the reaction system. The concentration of active carbons available for reaction with PCHDLi on the solid surface of the SWNTs was found to be approximately 2.0 mol %. The mass of PCHD attached to the SWNTs was effectively controlled by varying the molecular weight of the PCHD. The resulting PCHD‐grafted SWNTs exhibited excellent solubility in organic solvent, maintaining a highly stable homogeneous dispersion even after 3 months. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Single‐Walled Carbon Nanotubes Modified Gold Electrodes as an Impedimetric DNA Sensor

A gold surface modified with a self‐assembled monolayer of 11‐amino‐1‐undecanethiol (AUT) was used for the covalent immobilization of oxidized single‐walled carbon nanotubes (SWNTs). The as‐described SWNTs‐modified substrate was subsequently used to attach single‐stranded deoxyribonucleic acid (ssDNA) used as a substrate for DNA hybridization. Electrochemical impedance spectroscopy measurements were performed to follow the DNA hybridization process by using the redox couple [Fe(CN)₆]^3−/4− as a marker ion. Specifically, changes in charge transfer resistance obtained from the Nyquist plots were used as the sensing parameter of DNA hybridization. The substrate sensitivity towards changes in target DNA concentration, its selectivity toward different DNA sequences and its reusability are successfully demonstrated in this report.     

Spectroscopic Analysis of Two Distinct Equilibrium States for the Exchange Reaction of Sodium Cholate and Oligo‐DNA on Single‐Walled Carbon Nanotubes

Understanding the quantitative analysis of the transition adsorption structures of molecules on single‐walled carbon nanotubes (SWNTs) is of importance from the point of view of both fundamental science and applications of nanotubes. Absorption spectroscopy reveals that two different equilibrium states are existent for the exchange reaction of sodium cholate (SC) and oligo‐DNA (single‐stranded 20‐mer cytosine) on SWNTs. This is derived from the transitions of the adsorption structures of different chirality‐types of SWNTs and SC/DNA at certain SC concentrations below the critical micelle concentration of SC.     

Hybrids of Copolymers of Fluorene and C60‐Carrying‐Carbazole with Semiconducting Single‐Walled Carbon Nanotubes

Three different copolymers of C₆₀‐carrying‐carbazole and fluorene units with different copolymer composition ratios were designed and synthesized. On the basis of photoluminescence, atomic force microscopy, and Vis‐NIR and Raman spectroscopic analysis, we found that these copolymers solubilize only semiconducting single‐walled carbon nanotubes (sem‐SWNTs) to form copolymer/sem‐SWNT hybrids, in which energy transfer from the copolymer/C₆₀ moieties to the SWNTs was revealed. By comparing two possible hybrid structures with molecular‐mechanics simulations, the greatest stabilization was found when the C₆₀ moieties lay on the sem‐SWNT surfaces.     

Preparation of single‐walled carbon nanotubes‐induced poly(p‐oxybenzoyl) crystals

Crystallization of oligomers was applied for the preparation of single‐walled carbon nanotubes (SWNTs)/poly(p‐oxybenzoyl) (POB) crystals using SWNTs as a nucleating agent. Polymerization conditions were investigated to induce the crystallization of POB oligomers through SWNTs. SWNTs/POB plate‐like or lozenge‐shaped crystals were successfully prepared by direct polymerization of p‐hydroxybenzoic acid (HBA) in a mixed solvent of DMF/Py with TsCl in the presence of functionalized SWNTs. The size of the plate‐like crystals were ～200 nm to 3 μm. The crystals consisted of some layers, ～3 nm thick plates. Model reactions showed that esterification reactions proceed between functionalized SWNTs and HBA monomers in the polymerization system. The obtained crystals exhibited unique morphology and high crystallinity, producing a novel SWNT/POB hybrid. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1265–1277, 2008     

Deformation of single‐walled carbon nanotubes by interaction with graphene: A first‐principles study

The interaction between single‐walled carbon nanotubes (SWNTs) and graphene were studied with first‐principles calculations. Both SWNTs and single‐layer graphene (SLG) or double‐layer graphene (DLG) display more remarkable deformations with the increase of SWNT diameter, which implies a stronger interaction between SWNTs and graphene. Besides, in DLG, deformation of the upper‐layer graphene is less than in SLG. Zigzag SWNTs show stronger interactions with SLG than armchair SWNTs, whereas the order is reversed for DLG, which can be interpreted by the mechanical properties of SWNTs and graphene. Density of states and band structures were also studied, and it was found that the interaction between a SWNT and graphene is not strong enough to bring about obvious influence on the electronic structures of SWNTs. © 2015 Wiley Periodicals, Inc.     

Properties of single‐walled carbon nanotube‐based poly(phenylene vinylene) electroluminescent nanocomposites

Devices with varying concentrations of single‐walled carbon nanotubes (SWNTs) dispersed in three derivatives of poly(p‐phenylene vinylene) are prepared, and their electroluminescent properties evaluated. Increasing the concentration of SWNTs improves the electrical conductivity of the nanocomposites. However, an undesired increase in the electroluminescence (EL) turn‐on voltage is observed for the hybrids, possibly due to photoluminescence quenching of excitons by the SWNTs. At relatively low concentrations of SWNTs, there is an increase in the EL lifetime; in contrast, at relatively high concentrations of SWNTs, due to photoluminescence quenching by the nanotubes, significant reduction in brightness and faster degradation of the EL performance of the devices is observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

A New Amperometric Hydrazine Sensor Based on Prussian Blue/Single‐walled Carbon Nanotube Nanocomposites

A slow reaction process has been successfully used to synthesize Prussian blue/single‐walled carbon nanotubes (PB/SWNTs) nanocomposites. Electrochemical and surface characterization by cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) confirmed the presence of PB nanocrystallites on SWNTs. PB/SWNTs modified glassy carbon electrode (GCE) exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. The fabricated hydrazine sensor showed a wide linear range of 2.0×10^?6–6.0×10^?3 M with a response time less than 4 s and a detection limit of 0.5 μM. PB/SWNTs modified electrochemical sensors are promising candidates for cost‐effective in the hydrazine assays.     

Probing the Selectivity of Azomethine Imine Cycloaddition to Single‐Walled Carbon Nanotubes by Resonance Raman Spectroscopy

Selective covalent surface modification of single‐walled carbon nanotubes (SWNTs) is of great importance to various carbon nanotube‐based applications as it might offer an alternative method for enriching metallic and semiconducting nanotubes. Herein, we report on the surface modification of SWNTs through 1,3‐dipolar cycloaddition of 3‐phenyl‐phthalazinium‐1‐olate, which is a stable and reactive azomethine imine. For this reaction, microwave heating was found to be more efficient than conventional and solvent‐free heating. The sensitivity of cycloaddition to the molecular structure of SWNTs was probed using resonance Raman spectroscopy with three different laser excitations. Based on the obtained results, azomethine imine addition to the surface of nanotubes is selective for metallic and large‐diameter semiconducting SWNTs. Thermogravimetric analysis coupled with mass spectrometry showed that fragments released at high temperatures corresponded to the phenylphthalazine group, thus confirming the covalent surface functionalization. Modified SWNTs were further characterized by X‐ray photoelectron and UV/Vis‐NIR spectroscopies.     

Synthesis of water‐soluble single‐walled carbon nanotubes and its application in poly(vinyl alcohol) composites

A new type of water‐soluble single‐walled carbon nanotubes (SWNTs) was synthesized by grafting of dodecyl quaternary ammonium bromides. Results of Fourier transform infrared and proton nuclear magnetic resonance spectroscopic analyses confirmed the successful synthesis. Water‐soluble performance of functionalized SWNTs, i.e. N⁺‐SWNTs, has been studied in terms of solubility and stability. It was found that the solubility could reach up to 110 mg.l^?1 and as‐prepared solution possesses a good stability over the PH range of 6.87–11.25. Based on these properties, one of the important applications of N⁺‐SWNTs was demonstrated to prepare poly(vinyl alcohol) (PVA) composites. Owing to critical issues of uniform dispersion and enhanced interfacial PVA‐nanotube interaction having been simultaneously resolved to a reasonable extent, the composite film with only 0.3 wt% N⁺‐SWNTs showed an increase of 33% and 32% in tensile strength and Young's modulus, respectively, over neat PVA film. Moreover, a high optical quality and slightly increased glass transition temperature were also observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Band‐Gap Opening in Metallic Single‐Walled Carbon Nanotubes by Encapsulation of an Organic Salt

The encapsulation of viologen derivatives into metallic single‐walled carbon nanotubes (SWNTs) results in the opening of a band gap, making the SWNTs semiconducting. Raman spectroscopy, thermogravimetric analysis, and aberration‐corrected high‐resolution transmission electron microscopy confirm the encapsulation process. Through the fabrication of field‐effect transistor devices, the change of the electronic structure of the tubes from metallic to semiconducting upon the encapsulation is confirmed. The opening of a gap in the band structure of the tubes was not detected in supramolecular controls.     

Fabrication,Characterization, and Application of ‘Sandwich‐Type’ Electrode Based on Single‐Walled Carbon Nanotubes and Room Temperature Ionic Liquid

The much‐enhanced electrochemical responses of potassium ferricyanide and methylene blue (MB) were firstly explored at the glassy carbon electrode modified with single‐walled carbon nanotubes (SWNT/GCE), indicating the distinct electrochemical activity of SWNTs towards electroactive molecules. A hydrophobic room temperature ionic liquid (RTIL), 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆), was used as electrode modification material, which presented wide electrochemical windows, proton permeation and selective extraction ability. In consideration with the advantages of SWNTs and RTIL in detecting target molecules (TMs), a novel strategy of ‘sandwich–type’ electrode was established with TMs confined by RTIL between the SWNT/GCE and the RTIL membrane. The strategy was used for electrochemical detection of ascorbic acid (AA) and dopamine (DA), and detection limits of 400 and 80 fmol could be obtained, respectively. The selective detection of DA in the presence of high amount of AA could also be realized. This protocol presented many attractive advantages towards voltammetric detection of TMs, such as low sample demand, low cost, high sensitivity, and good stability.