Ozonolysis of functionalized single-walled carbon nanotubes

Room temperature ozonolysis of fluorinated SWNT and phenyl-sulfonated SWNT have been studied in perfluoropolyether (PFPE) solvents. Etching at the end caps (approximately 70 nm/hour for fluorinated SWNT/PFPE suspension with 1 g/l concentration) has been demonstrated to be the dominating effect during the ozonolysis of fluorinated SWNT. Base on characterization by AFM analysis, X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy, fluorination along the SWNT sidewalls protects F-SWNT from extensive functionalization by ozonolysis. An ozone reaction with fluorinated SWNT has been found to improve its solubility in 96% sulfuric acid. This allows oxidative cutting by ammonium peroxydisulfate without defluorination. In comparison to fluorinated SWNT, phenyl-sulfonated SWNT was found to be effectively and homogeneous cut by ozonolysis in a water suspension.     

Chemically functionalized water soluble single-walled carbon nanotubes modulate neurite outgrowth

We report the use of chemically-functionalized water soluble single-walled carbon nanotube (SWNT) graft copolymers for modulation of outgrowth of neuronal processes. The graft copolymers were prepared by the functionalization of SWNTs with poly-m-aminobenzene sulphonic acid and polyethylene glycol. When added to the culturing medium, these functionalized water soluble SWNTs were able to increase the length of various neuronal processes.     

Chemically functionalized water-soluble single-walled carbon nanotubes modulate morpho-functional characteristics of astrocytes

We report the use of chemically functionalized water-soluble single-walled carbon nanotubes (ws-SWCNTs) for the modulation of morpho-functional characteristics of astrocytes. When added to the culturing medium, ws-SWCNTs were able to make astrocytes larger and stellate/mature, changes associated with the increase in glial fibrillary acidic protein immunoreactivity. Thus, ws-SWCNTs could have more beneficial effects at the injury site than previously thought; by affecting astrocytes, they could provide for a more comprehensive re-establishment of the brain computational power.     

Poly(ethylene-co-vinyl alcohol) functionalized single-walled carbon nanotubes and related nanocomposites

Single-walled carbon nanotubes (SWNTs) were functionalized by poly(ethylene-co-vinyl alcohol) (EVOH) copolymer under carbodiimide-activated esterification reaction conditions. Similar to the parent EVOH copolymer, the EVOH-functionalized carbon nanotubes are soluble in highly polar solvent systems such as DMSO and hot ethanol-water mixtures. The soluble EVOH-SWNT sample was characterized by various techniques, including optical absorption, Raman, NMR, electron microscopy, and thermogravimetric analysis. The common solubility of EVOH and EVOH-SWNT allowed their intimate mixing in solution, and thus the fabrication of nanocomposites in which the SWNTs are homogeneously dispersed in the polymer matrix.     

Dispersions of functionalized single-walled carbon nanotubes in strong acids: solubility and rheology

The manipulation and processing of single-wall carbon nanotubes (SWNTs) is limited by their poor solubility in most common solvents. Covalent sidewall functionalization of SWNTs provides an excellent route to improve their solubility. Here we have studied the relationship between sidewall functionalization and phase behavior of solutions of functionalized SWNTs (f-SWNTs) in strong acids. We use centrifugation in conjunction with UV-Vis-nlR spectroscopy to quantify the solubility of f-SWNTs in strong acids. We image the dispersions of functionalized tubes by polarized light microscopy. We find that adding butyl groups increases marginally the solubility of SWNTs in 102% sulfuric acid in the isotropic phase; adding 9-nonadecyne groups roughly doubles the solubility of SWNTs. Viscosity measurements in dilute solutions are sensitive to de-bundling. We compare the viscosity-concentration dependence of dilute pristine and f-SWNTs to assess whether and how functionalization promotes de-bundling and stabilizes the tubes. The phase behavior and rheology of these f-SWNTs parallels with that of pristine SWNTs; 9-nonadecylated SWNTs have higher solubility and should be easier to process.     

Attachment of functionalized single-walled carbon nanotubes (SWNTs) to silicon surfaces

Single-walled carbon nanotubes (SWNTs) were functionalized by direct fluorination and subsequent reaction with 6-aminohexanoic acid for water-soluble carboxylic acid functionalized SWNTs (AHA-SWNTs). Both of the compounds were used as precursors to attach SWNTs to APTES coated silicon surfaces. AHA-SWNTs in aqueous solution were reacted with APTES self-assembled monolayers (SAMs) with coupling reagents N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS). The surface coverage is a function of concentration of AHA-SWNTs, solvent and coupling method. While for the fluorinated SWNTs (F-SWNTs), direct addition of F-SWNTs to preformed APTES SAMs at 90 degrees C shows essentially no reaction, in contrast to the one-pot reaction of F-SWNTs with APTES molecules in the presence of SWNTs on a silicon substrate. This reaction route provides a convenient method to attach SWNTs to silicon surfaces.     

Cutting single-walled carbon nanotubes

A two-step process is utilized for cutting single-walled carbon nanotubes (SWNTs). The first step requires the breakage of carbon-carbon bonds in the lattice while the second step is aimed at etching at these damage sites to create short, cut nanotubes. To achieve monodisperse lengths from any cutting strategy requires control of both steps. Room-temperature piranha and ammonium persulfate solutions have shown the ability to exploit the damage sites and etch SWNTs in a controlled manner. Despite the aggressive nature of these oxidizing solutions, the etch rate for SWNTs is relatively slow and almost no new sidewall damage is introduced. Carbon-carbon bond breakage can be introduced through fluorination to ～C(2)F, and subsequent etching using piranha solutions has been shown to be very effective in cutting nanotubes. The final average length of the nanotubes is approximately?100?nm with carbon yields as high as 70-80%.     

Formylation of single-walled carbon nanotubes

We report an improved, elegant method for the covalent formylation of single-wall carbon nanotubes (SWNTs) via formyl transfer from N-formylpiperidine, which could potentially open the gateway for more versatile chemical modification of carbon nanotube (CNT) walls than is possible via other reported functionalisation methods. The formylation reaction does not inflict damage upon the pristine CNT structure, unlike the currently commonly used carboxylation route, and involves much fewer steps, and takes considerably less time, than most other reported routes. The modified SWNTs have been characterised by Raman spectroscopy, ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy and "covalent tagging" with derivatising groups followed by thermogravimetric analysis-mass spectroscopy (TGA-MS). UV-vis-NIR spectroscopy shows that there is only limited disruption of the intrinsic electronic structure of the SWNTs. This is confirmed from estimates of the extent of functionalisation from TGA-MS, which suggest that it may be as low as 2 atomic per cent.     

Purification of single-walled carbon nanotubes

The discovery of carbon nanotubes (CNTs) created much excitement and stimulated extensive research into the properties of nanometer-scale cylindrical networks. From then on, various methods for the synthesis and characterization of aligned CNTs-both single-walled (SWCNTs) and multi-walled (MWCNTs) by different methods have been hotly pursued. Unfortunately, most methods currently in use produce raw multi component solid products, only a small fraction of which contains carbon nanotubes. The balance of the material is composed of residual catalyst particles (some of which are encased in concentric graphitic shells), fullerenes, other graphitic materials and amorphous carbon. These impurities cause a serious impediment for their detailed characterization and applications. If the carbon nanotube is ever to fulfill its promise as an engineering material, large, high quality aliquots will be required. A number of purification methods involving elimination processes such as physical separation, gas phase and liquid phase oxidation in combination with chemical treatments have been developed for nanotube materials. Though the quantitative determination of purity remains controversial, reported yields are best regarded with an appropriate level of skepticism on the method of assay. In this article, a review is given on the past and recent advances in purification of SWCNTs.     

Co-synthesis of single-walled carbon nanotubes and carbon fibers

A new vertical floating catalytic technique is developed and used to prepare both single-walled carbon nanotubes (SWNTs) and carbon fibers (CFs). Scanning electron microscopy (SEM) observation shows a clear separation of these two materials. Thin films of SWNTs can be peeled easily from the CF substrate which just acts as a catalyst support for the SWNT growth. The production process is also semicontinuous, resulting in a yield of ∼1.0 g h⁻¹ of SWNTs film with high purity. Structure and vibrational properties of these materials are investigated by electron microscopy and Raman spectroscopy, respectively.     

Chiral-angle distribution for separated single-walled carbon nanotubes

Chiral indices (n, m) of metallic and semiconducting single-walled carbon nanotubes (SWNTs) selectively separated via the density-gradient ultracentrifugation process were individually assigned by using an aberration-corrected transmission electron microscope (TEM) operated at 80 kV. Our statistical analysis revealed that armchair (n, n) and chiral (n, n-3) SWNTs with large chiral angles (>20 degrees) are dominant metallic nanotubes in the separated samples, whereas such a noticeable preference of particular indices was not observed for semiconducting nanotubes. Some significant discrepancies were found between the TEM and spectroscopic results on the major chiral indices and the metal/semiconductor ratios in these SWNTs.     

单壁碳纳米管的提纯方法

采用温控电弧炉，在600℃下，使用Fe／Ni/Mg催化剂大量制备了单壁碳纳米管。用两步纯化方法对单壁纳米管进行提纯：首先，原始的单壁碳纳米管在500℃，空气中加热30min；接着用37％的盐酸浸泡加热后的样品72h，水洗过滤后烘干,通过SEM、TGA、HRTEM和激光拉曼表征，纯化后单壁碳纳米管的纯度可高达95％，其直径范围为：1.24-1.38nm。     

Optical properties of single-walled carbon nanotubes functionalized with copolymer poly(3,4-ethylenedioxythiophene-co-pyrene)

Optical properties are reported for composites based on single-walled carbon nanotubes (SWNTs) and copolymer poly(3,4-ethylenedioxythiophene-co-pyrene) (PEDOT-Py) prepared by chemical polymerization of two monomers in the presence of carbon nanotubes. A charge transfer between SWNTs and the PEDOT-Py copolymer was demonstrated by Raman scattering. The increase in the relative intensity of the Raman lines peaked at 440–577 cm⁻¹, which were assigned to the ethylenedioxy ring vibrational modes, indicated a significant hindrance steric in the case of the composites based on the PEDOT-Py copolymer and metallic SWNTs. The increase in the absorbance of IR band peaked at 984 cm⁻¹ occurred simultaneously with the disappearance of the IR band at 1639 cm⁻¹. This finding was a consequence of the formation of new covalent bonds between SWNTs and the thiophene and benzene rings of the repeating units of the PEDOT-Py copolymer. The photoluminescence (PL) quenching process of the PEDOT-Py copolymer was induced by semiconducting SWNTs. The PL quenching of PEDOT-Py copolymer in the presence of SWNTs was demonstrated based on the energy level diagrams of the two constituents of the PEDOT-Py/SWNTs composite material.     

Optically active single-walled carbon nanotubes

The optical, electrical and mechanical properties of single-walled carbon nanotubes (SWNTs) are largely determined by their structures, and bulk availability of uniform materials is vital for extending their technological applications. Since they were first prepared, much effort has been directed toward selective synthesis and separation of SWNTs with specific structures. As-prepared samples of chiral SWNTs contain equal amounts of left- and right-handed helical structures, but little attention has been paid to the separation of these non-superimposable mirror image forms, known as optical isomers. Here, we show that optically active SWNT samples can be obtained by preferentially extracting either right- or left-handed SWNTs from a commercial sample. Chiral 'gable-type' diporphyrin molecules bind with different affinities to the left- and right-handed helical nanotube isomers to form complexes with unequal stabilities that can be readily separated. Significantly, the diporphyrins can be liberated from the complexes afterwards, to provide optically enriched SWNTs.     

Three dimensional single-walled carbon nanotubes

We report a simple fabrication method of creating a three-dimensional single-walled carbon nanotube (CNT) architecture in which suspended CNTs are aligned parallel to each other along the conventionally unused third dimension at lithographically defined locations. Combining top-down lithography with the bottom-up block copolymer self-assembly technique and utilizing the excellent film forming capability of polymeric materials, highly uniform catalyst nanoparticles with an average size of 2.0 nm have been deposited on sidewalls for generating CNTs with 1 nm diameter. This three-dimensional platform is useful for fundamental studies as well as technological exploration. The fabrication method described herein is applicable for the synthesis of other very small 1D nanomaterials using the catalytic vapor deposition technique.     

Chemically functionalized carbon nanotubes

Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.     

Biocompatibility of immobilized aligned carbon nanotubes

In vivo host responses to an electrode-like array of aligned carbon nanotubes (ACNTs) embedded within a biopolymer sheet are reported. This biocompatibility study assesses the suitability of immobilized carbon nanotubes for bionic devices. Inflammatory responses and foreign-body histiocytic reactions are not substantially elevated when compared to negative controls following 12 weeks implantation. A fibrous capsule isolates the implanted ACNTs from the surrounding muscle tissue. Filamentous nanotube fragments are engulfed by macrophages, and globular debris is incorporated into the fibrous capsule with no further reaction. Scattered leukocytes are observed, adherent to the ACNT surface. These data indicate that there is a minimal local foreign-body response to immobilized ACNTs, that detached fragments are phagocytosed into an inert material, and that ACNTs do not attract high levels of surface fouling. Collectively, these results suggest that immobilized nanotube structures should be considered for further investigation as bionic components.     

单壁碳纳米管束的排布

流体排布法是实现碳纳米管定向排列的一种简单的方法。采用流体排布法在具有浸润性图案化的基底上成功地对单壁碳纳米管(SWNTs)束进行了水平方向上的排布。将SWNTs悬浮液滴入光刻胶制成的微通道中,在流体剪切力作用下,弯曲的SWNTs在一定程度上会被拉伸并且平行地排列在纳米级宽度的微通道中。将排列好的SWNTs阵列转移到一些不同间距的金电极对上面,制作成碳纳米管场效应晶体管(CNTFET)。CNTFET的电性能测试结果表明,制备的SWNTs束可以制造出不同电极间距同时具有良好电性能的CNTFET。     

Band theory of single-walled carbon nanotubes

In this paper, a curvilinear coordinate system is used in space and in k-space to study the energy band of single-walled carbon nanotubes wrapped at a helical angle. Using this method, a general function of the bandgap associated with the radius of the tube and the helical angle is derived based on the tight-binding theory. The three-dimensional hexagonal Brillouin zone of the tube is on the surface of cylinder in the k-space. For two tubes with different diameters, there is a distance between the cylindrical Brillouin zones in the radial direction. The Brillouin zone varies with the radius of the tube and the number of cells on the circumference. For the metallic zigzag tubes, the bandgaps decrease discretely to zero at the corners of the Brillouin zones, and those corners are singular points of zero gaps. With the transformation of coordinates, the metallic zigzag type is proven to be equivalent to an armchair configuration. Electrical characteristics of the chiral effects are briefly highlighted.