Polymer crystallization-driven, periodic patterning on carbon nanotubes

We report herein a unique means to periodically pattern polymeric materials on individual carbon nanotubes (CNTs) using a controlled polymer crystallization method. One-dimensional (1D) CNTs were periodically decorated with polymer lamellar crystals, resulting in nano-hybrid shish-kebab (NHSK) structures. The periodicity of the polymer lamellae varies from 20 to 150 nm. The kebabs are approximately 5-10 nm thick (along CNT direction) with a lateral size of approximately 20 nm to micrometers, which can be readily controlled by varying crystallization conditions. Both polyethylene and Nylon 66 were successfully decorated on single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), as well as vapor grown carbon nanofibers (CNFs). The formation mechanism was attributed to "size-dependent soft epitaxy". Because NHSK formation conditions depend on CNT structures, it further provides a unique opportunity for CNT separation. The reported method opens a gateway to periodically patterning polymers and different functional groups on individual CNTs in an ordered and controlled manner, an attractive research field that is yet to be explored.     

A Review Featuring Fabrication,Properties and Applications of Carbon Nanotubes (CNTs) Reinforced Polymer and Epoxy Nanocomposites

Carbon nanotubes (CNTs) have long been recognized as the stiffest and strongest man-made material known to date.In addition,their high electrical conductivity has roused interest in the areas of electrical appliances and communication related applications.However,due to their miniature size,the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers.In order to enhance their chemical affinity to engineering polymer matrices,chemical modification of the graphitic sidewalls and tips is necessary.The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in this attempt to facilitate progress in this emerging area.Recently,carbonaceous nano-fillers such as graphene and carbon nanotubes (CNTs) play a promising role due to their better structural and functional properties and broad range of applications in every field.Since CNTs usually form stabilized bundles due to van der Waals interactions,they are extremely difficult to disperse and align in a polymer matrix.The biggest issues in the preparation of CNTs reinforced composites reside in efficient dispersion of CNTs into a polymer matrix,the assessment of the dispersion,and the alignment and control of the CNTs in the matrix.An overview of various CNT functionalization methods is given.In particular,CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion.In addition,discussions on mechanical,thermal,electrical,electrochemical and applications ofpolymer/CNT composites are also included.     

溶液法制备的碳纳米管薄膜的结构分析与场致电子发射机理研究

结合紫外光电子能谱和拉曼光谱对溶液法制备的碳纳米管薄膜的场致电子发射性能进行研究。采用溶液滴涂法制备的碳纳米管薄膜的场致电子发射开启电场约为3.33 MV/m,阈值电场约为5.44 MV/m,以福勒-诺得海姆(Fowler-Nordheim,FN)理论对电子发射进行解释,其发射的增强因子接近103。通过对紫外光电子能谱的分析,发现碳纳米管薄膜的低能量截止端在外加电场作用下逐步降低,表明纳米管薄膜的表面有效势垒在外加电场作用下逐步下降,从而使得碳纳米管薄膜的电子更加容易发射进入真空。结合拉曼光谱和电学特性的研究,发现界面过渡层的接触电阻与碳纳米管薄膜中的非晶碳成分均可以增强场致电子发射。     

Nanoparticle‐Assisted Alignment of Carbon Nanotubes on DNA Origami

Aligning carbon nanotubes (CNTs) is a key challenge for fabricating CNT‐based electronic devices. Herein, we report a spherical nucleic acid (SNA) mediated approach for the highly precise alignment of CNTs at prescribed sites on DNA origami. We find that the cooperative DNA hybridization occurring at the interface of SNA and DNA‐coated CNTs leads to an approximately five‐fold improvement of the positioning efficiency. By combining this with the intrinsic positioning addressability of DNA origami, CNTs can be aligned in parallel with an extremely small angular variation of within 10°. Moreover, we demonstrate that the parallel alignment of CNTs prevents incorrect logic functionality originating from stray conducting paths formed by misaligned CNTs. This SNA‐mediated method thus holds great potential for fabricating scalable CNT arrays for nanoelectronics.     

Low‐Temperature Growth of Carbon Nanotubes Catalyzed by Sodium‐Based Ingredients

Synthesis of low‐dimensional carbon nanomaterials such as carbon nanotubes (CNTs) is a key driver for achieving advances in energy storage, computing, and multifunctional composites, among other applications. Here, we report high‐yield thermal chemical vapor deposition (CVD) synthesis of CNTs catalyzed by reagent‐grade common sodium‐containing compounds, including NaCl, NaHCO₃, Na₂CO₃, and NaOH, found in table salt, baking soda, and detergents, respectively. Coupled with an oxidative dehydrogenation reaction to crack acetylene at reduced temperatures, Na‐based nanoparticles have been observed to catalyze CNT growth at temperatures below 400 °C. Ex situ and in situ transmission electron microscopy (TEM) reveal unique CNT morphologies and growth characteristics, including a vaporizing Na catalyst phenomenon that we leverage to create CNTs without residual catalyst particles for applications that require metal‐free CNTs. Na is shown to synthesize CNTs on numerous substrates, and as the first alkali group metal catalyst demonstrated for CNT growth, holds great promise for expanding the understanding of nanocarbon synthesis.     

A novel synthesis of polymer brush on multiwall carbon nanotubes bearing terminal monomeric unit

A novel approach to fabricate polymer brushes on the surface of carbon nanotubes (CNTs) is proposed. Carboxyl groups on the surface of chemically oxidized CNTs were reacted with hexamethylene diisocyanate, followed by a reaction with methacrylamide to give terminal vinyl groups‐functionalized CNTs, so called “CNT‐mer.” The synthetic procedure was investigated step‐by‐step and the synthesized CNT‐mer was used to grow polystyrene (PS) from CNTs by a simple in situ polymerization in the presence of a thermal initiator. By employing ¹H NMR, X‐ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and light scattering, the experimental results were verified. Using this approach, 45% PS with respect to CNTs are grafted on the surface of CNTs with about 4.0 nm thickness. This novel technique would provide a facile route to prepare tailor‐made polymer brushes on the surface of CNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6394–6401, 2006     

How a Zigzag Carbon Nanotube Grows

Owing to the unique structure of zigzag (ZZ) carbon nanotubes (CNTs), their ring‐by‐ring growth behavior is different from that of chiral or armchair (AC) CNTs, on the rims of which kinks serve as active sites for carbon attachment. Through first‐principle calculations, we found that, because of the high energy barrier of initiating a new carbon ring at the rim of a ZZ CNT, the growth rate of a ZZ CNT is proportional to its diameter and significantly (10–1000 times) slower than that of other CNTs. This study successfully explained the broad experimental observation of the lacking of ZZ CNTs in CNT samples and completed the theory of CNT growth.     

Bismaleimide/carbon nanotube hybrids for potential aerospace application: I. Static and dynamic mechanical properties

Two kinds of hybrids based on diallyl bisphenol A modified bismaleimide (BMI‐BA) and carbon nanotubes (CNTs) or aminated carbon nanotubes (A‐CNTs) were prepared, their static and dynamic mechanical properties were investigated in detail by using impact and flexural measurements as well as dynamic mechanical analysis (DMA). Results show that these mechanical properties of hybrids greatly depended on the nature (or the functional groups on CNTs) and loading in BMI‐BA matrix of hybrids. For example, the BMI‐BA/A‐CNT hybrid with a desirable amount of A‐CNTs has a higher impact strength than the original BMI‐BA resin, while all BMI‐BA/CNT hybrids have lower impact strength than the original BMI‐BA resin. DMA test shows that all hybrids have somewhat lower storage modulus and glass transition temperature than a pure polymer, which maybe attributed to the fact that both CNTs and A‐CNTs shift the curing peak to a higher temperature range and thus decrease the crosslinking density of networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Photoinduced Formation and Characterization of Electron–Hole Pairs in Azaxanthylium‐Derivatized Short Single‐Walled Carbon Nanotubes

2‐Azaxanthone, a nitrogenated derivative of the well‐studied organic chromophore xanthone, has been covalently bound through 2‐(ethylthio)ethylamido linkers to the carboxylic acid groups of short, soluble single‐walled carbon nanotubes (CNTs) of 450 nm average length, and the resulting azaxanthylium‐functionalized CNTs (AZX‐CNT, 8.5 wt % AZX content) characterized by solution ¹H NMR, Raman and IR spectroscopy and thermogravimetric analysis. Comparison of the quenching of the triplet excited state of AZX (steady‐state and time‐resolved) and of the transient optical spectra of CNTs and AZX‐CNT shows that the covalent linkage boosts the interaction between the azaxanthylium moiety and the short CNT units. The triplet excited state of the azaxanthylium derivative is quenched by CNT with and without covalent bonding, but when it is covalently bonded, the singular transient spectrum is compatible with the photogeneration of electron holes through electron transfer from CNT to excited azaxanthylium units.     

Chiral Carbonaceous Nanotubes Modified with Titania Nanocrystals: Plasmon‐Free and Recyclable SERS Sensitivity

Chiral carbonaceous nanotubes (CNT) were successfully used in plasmon‐free surface‐enhanced Raman scattering (SERS) for the first time. Further modification of TiO₂ nanocrystals on the chiral CNTs successfully realized the recycling of SERS substrate as chiral CNT/TiO₂ hybrids. The high SERS sensitivity of methylene blue (MB) over the chiral CNT/TiO₂ hybrids is ascribed to the laser‐driven birefringence induced by the helical structure, which provides much more opportunities for the occurrence of Raman scattering. The TiO₂ nanocrystals highly dispersed on the surface and inside the hollow cavity of chiral CNTs can completely degrade the MB under the solar light irradiation, leading to the self‐cleaning of SERS substrate. The present research opens a new way for the application of chiral inorganic materials in plasmon‐free SERS detection.     

On the Origin of Water Flow through Carbon Nanotubes

The transport of water molecules through carbon nanotubes (CNTs) is of primary importance for understanding water‐mediated biological activities as well as for the design of novel nanoporous materials. Herein, we analyze the water flow through CNTs by using molecular dynamics simulations with the hope of finding basic parameters determining the flow value. Of particular interest is that a simple equation as a function of water diffusion, occupancy and CNT size, can well describe the water flow through CNTs with different sizes. Specifically, both the simulation and equation flow exhibit power law relations with the CNT diameter and length, where the two exponents are close to each other. The water occupancy and translocation time also demonstrate interesting relations with the CNT size. The water dipole orientations and density profiles are also sensitive to the change of CNT size. These results greatly enhance our knowledge on the nature of water flow through CNTs and are helpful in predicting the water flow of CNTs up to the experimental length scale.     

Chitosan‐Functionalized Carbon Nanotubes as Support for the High Dispersion of PtRu Nanoparticles and their Electrocatalytic Oxidation of Methanol

Carbon nanotubes (CNTs) were non‐covalently functionalized with chitosan (Chit) and then employed as the support for PtRu nanoparticles. The functionalization was carried out at room temperature without the use of corrosive acids, thereby preserving the integrity and the electronic conductivity of the CNTs. Transmission electron microscopy reveals that PtRu nanoparticles were highly dispersed on the surface of Chit‐functionalized CNTs (CNT‐Chit) with small particle‐size. Cyclic voltammetry studies indicated that the PtRu nanoparticle/CNT‐Chit nanohybrids have a higher electrochemical surface area, electrocatalytic performance, and stability towards methanol oxidation compared to PtRu nanoparticles supported on the pristine CNTs.     

Carbon Nanotube‐phenolic Resin Composite Electrode Fabricated by Far Infrared‐assisted Crosslinking for Enhanced Amperometric Detection

The composite of carbon nanotube (CNT) and phenolic resin was prepared in a piece of fused silica capillary based on the far infrared‐assisted crosslinking of phenolic novolac resin in the presence of CNTs and hexamethylenetetramine for electrochemical sensing. The surface morphology and structure of the prepared materials were investigated by scanning electron microscopy, energy dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy. The results indicated that CNTs in the composite was adhered by the crosslinked phenolic resin to form an electrically conductive network. Many broken ends of CNTs appeared on the surface of the composite electrode in the form of a nanoelectrode array. The novel electrode was employed in the amperometric detection of synephrine and hesperidin in Citri Reticulatae Pericarpium in combination with capillary zone electrophoresis. The novel CNT‐based electrode owned the advantages of high sensitivity, low fabrication expense and excellent electrocatalytic performances, indicating great promise for the electrochemical detection in other analysis systems.     

Enhanced photocatalytic activity of mesoporous TiO2 aggregates by embedding carbon nanotubes as electron-transfer channel

Mesoporous multiwalled carbon nanotubes/titanium dioxide (CNTs/TiO(2)) nanocomposites with low loading amounts (0-0.5 wt%) of CNTs embedded inside mesoporous TiO(2) aggregates has been prepared by a simple one-pot hydrothermal method using titanium sulfate as titanium source. The as-prepared CNTs/TiO(2) samples are carefully characterized, analyzed and discussed. In contrast to previous reports with high CNT loading, our results indicate that a low CNT loading slightly influences the textural properties (including crystallite size, degree of crystallinity, specific surface areas, and pore volume etc.) and UV-light absorption of the mesoporous TiO(2) aggregates. The SEM and TEM results demonstrate that the CNTs are mostly embedded in the mesoporous TiO(2) aggregates. Moreover, chemical bonds are formed at the interface between CNTs and TiO(2), which is confirmed by the Raman, IR and XPS analyses. Significantly, we point out that PL analysis in terms of intensity of PL signals seems to not be a reliable way to monitor the recombination rate in the CNTs/TiO(2) composite, due to the quenching effect of CNTs. Instead, the analysis of transient photocurrent responses is introduced, which definitely reflects CNTs as fast electron transfer channels in chemically-bonded CNTs/TiO(2) composites with low CNT loading. Notably, the positive synergy effects of CNTs and TiO(2) depend on both the CNT loading amount and the state of interfacial contacts. In our study, only these chemically bonded CNTs/TiO(2) nanocomposites with appropriate loading amounts (<0.1 wt%) favor the separation of photogenerated electron-hole pairs and decrease their recombination rate and thus display significantly enhanced photocatalytic activity for degrading acetone in air under UV irradiation, as compared with pristine TiO(2) counterparts and commercial P25 photocatalyst. In contrast, a high CNT loading (>0.1 wt%) results in a decrease in photocatalytic activity; a simple mechanical mixing of CNTs and TiO(2) without forming chemical bonds at the interface also results in inferior photocatalytic performance.     

Carbon nanotube growth on high modulus carbon fibres: Morphological and interfacial characterization

Carbon nanotubes (CNTs) were grown directly on the surface of carbon fibres, using the catalytic chemical vapour deposition. FeCo bimetallic catalysts were deposited on carbon fibres using a simple wet impregnation method. CNTs were synthesized over the prepared catalysts by the catalytic decomposition of acetylene at 750^oC. The uniform CNT formation on the fibre surface was verified using scanning electron microscopy. Raman spectroscopy was employed to evaluate non‐destructively the CNT growth and the CNT quality. Thermo gravimetric analysis and differential thermal analysis were employed as destructive methods to confirm the spectroscopic data. Single CNT‐coated fibre fragmentation tests were performed to examine the interfacial shear strength (ISS) of the modified fibres. Acoustic emission was employed to monitor the fragmentation process in real time. Thus, the coated fibre structural integrity was assessed together with its stress transfer properties. Polarized optical microscopy was employed to cross validate the acoustic emission data. It was found that the ISS of the nanotube‐reinforced interphase was improved without affecting the fibre mechanical properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis,Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe³⁺, [Fe(CN)₆]^3? and KCl. Fourier transform infrared spectroscopy, UV‐vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe³⁺ to Fe²⁺ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer‐by‐layer technique. The thus‐prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H₂O₂ reduction.     

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active,Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom‐doped carbon (CNT/HDC) core–sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom‐containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom‐containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom‐doped nanocarbon catalysts in terms of half‐wave potential and kinetic current density. The four‐electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long‐term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.     

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active,Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom‐doped carbon (CNT/HDC) core–sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom‐containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom‐containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom‐doped nanocarbon catalysts in terms of half‐wave potential and kinetic current density. The four‐electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long‐term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.     

Curvature‐dependent adsorption of water inside and outside armchair carbon nanotubes

The curvature dependence of the physisorption properties of a water molecule inside and outside an armchair carbon nanotube (CNT) is investigated by an incremental density‐fitting local coupled cluster treatment with single and double excitations and perturbative triples (DF‐LCCSD(T)) study. Our results show that a water molecule outside and inside (n, n) CNTs (n = 4, 5, 6, 7, 8, 10) is stabilized by electron correlation. The adsorption energy of water inside CNTs decreases quickly with the decrease of curvature (increase of radius) and the configuration with the oxygen pointing toward the CNT wall is the most stable one. However, when the water molecule is adsorbed outside the CNT, the adsorption energy varies only slightly with the curvature and the configuration with hydrogens pointing toward the CNT wall is the most stable one. We also use the DF‐LCCSD(T) results to parameterize Lennard‐Jones (LJ) force fields for the interaction of water both with the inner and outer sides of CNTs and with graphene representing the zero curvature limit. It is not possible to reproduce all DF‐LCCSD(T) results for water inside and outside CNTs of different curvature by a single set of LJ parameters, but two sets have to be used instead. Each of the two resulting sets can reproduce three out of four minima of the effective potential curves reasonably well. These LJ models are then used to calculate the water adsorption energies of larger CNTs, approaching the graphene limit, thus bridging the gap between CNTs of increasing radius and flat graphene sheets. © 2016 Wiley Periodicals, Inc.     

聚乙烯链在碳纳米管侧壁吸附的动力学模拟研究

利用经典的分子动力学模拟方法对聚乙烯(PE)分子在两种不同类型的碳纳米管(CNT)中的吸附进行了研究. 计算了两者之间的扩散系数和相互作用能; 利用PE链自身的扭转角分布和取向参数对PE链构象进行了分析. 结果表明, PE链可以在CNT上很好的吸附, 且PE的构象和吸附位置主要与温度和CNT的半径有关, 与管的类型关系不大.