Layer-by-layer nanotube template synthesis

Electroless deposition of gold on the pore walls of polycarbonate templates is currently the best known method for controlling inside diameters of template-synthesized nanotubes. It would be very useful to have alternative template-based synthetic chemistries that yield nanotubes composed of other materials, but which still allow for precise control over the nanotube wall thickness and i.d. A film-formation process that is based on layer-by-layer deposition of the film-forming material along the pore walls of the template membrane provides this desired alternative synthetic chemistry. We describe here the use of Mallouk's alpha,omega-diorganophosphonate/Zr layer-by-layer film-forming method for preparing nanotubes within the pores of alumina template membranes. We have found that this method allows accurate, quantitative, and predictable control over the wall thickness, and thus i.d., of the layered nanotubes obtained.     

三步升温法合成阵列碳纳米管

本文使用结构简单的单温炉设备, 以二茂铁/三聚氰胺混合物为原料, 采用独特的三步升温方法于光滑的SiO₂衬底上合成出了大面积的阵列碳纳米管, 并对碳纳米管的形貌和结构进行了研究.     

以笼烯为接头的球棒式碳纳米管的电子结构

按照Hamada构造一维至三维球棒式碳纳米管,构造了一些球棒式的笼烯接头的具有C₃/C₅旋转轴的单层碳纳米管.在Hückel近似下,利用群论约化定理计算了它们的π电子结构,并对其稳定性进行了探讨.     

NMR chemical shifts of molecules encapsulated in single walled carbon nanotubes

We present density functional theory calculations of the nuclear magnetic resonance spectroscopy of molecules encapsulated within single walled carbon nanotubes. Ring currents in the nanotube induce shifts in the chemical shift of the nuclei comprising the encapsulated molecule. These changes in the chemical shifts are shown to have characteristic dependence on the chirality of the surrounding nanotubes.     

Single wall carbon nanotube amplification: en route to a type-specific growth mechanism

With the desire to mass produce any specific n,m type of single wall carbon nanotube (SWNT) from a small sample of the same material, we disclose here the preliminary work directed toward that goal. The ultimate protocol would involve taking a single n,m-type nanotube sample, cutting the nanotubes in that sample into many short nanotubes, using each of those short nanotubes as a template for growing much longer nanotubes of the same type, and then repeating the process. The result would be an amplification of the original tube type: a parent SWNT serving as the prolific progenitor of future identical SWNT types. As a proof-of-concept, we use here a short SWNT seed as a template for vapor liquid solid (VLS) amplification growth of an individual long SWNT. The original short SWNT seed was a polymer-wrapped SWNT, end-carboxylated, and further tethered with Fe salts at its ends. The Fe salts were to act as the growth catalysts upon subsequent reductive activation. Deposition of the short SWNT-Fe tipped species upon an oxide surface was followed by heating in air to consume the polymer wrappers, then reducing the Fe salts to Fe(0) under a H2-rich atmosphere. During this heating, the Fe(0) can etch back into the short SWNT so that the short SWNT acts as a template for new growth to a long SWNT that occurs upon introduction of C2H4 as a carbon source. Analysis indicated that the templated VLS-grown long SWNT had the same diameter and surface orientation as the original short SWNT seed, although amplifying the original n,m type remains to be proven. This study could pave the way for an amplified growth process of SWNTs en route to any n,m tube type synthesis from a starting sample of pure nanotubes.     

Distribution patterns and controllable transport of water inside and outside charged single-walled carbon nanotubes

The density distribution patterns of water inside and outside neutral and charged single-walled carbon nanotubes (SWNTs) soaked in water have been studied using molecular dynamics simulations based on TIP3P potential and Lennard-Jones parameters of CHARMM force field, in conjunction with ab initio calculations to provide the electron density distributions of the systems. Water molecules show different electropism near positively and negatively charged SWNTs. Different density distribution patterns of water, depending on the diameter and chirality of the SWNTs, are observed inside and outside the tube wall. These special distribution patterns formed can be explained in terms of the van der Waals and electrostatic interactions between the water molecules and the carbon atoms on the hexagonal network of carbon nanotubes. The electric field produced by the highly charged SWNTs leads to high filling speed of water molecules, while it prevents them from flowing out of the nanotube. Water molecules enter the neutral SWNTs slowly and can flow out of the nanotube in a fluctuating manner. It indicates that by adjusting the electric charge on the SWNTs, one can control the adsorption and transport behavior of polar molecules in SWNTs to be used as stable storage medium with template effect or transport channels. The transport rate can be tailored by changing the charge on the SWNTs.     

Rapid diffusion of CH4/H2 mixtures in single-walled carbon nanotubes

Equilibrium molecular dynamics (EMD) are used to examine the self-diffusion and macroscopic diffusion of CH4/H2 mixtures adsorbed inside a (10,10) single-walled carbon nanotube. EMD can be used to determine the macroscopic diffusion coefficients of adsorbed mixtures by evaluating the matrix of Onsager transport coefficients. Earlier studies have indicated the diffusion of light gases adsorbed as single components in carbon nanotubes is extremely rapid compared to that in other known nanoporous materials. The results presented here indicate that extremely rapid diffusion can also occur for mixtures of adsorbed molecules. The rapid diffusion of adsorbed molecules and the strong coupling between the fluxes of the adsorbed species in a mixture have interesting implications for uses of carbon nanotubes in membrane-based applications.     

Supramolecular self-assembly of amphiphiles on carbon nanotubes: a versatile strategy for the construction of CNT/metal nanohybrids, application to electrocatalysis

Homogeneous coating of carbon nanotubes with metallic nanoparticles was achieved using supramolecular auto-organization of amphiphilic molecules as template. The resulting Pd nanoparticles/carbon nanotube nanohybrids were then evaluated in electrocatalysis experiments, showing superior activity in ethanol oxidation compared to analogous systems.     

Modifying the response of a polymer-based quartz crystal microbalance hydrocarbon sensor with functionalized carbon nanotubes

This report compares the performance of polymer and carbon nanotube-polymer composite membranes on a quartz crystal microbalance (QCM) sensor for the detection of aromatic hydrocarbons (benzene, toluene, ethylbenzene, p-xylene and naphthalene) in aqueous solutions. Several different polymers (polystyrene, polystyrene-co-butadiene, polyisobutylene and polybutadiene) and types of functionalized carbon nanotubes (multi-walled and single-walled carbon nanotubes) were investigated at varying carbon nanotube (CNT) loading levels and film thicknesses. In a majority of instances, the difference in response between membranes comprising pure polymer and membranes containing 10% (w/w) carbon nanotubes were not statistically significant. However, a notable exception is the decreasing sensitivity towards p-xylene with increasing carbon nanotube content in a polybutadiene film. This variation in sensitivity can be attributed to a change in the sorption mechanism from absorption into the polymer phase to adsorption onto the carbon nanotube sidewalls. With much thicker coatings of 10% (w/w) carbon nanotube in polybutadiene, the sensitivity towards toluene was higher compared to the pure polymer. The increased toluene sensitivity may be partially attributed to an increase in the sorption capacity of a carbon nanotube polymer composite film relative to its corresponding pure polymer film. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements were performed to understand the mechanism of sorption and these studies showed that the addition of functionalized CNT to the polymer increases the absorption of certain types of hydrocarbons. This study demonstrates that carbon nanotubes can be incorporated into a polymer-coated QCM sensor and that composite films may be used to modify the QCM response and selectivity during the analysis of complex hydrocarbon mixtures.     

DNA‐Mediated Copper Nanoparticle Formation on Dispersed Single‐Walled Carbon Nanotubes

A new and facile method for the preparation of single‐walled carbon nanotubes (SWCNTs) decorated with Cu nanoparticles (CuNPs) formed on a double‐stranded DNA template in aqueous solution has been developed. A specially designed synthetic DNA sequence, containing a single‐stranded domain for the dispersion of carbon nanotubes and double‐stranded domains for the selective growth of CuNPs, was utilized. The final SWCNT/CuNP hybrids were characterized using fluorescence spectroscopy and transmission electron microscopy. The analyses clearly demonstrated the selective formation of uniform CuNPs on the carbon nanotube scaffold.     

Quantum Chemical Study of Water Adsorption on the Surfaces of SrTiO3 Nanotubes

We have studied the adsorption of water molecules on the inner and outer surfaces of nanotubes generated by rolling (001) layers of SrTiO₃ cubic crystals. The stability and the atomic and electronic structures of the adsorbed layers are determined by using hybrid density functional theory. The absorption energy and the preferred adsorbate structure are essentially governed by the nature of the surface of the nanotube. Dissociative adsorption prevails on the outer nanotube surfaces. The stability of the adsorbed layers on the inner surfaces is related to the possibility of the formation of hydrogen bonds between water molecules and surface oxygen atoms, and depends on the surface curvature. The presence of water molecules on the inner surface of the nanotubes leads to an increase of the electronic band gap. Externally TiO₂‐terminated nanotubes could be used for the photocatalytic decomposition of water by ultraviolet radiation.     

氧化铝模板上定向纳米碳管的快速生长及超声切短

在阳极氧化铝（AAO）模板上电沉积催化剂,快速生长了定向纳米碳管,纳米碳管以顶部生长模式生长.采用了超声的方法来切短露头于AAO模板的纳米碳管,增加纳米碳管膜的定向性.结果显示随着超声时间的增加,纳米碳管的定向性增加.位于纳米碳管膜顶部的催化剂在碳管切短的同时被去除,得到了顶部开口的纳米碳管.解释了纳米碳管被超声切短的机理.     

Metal induced molecular nano-extraction

We have previously devised a “scorpion” like system which is composed of a zigzag (8,0) single walled carbon nanotube attached to a 20 ringed graphene sheet by a glycine dimer species. Theoretical density functional theory calculations on a potential mechanism driven by a metal induced charge transfer process has been proposed for the extraction of molecules from nanotubes.     

Amphoteric doping of carbon nanotubes by encapsulation of organic molecules: electronic properties and quantum conductance

In order to investigate and optimize the electronic transport processes in carbon nanotubes doped with organic molecules, we have performed large-scale quantum electronic structure calculations coupled with a Green's function formulation for determining the quantum conductance. Our approach is based on an original scheme where quantum chemistry calculations on finite systems are recast to infinite, non-periodic (i.e., open) systems, therefore mimicking actual working devices. Results from these calculations clearly suggest that the electronic structure of a carbon nanotube can be easily manipulated by encapsulating appropriate organic molecules. Charge transfer processes induced by encapsulated organic molecules lead to efficient n- and p-type doping of the carbon nanotube. Even though a molecule can induce p and n doping, it is shown to have a minor effect on the transport properties of the nanotube as compared to a pristine tube. This type of doping therefore preserves the intrinsic properties of the pristine tube as a ballistic conductor. In addition, the efficient process of charge transfer between the organic molecules and the nanotube is shown to substantially reduce the susceptibility of the pi electrons of the nanotube to modification by oxygen while maintaining stable doping (i.e., no dedoping) at room temperature.     

Y型分支的碳纳米管的氧化铝模板法制备及其表征(英文)

利用两步氧化法,通过对氧化直流电压进行周期性调制可制备出带有Y型孔道的氧化铝模板;然后以金属钴为催化剂,乙炔为碳源,通过CVD法制取得到具有规则Y型分支的碳纳米管阵列.已制备出的碳管分支角度在20°～120°的范围内.实验表明,两段分支所成的角度以及分支的长度与合成氧化铝模板的脉冲电压调节规律有关,短脉冲,高氧化电压有利于生长出的短而密集的分支构型.     

Growth of conical carbon nanotubes by chemical reduction of MgCO3

Carbon nanotubes were synthesized by chemical reduction of magnesium carbonate with metallic lithium at 600 degrees C. The nanotubes with an average length of 13 microm and diameter of 60 nm are made of short coaxial conical cylinder tubular graphite sheets with their cone axis parallel to the tube axis, different from the ordinary carbon nanotubes, composed of concentric cylindrical graphite layers with their normal perpendicular to the tube axis. It is suggested that nanoscale rough surface of lithium formed at the interface between supercritical carbon dioxide and liquid lithium takes the roles of both the reductant for reduction of carbon dioxide to carbon and the template for growth of carbon nanotubes.     

DNA mediated assembly of single walled carbon nanotubes: role of DNA linkers and annealing

With the high demand for nanoelectronic devices, extensive research has focused on the use of single walled carbon nanotubes (CNTs) due to their high electron carrier mobility, large tensile strength, and single nanometer dimensions. Despite their promise, however, their applicability has been greatly hindered by the inherent difficulties of both separating nanotubes of different chiralities and diameters and positioning them from metallic tubes and positioning them in a precise location on a surface. In recent years, single stranded DNA (ssDNA) has been identified as a potential solution for both of these problems since DNA can be used to both separate the different types of CNTs as well as direct their organization. We demonstrate here the first principles on how to guide CNT assembly directly on surfaces from solution by specific DNA hybridization. It was found that the specific DNA sequence used to disperse the carbon nanotubes greatly influences the adsorption and specificity of nanotube binding to the surface. Furthermore, we demonstrate here that thermal annealing can correct misaligned tubes or incorrect binding. These studies provide an excellent foundation for employing two-dimensional DNA templates for CNT organization for nanoelectronic logic and memory based applications. Furthermore, using a single biomaterial to both sort and place CNTs in minimal steps would greatly help the throughput, manufacturability, and cost of such devices.     

Immobilized carbon nanotubes as matrix for MALDI-TOF-MS analysis: Applications to neutral small carbohydrates

In this work, we reported on the advantages of immobilized carbon nanotubes as a novel MALDI-matrix. Recently, carbon nanotubes have been reported to be an effective MALDI matrix for small molecules (Anal. Chem.2003, 75, 6191), as it can eliminate the interfering matrix peaks as well as form a web morphology to fully disperse the analyte and allow strong ultraviolet absorption for enhanced pulsed laser desorption and ionization. In our study, to overcome the problem that the carbon nanotube matrix may fly off from the target, a type of polyurethane adhesive, NIPPOLAN-DC-205, is introduced to immobilize carbon nanotubes on the target, which enables widespread application of carbon nanotubes as matrix for MALDI-MS analysis. At the same time, the properties of the carbon nanotubes as an efficient matrix remained after immobilization. The presence of NIPPOLAN-DC-205 increases the time for analysis at a particular desorption spot by minimizing the time-consuming search for "hot spots" and facilitating experiments such as post source decay (PSD) which need longer-lasting signals. Moreover, NIPPOLAN-DC-205 produces no interference peaks and can easily be cleaned with acetone. Fast evaporation technology may be used to enhance signal reproducibility in MALDI analysis using carbon nanotubes as matrix. Consequently, the applicability of the carbon nanotube as matrix for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of low molecular mass analytes is highly improved. The feasibility of the method employing polyurethane is demonstrated by comparison of the results produced from the carbon nanotube matrix with and without immobilization. In addition, neutral small carbohydrates, which are difficult to be ionized normally, can be cationized with high efficiency by MALDI-TOF-MS using the immobilized carbon nanotube matrix. The method was further applied to analyze peptides and detect urine glucose successfully.     

Transport diffusion of gases is rapid in flexible carbon nanotubes

Molecular dynamics simulations of rigid, defect-free single-walled carbon nanotubes have previously suggested that the transport diffusivity of gases adsorbed in these materials can be orders of magnitude higher than any other nanoporous material (A. I. Skoulidas et al., Phys. Rev. Lett. 2002, 89, 185901). These simulations must overestimate the molecular diffusion coefficients because they neglect energy exchange between the diffusing molecules and the nanotube. Recently, Jakobtorweihen et al. have reported careful simulations of molecular self-diffusion that allow nanotube flexibility (Phys. Rev. Lett. 2005, 95, 044501). We have used the efficient thermostat developed by Jakobtorweihen et al. to examine the influence of nanotube flexibility on the transport diffusion of CH4 in (20,0) and (15,0) nanotubes. The inclusion of nanotube flexibility reduces the transport diffusion relative to the rigid nanotube by roughly an order of magnitude close to zero pressure, but at pressures above about 1 bar the transport diffusivities for flexible and rigid nanotubes are very similar, differing by less than a factor or two on average. Hence, the transport diffusivities are still extremely large compared to other known materials when flexibility is taken into account.     

Linear and nonlinear optical characterization of a tetraphenylporphyrin-carbon nanotube composite system

We present a study of tetraphenylporphyrin composites formed with single-walled carbon nanotubes (SWNTs). Stable porphyrin/SWNT composite solutions were obtained by non-covalent bonding between the carbon nanotubes and conjugated tetraphenylporphyrin molecules. Transmission electron microscopy reveals porphyrin molecules adhering to the nanotube surface. We report on the first complete linear and nonlinear optical characterization of these nanocomposite materials. The composite solutions were found to be superior optical limiters to nanotubes alone, and to all porphyrin systems studied, including metalloporphyrins.