不同催化剂对热解法制备CNx纳米管的影响

CNx nanotubes was synthesized by thermal decomposition ethylenediamine catalyzed by pure iron, cobalt, nickel, and ferrocene. The effect of the catalyst on the CNx nanotubes’ morphology and yield was studied. The catalysis growth mechanism was also discussed. The CNx nanotubes with the “bamboo-like” structure and lower yield are produced when iron or ferrocene is used as the catalyst, whereas the curved CNx nanotubes with many pleats through the nanotube walls and higher yield are generated when cobalt is used. The CNx nanotubes catalyzed by nickel are only helix tubes with the diameter of about 500 nm. Raman spectroscopy studies show that the CNx nanotubes catalyzed by ferrocene have a worse crystallinity due to a higher nitrogen incorporation.     

Carbon nanotube formation and growth via particle-particle interaction

Carbon nanotubes are observed to form under a wide range of temperatures, pressures, reactive agents, and catalyst metals. In this paper we attempt to rationalize this body of observations reported in the literature in terms of fundamental processes driving nanotube formation. Many of the observed effects can be attributed to the interaction of three key processes: surface catalysis and deposition of carbon, diffusive transport of carbon, and precipitation effects. A new nanotube formation mechanism is proposed that describes the nanotube structures observed experimentally in a premixed flame and can account for certain shortcomings of the prevailing mechanism that has been repeatedly applied to explain nanotube formation in nonflame environments. The interacting particle model (IPM) attributes the initiation of nanotube growth to the physical interaction between catalyst particles. Coalescence of two (or more) catalyst particles leads to partial blocking of the particle surface, causing a disparity in carbon deposition over the particle surface. The resulting concentration gradient generates a net diffusive flux toward the interparticle contact point. Dimers that separate in this condition can support continuous nanotube growth between the particles. The model can also be extended to multiple particles to account for more complex morphologies. The IPM is consistent with many of the structures observed in the flame-produced material. The validity of the model is evaluated through analysis of diffusion dynamics and a force analysis of particle binding and separation. The IPM is also discussed in relation to identifying the requirements and best conditions to support nanotube growth in the premixed flame. The formation of nanotubes between particles as described by the IPM indicates that a single mechanism cannot completely describe nanotube synthesis; more likely, multiple pathways exist with varying rates that depend on specific process conditions.     

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.     

Linear nano-templates of styrene and maleic anhydride alternating copolymers

Poly(styrene-alt-maleic anhydride) (SMA) self-assembles in aqueous solution to form nanotube structures. These can be used as templates to linearly guide the growth of a secondary polymeric or inorganic material. Templates are made starting from a basic SMA solution, followed by slow pH decrease by dialysis against deionized water, until a 50% degree of protonation is reached. The nanotube structure is composed of multiple polymer chains, associating sideways by π-stacking to form the nanotube walls. The SMA templates were used to grow linear composites, which shows the applicability of the template properties and also confirms the nanotube association mechanism. Linear polymer composites were formed using this SMA template: pyrrole was polymerized, silver nitrate was reduced to silver and silver cyanide nanowires were grown.     

Direct electron transfer in nanostructured sol-gel electrodes containing bilirubin oxidase

Bilirubin oxidase encapsulated within a silica sol-gel/carbon nanotube composite electrode effectively catalyzed the reduction of molecular oxygen into water through direct electron transfer at the carbon nanotube electrode surface. In this nanocomposite approach, the silica matrix is designed to be sufficiently porous for substrate molecules to have access to the enzyme and yet provides a protective cage for immobilization without affecting biological activity. The incorporation of carbon nanotubes adds electrical connectivity and increases active electrode surface area. The standard surface electron transfer rate constant was calculated to be 59 s(-1) which indicates that the carbon nanotube side walls are primarily responsible for electron transfer. The use of direct electron transfer processes simplifies biofuel cell fabrication by eliminating the need for redox mediator and ion-conducting separators.     

The formation of low-dimensional inorganic nanotube crystallites in carbon nanotubes

The filling of carbon nanotubes, which vary in diameter and morphology, is directly observed by molecular dynamics computer simulation with a potential model which thermodynamically favors a four-coordinate bulk crystal structure. Inorganic nanotube (INT) structures form which are based on percolating hexagonal nets. For small carbon nanotube diameters the filling is shown to proceed via an "internal wetting" mechanism, which depends on the internal carbon nanotube area rather than the free volume. Both single- and double-walled INTs are predicted to form. The atomistic formation mechanisms are discussed and an intermediate structure identified. The INT structures, including the observed intermediate, are discussed by reference to a simple energy landscape. The formation energetics are discussed in terms of a simple analytical model which combines the INT strain energy and the tube-tube interactions. An effective phase diagram, which predicts the INT morphologies as a function of carbon nanotube diameter, is derived and discussed with respect to the analytical model.     

Theoretical study on interaction of hydrogen with single-walled boron nitride nanotubes. II. Collision, storage, and adsorption

Collision and adsorption of hydrogen with high incident kinetic energies on a single-walled boron nitride (BN) nanotube have been investigated. Molecular-dynamics (MD) simulations indicate that at incident energies below 14 eV hydrogen bounces off the BN nanotube wall. On the other hand, at incident energies between 14 and 22 eV each hydrogen molecule is dissociated at the exterior wall to form two hydrogen atoms, but only one of them goes through the wall. However, at the incident energies between 23 and 26 eV all of the hydrogen atoms dissociated at the exterior wall are found to be capable of going inside the nanotube and then to recombine to form hydrogen molecules inside the nanotube. Consequently, it is determined that hydrogen should have the incident energy >22 eV to go inside the nanotube. On the other hand, we find that the collisions using the incident energies >26 eV could result in damaging the nanotube structures. In addition our MD simulations find that hydrogen atoms dissociated at the wall cannot bind to either boron or nitrogen atoms in the interior wall of the nanotube.     

生长中纳米碳管的电子结构

利用第一原理的离散变分方法计算了生长中纳米碳管团簇的电子结构,发现悬挂键的存在导致管口处的电子结构明显地不同于管体,对应的非键合价电子不仅直接改变管口处碳原子之间的键合模式,而且进一步增强管口处碳原子之间的结合,促使碳原子只向管芯移动,这与实验中观察到的封闭顶端的几何形态相一致;而且降低碳管的化学稳定性.与完整型纳米碳管截然不同的电子结构决定了生长中纳米碳管在合成纳米材料过程中具有不同的作用行为.     

Bottom-up Synthesis and Thread-in-Bead Structures of Finite (n,0)-Zigzag Single-Wall Carbon Nanotubes

The last remaining synthetic target of finite single-wall carbon nanotube models, the zigzag nanotube, has been accomplished through bottom-up chemical synthesis. The zigzag nanotube was synthetically accessible without constructing long-sought yet elusive cyclacene structures but with a cycloarylene structure by devising its cutout positions. The persistent tubular shape was also perfected in this last model by cyclization of zigzag-shaped aromatic molecules with a synchronous topological arrangement. The crystal structure of this nanotube further revealed an entangled supramolecular assembly, which showed a novel way to align nanotube molecules by utilizing their open-end functional groups in a thread-in-bead molecular assembly.     

Carbon Nanotubes with Phthalocyanine-Decorated Surface Produced by NH3-Assisted Microwave Reaction and Their Catalytic Performance in Li/SOCl2 Battery

Multiwalled carbon nanotube (MWCNT)‐templated cobalt phthalocyanine (CoPc) assemblies are prepared by microwave reaction with the aid of NH₄Cl. The assemblies of CoPc/MWCNTs are added to the electrolyte of Li/SOCl₂ battery to show their potential application in the field of catalysis. The assemblies display a uniform coaxial nanotube structure. In the control test, the CoPc/MWCNTs synthesized without NH₄Cl exhibit the aggregation of the nanotubes of CoPc/MWCNTs. It indicates that the use of NH₄Cl as gas source is efficient in enhancing diffusion of the MWCNTs and controlling the growth of CoPc. The catalytic reduction of SOCl₂ can be carried out by CoPc molecules outside the assemblies and the MWCNTs inside the assemblies. The assemblies of CoPc/ MWCNTs exhibit excellent electrochemical catalytic activity to Li/SOCl₂ battery. The discharge energy of Li/SOCl₂ battery catalyzed by CoPc/MWCNTs is 144% higher than that of the battery without catalyst, and is 94% higher than the energy of Li/SOCl₂ battery catalyzed by bulk CoPc.     

Anodic oxidation of hydrazine at carbon nanotube powder microelectrode and its detection

Carbon nanotube powder microelectrodes (CNTPMEs) were used to study the anodic oxidation of hydrazine at Carbon nanotube (CNT)-the novel carbon material. It was found that the electrochemical behaviours were greatly improved at CNTs, indicating that the anodic oxidation could be catalyzed at CNTs. The kinetics parameters of this process were calculated, the heterogeneous electron transfer rate constant k was 0.0019 cm s(-1), (1-alpha)n(alpha) was 0.22. The CNTPMEs were also found with high sensitivity for hydrazine detection, could be used as hydrazine sensors.     

Controlling growth of aligned carbon nanotubes from porous silicon templates

Fabricating well-aligned carbon nanotubes, especially, on a silicon substrate is very important for their applications. In this paper, an aligned carbon nanotube array has been prepared by pyrolysis of hydrocarbons catalyzed by nickel nanoparticles embedded in porous silicon (PS) templates. High-magnification transmission electron microscopy images confirm that the nanotubes are well graphitized. The PS substrates with pore sizes between 10 and 100 nm play a control role on the growth of carbon nanotubes and the diameters of the tubes increase with the enlargement of the pores of the substrates. However, such a control role cannot be found in the macro-PS substrates.     

Rheology of concentrated carbon nanotube suspensions

The rheological properties of non-Brownian carbon nanotube suspensions are measured over a range of nanotube volume fractions spanning the transition from semidilute to concentrated. The polymer-stabilized nanotubes are "sticky" and form a quiescent elastic network with a well-defined shear modulus and yield stress that both depend strongly on nanotube volume fraction with different but related critical exponents. We compare controlled-strain-rate and controlled-stress measurements of yielding in shear flow, and we study the effect of slow periodic stress reversal on yielding and the arrest of flow. Our measurements support a universal scaling of both the linear viscoelastic and steady-shear viscometric response. The former allows us to extract the elastic shear modulus of semidilute nanotube networks for values that are near or below the resolution limit of the rheometers used, while the latter provides a similar extrapolation of the yield stress. A simple scaling argument is used to model the dependence of yield stress and elastic modulus on concentration.     

Supported coordination polymerization: a unique way to potent polyolefin carbon nanotube nanocomposites

Homogeneous surface coating of long carbon nanotubes is achieved by in situ polymerization of ethylene as catalyzed directly from the nanotube surface-treated by a highly active metallocene-based complex and allows for the break-up of the native nanotube bundles leading, upon further melt blending with HDPE, to high-performance polyolefinic nanocomposites.     

DNA-nanotube artificial ion channels

There is considerable interest in developing chemical devices that mimic the function of biological ion channels. We recently described such a device, which consisted of a single conically shaped gold nanotube embedded within a polymeric membrane. This device mimicked one of the key functions of voltage-gated ion channels: the ability to strongly rectify the ionic current flowing through it. The data obtained were interpreted using a simple electrostatic model. While the details are still being debated, it is clear that ion-current-rectification in biological ion channels is more complicated and involves physical movement of an ionically charged portion of the channel in response to a change in the transmembrane potential. We report here artificial ion channels that rectify the ion current flowing through them via this "electromechanical" mechanism. These artificial channels are also based on conical gold nanotubes, but with the critical electromechanical response provided by single-stranded DNA molecules attached to the nanotube walls.     

Van der waals interactions and decrease of the rotational barrier of methyl-sized rotators: a theoretical study

Rotational barriers of methyl-sized molecular rotators are investigated theoretically using ab initio and empirical force field calculations in molecular models simulating various environmental conditions experienced by the molecular rotors. Calculations on neopentane surrounded by methyl groups suggest that the neopentane's methyl rotational potential energy barrier can be reduced by up to an order of magnitude by locating satellite functional groups around the rotator at a geometry that destabilizes the staggered conformation of the rotator through van der Waals repulsive interactions and reduces the staggered/eclipsed relative energy difference. Molecular mechanics and molecular dynamics calculations indicate that this barrier-reducing geometry can also be found in molecular rotators surface mounted on graphite surfaces or carbon nanotube models. In these models, molecular dynamics simulations show that the rotation of methyl-sized functional groups can be catalyzed by van der Waals interactions, thus making very rigid rotators become thermally activated at room temperature. These results are discussed in the context of design of nanostructures and use of methyl groups as markers for microenvironmental conditions.     

Noncovalent functionalization of multiwalled carbon nanotubes: application in hybrid nanostructures

We developed a reproducible, noncovalent strategy to functionalize multiwalled carbon nanotubes (MWNTs) via embedding nanotubes in polysiloxane shells. (3-Aminopropyl)triethoxysilane molecules adsorbed to the nanotube surfaces via hydrophobic interactions are polymerized simply by acid catalysis and form a thin polysiloxane layer. On the basis of the embedded MWNTs, negatively charged gold nanoparticles are anchored to the nanotube surfaces via electrostatic interactions between the protonated amino groups and the gold nanoparticles. Furthermore, these gold nanoparticles can further grow and magnify along the nanotubes through heating in HAuCl4 aqueous solution at 100 degrees C; as a result these nanoparticles are joined to form continuous gold nanowires with MWNTs acting as templates.     

Catalyst volume to surface area constraints for nucleating carbon nanotubes

In this Article, we describe a carbon nanotube formation model in which sp2 carbon hemispheres form the embryonic caps from which a nanotube can grow. This requirement leads to a single wall carbon nanotube formation window concomitant with our systematic experimental findings, which show upper and lower diameter limits. Further, the successful formation of a nucleation cap (hemisphere) is governed by catalyst particle volume to surface area considerations. Single wall carbon nanotubes are only obtained when both the nanotube formation window and the precipitating catalyst size distribution cross over. The extent to which these two windows overlap establishes the mean diameter and diameter distribution of the obtained single wall carbon nanotubes.     

Challenges in Catalytic Hydrophosphination

Despite significant advances, metal‐catalyzed hydrophosphination has ample room for discovery, growth, and development. Many of the key successes in metal‐catalyzed hydrophosphination over the last decade have indicated what is needed and what is yet to come. Reactivity that is absent from the literature also speaks to the challenges in catalytic hydrophosphination. This Concept article discusses and highlights recent developments that address the ongoing challenges, and identifies areas in metal‐catalyzed hydrophosphination that are underdeveloped. Advances in product selectivity, catalyst design, and both unsaturated and phosphine substrates illustrate the ongoing development of the field. Like all catalytic transformations, the benefits are realized through catalyst, ligand, and conditions, and consideration of those features are the route to a yet more efficient and broadly applicable reaction.     

Effects of charge distribution on water filling process in carbon nanotube

Using umbrella sampling technique with molecular dynamics simulation, we investigated the nanofluidic transport of water in carbon nanotube (CNT). The simulations showed that a positive charge modification to the carbon nanotube can slow down the water column growth process, while the negative charge modification to the carbon nanotube will, on the other hand, quicken the water column growth process. The free energy curves were obtained through the statistical process of water column growth under different charge distributions, and the results indicated that these free energy curves can be employed to explain the dynamical process of water column growth in the nanosized channels. Supported by the National Natural Science Foundation of China (Grant Nos. 10425420 and 20773145), the Ministry of Science and Technology of China (Grant Nos. 2006CB806200 and 2006CB932100), and the Chinese Academy of Sciences including its CNIC Supercomputer Center.