碳纳米管/ZnO纳米复合体的制备和表征

通过将不同直径的ZnO纳米颗粒与碳纳米管连接制备了碳纳米管/ZnO纳米复合体. 将团聚的ZnO纳米颗粒分散并用表面活性剂CTAB使纳米颗粒带正电. 化学氧化碳纳米管使其带负电. ZnO/CTAB微团通过碳管表面羧基与CTAB的静电作用与碳纳米管连接形成纳米复合体. 研究了复合体形成的不同实验条件, 表征了碳纳米管/ZnO纳米复合体的结构并研究了纳米复合体的光学特性. 研究表明, 与碳纳米管连接的ZnO纳米颗粒是互不连接的并保持量子点的特性. 光致发光研究表明ZnO纳米颗粒的激发在纳米复合体中有淬灭.     

Single-walled carbon nanotube-based coaxial nanowires: synthesis, characterization, and electrical properties

We report herein the template-directed synthesis, characterization, and electric properties of single-walled carbon nanotube- (SWNT-) based coaxial nanowires, that is, core (SWNT)-shell (conducting polypyrrole and polyaniline) nanowires. The SWNTs were first dispersed in aqueous solutions containing cationic surfactant cetyltrimethylammonium bromide (CTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonyl phenyl ether (O pi-10). Each individual nanotube (or small bundle) was then encased in its own micellelike envelope with hydrophobic surfactant groups orientated toward the nanotube and hydrophilic groups orientated toward the solution. And thus a hydrophobic region within the micelle/SWNT (called a micelle/SWNT hybrid template) was formed. Insertion and growth of pyrrole or aniline monomers in this hybrid template, upon removal of the surfactant, produce coaxial structures with a SWNT center and conducting polypyrrole or polyaniline coating. Raman and Fourier transform infrared (FTIR) spectroscopy and scanning (SEM) and transmission (TEM) electron microscopy were used to characterize the composition and the structures of these coaxial nanowires. The results revealed that the micellar molecules used could affect the surface morphologies of the resulting coaxial nanowires but not the molecular structures of the corresponding conducting polymers. Electric properties testing indicated that the SWNTs played the key roles in the conducting polymer/SWNT composites during electron transfer in the temperature range 77 K to room temperature. Compared with the SWNT network embedded in the conducting polymers, the composites within which SWNTs were coated perfectly by the identical conducting polymers exhibited higher barrier heights during electron transfer.     

Controllable synthesis of conducting polypyrrole nanostructures

Wire-, ribbon-, and sphere-like nanostructures of polypyrrole have been synthesized by solution chemistry methods in the presence of various surfactants (anionic, cationic, or nonionic surfactant) with various oxidizing agents [ammonium persulfate (APS) or ferric chloride (FeCl3), respectively]. The surfactants and oxidizing agents used in this study have played a key role in tailoring the nanostructures of polypyrrole during the polymerization. It is inferred that the lamellar structures of a mesophase are formed by self-assembly between the cations of a long chain cationic surfactant [cetyltrimethylammonium bromide (CTAB) or dodeyltrimethylammonium bromide (DTAB)] and anions of oxidizing agent APS. These layered mesostructures are presumed to act as templates for the formation of wire- and ribbon-like polypyrrole nanostructures. In contrast, if a short chain cationic surfactant octyltrimethylammonium bromide (OTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonylphenyl ether (Opi-10) is used, sphere-like polypyrrole nanostructures are obtained, whichever of the oxidizing agents mentioned above is used. In this case, micelles resulting from self-assembly among surfactant molecules are envisaged to serve as the templates while the polymerization happens. It is also noted that, if anionic surfactant sodium dodeyl surfate (SDS) is used, no characteristic nanostructures of polypyrrole were observed. This may be attributed to the doping effect of anionic surfactants into the resulting polypyrrole chains, and as a result, micelles self-assembled among surfactant molecules are broken down during the polymerization. The effects of monomer concentration, surfactant concentration, and surfactant chain length on the morphologies of the resulting polypyrrole have been investigated in detail. The molecular structures, composition, and electrical properties of the nanostructured polypyrrole have also been investigated in this study.     

CNT@Fe3O4@C Coaxial Nanocables: One‐Pot,Additive‐Free Synthesis and Remarkable Lithium Storage Behavior

By using carbon nanotubes (CNTs) as a shape template and glucose as a carbon precursor and structure‐directing agent, CNT@Fe₃O₄@C porous core/sheath coaxial nanocables have been synthesized by a simple one‐pot hydrothermal process. Neither a surfactant/ligand nor a CNT pretreatment is needed in the synthetic process. A possible growth mechanism governing the formation of this nanostructure is discussed. When used as an anode material of lithium‐ion batteries, the CNT@Fe₃O₄@C nanocables show significantly enhanced cycling performance, high rate capability, and high Coulombic efficiency compared with pure Fe₂O₃ particles and Fe₃O₄/CNT composites. The CNT@Fe₃O₄@C nanocables deliver a reversible capacity of 1290 mA h g^?1 after 80 cycles at a current density of 200 mA g^?1, and maintain a reversible capacity of 690 mA h g^?1 after 200 cycles at a current density of 2000 mA g^?1. The improved lithium storage behavior can be attributed to the synergistic effect of the high electronic conductivity support and the inner CNT/outer carbon buffering matrix.     

Investigations into the mechanism of adsorption of carbon nanotubes onto aminopropylsiloxane functionalized surfaces

The factors that control carbon nanotube (CNT) adsorption onto aminopropyl siloxane (APS)-derivatized surfaces were investigated using two distinct types of well-characterized films with significant differences in their detailed structures. Both types of APS films showed a marked increase in CNT adsorption relative to untreated SiO2 surfaces but differed in the amount of CNTs adsorbed. To gain insight into the factors governing adsorption, the surface coverage of the CNTs was monitored as a function of the pH during the deposition, the surfactant used to suspend the CNTs, and the type and amount of salt added to the deposition solution. The adsorption is shown to be governed by electrostatic and VDW forces. In the case of complimentarily charged surfaces, the adsorption is proposed to occur through an ion exchange mechanism.     

Effect of Size and Temperature on Water Dynamics inside Carbon Nano-Tubes Studied by Molecular Dynamics Simulation

Water transport inside carbon nano-tubes (CNTs) has attracted considerable attention due to its nano-fluidic properties, its importance in nonporous systems, and the wide range of applications in membrane desalination and biological medicine. Recent studies show an enhancement of water diffusion inside nano-channels depending on the size of the nano-confinement. However, the underlying mechanism of this enhancement is not well understood yet. In this study, we performed Molecular Dynamics (MD) simulations to study water flow inside CNT systems. The length of CNTs considered in this study is 20 nm, but their diameters vary from 1 to 10 nm. The simulations are conducted at temperatures ranging from 260 K to 320 K. We observe that water molecules are arranged into coaxial water tubular sheets. The number of these tubular sheets depends on the CNT size. Further analysis reveals that the diffusion of water molecules along the CNT axis deviates from the Arrhenius temperature dependence. The non-Arrhenius relationship results from a fragile liquid-like water component persisting at low temperatures with fragility higher than that of the bulk water.     

Amphiphilic azobenzenesulfonic acid anionic surfactant for water-soluble, ordered, and luminescent polypyrrole nanospheres

Self-organized micelles of new renewable resource amphiphilic azobenzenesulfonic acid anionic surfactant were utilized to prepare water-soluble, luminescent, and highly ordered polypyrrole nanomaterials. The micellar behavior of the reaction medium was precisely controlled by varying the composition of pyrrole/surfactant ratio from 3 to 100 (up to 100 times lower amount of surfactant with respect to pyrrole), and polypyrrole nanospheres of 150-800 nm were prepared. Dynamic light scattering (DLS) and viscosity techniques were employed as tools to trace the factors, which control the mechanism of polypyrrole nanomaterials formation. DLS studies confirmed that the surfactant exists as in the form of spherical micelles of 4.8 nm diameter in water. Specific viscosity measurement revealed that the pyrrole+surfactant complexes in water exist in the form of either aggregated or isolated micelles depending upon their composition in the feed. SEM and TEM analysis confirmed that the aggregated micellar templates produced coral-like morphology, whereas uniform polypyrrole nanospheres of 150-400 nm were obtained at low micellar concentration. The nanomaterials formation was unperturbed by the variation of the oxidation agents such as ammonium persulphate (APS) or ferric chloride (FeCl3). WXRD analysis of the nanomaterials indicates that the anionic surfactant effectively penetrates into the polypyrrole chains, and a new peak at 2theta = 6.3 degrees (d-spacing = 14 A) was observed corresponding to highly ordered polymer chains. UV-vis and FT-IR confirmed the highly doped state, and the conductivity of the samples was obtained in the range of 10(-1) to 10(-2) S/cm by four-probe conductivity measurements. The azobenzenesulfonic acid anionic surfactant is luminescent in water, and its grafting on the polypyrrole nanospheres enhances the luminescent intensity with the quantum yield in the range of 2 x 10(-3) to 3 x 10(-4).     

基于静电吸附作用制备PPy/CNTs复合材料

通过添加十二烷基苯磺酸钠(SDBS), 在碳纳米管(CNTs)表面引入具有静电吸附作用的基团, 使吡咯单体附着于CNTs表面, 然后发生化学原位聚合, 得到了由片状聚吡咯(PPy)包覆CNTs所构成的PPy/CNTs复合材料, 开辟了一条易于工业化生产制备PPy/CNTs复合材料的途径. 所得材料和CNTs借助傅立叶变换红外光谱、扫描电子显微镜、透射电子显微镜等设备进行了成分和形貌的表征; 并将所得材料组装成电化学超级电容器, 进行了电化学性能测试. 研究结果表明, 加入SDBS后, 吡咯单体能很好地吸附于CNTs表面; CNTs的应用细化了PPy的颗粒, 改善了PPy的导电性能和机械性能, 使PPy/CNTs复合材料呈现出多孔状; 其电化学容量达到101.1 F·g-1(有机电解液), 是同样制备条件下所得纯PPy电化学容量(19.0 F·g-1)的5倍多, 约是所用纯CNTs电化学容量(25.0 F·g-1)的4倍.     

Structure and Dynamics of Adsorbed Dopamine on Solvated Carbon Nanotubes and in a CNT Groove

Advanced carbon microelectrodes, including many carbon-nanotube (CNT)-based electrodes, are being developed for the in vivo detection of neurotransmitters such as dopamine (DA). Our prior simulations of DA and dopamine-o-quinone (DOQ) on pristine, flat graphene showed rapid surface diffusion for all adsorbed species, but it is not known how CNT surfaces affect dopamine adsorption and surface diffusivity. In this work, we use molecular dynamics simulations to investigate the adsorbed structures and surface diffusion dynamics of DA and DOQ on CNTs of varying curvature and helicity. In addition, we study DA dynamics in a groove between two aligned CNTs to model the spatial constraints at the junctions within CNT assemblies. We find that the adsorbate diffusion on a solvated CNT surface depends upon curvature. However, this effect cannot be attributed to changes in the surface energy roughness because the lateral distributions of the molecular adsorbates are similar across curvatures, diffusivities on zigzag and armchair CNTs are indistinguishable, and the curvature dependence disappears in the absence of solvent. Instead, adsorbate diffusivities correlate with the vertical placement of the adsorbate’s moieties, its tilt angle, its orientation along the CNT axis, and the number of waters in its first hydration shell, all of which will influence its effective hydrodynamic radius. Finally, DA diffuses into and remains in the groove between a pair of aligned and solvated CNTs, enhancing diffusivity along the CNT axis. These first studies of surface diffusion on a CNT electrode surface are important for understanding the changes in diffusion dynamics of dopamine on nanostructured carbon electrode surfaces.     

Polypyrrole-coated natural rubber latex by admicellar polymerization

Admicellar polymerization has been used for the preparation of an electrically conductive polypyrrole coating on latex particles. An anionic surfactant, sodium dodecyl sulfate (SDS), was adsorbed onto natural rubber (NR) latex particles to form the surfactant bilayers after adjusting the pH below the point of zero charge of the latex surface. Adsorption of SDS and pyrrole adsolubilization were determined as a function of pyrrole and sodium chloride concentrations. Pyrrole caused a decrease in SDS adsorption at equilibrium. Sodium chloride increased the surfactant adsorption and the pyrrole adsolubilization. Thermogravimetric results showed the presence of polypyrrole. The conductivity of the polypyrrole-coated NR latex film prepared by admicellar polymerization without salt was the lowest; however, with salt addition, the conductivity of the film improved significantly. The oxidative polymerization technique resulted in a relatively higher conductivity than oxidative admicellar polymerization.     

In situ measurements of nanotube dimensions in suspensions by depolarized dynamic light scattering

We show that the dimensions of carbon nanotubes (CNTs) in suspension can be characterized by depolarized dynamic light scattering. Taking advantages of this in situ technique, we investigate in detail the influence of sonication procedures on the length and diameter of CNTs in surfactant solutions. Sonication power is shown to be particularly efficient at unbundling nanotubes, whereas a long sonication time at low power can be sufficient to cut the bundles with limited unbundling. We finally demonstrate the influence of CNT dimensions on the electrical properties of CNT fibers. Slightly varying the sonication conditions, and thereby the suspended nanotube dimensions, can affect the fibers conductivity by almost 2 orders of magnitude.     

Carbon nanotube-modified electrodes for electrochemical DNA-sensors

Glassy-carbon electrodes (GCEs) are modified with preoxidized multiwalled carbon nanotubes (CNTs). According to the data of atomic force microscopy, the layers of CNTs on GCEs possess a homogeneous nanostructurized surface. The voltammetric properties of a GCE/CNT depend on the modifier load. Guanine and deoxyguanosine monophosphate are strongly adsorbed on GCE/CNT and oxidized at +690 and +930 mV (pH 7.0), respectively. The oxidation current of guanine DNA nucleotides adsorbed on a GCE/CNT is significantly higher for the thermally denaturated biopolymer than for the native one. Our results are of interest for the development of sensors based on the electrochemical properties of nucleic acids.     

Review of recent studies on interactions between polymers and nanotubes using molecular dynamic simulation

Nanotubes have extraordinary properties, which have attracted the attention of many researchers from diverse fields. The interaction between carbon nanotube (CNT) or boron nitride nanotube (BNNT) and polymer/copolymer/surfactant has shown potential improvement in properties and performance. This paper reviews the recent studies in this field obtained from molecular dynamics simulation calculations, focusing on the interaction energies between nanostructure and polymer, radial distribution function, diffusion and radius of gyration and some other physical chemistry properties. Recent studies show that the intermolecular interaction in mentioned systems is strongly influenced by the specific monomer structure of polymers. The high values of intermolecular interaction energy of such composites offer that an efficient load transfer exists at the interface between nanotube and polymer, which is of a key role in the composite reinforcement practical applications. Our study reviewed the possibility of wrapping CNT/BNNT/CNT bundles by polymers and also the effects of CNTs/CNT bundles’ length on the conformational behavior of polymer adsorbed on these nanostructures.     

Synthesis of copper-core/carbon-sheath nanocables by a surfactant-assisted hydrothermal reduction/carbonization process

A simple hydrothermal method has been developed for the one-step synthesis of copper-core/carbon-sheath nanocables in solution. The obtained nanostructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM), Raman, and UV-vis spectrum analysis. These copper@carbon nanocables formed through the hydrothermal reduction/carbonization in the presence of surfactant cetyltrimethylammonium bromide (CTAB) acting as the structure-directing agent by hydrothermal treatment. HRTEM and selected-area electron diffraction (SAED) indicate that the resulted Cu nanowires had the preferred [110] growth direction. The influence of the reaction temperature, reaction time, and pH on the final products was investigated in detail. The possible formation mechanism for copper-core/carbon-sheath nanocables was also proposed. Amorphous carbon nanotubes can be obtained by etching the copper core in the nanocables.     

In situ AFM studies on self-assembled monolayers of adsorbed surfactant molecules on well-defined H-terminated Si(111) surfaces in aqueous solutions

The formation of self-assembled monolayers (SAMs) of adsorbed cationic or anionic surfactant molecules on atomically flat H-terminated Si(111) surfaces in aqueous solutions was investigated by in situ AFM measurements, using octyl trimethylammonium chloride (C8TAC), dodecyl trimethylammonium chloride (C12TAC), octadecyl trimethylammonium chloride (C18TAC)) sodium dodecyl sulfate (STS), and sodium tetradecyl sulfate (SDS). The adsorbed surfactant layer with well-ordered molecular arrangement was formed when the Si(111) surface was in contact with 1.0x10(-4) M C18TAC, whereas a slightly roughened layer was formed for 1.0x10(-4) M C8TAC and C12TAC. On the other hand, the addition of alcohols to solutions of 1.0x10(-4) M C8TAC, C12TAC, or SDS improved the molecular arrangement in the adsorbed surfactant layer. Similarly, the addition of a salt, KCl, also improved the molecular arrangement for both the cationic and anionic surfactant layers. Moreover, the adsorbed surfactant layer with a well-ordered structure was formed in a solution of mixed cationic (C12TAC) and anionic (SDS) surfactants, though each surfactant alone did not form the well-ordered layer. These results were all explained by taking into account electrostatic repulsion between ionic head groups of adsorbed surfactant molecules as well as hydrophobic interaction between their alkyl chains, which increases with the increasing chain length, together with the increase in the hydrophobic interaction or the decrease in the electrostatic repulsion by incorporating alcohol molecules into the adsorbed surfactant layer, the decrease in the electrostatic repulsion by increasing the concentration of counterions, and the decrease in the electrostatic repulsion by alternate arrangement of cationic and anionic surfactant molecules. The present results have revealed various factors to form the well-ordered adsorbed surfactant layers on the H-Si(111) surface, which have a possibility of realizing the third generation surfaces with flexible structures and functions easily adaptable to circumstances.     

Computer simulation of amino acid sorption on carbon nanotubes

A computer simulation of complexes of (6,6) open carbon nanotubes (CNTs) with neutral molecules, zwitterions and glycine, alanine, and phenylalanine amino acid anions is performed. In starting structures amino acids are arranged in three types: on the external side face, the open end, and inside CNT. The structure is optimized within the density functional theory with regard to the GD3 dispersion correction with and without taking into account solvation effects. It is found that the greatest CNT–amino acid interaction occurs in the neutral aqueous medium at dissociative chemisorption of the zwitterion (adsorption energy 80-90 kcal/mol) and in the basic medium at anion chemisorption (energy ~48-50 kcal/mol) on the open CNT end.     

Structure and properties of aqueous dispersions of sodium dodecyl sulfate with carbon nanotubes

The dispersing action of the surfactant (sodium dodecyl sulfate, SDS) on the carbon nanotubes (CNT) in aqueous medium has been studied. Electron microscopy, molecular docking, NMR and IR spectroscopies were applied to determine the physical-chemical properties of CNT dispersions in SDS—water solutions. It was established that micellar adsorption of the surfactant on the surface of carbon material and solubilization of SDS in aqueous medium contribute to improving CNT dispersing in water solutions. It was shown that the non-polar hydrocarbon radicals of a single surfactant molecule form the highest possible number of contacts with the graphene surface. Upon increase of the SDS in solution these radicals form micelles connected with the surface of the nanotubes. At the sufficiently high SDS concentration the nanotube surface becomes covered with an adsorbed layer of surfactant micelles. Water molecules and sodium cations are concentrated in spaces between micelles. The observed pattern of micellar adsorption is somewhat similar to a loose bilayer of surfactant molecules.     

Studies of the adsorption of oligomers and surfactants on carbon and steel surfaces in a hydrocarbon medium

The adsorption isotherms for an (amino) terminally functionalised, oligomeric polyisobutylene and for a series of alkylpropoxylate or alkylbutoxylate surfactant molecules on carbon particles, in isooctane, have been obtained. The isotherms on carbon show that the oligomer is the most strongly adsorbing species. The surfactants show some evidence of forming aggregates on the carbon surface at higher concentrations. Analysis of the adsorption isotherms indicate that the size of these aggregates is similar on the carbon particles and on steel balls, reported previously, but that in some cases the actual adsorbed amounts on the two surfaces differ considerably. Ellipsometric studies carried out in situ on steel surfaces in isooctane show that only the polymer gives a relatively thick adsorbed layer. Addition of surfactant reduces the adsorption of the oligomer. There are some differences between the thickness values reported previously using AFM, compared to those found in the current work using ellipsometry, but in both cases it would seem that some degree of multilayer adsorption is occurring for the oligomer on steel in isooctane.     

Preparation and Characterization of Electrodes Modified with Pyrrole Surfactant,Multiwalled Carbon Nanotubes and Metallophthalocyanines for the Electrochemical Detection of Thiols

Our aim was to prepare hybrid electrodes active towards the electrooxidation of thiols by the co‐immobilization of native carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc) from aqueous solutions. This strategy was adopted to avoid the oxidation of CNTs that can induce a modification of their exceptional properties. To do so, a hydrosoluble pyrrole surfactant was used to get homogeneous aqueous dispersions of CNTs and CoPc and to trap both materials on the electrode via the electropolymerization of the pyrrole surfactant. The hybrid electrodes exhibit a good electrocatalytic activity towards the oxidation of L ‐cysteine and glutathione. Their performances in terms of limit of detection (0.01 mM) are compatible with the detection of these thiols in biological samples.     

A combined streaming-potential optical reflectometer for studying adsorption at the water/solid surface

A novel in-situ streaming-potential optical reflectometry apparatus (SPOR) was constructed and utilized to probe the molecular architecture of aqueous adsorbates on a negatively charged silica surface. By combining optical reflectometry and electrokinetic streaming potentials, we measure simultaneously the adsorption density, gamma, and zeta potential, zeta, in a rectangular flow cell constructed with one transparent wall. Both dynamic and equilibrium measurements are possible, allowing the study of sorption kinetics and reversibility. Using SPOR, we investigate the adsorption of a classic nonionic surfactant (pentaethylene glycol monododecyl ether, C12E5), a simple cationic surfactant (hexadecyl trimethylammonium bromide, CTAB) of opposite charge to that of the substrate surface, and two cationic polyelectrolytes (poly(2-(dimethylamino)ethyl methacrylate), PDAEMA; (poly(propyl methacrylate) trimethylammonium chloride, MAPTAC). For the polyethylene oxide nonionic surfactant, bilayer adsorption is established above the critical micelle concentration (cmc) both from the adsorption amounts and from the interpretation of the observed zeta potentials. Near adsorption saturation, CTAB also forms bilayer structures on silica. Here, however, we observe a strong charge reversal of the surface. The SPOR data, along with Gouy-Chapman theory, permit assessment of the net ionization fraction of the CTAB bilayer at 10% so that most of the adsorbed CTAB molecules are counterion complexed. The adsorption of both C12E5 and CTAB is reversible. The adsorption of the cationic polymers, however, is completely irreversible to a solvent wash. As with CTAB, both PDAEMA and MAPTAC demonstrate strong charge reversal. For the polyelectrolyte molecules, however, the adsorbed layer is thin and flat. Here also, a Gouy-Chapman analysis shows that less than 20% of the adsorbed layer is ionized. Furthermore, the amount of charge reversal is inversely proportional to the Debye length in agreement with available theory. SPOR provides a new tool for elucidating aqueous adsorbate molecular structure at solid surfaces.