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.     

WC/CNT纳米复合材料制备及其对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过原位还原碳化技术, 将钨离子基团还原成碳化钨(WC)纳米微粒, 制备出WC/CNT纳米复合材料. 采用FTIR、XRD、SEM、HRTEM和N2吸附等分析测试手段对样品的形貌、晶相组成和微观结构特征进行了表征. FTIR和N2吸附结果表明, 硝化后, 在碳纳米管表面羧基化的同时比表面积增加; XRD结果表明, WC/CNT样品由碳纳米管、WC以及非化学计量比的氧化钨组成; SEM和HRTEM结果表明, WC纳米颗粒均匀地分散于碳纳米管的外表面,并与碳纳米管构成了复合材料. 采用循环伏安法测试了样品在碱性条件下对甲醇氧化的电催化性能, 结果表明, 复合材料对甲醇氧化的电催性能明显强于WC 和碳纳米管, 并在实验结果的基础上探讨了复合材料催化性能提高的原因.     

Metallized nanotube polymer composites via supercritical fluid impregnation

Although many metal decorated nanotubes and nanowires appear in the literature, well‐dispersed metal decorated nanotube polymer composites have rarely been reported because of the excessive density mismatch between the decorated nanotubes and polymer matrix. Here, we report a novel method to prepare well‐dispersed, highly functional, metallized nanotube polymer composites (MNPCs) that possess remarkably improved electrical conductivity and mechanical toughness. The MNPCs are prepared by supercritical fluid impregnation of an organometal compound into a premade well‐dispersed single wall carbon nanotube‐polymer composite film. The infused precursor preferentially migrates towards the nanotubes to undergo spontaneous reduction and form nanometer‐scale metal particles leading to an increase in the conductivity of the MNPC films. The environmentally friendly supercritical fluid impregnation process significantly improved the toughness of the composite films, regardless of the presence of metal. Additional functionality can be imparted into the resulting MNPC by infusing other precursors such as magnetic and catalytic metal compounds. © 2011 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys, 2012     

Single Nanoparticle Voltammetry: Contact Modulation of the Mediated Current

The cyclic voltammetric responses of individual palladium‐coated carbon nanotubes are reported. Upon impact—from the solution phase—with the electrified interface, the nanoparticles act as individual nanoelectrodes catalyzing the hydrogen‐oxidation reaction. At high overpotentials the current is shown to reach a quasi‐steady‐state diffusion limit, allowing determination of the tube length. The electrochemical response of the individual nanotubes also reveals the system to be modulated by the electrical contact between the electrode and carbon nanotube. This modulation presents itself as fluctuations in the recorded Faradaic current.     

Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

Electrocatalytic oxidation of ethylene glycol on Pt and Pt-Ru nanoparticles modified multi-walled carbon nanotubes

The synthesis and characterization of catalysts based on nanomaterials, supported on multi-walled carbon nanotubes (CNT) for ethylene glycol (EG) oxidation is investigated. Platinum (Pt) and platinum-ruthenium (Pt-Ru) nanoparticles are deposited on surface-oxidized multi-walled carbon nanotubes [Pt/CNT; Pt-Ru/CNT] by the aqueous solution reduction of the corresponding metal salts with glycerol. The electrocatalytic properties of the modified electrodes for oxidation of ethylene glycol in acidic solution have been studied by cyclic voltammetry (CV), and excellent activity is observed. This may be attributed to the small particle size of the metal nanoparticles, the efficacy of carbon nanotubes acting as good catalyst support and uniform dispersion of nanoparticles on CNT surfaces. The nature of the resulting nanoparticles decorated multiwalled carbon nanotubes are characterized by scanning electron microscopy (SEM) and transmission electron microscopic (TEM) analysis. The cyclic voltammetry response indicates that Pt-Ru/CNT catalyst displays a higher performance than Pt/CNT, which may be due to the efficiency of the nature of Ru species in Pt-Ru systems. The fabricated Pt and Pt-Ru nanoparticles decorated CNT electrodes shows better catalytic performance towards ethylene glycol oxidation than the corresponding nanoparticles decorated carbon electrodes, demonstrating that it is more promising for use in fuel cells.     

Synthesis and Catalytic Studies of Uniform Os &; Os–Pd Nanoparticles Supported on MWNTs

Os and Os–Pd nanoparticles supported on multi-walled carbon nanotubes were prepared by vacuum pyrolysis at 573 K using the [Os₃CO₁₀(NCMe)₂] and [Pd(acac)₂] as precursors. The nanoparticles prepared showed a narrow size distribution (Os: 1.8 nm; Os–Pd: 4.3 nm) and were decorated evenly on the surface of the nanotubes. By controlling the metal-to-nanotube ratio, Os nanotubes were prepared using the carbon nanotubes as a template. The catalysis of Os–Pd nanoparticles towards CVD carbon nanotube synthesis was studied. Dedicated to Professor Gunther Schmid on the occasion of his 70th birthday.     

Enhanced field emission from multiwall carbon nanotube films by secondary growth

We have studied nickel, gold, and ferritin coatings on catalytically grown multiwall carbon nanotubes as well as the generation of secondary nanotubes by resubmitting the decorated nanotubes to the chemical vapor deposition process. Nickel layers sputtered on nanotubes show a stronger interaction with the nanotube walls than gold coatings. At ambient temperature this results in a metal film that is more homogeneous for Ni than for Au. Surface mass transport at elevated temperatures leads to a transformation of the coating to nanoscale clusters on the nanotube surface. The resulting Au clusters are spherelike with a very small contact area with the nanotube whereas the Ni clusters are stretched along the tube axis and have a large contact area. Secondary nanotubes were established by growing nanotubes directly on the walls of primary nanotubes. Thin Ni layers or ferritin served as catalysts. We compared the field emission properties of samples with and without secondary nanotubes. The presence of secondary nanotubes enhances the field emission substantially.     

Effect of Hydrodynamic Forces on meso‐(4‐Sulfonatophenyl)‐Substituted Porphyrin J‐Aggregate Nanoparticles: Elasticity,Plasticity and Breaking

The J aggregates of 4‐sulfonatophenyl meso‐substituted porphyrins are non‐covalent polymers obtained by self‐assembly that form nanoparticles of different morphologies. In the case of high aspect‐ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small‐angle X‐ray scattering measurements in a disk‐plate rotational cell, and cone–plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles.     

Preparation of Au Nanoparticles Decorated Polyaniline Nanotube and Its Catalytic Oxidation to Ascorbic Acid

With sulfonated electrospun polystyrene fiber as a template, uniform polyaniline(PANI) nanotubes were fabricated via polymerization of aniline followed by template removal. Au nanoparticles(Au_nano) were decorated on the PANI nanotube successfully via auto-reduction of HAuCl₄ on the PANI nanotube. The morphology of the nanotubes was characterized by means of scanning electron microscopy(SEM) and transmittance electron microscopy(TEM). By varying precursor concentration and incubation time, Au_nano-PANI with different size of Au_nano was obtained conveniently. Glassy carbon electrode modified with the Au_nano decorated PANI nanotubes (Au_nano-PANI/GCE) was prepared and used seccessfully for the catalytic oxidation of ascorbic acid(AA). The results of differential pulse voltammetry indicate that there is a good linear relationship between the peak currents and the concentrations of AA in the range of 5-3000 μmol/L, with the limit of detection of 1 μmol/L(S/N>3). There is no mutual interference between AA and dopamine. The electrode has been successfully applied in the detection of AA in vitamin C tablet sample.     

扶手椅型单壁碳纳米管的结构和稳定性

用AM1和PM3两种方法对相同长度不同直径以及相同直径不同长度的扶手椅型单壁碳纳米管进行了优化, 并对AM1方法优化所得到的碳纳米管的几何结构进行了振动频率分析和p轨道轴矢量(POAV)分析, 发现了其热力学稳定性随碳纳米管直径和长度的变化规律, 讨论了各碳纳米管的张力、碳原子的杂化状态和共轭程度随碳纳米管直径的变化关系, 并与苯和C60做了比较。     

Dimensional changes as a function of charge injection in single-walled carbon nanotubes

Motivated by the central importance of charge-induced dimensional changes for carbon nanotube electromechanical actuators, we here predict changes in nanotube length and diameter as a function of charge injection for armchair and zigzag nanotubes having different diameters. Density functional theory with periodic boundary conditions is used, which we show provides results consistent with experimental observations for intercalated graphites. Strain-versus-charge relationships are predicted from dimensional changes calculated with a uniform background charge ("jellium") for representing the counterions. These jellium calculations are consistent with presented calculations that include specific counterions for intercalated graphite, showing that hybridization between the ions and the graphite sheets is unimportant. The charge-strain relationships calculated with the jellium approximation for graphite and isolated single-walled nanotubes are asymmetric with respect to the sign of charge transfer. The dependence of nanotube strain on charge approaches that for a graphite sheet for intermediate-sized metallic nanotubes and for larger diameter semiconducting nanotubes. However, the strain-charge curves strongly depend on nanotube type when the nanotube diameter is small. This reflects both the dependence of the frontier orbitals for the semiconducting nanotubes on the nanotube type and the pi-sigma mixing when the nanotube diameter is small.     

Apparent 'electrocatalytic' activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: occluded copper nanoparticles

The electrocatalytic detection of the anaesthetic halothane on a multiwalled carbon nanotube modified glassy carbon electrode is reported with a low limit of detection of 4.6 microM. A thorough investigation of the underlying cause of this apparent catalytic effect is undertaken by comparing the response of various carbon electrodes including glassy carbon, basal- and edge-plane pyrolytic graphite electrodes (bppg and eppg respectively) to increasing additions of halothane. The reduction of halothane is shifted by 250-300 mV to more negative potentials at an eppg electrode than that observed at the GC-CNT electrode. Therefore the results of this investigation show that, surprisingly, the electrocatalysis is not solely due to the introduction of edge-plane-like defect sites on the carbon nanotubes as is commonly found for many other substrates showing favourable voltammetry at nanotube modified electrodes. Instead, we reveal that in this unusual case the electroactive sites for the reduction of halothane are due to the presence of copper nanoparticles occluded within the carbon nanotubes during their production, which are never completely removed by standard purification techniques such as acid washing. This is only the third known case where apparent electrocatalysis by carbon nanotube modified electrodes is due to occluded metal-related nanoparticles within the nanotube structure, rather than the active sites being the edge-plane-like defect sites on the nanotubes. Furthermore this is the first case where the active sites are nanoparticles of copper metal, rather than metal oxide nanoparticles (namely oxides of iron(II)/(III)) as was found to be the case in the previous examples.     

Highly dispersed Pt nanoparticles immobilised on 3-amino-silane-modified MWNT materials for methanol oxidation

We demonstrate the use of molecular monolayers to enhance the nucleation of electrocatalytically active platinum nanocrystals onto carbon nanotubes. The multiwalled carbon nanotube (MWNT) is embedded within the polysiloxane shell with large amounts of hydrophilic amino groups outside after the siloxane is polymerized on the nanotube surfaces. Subsequent deposition of platinum nanoparticles led to high densities of 2- to 5-nm diameter Pt nanocrystals uniformly deposited along the length of the carbon nanotubes. The structure and nature of the resulting Pt/Si–MWNT composites were characterized by transmission electron microscopy and X-ray diffraction. Electrochemical measurements show that the molecular monolayers do not impede redox behavior of the electrode, and measurements of the electrocatalytic oxidation of methanol show very high catalytic efficiency.     

Thermal physics in carbon nanotube growth kinetics

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.     

Elution behavior of shortened multiwalled carbon nanotubes in size exclusion chromatography

We present a rigorous investigation on elution behaviors of ultrasonically shortened multiwalled carbon nanotubes in size‐exclusion chromatography. The size separation of five carbon nanotube samples that underwent ultrasonic shortening for varying lengths of time revealed the existence of three kinds of carbon species: large nanotubes, small nanotubes, and amorphous carbon species. Separation of the three different carbon species was confirmed by SEM analyses on the fractionated eluates and also by light scattering/UV absorbance double detection. The chromatographic peak intensity ratio between the large and small nanotubes suggested an increased amount of small carbon nanotubes upon longer mechanical treatment time. The effect of the concentration of carbon nanotube dispersion on elution behavior was examined, and the elution volume of the shortened nanotubes was found to decrease upon dilution while that of the large nanotubes showed the opposite tendency. Unusual elution behaviors of the multiwalled carbon nanotubes were also observed by altering the flow rate, and these behaviors could be explained by the longer equilibration time taken for large nanotubes to access the pores of the packing materials and a possible morphology change of small carbon nanotubes.     

Interactions of carbon nanotubes with pyrene‐functionalized linear‐dendritic hybrid polymers

A series of linear‐dendritic hybrid polymers, containing pyrene units at the periphery of aliphatic polyester dendrons, were prepared for the purpose of dispersing shortened single‐walled carbon nanotubes (SWNTs) in tetrahydrofuran (THF). The prepared hybrids contained 1, 2, 4, 8, or 16 (G0 through G4) pyrene units and a linear segment composed of polystyrene. It was found that a minimum of four pyrene units was necessary to form a strong enough interaction with SWNTs to enable steric stabilization in solution, when using a linear polymer segment of 11.5 kDa. Increasing either the number of pyrene units per polymer chain or the length of the polymer segment to 18.0 kDa did not improve nanotube solubility, whereas decreasing the polymer length resulted in significantly less effective nanotube dissolution. The G4 dendron alone, without the linear polystyrene segment, was also found to impart solubility to the nanotubes in THF. Interactions between the series of linear‐dendritic hybrids and full‐length multiwalled carbon nanotubes were also investigated, and it was found that the polymers exhibited strong interactions with the multiwalled carbon nanotube surface, resulting in the formation of stable solutions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1016–1028, 2010     

Nickel Hydroxide Nanoparticle Activated Semi‐metallic TiO2 Nanotube Arrays for Non‐enzymatic Glucose Sensing

Semi‐metallic TiO₂ nanotube arrays (TiO_xC_y NTs) have been decorated uniformly with Ni(OH)₂ nanoparticles without the aid of a polymer binder. The resulting hybrid nanotube arrays exhibit excellent catalytic activity towards non‐enzymatic glucose electro‐oxidation. The anodic current density of the glucose oxidation is significantly improved compared with traditional TiO₂ nanotubes decorated with Ni(OH)₂. Moreover, the Ni(OH)₂/TiO_xC_y NT‐based electrode shows a fast response, high sensitivity, wide linear range, good selectivity and stability towards glucose electro‐oxidation, and thus provides a promising and cost‐effective sensing platform for non‐enzymatic glucose detection.     

In Situ Fabrication of Noble Metal Nanoparticles Modified Multiwalled Carbon Nanotubes and Related Electrocatalysis

Using multiwalled carbon nanotubes (MWNTs) as templates, noble metal (Au, Ag, Pt or Pd) nanoparticles (NPs) were fabricated in situ by electrochemistry with a diameter of 40–60 nm. Further, catalytic behaviors of these composite materials were investigated. Experiments showed that such carbon nanotubes decorated with Pd NPs modified glassy carbon electrodes exhibited higher electrocatalytic ability to some molecules such as evolution of hydrogen, reduction of oxygen and oxidation of ascorbic acid. Atomic force microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry were used to characterize the film formation and their properties.     

Single‐Shell Carbon‐Encapsulated Iron Nanoparticles: Synthesis and High Electrocatalytic Activity for Hydrogen Evolution Reaction

Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single‐shell carbon‐encapsulated iron nanoparticles (SCEINs) decorated on single‐walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non‐noble‐metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low‐cost aerosol chemical vapor deposition method in a one‐step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications.