Electrochemical modification of vertically aligned carbon nanotube arrays

Electrochemical oxidation and reduction were utilized to modify vertically aligned carbon nanotube (CNT) arrays grown on a porous network of conductive carbon microfibers. Ultrafast and complete CNT opening and purification were achieved through electrochemical oxidation. Highly dispersed platinum nanoparticles were then uniformly and densely deposited as electrocatalysts onto the surface of these CNTs through electrochemical reduction. Using supercritical drying techniques, we demonstrate that the unidirectionally aligned and laterally spaced geometry of the CNT arrays can be fully retained after being subjected to each step of electrochemical modification. The open-tipped CNTs can also be electrochemically detached in full lengths from the supporting substrates and harvested if needed.     

Synthesis of vertically aligned carbon nanotube arrays on polyhedral Fe/Al2O3 catalysts

Polyhedral Fe/Al(2)O(3) catalysts prepared by an impregnation method were used for the synthesis of vertically aligned carbon nanotube (CNT) arrays from the pyrolysis of ethylene at 800 °C.     

Transferred vertically aligned N-doped carbon nanotube arrays: use in dye-sensitized solar cells as counter electrodes

We prepared vertically aligned nitrogen doped carbon nanotubes (CNTs) on a rigid glass substrate or flexible plastic substrate via a 'growth-detachment-transfer' process and the vertically aligned N-doped CNT arrays are employed as counter electrodes for novel dye-sensitized solar cells.     

An amperometric glucose biosensor based on glucose oxidase immobilized in electropolymerized poly(o-aminophenol) and carbon nanotubes composite film on a gold electrode.

An amperometric glucose biosensor is developed that is based on immobilization of glucose oxidase (GOD) in a composite film of poly(o-aminophenol) (POAP) and carbon nanotubes (CNT), which are electrochemically co-polymerized at a gold (Au) electrode. Because of the high surface per volume ratio and excellent electrical conductivity of CNT, the biosensor based on an Au/POAP/CNT/GOD electrode has lower detection limit (0.01 mM), larger maximum response current (0.24 mA cm(-2)) and higher sensitivity (11.4 mA M(-1) cm(-2)) than the values of the biosensor based on an Au/POAP/GOD electrode. Additionally, the biosensor shows fast response time, large response current, and good anti-interferent ability for ascorbic acid, uric acid and acetaminophen. Good reproducibility and stability of the biosensor are also observed.     

Wet Purification of Aligned Carbon Nanotube Arrays and Its Impact on the Morphology of the Carbon Nanotube Arrays

A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.     

湿法纯化碳纳米管阵列及其对碳纳米管阵列形貌的影响

采用酸溶液处理方法对垂直于衬底生长的碳纳米管阵列的纯化进行了研究. 利用扫描电子显微镜、X射线光电子能谱等手段对纯化前后的碳纳米管阵列的结构、形貌及化学组成进行表征. 实验结果表明, 通过控制条件, 酸溶液处理方法能够在有效地去除催化剂粒子等杂质的同时又保持阵列的相对完整性. 纯化后的碳纳米管阵列会促进其在电子学领域的进一步应用.     

Growth mechanism of long aligned multiwall carbon nanotube arrays by water-assisted chemical vapor deposition

Highly aligned arrays of multiwalled carbon nanotube (MWCNT) on layered Si substrates have been synthesized by chemical vapor deposition (CVD). The effect of the substrate design and the process parameters on the growth mechanism were studied. Adding water vapor to the reaction gas mixture of hydrogen and ethylene enhanced the growth which led to synthesis of longer CNT arrays with high density. Environmental scanning electron microscopy (ESEM), energy-dispersive spectroscopy (EDS), and atomic force microscopy (AFM) were used to analyze the CNT morphology and composition. Quadrupole mass spectroscopy (QMS) provided in-situ information on the gas spices within the reaction zone. On the basis of results, we verified the top growth mechanism and evaluated the reason of decline and stoppage of the CNT growth after extended period of deposition. Multilayered Si substrates with a top film of Al2O3, having appropriate roughness, provide favorable conditions to form catalyst islands with uniform distribution and size. Using water-assisted CVD process and optimized substrate design, our group succeeded to grow vertically aligned, patterned MWCNT up to 4-mm long. The arrays were of high purity and weak adhesion which allowed to be peeled off easily from the substrate.     

3-D carbon nanotube structures used as high performance catalyst for oxygen reduction reaction

We report a high performance oxygen reduction reaction (ORR) catalyst based on vertically aligned, nitrogen-doped carbon nanotube (VA-NCNT) arrays. Characterization in conditions analogous to the operation of a polymer electrolyte membrane fuel cell show ORR taking place on the catalyst at a favorable reduction potential with a superior current density and greater rate constant.     

Functionalized polypyrrole nanotube arrays as electrochemical biosensor for the determination of copper ions

A novel electrochemical biosensor based on functionalized polypyrrole (PPy) nanotube arrays modified with a tripeptide (Gly-Gly-His) proved to be highly effective for electrochemical analysis of copper ions (Cu²⁺). The vertically oriented PPy nanotube arrays were electropolymerized by using modified zinc oxide (ZnO) nanowire arrays as templates which were electrodeposited on indium–tin oxide (ITO) coated glass substrates. The electrodes were functionalized by appending pyrrole-α-carboxylic acid onto the surface of polypyrrole nanotube arrays by electrochemical polymerization. The carboxylic groups of the polymer were covalently coupled with the amine groups of the tripeptide, and its structural features were confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy. The tripeptide modified PPy nanotube arrays electrode was used for the electrochemical analysis of various trace copper ions by square wave voltammetry. The electrode was found to be highly sensitive and selective to Cu²⁺ in the range of 0.1–30 μM. Furthermore, the developed biosensor exhibited a high stability and reproducibility, despite the repeated use of the biosensor electrode.     

Reversible tuning of the wettability of carbon nanotube arrays: the effect of ultraviolet/ozone and vacuum pyrolysis treatments

Among diverse types of synthetic materials, arrays of vertically aligned carbon nanotubes have attracted the most attention, mainly because of their exceptional mechanical, electrical, optical, and thermal properties. However, their wetting properties are yet to be understood. In this present study, oxygenated surface functional groups have been identified as a vital factor in controlling the wetting properties of carbon nanotube arrays. The results presented herein indeed show that a combination of ultraviolet/ozone and vacuum pyrolysis treatments can be used to vary the surface concentration of these functional groups such that the carbon nanotube array can be repeatedly switched between hydrophilic and hydrophobic.     

取向碳纳米管/高分子新型复合材料的制备及应用

碳纳米管/高分子复合材料已经被广泛研究, 但长期以来存在一个共同而关键的挑战, 即碳纳米管无规聚集, 结构难以调控, 性能无法满足应用需要. 本工作提出了制备取向碳纳米管/高分子复合材料的一种新方法, 获得块状、膜状、纤维状复合材料, 制备的关键步骤是通过化学气相沉积法合成可纺的高质量碳纳米管阵列. 该方法简单易行, 具有较好的普适性. 由于碳纳米管取向排列, 复合材料具有优异的物理性能, 如碳纳米管取向后复合材料的机械强度和导电率可分别提高一个和三个数量级. 在此基础上, 进一步探讨取向碳纳米管/高分子复合材料作为新型电极在有机太阳能电池中的应用.     

An X-ray spectroscopy study of CdS nanoparticles formed by the Langmuir–Blodgett technique on the surface of carbon nanotube arrays

The composition and electronic structure of cadmium sulfide (CdS) nanoparticles formed by the Langmuir–Blodgett (LB) technique on clean silicon wafers and the surface of vertically aligned carbon nanotube (CNT) arrays are studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The samples were annealed in a vacuum at 175 °C and 225 °C to remove the organic matrix of the LB film. From the analysis of the XPS data the increased concentration of sulfate groups on the surface of CdS nanoparticles formed on CNTs and the electron density transfer from CdS to CNTs are determined. An increase in the LB film annealing temperature causes an increase in the degree of crystallinity and the CdS crystallite size and a decrease in the photoluminescence intensity of a CdS–CNT hybrid.     

Ordered networks of ZnO-nanowire hierarchical urchin-like structures for improved dye-sensitized solar cells

Quasi-1D ZnO nanowires (NWs) ordered as patterned 3D hollow hierarchical urchin-like structures have been prepared on transparent conducting substrates by electrodeposition. The ZnO NWs have been grown on self-assembled ordered polystyrene microspheres with electrical charge densities ranging from 5 to 30 C cm(-2) and organized arrays of mono and multi-urchin layers have been built. These layers have been sensitized by the highly absorbing D149 indoline organic dye. The optical characterizations and dye titrations have shown a significant increase in the light scattering and absorption as well as dye loading for the organized structures compared to randomly vertically aligned ZnO NWs grown under the same conditions. The dye-sensitized solar cells (DSSC) prepared using the sensitized layers have been characterized by current-voltage (J-V) measurements, IPCE and by electrochemical impedance spectroscopy. We show that the best performances are obtained for the 3D urchin monolayer structures. The conversion efficiency is increased by up to 4 times compared to their counterparts made of randomly dispersed vertical ZnO NWs. Impedance spectroscopy results show a very fast charge transfer in the ZnO NWs and urchin monolayers and that the electron lifetime is in the 4-14 ms range.     

In-situ growth of vertically aligned nickel cobalt sulfide nanowires on carbon nanotube fibers for high capacitance all-solid-state asymmetric fiber-supercapacitors

Fiber-supercapacitors(FSCs)are promising power sources for miniature portable and wearable electronic devices.However,the development and practical application of these FSCs have been severely hindered by their low volumetric capacitance and narrow operating voltage.In this work,vertically aligned nickel cobalt sulfide(Ni Co_2S_4)nanowires grown on carbon nanotube(CNT)fibers were achieved through an in-situ two-step hydrothermal reaction method.The as-prepared Ni Co_2S_4@CNT fiber electrode exhibits a high volumetric capacitance of 2332 F cm~(-3),benefiting from its superior electric conductivity,large surface area,and rich Faradic redox reaction sites.Furthermore,a Ni Co_2S_4@CNT//VN@CNT(vanadium nitride nanosheets grown on CNT fibers)asymmetric fiber-supercapacitor(AFSC)was successfully fabricated.The device exhibits an operating voltage up to 1.6 V and a high volumetric energy density of 30.64m Wh cm~(-3).The device also possesses outstanding flexibility as evidenced by no obvious performance degradation under various bending angles and maintaining high capacitance after 5000 bending cycles.This work promotes the practical application of flexible wearable energy-storage devices.     

The effects of the lengths and orientations of single-walled carbon nanotubes on the electrochemistry of nanotube-modified electrodes

The influence of both nanotube orientation and length on the electrochemical properties of electrodes modified with single-walled carbon nanotubes was investigated. Gold electrodes were modified with either randomly dispersed or vertically aligned nanotubes to which ferrocenemethylamine was attached. Electron transfer kinetics were found to depend strongly on the orientation of the nanotube, with electron transfer between the gold electrode and the ferrocene moiety being 40 times slower through randomly dispersed nanotubes than through vertically aligned nanotubes. The difference is hypothesized to be due to electron transfer being more direct through a single tube than that with electrodes modified with randomly dispersed nanotubes. With the vertically aligned nanotubes the rate constant for electron transfer varied inversely with the mean length of the nanotubes. The results indicate there is an advantage in using aligned carbon nanotube arrays over randomly dispersed nanotubes for achieving efficient electron transfer to bound redox active species such as in the case of bioelectronic or photovoltaic devices.     

Photocatalytic methane decomposition over vertically aligned transparent TiO2 nanotube arrays

We report here on a study of vertically aligned TiO(2) nanotube arrays grown by the one-step anodic oxidation technique and their photocatalytic performance for methane decomposition. Quantitative activity data as a function of film thickness is obtained.     

Preparation of dye-sensitized solar cells using template free TiO2 nanotube arrays for enhanced power conversion

Journal of Sol-Gel Science and Technology - By using the vertically aligned ZnO nanorod arrays (NRAs), TiO2 nanoparticles attached ZnO nanorods (TiO2@ZnO) and TiO2 nanotube arrays (NTAs) were...     

Erosion effects of atomic oxygen on carbon nanotube arrays in different incidence direction

The erosion effects of atomic oxygen (AO) in different incidence direction on carbon nanotube (CNT) arrays have been studied by ground‐based AO simulation facility. The surface morphologies and the molecular structures of CNT arrays before and after AO experiments have been characterized by scanning electron microscopy and Raman spectroscopy. It is shown that the morphologies of CNT arrays are quite different from those before AO experiments. It is presented that both bombardment effect and the oxidation effect of AO will contribute to the erosion effects on CNT arrays. Carbon nanotube arrays will be etched away in AO environment, but the AO erosion yield of CNT arrays is different with different AO incidence direction. It is proposed that the density of CNT‐based material may also affect the erosion yield.     

Aligned arrays of nanotubes and segmented nanotubes on substrates fabricated by electrodeposition onto nanorods

We describe an electrochemical-based approach to create vertically aligned nanotube arrays on substrates. Initially, nanoporous anodic alumina films are used as templates to electrodeposit nanorods, and then the alumina templates are removed and nanotube arrays are electrodeposited using the nanorod arrays as templates. We have used this approach to fabricate gold nanotube arrays using nickel nanorods as templates. By anodizing the ends of the nickel nanorods before gold electrodeposition, no deposition occurs at the ends of the rods, resulting in open-ended nanotubes. In addition, we have used layered nickel-gold nanorods as templates to create gold nanostructure arrays with alternating segments of filled and empty nanotubes. This approach is versatile and may be used to electrodeposit a wide range of nanotube materials with good control over the nanotube dimensions.     

Shear modulated percolation in carbon nanotube composites

A novel time-dependent percolation transition has been observed in sheared carbon nanotube (CNT) composites. At a fixed CNT filler loading, the electrical conductivities of CNT composites can change abruptly as much as 8 orders of magnitude as the shear processing time increases. Microstructure characterization shows that the CNTs have aligned along the shear flow direction, which leads to the dramatic increase of the percolation threshold and thereby the dramatic decreases of the electrical conductivities. Our results highlight the great importance of understanding the response of CNT dispersion states to the processing conditions.