Structure and purity of single walled carbon nanotube samples

Pulsed neutron diffraction has been used to characterize the microscopic structure and purity of single walled carbon nanotubes samples produced by arc discharge. We employed a time of flight diffractometer whose performance in measuring the microscopic structural properties of light-mass materials is well known and recognized. The extended Q-range of the instrument allows for a direct inversion of the data to determine the radial distribution function of the carbon atoms. This is compared with the corresponding function produced by computer simulation. In addition, the absolute calibration of the neutron diffraction data evidences anomalies in the diffraction spectra of the carbon nanotubes, especially at the level of the total scattering section, that could not be observed in previous neutron scattering experiments. These are attributed to the presence of a substantial amount of spurious carbonaceous material that was not quantitatively detected with more conventional diagnostic techniques.     

Low resolution Raman spectroelectrochemistry of single walled carbon nanotube electrodes

A new combination of a low-resolution Raman spectrometer with a minipotentiostat is presented in this work to perform in situ Raman measurements during electrochemical experiments with low-cost instrumentation. The instrumental setup has been used to study the electrochemical oxidation of transparent single walled carbon nanotube (SWCNT) films supported on non-conductive substrates. The spectroelectrochemical response provides the dependence of the characteristic signatures of the SWCNT bundles with the applied potential, which is similar to the response observed for SWCNT films deposited on conducting substrates. The evolution of both the electrical current and the Raman features differs considerably for pristine and oxidized films. The spectroscopic data reveal the occurrence of two kinds of irreversible breakdowns, “oxidative burning” and functionalization of the SWCNTs, in addition to reversible p-doping. 2D-correlation has been applied to analyze the evolution of the spectra with potential and has provided more detailed information than expected from a low spectral resolution spectrometer.     

Electrical conductivity of single walled and multiwalled carbon nanotube containing wool fibers

The main purpose of this study was producing conductive wool fabric applying carbon nanotubes. Raw and oxidized wool samples were treated with carbon nanotubes in the impregnating bath in the presence of citric acid as a crosslinking agent and sodium hypophosphite as a catalyst while sonicating them in the ultrasonic bath. Electrical resistance, washing durability, and color variation of treated samples were assessed. Through SEM images, the surface morphology of treated samples was studied confirming the surface coating through carbon nanotubes. According to the results, the electrical resistance of treated wool with carbon nanotubes reduced substantially. However, the single‐walled carbon nanotubes are more useful to increase the conductivity. In addition, the wool color changed into gray after the treatment. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Aligned millimeter-long carbon nanotube arrays grown on single crystal magnesia

Single crystal magnesium oxide (MgO) was found to be very beneficial to the growth of aligned carbon nanotube (CNT) arrays as long as 2.2 mm by chemical vapor deposition. Before growth, a thin film of catalyst (iron) was coated on the MgO by magnetron sputtering. Scanning electron microscopy was used to study the alignment and length, and transmission electron microscopy was used to exam the wall numbers, diameter, and graphitization. It was found that the number of walls as few as two can be controlled by the catalyst film thickness, whereas the length is a combined result of gas pressure, temperature, and time during growth. Water was found not to be a factor to the length of CNTs grown on MgO, but a significant factor when sapphire was used as the substrates.     

A molecular dynamics simulation of methane adsorption in single walled carbon nanotube bundles

The physisorption of methane in idealized bundles of single walled carbon nanotubes (SWCNT) is investigated in detail in this work employing computational. Several aspects related to the possible application of nanotubes as fuel gas containers are analyzed employing molecular dynamics simulations. The influence of the nanotube diameter on the adsorption capacity of the material and the distribution of the adsorbate are examined by considering bundles of carbon nanotubes with different morphologies. An increase of the load capacity with the nanotube diameter is observed, together with a qualitative change in the distribution of the adsorbed molecules. The effect of porosity is also studied from the point of view of the nanotube separation, finding that this leads to a significant increase in storage capacity in the case of bundles made of small diameter nanotubes. The role of temperature as a possible uptake/release triggering variable is also examined.     

Computer simulation of hydrogen physisorption in a Li-doped single walled carbon nanotube array

Hydrogen physisorption in a Li-doped single walled carbon nanotube (SWCNT) array is investigated by grand canonical Monte Carlo simulation. The optimization of hydrogen storage capacity at normal temperature and moderate pressure as a function of Li doping arrangement, doping-site position, doping ratio, and SWCNT array configuration is discussed and explained.     

Aluminum nitride‐single walled carbon nanotube nanocomposite with superior electrical and thermal conductivities

Development of aluminum nitride (AlN)‐single walled carbon nanotube (SWCNT) ceramic‐matrix composite containing 1‐6 vol% SWCNT by hot pressing has been reported in this article. The composites containing 6 vol% SWCNT are dense (~99% relative density) and show high dc electrical conductivity (200 Sm^?1) and thermal conductivity (62 Wm^?1K^?1) at room temperature. SWCNTs contain mostly metallic variety tubes obtained by controlled processing of the pristine tubes before incorporation into the ceramic matrix. Raman spectroscopy and field emission scanning electron microscopy (FESEM) of the fracture surface of the samples show the excellent survivability of the SWCNTs even after high‐temperature hot pressing. The results indicate the possibility of preparation of AlN nanocomposite for use in plasma devices and electromagnetic shielding.     

High‐yield synthesis of multi‐walled carbon nanotube by hydrothermal method

The evolution of multi‐walled carbon nanotubes (MWCNTs) under hydrothermal condition was investigated, because the hydrothermal method (HTM) has been utilised for commercial production of advanced engineering materials. To synthesise MWCNTs by hydrothermal process using mixed aqueous solution diethylenetriamine, polyethyleneglycol (PEG) and NaOH were used as starting materials. We investigated the effect of hydrothermal temperature, time, and amount of formative compounds. Hydrothermal reaction temperature was in the range from 150 to 180°C. The aim of the present work is to presentation hydrothermal synthesis as a new processing method for fabrication of MWCNTs, without the addition of metal catalyst. The homogeneity of hydrothermal processes, cheapness, and availability of amorphous carbon materials, without the need of catalyst, are advantages favouring the scaling‐up of the new method. The treatment of higher volumes would only require autoclaves with increasing load‐bearing capacity. Synthesised MWCNTs were analysed with a scanning electron microscope (SEM), a high resolution transmission electron microscope (HRTEM), thermo‐gravimetric analysis (TGA), and Raman spectroscopy. This result also presented a controllable way to synthesise MWCNTs with high purity. Indeed, present work will introduce new chapter in synthesising MWCNTs for scientific and engineering.     

CVD growth of carbon nanotube bundle arrays

Recent discovery of enhanced field emission current intensity from arrays of bundles of carbon nanotubes (CNT) has prompted this investigation of the growth of CNT bundle arrays by metal-catalyzed chemical vapor deposition (CVD), in order to understand and control the growth of these arrays. CNT bundle array growth has been characterized as a function of array geometric parameters: the CNT bundle diameter and inter-bundle spacing. We find that CNT bundle array growth varies significantly with bundle size and spacing, which we suggest is due to the formation of a volatile molecular byproduct of ethylene decomposition that enhances CNT growth in areas with high concentrations of metal catalyst. We have also studied and optimized CNT growth with respect to a variety of CVD process parameters, in order to control the length of the resultant CNT bundles. We find that the length of the CNT can be reliably controlled by varying either the reaction time or the gas pressure. Such control over CNT bundle length will be crucial in the incorporation of these bundle arrays into high-intensity electron field emission devices.     

Physical properties of carbon nanotube sheets drawn from nanotube arrays

We report mechanical, thermal, and electrical properties of novel sheet materials composed of multiwalled carbon nanotubes, drawn from a CNT array. At low loading there is some slippage of CNTs but at higher loading tensile strength σ₀ = 7.9 MPa and Young’s modulus E = 310 MPa. The room-temperature thermal conductivity of the CNT sheet was 2.5 ± 0.5 W m^?1 K^?1, giving a thermal conductivity to density ratio of κ/ρ = 65 W m^?1 K^?1 g^?1 cm³. The heat capacity shows 1D behavior for T > 40 K, and 2D or 3D behavior at lower temperatures. The room-temperature specific heat was 0.83 J g^?1 K^?1. The iV curves above 10 K have Ohmic behavior while the iV curve at T = 2 K is non-Ohmic, and a model to explain both ranges is presented. Negative magnetoresistance was found, increasing in magnitude with decreasing temperature (?15% at T = 2 K and B = 9 T). The tensile strength, Young’s modulus and electrical conductivity of the CNT sheet are low, in comparison with other CNT materials, likely due to defects. Thermal conductivity is dominantly phononic but interfacial resistance between MWCNTs prevents the thermal conductivity from being higher.     

碳纳米管阵列在电化学中的应用

高定向的碳纳米管阵列由于有优越的电导率、高比表面积、发达的多孔结构而具有良好的电化学性能如大容量、优异的速率性能和较长的循环寿命,这些独特的性质使其在电化学领域显现出巨大的应用潜力。本文简要介绍了碳纳米管阵列的制备,并从电化学储能、电化学催化和电化学传感器等领域综述近年来碳纳米管阵列在电化学应用中的最新研究进展,分析了其所面临的问题,并提出了未来碳纳米管阵列在电化学应用中的发展方向。关键词：碳纳米管阵列；电化学性能；储能；催化；传感器中图分类号：     

多孔氧化铝模板法制备取向碳纳米管阵列的研究进展

利用化学气相沉积技术在多孔氧化铝模板上可以制备取向碳纳米管阵列。通过调节阳极氧化参数可以改变模板的孔结构,进而可控制碳纳米管在孔道中生长的形貌。用这种方法制备的碳纳米管的直径、长度和密度可以选择性控制,这将有利于研究碳纳米管的性质和它在电化学及其他领域的应用。介绍了多孔氧化铝模板的形成原理以及碳纳米管在多孔氧化铝模板上的生长机理,讨论了阳极氧化条件、催化剂和气相沉积温度对碳纳米管特性的影响,并指出了这种技术中一些需深入研究的问题。     

Field emission from non-uniform carbon nanotube arrays

Regular arrays of carbon nanotubes (CNTs) are frequently used in studies on field emission. However, non-uniformities are always present like dispersions in height, radius, and position. In this report, we describe the effect of these non-uniformities in the overall emission current by simulation. We show that non-uniform arrays can be modeled as a perfect array multiplied by a factor that is a function of the CNTs spacing.     

Nanocrystalline TiO2 on single walled carbon nanotube arrays: Towards the assembly of organized C/TiO2 nanosystems

Arrays of single walled carbon nanotube bundles organized following different architectures have been coated by a homogeneous deposit of nanocrystalline titania. The nanotubes were grown treating nanosized C powders with atomic H in a purpose-designed chemical vapor deposition (CVD) reactor, the subsequent TiO₂ deposition was performed at 400 °C using the metal-organic CVD (MOCVD) technique and titanium tetraisopropoxide Ti(OⁱPr)₄ as a precursor. X-ray diffraction and Raman spectroscopy evidence the anatase structure of the TiO₂ coatings, formed by grains with an average size of about 55 nm. The structural and compositional characteristics of the TiO₂ deposits are not sensitive to the organization of the nanotube arrays, which maintain their pristine architectures. The adopted synthetic procedure opens a new route for the immobilization of anatase-type TiO₂ nanocrystallites onto geometrically varied structures and for the integration of composite nanotube/TiO₂ systems in effective devices.     

An efficient strategy for the purification of cloth-like single walled carbon nanotube soot produced by arc discharge

High purity single walled carbon nanotubes (SWCNTs) were prepared from arc discharge produced cloth-like soot by a new purification strategy, in which liquid oxidation and steam oxidation were combined with a freeze-drying process to remove the metallic and carbonaceous impurities. The process gives a product of >98% purity, which is acquired from a gram-scale dirty raw soot with an overall yield of ∼75% of the SWCNTs. The purity of the samples was characterized by thermogravimetric analysis, scanning and transmission electron microscopy, Raman and Vis-NIR spectroscopy, and magnetometry. A highly pure SWCNT sample with relative purity of 170.4% and I_G/I_D value of 78.92 is achieved. Experiments showed that HNO₃/HCl refluxing combined with freeze-drying is the key process that renders the crude SWCNTs hydrophilic with a large surface area, and thus remarkably increases the efficiency of the steam treatment to remove most of the carbonaceous impurities.     

Simultaneous voltammetric determination of dopamine and adenosine using a single walled carbon nanotube – Modified glassy carbon electrode

The simultaneous voltammetric determination of adenosine (ADS) and dopamine (DA) using a single wall carbon nanotube (SWCNT) modified glassy carbon electrode (GCE) is reported. This has physiological importance in controlling Parkinson’s disease. In phosphate buffer medium of pH 7.2, the concentration vs. peak current plots were linear in the range 1–100 μM for ADS and DA. A comparison of the voltammetric response of DA at acid-treated (purified and super-purified) and untreated SWCNT modified GCE indicates that the oxidation peak current of DA decreases considerably at the treated SWCNT modified GCE. This indicates that metallic impurities in nanotubes play a large role in enhancing the electrochemical current. The detection limit (3σ) and sensitivity observed for ADS and DA were 34.7 μM, 7 μM and 9.5 nA μM⁻¹, 77.9 nA μM⁻¹, respectively.     

Water transport control in carbon nanotube arrays

Based on a recent scaling law of the water mobility under nanoconfined conditions, we envision novel strategies for precise modulation of water diffusion within membranes made of carbon nanotube arrays (CNAs). In a first approach, the water diffusion coefficient D may be tuned by finely controlling the size distribution of the pore size. In the second approach, D can be varied at will by means of externally induced electrostatic fields. Starting from the latter strategy, switchable molecular sieves are proposed, where membranes are properly designed with sieving and permeation features that can be dynamically activated/deactivated. Areas where a precise control of water transport properties is beneficial range from energy and environmental engineering up to nanomedicine.     

Selective laser treatment and laser patterning of metallic and semiconducting nanotubes in single walled carbon nanotube films

Single wall carbon nanotubes (SWCNT) synthesized using mass production methods such as pulsed arc deposition consist of a mixture of metallic and semiconducting nanotubes. In this work, we report on an approach for the selective removal of either metallic or semiconducting SWCNT by a heat-treatment process with cw-lasers and pulsed lasers with specific wavelengths. The results show that using ultraviolet–visible radiation (with wavelengths between 473 nm and 632 nm) it is possible to remove predominantly metallic nanotubes. In contrast, near infrared lasers with 785 nm and 1064 nm wavelengths can be used to remove predominantly the semiconducting nanotubes. Finally, the fabrication of SWCNT films with an anisotropic distribution of metallic and semiconducting nanotubes is demonstrated using a direct laser interference pattering method.     

Large area synthesis of conical carbon nanotube arrays on graphite and tungsten foil substrates

Conical carbon nanotube (CCNT) arrays were synthesized over a large area of approximately 1 cm² or more on graphite and tungsten foil substrates. Experimental observations reveal that nucleation is caused by catalyst metal cluster in the initial stages, but the tapered morphology occurs due to the difference in the rates of vertical growth by attachment carbon atoms at edges of growing graphene sheets and radial growth with epitaxial nucleation of new graphene layers near bottom at the substrate. The above mechanism is supported through re-growth experiments on straight multi-walled nanotubes and growth kinetics data, which suggest a linear relationship between the growth rate and ratio of diameter to length (d/l) of CCNT.