Super-aligned Carbon Nanotube Arrays Research Articles

A 3D electrochemical biosensor based on Super-Aligned Carbon NanoTube array for point-of-care uric acid monitoring

Uric acid analysis is extremely important for gout prognosis, diagnosis and treatment. Previous technologies either lack specificity or exhibit poor performance, and thus could not meet the need of Point-of-Care (POC) uric acid monitoring. Here we present for the first time, a novel electrochemical biosensor based on 3D Super-Aligned Carbon NanoTube (SACNT) array to facilitate POC uric acid monitoring. The working electrode of the biosensor is composed of an orderly 3D SACNT array immobilized with uricase through a precipitation and crosslinking procedure. Such biosensor possesses a higher enzyme density, significantly larger contact area with reactants and could maintain the intact SACNT structure and its excellent conductivity after modification. The developed 3D SACNT array electrochemical biosensor benefits from high specific surface area, high electro-catalytic activity and large contact area with analytes, and demonstrates high sensitivity of 518.8 μA/(mM⋅cm2), wide linear range of 100–1000 μM and low limit of detection of 1 μM for uric acid. Dynamic uric acid monitoring has been achieved using the presented biosensor. And the obtained results in serum samples had no significant difference compared with those obtained using the FDA-approved electrochemical analyzer (Paired T-test, p > 0.05). These demonstrated that the technology can potentially be applied in POC monitoring of other biomolecules to improve prognosis, diagnosis and treatment outcomes of metabolic diseases.

High-temperature epitaxial graphite deposition on macroscopic superaligned carbon nanotube structures by a one-step self-heating method

By using superaligned carbon nanotube (SACNT) macrostructures as reinforcements, the one-step homoepitaxial growth of SACNT/graphite composites was achieved with a home-built experimental setup at temperatures as high as 2600 °C. Compared with traditional furnace heating method, this approach offers the advantages of increased convenience, high throughput and energy efficiency. This high-temperature homoepitaxy strategy was applied to three kinds of structures: SACNT yarn, SACNT film, and SACNT array. Because of the high temperature which exceeded 1800 °C, the samples after high-temperature homoepitaxy showed increased G/D peak area ratios in the Raman spectra, enhanced mechanical properties and improved thermal properties, all of which can meet the requirements of various applications.

Fast-response, agile and functional soft actuators based on highly-oriented carbon nanotube thin films

Highly-oriented carbon nanotube (CNT) film, which is made from super-aligned CNT array, is an even, tough and soft material. This CNT film has strong anisotropy in electrical and mechanical properties. The electrical conductivity and Young’s modulus of the CNT film (2.8 × 104 S m−1, 3000 MPa) along the CNT aligned direction are one magnitude larger than those (2.3 × 103 S m−1, 200 MPa) along the vertical direction. In virtue of easy preparation and good processability, it is competent as high-performance flexible electrodes for soft actuators, advanced film capacitors and batteries. Here, we use this highly-oriented CNT film as a heating electrode to make fast-response soft actuators. The actuator has a thin bilayer composite structure and is driven by current heating. It takes a typical miniaturized actuator only 0.9 s to perform fast and large-angle deformations (270° bending, curvature 4.8 cm−1), and its bending speed can reach 300° s−1 by low power driving (2.4 W). Based on this CNT film, graphical designs and fine processing were carried out to make patterned electrodes and functional actuators, such as cross-shaped and hand-shaped ones. Notably, a well-designed gripper-like actuator can even deftly grab and manipulate some tiny things, e.g. a grain of rice. Moreover, the anisotropic properties of the CNT film also effectively influence and regulate the deformation forms of the actuators. In virtue of good and unique performances in electrical, mechanical and thermal aspects, the high-oriented CNT film would have promising application prospects in various emerging soft devices.

Feasibility study of thin films deposited on a self-supporting carbon grid substrate target on the measurement of atomic inner-shell ionization cross-sections impacted by 3–30 keV electrons

In this paper, we have measured the , and X-ray production cross-sections of the W element and the K-shell ionization cross-sections of the Al element impacted by 3–30 keV electrons. A new kind of target consisting of a thin film deposited on a self-supporting carbon grid substrate has been used in this work. The self-supporting carbon grid substrate is made of several layers of super-aligned carbon nanotube arrays (the mass thickness of each layer of super-aligned carbon nanotube arrays is 20 μg/cm2). As a comparison, three kinds of targets consisting of a) the studied element deposited onto four layers of super-aligned carbon nanotube arrays and separated from each other by one layer of single carbon atoms, b) the studied element deposited directly onto four layers of super-aligned carbon nanotube arrays, and c) the studied element deposited directly onto two layers of super-aligned carbon nanotube arrays, were respectively prepared to figure out which type is fit for the measurement of inner-shell ionization cross-sections induced by 3–30 keV electrons. The experimental data are compared with the distorted-wave Born approximation (DWBA) theoretical predictions and with the available experimental data from other references. The results show that the first and the second targets are both suitable for the inner-shell ionization cross-section measurements by 3–30 keV electrons, but the third target is not. Besides, we present the M-shell X-ray production cross-sections of the W element by 5–30 keV electrons in this paper for the first time.

High-performance flexural fatigue of carbon nanotube yarns

Carbon nanotube yarns (CNTY) possess good specific strength and specific conductivity. As such, their potential for commercial applications is significant. Fatigue performance is a significant consideration in yarn/wire applications. In this study, the flexural fatigue performance of CNTY spun from super-aligned carbon nanotube arrays was investigated using a reversed bending test. The results showed that CNTY exhibited excellent resistance to pure flexural fatigue, significantly outperforming stainless steel wire; CNTY failed where a combination of flexural fatigue and tension–tension fatigue had special hollow fracture morphology, and CNTY resistance remained fundamentally unchanged in the combination fatigue process.

Improvement of sound absorption characteristics under low frequency for micro-perforated panel absorbers using super-aligned carbon nanotube arrays

Super-aligned carbon nanotube (SACNT) arrays are grown on the surface of micro perforated panel (MPP) in the hope of improving the acoustic performance of MPP absorbers by virtue of their unique properties. Scanning electron microscopy reveals that SACNT arrays did not block the perforations of MPPs or changed the perforation diameter due to their “super-aligned” nature, although MPPs are thickened. The absorption effect of SACNT arrays which are of the same and different lengths with different incident side on MPP absorbers are investigated, and standing wave tube method is used to determine the normal sound absorption coefficient. Results show that both of the lengths of SACNT arrays and the incident side have effects on the sound absorption performance of MPP absorbers. And generally SACNT arrays help to improve the sound absorption capacity of MPP absorbers in low-frequency regions only when the SACNT arrays surface is the incident side. SACNT arrays decrease absorption performance of MPP absorbers when the MPP surface is used as the incident side. Moreover, SACNT arrays are found to increase the acoustic ability of MPP absorbers with the same structure parameters monotonically at lengths up to 600μm in the condition that the SACNT arrays surface is used as the incident side.

High-strength composite yarns derived from oxygen plasma modified super-aligned carbon nanotube arrays

Spinning carbon nanotube (CNT) yarns from super-aligned carbon nanotube (SACNT) arrays is a promising approach to fabricate high-strength fibers. However the reported tensile strengths of the as-prepared fibers are far below that of an individual CNT. It is therefore still a challenge to improve their mechanical strengths. Here we report that the tensile strengths and Young’s moduli can be further improved to 2.2 GPa and 200 GPa respectively, if we first treat the SACNT array with oxygen plasma by using a reactive ion etching (RIE) facility, then dry spin yarns from it and make composite fibers with polyvinyl alcohol. According to the experimental results obtained using scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), the improvement is attributed to the oxygen RIE process, as it can create functional groups on the outer walls of CNTs and thus improve the interaction between the CNTs and the polymer molecules.

Hybrid super-aligned carbon nanotube/carbon black conductive networks: A strategy to improve both electrical conductivity and capacity for lithium ion batteries

Super-aligned carbon nanotube (SACNT) films drawn from SACNT arrays are uniformly introduced into LiCoO2–Super P composite cathodes by a cold-rolling method, and a hybrid conductive network consisting of SACNTs and carbon black powders is obtained. This attempt results in reduced percolation threshold and increased conductivity of the LiCoO2–Super P cathodes with addition of less than 0.01 wt% of SACNTs. The strength and flexibility of the LiCoO2–Super P–SACNT composites can be improved significantly due to the excellent mechanical properties of SACNTs. The continuous SACNT films play an important role for the formation of a homogeneous network for long-range conductive pathways. Super P is also an essential component to form short-range conductive pathways. By comparing with control samples that only contain Super P or SACNT films, we demonstrate that the LiCoO2–Super P–SACNT composites possess the best cycling stability (150 mA h g−1 at 0.1 C with a capacity retention of 99.7% after 50 cycles) and rate capability (87 mA h g−1 at 5 C). Combining both short-range and long-range conduction, the hybrid Super P-SACNT conductive network manifests itself as a promising strategy to improve the battery performances with a minimum amount of conductive fillers.

Aligned carbon nanotube coating on polyethylene surface formed by microwave radiation

Multifunctional carbon nanotube (CNT) architectures have been created on polyethylene (PE) surface by a microwave welding process. The continuous and aligned CNT films drawn from super-aligned CNT arrays can significantly absorb microwave energy and act as a network of nanosized thermal sources to locally melt the PE substrate beneath, leading to polymer wrapping around individual nanotubes. Uniform and highly conductive CNT/PE nanocomposite layer was formed without undermining the original alignment of the CNTs. CNT patterns have also been precisely fabricated on PE samples. The PE/CNT/PE bonds showed high interfacial strengths, which were affected by the duration of microwave radiation. With ultra-low content of CNTs introduced as antistatic agents, the dissipation of surface charges on PE substrate has been tremendously improved.

Superaligned arrays, films, and yarns of carbon nanotubes: a road toward applications

Carbon nanotube (CNT) array is a self-organized highly oriented structure, in which CNTs are vertically aligned on the substrate. Superaligned CNT array is a special kind of vertically aligned CNT array with the unique capability of being converted into pure CNT films or yarns simply by drawing in dry state. The as-converted CNT films are tens of nanometers in thickness, transparent, and highly conductive, with aligned CNTs parallel to the drawing direction. After passing through volatile solutions or being twisted, CNT films can be further condensed into shrunk yarns. These shrunk yarns possess high tensile strengths and Young’s moduli, and are good conductors. The continuous films and yarns have turned nanometer sized CNTs into a manipulable macroscopic object, brought the excellent properties into macroscopic applications, and opened up a road leading from nano-world to macro-world. In this paper, the applications of CNT films and shrunk yarns will be reviewed. Real products made from superaligned CNTs such as TEM grids, loudspeakers, and touch screens will be introduced.

Superaligned Carbon Nanotube Arrays, Films, and Yarns: A Road to Applications

A superaligned carbon nanotube (CNT) array is a special kind of vertically aligned CNT array with the capability of being converted into continuous fi lms and yarns. The as-produced CNT fi lms are transparent and highly conductive, with aligned CNTs parallel to the direction of drawing. After passing through volatile solutions or being twisted, CNT fi lms can be further condensed into shrunk yarns. These shrunk yarns possess high tensile strengths and Young’s moduli, and are good conductors. Many applications of CNT fi lms and shrunk yarns have been demonstrated, such as TEM grids, loudspeakers, touch screens, etc.

A polarized infrared thermal detector made from super-aligned multiwalled carbonnanotube films

Carbon nanotube (CNT) films, easily drawn from super-aligned CNT arrays with a largearea and a good compatibility with semiconductor technology, have been used as lightsensitive materials for infrared (IR) detection. A bolometric CNT detector madefrom one layer of super-aligned CNT film shows a 15.4% resistance change under10 mW mm − 2 of IR illumination and a fast characteristic response time of 4.4 ms due to its ultra-smallheat capacity per unit area in vacuum at room temperature. Besides the power intensitydetection, the anisotropic property of the super-aligned CNT films makes them idealmaterials to detect the polarization of IR light simultaneously, which provides greatpotential in infrared imaging polarimetry. Theoretical analyses have been carried out toinvestigate the influences of CNT film properties on the responsivity and response time ofthe detector.

Dry spinning yarns from vertically aligned carbon nanotube arrays produced by an improved floating catalyst chemical vapor deposition method

Carbon nanotube (CNT) yarn was drawn directly from super aligned CNT arrays synthesized by an improved floating catalyst chemical vapor deposition method. The synthesis of aligned CNT was performed as a multi-step interim reactant supply reaction to produce a double-layered CNT array in a horizontal quartz tube reactor. During the growth period, most impurities were blocked on the top surface of the first layer and therefore the top aligned CNT layer was unspinnable. However, the bottom CNT layer was super aligned CNTs, which were with clean surface and a tortuosity factor of 1.07. During the dry spinning process, the tangles, friction, and van der Waals interaction between CNTs served to hold them into CNT yarns. The tensile strength of the as-obtained CNT yarn can be further improved from 0.24 to 0.30GPa by twisting.

The effect of barrier layer-mediated catalytic deactivation in vertically aligned carbon nanotube growth

The effect of Al-barrier layer-mediated Fe-catalytic deactivation in vertically aligned carbon nanotube (CNT) growth was studied. The substrate surface morphology, catalytic diffusion and barrier layer oxidation were found to be dependent on the annealing temperature of the barrier layer, which ultimately affects CNT growth. The annealed barrier layer without complete oxidation was found to be suitable for top to bottom super aligned CNT arrays. The highest average CNT growth rate of up to 3.88 µm s−1 was observed using this simple approach. Details of the analysis are also presented.

Periodically striped films produced from super-aligned carbon nanotube arrays

We report a novel way to draw films from super-aligned carbon nanotube arrays at largedrawing angles. The obtained super-aligned carbon nanotube films have a periodicallystriped configuration with alternating thinner and thicker film sections, and the width ofthe stripes is equal to the height of the original arrays. Compared with ordinary uniformfilms, the striped films provide a better platform for understanding the mechanism ofspinning films from arrays because carbon nanotube junctions are easily observed andidentified at the boundary of the stripes. Further studies show that the carbon nanotubejunctions are bottleneck positions for thermal conduction and mechanical strength of thefilm, but do not limit its electrical conduction. These films can be utilized as striped andhigh-degree polarized light emission sources. Our results will be valuable for newapplications and future large-scale production of tunable super-aligned carbon nanotubefilms.

Fabrication and properties of aligned multiwalled carbon nanotube-reinforced epoxy composites

A method to fabricate continuous and aligned multiwalled carbon nanotube (CNT)/epoxy composites is presented in this paper. CNT/epoxy composites were made by infiltrating an epoxy resin into a stack of continuous and aligned multiwalled CNT sheets that were drawn from super-aligned CNT arrays. By controlling the amount and alignment of the continuous multiwalled CNT sheets, a CNT/epoxy composite with high content of well-dispersed CNTs can be obtained. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results show that the thermal stability of these CNT/epoxy composites was not affected by the addition of CNTs. The mechanical properties and electrical properties of the CNT/epoxy composites were dramatically improved compared to pure epoxy, suggesting that the CNT/epoxy composites can serve as multifunctional materials with combined mechanical and physical properties.

Controlled Growth of Super-Aligned Carbon Nanotube Arrays for Spinning Continuous Unidirectional Sheets with Tunable Physical Properties

We report controlled syntheses of super-aligned carbon nanotube (CNT) arrays with the desired tube-diameter, number of walls, and length for spinning continuous unidirectional sheets to meet a variety of industrial demands. The tube-diameter distribution of super-aligned arrays is well controlled by varying the thicknesses of catalyst films, and the length of them is tuned by the growth time. Further investigation indicates that the physical properties of the unidirectional sheets, such as electrical transport, optical transmittance, and light emission properties, can be well tuned by the tube-diameter- and length-controlled growth. This work extends the understanding of the super-aligned CNT arrays and will be very helpful in developing further applications.

Spinning and Processing Continuous Yarns from 4‐Inch Wafer Scale Super‐Aligned Carbon Nanotube Arrays

Carbon nanotubes (CNTs) are an extremely interesting type of material due to their unique 1D structure, and their excellent mechanical, thermal, and electrical properties. Many promising applications have been demonstrated. To exploit their excellent physical properties at a macroscopic level, it is desirable to create CNTs with macroscopic length. However, it has been very challenging to grow arbitrarily long CNTs. An alternative approach is to create long nanotube structures with many of them aligned into continuous yarns or ropes. In 2002, a breakthrough was made by our group to fabricate pure CNT yarns by directly drawing CNTs from super-aligned CNT arrays. Following that, Zhang et al. developed a draw– twisting spin method and demonstrated more interesting applications of the raw yarns. Since CNTs in the yarn are nearly parallel aligned, the CNT yarn is intrinsically an anisotropic material and has a special axis along the drawing direction, which demonstrates many fascinating properties and applications such as filaments for light bulbs, polarizers working in the UV region, thermal-field emitters, polarized-light emitters, transparent conducting membranes, etc. As these yarns are macroscopic objects, there is no doubt that they will be sought after for more and more applications as time goes on. However, to achieve real applications in the industry, some key issues have to be solved in advance. Currently many groups have achieved the growth of CNT arrays, but of these only two groups have reported spinning yarns from their arrays. The first question is why our CNT arrays can give rise to CNT yarn while others cannot? What is the critical factor that determines the ability for yarn formation? In our first paper and the recent paper of Zhang et al., the reported syntheses were carried out at atmospheric pressure (AP) in a tube furnace with diameters of 1–2 in. Can this synthesis be expanded to a larger scale at low pressure (LP) for commercial chemical vapor deposition (CVD) systems? The third problem is that, even though many applications have been demonstrated, the directly drawn-out yarns are very sticky due to their clean surfaces and extremely high surfaceto-volume ratio. It can easily to stick to the surfaces of other objects and can never be separated again, which greatly inhibits the real application of CNT yarns. Here, we show how these crucial problems were tackled by our group in the past two years. CNT arrays (or termed “CNT forests”) represent high-quality and highly ordered CNT structures, in which CNTs are nearly parallel aligned and perpendicular to the substrate. To date, a lot of groups have successfully synthesized CNT arrays since the initial papers were published. However, only two groups have reported that CNT yarns can be drawn from their arrays, which were defined as super-aligned arrays by us. We have tried to pull yarns from CNT arrays derived by a previously published method, which is denoted as a normal array, no yarns could be drawn out even though the height of the CNT array was above 1 mm. Now the question is what the difference is between normal and super-aligned arrays? Zhang et al. claimed that the formation of yarn was due to the disordered region at the top and bottom of the CNT array, which entangled together forming a loop. However we cannot agree with them based on the following points. First, in the normal array, the top and bottom part are more disordered and entangled than in the super-aligned array. Second, in our super-aligned array, the bottom part is highly ordered (see supporting information, Fig. S1) and without entanglement. Therefore, the disordered entanglement at the top may help the formation of yarn, but it cannot be the key factor for yarn formation. To elucidate the difference between normal and superaligned arrays, we performed comparative studies. Figure 1A is the transmission electron microscopy (TEM) image of C O M M U N IC A IO N S