Biomineralization of superhydrophilic vertically aligned carbon nanotubes

Vertically aligned carbon nanotubes (VACNT) promise a great role for the study of tissue regeneration. In this paper, we introduce a new biomimetic mineralization routine employing superhydrophilic VACNT films as highly stable template materials. The biomineralization was obtained after VACNT soaking in simulated body fluid solution. Detailed structural analysis reveals that the polycrystalline biological apatites formed due to the -COOH terminations attached to VACNT tips after oxygen plasma etching. Our approach not only provides a novel route for nanostructured materials, but also suggests that COOH termination sites can play a significant role in biomimetic mineralization. These new nanocomposites are very promising as nanobiomaterials due to the excellent human osteoblast adhesion.     

Growth kinetics of 0.5 cm vertically aligned single-walled carbon nanotubes

Half-centimeter-high mats of vertically aligned single-walled carbon nanotubes were grown at 600 degrees C by point-arc microwave plasma chemical vapor deposition. The mats were produced from 0.5 nm of an Fe catalyst layer, thus showing one of the highest catalytic yields of approximately 105 times. The growth process shows a lack of poisoning of the catalyst, in contrast to other reports. The experimental results confirm that the growth rate is ultimately limited by the gas phase diffusion of hydrocarbon radicals.     

Growth of vertically aligned carbon nanotubes on carbon fiber: thermal and electrochemical treatments

Composite electrodes of vertically aligned carbon nanotubes (VACNT) were synthesized on carbon fiber (CF) substrate by pyrolysis of camphor/ferrocene using a SiO₂ interlayer as a barrier against metal diffusion into the substrate. Two treatments were used to remove iron from CF/VACNT structure: thermal annealing at high temperature under inert atmosphere and electrochemical oxidation in H₂SO₄ solution. The composites were characterized by scanning electron microscopy and Raman scattering spectroscopy. Besides, the electrochemical behavior of CF/VACNT was analyzed by cyclic voltammetry and charge/discharge tests. CF/VACNT composite submitted to the electrochemical oxidation showed the best electrochemical performance, with high specific capacitance, which makes it very attractive as electrode for supercapacitors.     

Uniform, dense arrays of vertically aligned, large-diameter single-walled carbon nanotubes

Precisely controlled reactive chemical vapor synthesis of highly uniform, dense arrays of vertically aligned single-walled carbon nanotubes (SWCNTs) using tailored trilayered Fe/Al(2)O(3)/SiO(2) catalyst is demonstrated. More than 90% population of thick nanotubes (>3 nm in diameter) can be produced by tailoring the thickness and microstructure of the secondary catalyst supporting SiO(2) layer, which is commonly overlooked. The proposed model based on the atomic force microanalysis suggests that this tailoring leads to uniform and dense arrays of relatively large Fe catalyst nanoparticles on which the thick SWCNTs nucleate, while small nanotubes and amorphous carbon are effectively etched away. Our results resolve a persistent issue of selective (while avoiding multiwalled nanotubes and other carbon nanostructures) synthesis of thick vertically aligned SWCNTs whose easily switchable thickness-dependent electronic properties enable advanced applications in nanoelectronic, energy, drug delivery, and membrane technologies.     

Effects of carbon nanotubes on electro-optic characteristics in vertically aligned liquid crystal display

Size- and aggregation-controlled dispersion of thin multiwalled carbon nanotube (t-MWCNT) in negative dielectric anisotropic liquid crystal (LC) material exhibits remarkable improvement in electro-optic response time in vertically aligned LC cells. The physical properties such as birefringence, dielectric anisotropy and clearing temperature of nanotube dispersed LC material appear to be almost invariant to that of pristine LC. Nevertheless, the response time shows noticeable improvement, especially in decaying time associated with transition from maximum to minimum transmission, hence important for faster switching LC devices. The effect is attributed to that vertically aligned t-MWCNTs along the field direction play role of vertical alignment layer between LCs, consequently resulting in increased bend elastic constant of LCs.     

Electrochemistry of polystyrene intercalated vertically aligned single- and double-walled carbon nanotubes on gold electrodes

Electrochemical electrodes incorporating double- and single-walled carbon nanotubes (CNTs) were fabricated on cysteamine modified flat gold substrates. Through covalent coupling of the amine end groups with carboxyl functionalized CNTs, a dense forest of vertically aligned CNTs was produced. To these a 30 nm thick insulating polystyrene layer was spin coated, resulting in exposure of the uppermost carbon nanotube ends. The electrochemical performance of each electrode was then determined using the redox probe ruthenium hexaamine. Once surrounded by polymer, the double-walled CNTs (DWCNTs) showed an improved electron transfer rate, compared to the single-walled electrode. This improvement was attributed to the protection of the electronic properties of the inner wall of the DWCNT during the chemical modification and suggests that DWCNTs may offer a useful alternative to SWCNTs in future electrochemical sensors and biosensors.     

Sputtering deposition of Pt nanoparticles on vertically aligned multiwalled carbon nanotubes for sensing L-cysteine

A highly sensitive electrochemical sensor for determination of L-cysteine (CySH) is presented. It is based on vertically aligned multiwalled carbon nanotubes modified with Pt nanoparticles by magnetron sputtering deposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy and energy-dispersive. The electrochemistry of CySH was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The mechanism for the electrochemical reaction of CySH at the modified electrode at different pH values is discussed. The electrode exhibits a higher electrocatalytic activity towards the oxidation of CySH than comparable other electrodes. It displays a linear dependence (R ²?=?0.9980) on the concentration of CySH in the range between 1 and 500 μM and at an applied potential of +0.45 V, a remarkably low detection limit of 0.5 μM (S/N?=?3), and an outstandingly high sensitivity of 1.42?×?10³ μA?mM^?1?cm^?2, which is the highest value ever reported. The electrode also is highly inert towards other amino acids, creatinine and urea. The sensor was applied to the determination of CySH in urine with satisfactory recovery, thus demonstrating its potential for practical applications.

A solid-state pH sensor based on WO3-modified vertically aligned multiwalled carbon nanotubes

In this communication, a novel solid-state pH sensor based on WO₃/MWNTs nanocomposite electrode will be reported. WO₃ nanoparticles were homogeneously coated on vertically aligned MWNTs by magnetron sputtering. Potentiometric pH response of the WO₃/MWNTs electrode in Britton–Robinson buffers revealed a linear working range from pH 2 to12 with a slope of about ?41 mV pH^?1 and a response time less than 90 s. The stability of the electrode remained over a month. Moreover, the WO₃/MWNTs electrode displayed excellent anti-interference property. Compared to conventional pH sensors, the pH sensor based on WO₃/MWNTs nanocomposite electrode also showed excellent reproducibility, high stability and superb selectivity.     

A new recyclable Pd catalyst supported on vertically aligned carbon nanotubes for microwaves-assisted Heck reactions

Palladium supported on vertically aligned multi-walled carbon nanotubes (Pd/VA-CNTs) is used as catalyst for the C-C coupling reactions of p-iodonitrobenzene with styrene and ethyl acrylate under microwaves irradiation. Pd/VA-CNTs catalyst exhibits higher activity compared to Pd supported on activated charcoal, under the same reaction conditions. Due to the microwaves irradiation, the kinetics of the reaction is strongly accelerated compared to that obtained with a traditional heating mode. The macroscopic form of aligned CNTs support allows an easy recovery of the catalyst, avoiding a costly post-reaction filtration. In addition, the interaction between the active phase and the support leads to the negligible leaching of palladium during recycling tests. The observed results indicate that Pd/CNTs is a recyclable and stable heterogeneous catalytic system.     

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.     

Reversible electrowetting of vertically aligned superhydrophobic carbon nanofibers

Reversible electrostatically induced wetting (electrowetting) of vertically aligned superhydrophobic carbon nanofibers has been investigated. Carbon nanofibers on a 5 x 5 microm pitch were grown on Si substrates, electrically insulated with a conformal dielectric, and hydrophobized with fluoropolymer. This nanostructured scaffold exhibited superhydrophobic behavior for saline (theta approximately 160 degrees). Electrowetting induced a contact angle reduction to theta approximately 100 degrees. Competitive two-liquid (dodecane/saline) electrowetting exhibited reversibility on the same nanostructured scaffold. Without applied bias, ultra-fine-point tip (approximately 25 nm radius) nanofibers result in effectively zero capacitance with the overlying saline layer. Complete electrowetting of the substrate is confirmed as capacitance values increase by several orders of magnitude with increased wetting. These results demonstrate the applicability of reversible electrowetting on nanostructured scaffolds and use of nanofabricated structures that can be integrated with various micro- and nanoelectronic technologies.     

Proposed model for growth preference of plate-like nanohydroxyapatite crystals on superhydrophilic vertically aligned carbon nanotubes by electrodeposition

For the first time, the mechanism of growth of plate-like n-HA electrodeposited on superhydrophilic vertically aligned multi-walled carbon nanotubes (VACNT) is presented and a model for the specific growth preference is discussed. Results show that the carboxyl (carboxylic acid)/carboxylate functional groups directly attached on VACNT tips after oxygen plasma treatment were essential for the acceleration of the OH^? formation and the deposition of plate-like HA crystals. FEG-SEM, EDX and XRD showed that a homogeneous highly crystalline HA film, stoichiometric and with preferential growth in the (002) plane direction, was formed.     

Direct evidence for root growth of vertically aligned single-walled carbon nanotubes by microwave plasma chemical vapor deposition

The root growth mode of extremely dense and vertically aligned single-walled carbon nanotubes (SWNTs) synthesized by microwave plasma chemical vapor deposition was clarified by a new method, marker growth, which does not require transmission electron microscopy. SWNT layers were grown intermittently on a substrate, and a line between the layers was used as a marker to identify the growth mode. Micro-Raman spectroscopy revealed that the SWNT layers have the same diameter distribution.     

Control of carbon capping for regrowth of aligned carbon nanotubes

The regrowth of carbon nanotubes (CNTs) in a second growth stage after a first growth stage has been completely stopped has been found to be strongly related to the carbon capping present on their catalyst particles. It is shown that the undesirable carbon capping can be prevented from forming or removed and the nanotube growth can be rejuvenated by either control of plasma processing conditions during chemical vapor deposition or by inserting a room-temperature sputter etching process. The ability to cause sequential growth stages to take place in different directions makes it possible for us to clearly compare the occurrence and extent of CNT regrowth. Such a CNT regrowth process and understanding of controlling parameters can enable the creation of new nanowire configurations that could potentially be used for applications such as sharply bending nanointerconnections, nanosprings, bent AFM nanoprobes, or nanobarcodes.     

Large-scale synthesis of perpendicularly aligned helical carbon nanotubes

Large-scale perpendicularly aligned helical carbon nanotube arrays were prepared by co-pyrolysis of Fe(CO)5 and pyridine onto the pristine quartz glass plates in a tube furnace at 900-1100 degrees C under a mixture flow of Ar and H2. The resultant aligned helical carbon nanotubes could not only facilitate the structure-property characterization for helical carbon nanotubes but also allow them to be effectively incorporated into devices for practical applications.     

A highly sensitive hydrogen peroxide amperometric sensor based on MnO2-modified vertically aligned multiwalled carbon nanotubes

In this report, a highly sensitive amperometric sensor based on MnO₂-modified vertically aligned multiwalled carbon nanotubes (MnO₂/VACNTs) for determination of hydrogen peroxide (H₂O₂) was fabricated by electrodeposition. The morphology of the nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometer and X-ray diffraction. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were applied to investigate the electrochemical properties of the MnO₂/VACNTs nanocomposite electrode. The mechanism for the electrochemical reaction of H₂O₂ at the MnO₂/VACNTs nanocomposite electrode was also discussed. In borate buffer (pH 7.8, 0.20 M), the MnO₂/VACNTs nanocomposite electrode exhibits a linear dependence (R = 0.998) on the concentration of H₂O₂ from 1.2 × 10⁻⁶ M to 1.8 × 10⁻³ M, a high sensitivity of 1.08 × 10⁶ μA M⁻¹ cm⁻² and a detection limit of 8.0 × 10⁻⁷ M (signal/noise = 3). Meanwhile, the MnO₂/VACNTs nanocomposite electrode is also highly resistant towards typical inorganic salts and some biomolecules such as acetic acid, citric acid, uric acid and d-(+)-glucose, etc. In addition, the sensor based on the MnO₂/VACNTs nanocomposite electrode was applied for the determination of trace of H₂O₂ in milk with high accuracy, demonstrating its potential for practical application.     

Composites based on polyaniline and aligned carbon nanotubes

Composites based on aligned carbon nanotubes and polyaniline are prepared via the electrochemical polycondensation of aniline in a sulf uric acid solution. The structure of the composites and the character of interaction of polyaniline and the surface of carbon nanotubes are studied by scanning and transmission electron microscopy, X-ray diffraction, and IR and X-ra y photoelectron spectroscopy. It is shown that in the composites, electron density is transferred from the carbon nanotube to the polyaniline film. The occurrence of polyaniline on the surface of nanotubes increases the mean current in cyclic voltammograms of the composite material and leads to a marked increase in the calculated specific capacity of electrodes formed on its basis.     

Bimetallic nanoparticles aligned at the tips of carbon nanotubes

Cluster-derived bimetallic nanoparticles have been deposited onto multi-wall carbon nanotubes and shown to be generally homogeneously dispersed, of uniform small sizes, of the same composition as the starting mixed-metal clusters, and to have a tendency to align at the tips of the tubules.