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.     

Self-assembly of vertically aligned gold nanorod arrays on patterned substrates

Nanorods standing at attention! A self-assembly technique based on convective and capillary forces was used for the direct fabrication of standing arrays of gold nanorods on lithographically predefined areas. The hexagonal close-packed structure of gold nanorods creates an ideal substrate for surface-enhanced Raman spectroscopy.     

Dendron growth from vertically aligned single-walled carbon nanotube thin layer arrays for photovoltaic devices

Single-walled carbon nanotube arrays attached to conductive transparent electrodes have previously shown promise for use in photovoltaic devices, whilst still retaining light transmission. Here, chemical modification of these thin (<200 nm) arrays with PAMAM-type dendrons has been undertaken to enhance the photoresponse of these devices. The effect of modification on the electrode was measured by differential pulse voltammetry to detect the dendrons, and the effect on the nanotubes was measured by Raman spectroscopy. Solar simulator illumination of the cells was performed to measure the effect of the nanotube modification on the cell power, and determine the optimal modification. Electrochemical impedance spectroscopy was also used to investigate the equivalent electronic circuit elements of the cells. The optimal dendron modification occurred with the second generation (G-2.0), which gave a 70% increase in power over the unmodified nanotube array.     

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.     

Molecular beam-controlled nucleation and growth of vertically aligned single-wall carbon nanotube arrays

The main obstacle to widespread application of single-wall carbon nanotubes is the lack of reproducible synthesis methods of pure material. We describe a new growth method for single-wall carbon nanotubes that uses molecular beams of precursor gases that impinge on a heated substrate coated with a catalyst thin film. In this growth environment the gas and the substrate temperature are decoupled and carbon nanotube growth occurs by surface reactions without contribution from homogeneous gas-phase reactions. This controlled reaction environment revealed that SWCNT growth is a complex multicomponent reaction in which not just C, but also H, and O play a critical role. These experiments identified acetylene as a prolific direct building block for carbon network formation that is an order of magnitude more efficient than other small-molecule precursors. The molecular jet experiments show that with optimal catalyst particle size the incidence rate of acetylene molecules plays a critical role in the formation of single-wall carbon nanotubes and dense vertically aligned arrays in which they are the dominant component. The threshold for vertically aligned growth, the growth rate, the diameter, and the number of walls of the carbon nanotubes are systematically correlated with the acetylene incidence rate and the substrate temperature.     

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.     

Facile solution route to vertically aligned, selective growth of ZnO nanostructure arrays

For any future cost-effective applications of inorganic nanostructures, in particular, hybrid photovoltaic cells, it is essential that these inorganic nanomaterials be solution processable and selectively printable. This letter reports the selective growth of single-crystal ZnO nanostructures based on the microcontact printing of an inorganic nanocrystal seeding film. The pattern-transfer quality is dependent on the concentration of the inking solution. Variable yet controllable anisotropic growth of ZnO nanowires has been demonstrated on the transferred patterns of ZnO nanocrystal films. The patterning and growth of these highly ordered arrays of ZnO nanostructures employ a simple soft lithography technique and mild reaction conditions at low temperature and in the absence of harmful organic additives.     

Growing ordered arrays of vertically aligned copolymer nanowires for supercapacitors with high stability

Journal of Solid State Electrochemistry - In this report, we present a novel platform to study the formation of delicate ordered vertically aligned copolymer nanowires array with EDOT and Py as the...     

Modification of vertically aligned carbon nanotube arrays with palladium nanoparticles for electrocatalytic reduction of oxygen

A novel type of palladium nanoparticles-modified multiwalled carbon nanotubes composite-electrode with electrocatalytic activity for oxygen reduction is presented. The nanocomposite was prepared by magnetron sputtering deposition with Pd in Ar atmosphere on MWNTs, which were synthesized on Ta plates by chemical vapor deposition. Both scanning electron microscopy and transmission electron microscopy were employed to observe the surface morphology. The Pd nanoparticles, with diameters around 5 nm, are dispersed at the tips and on the sidewalls of the MWNTs. Voltammetry, amperometry and electrochemical impedance measurements were used to demonstrate the strong electrocatalytic activity of the nanocomposite in acid solution. Compared to the bare MWNT electrode, the PdNPs/MWNT nanocomposite shows a positive shift of the O₂ reduction current at onset potentials from +400 to +500 mV, a concurrent 1.5-fold increase in the O₂ reduction peak current with high stability. The successful preparation of PdNPs/MWNTs nanocomposite by magnetron sputtering deposition opens a new path for an efficient dispersion of promising nanoparticles for fuel cells and O₂ sensors.     

Production and properties of fibers spun from nylon 6/lithium chloride mixtures

The possibility of producing high-modulus nylon 6 fibers by incorporation of lithium chloride (LiCl) in the polymer prior to spinning and drawing has been examined. Samples containing 2% and 4% LiCl (w/w) together with an unsalted control were studied. Particular attention was given to optimizing the spinning process by varying the melt temperature and the draw-down. The spun fibers were subsequently drawn in a tensile testing machine at 135°C, preliminary studies having established that this was desirable for the production of high-modulus material. The influence of annealing after drawing was also examined. Drawn fiber moduli in the range 8–9 GPa were obtained, compared with ca. 5–6 GPa for unsalted material. Limited structural studies (birefringence and wide-angle x-ray diffraction) suggest that the enhancement of modulus is due to an increase in the stiffening effect of extended molecules in the noncrystalline regions. Dynamic mechanical measurements show that there is reduced chain mobility in the disordered regions of the polymer, suggesting strong polymer-ion interactions. The salt can be readily removed by washing the fibers in boiling water, with significant reduction in moduli. This militates against commercial application of the salted fibers.     

A quantum dot sensitized solar cell based on vertically aligned carbon nanotube templated ZnO arrays

We report on a quantum dot sensitized solar cell (QDSSC) based on ZnO nanorod coated vertically aligned carbon nanotubes (VACNTs). Electrochemical impedance spectroscopy shows that the electron lifetime for the device based on VACNT/ZnO/CdSe is longer than that for a device based on ZnO/CdSe, indicating that the charge recombination at the interface is reduced by the presence of the VACNTs. Due to the increased surface area and longer electron lifetime, a power conversion efficiency of 1.46% is achieved for the VACNT/ZnO/CdSe devices under an illumination of one Sun (AM 1.5G, 100 mW/cm²).     

Synthesis and photocatalytic properties of vertically aligned Bi2S3 platelets

Vertically aligned Bi₂S₃ platelets have been synthesized on FTO substrate via a simple hydrothermal process. X-ray diffraction analysis confirms the orthorhombic structure of the platelets. The results of scanning electron microscopy show that the Bi₂S₃ platelets interconnect with each other. The length of platelets is about 5 μm and the thickness ranges from 50 to 150 nm. The photocatalytic activity studies reveal that the synthesized Bi₂S₃ platelets exhibit excellent photocatalytic performance in rapidly degrading aqueous methylene blue dye solution under UV irradiation. A degradation ratio of 56% was obtained for the Bi₂S₃ platelets at 120 min and about 99% at 240 min. These results suggest that Bi₂S₃ platelets will be an interesting candidate for photocatalytic detoxification under UV light.     

Patterned growth of vertically aligned silicon nanowire arrays for label-free DNA detection using surface-enhanced Raman spectroscopy

Patterning is of paramount importance in many areas of modern science and technology. As a good candidate for novel nanoscale optoelectronics and miniaturized molecule sensors, vertically aligned silicon nanowire (SiNW) with controllable location and orientation is highly desirable. In this study, we developed an effective procedure for the fabrication of vertically aligned SiNW arrays with micro-sized features by using single-step photolithography and silver nanoparticle-induced chemical etching at room temperature. We demonstrated that the vertically aligned SiNW arrays can be used as a platform for label-free DNA detection using surface-enhanced Raman spectroscopy (SERS), where the inherent “fingerprint” SERS spectra allows for the differentiation of closely related biospecies. Since the SiNW array patterns could be modified by simply varying the mask used in the photolithographic processing, it is expected that the methodology can be used to fabricate label-free DNA microarrays and may be applicable to tissue engineering, which aims to create living tissue substitutes from cells seeded onto 3D scaffolds.

Patterned growth of vertically aligned ZnO nanowire arrays on inorganic substrates at low temperature without catalyst

We report an approach for growing aligned ZnO nanowire arrays with a high degree control over size, orientation, dimensionality, uniformity, and possibly shape. Our method combines e-beam lithography and a low temperature hydrothermal method to achieve patterned and aligned growth of ZnO NWs at <100degreesC on general inorganic substrates, such as Si and GaN, without using catalyst. This approach opens up the possibility of applying ZnO nanowires as sensor arrays, piezoelectric antenna arrays, two-dimensional photonic crystals, IC interconnects, and nanogenerators.     

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.     

Centrifugally spun poly(ethylene oxide) fibers rival the properties of electrospun fibers

Centrifugal force spinning (CFS), also known as centrifugal spinning, forcespinning, or rotary jet spinning, provides considerably higher production rates than electrospinning (ES), but the more widespread use of CFS as an alternative depends on the ability to produce fibers with robust thermal and mechanical properties. Here, we report the CFS of poly(ethylene oxide) (PEO) fibers made using a spinning dope formulated with acetonitrile (AcN) as the volatile solvent, and we describe the thermal and mechanical properties of the centrifugally-spun fibers. Even though the formation, diameter, and morphology of electrospun and centrifugally-spun PEO fibers are relatively well-studied, the article presents three crucial contributions: the pioneering use of PEO solutions in AcN as spinning dope, characterization of crystallinity and mechanical properties of the centrifugally-spun PEO fibers, and a comparison with the corresponding properties of electrospun fibers. We find that fiber formation occurrs for the chosen CFS conditions if polymer concentration exceeds the entanglement concentration, determined from the measured specific viscosity. Most significantly, the centrifugally spun PEO fibers display crystallinity, modulus, elongation-at-break, and fiber diameter that rival the properties of electrospun PEO fibers reported in the literature.     

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.     

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.     

Membranes of vertically aligned superlong carbon nanotubes

In the present work, we have developed a simple but effective method to prepare superlong vertically aligned carbon nanotubes (SLVA-CNT) and epoxy composite membranes, and we have demonstrated that various liquids, including water, hexane, and dodecane, can effectively pass through the SLVA-CNT membranes. These results were confirmed by molecular dynamics simulations. While the mechanical densification was used to further enhance the flow transport through the SLVA-CNT membranes, we developed in this study a magnetic-nanoparticle switching system to turn on and off the flow through the nanotube membrane by simply applying an alternating voltage. The methodologies developed in this study should have a significant implication to the development of various smart membranes for advanced intelligent systems.     

Structure and properties of novel fibers spun from cellulose in NaOH/thiourea aqueous solution

Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing.