Oxide Nanotube Arrays Research Articles

Highly-ordered dye-sensitized TiO2 nanotube arrays film used for improving photoelectrochemical electrodes

Thin titanium oxide nanotube arrays (TNAs) films were synthesized by anodization of titanium foil in an aqueous dimethyl sulfoxide solution using a platinum foil counter electrode. TNAs up to 6.8 μm in length, 120 nm in inner pore diameter, and 20 nm in wall thickness were obtained by 40 V potentials anodization for 24 h. Their microstructures and surface morphologies were characterized by XRD, TEM, SAED and UV-vis spectroscopy. The photoelectrochemical properties of as-prepared unsensitized and dye-sensitized TNAs electrodes were examined under simulated solar light (AM 1.5, 100 mW/cm2) illumination. The results showed that the photocurrent of the dye-sensitized TNAs electrodes reached 6.9 mA/cm2, which was 6 times more than that of the dye-sensitized TiO2 nanoparticles (TNPs) electrodes. It implied that the electron transport process and the charge recombination suppression within TNAs electrodes were much more favorable in comparison with that in the TNPs electrodes. Electrodes applying such kind of titania nanotubes will have a potential to further enhance the efficiencies of TNAs-based dye-sensitized solar cells.

Study on the Anticorrosion, Biocompatibility, and Osteoinductivity of Tantalum Decorated with Tantalum Oxide Nanotube Array Films

With its excellent anticorrosion and biocompatibility, tantalum, as a promising endosseous implant or implant coating, is attracting more and more attention. For improving physicochemical property and biocompatibility, the research of tantalum surface modification has increased. Tantalum oxide (Ta(2)O(5)) nanotube films can be produced on tantalum by controlling the conditions of anodization and annealing. The objective of our present study was to investigate the influence of Ta(2)O(5) nanotube films on pure tantalum properties related with anticorrosion, protein adsorption, and biological function of rabbit bone mesenchymal stem cells (rBMSCs). The polarization curve was measured, the adsorption of bovine serum albumin and fibronectin to Ta(2)O(5) nanotubes was detected, and the morphology and actin cytoskeletons of the rBMSCs were observed via fluorescence microscopy, and the adhesion and proliferation of the rBMSCs, as well as the osteogenic differentiation potential on tantalum specimens, were examined quantificationally by MTT and real-time PCR technology. The results showed that Ta(2)O(5) nanotube films have high anticorrosion capability and can increase the protein adsorption to tantalum and promote the adhesion, proliferation, and differentiation of rBMSCs, as well as the mRNA expression of osteogenic gene such as Osterix, ALP, Collagen-I, and Osteocalcin on tantalum. This study suggests that Ta(2)O(5) nanotube films can improve the anticorrosion, biocompatibility, and osteoinduction of pure tantalum, which provides the theoretical elaboration for development of tantalum endosseous implant or implant coating to a certain extent.

A gold-coated titanium oxide nanotube array for the oxidation of borohydride ions

Highly ordered titanium dioxide nanotube (≈100–200nm pore diameter) arrays, were formed on a titanium foil by anodising at a cell voltage of 60V, in two stages. The nanotube arrays were over-coated with nanoparticulate gold using physical vapour deposition (PVD) sputtering resulting in a well dispersed coating. The electrodes were used to study the oxidation of 20×10−3moldm−3 borohydride ions in 3moldm−3 NaOH, at 298K, by cyclic voltammetry. The gold-coated titanium oxide nanotube array electrodes provided higher electrical charge per unit mass of gold and unit area that a gold nanoparticle deposit on carbon and gold adsorbed on hydrothermally synthesised titanate nanotubes offering a reliable and low cost technique to produce a high surface area anode for a direct borohydride fuel cell.

PHOTOCATALYTIC ACTIVITY AND PHOTOCURRENT PROPERTIES OF TiO2 NANOTUBE ARRAYS INFLUENCED BY CALCINATION TEMPERATURE AND TUBE LENGTH

In this article, titanium oxide nanotube arrays (TiO2–NTAs) were fabricated by anodic oxidation in an ethylene glycol (EG) electrolyte solution containing 0.25 wt.% NH4F. By varying anodized time and annealed temperature, the obtained nanotube arrays behaved different photocatalytic (PC) activities and photocurrent properties. These samples were characterized by scanning electronic microscope (SEM), X-ray powder diffraction (XRD). It was indicated in SEM images that TiO2 nanotube manifests highly ordered structure which, however, has been completely destroyed when the temperature comes to 800°C. XRD manifested that TiO2 nanotubes with various kinds of length all possessed anatase crystallite when annealed at 500°C; meanwhile, with certain length, TiO2–NTAs annealed at series calcination temperature range of 300–600°C also presented anatase crystallite, which is gradually enhanced with the increment of temperature. At 700°C, mixed structure was observed which was made up of proportions of overwhelming anatase and toothful rutile. Methyl blue (MB) degradation and photocurrent measurement testified that TiO2–NTAs under 4 h oxidation and 3 h of 600°C calcination manifested the highest activity and photocurrent density.

The effect of highly ordered titania nanotube structures on hydrogen gas detection

Different titanium oxide nanotubes were synthesized by anodizing the surface of titanium foil in two electrolyte solutions containing hydrofluoric acid and ethylene glycol. The samples were heat‐treated in a furnace. The microstructure and phase transformations of the nanotubes were investigated by X‐ray diffraction and field emission–scanning electron microscope. The nanoscale geometry of the nanotubes is responsible for the outstanding hydrogen gas sensitivities. A remarkable variation in electrical conductance has been observed in titanium oxide nanotube arrays that were prepared in hydrofluoric acid. This sensor exhibits a large resistance variation in the presence of very small quantities of hydrogen gas at 25 °C. The sensors show reversibility, repeatability, negligible drift, and wide dynamic range. Copyright © 2012 John Wiley & Sons, Ltd.

Synthesis of Self-Aligned Titanium Oxide Nanotube Arrays in Ammonium Fluoride-Ethylene Glycol Electrolytes with Different Water Contents

The aim of this research is to fabricate of TiO2 nanotube arrays by potentiostatic anodisation process on titanium sheets. Anodisation is carried out under various applied potentials ranging from 20 to 30 volts for 1-3 hours at room temperature. Anodised were conducted in 1-4 wt% NH4F, water-based electrolyte and ethylene glycol-based electrolyte. The morphology of the anodised surfaces were characterised by scanning electron microscopy. When titanium sheets were anodised in various conditions, surface morphology of anodised titanium change remarkably with the changing of applied voltages, chemical composition of the electrolyte and anodisation time. The results of the present work show that the highly ordered and uniformly distributed TiO2 nanotubes on titanium substrate can be fabricated by using mixtures of NH4F, ethylene glycol and water with appropriate conditions. Moreover, the anodisation potential and the water content play significant roles in the formation of TiO2 nanotube with different inner tube diameters. The length of TiO2 nanotube was controlled by anodisation time.

Vertical oxide nanotubes connected by subsurface microchannels

We describe the fabrication of arrays of oxide nanotubes using a combination of bottom up and top down nanofabrication. The nanotubes are made from epitaxially grown semiconductor nanowires that are covered with an oxide layer using atomic layer deposition. The tips of the oxide-covered nanowires are removed by argon sputtering and the exposed semiconductor core is then selectively etched, leaving a hollow oxide tube. We show that it is possible to create fluidic connections to the nanotubes by a combination of electron beam lithography to precisely define the nanotube positions and controlled wet under-etching. DNA transport is demonstrated in the microchannel. Cells were successfully cultured on the nanotube arrays, demonstrating compatibility with cell-biological applications. Our device opens up the possibility of injecting molecules into cells with both spatial and temporal control. Open image in new window

Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays.

Vertically aligned iron oxide nanotube arrays and porous magnetite nanostructures as three-dimensional electrodes for lithium ion microbatteries

The simple preparations of vertically aligned iron oxide nanotube arrays and porous magnetite nanostructures and their application as three-dimensional electrodes for lithium ion microbatteries are introduced. Nanotube arrays are well formed across a very large area with a ∼40 nm nanotube diameter. The nanotubes change to be porous nanostructures like nano-pillar arrays after heat treatment under 10% H2. These two structures allow the omission of conductive agents and binder in the battery assembly. In addition, the structural advantages for lithium ion and electron transport are exhibited through excellent cyclic stability and rate capability even at very high current density, which can complete one charge/discharge in a few minutes.

Heat treatment and electrochemical activation of titanium oxide nanotubes: The effect of hydrogen doping on electrochemical behavior

During the course of the present study, highly dense arrays of titanium oxide nanotubes (TON) were fabricated by anodization of titanium foil in aqueous fluoride solutions. The obtained TON arrays were then subjected to annealing and electrochemical treatment, followed by characterization using scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance (EI) techniques. By combining the effects of annealing and cathodic potential treatment, the cyclic voltammetry shows that the TON arrays catalyze the hydrogen evolution in acidic medium. This catalytic activity was not observed when the rutile phase started to form in TON arrays. EI results show that TON conductivity is substantially improved by cathodic potential treatment only when it contains the anatase phase. This was also confirmed by the cyclic voltammetric scan for the Fe(CN) 6 3−/Fe(CN) 6 4− couple, where a smaller peak separation between anodic and cathodic peaks was observed, rather than as-anodized TON.

Influence of Structure Parameters and Crystalline Phase on the Photocatalytic Activity of TiO2 Nanotube Arrays

Titanium oxide nanotube arrays (TiO2-NTAs) with different diameters and lengths are prepared by anodization of titanium foils in a water/ethylene glycol solution (5:95 V/V) containing 0.3 wt% NH4F. The effects of the diameters, lengths and crystalline phases of the NTAs on the photocatalytic (PC) activity are systematically evaluated. Larger pore diameter results in higher PC activity. The PC activity increases initially and then decreases with lengths for TiO2-NTAs and the optimal length that yields the highest PC activity is observed to be 6.2 microm. The crystalline phase and corresponding PC activity depend on the calcination temperature and their relationship is also investigated. The amorphous-to-anatase and anatase-to-rutile phase transitions initially occur at 300 and 500 degrees C, respectively. The PC activity of TiO2-NTAs initially increases with calcination temperature from 250 to 500 degrees C and then decreases at higher calcination temperature. The enhanced PC activity observed from the samples annealed at 250-450 degrees C is attributed to the better anatase crystalline structure at higher calcination temperature. The highest PC activity with regard to photodecomposition of methyl orange is observed from TiO2-NTAs calcined at 500 degrees C, which coincides with the anatse-to-rutile phase transformation. The synergistic effect of the anatase TiO2-NTAs and rutile barrier layers facilitate interfacial electron transfer consequently enhancing the PC activity. Further elevation of the calcination temperatures to 550 and 600 degrees C exhibits diminished PC activity because the NTs become shorter due to conversion of the bottom of anatase NTs into rutile film.

The Fabrication and Property of Hydrophilic and Hydrophobic Double Functional Bionic Chitosan Film

A new kind of hydrophobic bionic chitosan film was fabricated by simulating the surface structure of lotus leaf. The titanium oxide nanotube array was used as templates. Scanning electron microscopy (SEM) images show that one side of this films have nano-scale rough surface with spherical protrusions alike the surface of lotus leaf. The diameter of the protrusions is about 100 nm, which is equal to diameter of the titanium oxide nanotube. The water contact angle of chitosan films is up to 120 degrees and it is hydrophobic. The other side of the film is flat and the contact angle is 70 degrees. That indicated that the hydrophilism of natural materials is connected with the surface structures. The double functional chitosan films, one side is hydrophilic, the other is hydrophobic, can be made by an easy method. This method is non-toxic and clean. The double functional chitosan film will improve the application of chitosan films in medicine.

The formation of micrometer-long TiO2 nanotube arrays by anodization of titanium film on conducting glass substrate

Micrometer-long titanium oxide nanotube arrays, tens of nanometers in diameter, were fabricated by anodization of titanium film coated on a conducting glass substrate. The Ti film was deposited by magnetron sputtering at room temperature. The effect of anodizing conditions on the formation of TiO 2 nanotubes was investigated. The results indicate that dense and uniform Ti film deposited under 150 W at room temperature was favorable for the formation of ordered nanotube arrays. The average diameter of the TiO 2 nanotubes varied from 35 to 95 nm when the anodization potential changed from 10 to 40 V. Micrometer-long nanotubes (1.1 μm) with good adhesion to the substrate could be obtained in 0.5 wt% NH 4 F/glycerol at 30 V for 2 h. After heat treatment, the crystalline anatase nanotubes show enhanced photoelectrochemical activity compared with those anodized in 1 M H 3 PO 4/0.5 wt% HF. This is attributed to the increased light-harvesting abilities.

Superparamagnetic behavior in cobalt iron oxide nanotube arrays by atomic layer deposition

Cobalt iron oxide nanotube arrays with various wall thicknesses were prepared by atomic layer deposition in porous anodic alumina template. Nanotubes uniform in thickness and homogeneous in composition can be obtained with aspect ratios on the order of 50. These nanotubes have a polycrystalline spinel structure. Both the mean grain size and the grain size distribution increase with the tube wall thickness. Correspondingly, their magnetic properties (remanence and coercive field) also have a strong dependence on the thickness for measurements carried out at 300 K. This dependence is attributed to the superparamagnetic behavior of the grains that constitute the nanotube.

Fabrication, biomolecular assembly and electrochemical biosensing applications of highly ordered Ti–Pd alloy oxide nanotube arrays

Pd–TiO 2 nanotube arrays (Pd–TNTs) which are highly ordered and vertically grown on Ti–0.2Pd alloy were fabricated by electrochemical anodization for the first time. The obtained Pd–TNTs were utilized as a “super vessel” for assembly of myoglobin (Mb) and biosensing applications. Experimental results demonstrate that the resulting Pd–TNTs display an enhanced capability for the immobilization of myoglobin. The direct electrochemistry of the immobilized Mb is dramatically facilitated, indicated by a couple of well-defined redox peaks and a very large electron transfer rate constant ( k s) of 20.7 s − 1 . Furthermore, Mb/Pd–TNTs present excellent electrocatalytic activity for the detection of trichloroacetic acid with a wide linear range from 0.5 to 96 μM and a low detection limit of 94 nM (3 N/S). Pd–TNTs with highly ordered nanotubular structure open a facile way to obtain ideal materials for biomolecular assembly and construct electrochemical biosensors.

Polypyrrole/Titanium Oxide Nanotube Arrays Composites as an Active Material for Supercapacitors

The authors present the first reported use of vertically oriented titanium oxide nanotube/polypyrrole (PPy) nanocomposites to increase the specific capacitance of TiO2 based energy storage devices. To increase their electrical storage capacity, titanium oxide nanotubes were coated with PPy and their morphologies were characterized. The incorporation of PPy increased the specific capacitance of the titanium oxide nanotube based supercapacitor system, due to their increased surface area and additional pseudo-capacitance.

Highly ordered iron oxide nanotube arrays as electrodes for electrochemical energy storage

Highly ordered α-Fe 2O 3 nanotube arrays have been fabricated by a simple and cost-effective anodization method on iron foils. The α-Fe 2O 3 nanotube arrays exhibit high specific capacitance (138 F·g − 1 at 1.3 A·g − 1 ), remarkable rate capability (91 F·g − 1 at 12.8 A·g − 1 ) and good cycling stability (the capacitance retention close to 89% after 500 cycles), due to the unique nanostructures of the α-Fe 2O 3 nanotube arrays, which providing high surface area, fast ion transport pathways and robust structures. These features made the α-Fe 2O 3 nanotube array electrode very attractive for supercapacitor applications.

Formation of the Microstructure of TiO2 Film Through Anodic Oxidation of Titanium

Recent titanium oxide nanotube arrays have attracted attention for their applications. Titanium oxide nanotubes were prepared under potentiostat conditions (10 – 60 V) for various times (1 min – 3 hr). SEM observations revealed that the pore sizes of the nanotubes have a tendency to increase with an increase in the applied potential in the NH4F-glycerol-H2O electrolyte. Some corrosive pores were observed on the surface of titanium substrate at 40 V for 1 minute at 40°C. The pores covered the surface of the titanium substrate after 10 minutes, and some small pores were observed in the inner part of the pores, which should correspond to the combining of some small adjacent pores into a large one. The combining of the tubes were observed after 2 h and 3 h anodization times, and the nanotube arrays seem to be formed upward from the SEM side-views. The photocatalytic activity of the titanium oxide nanotubes was evaluated according to the JIS standard (JIS R 1703–2). The R factor of the titanium oxide nanotube arrays formed at 40 V and 40°C for a 3h the anodization time was 9.71 n mol/l·min, which was twice that of the titanium oxide thin film obtained by the rf-sputtering method.

Ordered Arrays of Ti-Mn Oxide Nanotubes for High Capacity Li-Ion Battery

Ordered arrays of vertically oriented Ti-Mn oxide nanotubes were synthesized by a simple anodization method. XRD pattern showed presence of TiO2 in the form of anatase and rutile in addition to Mn2O3 after annealing at 500 ºC. An experimental battery with Ti-Mn oxide nanotubes as anode and LiCoO2 cathode was assembled and charge-discharge experiments were carried out at different rates. At 1 C discharge rate, the nominal capacity was about 474 mAh/g and remained constant even after 30 cycles. The discharge behavior showed two components; the first with a decreasing potential possibly owing to super capacitor like behavior of the nanotubes and the second component with a plateau potential at 1.9 V owing to Li-ion extraction from the nanotubular walls. Vertical orientation of the nanotubes, contact of the individual nanotubes with the substrate and Mn incorporation in the TiO2 ensured faster diffusion and better charge transportation than conventional TiO2 anode.

Effect of Anode-Cathode Spacing on Anodic Formation of Self-Organized TiO<sub>2</sub> Nanotube Arrays

We report on the effect of anode-cathode spacing on the fabrication of TiO2 nanotube arrays by using a facile two-electrode anodization system. The experimental results show that the formation of nanotubes is affected by the anode-cathode spacing and the possible mechanism is also discussed. The as-formed TiO2 nanotube arrays were mainly examined by using a field emission scanning electron microscope. The present results are believed to be generalized to fabricate self-organized oxide nanotube arrays in other anodizing systems.