Ordered Titanium Dioxide Nanotube Research Articles

Fabrication of Highly Ordered Titania Nanotubes in Viscous Organic Electrolytes

The TiO2 nanotubes with a highly ordered structure on titanium were grown by a self-organized electrochemical anodization with viscous organic electrolytes containing small additions of fluorides as the supporting electrolyte. The structure and composition of the as-anodized nanotubes were characterized by field emission scanning electron microscopy. The formation mechanism of the nanotubes was discussed.

Preparation and hydrogen gas sensitive characteristics of highly ordered titania nanotube arrays

In this paper, we report the growth and characteristics of titania nanotube arrays prepared by anodic oxidation and then annealed in an oxygen atmosphere at 500°C. The titania nanotube arrays presented high sensitivity to hydrogen gas. The crystalline phase of the samples was checked by X-ray diffraction (XRD). The differences in the nanotubes morphology attributed to the etched samples due to anodization potential, reaction time and the electrolyte concentration were analyzed by scanning electron microscopy (SEM). The gas sensitive parameters of the samples were obtained from resistance, the response time and the recovery time at different temperatures.

Preparation and photoelectrochemical properties of a hybrid electrode composed of polypyrrole encapsulated in highly ordered titanium dioxide nanotube array

We demonstrated in this paper that polypyrrole encapsulated in highly ordered TiO 2 nanotubes array (PPy/TiO 2 NTs) electrode could be obtained via two steps: (1) electrosynthesis of TiO 2 nanotube array in HF solution by anodization method; (2) followed by electropolymerization of pyrrole encapsulated in the TiO 2 nanotubes array. The morphological characteristics and structures of PPy/TiO 2 NTs electrode were examined by field-emission scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. The photoelectrochemical properties were studied in a three-electrode cell with 0.5 M Na 2SO 4 solution as supporting electrolyte. The photocurrent was dramatically enhanced on the PPy/TiO 2 NTs electrode, comparing with that on bare TiO 2 NTs electrode. A photocurrent density of 1.52 mA cm − 2 and the incident photon to electron conversion efficiency of 73.21% were obtained under an UV illumination of 10 mW cm − 2 .

The formation mechanism of titania nanotube arrays in hydrofluoric acid electrolyte

Self-organized and highly ordered titania nanotube arrays (TNAs) were prepared through electrochemical anodic oxidization on a titanium foil in 0.5 wt.% hydrofluoric acid (HF) electrolyte. The current density and morphology images during the formation process of TNAs were studied. Results show that the formation of TNAs includes the following processes. Initially, dense oxide of titania was rapidly formed on the titanium surface, followed by small pore formation. The adjacent small pores were then integrated and become larger pores. At the same time, small tubes were transformed. These small tubes were further integrated into larger tubes until the primary tube formation. Finally, the tubular structure was gradually optimized and eventually developed into the highly ordered TNAs. A model was proposed to explain the formation mechanism of TNAs fabricated on a titanium foil in HF acid electrolyte.

Fabrication and characterization of highly-ordered titania nanotubes via electrochemical anodization

Highly ordered titania nanotube arrays are fabricated via anodization process in electrolytes containing HF and acetic acid. Graphite was used as cathode. The size of titania can be controlled by changing anodizing voltage and bath temperature. From FE-SEM images, we observed the microstructure of titania nanotubes. Whereas, these nanotubes were amorphous; to induce crystallinity, the products were annealed at different temperatures. XRD analysis shows that the anatase and rutile phase emerge at different conditions. The optical properties were characterized via UV–vis absorption analysis. On the basis of these work, a discussion on the growth mechanism of nanotube structure was presented in this paper.

Photoelectrochemical oxidation behavior of methanol on highly ordered TiO2 nanotube array electrodes

The highly ordered titanium dioxide nanotube array (HOTDNA) electrodes were prepared in hydrofluoric acid solution by electrochemical anodic oxidation technique on a pure titanium sheet. The HOTDNA electrodes were characterized by X-ray diffraction, SEM microscopy, and UV–vis spectra. It has shown high density, well ordered and uniform titanium dioxide nanotube array film covered on these electrodes and the TiO2 structure depending on the heating condition, the anatase phase of TiO2 appeared when heating to 500 °C. The photoelectrochemical characteristics of methanol in 0.5 M Na2SO4 on the HOTDNA electrodes were investigated. The cyclic voltammetry, photocurrent-time and open-circuit photopotential response of methanol on the HOTDNA electrode were represented and significant photogenerated current was observed upon illumination in the UV regions with the light of 253.7 nm central wavelength. The effect of variables such as light intensity, applied potential, and methanol concentration on the photoelectrochemical response was investigated. It was found that the photocurrent was greatly influenced by these factors.

Photoelectrocatalytic Activity of Highly Ordered TiO2 Nanotube Arrays Electrode for Azo Dye Degradation

A highly ordered titanium dioxide nanotube arrays (HOTDNA) electrode was prepared in hydrofluoric acid solution by electrochemical anodization technique on a pure titanium sheet. The HOTDNA electrode was characterized by FE-SEM microscopy, X-ray diffraction, and UV-vis spectra. The linear-sweep photovoltammetry response on the HOTDNA electrode is presented in this work. The photogenerated current of 0.3 mA/cm2 was observed significantly upon illumination with applied potential of 0.5 V in the UV regions at the central wavelength of 253.7 nm. Photoelectrocatalytic (PEC) and photocatalytic (PC) activities of the HOTDNA electrode were evaluated in the degradation of methyl orange (MeO) in aqueous solution. A set of optimized conditions such as anodic potential, calcinations temperature, and MeO concentration on the PEC activity was investigated. The PEC and PC activities of HOTDNA electrode were compared. We concluded that the HOTDNA electrode was an effective photoelectrode for achieving an enhanced MeO degradation.

Fabrication and Catalytic Properties of Co−Ag−Pt Nanoparticle-Decorated Titania Nanotube Arrays

Highly ordered titania nanotube arrays are fabricated by anodic oxidation of titanium in a fluoride-ion-containing electrolyte. In this work Co−Ag−Pt nanoparticles, approximately 20 nm in diameter, are electrochemically deposited inside the nanotubes and the catalytic properties of the resultant architecture examined using Mn2+/Mn3+ as the probe. The effect of Co, Ag, and Pt loading content on the catalytic activity is investigated. In comparison to a Pt electrode, the oxidation potential of the Co−Ag−Pt/titania nanotube array electrode is negatively shifted by 93 mV and the peak current increased by a factor of 9.

Effect of water content of ethylene glycol as electrolyte for synthesis of ordered titania nanotubes

Anodization of Ti using fluoride containing polyhydric alcohols such as ethylene glycol or glycerol as electrolyte results in ordered arrays of TiO 2 nanotubes with a smooth surface and a very high aspect ratio. However, the reproducibility of the result is affected by many experimental parameters, notably the water content. In this investigation, anodizations of Ti foil in anhydrous ethylene glycol +0.2 wt% NH 4F solution (EG solution) with 0–1.0 wt% water additions were carried out at 20 V for 45 min in a dry-argon filled controlled-atmosphere glove box. It was observed that a minimum amount of 0.18 wt% of water addition was required to form a well ordered TiO 2 nanotubular arrays. When the anhydrous EG solution was reused for third time, ordered arrays of nanotubes started to form. When the water addition to the EG solution was more than 0.5 wt%, formation of ridges was observed on the nanotubes. XPS results showed presence of un-anodized Ti element in the anhydrous condition and presence of organic and (NH 4) 2TiF 6 type compounds in all the anodized samples in addition to the regular TiO 2 phase. The results underline the influence of water content and local pH condition to form the ordered nanotubular arrays.

Bioelectrocatalytic application of titania nanotube array for molecule detection

A bioelectrocatalysis system based on titania nanotube electrode has been developed for the quantitative detection application. Highly ordered titania nanotube array with inner diameter of 60nm and total length of 540nm was formed by anodizing titanium foils. The functionalization modification was achieved by embedding glucose oxidases inside tubule channels and electropolymerizing pyrrole for interfacial immobilization. Morphology and microstructure characterization, electrochemical properties and bioelectrocatalytic reactivities of this composite were fully investigated. The direct detection of hydrogen peroxide by electrocatalytic reduction reaction was fulfilled on pure titania nanotube array with a detection limit up to 2.0×10−4mM. A biosensor based on the glucose oxidase–titania/titanium electrode was constructed for amperometric detection and quantitative determination of glucose in a phosphate buffer solution (pH 6.8) under a potentiostatic condition (−0.4V versus SCE). The resulting glucose biosensor showed an excellent performance with a response time below 5.6s and a detection limit of 2.0×10−3mM. The corresponding detection sensitivity was 45.5μAmM−1cm−2. A good operational reliability was also achieved with relative standard deviations below 3.0%. This novel biosensor exhibited quite high response sensitivity and low detection limit for potential applications.

Photoelectrochemical application of nanotubular titania photoanode

Titania/titanium (TiO 2/Ti) electrodes with tailored surface structure have been fabricated by galvanostatic–potentiostatic anodization process. Highly ordered titania nanotubes array can be prepared by electrolyzing titanium foil at 20 V for 40 min in HF–H 3PO 4 electrolyte. Comparatively, micro-structured and crystallized TiO 2 multiporous film can be prepared at 20–40 V for 6 h in H 2SO 4–H 3PO 4–H 2O 2–HF electrolyte. The morphological characteristics and crystal behaviors of both nanotubular and micro-structured TiO 2 films are investigated by field emission scanning electron microscopy and X-ray diffraction measurement. Photoelectrochemical properties of TiO 2/Ti film electrodes are examined by anodic photocurrent response and cyclic voltammetry measurement. Photocatalytic and photoelectrocatalytic application are investigated by using either nanotubular TiO 2/Ti thin-film or micro-structured TiO 2/Ti thick-film electrodes as photoanodes for recalcitrant organic pollutant degradation.

Transparent Highly Ordered TiO2 Nanotube Arrays via Anodization of Titanium Thin Films

Titanium thin films, 400 nm to 1000 nm thick, fabricated by radio frequency (rf) sputter deposition are anodized in an electrolyte containing acetic acid and hydrofluoric acid to form optically transparent films of highly ordered titania nanotube arrays. Real-time monitoring of the anodization current, at a fixed potential, is used to controllably eliminate the Ti layer underneath the titanium oxide nanotube array without disturbing the architecture. Fabrication variables critical to achieving the transparent nanotube-array film include annealing temperature of the anodized, initially amorphous nanotube array and Ti-film sputter deposition variables, including rate, film thickness, and substrate temperature. Structural investigations on the transparent nanotube arrays reveal only the presence of the anatase phase even after annealing at 500 °C. In contrast, both rutile and anatase phases were observed in films with a metal layer underneath the nanotubes and annealed in an oxygen ambient above 430 °C. Rutile growth occurs at the nanotube–metal interface as metal oxidation takes place during annealing. The average refractive index of the transparent nanotube-array film is found to be 1.66 in the UV-vis range, with a calculated porosity of 67 %; the bandgap is determined as 3.34 eV, with a bandgap tail extending to 2.4 eV.

Visible light photoelectrochemical and water-photoelectrolysis properties of titania nanotube arrays

We examine the visible light water-photoelectrolysis and photoelectrochemical properties of highly ordered titania nanotube arrays as a function of nanotube crystallinity, length (up to 6.4 μm), and pore size. Most noteworthy of our results, under visible light AM 1.5 illumination (100 mW/cm 2) the titania nanotube array photoanodes (1 cm 2 area), pore size 110 nm, wall thickness 20 nm, and length 6 μm, generate hydrogen by water photoelectrolysis at a rate of 175 μL/h, with a photoconversion efficiency of 0.6%. The energy–time normalized hydrogen evolution rate is 1.75 mL/h W. The oxygen bubbles evolving from the nanotube array photoanode do not remain on the sample, hence the output remains stable with time irrespective of the duration of hydrogen production.

Enhanced Photocleavage of Water Using Titania Nanotube Arrays

In this study highly ordered titania nanotube arrays of variable wall thickness are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness and length of the nanotubes can be controlled via anodization bath temperature. We find that the nanotube wall thickness is a key parameter influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner pore diameter nanotube arrays, those fabricated in a 5 degrees C anodization bath, 224 nm length and 34 nm wall thickness produced a photoanodic response that was thrice that of a nanotube array fabricated in a 50 degrees C anodization bath, 120 nm length and 9 nm wall-thickness. At high anodic polarization, above 1 V, the quantum efficiency under 337 nm illumination was greater than 90%. For the 5 degrees C anodization bath samples (22 nm pore-diameter, 34 nm wall thickness), upon 320-400 nm illumination at an intensity of 100 mW/cm(2), hydrogen gas was generated at the power-time normalized rate of 960 micromol/h W (24 mL/h W) at an overall conversion efficiency of 6.8%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.

A Sentinel Sensor Network for Hydrogen Sensing

A wireless sensor network is presented for in-situ monitoring of atmospheric hydrogen concentration. The hydrogen sensor network consists of multiple sensor nodes, equipped with titania nanotube hydrogen sensors, distributed throughout the area of interest; each node is both sensor, and data-relay station that enables extended wide area monitoring without a consequent increase of node power and thus node size. The hydrogen sensor is fabricated from a sheet of highly ordered titania nanotubes, made by anodization of a titanium thick film, to which platinum electrodes are connected. The electrical resistance of the hydrogen sensor varies from 245 Ω at 500 ppm hydrogen, to 10.23 kΩ at 0 ppm hydrogen (pure nitrogen environment). The measured resistance is converted to voltage, 0.049 V at 500 ppm to 2.046 V at 0 ppm, by interface circuitry. The microcontroller of the sensor node digitizes the voltage and transmits the digital information, using intermediate nodes as relays, to a host node that downloads measurement data to a computer for display. This paper describes the design and operation of the sensor network, the titania nanotube hydrogen sensors with an apparent low level resolution of approximately 0.05 ppm, and their integration in one widely useful device.