Nanotube Array Thin Films Research Articles

A strategy to improve the performance of TiO2 nanotube array film photocatalysts by magnetron-sputtered amorphous BiFeO3

Amorphous BiFeO3/TiO2 nanotube array thin films were prepared on indium tin oxide glass using an anodic oxidation technique coupled with magnetron sputtering. The morphology, structure, optical properties, photoelectrochemical properties, and photocatalytic activity of heterostructured nanotube array thin films with different morphologies of BiFeO3 were studied. HRTEM observations show the interface between amorphous BiFeO3 and anatase TiO2. The amorphous BiFeO3/TiO2 nanotube array thin films show enhanced visible-light absorption and outstanding separation and transfer of photoinduced charges. The BFO3-TNA sample shows excellent photocatalytic activity. By using it, 97.6% of chromium (VI) can be removed in 60 min under visible-light illumination. This work will provide a feasible route to further enhance the photocatalytic activities of visible-light responsive TiO2 nanotube array thin films as photocatalysts for rapidly removing chromium (VI) from water.

On the reflection and diffraction of carbon nanotube array thin film

A theory for determining the effective refraction index of carbon nanotube array thin film is developed based on Fresnel’s equation of wave normals. Here, the theory of a metallic film is used to determine the reflectivity and then to analyze the results of previous experiments on the optical properties of vertically aligned carbon nanotube arrays for different polarized incident lights. Both transverse electric-polarized lights and transverse magnetic-polarized lights are investigated, and the results agree well with the available experimental data. In a different case, when considering the weighted average of the polarized lights, the theoretical reflectivity for a non-polarized incident light is in excellent agreement with the experimental data. The refraction efficiency of a grating-patterned carbon nanotube array thin film is also investigated using the Fraunhofer diffraction theory. Based on the comparison of the theoretical and experimental results, it is concluded that the proposed theoretical model reveals the optical behavior of a carbon nanotube array thin film.

Investigation on voltaic effect based on one-dimensional TiO2 nanotube array thin film

This work is to develop a high-reliability long-life high-conversion-efficiency radio-isotope microbattery in order to meet power requirements of micro-electromechanical systems, micro-sensors, micro-actuators, wireless sensing net, and other electron devices working in harsh circumstances, such as polar, desert, subsea, outer surface, etc. Compared with traditional dry batteries, chemical batteries, fuel cells and solar cells, the radioactive isotope batteries have long service life, higher energy density, strong adaptability to environment, good work stability, no maintenance, and miniaturized size, etc. These advantages make the voltaic battery an attractive alternative. In this paper we present a voltaic battery with enhanced voltaic effect by using a wide-bandgap semiconductor TiO2 nanotube array thin film. An electrochemical anodic oxidation method is used to prepare the vertically oriented and highly ordered TiO2 nanotube array film on Ti plate. Electrolyte solution consists of ammonium fluoride, ethylene glycol, and deionized water. The structure (TiO2 nanotube array with diameter about 80-100 nm, wall thickness about 15-25 nm, and length 9 m) is characterized by field emission scanning electron microscope. The microstructure of the TiO2 nanotube array is characterized using X-ray diffraction. The effects of annealing condition on optical and electrical properties are studied. The electrical property is characterized by Keithley model 2450 source meter semiconductor characterization system in dark at room temperature. The voltaic batteries are assembled as a sandwiched structure (63Ni/TiO2 nanotube arrays film/Ti) using a radioisotope 63Ni plate and TiO2 nanotube array films. The experimental results show that the black TiO2 nanotube array film annealed at 450 ℃ in argon atmosphere could creates high visible-ultraviolet absorption due to a great many of oxygen vacancy defects generated in TiO2 nanotube array film. The oxygen vacancy signals are found by electron spin resonance. Compared with the planar structure, the nano-porous array structure has strong absorption to particles:most of the particles enter into the pores and are reflected or absorbed by the surface of the tube walls. With a 10 mCi 63Ni radiation source, the voltaic battery using black TiO2 nanotube array film can generate an open-circuited voltage of 1.02 V, a short-circuited current of 75.52 nA, and a maximum effective conversion efficiency of 22.48%.

Enhanced Photoelectrochemical Performance of Coaxial-Nanocoupled Strontium-Rich SrTiO3/TiO2 {001} Nanotube Arrays

The composition of a photocatalyst is the fundamental determinant of its photoability. Recently, significant attention has been focused on the ternary oxide epitaxial overlayers. Here, a highly active {001} facet dominant coaxial-nanocoupled SrTiO3/TiO2 nanotube array thin film was fabricated by a modified two-step anodization combined with a hydrothermal process. Through photoelectrochemical (PEC) measurements, such a coaxial-nanocoupled SrTiO3/TiO2 {001} surface reconstruction can definitely improve its PEC performance. The enhanced PEC performance and strongest photocurrent response of SrTiO3/TiO2 nanotubes (STNs) with a 2 h hydrothermal treatment were ascribed to the fast electron transfer in coaxial nanoarchitecture.

Nitrogen-doped TiO2 nanoparticles better TiO2 nanotube array photo-anodes for dye sensitized solar cells

Power conversion efficiency of dye sensitized solar cell (DSSC) is closely related to photo-anode's structure. It has been believed that titanium dioxide (TiO2) nanotube array thin film is one of the best photo-anode candidates for DSSC. However, the insufficient internal surface area and wide band gap of pure anatase limit their power conversion efficiency. Here we report a novel TiO2 nanotube array film synthesized by anodization followed by surface modification with nitrogen (N) doped TiO2 nanoparticles using a solvothermal method. The incorporation of N doped TiO2 nanoparticles along the wall of TiO2 nanotubes not only provides a large surface area for dye loading, but also increases the conductivity of the electrode, generating an overall power conversion efficiency of 2.53%, which is 68% higher than that with pure TiO2 nanotube array (with the length of 1.8μm) photoanode. When the length of TiO2 nanotube increased to 4.1μm, the overall power conversion efficiency can be improved to be 4.9%, which is higher than the previous reported results using the same length of nanotube.

Formation Process of TiO2 Nanotube Arrays Prepared by Anodic Oxidation Method

TiO2 nanotube array thin films have great potential in many fields, such as solar cell, photo catalyst, photo-induced cathodic protection for metals and bioactivity. In order to investigate the formation process of the TiO2 nanotube array thin films, the EIS spectrum and current density were measured during the anodic oxidation. The results showed that the formation process could be divided into four stages. The current density decreased sharply at the first stage, and then increased at the second stage, followed by declining and finally remained constant value. In addition, the current density increased with the anodic voltage. The EIS spectrum varied in different stage. The simulated circuit was composed three sections, the first sections indicated the resistance of the electrolyte, the second one gave the double layer structure between the electrolyte and titanium electrode, the third one was a inductive loop, which represented the anions absorbed on the surface of the TiO2 nanotube's wall. The more cations were absorbed, the higher value of the inductive loop would be. The EIS results showed that the value increased with the outer voltage, which means that more cations were absorbed under the higher anodic voltage.

Kinetics and Physicochemical Process of Photoinduced Hydrophobic ↔ Superhydrophilic Switching of Pristine and N-doped TiO2 Nanotube Arrays

Visible-light-active near superhydrophobic ↔ superhydrophilic switching vertically aligned anatase TiO2 and TiO1.84N0.14 nanotube array thin films were synthesized by anodizing Ti foils in ethylene glycol + NH4F + water electrolyte-containing urea as nitrogen source. Compared with pristine TiO2, N-doped TiO2 nanotube arrays underwent hydrophobic to superhydrophilic transition faster under sunlight. The UV-light-induced hydrophobic-to-superhydrophilic conversion rates in the hydrophobic and hydrophilic regimes for pristine and N-doped samples are 0.2178 min–1, 0.9534 min–1 and 0.5185 min–1, 1.376 min–1 respectively. The corresponding sunlight induced conversion rates for the pristine and N-doped samples are 0.015 min–1, 0.061 min–1 and 0.013 min–1, 0.152 min–1 respectively. The reverse hydrophobic conversion, when kept in dark, was found to follow a single curve with rates 8.94 × 10–5 and 4.06 × 10–5 min–1 for the pristine and doped samples respectively. The major physicochemical process behind the hydrophobic ↔ superhydrophilic transition is found to be decomposition of surface carbonaceous species and their adsorption, respectively, by surface X-ray photoelectron spectroscopy before and after photoirradiation.

Electrochemically synthesized visible light absorbing vertically aligned N-doped TiO2 nanotube array films

Visible light absorbing vertically aligned N-doped anatase nanotube array thin films were synthesized by anodizing Ti foils in ethylene glycol+NH4F+water mixture containing urea as nitrogen source. Different nitrogen concentrations were achieved by varying the urea content in the electrolyte. The structure, morphology, composition and optical band gap of the nanotube arrays were determined by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy, respectively. The substitution of O2− ions by N3− ions in the anion sublattice as well as the formulae of the doped samples was confirmed from the results of XPS. The optical band gap of the nanotube arrays was found to decrease with N-concentration. The sample with the highest concentration corresponding to the formula TiO1.83N0.14 showed two regions in the Tauc's plot indicating the presence of interband states.

Enhanced Field Emission Properties of Electrochemically Synthesized Self-Aligned Nitrogen-Doped TiO2 Nanotube Array Thin Films

Vertically aligned TiO2-δ and TiO2–3yN2y nanotube array thin films were synthesized electrochemically in a single step. N-Doping at different levels was achieved by using different concentrations of urea, as nitrogen precursor, in the electrolyte. The GIXRD and Raman studies revealed that the nanotube arrays are of anatase phase. The field emission measurements showed low turn-on fields of 10, 9.21, and 6.54 V/μm at 3.88, 4.12, and 4.74 at% of N-doping, respectively, implying enhanced field emission upon N-doping as well as an increase in electron emission with increase in N-doping. The electron emission current was found to be stable for a period of 5 h. The high electron emission current and low threshold field on N-doping is due to the presence of localized donor states below the conduction band minimum, as a result of oxygen vacancies, created by N-doping, and introduction of localized N 2p states above the valence band minimum by the doped nitrogen .

Low Temperature Heat Treatment of Anodic TiO<SUB>2</SUB> Nanotube Array Thin Film and Their Photo-Electrochemical Properties

Low Temperature Heat Treatment of Anodic TiO<SUB>2</SUB> Nanotube Array Thin Film and Their Photo-Electrochemical Properties

The Influence of Annealing Temperatures on the Crystalline and Photocatalytic Abilities of Anodized TiO<sub>2</sub> Nanotube Arrays

The TiO2 nanotube array thin films were fabricated on pure Ti plates by anodization process and annealed at 450oC, 500oC and 550oC for 30 minutes, respectively. The methylene blue (MB) degradation test was further conducted to evaluate the effects of annealing on the photocatalytic ability of TiO2 nanotube array. It was observed that better photocatalytic ability was found for the thin film annealed at 450oC, which was mainly the anatase phase. On the other hand, the anatase/rutile mixed phases were discovered on thin films annealed at 500oC and 550oC, respectively. In this work, the photocatalytic ability of TiO2 nanotube array with mixed anatase/rutile phases was not comparable to that reported in literature. It was suggested that the MB degradation ability was not only related to the crystallinity structure, but also strongly influenced by the surface characteristics of TiO2 nanotube array thin film.

In-situ preparation of multi-layer TiO 2 nanotube array thin films by anodic oxidation method

The multi-layer TiO 2 nanotube array thin films have been formed by anodic oxidation method via adjusting the outer voltage during oxidation process in glycerol electrolyte containing 0.3% NH 4HF 2. The diameter of the nanotube array increases with the outer voltage, and the length of nanotube in every layer increases with the anodic oxidation time. These multi-layers bring new possibilities to tailor the properties of the TiO 2 nanotube array thin films formed via anodic oxidation method. Further, such multi-layer structure provide a new approach to evaluate the growth rate of TiO 2 nanotube, which will help us to understand more deeply the formation mechanism of the TiO 2 nanotubes. The growth rate of TiO 2 nanotube array is respectively 1.2 and 3.6 μm/h under the anodic voltage of 30 V and 60 V. These multi-layer TiO 2 nanotube array thin films may exhibit lots of potential applications in photoelectrochemical fields.

Effect of Crystallization Methods on Morphology and Photocatalytic Activity of Anodized TiO2Nanotube Array Films

Highly ordered TiO2 nanotube array (TNs) thin films were prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution containing Na2SO4, H3PO4, NaF, and sodium citrate and then treated by calcination, vapor-thermal, and hydrothermal methods, respectively. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of the film samples was evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation. The production of hydroxyl radicals (•OH) on the surface of UV-irradiated samples was detected by a photoluminescence technique using terephthalic acid as a probe molecule. The transient photocurrent response was measured by several on−off cycles of intermittent irradiation. It was found that post-treatment exhibited a great influence on the morphology, crystallization, and photocatalytic activity of TNs th...

Fabrication of Oriented TiO<sub>2</sub>-Based Nanotube Array Thin Films

In this study, we have successfully developed the technology to grow the nanotube array thin films from dip-coated titania using hydrothermal method. The nanotube array thin film strongly adhered onto the substrate, was formed in short time reaction at 140°C. Even a self-supporting films, consisted of vertically aligned nanotube in large part, were formed after long time reactions at 140°C with 10 μm in thickness. The most probable formation mechanism of TiO2-based nanotube array thin films is discussed.

Formation of Vertically Oriented TiO2 Nanotube Arrays using a Fluoride Free HCl Aqueous Electrolyte

Described is the synthesis of TiO2 nanotube array thin films by anodization of Ti foil in an aqueous HCl electrolyte. This process represents an alternative electrolyte that can be utilized instead of fluoride-containing electrolytes. Nanotube arrays up to 300 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained by using a 3 M HCl aqueous electrolyte for anodization potentials between 10 and 13 V. An anodization voltage of up to 20 V could be used if it was increased stepwise with a resulting nanotube length of approximately 600 nm; however, the resulting nanotubes are not as well-ordered as those fabricated by a constant anodization voltage. The addition of a low concentration of H3PO4 as a buffering medium in the concentration range 0.01−0.1 M expands the anodization voltage up to 14 V but the architectures formed more closely resemble rods than tubes.