Anatase Nanotubes Research Articles

Controlling the Synthetic Pathways of TiO<SUB>2</SUB>-Derived Nanostructured Materials

A comprehensive study of the hydrothermal synthesis of TiO2-derived nanostructured materials, including layered protonic trititanate (H2Ti3O7), metal-ion exchangeable titanate (Na(x)H(2-x)Ti3O7), TiO2(B) and anatase nanotubes and TiO2-anatase nanowires, was conducted. Nanoscaled tubular structures were found to be already present in the samples derived from prolonged hydrothermal process of bulk anatase TiO2 and could be converted to various types of nanotubes, nanowires or nanorodes by post-synthesis treatments. 0.1 M HCI acid wash and air annealing were the two key parameters to select the types of nanotubes/nanowires as the final products. XRD, Raman, TG, and XPS core level and valence band studies were carried out to elucidate our proposed synthetic pathways.

Enhanced photochromism of Ag loaded self-organized TiO 2 nanotube layers

The present work investigates the photochromic behavior of Ag nanoparticles loaded onto self-organized TiO 2 nanotube layers grown by anodization of Ti in fluoride containing electrolytes. Ag nanoparticles (∼10 nm) were deposited photocatalytically on the layers. These Ag/TiO 2 structures show considerable photochromic activity in the visible range. Optical images and reflectance spectra show that the Ag loaded nanotubes have much higher photochromic contrast than the Ag loaded compact TiO 2 layers. Significantly increased switching speed is observed for the Ag loaded nanotubes, with a faster kinetics for the longer nanotubes. These photochromic effects are significantly stronger for amorphous nanotubes than for crystalline anatase nanotubes.

Synthesis of TiO 2 nanotube networks from the mineralization of swim bladder membrane in supercritical CO 2

In this work, a green route to prepare TiO 2 nanotube networks using swim bladder (SB) membrane as a bio-template was reported. In this method, the SB membrane was first dried with CO 2 extraction, which resulted in the fibrous structures of SB membrane. With the CO 2-dried SB membrane as bio-template, TiO 2 were obtained via the surface sol–gel reaction of titanium isopropoxide on the fibers of SB membrane in supercritical CO 2, followed by the removal of SB membrane calcined at 600 °C. The resulting TiO 2 was characterized with scanning electron microscopy, transmission electron microscopy and X-ray diffraction. It was indicated that ordered anatase nanotube networks were produced. Compared to the conventional sol–gel method, the protocol adopted in this work could produce TiO 2 nanotubes with regular and ordered structures.

Rate Characteristics of Anatase TiO2 Nanotubes and Nanorods for Lithium Battery Anode Materials at Room Temperature

Anatase nanotubes and nanorods were prepared by annealing mixed and anatase nanotubes at 300 and , respectively. The first discharge capacities of anatase nanotubes and nanorods were and , respectively. Irreversible capacity ratios were 14 and 15% for anatase nanotubes and nanorods, respectively. Capacity retention of the nanotubes was 81%, and that of the nanorods was 40% after . In contrast to nanotubes, the high rate performance of nanorods strongly depended on the electrode density of the electrode. Nanorods with showed 200 and at 0.5 and rates, respectively. However, nanotubes showed no capacity decrease at 0.5 or under an electrode density of either 1 or . Under , nanotubes showed 245 and at 0.5 and rates, respectively.

Super-hydrophilic and transparent thin films of TiO2 nanotube arrays by a hydrothermal reaction

Titanate nanotube arrays were grown on sapphire substrates by sputtering deposition of titanium films and a subsequent hydrothermal treatment in an aqueous NaOH solution. Post annealing in air transformed the crystals from a titanate structure to an anatase structure. Titanate and anatase nanotube arrays were optically transparent and adhered well to the substrates. Both titanate and anatase nanotube films exhibited high-hydrophilic states with water contact angles below 5° even after dark storage for more than three months due to their surface nanostructures. UV illumination caused super-hydrophilic states with 0° water contact angles, i.e. band-gap excitations decreased the initial water contact angles in dark conditions (∼3.5°) to 0°. The hydrophilicizing rate of the anatase nanotubes was faster than that of the titanate nanotubes because the anatase nanotubes had a higher crystallinity and more absorbed photons.

Anatase nanotubes as support for platinum nanocrystals

Anatase nanotubes were successfully produced via the sol–gel process involving organic titanium precursors and multi-walled carbon nanotubes as template. Controlled heat treatments were carried out in order to remove any solvents and to crystallise the initial amorphous titania coating into anatase. In order to use these structures for catalyst support, platinum particles were formed by the impregnation with hexachloroplatinic acid and subsequent calcination and reduction to obtain a final loading of 4 wt% platinum. This impregnation step was carried out either with the carbon nanotube former still present with subsequent heat treatment to remove the carbonaceous template (sample A) or with the carbon nanotube former already removed (sample B). The materials were characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy.

Low-reflective and super-hydrophilic properties of titanate or titania nanotube thin films via layer-by-layer assembly

Transparent nanotube films of hydrogen titanate were fabricated by a layer-by-layer self assembly. Titania (anatase) nanotube films were also obtained by annealing titanate nanotube films at 673 K in air. Both types of film had an optically low reflectivity and a high transparency compared to polycrystalline anatase thin films. The low reflectivity and the high transparent properties of the nanotube films are due to their nanostructural porosity, i.e. the inner cavities of the nanotubes and the void spaces between nanotubes. Thin films of titanate and titania nanotubes became super-hydrophilic with a water contact angle of zero degrees under UV illumination, but the water contact angle of polycrystalline anatase thin films did not decrease below five degrees. The highly hydrophilic surfaces of the nanotubes are attributed to their nanostructural morphologies.

Ion Implantation and Annealing for an Efficient N-Doping of TiO2 Nanotubes

Self-organized anodic titania nanotube layers were doped with nitrogen successfully using ion implantation. Photoelectrochemical measurements combined with XRD measurements show that the damage created by ion bombardment (that leads to a drastic decrease of the photoconversion efficiency) can be “annealed out” by an adequate heat treatment. This results in a N-doped crystalline anatase nanotube structure with strongly enhanced photocurrent response in both the UV and the visible range.

Reconstruction of Lepidocrocite Nanosheets into Anatase TiO2 by Rolling in Low Temperature

Abstract Highly crystallized anatase nanotubes and nanorods were prepared by rolling of molecular nanosheets, i.e., lepidocrocite, by surfactant-assisted hydrothermal method in low temperature (413 K). Alcohol played an important role for deintercalation of the surfactant between lepidocrocite nanosheets. Morphology of nanoscale anatase TiO2 materials was controlled by choosing pH and composition.

Structure, stability and electronic properties of TiO2 nanostructures

AbstractThe structural properties, the stability and the electronic properties of various nanostructures based on the titania layer modifications (anatase and lepidocrocite) are studied using the density‐functional‐based tight‐binding method (DFTB). The anatase nanotubes were found as the most stable nanostructure of TiO2. Based on the results of the calculations of the anatase nanostructures a model of their stability was developed. All anatase nanoforms are semiconductors with a direct band gap (∼4.2 eV). The lepidocrocite nanotubes are semiconductors with an indirect band gap (∼4.5 eV). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrochemical Performance of Anatase Nanotubes Converted from Protonated Titanate Hydrate Nanotubes

Titanium oxides with one-dimensional nanostructure are of significant interest for the electrochemical lithium insertion and extraction because of their large specific surface area and numerous surface defects. Nanotubes with 10-15 nm outer diameters and 200 ∼ 400 nm long were prepared by a reaction between rutile and caustic soda under hydrothermal conditions. These nanotubes are protonated titanate and can be converted into the anatase nanotubes after calcination at 500°C in argon atmosphere. The anatase nanotubes exhibited a high reversible discharge capacity, excellent high-rate discharge capability, and good cycle stability under the large current density.

Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning

Hollow nanofibers with walls made of inorganic/polymer composites or ceramics have been prepared by electrospinning two immiscible liquids through a coaxial, two-capillary spinneret, followed by selective removal of the cores. The capability and feasibility of this technique have been demonstrated by the fabrication of titania/polymer or anatase nanotubes whose size and wall thickness could be independently varied by controlling a set of experimental parameters. The presence of a sol−gel precursor in the sheath liquid was necessary for the formation of stable, coaxial jets and hollow fibers with robust walls. The circular cross-section, uniform size, and well-controlled orientation of these long hollow nanofibers are particularly attractive for use in fabricating fluidic devices and optical waveguides.

Morphology transcription with TiO 2 using chemical solution growth and its application for photocatalysts

Macro- and microscopic morphologies of anatase TiO 2 were successfully controlled by a direct growth technique in supersaturated solutions using various kinds of templates. Woven fibers consisting of nanometer-sized anatase TiO 2 particles were prepared using organic fibers as a template. Anatase nanotubes were obtained with anodized porous alumina having straight channels of 100–200 nm in diameter. The micrometer-scale structures of plant tissues were also transcribed with anatase. The fibrous ceramics having well-organized structures were confirmed to be applicable for photocatalytic applications relating to gas reactions.