Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

We report on the microstructure and dynamics of electron transport and recombination in dye-sensitized solar cells (DSSCs) incorporating oriented TiO2 nanotube (NT) arrays. The morphology of the NT arrays, which were prepared from electrochemically anodized Ti foils, were characterized by scanning and transmission electron microscopies. The arrays were found to consist of closely packed NTs, several micrometers in length, with typical wall thicknesses and intertube spacings of 8−10 nm and pore diameters of about 30 nm. The calcined material was fully crystalline with individual NTs consisting of about 30 nm sized crystallites. The transport and recombination properties of the NT and nanoparticle (NP) films used in DSSCs were studied by frequency-resolved modulated photocurrent/photovoltage spectroscopies. While both morphologies display comparable transport times, recombination was much slower in the NT films, indicating that the NT-based DSSCs have significantly higher charge-collection efficiencies than...

Enhanced Charge-Collection Efficiencies and Light Scattering in Dye-Sensitized Solar Cells Using Oriented TiO2 Nanotubes Arrays

A review on highly ordered, vertically oriented TiO2 nanotube arrays: Fabrication, material properties, and solar energy applications

Tubular and fibrous nanostructures of titanates have recently been
synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed. The crystal structures, morphologies, and mechanism of formation
of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar-cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.

Protonated Titanates and TiO2 Nanostructured Materials: Synthesis, Properties, and Applications

Smooth anodic TiO2 nanotubes.

Tailoring the wettability of TiO2 nanotube layers

Self-organized porous WO3 formed in NaF electrolytes

The present work reports the fabrication of self-organized porous oxide-nanotube layers on the biomedical titanium alloys Ti-6Al-7Nb and Ti-6Al-4V by a simple electrochemical treatment. These two-phase alloys were anodized in 1M (NH(4))(2)SO(4) electrolytes containing 0.5 wt % of NH(4)F. The results show that under specific anodization conditions self-organized porous oxide structures can be grown on the alloy surface. SEM images revealed that the porous layers consist of arrays of single nanotubes with a diameter of 100 nm and a spacing of 150 nm. For the V-containing alloy enhanced etching of the beta phase is observed, leading to selective dissolution and an inhomogeneous pore formation. For the Nb-containing alloy an almost ideal coverage of both phases is obtained. According to XPS measurements the tubes are a mixed oxide with an almost stoichiometric oxide composition, and can be grown to thicknesses of several hundreds of nanometers. These findings represent a simple surface treatment for Ti alloys that has high potential for biomedical applications.

Luciano Taveira

Papers

Smooth anodic TiO2 nanotubes.

Tailoring the wettability of TiO2 nanotube layers

Self-organized porous WO3 formed in NaF electrolytes

Self‐organized nanotubular oxide layers on Ti‐6Al‐7Nb and Ti‐6Al‐4V formed by anodization in NH4F solutions

Self-organized TiO2 nanotubes prepared in ammonium fluoride containing acetic acid electrolytes