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

Nanoporous anodic aluminium oxide has been widely used for the development of various functional nanostructures. So far these self-organized pore structures could only be prepared within narrow processing conditions. Here we report a new oxalic-acid-based anodization process for long-range ordered alumina membranes. This process is a new generation of the so-called "hard anodization" approach that has been widely used in industry for high-speed fabrication of mechanically robust, very thick (>100 microm) and low-porosity alumina films since the 1960s. This hard anodization approach establishes a new self-ordering regime with interpore distances, (D(int))=200-300 nm, which have not been achieved by mild anodization processes so far. It offers substantial advantages over conventional anodization processes in terms of processing time, allowing 2,500-3,500% faster oxide growth with improved ordering of the nanopores. Perfectly ordered alumina membranes with high aspect ratios (>1,000) of uniform nanopores with periodically modulated diameters have been realized.

/pdf/fast-fabrication-of-long-range-ordered-porous-alumina-1bigpxis0y.pdf

Fast fabrication of long-range ordered porous alumina membranes by hard anodization

The present paper gives an overview and review on self-organized TiO2 nanotube layers and other transition metal oxide tubular structures grown by controlled anodic oxidation of a metal substrate We describe mechanistic aspects of the tube growth and discuss the electrochemical conditions that need to be fulfilled in order to synthesize these layers Key properties of these highly ordered, high aspect ratio tubular layers are discussed In the past few years, a wide range of functional applications of the layers have been explored ranging from photocatalysis, solar energy conversion, electrochromic effects over using the material as a template or catalyst support to applications in the biomedical field A comprehensive view on state of the art is provided

TiO2 nanotubes: Self-organized electrochemical formation, properties and applications

Platinum-based nanostructured materials: synthesis, properties, and applications.

Fabrication of ideally ordered nanoporous alumina films and integrated alumina nanotubule arrays by high-field anodization

Various ordered nanoporous alumina films with arbitrary pore intervals from 130 to 980 nm were fabricated on aluminum by a critical-potential anodization approach with sulfuric, phosphoric, oxalic, glycolic, tartaric, malic, and citric acid electrolytes under 70-450 V. The pore intervals of the porous alumina films were linearly proportional to applied potentials, with corresponding dominated territories to the electrolytes. In addition to pore interval, the self-ordering extent of pore arrangement was also improved with increasing anodizing potentials, leading to highly ordered porous alumina films at critical-high potentials. A cell separation phenomenon occurred for the films formed in sulfuric and glycolic acid solutions at the critical potentials, thus leading to the formation of highly ordered alumina nanotubule arrays. The critical-potential anodization in the other electrolytes produced self-organized porous alumina films with two-layered pore walls and pore bases. The basic principle for achieving porous alumina films with desired pore intervals is controlling the balance of the growth of barrier layer and the pore generation by adjusting the acidity, the concentration, and temperature of electrolytes. The porous alumina films formed in various electrolytes were transparent, and the transmittances of the films were inversely proportional to the applied potentials or the pore intervals.

Large-Scale Fabrication of Ordered Nanoporous Alumina Films with Arbitrary Pore Intervals by Critical-Potential Anodization

A transparent porous alumina nanostructure was formed on a glass covered tin-doped indium oxide ~ITO! substrate by anodization of a highly pure sputtered aluminum layer. Details of the fabrication and microstructures of porous anodic alumina films are described and a possible mechanism of anodization is outlined. The variation of anodic current density reflects three processes, i.e., ~i! anodization of the sputtered aluminum layer, ~ii! transition of electrolysis from aluminum to the underlying ITO film, and~iii! electrochemical reactions on the ITO film beneath the anodic alumina film. As all the aluminum is completely anodized, the resultant oxide films on the ITO/glass substrate possess a parallel porous structure ~f80-100 nm, cell size in ;350 nm! with a thin arched barrier layer ~;80 nm! and exhibit a high transmittance in the ultraviolet-visible light range ~75-100% transmittance 300-900 nm!.

Formation and Microstructures of Anodic Alumina Films from Aluminum Sputtered on Glass Substrate

Three-dimensional highly porous TiO2-4%SiO2-1%TeO2/Al2O3/TiO2 composite nanostructures (φ30-120 nm) directly fixed on glass substrates were fabricated by anodization of a superimposed Al/Ti layer sputter-deposited on glass and a sol-gel process. The porous composite nanostructures exhibited enhanced photocatalytic performances in decomposing acetaldehyde gas under UV illumination, which can be mainly ascribed to the combination of their large surface areas (7750-14770 m(2)/m(2)), high porosities (34.2-45.6%), and transparency. Specially, the composite nanostructure with ∼φ120 nm pores calcined at 500 °C showed the highest photocatalytic activity that is 6-10 times higher than commercial P-25 TiO2 under the experimental conditions.

Highly Porous (TiO2-SiO2-TeO2)/Al2O3/TiO2 Composite Nanostructures on Glass with Enhanced Photocatalysis Fabricated by Anodization and Sol-Gel Process.

Titania nanostructures with larger surface areas are fabricated on a glass substrate by anodization of sputtered aluminum and the sol−gel process, and the structural characteristics of the nanostructures are investigated. Highly pure aluminum film (99.99%, ≈2 μm), which is deposited on a glass substrate with a conductive tin-doped indium oxide (ITO) layer, is first anodized potentiostaticly in a phosphoric acid solution to obtain porous alumina structures. The anodic alumina is then used as a host or template to synthesize porous Al2O3/TiO2 composite nanostructures through a sol−gel process. Finally, a TiO2 nanotubules array with contours of porous anodic alumina is fabricated on glass by removing the alumina template selectively. The resultant TiO2 is 4−20 nm polycrystalline of anatase structure with (101) preferential orientation. Titania nanostructures have large surface areas and exhibit a high transmittance in visible light and a strong absorbance within ultraviolet range in UV−vis spectra. Moreover,...

Song-Zhu Chu

Papers

Fabrication of ideally ordered nanoporous alumina films and integrated alumina nanotubule arrays by high-field anodization

Large-Scale Fabrication of Ordered Nanoporous Alumina Films with Arbitrary Pore Intervals by Critical-Potential Anodization

Formation and Microstructures of Anodic Alumina Films from Aluminum Sputtered on Glass Substrate

Highly Porous (TiO2-SiO2-TeO2)/Al2O3/TiO2 Composite Nanostructures on Glass with Enhanced Photocatalysis Fabricated by Anodization and Sol-Gel Process.

Synthesis and Characterization of Titania Nanostructures on Glass by Al Anodization and Sol−Gel Process