Po Chun Chen, Chien Chon Chen* and Shih Hsun Chen* Pages 373 - 393 ( 21 )
Background: We present a review on recent progress in the research and development of titanium dioxide (TiO2) nanomaterials. Based on the studies reported in the literature, titanium oxide nanoparticles and nanotubes (NPs and NTs) can be fabricated by inexpensive methods, such as solgel deposition and anodization process. Typically, TiO2 NPs are synthesized in a particle size less than 10 nm, and the featured dimensions of TiO2 NTs are about 100 nm in pore diameter, 1010 pores/cm2 in pore density, 25 nm for wall thickness, and several microns in length perpendicular to surface.Methods: Anodic oxide films are normally amorphous because of the formation of defect clusters and the presence of considerable internal mechanical stresses. However, a careful pre-polishing procedure and a slow increasing rate in anodizing voltage (0.1 mV/s) is beneficial to fabricate crystalline epitaxial thin films. Furthermore, with an ultra-slow anodizing condition up to 1 V (saturated calomel electrode; SCE), crystalline TiO2 with a thickness of 1.65 nm can be formed. Results: In order to increase the effective surface area of TiO2, the TiO2 NPs are deposited on TiO2 NT surfaces. The effect of the TiCl4 treatment on TiO2 NT films has been reported to increase the surface area, and thus to enhance the photocatalytic applications. During the deposition process, the Ti(OH)4 is formed from TiF4 or TiCl4 solution by controlling pH value and temperature. Then, the Ti(OH)4 can be transformed to TiO2 after heat treatment. TiO2 NTs/NPs have a larger surface area than a compact TiO2 film, more materials can be absorbed on the TiO2 NT surface. With the anodic electrolyte of a higher pH value, the TiO2 NT film with a longer length and a higher surface area will be produced. Large-scale manufacturing of high-quality and inexpensive TiO2 NTs/NPs film can be potentially utilized for academic research and industrial applications. Conclusion: The dense TiO2 film can be formed on matrix Ti through heat-treatment or interference anodization methods. However, anodizing titanium foil in a F− ions and minimizing water content in non-aqueous organic polar electrolyte are beneficial for the formation of closely packed and vertically aligned nanotubes.
Anodization, nanoparticle, nanotube, photocatalyst, sol-gel, TiO2
Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei 10643, Department of Energy Engineering, National United University, Miaoli 36063, Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 10607