Growth of TiO 2 nanotube arrays in semiconductor porous anodic alumina templates
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A. Nourmohammadia) Department of Nanotechnology, Faculty of Advanced Science and Technologies, University of Isfahan, Isfahan 81746-73441, Iran
M.H. Feiz Department of Physics, Faculty of Science, University of Isfahan, Isfahan 81746-73441, Iran (Received 9 December 2013; accepted 25 August 2014)
The aim of this research study is to produce high-quality TiO2 nanotube arrays using porous alumina templates. The templates are fabricated through anodizing bulk aluminum foils which can be utilized for the production of thick alumina templates. To produce the nanotube arrays, the alumina template pores are filled with the precursor sol by applying a DC electric field. Then, the deposited nanotubes are heat treated at 320 °C for 2 h and, subsequently, sintered for 2 h at 400 and 750 °C to obtain nanotubes with pure anatase and rutile phases, respectively, as confirmed by x-ray diffraction data. Scanning and transmission electron microscopy (SEM and TEM) investigations show that the nanotubes have been deposited in the channels of the nanoporous alumina template. Also, SEM investigations show the existence of a vast area of TiO2 nanotube arrays when we use semiconductor alumina templates.
I. INTRODUCTION
The properties of titanium dioxide nanostructures depend on their charge transfer efficiency, their surface area (i.e., m2/g), and solar energy absorption. All these specifications are related to the geometry of the nanostructures. Synthesis of one-dimensional nanostructures such as nanotubes and nanorods are thus desirable because of their supreme charge transfer efficiency. Among these nanostructures, the advantage of producing TiO2 nanotubes is their higher surface activity owing to higher surface area. A well-ordered array of high aspect ratio TiO2 nanotubes, which is perpendicular to a conductive substrate surface, is the ideal geometry for charge transfer along the nanotubes from the medium environment toward the substrate. Experience has shown that a well-ordered TiO2 nanotube array will receive more light than a disordered one under the same illumination.1 Besides, high aspect ratio (length to diameter) nanotubes can harvest more solar energy.1 Hence, many efforts have already been carried out to obtain such nanotube arrays.2 So far, various methods have been utilized to produce TiO2 nanotubes including the conventional templatebased sol–gel process,3 anodic oxidation of titanium a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.275 2432
J. Mater. Res., Vol. 29, No. 20, Oct 28, 2014
http://journals.cambridge.org
Downloaded: 13 Mar 2015
foils,4,5 photoelectrochemical etching,6,7 hydrothermal synthesis,8 sol vacuum infiltration,9 and sol–gel electrophoresis.10 Fabrication of TiO2 nanotube arrays via anodizing titanium foils was reported for the first time in 2001 by the Grimes’ group.11 Since then, this method has been extensively studied and used in producing TiO2 nanotubes because of its simplicity.12 However, direct technological use of these anodized nanotub
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