Self-organized TiO 2 nanotube arrays by anodization of Ti substrate: Effect of anodization time, voltage and medium comp
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N.R. de Tacconi and C.R. Chenthamarakshan Center for Renewable Energy Science and Technology (CREST), Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019
P. Kajitvichyanukul Department of Environmental Engineering, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
K. Rajeshwara) Center for Renewable Energy Science and Technology (CREST), Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019 (Received 2 May 2007; accepted 27 July 2007)
This study probes the relationship between the morphology of anodic titania (TiO2) layers grown on Ti foil substrates and their subsequent photoelectrochemical response in 0.5 M Na2SO4 supporting electrolyte. The effects of anodization variables (voltage and time) and anodization medium composition [water, glycerol, poly(ethylene glycol), ethylene glycol] along with fluoride ion concentration on the oxide layer of morphology and photoresponse are described. The degree of order of the self organized TiO2 nanotube arrays and the extent to which these arrays organize themselves over the entire substrate surface are key variables dictating the corresponding quality of the resultant photoresponse.
I. INTRODUCTION
Tailoring the structure and morphology of semiconductor materials on a nanometer size scale has fundamental and practical importance. Nanotubular semiconductor structures are of particular interest because of their unusual electronic transport and mechanical strength characteristics. In this regard, titania (TiO2) nanotubes and nanotube arrays have been the subject of many recent studies.1–12 In these studies, templates derived from track-etch polymer membranes, anodic alumina or polystyrene (latex) spheres13 have been deployed to house TiO2 nanotubes and nanowires using either solution (e.g., sol-gel) chemistry or electrodeposition. However, template-free approaches are rather more versatile for growing one-dimensional (1D) semiconductor structures. Thus, TiO2 hollow fibers were prepared from supramo-
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0391 3186 J. Mater. Res., Vol. 22, No. 11, Nov 2007 http://journals.cambridge.org Downloaded: 07 Jul 2014
lecular precursor assemblies.14 Nanotubes of TiO2 were synthesized by hydrothermal treatment,15,16 for example, of crystalline TiO2 particles with aqueous NaOH.15 Using a seed layer of ZnO nanorods on Si substrate, aligned TiO2 nanotube and nanowire arrays were prepared by liquid phase deposition.17 Aligned rutile and anatase TiO2 nanorods as well as anatase TiO2 nanowalls were synthesized by a template- and catalyst-free metal organic chemical vapor deposition.18 Finally, a seed layer of TiO2 nanoparticles on Ti foil was used to prepare large oriented arrays and continuous films of TiO2-based nanotubes.19 Another attractive template-free approach for preparing nanotubes, especially aligned arrays of nanotubes, is anodic oxidation of the parent metal in carefully tun
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