Titanium Dioxide Nanotube Arrays Fabricated by Anodizing Processes

Abstract

Extended and oriented nanostructures are desirable for many applications, but direct fabrication of complex nanostructures with well-aligned morphology, orientation, and surface architectures remains a significant challenge. Here, we study a simple electrochemical anodizing process to fabricate arrays of titanium ͑Ti͒ nanotubes without the use of a template. The nanotubes are formed perpendicular to the metal substrate as an open-ended array in a continuous, well-aligned conformation. The hole size and separation have been found to be dependent on the anodizing voltage and on anodizing time. It was found that the nanotube deposition process had a low faradaic efficiency, and a large fraction of the Ti was transformed into soluble species in the anodizing bath. The TiO 2 nanotubes have uniform diameters that make them suitable for electrochemical intercalation hosts for Li + ions and other applications.Nanoscale one-dimensional materials, such as nanowires, nanorods, nanofibers, and nanotubes, have attracted interest recently due to their importance in basic scientific research and potential technology applications. 1-3 Specifically, many important metal oxides with nonlayered structure such as TiO 2 , ZnO, MnO 2 , ZrO 2 , and Co 3 O 4 have attracted attention in the fabrication of nanotube structures, despite the high rigidity of the crystal structure. Most of the important progress includes fabrication of the metal oxide nanotubes from anodic aluminum oxide templates ͑AAO͒ and supramolecular templates with various sol-gel methods that transfer materials onto inner or outer surfaces of templates. A recent example of this procedure is the work of Hoyer 4 on TiO 2 nanotubes.The study of TiO 2 films formed on the parent metal has an extensive literature because they provide excellent corrosion protection. However, precursor sites for pitting corrosion 5-7 were discovered in our laboratory recently. The oxide films formed on Ti in sulfuric and hydrochloric acids, and on a wide range of other electrolytes, are normally fully dense, and nanotube structures are completely absent.Several research groups have studied oxide nanotubes, including TiO 2 ͑TONT͒. In the context of the present paper, Zwilling et al. 8 have anodically grown highly porous oxide layers on pure Ti and Ti-6A1-4V alloy in hydrofluoric acid ͑HF͒ solution with or without acetic acid and chromic acid additions. Another group has discussed the morphology of well-aligned nanotube Ti oxide structures fabricated by anodizing and has described details of preparation and modification by heat treatment to form suitable materials for hydrogen sensing systems. 9-14 Schmuki and co-workers 15-17 have explored the effect of solution pH on the size and shape of the TONT formed by anodization. Especially noteworthy is the length of nanotubes formed in near-neutral pH solutions of fluoride. 17 In recent work, Sklar et al. 18 reported a variety of solution compositions that were used for anodic formation of TONT. In a recent paper from our laboratory, ZrO 2 nanotube arr...

Photo-assisted electrodeposition of an electrochemically active polypyrrole layer on anatase type titanium dioxide nanotube arrays

“…The initiation of electropolymerization in LiClO 4 solution in the dark is less obvious to explain. Since during the synthesis, alternative anodic and cathodic scans are applied on the substrate, hydrogen insertion into the TiO 2 nanotubes can be promoted, increasing progressively the doping level of the semiconductor and consequently its conductivity [16,[26][27][28]. A similar explanation has been given in the case of the WO 3 /PPy system, for which the electroactivity in the dark in the anodic range has been attributed to H + uptake [12].…”

“…The impedance and voltammetric results show that once the coverage rate is complete, the TiO 2-polypyrrole junction behaves like a conductor in the dark, although the underlying Miyauchi et al [29], from reference [28], and from the estimation of the energy of the conduction band for TiO 2 -NTA (Fig. 10b), the electron transfer process between the oxide and the polymer is schemed in Fig.…”

“…[27]). The conversion of the vacuum scale to the potential scale is made using E SCE = -4.70 eV [28]. …”

Fabrication and photoluminiscent properties of titanium oxide nanotube arrays

“…The first and the second peaks result from the electronic transition from the bottom of the conduction band to the top of the valence band, according to the electronic structure of anatase (3.2 eV) and rutile (3.0 eV), respectively. The nanotubes annealed at 700 °C collapse and the tubular structure is converted to nanowires or nanorods, 23 which leads to quantum size effect, and hence reduces the blue shifts of the first and the second peaks. The peaks located at 465.0 nm and 510.5 nm can be ascribed to the electronic transition originated from defect levels in the band gap.…”

Surface-assisted laser desorption/ionization mass spectrometry on titania nanotube arrays

“…Furthermore, titania is quite stable at ambient condition. After anodizing processes [40], titania nanotube arrays (NTAs) are generally formed. We found that background interference was almost absent in the titania NTAs during laser desorption/ionization.…”