Effect of Titanium Matrix Structure on Growth Morphology of Anodized TiO₂ Nanotube Arrays for Applications in Photoelectrochemical Performances

Abstract

In the application of a solar cell and photocatalytic system, anodized titanium dioxide nanotube arrays (TNTs) have one-dimensional highly ordered nanotube structure, so they have attracted much attention. In order to form ordered TNTs, many factors, such as voltage, anodizing time, solvent type, and so on, need to be controlled. However, these factors have mainly focused on the effect of external conditions, while the effect of internal factors such as the crystal structure of the titanium substrate on the growth of nanotubes have been less investigated. In this paper, the titanium substrate tissue structure with a (002) preferred orientation was obtained by a rolling treatment. On this basis, TNTs with highly ordered structure were constructed, and the effect of the titanium substrate structure on the nanotube growth morphology was investigated. The changes in morphology were characterized by scanning electron microscopy, and the relationship between the changes in the crystal structure and morphology of TNTs was systematically analyzed by combining metallographic structure and X-ray diffraction data. The changes in the electrochemical behavior of the titanium substrates after rolling were examined through electrochemical methods. The above results show that there are a large number of dislocations and microscopic internal stresses in the grain structure of the titanium substrate after rolling, which leads to improvement of the corrosion resistance of the materials. The changes in the microstructure of these materials make the nanotube arrays have highly ordered structure and better photoelectrochemical properties, which provides an idea for improving their applications in photoelectrochemistry.

Plasma-Assisted N-Doped TiO2 Nanotube Array as an Active UV–vis Photoanode

“…Ultimately, this leads to a shift in optical response toward the visible range. ,,, This is possible because the replacement of oxygen atoms in the TiO 2 lattice with nitrogen atoms is effective due to their similar size and relatively low ionization energy and to the stability of the Ti–N–O bonds that are formed. ,,, It is well known that photocatalytic processes involving TiO 2 are heterogeneous and that the surface area of the catalyst plays an important role. The structural properties of TiO 2 , such as its crystallinity, particle size, grain size, porosity, and surface area, are all affected by the TiO 2 synthesis method, doping method, and the type of dopant. ,,− Therefore, nanostructures based on TiO 2 nanotubes obtained by the anodic oxidation of titanium have been widely used in recent years as photocatalysts (photoanodes) due to their particular properties . Such materials are characterized by strong light-scattering effects due to their characteristic morphology, that is, densely packed tubes of a certain height that can be separated from each other. ,− In addition, highly ordered nanotubes that are vertically oriented to the metallic Ti substrate provide a high degree of electron mobility along the axis of the tubesa unidirectional charge transfer. ,, Another advantage is that it is relatively easy to control their crystalline form or degree of crystallinity (anatase, rutile, and a mixture of anatase and rutile) through temperature processes. ,,− These properties have been used effectively in various types of light-induced reactions, such as degradation of various types of dyes (methylene orange, , methylene blue, − rhodamine B, and azo dye (RB5)), pesticides (acephate), phenols, and the production of hydrogen. ,,,− Despite these advantages, a limitation in the use of nanotubes in photocatalysis as broadly understood is the nature of titanium oxide itself, and therefore its physical and chemical properties, as mentioned above.…”

“…Clearly visible peaks of the Ti substrate are associated with the direct growth of nanotubes on titanium foil, see Figure 2b. The sample subjected to heat treatment at 450 °C in UHV conditions shows extra three distinct peaks at about 2θ = 25.0°, 48.0°, and 55.0°corresponding to anatase reflections (101), (200), and (211), respectively 20.…”