Growth and Optimization Processes Towards Self-Organized and Highly Ordered Titanium Dioxide Nanotubes for Photocatalytic Applications
Abstract
Highly- ordered and self-organized titanium dioxide nanotubes (TNT) for photocatalytic activity were fabricated by anodization method, and characterized using scanning electron microscopy, X-ray diffraction, UV-Vis spectrophotometry, and profilometry. Anodization electrolyte preparation and growth conditions were studied towards the growth of ordered TNTs by systematically varying electrolyte composition and mixing procedures. TNTs were grown by anodizing pure titanium foils in a third generation electrolyte consisting of 0.2 M ammonium fluoride and water. For optimization purposes, the samples were anodized at a constant DC voltage of 60 V for two hours while varying the electrolyte composition by employing different ways of mixing the electrolyte so as to achieve a homogeneous solution. The concentration of fluoride was varied between 0.005 M to 0.3 M, while the water content was varied between 3 and 50 vol %. Introducing a two-step anodization procedure, improved TNT structures were achieved. The as-prepared TNTs between 87 nm and 170 nm; and wall thickness between 20 nm to 40 nm depending on anodizing conditions were amorphous, and were found to transform into highly crystalline anatase structure upon calcination at 400oC. The physical dimensions of the TNTs varied with length between about 7.2 nm to 46 nm; inner diameter. The TNTs were shown to be active for methylene blue photo-degradation, and that reaction rate was shown to be more than twice as high on the two-step anodized TNTs.
Keywords
Anodization, Tio2, Nanotubes, Photocatalysis.