Preparation of titanium(IV) oxide film on a hard alumite substrate
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TiO2 was deposited onto hard alumite (Al/Al2O3/TiO2) by alternating current electrolysis and precipitation in (NH4)2[TiO(C2O4)2] solution at various temperatures, where the hard alumite was prepared by the anodic oxidation of aluminum in sulfuric acid (Al/Al2O3). The TiO2 electrodeposition mainly occurred at temperatures lower than about 50 °C, while the TiO2 deposition due to TiO(C2O4)22− adsorption onto alumina predominantly occurred at temperatures higher than about 50 °C. The amount of deposited TiO2 increased with the increase in the deposition temperature, leading to high photocatalytic activity. The deposited TiO2 at 90 °C followed by heat-treatment at 550 °C had an anatase structure and showed a high photocatalytic activity for the decomposition of acetaldehyde even under fluorescent lamp illumination. The Al/Al2O3/TiO2 prepared at 50 °C was optimal for practical use, because of a relatively high activity and the sufficient adhesion strength between the TiO2 and the Al/Al2O3 substrate due to the presence of the deposited TiO2 in the pores of the alumina film.
I. INTRODUCTION
TiO2 is a promising material as a photocatalyst for photodecomposition reactions such as the photolysis of water1–6 and decomposition of some chemical compounds7–15 under illumination. Various preparation and fixation methods for the TiO2 photocatalyst have already been reported.14,16–28 The sol-gel or a similar method is most important11–14,18–22 because the prepared TiO2 has a small size and therefore a high specific surface area. This is preferable for a catalyst,20–29 although the cost for preparation of these types of TiO2 is generally high. Consequently, a low-cost preparation and fixation of the TiO2 photocatalyst with nano-sized particles is necessary for practical use. Aluminum is widely used as a building material because it is relatively cheap and light. Generally, aluminum is electrochemically oxidized to produce an alumite (aluminum with a porous alumina film, denoted by Al/ Al2O3), which protects against corrosion.30,31 It is well known that the alumite prepared by anodic oxidation in sulfuric and phosphoric acids has self-organized and nano-sized pores.30–33 Some metal and metal oxides can be deposited in the pores of the alumina film by alternating current (ac) and/or direct current (dc) electrolysis, and a)
e-mail: [email protected] J. Mater. Res., Vol. 17, No. 9, Sep 2002
http://journals.cambridge.org
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some metal deposited alumite is used as “colored alumite.”30,34 Alumite will be useful as a substrate for the TiO2 photocatalyst film because the alumite has nano-sized pores and may act as a carrier of the catalyst. We developed new low-cost electrochemical methods for directly depositing the TiO2 photocatalyst onto an Al/Al2O3 substrate (denoted by Al/Al2O3/TiO2). In these cases, the electrodeposition was made by two-step35 or onestep36 electrolysis. In the former case, the as-deposited TiO2 consisted of mixtures of the anatase, rutile, and amorphous phases, and showed hig
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