Effect of calcination temperature on morphology and photoelectrochemical properties of anodized titanium dioxide nanotube arrays

Highly ordered TiO(2) nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH(4)F and then calcined at various temperatures. The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation. The production of hydroxyl radicals ((center dot)OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule. The transient photocurrent response is measured by several on-off cycles of intermittent irradiation. The results show that low temperatures (below 600 degrees C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca. 600 degrees C. At 800 degrees C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed. The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600 degrees C) due to the enhancement of crystallization. Especially, at 600 degrees C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures. With further increase in the calcination temperature from 600 to 800 degrees C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas. (C) 2009 Elsevier B.V. All rights reserved.