Effect Of Calcination Temperature On Morphology And Photocatalytic Properties Of Anodized Titanium Dioxide Nanotube Arrays

In 21 st century, environment and energy are two important issues to the humanity, and using solar energy directly as light source becomes an ideal technology of environmental pollution improvement and clean energy production. In recent years, titanium dioxide and other semiconductor photocatalytic materials have been intensively investigated for their wide potential application in environment field such as sensors, solar cells and photocatalytic degradation of pollution since Fujishima and Honda discovered the photocatalytic splitting of water on TiO2 electrodes in 1972. Among various oxide semiconductor photocatalysts, titania has been proved to be the most suitable photocatalyst for its biological and chemical inertness, nontoxicity, cost effectiveness and strong oxidizing power. Although TiO2 photocatalytic material has a low efficient utilization of solar energy, the preparation of photocatalyst with high photocatalytic activity, the immobilization of powder photocatalyst, and the improvement of photocatalyst performance are priorities to be considered. Herein, valuable explorations have been carried out on the synthesis of anodized titanium dioxide nanotube arrays and Bi2O3/TiO2 composite photocatalysts. The main points could be summarized as follows:Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F 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 (·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℃) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca.600℃. At 800℃, 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℃) due to the enhancement of crystallization. Especially, at 600℃, 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℃, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas.Bismuth-incorporated titania hollow microspheres are fabricated by an impregnating-calcination method. The results show that Bi-incorporating greatly enhances the visible-light photocatalytic acitivity of TiO2 hollow microspheres. When the atomic ratio of Bi/Ti (RBi) increases from 0 to 0.5, the photocatalytic activity of the samples increases. Especially, at RBi= 0.5, it shows the highest photocatalytic activity.