Effects of calcination temperature on the photocatalytic activity and photo-induced super-hydrophilicity of mesoporous TiO2 thin films

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Abstract
Mesoporous TiO2 nanometer thin films were prepared on fused quartz by the dip-coating sol–gel method from a system containing a triblock copolymer as a template (or pore-forming agent), and then calcined at different temperatures. These films were characterized by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, BET surface area and UV-visible spectrophotometry. The photocatalytic activity and photo-induced super-hydrophilicity of the films were evaluated by the photocatalytic degradation of acetone and water contact angle measurement in air, respectively. It was found that the thin films calcined at 700 °C not only show the highest photocatalytic activity, but also possess the greatest light-induced hydrophilicity and the slowest conversion rate from the hydrophilic to a hydrophobic state. The former is attributed to the fact that the films calcined at 700 °C are composed of anatase and rutile, which is beneficial in enhancing the transfer of photo-generated electrons from the anatase to the rutile phase, reducing the electron–hole combination rate in anatase and enhancing its activity. The high light-induced hydrophilicity and slow hydrophilic to hydrophobic conversion rate are due to the synergetic effect of good photocatalytic activity, sufficient surface hydroxyl content and a degree of surface roughness. Because of their high specific surface areas and mesoporous structures, the photocatalytic activity of mesoporous TiO2 thin films is higher than that of conventional TiO2 thin films.
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