Effect of preparation conditions on properties of titanium dioxide aerogel

Abstract

Titanium dioxide was synthesized using titanium isopropoxide as a precursor via a sol-gel method. The effect of solvent on properties of TiO2 was investigated by using two different alcohols, i.e. ethanol and methanol as a solvent in the synthesis. The resulting wet gel was dried under two different conditions: firstly, under ambient atmosphere to form TiO2 xerogel and secondly, under critical drying condition using supercritical CO2 to form TiO2 aerogel. After drying, heat treatment of the gels was performed under a flow of either air or nitrogen at a temperature ranging from 350 oC to 600 °C in order to study the effect of calcination condition on properties of TiO2. The specific surface area and pore volume of as-synthesized aerogels were significantly higher than those of as-synthesized xerogel. More organic residue remained in as-synthesized aerogel than in xerogel. The phase transformations from amorphous to anatase and from anatase to rutile in aerogel occurred at a higher temperature than that of the phase transformations in xeroge did. The photocatalytic activities of TiO2 catalysts were evaluated for degradation of ethylene in a gas phase under UV illumination. The photocatalytic activities of xerogel samples were higher than those of aerogel, which indicated that the photocatalytic activities did not depend on specific surface area. TiO2 sample that was prepared with ethanol as a solvent and was calcined at 400 oC exhibited the maximum photocatalytic activity while the maximum photocatalytic activity of TiO2 that was prepared with methanol as a solvent was observed in the sample that was calcined at 500 oC. The result may be attributed to the amount of Ti3+ surface defects and the crystallinity of anatase in TiO2.