Enhanced photocatalytic activity of titanium dioxide/allophane mixed powder by acid treatment

• Photocatalyst was prepared by acid treatment of TiO2/allophane mixed powder.
• Amorphous silica was formed by selective dissolution of Al component in allophane.
• The obtained TiO2/silica composite showed high rate of removal of acetaldehyde.
• The enhanced property was ascribed to the silica-dispersed microstructure.

The TiO2/allophane mixed powders at various mixing ratios were acid-treated to obtain a highly active photocatalyst. It was found that amorphous silica surrounding TiO2 particles was formed after acid treatment by selective dissolution of alumina component in the allophane. The photocatalytic activity of the mixed powder, evaluated by the photocatalytic decomposition rate for gaseous acetaldehyde, was improved by the acid treatment when the mixing ratio of allophane was higher than 5 mass% in spite of the decrease of specific surface area (SSA), while that of the pure-TiO2 powder was decreased maybe because of the increase of Ti3 + defects density on its surface. As for the pure-allophane powder, SSA and adsorption rate for acetaldehyde were decreased by acid treatment. In addition, it was found that the acid treatment of allophane was needed to be performed in the presence of TiO2 to obtain a highly active photocatalyst from the result of the comparative experiments using mixed powder of acid-treated TiO2 powder and acid-treated allophane powder. Based on these results, it was concluded that the silica-dispersed microstructure of the nanocomposite was suitable for the efficient removal of acetaldehyde.

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