Preparation of Wormhole-like Mesoporous TiO2 with an Extremely Large Surface Area and Stabilization of Its Surface by Chemical Vapor Deposition

Abstract

Mesoporous titania with BET surface area over 1200 m²/g^-1 was synthesized by primary amine templating. Dodecyl-, tetradecyl-, and hexadecylamines gave intense XRD patterns with narrow pore-size distributions in which the most probable diameter changed according to the carbon chain length. Thermal treatment was necessary for the formation of a stable structure, which strongly depends on the vapor pressure during the process. No diffraction patterns were observed above 2θ = 10°, suggesting the amorphous nature of the mesoporous titania. UV−vis and XANES spectroscopies demonstrated that the local structure of titanium was mainly 5-coordinated and O_h (6-coordinated) Ti. Chemical vapor deposition (CVD) of titanium isopropoxide followed by its decomposition with water vapor was carried out to improve the thermal stability of template-extracted titania. Although this CVD treatment resulted in a decrease in the BET surface area by 20%, the treated TiO₂ showed high thermal stability; surface areas higher than 500 m²/g^-1 were retained after calcination at 573 K for 24 h.