Preparation and Formation Mechanism of Mesoporous Titania Particles Having Crystalline Wall

Abstract

Mesoporous titania particles having anatase-type crystalline wall were prepared using a low-temperature crystallization technique. Crystalline mesoporous titania was obtained through the sol−gel process of titanium oxysulfate sulfuric acid hydrate (TiOSO4·xH2SO4·xH2O) at 333 K in the presence of cetyltrimethylammonium bromide (C16TAB), a cationic surfactant. The mesoporous titania with hexagonal structure was formed according to the following mechanism. Nuclei of ultrafine titanium hydroxide oxide (TiO(OH)2) were formed from TiOSO4 on the periphery of the surface of cationic C16TAB micelles at the primary stage of sol−gel reaction. Then, heat treatment at 333 K induced the transformation of the particle wall from TiO(OH)2 to anatase nanocrystal, which resulted in the formation of mesoporous titania with a crystalline wall. Moreover, the presence of bromide ion (Br-), the counterion of C16TAB, was shown to suppress the collapse of mesostructure by retarding the transition from anatase to rutile.