Preparation and Formation Mechanism of Mesoporous Titania Particles Having Crystalline Wall

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 (TiOSO 4 · x H 2 SO 4 · x H 2 O) 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 TiOSO 4 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.