Sol-gel synthesis and morphological control of nanocrystalline TiO2 via urea treatment

Nanocrystalline TiO2 rods and hollow tubes with an engraved pattern on the surface have been prepared by a novel anionic template-assisted sol-gel synthesis via urea treatment and under hydrothermal condition. X-ray diffractometry (XRD) results indicate that these nanocrystallines consist predominantly of anatase TiO2, with minor amounts of rutile and brookite. Scanning and transmission electron microscopy (SEM and TEM) analyses reveal these rods and hollow tubes may result from the aggregates of nanorods of similar to 10 nm in diameter. The crystallographic faceting found from TEM further reveals the polymorphic nature of the nanocrystalline TiO2 thus prepared. A reverse micelle formation mechanism taking into account the hydrothermal temperature, the pH effect of the sol-gel system, the isoelectric point, the formation of micelles, and the electrostatic interaction between the anionic surfactant and the growing TiO2 particulates is proposed to illustrate the competition between the physical micelle assembly of the ionic surfactants and the chemical hydrolysis and condensation reactions of the Ti precursors. (C) 2007 Elsevier Inc. All rights reserved.