QEXAFS and UV/Vis Simultaneous Monitoring of the TiO2-Nanoparticles Formation by Hydrolytic Sol−Gel Route

Abstract

The hydrolysis of titanium(IV) tetraisopropoxide and the following condensation and aggregation to titania nanoparticles under slow water solution addition were concomitantly investigated by in situ QEXAFS and UV/vis spectroscopies. The amount of dominant titanate species in the solution was determined as a function of time, temperature, and water addition rate. Resulting from fast hydrolysis and condensation of isopropoxide precursors an intermediate oligomeric species is initially formed at the early stages of the reaction. This oligomeric species has been identified as a dodecatitanate species with Ti11O13 or Ti12O16 molecular framework. At the subsequent stage of the reaction corresponding to slower processes compared to the fast hydrolysis, titania nanoparticles are formed by a cluster−cluster growth mechanism involving the consumption of the dodecatitanate species following a pseudo first-order reaction. Finally, at the advanced stage, sudden aggregation of titania nanoparticles occurs at a given th...