FT-Raman Spectroscopy of Modified Tetraisopropyltitanate Hydrolysates

Abstract

Modification of metal alkoxides with complexing agents, such as carboxylic acids, which act both as a catalyst and a ligand, is commonly used in sol-gel processing to alter the hydrolysis and condensation rates of the alkoxide. Hydrolysates produced by the reaction of modified tetraisopropyltitanate with water were X-ray-amorphous but exhibited spectra similar to the spectrum of rutile; broad bands assigned to the E _g and A_1g Ti-O stretching modes of the “rutile-like” phase were observed at ca. 425 and 605 cm^-1, respectively. During peptization of the hydrolysate with nitric acid at 60 °C, the intensity of these bands decreased substantially, and new peaks appeared at 154, 405, 515 and 630 cm^-1 which were assigned to the ${\delta _{O - Ti - O}}({E_g}),{\delta _{O - Ti - O}}({B_{1g}}),{\nu _{Ti - O}}({A_{1g}}/{B_{1g}})$ and ${v_{Ti - O}}\left( {{E_g}} \right)$ modes, respectively, of anatase. However, the hydrolysates were also found to undergo a similar phase change when processed at the same temperature in the absence of peptizing agents, but the rate of transformation was slower. The carboxylic acid also had a significant influence on the induction time for the phase change, with the transformation occurring more slowly with increasing carboxylate chain length.