Preparation and properties of silica hybrid gels containing phytic acid

Silica-phosphate mixed gels have been prepared by the sol-gel process from tetramethoxysilane and phytic acid (IP6H12). They contain inositol phosphate ester units anchored by covalent P-O-X bonds (X = P or Si) as isolated polyphytate clusters either embedded or bound in the amorphous network. P-31 NMR of the liquid phases at low temperature was used to monitor the initial steps of hydrolysis-condensation reactions at the sol stage. Dried gels have been characterized by C-13, Si-29 and P-31 MAS NMR, powder X-ray diffraction and FTIR. The ability of these gels to sequestrate metallic ions, such as La3+ and Zn2+, on the open phosphate sites has been investigated. The resulting samples undergo structural modifications during the heat treatment which leads to the formation of silica-lanthanum phosphate and silica-zinc pyrophosphate mixtures. The specific influence of the inserted cation on the structure of the final silica-phosphate obtained at 600 and 900 degrees C is discussed.