Abstract

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. ³¹P 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 ¹³C, ²⁹Si and ³¹P 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 °C is discussed.