Preparation and properties of silica hybrid gels containing phytic acid

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.