Correlation between gelation time, structure and texture of low-doped silica gels

Abstract

It is shown how the properties of a porous silica xerogel prepared using a classical sol–gel synthesis can be fine-tuned by a minor modification of the composition. The addition of a doping cation (Cu²⁺, Ca²⁺, Na⁺⋯) in trace quantities in the silica sol was found to exert a dramatic effect at all stages of material preparation. An investigation of both liquid and solid phases is presented, making it possible to highlight strong correlations. The time-resolved speciation of Si-containing moieties in the sol was found to be an indication of the structuration of the gel, which was reflected by the porosity and by the molecular structure of the resulting porous material. Based on a careful comparison of several slightly doped silica gels, a model is proposed which makes it possible to predict the structure and the texture of a silica gel from data recorded early in the liquid phase.