Adsorption properties of crystalline silicas: (II) Adsorption of anionic surfactants and delamination

Abstract

Lamellar crystalline silicas (crystalline silicic acids, chemical composition SiO2·xH2O; examples: H4Si14O30·xH2O, H4Si20O42·xH2O) are distinguished from the amorphous forms by their layered structure and exceptional adsorption properties. One outstanding example is the reaction with anionic surfactants. Several types of crystalline silicas (typical H4Si20O42·xH2O) can intercalate ionic pairs consisting of surfactant anion and gegen ion into the interlayer space. The saturation value of SDS adsorption is 0.475 mmol SDS/g H4Si20O42·3H2O. The acid H4Si14O30·xH2O adsorbs anionic surfactants at the external surfaces only (saturation value 0.04 mmol/g H4Si14O30·0.8 H2O). When anionic surfactants are adsorbed in the interlayer space, the layer separation increases to such an extent that the crystals disarticulate in a fan-like manner or delaminate into thinner packets of layers or smaller aggregates. Washing-out the SDS ionic pairs or drying reconstitutes the parallel layer orientation and leads to re-aggregation of the packets and fragments.