Colloidal Zeolite-Preparation, Properties and Applications

A method for the preparation of stable colloidal suspensions containing discrete molecular sieve crystals is presented. The hydrothermal synthesis of the all-silica tetrapropylammonium silicalite-1 molecular sieve illustrates the preparation. The discrete colloidal crystals ( < 150 nm) are aggregates of plate-like primary particles and they are stabilized in aqueous solution via steric forces that arise as a result of the strong adsorption of the tetrapropylammonium cation on the siliceous surface. The silicalite-1 surface charge is a function of pH as shown by electrophoretic measurements. These properties may be utilized for fabricating advanced materials. An example of the application of the colloidal materials is illustrated by the preparation of a thin silicalite-1 film on a non-charged gold substrate. Knowledge of the surface chemistry of the participating interfaces and the properties of the colloidal crystals allows for the preparation of microporous films with a thickness less than 300 nm.