Direct wet deposition of zeolite FAU thin films using stabilized colloidal suspensions

Abstract

Seeded growth is the most popular approach to the preparation of zeolite thin films and membranes. Herein, we report a simplified method of fabricating zeolite Faujasite (FAU) thin films through the direct wet deposition of zeolite FAU thin films using stabilized colloidal suspensions. Zeolite FAU suspensions are stabilized by adjusting the pH values and the suspensions are spin-coated on a silicon wafer substrate to form dense zeolite FAU thin films. Dynamic light scattering (DLS) was used to investigate the colloidal properties of the zeolite FAU suspensions. The time-dependent hydrodynamic radius Rh was derived from DLS measurements for use as a quantitative measure of colloidal stability. It was found that high pH values destabilize the colloidal suspensions. Thin film samples cast using the relatively stable zeolite FAU suspensions yielded thin films with uniform morphology. In thin films formed from suspensions with a high pH value, the zeolite FAU crystals transformed into a dense phase. We also measured the relative permittivity (εr) of the thin film samples cast from various suspensions. At a low frequency (<100 kHz), thin films that compose zeolite FAU crystals presented higher εr values than did those possessing nonporous particles. The high εr values of the zeolite FAU thin films can probably be attributed to the physical adsorption of water. At a high frequency (1000 kHz), water had far less effect on εr values and thin films with a zeolite FAU structure presented εr values characteristic of low-dielectric constant (low-k) thin films.