Sorption in Zeolites Modified for Use in Organic−Inorganic Hybrid Membranes

Adding zeolites to polymer matrixes can provide improved materials for membrane-based separation of gases. To create such materials, the sorption in and diffusion through the zeolites must be relatively unhindered by the process of modification and bonding to the polymer. An attractive approach to achieve the stabilization and bonding of the zeolite phase involves silane treatment of external zeolite surfaces prior to dispersion. This study shows that standard treatments to achieve the silylation in an aqueous alcohol mixture with the assistance of ultrasonic energy can cause surprising and undesirable alterations in the sieve properties. Using zeolite 4A as a model and γ-aminopropyldimethylethoxysilane in both ethanol−water and isopropanol−water mixtures, the extent of sieve sorption property changes during reaction in the presence of ultrasound exposure is illustrated. Control studies with these alcohol−water systems further identify the impact of the alcohol type on the zeolite. Oxygen sorption kinetics and equilibria are reported for the modified and unmodified zeolite after activation and drying under typical conditions used for forming such hybrid materials. It is concluded that sonication appears to drive both isopropanol and ethanol into the sieves; however, drying at 250 °C appears to enable recovering most of the intrinsic sieve sorption and transport properties.