Silicalite-1 crystallization on glass fiber filter discs

Silicalite-1 was in situ crystallized from clear synthesis solutions onto commercial millipore glass fiber filters. The filters with diameter 2.5 cm were soaked in the precursor mixtures and hydrothermally treated at 80 °C or 150 °C for time up to 150 h. After the synthesis, the filters were treated in an ultrasonic bath for 15 min with a 0.1 M ammonia solution. The disc composites prepared at 80 °C swelled during synthesis, were easy to disintegrate upon subsequent manipulations and wrinkled when dried. The calcined materials were brittle with a porcelain-like appearance. The filters synthesized at 150 °C, both as synthesized and calcined, seemed identical in shape and mechanical characteristics to the initial glass fiber filters. Prolongation of the treatment at 150 °C up to 100 h led to densified fiber discs according to the SEM study but without visual changes in their mechanical strength. The difference in crystallization at the two different temperatures was attributed to the slower nucleation process at 80 °C, which resulted in greater dissolution of the fiber units and a certain inhibition of the crystallization process caused by the changed chemical environment at the fiber-synthesis solution interface. The silicalite-1/filter composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), chemical analysis and N2 adsorption measurements.