On the feasibility of the sonochemical preparation of hierarchical faujasite-type zeolites as an alternative to ultrasonic‑assisted alkaline treatment.

Using sonochemistry to synthesize hierarchical faujasite-type zeolites could offer a promising alternative to traditional alkaline-solution manufacturing. This approach could eliminate the need for costly and often hazardous reagents, thereby lowering production expenses and supporting green chemistry initiatives. Unlike conventional zeolite hierarchization, this innovative method could replace alkaline desilication of microporous zeolites entirely with ultrasonic pretreatment of the gel, followed by hydrothermal crystallization of the zeolite product. Selecting faujasite from over 260 possible zeolite structures highlights its broad utility in the chemical industry. The synthesized systems were analyzed for crystallinity, structure, Si/Al ratio, chemical states of silicon and aluminum, morphology, and acidity. Results showed that increasing ultrasound exposure time led to smaller crystallites and reduced microporosity, resembling effects obtained via standard alkaline desilication of parent microporous zeolites. Hence, it could be concluded that the sonicated zeolites were hierarchical materials at first sight. Nevertheless, significant drops in microporosity, accompanied by distinct fragmentation and a relatively low drop in Si/Al ratios, suggested existing interparticle voids rather than intracrystalline mesopores and macropores. Therefore, the sonicated materials reported in this work can be described as seemingly hierarchical faujasites. Furthermore, the sonicated faujasites exhibited high sensitivity to further modification, prompting further optimization studies, including zeolite structures with higher starting Si/Al ratios.