Rapid and Facile Synthesis of Nanosized Silicalite‑1 Zeolites from Solid Silica in a Semisolid-like System via a Two-Step Crystallization Method

Nanosized zeolites have been found in extensive applications. Herein, a rapid two-step crystallization process (8 h) in a semisolid-like gel system, constructed by simply mixing and grinding solid silica gel, NaOH with TPAOH aqueous solution without extra water addition and any other additives, for the first time is demonstrated to synthesize nanosized silicalite-1 zeolites (∼66 nm) with high crystallinity and high product yield (>90%). The obtained nanosized silicalite-1 zeolites exhibit a large BET surface area (418 m² g^–1), a high micropore surface area (316 m² g^–1), and a rich micropore volume (0.14 cm³ g^–1). The rapid evolution process of nanosized zeolites could be decoupled into the nucleation stage at low temperatures and the crystallization stage at high temperatures during the two-step crystallization process. Importantly, the semisolid-like gel ensures fast nucleation. Moreover, in the later crystallization period, the fast crystal growth and inhibited ripening endow nanosized zeolite crystals with good crystallinity through a mass transfer-confined space. The obtained silicalite-1 zeolites were successfully applied in the preparation of (h0h)-oriented MFI zeolite membranes on hollow fibers, showing the flux up to 5.44 kg m^–2 h^–1 and the separation factor of 70 during the pervaporation test (5 wt % ethanol/water solution, 60 °C). This research develops a state-of-the-art synthetic approach for the efficient preparation of high-quality MFI-type nanozeolites.