Nanoblock Aggregation-Disaggregation of Zeolite Nanoparticles: Temperature Control on Crystallinity

摘要

During the induction period of silicalite-1 formation at 80 °C, primary nanoblocks of 8- 11 nm self-assemble together into fragile nanoflocculates of ca. 60 nm that dislocate and reappear according to a slow pseudoperiodical process. Between 22 and 32 h, the nanoflocculates grow up to 350 nm and contain ill- and well-oriented aggregates of ca. 40 nm. After 48 h, only ill-faceted monodomains of ca. 90 nm remains, which self-assemble into larger flocculates of ca. 450 nm. For crystal growth performed at 90 °C, most of the final aggregates exhibit ill-oriented assembly. This is consistent with a trial-and-errorblock-by-block building mechanism that turns into an irreversible and apparently faster process at 90 °C, causing definitively ill-oriented product. The nanoblocks, aggregates, and flocculates were characterized in nondiluted, nondiluted and ultrasonicated, or diluted and ultrasonicated solutions, using mainly dynamic light scattering and cryo-high-resolution transmission electron microscopy at various tilted angles.