Ultrasonic-assisted rapid liquid-phase exfoliation of MFI-type zeolite nanoparticle aggregates

The preparation of dispersible MFI-type zeolite nanoparticles with open micropores is challenging. Herein, a rapid and effective ultrasound-assisted liquid-phase exfoliation method along with a freeze-drying process for redispersion of calcined Silicalite-1 (S-1) zeolite nanoparticle aggregates using 3-aminopropanol as an exfoliating agent is demonstrated. The exfoliation of S-1 zeolite nanoparticles is characterized by X-ray diffraction, scanning electron microscopy and DLS particle size analysis. The effects of drying methods of as-synthesized zeolite nanoparticle suspension, zeolite contents in frozen nanoparticle suspension, exfoliating agent concentrations, and zeolite doses in ultrasonic suspension on exfoliation efficiency are systematically investigated. It is found that the S-1 zeolite nanoparticle (∼70 nm) achieves a yield up to 95 % through a 30 min ultrasonic exfoliation in a 3-aminopropanol solution along with a freeze-drying process. The proposed exfoliation mechanism involves two primary stages: guest molecule insertion followed by water expansion, both substantially enhanced by tip sonication. This work offers a comprehensive understanding of the exfoliation process, provides valuable insights into the dispersion of sintered zeolite nanoparticles.