Ultra-Fast Crystallization of Nanozeolite via Hydroxyl Radicals Generated by Electron-Beam-Induced Radiolysis.

Abstract

The development of nanozeolites is crucial for advancing applications in catalysis, adsorption, and separation due to their unique structural and functional properties. Herein, we demonstrate the ultra-fast crystallization of RHO-type nanozeolite (in just a few tenths of a seconds) in a colloidal aluminosilicate suspension is demonstrated and is observed by transmission electron microscopy. Nucleation occurs almost instantaneously, within 5 s, under electron beam irradiation, followed by rapid, homogeneous crystal growth completed within 14-20 s. The crystallization of RHO nanocrystals is driven by hydroxyl radicals (OH^•) generated through radiolysis, allowing for real-time tracking of nanozeolite formation. By systematically varying the electron dose rate from 0.66 to 80.7 e^- Å^-2 s^-1, its critical role in controlling induction time, nucleation density, and particle coalescence is demonstrated. The latter stages involve Ostwald ripening, resulting in the formation of larger RHO nanocrystals. Notably, coalescence occurs earlier at higher electron doses (80.7 e^- Å^-2 s^-1) due to accelerated nucleation from a higher generation of OH^• radicals. These findings provide direct evidence of the ultra-fast kinetics of nanozeolite nucleation and growth, highlighting the pivotal role of hydroxyl radicals in driving amorphous nanoparticle formation and stabilizing zeolite crystallites with uniform crystals size.