Mesocrystal morphology regulation by “alkali metals ion switch”: Re-examining zeolite nonclassical crystallization in seed-induced process

Abstract

HypothesisIt is a Holy Grail to realize the goal-oriented synthesis of zeotype crystals via direct thermodynamic/kinetic control of crystallization in the simplest inorganic system. Especially, the most commonly used counter cations (i.e., Na+ and K+) are in turn believed to play merely the role of balancing charges and stabilizing frameworks, which make the simple ion-based morphology/porosity control remain big challenges. ExperimentsWe re-examined the role of Na+ and K+ to fine-tune the classical/nonclassical crystallization process in a seed-induced system with the simplest composition (Si/Al sources, inorganic alkali, and H2O), and proposed an “ion switch” strategy. By analyzing the multiple growth curves, tracking the precursor evolution, and observing epitaxial crystallization behavior, a distinctive “ion switch”-worked nonclassical mechanism was uncovered. FindingsBy the “ion switch” strategy, ZSM-5 mesocrystals were fine-regulated with diverse architecture from single crystal to nanocrystallite assembly and intracrystal mesopore-enriched crystal. Such simple ions-controlled crystallization was achieved through microstructure heterogeneity of zeolitic building-blocks triggered by different counterions and their corresponding assembly behavior from oriented attachment to random deposition. Furthermore, this protocol can be extended to a wider H2O/SiO2 range, mixed Na+/K+ systems, and other alkali metal ions from Li+ to Cs+, and ZSM-5 mesocrystals with extended morphologies can be obtained.