Preparation of Hierarchical ZSM-5 Sheets with Diverse Quaternary Ammonium Hydroxides as Etching Agents

To address the inherent diffusion limitations in zeolites, the preparation of hierarchical zeolite sheets with a lower internal diffusion resistance is highly desired. Herein, we present a facile strategy for producing hierarchical ZSM-5 zeolite sheets (Z5-HSs) via alkaline etching of the coffin-shaped bulk counterparts with diverse quaternary ammonium hydroxides (i.e., TMAOH, TEAOH, TPAOH, and TBAOH). Our results demonstrate that ZSM-5 sheets with a hierarchical structure could be obtained by rational control of the initial Si/Al ratio, irrespective of the etchant variety employed. The final Si/Al ratio of the obtained sheets can be tuned in the range of 11-55. Furthermore, our results reveal two distinct etching mechanisms governed by the etchant type: an "outside-in" process for TMA⁺, driven by its strong surface affinity, and a dissolution-recrystallization pathway for the larger TEA⁺, TPA⁺, and TBA⁺ cations. To the best of our knowledge, this work demonstrates for the first time that the synergistic effect of framework aluminum enables weakly templating TBAOH to successfully form uniform sheets, a result not achievable with pure-silica zeolites. These findings highlight the critical interplay between etchant choice and zeolite composition and significantly expand the toolbox for the precise microstructural tailoring of zeolites.