Oriented Aggregation of Silicalite-1 Subcrystals into MFI Zeolite Crystals

This is the authors' abstract. We don't add key points for this paper.

Precursor nanoparticles that form spontaneously on hydrolysis of silica source in aqueous solutions of tetrapropylammonium (TPA) hydroxide evolve to (TPA)- silicalite-1, a molecular-sieve crystal that serves as a model for the self-assembly of porous inorganic materials in the presence of organic structure-directing agents. The structure and role of these nanoparticles are of practical significance for the fabrication of 3-dimensional (3D) ordered porous materials and molecular-sieve films, but still remain elusive. Here we show experimental findings of nanoparticle and crystal evolution by controllable manipulation of silicalite-1 synthesis. We have investigated detailed structural features of MFI precursors, which involves precise temperature control during synthesis, fine purification of 6–10 nm silicalite-1 subcrystals (SCs) as starting materials, and subsequent compression via an ice-templating method. SCs aggregate into MFI crystals with unidirectional orientation─indicating that SCs possess at least partial MFI structure and a slab-like morphology. This synthetic route is not only facile and environmentally friendly but also highly reproducible. We believe this method holds great promise for advancing the application of membrane-based separation processes in the natural gas industry and organic liquid separation.