Dissolution–Recrystallization Formation of Huge Thin 2D Silicalite Lamella for Promoted Sorption

Abstract

AbstractAn all silica MEL‐type silicalite‐2 nanocrystal is hydrothermally treated in coexistence with cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) at ordinary and elevated temperatures. From monitoring its structural transition process by various physico‐chemical methodologies, it is found that, instead of simple delamination, silicalite‐2 nanocrystal changes with a dissolution and recrystallization mechanism by treatment at an elevated temperature and for a long time, that is, it is first dissolved and then reorganized to huge 2D platelets via an intermediate step forming periodic mesoporous material. The newly formed nanoplatelets (h‐nanoplatelets) from in‐plane growth along a (or b)‐, c‐directions (normal to b (or a)‐axis) are of silicalite (either MEL or MEL/MFI intergrowth)‐type framework topology with a thickness of 3.3 nm (the equivalent of ≈1.6 unit cell) and interspersed with a minor part of small square‐like MFI‐type nanoplatelets (s‐nanoplatelets). The h‐nanoplatelets have expanded lattice parameters and a larger micropore size compared to the parent silicalite‐2 nanocrystal and s‐nanoplatelets, whose micropore structure are modified so as to benefit from both equilibrium adsorption and desorption‐recovering ability of organic contaminants particularly at a low vapor pressure range. This is the first report regarding the dissolution–recrystallization formation of 2D lamella‐type silicalites mediated by popular types of surfactant and base species.