MCM-22 Zeolite-Induced Synthesis of Thin Sodalite Zeolite Membranes

A novel strategy for synthesizing the high-performance thin and compact sodalite zeolite membrane over rough α-Al2O3 support was developed. The synthesis involved the deposition of a layer of flaky MCM-22 zeolite crystals over support and the subsequent hydrothermal crystallization of sodalite zeolite. It was identified that the sodalite zeolite membrane possessed a thickness of ca. 700 nm with almost no defect, and a water/ethanol separation factor higher than 10 000 at a permeation flux of 4.4 kg·m–2·h–1 could be achieved. A possible mechanism for the formation of high-performance sodalite zeolite membrane was also proposed, which involved first the decomposition of MCM-22 zeolite crystals into small fragments containing double six-membered rings (D6R) and subsequently the nucleation and crystallization of sodalite initiated by the D6R-containing species over the surface of support from the strongly alkali synthesis sol. The study showed that the predeposition of a layer of flaky MCM-22 zeolite crystals over the surface of support was crucial for the generation of thin and compact sodalite membranes, as it not only improved the surface flatness but also led to the in situ nucleation and crystallization of sodalite zeolite crystals. This method combines 2D-material film-forming technology with 3D-material film-forming technology, thus providing a new approach for preparing thin and defect-free membranes.