Strategies to control zeolite particle morphology

Aluminosilicate zeolites with controllable morphology have attracted considerable attention due to their potential applications in catalysis, adsorption, and separation technologies, as well as the biomedical field. However, the rational design and preparation of zeolites with the required morphology have not been achieved because the zeolite crystallization mechanism has not been fully understood, and therefore, the nucleation and crystal growth processes cannot be oriented. This paper reviews the progresses achieved in zeolite morphology control. The chemical compositions of the synthesis gel, including template (or the structure-directing agent) and framework heteroatoms, silica and alumina sources, alkali metal cations and mineralization ions, crystallization conditions, and synthesis methods have a considerable impact on the crystal morphology. The oriented assembly of zeolite crystals into special morphologies, such as hierarchical porous structures, zeolite membranes, hollow zeolite spheres, and core@shell-structured zeolites, can be realized by using soft and/or hard template methods and adjusting the synthesis and crystallization conditions. In addition, zeolite crystallization and crystal assembly mechanisms are investigated for providing an overall insight into the regulation of zeolite crystal morphology.