Amorphous metal-organic frameworks: From synthesis strategies to emerging applications

Abstract

Amorphous metal-organic frameworks (AmMOFs) have emerged as alternatives to their crystalline counterparts due to their unique structures, diverse properties, and wide applications. AmMOFs usually combine the advantages of crystalline MOFs (CrMOFs) including high surface area, exceptional chemical and thermal stabilities, chemical functionalities, and tunable pore sizes/shapes, with the emerging properties of amorphous counterparts including the absence of grain boundaries, abundant defects and active sites, isotropy, high flexibility, and enhanced mechanical robustness. Although the number of reports on AmMOFs is much lower than those on CrMOFs, in some examples they exhibit improved properties and have also attracted increasing attention in the recent years, thereby they will possess great potential in the future technologies. This review aims to highlight the recent progress of AmMOFs in synthesis methods, structure-property relationships, and emerging applications. In this regard, we highlight the superiority of AmMFs compared to their crystalline counterparts, then describe two primary approaches for preparing AmMOFs including: 1) top-down: amorphization of pre-synthesized CrMOFs via different treatment methods, and 2) bottom-up: direct synthesis of AmMOFs. Additionally, we highlight the recent progress of AmMOFs in different fields including biomedical, catalysis/photocatalysis, energy storage and conversion, chemical sensing, gas adsorption and separation, and water/wastewater treatment applications.