Anisotropy of metal–organic framework and their composites: properties, synthesis, and applications

Abstract

Metal–organic frameworks (MOFs) are potentially promising materials for a variety of applications in several fields owing to their distinctive structural properties, such as ultrahigh surface area, tailorable porosity and structural diversity. The ability to deliberately synthesize anisotropic MOFs and their composites holds great promise for applications in various fields, and constructing and designing anisotropic MOFs and their composite structures provide further performance-enhancing opportunities. This review thoroughly examines recent advancements in the properties, synthesis mechanisms, and applications of anisotropic MOFs. The discussion begins by highlighting the morphological anisotropies exhibited by MOFs and focuses on their abilities to form different structures. The physical anisotropies of MOFs are subsequently discussed, emphasizing their unique properties, such as their thermal, electronic, photonic, and magnetic anisotropies. The synthesis methods used to achieve anisotropic MOF microstructures are then explored, including modulation, template, etching, epitaxial-growth, self-assembly, and recrystallization techniques. These methods enable the morphology, size, and orientation a MOF microstructure to be precisely controlled, thereby enhancing anisotropic properties. Finally, we highlight the possible uses of anisotropic MOF microstructures in photocatalysis, electrocatalysis, and gas-separation applications.