Macroscopic alignment of metal-organic framework crystals in specific crystallographic orientations

With the growing interest in metal-organic frameworks (MOFs) and their potential applications, it has become crucial to discover novel MOFs and modify their constituent components. One promising strategy for enhancing the properties of MOFs is the alignment of crystals in specific orientations, which induce anisotropic properties in particular facets. The integration of oriented MOFs at the macroscopic level can be achieved through two main approaches: the direct growth in an oriented manner and the alignment of pre-formed crystals. Direct growth methods involve the adsorption of precursor molecules on substrates, initiating the guided growth based on factors like lattice parameters, surface interactions, and differential growth rates of crystal facets. Integrating MOFs with other substrates in an oriented manner generates novel architectures with unique properties. Another approach is to create alignment using pre-formed MOF crystals, which mainly involves external forces, interfaces of synthetic media, and their assembly. This strategy offers greater flexibility in material selection because of the wide range of pre-existing MOF structures of different compositions. Furthermore, it enables the fabrication of highly ordered alignment over large areas. Ideally, perfectly aligned MOF crystals can mutually synchronize with each other to act like a large single-crystal, ultimately facilitating the full utilization of the directional anisotropic properties over a large area. This review focuses on the preparation strategies and examples of macroscopically oriented MOFs. This review explores synthetic strategies for macroscopic aligned MOFs, enhancing properties without structural designs or post-synthetic reactions.