Post-synthetic modification of metal-organic framework-based membranes for enhanced molecular separations

Metal-organic frameworks (MOFs) are a class of porous crystalline materials constructed by polynuclear metal clusters and organic linkers. In recent years, research efforts have been switching from fundamental studies of MOFs to the exploration of engineered forms of MOFs for specific applications. Particularly, MOF-based membranes have been extensively studied for challenging molecular separations. The design of high-quality MOF membranes with highly efficient separation performance requires controllable manipulation and functionalization of MOF structures. In-situ modification and post-synthetic modification (PSM) are two efficient ways to manipulate MOF structures. Comparing these two approaches, PSM is more appealing as it allows for the functionalization of diverse MOFs, while the in-situ modification is limited to a restricted set of MOF candidates. This review focuses on recent advances in the post-synthetic modification of MOFs and their membranes for enhanced molecular separation applications. Different categories of post-synthetic modification methods are summarized. Representative examples of post-synthetically modified polycrystalline MOF membranes and MOF composite membranes are discussed. Furthermore, the significant contributions of post-synthetic modification to the enhanced molecular separation performance of MOF membranes are highlighted. Last but not least, challenges and opportunities for bringing MOF membranes from the laboratory scale to practical separation applications are presented to guide the future development of MOF membranes with industrially attractive molecular separation performance.