Creating hierarchical pores in metal-organic frameworks via postsynthetic reactions

Metal-organic frameworks (MOFs) demonstrate promise for a multitude of applications owing to their high porosity and surface area. However, the majority of conventional MOFs possess only micropores with very limited accessibility to substances larger than 2 nm-especially functional biomacromolecules like some proteins. It is challenging to create an appropriately large pore size while avoiding framework collapse in MOFs. Herein, we present the generation of mesopores in microporous MOFs through three facile and effective techniques, namely Soxhlet washing, linker hydrolysis and linker thermolysis. These postsynthetic elimination approaches have been applied in selected MOFs, including PCN-250, PCN-160 and UiO-66, and controllably generate MOFs with hierarchical pores and high stability. Our work demonstrates reproducible and straightforward methods resulting in hierarchically porous materials that possess the benefits of mesoporosity while borrowing the robustness of a micropore framework. All the procedures can be conducted reliably at a multigram scale and operation time less than 6 h, representing a significant effort in the field of MOF synthesis. These hierarchically porous MOFs show great promise in a wide range of applications as efficient adsorbents, catalysts and drug carriers.