Pressure-Driven Loading of Large Guests in Metal-Organic Frameworks

Confining guest molecules within metal-organic frameworks (MOFs) allows their physical and chemical properties to be harnessed in their heterogenized form. However, apart from the loading of small molecules that can freely diffuse into and out of MOF pores, there is not yet a general and efficient strategy for loading and confining bulky organic molecules into MOFs with small apertures. In this work, we demonstrated that pressure can be employed to facilitate the diffusion of guest molecules into the cavities of UiO-66 and UiO-66-NH₂, even when the aperture sizes are smaller than the guests. This approach enables rapid and high-capacity loading of liquids or meltable solids that otherwise cannot be incorporated under atmospheric pressure. By studying the loading mechanism, we found that applying pressure can activate local geometric rearrangements of the MOF cavities and guests, enabling physical confinement of the guests within MOFs. As a result, a wide range of guest molecules can be readily encapsulated using our strategy, allowing for broad potential applications, including heterogeneous catalysis, postsynthetic modifications, and drug release.