Stepwise Node-Locking of a Mesoporous Zirconium Metal–Organic Framework Toward Enhanced Cycle Stability for Water Adsorption

Zr-based metal–organic frameworks (Zr-MOFs) with exceptional chemical stability have shown promising applications in water adsorption-based humidity control. However, due to the strong surface tension during the desorption of water, MOFs with both high water uptake capacity and high mechanical cycle stability are still rare. Through a hierarchical Zr-MOF (NU-601) with both micro- and mesopores showing high stability in water but fragility against the evacuation of solvent molecules as an illustration, we presented a stepwise strategy of locking Zr₆ nodes by auxiliary ligands from monodentate to bidentate, from monotopic to ditopic, and from nonstructural saturation to structural saturation, eventually realizing structural coordination saturation. The obtained new Zr-MOF (NJTech-4) with saturated (12-connected) Zr₆ nodes shows high water vapor uptake (995 cm³ g^–1) and excellent cycle stability, making it one of the suitable candidates for water-adsorption-based applications. Our experiments suggest that bidentate chelation of auxiliary ligands on Zr₆ clusters is a solution for stabilizing the nodes, which contributes to better cycle and thermal stability. Introducing supportive structural coordination could further strengthen the structure robustness against capillary forces, retaining a high water uptake capacity during the continuous removal of water from the pore.