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.