Exceptional Mechanical Stability of Highly Porous Zirconium Metal–Organic Framework UiO-66 and Its Important Implications

Metal–organic frameworks (MOFs)
with high porosity usually
exhibit weak mechanical stabilities, in particular, rather low stabilities
against shear stress. This limitation remains one of the bottlenecks
for certain applications of porous MOFs, such as gas storage or separation
that requires dense packing of the MOF powders under mechanical compression
without collapsing the pores. We found that UiO-66, a prototypical
Zr-MOF with high porosity, exhibits unusually high shear stability.
Its minimal shear modulus (Gmin = 13.7
GPa) is an order of magnitude higher than those of other benchmark
highly porous MOFs (e.g., MOF-5, ZIF-8, HKUST-1), approaching that
of zeolites. Our analysis clearly shows that the exceptional mechanical
stability of UiO-66 is due to its high framework connections (i.e.,
the high degree of coordination of Zr–O metal centers to the
organic linkers). Our work thus provides important guidelines for
developing new porous MOFs targeting at high mechanical stabilities.