Ultrahigh Surface Area Zirconium MOFs and Insights into the Applicability of the BET Theory

An isoreticular series of metal–organic
frameworks (MOFs)
with the ftw topology based on zirconium oxoclusters
and tetracarboxylate linkers with a planar core (NU-1101 through NU-1104) has been synthesized employing a linker
expansion approach. In this series, NU-1103 has a pore
volume of 2.91 cc g–1 and a geometrically calculated
surface area of 5646 m2 g–1, which is
the highest value reported to date for a zirconium-based MOF and among
the largest that have been reported for any porous material. Successful
activation of the MOFs was proven based on the agreement of pore volumes
and BET areas obtained from simulated and experimental isotherms.
Critical for practical applications, NU-1103 combines
for the first time ultrahigh surface area and water stability, where
this material retained complete structural integrity after soaking
in water. Pressure range selection for the BET calculations on these
materials was guided by the four so-called “consistency criteria”.
The experimental BET area of NU-1103 was 6550 m2 g–1. Insights obtained from molecular simulation
suggest that, as a consequence of pore-filling contamination, the
BET method overestimates the monolayer loading of NU-1103 by ∼16%.