Rational Tuning of Water Vapor and CO2 Adsorption in Highly Stable Zr-Based MOFs

We report the synthesis of a novel and highly robust monomethyl-functionalized Zr-based MOF (UiO-66-MM) by presynthesis functionalization of the BDC ligand. UiO-66-MM is isostructural to UiO-66 and is characterized by PXRD, FTIR, N-2 adsorption, NMR, and TGA. Grand canonical Monte Carlo (GCMC) simulations are performed to confirm the increase in adsorbate-adsorbent interactions for CO2 and CH4 observed during the experimental measurements. This enhancement is due to the presence of the methyl group in UiO-66-MM, which increases the adsorption potential by constricting the pore diameter. However, UiO-66-MM is less hydrophilic than the parent UiO-66 due to the nonpolar methyl groups and adsorbs almost 30% less water than UiO-66. This new MOF also has a much higher CO2/CH4 selectivity under dry conditions due to enhanced van der Waals interactions with CO2. Hence, we expect UiO-66-MM to exhibit superior performance over the parent MOF in humid gas separations.