A Combined Experimental−Computational Investigation of Carbon Dioxide Capture in a Series of Isoreticular Zeolitic Imidazolate Frameworks

摘要

A series of five zeolitic imidazolate frameworks (ZIFs) have been synthesized using zinc(II) acetate and five different 4,5-functionalized imidazole units, namely ZIF-25, -71, -93, -96, and -97. These 3-D porous frameworks have the same underlying topology (RHO) with Brunauer−Emmet−Teller surface areas ranging from 564 to 1110 m2/g. The only variation in structure arises from the functional groups that are directed into the pores of these materials, which include −CH₃, −OH, −Cl, −CN, −CHO, and −NH₂; therefore these 3-D frameworks are ideal for the study of the effect of functionality on CO₂ uptake. Experimental results show CO₂ uptake at approximately 800 Torr and 298 K ranging from 0.65 mmol g−1 in ZIF-71 to 2.18 mmol g−1 in ZIF-96. Molecular modeling calculations reproduce the pronounced dependence of the equilibrium adsorption on functionalization and suggest that polarizability and symmetry of the functionalization on the imidazolate are key factors leading to high CO₂ uptake.