A Combined Experimental-Computational Study on the Effect of Topology on Carbon Dioxide Adsorption in Zeolitic Imidazolate Frameworks

Abstract

We report CO2 adsorption data for four zeolitic imidazolate frameworks (ZIFs) to 55 bar, namely ZIF-7, ZIF-11, ZIF-93, and ZIF-94. Modification of synthetic conditions allows access to different topologies with the same metal ion and organic link: ZIF-7 (ZIF-94) having sod topology and ZIF-11 (ZIF-93) having the rho topology. The varying topology, with fixed metal ion and imidazolate functionality, makes these systems ideal for studying the effect of topology on gas adsorption in ZIFs. The experiments show that the topologies with the smaller pores (ZIF-7 and 94) have larger adsorptions than their counterparts (ZIF-11 and 93, respectively) at low pressures (<1 bar); however, the reverse is true at higher pressures where the larger-pore structures have significantly higher adsorption. Molecular modeling and heat of adsorption measurements indicate that while the binding potential wells for the smaller-pore structures are deeper than those of the larger-pore structures, they are relatively narrow and cannot accommodate multiple CO2 occupancy, in contrast to the much broader potential wells seen in the larger pore structures.

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

“…The BET surface area derived from the N 2 isotherm were 424 m 2 g −1 and 506 m 2 g −1 respectively (Fig. S2), which is close to what has previously been reported (471 and 480 m 2 g −1 ) [39,50]. TGA analysis of the asprepared ZIF-94 in air showed a thermal stability up to~225°C with 20% weight loss due to THF and methanol removal (Fig.…”

“…ZIF-94 crystals were synthesized in this work by replacing dimethylformamide (DMF), previously used for synthesis of ZIF-94 [39], with a 2:5 ratio mixture of methanol: THF. A reaction yield of 82% for lab scale synthesis and 99% for up scaling, with respect to zinc were achieved.…”

“…The higher CO 2 uptake is attributed to the smaller pore diameter of ZIF-94 (9.1 Å) compare to other ZIFs. As it was reported, small pores are advantageous when considering CO 2 adsorption in the low-pressure regime [39]. ZIF-94/SIM-1 has already been used as membrane material in some publications.…”

Understanding the breathing phenomena in nano-ZIF-7 upon gas adsorption

“…Indeed, traditional synthesis for involves N,N-dimethylformamide (DMF) as a solvent with the associated difficulty to completely remove DMF from the inner cavities. 13,17,18 With this in mind, the main goal of this manuscript is to evaluate the breathing phenomena in small nanocrystals of ZIF-7 prepared using a solvent exchange approach. Under these conditions we will be able to completely remove unreacted chemicals together with the DMF used during the synthesis, thus leaving behind a perfect solvent-free porous structure.…”

Storage and separation of CO2 and CH4 in boron imidazolate frameworks: a theoretical study from Monte Carlo simulation

“…This model can reproduce the experimental gas-phase quadrupole moment of carbon dioxide by placing partial charges on C (+0.70 e) and O (−0.35 e) atoms. The potential parameters of BIF atoms were taken from the universal force field (UFF) of Rappe et al [30], which has been widely used to study the adsorption of different gases on nanoporous materials [23,[31][32][33]. Lorentz-Berthelot mixing rules were used to calculate mixed Lennard-Jones parameters.…”