Computational Investigation of the Role of Topology and Functionalization on ZIF Stability

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal organic frameworks (MOFs) composed of Zn centers connected by imidazolate ligands. ZIFs exhibit high thermal and hydro stability, and are therefore attractive candidates for separations or adsorptions processes. However, little is known about their chemical stability in the presence of acidic conditions typical to flue gases. This work establishes a computational approach for predicting ZIF stability upon exposure to humid air, humid SO₂, and humid CO₂. We create mechanistic models for the complicated water-acid gas reaction complexes and use periodic density functional theory (DFT) calculations to determine the most favourable configurations. Calculations are designed to separate and independently probe the effects of framework topology and linker functionalization in ten ZIF materials. The results show good agreement with experimental stability observations, indicating that we have a reasonable physical understanding for ZIF stability in acid gas environments. Additionally, we propose a kinetic model for degradation that extracts rate constants consistent with time-dependent BET surface area measurements. In conclusion, we demonstrate that by combining kinetic theory with first principles calculations of bond-breaking events, we can accurately predict the likelihood and timescale of complex bulk structural degradation