Computational characterization of disordered metal-organic frameworks

Abstract

Metal-organic frameworks (MOFs) are a class of crystalline nanoporous adsorbents with numerous applications due to their highly tunable physical and chemical properties. However, MOFs are limited by their susceptibility to degradation in humid and acid environments common to many industrial processes. We focus on zeolitic imidazolate frameworks (ZIFs), a MOF subclass with high thermal stability which can be synthesized in many topologies. In this thesis, we study disorder in ZIFs at local and superlattice length scales by building computational models of defects, simulating bulk properties of the defect material, and comparing our theoretical insights against experimental measurements. We first demonstrated that inherent extended defects such as stacking faults are favorable, suggesting that these defects will be introduced during synthesis and are therefore prevalent in real ZIF materials. Then we consider degradation induced by exposure to H2O, CO2, SO2, and NO2 on a broad set of ZIFs. While simulation alone cannot fully predict ZIF stability, it will be valuable in elucidating new degradation pathways of more complex attacking species. Following on this work, we investigated how local defects accumulate until the bulk structure degrades. The mechanism we proposed explains favorable defect propagation as a means to reduce or eliminate the strain energy. Finally, we performed meta-analysis on a fundamental question: how reproducible is MOF synthesis research? While our findings are not encouraging, we propose an “Olympic medal” hierarchy standard and suggest ways the research community can improve reproducibility.