(757b) Towards a Generalized Understanding of Acid Gas Interactions with ZIF Materials 

Zeolitic Imidazolate Frameworks (ZIFs) are a set of nanoporous metal-organic frameworks (MOFs) with tunable porosity and functionality. Among MOFs, they also show relatively good stability with respect to temperature and humidity. These characteristics lead to their potential applications as membranes or adsorbents in separation processes, in which they would be exposed to a variety of molecular species including acid gases. However, there is very little systematic knowledge of the effects of acid gas exposure on the structure and separation properties of ZIFs, in particular the mechanistic aspects of ZIF degradation by acid gases as well as the effects of differences in ZIF crystal topology and linker composition on their stability. ^1-2 The objective of this work is to develop a generalized understanding of ZIF stability in acid gases. The stability of ten ZIF materials (of differing structural topologies such as SOD, RHO and ANA) under different environments such as humid air, liquid water, dry, humid and aqueous SO₂, dry and humid CO₂ are investigated in detail. Combined characterization by several techniques (PXRD, N₂ physisorption, EDX, XPS, and FTIR) allowed us to track the structural and compositional properties before and after exposure. All ZIFs studied were found to be stable under dry acid gas environments in this study while a few ZIFs underwent transitions into non-porous phases under humid air or liquid water exposure. Most ZIFs were found to be unstable under long-term humid SO₂ or CO₂exposure. We present quantitative kinetic data and parameters for the degradation of ZIFs, and discuss in detail the effects of topology and linker composition. This work provides a comprehensive guide to the acid gas stability of ZIF materials, and the main features could be extended to other classes of MOFs and to understand stability under exposure to other kinds of reactive species.

References

1. Bhattacharyya, S.; Pang, S. H.; Dutzer, M. R.; Lively, R. P.; Walton, K. S.; Sholl, D. S.; Nair, S., Interactions of SO₂-Containing Acid Gases with ZIF-8: Structural Changes and Mechanistic Investigations. J.Phys.Chem.C 2016, 120, 27221-27229.

2. Pang, S. H.; Han, C.; Sholl, D. S.; Jones, C. W.; Lively, R. P., Facet-Specific Stability of ZIF-8 in the Presence of Acid Gases Dissolved in Aqueous Solutions. Chem. Mater. 2016, 28, 6960-6967.