(302e) Structural Modification of Metal Organic Frameworks for Steam Stable CO2 Adsorbents

The heightened global concern over increasing CO₂ concentrations in the atmosphere have led to intensive research on CO₂ mitigation strategies, specifically on the ways to capture CO₂ from post-combustion flue gas. Porous adsorbent materials may represent promising pathway to capture the greenhouse gas in a simple and cost-efficient way.¹ Among adsorbents, metal organic frameworks (MOFs) featuring high surface areas and chemical tunability have demonstrated competitive CO₂ adsorption capacities under the CO₂ capture conditions simulating the flue gas.² However, most of the research employing MOFs as a CO₂ adsorbent have been carried out under dry conditions, which is far from the realistic conditions. To use MOFs for practical CO₂ capture applications such as for the flue gas, the material stability of MOFs under humid conditions should be evaluated.

In this work, structural changes and CO₂ capture performance of MOFs was studied under humid CO₂ capture conditions using accelerated steam treatment tests. Traces of structural degradation based on XRD patterns and porosity measurements as well as dramatic loss of its CO₂ capture capacity was observed when the bare Mg/DOBDC was exposed to the humidity. To improve materials stability, pore surface modification with ethylene diamine groups was performed using post-synthesis functionalization procedures used in the previous work.³ Materials stability of the Mg/DOBDC under humid conditions was assessed before and after functionalization and analyzed using characterization techniques including XRD, surface area and pore size analyzer, TGA, etc. Amine functionalization was hypothesized to shield open metal sites of the framework from water molecules therefore protecting material from degradation. It was found that while some degradation occurred still, CO₂ capacities were almost completely regenerated after steam treatment. 

            (1)      Choi, S.; Drese, J. H.; Jones, C. W. ChemSusChem 2009, 2, 796.

            (2)      Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T. H.; Long, J. R. Chemical Reviews 2012, 112, 724.

            (3)      Choi, S.; Watanabe, T.; Bae, T.-H.; Sholl, D. S.; Jones, C. W. The Journal of Physical Chemistry Letters 2012, 3, 1136.