(395ad) Experiment and Simulation Study of Carbon Dioxide/Mixed Gas Adsorption in Elastic Layered Metal-Organic Frameworks

Elastic Layered Metal-organic framework (ELM) adsorbents are flexible two-dimensional coordination polymers that undergo abrupt reversible gated adsorption from an empty collapsed structure to a filled expanded state by cooperative sorption of guest molecules between square grid layers. The ELM gating transition is distinct from condensation transition commonly observed for other porous carbons as it is induced by ELM structural rearrangement rather than by pore size effects.

We report experimental measurement of CO₂ sorption isotherms on ELM11 [Cu(BF₄)2(bpy)2], ELM-12 [Cu(OTf)2(bpy)2] and ELM-22 [Co(OTf)2(bpy)2] (bpy=bipyridine; OTf = trifluoromethanesulfonate) at supercritical temperatures. We also present the hybrid Monte Carlo – molecular dynamics simulation results of CO₂ sorption selectivity for separation of CO₂ from post-combustion (CO₂/N₂) flue gas mixture and CO₂/H2 syngas mixture. Simulated CO₂ capacities above the gating pressure and CO2 isosteric heat of adsorption agree well with ELM-11 and ELM-12 experimental data. The spatial density distribution of pure CO₂ and gas mixtures adsorbed within the framework structure is mapped and transition in the preferred orientations of CO₂ within ELM-12 is noted.  The possibility for tuning the structure for higher adsorption capacity as well as selectivity will also be discussed.