The current challenges of carbon dioxide capture are focused on reducing the energy consumption per unit capture of CO₂. Therefore, developing sorbents that combine the characteristics of selective chemisorption and low regeneration energy consumption is highly desired. We focus on the exploration of this sorption chemistry in metal-organic frameworks (MOFs) and report a series of eleven amino acid functionalized MOF structures (MOF-808-AA), in which we devised MOF-808 as the basis for generating the amino acid functionalized forms, and the amino acid moieties are strongly bound to the backbone. We showed that MOF-808, when functionalized with amino acids where their carboxylate is bound directly to the Zr(IV), produces pores capable of selectively binding CO₂ from flue gas with potentially low energy requirements.
We measured and confirmed their enhanced CO₂ capture performance in the presence of water through sorption studies. These involved single-component sorption isotherms, CO₂/H₂O binary sorption isotherms, and dynamic breakthrough experiments. We further explored the mechanistic aspects of CO₂ binding in the presence of water and confirmed the formation of bicarbonate using evidence from solid-state nuclear magnetic resonance (NMR) spectroscopy. We found that this construct creates an environment inside the pores where CO₂ uptake under humid conditions leads to the formation of bicarbonates, therefore requiring no application of heat to regenerate the material. In this way, the application of a rough vacuum is sufficient to remove the CO₂. We then applied the CO₂ capture and release process in vacuum swing adsorption (VSA). A member of the MOF-808-AA series was subjected to a simulated coal flue gas and found to take up CO₂ and release it without heating. These studies, for the first time, combine humidity-enhanced CO₂ uptake and low-energy vacuum swing adsorption processes for post-combustion CO₂ capture.

Conceptual illustration of MOF-808-AA sorbents and their capture of CO<sub>2</sub> from flue gas driven by vacuum.

Conceptual illustration of MOF-808-AA sorbents and their capture of CO₂ from flue gas driven by vacuum.

Mark Doherty

Appearances