Controlling Cooperative CO2 Adsorption in Diamine-Appended Mg2(dobpdc) Metal–Organic Frameworks

Journal of the American Chemical Society

5 years ago

Controlling Cooperative CO2 Adsorption in Diamine-Appended Mg2(dobpdc) Metal–Organic Frameworks

Abhoyjit S. Bhown, Phillip J. Milner, Rebecca L. Siegelman, Adam H. Berger, Jeffrey D. Martell, Miguel I. Gonzalez, Thomas M. McDonald, Jarad A. Mason, Jeffrey R. Long

In the transition to a clean-energy future, CO₂ separations will play a critical role in mitigating current greenhouse gas emissions and facilitating conversion to cleaner-burning and renewable fuels. New materials with high selectivities for CO₂ adsorption, large CO₂ removal capacities, and low regeneration energies are needed to achieve these separations efficiently at scale. Here, we present a detailed investigation of nine diamine-appended variants of the metal–organic framework Mg₂(dobpdc) (dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) that feature step-shaped CO₂ adsorption isotherms resulting from cooperative and reversible insertion of CO₂ into metal–amine bonds to form ammonium carbamate chains. Small modifications to the diamine structure are found to shift the threshold pressure for cooperative CO₂ adsorption by over 4 orders of magnitude at a given temperature, and the observed trends are rationalized on the basis of crystal structures of the isostructural zinc frameworks obtained from in situ single-crystal X-ray diffraction experiments. The structure–activity relationships derived from these results can be leveraged to tailor adsorbents to the conditions of a given CO₂ separation process. The unparalleled versatility of these materials, coupled with their high CO₂ capacities and low projected energy costs, highlights their potential as next-generation adsorbents for a wide array of CO₂ separations.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b05858

DOI: 10.1021/jacs.7b05858