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

Abstract

In the transition to a clean-energy future, CO 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 CO adsorption, large CO 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 Mg(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) that feature step-shaped CO adsorption isotherms resulting from cooperative and reversible insertion of CO into metal-amine bonds to form ammonium carbamate chains. Small modifications to the diamine structure are found to shift the threshold pressure for cooperative CO 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 CO separation process. The unparalleled versatility of these materials, coupled with their high CO capacities and low projected energy costs, highlights their potential as next-generation adsorbents for a wide array of CO separations.

Tuning carbon dioxide capture capability with structural and compositional design in mmen‐(Mg,Zn) (dobpdc) metal‐organic framework: density functional theory investigation

“…The E ads was calculated using the definition in Eqn . In checking for validity, for x = 0 or mmen‐Mg 2 (dobpdc), our calculated E ads of −79.01 kJ/mol agrees well with experimental value of 78.80 kJ/mol. Nevertheless, for x = 1 or mmen‐Zn 2 (dobpdc), an experimental value for E ads is yet to be reported…”

Tuning Expanded Pores in Metal–Organic Frameworks for Selective Capture and Catalytic Conversion of Carbon Dioxide

“…As shown in Figure a, 1 demonstrates CO 2 uptake of 101.0 cm 3 g −1 at 273 K and 1 bar, and 75.1 cm 3 g −1 at 298 K and 1 bar, with selectivities for CO 2 /N 2 mixtures (CO 2 /N 2 =15:85 v/v) as high as 60.4 at 273 K and 35.9 at 298 K (calculated by IAST method; Figures S4 and S5). In addition, the isosteric heat of adsorption ( Q st ) for CO 2 was calculated based on the isotherms of 273 and 298 K by using the Clausius–Clapeyron equation . Similar sorption enthalpies and trends with increasing CO 2 uptake indicate that these three materials have comparable affinities towards CO 2 with only slight differences (Figure S6).…”

Chemical Crystallography at the Advanced Light Source

“…Recent work at the University of California, Berkeley [70], has shown that when N-alkylated ethylenediamines are appended to the Zn2(dobpdc) (dobpdc 4− = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) coordination framework ( Figure 14) it is possible for CO2 molecules to be inserted into the M-NH2R bond to give coordinated zwitterionic ammonium carbamate ligands. The coordinated carbamate anion then forms hydrogen bonds to the ammonium end of an adjacent ligand.…”