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

Abstract

© 2018 Society of Chemical Industry and John Wiley & Sons, Ltd. This paper presents a materials design for tuning the CO2-capture capability of mixed-metal-organic framework mmen-(ZnxMg1-x)2(dobpdc) using density functional theory. The structural stability of a mixed-metal structure with respect to its parent single-metal species was investigated via energy of mixing (ΔEmix). We found that the ΔEmixof all mixed-metal structures are negative, signifying exothermic mixing. This then indicates that mixed-metal structures are energetically preferable compared with their non-interacting single-metal species. Moreover, the magnitudes of ΔEmixof all mixed-metal structures are lower than 1 kJ/mol, implying an ‘ideal mixing’. Density-of-state analysis also reveals that the electronic structures of both Mg and Zn in mixed-metal structures are not significantly different from those in parent single-metal species, suggesting weak chemical interaction between Mg and Zn in mixed-metal structures. For CO2-adsorbed mmen-(ZnxMg1-x)2(dobpdc), we found that the adsorption energy (Eads) is a linear function of mixing ratio (x), and does not depend on how Mg and Zn atoms are arranged in forming different mixed-metal structures. This can be described by the weak chemical interaction between Mg and Zn in a mixed-metal structure. Consequently, Eadscan then be predicted conveniently from the mixing ratio, while the adsorption properties of parent single-metal species can be tuned with the proposed mixed-metal method. We then expect that the knowledge of materials design using a mixed-metal approach presented in this work would benefit the community in providing the ability to tune CO2capture capability efficiently in the materials studied. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.