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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 ΔEmix of 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 ΔEmix of 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, Eads can 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 CO2 capture capability efficiently in the materials studied. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

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Local structure of lead zinc niobate (PZN) ceramic, synthesized via B-site oxide precursor route in atmospheric pressure, was investigated using synchrotron x-ray absorption spectroscopy (XAS) technique. The x-ray absorption near-edge structure (XANES) simulation was first carried out. The XANES simulation results indicate that the PZN ceramic is in pyrochlore phase having Zn 2þ substituted on Nb 5þ site. Afterwards, the extended x-ray absorption fine structure (EXAFS) analysis was performed to extract the bond length information between Zn 2þ and its neighboring atoms. From the EXAFS fitting, the bond length between Zn 2þ and Pb 2þ in the pyrochlore phase was found to be longer than the previously reported bond length in the perovskite phase. Further, with the radial distribution information of Zn 2þ 's neighboring atoms, the formation energies along the precursor-to-pyrochlore and precursor-to-perovskite reaction paths were calculated using the density functional theory (DFT). The calculated results show that the formation energy of the perovskite phase is noticeably higher than that of the pyrochlore phase, which is influenced by the presence of energetic Pb 2þ lone pair, as the perovskite phase has shorter Zn 2þ to Pb 2þ bonding. This therefore suggests the steric hindrance of Pb 2þ lone pair and the mutual interactions between Pb 2þ lone pair and Zn 2þ are main causes of the instability of lead zinc niobate in the perovskite structure and confirm the efficacy of XAS and DFT analysis in revealing local structural details of complex pyrochlore materials. V C 2013 AIP Publishing LLC. [http://dx.

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