Implementation of a Core-Shell Design Approach for Constructing MOFs for CO 2 Capture.

Adsorption-based capture of CO 2 from flue gas and from air requires materials that have a high affinity for CO 2 and can resist water molecules that competitively bind to adsorption sites. Here, we present a core-shell metal-organic framework (MOF) design strategy where the core MOF is designed to selectively adsorb CO 2 , and the shell MOF is designed to block H 2 O diffusion into the core. To implement and test this strategy, we used the zirconium (Zr)-based UiO MOF platform because of its relative structural rigidity and chemical stability. Previously reported computational screening results were used to select optimal core and shell MOF compositions from a basis set of possible building blocks, and the target core-shell MOFs were prepared. Their compositions and structures were characterized using scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction. Multigas (CO 2 , N 2 , and H 2 O) sorption data were collected both for the core-shell MOFs and for the core and shell MOFs individually. These data were compared to determine whether the core-shell MOF architecture improved the CO 2 capture performance under humid conditions. The combination of experimental and computational results demonstrated that adding a shell layer with high CO 2 /H 2 O diffusion selectivity can significantly reduce the effect of water on CO 2 uptake.