Mechanisms of CO₂and H₂O co-adsorption in pyrazine-linked hybrid ultramicroporous materials

Sorption-based carbon-separation applications using porous materials are often severely limited by the inevitable presence of water, thus greatly affecting their performance. An entirely unexpected breakthrough has been achieved with ultramicroporous materials. There are very few materials that can perform well in the presence of water and the MFSIX-3 series (M=Ti or Si) is leading this class of materials and has become the new benchmark for CO₂ capture. Despite this exciting development, the mechanisms by which MFSIX-3 is capable to retain its excellent performance in the presence of water remain unknown. Herein, we combine in situ infrared spectroscopy with ab initio calculations to provide insights into the co-adsorption of H₂O and CO₂ in prototypal pyrazine-linked HUMs. An in-depth study of binding sites and sorption mechanisms reveal the following: (i) conclusive experimental evidence that both CO₂ and H₂O molecules occupy the same pore; (ii) synergistic sorbate-sorbent interactions that enable co-adsorption in such a narrow ultramicropore; and (iii) the beneficial effects induced by higher humidity. Our results provide bottom-up design principlesto custom-design their pore size/chemistry and allow for new carbon capture benchmarks, even in the presence of humidity.