Elucidating the Competitive Adsorption of H ₂ O and CO ₂ in CALF-20: New Insights for Enhanced Carbon Capture Metal–Organic Frameworks

In light of the pressing need for efficient carbon capture solutions, our study investigates the simultaneous adsorption of water (H 2 O) and carbon dioxide (CO 2 ) as a function of relative humidity in CALF-20, a highly scalable and stable metal–organic framework (MOF). Advanced computer simulations reveal that due to their similar interactions with the framework, H 2 O and CO 2 molecules compete for the same binding sites, occupying similar void regions within the CALF-20 pores. This competition results in distinct thermodynamic and dynamical behaviors of H 2 O and CO 2 molecules, depending on whether one or both guest species are present. Notably, the presence of CO 2 molecules forces the H 2 O molecules to form more connected hydrogen-bond networks within smaller regions, slowing water reorientation dynamics and decreasing water entropy. Conversely, the presence of water speeds up the reorientation of CO 2 molecules, decreases the CO 2 entropy, and increases the propensity for CO 2 to be adsorbed within the framework due to stronger water-mediated interactions. Due to the competition for the same void spaces, both H 2 O and CO 2 molecules exhibit slower diffusion when molecules of the other guest species are present. These findings offer valuable strategies and insights into enhancing the differential affinity of H 2 O and CO 2 for MOFs specifically designed for carbon capture applications.