Elucidating the Competitive Adsorption of HO and CO 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 (HO) and carbon dioxide (CO) 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, HO and CO 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 HO and CO molecules, depending on whether one or both guest species are present. Notably, the presence of CO molecules forces the HO 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 molecules, decreases the CO entropy, and increases the propensity for CO to be adsorbed within the framework due to stronger water-mediated interactions. Due to the competition for the same void spaces, both HO and CO 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 HO and CO for MOFs specifically designed for carbon capture applications.