Tunable CO2 capture in n-ethylethylenediamine functionalized Mg2-MOF-74: unraveling the role of diamine basicity in reactivity and adsorption capacity

Mitigating CO₂ emissions requires the development of highly efficient, tunable, and selective adsorption materials. In this study, we explore the potential of diamine functionalized Mg₂-MOF-74 for CO₂ capture using density functional theory (DFT) calculations.N-Ethylethylenediamine (e2) exhibits favorable CO₂ adsorption energy and a low energy barrier for the rate-determining step (RDS) in the capture process, making it an effective diamine for MOF functionalization. Additionally, this study examines the influence of e2 basicity (pKa) on adsorption mechanisms, reaction barriers, and overall CO₂ uptake capacity. Our results reveal that while the neutral e2 exhibits a high RDS energy barrier, its mono- and doubly deprotonated forms significantly lower these barriers. In particular, the energy barriers for CO₂ insertion at both amine sites in the doubly deprotonated system are significantly lower (0.23–0.40 eV). We find that the doubly deprotonated e2/Mg₂-MOF-74 framework enhances reactivity at both amine sites, enabling the efficient capture of up to 24 CO₂ molecules. The moderate adsorption energy of −0.98 eV at high CO₂ coverage suggests facile desorption, promoting efficient MOF regeneration. Furthermore, our analysis indicates that a solvent environment with a pH of ∼12 favors the formation of the doubly deprotonated e2 species, further optimizing CO₂ adsorption performance