Electronic structure dictates performance: why Mg-MOF-74 outperforms its peers in direct air capture of CO₂.

contextThe urgent need for scalable direct air capture (DAC) technologies is hindered by the lack of adsorbents that efficiently capture CO₂ from ambient air. While metal-organic frameworks (MOFs) such as the M-MOF-74 series show promise, a systematic electronic-level comparison of their DAC suitability is lacking. This study fills that gap by a systematic, electronic-level comparison of five M-MOF-74 variants (Mg, Ni, Co, Mn, Zn) using integrated DFT-GCMC analysis, establishing a clear structure-property relationship for DAC. Results identify Mg-MOF-74 as the optimal candidate, achieving the highest CO₂ uptake (5.03 mmol/g) and strongest binding energy (34.3 kJ/mol), which are attributed to its favorable electronic structure and open metal sites. We identify an optimal electronic configuration, moderate band gap, clear valence band maximum-conduction band minimum separation, and well-defined adsorption sites, which maximizes strong, selective physisorption at open metal sites. The work thus provides a blueprint for targeted material design, though the moisture sensitivity of Mg-MOF-74 underscores the need for hydrophobic functionalization in practical applications.

methodsDensity functional theory (DFT) calculations were performed using the Dmol