A Computational Study of Alkali Metal-Anchored 3D-COFs for Efficient CO2 Capture and Separation: Effects of Metal Type and Concentration.

Excessive CO2 emissions have promoted carbon capture, utilization, and storage (CCUS) as an advanced technology to alleviate environmental degradation. Developing high-performance adsorbents is essential for effective CCUS processes. In this study, a 3D-COF constructed with CuPcOC and benzidine was designed and incorporated with alkali metals (AMs) to form 3D-COF-nAMs. The CO2 capture and separation effects of AM doping types and concentrations were systematically explored (AM = K, Na, Li; n = 1, 2). The results showed that CO2 adsorption capacity increased with the atomic number of the AMs, with 3D-COF-1K exhibiting the highest adsorption capacity of 221.16 cm3 cm-3. However, for K-anchored structures, CO2 adsorption was reduced at higher doping concentrations. Further analysis of pore characteristics, structural stability, electronic structure, adsorption configuration, radial distribution function, isosteric heat of adsorption, van der Waals and Coulomb interactions revealed the intrinsic mechanism of AM anchoring. Moreover, a quantitative structure-property relationship, X= ω1Eχ+ ω2R, was established to correlate electronegativity (χ), charge transfer amount (E), and atomic radius (R). Linear fitting results under different doping concentrations confirmed its reliability. This work provides a theoretical basis for the rational design of COF-based adsorbents in CO2 separation technology.