Coordination environment regulated Li-COFs for efficient CO2 capture and separation over N2 and CH4

The urgency to reduce excessive CO2 emissions has driven the development of CO2 adsorbents. Metal-covalent organic frameworks (M-COFs) are a promising adsorbent that bridges the gap between metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). Herein, the CO2 capture and separation performances of Li-COF-XYs (XY=OO, ON, NN, NS, and SS) were investigated at 298 K and 0-1.0 bar using Grand Canonical Monte Carlo (GCMC) and Density Functional Theory (DFT). The analysis of structure and pore characteristics confirms the structural stability and excellent pore environment for CO2 adsorption of Li-COF-XYs. The formation of X-Li-Y creates strong CO2 adsorption sites, making Li-COF-XYs effective for CO2 capture and separation. This effect becomes more pronounced as the electronegativity of the coordination atoms increases. Moreover, the CO2 capture capacity is affected by pore size under a similar coordination environment. Therefore, Li-COF-ON has the highest CO2 capture capacity of 7.99mmol g(-1) with CO2 selectivity over N-2/CH4 of 127.26/86.45 at 298 K and 1.0 bar. The internal mechanism by which the coordination environment influences CO2 capture and separation is elucidated by the distribution of gas adsorption, adsorption energy, isothermal adsorption heat, and interactions. This work provides theoretical insights for the development of M-COFs for CO2 capture and separation.