Screening and preparation of functionalized TpBD-COFs for CO₂ capture

Covalent organic frameworks (COFs) with high specific surface area, ordered pore wall, modified porous surface and customizable chemical structure have been widely used in CO₂ capture. However, the screening of functionalized COFs suitable for CO₂ capture still relies on experiments, which will require a long experimental period with blindness and randomness. Herein, we chosed three electron withdrawing groups (–NO₂, –CN and −Br) and three electron donating groups (–CH₂NH₂, –CH₃, –OCH₃) to explore the effect of electron withdrawing ability of functional groups on the CO₂ adsorption capacity. Grand canonical Monte Carlo (GCMC) method was used to simulate the adsorption capacity of CO₂ over X-TpBD-COFs (X=–NO₂, –CN, −Br, –CH₂NH₂, –CH₃, –OCH₃). As the result, NO₂-TpBD-COF had the highest adsorption capacity among the six functionalized X-TpBD-COFs at 100 kPa and 25 ℃ (49.37 cm³/g), while OCH₃-TpBD-COF had the lowest adsorption capacity among them (23.51 cm³/g at 25 ℃ and 100 kPa). The order of binding energy was basically the same as the order of adsorption capacity when the synergistic interactions between functional groups and oxygen atoms in Tp were considered according to density functional theory (DFT). Molecular dynamics (MD) showed that the diffusion and distribution of CO₂ were mainly effected by pore structures. To verify the simulation results, NO₂-TpBD-COF and OCH₃-TpBD-COF were successfully prepared by solvothermal method. The CO₂ adsorption capacities of these two COFs were basically consistent with the conclusion obtained by the simulations. This study provided a way for simulation to guide accurate and rapid experimental design of COF materials for CO₂ capture.