Tracking CO₂ capture and separation over N₂ in a flexible metal–organic framework: insights from GCMC and DFT simulations

Investigations on the structural transition and property of the intermediate structures are significant to understand the gas adsorption and separation performance in flexible metal–organic frameworks (MOFs). Herein, theoretical investigations were conducted to track CO₂/N₂ adsorption and separation in the flexible bridged phenyl MOF 1. Results showed the closed pore form 1B expanded and exhibited the intermediate states of 1B_x (x = 9.8, 10.34, 11.3, 12.5, and 14.1) with the adsorption of CO₂. The adsorption performance–structure–pressure relationship was built based on the adsorption isotherms, and 1B_9.8, 1B_10.34, 1B_11.3, 1B_12.5, and 1B_14.1 were the structures of 1B with adsorbed CO₂ at 26.3, 29.2, 29.5, 33.7, and 37.1 bar at 298 K, respectively. The CO₂/N₂ selectivity was plotted based on the structure–pressure relationship. The interaction and gas distribution analyses demonstrated that the adsorption site changed during the structural transition in the adsorption process, which played a significant role in CO₂ adsorption and separation. This work provided significant guidelines for elucidating the gas adsorption and separation in flexible adsorbent materials.