Substituent Engineering in Pore-Space-Partitioned Metal–Organic Frameworks for CO₂ Selective Adsorption and Fixation

Comprehensive understanding of substituent groups located on the pore surface of metal–organic frameworks (which we call substituent engineering herein) can help to promote gas adsorption and catalytic performance through ligand functionalization. In this work, pore-space-partitioned metal–organic frameworks (PSP MOFs) were selected as a platform to evaluate the effect of organic functional groups on CO₂ adsorption, separation, and catalytic conversion. Twelve partitioned acs metal–organic frameworks (pacs-MOFs, named SNNU-25-R_n here) containing different functional groups were synthesized, which can be classified into electron-donor groups (−OH, −NH₂, −CH₃, and −OCH₃) and electron-acceptor groups (−NO₂, −F, −Cl, and −Br). The experimental results showed that SNNU-25-R_n with electron donors usually perform better than those with electron acceptors for the comprehensive utilization of CO₂. The CO₂ uptake of the 12 SNNU-25-R_n MOFs ranged from 30.9 to 183.6 cm³ g^–1 at 273 K and 1 bar, depending on the organic functional groups. In particular, SNNU-25-OH showed the highest CO₂ adsorption, SNNU-25-CH₃ had the highest IAST of CO₂/CH₄ (36.1), and SNNU-25-(OH)₂ showed the best catalytic activity for the CO₂ cycloaddition reaction. The −OH functionalized MOFs with excellent performance may be attributed to the Lewis acid–base and hydrogen-bonding interactions between −OH groups and the CO₂ molecules. This work modulated the effect of the microenvironment of MOFs on CO₂ adsorption, separation, and catalysis in terms of substituents, providing valuable information for the precise design of porous MOFs with a comprehensive utilization of CO₂.