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 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 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 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.