Enhanced Selective Co2 Adsorption in Mofs: Balance between Open Metal Sites Concentration and Pore Size

Abstract

Developing efficient CO2 capture materials is crucial for alleviating excessive CO2 emission. Herein, basing on ZnOFFIVE-1, a series of ZnOFF-X-nLi structures (X = small (S), medium (M), or large (L) ligand; n = 4 or 8) are designed to achieve the balance between open metal sites (OMSs) concentration and pore size for high-performance selective CO2 adsorption. The incorporation of OMSs Li, acting as Lewis acidic centers, creates favorable adsorption sites and enhances the host-guest interaction but would lead to some blockage in the pore channels. Increasing ligand length could remit the blockage, but the excessive pore size enlargement would weaken the synergistic effect between adsorption sites. ZnOFF-M-8Li, with the optimal balance, exhibits the largest CO2 capture capacity of 12.54 mmol g–1 and selectivity of 337.57/241.77 over N2/CH4 at 298 K and 100 kPa. Pore characteristics, gas distribution, adsorption isothermal heat, and van der Waals and Coulomb interactions are analyzed to elucidate the optimal balance between OMSs concentration and pore size. This study outlines the importance of balance between OMSs concentration and pore size for enhancing the selective CO2 adsorption performance.

Keywords: CO2 capture and separation, MOF, OMSs concentration, Pore size, Synergistic effect