Development of Ni_x/Mg_1−x-MOF-74 for highly efficient CO₂/N₂ separation

To enhance the separation selectivity of Mg-MOF-74 towards CO₂ in a CO₂/N₂ mixture, a series of Mg-MOF-74 and Ni_x/Mg_1−x-MOF-74 adsorbents were prepared by solvothermal synthesis in this paper. It was found that the adsorption capacity of Mg-MOF-74 for CO₂ could be effectively increased by optimizing the amount of acetic acid. On this basis, the bimetal MOF-74 adsorbent was prepared by metal modification. The multi-component dynamic adsorption penetration analysis was utilized to examine the CO₂ adsorption capacity and CO₂/N₂ selectivity of the diverse adsorbent materials. The results showed that Ni_0.11/Mg_0.89-MOF-74 showed a CO₂ adsorption capacity of 7.02 mmol/g under pure CO₂ atmosphere and had a selectivity of 20.50 for CO₂/N₂ under 15% CO₂/85% N₂ conditions, which was 10.2% and 18.02% higher than that of Mg-MOF-74 respectively. Combining XPS, SEM and N₂ adsorption-desorption characterization analysis, it was attributed to the effect of the more stable unsaturated metal sites Ni into the Mg-MOF-74 on the pore structure and the synergistic interaction between the two metals. Density Functional Theory (DFT) simulations revealed that the synergistic interaction between modulated the electrostatic potential strength and gradient of the material, which was more favorable for the adsorption of CO₂ molecules with small diameters and large quadrupole moment. In addition, the Ni_0.11/Mg_0.89-MOF-74 showed commendable cyclic stability, underscoring its promising potential for practical applications.