Enhancing Co2 Adsorption Selectivity of Mof-199 by the Synergistic Effect of Mg Metal Doping and Polyethyleneimine Impregnation

The fine-tuning of metal-organic frameworks (MOFs) can enable the development of effective adsorbents for the selective capture of less polarizable carbon dioxide (CO2) from flue gases. In this work, a series of bi-metallic MOFs with different doping concentrations (1-10 mol%) of magnesium (Mg) metal were synthesized by in situ metal substitution followed by post-synthetic functionalization with 10-50 wt.% polyethyleneimine (PEI). Detailed characterization confirmed the successful incorporation of the secondary metal and amine group into the MOF framework. Results showed that only up to 2 mol% of copper (Cu) can be substituted by Mg metal in the framework of MOF-199; further increase in Mg content disrupts the electrostatic equilibrium, leading to the formation of carbon matter-based copper nanoparticles instead. The sorption results showed that 1 and 2 mol% Mg-doped MOFs (MOF@Mg1 and MO@Mg2) demonstrated a CO2 uptake of 7.93 and 8.61 (mmol/g) respectively, at 1 bar and 273.15 K, showing 8.48 and 17.78% increase in adsorption capacity compared to the pristine MOF. Furthermore, 40 wt.% PEI-loaded MOF exhibited a 9.52% enhancement in CO2 adsorption selectivity. This work provides valuable insights into the synergistic effects of secondary metal doping and PEI impregnation on the morphology, structure, and CO2 adsorption performance of MOF-199.