Synergistic tuning mixed matrix membranes by Ag+-doping in UiO-66-NH2/polymers of intrinsic microporosity for remarkable CO2/N2 separation

Novel mixed matrix membranes (MMMs) with superior CO2/N2 separation properties are of great importance for post-combustion CO2 capture from flue gas. Metal-organic frameworks (MOFs) as one of the most attractive porous fillers for MMMs fabrication, are considered to provide a solid molecular sieving mechanism for enhancing CO2/N2 selectivity. However, it causes the reduction in gas permeability and limits its further industrialization. Herein, we proposed a new strategy for filler functionalization by doping silver ions (Ag+) into UiO-66-NH2 nanoparticles through the double-solvent method and used for the preparation of advanced MMMs. The double-solvent method is benefits for the enrichment of Ag+ in the hydrophilic pores of UiO-66-NH2. As a result, the prepared novel MMMs called Ag+@UiO@PIM-1 with the polymers of intrinsic microporosity (PIMs) as polymer matrix, show outstanding CO2 permeability. According to the mixed gases (CO2/N2 = 10:90) permeation experiments under 25 °C and 2 bar, the membrane with 30%Ag+@10%UiO loading achieves more than 65% increase in CO2/N2 selectivity (∼30) and 120% in CO2 permeability (>15,000 Barrer) compared to the pristine PIM-1 membrane. By optimizing the Ag+ doping amount and Ag+@UiO loading content, the separation performance exceeds the 2019 CO2/N2 upper bound. To figure out the separation mechanism, the pore texture properties and CO2 affinity of the functional filler (Ag+@UiO) together with the membrane structure were characterized by XPS, PXRD, SEM, gas sorption, etc. The synergistic mechanisms by combing CO2 facilitated transport and molecular sieving from pore regulation were identified to enable advanced CO2/N2 membrane separation.