| MOFs-based mixed matrix membranes have good prospects for CO2 separation.However,the“gate-opening”effect of MOFs renders the increase of effective separation size,making it difficult to achieve accurate screening of CO2/N2?CH4?.In-situ synthesis and post-synthesis modification methods are used to adjust the pore size of the MOF,which requires toxic reagents,strict operation requirements,and tends to damage the crystal structure.To this end,this paper proposes to use Ionic Liquids?ILs?to post-modify the cage size of MOF.Through the occupancy of ionic liquids in the cage cavity,the effective separation size of MOF is adjusted to increase the transmission resistance of large-size gas molecules through MOF,which attributes to efficient screening of mixed matrix membranes for gas pairs of different sizes.First,select ZIF-8 as the research object,through the adsorption-infiltration two-step method,the ionic liquid molecules are adsorbed on the surface of ZIF-8,and then heated to dilate the aperture window of ZIF-8,so that the ionic liquid molecules infiltrate under the driving force of temperature and concentration.[Bmim][PF6]@ZIF-8 composite materials with different[Bmim][PF6]concentrations were prepared.[Bmim][PF6]and ZIF-8 are successfully combined and have interaction forces with each other.TGA result reveals approximate[Bmim][PF6]concentrations in the[Bmim][PF6]@ZIF-8 composite.[Bmim][PF6]successfully occupied the ZIF-8 cage cavity,so that the effective separation size of ZIF-8 is tuned.[Bmim][PF6]@ZIF-8/Pebax-based mixed matrix membranes were prepared.During the membrane formation process,only trace ionic liquid molecules reach the surface of ZIF-8,but the content is similar,indicating that the ionic liquid is effectively confined in the ZIF-8 cage.The gas permeation tests shows that the 25%loading[Bmim][PF6]8@ZIF-8 has the best separation performance(PCO2=113Barrer,?CO2/N2=84.5),which is 68%higher than[Bmim][PF6]/ZIF-8 membranes,while PCO2 loses only 22.5%,transcend than the 2008 Robeson.As the content of ionic liquid in the ZIF-8 cage increases,the CO2/N2 separation selectivity of the mixed matrix membrane further increases,ionic liquid is confined into the ZIF-8 cage and the cage size of ZIF-8 is tuned accurately between the sizes of CO2 and N2 by adjusting IL concentration.In order to verify the universality of IL regulating the sieve pore size of MOFs,the same cation[Bmim]was selected,but the anion[Tf2N]with greater steric hindrance[Bmim][Tf2N]@ZIF-8 composite was prepared.[Bmim][PF6]@ZIF-71composite material was prepared by selecting ZIF-71 with similar topological structure but larger window size.With the increase of IL content,the surface adsorption of ZIF-8 and ZIF-71 gradually decreased,and the pore volume decreased.15wt.%loading[Bmim][Tf2N]8@ZIF-8 membrane has the best performance(PCO2=108.3 Barrer,?CO2/N2=86.7),[Bmim][PF6]@ZIF-71 membrane has a PCO2 of 72Barrer,?CO2/N2 can reach 89.After changing the size of ZIF and the more occupancy ionic liquid,the membrane still has excellent CO2/N2 separation selectivity. |
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