Preparation Of MOFs/PI Mixed Matrix Membranes In Situ And Gas Separation

Thermally rearranged polymer and carbon molecular sieves membrane?CMS?are new types of high-performance materials which have superior performance lying above the Robeson upper-bound limit of polymers.The aromatic polyimide?PI?was used as the membrane material,the metal organic frameworks UiO-66 nanoparticles with high thermal stability and adjustable pore structure were used as dopants in this paper,and we synthesized the UiO-66/PI mixed matrix menbranes in situ following by solvent evaporation and thermally rearrangement.The effects of UiO-66 loading,constant treatment time and thermal treatment temperature on the UiO-66/PI thermally rearranged membranes structure and performance were studied.Functionalization UiO-66-NH₂ and UiO-66-?COOH?₂ MOFs were further prepared to synthesis functionalized UiO-66/PI mixed matrix carbon membranes.The structure and performance of MOFs and membranes were characterized by analysis techniques such as field emission scanning electron microscope?FF-SEM?,X-ray diffractometer?XRD?,and Fourier transform infrared analyzer?FTIR?.The results show that:?1?The morphology and size of UiO-66 crystal were influenced by the crystallization condition and the type of regulators.The crystallization temperature and time can change the crystal relative crystallinity and the addition of the modifier can affect the connection between the metal ion and the ligand.The crystals prepared with the basic regulator NH₄OH are easy to agglomerate.The crystals prepared with the strong acid regulator HF are rod-shaped and the size is not uniform,while the crystals prepared with the weak acid HAc are uniform in size.The crystals size gradually grows up leading to an octahedron structure with the amount of HAc gradually increases.When the HAc amount is 0.6 ml,the size of UiO-66 crystal is around150nm,the BET specific surface area is 1429 m³/g and the thermal stability is as high as 520?.?2?The UiO-66 nanoparticles were dispersed uniformly into the polymeric matrix by the in-situ doping method.After thermal treatment,the crystal structure of UiO-66 was still maintained and the interchain distance was further enlarged.The gas permeabilities and selectivities for CO₂/CH₄ and CO₂/N₂ of the MMMs were both improved due to the incorporation of UiO-66.Compared with the membrane without incorporating UiO-66,the CO₂permeability of the thermally rearranged MMMs with 3 wt.%loading could be as high as 3316Barrer,which was 1.74 times higher.Meanwhile,the selectivities of CO₂/N₂ and CO₂/CH₄ were increased from 24.4 and 27.5 to 35.7 and 33.2 respectively.In addition,the gas permeabilities of the membranes were further enhanced when the thermal treatment time was extended.When the thermal time was 5 h,the CO₂ gas permeability was 11950 Barrer and the corresponding CO₂/CH₄ selectivity was 19.The separation performance for CO₂/CH₄ and CO₂/N₂ of the UiO-66/PI thermally rearranged MMMs prepared in this work was beyond the upper bound of 2008Robeson.?3?In-situ introduction of functionally modified UiO-66-NH₂ and UiO-66-?COOH?₂improves the gas selectivity of mixed matrix carbon membranes.The thermal decomposition of the functional groups-NH₂ and-COOH would enriched the microporous structure system of the mixed matrix carbon membranes thus the gas separation performance were improved.The CO₂ permeabilities are up to 16448 and 17551 Barrer,at the same time the gas selectivities of CO₂/N₂ and CO₂/CH₄ are up to 33.4,38.8 and 31.4,34.1 when the thermal treatment temperature is 550?and the loading of UiO-66-NH₂ and UiO-66-?COOH?₂ are 3 wt.%.The membranes show good application prospects in the field of CO₂ separation and capture.