| Two-dimensional porous materials have become a hot topic in the forefront of material science research due to their ultra-thin thickness and unique physical/chemical properties and have achieved remarkable research results in many fields such as gas separation.However,there are still many bottleneck issues in the development of two-dimensional porous material gas separation membranes,such as difficulties in preparing ultra-thin two-dimensional nanosheets,high cost of commonly used inorganic porous substrates,complex traditional membrane preparation methods,and imperfect gas separation mechanism system.Therefore,the development of simple effective methods for preparing twodimensional material gas separation membranes is an urgent and competitive problem that needs to be solved in the field of gas separation membranes.In this thesis,the high-permeance and low-cost glass fiber(GF)filter is used for the first time as an inorganic porous substrate for the preparation of gas separation membrane,and a method for preparing two-dimensional material gas separation membranes with staggered stacked nanosheet structures is creatively developed,that is,the centripetal force assisted vacuum filtration method.Representative two-dimensional materials with different structural properties are selected,and graphene oxide(GO)and metal-organic framework(MOF)composite membranes are then successfully prepared,and their H2/CO2 separation performances are evaluated,while the gas separation mechanisms are clarified.The results expand the application of two-dimensional nanomaterials in the field of gas separation.1.The GF-supported GO lamellar membranes(GO/GF composite membranes)are prepared by directly depositing diluted commercial GO dispersions with different concentrations on the surface of GF filters using centripetal force-assisted vacuum filtration method.The orderly interlocked nanosheet stacking structure and minimized substrate transport resistance enable the GO/GF composite membranes to combine high H2 permeance and high H2/CO2 selectivity.The optimized GO/GF composite membrane displays a H2 permeance of 93 5 ± 51 gas permeance units(GPU)and an H2/CO2 selectivity of up to 1379± 95.A low-temperature partial reduction strategy is used to precisely tailore the interlayer spacing of the GO/GF composite membrane,and the H2/CO2 selectivity of the quasi-reduced GO/GF(q-rGO/GF)composite membrane is significantly improved due to the synergistic effect of strict channel size sieving and retained functional group interactions.The q-rGO/GF composite membrane displays a H2 permeance of 783 ± 50 GPU and an ultra-high H2/CO2 selectivity as high as 3636 ± 312,which is the highest selectivity for H2/CO2 separation membranes reported thus far.In addition,the gas separation performance of the q-rGO/GF composite membrane is quite stable,and there is no performance degradation during a 120-h test.2.For the first time,the amino-functionalized isoreticular metal organic framework-3(IRMOF-3)nanosheets are filled into macroporous GF filters to prepare IRMOF-3 nanosheet-filled GF(IRMOF3@GF)composite membranes.The filled membrane structure combines stable nanosheet attachment with high MOF filling amount,which can solve the limitations of structure and synthesis method of traditional supported MOF polycrystalline membranes.The filled membrane structure can also fully utilize the performance advantages of two-dimensional MOF nanosheets to achieve efficient gas separation.The optimized IRMOF-3@GF filled membrane exhibits a H2 permeance of 974 ± 41 GPU and an impressively high H2/CO2 selectivity of 1341 ± 134,which sets a new record for MOF-based gas separation membranes reported thus far.In addition,Grand Canonical Monte Carlo(GCMC)simulations are performed to investigate the H2/CO2 separation mechanism of the IRMOF-3@GF filled membrane and the results suggest a synergistic separation mode based on selective adsorption and size exclusion.The innovative filled-membrane fabrication route and the presented gas separation mechanism offer a new strategy to design and prepare MOF nanosheet-based gas separation membranes.3.Two-dimensional zeolitic imidazolate framework(ZIF)nanosheet membranes are in situ grown on the GF filters by a drop-percolation synthesis method.The as-prepared ZIF-L/GF composite membrane shows excellent H2/CO2 separation performance with a H2 permeance of up to 1922±533 GPU and a H2/CO2 selectivity of 236 ± 89.The ZIF-L/GF composite membrane also displays excellent thermal stability and good durability with no performance degradation during a 150-h test.For comparison,the GF-supported ZIF-L nanosheet membrane and ZIF-8 nanosheet membrane are prepared using centripetal force-assisted vacuum filtration method.Although the H2/CO2 selectivity of the ZIF-L nanosheet membrane and the ZIF-8 nanosheet membrane is higher than that of the ZIF-L/GF composite membrane,their H2 permeance is much lower than that of the ZIF-L/GF composite membrane.The in situ droppercolation synthesis process is much simpler and more economic than the nanosheet dispersion-vacuum filtration method,and the resultant ZIF-L/GF composite membrane holds great potential for practical applications due to the combination of high H2 permeance and high H2/CO2 selectivity.4.GO nanosheets are directly composited with IRMOF-3 nanosheets and ZIF-L nanosheets,respectively,and the GO/IRMOF/GF composite membranes and the GO/ZIF/GF composite membranes are prepared by mixed dispersion-centripetal force-assisted vacuum filtration method,respectively.Through structural characterization and gas separation performance tests,two different two-dimensional materials with excessive differences in lateral sizes and thickness are found to be difficult to achieve a composite effect.Both the GO/IRMOF/GF composite membrane and the GO/ZIF/GF composite membrane exhibit the structural characteristics of the GO lamellar membranes.The H2 permeance of the GO/IRMOF/GF-4 composite membrane and the GO/ZIF/GF-4 composite membrane is 817 and 1739 GPU,respectively,while the H2/CO2 selectivity is 894 and 741,respectively.Although the GO/IRMOF/GF composite membrane and the GO/ZIF/GF composite membrane exhibit fine gas separation performance,their application potentials are not as good as the IRMOF-3@GF filled membranes and the ZIF-L/GF composite membranes. |
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