| As an important energy-efficient and environmentally friend separation process,membrane separation has been widely applied in various fields,such as gas separation,water treatment,solvent purification,etc.Metal-organic frameworks?MOFs?are crystalline materials,and possess a series of extraordinary features,such as uniform pore sizes,large surface areas,large diversity in structures and special adsorption a nities,etc.MOF membranes offer unique opportunities to overcome the limitations of Robeson's“upper-bound”in membrane-based separation,and therefore have received considerable attention in recent years.Various substrates have been employed to support MOF membranes for separation applications.Among them,inorganic substrates,such as metal net,aluminium oxide and titanium dioxide,are mostly studied.Since polymeric membranes have the advantages of low cost,high processing ability and large membrane areas compared with inorganic substrates,the polymeric membranes as substrates will be of good benefit to industrial applications.So far,there are only a few reports concerning the successful MOFs growing on a polymer surface.In this context,we focused on developing serials of MOF/polymer hollow fiber composite membranes with comparative separation performance.To overcome the issues of coverage,adhesion,compression,chemical resistance and swelling in fabrication of MOF/polymer composite membrane,the substrates were modified to fabricate continuous MOF/polymer hollow fiber composites membranes.Furthermore,the mixed matrix membrane and continuous MOF layer were integrated as well as the continuous MOF layers were in situ transformed to further improve the separation performance of the prepared membranes.The main research contents and results are as follow:?1?Based on the chemical modification of the polyacrylonitrile?PAN?hollow fiber,the MOF/PAN hollow fiber composite membranes were successfully fabricated.The produced-COO-can serve as covalent linkers to enhance the nuclei sites on hollow fiber.Because of the dehydrogenation,cyclization and crosslinking reactions of the PAN hollow fiber during solvothermal treatment,the compression strength of the obtained membranes were improved greatly.Because the dense skin layers of the PAN hollow fiber were damaged and then formed macroporous structure,the prepared CuBTC/PAN hollow fiber membrane exhibited moderate selectivity and high H2 permeance of 9.63×10-5 mol m-2 s-1 Pa-1.?2?Based on the reaction between the polyvinylidene fluoride?PVDF?and the reagents with two primary amines,a new ammoniation-based chemical modification strategy was established for synthesis of continuous and uniform MOF/PVDF hollow fiber composite membranes.Ammoniation can promote the PVDF hollow fibers to produce amino groups,form a nanoparticle structure,and be well cross-linked;therefore,the high-density heterogeneous nucleation sites for MOFs growth as well as the thermal stability and chemical resistance of composite membranes can be greatly improved.Besides the high-quality layers of representative CuBTC and ZIF-8 were synthesized,the ZIF-7 and NH2-MIL-53 membranes were also fabricated under harsh synthetic conditions in DMF precursor solutions.The prepared MOF/PVDF composite membranes exhibited excellent performance.For examples,ZIF-7/PVDF membrane exhibited H2 permeance of 13.29×10-7 mol s-1 m-2 Pa-1,as well as H2/N2and H2/CO2 selectivities of 18.30 and 16.32,respectively;NH2-MIL-53/PVDF membrane showed high H2 permeance of 54.20×10-7 mol s-1 m-2 Pa-1,H2/N2 and H2/CO2 slectivities of 27.85 and 30.37.?3?Based on the ammoniated PVDF hollow fiber,a non-activation ZnO array was fabricated by solvothermal processing the 2-methylimidazole-contained precursor,and employed as buffering layer to obtain the MOF/ZnO/PVDF hollow fiber composite membranes.Because ZnO array across the dense layer of the PVDF hollow fiber and contained the 2-methylimidazole,the crack-free and uniform MOF membranes were successfully grew on the ZnO/PVDF hollow fiber substrate without any activation procedure.Moreover the MOF layer adhered to the hollow fiber strongly.The fabricated MOF/PVDF membranes had excellent H2 permselectivity.For the ZIF-7/ZnO/PVDF membrane,the seletivities for H2/N2 and H2/CO2 were20.27 and 18.43,respectively,and the permeance of H2 can reach as high as23.54×10-7 mol s-1 m-2 Pa-1,which was better than the ZIF/PVDF membranes without ZnO buffering layer.?4?Based on the integration of the mixed matrix membranes and continuous MOF membranes,the trinity membranes containing substrates,MOF-PDMS mixture layers and continuous MOF layers were synthesized.Because the MOF-PDMS mixture layers can serve as seeds,the well inter-grown MOF layers were grew on the MOF-PDMS mixture layer successfully.Since the large CuBTC penetrated through the entire mixture layers,the trinity CuBTC membrane showed good performance in CO2 capture,with excellent selectivities of H2/CO2?21.03?and N2/CO2?7.23?.?5?Based on the transformantion of the CuBTC/PVDF hollow fiber composite membrane,the mild multivalent cation substitution was employed to fabricate the CuBTC/MIL-100/PVDF hollow fiber composite membranes.Through this strategy,the unstable and easily fabricated MOF particles were first transformed to obtain the stable MOFs with completely different topology structure,which are usually fabricated in relatively harsh synthetic conditions.Then the common MOF membrane was in situ transformed to another MOF membrane,which is hard to be synthesized in conventional methods at present.Moreover,the pore size can be reduced through immobilizing the metal salt residue in cavities and the appropriate crystal facets of MOFs can be exposed to achieve competitive molecular sieving ability.The promising candidates of MOF membranes were designed and synthesized.For example,the CuBTC/MIL-100 membrane exhibited 89,171,241 and 336 times higher H2 permeance than that of CO2,O2,N2 and CH4,respectively. |
PDF Full Text Request