Design,Preparation And Catalytic Application Of Ionic Liquid-Covalent Organic Framework Hybrids

The ionic liquid-covalent organic framework(IL-COF)hybrids have inherited the controllable pore structure,high specific surface area and various surface properties from COFs and high selectivity of special structure regulation from ILs,which provides the idea to design efficient catalyst in molecular aspect for the heterogeneous catalytic process.The development of high activity,high selectivity and high stability of IL-COF hybrids is the key and problem to realize its application in catalysis field.In this work,taking dehydration of sorbitol and cycloaddition of epoxides with CO2 as typical catalytic reaction process,investigations are conducted including new methods for the synthesis of IL-COF hybrids,the structure-activity relationship between hybrids and catalytic performance,and synergistic catalytic mechanisms by ILs and porous COFs.The four innovative works have been carried out as follows:(1)The Br(?)nsted ionic liquids-covalent organic framework(BIL-COF)hybrids were successfully prepared via one-pot in situ self-assembly method to solve the problem of low isosorbide yield in the dehydration of sorbitol.The effects of amounts of BILs on the crystallinity,pore structure,morphology and acidity of BIL-COF hybrids were investigated.Based on the characterization and experiments,the hydrogen bond interaction between BILs guest and COFs host in BIL-COF hybrids was studied.The catalytic performance of BIL-COF hybrids synthesized via in-situ self-assembly method and direct impregnation was subsequently compared in terms of dehydrative transformation of sorbitol to isosorbide.Under the optimal conditions,the yield of isosorbide could reach up to 97%,which is the highest value in the reported literature.(2)The basic poly(ionic liquid)-covalent organic framework(PIL-COF)hybrids were prepared by chemical grafting method,which realized the efficient conversion of sorbitol under mild conditions.The regular understanding between PILs loading and the crystallinity,porosity and alkali content of PIL-COF hybrids was obtained and proved the successful combination of PILs and COFs based on the characterization.It was clear that the alkali content,alkali strength and porous structure of PIL-COF hybrids were the key factors affecting the catalytic efficiency.The effects of temperature,reaction time,catalyst dosage and solvents on catalytic performance were examined.The yield of isosorbide catalyzed by PIL-COF reached up to 83%at 140?for 12 h,which outperformed individual PIL.Finally,the reaction mechanism of base-catalyzed sorbitol and DMC to produce isosorbide was proposed based on the detection of intermediates.(3)The porous poly(ionic liquid)@covalent organic framework(PPIL@COF)hybrids with core-shell structure were designed via surface functionalization and interfacial growth to achieve highly efficient conversion of CO2 under mild conditions.The core-shell structure of PPIL@COF hybrids was proved through characterization analysis.The effects of the ratio of PPIL and COFs on the contents of catalytic sites,CO2 adsorption capacity and catalytic performance of PPIL@COF hybrids were explored.The synergistic effects of hydroxyl groups and bromide anions at interface was revealed.The PPIL@COFA-40 exhibited excellent catalytic performance in the cycloaddition of epoxides with CO2 in the absence of solvents and any co-catalyst under mild conditions(100?),producing cyclic carbonates with excellent yields(93?96%).(4)The fabrication of poly(ionic liquid)-macroporous covalent organic framework(PIL-MCOF)hybrids with microporous and macroporous structures was accessed via hard-template method followed by in-situ synthesis of linear PILs in channels of COFs.The PIL-MCOF hybrids avoided the harsh conditions in cycloaddition reaction through enhancing CO2 adsorption capacity,the diffusion and mass transfer of the substrate.The porosity and amounts of catalytic sites of the resultant PIL-MCOF hybrids could be tuned through the size,solid content modulation of templates and contents of introduced linear PILs.The experimental results proved the versatility of PIL-MCOF hybrids that micropore improved pore volume,enhanced CO2 adsorption and macropore enhanced diffusion and mass transfer.The PIL-MCOF hybrids could produce propylene carbonate with 99%yield under 1 MPa CO2 at 90 ? in the absence of solvents and any co-catalyst.