Studies On Photocatalysis And Separation Properties Of Ionic Framework Organic Porous Materials

Ionic framework organic porous materials are newly emerging materials.In sharp contrast to charge-neutral porous materials,the framework structure of ionic organic porous materials is charged.Therefore,they have some unique properties and functions different from those of neutral porous materials.Among various organic porous materials,Metal organic frameworks?MOFs?and Covalent organic frameworks?COFs?have attracted great research interest due to their unique structural characteristics and abundant component forms.They exhibit higher porosity and larger specific surface area than conventional porous materials.Moreover,they are also more flexible in the selection and combination of ligands,so we can easily adjust the functional groups,active sites,and physical and chemical properties of MOFs/COFs materials according to the needs,and then design and prepare MOFs/COFs materials with rich structures and diverse properties.However,most of the framework structures of MOFs and COFs that have been reported are charge-neutral.In particular,there are very few reports on COFs materials with ionic framework.Compared with MOFs and COFs with charge-neutral framework structure,MOFs and COFs with ionic framework structure have shown unique advantages in the field of gas storage,catalysis,separation,water purification and other fields,which has attracted extensive attention in the academia and gradually become a hot research field.Based on the above research background,this paper carried out a series of research work focusing on the design,synthesis and application of ionic framework MOFs and COFs.And the performance of ionic framework MOFs and COFs in photocatalysis and selective separation was mainly studied in this paper.The research results mainly include the following aspects:1.Preparation of metal organic frameworks composite luminescent materials and study on its photocatalytic performance for singlet oxygen generationMOFs have shown great potential in the field of photocatalysis.On the basis of previous work,an anionic framework MOF,bio-MOF-1,was synthesized,which shows excellent photophysical properties and chemical stability.At the same time,three cationic ruthenium complexes?RCs?were also synthesized successively.Since the charge properties of bio-MOF-1 and RCs are opposite to each other,thus we have successfullyconstructedacompositematerialluminescencesystem,bio-MOF-1&RCs,with two-photon up-conversion excitation emission ability by ion exchange method.The experimental results show that the composite material system can greatly improve the two-photon up-conversion luminescence efficiency of the photosensitizer molecules RCs in the near-infrared region?Optical window in biological tissue?,and thus improve the ability of RCs to generate singlet oxygen?¹O₂?.In addition,in view of the biological properties of the components involved in the composite material,therefore,bio-MOF-1&RCs has potential photodynamic therapy?PDT?value.2.Preparation of two-dimensional cationic covalent organic frameworks membrane and study on its selective molecular sieving performanceDue to its unique lamellar structure and vertically distributed channels,two-dimensional COFs have shown excellent performance in the field of selective separation.However,it still faces tough challenges to prepare a high-quality and large-area 2D COFs membrane material,especially the COFs membranes with ionic framework are rarely reported.Based on the above research background,we designed and prepared COF membrane,EB-COF:Br,with cationic framework structure.First,EB-COF:Br nanosheets grew at the two-phase interface of dichloromethane and water by interfacial crystallization process,and then EB-COF:Br membrane was successfully prepared by the layer-by-layer self-assembly strategy between COFs nanosheets.Further,experimental results show that cationic EB-COF:Br membrane has high selectivity in separating molecules/ions with different sizes and charges.EB-COF:Br membrane has an interception efficiency of more than 98%for anionic dye molecules,while it has a weak interception performance for cationic and neutral dye molecules.Meanwhile,EB-COF:Br membrane also showed excellent solvent permeation flux.The highly selective separation performance of EB-COF:Br membrane results from its unique dual control separation process by both nano-pore size and charge,while the excellent solvent permeation flux is due to its high porosity and plentiful vertically distributed channels.Therefore,EB-COF:Br membrane can be used for the selective separation of complex mixtures.3.Preparation of large-scale anionic covalent organic framework membrane and study on its selective separation performanceBased on our previous work,we further optimized the preparation method of COFs membranes.A novel COF membrane with anionic framework structure,TpPa-SO₃Na,was designed and prepared successfully.First,we designed and synthesized a monomer with sodium sulfonate group?-SO₃Na?:Pa-SO₃Na,and then obtained an anionic COF membrane,TpPa-SO₃Na,with excellent crystallization property by interfacial crystallization process.TpPa-SO₃Na membrane has excellent properties of structure and separation,which can be directly used for molecular/ionic selective separation.Experimental results show that the anionic COF membrane can efficiently and selectively separate molecules/ions with different charge properties.The membrane has such excellent separation performance,apart from the inherent physical size cut-off effect in the nano channels of the membrane,more importantly,there is electrostatic interaction between the ionized channel wall in membrane and the separated components.The strong electrostatic effect can achieve the selective recognition and retention of molecules/ions with different charge properties.Compared with EB-COF:Br membrane,TpPa-SO₃Na membrane has fewer defects,better integrity,higher mechanical and chemical stability,and thus has better potential of selective separation.