Synthesis Of New Membrane Materials And The Application Of Efficient Separation

Membrane separation technology is widely used in many fields of industry and human activities,such as water treatment,fine chemical production,biopharmaceuticals and energy.The separation process is one of the huge energy consumption parts in chemical production,and the energy consumption for separation and purification accounts for 50%of the energy consumption for the entire industry.Due to its high efficiency and energy saving characteristics,membrane separation technology is an important means to reduce global energy consumption and pollution emissions.The prerequisite and key to the application of membrane separation is to develop membrane with high separation performance.Metal-organic frameworks(MOFs)or covalent-organic frameworks(COFs)have ultra-high porosity,regular pore structure and easy functionalization.Therefore,MOFs/COFs are an ideal candidate material for preparing membrane.However,there are still many challenges in the development of MOFs/COFs membrane,such as its complicated preparation process,general separation performance,and unsatisfactory membrane stability.In response to the above problems,this paper proposes to design and construct MOFs/COFs membrane with special pore structure and physical and chemical properties according to the requirements of the separation system to prepare high-performance membrane.Benefiting from the diversity of MOFs/COFs component units and easy post-modification and functionalization,this thesis prepares membrane with high separation performance from the perspectives of pre-synthesis and post-synthesis modification.The specific research content of this paper is as follows:1.By designing and synthesizing the ligands of MOFs,the photo-switch group is introduced into the MOFs skeleton to prepare Cu(AzDC)(4,4'-BPE)_0.5 membrane with light response.When the Cu(AzDC)(4,4'-BPE)_0.5 membrane is irradiated by ultraviolet light(UV)/visible light(Vis),the photosensitive groups in the MOFs skeleton undergo a reversible cis/trans conformational transition,which in turn affects the interaction force between gas molecules and Cu(AzDC)(4,4'-BPE)_0.5 membrane pores,and realized the remote intelligent control of membrane permeability through external stimulation.2.Through the post-synthesis modification strategy,the azophenyl group with light response characteristics is introduced into the COFs membrane skeleton,so that the prepared membrane has the characteristics of light intelligence and controllability.The[OH]_25%-COF-300 membrane containing hydroxyl was successfully prepared by the in-situ growth method,and then reacted with 4-phenylazobenzoyl chloride for post-synthesis modification to prepare[N=N]_25%-COF-300 membrane.Under UV/Vis irradiation,the photosensitive group of azobenzene in[N=N]_25%-COF-300 membrane undergoes a reversible cis/trans isomerization,which changes the permeability and separation factor of mixture gas through the membrane.The[N=N]_25%-COF-300membrane showed good stability in 80 h continuous separation test,making it feasible to apply to the H₂/CO₂ separation system.3.Through the post-modification functionalization strategy,a new type of high-efficiency nanofiltration separation membrane,IISERP-COOH-COF1 membrane,was prepared based on the ring-opening reaction.Post-modification functionalization not only reduce the pore size of the IISERP-COF1 membrane,but also reduce non-selective permeation caused by intercrystalline defects,thereby improving membrane separation selectivity.The post-modified synthetic membrane has excellent nanofiltration separation performance and has the potential for seawater desalination applications.4.The post-modification functionalization strategy is adopted to introduce cationic groups into the COFs framework,thereby weakening the force between the COFs layers,and exfoliating the COFs into 2D nano-sheets,and then the BTADHBD-Me₃N⁺Cl^-membrane is obtained by vacuum filtration.BTADHBD-Me₃N⁺Cl^-membrane has high dye rejection rate and excellent water flux for various types of dye aqueous solution.Thanks to the nano-channels perpendicular to the surface of the BTADHBD-Me₃N⁺Cl^-membrane,the BTADHBD-Me₃N⁺Cl^-membrane exhibits a better performance than the graphene oxide(GO)membrane.