Two Dimensional Supramolecular Frameworks: Construction And Membrane Separation

Ordered porous framework materials,like metal-organic framework,covalent-organic framework,have received extensive attentions for their permanent and tunable pore structures.However,their crystalline or microcrystalline forms inherently limit the progress of frameworks toward membrane and device.The collaboration of building blocks,connection bonding types and bonds angles are the key factors for the formation of framework structures.The dynamic and reversible non-covalent interactions are proved to be suitable for the multicomponent assembly towards multi-scale soft materials.The modularization design,dynamic and reversible as well as self-sorting features indicate that the supramolecular frameworks prepared via supramolecular assembly strategy possess flexible and processable.However,while bring about the flexibility,the degree of freedom of the system is enhanced,and the interfacial energy between the building blocks and the medium usually drives molecules close packing.Therefore,it is particularly important to screen the suitable molecular modules and driving forces,which has prominent significance for guiding the synthesis of processable supramolecular frameworks.In this thesis,using the assembly of polyoxometalate?POM?complex as the starting point,we designed and synthesized a series of pillar[5]arene modified polyoxometalate complexes as the building blocks,to construct the supramolecular polymer/frameworks through the directional host-guest interaction,coordinating the steric effect and the amphiphilic of components,the flexible two-dimensional supramolecular framework was prepared driven by the surface free energy,and then successfully processed into membranes for molecular sieving,nanoparticles separation and liquid separation with selectivity.Firstly,we synthesized the pillar[5]arene and cyano group covalently modified MnMo₆ clusters respectively as the supramolecular monomers,to construct the[2+2]type linear supramolecular polymers.Through the electrostatic interaction intergrated functional surfactants,the supramolecular polymers exhibit both chiral and AIE properties.Furthermore,the water-dispersed supramolecular polymer nanoparticles can be prepared via simple ultrasonication treatment,without addition of the other surfactants.Moreover,the adsorption of the trace dyes with high efficiency was realized in water.This research not only paves a way for the multifunctional integration of linear supramolecular polymers,but also provides a reference for the preparation of processible soft supramolecular materials with precise and sophisticated structures.Secondly,changing the guest to triazine with three cyano groups,the[2+3]type2D supramolecular framework was obtained in chloroform.The framework has a hexagonal extended arrangement in the 2D plane and pack into a graphite-like structure through a layer-by-layer pathway out-plane.Furthermore,large-scale ultra-thin flexible two-dimensional nanosheets were exfoliated in DMSO/H₂O with a suitable ratio.And then,the separation membranes were prepared through controlled vacuum filtration on a supporting matrix.Based on the uniformed and nanosized pores,the membrane can be used for separation Au nanoparticles with size selectivity.Moreover,dyes with opposite charges were separated due to the negative surface of the membrane.These results offer the idea for the preparation and solution process of 2D supramolecular frameworks,and the opportunities for the function collection of supramolecular frameworks.Thirdly,by introducing of the flexible electrostatic interaction,the[4+2]type supramolecular framework gel was obtained through the host-guest interaction between the ion complex host that is prepared by cation pillar[5]arene encapsulated four charged POMs,and the ditopic guest under sonication.The rheological experiment proved that the framework gel has excellent self-healing properties,and the framework fibers are highly swellable in specific solvents,therefore,the membrane material was rapidly prepared by simple spin coating on different substrates.The fiber framework dose not dissociate under dilution and immersion,indicating the sufficient structural stability of the supramolecular framework driven by intermolecular interactions,as a consequence,the on-demand oil/water separation and immiscible organic liquid separation were realized with high efficiency.Due to the nano-size pores and the amphiphilic features of the frameworks,the surface properties of the membrane can be facilely modulated via filling a joystick liquid and then a liquid as requested,and then,it can be used for in-situ consecutive switchable liquid separation of immiscible liquids.The feasibility of the separation and switching processes was verified by free energy calculation and dissipative particle dynamics simulation,respectively.The cracked membrane can be recovered to its continuous state in the atmosphere of the gel-forming solvent,and maintained well flux and separation efficiency after manifold cycles,reflecting the advantages of non-covalent bonds in recycling.These results showed that the synergistic combination of nondirective and directional non-covalent interactions is an effective strategy for the preparation of flexible supramolecular frameworks.For the first time,the supramolecular materials constructed from small molecules through non-covalent bonds have shown the effective applications in liquid separation.At the same time,the strategy of membrane surface switching not only provides new ideas for designing switchable liquid separation membrane materials,but also is expected to be applied to other selective separation processes,such as emulsion separation,protein separation,etc.In conclusion,we have shown effective strategy to prepare the flexible two-dimensional supramolecular framework,the pillar[5]arene modified POM complex as the building block and then the extended framework connected through the host-guest interaction and free energy.Among them,the mobile electrostatic interaction endows the framework with dynamic flexiability,and the directional host-guest interaction provides a guarantee for the periodically extension of the framework structure.The stability of the multiple interactions and abundant structural properties make supramolecular framework membranes show excellent separation performance in various nano-separation processes.The research results in this thesis not only provide new ideas for the preparation of processable framework materials,but also broaden the application of supramolecular materials in the field of membrane separation.