Ultrafine And Reversible Emulsion Separation Of Supramolecular Framework

Due to the complicated practical situation in industrial production and life,emulsions exist in various types,forms,and sizes.It is still a challenge faced by emulsion separation technology to satisfy the increasingly ultrafine and diverse treatment requirements.From the perspective of interface science,porous materials with special wettability exhibit different wetting behaviors for two liquids by reasonably designing the surface energy and roughness of the materials and further achieving efficient treatment of emulsions through size screening or demulsification effect.However,the development of unique wettability materials for emulsion separation is challenged by the existence of the rich variety of liquid pairs(including various types of oil-water emulsions and organic emulsions),the diverse polarities of continuous phases,the enhanced system stability by the surfactants,and the difficulty in trapping ultrafine droplets.Therefore,new ultrafine and intelligent emulsion separation materials still need to be developed.Driven by noncovalent interactions,the supramolecular framework(SF)is formed with nanoscale pore size and designable surface composition,which can be applied in the separation of molecular,particle,and liquid.The flexibility of SF offers opportunities for the preparation of intelligent materials due to the dynamically reversible intermolecular interactions,and the flexibility of its structure facilitates its further processing into composite materials with good compatibility.In this thesis,based on the functional synergy theory,this work utilized SF and auxiliary components with suitable properties to obtain a series of SF composite materials.The obtained materials with unique permeation channels,designable wetting properties,and good processing performance achieve efficient and switchable separation of nanosized oil-water emulsions and switchable separation of organic liquid emulsions.First,a method to modify graphene oxide(GO)with good hydrophilicity onto SF materials was proposed.GO-assisted SF composite membrane can be prepared by successive pumping of two materials onto a commercial matrix and used to separate oilin-water emulsion with nanosized droplets.The SF containing covalently modified polyoxometalates(POMs)as one of the building blocks enables the composite membranes to trap the dispersed tiny droplets in the emulsions through nanoscale pores but also to drive the demulsification process by electrostatic interaction using the stable negatively charged surface.The hydrophilic graphene oxide modified on the composite membrane endows the membrane with enhanced water affinity,leading to the enhanced underwater hydrophobicity of the composite membrane.Based on the separation mechanism of size screening and demulsification effect,the composite membrane can treat oil-in-water nanosized emulsions stabilized by non-ionic,anionic,and cationic surfactants.The TOC content in the filtrate is less than 10 ppm,which corresponds to high separation efficiency.Especially for the emulsions containing ionic surfactant,no residual droplets were detected in the filtrate by DLS.The composite membrane with an antifouling effect obtained a high separation permeability and recovery rate of flow rate,which allow stable separation for multiple cycles.In the present part,two components with different structural and surface characteristics were combined and high-performance separation of oil-in-water nanosized emulsions under function synergy was achieved.Second,to expand the applicability of SF composites in emulsion separation,the types of SF and auxiliary materials were changed.The SF assembly electrostatically containing POMs was blended with the polymer polycaprolactone(PCL)under good compatibility.Thanks to the improvement of the mechanical properties in the system by polymer,the free-standing polymer-assisted SF fiber membrane was prepared by a simple casting and peeling method.PCL also fills the gap between the assembled fibers,allowing the composite film to exhibit nanoscale intercept size derived from the framework pores.In addition,the intelligently responsive wetting property of the SF regulated by the joystick solvent endows the composite membrane with the in-situ conversion of the underwater superhydrophobicity and the underoil superoleophobicity.Due to the above properties,the composite membrane in the corresponding wetting state can accurately sieve the ultrafine nanoparticles dispersed in hydrophobic organic solvents and water.More importantly,the material realized the on-demand separation of water-in-oil and oilin-water emulsions,no matter containing a surfactant or not,through simple filtration.For the nanoparticles and emulsion drops,the queue value of the composite membrane is about 3 nm.Notably,the above separation can be carried out in situ and continuously multiple times and maintain stable separation performance during the circulation process.Third,the first two parts have progressed from oil-in-water emulsion separation to switchable treatment of oil-water ones,but the expansion towards the separation of abundant organic liquid emulsion remains challenging.Based on the goal of separating multi-component and multi-form organic liquid mixtures,the same supramolecular skeleton material as in the previous part was chosen to modify the three-dimensional(3D)sponge matrix by a dip-coating method.The polymer PCL which has good compatibility with the SF assembly and the sponge matrix was used as the auxiliary component to obtain an SF-modified sponge with a firm modified layer.Benefiting from the reversible wettability of SF under the different wetting states of polar and non-polar liquids,the modified sponge material exhibits controllable under-liquid double lyophobic under the control of the joystick solvent,that is,repel polar liquids in non-polar liquids and repel non-polar liquids in polar liquids.The 3D sponge matrix brings abundant pores to the modified material to provide sufficient storage space.The relatively large pores corresponding to high flux are conducive to the flow of viscous liquid.In addition,the interconnected and tortuous channels provide an environment for the coalescence of droplets in the emulsion,which helps separate the emulsions through a demulsification mechanism.According to the above properties,the sponge connected to the pump quickly absorbed non-polar liquids on polar liquids in large volumes.Notably,the material realized the unreported switchable separation of organic liquid emulsions through filtration with high separation efficiency and permeability.And the entire process could circulate continuously in situ.The separation process by adsorption or filtration is suitable for organic liquid pairs containing high-viscosity formamide and ethylene glycol.In conclusion,a series of supramolecular framework composites with special permeation channels,designable wettability,and good processability were constructed by selecting different types of auxiliary materials with unique properties to composite with supramolecular frameworks.The introduction of auxiliary components into the supramolecular assemblies not only improved the mechanical properties of the composite systems but also produced materials with good processability.It also brought about improved and expanded functionalization based on synergistic effects,realizing efficient and on-demand treatment towards nano-sized oil-water emulsions,as well as switchable separation of organic liquid emulsions.The results of this thesis have developed new materials for the on-demand separation of nanosized emulsions and organic liquid emulsions,which has not been achieved before.Also,the means of adding auxiliary materials to achieve a functional synergy effect provides new ideas for the application of supramolecular framework materials in separation and has reference value in the fields of catalysis,optoelectronics,and biomaterials.