Preparation And Properties Of Fluorine-Containing Solvent-Resistant Nanofiltration Membranes Based On Interfacial Polymerization

The separation is an important process in the chemical and pharmaceutical industries.Pressure driven membrane separation is considered to be an efficient,low energy consumption,phase change free,and environmentally friendly separation process.Solvent resistant nanofiltration（SRNF）is an emerging technology.The SRNF membranes are used for separation and purification processes in organic solutions.Interfacial polymerization（IP）is the most common method for preparing composite nanofiltration membranes,which has the advantages of simple operation and strong controllability.Currently,the research on solvent resistant nanofiltration membranes mainly focuses on improving the solvent permeability and solute retention of the membranes,as well as improving the solvent resistance of the membranes.It is very difficult for existing SRNF membranes to both exhibit excellent permeability and selectivity.In other words,the improvement of one aspect is often accompanied by the sacrifice of the other.In addition,for many current nanofiltration membranes,it is very difficult to withstand many highly polar organic solvents,such as DMF.This makes them difficult to apply under extreme conditions.It is well known that fluoropolymers have high heat resistance,chemical resistance,durability,and weather resistance.and it has great potential as an excellent material for preparing solvent resistant nanofiltration membranes.However,due to the difficulty in dissolving fluorinated monomers in water,there have been few previous reports on this issue.With the application of ionic liquids in interfacial polymerization,it provides a new idea for the preparation of solvent resistant nanofiltration membranes using fluoropolymers.Based on the interfacial polymerization method,an interfacial polymerization on the surface of polyacrylonitrile（PAN）support membranes was carry out to prepare fluorinated film composite（TFC）membranes utilizing a mixed solvent system composed by ionic liquid and aqueous solution.Subsequently,hydrazine hydrate was used as a crosslinking agent to integrally crosslink the PAN base membrane,polyester selective layer,and the interface therein.The fluorinated integrally crosslinked composite membrane was then obtained.Finally,aggregation induced luminescence（AIE）monomers were added to interfacial polymerization to synthesize AIE fluorescent membranes with fluorescence characteristics.The three membranes obtained have excellent nanofiltration performance and solvent resistance.The specific work is as follows:（1）In order to improve the filtration performance and solvent resistance of SRNF membranes,the fluorinated monomer hexafluorobisphenol A（BPAF）and bisphenol A（BPA）were selected as monomers for interfacial polymerization in this work.To increase their solubility,a mixed solvent of water/ionic liquid was used instead of the traditional aqueous phase of interfacial polymerization.Fluorinated poly（aryl ester）TFC membranes were synthesized on PAN based membranes by interfacial polymerization using trimesoyl chloride（TMC）as an organic monomer.The surface morphology,structure,nanofiltration performance,and long-term solvent resistance of fluorinated TFC membranes were characterized.The results confirmed that the addition of fluorinated monomer can adjust the surface morphology and roughness of TFC membranes.The high viscosity of ionic liquid and the addition of fluorinated monomer can slow down the interfacial polymerization reaction,which is conducive to the formation of thinner selective layer films.In addition,the introduction of fluorinated monomer can also help improve the solvent resistance of TFC membranes.The permeability of the membrane sample PAN-F-0.5 to methanol is as high as124.05 L m^-2h^-1bar^-1.The molecular weight cutoff value（MWCO）of the resulting membrane is approximately 450 g mol^-1.PAN-F-0.5 still exhibits excellent performance after continuous immersion in DMF for 90 days（room temperature）and 7 days（80°C）,respectively.The results show that the fluorinated TFC membrane has excellent filtration performance and solvent resistance.（2）In order to further improve the solvent resistance of fluorinated TFC membranes,the fluorinated TFC membranes prepared by interfacial polymerization were crosslinked with hydrazine hydrate.In this chapter,hydrazine hydrate was used as a crosslinking agent to crosslink the polyacrylonitrile base film,fluoropolyester layer,and the interface between them.The effects of temperature and time of the crosslinking reaction were investigated,and a hydrazine hydrate overall crosslinked film was prepared.The surface morphology,structure,nanofiltration performance,and long-term solvent resistance of the hydrazine hydrate monolithic membranes were characterized.The results confirmed that the overall crosslinking of hydrazine hydrate can tightly bind the support layer and the selective layer of TFC membranes,increasing their solvent resistance.In addition,after overall post crosslinking,the surface trifluoromethyl content of the fluorinated membrane decreased,the number of amino groups increased,and the separation layer became thinner,enhancing the solvent permeability of the TFC membranes.The molecular weight cutoff value（MWCO）of the resulting membrane is about 500 g mol^-1.（PAN-F-90-3）_xstill maintains excellent permeability and retention after continuous immersion in NMP at room temperature for 90 days and immersion at 80°C for 10 days.The results show that the overall crosslinking of hydrazine hydrate endows the TFC membranes with strong solvent resistance.（3）In order to study nanofiltration membrane materials with intelligent fluorescence response,fluorescent monomer with aggregation induced emission（AIE）effects was added to interfacial polymerization.Firstly,the fluorescent monomer TPE-1 was synthesized through a one-step organic synthesis reaction,which has a typical AIE effect.AIE fluorescent TFC membranes were obtained by interfacial polymerization of the prepared fluorescent monomer into aqueous monomers on PAN matrix membranes.The structure and fluorescence properties of TPE-1 were characterized.Subsequently,the surface morphology,structure,nanofiltration performance,and fluorescence properties of AIE fluorescent TFC membranes were characterized.The results show that TPE-1 can be interfacial polymerized onto TFC membranes and retain the fluorescence characteristics of AIE after polymerization.The prepared AIE fluorescent TFC membranes have good nanofiltration performance and can emit stable fluorescence.