Design,Fabrication And Filtration Performance Of Solvent Resistant Mixed Matrix Membranes

Polyacrylonitrile(PAN)with good chemical stability,film forming abilities is one of the most important polymers in membranes preparation,which have been widely researched in the field of ultrafiltration,nanofiltration,dialysis and pervaporation.However,the defects of low flux,low anti-fouling properties in PAN membranes have limited its large-scale applications.In order to solve above-mentioned key problems,PAN-based mixed matrix membranes(MMMs)incorporated into graphene oxide(GO),SiO2 and TiO2 nanoparticles were fabricated in-situ after the membranes structural designs.Through the investigation on membranes pore structures,chemical structures,hydrophilicity and flux,the GO on the the structures and permeability of MMMs were systematic researched and the method to ameliorate the PAN membranes pore structures,porosity,flux and anti-fouling performances.Based on these,the method to increase the thermal and chemical stabilities were researched.Through the systematic discussion on change rules of chemical structures and TiO2 influence rules during thermal crosslinking process,the approaches to avoid the molten of MMMs pores.And a novel embedded flexible TiO2/PAN composite membranes were fabricated.The following research results have been achieved:(1)Through the structure design,GO/SiO2/PAN and GO/TiO2/PAN MMMs with high flux,high porosity,good hydrophilicity and anti-fouling properties were fabricated in-situ;The effects of GO on the structures and permeability of MMMs in NIPS process were systematic researched,and the synergistic effects between GO and SiO2,TiO2 nanoparticles were also revealed.1)The generated GO/SiO2/PAN MMMs have typical finger-like pores which is upright and hole-through,porosity bottom surfaces;Its porosity,pure water contact,water flux and flux recovery rate(FRR)are 79.6%,53.5°,387.0L/(m2·h)and 85.6%,respectively.The incorporation of GO increased the PAN phase separation rates,which induce GO/SiO2/PAN membranes with thin skin-layers and high porosity;Meanwhile,SiO2 were fixed on the surfaces of GO sheets through C-N covalent bond.And through the migration of GO sheets,the hydrophilicity,flux and anti-fouling performances of PAN MMMs were greatly improved.2)The silicic metal alkoxide was changed into easier hydrolytic tetrabutyl titanate(TBT)and a novel GO/TiO2/PAN MMMs were prepared in situ.Compared with GO/SiO2/PAN MMMs,the porosity,pure water contact angle,water flux and FRR of GO/TiO2/PAN MMMs are 88.8%,40.7°,1487.6 L/(m2 h)and 87.7%,respectively.The differences with GO/SiO2/PAN MMMs are that the incorporation of GO not only decreased the thickness of the MMMs skin layer obviously,but also generated the "pore-forming agent" of TiO2 nanoparticles during its surface migration,which further increased the porosity and hydrophilicity of the MMMs and the flux and anti-fouling performances were greatly improved eventually.(2)The well solvent resistant TiO2/PAN thermal crosslinked membranes were fabricated by the method of thermal crosslinking.Through the systematic researches in structure changes and the effects of TiO2,we discovered that under the proper thermal crosslinking temperature and high air flow,lengthening the thermal crosslinking times is in favour of stabilization of the membranes pore structures;The incorporation of TiO2 nanoparticles can avoid the meltdown and collapse of membranes pores effectively and well keep the MMMs original finger-like and sponge-like pores;The mechanism of the effects of TiO2 nanoparticles on the PAN thermal-crosslinked membranes pore structures were also investigated.(3)In order to solve the problem of the poor heat resistance of non-wovens in the traditional polymeric composite membranes,the embedded flexible TiO2/PAN composite membranes were designed and fabricated by means of embedding a novel high temperature resistance flexible porous supports,though the method of soaking coating,in-situ fabrication and NIPS process,and the solvent resistant flexible thermal crosslinked TiO2/PAN composite membranes were finally generated through thermal crosslinking method.The prepared flexible thermal crosslinked TiO2/PAN composite membranes can keep the original finger-like and sponge-like pores structures,tolerate the dissolution from strong polar solvents such as DMF,nd have nanofiltration performances with the Na2SO4 rejection rate of 47.7%due to the shrink of the pores on the top surfaces and the finger-like pores walls during the thermal crosslinking process.Therefore,a novel method to fabrication solvent resistant nanofiltration membranes were discovered in our research works.