Functional Modification Of PVDF Membrane By Composite Thermally Induced Phase(NTIPS)

Membrane separation process as a new separation,purification and purification technology,because of its low energy consumption,high efficiency,is now widely used in the process of industrialization,showing a great application prospect.Polyvinylidene fluoride(PVDF)is a kind of membrane material with excellent performance.It has strong chemical stability,mechanical strength and thermal stability.It can be used outdoors for a long time.However,the surface hydrophilicity of polyvinylidene fluoride(PVDF)is poor,and membrane pollution such as protein adsorption is easy to occur in practical application,which causes blockage of membrane pores,reduces the separation efficiency and shortens the service life of membrane components.The most commonly used method to prepare PVDF membrane is phase transformation,which mainly includes non-solvent-induced phase separation(NIPS)and thermally induced phase separation(TIPS).In this study,the two commonly used technologies were combined to prepare a composite membrane with both non-solvent-induced phase separation(NIPS)and thermally induced phase separation(TIPS)membrane structures through composite thermoinduced phase separation(NTIPS),and the membrane was blended and modified by UIO66 and UIO66@PDA.On the one hand,NTIPS membrane with NIPS fingerlike pore structure and TIPS double-continuous network structure was realized.On the other hand,the anti-fouling performance and pure water flux of PVDF membrane were effectively improved by using the hydrophilicity and uniform dispersion of UIO66 and UIO66@PDA nanoparticles.Some ideas were provided for the preparation of composite membranes with good anti-pollution properties.The main content of this paper includes the following four parts:(1)Pure PVDF membrane,UIO66-PVDF membrane and UIO66@PDA-PVDF membrane were prepared by composite thermally induced phase separation(NTIPS).XRD,FT-IR,DSC,SEM,TGA and other testing methods were used to test the crystal structure,molecular structure and contact Angle of the membrane.The microstructure and mechanical properties of the membrane were characterized and analyzed.The results showed that UIO66 and UIO66@PDA mixed in PVDF membrane retained their own properties and improved the thermal stability of the membrane.(2)The hydrophilicity and filtration performance of pure PVDF membrane and PVDF composite membrane were measured and studied.The results showed that both UIO66 and UIO66@PDA improved the hydrophilicity of the membrane and reduced the contact Angle of the composite membrane.When the amount of Fe was 1.0wt%,the contact Angle of the membrane was the minimum and the hydrophilicity was the best.With the addition of UIO66 and UIO66@PDA,the water flux of the composite membrane firstly increases and then gradually decreases,and the rejection rate changes in a small range.When the content of modified substances is large,the nanoparticles agglomerate and clog the membrane holes,resulting in membrane defects,which affect the membrane flux and rejection rate.The addition of modified particles also affects the average pore size and porosity of the membrane and the permeability of the membrane.(3)The stability and anti-fouling performance of pure PVDF membrane and PVDF composite membrane were studied.Compared with the pure PVDF membrane,both UIO66 and UIO66@PDA improved the anti-protein adsorption performance of the membrane.With the addition of UIO66 and Na N nanoparticles,the types of pollutants adsorbing on the surface of the composite membrane changed.When the addition amount of Na N was 1.0wt%,Compared with pure PVDF membrane,the flux recovery ratio(FRR)of the composite membrane increased significantly,which was about 44%higher than that of pure PVDF membrane.Moreover,the irreversible fouling rate of PVDF composite membrane decreased,which indicated that the anti-fouling performance of PVDF composite membrane was effectively improved,and the enhanced anti-fouling ability of the membrane could prolong the operating cycle of the membrane in the process of water treatment.In addition,the composite membrane showed good acid and alkalinity resistance.(4)The different temperature of coagulation bath has a great influence on the structure and properties of the membrane.With the increase of the temperature of coagulation bath,the pore size on the surface of the membrane will gradually increase.The porosity of the membrane is mainly affected by the polymer concentration and has little change with the increase of the temperature of coagulation bath.However,the pure water flux increases with the increase of the temperature of coagulation bath,and the rejection rate decreases with the increase of the temperature.