Research On The Structure And Separation Performance Of Nanofiltration Membrane Modified By In-situ Growth Of Titanium Dioxide Nanoparticle

Membrane separation technology has shown great advantages in water treatment due to its high separation efficiency and high water reuse rate.However,the low water flux of separation membranes,the serious phenomenon of membrane contamination and the inability of a single membrane separation technology to fully remove pollutants are the bottlenecks that restrict the development of membrane separation technology.Therefore,the research and development of modified membranes with high flux and anti-pollution are of great theoretical significance and application value in the field of water treatment.In this thesis,from the perspective of membrane material design,we take separation membrane modification as the core of research,test the nanofiltration membrane performance by sieving nanofiltration membranes with different preparation conditions,and prepare modified nanofiltration membranes by the modification method of in situ growth of titanium dioxide interlayer and surface modification layer.The results show that the enhancement of hydrophilic and charge properties and the increase of roughness are all beneficial to improve the affinity of nanofiltration membrane for water molecules,increase the resistance to the adsorption and accumulation of contaminants on the surface of separation membrane,and expand the contact area between water molecules and membrane surface,thus causing the improvement of water flux and recovery rate of nanofiltration membrane;the hydrophilic and charge surface properties of titanium dioxide nanoparticles are beneficial to the optimization of structural parameters of separation membrane,and the nanoparticles and The nano-channels between nanoparticles and polymers can provide additional water channels for the nanofiltration membrane,further reducing the transmembrane resistance of water molecules,enhancing the diffusion rate of water molecules transported in the membrane,and improving the macroscopic water flux of the nanofiltration membrane.To address the problems of low flux and poor resistance to contamination and chlorine in nanofiltration membranes,interfacial polymerization（IP）was used to synthesize a polyamide（PA）separation layer by interfacial polymerization of piperazine（PIP）and homophthaloyl chloride（TMC）on the surface of polysulfone（PSF）ultrafiltration membrane,and then the polyamide nanofiltration membrane was modified by the strategy of in situ synthesis of titanium dioxide.The titanium dioxide interlayer was introduced between the polysulfone ultrafiltration membrane and the PA layer,and the titanium dioxide surface modification layer was introduced on the surface of the PA layer.The data showed that the nanofiltration membrane with titanium dioxide interlayer structure achieved the expected high flux nanofiltration membrane,and the highest water flux was achieved by the titanium dioxide surface modified nanofiltration membrane,and the retention rate of Na₂SO₄was maintained at 97%by the nanofiltration membrane modified by the introduction of titanium dioxide interlayer compared with the polyamide nanofiltration membrane,while the water flux reached 75 L/（m²·h）;the nanofiltration membrane modified by the titanium dioxide surface modified layer The water flux was 86 L/（m²·h）,and the Na₂SO₄removal rate was maintained at 95%by eliminating the performance shielding of the titanium dioxide layer by the polyamide layer.The flux recovery rate was 88.9%and the flux decrease rate was 26.4%for the titanium dioxide intermediate layer modified nanofiltration membrane,while the flux recovery rate was 90.5%and the flux decrease rate was only 19.1%for the titanium dioxide surface modified layer modified nanofiltration membrane.After the static chlorine resistance test,both modified nanofiltration membranes showed good chlorine resistance,but the titanium dioxide surface-modified layer-modified nanofiltration membrane showed stronger chlorine resistance,and the presence of the surface-modified layer effectively shielded the chlorination sites on the surface of the nanofiltration membrane,which maximized the chlorine resistance of the nanofiltration membrane.Both modification methods significantly improved the performance of the nanofiltration membranes,and the stability of both modified membranes was good.The research results provide theoretical and technical support for the preparation of high-performance modified separation membranes.