Preparation And Separation Performance Of TiO₂ And CMCS Modified PVDF Ultrafiltration Mambrance

Polyvinylidene fluoride material is widely used in the field of membrane separation due to its good chemical stability,excellent radiation resistance and high mechanical properties.The improvement of the hydrophilicity of PVDF materials is very important for improving the membrane’s anti-pollution property and prolonging the membrane’s service life.Blending modification methods are widely used because of their simple operation.Blending modification materials can be divided into two categories: organic materials and inorganic materials,both of which can improve the comprehensive performance of ultrafiltration membranes to a certain extent.In this paper,monochloroacetic acid method was used to prepare N,O-carboxymethyl chitosan from chitosan.The infrared,XPS elemental analysis and thermogravimetric characterization of the product were used to confirm the existence of the functional group carboxyl group,which confirmed The product is N,O-carboxymethyl chitosan,the substitution degree of N,O-carboxymethyl chitosan is determined by titration,and the best preparation process is finally determined: the quality of chitosan and monochloroacetic acid When the ratio is1:4.5,the reaction time is 5 h,the reaction temperature is 60 °C,and the Na OH mass fraction is 45 wt%,N,O-carboxymethyl chitosan with a degree of substitution of 0.97 can be prepared.Titanium dioxide（TiO₂）was used as the modified material,and TiO₂/PVDF ultrafiltration membrane was prepared by immersion precipitation phase transformation method.The effect of TiO₂ content on the performance of ultrafiltration membrane was analyzed.The experimental results show that the addition of nano-TiO₂ can appropriately improve the ultrafiltration membrane Hydrophilicity,but when the amount of TiO₂ is too much,the permeability and anti-fouling ability of the membrane are affected.The mechanical properties of the membrane are less affected by the increase in the content of nano-TiO₂,and the optimal doping amount of titanium dioxide is finally determined to be 1.0 wt%.At this time,the water flux of the ultrafiltration membrane is 677.8 L·m^-2·h^-1,The rejection rate was 79.5 %,the porosity was 80.9 ± 0.014,the water contact angle was 71.4°,and the FRR value reached 90 %.N,O-carboxymethyl chitosan（CMCS）was used as the modified material to prepare CMCS/PVDF ultrafiltration membrane.The influence of the doping amount of CMCS on the performance of ultrafiltration membrane was investigated.The experimental results showed that the addition of CMCS had little influence on themechanical properties of ultrafiltration membrane.When the doping amount of CMCS is 0.2wt %,the modification effect of ultrafiltration membrane is the best.At this time,the water flux of ultrafiltration membrane is 466 L·m^-2·h^-1,the retention rate is 86.48%,the water contact Angle is 71.0°,the porosity is 85.7 ± 0.023,and the FRR value reaches 89.45%.