Construction And Evaluation Of Anti-fouling Interface Based On Super-hydrophilic PVDF-g-PAA Ultrafiltration Membrane

The construction of anti-fouling membrane interface is the core to solve the membrane fouling problem.In this paper,the super-hydrophilic poly（vinylidene fluoride）-grafted polyacrylic acid（PVDF-g-PAAS）ultrafiltration membrane was prepared by a one-pot method,and the Mg（OH）2 composite super-hydrophilic ultrafiltration membrane and visible light-Fenton self-cleaning ultrafiltration membrane PVDF-g-PAA@FeOOH（FASF）were prepared by the in situ mineralization of Mg²⁺and Fe³⁺,respectively.The preparation parameters,physicochemical properties,ultrafiltration and anti-fouling properties of three kinds of ultrafiltration membranes were studied.The main research contents are as follows:（1）The super-hydrophilic poly（vinylidene fluoride）-grafted polyacrylic acid（PVDF-g-PAAS）ultrafiltration membrane（FAS）was prepared by a one-pot ultrafiltration membrane preparation technology which combines radical-initiated graft copolymerization with the process of membrane conversion from submerged precipitation phase using alkaline polyvinylidene fluoride（HPVDF）as the base polymer and acrylic acid（AA）as the graft monomer.The effects of material ratio,material-liquid ratio,coagulating bath temperature and alkali concentration on physical and chemical properties,microstructure and ultrafiltration properties of FAS were studied.The results showed that the initial WCA of the FAS was lower than 60°and completely wetted within10 s,and the Zeta potential was negative and decreased with the increase of pH.The membrane structure parameters were greatly affected by the material ratio and the material-liquid ratio.When the material ratio increased from 3/12 to 9/12,the undulating cortex appeared on the FAS surface,the micropores increased,the cross-section pores transitioned from finger to sponge,the pure water flux decreased,and the rejection rate of bovine serum albumin（BSA）remained above 90%.As the temperature of coagulating bath increases,the FAS sublayer structure becomes more loose and denser with the increase of alkali concentration.Ratio flux reduction of FAS is lower than 65%and the flux recovery rate is higher than 80%during BSA ultrafiltration,which shows good anti-fouling performance.The grafting rate was the highest when the feed ratio was 6/12.The pure water flux of the FAS12-6 prepared in a 60℃0.05 mol·L^–1 alkaline gel bath was565.83 L·m^–2·h^–1,and the flux recovery rate reached 94.62%,which decreased below 8%after 4 cycles.（2）Two kinds of nano Mg（OH）2 composite PVDF-g-PAA super-hydrophilic ultrafiltration membrane FAMS and FAMM were prepared by surface in situ mineralization and membrane matrix in situ mineralization using the coordination of carboxyl groups in the FAS to the Mg²⁺.The effects of the base membrane composition and the addition MgCl2·6H2O inorganic precursors on the physical and chemical properties,microstructure and ultrafiltration properties of the composite membrane were studied respectively.The anti-fouling properties of the two membranes were investigated.The results showed that:the porosity of the FAMS pore after mineralization on the FAS surface decreased significantly,and the pure water flux decreased,but the hydrophilicity increased significantly.The high grafting rate and surface smoothness of FAS are beneficial to improve the mineralization and uniformity of Mg（OH）2 nanoparticles.The increase MgCl2·6H2O addition in the PVDF-g-PAA system is beneficial to increase the hydrophilicity and pure water flux of the FAMM,but the gel will be formed after the content of the gel is higher than 4%.The recovery rates of FAMS and FAMM cleaning flux were as high as 96.80%and 97.21%.After four cycles BSA stable flux decay was lower than 7%,demonstrated better and more stable anti-pollution performance than FAS.（3）The composite ultrafiltration membrane PVDF-g-PAA@Fe OOH（FASF）with visible light photo-Fenton self-cleaning function was prepared by in situ mineralization on the surface of FAS based on the principle that the membrane was immobilized by coordination with carboxyl groups and could be hydrolyzed to formβ-FeOOH nanoparticles under acidic conditions.Methylene blue（MB）and BSA was used as simulants,the visible light photo-Fenton reaction activity and photocatalytic self-cleaning properties of FASF were investigated by static photocatalytic degradation and ultrafiltration experiments,respectively.The results showed that:the FASF surfaceβ-FeOOH content increased and the hydrophilicity increased significantly with the increase of grafting rate and mineralization time in the FAS,but the absolute value of Zeta potential and pure water flux decreased.FASF has a high visible light photo-Fenton reaction activity,and the FASF6,of 24 h of mineralization has a degradation rate of more than 90%within 40 min for 20 mg·L^–1 MB solution.The flux recovery rate of FASF at30 min of visible light photo Fenton cleaning after BSA contamination is close to 100%.the flux can still maintain 97%of the initial flux after 4 BSA filtration cycles,showing excellent resistance to BSA contamination and visible light photo-Fenton self-cleaning.