PDA Intermediated ZIF-8 Membrane For Monovalent Selective Anion Exchange Membrane

A monovalent anion selective film with continuous and stable ZIF-8 crystal layer was synthesized in aqueous solvent at room temperature using commercial anion exchange membrane as substrate and Zn²⁺modified PDA coating as intermediate layer.Compared with the original membrane,the monovalent selectivity and monovalent anionic flux of the ZIF-8/Hmim-PDA/AEM membrane were significantly improved,and the stability and anti-organic pollution performance of the modified membrane were good.The successful synthesis of ZIF-8 on the membrane surface was verified by the changes of chemical structure and elemental composition of the membrane surface and the morphology of the membrane surface and section.The water contact Angle of the film was analyzed.Although the hydrophobic ZIF-8 material was introduced,the hydrophilicity of the film was not significantly affected compared with that of the original film（25.1°）and the modified film（28.3°）.ZIF-8/Hmim-PDA/AEM showed good selective permeability(P(Cl^-:SO₄^2-)=10.96),and the univalent ion flux increased by 377.71%compared with AEM.The total resistance of modified film surface is5.59Ω·cm²,which only increases by 2.29Ω·cm² compared with the original film.ZIF-8/Hmim-PDA/AEM showed good stability in long-term operation,and the fluctuation error of water ion concentration in 20h electrodialysis process was less than 0.002mol/L.PDA coating and Hmim activation technology can improve the non-polarity of the membrane,enhance the repulsion between the membrane and humus,and enhance the anti-pollution performance.The effects of deposition time in PDA solution,activation time of Hmim and ratio of synthetic mother solution on the monovalent selectivity and energy consumption in electrodialysis process were investigated.The membrane samples were prepared according to three factors and two levels.The relative optimal modification conditions are as follows:PDA deposition time 16h,Hmim activation time 3h,Zn（NO₃）₂·6H₂O:Hmim:H₂O molar ratio 1:75:6000.At the same time,J_CL^- is 3.6×10^-6mol·cm^-2·min^-1,j_SO4^2-is only 0.5×10^-6mol·cm^-2·min^-1.The anionic separation efficiency reached 75.5%,and the interaction between sodium alginate,humic acid,bovine serum protein and membrane was mutually repellent,indicating that no.8membrane had a good anti-pollution effect.The severity of organic matter to membrane pollution was SA>HA>BSA.In the coagulation stage of pollutants,the mutual attraction of BSA-BSA will aggravate membrane pollution.