Investigations On Preparation And Properties Of Sandwich Polyamide Nanofiltration Membrane Containing ZIF-8

Nanofiltration technology is an important means to solve the demand of human society for water resources,and the process of water quality purification can be realized through nanofiltration membrane.The purpose of introducing MOFs material into nanofiltration membrane is to alleviate the"Tradeoff"effect and improve the performance of nanofiltration.In view of the limitations of some MOFs nanofiltration membranes in interception.In this study,MOFs branched ZIF-8 was used as substrate to prepare film nanocomposite（TFN）film with polyamide sandwich nanoparticles,and poly（4-styrenesulfonate）sodium（PSS）and tannic acid（TA）were used as auxiliary modifiers to prepare PSS-TFN film and TA-TFN film,which not only had good retention effect on divalent salt ions and dyes with smaller molecules（lower than 600Da）,but also showed good anti-fouling properties.It provides a certain reference value for the study of MOFs nanofiltration membrane.First of all,ZIF-8 is directly modified by PSS,PSS inhibits the nucleation of ZIF-8 and makes its dispersion more uniform,and the subsequent synthesis of polyamide also has a good synthesis environment,thus the PSS-TFN film is obtained.The surface of PSS-TFN film is compact and smooth,has very low roughness and good hydrophilicity,and has more negative charge.The water flux of the membrane is 35.06Lm^-2h^-1,which is 122%higher than that of the thin film composite membrane（TFC）.The negative group of PSS,the cavity structure of ZIF-8 and the integrity of PA play a key role in its retention performance.The experimental results show that the rejection rates of PSS-TFN membrane to Na₂SO₄,Na Cl,Mg SO₄ and Mg Cl₂ are 92.06%,59.16%,53.64%and 29.4%,respectively.The rejection rates of acid fuchsin（AF）,sunset yellow（SY）,methyl orange（MO）and methylene blue（Mn B）were 99.35%,97.94%,94.70%and 92.53%,respectively.The rejection performance was much better than that of TFC and TFN membranes.Secondly,using TA to regulate ZIF-8 is another effective method to prepare high performance nanofiltration membrane.Plant polyphenol tannic acid can firmly adhere to the substrate surface by covalent or non-covalent bonding,in which phenolic hydroxyl groups can chelate with Zn²⁺in ZIF-8,providing more binding sites for ZIF-8 and enriching ZIF-8,thus affecting the PA layer.Through electron microscope analysis,the surface smoothness of TA-TFN film is much better than that of TFC film,and the thickness of PA layer is greatly reduced.The TA-TFN membrane showed good hydrophilicity,and the Zeta potential showed that it showed a high negative potential in water.The pure water flux of the optimized TA-TFN membrane was about 29.00 Lm^-2h^-1,and the rejection rates of Na₂SO₄,Mg SO₄,Na Cl and Mg Cl₂ were 90.26%,71.20%,63.13%and 34.43%respectively,and the rejection rates of AF,SY,MO and Mn B 4 kinds of dyes were 98.57%,98.05%,97.8%and 96.91%,respectively.Finally,sodium alginate（SAA）,bovine serum albumin（BSA）and lysozyme（Lys）were used as model pollutants to mix with Na₂SO₄ solution for the filtration test of PSS-TFN,TA-TFN membrane and control group TFC,TFN membrane to compare their antifouling performance.The results showed that the antifouling performance of PSS-TFN membrane is the highest,TA-TFN membrane is the same as TFN membrane,and the TFC membrane is the worst.The theoretical calculation results from x DLVO are completely consistent with the order of the antifouling performance of the membrane,which explains the membrane fouling behavior microscopically and delineates the applicable scope of PSS-TFN and TA-TFN membranes in antifouling.