Study On Properties Of Self-sealed PA/ZIF Nanofiltration Membranes By In Situ Counter-Diffusion Growth

As a low pressure separation technology,nanofiltration membrane has a pore size range of 0.5-2 nm,which can be used to isolate inorganic salts and small molecular organic matter?such as dyes and so on?.The most advanced thin film composite nanofiltration?TFC-NF?membranes are based on cross linked polyamide?PA?active layers formed by interfacial polymerization?IP?on the ultrafiltration membrane supports.The efforts in increasing their separation efficiency by operating under higher water permeance are generally thwarted by the tradeoff in salt rejection?such as Na₂SO₄?and antifouling resistance capability.Therefore,the focus of the research for nanofiltration membranes remains in the efforts of boosting up their water permeance without sacrificing their salt rejection and antifouling capability.In this paper,firstly we start from constructing nanofiltration membrane with high water flux.The structure and properties of polyamide nanofiltration membrane are adjusted by introducing zinc nitrate hexahydrate during the interfacial polymerization of PIP and TMC.The preloaded zinc nitrate and PIP complexation limits the diffusion rate of aqueous monomers so that the membrane surface forms a striped polyamide Turing structure with larger nanopore?about 9.3??.TFC-Zn membrane keeps a fairly high dye rejection??90%?and shows 4 times the water permeation flux??117.2L/?m²·h??of the primary TFC membrane.Subsequently,in order to improve the desalination performance of the nanofiltration membrane.A water channel is constructed on the surface of the polyamide membrane by introducing ZIF material to block the larger nanopore of the membrane using as in situ counter-diffusion method.The reaction of organic ligands and metal ions will mainly take place at the defects of the polyamide seperation layer,which will in situ form insoluble materials to seal these defects.Therefore,the formal ZIF nanoparticle matrix with a 3.0?3.5?pore structure not only helps water molecules pass through the membrane material,but also prevents Na₂SO₄ inorganic salt penetration.TFN-ZIF membranes show not only 3?4 times higher water flux than TFC membranes,but also retain comparably high salt rejection and antifouling resistance capability.ZIF-8 was chosen as a model to study the effect of Zn loading levels,counter-diffusion reaction time on the structures and properties formed TFN-ZIF membranes.The ZIF-8 material was extended to ZIF-7 and ZIF-90,and the effect of the imidazole ligand structure on the structure and properties of the mix matrix membrane was investigated.The universality of the method was verified.