High Water Permeating Thin Film Composite Polyamide Nanofiltration Membranes Showing Thermal Responsive Gating Properties

The water flux,salt retention and pollution resistance of Nanofiltration membranes play significant roles in water treatment and desalination.Therefore,this paper mainly studies the factors that affect these three parameters of nanofiltration membranes.Interfacial polymerization was used to prepare a polyamide nanofiltration membrane,and then the surface of the nanofiltration membrane was grafted with dimethyl methacrylate（DMAEMA）and 1,3-propanesultone（1,3-PS）to prepare new high permeability nanofiltration membranes.The effects of graft chain length,degree of amphoteric ionization and test temperature on the performance and anti-fouling property of nanofiltration membranes were studied.On the polysulfone ultrafiltration membrane,a polyamide nanofiltration membrane was prepared by an interfacial polymerization method using an aqueous piperazine solution and a trimesyl chloride n-hexane solution.O n this basis,a novel high permeability nanofiltration membrane was prepared by modification on the surface of the polyamide nanofiltration membrane.Firstly,DMAEMA chains were grafted onto the surface of polyamide nanofiltration membranes.Secondly,a zwitterionic nanofiltration membrane was prepared using a ring-opening reaction of1,3-PS.The membrane was characterized by FTIR,XPS,CA,Zeta potential,SEM,AFM and XRD on the chemical structure,hydrophobicity,chargeability and surface micromorphology of DMAEMA modified nanofiltration membranes and zwitterionic nanofiltration membranes.The cross-flow filtration experimental device tests the membrane for the separation performance of inorganic salt solution and the anti-pollution performance of BSA solution.FTIR and XPS characterization results show that DMAEMA modified nanofiltration membranes and zwitterionic nanofiltration membranes were successfully prepared.The functional layer becomes thicker,the roughness increases slightly,the water contact angle decreased,and the surface negative charg reduced.Membrane separation performance was tested using Na₂SO₄ inorganic salt solution.The results show that the modified membrane has good separation performance for Na₂SO₄.Among them,the DMAEMA modified nanofiltration membrane（NF-4）has a retention rate of about 94%for Na₂SO₄ and a water permeability of 11.9 L/（m²·h·bar）;the retention rate of zwitterionic nanofiltration membrane NF-4-6 to Na₂SO₄ is about 90%,and the water permeability is about 14L/（m²·h·bar）.In addition,the change of water permeability shows that the modified nanofiltration membrane has the upper critical solution temperature（UCST）.The UCST thermal response temperature ranges of NF-8 and NF-8-6 are between 30?C-35?C and 25?C-30?C,respectively.Finally,the antifouling of the membranes was tested using an aqueous BSA solution.The results showed that when all tests were performed at a low temperature of 25?C,the membrane was less polluted and easier to clean.When polluted at a high temperature of 40?C and cleaned at a low temperature of 25?C,due to the high degree of pollution of the membrane,it is not easy to clean.Under low temperature cleaning at 25?C,the flux recovery rates of the three membranes NF-0,NF-4,and NF-4-6 are respectively 58.0%,27.9%,34.7%;under high temperature cleaning at 40?C the flux recovery rates of NF-0,NF-4,and NF-4-6 membranes were increased to 89.8%,74.8%,and 88.3%,respectively.And the flux of the membrane was largely restored.