Preparation And Separation Performances Of Composite Nanofiltration Membranes With Tannic Acid Based Selective Layers

As a burgeoning technology,nanofiltration?NF?can readily separate molecules ranging from 200 to 1000 Da and multivalent ions in aquatic systems,and has wide application prospects in the treatment of dye wastewater,wastewater recycling and seawater purification.However,it is still a challenge to use low-cost materials simple strategies to prepare high performance NF membranes in a simple method.As a Plant polyphenol,tannic acid?TA?extracted from various plant tissues has rich physicochemical properties and universal adhesion,providing new ideas for the preparation of high-performance composite NF membranes.The composite NF membrane prepared by the co-deposition method only has a good rejection on the dye solution,but the inorganic salt rejection is not high.In this study,a series of composite NF membranes with TA based selective layers were prepared by different methods.The study mainly discusses the construction of a simple NF membrane preparation method to improve the separation performance of the NF membranes.The physical and chemical properties and separation performance of these composite NF membranes were systematically studied.Co-deposition between TA and amine was used to prepare high performance NF membranes.The physical and chemical properties and separation performance of composite NF membranes can be effectively adjusted by optimizing the amine molecular weight.The membranes prepared by TA and various amine were characterized by X-ray photoelectron spectroscopy?XPS?,attenuated total reflectance fourier transform infrared?ATR-FTIR?,scanning electron microscopy?SEM?,zeta potential and water contact angle measurement.It was found that amine with low molecular weight such as ethylenediamine?EDA?and diethylenetriamine?DETA?facilitates the co-deposition onto membrane surface,while polyethylene polyamine?PEPA?and branched polyethylenimine 600?PEI 600?enhance the precipitation in solution.TA/DETA co-deposited membrane?co-deposition time was 12 h?shows a MgCl₂ rejection of 83.5%,which is higher than the reported TA based NF membranes,meanwhile exhibits a pure water permeance of 4.5 L m^-2 h^-1 bar^-1.AgNO₃ oxidation assisted co-deposition between TA and DETA was used to prepare high performance composite nanofiltration membranes.The addition of AgNO₃ can shorten the co-deposition time?co-deposition time was 5 h?,and facilitate the formation of silver nanoparticles on the nanofiltration membrane surface,thereby improving the antibacterial performance of the NF membranes.The effects of Ag NO₃ concentration and co-deposition time on the structure,surface properties and separation performance of NF membranes were systematically investigated.The optimal NF membrane exhibited excellent separation performance,with a MgCl₂ rejection of 82%.Furthermore,the optimal NF membrane shows excellent protein resistance,and improved antibacterial activity for E.coli,which benefit for the long-term use of the composite NF membrane.Tannic acid and hydrophilic Jeffamine?JA?containing amino groups were used in a layer-by-layer?LBL?process to fabricate composite NF membranes.Alternately immersing a polyacrylonitrile substrate into individual TA and JA buffer solutions could readily construct a NF membrane selective layer without any pre-treatment to the substrate.The optimised membrane showed a high pure water permeance of 37 L m^-2 h^-1 bar^-1 whilst maintaining rejections higher than 90%towards various dyes with molecular weights ranging from 269 to 1017 g moL^-1.Particularly,the obtained membrane exhibited excellent anti-fouling and long-term performance attributed to the hydrophilic membrane surface and covalent bonds in the selective layer.