Preparation And Performance Study Of Composite Nanofiltration Membrane Regulated By Polycaffeic Acid Intermediate Laye

The separation property of nanofiltration membrane is constrained by the permeability-selectivity upper bound.This subject aims to prepare a composite nanofiltration membrane with high permeability and rejection.The poly（caffeic acid）（PCA）interlayer structure was introduced between the polyacrylonitrile substrate and the polyamide separation layer.The polyamide composite nanofiltration membrane with interlayer structure（PAN-PCA_n-PA membrane）was prepared.The functional groups and surface elemental compositions of membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy,respectively.The surface and cross-section morphologies of membranes were observed by scanning electron microscope.The surface roughness of membranes was measured by atomic force microscopy.The properties of the membranes surface were analyzed by contact angle,Zeta potential and pore size distribution.According to experimental results,the crosslinking degree of polyamide layer of the PAN-PCA_n-PA membrane is enhanced.The average pore size of PAN-PCA_n-PA membrane is about 0.32 nm.The hydrophilicity and negative charge of the PAN-PCA_n-PA membrane increase.In addition,there is a“gutter”structure between the polyamide layer and the substrate in PAN-PCA_n-PA membrane.The water flux and rejection of composite membrane as indexes,the effect of preparation parameters on the membrane performance were extensively investigated.According to the results,the deposition of 0.5 wt%PCA for 2 h,aqueous solution of0.7 wt%PIP,organic solution of 0.2 wt%TMC,aqueous immersion time of 3 min,interfacial polymerization time of 1.5 min,standing time of 30 min,heat treatment at 60℃ for 20 min.Compared with the PAN-PA membrane,the introduction of the PCA interlayer increases the flux of the PAN-PCA₂-PA membrane by about 86%,reaching17.7 L·m^-2·h^-1·bar^-1,while the rejection to Na₂SO₄ is 98.9%.The use of PCA interlayer not only improves the formation of polyamide rejection layers,but also provides an optimized water transport path,which enables PAN-PCA₂-PA membranes to overcome the longstanding trade-off between membrane permeability and selectivity.The PAN-PCA₂-PA membrane exhibits the order of rejection to different salt:Na₂SO₄（98.9%）>Mg SO₄（95.8%）>Mg Cl₂（60.5%）>Na Cl（30.2%）.In addition,the selectivity of Na Cl/Na₂SO₄ is 63.5.the selectivity of Cl^-/SO₄^2-is 75.9,the selectivity of Na⁺/Mg²⁺is 3.6.PAN-PCA₂-PA membrane has a good selective separation performance,the theoretical basis for PAN-PCA₂-PA membrane practical application is provided.