Modification And Preparation Of High Performance Separation Membrane By Layer-by-layer Self-assembly Technology

Layer-by-layer self-assembly（LbL）technology is a common technology for modifying and preparing high performance separation membrane with the advantages of simple operation,no special requirements for operating environment,and have abundant membrane-forming materials,etc.In this paper,aiming at the problems of poor anti-pollution performance of polysulfone（PSf）membrane and complicated preparation process of traditional thin film composite（TFC）membrane,sodium lignosulfonate（LS）and polyethyleneimine（PEI）are selected as cheap hydrophilic modification materials,PSf membrane is modified by LbL technology to improve its hydrophilicity and anti-pollution performance,also TFC nanofiltration（NF）membrane is prepared by LbL technology combined with glutaraldehyde（GA）crosslinking for heavy metal ion removing,and the influence law between different preparation conditions and membrane performance is mainly studied.The specific work is as follows:（1）Lignin is the second most abundant and low-cost natural polymer,but its high value-added utilization is still lack of effective and economic ways.In this paper,LS was introduced to fabricate antifouling membrane surfaces via layer-by-layer self-assembly with PEI.The LS/PEI multilayers were successfully deposited on the PSf membrane,as demonstrated by ATR-FTIR,XPS,Zeta potential measurements,AFM,and SEM.Meanwhile,the effect of the number of bilayers was investigated in detail on the composition,morphologies,hydrophilicity,and antifouling performance of the membrane surface.As a result,with the bilayer numbers increase to 5,the PSf membrane shows smooth surface with small roughness,and its water contact angle reduces to 44.1°,indicating the improved hydrophilicity.Accordingly,the modified PSf membrane with 5 LS/PEI bilayers repels the adsorption of protein,resulting in good antifouling performance.This work provides a green,facile,and low-cost strategy to construct antifouling membrane surfaces.（2）A novel NF membrane was prepared by LbL assembly of PEI and LS followed by cross-linking.The surface composition,morphology and property of PEI/LS bilayer were detailedly investigated by FTIR/ATR,XPS,SEM,AFM,and water contact angle test.Moreover,the NF performance of PEI/LS LbL assembly membranes can be modulated by bilayer number,polyelectrolyte concentration and salt content.The water flux reduced while the salt rejection greatly improved as increasing the bilayer numbers,PEI concentration,or Na Cl content.More than 95%Mg SO₄and Mg Cl₂,as well as 80%Na Cl can be rejected by a NF membrane prepared by 6 PEI/LS bilayers,1 wt%PEI,0.5 wt%LS and 1 M Na Cl.Furthermore,this NF membrane can be used to remove more than 95%heavy metal ions(Cd²⁺,Zn²⁺,Mn²⁺,Cr²⁺,Cu²⁺and Ni²⁺).This work proposed a promising NF membrane by using PEI/LS as low cost polyelectrolytes and facile LbL assembly method,which should receive much attention in water purification.