Construction Of Sodium Ligninsulfonate Based Composite Nanofiltration Membrane And Separation For Anionic Dye Solution

The production of anionic dye water is huge,since anionic dyes have many kinds and wide applications.The separation by conventional methods can not meet the discharge standard because of the small molecular weight and difficult separation of anionic dyes,which leads to serious water pollution and endangers human health.Membrane separation technology has a high potential in the purification of dye water,which can be attributed to its advantages of green,high purity separation,high separation efficiency and no secondary pollution.The composite nanofiltration membrane has excellent retention performance for substances with molecular weight of 200-1000Da,and its thin functional layer is helpful to the rapid passage of water molecules.Therefore,the composite nanofiltration membrane has great development prospects in the separation of dye water.However,the membrane fouling and the intrinsic trade-off between permeance and retention rate of the polymer based composite nanofilms usually lead to the decline of membrane separation performance.In this work,started from the design of materials and based on Donnan exclusion theory,sodium lignosulfonate based composite nanofilms with excellent anionic dyes removal performance were constructed by interfacial polymerization method.Meanwhile,the separation mechanisms of the fabricated composite nanofilms were discussed through the separation test of dye solutions.This work may provide a new strategy for the construction of novel composite nanofilms.Based on Donnan exclusion theory,a new lignosulfonate/trimesoyl chloride（SLS/TMC）composite nanofiltration membrane was prepared by interfacial polymerization using green and renewable sodium lignosulfonate with a large number of sulfonic groups and phenol and alcohol hydroxyl groups in its molecular structure as the aqueous solute of interfacial polymerization.The sulfonic groups in ligninsulfonate endows the SLS/TMC composite nanofilm with highly negatively charged surface.The membrane shows highly negatively charged surface in the p H range of 3-10.The Zeta potential of the membrane surface is-88.5 m V at p H 8 and-58.1 m V at p H 3.Meanwhile,the surface roughness of the SLS/TMC composite nanofilm is low.Therefore,the rejection rates of the SLS/TMC composite nanofilm for rose bengal,methyl blue,and reactive brilliant blue were all above 99.5%,and it can maintain stable separation performance at different p H dye solutions separation.At the same time,the SLS/TMC composite nanofilm presented excellent anti-dye fouling performance,and the flux recovery rate was up to 99.1%.In order to improve the permeation flux of composite nanofiltration membrane,the lignosulfonate-cyclodextrin/trimesoyl chloride（SLS-CD/TMC）composite nanofilm was fabricated by addingβ-cyclodextrin（β-CD）to the aqueous solution of sodium lignosulfonate which was used for interfacial polymerization.The inner cavity structure ofβ-CD can provide a channel for water passing through,thereby reducing the permeation resistance of water.Meanwhile,the intrinsic hydrophilicity ofβ-CD enhanced the hydrophilicity of the SLS-CD/TMC composite nanofilm surface.The SLS also endowed the membrane with highly negatively charged surface in the p H range of 3-10.Therefore,the SLS-CD/TMC composite nanofilm can maintain a high dye rejection（>99.5%）while the permeance increased to 33.7 L m^–2h^–1bar^–1 in the separation of methyl and congo red solutions.Meanwhile,the SLS-CD/TMC composite nanofilm showed excellent anti-fouling performance in the process of anionic dye solution separation.In order to improve the anti-bacterial property and permeation flux of composite nanofiltration membrane,based on the reduction ability of SLS to Ag+and the stabilization ability of SLS to silver nanoparticles（Ag NPs）,lignosulfonate-silver nanoparticle/trimesoyl chloride（SLS-Ag NP/TMC）composite nanofilm with uniform distribution of Ag NPs in the active layer was fabricated by adding Ag NO3 to the SLS aqueous solution which was used for the interfacial polymerization.The Ag NPs can effectively reduce the permeation resistance of water by constructing water molecular channels at the interface,and the intrinsic hydrophilicity of Ag NPs reduced its initial water contact angle from 67.2°to 55.8°.In addition,the anti-bacterial property of Ag NPs endowed the SLS-Ag NP/TMC composite nanofilm with improved anti-bacterial property.The SLS also endowed the membrane with highly negatively charged surface in the p H range of 3-10.Therefore,the SLS-Ag NP/TMC composite nanofilm demonstrated a high permeance of 41.7 L m^–2h^–1bar^–1 with CR rejection rate of 99.8%for the separation of the CR solution.Meanwhile,the SLS-Ag NP/TMC composite nanofilm presented excellent anti-anionic dye fouling performance.