The Study Of Performance And Preparation Of Pan-based Loose Nano-filtration Membrane

In China,the direct discharge of 2.37 billion tons of printing and dyeing wastewater annually seriously threatens the ecological environment and human health.There are not only macromolecule organic compounds?dyes,slurries,oils and fibers?,but also a large number of inorganic salts?Na₂CO₃,Na₂SO₄ and NaCl?in the wastewater.Divalent inorganic salts?Na₂CO₃ and Na₂SO₄?and dye molecules?commonly reactive red and congo red?are highly rejected?R>90%?in traditional commercial nanofiltration?NF?membrane treatment,which not only reduces the quality of rejected dyes,but also increases the difficulty of recovery of dyes and inorganic salts.Therefore,this paper is aimed to preparing loose NF membranes for the separation of dyes and electrolytes.The details are as following:?1?A novel free radical graft copolymerization route was used to prepare the catechin?CA?–grafted?CS?chitosan loose NF membrane for the separation of dye–salt mixture.Using vitamin C and hydrogen peroxide as initiator,CA,the eco-friendly natural material,was grafted onto CS through the free radical reaction and self-cross-linking.Then,the conjugate were deposited on HPAN substrate by electrostatic interaction.FT–IR,XPS,SEM,AFM and electrokinetic analyzer were used to observe the microstructure and element composition of the membrane.The results showed that the loose NF membrane displayed the 98.5%rejection for crystal violet with the permeate flux of 72 L m^-22 h^-11 MPa^-1 and inorganic salts rejection was as following:R_{Na2 SO4}?4.8%?<R_NaCl?12.5%?<RMgSO4?15.8%?<RMgC l2?16.2%??Meanwhile,the membrane showed stable separation performance during the 60 h filtration experiment.In addition,a high removal rate of 82%for NaCl with a dye loss rate of 10%was also observed in the constant-volume dye purification process.?2?A novel chelation–assisted in situ self-assembly strategy was applied to assemble the loose vitamin E succinate?VES?/AgCl–polyethyleneimine?PEI?NF membrane.Using this route,the Ag⁺–PEI chelate complex layer on the HPAN substrate was served as the templates to synthesize the VES-functionalized-AgCl nanoparticle.The generated nanoparticles grew into the polymer in situ and possessed a uniform distribution in the selective layer,which improved the membrane flux by about 50%.The loose NF membrane prepared at optimum conditions possessed the crystal violet rejection of 99.2%with the flux of 106.5 L m^-2 h^-11 MPa^-11 and inorganic salts rejection was as following:RMg Cl2?6.2%?<RNaCl?8.3%?<RMgSO4?9.6%?<RNa2 SO4?12.8%?.Meanwhile,the membrane had excellent dye desalination ability under different feed concentration,feed pH and operating pressure.In addition,low Ag⁺release rate?2.84%?and 60 h filtration experiment showed that the membrane had good stability.