Preparation And Properties Of Layer-by-layer Self-assembled Composite Films Based On Chitosan/sodium Alginate

There are a large number of inorganic salts in dye recycling in dyeing wastewater,which affects the stability and purity of dyes.To solve this problem,in this study,hydrolyzed polyacrylonitrile（HPAN）was used as the base membrane,Chitosan（CS）with positive charge was used as polyelectrolyte cation,and sodium alginate（SA）with negative charge was used as polyelectrolyte anion,and calcium chloride（Ca Cl₂）was used as ionic crosslinking agent.The HPAN-（CS/SA）n composite membrane was prepared by alternately depositing cationic and anionic polyelectrolyte on the surface of HPAN membrane.Scanning electron microscopy（SEM）and energy dispersive spectroscopy（EDX）were used to observe the surface,cross-sectional morphology and element distribution content of the base membrane and HPAN-（CS/SA）_n membrane.The HPAN-（CS/SA）_n composite membrane was characterized by FTIR,contact angle,Zeta potential,atomic force microscope（AFM）,and the success of hydrolysis modification and layer-by-layer self-assembly process of PAN base membrane were verified.With the permeation flux and rejection rate of composite membrane as indexes,theeffects of assembly layers,polyelectrolyte concentration,cross-linking agent concentration,assembly method and base film material in LBL assembly process were investigated.and the optimal conditions were determined as follows:the assembly layers were 3 layers,the concentration of chitosan and sodium alginate was 0.3 wt%,and the concentration of calcium chloride was 2.5 wt%.Under these conditions,HPAN-（CS/SA）₃ composite membrane has good dye retention performance.Under the operating pressure of 0.1MPa,the rejection rate of the composite membrane for Congo red is over 99.00%,and the permeation flux is 54.84 L/m² h.secondly,the rejection rate for bovine serum albumin（BSA）is 98.00%and the flux recovery rate is 92.69%,which shows that the composite membrane is good anti-pollution performanceUsing Bright blue G250,Congo red and Direct black 38 as dye components and Na Cl、Na₂SO₄ as salt components of feed solution,dye desalination experiments were carried out using HPAN-（CS/SA）₃ membrane.The results show that the rejection rate of HPAN-（CS/SA）₃ membrane for three dyes is above 98.00%,the rejection rate for Na₂SO₄ is below 25.00%,and the rejection rate for Na Cl is below 14.00%,which realizes the separation of dye and salt in dye wastewater,indicating that the composite membrane has a good application prospect in dye desalination.