Preparation And Performance Study Of Chitosan/sodium Alginate Modified Polyamide Nanofiltration Membrane Based On Chitosan/alginate

With the development of society,the global water shortage has become very serious,and there is a huge demand for efficient water treatment technologies.However,commercial nanofiltration membranes currently available in the market are less effective in separating mono-and divalent ions and have low permeation performance.Therefore,the development of high permeation selective nanofiltration membranes has become a market demand and a trend for enterprise development.In this project,polyethersulfone（PES）was selected as the base membrane,and chitosan（CS）and sodium alginate（SA）were used as membrane materials to prepare three different composite membranes.PIP-CS/TMC composite nanofiltration membranes were prepared by interfacial polymerization with CS and piperazine（PIP）as the aqueous phase and homophthalic trichloride（TMC）as the organic phase;SA/PES composite nanofiltration membranes were prepared by coating-crosslinking method with SA as the casting solution and glutaraldehyde as the crosslinking agent;SA-coated PES membranes were used as the intermediate layer,on which CS+PIP as the aqueous phase and The SA/CS composite membrane with a three-layer composite structure was prepared by introducing an interlayer-assisted interfacial polymerization method using TMC as the organic phase to form a polyamide membrane on the SA/PES membrane.The composite membrane structure was characterized by ATR-FTIR,SEM,zeta potential meter and contact angle meter to investigate the relationship between the composite membrane structure and membrane separation performance,and the optimal membrane production parameters and desalination performance of the composite membrane were investigated by a laboratory staggered flow device,etc.The main results are as follows.（1）The best performance of PIP-CS/TMC composite membrane was achieved at CS concentration of 1 g/L,aqueous phase reaction time of 0.5 min,interfacial polymerization time of 0.5 min,and heat treatment temperature of 80°C.The pure water flux reached 48.2 L·m^-2·h^-1;the retention order of four inorganic salts was R（Na₂SO₄:83.22%）>R（Mg SO₄:64.67%）>R（Na Cl:21.04%）>R（Mg Cl₂:19.38%）;the selectivity of Na Cl/Na₂SO₄was 4.63;the retention rate of SO₄^2-was 91%;the retention rate of Cl^-was 5.3%;the separation coefficient of Cl^-/SO₄^2-was 10.05;the retention effect of BSA was very strong,and the retention rate was stable at 98%or more.The modified membrane has good permeation performance and strong retention effect on inorganic salts,which can achieve high efficiency desalination and good separation effect on mono/divalent ions.（2）The SA/PES composite nanofiltration membrane performed best at SA concentration of 2.5 wt%,glutaraldehyde concentration|0.9 wt%,cross-linking time of2h,and cross-linking temperature of 30°C.At this time,the pure water flux of the membrane was 7.8 L·m^-2·h^-1;the retention rate of Na₂SO₄was 84.41%;the retention order of the four inorganic salts was Na₂SO₄（84.41%）>Mg SO₄（47.71%）>Na Cl（30.12%）>Mg Cl₂（19.38%）,the retention rate of SO₄^2-was 84.16%;the retention rate of Cl^-was 9.09%;the separation coefficient of Cl^-/SO₄^2-was 5.74;the retention rate of BSA was 98.7%.At p H=7,the zeta potential of SA/PES composite membrane increased from-34.90 m V to-70.36 m V,and the composite membrane was negatively charged,which had good retention effect on divalent anion and could achieve high efficiency desalination.（3）The best performance of SA/CS composite membrane was achieved when the concentration of SA was 2.5 wt%and the concentration of CS was 1 g/L.The flux of pure water was 11.45 L·m^-2·h^-1,which was improved compared with that of SA/PES membrane;the retention order of four inorganic salts was Na₂SO₄（92.82%）>Mg SO₄（52.87%）>Na Cl（34.54%）)>Mg Cl₂（21.93%）,the retention rate of SO₄^2-was 90%;the retention rate of Cl^-was 6%;the separation coefficient of Cl^-/SO₄^2-was:9.08;and the retention rate of BSA was 93.5%,the retention rates of SA/CS composite membrane for Na₂SO₄,Na Cl,and Mg Cl₂were greater than those of PIP-CS/TMC composite membrane and SA/PES composite membranes.This indicates that the three-layer composite membrane prepared by coating method assisted interfacial polymerization is more dense than the composite membrane prepared by coating alone and interfacial polymerization alone,which improves the salt retention and has good separation of mono/divalent ions.The nanofiltration membranes prepared in this paper all have excellent salt retention as well as mono/divalent ion separation performance,which provides an idea for highly selective permeability nanofiltration membranes.