Modification And Separation Performance Of Polyethersulfone Composite Membrane

Dyestuffs have gradually penetrated into various industries such as textiles,beverages,cosmetics,food and daily necessities.In the dye synthesis process,due to the immature dye processing technology,a large part of the dye liquor is discharged into the environment.Most dye molecules have an aromatic molecular structure,which is a complex,highly stable,and difficult-to-degrade material.The discharge of these harmful substances into the environment can cause harm to organisms.Since inorganic salts（mainly sodium chloride（NaCl）and sodium sulfate（Na₂SO₄））are used in dye synthesis to purify dye products by salting out and rinsing,salt-containing dye wastewater is inevitably produced.The adsorption method has a good removal efficiency for most pollutants in wastewater,but the adsorbent is difficult to regenerate,and the adsorption performance will decrease after regeneration.The membrane separation technology can effectively remove dyes in wastewater.Due to good selectivity,membrane separation technology has been increasingly used in the textile and printing and dyeing industries for wastewater treatment.In this paper,the hydrophilic additive polyvinylpyrrolidone（PVP）of different concentrations（1～16wt%）was mixed into the polyethersulfone（PES）membrane by the method of non-solvent induced phase separation.Then,polydopamine（PDA）modification was performed on the surface of the prepared membrane.By optimizing the conditions of preparation,PDA-modified ultrafiltration membrane with the best hydrophilicity was prepared.In addition,a detailed comparison of the different PVP content（PES membrane）and the shape of the membrane modified with PDA（PDA/PES membrane）on the surface were carried out,such as appearance,structure,surface hydrophilicity,permeation flux,bovine serum albumin（BSA）rejection rate,dye rejection rate,anti-fouling performance and stability.It is found that PDA/PES membrane has excellent performance and finger-like pore structure.When the PVP content reaches 10wt%,the contact angle of the PDA-modified membrane（PES-10-PDA）is the smallest,indicating that the membrane has the highest hydrophilicity.Through the retention experiment of BSA solution,it is found that the retention rate of PES-10-PDA membrane can reach more than 70%.In addition,the modification of PDA significantly improves the stain resistance of the film.When the PVP content reached 10wt%,the flux recovery rate of the modified membrane reached 91.23%.The stability test results show that the flux of the PDA/PES membrane is basically unchanged after being immersed in a certain concentration of acid-base solution for 15 days.It shows that the PDA modified membrane has good chemical stability.This simple manufacturing process and excellent performance show that the modified membrane has the potential to deal with fouling.Based on the preparation of the PES membrane in the previous step,nanofiltration membrane effectively removed dyes from wastewater is prepared.First,the PES membrane is further modified.The styrene-maleic anhydride（SMA）,PES,and PVP were mixed to prepare more hydrophilic base membrane.On the basis of PDA modifying base membrane,titanium dioxide（TiO₂）and polyethyleneimine（PEI）are co-deposited on the surface of the membrane to obtain new composite membrane（TiO₂/PEI/PDA-SMA/PES）with excellent dye/salt separation performance.SEM,AFM,FTIR,zata potential and contact angle were used to characterize the prepared membrane.In addition,the influence of TiO₂ content on membrane permeability and rejection is also discussed.The results showed that when the addition amount of TiO₂ was 10 g·L^-1,the hydrophilicity of the membrane reached the highest.Compared with PES pure membrane,TiO₂-2/PEI/PDA-SMA/PES membrane(73.2 L·m^-2·h^-1·bar^-1)has high water permeability and high dye rejection rate（Congo Red,Rhodamine B and Crystal Violet are respectively 98.6%,92.3%and 90.4%）and satisfactory salt permeability(Na₂SO₄,NaCl,Mg₂SO₄ and MgCl₂ respectively 39.5,36.4,30.6 and 29.4 L·m^-2·h^-1·bar^-1),the surface of the membrane shows a typical positively charged feature.At the same time,even when the salt concentration is as high as 60 g·L^-1,the membrane can still maintain high dye/salt separation performance(90.08%dye rejection rate,17.4 L·m^-2·h^-1·bar^-1 permeability of the salt solution).In addition,the TiO₂-2/PEI/PDA-SMA/PES membrane showed high stability in the 30-hour flux test.In addition,TiO₂ nanoparticles modified by N-[3-（trimethoxysilyl）propyl]ethanedi（AAPTS）were synthesized,and the ammoniated TiO₂ nanoparticles were mixed into m-phenylenediamine.Then,the polyamide thin film nanocomposite（TFN）membrane was prepared by interfacial polymerization with trimellityl chloride on the PES base membrane.By analysis of ATIR,SEM,AFM and Zeta potential,the chemical structure,surface morphology,roughness and electrode potential of TFN membrane of ammoniated TiO₂ at different concentrations were tested.The results show that compared with polyamide membrane（TFC membrane）,the water flux of the membrane containing 0.6wt%TFN is 78.9L·m^-2·h^-1·bar^-1.At the same time,the membrane has high dye rejection（for example,95%for Congo red,98%for reactive black,and 97%for methyl blue）and low salt rejection（for example,16.9%for Na₂SO₄）.The rejection rate of methyl blue/Na₂SO₄ mixture is similar to that of dye or salt solution（the rejection rate of methyl blue is more than 96.0%,and the rejection rate of Na₂SO₄is less than 15%）.In addition,the membrane exhibits ideal stability,and the flux value does not change significantly during 15 hours of filtration.