Research On Antifouling Modification And Properties Of Nanofiltration Membrane Based On The Sulfonamide Monomer

Nanofiltration membranes possess the unique advantages of high separation accuracy,environmental protection and low energy consumption,which are mainly used in wastewater treatment,seawater desalination and drinking water preparation.In practical application,nanofiltration membranes usually face the challenges such as membrane contamination and chlorination degradation,which lead to decreased separation performance,shortened service life and increased operating costs.In order to solve the problem that nanofiltration membranes are vulnerable to pollution and chlorination degradation,this study developed a modified nanofiltration membrane with excellent pollution resistance and chlorine resistance by using two-step surface modification method.Specific research contents are as follows:（1）The hydrophilic polytetrafluoroethylene（PTFE）microporous membrane was used as the experimental substrate.The MPD/TMC pristine membrane was prepared by interfacial polymerization of m-phenylenediamine（MPD）aqueous solution and tribenzoyl chloride（TMC）organic solution.2-Aminophenol-4-sulfonamide（APSA）was added to the aqueous solution to obtain APSA modified nanofiltration membrane,and the optimum preparation conditions were determined by anti-contamination test of the bovine albumin（BSA）.Fourier infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,Zeta potential and water contact Angle were employed to characterize the chemical composition,surface morphology,electrical properties and hydrophilicity of the modified nanofiltration membrane surface.The separation performance,antifouing resistance and chlorine resistance of the modified nanofiltration membrane were tested and analyzed by the cross flow device.FTIR spectra showed that S-O and S-N characteristic absorption peaks appeared in the APSA modified nanofiltration membrane,which proved that APSA monomer was successfully introduced into the modified nanofiltration membrane.SEM images indicated that the separation layer of the modified nanofiltration membrane surface was denser and showd a smaller"nodular"structure.Zeta potential results testified that the modified nanofiltration membrane surface had lower negative charge at p H=7.The water contact angle of the modified nanofiltration membrane was only 19.7°,while the MPD/TMC membrane reached 43.3°,indicating that the modified nanofiltration membrane was more hydrophilic.The separation performance of the modified nanofiltration membrane was tested and analyzed by the cross-flow device.The molecular weight cut-off（MWCO）of the APSA modified nanofiltration membrane was 642 Da,and the rejection rates of magnesium sulphate（Mg SO₄）and sodium sulphate（Na₂SO₄）reached 96.0%.The antifouling performance test showed that the flux recovery rates（FRR）of the modified nanofiltration membrane for BSA and humic acid（HA）were 96.4%and96.8%,which were significantly higher than those of the MPD/TMC membrane（83.5%and 78.8%）.The chlorine resistance of the two membranes was tested.By comparing the results before and after chlorination,the separation and antifouling performance of the modified nanofiltration membrane after chlorination were significantly higher than that of the pristine membrane,and the decline rate was also lower than that of the pristine membrane.The above test results showed that the modified nanofiltration membrane has excellent separation,antifouling and chlorine resistance.（2）In order to further improve the antifouling performance of nanofiltration membrane,APSA modified nanofiltration membrane was used as the experimental base membrane.Polyvinyl alcohol（PVA）polymer was grafted onto the surface of APSA modified nanofiltration membrane with glutaraldehyde（GA）crosslinking agent to obtain APSA-GA-PVA modified nanofiltration membrane,and the optimal preparation conditions were discussed.It could be known from FTIR analysis:APSA-GA-PVA modified nanofiltration membrane certified the aldehyde group（-CHO）and the ester group（O=C-O）new characteristic absorption peaks,indicating that GA and PVA were successfully grafted onto the modified nanofiltration membrane surface.APSA-GA-PVA modified nanofiltration membrane presented a"spider"structure and the surface was more flat by SEM images.Zeta potential analysis indicated that the surface of APSA-GA-PVA modified nanofiltration membrane possessed a lower negative charge at p H=7.The water contact angle value of APSA-GA-PVA modified nanofiltration membrane was14.8°,which was lower than 19.7°of APSA modified nanofiltration membrane,demonstrating that the modified nanofiltration membrane was more hydrophilic.The separation performance test of APSA-GA-PVA modified nanofiltration membrane:MWCO was 571 Da,and the water flux and rejection rate of Mg SO₄ was up to 98.6%,showing better separation performance.The test results of antifouling performance exhibited that the FRR of APSA-GA-PVA modified nanofiltration membrane for BSA and HA were 98.5%and 98.7%,which were higher than that of APSA modified nanofiltration membrane.In addition,In order to explore the effect of APSA-GA-PVA modified nanofiltration membrane on pollutant,three cyclic pollution experiments were conducted.The test results showed that the FRR value of the modified nanofiltration membrane for BSA was up to 94.7%,indicating that the modified nanofiltration membrane grafted with PVA had better antifouling ability.