| With the continuous development of membrane technology in the industrial and academic fields,it has become a cost-effective method of sewage treatment due to its low energy consumption,high separation efficiency and relatively simple process.But under normal circumstances,most of the membranes are hydrophobic.During the filtration process,problems such as low flux,high required transmembrane pressure,easy contamination,and low service life will be encountered.Hydrophilic modification of membranes is an effective way to solve the above problems.Polyvinylidene fluoride(PVDF)membrane has the advantages of high chemical stability,good acid and alkali resistance,and good toughness,so it is widely used.In this study,poly(styrene-co-maleic anhydride)(PSMA)and poly(glycidyl methacrylate-co-poly(ethylene glycol)methyl ether methacrylate)(P1)were used to react with Polyethyleneimine(PEI)through the coating method to make the PVDF membrane hydrophilic,respectively.The cross-linking reaction between PSMA、P1and PEI made the coating more stable,PEI endowed PVDF membrane with superhydrophilic,underwater superoleophobic and other properties.Firstly,PSMA and PEI were used to coat the PVDF membrane by dip coating strategy to improve its hydrophilicity.The same modification method was used to modify cotton fabric,nylon mesh and stainless steel mesh as a control.PSMA was dip-coated first,and then PEI was dip-coated to produce a cross-linked polymer coating.The coating process could be completed within 30 minutes.Through scanning electron microscopy(SEM),attenuated total reflection flourier transformed infrared spectroscopy(ATR-FTIR)and X-ray photoelectron spectroscopy(XPS)characterization,the successful coating of the cross-linked copolymer on the surface of the membrane was verified.All of the modified membranes had superhydrophilic,underwater superoleophobic and dynamic underwater anti-oil performance.Water droplets could spread immediately on the surface of the modified membranes.The underwater oil contact angle on the surface of all modified membranes was greater than 155°,which is significantly changed compared with the pristine membranes.All modified membranes could realize the separation of oil/water mixture,and the separation efficiency was above 99.0%;the modified PVDF membrane had the best performance in oil/water emulsion separation due to its small pore size,and the separation efficiency was up to 98.5%.The modified PVDF membrane can also withstand acid and alkali soaking and long-term repeatedfiltration.Secondly,in order to make the coating modification process safer and more environmentally friendly,the water-soluble polymer P1 and PEI were sprayed alternately on the PVDF membranes by spraying method to obtain a stable cross-linked coating multifunctional PVDF membrane.SEM,ATR-FTIR and XPS characterizations verified that the polymers were successfully cross-linking coated on the surface of the membranes.For the separation of oil-water mixtures,the coated membrane exhibited an oil removal rate exceeding 99.0%,and the separation efficiency for oil/water emulsions exceeded 98.0%.After filtering BSA and washing with water,the flux recovery rate(FRR)of the coated membrane could reach 96.7%.The adsorption and removal efficiency of the coated membrane M3(P1 and PEI were sprayed three times respectively)for congo red(CR),methyl orange(MO),methylene blue(MB)and crystal violet(CV),Pb(Ⅱ),Cu(Ⅱ)and Cd(Ⅱ)were 82.4 %,83.9%,6.3%,26.8%,90.6%,91.3% and 86.2%,respectively.Therefore,it could be used to remove anionic dyes and heavy metal ions in wastewater.The antibacterial properties of the coated membrane were also confirmed by the inhibition zone test and confocal laser scanning microscope(CLSM)analysis.In addition,the cross-linking reaction between polymers also made the coated membranes excellent in durability and reusability.Most importantly,the modification method only used water as a solvent,which ensures the safety and environmental protection of the coating modification process. |
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