| Polyamide thin-film composite reverse osmosis membrane has been sucessfully used in the fields such as concentration of industrial fliuds,treatment of wastewater and desalination of seawater for its high rejection and low energy consumption.However,membrane fouling and performance degradation are the key technical issues that limit the extensive application of polyamide reverse osmosis membranes.Therefore,it is of great theoretical and practical significance to improve the anti-fouling polyamide reverse osmosis membrane and to restore separation performance of the degraded membrane.In this study,the carboxyl groups on the surface of polyamide reverse osmosis membrane were activated by EDC\s-NHS,and three monomers containing amino group such as sulfamic acid,diethanolamine and piperazine were grafted in-situ onto the surface of polyamide composite reverse osmosis membrane through amidation to tune membrane surface physico-chemical property and thus improve the antifouling properties of the membrane on specific pollutant.Sericin molecules were also grafted in-situ onto the surface of the degraded polyamide membrane for performance restoration by investigatng the effects of factors including activator concentration,EDC\s-NHS ratio,the reaction pH and sericin concentration.Membrane surface chemical structure,morphology,charge and hydrophilicity were investigated by Fourier transform infrared spectroscopy?ATR-FTIR?,atomic force microscopy?AFM?,surface zeta potential and static water contact angle.Membrane reverse osmosis performance and antifouling property were evaluated through cross-flow permeation tests.The conslusions obtained are as follows:?1?Monomers containing amino group inclouding diethanolamine,sulfamic acid and piperazine could be grafted onto the surface of the polyamide reverse osmosis membranes through the activation of the carboxyl groups on membrane surface of by EDC\s-NHS.The in-situ grafting of monomer could effectively tune membrane surface charge and hydrophilicity and thus enhance membrane antifouling property,while had no influence on membrane permeaability and selectivity.?2?The grafting of aminosulfonic acid could enhance membrane surface hydrophilicity and negative charge.The zeta potential at neutral pH increased from-46.82 mV to-55.49 mV?pH=7?and the contact angle decreased from 36.1°to 27.6°.Compared with the virgin membrane,the fouling resistance to bovine serum albumin of the modified membrane was significantly improved,showing a decrease of flux recovery ratio from 87.7%to 94.6%.Surface grafting of diethanolamine resulted in an enhanced surface hydrophilicity and a decreased surface negative charge.After modification,membrane surface water contact angle and zeta potential at neutral pH decreased to-29.53 mV and 21.9°,respectively,and the membrane fouling resistance to sodium alginate was significantly improved,showing a sharp increase of flux recovery ratio from 87.8%to 99.4%.The grafting of piperazine had no effect on membrane surface hydrophilicity but led to a decrease of surface negative charge from-46.82 mV to-16.49mV at neutral pH.The modified membrane exhibited an ehnaced anti-fouling property to both sodium alginate and dodecyl trimethyl ammonium bromide and a weakened fouling resistance to bovine serum protein.?3?The treatment of partially degraded polyamide composite reverse osmosis membrane with EDC\s-NHS could restore membrane salt rejection 93.5%to 95.0%.The peak area ratio of 1660cm-1 to 1490cm-1 in ATR-FTIR spectrum increased by 10%after treatment,indicating that EDC\s-NHS could activate the carboxyl groups on the membrane surface and react with amino groups on the membrane to form amide bonds.On the other hand,compared with sericin coatted membrane,the increasement of the peak area ratio of 1660cm-1 to 1490cm-1 could be futher increased by 15%through the treatment of EDC\s-NHS followed by sericin aqueous solution,corresponding to a futher increase of salt rejection to 97.0%.The results revealed that EDC\s-NHS could simultaneously activate the carboxyl groups of the membrane to react with the amino groups of sericin molecules through amidation reaction.Long-term running experiments showed that the restored membrane possessed good performance stability. |
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