| Exacerbated by accelerated urbanization,industrialization and rapid population growth,water contamination and scarcity have evolved to be of critical global concerns.Due to the numerous advantages of reliable selectivity,ease of use,wide application range and compactness,membrane-based separation technologies work as the most in-demand means for seawater desalination and water purification.Of all the existing membrane technologies,thin-film composite polyamide?TFC PA?membrane is the state-of-the-art applications for the nanofiltration?NF?,reverse osmosis?RO?,and forward osmosis?FO?processes,offering strong mechanical integrity,steady water permeability and superior salt rejection.However,membrane fouling and chlorination susceptibility are two main problems that restrict the further development of TFC membrane.Therefore,it is of upmost interest to develop chlorine-resistant and improved antifouling TFC polyamide membranes for the economical and sustainable operation of desalination process.Herein,the TFC PA membrane was modified via a simple layer-by-layer interface polymerization method?LBL-IP?,and thus a zwitterions-containing polyamide membrane,so-called QDAP modified membrane,was successfully prepared.Chlorine resistance and antifouling performances of the modified TFC PA membrane were examined in the RO and FO processes.?1?In situ surface modification of thin-film composite polyamide membrane with zwitterions for the enhanced chlorine-resistance and transport properties2,6-diaminopyridine?2,6-DAP?was used to in-situ modify the polyamide selective layer of TFC membrane via layer-by-layer interfacial polymerization?LBL-IP?,followed by its quaternization with 3-bromopropionic acid?3-BPA?.The impacts of such modification with 2,6-DAP and 3-BPA on the PA surface properties including hydrophilicity,roughness and zeta potential were investigated.The mass transport properties were also evaluated in both of the cross-flow RO and FO processes.The modified TFC membrane was found to achieve an improved water permeability with enhanced perm-selectivity.The QDAP modified membrane was also demonstrated to exhibit an excellent chlorine resistance of 16,000 ppm·h,remarkably higher than2,000?12,000 ppm·h for the previously reported TFC polyamide membranes in literature.Chlorination-resistant mechanism was explained by the formation of zwitterions on the TFC PA membranes,and prevention of the chlorine-attack and the Orton rearrangement of benzene ring of the PA layer.The A/B ratio of the chlorinated QDAP membrane was measured in the RO process to be 21.86 bar-1?A,4.81±0.17LMH/bar and B,0.22±0.06 LMH?.This value is significantly higher than the reported values(2.32-13.75 bar-1)in literature.In general,our optimal QDAP membranes exhibited better performances than the conventional PA ones,and thus could serve as a promising alternative for the later industrial applications.?2?Optimization and organic fouling behavior of zwitterion-modified thin-film composite polyamide membrane for water reclamation:A comprehensive studyThe organic antifouling performance of the QDAP modified membranes was comprehensively evaluated during the reverse osmosis process.The model surfactants and proteins with either positive or negative charges were of use to evaluate the organic fouling behavior of the membrane.Main findings are the following including:?1?not only did the QDAP-grafted membrane show clearly less flux decline,the flux recovery thereof was also much more improved than the unmodified membrane irrespective of the considered foulant types;?2?for different foulants,Dodecyl Trimethyl Ammonium Chloride?DTAC?posed the worst fouling potential due to its low molecular weight and positive charge,when DTAC was added as a model foulant into the feed solution;?3?the use of quartz crystal microbalance with dissipation?QCM-D?was capable of interpreting the fouling mechanism of different organic foulants on the polyamide surface by providing the detailed information of foulant layer including the foulant adsorption rate,adsorbed mass amount and the structural information.The adsorption rate of foulants by QDAP modified membrane is slow,and the foulants formed on the modified membrane surface are softer and looser,which are easy to be washed off through physical cleaning,thus improving the antifouling performance of TFC PA membrane.To conclude,the TFC PA membrane was modified via layer-by-layer interfacial polymerization method.The recently developed zwitterions-containing QDAP modified membrane consistently perform an improvement of chlorine resistance,antifouling potential and permeability without compromising salt rejection and membrane integrity.As such,this work provides a facile surface-engineering approach to fabricate the antifouling and chlorine-resistant TFC polyamide membranes. |
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