| As one of the emerging technologies for water treatment,reverse osmosis（RO）can reject most ions in the feed water,producing the permeate water with exceptionally high quality.At present,the commercial RO membrane is fabricated and assembled based on a polyamide chemical structure.However,such a chemical composition is extremely vulnerable to the attack of disinfection reagents,which were critically needed to inhibit the growth of microorganisms.To address this issue,we report the molecular design,fabrication,and application of new membrane materials with chlorine resistance.Details are presented as follows:（1）A new sulfonated diamine monomer,4,4’-（（1,4-phenylenebis（methylene））bis（azan ediyl））dibenzenesulfonic acid（PMABSA）was synthesized and used as the sole aqueou s reactant to fabricate a novel reverse osmosis（RO）membrane with trimesoyl chloride（TMC）,in place of conventional m-phenylene diamine（MPD）.The separation perfor mance of the PMABSA/TMC membrane was optimized by the response surface metho d（RSM）by means of evaluating the pure water permeability（PWP）and salt rejection（R）to Na Cl,and optimal results of PWP of 1.18±0.03 L m-2h-1bar-1,and R of 98.2±0.4%,respectively,were achieved at 1.55 MPa.Owing to the rigid benzene ring in the center of the molecule,which may have a blocking effect during the interfacia l polymerization（IP）process,the resulting barrier layer was less compact and had lo w thickness.Both molecular dynamics（MD）simulation and positron annihilation spect roscopy（PAS）revealed the creation of sufficient free volumes in the sulfonated polya mide matrix.Regardless of the slightly lower water permeation,the PMABSA/TMC m embrane exhibited a superior rejection ability to all the ions compared to that of com mercial SW30HR（Dow Chemical）in a model seawater separating test.Overall,all the results indicated the great potential of the novel membrane as a new choice of non-MPD RO membrane for seawater desalination.（2）Anewsulfonateddiaminemonomer,namely3,3’-（ethane-1,2-diylbis（azanediyl））bis（2,6-dimethylbenzenesulfonic acid）（EDADMBSA）,was designed and synthesized in order to fabricate a novel thin-film composite（TFC）reverse osmosis（RO）membrane by using the interfacial polymerization（IP）technique with trimesoyl chloride（TMC）.In particular,EDADMBSA was employed as the sole reactant in the aqueous phase during the IP process,instead of the conventional m-phenylene diamine（MPD）.Due to the presence of two methyl groups next to a phenylamino group that could exert a strong steric hindrance influence,the rotation of the polyamide main chain was significantly enforced,as clearly illustrated by a molecular dynamics simulation.In this manner,sufficient free volumes were generated in the polymer matrix,allowing for a lower water penetration resistance.The optimal pure water permeability（PWP）attained with this EDADMBSA/TMC membrane was as high as 1.9±0.2 L m-2h-1bar-1,which is 2.6-2.7 times greater than that of a self-made MPD/TMC membrane under the same test conditions.Furthermore,the unique methyl substituents could also serve as void occupiers,allowing the TFC membrane to retain a reasonably high water-solute selectivity.Compared to commercial BW30FR（Dow Chemical）,the novel membrane displayed a superior ability to reject all the ions in a simulated desalination test,revealing its promising potential as a separation medium for brackish water desalination.（3）Polyamide reverse osmosis（RO）membranes suffer performance decay when exposed to free chlorine because of their unique chemical structure.The decay limits their lifespan and increases operating cost.In this study,the secondary interfacial polymerization（SIP）method was performed,for the first time,using isophthaloyl chloride（IPC）as the chain-terminating reagent,to eliminate the negative effect when the unreacted amino groups interact with chlorine.The surface Zeta potential of the as-prepared membrane remained almost constant over a wide p H range,which greatly demonstrated the high conversion ratio of the end-capping procedure.However,neither the surface morphology nor the separation properties,i.e.,pure water permeability and salt rejection,were conspicuously influenced.Because of the absence of the terminated amino groups in the polyamide layer,the IPC-modified membrane exhibited significantly improved chlorine resistance,particularly at high p H.Its desalination performance remained unchanged as the total chlorine exposure approached 10,000 ppm·h,whereas only 80.3%of the Na Cl was rejected by the unmodified membrane under the same conditions.The chlorine resistance of both types of membrane declined as the solution p H decreased to neutral or acidic;however,the chlorine resistance of the membrane treated with IPC generally declined more slowly than that of the membrane without IPC treatment.Such SIP technology can be applied directly to the commercial SW30seawater desalination membrane,making it more tolerant to free chlorine.Overall,our results strongly proved the IPC-assisted end-capping process as a promising,practicable,and scalable technology for enhancing the chlorine resistance of an RO membrane.（4）Chlorination is a common practice to prevent biofouling in municipal water supply,wastewater reuse,and seawater desalination.However,polyamide thin-film composite reverse osmosis（RO）membranes the premier technology for desalination and clean water production structurally deteriorate when continually exposed to chlorine species.Here,we use layer-by-layer interfacial polymerization of 3,5-dihydroxybenzoic acid with trimesoyl chloride to fabricate a polyester thin-film composite RO membrane that is chlorine-resistant in neutral and acidic conditions.Strong steric hindrance and an electron-withdrawing group effectively prevented direct aromatic chlorination,and residual-OH groups were capped with isophthaloyl dichloride to preclude reaction with active chlorine.The poly（isophthalester）membrane exhibited high salt rejection（99.1±0.2%）and water permeability(2.97±0.13 L m-2h-1bar-1),even after demonstrating biofouling prevention with chlorine(50 mg L-1of Na OCl for 15 minutes).We anticipate our chlorine-resistant membrane to significantly advance reverse osmosis desalination as a sustainable technology to meet the global challenge for water supply.In summary,our progress in chlorine-resistant polyester RO membranes may improve the reliability of RO technology,promote structural reform of the processing flow,and reduce the cost of desalination and waste water reuse.However,this work is certainly not finished and will require close collaboration between academia and industry to scale-up and commercialize the technology. |
PDF Full Text Request