| Polyamide thin film composite membrane has been widely applied in fields of desalination, pharmacy, biochemical fabrication and so on, since it possesses high flux and ion rejection. However, the sensitivity of polyamide membrane to active chlorine remains a remarkable issue. To solve this problem, considerable researches attempted to improve the membrane’s chlorine-resistance through tailoring chemical structure or grafting and coating methods. In spite of some progress ever made, there still exist mainly two drawbacks in previous work. Firstly, modified membranes are always accompanied by deterioration in separation performance. Secondly, most chlorine-resistance improvements are irreversible process which can’t be regenerated after a long-term operation, so their protective fuctions are questionable in practice. Aimed to settle above two issues, this doctoral thesis tried to modify polyamide membranes through three pathways including glycylglycine-grafting, formaldehyde-reducing followed by glutaraldehyde-crosslinking, and nano-polypyrrole incorporation. By utilizing those modification, we promoted the chlorine-resistance on the premise of excellent separation performance, even, the modified membranes can be recovered to originally intact state after chlorine-attaching by some special treatment. That’s to say, a renewable anti-chlorine ability was granted. In the last part, one kind of high-flux polyamide membrane catalyzed by compound acid-acceptor was fabricated and graft-modified by glycylglycine subsequently, which helped us successful to obtain polyamide reverse osmosis membrane with both good separation performance and chlorine-resistance. This thesis mainly cover these four parts:(1) Surface modification by glycylglycine-grafting to supply polyamide membrane with renewable chlorine-resistance:Acylation reaction was catalyzed by EDC/NHS solution between amines of glycylglycine and carboxy groups of polyamide surface, results showed that the graft reduced flux but improved chlorine-resistance evitably, which was limited; Comparison were made on separation performance, chlorine content and zeta potential of surface before and after chlorination and reduction treatment during a "acidic chlorination-basic reduction" treatment to modified membrane. Results showed that the deteriorated performance caused by chlorination can be recoved by subsequent basic reduction, which was verified stem from the grafted glycylglycine with reversible chlorination ability. Moreover, zeta potential parameter was discovered to vary among with glycylglycine chlorination process, which may be used to monitor chlorine-substitution progress.(2) Surface modification by formaldehyde-reducing and following glutaraldehyde-crosslinking to improve chlorine-resistance while maintaining performance:Reduction by formaldehyde/phosphoric acid solution can help to remove chlorine-sensitive amide N-H points and then generate hydroxymethyl groups. Following crosslink reaction by glutaraldehyde created ether linkages between polyamide chains. Results showed that the ion rejection decreased after reduction but recovered by crosslink reaction. Ultimately, chlorine-resistance was reinforced notably; Comparison were made on surface hydrophilicity, functional groups and morphology before and after the modification process. Results showed that modification helped to make membrane more hydrophilic. Besides, the deterioration of H bonds caused by reduction and the formation of ether bonds caused by crosslinking reaction were both justified.(3) Nano-polypyrrole incorporation into polyamide layer to generate renewable chlorine-resistance:Polypyrrole nanoparticles were prepared in a chemical oxidation method and then scattered into organic phase during interfacial polymerization. Results showed that obtained nanoparticles was in a diameter close to that of polyamide layer. While those nanoparticles were incorporated into selective layers, its chlorine-resistance was promoted successfully; "NaCIO chlorination-Na2S3O3 reduction" cyclic treatement was used to this modified membrane and chlorine content was quantified. Results showed that the chlorine-resistance of modified membrane can be recovered by Na2S3O3.(4) A new acid acceptor consisting of crown ether (18-crown-6)/KOH was utilized to catalyze interfacial polymerization reaction for polyamide reverse osmosis membrane fabrication. The 18-crown-6 will form a complex compound with KOH, then facilitating KOH to diffuse from aqueous to organic phase. So KOH can work more efficiently to catalyze the polymerization. Afterwards, glycylglycine-grafting was used to treat this kind of membrane. Results showed that membrane’s chlorine-resistance improvement was more effective that bare membrane case, since acid acceptor can help to generate more carboxy groups on surface for graft reaction and so more glycylglycine molecules can be loaded onto membrane. |
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