Crown ether interlayer-modulated polyamide membrane with nanoscale structures for efficient desalination

Nanoscale thin-film composite(TFC)polyamide membranes are highly desirable for desalination owing to their excellent separation performance.It is a permanent pursuit to further improve the water flux of membrane without deteriorating the salt rejection.Herein,we fabricated a high-performance polyamide membrane with nanoscale structures through introducing multifunctional crown ether interlayer on the porous substrate impregnated with m-phenylenediamine.The crown ether interlayer can reduce the diffusion of amine monomers to reaction interface influenced by its interaction with m-phenylenediamine and the spatial shielding effect,leading to a controlled interfacial polymerization(IP)reaction.Besides,crown ether with intrinsic cavity is also favorable to adjust the IP process and the microstructure of polyamide layer.Since the outer surface of the nanocavity is lipophilic,crown ether has good solvency with the organic phase,thus attracting more trimesoyl chloride molecules to the interlayer and promoting the IP reaction in the confined space.As a result,a nanoscale polyamide membrane with an ultrathin selective layer of around 50 nm is obtained.The optimal TFC polyamide membrane at crown ether concentration of 0.25 wt.%exhibits a water flux of 61.2 L·m^(−2)·h^(−1),which is 364%of the pristine TFC membrane,while maintaining a rejection of above 97%to NaCl.The development of the tailor-made nanoscale polyamide membrane via constructing multifunctional crown ether interlayer provides a straightforward route to fabricate competitive membranes for highly efficient desalination.

Surface Modification of Commercial Aromatic Polyamide Reverse Osmosis Membranes by Crosslinking Treatments

Crosslinking treatments for a commercially available aromatic polyamide reverse osmosis membrane were carried out to improve its chlorine resistance.The crosslinking agents including 1,6-hexanediol diglycidyl ether,adipoyl dichloride and hexamethylene diisocyanate ester with long flexible aliphatic chains and high reactivity with N-H groups were used in the experiments.Attenuated total reflective Fourier transform infrared spectra verified the successful preparation of highly crosslinked membranes by crosslinking treatments.It was suggested that the crosslinking agents were connected to membrane surface through the reactions with amine and amide Ⅱ groups,which is confirmed by surface charge measurements.Based on contact angle measurements,crosslinking treatments decreased membrane hydrophilicity by introducing methylene groups to membrane surface.With increasing amount of crosslinking agent molecules connected to membrane surface,the hydrolysis of unconnected functional groups of crosslinking agent produced polar groups and increased membrane hydrophilicity.The highly crosslinked membranes showed higher salt rejections and lower water fluxes as compared with the raw membrane.Since the active sites(N-H groups) vulnerable to free chlorine on membrane surface were eliminated by crosslinking treatments,the chlorine resistances of the highly crosslinked membranes were significantly improved by slighter changes in both water fluxes and salt rejections after chlorination.