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Tight ultra-filtration (TUF) membranes were constructed by in situ growing zinc imidazole frameworks micro-crystalline leaves (ZIF-L) in polyethylene imine (PEI) and polydopamine (PDA) deposit layers on porous polyethylene (PE) substrates. The effects of preparation conditions on the surface physical and chemical structures as well as on the dye/salt separation performance of the formed TUF membranes were systematically investigated. By inserting selective water permeation channels and increasing contacting surface areas, in situ-grown ZIF-L arrays tightly cross-linked in the coating matrix greatly increased water permeation without trading off dye/salt retention selectivity. The morphology of the included ZIF-L particles could be varied by adjusting the ligand/Zn molar ratio (α) in the preparation processes. Optimized PDA-PEI/ZIF-L@PE TUF membranes containing ZIF-L of cross-cross block morphology showed very high pure water permeability of 180 ± 20 L·m−2·h−1·bar−1 (LMHB) and retention selectivity (S CR/Na2SO4 and S MB/Na2SO4) of 267 and 43, respectively, as well as excellent stability and anti-fouling properties. [Display omitted] • Lower cost-based TUF membranes were prepared for effective dye/salt separation. • In situ-grown ZIF-L increased water flux without losing dye retention selectivity. • PEI and PDA coating greatly enhanced the stability of ZIF-L in water. • Morphology of ZIF-L was tuned for improving membrane performance. • Protonation of the -NH- groups increased positive charge and water flux. [ABSTRACT FROM AUTHOR]

Highlights • TFC membrane with an asymmetric separation layer was fabricated for nanofiltration. • The membrane was fabricated via IP process followed by secondary interface reaction. • High efficient nanofiltration of anionic dye aqueous solution was achieved. • Steady-state water flux was improved by at least 36.0%. • Steady-state flux decline was lowered by more than 23.5%. Abstract The development of high performance membrane is crucial for enhanced separation efficiency of nanofiltration process in treating wastewaters from dye and textile industries. In this work, a novel thin-film composite nanofiltration membrane with an asymmetric separation layer composed of relatively compact skin and loose body was designed and fabricated for improved perm-selectivity and antifouling property. Nascent composite membrane with loose poly(piperazine amide) (PA) separation layer was interfacially synthesized and performed with secondary surface reaction using an aqueous tannic acid (TA) solution. Membrane characterizations verified the formation of compact TA skin on top of the loose PA layer through forming covalent bonds via esterification reaction. Compared with the composite nanofiltration membrane with PA symmetric separation layer having the same glucose rejection of about 82.0%, the permeability to pure water of the composite membrane with PA/TA asymmetric separation layer was higher by 28.0%, the water fluxes to aqueous solutions dissolved with model anionic dyes of alizarin yellow R, sunset yellow and Congo red under steady state were higher by 50.3, 43.9 and 36.1%, and the steady-state flux declines were lowered by 27.8, 43.4 and 23.5%, respectively. Furthermore, the PA/TA-based membrane also exhibited better antifouling property and rejection ability to alizarin yellow R. [ABSTRACT FROM AUTHOR]