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Surface modification is an efficient post-treatment method to optimize the properties of nanofiltration (NF) membranes. Here, we report a facile surface modification strategy coupling with heat curing for grafting monoethanolamine (MEA), a monomer containing both a primary amine and a primary alcohol group, onto a nascent polyamide NF membrane. With grafting 0.5 wt% MEA at 50 °C, the pure water permeability of the polyamide NF membranes was improved from 7.9 to 19.5 L m−2 h−1 bar−1 due to their enhanced physicochemical property, such as superior hydrophilicity, rough surface morphology, and enlarged membrane pores. Meanwhile, the rejection of Na 2 SO 4 remained above 97.5%. More importantly, the optimal membrane modified with 0.5 wt% MEA exhibited a high Na 2 SO 4 rejection of 99.1% and a negative NaCl rejection of −20.1% when treating a mixed salt solution containing 2 g/L Na 2 SO 4 and 2 g/L NaCl. Our study provides a novel insight for the fabrication of high permselectivity NF membranes via surface modification. Image 1 • Surface grafting was creatively coupled with heat curing in water. • Monoethanolamine molecule was successfully grafted onto the nascent membrane, rendering a better hydrophilic nanofiltration membrane. • The modified membrane exhibited enhanced pure water permeability of 19.5 L m−2 h−1 bar−1. • The modified membrane owned superior Cl−/SO 4 2− selectivity. [ABSTRACT FROM AUTHOR]

In this study, we utilized the NaOH solution as a heat-treating medium to replace the conventional oven-heating process after interfacial polymerization for the RO membrane fabrication. XPS result confirmed that the nascent RO membrane possessed a gradient cross-linking density along the polyamide layer depth, which is relatively loose on top and dense facing the substrate. The top loose polyamide could be exfoliated under NaOH treatment. The TFC membrane treated in a 1.5 mol L-1 NaOH solution exhibited a pure water flux nearly 3 times higher than that heat-treated in a water bath and also maintained a high NaCl rejection. In consideration of the practical operation process, membrane stability was evaluated, and the results showed that the membrane heat-treated by 1.5 mol L-1 NaOH solution possessed good long-term and pH stability. Thus, the facile heat-treating strategy provides a new path for fabricating high flux TFC-RO membranes. • Novel heat-treating medium of NaOH solution was utilized to fabricate the novel RO membrane. • The top loose layer of the nascent polyamide membrane could be exfoliated under NaOH treatment. • The modified heat-treating strategy showed great superiority over traditional oven-heating process. [ABSTRACT FROM AUTHOR]

In this study, the impacts of heat curing conditions on the morphology and permeability of polyamide nanofiltration (NF) membranes were comprehensively investigated. The surface chemical composition, morphology, charge property, hydrophilicity and NF performance of the resulting membranes were studied. In order to preserve the instantaneous polyamide layer morphology, freeze drying process was employed after heat curing. Results showed that the surface roughness of the polyamide selective layer increased first and then decreased with curing time. The tunable morphology of polyamide NF membranes can be acquired by adjusting the curing temperature and time. The nascent membrane without heat curing exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and maintained Na 2 SO 4 rejection of 97.4%. Increasing the curing time, the permeability of the NF membranes was greatly diminished. This work provided novel viewpoint about the effects of heat curing on morphology and permeability for high-performance polyamide NF membrane. • Interfacial polymerization is terminated by liquid nitrogen to preserve the instantaneous polyamide layer morphology. • Polyamide layer roughness increases first and then decreases as a function of the heat curing time. • The nascent membrane exhibited excellent pure water permeability of 16.7 L m−2 h−1 bar−1 and Na 2 SO 4 rejection of 97.4%. [ABSTRACT FROM AUTHOR]

• A novel TFC NF membrane was fabricated by incorporation of β-CD into polyamide backbone. • The effect of β-CD on the NF membrane performance was studied thoroughly. • Such NF membrane showed a high permselectivity performance. Based on the Freeman theory, tailoring polymer backbone stiffness can improve membrane performance. Therefore, a rigid monomer—bisphenol F—to enhance the backbone stiffness of polyester/polyamide was utilized to prepare high performance nanofiltration (NF) membranes in the previous work. Here, the three-dimensional (3D) hollow-bowl-structure monomer—beta cyclodextrin (β-CD)—is added into the polyester/polyamide backbone to fabricate a 3D-microstructure NF membrane. With the incorporation of β-CD, the pure water flux (PWF) increases by 68% (up to 152 L m−2 h−1, 0.6 MPa), while the rejection of Na 2 SO 4 remains high (96.8%). Surprisingly, such NF membrane exhibits a very low rejection of NaCl (1.1%) and high rejection of Na 2 SO 4 (up to 95.8%) when dealing with a Na 2 SO 4 /NaCl mixed solution. The fabricated 3D-microstructure NF membrane shows the potential to be applied in the monovalent/divalent anion separation field. [ABSTRACT FROM AUTHOR]