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Nanofiltration (NF) membranes with both high permeability and salt rejection are in dire need for water treatment. Generally, heat treatment is an essential step for fabricating polyamide NF membranes. Conventional heat treatment in an oven causes membrane pore shrinkage and over cross-linking, which often leads to a severe loss of permeation performance. Herein, we report a single-step method by heat-treating membranes in non-neutral solutions to avoid pore shrinkage and generate graded hydrolysis in membrane selective layer. As confirmed by the XPS result, the polyamide NF membrane fabricated via controlled hydrolysis possesses a gradient cross-linking degree vertically along the membrane surface. This optimal polyamide NF membrane had a superior pure water permeability (PWP) of 27.5 L m−2 h−1 bar−1 and high Na 2 SO 4 rejection of 98.5%. Such controlled hydrolysis approach provides novel strategy for fabricating high performance polyamide membranes. • Heat treatment in water was employed to avoid pore shrink and over cross-linking of the polyamide active layer. • The performance of NF membrane with gradient cross-linked structure can be easily tuned by adjusting the pH value of water. • The optimal membrane owns a superior pure water permeability of 27.5 L m−2 h−1 bar−1 and a high Na 2 SO 4 rejection of 98.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • TFN(O) membrane exhibits a high flux of 30.4 L∙m−2∙h−1∙bar−1 with 96% rejection for TCE. • The molecular orientation of n-hexane is affected by UiO-66. • The asymmetric distribution of UiO-66 in PA layer has been studied. • The tandem model of dissolution and diffusion in NF is applied to the MD simulation. Chlorinated hydrocarbons (CHC) are highly toxic to human health and the ecological environment. In this study, thin-film nanocomposite (TFN) membranes doping with UiO-66 were prepared and applied to the CHC removal in groundwater. TFN membranes with UiO-66 asymmetrically distributed in the polyamide (PA) layer were prepared by incorporating UiO-66 in the aqueous phase and the organic phase, respectively. Molecular dynamics (MD) simulation was applied to do further mechanism research. The water boundary layer surrounding UiO-66 induces a wrinkled phase interface when UiO-66 is dispersed in the aqueous phase. Also, the dissolution-diffusion model was used for investigating nanofiltration (NF) process. Water molecules show a faster dissolution rate and a higher dissolution equilibrium on the UiO-66 surface. UiO-66 exhibits twice the water number density relative to the PA due to super-hydrophilicity, which provides a greater driving force for the mass transfer of water. In addition, the diffusion coefficient of water in the UiO-66 pore is about 1.5 times that in PA. As a result, TFN(O) membrane exhibits a high pure water flux of 30.4 L∙m−2∙h−1∙bar−1 with the trichloroethylene (TCE) and trichlorobenzene (TCB) rejection above 96%. This work provides a solution for CHC removal of groundwater and a mechanistic explanation for the interfacial polymerization (IP) and separation process of doped nanoparticles. [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]