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[Display omitted] • A novel polyamide loose NF membrane was prepared from aqueous monomer (piperazine-2-carboxylic acid). • The loose NF membrane formation mechanism was clarified. • The loose NF membrane exhibited high water permeance and outstanding separation selectivity of dye/salt. • The loose NF membrane demonstrated excellent antifouling performance. Dye effluent is regarded as one of the most hazardous industrial effluents. Although loose nanofiltration (NF) membranes have been considered as an effective alternative technique for treating dye effluent, their development is still constrained by subpar permeance, separation efficiency and anti-fouling performance. In this work, a novel loose polyamide (PA) NF membrane was designed employing a conventional interfacial polymerization process using piperazine-2-carboxylic acid (PIP-COOH) and trimesoyl chloride as aqueous and organic phase monomers, respectively. The presence of unique electron-absorbing carboxyl groups on the PIP-COOH monomer not only provided abundant negative charge on the membrane surface, but also greatly reduced the reactivity, diffusion rate and solubility in n-hexane of the aqueous monomer, allowing for the formation of a more relaxed and smoother active layer. The balanced combination of pore size screening and Donnan effect achieved precise separations with high permeability. Moreover, the interaction of the carboxyl groups with the backbone structure increased the free volume of the PA layer and improved permeability significantly. The PIP-COOH/TMC membrane prepared under the optimal conditions exhibited high water permeance of 598.1 L·m−2·h−1·MPa−1, high reactive red rejection (99.3%) and low NaCl rejection (5.4%). Furthermore, the membrane possessed exceptional anti-fouling performance thanks to the ultra-smooth surface with crucial antifouling index flux recovery ratio as high as about 99%, which showed unexpected application possibilities. In conclusion, this study offers a potential novel membrane material for the development and application of loose NF membranes in the treatment of colored effluent. [ABSTRACT FROM AUTHOR]

The regulation of interfacial polymerization (IP) is the critical procedure for the preparation and industrialization of thin film composite (TFC) nanofiltration (NF) membranes. However, the IP control is still a huge challenge based on the extremely rapid reaction rate during the fabrication of the membrane. Herein, a new strategy was developed to modulate the IP process to increase the NF membrane performance. The aldehyde oxidized dextran (ODex) interlayer was deposited on the polysulfone ultrafiltration substrate, and the enamine would form between the secondary amines of aqueous phase monomer piperazine (PIP) and aldehyde groups of the ODex. Based on the by-products of IP, the enamine gradually decomposed reversibly in a hydrogen ion environment and the immobilized PIP was released and continued to react with organic phase monomer trimesoyl chloride (TMC). Accordingly, a thinner and exhibiting nanowire structures separation layer with fewer defects was obtained. The permeance of the optimal NF membrane with 0.7 wt% ODex interlayer deposition concentration could reach up to 208 ± 10.4 Lm−2h−1MPa−1, which was more than 2.5 times permeance of the ordinary NF membrane, and the rejection rate for Na 2 SO 4 could reach 99.3 ± 0.3%. In addition, the mono- and divalent ion selectivity of the modified membrane was also greatly improved (α NaCl/Na2SO4 = 115). This study provides a new idea for the regulation of IP process, thereby suggesting a reasonable proposal for improving the performance of TFC NF membranes. [Display omitted] •The enamine was formed between the secondary amines of piperazine and the aldehyde group on the oxidized dextran interlayer. •The interfacial polymerization procedure was effectively regulated by a reversible enamine reaction. •The effect of enamine reversible reaction on the structure of nanofiltration membrane was discussed in detail. •The performance of modified NF membranes for monovalent/divalent salts selectivity was significantly improved. [ABSTRACT FROM AUTHOR]

The thin-film composite (TFC) nanofiltration (NF) membrane is a novel kind of membrane that has been extensively studied in recent years and broadly applied in desalination and wastewater treatment. The improvement of separation performance by optimizing the structure and morphology of NF membranes can significantly reduce energy consumption and bring more economic benefits. In this work, glutaraldehyde (GA) was used to crosslink polyethyleneimine (PEI) and dextran nanoparticles (DNPs) to construct an interfacial coating interlayer on polysulfone (PSF) ultrafiltration (UF) substrate. Subsequently, the polyamide (PA) NF membranes were fabricated by interfacial polymerization (IP) between piperazine (PIP) and trimesoyl chloride (TMC). DNPs were semi-encapsulated in the PEI coating and the exposed nanoparticles would be embedded in the PA layer for forming interfacial channels after IP. The interlayer not only affected the adsorption and diffusion of aqueous phase monomers to form a thin membrane, but also improved the membrane density to prevent selective defects associated with the incorporation of nanoparticles. The pure water permeance of the interlayered-TFC NF membrane was determined as 313.3 Lm−2h−1MPa−1, which was approximately four-fold that of the pristine membrane. The retention rate of various divalent salts of the NF membrane also significantly improved, and the retention rate of Na 2 SO 4 exceeded 99%. This innovative method of interlayer modification has exhibited great potential in rapid desalination and wastewater recovery, providing new possibilities for the preparation of industrial high-performance NF membranes. [Display omitted] • An innovative interlayer combining DNPs and PEI coating was successfully constructed. • DNPs were semi-encapsulated in the PEI coating to formed interfacial channels favorable for water passage. • The flux of the interlayer-modified NF membrane increased nearly 4 times with the retention rate of Na 2 SO 4 above 99%. • NF membrane exhibited excellent monovalent/divalent ion selectivity. [ABSTRACT FROM AUTHOR]

In recent years, the global demand for lithium resources has grown substantially due to the rapid development of the new energy industry. The nanofiltration (NF) technique is a feasible method to extract lithium from salt-lake brine, and the high Mg2+/Li+ separation selectivity of the NF membrane is the crucial factor in the NF separation process. In this work, the polyamide (PA) layer was prepared on the polyphenol/PEI interlayer-modified polysulfone (PSF) substrate to endow the NF membrane with decreased pore size and weakened electronegativity. Enhanced steric hindrance effect and reduced electrostatic attraction between Mg2+ and PA layer increased the Mg2+ rejection, thereby improving the Mg2+/Li+ separation factor of the NF membrane. Furthermore, the positively charged polyphenol/PEI interlayer hindered the permeation of Mg2+ through the Donnan effect, further enhancing the Mg2+/Li + separation factor. A separation factor up to 50.7 for Mg2+/Li+ was achieved by extracting lithium from simulated brine using the obtained NF membrane. In addition, the NF membrane exhibited a permeability of 18.6 L m−2 h−1·bar−1 and excellent long-term stability, which greatly improved the Mg2+/Li+ separation efficiency and reduced energy consumption. Therefore, this work provides a simple strategy for preparing NF membranes with high Mg2+/Li+ separation factor and permeability. [Display omitted] • Dual-electric layer NF membranes with positively charged interlayer and negatively charged separation layer. • The high Mg2+/Li+ separation selectivity is attributed to the synergy between the steric hindrance effect and Donnan exclusion. • The Mg2+/Li+ selectivity of NF membranes can be adjusted by changing the preparation conditions of the interlayer. • Permeability - selectivity trade-off was well addressed. [ABSTRACT FROM AUTHOR]