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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]

[Display omitted] • Carboxylated starch nanoparticles (CSNPs) were synthesized and embedded in the separation layer of the nanofiltration membrane. • The aggregated or large CSNPs adsorb the aqueous phase to build an aqueous template during the interfacial polymerization transferring the reaction interface. • The compatibility problem of nanoparticles and separation layer was effectively solved. • The S NaCl/Na2SO4 of the modified nanofiltration membrane reached 180 with more than 2 times improvement in flux. The challenge of poor compatibility between nanoparticles and separation layers in thin film nanocomposite (TFN) nanofiltration (NF) membranes has always plagued the researchers. In this work, a carboxylated starch nanoparticles (CSNPs) were introduced into the polyamide (PA) separation layer of NF membrane by the IP reaction between trimesoyl chloride (TMC) and piperazine (PIP). The agglomerated or large size CSNPs could transfer the reaction interface above the particles through the formation of a water template by adsorption of aqueous phase monomers, which shaped the defect-free separation layer. Furthermore, the reduced thickness and increased density of the separation layer greatly enhanced the separation selectivity of the nanofiltration membrane thanks to the introduction of hydrophilic groups of nanoparticles. The modified membrane achieved a nearly 5-fold improvement in separation selectivity for NaCl and Na 2 SO 4 (S NaCl/Na2SO4 = 180) and a 2-fold increase in the water permeance. In addition, the modified NF membrane also possessed better chlorine-resistance property based on the formation of polyarylester between the reaction of hydroxyl groups in CSNPs and acyl chloride groups in TMC. Such novel aqueous-phase additives provide new insights to effectively solve the compatibility problem between the nanoparticles and separation layers, which is favorable for the commercial production of NF membrane. [ABSTRACT FROM AUTHOR]

The thin-film composite (TFC) nanofiltration (NF) membrane is an excellent choice to solve water shortage based on the advantages of high flux and selective separation. However, the current NF membrane still causes a tremendous amount of energy consumption in the practical applications due to the limitation of flux. In this work, dextran nanoparticles (DNPs) with the cross-linked organic components, numerous hydrophilic groups and internal cavities were added into the aqueous phase solution, and novel NF membranes were fabricated by adjusting the concentration and particle size of DNPs to control the interfacial polymerization (IP) reaction. After modification, the decrease of membrane thickness and the increase of surface hydrophilicity improved the separation performance of NF membrane. The water flux of NF membrane with 0.5 wt% DNPs doping was up to 211.2 Lm−2h−1MPa−1, which was more than twice as high as the unmodified membrane with Na 2 SO 4 retention up to above 98%. It was also worth mentioning that the modified membrane indicated excellent monovalent/divalent ion selectivity and anti-fouling performance. This strategy of improving membrane performance by controlling the concentration and particle size of the aqueous phase additives with the advantages of simplicity and universality provides a certain impetus for the development of TFC membrane. • Dextran nanoparticles were successfully incorporated into the separation layer of NF membrane. • The water flux of the DNPs-modified NF membrane increased 2–3 times without sacrificing the Na 2 SO 4 retention. • The influence of the particle size and concentration of DNPs was discussed detailedly. • The anti-fouling performance and monovalent/divalent ion selectivity of the membrane improved. [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]