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[Display omitted] • Monomers developed in recent years for preparation of TFC membranes is summarized. • The relationship between monomer structure and membrane properties is established. • The application problems of the IP monomers are summarized. • The outlook for future development of the monomer is also discussed. The thin-film composite (TFC) membranes fabricated by interfacial polymerization (IP) can be applied in the fields of nanofiltration (NF) and reverse osmosis (RO), which has the unparalleled advantages, such as high selectivity and permeability, small capital investment and low energy consumption, thus attracting great research interest in industry and academia field. The performance of TFC membranes is determined by their microstructure and physicochemical properties while IP monomer plays a decisive role regarding both. Over the past few decades, the researchers have paid intensive and sustained efforts to develop new IP monomers. This paper reviews these monomers and the corresponding membranes developed in recent years with the aim of establishing an intrinsic relationship between monomer structure and membrane properties. The excellent performances based on new monomers in enhancing the permeability, selectivity, anti-fouling and chemical stability of NF and RO membranes for liquid treatment are highlighted. Finally, various problems in the monomer development are summarized and the outlook for future development is also discussed. [ABSTRACT FROM AUTHOR]

[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 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]

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]

• Novel polyarylate NF membranes were prepared with oligomeric phenolic resin monomer. • NF membrane exhibited a high Na 2 SO 4 rejection rate and excellent chlorine-resistance. • The influence of preparation parameters on the NF membrane performance was investigated. Conventional water treatment polyamide nanofiltration (NF) membranes often suffer from the degradation of sodium hypochlorite (NaOCl) in sewage or during the process of membrane cleaning and deteriorate the separation performance, which significantly increases the treatment cost. Herein, a novel polyacrylate composite NF membranes were prepared by interfacial polymerization using oligomeric phenolic resin (OPR) and trimesoyl chloride (TMC) as aqueous and organic phase monomer respectively on the polyethersulfone (PES) ultrafiltration supporting membranes. The fabrication parameters, including the pH of the aqueous solution, reaction time and the concentration of the monomer, on the performance of the composite NF membranes were optimized. A series of characterization indicated that the surface of the NF membranes was negatively charged, the molecular weight cut-off (MWCO) and the pore diameter of the polyacrylate membrane were 400 Da and 0.47 nm, respectively. At the optimized preparation conditions, the NF membrane exhibited high Na 2 SO 4 rejection of 98.2% and water flux of 2.42L·m−2·h−1·bar−1, which was superior to most of the polyacrylate NF membranes reported in recent years. Compared with the polyamide membrane, the prepared polyacrylate membrane demonstrated better chlorine-resistant property and still maintained 92.0% Na 2 SO 4 rejection after being treated with NaOCl solution. Moreover, the NF membrane preserved excellent long-term operation stability. The chlorine-resistant NF membrane constructed from OPR monomer has a broad application prospect in the field of high chlorine wastewater treatment. [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]

[Display omitted] • Nanofiltration membranes with strong negative charge were prepared by a new aqueous monomer 2,4,6-trimethyl-3,5-diaminobenzenesulfonamide (TMDBSA) through the traditional interfacial polymerization process without any post-treatment. • The membrane has high water permeability (19.6 L m−2 h−1 bar−1) and >98.3% methyl blue rejection. • It owns separation stability for the removal of MB in a harsh acid environment. • It has excellent antifouling performance and long-term stability during the filtration tests. • It demonstrates great practical application potential for treating acidic anionic dyes solutions. Nanofiltration (NF) membranes with negative surface charge are of critical significance for the efficient removal of anionic dyes from wastewater. In this work, a novel negatively charged NF membrane was prepared from a new sulfonamide monomer, 2,4,6-trimethyl-3,5-diaminobenzenesulfonamide (TMDBSA) and trimesoyl chloride (TMC) via interfacial polymerization. The unique diamino-sulfonamide structure of TMDBSA would be conducive to the formation of a poly (amide-sulfonamide) (PASA) layer with enhanced negative charge while maintaining the appropriate degree of crosslinking. The TMDBSA-TMC membrane prepared at optimized condition exhibits both high water permeability (19.6 L m−2h−1 bar−1) and superior rejections of anionic dyes with different molecular weights (e.g. 98.3% rejection for methyl blue), reveals that Donnan exclusion dominates the rejection mechanism. More importantly, benefiting from the strong negatively charged surface and PASA structure, the TMDBSA-TMC membrane shows separation stability for the removal of methyl blue in a broad pH range, even under a harsh acid environment. Meanwhile, the membrane has excellent antifouling performance and long-term stability during the filtration tests. The newly developed negatively charged NF membrane demonstrates great practical application potential for the removal of anionic dyes with small molecular weights. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) membrane is of great significance for desalination of light brine and purification of drinking water. Although the development of novel preparation methods and membrane materials has improved the separation performance, it is still a major challenge to promote NF membrane toward industrial production with simpler and more controllable process. Herein, the polyphenol intermediate layer was designed by 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) with twist structure and polyethyleneimine (PEI) co-deposition to increase the surface hydrophilicity and electropositivity of the polysulfone ultrafiltration substrate. Subsequently interfacial polymerization (IP) was carried out on the polyphenol intermediate layer to assemble a polyamide ultrathin selective layer using trimesoyl chloride and piperazine monomer. Through adjusting the co-deposition time of TTSB and PEI, a unique nano-pleated structure was successfully formed on the thin-film composite membrane surface. The water permeance of the membrane was determined as 23.7 L m−2 h−1 bar−1 with 99.4% Na 2 SO 4 rejection, which was almost triple fold of the flux of the controller membrane without the intermediate layer. Our results provide an efficient and convenient way to fabricate the advanced NF membrane with higher divalent/monovalent ion selectivity and water permeance simultaneously, which will provide advices for the gas separation and pervaporation membranes with the IP method. • Novel TTSBI-PEI interlayer-based polyamide membrane was fabricated by interfacial polymerization. • The nano-pleated structure on the selective layer improved the water flux without deterioration of Na 2 SO 4 rejection. • The novel nanofiltration membrane exhibited excellent long-term stability. [ABSTRACT FROM AUTHOR]