Na2SO4 Rejection Research Articles

One-step rejuvenation for prolonging running lifespan of nanofiltration membranes

Commercial nanofiltration (NF) membranes based on polyamides may experience a decline in permeation performance after prolonged operation. The short lifespan of NF membranes will lead to waste and additional carbon emissions. Thus, rejuvenating membranes and extending their lifespan seem more meaningful than investigating new materials. In this paper, polyamide NF membranes were modified with various polyphenol monomers to improve their permeation performance. The effects of different polyphenols on pore size, surface morphology, and permeation performance of the NF membranes were thoroughly investigated. After modification with tannic acid, the NF membrane exhibits improved salt rejection while experiencing an acceptable decrease in water flux. It should be noted that the commercial NF membrane element fabricated by Koch can recover its Na2SO4 rejection from 83.0% to 94.2% and demonstrate long-term stability after rejuvenation with tannic acid. Combined with the environmental friendliness of polyphenols, this straightforward modification method has the potential for prolonging the operational lifespan of industrial NF membrane products.

In-situ interfacial polymerization of zwitterionic nanofiltration membranes with anti-scaling performance

Mineral scaling caused by multivalent metal ions can significantly hinder the long-term operation of nanofiltration membranes. In this study, in-situ interfacial polymerization including a posttreatment by using a citric acid solution was employed in order to mitigate scaling on the membrane surface. Under the optimal conditions (15 ​min of posttreatment with a 2 ​M citric acid solution), the membrane water permeance increased from 5.76 ​± ​0.2 to 15.1 ​± ​1.8 ​L⋅m−2⋅h−1·bar−1 for the pristine and the optimal membrane, respectively. The molecular weight cut-off of the optimal membrane was 399 ​Da, which allows for the removal of organic micropollutants in groundwater. Furthermore, the resulting membrane showed a Na2SO4 and CaCl2 rejection of 92.5 ​± ​1.9 and 11.4 ​± ​1.3%, respectively. During the anti-scaling tests, the membrane fabricated with this strategy exhibited a minor decline of the water permeance of 33.5% when subjected to the same water recovery process, opposed to 65.8% for the pristine membrane. This proposed fabricating procedure thus provides an effective strategy for retarding membrane scaling in desalination applications.

Phytic acid and ferric chloride compound additives-regulated interfacial polymerization for high-performance nanofiltration membrane

To balance the permeability-selectivity trade-off effect of the polyamide nanofiltration membrane, interfacial polymerization regulation strategy is widely used to optimize the physicochemical structure of the polyamide film. In the present work, the compound additives of phytic acid and ferric chloride were added into the aqueous phase to regulate the interfacial polymerization process. On the one hand, a lot of piperazine monomers will be adsorbed around the phytic acid molecules due to the electrostatic interaction between phosphoric acid groups and amino groups. Meanwhile, the phytic acid molecules and ferric ions can form a complex in the piperazine solution, which results in a low diffusion rate of the other piperazine monomers without adsorbed on the phytic acid and ferric chloride complex due to steric hindrance. The synergistic effect of electrostatic interaction and steric hindrance leads to the optimized nanofiltration membrane with a thinner and looser polyamide structure. The best-performing nanofiltration membrane exhibits an approximately four-fold water permeance (28.4 L m−2 h−1 bar−1) compared with the controlled M0 nanofiltration membrane (6.5 L m−2 h−1 bar−1) without obviously sacrificing the Na2SO4 rejection (96.9 %). This simple interfacial polymerization regulation strategy provides a novel insight for the preparation of high-performance NF membrane.

C3N4-interlayer-mediated interfacial polymerization of homopolymer nanofiltration membranes for efficient water purification

Interlayered thin film composite (TFNi) membranes have been shown to achieve high-quality polyamide (PA) skin layers with enhanced permeability and selectivity. Herein, we demonstrate the construction of a hydrophilic interlayer by polymeric graphitic carbon nitride (g-C3N4) for optimizing the interfacial polymerization of the nanofiltration membrane. Due to the effective enrichment and the slowed diffuse rate of amine monomer solutions, g-C3N4 modification decreases the thickness of the PA skin layer and increases the electronegativity of membranes. The best TFNi membrane exhibits a high water permeance of 31.82 L m−2 h−1 bar−1, nearly twice as high as that of the membrane without g-C3N4 interlayer, while maintaining a comparably Na2SO4 rejection efficiency. The stronger hydrophilicity and more negatively charged surface of the TFNi membrane effectively retarded membrane fouling, contributing to the high-efficiency removal of harmful drugs from actual surface water, with more than two times higher water flux that of commercialized NF270 membrane. This work provides a facile strategy to synthesize TFNi membranes with great application potential for high-performance nanofiltration.

Enhancing the perm-selectivity of thin-film nanocomposite membranes intercalated with cyclodextrin-chelated Metal-Organic Framework via modulated interfacial polymerization

Nanofiltration (NF), an exceedingly promising technology, has been extensively implemented within the domain of desalination. The pursuit of optimizing water permeance, while upholding outstanding rejection rates to ameliorate the vexing permeability-selectivity trade-off effect, has raised tremendous concerns. Herein, a novel approach has been proposed, involving the construction of a cyclodextrin-chelated Metal-Organic Framework (MOF) interlayer through vacuum-assisted filtration, aimed at orchestrating the interfacial polymerization (IP) process and sculpting the membrane morphologies of polyamide membranes. The results demonstrated that cyclodextrin-chelated MOF interlayer produced a “gutter” effect for faster water transport and enhanced the interaction of the substrate and PA layer. Simultaneously, the interlayer helped to alleviate the diffusion rate of piperazine (PIP) via the interactions (e.g., hydrogen bonds, electrostatic attraction and steric hindrance) between interlayer and PIP, leading to a lower cross-linking degree and a defect-free thinner active layer. Meanwhile, cyclodextrin with intrinsic nano-cavity created more free volume for water transport inside the polymer. Furthermore, the crumpled interlayer established a hydrophilic undulated interface, followed by the generation of micro-wrinkled polyamide layer with larger filtration areas. The optimal membrane exhibited a high permeability of 39.59 L/m2 h bar, nearly 6.5 times than that of the original membrane, while maintaining a remarkable Na2SO4 rejection of 95.71 %. The strategic deployment of cyclodextrin-chelated MOF interlayers in membrane modification held the potential to efficaciously mitigate the trade-off effect, thereby presenting a promising avenue for the realization of highly-efficient desalination processes.

Hydrophilic carbon-carbon covalent linkage network structure for strong acid/alkali resistant and antifouling nanofiltration membrane

The nanofiltration (NF) membrane plays a crucial role in wastewater treatment by separating ions and molecules. However, traditional polyamide (PA) thin-film composite (TFC) NF membranes have limitations in durability under acidic or alkaline conditions and are prone to fouling, which limits their applications and increases costs. In this study, we have successfully developed a new nanofiltration membrane with an active layer composed of hydrophilic carbon-carbon covalent bond linkage network through UV irradiation-initiated polymerization of a kind of sulfobetaine - [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS) - or acrylic acid (AA) on the surface of poly (ether sulfone) (PES) substrate. The carbon-carbon covalent bond (C–C) chemistry used in the preparation of the NF membrane results in exceptional durability towards acid and base, enabling it to maintain its ion separation efficiency (up to 94.2 % and 90.3 % of the initial Na2SO4 rejections) under strong acidic (20 % (w/v) H2SO4) and strong alkaline (2 M NaOH) conditions. Additionally, the water-attracting nature of polyDMAPS and PAA effectively prevents the fouling of protein and bacteria on the NF membrane surface. This breakthrough in manufacturing NF membranes significantly improves their environmental durability, making them suitable for use in highly acidic or alkaline environments (e.g., pH < 0 and pH > 14), including heavily contaminated ones.

Aminal-Linked Covalent Organic Framework Membranes Achieve Superior Ion Selectivity.

High-salinity wastewater treatment is perceived as a global water resource recycling challenge that must be addressed to achieve zero discharge. Monovalent/divalent salt separation using membrane technology provides a promising strategy for sulfate removal from chlor-alkali brine. However, existing desalination membranes often show low water permeance and insufficient ion selectivity. Herein, an aminal-linked covalent organic framework (COF) membrane featuring a regular long-range pore size of 7Å and achieving superior ion selectivity is reported, in which a uniform COF layer with subnanosized channels is assembled by the chemical splicing of 1,4-phthalaldehyde (TPA)-piperazine (PZ) COF through an amidation reaction with trimesoyl chloride (TMC). The chemically spliced TPA-PZ (sTPA-PZ) membrane maintains an inherent pore structure and exhibits a water permeance of 13.1Lm-2h-1bar-1, a Na2SO4 rejection of 99.1%, and a Cl-/SO4 2- separation factor of 66 for mixed-salt separation, which outperforms all state-of-the-art COF-based membranes reported. Furthermore, the single-stage treatment of NaCl/Na2SO4 mixed-salt separation achieves a high NaCl purity of above 95% and a recovery rate of ≈60%, offering great potential for industrial application in monovalent/divalent salt separation and wastewater resource utilization. Therefore, the aminal-linked COF membrane developed in this work provides a new research avenue for designing smart/advanced membrane materials for angstrom-scale separations.

Thin film nanocomposite nanofiltration with tannic acid-Fe(III) complexes functionalized Ti3C2Tx for enhanced divalent-salinity-water separation with a superior durability

Incorporating nanomaterials for a thin film nanocomposite (TFN) layer has been verified effective to improve the separation performance of nanofiltration (NF) membranes, whereas the poor compatibility between nanomaterials and polyamide (PA) matrix leads to a decrease in the salt rejection and pollution resistance. In this study, inspired by a new interface-bridging idea, Ti3C2Tx was bonded with tannic acid-Fe(III) (TA-Fe(III)) complexes, and then incorporated into a PA matrix for the first time to obtain a novel TFN NF membrane. The introduction of TA-Ti3C2Tx was found to effectively reduce the diffusion of piperazine, and thus result in the induction of a thinner, lower roughness, more hydrophilic, and defect-free PA layer. With the addition of 0.015 wt% TA-Ti3C2Tx, the TFN membrane obtained the highest water permeability of 12.17 L m−2 h−1 bar−1, almost twice that of the pristine membrane, with a high Na2SO4 rejection above 97 %. In addition, the TA-Ti3C2Tx-filled TFN membranes were verified to exhibit excellent antifouling performance and pressure resistance with a high durability, which is crucial for the practical application in salinity water treatment. This study provides an effective strategy to tailor the interfacial microstructural of nanoparticle-filled NF membranes for superior divalent-salinity-water separation.

Regulation of interfacial polymerization by organic base for high-permselective nanofiltration

In the synthesis of the polyamide nanofiltration (NF) membrane, the hydrogen chloride is a by-product generated at the organic interface from interfacial polymerization, which reduces the reactivity of amine monomers due to protonation. Herein, a strategy of addition of an organic base in the organic phase to neutralize the H+ was reported. The performances of the membranes produced using three organic bases with different chain lengths were explored. The results showed that the organic base neutralized the H+ and promoted the rate of interfacial condensation reaction, which facilitated the formation of a dense and thin polyamide layer. Moreover, compared to control membrane, the membrane modified by organic base exhibited higher water permeance without sacrificing salt rejection. Higher diffusion rate of HCl through PES substrate compared to NF membrane indicated that HCl diffusion was mainly affected by the resistance of polyamide layer. Molecular simulations demonstrated that triethylamine (TEA) has lower energy barrier of neutralization and higher reaction heat in comparison with tripropylamine and N, N-diisopropylethylamine. The TEA modified membrane thereby displayed a permeance up to 24.3 L h−1 m−2 bar−1 and Na2SO4 rejection of 98.8 %. This work provided a promising strategy for the regulation of interfacial polymerization in achieving high-permselective nanofiltration.

Synergistic effect of POSS and chitosan on highly enhancing the separation selectivity and antifouling capacity of polyamide membranes

The trade-off limit between permeability and selectivity, along with membrane fouling, has consistently posed significant challenges impeding the practical implementation of water purification membranes. In this paper, a combination of polyhedral oligomeric silsesquioxanes (POSS) and chitosan is introduced into the polyamide layer through interfacial polymerization and crosslinking to optimize the physical, chemical structure of membrane simultaneously. The resulting P/CS-2-POSS-2 membrane exhibits a notable water flux of 221.3 L m−2 h−1 MPa−1 and a substantial Na2SO4 rejection of 97.1 %. The selectivity of water molecules over sulfates in the optimized hybrid membrane is approximately 4 times greater than that observed in the pristine polyamide membrane. This finding underscores the success of the developed method in mitigating the trade-off between permeability and selectivity. Furthermore, the hybrid membranes exhibit superior antifouling properties, as evidenced by an impressive flux recovery ratio of 95.8 % for bovine serum albumin. Additionally, the mass transport properties of the prepared membranes are explored via molecular dynamics (MD) simulations. The results highlight that chitosan primarily enhances the membrane's hydrophilicity, whereas POSS predominantly regulates the membrane's pore size. Both fillers synergistically enhance the comprehensive performance of the membrane by effectively utilizing steric hindrance and the Donnan effect.

High mono/divalent selectivity thin film composite membrane prepared at 1,2-propanediol/hexane organic-organic interface

A new organic-organic phase interface was constructed for the interfacial polymerization to control the formation of polyamide. 1,2-propanediol was introduced to dissolve reactive amines to extend optional amines and reduce the hydrolysis of acyl chloride. The properties of the 1,2-propanediol/hexane interface such as interfacial intension, partition coefficient, and interface thickness were investigated and compared with the water/hexane system. The thin film composite (TFC) membranes prepared at different phase interfaces via interfacial polymerization were systematically characterized and explored. Compared to the conventional TFC membrane, a smoother and thinner polyamide skin layer with more hydrophilicity was fabricated. The optimum 1,2-propanediol based membrane displayed a high Na2SO4 rejection of 99.1% and mono/divalent ion selectivity of 98. This organic-organic interfacial polymerization not only provided a simple strategy to fabricate smooth polyamide nanofilms but also offered a feasible way for preparing polyamide membranes with good ion sieving performance that was in demand in nanofiltration.

Phospho-modified polyamide nanofiltration membranes with high permeability by using alendronate sodium as additives

The conventional in-situ interfacial polymerization (IP) process, characterized by its rapid reaction rate, is known to be an uncontrollable process that can lead to defects in the performance of nanofiltration (NF) membranes. Herein, a novel NF membrane with a phosphorylated polyamide (PA) network was prepared through a controlled IP process with the addition of alendronate sodium (AS). The phosphoric acid groups of AS can restrain the diffusion of PIP, due to the synergistic interactions with piperazine (PIP) including electrostatic interaction and hydrogen bonding. Moreover, the amine groups of AS could react with trimesoyl chloride (TMC) in organic phase, which incorporated AS into the PA networks. Consequently, a more negatively-charged ionic PA layer with looser, rougher and more hydrophilic structure was obtained. The prepared membrane exhibited a water permeance of 25.0 L·m−2·h−1·bar−1 which was almost two-fold higher than that of NF membranes prepared without additives, while keeping an excellent salt rejection performance (Na2SO4 rejection >97 %), even in a high salt concentration (7.0 g/L). Furthermore, the membrane demonstrated high rejections for different dyes, long-term operation stability and comparable anti-fouling ability against typical contaminants. This work provided a facile and rational approach to preparing ionic NF membranes with high permeability.

Thin film composite polyamide nanofiltration membranes with interlayer constructed with core-shell structured polystyrene-polyacrylamide nanospheres for antibiotics separation

Nanofiltration (NF) is an efficient and economic separation technology which has great application potential in solving worldwide water shortage. Constructing interlayer is an effective approach to fabricate thin film composite (TFC) polyamide (PA) NF membranes with better performance. Herein, the polystyrene-polyacrylamide nanospheres with core-shell structure were synthesized using an emulsion polymerization method. The PA NF membranes were prepared via interfacial polymerization (IP) on the mixed cellulose esters microfiltration (MCE MF) membranes which modified with the core-shell structured nanospheres. The fabricated PA NF membranes showed good performance with a pure water permeability of 18.9 L·m−2·h−1·bar−1 and Na2SO4 rejection of 97.4 %. The NF membranes also showed good antibiotics separation performance with rejection to levofloxacin (LEV), penicillin G (PG), tetracycline (TC), and erythromycin (ERY) of 97.1 %, 86.9 %, 92.2 %, and 96.4 %, respectively and efficient separation to antibiotics and NaCl. This work provides a feasible strategy to construct an interlayer of PA NF membranes with the core-shell structured polystyrene-polyacrylamide nanospheres.

Ionic liquid-functionalized antibiofouling nanofiltration membranes

Nanofiltration membranes hold great potential for water treatment applications, but are susceptible to fouling issues. In this study, we demonstrate the fabrication of NF membranes with high permeability, high rejection, antibiofouling and scaling resistance. The membrane was prepared through interfacial polymerization by doping the aqueous phase with 1-aminoethyl-3-methylimidazolium tetrafluoroborate ionic liquid. The TFC-0.2 membrane exhibited a more open nanoporous structure, resulting in an increased permeability from 5 ± 0.5 L·m−2·h−1·bar−1 (LMH/Bar) to 11.1 ± 0.4 LMH/Bar, while maintaining a comparable salt rejection performance to the original TFC membrane. Additionally, the TFC-0.2 membrane demonstrated excellent retention performance, with a removal efficiency exceeding 90 % for emerging contaminants such as antibiotics and PFOA. Notably, the TFC-0.2 membrane exhibited significant differences in the rejection of Na2SO4 and CaCl2, indicating its strong resistance to gypsum fouling. Furthermore, it is worth highlighting that the TFC-0.2 membrane displayed remarkable antibiofouling performance due to the bactericidal properties of AMIT. This capability allowed for the sterilization of bacteria at the early stage of attachment to the membrane surface, effectively mitigating biofouling. The findings of this study offer a simple yet effective strategy for fabricating high-performance nanofiltration membranes with exceptional antifouling properties.

Nano‐confined Supramolecular Assembly of Ultrathin Crystalline Polymer Membranes for High‐Performance Nanofiltration

AbstractPolymer membranes with high permeability, high salt rejection, and mechanical integrity are desirable in water treatment and purification. However, it remains a daunting challenge to achieve ultrathin yet robust polymer membranes harvesting all the above features for nanofiltration. Here, a new approach of nano‐confined supramolecular assembly to fabricate ultrathin crystalline polymer membranes with a modulus of 1 GPa and a thickness of 6.5 nm is reported. The microdroplet carrying amphiphilic tetra‐oligomers can quickly spread at the air–‐water interface, where the hydrophilic motifs such as carbonyl and hydroxyl groups can reconfigurably anchor down to water molecules via abundant hydrogen bonding interactions, significantly promoting the alignment and orientation of hydrophobic alkyl chains within the nano‐confined space. The resultant nano‐films exhibit mechanical robustness as well as excellent ion sieving with improved NaCl rejection of 81.3% and unprecedented Na2SO4 rejection of 99.9% without compromising water permeation, outperforming the reported and commercial state‐of‐the‐art polymer membranes. This work enables the rapid production of over 100 cm2 ultrathin crystalline polymer membranes with great nanofiltration potential and highlights the critical role of supramolecular assembly in the chemical and structural configurations in a nano‐confined space.

Innovative construction of nano-wrinkled polyamide membranes using covalent organic framework nanoflowers for efficient desalination and antibiotic removal

In recent years, the scientific community has identified the intriguing potential of polyamide (PA) nanofiltration (NF) membranes with nano-wrinkled structures, promising to transcend the longstanding permeability-selectivity trade-off inherent in conventional membranes. The present study advances this frontier by masterfully employing covalent organic framework (COF) nanoflowers, meticulously constructed on substrate surfaces using a sophisticated layer-by-layer self-assembly technique. This innovation mediates the interfacial polymerization (IP) process, integral to PA NF membrane fabrication. Through rigorous analysis employing scanning electron microscopy and atomic force microscopy, the derived PA membrane was found to exhibit a distinctive nano-wrinkled morphology. Remarkably, this novel structure yielded a pure water permeance nearly threefold that of control membranes with conventional nodular PA layers. This enhancement is attributed to a synergistic combination of factors that includes increased surface hydrophilicity, greater surface area, thinner PA layer, and an optimized water transport pathway. Furthermore, this membrane demonstrated an impressive 98.7 % Na2SO4 rejection rate, greater than 96.4 % rejections for four critical antibiotics, and commendable stability in flux with superior anti-fouling characteristics. These groundbreaking insights open new avenues for the development of high-performance nano-wrinkled PA membranes, with far-reaching implications for various environmental applications.

Advanced ion separation in polyamide nanofiltration membranes via interfacial polymerization regulated by dynamic polyphenol-metal coordination

Developing advanced nanofiltration membranes (NFMs) for inorganic salt ions separation remains a significant challenge in the value-added process of water treatment. Herein, we engineered a highly permeable-selective TA/Fe/Ca/PA-p NFM through a novel strategy for the interfacial polymerization (IP) regulated by the dynamic polyphenol-metal coordination. Interestingly, the dynamic coordination occurred after the substrate surface was first modified with tannic acid (TA) and Fe3+ and then coated with an aqueous phase solution containing piperazine (PIP) and Ca2+. In this process, the coordination competition between Fe3+ and Ca2+ for TA and the conversion of TA/Fe3+ bis-complex into tris-complex were conducive to forming more uniform TA/Fe/Ca complex on the substrate surface. Meanwhile, TA can also perform Michael addition with PIP to control the diffusion of PIP to the organic phase. Following the IP reaction, the nascent TA/Fe/Ca/PA NFM underwent post-treatment in a sodium citrate (SC) solution to dissociate the TA/Fe/Ca complex by further applying the dynamic coordination, resulting in a crumpled and thinner separation layer with desirable surface properties. The optimized TA/Fe2/Ca/PA-p NFM exhibited a pure water permeability of 36.1 L m−2 h−1⋅bar−1, nearly 2.4 times higher than that of the original PA NFM. Correspondingly, the Na2SO4 rejection reached 99.4 % and its Cl−/SO42− separation factor was 118.3. This outstanding permselectivity was mainly attributed to the decreased mass transfer resistance, the expanded effective permeability area, and the increased negative charge on the membrane surface. Additionally, the TA/Fe2/Ca/PA-p NFM was endowed with good operational stability, pressure resistance, and antifouling performance. This eco-friendly and cost-effective approach paves the way for fabricating high-performance NFMs and demonstrates the great potential of dynamic polyphenol-metal coordination in water treatment.

Ternary deep eutectic solvent enhanced the diffusion control of amine monomer for highly permeable and anti-fouling polyamide nanofiltration membranes

Thin-film composite nanofiltration (TFC NF) membranes have been widely used in water treatment, while the common active polyamide (PA) separation layer suffers the problems of excessive mass transfer resistance and fouling. In this work, a novel ternary deep eutectic solvent (DES) of citric acid/choline chloride/glycol as an additive in the aqueous phase was focused on regulating the formation of PA layer. The ternary DES can interact with piperazine (PIP) via hydrogen bonding and electrostatic interaction, synergistically enhancing the diffusion control of PIP with viscosity modulation during interfacial polymerization. Notably, a thinner and rougher separation layer with a cellular-like structure was obtained by optimizing the ratio of citric acid in ternary DES. Accordingly, the optimized TFC10%-3 membrane maintained an excellent Na2SO4 rejection (98.8 %) and a 104.7 % increase in pure water permeance (39.5 L·m−2·h−1·bar−1) compared to the original membrane, outperforming commercial membranes and the most NF membranes reported in the literature. Besides, the introduction of citric acid in PA layer increased the surface hydrophilicity and electronegativity of TFC10%-3 membrane, resulting in a higher flux recovery rate (FRR = 93.2 %) of TFC10%-3 membrane than that of TFC10%-0 membrane (FRR = 83.9 %). This study provides a feasible design strategy for the preparation of highly permeable and anti-fouling TFC NF membranes and enrichs the application of ternary DES in water treatment.

Polyamide nanofiltration membrane fabricated via a metal-chelate strategy for high-flux desalination

Nanofiltration (NF) technology, utilizing polyamide (PA) membranes fabricated through interfacial polymerization (IP), has found extensive application in desalination processes. The pursuit of enhancing water permeance while maintaining high rejection rates of NF membranes has garnered substantial research attention. This study proposed a metal-chelate strategy by incorporating calcium chloride (CaCl2) as an aqueous additive during the IP process and employing EDTA-4Na for post-treatment. In the presence of Ca2+, the EDTA-4Na-soaked membrane achieved suitable swelling to better regulate membrane pores, which benefited water flux enhancement and avoided severe structural defects. Meanwhile, the modified membrane also showed a more hydrophilic and negatively charged surface, leading to a significant performance in removing Na2SO4. As a result, the optimized membrane exhibited a water flux of 24.6 L m−2 h−1 bar−1, nearly 3 folds that of the initial PA membrane, while maintaining a satisfactory Na2SO4 rejection (97.2 %). Moreover, the obtained membrane showed good operation stability and anti-fouling properties during long-term use. This work proves that the metal-chelate strategy can be an efficient modification method and inspires the fabrication of high-performance NF membranes with coupling processing.

Modulating interfacial polymerization via 1-methylimidazole as reactive additive for nanofiltration membrane with high-performance

Nanofiltration (NF) membrane technology has become the most critical alternative to resolve fresh water resources shortage and water pollution. Preparing polyamide (PA) NF membrane with excellent water permeance and mono/multivalent salts selectivity is highly desired. Herein, we introduced 1-methylimidazole (1-MI) as a reactive additive into interfacial polymerization (IP) to prepare NF membrane and attempted to improve the NF membrane performance. 1-MI modified NF membranes exhibited enlarged pore size and thickness of PA layer, as well as a smooth and hydrophilic membrane surface, the water permeance improved from 7.7 L/(m2·h·bar) of Virgin-NF to 13.1 L/(m2·h·bar) of 1-MI-0.05-NF. The Na2SO4 rejection was maintained at 95.01% while NaCl rejection dramatically reduced from 25.79% to 13.29%, and the Cl−/SO42− selectivity slightly increased from 21.47 to 23 under the mixed salts solution as feed. The enhancement of water permeance was ascribed to the looser PA layer and enhanced hydrophilicity. The retaining Na2SO4 rejection was attributed to electrostatic repulsion caused by more carboxylic acid groups, and the decreased NaCl rejection was ascribed to the looser PA layer. Besides, the modified membrane had an acceptable pH stability. In summary, 1-MI modified NF membrane was suitable for the separation of monovalent/divalent anionic salts.