Na2SO4 Rejection Research Articles

Gradient crosslinking optimization for the selective layer to prepare polyvinyl alcohol (PVA) nanofiltration (NF) membrane: The enhanced filtration performance and potential rejection for EDCs

Polyvinyl alcohol (PVA) has been employed and crosslinked as the selective layer of NF membranes with enhanced hydrophilicity. However, the influences of different crosslinking methods and agents on the reaction mechanism and membrane performance still need to be comprehensively studied. In this study, NF membranes were prepared by coating crosslinking (CC-membrane) and gradient crosslinking (GC-membrane) methods. Compared with CC-membrane, the GC-membrane possessed a 65% higher flux with Na2SO4 rejection around 90%, under the optimal preparation conditions with PVA content of 0.10%, curing at 80 °C for 10 min. Crosslinking agents including 1,3,5-benzenetricarboxylic acid (TMA), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA) with different spatial structure were used to optimize the GC-membrane. As confirmed by SEM, XPS, FTIR and contact angle tests, the 6FDA-GC membrane showed a thinner, smoother and more hydrophilic selective layer, and kept an excellent balance between the water flux (88.6 L/m2h) and Na2SO4 rejection (88.7%). This is because the 6FDA with a large molecule and flexible spatial structure could form a more integrated crosslinking structure compared to PMDA. Meanwhile, the 6FDA-GC membrane showed rejections of over 80% towards the endocrine-disrupting compound 17α-Ethinylestradiol and exhibited stable antifouling ability and durability. Overall, this work studied systematically the influences of various crosslinking agents on the GC-membrane, and verified the potential of hydrophilic PVA membranes for nanofiltration.

Polyamide membranes with nanoscale ordered structures for fast permeation and highly selective ion-ion separation

Fast permeation and effective solute-solute separation provide the opportunities for sustainable water treatment, but they are hindered by ineffective membranes. We present here the construction of a nanofiltration membrane with fast permeation, high rejection, and precise Cl-/SO42- separation by spatial and temporal control of interfacial polymerization via graphitic carbon nitride (g-C3N4). The g-C3N4 nanosheet binds preferentially with piperazine and tiles the water-hexane interface as revealed by molecular dynamics studies, thus lowering the diffusion rate of PIP by one order of magnitude and restricting its diffusion pathways towards the hexane phase. As a result, membranes with nanoscale ordered hollow structure are created. Transport mechanism across the structure is clarified using computational fluid dynamics simulation. Increased surface area, lower thickness, and a hollow ordered structure are identified as the key contributors to the water permeance of 105 L m2·h−1·bar−1 with a Na2SO4 rejection of 99.4% and a Cl-/SO42- selectivity of 130, which is superior to state-of-the-art NF membranes. Our approach for tuning the membrane microstructure enables the development of ultra-permeability and excellent selectivity for ion-ion separation, water purification, desalination, and organics removal.

Nanovehicle-assisted monomer shuttling enables highly permeable and selective nanofiltration membranes for water purification

Fabricating nanofiltration membranes with high water permeance and selectivity is crucial to efficient water purification. However, achieving such a goal with a simple and cost-effective approach that is compatible with existing membrane manufacturing infrastructure remains a substantial technical challenge. Here we show a strategy of nanoemulsion-regulated interfacial polymerization (NERIP) based on nanovehicle-assisted monomer shuttling for fabricating highly permeable and selective nanofiltration membranes. In NERIP, the nanovehicles, which are surfactant-stabilized oil droplets (in water) enriched with piperazine (PIP), enter and merge into the hexane phase to initiate the polymerization between PIP and trimesoyl chloride. This nanovehicle-assisted monomer shuttling results in the formation of polyamide ‘bubbles’ that later collapse into nanocraters. The nanocrater structure substantially increases the surface area and void fraction of the polyamide layer. The PIP shuttling also accelerates the polymerization reaction, enabling the formation of a thin and highly cross-linked polyamide layer with a more uniform pore size distribution. These structural superiorities yield an unprecedentedly high performance with a water permeance of 36.8 ± 1.9 l m−2 h−1 bar−1 and a Na2SO4 rejection of 99.6 ± 0.1%. NERIP creates a new dimension to fabricate highly permeable and selective nanofiltration membranes for desalination and water purification. The development of advanced nanofiltration membranes should be compatible with existing manufacturing process to be practically useful. A process based on nanoemulsion-regulated interfacial polymerization allows the fabrication of low-cost and high-performance membranes.

Polyamide/polyethylene thin film composite (PA/PE-TFC) NF membranes prepared from reverse-phase interface polymerization (RIP) for improved Mg(II)/Li(I) separation

Polyamide/polyethylene thin film composite (PA/PE-TFC) NF membranes were prepared from reverse-phase interface polymerization (RIP) for improved Mg(II)/Li(I) separation. RIP processes between 1,3,5-benzenetricarbonyl chloride (TMC) in bottom organic phase and piperazine (PIP) in upper aqueous phase were developed to form continuous and intact surface PA separation layers on PE porous substrates thinner than traditional polysulfone (PSF) based substrates. After activation with isopropyl alcohol (IPA), PA/PE-TFC-IPA NF membranes were formed, whose NF performance could be tuned by adjusting the preparation conditions. When TMC concentration was kept at 0.15 % w/v, RIP with low PIP concentration (0.025 wt%) yield PA/PE-TFC-IPA NF membranes with negatively charged surfaces, high Na2SO4 rejection rate (95 % ± 3 %) and water permeance (13–19 L·m−2·h−1·bar−1). RIP with high PIP concentration (0.3 wt%) formed PA/PE-TFC-IPA NF membranes with less negative surfaces, high MgCl2 rejection rate (94.3 ± 0.7 %), low water permeance (4.8 ± 0.3 L·m−2·h−1·bar−1), and high Mg(II)/Li(I) separation coefficient SLi/Mg (18 ± 1) for 1000 ppm LiCl and MgCl2 mixed solution. PA/PE-TFC-IPA NF membranes also showed good long-term stability and improved anti-fouling performance for positively charged pollutants, bearing high potential for applications in the lithium extraction processes.

Poly(vinyl alcohol)-based highly permeable TFC nanofiltration membranes for selective dye/salt separation

Loose nanofiltration (LNF) membranes possessing high water permeance and outstanding dye/salt selectivity are highly desirable for fractionating dyes and salts for textile wastewater. Herein, inexpensive and nontoxic poly(vinyl alcohol) (PVA) was utilized as an aqueous monomer via interfacial polymerization to fabricate novel highly permeable LNF membranes upon activation by sodium hydroxide. Systematic chemical and structural analyses indicated that the prepared polyester membrane formed was loose, hydrophilic, and negatively charged. The properties of the LNF membranes were optimized by adjusting the curing temperature (70 °C–100 °C). The optimized PVA-based membrane (PVA-M70°C) showed excellent water permeability (52.6 L m−2 h−1 bar−1), favorable dye rejection (> 90.0 %) and low salt rejection (NaCl and Na2SO4 rejection rates were lower than 5 % and 18 %, respectively). Furthermore, the PVA-M membrane demonstrated excellent antifouling properties and long-term stability. Considering the biodegradable nature and low cost of PVA, PVA-based polyester membranes show great promise for LNF membrane production on an industrial scale. This work advances the use of PVA as a green aqueous monomer in fabricating highly permeable LNF membranes for efficient dye/salt selectivity.

Antifouling thin-film nanocomposite NF membrane with polyvinyl alcohol-sodium alginate-graphene oxide nanocomposite hydrogel coated layer for As(III) removal

Removal of As(III) from the polluted waters is a challenge. It should be oxidized to As(V) for increasing its rejection by RO membranes. However, in this research, As (III) is directly removed by a high permeable and antifouling membrane prepared through the surface coating and in-situ crosslinking procedure of polyvinyl alcohol (PVA) and sodium alginate (SA) as coating materials containing graphene oxide as a hydrophilic additive on a polysulfone support with glutaraldehyde (GA) chemical crosslinking agent. The properties of the prepared membranes were evaluated through contact angle, zeta potential, ATR-FTIR, SEM, and AFM. The addition of GO in the polymeric networks of SA and PVA hydrogel coating layers led to a better hydrophilicity and a smoother surface and a higher negative surface charge resulted in improvment of permeability and rejection of membranes. Among the prepared hydrogel-coated modified membranes, SA-GO/PSf indicated the highest pure water permeability (15.8 L m−2 h−1 bar−1) and BSA permeability (9.57 L m−2 h−1 bar−1), respectively. The best desalination performance (NaCl, MgSO4, and Na2SO4 rejections of 60.0%, 74.5%, and 92.0%, respectively) and As(III) removal (88.4%) along with satisfactory stability and reusability in cyclic continuous filtration was reported for PVA-SA-GO membrane. In addition, the PVA-SA-GO membrane indicated improved fouling resistance toward BSA foulant with the lowest flux decline of 7%.

Incorporation of Functionalized Halloysite Nanotubes (HNTs) into Thin-Film Nanocomposite (TFN) Nanofiltration Membranes for Water Softening

Incorporating nanoparticles (NPs) into the selective layer of thin-film composite (TFC) membranes is a common approach to improve the performance of the resulting thin-film nanocomposite (TFN) membranes. The main challenge in this approach is the leaching out of NPs during membrane operation. Halloysite nanotubes (HNTs) modified with the first generation of poly(amidoamine) (PAMAM) dendrimers (G1) have shown excellent stability in the PA layer of TFN reverse-osmosis (RO) membranes. This study explores, for the first time, using these NPs to improve the properties of TFN nanofiltration (NF) membranes. Membrane performance was evaluated in a cross-flow nanofiltration (NF) system using 3000 ppm aqueous solutions of MgCl2, Na2SO4 and NaCl, respectively, as feed at 10 bar and ambient temperature. All membranes showed high rejection of Na2SO4 (around 97-98%) and low NaCl rejection, with the corresponding water fluxes greater than 100 L m-2 h-1. The rejection of MgCl2 (ranging from 82 to 90%) was less than that for Na2SO4. However, our values are much greater than those reported in the literature for other TFN membranes. The remarkable rejection of MgCl2 is attributed to positively charged HNT-G1 nanoparticles incorporated in the selective polyamide (PA) layer of the TFN membranes.

Preparation of composite nanofiltration membrane with interlayer for pharmaceutical rejection

It is necessary to prepare a nanofiltration (NF) membrane with high water permeability and excellent pharmaceutical selectivity. In this study, polydopamine/poly(sulfobetaine methacrylate) (PDA/PSBMA) was selected as the interlayer to improve the water permeance of polyamide (PA) composite NF membrane. The introduction of the PDA/PSBMA interlayer led to an increase in the degree of crosslinking of the PA layer and the formation of cracks inside and below the PA layer. As a result, a negatively charged NF membrane with a molecular weight cut-off (MWCO) of 348 Da and an average pore size of 0.23 nm was obtained. The pure water permeance of the optimal NF membrane was 22.0 L·m−2·h−1·bar−1, and the Na2SO4 rejection was 98.9%. Meanwhile, this NF membrane showed excellent rejection of antibiotics. The rejections of erythromycin (ERY), tetracycline hydrochloride (TC), and cephalexin (CA) were 100.0%, 99.4%, and 97.5%, respectively. The separation coefficients of NaCl/TC and NaCl/ERY were as high as 108.2 and 80.8, respectively. In addition, this NF membrane demonstrated outstanding properties in terms of antifouling and long-term stability. The NF membrane with PDA/PSBMA interlayer has excellent potential for pharmaceutical wastewater treatment and antibiotic extraction.

Highly permeable polyamide-holey graphene oxide composite membrane prepared by pressure spray interface polymerization for desalination

The rise of reverse osmosis membranes (RO) has attracted significant attention, which is pivotal to addressing the water shortage. Superior permeability and high selectivity are extremely critical criteria for RO membranes. Therefore, in this study, we reported a novel strategy: pressure spray interface polymerization (PSIP) to prepare ultrathin RO composite membranes. In the approach, besides the developed novel technique, highly permeable holey graphene oxide (HGO) containing nanopores was also used to refine the size of the transport nanochannels during the reaction of m-phenylenediamine (MPD) and the trimethyl chloride (TMC). Meanwhile, the electrostatic interaction between the HGO and MPD provided a solid guarantee for good dispersion in the composite membrane. The resultant pressure spray interface polymerization-highly permeable holey graphene oxide (PSIP-HGO) composite membrane displayed high salt rejection and water permeance, which showed high water permeance of 4.0 Lm−2h−1bar−1 and Na2SO4 rejection of 95% in a concentration of 2000 ppm under 5 bar. Moreover, the PSIP-HGO membrane showed outstanding long-term stability and high chemical stability. Therefore, our work may provide a feasible pathway for designing advanced RO membranes for water desalination.

Silicification-interlayered nanofiber substrates regulated crumpled ultrathin polyamide nanofilms for highly enhanced nanofiltration

Thin-film nanofiber composite (TFNC) membranes have shown great potentials for highly efficient nanofiltration. However, it remains a challenge to construct defect-free ultrathin polyamide nanofilms with designed crumpled structures on polymeric nanofiber substrates via traditional interfacial polymerization (IP) to realize high permeability and selectivity synchronously. Herein, a novel strategy is reported to regulate the polyamide nanofilm by a silicification-interlayered nanofiber substrate with hydrophilic and rugged surface. The silica interlayer could enrich piperazine (PIP) monomers in aqueous solutions and control the releasing towards the interfacial reaction zone, enabling the homogeneous IP reaction and the reduced thickness of PA nanofilms. The silicified nanofiber substrate can also serve as a templating support to crumple the PA nanofilms and thus increase their effective infiltrating area. Furthermore, deep insight has been taken into the intermolecular interactions in the IP system and the fundamental mechanism of the silicification-interlayered nanofiber substrate regulating the IP process via density function theory (DFT) and dissipative particle dynamics (DPD) simulations. The membrane morphologies were observed by SEM and AFM, and chemical structures of membrane surfaces were characterized by FTIR/ATR, XPS and XRD in detail. The hydrophilicity and charged properties of different membrane surfaces were analyzed by water contact angle and Zeta potential tests, respectively. As a result, an ultrathin crumpled PA nanofilm is generated on top of the nanofiber substrate as selective layer, enabling the composite membrane with enhanced water permeability of 19.6 L m−2 h−1 bar−1 (approximately two folds higher than that of the pristine PA membranes) and high Na2SO4 rejection of 96.5%. Meanwhile, the prepared membranes reveal good structural stability not only under different operation pressures but also during long-term filtration processes. This work is believed to provide a facile approach to engineer advanced TFNC membranes with high-efficiency nanofiltration performance.

Kosmotropes and chaotropes: Specific ion effects to tailor layer-by-layer membrane characteristics and performances

So-called specific ion effects strongly impact physicochemical phenomena in among others, morphologies of polymeric membranes. This can be correlated to the identity of the ions, rather than just to their charge or concentration. We use this effect to tune the properties of layer-by-layer membranes prepared with the polyelectrolytes polydiallyldimethylammonium chloride and polystyrene sodium sulfonate. To systematically study this, membranes were prepared using different salts (NaBr, NH4Cl, MgCl2, NaCl, LiCl, MgSO4, NaH2PO4, (NH4)2SO4, Na2SO4). The specific ion effects were evaluated thanks to the classification of salts and PEs into kosmotropes (well hydrated) and chaotropes (poorly hydrated) following the law of matching water affinities (LMWA). The impact of the type of anions and cations on the multilayer formation and membrane performances was evaluated. Membranes prepared with kosmotropic salts achieved stable performances after only 4 bilayers, and almost 6 times higher water permeabilities than membranes prepared with chaotropic salts without compromising and often even improving the membrane's size exclusion behaviour. The salts used tuned the membranes charge: Kosmotropic salts delivered negatively charged membranes with Na2SO4 and MgCl2 retentions till 97% and 10% respectively, while chaotropic salts formed more positively charged membranes with reversed behaviour with Na2SO4 and MgCl2 rejection of 20 and 89%.

Polyamide nanofiltration membrane fabricated with ultra-low concentration triaminoguanidine showing efficient desalination performance

Tuning the reactivity and diffusion of amine monomers in interfacial polymerization (IP) process could efficiently regulate the formation and structure of the polyamide (PA) selective layer. Herein, novel thin-film composite NF membranes with dense and ultrathin PA selective layer were fabricated using 1,3,5-benzenetricarbonyl trichloride (TMC) and ultra-low concentration triaminoguanidine (Tg) as reactive monomers. Fabrication parameters, including Tg concentration, NaOH concentration and reaction time, were systematically explored to optimize the desalination performance of PA-Tg NF membrane. During the stability test over 48 h, PA-Tg-0.06 membrane displayed a water permeance of ∼12 L m−2 h−1·bar−1 and Na2SO4 rejection of ∼99%. Meanwhile, detailed comparisons were made between PA-Tg NF membrane and a typical NF membrane fabricated with PIP as an aqueous monomer, including characteristics of the monomers as well as the structure, water permeance, salt rejection and antifouling property of the membranes. Molecular dynamics simulation and interfacial diffusion experiments indicated that the Tg monomer exhibited a higher reactivity but a lower diffusivity than the PIP monomer, making it feasible for the fabrication of PA-Tg NF membrane with ultra-low concentration of Tg monomer. In addition, compared with the PA-PIP membrane, the PA-Tg membrane exhibited a smoother, more hydrophilic and negatively charged surface, as well as a thinner and denser selective layer, thereby showing a higher water permeance, salt rejection and stronger fouling resistance.

Chlorine resistant polyamide desalination membrane prepared via organic-organic interfacial polymerization

Desalination of seawater, brackish water and urban sewage is an important way to solve the global water shortage. Polyamide (PA) membranes, including reverse osmosis (RO) membrane and nanofiltration (NF) membrane, are the primary technology for seawater desalination and clean water production. However, traditional thin-film composite PA (TFC-PA) membranes prepared from interfacial polymerization (IP) of amine monomers (either piperazine or m-phenylenediamine) in water and acyl chloride monomers in organic solvent are incapable of tolerating strong acid and chlorine environment. Here, we develop a new IP process, which takes place at the immiscible interface between dimethylacetamide (DMAc) and hexane (referred to as organic/organic IP), to prepare both chlorine-resistant and acid-resistant TFC-PA membranes. Compared to conventional water/oil IP process, the organic/organic IP process can adapt more kinds of amine monomers rather than just PIP, such as tetra (4-aminophenyl) methane (TMAP), tris (4-aminophenyl) amine (TAPA), and 4,4′,4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TTA), which we studied in this work, thereby extending the PA molecular structure and enabling the membranes with greatly improved chemical stability. Among them, the TAPM-based TFC-PA membrane exhibits a NaCl rejection of 95.9% and no obvious NaCl rejection deterioration after soaking in a high concentration of NaClO (1000 ppm, pH 7) for more than 30 h, indicating excellent chlorine resistance. The TTA-based TFC-PA membrane shows a Na2SO4 rejection of 97% and remains unchanged after being exposed to a wide pH scan of 2–12. The Organic/organic IP provides a new and easy-to-operate platform for designing chlorine and acid resistant TFC-PA membranes, which will greatly improve their environmental stability as the most advanced desalination membrane at present.

Catalytic template assisted interfacial polymerization for high‐performance acid‐resistant membrane preparation

AbstractHighly permeable acid‐resistant nanofiltration (NF) membranes are of critical significance for the efficient treatment of acidic streams. Enhancing permeability while maintaining the high solute rejection of acid‐resistant NF membranes remains a great challenge due to the low reactivity of monomers. In this work, a novel catalytic template assisted interfacial polymerization (IP) strategy of 3‐aminobenzenesulfonamide (ABSA) and trimesoyl chloride (TMC) was provided to prepare a poly(amide‐sulfonamide) membrane. Aminopyridine doped graphene quantum dots rich in acylation catalytic sites and ZIF‐8 nanoparticles are co‐loaded on a substrate as template. Benefiting from the enhanced phase integrity and self‐inhibition effect of the template assisted IP process, the resulting ultra‐thin acid‐resistant membrane exhibits an excellent water permeance (20.4 Lm−2h−1bar−1) with a high Na2SO4 rejection of 90.5%, which outperforms almost all the reported acid‐resistant NF membranes. Our work paves a versatile way for synthesis of special separation membranes.

Assembly of polyamide nanofilms for nanofiltration membranes with ultra-high desalination performance

A method of assembling nanofilms for nanofiltration (NF) composite membranes with ultra-high desalination performance was developed in this work. A series of graphene quantum dots enhanced polyamide (GPA) nanofilms were primarily prepared via support-free interfacial polymerization. Subsequently, the NF composite membranes with two GPA nanofilms (GPA-GPA) layer-by-layer (LBL) assembly were elaborately designed to achieve effective desalination process. The residual amine groups and acyl chloride groups on the surfaces of GPA nanofilms reasonably formed a nascent polyamide (PA) interlayer between two functional layers. The separation performance of GPA-GPA assembly membranes was dramatically developed through the in-situ formed PA interlayer with network pore structure. Most of assembled NF membranes exhibited Na2SO4 rejection rate above 99.5%, and the permeance was above 20.0 L m−2 h−1 bar−1. This creative strategy of in-situ constructing PA interlayer opened up an innovative path for the design of NF membranes with excellent desalination performance.

Incorporating ionic carbon dots in polyamide nanofiltration membranes for high perm-selectivity and antifouling performance

Recent advances in nanotechnology have brought great opportunities to the developing next-generation nanofiltration membranes for addressing the concern of global water scarcity and energy crisis. Carbon dots have been deemed as a promising nanomaterial for enhancing the nanofiltration performance of polymeric membranes. Herein, carbon dots with cationic amine groups (PEI-CDs) and those with anionic sulfonate groups (PS-CDs) are incorporated into the polyamide selective layer of thin-film nanocomposite (TFN) membranes to create charged nanovoids (free volume) between the carbon dots and the surrounding polyamide network for high-efficiency nanofiltration. The positively charged amine group-based and negatively charged sulfonate group-based nanovoids in the resultant TFN-PEI-CDs and TFN-PS-CDs membranes, respectively, provide alternative pathways for efficient water permeation while effectively rejecting divalent ions via the Donnan and dielectric exclusion effects, thereby overcoming the recurring trade-off between permeability and selectivity encountered by dense polymeric membranes. In particular, the creation of negatively charged nanovoids enables the TFN-PS-CDs membrane to achieve one of the best performances among the recently reported nanofiltration membranes, by showing a nearly tripled pure water permeability of 30.9 L m−2 h−1 bar−1 as well as a higher Na2SO4 rejection rate of 99.4% than the membrane with a pristine polyamide selective layer. Moreover, the TFN membranes demonstrate greater resistance to foulants with charges of the same sign as the nanovoids. This work provides insights into the design of nanovoids with desired properties in other polymeric membranes for high-efficiency filtration processes.

Dually charged polyamide nanofiltration membrane incorporated UiO-66-(NH2)2: Synergistic rejection of divalent cations and anions

Traditional polyamide nanofiltration membranes suffer from permeability-selectivity trade-off limitation and unsatisfactory rejection for divalent cations. Herein, a novel dually charged membrane was constructed by incorporating positively charged UiO-66-(NH2)2 into the negatively charged polyamide layer. Thanks to the customizable nanochannels of metal-organic frameworks, the amino-rich nanochannels of UiO-66-(NH2)2 could be fabricated through a ligand replacement strategy. UiO-66-(NH2)2 played a crucial role in the enhanced rejection of divalent cations, meanwhile negatively charged polyamide surface guaranteed the efficient Na2SO4 rejection. Satisfactory rejections of CaCl2 (96.07 %) and Na2SO4 (90.62 %) were achieved simultaneously by optimal TFN-D5. Meanwhile, TFN-D5 owned the greatly-improved water permeance of 19.44 LMH/bar, which was about 1.5 times better than that of the TFC-control. Calculations based on density functional theory further confirmed UiO-66-(NH2)2 rejected Ca2+ efficiently since the migration energy barrier across UiO-66-(NH2)2 was an order of magnitude higher than that of UiO-66-NH2 and UiO-66. Moreover, the desirable rejections were beyond 94 % towards many divalent cation salts including MgCl2, NiCl2, PbCl2, MnCl2, CdCl2 and ZnCl2. Thus, this work provided an efficient way to realize the synergistic removal of both divalent cations and anions.

Additive manufacturing of defect-healing polyamide membranes for fast and robust desalination

Polyamide membranes that can exclude salts from water have found significant success in desalination applications. The polyamide thickness is difficult to control, as it is closely coupled with other properties including monomer chemistries and substrate structures. In this work, an additive manufacturing strategy using spray-coating to prepare large-area polyamide composite membranes with tunable thickness is explored. Using spray-coating, composite membranes comprising polyamide layers and carbon nanotube (CNT) layers on top of porous substrates are additively constructed. In the context of mediation by CNT layers, thickness control is decoupled from other properties. As a result, the polyamide thickness can be independently adjusted by changing monomer concentrations, and water permeance is found to be related to the thickness. A large-area membrane with a size of 30 × 30 cm2 is successfully prepared under optimal conditions, and exhibits large water permeance of 34.1 L m−2 h−1 bar−1 and high Na2SO4 rejection rate of 95.6%. Importantly, the additive nature holds the ability to eliminate defects possibly existing through multiple spraying, affording defect-healing characteristic. This work allows envisioning a turning point that additive manufacturing is shifting the long-standing paradigm in the preparation of high-performance separation membranes.

Microporous poly(triaminoguanidinium-amide) nanofilms with sub-nm precision for ultra-low molecular weight cut-off in nanofiltration

Poly(triaminoguanidinium-amide) membranes show a high water permeance (19 L m−2 h−1 bar−1) with an ultra-low molecular weight cut-off of 163–200 g mol−1, a high rejection of Na2SO4 (≃99.7%), and a high selectivity between NaCl and Na2SO4 (≃140).

Enhancing the desalination performance of polyamide nanofiltration membranes via in-situ incorporation of zwitterionic nanohydrogel

Designing a nanofiltration (NF) membrane with distinguished high permeability and ion selectivity is attractive for handling hypersaline wastewater. In this work, we used zwitterionic nanogels (ZNGs) as aqueous additives to prepare NF membranes by interfacial polymerization (IP), and comprehensively investigated the chemical composition of the nanogels on the performance of NF membranes. The outcome of characterizations demonstrated that the nanogels mainly exist as an interlayer between the polyethersulfone (PES) substrate and polyamide (PA) layer, which elevated the hydrophilicity and electronegativity of the membrane surface. In addition, due to the stronger steric hindrance, electrostatic interaction and interlayer-promoted gutter effect, the optimized NF membrane prepared with the addition of 0.015 wt% amine functionalized PSB (SBMA-AH) in aqueous solution exhibited an exceptional water permeability of 20.6 L m−2 h−1 bar−1 and high Na2SO4 rejection of up to 99.5 %, as well as high selectivity of 160.1 for separating Cl−/SO42−. The membrane also displayed superior performance stability under different salt concentrations and pressures. The outstanding desalination performance of the as-prepared NF membrane enables it a promising candidate for hypersaline wastewater treatment.