Commercial Nanofiltration Membranes Research Articles

PA/APVC nanofiltration membrane from reactive positively charged substrate membrane

Efficient Li+ and Mg2+ from natural seawater and salt lakes using nanofiltration is essential for efficient extraction of lithium resources and to address the global energy shortage. The combination of size sieving and the Donnan effect is crucial for optimal selectivity. We proposed a positively charged reactive support layer to design dual positively charged layer to enhance the magnesium-lithium separation. The positively charged support layer was prepared by ammoniating the PVC membrane with PEI, and then reacted with TMC to successfully prepare a dual positively charged layer PA/APVC nanofiltration membrane with high Li+/Mg2+ selectivity. The reactive support layer not only established a covalent bond connection with the PA layer, which increased the stability of the active layer, but also showed a positive charge (23.59 mV at pH=7) after ammonization, which further enhanced the Mg2+ repulsion from 82.57 % to 98.56 %. Furthermore, the highest separation factor achieved was 23.34 when a mixed solution containing Mg2+ and Li+ in a mass ratio of 50:1 was utilized, which was 13.48 times that of commercial nanofiltration membranes. The utilization of a reactive substrate membrane in the fabrication process of the PA/APVC membrane offers innovative prospects for future investigations on magnesium-lithium separation, contributing to the advancement of nanofiltration membranes.

Process optimization for the removal of sodium diclofenac from water using a green polymeric membrane

New polymeric membranes for water treatment have been regularly developed and reported by the scientific community; however, process optimization based on the application purpose is necessary to achieve the best performance. In this work, a previously developed “green” polymeric membrane was employed to investigate the influence of process parameters on the removal of sodium diclofenac (DCF) from water. The “green” classification relies on the membrane components (poly(vinyl alcohol) – PVA, citric acid, glycerol, and green synthesized silver nanoparticles) and the mild conditions for its preparation. The parameters studied were the compaction and operational pressure (1.0 – 5.0 bar), feed temperature (10 – 25 °C), DCF concentration (0.002 – 0.010 g L−1), and feed pH (4.0 – 10.0). The results showed a positive influence of pressure on DCF removal (from 54 % to 75 %, within a range of 1.0–5.0 bar) due to the PVA structure densification, as well as the temperature (from 61 % to 82 %, within a range of 10–25 °C) because of the increased water affinity. The DCF concentration influenced the absorption of DCF into the membrane, reaching the maximum of 73 % of DCF removal at 0.007 – 0.010 g L−1. The feed pH determined the mechanism of removal but had a minor influence on the final performance (from 73 % of DCF removal at acidic pH to 77 % at alkaline conditions). The optimized conditions of 5 bar, 25 °C, 0.008 g L−1 DCF, and pH ∼5.75 promoted a permeability of 0.024 L m−2 h−1 bar−1 with 80 % DCF removal. This performance is comparable to that observed for commercial nanofiltration membranes but offers the advantage of a membrane fabricated and operated using a sustainable approach.

A Janus membrane with electro-induced multi-affinity interfaces for high-efficiency water purification.

Drinking water with micropollutants is a notable environmental concern worldwide. Membrane separation is one of the few methods capable of removing micropollutants from water. However, existing membranes face challenges in the simultaneous and efficient treatment of small-molecular and ionic contaminants because of their limited permselectivity. Here, we propose a high-efficiency water purification method using a low-pressure Janus membrane with electro-induced multi-affinity. By virtue of hydrophobic and electrostatic interactions between the functional interfaces and contaminants, the Janus membrane achieves simultaneous separation of diverse types of organics and heavy metals from water via single-pass filtration, with an approximately 100% removal efficiency, high water flux (>680 liters m-2 hour-1), and 98% lower energy consumption compared with commercial nanofiltration membranes. The electro-induced switching of interfacial affinity enables 100% regeneration of membrane performance; thus, our work paves a sustainable avenue for drinking water purification by regulating the interfacial affinity of membranes.

Characterization and performance evaluation of in-house ultrafiltration membrane coupled with photocatalysis for 17α-methyltestosterone hormone removal.

17α-methyltestosterone (MT) hormone is a synthetic androgenic steroid hormone utilized to induce Nile tilapia transitioning for enhanced production yield. This study specifically focuses on the removal of MT through the utilization of photocatalytic membrane reactor (PMR), which employs an in-house polyvinylidene fluoride (PVDF) ultrafiltration membrane modified with 1% nanomaterials (either TiO2 or α-Fe2O3). The molecular weight cut-off (MWCO) of the in-house membrane falls within the ultrafiltration range. Under UV95W radiation, the PMR with PVDF/TiO2 and PVDF/α-Fe2O3 membranes achieved 100% MT removal at 140 and 160 min, respectively. The MT removal by the commercial NF03 membrane was only at 50%. In contrast, without light irradiation, the MT removal by all the membranes remained unchanged after 180 min, exhibiting lower performance. The incorporation of TiO2 and α-Fe2O3 enhanced water flux and MT removal of the membrane. Notably, the catalytic activity was limited by the distribution and concentration of the catalyst at the membrane surface. The water contact angle did not correlate with the water flux for the composited membrane. The degradation of MT aligned well with Pseudo-first-order kinetic models. Thus, the in-house ultrafiltration PMR demonstrated superior removal efficiency and lower operational costs than the commercial nanofiltration membrane, attributable to its photocatalytic activities.

Constructing high-performance nanofiltration membranes using nanofiber supports: Effects of structural stability and polyvinyl alcohol interlayers

Nanofiber supports are promising candidates for constructing high-performance nanofiltration (NF) membranes due to their unique interconnected pores and high porosity. Conventional nanofiber supports usually possess excessive surface roughness and low structural stabilities, influencing the formation of polyamide separation layers. However, research on the effects of nanofiber support properties on the NF membrane performances is relatively few. In this study, we systematically evaluated the effects of structural properties of the nanofiber supports on the performances of the fabricated thin-film nanofiber composite (TFNC) NF membranes. The polyimide (PI) support with heat-pressing post-treatments owns a smooth surface and high structural stability due to the welding and compaction of the PI nanofibers. This promoted the formation of a polyamide separation layer with high smoothness and low fouling tendencies. Consequently, the mechanical strength and long-term operation stability of the TFNC-PI NF membrane were much stronger than that of the membranes with polyacrylonitrile (PAN) and PVDF nanofiber supports. Membrane performance analyses illustrated that the TFNC NF membranes possess notable higher water permeance while slight lower salt rejection than the commercial NF membrane. Compared to TFNC-PAN NF membranes (18∼20 L m-2h−1 bar−1), the water permeance of the structurally stable TFNC-PI NF membrane was relatively low (15–16 L m-2h−1 bar−1) due to its smaller surface filtration area and membrane pore size. Further attempts illustrated that constructing interlayers with 2 wt% polyvinyl alcohol (PVA) coating solutions resulted in the formation of clear and regular Turing structures in the polyamide surface layer. It notably enhanced the water permeance of the membrane by ∼30 % without compromising the salt rejection capability of the membrane. This study provides fundamental insights into the effects of nanofiber support properties on NF performance and feasible pathways to construct high-performance TFNC NF membranes.

Selection of membrane for production of drinking water from surface and groundwater by nanofiltration

The aim of the work was to select a nanofiltration membrane that would ensure effective simultaneous co-removal of pollutants present in surface and groundwater, including contaminants such as bisphenol A and PFAS compounds. Series of membrane filtrations was carried out using 12 commercial nanofiltration membranes (NFX, NFG, NF270, NF90, DK, DL, TS80, SB90, TS40, XN45, NPO30, NPO10) under various operating parameters. The conducted tests showed that among tested membranes the membrane most suitable for the production of drinking water from model waters is the NF90 membrane by Dow Filmtec. Regardless of the composition of the water, its pH and transmembrane pressure, the water produced using NF90 membrane each time met the legal requirements in terms of heavy metals (chromium total, silver, nickel, lead, arsenic), iron, manganese, sulfates, chlorides, fluorides, nitrates, sodium, PFAS, tetrachlorethylene, bisphenol A and KMnO4 index. In addition, tests carried out to verify the susceptibility of the produced water to the formation of disinfection by-products (DBP - ∑THM and halogenoacetic acids) showed that DBP concentrations in produced water did not exceed the values permitted by law.

A homogeneous carbon nitride nanomodifier for promoting the water permeation of polyamide desalination membranes

Nanomaterial modification provides an effective way to enhance the separation performance of nanofiltration membranes, but the limited hydrophilicity of conventional nanostructures causes their poor solubility in solvents, affecting the quality of polyamide membranes for performance enhancement. Herein, we explored quasi-water soluble carbon nitride as a homogeneous modifier to improve the nanofiltration performance of polyamide membranes. With sufficient hydroxyl, amino, and cyano groups, the introduced quasi-water soluble carbon nitride significantly enhanced the surface hydrophilicity of the support membrane, resulting in the formation of an ultrathin functional layer for high-efficiency desalination. The high permeation flux of 108.64 L m-2h−1 (4 bar) was even twice and three times higher than those of the pristine polyamide membrane and commercial nanofiltration membranes, with a high Na2SO4 barrier rate of 98.84 % and a Cl-/SO42- selectivity of 76. This work provides an effective way to precisely regulate the structure of nanofiltration membranes for high-performance water purification.

Are Hansen solubility parameters relevant in predicting the post-treatment effect on polyamide-based TFC membranes?

This study investigates the impact of solvent post-treatment on polyamide-based thin film composite (TFC) membranes, specifically examining the effect on commercial nanofiltration (NF) and reverse osmosis (RO) membranes. Na2SO4 rejection and increase in pure water permeance (PWP) were considered as the output parameters. The disparity in Hansen solubility parameters (HSP) between the post-treatment solution and the polyamide layer of the TFC membrane, denoted by Ra, is well adapted to understand the enhancement in water permeance through the membranes upon treatment. Aqueous solutions of dimethylformamide with a Ra value of 4, acetonitrile with a Ra value of 8.3, and ethanol with a Ra value of 12.7 were used as the post-treatment solutions. Our experimental design, based on the Box-Behnken design of Response Surface Methodology, incorporates variables such as the concentration of the solvent in the solution (% v/v), Ra value, and treatment time (s). Our findings demonstrate that the effect of post-treatment on the TFC membranes is not governed by the Ra value. Notably, while the post-treatment with the aqueous solution of acetonitrile, 80% v/v for 30 s, had considerable effects on NF membranes (124.5% enhancement in PWP; reduction of 3.5% in Na2SO4 rejection), its impact on RO membranes was negligible. Several factors explain this discrepancy, including the limitations of the HSP model for composite polymers, the inaccuracy of the PWP or salt rejection as a swelling indicator, variations in the HSP values of the polyamide layers for different membranes, and possible modifications in the interface between the support membrane and the polyamide layer. In summary, our study provides insights into the complex interactions between solvents and composite membranes, indicating that HSP alone is not a decisive factor in predicting post-treatment effects on polyamide-based TFC membranes.

Evaluation of commercial nanofiltration and reverse osmosis membrane filtration to remove per-and polyfluoroalkyl substances (PFAS): Effects of transmembrane pressures and water matrices.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are now widely found in aquatic ecosystems, including sources of drinking water and portable water, due to their increasing prevalence. Among different PFAS treatment or separation technologies, nanofiltration (NF) and reverse osmosis (RO) both yield high rejection efficiencies (>95%) of diverse PFAS in water; however, both technologies are affected by many intrinsic and extrinsic factors. This study evaluated the rejection of PFAS of different carbon chain length (e.g., PFOA and PFBA) by two commercial RO and NF membranes under different operational conditions (e.g., applied pressure and initial PFAS concentration) and feed solution matrixes, such as pH (4-10), salinity (0- to 1000-mM NaCl), and organic matters (0-10mM). We further performed principal component analysis (PCA) to demonstrate the interrelationships of molecular weight (213-499 g·mol-1 ), membrane characteristics (RO or NF), feed water matrices, and operational conditions on PFAS rejection. Our results confirmed that size exclusion is a primary mechanism of PFAS rejection by RO and NF, as well as the fact that electrostatic interactions are important when PFAS molecules have sizes less than the NF membrane pores. PRACTITIONER POINTS: Two commercial RO and NF membranes were both evaluated to remove 10 different PFAS. High transmembrane pressures facilitated permeate recovery and PFAS rejection by RO. Electrostatic repulsion and pore size exclusion are dominant rejection mechanisms for PFAS removal. pH, ionic strength, and organic matters affected PFAS rejection. Mechanisms of PFAS rejection with RO/NF membranes were explained by PCA analysis.

Structure and transport properties of self-assembled nanofiltration membranes based on sustainably derived materials

The development of functional polymers using sustainable resources is an increasingly important pursuit. Unsaturated fatty acids represent a potentially interesting class of renewable materials for this purpose. Their unsaturated carbon bonds permit crosslinking to form solid polymers. Additionally, their carboxylic acid functional groups provide for the display of specific surface chemistry within the resulting polymers, and also enable chemical derivatization. Here, we explore the fabrication of nanometer-scale size-selective membranes using conjugated linoleic acid derived monomers. Potassium salt conjugated linoleic acid surfactants (KCLA) self-assembled to form hexagonally packed cylinders (HI) in an aqueous medium containing glycerol. This structure provides a highly ordered medium with aqueous-continuous channels for nanofiltration. The HI mesophase was crosslinked with the addition of bifunctional comonomers and the ordered structure was retained with good fidelity in the resulting thin polymer films (< 400 nm thick). These film function effectively as nanofiltration membranes, with a size cut-off of approximately 1.2 nm for charged solutes, while maintaining a high permeance of ∼ 9 LMH/bar. This performance is on par with several commercial nanofiltration membranes and these materials are therefore of potential interest for advancing sustainability concerns in practical nanofiltration applications.

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.

Catalytic pre-coat on ceramic nanofiltration membranes for segregation and Fenton cleaning of high-resistance colloids in direct surface water treatment

Ceramic nanofiltration (NF) is a promising alternative for direct surface water treatment, but is hampered for full-scale applications by fouling and a lack of eco-friendly cleaning regimes. In this work, an innovative reactive pre-coat layer, consisting of an iron oxychloride catalyst, was constructed on top of commercial ceramic NF membranes, for segregating a large-sized colloid fraction in canal water and Fenton cleaning with a hydrogen peroxide (H2O2) solution. The large-sized colloids (3−30 μm) were identified as dominant substances fouling the TiO2 separation layer of the pristine membranes, leading to a fast increase in their filtration resistance, in contrast to the small-sized colloids (<0.04 μm) and natural organic matter (NOM). As a consequence, the catalyst pre-coat layer with a pore size of 0.1–0.5 μm was able to segregate the large-sized colloids from the TiO2 separation layer during direct filtration of the raw water. Moreover, filtration under an acceptable flux of around 23 L m−2 h−1 did not cause pore clogging in the catalyst pre-coat. In addition, Fenton oxidation initiated by the catalytic pre-coat efficiently restored the filtration resistance, whereas sole H2O2 flush of the pristine membrane was not effective. In the meantime, the TiO2 separation layer of the membrane exerted a high NOM rejection of approximately 90%, measured as dissolved organic carbon, while the catalyst pre-coat on the membrane remained active in Fenton cleaning, over five one-day cycles. The findings of this work may provide guidance on the structural and functional design of a catalytic pre-coat layer for a dual purpose of foulant segregation and oxidative removal, particularly in response to key fouling-causing substances, during membrane-based treatment of real water matrices.

Effect of pH by Manganese Salts and Natural Organic Matter on Nanofiltration Membrane Fouling

This research aimed to determine the removal performance of manganese affected from solution pH of combined manganese salts with natural organic matter (NOM) using commercial nanofiltration (NF) membrane. The filtration experiments were tested under a dead-end filtration test cell. Variational factors used in this study were the types of manganese salts (i.e. manganese chloride (MnCl2), manganese sulfate (MnSO4), and manganese nitrate (Mn(NO3)2)) with the solution pH of 3, 5, and 7, and ionic strength of 0.01 mol/L. Water samples were prepared with NOM concentration of 10 mg/L, while the operating pressure was operated constant at 60 psig. Experimental results found that the MnSO4 salt provided the highest manganese removal efficiency of 95%, while the removal efficiencies of MnCl2 and Mn(NO3)2 were about 84.86% and 70.7%, respectively. Solution fluxes were not significantly different. In the presence of NOM concentration of 10 mg/L, solution pH of 3–7, it was found that low solution pHs for all conditions provided the highest manganese removal. The removals of NOM were relatively high more than 97%. The mathematical fouling model was done with cake filtration model (CFM) due to NOM accumulation on NF membrane surface.

Evaluation of nanofiltration and reverse osmosis membranes for efficient rejection of organic micropollutants

Nanofiltration (NF) and reverse osmosis (RO) membranes have revolutionized water treatment processes. However, emerging separations, such as the removal of organic micropollutants (OMPs), pose a challenge for traditional RO and NF membranes due to either low water permeance (RO) or inadequate OMP rejection (NF). In this work, we investigated the rejection of thirteen frequently detected OMPs at environmentally relevant low feed concentration of 12 μg/L by using a wide range of commercial RO and NF polyamide thin-film composite (TFC) membranes and an in-house prepared NF membrane. The membranes were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle, and surface charge measurements. We investigated removal capabilities of OMPs at standard brackish water RO operating conditions (i.e., 15.5 bar transmembrane pressure, pH 8) and also examined the effect of feed solution transmembrane pressure on membrane performance. The rejection of ionic OMPs was strongly influenced by electrostatic repulsion effects, whereas rejection of non-ionic solutes was primarily driven by size exclusion and hydrophobic/hydrophilic interactions. The best performing TFC membranes — a lab-made semi-aromatic piperazine-based NF polyamide membrane and a fully aromatic commercial polyamide NF membrane (NF1) — displayed excellent rejection of OMPs comparable to a commercial RO seawater membrane (RO4), but exhibited ∼2-fold and ∼6-fold higher water permeance, respectively.

Enhancing nanofiltration membrane selectivity between mineral salts and organic pollutants by sulfonic acid functionalization for drinking water treatment

Efficient removal of natural organic matter (NOM) and organic micropollutants (OMPs) while preserving essential mineral salts is a critical goal of high-quality drinking water production, which has not been satisfyingly achieved by available nanofiltration (NF) membranes. In this study, a facile modification strategy was developed to enhance membrane salt/organics selectivity, purposely utilizing the advantages of sulfonic acid groups including high hydrophilicity, strong acidity and low complexation propensity for divalent cations. The post-treatment using a heated alkaline solution of taurine endowed the membrane with reduced active layer thickness, properly enlarged pore size and more favorable surface characteristics inheriting from grafted sulfonic acid groups. Compared to the control one, the optimal modified membrane exhibited a more than doubled water permeance and significantly reduced rejections of Ca2+ and Mg2+, while maintaining a high removal capacity for OMPs. The membrane superiority in the rejection selectivity between mineral salts and NOM was further demonstrated for natural surface water treatment, which outperformed a variety of commercial NF membranes. Improved dual resistance to Ca2+-involved organic fouling and scaling was also achieved by the sulfonic acid functionalized membrane with a higher passage of Ca2+. This study provides insights on the fit-for-purpose enhancement of membrane performance for more efficient water treatment.

Polyelectrolyte multilayers modification of nanofiltration membranes to improve selective separation of mono- and multivalent cations in seawater brine

Nowadays, brine produced in the Reverse Osmosis (RO) seawater desalination plants is a significant and largely untapped source of critical minerals and metals, which is usually discharged into the seas as wastewater. As a front face stage in the brine mining process, nanofiltration (NF) membranes can be used to separate brine stream into monovalent and multivalent ion-rich streams. Since high separation factors are required in seawater RO brine, polyelectrolyte multilayers with Layer-by-Layer (LbL) technique were used in this study to modify commercial polyamide NF membranes and improve their performance. Two common polyelectrolytes, poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated onto two poly-piperazine polyamide NF membranes (NF270 and Desal-5 DL). The effects of the bilayers number and the outer layer charge on membranes’ performance were studied using two crossflow filtration setups with two different membrane sizes to find the membrane with the higher monovalent/multivalent separation factor. Desal-5 DL membrane coated with 5.5 bilayers provided the highest selectivity factors for mono/multivalent cations (> 21), the highest average rejection of multivalent cations group (about 95.7%) for short-term experiments. Another interesting result was the increase in water permeance of the Desal-5 DL membrane after it was coated with 5.5 bLs (indicating more than 20% improvement in pure water permeance). In addition, the stability test with brines at 20 bar showed that this membrane was stable over an extended period of filtration (22 hours) with an even higher selectivity factor of 34 and multivalent cations rejection of 97.7% on average.

Surface modification of FeⅢ-juglone coating on nanofiltration membranes for efficient biofouling mitigation

Nanofiltration membranes have increasingly played a vital role in the purification of surface water and the recycling of wastewater. However, the problem of membrane biofouling, which leads to shortened service life and increased energy consumption, has hindered the widespread application of nanofiltration membranes. In this study, we developed functionalized nanofiltration membranes with anti-adhesive and anti-biofouling properties by coordinating FeIII and juglone onto commercial nanofiltration membranes in a facile and viable manner. Due to the hydrophilic nature of the FeⅢ-juglone coating as well as its ultra-thin thickness and minimal impact on the membrane pores, the permeance of the optimally modified membrane even increased slightly (14 %). The outstanding anti-adhesive property of the FeⅢ-juglone coating was demonstrated by a significant reduction in the adsorption of proteins and bacteria. Furthermore, the modified membranes exhibited lower flux decline amplitude and reduced biofilm deposition during dynamic fouling experiment, further supporting the outstanding anti-biofouling performance of the nanofiltration membrane after the modification with FeⅢ-juglone coating. This study presents a novel and feasible approach for simultaneously improving the water permeance, anti-adhesive property and anti-biofouling property of commercial nanofiltration membranes.

Removal of antibiotics and estrogens by nanofiltration and reverse osmosis membranes

The separation behavior of a variety of emerging contaminants, including nine antibiotics and six estrogens commonly reported in natural environment, by four commercial nanofiltration and reverse osmosis (NF/RO) membranes at various water conditions (pH, concentration) was investigated. The contaminant rejection at pH 6.0 followed a decreasing trend of XLE (94%–100%) ≈ NF90 (88%–100%) ＞ NF270 (25%–85%) ＞ DL (16%–75%). The dense structures of NF90 and XLE reflected by their small effective pore radii (0.30–0.31 nm) contributed mainly to their high rejection, demonstrating the important role of size exclusion. For the negatively charged loose NF270 and DL membranes (0.40–0.45 nm), charge repulsion made additional contribution, which is markedly reflected by their greater rejection to charged antibiotics than neutral estrogens (45%–85% vs. 25%–60% by NF270). The correlation between rejection data and normalized molecular sizes at pH 4.0 and 9.0 intuitively demonstrated the individual role of size exclusion and charge repulsion. The adsorption by membranes was mainly responsible for the initial compound reduction in feedwater by 6%–25% within 3 h, while only 0.3%–5.6% was attributed to self-degradation. The adsorption capacity was determined, which might be mainly governed by hydrophobic interaction. The resolved controlling factors and mechanisms will contribute to the accurate prediction and membrane selection for trace contaminant removal by membrane process.

Multipass Nanofiltration for Lithium Separation with High Selectivity and Recovery.

Nanofiltration (NF) is a promising and sustainable process to extract Li+ from brine lakes with high Mg2+/Li+ mass ratios. However, a trade-off between Li/Mg selectivity and Li recovery exists at the process scale, and the Li/Mg selectivity of commercially and lab-made NF membranes in a single-pass NF process is insufficient to achieve the industrially required Li purity. To overcome this challenge, we propose a multipass NF process with brine recirculation to achieve high selectivity without sacrificing Li recovery. We experimentally demonstrate that Li/Mg selectivity of a three-pass NF process with a commercial NF membrane can exceed 1000, despite the compromised Li recovery as a result of co-existing cations. Our theoretical analysis further predicts that a four-pass NF process with brine recirculation can simultaneously achieve an ultrahigh Li/Mg selectivity of over 4500 and a Li recovery of over 95%. This proposed process could potentially facilitate efficient NF-based solute-solute separations of all kinds and contribute to the development of novel membrane-based separation technologies.

Nanofiltration Membranes for the Removal of Heavy Metals from Aqueous Solutions: Preparations and Applications.

Water shortages are one of the problems caused by global industrialization, with most wastewater discharged without proper treatment, leading to contamination and limited clean water supply. Therefore, it is important to identify alternative water sources because many concerns are directed toward sustainable water treatment processes. Nanofiltration membrane technology is a membrane integrated with nanoscale particle size and is a superior technique for heavy metal removal in the treatment of polluted water. The fabrication of nanofiltration membranes involves phase inversion and interfacial polymerization. This review provides a comprehensive outline of how nanoparticles can effectively enhance the fabrication, separation potential, and efficiency of NF membranes. Nanoparticles take the form of nanofillers, nanoembedded membranes, and nanocomposites to give multiple approaches to the enhancement of the NF membrane's performance. This could significantly improve selectivity, fouling resistance, water flux, porosity, roughness, and rejection. Nanofillers can form nanoembedded membranes and thin films through various processes such as in situ polymerization, layer-by-layer assembly, blending, coating, and embedding. We discussed the operational conditions, such as pH, temperature, concentration of the feed solution, and pressure. The mitigation strategies for fouling resistance are also highlighted. Recent developments in commercial nanofiltration membranes have also been highlighted.