Nanofiltration Membranes Research Articles

Synergistic Optimization Strategies for SA-PVA Hydrogel Nanofiltration Membrane Performance by MWCNTs and TiO2

Synergistic Optimization Strategies for SA-PVA Hydrogel Nanofiltration Membrane Performance by MWCNTs and TiO2

Design of Loose Nanofiltration Membranes by Tailoring Hydrophilicity and Molecular Mass of Deep Eutectic Solvent Additives: Thermodynamics and Kinetics of Phase Inversion

Design of Loose Nanofiltration Membranes by Tailoring Hydrophilicity and Molecular Mass of Deep Eutectic Solvent Additives: Thermodynamics and Kinetics of Phase Inversion

Nanofiltration Membrane with Enhanced Ion Selectivity Based on a Precision-Engineered Ultrathin Polyethylene Supporting Layer.

Nanofiltration (NF) technology is increasingly used in the water treatment and separation fields. However, most research has focused on refining the selective layer while overlooking the potential role of the supporting layer. With expertise in ultrathin polymer films, particularly in the production of polyethylene (PE) membranes, we explore the possibility of improving NF membrane performance by precisely controlling the structure and surface properties of the ultrathin supporting layer in this work. Here, we introduced an innovative NF membrane that used a submicrometer ultrathin PE membrane produced through a biaxial stretching process, which is significantly thinner than commercial PE membranes available on the market. The core innovations are as follows: first, we focused on precise control of the supporting layer rather than just the selective layer, achieving significant enhancements in overall NF membrane performance; second, the ultrathin PE supporting layer served as a tunable interface for interfacial polymerization, offering possibilities for structural control of the selective layer and advancing membrane performance innovations. The resulting NF membrane boasts an overall thickness of ∼630 nm, which represents the thinnest NF membrane documented to date. This ultrathin NF membrane showed an ultrahigh Cl-/SO42- selectivity of 338.03, placing it at the forefront of existing literature. This study sheds light on the important role of the supporting layer in the preparation of selective layers. We believe that this approach has the potential to contribute to the development of ultrathin, high-performance NF membranes.

Interfacially Cross-Linked Polydopamine/Polybenzimidazole Composite Membranes for Organic Solvent Nanofiltration.

Interfacial cross-linking was used to prepare composite organic solvent nanofiltration (OSN) membranes comprising a polydopamine (PDA) active layer formed on a polybenzimidazole (PBI) substrate. Dibromo-p-xylene (DBX) was employed as a cross-linking agent to make the composite membranes chemically stable against harsh polar aprotic solvents. The interfacial cross-linking of PDA/PBI allowed for finely tuning the molecular weight cutoff (MWCO) of the membrane, resulting in a membrane with precise molecular separation capabilities for OSN. The morphology and surface properties of the membranes were characterized, and a membrane with a MWCO of 286 Da was investigated for OSN of a series of solvents. The membrane permeance was in the order of acetonitrile (MeCN) > methanol (MeOH) > acetone > toluene > dimethylformamide (DMF) > heptane > ethanol (EtOH) > isopropanol (IPA) > tetrahydrofuran (THF). The membranes displayed a sharp pore size distribution, yielding a rejection rate of over 99% for Rose Bengal (RB, MW 1020 g/mol) and Remazol brilliant blue (RBB, MW 626.5 g/mol) from DMF and EtOH solutions. When it came to methyl orange (MO, MW 327.3 g/mol) that had a molecular weight closer to the MWCO of the membrane, the membrane still displayed a high rejection rate of 95% and 99% in nanofiltrating solvents DMF and EtOH, respectively. In addition, it was demonstrated that the membrane was able to effectively fractionate mixed solutes having molecular weights appropriate for the MWCO rating of the membrane during OSN.

Nanofiltration Membranes Containing a Metal–Polyphenol Network Layer: Using Casting Solution pH as a Tool to Tailor the Separation Performance

Nanofiltration Membranes Containing a Metal–Polyphenol Network Layer: Using Casting Solution pH as a Tool to Tailor the Separation Performance

Organic Solvent Nanofiltration Membrane with In Situ Constructed Covalent Organic Frameworks as Separation Layer

Organic solvent nanofiltration (OSN) technology is advantageous for separating mixtures of organic solutions owing to its low energy consumption and environmental friendliness. Covalent organic frameworks (COFs) are good candidates for enhancing the efficiency of solvent transport and ensuring precise molecular sieving of OSN membranes. In this study, p-phenylenediamine (Pa) and 1,3,5-trimethoxybenzene (Tp) are used to construct, in situ, a TpPa COF skin layer via interfacial polymerization (IP) on a polyimide substrate surface. After subsequent crosslinking and activation steps, a kind of TpPa/polyimide (PI) OSN membrane is obtained. Under optimized fabrications, this OSN membrane exhibits an ethanol permeance of 58.0 LMH/MPa, a fast green FCF (FGF) rejection of 96.2%, as well as a pure n-hexane permeance of 102.0 LMH/MPa. Furthermore, the TpPa/PI OSN membrane exhibits good solvent resistance, which makes it suitable for the separation, purification, and concentration of organic solvents.

Polyamide-Crystalline Covalent Organic Framework Dual-Layer Nanofiltration Membrane with Improved Ion Selectivity

Polyamide-Crystalline Covalent Organic Framework Dual-Layer Nanofiltration Membrane with Improved Ion Selectivity

Carbon-Doped TiO2 Nanofiltration Membranes Prepared by Interfacial Reaction of Glycerol with TiCl4 Vapor

In the pursuit of developing advanced nanofiltration membranes with high permeation flux for organic solvents, a TiO2 nanofilm was synthesized via a vapor–liquid interfacial reaction on a flat-sheet α-Al2O3 ceramic support. This process involves the reaction of glycerol, an organic precursor with a structure featuring 1,2-diol and 1,3-diol groups, with TiCl4 vapor to form organometallic hybrid films. Subsequent calcination in air at 250 °C transforms these hybrid films into carbon-doped titanium oxide nanofilms. The unique structure of glycerol plays a crucial role in determining the properties of the resulting nanopores, which exhibit high solvent permeance and effective solute rejection. The synthesized carbon-doped TiO2 nanofiltration membranes demonstrated impressive performance, achieving a pure methanol permeability as high as 90.9 L·m−2·h −1·bar−1. Moreover, these membranes exhibited a rejection rate of 93.2% for Congo Red in a methanol solution, underscoring their efficacy in separating solutes from solvents. The rigidity of the nanopores within these nanofilms, when supported on ceramic materials, confers high chemical stability even in the presence of polar solvents. This robustness makes the carbon-doped TiO2 nanofilms suitable for applications in the purification and recovery of organic solvents.

Nanofiltration membrane performance in recirculating aquaculture systems: modeling permeate concentration with diverse pre-treatment configurations

Nanofiltration membrane performance in recirculating aquaculture systems: modeling permeate concentration with diverse pre-treatment configurations

Weakly-negatively-charged loose nanofiltration membranes tailored by polyethyleneimine for dye/salt separation

Loose nanofiltration membranes with a weakly negatively charged surface were made from interfacial polymerization between natural hydrophilic polymer carboxylated chitosan (C-CS) and trimesoyl chloride (TMC) firstly and further depositing branched polyethyleneimine (PEI) on top of the surface to tailor the membrane structures and surface charge properties. This kind of membrane was exploited for dye/salt separation in textile wastewater treatment. The effects of contents and molecular weights of PEI on the morphologies, surface charge, hydrophilicity, pore size, and dye/salt separation performance of the membrane were comprehensively investigated. We found that the top layer of PEI with a moderate molecular weight is suitable to form a loose structure for dye/salt separation. The optimized membrane has a comparable high water permeability (44.4 L/m2.h.bar), a low salt rejections (2.6 % for Na2SO4, 7.7 % for NaCl, and 6.8 % for MgCl2), a relatively high dye rejection (96.9 % for Congo Red, 85.4 % for Methyl Blue, 51.1 % for Bromophenol Blue, and 48.3 % for Reactive Black 5), and an extremely high CR/Na2SO4 fractionation ratio (37.27). Moreover, the resultant membrane shows excellent anti-fouling performance after 5 cycles (50 h) of filtration. It maintains a high Congo Red rejection during a 10-day long-term run. This study shows an easy way to fabricate and adjust the properties of loose nanofiltration membranes that work well for dye/salt separation using common and low-cost polymers. It shows promising potential in the application of textile wastewater treatment and resource recovery.

Poly(bis(1‐methylpiperazin‐1‐ium‐amide) Nanofilm Composite Membrane with Nanochannel‑Enabled Microporous Structure and Enhanced Steric Hindrance for Magnesium/Lithium Separation

AbstractEfficient lithium/magnesium (Li+/Mg2+) separation attainment is fundamental to the extraction of lithium from brine by nanofiltration membrane separation process, which is essential for resource recovery and a circular water economy. However, for poly(piperazine‐amide) nanofilm composite membranes, the higher electronegativity affects the Mg2+ rejection and consequently Li+/Mg2+ separation performance. Manipulating the positive charge density and pore size regulation of the nanofiltration membranes are determinative of the Li+/Mg2+ separation performance improvement. Here, a new monomer 1,1′‐(hexane‐1,6‐diyl)bis(1‐methylpiperazin‐1‐ium) bromide containing bis‐quaternary ammonium cations is employed as a molecular building block to fabricate polyamide nanofilms via interfacial polymerization. The dual quaternary ammoniums and the rod‐shaped conformation of the monomer confer enhanced electropositivity, steric hindrance, loosely packed microporous network structure (pore diameter∼0.8–1.35 nm), and high free volume. The resultant membrane exhibits high water permeance of 28.34 L m−2 h−1 bar−1 with good Li+/Mg2+ selectivity of up to 76.9. In addition, the membrane also exhibits chlorine stability performance owing to the lack of the chlorine sensitive −NH groups in the formed tertiary amide structures. Computational insights on the structural properties, nanofilm formation, and transmembrane water and ion transport behaviors are provided. This study offers insightful theoretical and technological concepts to design and construct membrane materials for energy‐efficient separations.

High performance composite hollow fiber nanofiltration membrane fabricated via the synergistic effect of co-solvent assisted interfacial polymerization and macrocyclic polyamine incorporation

The necessity for high-performance thin film composite (TFC) nanofiltration (NF) membranes for drinking water and wastewater treatment is becoming increasingly apparent in the face of the global water crisis. In this work, co-solvent (acetone) assisted interfacial polymerization (CAIP) and incorporating macrocyclic polyamine (Cyclen) as an aqueous co-monomer were employed to fabricate hollow fiber (HF) NF membrane and to enhance the permeability and the selectivity, respectively, thereby overcoming the inherent trade-off effect. The effects of Cyclen and acetone on the separation performance were comprehensively investigated, and the interfacial polymerization conditions were optimized. The optimal HF NF membrane exhibits a 68.6 % increment in water permeance relative to the baseline membrane while without sacrificing the Na2SO4 rejection which is as high as 99.2 %. In particular, it exhibits a superior high pure water permeability of 222.5 L m−2 h−1 MPa−1, ranking among the highest observed for HF NF membranes in the existing literature. Moreover, it exhibits excellent acid resistance as well as fouling resistance. This research paves a novel approach for developing high-performance HF NF membranes for water and wastewater treatment.

Ultra-fast interlayer construction strategy for the preparation of NF membranes with high Li+/Mg2+ separation performance

Nanofiltration (NF) membranes have demonstrated significant potential in lithium extraction from salt-lake brines due to their superior selectivity in separating monovalent cations from divalent cations. In this paper, NF membranes with high permeate flux and high lithium-magnesium separation factor (SLi,Mg) were prepared by using a polyamide (PA) layer as the separation layer, RA-PEI as the interlayer, and a polysulfone (PSf) membrane as the substrate membrane. Notably, the RA-PEI co-deposition modification method is an ultra-fast substrate modification method, requiring only 1s for modifying PSf substrates. At the same time, RA-PEI firmly adheres to the surface of the PSf substrate by the synergistic effects of intermolecular hydrogen bonding interactions and π-π interactions. This was further verified by comparing the adsorption energies of different kinds of organic interlayers and PSf substrates obtained from molecular dynamics (MD) simulations. Correlation characterization showed that the RA-PEI interlayer endowed the NF membranes with reduced average pore size as well as attenuated electronegativity, thus realizing the efficient separation of Mg2+ and Li+. The performance assessment showed that the membrane containing RA-PEI interlayer exhibited excellent separation performance and permeate flux in simulated salt-lake brine (2000 ppm, WMg/Li = 20), where SLi,Mg (92.8) and permeate flux (16.7 L·m−2·h−1·bar−1) were improved by 7.8 and 2.2 times, respectively, in comparison to the pristine NF membrane. Therefore, this work provides a useful contribution to the practical use of NF membranes for lithium extraction from salt lakes.

Multifunctional role of surfactant in fabricating polyamide nanofiltration membranes for Li+/Mg2+ separation

Extracting Lithium from salt-lake brines can effectively alleviate global lithium scarcity. Separating the co-existing Mg2+ ions from Li+ ions in the brines is essential. While thin-film composite (TFC) nanofiltration (NF) membrane show potential for this separation, commercial NF membranes with negatively charged surfaces fail to meet the high rejection requirement for Mg2+ ions due to the electrostatic attractions between membranes and cations. Positively charged NF membranes fabricated by interfacial polymerization (IP) between aqueous phase polyethylenimine (PEI) and hexane phase trimesoyl chloride (TMC) have shown promise for Li+/Mg2+ separation. However, lithium extraction efficiency is greatly limited by the relatively low permeance and high lithium rejection of the membrane caused by an excessively cross-linked structure. Therefore, optimizing the pore size while maintaining the positive charge of PEI/TMC-based TFC membranes is necessary. We propose adding anionic surfactants to the aqueous PEI solution to modulate PEI/TMC-based NF membrane formation. Surfactants control PEI diffusion in IP through their interactions and improve reaction uniformity at the water-hexane interface. This results in a narrow pore size distribution of the PA network. In this study, three sulfate surfactants with varying alkyl chain lengths were used to control membrane formation. Results showed that sodium n-decyl sulfate (SDES), the shortest sulfate surfactant, improved membrane performance most effectively. The optimized membrane exhibited a crumpled surface and relatively loose pore structure with narrow pore size distribution. It demonstrated a pure water permanence of 5.65 L m−2 h−1 bar−1, high MgCl2 rejection of 92.6 %, and low LiCl rejection of 21.5 %. After filtering a Mg2+ and Li+ binary mixture solution, the Mg2+/Li+ ratio decreased significantly from 40 (feed) to 3.08 (permeate). This study provides an efficient strategy for preparing PEI/TMC-based NF membranes with favorable Li+/Mg2+ separation performance.

Fabrication of tight polyamide nanofiltration membrane by using a pyridine-diamine precursor for heavy metal ions removal

Nanofiltration offers a promising solution for removing heavy metal ions from wastewater, thereby mitigating ecological and environmental risks. In this study, we synthesized a novel pyridine-diamine precursor 2,6-dipiperazine pyridine (PyBPIP), and employed it as the sole aqueous monomer to fabricate tight polyamide (PA) nanofiltration (NF) membranes via interfacial polymerization (IP) method with trimesoyl chloride for the separation of heavy metals. The resulting membrane features an ultrathin PA functional layer (approximately 60 nm), a lower molecular weight cut-off of 251 Da, and a weakly negatively charged surface. This NF membrane exhibits competitive water permeance of approximately 7.67 LMH/bar and excellent rejection rates exceeding 98 % for various heavy metals ions including Zn2+, Mn2+, Cu2+, along with outstanding separation performance for other divalent cations. Additionally, the NF membrane also exhibits robust stability during the 72-h operational test. In summary, this study demonstrates the feasibility of designing suitable monomers for the preparation of highly perm-selective NF membranes for the removal of heavy metal ions in wastewater.

Stepwise increasing TMC concentration in NF membranes fabrication for controlled PA layer thickness, compactness, and charge distribution: Maintaining high permeance, enhancing desalination, and mechanistic insights

Piperazine (PIP)-based polyamide (PA) nanofiltration (NF) membranes exhibit limited rejection of divalent cations due to their negatively charged surfaces and insufficient compactness, restricting their broader application in various water treatment processes. To overcome this challenge, a novel strategy—stepwise increasing TMC concentration (SITC) during the interfacial polymerization (IP)—was proposed to optimize the PA layer structure. Conventional PA layer demonstrates a vertical diffusion structure: a compact barrier region underneath a thick and loose region. The regulatory goal of SITC is to enhance compactness while minimizing the increase in hydraulic resistance. The regulatory mechanism suggested SITC could regulate the IP reaction in both over time (throughout the IP process) and across the reaction region. During the initial IP stage, SITC reduced the reaction rate and increased PIP/TMC ratio in the bottom reaction zone, thereby improving the compactness and potential of final bottom barrier region. Thus, SITC can effectively restrict the permeation of cations, significantly increasing MgCl2 rejection from 33.70 % to 92.12 %. In the subsequent diffusion-limited stage, SITC enhanced the restriction on PIP diffusion, decreasing the thickness of the final upper loose region and surface potential. Those advantageous characteristics allowed the membrane to maintain a high rejection for Na2SO4 (>98.44 %). Concurrently, the membrane maintained a high water permeance (13.00 L·m−2·h−1·bar−1), attributed to the thin (16.69 nm) and optimized compactness distribution of its PA layer. This study provided a novel mechanism insight into the functional customization of NF membranes by decoupling the synthesis-property-performance relationship.

The importance of ionic hydration in the transport of monovalent anions through nanofiltration membranes

The importance of ionic hydration in the transport of monovalent anions through nanofiltration membranes

Enhancing nanofiltration performance with tannic acid and polyvinyl alcohol interlayers for improved water permeability and selective solute rejection

Global water shortages have significantly intensified the demand for efficient and sustainable water purification technologies. Nanofiltration (NF) plays a crucial role in desalination, providing distinct advantages by removing a variety of pollutants including heavy metals and organic compounds, all while consuming minimal energy. Traditional NF membranes often struggle to balance high rejection with satisfactory permeability. This study advances NF technology by utilizing polysulfone as a durable substrate and introducing tannic acid (TA)-polyvinyl alcohol (PVA) interlayer to enhance structural robustness and functional capabilities of membranes. Through streamlined one-step coating followed by precise interfacial polymerization, this approach optimizes monomer piperazine storage and dispersion on substrate, effectively controlling its diffusion rate, resulting in a thinner polyamide (PA) layer. These strategic enhancements not only lead to a significant increase in permeability to 216.3 L·m−2·h−1·MPa−1 and an impressive rejection for Na2SO4 of 99.04 % but also ensure enhanced long-term operational stability. The innovative TA-PVA interlayer sets new benchmarks for high-performance NF membranes by combining environmental friendliness with cost-effectiveness, making it ideal for large-scale industrial applications. This unique composition promotes sustainability and economic efficiency in water treatment technologies, and underscoring the vast potential for expanding the production and application of advanced NF systems.

Anhydrous interfacial polymerization induced by isopropanol to construct high permeance polyamide membranes for organic solvent nanofiltration

Anhydrous interfacial polymerization induced by isopropanol to construct high permeance polyamide membranes for organic solvent nanofiltration

Crystalline Covalent organic framework membrane with tailored chargeability for efficient pharmaceutical rejection by in-situ functionalization of polyethylene-imine

The nanofiltration (NF) membrane with better hydrophilicity, uniform pore size distribution, and dually charged properties is highly desirable to improve the pharmaceutical rejection, especially for the neutral and positively charged pharmaceuticals. Herein, a TpPa membrane was first in-situ crystallized via PTSA-mediated interfacial catalytic polymerization (ICP) strategy using 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa), followed by post-functionalization with PEI to narrow pore size, improve hydrophilicity, and tailor membrane charges to enhance pharmaceutical rejection. PTSA was used as a catalyst to enhance the crystallinity of the TpPa membrane. The PEI introduction narrowed the pore radius from 0.382 nm to 0.272 nm, improved surface hydrophilicity from 74.8°to 37.0°, and shifted surface charge from -19.25 mV to 11.15 mV. This PEI-functionalized TpPa (TpPa-PEI) layers exhibited heterogeneous charges on both sides with a positively charged top and negatively charged bottom. MgCl2 rejection increased from 13.67% to 83.0% without sacrificing water permeance. Additionally, pharmaceutical rejection and the water permeance of the optimal TpPa-PEI membrane exceeded those of the TpPaIP-PEI membrane fabricated without PTSA by about 3.3 and 1.3 times, respectively. Furthermore, compared to the pristine TpPa membranes, the substantially enhanced electropositivity of the optimal TpPa-PEI membrane led to 3-5 times increase in positively charged pharmaceutical rejection (94.1% for propranolol, 97.2% for sulpiride, and 71.2% for metformin). The synergy of negatively charged bottom TpPa-PEI layers and reduced pore size maintained sulfadiazine rejection of 62.1%. Mechanistic study confirmed that PEI penetrated 100 nm into the TpPa layer and cross-linked with the aldehyde groups, leading to tailored chargeability, improved hydrophilicity, and reduced pore size. Via a PEI cross-linking strategy, sub-nanometer channels of crystalline COF layers can be rationally designed, featuring precisely tailored chargeability and hydrophilicity, promising functionalization of the membrane pores and remarkably robust for water reuse.