Polyamide Membranes Research Articles

Synthesis of polyamide-based RO membranes for saline water treatment

Reverse osmosis (RO) technology is a widely used method for converting seawater into fresh water, known for its high efficiency and broad applications. This study focuses on optimizing the synthesis conditions for polyamide (PA) membranes, including the concentrations of m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the choice of solvent, soaking time, and reaction time. FTIR and SEM analysis confirmed the successful synthesis of the PA layer and revealed that the surface morphology of the membrane was significantly influenced by synthesis conditions. Mechanical testing demonstrated that the optimized membranes exhibited high tensile strength (41.18 MPa) and low elongation at break (11.69%), indicating a robust but relatively brittle material. The study determined that the optimal conditions were 1.0 wt.% MPD and 0.1 wt.% TMC, hexane as a solvent, a soaking time of 2 min, and a reaction time of 60 sec, achieving a maximum salt rejection of 86.45%. These findings are critical for enhancing RO membrane efficiency and addressing the global demand for clean water.

Interfacial self-organization of large-area mixed-dimensional polyamide membranes for rapid aqueous nanofiltration

Interfacial self-organization of large-area mixed-dimensional polyamide membranes for rapid aqueous nanofiltration

Natural composite hydrogel regulated interface polymerization to prepare high performance nanofiltration membranes with wrinkled structure

Composite hydrogels offer significant potential in the development of nanofiltration membranes. Nonetheless, fabricating defect-free and ultra-thin polyamide membranes with wrinkled structure on three-dimensional composite hydrogel substrates through conventional interfacial polymerization remains a considerable challenge. Achieving both enhanced water permeability and ionic selectivity simultaneously is particularly challenging. In this study, a hydroxyl-enriched natural composite hydrogel, carboxyl methylated Astragalus gum/acid-soluble chitosan/multi-walled carboxylated carbon nanotubes (CTG/CS@CNT-COOH), was introduced as an intermediate layer to improve the process. This interlayer effectively enhanced PIP retention and reduced its diffusion rate into the organic phase by over 90 % through hydrogen bonding and physical barriers. The resulting polyamide layer, with a thickness of only 79.0 nm, exhibited a desirable wrinkled structure. SEM and AFM were employed to assess membrane morphology, while ATR-FTIR and XPS provided a detailed characterization of the membrane surface chemistry. The hydrophilicity and charge properties of various membranes were examined using water contact angle and zeta potential measurements. Notably, the modified thin-film composite membrane (TFC4) demonstrated exceptional pure water permeance, reaching 23.31 L m−2 h−1·bar−1, compared to 8.63 L m−2 h−1·bar−1 for TFC membrane lacking the composite hydrogel, alongside a Na2SO4 rejection rate of 98.38 %. Furthermore, the membrane exhibited strong fouling resistance and maintained structural integrity throughout extended filtration tests. This study presents a straightforward strategy for developing high-performance TFC membranes with enhanced efficiency.

High performance, pH-resistant membranes for efficient lithium recovery from spent batteries

Cation separation under extreme pH is crucial for lithium recovery from spent batteries, but conventional polyamide membranes suffer from pH-induced hydrolysis. Preparation of high performance nanofiltration membranes with excellent pH-resistance remains a challenge. Here we synthesize a high performance nanofiltration membrane (1,4,7,10-Tetraazacyclododecane (TAD)−1,3,5-Tris(bromomethyl)benzene (TBMB) thin film composite membranes (TFCMs)) with excellent pH-stability through interfacial quaternization reaction between TAD and TBMB. Due to the high stability of “C-N” bonds in TAD-TBMB TFCMs, its separation performance is stable even after 70 days immersion in concentrated acid (3 M H2SO4, HNO3, or HCl) and base (3 M NaOH), which is at least 15 times more stable than benchmark commercial membranes. The membrane shows an overall separation performance (11.3 L m−2 h−1 bar−1 (LMHB), RCo2+: 97% in 2 M H2SO4) due to the size sieving and the intensified charge repulsion, outperforming many of the state-of-the-art membranes. Finally, the TAD-TBMB TFCM remains stable during 30-days continuous nanofiltration of 2 M H2SO4 and leachate (2 M H2SO4, ions: 6.2 g L−1) from spent batteries.

Analysis of Metal-Organic Framework and Polyamide Interfaces in Membranes for Water Treatment and Antibacterial Applications.

Integrating biocidal nanoparticles (NPs) into polyamide (PA) membranes shows promise for enhancing resistance to biofouling. Incorporating techniques can tailor thin-film nanocomposite (TFN) membranes for specific water purification applications. In this study, silver-based metal-organic framework Ag-MOFs (using silver nitrate and 1,3,5-benzentricarboxylic acid as precursors) are incorporated into PA membranes via three different methods: i) incorporation, ii) dip-coating, and iii) in situ ultrasonic techniques. The characterizations, such as top-surface and cross-section scanning and transmission microscopy, reveal that the incorporation methods for the modified TFN membranes substantially control morphology and surface characteristics. For example, the in situ ultrasonically interlayered Ag-MOFs showed the largest pores (average pore diameter of 14 Å ± 0.1), resulting in the highest water permeance (water flux of 10.9 LMH/bar for Na2SO4). It also show superior antifouling and anti-biofouling performance, with a flux recovery ratio (FRR) of 94.1% in both fouling tests due to its improved surface hydrophilicity and the antibacterial properties of incorporated Ag-MOFs. Conversely, the surface-grafted dip-coated Ag-MOFs offered the highest salt rejection, attributed to its highly negatively charged surface and a dense PA network with narrow pores (average pore diameter of 10 Å ± 0.06).

Interfacial Polymerization of Aromatic Polyamide Reverse Osmosis Membranes.

Polyamide membranes are widely used in reverse osmosis (RO) water treatment, yet the mechanism of interfacial polymerization during membrane formation is not fully understood. In this work, we perform atomistic molecular dynamics simulations to explore the cross-linking of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers at the aqueous-organic interface. Our studies show that the solution interface provides a function of "concentration and dispersion" of monomers for cross-linking. The process starts with rapid cross-linking, followed by slower kinetics. Initially, amphiphilic MPD monomers diffuse in water and accumulate at the solution interface to interact with TMC monomers from the organic phase. As cross-linking progresses, a precross-linked thin film forms, reducing monomer diffusion and reaction rates. However, the structural flexibility of the amphiphilic film, influenced by interfacial fluctuations and mixed interactions with water and the organic solvent at the solution interface, promotes further cross-linking. The solubility of MPD and TMC monomers in different organic solvents (cyclohexane versus n-hexane) affects the cross-linking rate and surface homogeneity, leading to slight variations in the structure and size distribution of subnanopores. Our study of the interfacial polymerization process in explicit solvents is essential for understanding membrane formation in various solvents, which will be crucial for optimal polyamide membrane design.

Selective-layer polysulfone membranes based on unfunctionalized and functionalized MoS2/polyamide nanocomposite for water desalination.

Recently, reverse osmosis (RO) has become the most widely used process in membrane technology. It has aroused great interest in water desalination through membranes. According to recent studies, the surface properties of support layers in thin film membranes are crucial for improving reverse osmosis performance. Surface polymerization was used to produce the membranes in this work, with the polyamide acting as a selective layer on the polysulfone support film. Three membranes were produced with different proportions of molybdenum sulfide (MoS2) nanopowder. The effectiveness of the membranes was improved by increasing water permeability while maintaining excellent salt retention. All membranes produced were tested using various characterization methods including scanning electron microscope, Brunauer-Emmett plate, and zeta potential. The water permeability of the polyamide membrane with PA-MoS2 (0.015% w/v) was 29.79 L/m2 h bar, more than the PA-MoS2 membranes (0.005% w/v, 19.36 L/m2 h) and PA-MoS2 (0.01% w/v, 3.63 L/m2 h bar). Under the same conditions, salt rejection of more than 96.0% for NaCl and 97.0% for MgSO4 was also observed. According to the SEM, the 0.015% PA-MoS2 membrane exhibited lower surface roughness, greater hydrophobicity, and a higher water contact angle. Due to the hydrophobic nature of MoS2, these properties resulted in the lowest salt rejection.

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

Highly permeable polyamide (PA) membranes with precise molecular sieving capabilities are crucial for energy-efficient chemical separations. There is a critical need to design solvent-stabilized membranes with enhanced permeance to improve separation efficiency. In this work, we propose a novel anhydrous interfacial polymerization (IP) method, where flexible polyethyleneimine (PEI) and rigid p-phenylenediamine (PPD) are uniquely dissolved in isopropanol (IPA) and subsequently crosslinked with trimethyl chloride (TMC) in situ to fabricate high-performance PA membranes. Notably, the use of IPA as a solvent represents a significant advancement in membrane fabrication. This approach resulted in PA membranes with a relatively loose selective layer compared to traditional PA membranes, allowing for exceptionally high solvent permeance while maintaining strong rejection performance in organic solvent nanofiltration (OSN). The obtained PEI + PPD/TMC PA membranes demonstrated outstanding ethanol (EtOH) permeance of 46.44 L m−2 h−1 bar−1 in the organic solvent system, along with good rejection for small organic molecules, such as 93.84% for Eriochrome Black T (EBT, 461.38 Da). In addition, the performance of the PEI + PPD/TMC PA membranes remained at a high level even during 510 min of continuous cross-flow filtration, under high pressure (5 bar) testing, and after 6 cycles of separation, which demonstrated their good stability in long-term service. This work establishes a robust foundation for employing anhydrous IP reactions and innovative solvent systems, such as IPA, to develop high-permeance PA membranes.

Ceramic supported polyamide composite nanofiltration membrane with a glutaraldehyde cross-linked chitosan interlayer

Interfacial polymerization has been applied to prepare polyamide (PA) membrane on ceramic substrate. However, the low compatibility of the organic PA layer with the ceramic substrate and the intrusion of the PA layer into the ceramic substrate impedes the performance of the obtained membrane. Herein, building on previous work, a thinner interlayer (a glutaraldehyde (GA) cross-linked chitosan (CCM) interlayer) is constructed on a ceramic ultrafiltration substrate (∼5 nm) for the subsequently interfacial polymerization to improve the performance of the obtained membrane. FTIR, XPS and FESEM analyses confirm the successful construction of a smooth interlayer with a thickness of ∼250 nm and the subsequently formation of a homogeneous, rough polyamide (PA) layer with a thickness of ∼15 nm. The obtained membrane has a hydrophilic surface and a negative charged property. The molecular weight cut-off (MWCO) of the obtained membrane is 404 Da. A thinner interlayer of the composite membrane leads to a water flux of 149.46 L m−2 h−1 (0.4 MPa) with rejections of Na2SO4 84.71 %, MgSO4 81.07 %, MgCl2 63.39 %, CaCl2 58.7 %, and NaCl 51.87 %. The interlayer regulates the macroporous structure of the ceramic substrate to prevent the intrusion of the PA layer. Furthermore, the interlayer enhances the connection between the PA layer and the ceramic substrate, which enhances the stability of the PA/CCM membrane (stable performance during 20 h continuous filtration). Overall, this work provides a simple way (construct a glutaraldehyde (GA) cross-linked chitosan interlayer) to prepare composite nanofiltration membranes on ceramic substrate, which has potential applications in dyes desalination.

Membranes of Amphiphilic Polyamide 1012 Prepared via Mixed ‘Non-solvents’ Evaporation Induced Phase Separation

Membranes of Amphiphilic Polyamide 1012 Prepared via Mixed ‘Non-solvents’ Evaporation Induced Phase Separation

Nanofoamed Polyamide Membranes: Mechanisms, Developments, and Environmental Implications.

Thin film composite (TFC) polyamide membranes have been widely applied for environmental applications, such as desalination and water reuse. The separation performance of TFC polyamide membranes strongly depends on their nanovoid-containing roughness morphology. These nanovoids not only influence the effective filtration area of the polyamide film but also regulate the water transport pathways through the film. Although there have been ongoing debates on the formation mechanisms of nanovoids, a nanofoaming theory─stipulating the shaping of polyamide roughness morphology by nanobubbles of degassed CO2 and the vapor of volatile solvents─has gained much attention in recent years. In this review, we provide a comprehensive summary of the nanofoaming mechanism, including related fundamental principles and strategies to tailor nanovoid formation for improved membrane separation performance. The effects of nanovoids on the fouling behaviors of TFC membranes are also discussed. In addition, numerical models on the role of nanovoids in regulating the water transport pathways toward improved water permeance and antifouling ability are highlighted. The comprehensive summary on the nanofoaming mechanism in this review provides insightful guidelines for the future design and optimization of TFC polyamide membranes toward various environmental applications.

Ionic Liquid‐Filled Polyamide Microcapsules Obtained by Interfacial Polymerization

AbstractMicroencapsulated ionic liquids (ILs) have a wide range of exciting properties. They can be synthesized by a variety of methods, of which interfacial polymerization represents a very simple, fast, and reliable production process, but the number of available shell materials that can be obtained by this method is limited. However, recent advances in the field of interfacial polymerization have described the formation of a polyamide membrane at the IL/organic phase interface, which is extended in this work to the first microencapsulation of ILs with a polyamide shell, providing an additional and versatile shell material. The IL‐filled microcapsules are obtained using a surfactant‐free synthesis process and inexpensive, low‐toxicity monomers and solvents and feature an exceptionally high core‐to‐shell weight ratio enabling a broad range of possible applications.

Bubble Drainage Assisted Fabrication of Polyamide Membranes with Crater-like Structures for Efficient Desalination.

Bubble drainage (BD) occurs in various natural phenomena and industrial activities, in which bubbles rise toward the water surface and create a progressively thinned two-sided liquid film, called a lamella. Surfactant, as an important regulator in the BD process, not only assembles on both sides of the lamellae, generating a configuration of lamellae sandwiched by monolayers of surfactants (lamellae/MS), but also induces interfacial deformation by lowering interfacial tension. Herein, we developed a strategy of BD assisted interfacial polymerization for the fabrication of polyamide (PA) membranes. The regulated interfacial deformation at the water-oil interface produced a membrane with crater-like structures, which greatly increased the surface area of the PA membrane. Moreover, the lamellae/MS configuration served as a reservoir to spontaneously enrich amine monomers and thus modulate the diffusion-reaction kinetics. The resulting PA membranes exhibited superior separation performance with a water permeance of 44.7 L m-2 h-1 bar-1 and a Na2SO4 rejection of 99.2%.

Carbon nanotube intermediate layer intercalation and its influence on surface charge of thin film composite membrane

The surface charge of a separation membrane is a critical factor affecting its performance in ion separation and fouling resistance. Thin-film composite (TFC) polyamide (PA) membrane, commonly used in water treatment, often suffer from excessive surface negative charges, which significantly limits their application and fouling resistance. To address this issue, this work introduces a carbon nanotubes (CNT) intermediate layer to adjust the surface charge of TFC PA membranes, aiming to achieve a PA layer with neutral properties. Novel grazing-incidence wide-angle x-ray scattering (GIWAXS) measurements were employed to elucidate the effect of CNT on the molecular chain stacking of PA. The CNT intermediate layer was found to influence the PA cross-linking, which is related to surface negative charge, by controlling the storage and release of the m-phenylenediamine monomer during interfacial polymerization. The neutral CNT-TFC membrane demonstrated improved NH4+ retention and increased resistance to fouling by protein, surfactant, and E. coli. However, other surface properties, such as roughness and hydrophilicity, could counteract the antifouling benefits of a neutral surface. This work provides insights into additional advantages of CNT intermediate layer intercalation in TFC PA membranes, such as enhanced cross-linking and surface charge control.

Rapid solvent transport and tunable molecular sieving enabled by ultrathin alkyl-chain-engineered polyamide membranes

Organic solvent nanofiltration (OSN) has emerged as a promising separation technology for the chemical and pharmaceutical industries due to its low energy consumption and eco-friendliness. However, traditional polyamide-based membranes used in OSN often exhibit low permeance for organic solvents and it is difficult to precisely control the pore structure. In this study, we report a facile approach to fabricate ultrathin alkyl-chain-engineered polyamide nanofilms via free-standing interfacial polymerization for high-performance selective separations. The membranes were prepared via a “two birds one stone” strategy, enabled by post-treatment in aliphatic amine solution, simultaneously regulating the pore size and optimizing the membrane chemical property. This enables the membrane with high solvent permeance, especially for non-polar solvents (heptane at ∼22.2 L m−2h−1 bar−1, toluene at ∼16.8 L m−2h−1 bar−1), while maintaining excellent molecular sieving capability. Notably, the molecular weight cut-off (MWCO) can be regulated by introducing alkyl chains of varying lengths to their pores. The exceptional solvent permeance and tunable molecular sieving property make the membranes promising for high value-added products purification in the pharmaceutical industry and crude oil separation.

Green fabrication of polyamide nanofiltration membranes with ultra-low chemical consumption by vacuum filtration-spraying assisted interfacial polymerization

Polyamide nanofiltration membranes, due to their exceptional advantages of high separation efficiency and low energy consumption, have been widely used for hardwater softening, wastewater treatment and brackish water desalination. Despite extensive progress, the conventional fabrication process of polyamide membranes suffers from high chemical consumption (e.g., organic solvent), thus posing a tough challenge in how to harness the minimized chemical dosage for manufacturing intact polyamide membranes. Herein, we report a facile and green strategy to fabricate high-performance polyamide nanofiltration membranes with ultra-low organic solvent consumption, by virtue of vacuum filtration-spraying assisted interfacial polymerization (VSAIP) of piperazine and trimesoyl chloride. With this VSAIP method, uniform and intact polyamide membranes can be fabricated even under an ultra-low organic solvent dosage of 0.0398 L/m2, saving about 95 % organic solvent consumption compared with conventional methods. The results of SEM and AFM images and XPS spectra reveal that the VSAIP-enabled membranes show comparable morphologies and thickness as well as unaltered chemical composition. We further show that the VSAIP method can be applied for high-throughput production of polyamide nanofiltration membranes in a diameter of 30 cm, exhibiting excellent salt rejection (RNa2SO4 = 98.1 %) and high water permeance (22.4 L m−1 h−1 bar−1), comparable with the recently reported state-of-the-art nanofiltration membranes. The low organic solvent consumption and outstanding nanofiltration performance make VSAIP promising in green manufacturing of advanced membranes.

Janus-structured MXene-PA/MS with an ultrathin intermediate layer for high-salinity water desalination and wastewater purification

Solar-driven interfacial evaporation presents significant potential for seawater desalination and wastewater purification. However, prolonged operation in marine environments often results in salt accumulation, which adversely impacts the performance and lifetime of system. Despite the progress in material design, achieving efficient evaporation while mitigating salt crystallization remains challenging in high-salinity water. In this study, we synthesized a hierarchically structured C18H37-MXene/PA/MS evaporator employing a simple yet effective methodology specifically designed for applications in high-salinity water environments. The evaporator features a dual-region configuration, with an upper hydrophobic light-absorbing layer comprising modified MXene and polyamide (PA) membranes and a hydrophilic lower layer consists of hydrophilic melamine sponge (MS). This innovative design, incorporating an ultra-thin polyamide interlayer, significantly enhances interfacial stability, thereby mitigating the interfacial separation typically observed in conventional Janus materials during prolonged usage. Furthermore, the meticulous control over the thickness of the hydrophobic layer (5.54 μm) ensures optimal thermal insulation properties of the material. Consequently, the C18H37-MXene/PA/MS evaporator demonstrates an impressive evaporation rate of 1.49 kg m−2 h−1 under 1 sun illumination, with a high energy efficiency of 92.8 %. Furthermore, the Janus architecture ensures steady performance in high salinity conditions, sustaining a high evaporation rate of 1.46 kg m−2 h−1 even in a 20 wt% NaCl solution. Furthermore, under natural sunlight, the daily freshwater yield reaches 8.91 kg m−2. The exceptional evaporation efficiency and robust salt resistance highlight its strong potential for water desalination and wastewater treatment, contributing to the advancement of sustainable water resource management.

Pattern size relative to oil droplet size effect on oil fouling in nanofiltration

Membrane fouling is a major issue in many membrane applications. There are numerous methods used in attempt to mitigate membrane fouling, with one method being membrane surface patterning. However, it is still unclear how the ratio of foulant size to pattern size affects membrane fouling. In this study, we investigated constant foulant size while varying the pattern size on the membrane surface to be smaller than (300-nm), equal to (10-μm), and larger than (50-μm) the foulant (10-μm) on polyamide nanofiltration membranes. These membranes were compared to a commercial nanofiltration membrane and a control flat synthesized membrane. The membranes were tested with water, 2000 ppm Na2SO4, and three cycles of a n-dodecane (as oil) brine solution in a dead-end cell to assess the fouling resistance and flux recovery ability of each polyamide membrane type. From the fouling experiments, it was determined that none of the pattern sizes significantly affect the flux recovery ratio, but smaller than and larger than patterns decreased the fouling rate on the polyamide membranes by a small margin.

Screening of the biphenyl polyamides nanofilms appropriate for molecular separation in organic solution feed

Developing polymeric separation membranes that combine excellent solvent stability, high permeability, and customizable molecular weight interception remains a challenge. Herein, thin-film composite (TFC) polyamide (PA) membranes with poly(ether ether ketone) (PEEK) support and biphenyl-centered polyamides active layer were fabricated through interfacial polymerization technique for the first time. Enhanced solvent stability was exhibited by the fabricated membranes due to the intrinsic resistance to organic solvents possessed by PEEK and biphenyl polyamides. The separation performance of the obtained membranes was systematically studied by relating to the properties of PA nanofilms in terms of nano-mechanical strength, morphologies, and microporosity. The organic solvent nanofiltration (OSN) performance of the resultant membranes in terms of permeability and molecular weight cut-off (MWCO) could be regulated. The optimized membrane exhibited a pure solvent permeability as high as 21.6 L m−2 h−1 bar−1 for acetonitrile and 14.0 L m−2 h−1 bar−1 for methanol. It also showed excellent long-term durability with almost unchanged permeability as well as solute retention remained above 97.8 % after a cumulative OSN operation of N, N-Dimethylformamide (DMF) based feed for 240 h. In particular, OSN membrane with targeted MWCOs covering the range of 170–370 g·mol−1 could be fabricated by selecting appropriate biphenyl acyl chlorides as building blocks. This approach offers a scalable and versatile platform for the development of solvent-stable, highly permeable, and customizable MWCO membranes for process-oriented OSN.

Self-assembled nanoflower-mediated interfacial polymerization through tunable intra- and inter-layer channels to boost total heat exchange performance

Total heat exchange membranes (THEMs) are vital for minimizing energy consumption and enhancing indoor air quality in energy recovery ventilation (ERV) systems. Manipulating the surface morphology of polyamide (PA) membranes via nanofiller-mediated interfacial polymerization is key to advancing total heat recovery performance. This study presented the fabrication of PA thin-film nanocomposite (TFN) membranes by integrating self-assembled poly(amic acid-imide) nanoflowers (P(AA-I)-NFs) with intertwined nanosheets into the organic phase. This facile approach effectively eliminated nonselective interphase voids and defects, owing to the superior polymer affinity of the organic nanoflowers. The finely tuned intra- and inter-layer channels within P(AA-I)-NFs significantly impacted monomer mass transfer, facilitated the shuttle effect, expanded the interfacial polymerization zone, and led to the formation of a rougher, thicker PA layer with enhanced surface area. The optimized P(AA-I)-NFs/PA TFN membranes exhibited outstanding performance, including CO₂ permeability of 0.51 GPU, water vapor permeability of 656.59 GPU, and an enthalpy exchange efficiency of 71.47 %, surpassing the trade-off limitations typically observed in commercial and other advanced THEMs. These findings underscored the potential of P(AA-I)-NFs-mediated TFN membranes as highly competitive candidates for next-generation ERV systems.