Polyamide Thin Film Composite Membranes Research Articles

Polyamide Thin-Film Composite Membranes with Enhanced Interfacial Stability for Durable Organic Solvent Nanofiltration

Polyamide Thin-Film Composite Membranes with Enhanced Interfacial Stability for Durable Organic Solvent Nanofiltration

The Preparation and Performance Study of Polyamide Film Based on PDA@MWCNTs/PVDF Porous Support Layer.

It is urgent to develop a polyamide (PA) thin-film composite (TFC) membrane with a new method in this study by designing and constructing a new nanomaterial support layer instead of the conventional support layer. Polydopamine-wrapped single-walled carbon nanotubes (PDA@MWCNTs) as the place of the polymerization reaction can optimize the PA film structure and performance. The resulting composite membrane presents a higher water flux of 15.8 L·m-2·h-1·bar-1 and a rejection rate of 97% to Na2SO4, simultaneously maintaining this high separation performance in 300 min. It is a new ideal to construct novel support layer by using inorganic nanoparticles and organic polymer nanofiber membranes.

Construction of skyloft-like polyamide membrane on tubular ceramic support for high-flux nanofiltration

Polyamide (PA) thin-film composite membrane has been widely used in water/wastewater treatment, but construction of such membrane on a three-dimensional inorganic macroporous support remains a challenge, thus limiting the further application under harsh conditions. Herein, we propose a skyloft-like PA membrane on a commercial tubular ceramic macrofiltration support. This membrane built on stilts comprises an ultrathin PA canopy of ∼ 33 nm and pillars (∼1 μm-thick) of vertically aligned CoAl-layered double hydroxide (LDH) nanosheets and covalent organic framework (COF) nanospheres. The prepared PA/OH-COF/F-COF/LDH membrane shows a high water permeance of up to 736.6 L m-2h−1 MPa−1 together with a satisfactory rejection rate of > 90 % for various small molecules including dyes and antibiotics (> ∼1 nm). The resultant membrane also demonstrates a good dye desalination performance (with a selectivity of up to 197), illustrating an outstanding permselectivty. A long-term and continuous cross-flow nanofiltration indicates a robust stability of the membrane.

Acid and chlorine-resistant cations selective nanofiltration membranes derived from Hoffmann alkylation reaction

Conventional polyamide and polyester thin film composite membranes (TFCMs) are susceptible to harsh conditions, because the amide and ester bonds in them will degrade under extreme pH or chlorine oxidants. This work addressed this problem by preparing TFCMs through the Hoffmann alkylation reaction. Two monomers, i.e., 1,4,7,10-Tetraazacyclododecane (TAD) and 1,2,4,5-Tetrakis(bromomethyl)benzene (TBB), were designed and underwent interfacial alkylation on polyacrylonitrile substrate. The TAD-TBB TFCMs feature high positive charge, and show good repulsion (>90%) to divalent cations. Benefiting from the stability of “C-N-C” bonds in TAD-TBB network, both the permeance (13.7 L m−2 h−1 bar−1) and cation rejection (90.3%–91.4%) of the TAD-TBB TFCMs are stable after being immersed in 2 M HCl for 21 days. Meanwhile, the TAD-TBB TFCMs maintained good separation performance (permeance: 13.9 L m−2 h−1 bar−1, MgCl2 rejection: 90.5%–92.2%) after a total free chlorine exposure of 96000 ppm h (200 ppm for 480 h). This work reported the preparation of cation-selective membranes stable in harsh environments.

Polyamide Nanofilms through a Non‐Isothermal‐Controlled Interfacial Polymerization

AbstractEfficient thin film composite polyamide (PA) membranes require optimization of interfacial polymerization (IP) process. However, it is challengeable owing to its ultrafast reaction rate coupled with mass and heat transfer, yielding heterogeneous PA membranes with low performance. Herein, a non‐isothermal‐controlled IP (NIIP) method is proposed to fabricate a highly permeable and selective PA membrane by engineering IP at the cryogenic aqueous phase (CAP) to achieve synchronous control of heat and mass transfer in the interfacial region. The CAP also enables the phase transition of the aqueous solution from the liquid to solid state, providing a more comprehensive understanding of the fundamental mechanisms involved in different phase states in the IP process. Consequently, the PA membrane exhibits excellent separation performance with ultrahigh water permeance (42.9 L m−2 h−1 bar−1) and antibiotic desalination efficiency (antibiotic/NaCl selectivity of 159.3). This study provides new insights for the in‐depth understanding of the precise mechanism linking IP to the performance of the targeting membrane.

Economic assessment for TFC-RO membranes production for water desalination

Cutting-edge membranes employed in various desalination applications are polyamide thin-film composite (TFC) membranes, created through interfacial polymerization (IP). Despite their widespread use in desalination, these membranes face several technical impediments in real-world applications. In recent years, there has been notable attention directed towards graphene oxide (GO) and materials derived from it, particularly in the field of membrane synthesis and functionalization. Capitalizing on their distinctive and adjustable characteristics, numerous nanomaterials based on GO have been explored and employed as efficient nanofillers in diverse membrane applications, ranging from water treatment and purification to desalination. The research contributes to (1) the developed concept of reverse osmosis membrane production, and the description of the step-by-step process design to produce modified reverse osmosis membranes(longer lifetime membranes with chlorine resistant properties); (2) the improved methodology for assessing the economic efficiency of reverse osmosis membrane manufacturing process adjusted to the specifics of the process design and the time factor; and (3) substantiation of the economic efficiency of the reverse osmosis membrane production project without and including the time factor impact.The project’s net present value is 664,074.76 EUR, with an internal rate of return of 13.20 %, while the return on investment is 21.23 %. The discounted payback period is longer than the simple payback period by 24.32 % but still acceptable at 9.15 years. The product profitability is 17.99 %. The comparative analysis of previous publications presenting alternative reverse osmosis modules revealed a market potential for new reverse osmosis modules and a sufficient reserve of the business.

Solvent-free polyamide TFC membrane fabrication based on TMC vaporization for saline water recovery

While thin film composite (TFC) membranes have dominated the global desalination process, using large amounts of organic solvent during membrane manufacturing remains a major concern. Thus, a greener approach to prepare TFC membranes based on solvent-free trimesoyl chloride monomer vaporization is presented in this work. This study fabricated the solvent-free membranes by varying relevant parameters during the vapor interfacial polymerization (VIP) process and studied their impacts on the membrane properties. Evidently, the VIP membranes exhibited thinner polyamide layers than conventionally prepared membrane following the slow polymerization rate. This resulted in higher pure water permeability (2.93 L/m2.h.bar) than the conventional membrane (2.53 L/m2.h.bar) when both membranes were tested at 8 bar. Despite demonstrating slight decrease in salt rejection, the saline water recovery performance of VIP membrane was unaffected, as high salt rejection was unnecessary. Under the best synthesis conditions, a VIP membrane with lower salt rejection could rival the conventional membrane with a >98 % dye rejection while attaining substantially higher NaCl/dye selectivity (up to 330) than the conventional ones (68.75). Pertinently, the study findings demonstrated the potential of the solvent-free IP-fabricated TFC membrane for saline water recovery.

Reducing Chloride Ion Permeation during Seawater Electrolysis Using Double-Polyamide Thin-Film Composite Membranes.

Low-cost polyamide thin-film composite membranes are being explored as alternatives to expensive cation exchange membranes for seawater electrolysis. However, transport of chloride from seawater to the anode chamber must be reduced to minimize the production of chlorine gas. A double-polyamide composite structure was created that reduced the level of chloride transport. Adding five polyamide layers on the back of a conventional polyamide composite membrane reduced the chloride ion transport by 53% and did not increase the applied voltage. Decreased chloride permeation was attributed to enhanced electrostatic and steric repulsion created by the new polyamide layers. Charge was balanced through increased sodium ion transport (52%) from the anolyte to the catholyte rather than through a change in the transport of protons and hydroxides. As a result, the Nernstian loss arising from the pH difference between the anolyte and catholyte remained relatively constant during electrolysis despite membrane modifications. This lack of a change in pH showed that transport of protons and hydroxides during electrolysis was independent of salt ion transport. Therefore, only sodium ion transport could compensate for the reduction of chloride flux to maintain the set current. Overall, these results prove the feasibility of using a double-polyamide structure to control chloride permeation during seawater electrolysis without sacrificing energy consumption.

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

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

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.

Ultrahigh-permeance polyamide thin-film composite membranes enabled by interfacial polymerization on a macro-porous substrate toward organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes have become a powerful separation platform in a myriad of chemical and pharmaceutical fields owing to their superior merits in high separation efficiency and low energy consuming. Despite extensive progress in exploiting polyamide thin film composite (TFC) membranes for OSN, they are heavily limited by inferior solvent permeability, especially when using conventional low-porous polyimide as TFC substrate. Herein, we report a facile substrate engineering strategy to leverage macro-porous Nylon66 microfiltration membrane to replace the conventional low-porous polyimide substrates for fabricating TFC membranes by interfacial polymerization, enabling high and robust solvent permeability during OSN. Distinct from conventional polyimide, Nylon66 substrates take advantage of their high porosity, macro-porous size and excellent hydrophilicity to realize more monomers storage and uniform monomers distribution, allowing to create crumpled and defect-free polyamide layers. With this method, the polyamide TFC membranes show a 2.1-fold increase in ethanol permeance (up to 16.0 L h−1 m−2 bar−1) meanwhile possessing 98 % rejection of dye, surpassing the most reported TFC membranes. We also demonstrate that the TFC membranes exhibit excellent long-term stability in both polar and non-polar solvent, as well as hold huge promise in the precise separation of dye mixture, pharmaceutical ingredient, and catalyst.

Constructing nanofiltration membrane on hydrophobic PVDF and PTFE substrates via reverse interfacial polymerization

Polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE) porous membranes are ideal substrates for preparing thin-film composite (TFC) polyamide (PA) membranes with improved solvent resistance. However, it remains difficult to construct PA skin layers on PVDF and PTFE substrates via conventional interfacial polymerization (IP) due to the hydrophobic nature of these materials. To address this challenge, a reverse IP process was proposed to construct a defect-free PA skin layer on PVDF and PTFE substrates, in which the hydrophobic PVDF and PTFE substrates were soaked with the organic phase to ensure uniform coverage of reacted solution on the substrates. This novel strategy can effectively tackle the issue of uneven wetting of the aqueous phase on hydrophobic substrates in the conventional IP process. The resultant TFC membranes (i.e. Mrev-PVDF and Mrev-PTFE) exhibit excellent nanofiltration (NF) performance in both aqueous and organic solutions. Mrev-PVDF and Mrev-PTFE have MgCl2 rejections of 96.12% and 95.17%, alongside the water permeances of 12.8 LMH/bar and 11.2 LMH/bar, respectively (Mrev-PTFE was activated with DMF). It is further shown that Mrev-PVDF and Mrev-PTFE could also reject 99.4% and 98.5% of Congo red in methanol solution at solvent permeances of over 3.3 LMH/bar, while they also perform excellently in other polar protic solvents. Consequently, this work opens a new window for constructing high-performance TFC PA membranes on hydrophobic substrates and expands the application of the TFC PA NF membrane.

Biomimetic peptoid-assisted fabrication of antibiofouling thin-film composite membranes

Polyamide (PA) thin-film composite (TFC) membranes are extensively used in water purification but suffer from chronic biofouling, which has spurred extensive research on the development of antibiofouling membranes. In this study, we present a facile method to fabricate a biofouling-resistant, high-performance PA TFC membrane by adding a biomimetic antimicrobial peptoid (i.e., oligo-N-substituted glycines) to the reaction medium during an interfacial polymerization (IP) process. The amphiphilic peptoid facilitates IP by acting like a surfactant, thereby enabling the formation of a highly crosslinked and permeable PA separation layer. Consequently, the peptoid-added TFC (pept-TFC) membrane exhibits superior separation performance compared with pristine, commercial, and other laboratory-made TFC membranes. Furthermore, because the peptoid is strongly incorporated into the PA separation layer network, the resultant pept-TFC membrane is endowed with excellent antimicrobial and antibiofouling properties. Importantly, the enhanced separation and antibiofouling performances of the pept-TFC membrane persist during long-term membrane operation, indicating the robust implantation of the peptoid and permanent changes in the structure and properties of PA. The proposed strategy provides a versatile and environmentally benign platform for fabricating functional membranes by simply employing structurally tailored peptoids with specific functions.

Modulation of charge properties inside thin-film composite polyamide membranes towards enhanced nanofiltration performance

Nanofiltration (NF) is receiving increasing attention worldwide as a high-efficiency technology for water purification. One viable approach to enhance the performance of NF membranes involves the meticulous optimization of their physicochemical and structural attributes through the introduction of additives. Nonetheless, the predominant NF membrane additives currently accessible primarily exert their influence at the membrane's surface. In this context, we introduce a novel strategy for fabricating polyamide (PA) NF membranes endowed with augmented negative charge density, capable of permeating the innermost stratum of the separation layer. This innovation hinges on the straightforward inclusion of 2-Methylimidazole (Hmim) into the aqueous phase. The ramifications of Hmim's incorporation of the structural configuration, morphological composition, physicochemical characteristics, and overall performance of the thin-film composite (TFC) membrane were meticulously scrutinized through an array of comprehensive characterizations. The integration of Hmim affords PA nanofiltration membranes the remarkable capability to achieve a rejection rate as formidable as 99.5% for Na2SO4 and 42.8% for NaCl, all the while maintaining an unswerving flux. As a result, a high SO42-/Cl- separation factor of up to 116.1 was achieved. Our work provides insights and directions for the development of additives in the preparation of NF membranes.

Zwitterionic material for construction of an antifouling polyamide thin film composite membrane

Zwitterionic materials containing equal proportions of positively and negatively charged groups have been used to provide membranes with antifouling capabilities. This study focuses on the modification of a commercially available polyamide thin-film composite membrane with a zwitterionic material and investigates its effectiveness in fouling mitigation. The zwitterionic material, sulfobetaine vinylimidazole (SBVI), was synthesized by reacting 1,3-propane sulfone with 1-vinyl imidazole. A NF90 polyamide membrane functionalized with propagyl bromide was modified by the polymerization of SBVI on its surface. Various techniques were used to verify the successful modification of membranes. The water flux and salt rejection of the pristine and modified membranes were measured under comparable stabilization conditions, and showed an increase in salt rejection and a decrease in permeability for the modified membrane because of additional membrane resistance. However, fouling tests conducted with a wide range of foulants in cross-flow filtration mode showed a lower fouling ratio and higher recovery ratio for the modified membrane than for the pristine membrane. The enhancement in the antifouling characteristics of the modified membrane was mainly attributed to the improvement in hydrophilicity resulting from the zwitterionic brushes. Our results demonstrated the fouling resistance is further reinforced in an ionic environment through the “salting-in” effect.

Sustainable β- and γ-cyclodextrins for development of highly permeable thin film composite nanofiltration membranes

The use of macromolecules, such as cyclodextrins (CDs), given their porosity and compatibility with organic materials, are very attractive for the progress of polymeric membranes in nanofiltration (NF) of aqueous dye solutions. Two types of membranes were fabricated. Firstly, β- and γ-CDs were incorporated to polyamide (PA) thin film composite (TFC) membranes. These membranes, named CD/MPD-TMC, were prepared by conventional interfacial polymerization —i.e., an aqueous solution of m-phenylenediamine (MPD) followed by a solution of trimesoyl chloride (TMC) in hexane— by replacing a certain amount of the MPD monomer with varying proportions of CDs. Secondly, two-step double-IP (TD-IP) membranes were fabricated as follows: CDs were deposited atop the polymer support, followed by addition of TMC —forming a polyester (PE) layer—, and subsequently the membrane surface was modified with MPD molecules. In both CD/MPD-TMC and TD-IP membranes, the presence of CDs improved the membrane performance, the latter configuration leading to much higher water permeances. The TD-IP membrane using β-CD achieved the highest water permeance of 10 L m−2 h−1·bar−1 (LMH bar−1) and a rejection of acridine orange dye (265 Da) greater than 98 %. This represents a 6-fold increase in water permeance compared to bare PA (1.6 LMH bar−1). The enhanced water transport was mainly attributed to the more hydrophilic nature of the membranes and the presence of a PE layer with a porous structure and high pore connectivity. High dye rejection resulted from electrostatic and Donnan repulsions due to surface modification with MPD molecules.

A sustainable approach for the removal of pharmaceutical contaminants from effluent using polyamide thin-film composite membranes integrated with Zn-based metal organic frameworks.

This study addresses the significant concern of pharmaceutical contaminants, including antipyretic and antibiotic drugs, in municipal and industrial wastewater, impacting both the environment and human health. We investigate incorporating zinc-based metal-organic framework (Zn-MOF) nanofillers into polyamide layers, developing thin-film composite (PA-TFC) nanofiltration membranes via interfacial polymerization to remove paracetamol, ibuprofen, and amoxicillin from simulated wastewater. Characterization confirms Zn-MOF's presence in the PA-TFC membrane, affecting structural topology, pore size, contact angles, and zeta potential. Zn-MOF nanofillers strongly adhere to the polyamide layer, influencing membrane surface chemistry and morphology. The newly developed MOF/PA-TFC nanofiltration membranes demonstrate a remarkable water flux of up to 35 LMH, showcasing superior removal efficiency for the three pharmaceutical contaminants when compared to PA-TFC membranes. Specifically, the rejection rates for paracetamol, ibuprofen, and amoxicillin are notably high at 93%, 98%, and 99%, respectively. Consequently, this study establishes MOF/PA-TFC nanofiltration membranes as a highly efficient solution for removing emerging pharmaceutical contaminants from environmental water, promoting sustainability and safeguarding water resources.

Relative Insignificance of Polyamide Layer Selectivity for Seawater Electrolysis Applications.

Low-cost polyamide thin-film composite (TFC) membranes are being explored as alternatives to cation exchange membranes for seawater electrolysis. An optimal membrane should have a low electrical resistance to minimize applied potentials needed for water electrolysis and be able to block chloride ions present in a seawater catholyte from reaching the anode. The largest energy loss associated with a TFC membrane was the Nernstian overpotential of 0.74 V (equivalent to 37 Ω cm2 at 20 mA cm-2), derived from the pH difference between the anolyte and catholyte and not the membrane ohmic overpotential. Based on analysis using electrochemical impedance spectroscopy, the pristine TFC membrane contributed only 5.00 Ω cm2 to the ohmic resistance. Removing the polyester support layer reduced the resistance by 79% to only 1.04 Ω cm2, without altering the salt ion transport between the electrolytes. Enlarging the pore size (∼5 times) in the polyamide active layer minimally impacted counterion transport across the membrane during electrolysis, but it increased the total concentration of chloride transported by 60%. Overall, this study suggests that TFC membranes with thinner but mechanically strong supporting layers and size-selective active layers should reduce energy consumption and the potential for chlorine generation for seawater electrolyzers.

Investigating the efficiency of a ceramic-based thin-film composite nanofiltration membrane for dyes removal

This study focuses on producing polyamide thin-film composite (TFC) ceramic membranes using interfacial polymerization, resulting in a polyamide layer on ceramic tubular substrates (Al2O3). These Al2O3 substrates possess robust mechanical and physical traits, featuring a porous surface structure. TFC membranes exhibit a thin, dense structure with root-like nanostructures on the ceramic base, with a thickness of around 260 nm. Atomic force microscopy confirms the smoother surface of TFC membranes with an average roughness value of 18 nm compared to ceramic tubular substrates. TFC membranes exhibit negative zeta potentials within a pH range of 4.7–10, while ceramic tubular substrates show more complex zeta potential behavior. Both substrate and TFC membranes are hydrophilic, with the TFC membrane having a slightly higher water contact angle (approximately 43 ± 1°). Zeta potential analysis reveals a negative potential of around −23 mV for the TFC membrane. In water permeability tests, the ceramic tubular substrate membrane demonstrates high permeability, whereas the TFC membrane displays slightly lower permeability (28 ± 0.8 L/m2 h bar) due to the presence of the polyamide selective layer. Importantly, the TFC membrane significantly enhances organic dye rejection compared to the ceramic tubular substrate, with rejection rates of 95% for CR, 92% for BTB, and 86% for MB. Rejection performance is mainly influenced by size exclusion and dye molecular charge. These novel TFC ceramic nanofiltration membranes offer improved water permeability while maintaining selectivity, holding promise for effectively removing organic pollutants in water treatment applications.

Complexation of cellulose nanocrystals and amine monomer for improved interfacial polymerization of nanofiltration membrane

Thin film composite (TFC) polyamide membranes prepared by the interfacial polymerization (IP) of reactive monomers are widely utilized for desalination. However, the trade-off between the permeability and selectivity of TFC membranes limits further improvements in separation performance. In this study, the complexation of amine monomers with cellulose nanocrystals (CNC) and subsequent deposition on a substrate for the IP reaction was employed to modify the polymerization process and the resulting interlayered-thin film nanocomposite (i-TFN) membrane structure. This method can optimize the amine loading and distribution for the IP reaction, and CNC with favorable functional groups can limit the release and diffusion behavior of the amine monomer, resulting in a crumpled membrane structure with a retained continuous polymer network. The optimized membrane had a three-fold higher water permeance than the pristine membrane without compromising salt rejection performance. This study provides a strategy for regulating the monomer distribution and reaction at the IP interface for improved performance.