Interfacial Polymerization Process Research Articles

A Nanofiltration Membrane Preparation Process Based on Polyethyleneimine Diffusion Modulation and Surface Modification

ABSTRACTNanofiltration (NF) membranes play a huge role in industrial manufacturing with their unique selective permeability. Membrane material and structure are the main factors affecting the effectiveness of NF separation. Typically, NF membranes are produced by interfacial polymerization (IP). Therefore, control of the IP process is particularly important. This work provides a NF membrane preparation process by combining internal modulation of the separation layer and surface modification. The diffusion of polyethyleneimine (PEI) molecules is accelerated by the introduction of ethanol and cetyltrimethylammonium bromide into the PEI aqueous phase solution, resulting in the formation of a loose interior. In addition, the high selectivity is maintained by high molecular weight PEI modifying. After optimizing the process, the NF membrane permeate flux and selectivity can be increased compared to the blank group (MgCl2 desalination from 90% to 97%, permeate flux from 17 to 35 L m−2 h−1). The resulting PEI/TMC NF membranes also show excellent separation properties in mixed salt applications for magnesium‐lithium separation.

Enhancing PPCP and salt separation in polyamide nanofiltration membranes with polydopamine and ZnO functionalized nanofiber support

Achieving the removal of pharmaceuticals and personal care products (PPCPs) while selectively rejecting divalent cations like Ca2⁺ and Mg2⁺ without compromising water productivity and recovery remains a challenge for existing commercial nanofiltration (NF) membranes used in drinking water treatment. These challenges stem from the limited pore size and insufficient negatively charged surface density of conventional NF membrane. This study employed a polydopamine-coated nanofibrous membrane, uniformly embedded with in-situ grown ZnO nanoparticles, as a porous support layer. In the interfacial polymerization process, the fabricated substrate regulated the diffusion of aqueous monomers, thereby optimizing the polyamide layer on composite NF membrane with thinner thickness, stronger surface density, crumple structure and appropriate pore size. This resulting membrane demonstrated excellent PPCP rejection while maintaining high permeability to essential minerals. Under optimal conditions, the designed membrane achieved an impressive water flux at about 21 L m⁻2 h⁻1 bar⁻1 and showed significant selectivity for PPCP and divalent cation, with diclofenac sodium rejection exceeding 90 % and Ca2⁺ rejection of below 20 %. The incorporation of ZnO nanoparticles enlarged the active filtration surface and created additional water pathways, resulting in a water permeation rate that was double that of a pristine NF membrane, without compromising PPCP/divalent cation selectivity. This work provides valuable insights and important correlations for developing NF membranes aimed at enhancing water production while preserving selectivity for PPCP/divalent cation.

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.

Synthesis and characterization of L-Arg-polypyrrole@g-C3N4 nanocomposite for highly efficient removal of orange G dye: Mechanistic insights and RSM@BBD optimization

Dye pollution, specifically orange G dye (OG dye) has been substantial threat owing to its poisonous to both human health and ecosystems. Thus, developing adsorbents with high stability, strong adsorption efficiency, easy separation, and excellent regenerability remains a challenge. In the present research, L-Arg-PPy@g-C3N4 nanocomposite was crafted through an interfacial polymerization process. OG adsorption onto L-Arg-PPy@g-C3N4 was optimized in batch mode using response surface methodology coupled with box-Behnken design (RSM@BBD) to assess the adsorbent dose, pH and initial OG concentration. The developed composite proficiently eliminates 94.87 % of OG dye molecules at 1 g·L−1 with a reaction time approaching 60 min, with high uptake efficacy of 23.31 mg·g−1. The Langmuir isotherm and pseudo-second-order kinetic models effectively describe the adsorption process in both aqueous solution and wastewater. Based on XPS/FT-IR analysis, the OG dye mechanism is mainly driven by π-π interactions, hydrogen bonding and electrostatic attractions. The adsorbent efficacy achieved 88.3 % removal in real wastewater treatment. This slight detriment was explained by the individual study of co-interfering ions. Reusability tests confirmed the adsorbent’s excellent regeneration capability for purifying wastewater containing OG dye molecules maintaining 73.8 % removal capacity during 4 cycles. These findings confirm the potential of the developed L-Arg-PPy@g-C3N4 as an effective filter for OG removal from wastewater.

Wet-coating amino-functionalized PDMS interlayer boosting thin film composite membranes for efficient CO2 separation

Membrane separation is in the spotlight as one of the most cost-effective technologies without chemicals for carbon capture. This work aims to fabricate thin film composite (TFC) membranes for boosting CO2 separation. Commercial polysulfone (PSf) flat sheet membranes pre-treated with ethanol solutions were used as support materials by coating with amino-functionalized cross-linked polydimethylsiloxane (PDMS) interlayer. It is worth noting that the developed amino-functionalized PDMS interlayer based on a novel wet-coating method to avoid the penetration of coating solution, which provides better compatibility with the coated polyamide selective layer and also the facilitated transport for CO2 permeation. A thin CO2-selective layer was obtained by interfacial polymerization (IP) between trimesoyl chloride (TMC) in the organic phase and diethylene glycol bis(3-aminopropyl) ether (DGBAmE or EO3) in the aqueous phase to enhance the CO2/N2 selectivity. Both the IP process and the membrane preparation parameters such as heat-treatment temperature, and monomer concentration were systematically optimized. It was found that the best membrane prepared with 9.9 mmol/L TMC monomer solution presents a CO2 permeance of 81 GPU and a CO2/N2 selectivity of 65, which was significantly enhanced from the non-selective supports. This work provides a facile approach for tuning the TFC membrane performance for CO2 separation and can be extended to make high-performance membranes for industrial CO2 capture by selecting more permeable supports.

Fabrication of green xylose-based nanofiltration membrane with enhanced performance and chlorine resistance

Nanofiltration technology has been widely used in drinking water purification due to its excellent permeance and selectivity properties, especially in small molecular solute separation. However, using oxidizing agents in the pretreatment process for fouling control threatens the nanofiltration membrane structure, leading to the deterioration of the separation performance. Herein, we fabricate a polyester nanofiltration membrane utilizing xylose as an aqueous monomer in the interfacial polymerization process. Due to abundant hydroxyl groups and low reactivity of xylose monomers, the polyester membrane possessed a hydrophilic and thin separation layer, which led to high water permeance with the optimal value of 28.7 L·m−2·h−1·bar−1. Possessing highly cross-linking structures and negatively charged surfaces, the fabricated polyester membranes showed an excellent Na2SO4 rejection of up to 95.4 %. In addition, the low electron-donating property of polyester membranes ensured their chemical stability toward active chlorine. This endows relatively stable performance of the polyester membrane after chlorine resistance tests in a wide pH range. This study presents a feasible approach employing green monomers for fabricating nanofiltration membranes with outstanding separation performance and robust chlorine resistance.

COFs functionalized self-cleaning loose nanofiltration membranes for efficient dye/salt separation

In spite of the fact that loose nanofiltration membrane (LNFM) technology has certified inspiring prospects in the remediation of dyestuff-comprising wastewater, omnipresent membrane fouling deteriorates its separation competence and hinders its practical application. Herein, a neoteric LNFM with finely tuned anti-fouling and self-cleaning properties was manufactured via the reformative phase inversion procedure integrated with the correctional interfacial polymerization process. By altering the casting solution (i.e., adding nano additives) and coagulation bath (i.e., applying melamine aqueous solution rather than pure water) recipes, the porphyrin-based covalent organic framework (COF-366) and melamine monomers were introduced into the polymeric matrix ingeniously in one step, participating the subsequent interfacial polymerization reaction straightly. The COF-366 with photocatalytic degradation performance and hydrophilicity bestows the resultant LNFM with superior decomposing capacity for organic micro-pollutants under visible light irradiation and better operation durability. Moreover, this substrate-confined amine diffusion combined with the high polarity of melamine enables the formation of a thinner nanofilm for easy mass transport. The best-performing LNFM invented in this work exhibited a high water permeance up to 65 L m−2 h−1 bar−1, excellent dye retention (95.7% against methyl blue), and salt/dye discrimination (27.1 for methyl blue and Na2SO4 selectivity) abilities. Eventually, the membrane could recover to original separation efficacy after the cyclic degradation testing. Overall, this work demonstrates an extensive perspective to pioneer an advanced self-cleaning membrane for dye/salt fractionation.

Incorporation of Graphene Oxide Quantum Dots in Gradient Layers of Polyethersulphone Nanofiltration Membranes for Nitrate Rejection from Aqueous Solution.

Graphene oxide quantum dots (GOQDs) have been widely used to prepare nanofiltration membranes due to the merits of excellent dispersity, ultrasmall size, and unique properties related to graphene. In this study, we first prepared the polyethersulphone-based nanofiltration (PES-NF) membrane via an interfacial polymerization process using a piperazine and m-phenylenediamine mixed solution as the aqueous phase. Then GOQDs were incorporated into the top-down gradient structured layers (i.e., ultrathin layer, interlayer, and substrate membrane layer) of the nanofiltration membrane, and subsequently the effect of GOQD addition on the nitrate rejection was evaluated. Compared with the pristine PES-NF membrane without the incorporation of GOQDs, the fabricated NF membrane (GOQD/PES-NF-2) incorporating GOQDs at both the ultrathin layer and interlayer exhibits more remarkable performances (an acceptable permeation flux of 52.2 L m-1 h-1 and excellent nitrate rejection of 96.3% at 0.6 MPa), the permeation flux of this membrane increases by nearly 2.4 times, and its nitrate rejection also shows a slight enhancement (∼7.6%) compared with those of PES-NF. Remarkably, at the operating pressure much lower than that required by reverse osmosis membranes, the GOQD/PES-NF-2 membrane possesses an equivalent monovalent ion rejection to reverse osmosis membranes but a higher permeation flux. Furthermore, the result of a 7 day continuous stability test validates the excellent durability of the GOQD/PES-NF-2 membrane, and its antifouling and chlorine resistance performances also outperform those of the PES-NF membrane.

Enhancing separation performance of thin film nanocomposite membranes by self-etching of polydopamine-modified calcium carbonate during interfacial polymerization process

The acid-accepting and gas-generating properties, along with the formation of extensive nanovoids, make CaCO3 nanoparticles attractive as sacrificial nanofillers for fabricating thin-film composite (TFN) nanofiltration membranes. However, challenges such as severe agglomeration and limited acid etching efficiency of the nanoparticles hinder the pursuit of superior membrane performance. In this study, the dispersion and compatibility of CaCO3 nanoparticles within the membrane matrix were improved by modifying them with a polydopamine (PDA) coating. The abundant phenolic hydroxyl groups of PDA enhanced the hydrophilicity and negative charges of membrane surface. Additionally, the PDA capsule increased the etching extent of the CaCO3 nanoparticles by improving the nanoparticle dispersion and generating additional acid, which created sufficient water channels within the polyamide layer. It was demonstrated that incorporating 45 μg/cm2 of PDA-modified CaCO3 nanoparticles doubled the water permeance to 16.7 LMH/bar, while maintaining a low molecular weight cut-off of 249 Da and achieving rejections over 90 % for five types of per- and polyfluorinated substances. The PDA modification also overcame the membrane stability issue caused by the agglomerated CaCO3 nanoparticles. This study provides a novel strategy for applying properly modified self-etching nanofillers in TFN membrane development, showing great potential for water treatment applications.

Construction of sub-10nm ultra-thin polyamide layer using porous GOQDs-AGQDs interlayer

The application of high-performance polyamide nanofiltration membranes with controllable structures shows promising prospects in fields such as seawater desalination and wastewater treatment. In this study, a high-performance polyamide composite nanofiltration membrane with sub-10nm ultra-thin separation layer was designed and fabricated using a hydrophilic porous GOQDs-AGQDs (graphene oxide quantum dots-amino graphene quantum dots) interlayer to reconstruct the substrate architecture. The GOQDs-AGQDs interlayer not only improved the uniformity and smoothness of the microporous substrate, but also could form hydrogen bond with amine monomers to effectively inhibit its diffusion, thereby effectively slowing down the interfacial polymerization process and facilitating the formation of an ultra-thin, smooth and dense polyamide (PA) layer. The results demonstrate that the optimized PA/GOQDs-AGQDs/PES membrane achieved a PA separation layer thickness as low as 9.4 nm, with a permeation flux of 27.2 L·m−2 ·h−1·bar−1, nearly three times that of the original PA/PES membrane. Simultaneously, it enhanced the Na2SO4 rejection rate to 97.1 %, achieving synchronous improvements in permeability and selectivity. Additionally, the PA/GOQDs-AGQDs/PES composite membrane exhibited relatively low surface roughness and demonstrated excellent long-term stability. This work presents a novel strategy for the controllable fabrication of high-performance nanofiltration membranes.

Monitoring the process of interfacial polymerization for fabrication of polyamide reverse osmosis membrane via molecular simulation based on π-π interaction between surfactant and monomer

Accurate regulation of the interfacial polymerization (IP) process is prerequisite for preparation of thin film composite reverse osmosis (RO) membranes with ideal polyamide (PA) layers, and surfactant assembly-regulated IP (SARIP) is proved to be an effective approach. However, mechanism in molecular level for modulation of IP based on surfactants is still inadequate. Here, sodium dodecylbenzene sulphonate (SDBS) and sodium dodecyl sulfate (SDS) have been chosen as surfactants to make comparison of the IP process based on π-π interaction between surfactant and monomer via molecular simulation. As illustrated by Molecular Dynamics (MD) simulations, surfactants enlarge the width of the miscible zone, increase the diffusion rate together with the relative concentration of MPD in the miscible zone, as well as regulate the position of IP reaction towards the aqueous phase. Compared to SDS, SDBS makes the diffusion of MPD in good order, thus avoiding the severe variation in structure and morphology on PA layer. As calculated by DFT, higher interaction energy between the phenyl group of MPD and SDBS based on the π-π interaction is achieved, leading to uniform distribution of MPD close to the phenyl group of SDBS instead of escaping violently into miscible zone. Thus, strong consistency between the position of IP reaction and the height of the phenyl group in SDBS is emerged, which further explains the intrinsic reason for the variation of the IP position and the modulation of the PA microstructure. The mechanism for IP regulation based on SARIP at molecular level is finally proposed via molecular simulation, providing new idea for the preparation of high-performance RO membranes.

Modulating low-temperature interfacial polymerization with NaHCO3 for high-performance ultrathin nanofiltration membranes

Conventional interfacial polymerization (IP) encounters significant challenges in achieving the desired nanofiltration (NF) membrane structure, owing to uncontrolled diffusion and ultrafast polymerization. Our study introduced carbonates into the low-temperature interfacial polymerization (LTIP) process to precisely regulate the diffusion of amine monomers and polymerization kinetics. Carbonates in the aqueous phase restrict the diffusion of amine monomers while promoting the generation of nanobubbles. Further utilization of the low-temperature oil phase not only retards polymerization but also facilitates the formation of foam nanostructures in the polyamide layer. Density functional theory calculations and molecular dynamics simulations revealed the mechanisms underlying the regulation of amine monomer diffusion and gas-bubble release by carbonates and LTIP. The fabricated membrane has a smoother, ultrathin separation layer while maintaining a high permeability of 35.0 L·m−2·h−1·bar−1 (nearly doubled compared with the pristine membrane) and high Na2SO4 rejection of 99.5 %. This study confirms the practicality of the carbonate-modulated LTIP strategy.

Diffusion-Regulated Interfacial Polymerization of Hierarchically Microporous Polyamide Membranes for Permselective Gas Separations.

Interfacial polymerization has emerged as a robust method for fabricating task-specific polyamide (PA) membranes. However, the limited microporosity of highly cross-linked PA membranes constrains their effectiveness in gas separation applications. Herein, we introduce an ionic liquid (IL)-regulated interfacial polymerization process to fabricate polyamide nanofilms incorporating kinked tetrakis (4-aminophenyl) methane monomers. In situ ultraviolet-visible spectroscopy demonstrates that the diffusion of 1,3,5-benzenetricarbonyl trichloride (TMC) toward the interface increases with the IL/H2O ratio, leading to the formation of a more compact membrane with a higher cross-linking degree. The PA-TAM7/3-60 min membrane exhibits a CO2 permeance of 29.8 GPU and a CO2/CH4 selectivity of 109, exceeding the 2008 Robeson upper bond. Additionally, the highly cross-linked structure imparts the membranes with notable plasticization resistance. Mixed-gas tests (CO2/CH4 = 50/50, v/v) reveal that the PA-TAM7/3-60 min membrane experiences only a 2% reduction in CO2 permeance and a 10% decrease in CO2/CH4 selectivity at a CO2 partial pressure of 300 PSIG, compared to its performance at 30 PSIG. The ease of tuning membrane structure and gas separation performance, along with its excellent plasticization resistance, underscores the potential of these PA membranes for task-specific gas separations.

Synergistic preparation of organic solvent nanofiltration membranes from polydopamine/polyethyleneimine interlayers with aminated attapulgite

This study utilized polydopamine (PDA)/polyethyleneimine(PEI) as the hydrophilic interlayer and added aminated attapulgite (ATP-NH2) to the aqueous phase monomer for interfacial polymerization (IP) to synergistically create nanofiltration membranes resistant to organic solvents. The hydrophilic nature of the PDA/PEI interlayer facilitates the rapid passage of polar solvents and results in excellent adhesion, ensuring tight bonding between the ultrafiltration support membranes and the active layer. Furthermore, the incorporation of the ATP-NH2 nanoparticles played a pivotal role in regulating the IP process. The resulting nanofiltration membranes, produced through the combined efforts of these components, achieved an optimal methanol permeation flux of 14.05 L m−2h−1 bar−1, with a rejection rate of Evans blue dye maintained at 99.42 %. Despite being exposed to N, N-dimethylformamide (DMF) at 80 ℃ for a period of 5 days, the nanofiltration membranes maintained both their exceptional separation effectiveness and stability. These findings suggest promising application prospects for the developed nanofiltration membranes.

Modular Customized Biomimetic Nanofluidic Diode for Tunable Asymmetric Ion Transport.

Artificial ion diodes, inspired by biological ion channels, have made significant contributions to the fields of physics, chemistry, and biology. However, constructing asymmetric sub-nanofluidic membranes that simultaneously meet the requirements of easy fabrication, high ion transport efficiency, and tunable ion transport remains a challenge. Here, a direct and flexible in situ staged host-guest self-assembly strategy is employed to fabricate ion diode membranes capable of achieving zonal regulation. Coupling the interfacial polymerization process with a host-guest assembly strategy, it is possible to easily manipulate the type, order, thickness, and charge density of each module by introducing two oppositely charged modules in stages. This method enables the tuning of ion transport behavior over a wide range salinity, as well as responsive to varying pH levels. To verify the potential of controllable diode membranes for application, two ion diode membranes with different ion selectivity and high charge density are coupled in a reverse electrodialysis device. This resulted in an output power density of 63.7W m-2 at 50-fold NaCl concentration gradient, which is 12 times higher than commercial standards. This approach shows potential for expanding the variety of materials that are appropriate for microelectronic power generation devices, desalination, and biosensing.

Capping-grafting synergistic strategy for the preparation of high-performance Mg2+/Li+ separation nanofiltration membranes

Polyethyleneimine (PEI) nanofiltration (NF) membranes demonstrate remarkable effectiveness in separating lithium and magnesium from salt lakes, attributed to their positively charged surface. However, undesired permeability resulting from densely cross-linked structures limits the further industrial applications and development of PEI NF membranes. Herein, a high permeable Mg2+/Li+ separation NF membrane with stronger internal and surface positive charge was fabricated using 1-Aminopyridinium iodide (1-AI) for the first time through a capping-grafting synergistic strategy. On the one hand, the monoamine character of 1-AI can realize the end-capping (EC) effect on the acyl chloride monomers in the interfacial polymerization process, which can contribute to a reduction in the cross-linking degree of the membrane. On the other hand, 1-AI with a quaternary ammonium group as the surface grafting (SG) agent can significantly improve the surface positive charge property of the membrane. The synergistic effect of capping-grafting not only rendered the membrane looser and effectively enhanced the surface positive charge of the membrane, but also increased the depth of grafting modification, leading to a notable rise in the internal positive charge of the membrane. After the capping-grafting treatment, the water permeance of the PEI-EC/SG membrane reached 19.8 L·m−2·h−1·bar−1, approximately 4.5 times that of the original PEI membrane, while keeping an ideal MgCl2 rejection rate (97.1%) and exhibiting good Mg2+/Li+ selectivity (27.7). This work demonstrates the advantages of the capping-grafting synergistic method in regulating membrane structure for improving permeability as well as the surface and internal charge properties of the membrane for enhancing ion selectivity.

Polyamide nanofiltration membranes with enhanced surface charge difference via large aqueous monomer

The charge properties of polyamide membranes play a crucial role in the selective ionic and molecular sieving processes. These polyamide membranes fabricated through interfacial polymerization normally exhibit a front surface enriched with carboxyl groups and a rear surface enriched with amine groups, rendering it with a Janus surface charge. However, this disparity in charge properties between the two surfaces has not been thoroughly investigated, despite its importance in understanding the membrane formation mechanism. In this study, polyethylenimine (PEI, Mw = 70000 Da) and piperazine (PIP, Mw = 86 Da), with distinct molecular size, were employed as aqueous monomers to react with trimesoyl chloride (TMC) at a support-free water hexane interface to synthesize polyamide nanofiltration membranes. The charge differences in the rear and front surface of PEI/TMC and PIP/TMC nanofiltration membrane was fully explored. The PEI/TMC membrane demonstrated a great charge disparity between the two surfaces with a negatively charged (isoelectric point = 5.62) front surface and a positively charged (isoelectric point = 9.59) rear surface. As a result, the rear surface exhibits a higher MgCl2 rejection (95.6 %) than the front surface (88.9 %). In contrast, the PIP/TMC membrane exhibited a similar negative charge and salt rejections on both surfaces. Moreover, the rear surface of PEI/TMC membrane exhibited a great anti-fouling performance to positively charged lysozyme (FDR = 51.1 %, FRR = 88.8 %). This work provides valuable insights into the mechanisms of an interfacial polymerization process

Synthesis and Characterization of Polyaniline / [BMIM][BF4] Polyionic Liquid by Interfacial Polymerization

Polyaniline (PANI) was prepared by polymerization via the chemical oxidation of aniline monomer with ammonium persulfate as the initiator. The interfacial polymerization method was used to prepare PANI/1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] polyionic liquid (PIL). The obtained PANI/ [BMIM][BF4] PIL was investigated by the XRD, EDX, SEM, FTIR, and UV-Visible characterizations. X-ray diffractogram of PANI showed five prominent characteristic peaks at 27.1°, 24o, 21.8°, 19.8°, and 18.2°. This demonstrates the semi-crystalline character of the polyaniline produced through the interfacial polymerization process. Incorporation of [BMIM][BF4] into PANI reduced the crystalline phase and enhanced amorphicity. From the EDX pattern, several elements appeared in this test; oxygen had of the highest weight percentage of 54.2%. The SEM image showed a clear hierarchal porous structure with nano-sticks particles and forms a cross-linked framework between PANI and [BMIM][BF4]. From FTIR spectra of PIL, a prominent absorption peak at 3163.26 cm-1 was noted because of the N-H stretching vibrations present in the polymer. The UV-Vis spectra for PANI/[BMIM][BF4] polyionic liquid showed three peaks between 200 and 1060 nm. These bands result from π → π* and n → π* transitions, which are related to the excitement absorption of benzenoid and quinoid groups.

Fabrication of ultra-permeable membranes with antibiofouling capability by incorporating bifunctionalized zeolite

Poor water permeance and biofouling significantly limit the application of nanofiltration (NF) membranes in wastewater treatment and seawater desalination. Herein, bifunctionalized FAU-Ag-OH zeolites, featuring abundant hydroxyl groups and silver ions on their surface, were designed and incorporated into polyamide (PA) layer of a thin-film nanocomposite (TFN) membrane, effectively enhancing the antibiofouling properties and water permeance of membrane. The plentiful hydroxyl groups and well-dispersed silver ions on the bifunctionalized FAU-Ag-OH zeolites impart the membrane with more negative surface charge, increased hydrophilicity, and superior antibiofouling property. Additionally, the doped FAU-Ag-OH zeolites can retard the diffusion of piperazine during interfacial polymerization (IP) process and have improved chemical compatibility with polymers, which results in desirable membrane structure. Consequently, the optimal M–0.05 membrane containing FAU-Ag-OH zeolites exhibited a 2.3-fold increase in water permeance (18.8 ± 2.0 L m−2 h−1 bar−1) and enhanced antibiofouling ability (with antibacterial efficiency up to 95.4 % and flux recovery ratio up to 85 %) compared with the TFC membrane. The successful fabrication of such membrane with enhanced antibiofouling properties and improved water permeance is expected to promote the application of NF membranes in water treatment.

Thin-film composite (TFC) membranes incorporated with hydrophilic additives and layered double hydroxides (LDHs) for effective brackish water (BW) desalination

To overcome the limited water permeability of thin-film nanocomposite (TFN) membranes for brackish water reverse osmosis (BWRO) processes, we have incorporated a few amine or hydroxyl group terminated hydrophilic additives during interfacial polymerization when fabricating RO membranes and found that the membrane comprising 1 wt% 2-(2-hydroxyethyl)pyridine (2-(2-pyridyl)ethylahydroxide, PEH) has the best BWRO performance. The membrane was subsequently infiltrated with layered double hydroxide (LDH) nanoparticles by a post ethanol activation and could deliver a water permeability of 4.18 LMH bar−1 which is 100 % more than the control membrane without much compromising the salt rejection. The newly developed process not only incorporates nanofillers with the advantages of simplicity and decoupling from the interfacial polymerization process, but also endows the TFN membranes with enhanced separation performance. The study may provide useful insights to incorporate nanofillers by the solvent activation approach for the fabrication of TFN membranes.