Polyamide Layer Research Articles

A “self-driven” roving membrane with enhanced water-pumping and dye rejection performance

Considering that traditional membrane treatment of dyeing wastewater requires extra driving pressure, this work successfully prepared a roving membrane powered by the siphoning and wicking effects of the roving to separate dyes from dyeing wastewater. In this work, we found that bamboo pulp roving had the optimal siphoning and wicking performance, making it the focus for subsequent research. At the optimized interfacial polymerization parameters, the prepared roving membrane exhibited the optimal water-pumping and dye rejection performance, which reached 9.11 g/h and 99.58 %, respectively. The diameter of the rovings wrapped in polyamide layer became smaller and the wicking performance was improved. In addition, the thickness of polyamide layer with uniformly distributed nanoTiO2 decreased, and the crosslinking degree was enhanced. Ultraviolet light further contributed to the enhanced water-pumping and dye rejection performance of the piperazine/TiO2/trimesoyl chloride roving membrane. During the 120-h continuous filtration, the water-pumping and rejection performance was stable with only small fluctuations. Importantly, high dye retentions and water-pumping rate were achieved. In this study, we successfully prepared a membrane that is easy to use and does not require extra driving pressure, providing a new approach for dye wastewater treatment.

Thermally stable thin-film composite nanofiltration membranes derived from 3,3′-diaminobenzidine

The rapid development of modern industrialization has put forward high demands on separation and purification technologies. To reduce energy consumption, improve efficiency, and enhance process flexibility, nanofiltration membranes for high temperature separation have become more and more important. Herein, we report the use of 3,3′-diaminobenzidine (DAB) as the aqueous phase monomer and trimesoyl chloride (TMC) as the organic phase monomer to engineer thermally resistant nanofiltration membranes via interfacial polymerization. The incorporation of DAB enhances the rigidity of the cross-linked polyamide network, reduces segmental thermal motion at high temperature, and improves the thermal stability of the composite membrane. The variations in fractional free volumes of the nanofiltration membranes were analyzed at different temperatures by molecular dynamics (MD) simulation, which have also been confirmed by experiments. The findings reveal that incorporating a rigid monomer into the polyamide layer can significantly enhance the thermal resistance. The resultant composite membrane exhibits outstanding resistance to high-temperature feed solutions, boasting a highly stable rejection rate (97.0 %) to Na2SO4 between 25–85 °C. Remarkably, even under sustained operation at 85 °C for 12 h, the rejection rate is consistently stable. This work presents a novel system for the design of thermally stable nanofiltration membranes for high temperature separation.

High-flux polyamide nanofiltration membranes tuning by polydopamine-modified boron nitride nanosheets: Accelerating Mg2+/Li+ separation

As a promising technology for lithium extraction from salt lakes, nanofiltration membranes still face challenges in balancing between permeability and selectivity. In this paper, highly dispersed functionalized boron nitride nanosheets (BNNSs-NH2) were prepared by modifying exfoliated boron nitride nanosheets (BNNSs) with polydopamine, which were incorporated into a polyamide (PA) layer by aqueous phase conditioning to prepare positively charged polyamide nanofiltration membranes. Scanning electron microscopy (SEM) showed that the PDA nanoclusters on the surface of the BNNSs can disrupt the regular stacking parallel to the membrane surface. Energy spectrum (EDS) of SEM and X-ray photoelectron spectroscopy (XPS) etching further revealed that BNNSs-NH2 were dispersed within PA layer, creating transmembrane channels for molecular diffusion. The results showed a pure water permeance of 8.55 ± 0.24 L/m2 h bar, indicating that the stabilized intercalation of BNNSs-NH2 in the PA layer synergistically improved the water permeability. Meanwhile, the retention rate of MgCl2 remained at 94 %, which was attributed to the enhanced compatibility between BNNSs-NH2 and polyamide matrix by the polydopamine coating (PDA) on the surface, as well as the Dornan effect repulsion by the enhanced positive charge on the membrane surface. After the three-stage nanofiltration of membrane, the Mg2+/Li+ ratio decreased from 50 to 0.12. Overall, this method balances permeability and selectivity by adjusting pore size and positive charge, potentially offering new ideas and insights for the preparation and development of nanofiltration membranes for Mg2+/Li+ separation.

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.

Turing structured nanofiltration membrane fabricated by sulfonated cellulose nanocrystals mediated interfacial polymerization for enhanced permeability separation performance

Preparing Turing structure nanofiltration (NF) membrane is a representative strategy to obtain high permeability and selectivity. However, getting a tailored Turing structure by adjusting the interfacial polymerization (IP) process remains a significant challenge. Herein, sulfonated cellulose nanocrystals (S-CNC) with excellent hydrophilicity and negative surface charges were selected as aqueous phase additives to explore their influence on the morphology and composition of polyamide (PA) layer as well as its NF performance. It was found the surface morphology of the PA layer was effectively changed by adjusting the content of S-CNC in the aqueous phase. As the content of S-CNC increased, the Turing structure underwent a series of evolutions, from an “octopus leg structure” to a densely packed ridge-valley structure to a large ridge-valley structure filled with dense nodular particles. Finally, it changed back to the typical PA morphology of densely distributed nodular particles. By exploring the interaction between S-CNC and piperazine (PIP), it was demonstrated that the hydrogen bond and electrostatic interaction between S-CNC and PIP synergistically inhibited the diffusion of PIP, thus resulting in various Turing structures. Benefiting from the unique Turing structure, the prepared SCNF-10 NF membranes showed excellent permeability and separation properties with pure water permeability (PWP) of 16.9 LMH bar−1 and Na2SO4 rejection rate of 98.0 %. SCNF-10 NF membranes also exhibited good selectivity with a separation factor of 34.6 for mono-bivalent salts and long-term permeation stability. It is anticipated that this regulation strategy for various Turing structures preparation can provide a deeper understanding of the application of cellulose nanocrystals to NF membranes in the later stage, which will also promote the development of the high performance of NF membranes.

A novel TFNi pervaporation membrane with g-C3N4 quantum dots for high-efficiency IPA dehydration

Pervaporation (PV) shows significant potential for the highly selective isopropanol (IPA). The pursuit of developing PV membranes with outstanding separation effect and enduring high purity permeation is an indispensable goal. Based on polyamide (PA) separation layers, a polydopamine (PDA) mixed g-C3N4 quantum dots (gCNQDs) coating as the interlayer was deposited onto a porous ceramic hollow fiber substrate to fabricate thin-film nanocomposite membranes with an interlayer (TFNi). The nanocomposite interlayer enabled the formation of a smoother and highly separated selective polyamide layer. The separation factor exhibited a 31-fold enhancement with the augmentation of the blending fraction of gCNQDs during the PDA coating process. The resulting TFNi membrane attained an exceedingly high separation factor of 10270 ± 90 with a permeate water concentration of 99.9% and demonstrated a satisfactory flux of 1.40 ± 0.08 kg⋅m-2⋅h-1 during the PV process of 90 wt% IPA dehydration at 60 °C. This study presents a fresh perspective on the implementation of nanocomposite interlayers, which is expected to expand the application of high-performance TFNi membranes in PV dehydration processes.

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.

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 interfacial polymerization by combination of organic phase additives and trimesoyl chloride for preparing high-performance thin-film nanocomposite reverse osmosis membranes

Incorporating hydrophilic nanoparticles into organic phase during interfacial polymerization (IP) to establish covalent bonds with organic phase monomers has proven to be a successful approach for fabricating high-performance thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, the effect of covalent bonds number on the membrane structure and properties remains uncertain. Herein, hydrochloric acid doped polyaniline (PANI-HCl) with a small amount of amine groups and inherent polyaniline (PANI-base) nanomaterials with a larger amount of amine groups were prepared as organic phase additives for preparing high-performance TFN RO membranes. The amine groups on the nanoparticles can bond covalently with the acyl chloride groups of trimethyl chloride (TMC), leading to the accumulation of TMCs at organic/aqueous interface and accelerates IP reaction rate, resulting in a thinner, denser polyamide layer with more leaf-like structures and free volume. The water permeance of the PANI-base-RO membrane was improved by 62.5 % from 0.8 to 1.3 Lm−2h−1bar−1, and the NaCl rejection was improved from 97.6 % to 99.4 % compared with the pristine membrane. Overall, this work highlights the beneficial impact of organic phase additives with more amine groups on enhancing the desalination performance of RO membranes, providing valuable insights for the structural design of additives and dispersing medium selection.

Advanced lithium extraction nanofiltration membrane with fast transport channels via competitive diffusion and reaction of rigid electropositive phenylbiguanide molecules

The utilization of nanofiltration membranes for lithium extraction from Salt-Lake holds the potential to address lithium resource scarcity and drive energy transformation. Nevertheless, the trade-off effect between water permeability and Mg2+/Li+ separation selectivity poses a challenge in the application of these membranes. In this work, rigid-flexible interpenetration and competitive diffusion reaction strategies were proposed to regulate the pore structure and charge density of the functional layer, thus enhancing the overall separation performance of nanofiltration membrane. Phenylbiguanide (PBG) possessing rigid structure, high positive charge density, and low energy transfer barrier was embedded into flexible polyethyleneimine-based polyamide network. This integration facilitated the formation of continuous and semi-permanent microcavities with rigid-flexible coupled structure, and meanwhile, elevated the density of positive charges. Consequently, the modification extended the water molecular transport channels within the functional layer, leading to a notable enhancement in pure water flux, from 7.40 to 26.43 L m−2h−1. In addition, due to the faster diffusion of PBG than polyethyleneimine with high molecular weight (70000 Da, as aqueous monomer in this work), it could react with excess 1,3,5-trimesoyl chloride (TMC) on the surface of initial membrane to form a new polyamide layer, which repaired the defects in the functional layer and also enhanced the charge density inside pore channels. Therefore, Mg2+/Li+ separation selectivity factor increased from 3.79 of TFC membrane to 22.98 of PBG membrane, i.e., by about 6 times. This study provided an effective strategy to develop nanofiltration membranes with both good water permeability and Mg2+/Li+ selectivity.

Controllable Design of Polyamide Composite Membrane Separation Layer Structures via Metal-Organic Frameworks: A Review.

Optimizing the structure of the polyamide (PA) layer to improve the separation performance of PA thin-film composite (TFC) membranes has always been a hot topic in the field of membrane preparation. As novel crystalline materials with high porosity, multi-functional groups, and good compatibility with membrane substrate, metal-organic frameworks (MOFs) have been introduced in the past decade for the modification of the PA structure in order to break through the separation trade-off between permeability and selectivity. This review begins by summarizing the recent progress in the control of MOF-based thin-film nanocomposite (TFN) membrane structures. The review also covers different strategies used for preparing TFN membranes. Additionally, it discusses the mechanisms behind how these strategies regulate the structure and properties of PA. Finally, the design of a competent MOF material that is suitable to reach the requirements for the fabrication of TFN membranes is also discussed. The aim of this paper is to provide key insights into the precise control of TFN-PA structures based on MOFs.

Fabrication of cellulose nanocrystals-incorporated dense Janus membranes for enhanced desalination and oily saline wastewater treatment via membrane distillation

Conventional hydrophobic membranes used in membrane distillation (MD) face significant challenges, such as severe membrane fouling and wetting, when treating surfactant-containing oily wastewater. Current strategies to modify surfaces for anti-fouling and anti-wetting purposes are often complex and time consuming, potentially compromising the flux in MD. This study investigates the characteristics and performance of novel fabricated Janus membranes for the treatment of oily hypersaline wastewater in membrane distillation applications. Janus membranes, which have a dense polyamide layer containing cellulose nanocrystal nanoparticles, were synthesized using the reverse interfacial polymerization (R–IP) method on a polyvinylidene fluoride (PVDF) substrate. Characterization using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) revealed that the modified Janus membranes exhibited an enhanced hydrophilicity and structural integrity due to the incorporation of cellulose nanocrystal nanoparticles. The fabricated membranes showed a dense surface layer without visible pores or cracks, with micron-scale patterned structures and widely distributed wrinkles, particularly at higher concentrations of cellulose nanocrystal nanoparticles. The desalination performance was evaluated in an air gap membrane distillation setup, where the modified Janus membranes demonstrated higher water vapor fluxes and stable salt rejection, even in the presence of surfactants. The wettability and fouling resistance of the Janus membranes were evaluated, with the PVDF-RIP0.5C membrane showing the highest hydrophilicity and underwater oleophobicity, thereby preventing oil adhesion and membrane fouling. These results underline the potential of Janus membranes with incorporated cellulose nanocrystal nanoparticles for efficient desalination and treatment of oily saline wastewater in the MD process.

Polyamide nanofiltration membrane modified with defective covalent organic framework interlayer for selective ion sieving

Generally, thin-film composite (TFC) membranes prepared using piperazine (PIP) and trimesoyl chloride (TMC) exhibit good Na2SO4 rejection, but their MgCl2 rejection is not satisfactory. In this study, a defective covalent organic framework (COF) interlayer with residual unreacted amine groups was fabricated via interfacial polymerization (IP) by changing the catalyst concentration. Introduction of the COF layer into a polyamide (PA) separation membrane modified the pore size of the PA layer, thereby improving the rejection of divalent cations. The pore size of the PA layer decreased and the surface morphology of the membrane was converted from nodular to a hybrid morphology of “ridge-and-valleys’’ and nodules, indicating that the residual unreacted amine groups on the COF interlayer successfully reacted with the acyl chloride groups. The optimal membrane (PIP/COF-A/PES) exhibited high rejection of divalent ions (Na2SO4 of 98.3% and MgCl2 of 94.3%), and the membrane showed excellent capability for separating mono/divalent ions. Overall, a method of preparing nanofiltration membranes by modifying the PA layer to enhance the rejection of divalent cations was demonstrated.

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.

Engineering mineralized interlayers for enhanced nanofiltration: Synergistic modulation of polyamide layer structure and catalytic self-cleaning performance

High permselectivity and antifouling/self-cleaning nanofiltration (NF) membranes are ideal materials for water treatment, and this vision is expected to be reached through the design of multifunctional self-cleaning interfaces. In this study, we employed metal - polyphenol network (MPN) to mediate in situ mineralization of porous substrates, enabling simultaneous modulation of interfacial polymerization (IP) and catalytic self-cleaning. The findings demonstrate that the mineralized layers employ an interlayer modulation strategy to produce a polyamide (PA) layer that is more hydrophilic, thinner, and structurally denser. As a result, the resulting PA-Fe3O4-PSF membrane exhibited a 2.5-fold increase in permeance (19.2 L m−2 h−1 bar−1) and a 7.3-fold enhancement in Cl−/SO42− selectivity (66.4), compared to the control membrane (PA-PSF). Additionally, its highly polarized membrane surface significantly improved its antifouling performance. Compared to membranes with mineralized layers on the surface (Fe3O4-PA-PSF), PA-Fe3O4-PSF constructs a confined space that facilitates more efficient regeneration through in situ catalytic self-cleaning and ensures greater stability during multiple fouling-regeneration cycle operations. This study paves the way for fabricating multifunctional NF membranes with sustainable applications in material concentration, wastewater treatment, and environmental remediation.

Performance regulation of the TFC NF membrane via the introduction of oleic acid into different organic solvents

AbstractBACKGROUNDTailored design of high‐performance nanofiltration membranes is desirable. The physicochemical properties of the organic phaseare essential for the preparation of nanofiltration membranes. Therefore, byfine‐tuning the organic phase, it is possible to achieve nanofiltrationmembranes with enhanced performance.RESULTSIn this work, oleic acid, a naturally extracted fatty acid, wasintroduced into three different organic solvents (n‐heptane, n‐octane andisopar G) to construct special oil phases for interfacial polymerization. Testingresults showed that proper dosage of oleic acid addition can effectivelydecrease the nanofiltration membrane pore size and enhance the salt rejectionregardless of the solvent type. Taking n‐octane as example, 5% oleic acidaddition in it can decrease the mean pore size from 0.500 nm to 0.341 nm and improve the MgSO4 rejection from 52.4% to 95.5%. Further characterizationindicated that the introduction of oleic acid into organic solvent cansignificantly reduce the interfacial tension and promote the diffusion of piperazinefrom aqueous phase to the oil phase. In addition, oleic acid could react with piperazineand produce some white particles that could be embed into the polyamide layer, thus altering the surface morphology.CONCLUSIONIn this work, a novel modified thin film composite nanofiltration membrane was prepared by a simple and controllable oleic acid assisted interfacial polymerization strategy, which exhibits good water permeability, solute selectivity and antifouling property. Without changing the existing process, our strategy opens up a simple, environmentally friendly and operable route for the synthesis of thin film composite nanofiltration membranes. © 2024 Society of Chemical Industry (SCI).

High-Performance Nanofiltration Membrane with Dual Resistance to Gypsum Scaling and Biofouling for Enhanced Water Purification.

Nanofiltration (NF) technology is pivotal for ensuring a sustainable and reliable supply of clean water. To address the critical need for advanced thin-film composite (TFC) polyamide (PA) membranes with exceptional permselectivity and fouling resistance for emerging contaminant purification, we introduce a novel high-performance NF membrane. This membrane features a selective polypiperazine (PIP) layer functionalized with amino-containing quaternary ammonium compounds (QACs) through an in situ interfacial polycondensation reaction. Our investigation demonstrated that precise QAC functionalization enabled the construction of the selective PA layer with increased surface area, enhanced microporosity, stronger electronegativity, and reduced thickness compared to the control PIP membrane. As a result, the QAC NF membrane exhibited an approximately 51% increase in water permeance compared to the control PIP membrane, while achieving superior retention capabilities for divalent salts (>99%) and emerging organic contaminants (>90%). Furthermore, the incorporation of QACs into the PIP selective layer was proved to be effective in mitigating mineral scaling by allowing selective passage of scale-forming cations, while simultaneously exhibiting strong antimicrobial properties to combat biofouling. The in situ QAC incorporation strategy presented in this study provides valuable guidelines for the fit-for-purpose design of the selective PA layer, which is crucial for the development of high-performance NF membranes for efficient water purification.

N-oxide connected zwitterionic polyamide nanofiltration membrane for efficient antibiotic/salt separation

Nanofiltration membrane technology for antibiotic desalination in fermentation broth represents a low-energy and high-purity approach. However, it is constrained by the low perm-selectivity and susceptibility to membrane fouling. Here, we develop a novel zwitterionic nanofiltration membrane by incorporating an N-Oxide directly connected zwitterion N,N-bis(3-aminopropyl)methylamine N-oxide (DNMAO) into the nascent polyamide layer via interfacial polymerization. The N-Oxide derived zwitterion created a looser crosslinking network in addition to the trimesoyl chloride-piperazine (TMC-PIP) network, which was supported by Stokes radius related with molecular weight cut-off measurement, and Brunauer-Emmett-Teller Ar adsorption isotherms. Moreover, the directly connected groups (N+-O-) without spacers endow excellent hydration ability and mitigate membrane fouling. The optimized membrane exhibits a water flux of 114.9 L m−2 h−1 and exceptional anti-fouling performance with a flux recovery ratio as high as about 96.4 %. Furthermore, the salt/antibiotic separation factor maintained at 41.1 when continuously filtrating NaCl/erythromycin (ERY) mixed solution for 7 h, which showed a great potential in antibiotic purification.

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.