Improved antifouling properties of polyethersulfone membrane by blending the amphiphilic surface modifier with crosslinked hydrophobic segments

Zwitterionic Tröger's Base Microfiltration Membrane Prepared via Vapor-Induced Phase Separation with Improved Demulsification and Antifouling Performance

The fouling of separation membranes has consistently been a primary factor contributing to the decline in membrane performance. Enhancing the surface hydrophilicity of the membrane proves to be an effective strategy in mitigating membrane fouling in water treatment processes. Zwitterionic polymers (containing an equimolar number of homogeneously distributed anionic and cationic groups on the polymer chains) have been used extensively as one of the best antifouling materials for surface modification. The conventional application of zwitterionic compounds as surface modifiers is intricate and inefficient, adding complexity and length to the membrane preparation process, particularly on an industrial scale. To overcome these limitations, zwitterionic polymer, directly used as a main material, is an effective method. In this work, a novel zwitterionic polymer (TB)-zwitterionic Tröger's base (ZTB)-was synthesized by quaternizing Tröger's base (TB) with 1,3-propane sultone. The obtained ZTB is blended with TB to fabricate microfiltration (MF) membranes via the vapor-induced phase separation (VIPS) process, offering a strategic solution for separating emulsified oily wastewater. Atomic force microscopy (AFM), scanning electron microscopy (SEM), water contact angle, and zeta potential measurements were employed to characterize the surface of ZTB/TB blended membranes, assessing surface morphology, charge, and hydrophilic/hydrophobic properties. The impact of varying ZTB levels on membrane surface morphology, hydrophilicity, water flux, and rejection were investigated. The results showed that an increase in ZTB content improved hydrophilicity and surface roughness, consequently enhancing water permeability. Due to the attraction of water vapor, the enrichment of zwitterionic segments was enriched, and a stable hydration layer was formed on the membrane surface. The hydration layer formed by zwitterions endowed the membrane with good antifouling properties. The proposed mechanism elucidates the membrane's proficiency in demulsification and the reduction in irreversible fouling through the synergistic regulation of surface charge and hydrophilicity, facilitated by electrostatic repulsion and the formation of a hydration layer. The ZTB/TB blended membranes demonstrated superior efficiency in oil-water separation, achieving a maximum flux of 1897.63 LMH bar-1 and an oil rejection rate as high as 99% in the oil-water emulsion separation process. This study reveals the migration behavior of the zwitterionic polymer in the membrane during the VIPS process. It enhances our comprehension of the antifouling mechanism of zwitterionic membranes and provides guidance for designing novel materials for antifouling membranes.

Hydrophobicity of molecular-scale textured surfaces: The case of zeolitic imidazolate frameworks, an atomistic perspective

Hydrophobicity has proven fundamental in an inexhaustible amount of everyday applications. Material hydrophobicity is determined by chemical composition and geometrical characteristics of its macroscopic surface. Surface roughness or texturing enhances intrinsic hydrophilic or hydrophobic characteristics of a material. Here we consider crystalline surfaces presenting molecular-scale texturing typical of crystalline porous materials, e.g., metal-organic frameworks. In particular, we investigate one such material with remarkable hydrophobic qualities, ZIF-8. We show that ZIF-8 hydrophobicity is driven not only by its chemical composition but also its sub-nanoscale surface corrugations, a physical enhancement rare amongst hydrophobes. Studying ZIF-8's hydrophobic properties is challenging as experimentally it is difficult to distinguish between the materials' and the macroscopic corrugations' contributions to the hydrophobicity. The computational contact angle determination is also difficult as the standard "geometric" technique of liquid nanodroplet deposition is prone to many artifacts. Here, we characterise ZIF-8 hydrophobicity via: (i) the "geometric" approach and (ii) the "energetic" method, utilising the Young-Dupré formula and computationally determining the liquid-solid adhesion energy. Both approaches reveal nanoscale Wenzel-like bathing of the corrugated surface. Moreover, we illustrate the importance of surface linker termination in ZIF-8 hydrophobicity, which reduces when varied from sp3 N to sp2 N termination. We also consider halogenated analogues of the methyl-imidazole linker, which promote the transition from nanoWenzel-like to nanoCassie-Baxter-like states, further enhancing surface hydrophobicity. Present results reveal the complex interface physics and chemistry between water and complex porous, molecular crystalline surfaces, providing a hint to tune their hydrophobicity.

Surface Segregation Methods toward Molecular Separation Membranes

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

Antifouling improvement of a polyacrylonitrile membrane blended with an amphiphilic copolymer

The amphiphilic copolymer polyacrylonitrile-co-poly(hydroxyethyl methacrylate) (PAN-co-PHEMA) was readily blended with polyacrylonitrile (PAN) to fabricate a flat-sheet blending membrane through non-solvent induced phase separation (NIPS). In the membrane-forming process, the hydrophilic PHEMA chains are uniformly distributed on the surface, as revealed by the energy-dispersive X-ray tests. The sponge-like sub-layer embedded with droplet-shaped structures is formed at the cross-sections of membranes, because of the high viscosity of the casting solution. With the increase of copolymer concentration, the mean pore size of the blending membranes increases from 26.9 to 99.8 nm, leading to the increase of membrane flux from 93.6 to 205.4 l/(m2h). The incorporation of PAN-co-PHEMA copolymer endows the blending membrane with a rough surface microstructure and enhanced hydrophilicity. The rejection ratio of membranes for emulsified pump oil reaches 99.9%, indicating a prominent separation performance. In the cycle permeation experiments, the flux recovery ratio of the blending membranes is as high as 99.6%, which is much higher than those of PAN membrane. The irreversible fouling of blending membranes induced by oil adsorption is alleviated, and converted into reversible fouling, owing to the reduction of the adhesion force between foulant and membrane surface. These results suggest that the anti-fouling property of PAN membranes has been dramatically strengthened via the addition of PAN-co-PHEMA copolymer.

Iron-containing poly(ionic liquid) membranes: a heterogeneous Fenton reaction and enhanced anti-fouling ability

Iron-containing poly(ionic liquid) membranes were prepared by Cu(0)-mediated reversible deactivation radical polymerization, which was achieved to catalyze a heterogeneous Fenton reaction and realize self-cleaning of the membrane surface.

Antimicrobial Hydrophilic Membrane Formed by Incorporation of Polymeric Surfactant and Patchouli Oil

Membrane properties are highly affected by the composition of the polymer solutions that make up the membrane material and their influence in the filtration performance on the separation or purification process. This paper studies the effects of the addition of pluronic (Plu) and patchouli oil (PO) in a polyethersulfone (PES) solution on the membrane morphology, membrane hydrophilicity, and filtration performance in the pesticide removal compound in the water sample. Three types of membranes with the composition of PES, PES + Plu, and PES + Plu + patchouli oil were prepared through a polymer phase inversion technique in an aqueous solvent. The resulting membranes were then analyzed and tested for their mechanical properties, hydrophilicity, antimicrobial properties, and filtration performance (cross-flow ultrafiltration). The results show that all of the prepared membranes could reject 75% of the pesticide. The modification of the PES membrane with Plu was shown to increase the overall pore size by altering the pore morphology of the pristine PES, which eventually increased the permeation flux of the ultrafiltration process. Furthermore, patchouli oil added antimicrobial properties, potentially minimizing the biofilm formation on the membrane surface.

The development of an antifouling interpenetrating polymer network hydrogel film for salivary glucose monitoring

Owing to its rapid response and broad detection range, a phenylboronic acid (PBA)-functionalized hydrogel film-coated quartz crystal microbalance (QCM) sensor is used to non-invasively monitor salivary glucose in diabetic patients. However, nonspecific protein adsorption on the PBA-functionalized hydrogel film can cause dramatic loss of sensitivity and accuracy of the sensor. A traditional zwitterionic polymer surface with ultra-low protein fouling can hinder the interaction of PBA in the hydrogel matrix with glucose molecules owing to its steric hindrance, resulting in poor glucose sensitivity of the sensor. Herein, we developed a novel hydrogel film that enhanced the antifouling properties and sensitivity of the QCM sensor by infiltrating a glucose-sensitive monomer (i.e., PBA) into a zwitterionic polymer brush matrix to form an interpenetrating polymer network (IPN). The IPN hydrogel film could minimize the glucose sensitivity loss since the antifouling polymer distributed in its matrix. Moreover, a stable hydration layer was formed in this film that could prevent water from transporting out of the matrix, thus further improving its antifouling properties and glucose sensitivity. The experimental results confirmed that the IPN hydrogel film possessed excellent resistance to protein fouling by mucin from whole saliva with reductions in adsorption of nearly 88% and could also enhance the glucose sensitivity by nearly 2 fold, compared to the PBA-functionalized hydrogel film. Therefore, the IPN hydrogel film provides improved antifouling properties and sensitivity of the QCM sensor, which paves the way for non-invasive monitoring of low concentrations of glucose in saliva.

A Self-Cleaning Heterostructured Membrane for Efficient Oil-in-Water Emulsion Separation with Stable Flux

Lack of clean water is a major global challenge. Membrane separation technology is an ideal choice for the treatment of industrial, domestic sewage owing to its low energy consumption and cost. However, membranes are highly susceptible to contamination, particularly during wastewater treatment, which has limited their practical applications in this field. Similarly, the flux of the membrane decreases with prolonged use due to its reduced interlayer spacing. Preparation of membranes with anticontamination properties and stable flux is the key to addressing this problem. In this study, a 2D heterostructure membrane with visible-light-driven self-cleaning performance is prepared via a self-assembly process. Notably, the addition of palygorskite increases the interlayer spacing of the graphene and heterojunction structures, which increases the flux of the membrane and avoids a decrease of the interlayer spacing of the membrane under pressure. The presence of a heterojunction with visible light catalytic properties effectively avoids membrane fouling and avoids a sharp decrease of the permeation flux. Importantly, the prepared 2D membrane has excellent separation performance for oil-water emulsions with both high flux and efficiency. These features suggest great potential for the prepared 2D membrane in wastewater treatment applications.

Preparation and performance of poly(4-vinylpyridine)-b-polysulfone-b-poly(4-vinylpyridine) triblock copolymer/polysulfone blend membrane for separation of palladium (II) from electroplating wastewaters

In order to separate palladium (II) from electroplating wastewaters, poly(4-vinylpyridine)-b-polysulfone-b-poly(4-vinylpyridine) (P4VP-PSF-P4VP) / polysulfone blend membranes were fabricated by combining non-solvent induced phase separation, surface segregation and self-assembly of block copolymer. Amphiphilic P4VP-PSF-P4VP was used as the membrane base material, which was synthesized by introducing the functional monomer of 4-vinylpyridine (4-VP), and polysulfone as the additive. Effects of blend ratio and 4-VP content on membrane performance, such as structure, hydrophilicity, pure water flux and adsorption capacity towards Pd (II), were investigated. The membranes exhibited dense surface structure and low roughness due to surface segregation and self-assembly of P4VP-PSF-P4VP. The presence of 4-VP increased hydrophilicity and water flux of membrane, and it also provided good adsorption capacity towards Pd (II) (up to 103.1 ± 5.15 mg/g). Further, the membrane was used to separate Pd (II) from simulated wastewaters during filtration. It showed good rejection ability and high selectivity towards Pd (II) in co-existence of Cu (II) and Ni (II), and selectivity coefficients of Pd/Cu and Pd/Ni are 41.9 ± 1.88 and 97.8 ± 4.32, respectively. In filtration process of actual electroplating wastewater, the membrane also exhibited excellent rejection performance (Pd (II) rejection reached up to 96.8 ± 2.71%). Perhaps it is suitable for future practice applications.

Current Advances in Biofouling Mitigation in Membranes for Water Treatment: An Overview

Membranes, as the primary tool in membrane separation techniques, tend to suffer external deposition of pollutants and microorganisms depending on the nature of the treating solutions. Such issues are well recognized as biofouling and is identified as the major drawback of pressure-driven membrane processes due to the influence of the separation performance of such membrane-based technologies. Herein, the aim of this review paper is to elucidate and discuss new insights on the ongoing development works at facing the biofouling phenomenon in membranes. This paper also provides an overview of the main strategies proposed by “membranologists” to improve the fouling resistance in membranes. Special attention has been paid to the fundamentals on membrane fouling as well as the relevant results in the framework of mitigating the issue. By analyzing the literature data and state-of-the-art, the concluding remarks and future trends in the field are given as well.

Triple-Layer Nanocomposite Membrane Prepared by Electrospinning Based on Modified PES with Carbon Nanotubes for Membrane Distillation Applications

In this work, a novel triple-layer nanocomposite membrane prepared with polyethersulfone (PES)/carbon nanotubes (CNTs) as the primary bulk material and poly (vinylidene fluoride-co-hexafluoro propylene) (PcH)/CNTs as the outer and inner surfaces of the membrane by using electrospinning method is introduced. Modified PES with CNTs was chosen as the bulk material of the triple-layer membrane to obtain a high porosity membrane. Both the upper and lower surfaces of the triple-layer membrane were coated with PcH/CNTs using electrospinning to get a triple-layer membrane with high total porosity and noticeable surface hydrophobicity. Combining both characteristics, next to an acceptable bulk hydrophobicity, resulted in a compelling membrane for membrane distillation (MD) applications. The prepared membrane was utilized in a direct contact MD system, and its performance was evaluated in different salt solution concentrations, feed velocities and feed solution temperatures. The results of the prepared membrane in this study were compared to those reported in previously published papers. Based on the evaluated membrane performance, the triple-layer nanocomposite membrane can be considered as a potential alternative with reasonable cost, relative to other MD membranes.

Self-associating cellulose-graft-poly(ε-caprolactone) to design nanoparticles for drug release

The growing interest in the use of polysaccharides nanoparticles for biomedical applications is related to the recent progresses on the synthesis of cellulose-based polymers with the specific functionalities. In particular, cellulose graft copolymers are emerging as amphiphilic materials suitable to fabricate smart nanoparticles for drug delivery applications. In this work, a cellulose-graft-poly(ε-caprolactone) (cell-g-PCL) was synthetized and characterized by FTIR, TGA and DSC in order to validate the synthesis process. We demonstrated that fast evaporation processes promoted cell-g-PCL self-assembly to form nanomicellar structures with hydrodynamic radius ranged from 30 to 60 nm as confirmed by TEM analysis. Moreover, the application of controlled electrostatic forces on solvent evaporation - namely electrospraying - allowed generating round-like nanoscaled particles, as confirmed by SEM supported via image analysis. We demonstrated also that sodium diclofenac (DS) drastically influenced the mechanism of particle formation, favoring the deposition of erythrocyte-like particles with highly concave surfaces, not penalizing the encapsulation efficiency of nanoparticles (>80%). The release profile showed a fast delivery of DS - about 60% during the first 24 h - followed by a sustained release - about 20% during the next 6 days - strictly related to the peculiar weak interactions among amphiphilic polymer segments and water molecules, thus suggesting a successful use of electrosprayed cell-g-PCL nanoparticles for therapeutic treatments in nanomedicine.

Amphiphilic Block Copolymer of Poly(dimethylsiloxane) and Methoxypolyethylene Glycols for High-Permeable Polysulfone Membrane Preparation

Poly(dimethylsiloxane)-block-methoxypolyethylene glycols (PDMS-b-mPEG) were synthesized by Steglich esterification. The high-permeable membrane (PSf/PDMS-b-mPEG) was prepared by using PDMS-b-mPEG as additives. The successful synthesis of PDMS-b-mPEG was confirmed by nuclear magnetic resonance. Field emission scanning electron microscopy images show that the distribution of finger-like macroporous and sponge-like macroporous can be modulated by controlling the ratio of the hydrophilic/hydrophobic components of additives. The distribution of additives and membrane wettability are validated with X-ray photoelectron spectroscopy and water contact angle test. The permeability of the blended membrane, especially for the membrane PSf/PDMS-b-mPEG1900 (M3), was remarkably improved. The water permeability of M3 (239.4 L/m²·h·bar) was 6.6 times that of the unblended membrane M0 (42.5 L/m²·h·bar). The findings of protein BSA filtration show that the flux recovery ratio of M3 is 89.2% at a BSA retention rate of about 80%, which demonstrates that the polysulfone membranes blended with PDMS-b-mPEG have excellent antifouling performance and extraordinary permeability.

Radical Cation Initiated Surface Polymerization on Photothermal Rubber for Smart Antifouling Coatings

Biofouling on surfaces of various materials has attracted considerable attention in biomedical and marine industries. Surface grafting based on covalent surface-initiated polymerization offers a popular route to address this problem by providing diverse robust polymer coatings capable of preventing the biofouling in complex environments. However, the existing methods for synthesizing polymer coatings are complicated and rigorous, or require special catalysts, greatly limiting their practical applications. In this work, a radical-cation-based surface-initiated polymerization protocol to graft the surface of darkened trans-polyisoprene (TPI) rubber with a thermo-responsive smart polymer, poly(N-isopropylacrylamide) (PNIPAM), through a simple iodine doping process is reported. A series of characterizations were performed to provide adequate evidence to confirm the successful grafting. Combining the thermal sensitivity of PNIPAM with the photothermal conversion ability of the darkened rubber, efficient bacteria-killing and antifouling capabilities were successfully achieved as a result of temperature-controlled iodine release and switchable amphiphilicity of PNIPAM.

Asymmetric Aerogel Membranes with Ultrafast Water Permeation for the Separation of Oil-in-Water Emulsion

Owing to highly porous and low density attributes, aerogels have been actively utilized in catalysis and adsorption processes, but their great potential in filtration requires exploitation. In this study, an asymmetric aerogel membrane is fabricated via one-pot hydrothermal reaction-induced self-cross-linking of poly(vinyl alcohol) (PVA), which exhibits ultrafast permeation for the separation of oil-in-water emulsion. Meanwhile, carbon nanotubes are added to improve the mechanical strength of the aerogel membranes. The self-cross-linking of PVA forms the supporting layer, and the exchange of water and vapor at the interface of PVA solution and air generates the separating layer as well as abundant hydroxyl groups on the membrane surface. The density, porosity, pore size, and wettability of the aerogel membrane can be tuned by the PVA concentration. Owing to high porosity (>95%) and suitable pore size (<85 nm), the aerogel membrane exhibits high rejection (99.0%) for surfactant-stabilized oil-in-water emulsion with an ultrahigh permeation flux of 135.5 × 10³ L m^-2 h^-1 bar^-1 under gravity-driven flow, which is 2 orders of magnitude higher than commercial filtration membranes with similar rejection. Meanwhile, the aerogel membrane exhibits superhydrophilicity, superoleophobicity underwater, and excellent antifouling properties for various surfactant-stabilized oil-in-water emulsions, as indicated by the fact that the flux recovery ratio maintains more than 93% after five cycles of the filtration experiment. The findings in this study may offer a novel idea to fabricate high-throughput filtration membranes.

Recent advances in hydrophilic modification and performance of polyethersulfone (PES) membrane via additive blending

The blending of additives in the polyethersulfone (PES) matrix is an important approach in the membrane industry to reduce membrane hydrophobicity and improve the performance (flux, solute rejection, and reduction of fouling). Several (hydrophilic) modifications of the PES membrane have been developed. Given the importance of the hydrophilic modification methods for PES membranes and their applications, we decided to dedicate this review solely to this topic. The types of additives embedded into the PES matrix can be divided into two main categories: (i) polymers and (ii) inorganic nanoparticles (NPs). The introduced polymers include polyvinylpyrrolidone, chitosan, polyamide, polyethylene oxide, and polyethylene glycol. The introduced nanoparticles discussed include titanium, iron, aluminum, silver, zirconium, silica, magnesium based NPs, carbon, and halloysite nanotubes. In addition, the applications of hydrophilic PES membranes are also reviewed. Reviewing the research progress in the hydrophilic modification of PES membranes is necessary and imperative to provide more insights for their future development and perhaps to open the door to extend their applications to other more challenging areas.

Morphology and performance of polyvinyl chloride membrane modified with Pluronic F127

Background: Attempts to modify the morphology of membrane for application in industrial separation are being undertaken by many researchers. The present study discusses the morphological modification of polyvinyl chloride (PVC) membrane by combining the hydrophilic surfactant Pluronic F127 (PF127) in a polymer solution to improve the performance of the membrane.  Method: The membrane is formed using the non-solvent induced-phase separation (NIPS) method. PF127 is added to the membrane solution as a membrane modifying agent. The effects of the surfactant concentration in the dope solution on the permeability of pure water, solute rejection, hydrophilic characteristics, and membrane morphology are investigated. Results: Higher concentrations of PF127 had a significant effect on the permeability of pure water. The highest membrane permeation was 45.65 l/m 2.hr.atm with the addition of 7% PF127 additive. Conclusion: PF127 is successfully proposed as a membrane pore-forming agent in this work; the blending of this additive in appropriate amounts in the polymer solution is adequate to improve the performance of the PVC membrane.

Morphology and performance of polyvinyl chloride membrane modified with Pluronic F127

Background: Attempts to modify the morphology of membrane for application in industrial separation are being undertaken by many researchers. The present study discusses the morphological modification of polyvinyl chloride (PVC) membrane by combining the hydrophilic surfactant Pluronic F127 (PF127) in a polymer solution to improve the performance of the membrane.  Method: The membrane is formed using the non-solvent induced-phase separation (NIPS) method. PF127 is added to the membrane solution as a membrane modifying agent. The effects of the surfactant concentration in the dope solution on the permeability of pure water, solute rejection, hydrophilic characteristics, and membrane morphology are investigated. Results: Higher concentrations of PF127 had a significant effect on the permeability of pure water. The highest membrane permeation was 45.65 l/m 2.hr.atm with the addition of 7% PF127 additive. Conclusion: PF127 is successfully proposed as a membrane pore-forming agent in this work; the blending of this additive in appropriate amounts in the polymer solution is adequate to improve the performance of the PVC membrane.

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Preparation and characterization of an amphiphilic polyamide nanofiltration membrane with improved antifouling properties by two-step surface modification method

Membrane fouling is an urgent problem needing to be solved for practical application of nanofiltration membranes. In this study, an amphiphilic nanofiltration membrane with hydrophilic domains as well as low surface energy domains was developed, to integrate a fouling-resistant defense mechanism and a fouling-release defense mechanism. A simple and effective two-step surface modification of a polyamide NF membrane was applied. Firstly, triethanolamine (TEOA) with abundant hydrophilic functional groups was grafted to the membrane surface via reacting with the residual acyl chloride group of the nanofiltration membrane, making the nanofiltration membranes more hydrophilic; secondly, the 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), well-known as a low surface energy material, was covalently grafted on the hydroxyl functional groups through hydrogen bonding. Filtration experiments with model foulants (bovine serum albumin (BSA) protein solution, humic acid solution (HA) and sodium alginate solution (SA)) were performed to estimate the antifouling properties of the newly developed nanofiltration membranes. As a result of surface modification proposed in this study the antifouling properties of an amphiphilic modified F-PA/PSF membrane were enhanced more than 10% compared to the PA/PSF specimen in terms of flux recovery ratio.

Schematic diagram of amphiphilic NF membrane by a two-step modification.

Synergy of the mechanical, antifouling and permeation properties of a carbon nanotube nanohybrid membrane for efficient oil/water separation

For water treatment applications, fabricating a high permeation flux membrane with super-strong mechanical strength and excellent long-term antifouling properties remains a great challenge. In this study, robust, antifouling carbon nanotube (CNT) nanohybrid membranes have been fabricated for oil/water separation. Polyethyleneimine (PEI) with abundant amino groups and a hyperbranched structure is utilized to construct a nanocoating on a CNT surface to enhance their hydrophilicity through multiple interactions between PEI and CNTs. Secondly, the vacuum-assisted self-assembly method is utilized to fabricate free-standing membranes by filtration of CNT dispersions. Finally, trimesoyl chloride (TMC) is utilized to post-modify membranes to enhance the mechanical strength and hydrophilicity and change the surface charge through reaction between amino groups and acyl chloride groups as well as hydrolysis of acyl chloride groups into carboxyl groups. The controlled stacking of CNTs renders membranes with a hierarchical nanostructure and a high porosity, leading to high water flux. The physical and chemical crosslinking renders membranes with high mechanical strength, as measured by atomic force microscopy (AFM) and tensile strength tests. The high hydrophilicity and negatively charged surface render membranes with good antifouling properties, as evaluated by filtration experiments of various oil-in-water emulsions. This study may reveal the great prospects of CNT-based membranes with superior comprehensive properties in water treatment relevant applications.

Preparation and performance optimization of PVDF anti-fouling membrane modified by chitin

The poly(vinylidene fluoride) (PVDF)/chitin (CH) blend membranes were prepared by the immersion phase inversion method using N,N-dimethylacetamide (DMAc)/lithium chloride (LiCl) as the co-solvent. It was found that blending CH with PVDF allowed membranes to have a better hydrophilicity, penetrability, antifouling and antibacterial performance. In order to improve the performance of PVDF/CH blend membranes further, water/ethanoic acid (HAc) solutions with different compositions were employed as coagulation baths. The effects of HAc volume percentage in coagulation baths on the surface composition, morphology, wettability, water flux, antifouling and antibacterial property of PVDF/CH membrane were investigated. The results indicated that the content of CH on the surface of the membrane increased with the increase of HAc concentration in coagulation baths, which contributed to an improvement of hydrophilicity. The increasing HAc content in coagulation baths also led to a change from finger-like pores to sponge-like pores and a decrease of porosity for PVDF/CH blend membranes. When increasing HAc concentration, the antifouling performance of the blend membranes was improved. Meanwhile, the amidogen of CH on PVDF/CH membrane surfaces could suppress the growth of bacteria, and the blend membrane showed an improved antibacterial performance with the volume ratio of HAc increasing.