Membrane Pore Structure Research Articles

Template-assisted fabrication of polyether ether ketone hollow fiber membrane for highly efficient separation of binary dye mixtures

Poly(ether ether ketone) (PEEK) is among the most reliable membrane materials in membrane-based separation processes due to its excellent properties especially under harsh environment. Successfully implementing the controllable construction of the pore structure into the fabrication process of PEEK hollow fiber membranes (HFMs) can make a significant contribution to addressing the issue of membrane selectivity and permeability. Herein, we developed a flexible route for manufacturing PEEK HFMs by melt-spinning technology combined with the template-assisted crystallization process. This route effectively reduced the amount of organic solvent in the membrane preparation process, and the crystallization induced strategy remarkably improved the connectivity of membrane pore structure and fixed pore structure of PEEK HFMs. Furthermore, we conducted a comprehensive investigation into the separation mechanism and performance stability of the prepared membranes in binary dye mixtures. The results unveiled that the suitable pore structure of the PEEK HFMs that maintained a high salt permeability with a high dye retention, synergized with strong negative charge contributed to excellent performance in dye/salts or dye/dye binary mixtures separations. A long-term stability of PEEK HFMs for treatment of the simulated textile wastewater with rejection coefficient of above 99% to dyes like congo red (CR) and a low NaCl rejection (<10%) indicated that PEEK HFMs have a bright prospect in dye/salt separation for water purification and resource reclamation.

Improved enantioselective permeation in cellulose membrane-supported metal–organic framework via polyvinylpyrrolidone as the pore-forming agent

Chiral membranes have limited permeability and selective trade-off, which has been a major problem in chiral membrane separations. To address this issue, the carboxylated cellulose (CC) membranes were prepared with small pore size and low resistance substrate by regulating the amount of polyvinylpyrrolidone (PVP) and casting solution, and the CC@CuLBH composite membrane with chiral separation capability was fabricated by in situ formation of well-dispersed [Cu(L-mal)(Bipy)]·H2O (CuLBH) with the carboxyl group on the surface of CC membrane as the metal anchor points. Under the optimal conditions, the CC@CuLBH membrane showed good chiral separation ability with an ee value of 60% for R-1-(1-naphthyl)ethanol (R-NE). Compared with the CC/CuLBH membrane formed by physical blend, the CC@CuLBH membrane exhibited improved enantioselective permeation for R-NE enantiomer. Both the unique chiral microenvironment of CuLBH and the regular pore structure of CC membrane, in addition to their synergistic effects resulted in the highly permeable and enantioselectivity for the CC@CuLBH composite membrane, which broadened the preparation method of chiral membrane.

Engineered Bacterial Biomimetic Vesicles Reprogram Tumor-Associated Macrophages and Remodel Tumor Microenvironment to Promote Innate and Adaptive Antitumor Immune Responses.

Tumor-associated macrophages (TAMs) are among the most abundant infiltrating leukocytes in the tumor microenvironment (TME). Reprogramming TAMs from protumor M2 to antitumor M1 phenotype is a promising strategy for remodeling the TME and promoting antitumor immunity; however, the development of an efficient strategy remains challenging. Here, a genetically modified bacterial biomimetic vesicle (BBV) with IFN-γ exposed on the surface in a nanoassembling membrane pore structure was constructed. The engineered IFN-γ BBV featured a nanoscale structure of protein and lipid vesicle, the existence of rich pattern-associated molecular patterns (PAMPs), and the costimulation of introduced IFN-γ molecules. In vitro, IFN-γ BBV reprogrammed M2 macrophages to M1, possibly through NF-κB and JAK-STAT signaling pathways, releasing nitric oxide (NO) and inflammatory cytokines IL-1β, IL-6, and TNF-α and increasing the expression of IL-12 and iNOS. In tumor-bearing mice, IFN-γ BBV demonstrated a targeted enrichment in tumors and successfully reprogrammed TAMs into the M1 phenotype; notably, the response of antigen-specific cytotoxic T lymphocyte (CTL) in TME was promoted while the immunosuppressive myeloid-derived suppressor cell (MDSC) was suppressed. The tumor growth was found to be significantly inhibited in both a TC-1 tumor and a CT26 tumor. It was indicated that the antitumor effects of IFN-γ BBV were macrophage-dependent. Further, the modulation of TME by IFN-γ BBV produced synergistic effects against tumor growth and metastasis with an immune checkpoint inhibitor in an orthotopic 4T1 breast cancer model which was insensitive to anti-PD-1 mAb alone. In conclusion, IFN-γ-modified BBV demonstrated a strong capability of efficiently targeting tumor and tuning a cold tumor hot through reprogramming TAMs, providing a potent approach for tumor immunotherapy.

Electrospun membranes of diselenide-containing poly(ester urethane)urea for in situ catalytic generation of nitric oxide

Nitric oxide (NO) plays an important role as a signalling molecule in the biological system. Organoselenium-coated or grafted biomaterials have the potential to achieve controlled NO release as they can catalyse decomposition of endogenous S-nitrosothiols to NO. However, such biomaterials are often challenged by the loss of the catalytic sites, which can affect the stability in tissue repair applications. In this work, we prepare a diselenide-containing poly(ester urethane)urea (SePEUU) polymer with Se–Se in the backbone, which is further electrospun into fibrous membranes by blending with poly(ester urethane)urea (PEUU) without diselenide bonds. The presence of catalytic sites in the main chain demonstrates stable and long-lasting NO catalytic activity, while the porous structure of the fibrous membranes ensures uniform distribution of the catalytic sites and better contact with the donor-containing solution. PEUU/SePEUU50 in 50/50 mass ratio has a physiologically adapted rate of NO release, with a sustained generation of NO after exposure to PBS at 37 °C for 30 d. PEUU/SePEUU50 has a low hemolysis and protein adsorption, with mechanical properties in the wet state matching those of natural vascular tissues. It can promote the adhesion and proliferation of human umbilical vein endothelial cells in vitro and control the proliferation of vascular smooth muscle cells in the presence of NO generation. This study exhibits the electrospun fibrous membranes have potential for utilizing as hemocompatible biomaterials for regeneration of blood-contacting tissues.

Numerical simulation of droplet dispersion within meso-porous membranes

Analysis of membrane processes in fluid processing, and their main influencing operating conditions are relevant in a variety of industrial applications. Increasing regulatory scrutiny and environmental considerations are forcing industries across all sectors, from food and pharma to oil and gas, to further understand and optimise the handling and formulation of liquid systems for efficient process design. In a generic setup for emulsification and liquid formulation the flow and dispersion behaviour of a liquid oil droplet on its way through a porous water filled membrane is analysed. A set of high-resolution numerical simulations of a single oil droplet dispersed in water through a porous membrane structure with varying contact angles is performed. In this work cluster analysis of volume-of-fluid simulation results to obtain statistical droplet size distributions is conducted and further analysed to highlight the effect of the contact angle as well as pressure drop on the dynamics of the system. It is observed that based on the membrane surface activity the droplet behaviour changes from filtration with coalescence when the membrane is lipophilic to emulsification with droplet break-up when the membrane is lipophobic. Furthermore, the pressure drop is identified as a key factor for the dynamics of the droplet process and the frame in which it occurs. These results highlight that the membrane wettability is a determining factor for the emulsification or filtration effectiveness of a membrane for various applications.

A novel Polyethersulfone/Chamomile (PES/Chm) mixed matrix membranes for wastewater treatment applications

In order to address the limitation of low flux in ultrafiltration (UF), a suitable additive is introduced into the base polymer to modify the membrane morphology, thereby enhancing flux rates. In this study, chamomile leaf nanoparticles (Chm NPs) were investigated as a novel green material for utilizing in UF membrane synthesizes. To enhance comprehension of the influence of Chm on the synthesis of PES UF membranes, a series of membranes were fabricated by including different quantities of Chm into the casting solution; (0, 0.5, 1.5, and 2 wt. %.). The synthesized membranes were fully characterized, through the porosity, pore size, hydrophilicity, membrane morphology, and UF efficiency. Manufactured PES/Chm membranes demonstrated significantly increased permeate water flux (PWF) (up to 498 kg/m2 h), which was four times that of the pristine PES membrane (116 kg/m2 h), besides that the bovine serum albumin (BSA) and Congo red dye (CR) rejection of PES/Chm membranes was still kept high. The enhanced PWF was mostly due to the more porous membrane structure and increased hydrophilicity. Meanwhile, the higher surface hydrophilicity of the PES/Chm membranes resulted in greater antifouling performance and the high flux recovery ratio (FRR) of 93 %. Based on the results of this research, the Chm may be used as a novel green additive with substantial application potential in the fabrication of UF membranes wastewater treatment.

Chalcopyrite functionalized ceramic membrane for micropollutants removal and membrane fouling control via peroxymonosulfate activation: The synergy of nanoconfinement effect and interface interaction

This work developed a novel chalcopyrite (CuFeS2) incorporated catalytic ceramic membrane (CFSCM), and comprehensively evaluated the oxidation-filtration efficiency and mechanism of CFSCM/peroxymonosulfate (PMS) for organics removal and membrane fouling mitigation. Results showed that PMS activation was more efficient in the confined membrane pore structure. The CFSCM50/PMS filtration achieved almost complete removal of 4-Hydroxybenzoic acid (4-HBA) under the following conditions: pH = 6.0, CPMS = 0.5 mM, and C4-HBA = 10 mg/L. Meanwhile, the membrane showed good stability after multiple uses. During the reaction, SO4•− and •OH were generated in the CFSCM50/PMS system, and SO4•− was considered to be the dominant reactive species for pollutant removal. The roles of copper, iron, and sulfur species, as well as the possible catalytic mechanism were also clarified. Besides, the CFSCM50/PMS catalytic filtration exhibited excellent antifouling properties against NOM with reduced reversible and irreversible fouling resistances. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis showed an increased in repulsive energy at the membrane-foulant interface in the CFSCM50/PMS system. Membrane fouling model analysis indicated that standard blocking was the dominant fouling pattern for CFSCM50/PMS filtration. Overall, this work demonstrates an efficient catalytic filtration process for foulants removal and outlines the synergy of catalytic oxidation and interface interaction.

Constructing hierarchically elongated porous structure in ultrathin ultrahigh molecular weight polyethylene membrane: Achieving high selectivity with remained permeability

Anisotropic pores with a high aspect ratio exhibit higher permeability as well as selectivity than circular pores. Herein, highly selective porous membranes exhibiting elongated slit-like pores and disk-like interlayer large pores are fabricated successfully by biaxial stretching and further constrained uniaxial stretching of ultrahigh molecular weight polyethylene gel films. The thickness and the surface roughness of the porous membrane decrease, and the pore size distribution become narrow during biaxial stretching, while the porous structure become elongated during constrained uniaxial stretching. The thickness decreases from 173.23 μm to 2.33 μm, which reduces the resistance to water passage and then increases the water permeability from approximately 540 L/ (m2 h bar) to 780 L/ (m2 h bar). Due to the presence of mineral oil, the porosity is maintained and even high ratios of constrained uniaxial stretching do not close the pores. The elongation of the porous structure resulted in a significant reduction of the membrane pore size. At a total stretching ratio of 144 times, the pore size of the porous membrane with only biaxial stretching is 0.098 μm, while that of the porous membrane with biaxial stretching and further constrained uniaxial stretching is 0.048 μm. The separation accuracy and stability of the porous membrane improve distinctly, ascribing that the small pore size can reject small particles and prevent the particles from entering the membrane. This study provides one novel strategy to regulate the porous structure of porous polymer membranes for improving the separation efficiency.

Advancing Breathability of Respiratory Nanofilter by Optimizing Pore Structure and Alignment in Nanofiber Networks.

Respiratory masks are the primary and most effective means of protecting individuals from airborne hazards such as droplets and particulate matter during public engagements. However, conventional electrostatically charged melt-blown microfiber masks typically require thick and dense membranes to achieve high filtration efficiency, which in turn cause a significant pressure drop and reduce breathability. In this study, we have developed a multielectrospinning system to address this issue by manipulating the pore structure of nanofiber networks, including the use of uniaxially aligned nanofibers created via an electric-field-guided electrospinning apparatus. In contrast to the common randomly collected microfiber membranes, partially aligned dual-nanofiber membranes, which are fabricated via electrospinning of a random 150 nm nanofiber base layer and a uniaxially aligned 450 nm nanofiber spacer layer on a roll-to-roll collector, offer an efficient way to modulate nanofiber membrane pore structures. Notably, the dual-nanofiber configuration with submicron pore structure exhibits increased fiber density and decreased volume density, resulting in an enhanced filtration efficiency of over 97% and a 50% reduction in pressure drop. This leads to the highest quality factor of 0.0781. Moreover, the submicron pore structure within the nanofiber networks introduces an additional sieving filtration mechanism, ensuring superior filtration efficiency under highly humid conditions and even after washing with a 70% ethanol solution. The nanofiber mask provides a sustainable solution for safeguarding the human respiratory system, as it effectively filters and inactivates human coronaviruses while utilizing 130 times fewer polymeric materials than melt-blown filters. This reusability of our filters and their minimum usage of polymeric materials would significantly reduce plastic waste for a sustainable global society.

Beyond Symmetry: Exploring Asymmetric Electrospun Nanofiber Membranes for Liquid Separation

AbstractComposite membranes with asymmetric traits have gained attention in liquid separation, featuring gradient chemical and physical attributes that align or oppose mass transfer direction. Chemically asymmetric configurations harness internal driving forces to heighten separation efficiency, rendering them an appealing option for heightened separation efficiency and fouling prevention. Concurrently, the internal hierarchical structure differences within composite membranes—such as fiber‐based structural adjustments and the gradient density of functional layers—yield the dual benefits of effective liquid repelling and heightened transport efficiency. Unlike conventional phase‐change methods, electrospinning technology possesses advantages in constructing and governing composite fibrous membrane materials with asymmetric chemistry and hierarchical structures, driven by its adaptable stacking methodologies. Notably, the inherent pore structure of electrospun nanofibrous membranes emerges as a proven solution for minimizing transport resistance. In recent times, interest has surged in electrospun nanofibrous membranes endowed with internal asymmetric properties. However, the spotlight has predominantly graced Janus membranes, spotlighting opposite wettability on different sides, leaving other facets of asymmetric membrane enhancement somewhat underexplored. This comprehensive work unveils recent strides in design, fabrication, facilitated transport mechanisms, and real‐world liquid separation applications, all under the aegis of electrospun nanofiber membranes, each endowed with distinct asymmetric properties.

Insight of multifunctional Cu-alginate hydrogel membrane for precise molecule/ion separation applications

Membrane technology has garnered significant attention for its role in addressing the challenges of molecule/ion separation processes, yet it remains hindered by issues such as membrane fouling, including organic and biofouling. While calcium alginate (CaAlg) membranes have demonstrated remarkable antifouling and molecule/ion separation properties, they suffer from high swell ability and poor mechanical performance. This study introduces a one-step ion-crosslinking method to fabricate a series of copper alginate (CuAlg) hydrogel membranes. These membranes are then assembled into a dual-layer structure with a modified hydrophilic and mechanically robust microfiltration fiber support layer (MHSL). Notably, the CuAlg/MHSL membrane exhibits excellent separation performance, characterized by high selectivity and flux recovery rate. This membrane significantly enhances the long-term molecule/ion separation performance through improved mechanical strength, anti-swelling properties, and antimicrobial capabilities. In addition, the decreased thickness of the CuAlg/MHSL membrane enables higher flux rates, proving beneficial in cases of CaAlg membranes' inability to perform well under high-salt conditions. To further investigate the pore structure and anti-swelling mechanism of the CuAlg membrane, molecular dynamics (MD) simulations are conducted. Additionally, a life cycle analysis comparing the CuAlg hydrogel with various traditional polymers assesses their respective environmental impacts, highlighting the eco-friendliness of the hydrogel as a membrane substrate. These findings provide valuable insights for developing sustainable hydrogel membranes with stable performance and high separation efficiency in molecular/ion separation applications.

Synthesis and Characterization of PES/PEG/PVA/SiO2 Nanocomposite Ultrafiltration Membrane

This study aims to synthesis and characterize PES/PEG/PVA/SiO2 composite membranes. The composite membranes were synthesized by phase inversion method with composition (% w/w) Polyethersulfone/ PES (17.25), Polyvinylalcohol/ PVA (3.58; 0.85; 1.43; 2.57; 3.57, Polyethylene glycol/ PEG (3.72), Silica/SiO2 (0.35; 0.85; 1.43; 2.57; 3.57), and Dimethyl acetamide/DMAc solvent. Composite membranes were characterized using FTIR spectroscopy, X-ray diffraction, Scanning Electron Microscopy (SEM), and water contact angle. The results showed that the interaction between PES, PVA, and SiO2 was indicated by a shift in the typical absorption spectrum of the FTIR. SEM cross-sectional photos showed that the addition of PVA and SiO2 caused significant changes in the morphology and pore structure of the PES membrane. The results of the X-ray diffractogram (X-Ray) showed a shift in the typical diffraction peaks of PES, PEG, PVA and the presence of new diffraction peaks of SiO2. The crystallinity of the membrane increased from 34.99% to 57.25% which indicated that the composite membrane was successfully synthesized. The addition of PEG/PVA/SiO2 also increased the hydrophilicity of the composite membrane. Based on these findings, it can be concluded that the PES/PEG/PVA/SiO2 composite membrane has been synthesized through the phase inversion method with the optimum composition of PES: PEG: PVA: SiO2 was 17.25%: 3.72%: 0.85%: 0.35%, respectively. The addition of PEG/PVA/SiO2 increased the hydrophilicity and modified the morphological structure of the PES membrane.

Insight into polydopamine coating on microfiltration membrane with controlled surface pore size for enhanced membrane rejection

Membrane modification with polydopamine (PDA) is a common practice to enhance membrane selectivity and improve membrane compatibility with nanoparticles or thin films. Depending on the membrane surface properties, dopamine can deposit or penetrate into microporous membranes, leading to alteration in the membrane's physicochemical properties and consequently its performance. In this study, microfiltration (MF) polyethersulfone membranes with varying surface pore sizes were fabricated by manipulating the precasting time (solvent evaporation time of 3s, 15s, 30s and 60s) prior to non-solvent induced phase separation (NIPS) process. Notably, the coating of PDA slightly reduced the membrane's surface pore size and membrane's porosity. M60 membrane which possessed the smallest mean surface pores (∼300 nm), exhibited PDA clusters predominantly formed on top of the membrane surface. With an increase in surface pore size, dopamine can penetrate the porous structure of the MF membrane, leading to the polymerization of dopamine into PDA aggregates on both the membrane surface and inner pores. The M30 membrane had the largest surface pore size (∼500 nm), showing the formation of large PDA globules in the finger-like pores. The membrane (M30P) experienced significant narrowing of the inner pores, resulting in reduced water permeability. Overall, all PDA-coated membranes exhibited improved sucrose rejection (85–95%) compared to the uncoated ones (64–83%). These finding provides insight into the polymerization mechanism of dopamine on porous membranes prior to the incorporation of nanomaterials or thin film coating.

Optimization of porous layer structure of high-temperature proton exchange membrane fuel cell based on deep learning and Monte Carlo method

The optimization of the membrane electrode assembly (MEA) is a crucial aspect in improving the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Through experimental validation, a three-dimensional HT-PEMFC computational fluid dynamics (CFD) model was established to simulate the transport of charge, mass, and momentum across various porous layers. A deep neural network (DNN) was designed to quantify the influence of porous layer structures on cells performance and determined the optimal solution of the MEA parameters for different Pt loadings. The training data of DNN were generated using 11 porous layer structural parameters selected via a Monte Carlo method, and their corresponding current densities predicted by the validated HT-PEMFC CFD model. The DNN model showed an average relative error of only 0.76% in predicting current density when compared to CFD simulations. Using a bi-objective genetic algorithm (GA) in conjunction with the DNN model, the optimized cell power densities at a voltage of 0.4 V and Pt loadings of 0.3 mg/cm2 and 0.5 mg/cm2 are 18% and 9% higher than the maximum values reported in the literature, respectively. The proposed approach combining DNN model and GA can serve as a useful guide for the design of HT-PEMFC in practical applications.

Fabrication of hydrophobic PI nanofibrous membrane with controllable pore structures

Polyimide (PI) has garnered increasing attention in the field of membrane technology owing to its excellent comprehensive performance. In this work, PI nanofibrous membranes with a controllable pore structure were fabricated by the thermal imidization of electrospun polyamide acid (PAA) nanofibrous membranes. Polytetrafluoroethylene (PTFE) and poly(tetrafluoroethylene-hexafluoropropylene) (FEP) particles were introduced into the PAA nanofibrous membrane with the aim of enhancing the membrane's hydrophobicity and regulating its pore structure by electrospraying the PTFE/FEP mixed aqueous dispersion. During the thermal imidization process, melt casting of FEP particles occurred, leading to the adhesion of PI nanofibrous membranes and subsequent regulation of the membrane's pore structure. Meanwhile, due to the imidization temperature being lower than PTFE’s melting temperature, the unmelted PTFE particles would further enhance the membrane’s hydrophobicity. We have successfully provided a novel method for fabricating PI nanofibrous membranes with controllable pore structures and excellent hydrophobicity to expand their applications in membrane separation. Owing to the hydrophobicity and lipophilicity, the obtained PI nanofibrous membranes were applied to oil-water (kerosene/water) separation to characterize the separation performance. The results showed that, following the regulation of the pore structure, the PI nanofibrous membranes exhibited a high oil flux (203.83 L/m2·h) and separation efficiency (＞99.00%) without external pressure.

Electrospun Nanofiber Membranes with Various Structures for Wound Dressing.

Electrospun nanofiber membranes (NFMs) have high porosity and a large specific surface area, which provide a suitable environment for the complex and dynamic wound healing process and a large number of sites for carrying wound healing factors. Further, the design of the nanofiber structure can imitate the structure of the human dermis, similar to the natural extracellular matrix, which better promotes the hemostasis, anti-inflammatory and healing of wounds. Therefore, it has been widely studied in the field of wound dressing. This review article overviews the development of electrospinning technology and the application of electrospun nanofibers in wound dressings. It begins with an introduction to the history, working principles, and transformation of electrospinning, with a focus on the selection of electrospun nanofiber materials, incorporation of functional therapeutic factors, and structural design of nanofibers and nanofiber membranes. Moreover, the wide application of electrospun NFMs containing therapeutic factors in wound healing is classified based on their special functions, such as hemostasis, antibacterial and cell proliferation promotion. This article also highlights the structural design of electrospun nanofibers in wound dressing, including porous structures, bead structures, core-shell structures, ordered structures, and multilayer nanofiber membrane structures. Finally, their advantages and limitations are discussed, and the challenges faced in their application for wound dressings are analyzed to promote further research in this field.

Large Scalable High Ion Conductive and Selective Double Layer Membrane Achieved through Dual Ion Conducting Mechanisms

As the share of sustainable energy sources in the electricity supply rises, large-scale energy storage becomes increasingly important. All vanadium flow batteries, as one of the most promising large-scale energy storage methods, have reached the commercialization stage because of their unique feature of uncoupling power and energy, as well as the advantages of long life, high safety, and low cost. The ion-selective membrane is an essential part of flow batteries, which allows specific ions to pass through to maintain a neutral charge and prevents the crossover of active species to maintain the capacity. However, the high cost and low ion-selectivity of the commercialized ion-selective membranes (i.e., Nafion membranes) hindered the further promotion of the flow batteries. Herein, we developed a large scalable double-layer ion selectivity membrane with a unique bifunctional nanoporous boron nitride (PBN) ion selective layer and a low-cost porous polyetherimide (PEI) ion conductivity and support layer. PBN was synthesized by a large scalable template-free method, which was further decorated with Nafion resin. The nano-sized and tortuous pores of the PBN can effectively block the crossover of vanadium ions and provide excellent ion selectivity based on the pore size exclusion mechanism. Furthermore, the super-acidic sulfonic acid groups of Nafion decorated on the nanoporous structure of PBN provide high-speed proton transfer channels that increase proton conductivity through both Grotthuss and vehicle mechanisms. The low-cost porous PEI ion conductivity and support layer was prepared by the phase separation method. The well-aligned asymmetric finger-like porous structure of the PEI membrane provides excellent ion conductivity. The addition of a hydrophilic polymer additive, polyvinylpyrrolidone, further increased its ion conductivity. The PBN–PEI double layer membrane, prepared by a simple spray coating method, demonstrated an excellent ion selectivity (1.49×108 mS cm−3 min), which is almost 15 times higher than that of the pristine PEI membrane (6.71×106 mS cm−3 min) while maintaining high ion conductivity (64 mS cm−1). The PBN–PEI membrane achieved superior performance (97% of coulombic efficiency, 94% of voltage efficiency, and 91% of energy efficiency at 40 mA cm−2) than the Nafion 115 membrane in the all-vanadium flow battery with higher discharge capacity at all current densities and high stability with a lower capacity fading rate (0.17% per cycle vs. 0.74% per cycle at 100 mA cm−2). The PBN–PEI membrane also demonstrated a stable operation in the all-vanadium flow battery at a current density of 100 mA cm−2 over 700 cycles. The work presented the remarkable performance of the ultra-thin PBN bifunctional layer in terms of ion conductivity and selectivity; the combination with the low-cost high ion-conductive porous PEI membrane and a simple fabrication process demonstrated a great potential for commercialization of the PBN-PEI double-layer membrane.

A simple and effective approach to regulate and control pore structure of electrospun PTFE nanofiber membrane

Owing to its outstanding hydrophobicity, thermal stability, and chemical resistance, polytetrafluoroethylene (PTFE) has always been the ideal material in the field of membrane contactors. However, the pore structure regulation of the PTFE membrane is challenging due to its poor processability. Herein, a novel and simple strategy to adjust the pore structure of the electrospun PTFE nanofiber membrane was proposed by introducing sodium alginate (SA) into the PTFE/PVA spinning solution. The pore structure of the PTFE nanofiber membrane gradually changed from the nanofiber network to the “sea-island” structure with the increase of SA addition from 0 to 2.5 %, which brought about a decrease in membrane pore size from 1.49 to 0.58 μm. Meanwhile, with the increase of SA addition, there was an obvious improvement in the mechanical properties of obtained PTFE nanofiber membrane because of the higher packing density of PTFE/PVA/SA precursor nanofiber. Finally, the obtained PTFE nanofiber membrane was utilized in the membrane emulsification (ME) process, which exhibited excellent emulsion performance in terms of 0.30 μm average droplet size of Water-in-oil (W/O) emulsion (remaining stable for 30 days).

An efficient immersing strategy for enhancing the separation performance of microfiltration carbon membranes for oily wastewater

Here, an immersing strategy was designed to modify the porous structure of microfiltration carbon membranes (MFCMs) made by the pyrolysis of phenolic resin-based plates. The thermal stability of precursors, the functional groups, porous structure, microcrystalline structure, microscopic morphology and surface wettability of MFCMs were characterized by TGA, FT-IR, XRD, SEM, TEM and water contact angle, respectively. The effects of the concentration of immersing solution, soaking time and operational conditions on the separation performance of MFCMs for oily wastewater were investigated. In addition, the anti-fouling ability of the MFCMs was further examined. The results showed that the average pore size and porosity of MFCMs decreased after immersing modification. When the modification condition was adopted at the immersing solution concentration of 3% and soaking time of 60 s, the resultant MFCMs exhibited the minimum average pore size of 0.13 μm and a porosity of 31.96%. At the same time, the optimal separation performance was achieved at 99.85% for oil rejection and 392.16 Kg/m2•h•MPa for water permeation flux. In addition, the oil rejection almost remains intact during antifouling ability test, except for a slight drop trend of water permeation flux. It is evident that the facile immersing protocol holds a promise for effectively modifying MFCMs in the treatment of oily wastewater.

PH-Swing membrane adsorption of perfluoroalkyl substances: Anion-exchange brushes and role of water chemistry

The pH-swing membrane adsorption, aiming for effective removal, high membrane permeability, and facile regeneration, was developed to remediate emerging perfluoroalkyl contaminants. Compared to the collapse transformation of deprotonated tertiary-amine brushes at neutral pH (pKb: ∼5.82), the quaternary-ammonium (QA) brushes endowed consistent membrane pore structure and higher isoelectric point (pHIEP: 11.2 versus 7.5), resulting in a suitable pH-swing adsorption/desorption range towards groundwater conditions. Such QA-grafted membranes (QA loading: 1.1 mmol/g) not only presented >90 % removal of perfluorooctanoic acid (PFOA) at a treatment capacity of 570 L per m2 of membrane area, but also enabled effective membrane regeneration that >97 % desorption was achieved at pH 12.5 and 5 % methanol. The remediation is driven by synergetic electrostatic and hydrophobic interactions, as demonstrated by (1) the zeta-potential dependent removal performance and (2) the greater maximum adsorption capacity towards the more hydrophobic perfluorooctane sulfonate than PFOA (Qm: 0.65 mmol/g and 0.44 mmol/g, respectively). Within three pH-swing adsorption/regeneration cycles, a total PFOA removal of 82.4 % was achieved with a treatment capacity of 2,930 L/m2. The impacts of ionic strength, ionic types, and natural organic matters were evaluated. Overall, the pH-swing strategy is an effective method with high permeability (165.6 L m−2h−1bar−1), stability, and tunable adsorption/regeneration processes.