Membrane Pore Structure Research Articles

Finely tailored pore structure of polyamide nanofiltration membranes for highly-efficient application in water treatment

• PIP has been applied as a structure regulator to enlarge pores of PA NF membranes. • The addition of PIP enhances the permeance by 97.3% with rejection of MO above 98%. • TPC has been deployed for narrowing pore size distribution of the PA NF membranes. • The incorporation of TPC enhances rejection to positive multi-valent ions greatly. • The finely tailored membranes show strong promise in waste water treatment. With fine pore structures and abundant surface charge, polyamide nanofiltration membranes have been widely deployed for separating small active organic molecules and multi-valent ions. However, lack of highly permeable membranes with excellent rejection towards target molecules hampers the widespread application of the polyamide (PA) nanofiltration membranes on a large scale. In current study, we conceive a facile strategy to regulate the molecular structure of polyamide selective layer through introducing piperazine (PIP) or terephthaloyl chloride (TPC) as a structural regulator during the interfacial polymerization between polyethyleneimine (PEI) and trimesoyl chloride (TMC). On the one hand, adding PIP to aqueous solution enlarges the length between the crosslinked networks, thereby enhancing the pure water permeance by 97.3% (to 23.70 L m −2 h −1 bar −1 ). Interestingly, the membranes exhibit excellent performance for dyes separation (rejection greater than 98%) and molecular weight cut-off (MWCO) about 554.34 Da under the optimum separation conditions. On the other hand, the introduction of TPC could assist the formation of crosslinked structures, thereby narrowing the pore size distribution of the membranes. The well-designed membranes reject above 98% PbCl 2 with permeance about 6.36 L m −2 h −1 bar −1 and MWCO below 150 Da under the optimum operation conditions, which is preferable to the state-of-art PA membranes. Excitingly, all of the well-designed membranes demonstrate excellent anti-fouling performances. In summary, with finely tailored pore structure, high permeance and high rejection, and excellent anti-fouling performance, the obtained membranes show strong promise in treating effluence from printing and dyeing industry, and metallurgy and mining industry, respectively.

Janus electrocatalytic flow-through membrane enables highly selective singlet oxygen production

The importance of singlet oxygen (1O2) in the environmental and biomedical fields has motivated research for effective 1O2 production. Electrocatalytic processes hold great potential for highly-automated and scalable 1O2 synthesis, but they are energy- and chemical-intensive. Herein, we present a Janus electrocatalytic membrane realizing ultra-efficient 1O2 production (6.9 mmol per m3 of permeate) and very low energy consumption (13.3 Wh per m3 of permeate) via a fast, flow-through electro-filtration process without the addition of chemical precursors. We confirm that a superoxide-mediated chain reaction, initiated by electrocatalytic oxygen reduction on the cathodic membrane side and subsequently terminated by H2O2 oxidation on the anodic membrane side, is crucial for 1O2 generation. We further demonstrate that the high 1O2 production efficiency is mainly attributable to the enhanced mass and charge transfer imparted by nano- and micro-confinement effects within the porous membrane structure. Our findings highlight a new electro-filtration strategy and an innovative reactive membrane design for synthesizing 1O2 for a broad range of potential applications including environmental remediation.

Applied organic-inorganic nanocomposite of PLA-TiO2 for preparing polysulfone membrane: structure, performance and UV-assisted cleaning strategy.

Blended organic copolymer (or homopolymer) and inorganic nanoparticles have been widely used (separately or simultaneously) for optimizing membrane pore structure and surface functionality. However, the prepared membranes suffer from degraded stability and insufficient integrity due to the high solubility or incompatibility of the blending additives. In this work, an organic-inorganic nanocomposite (i.e., PLA-TiO2) was designed, and employed for PSF membrane preparation. The Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis confirmed that bidentate chelating dominated the bonding mechanism between PLA and TiO2. The resultant PSF/PLA-TiO2 membranes possessed a highly porous surface with narrowed pore size distribution, demonstrating the strong pore forming ability of PLA-TiO2 for membrane preparations. Moreover, owing to the distinct inorganic-organic molecular conformation, the PLA-TiO2 exhibited enhanced stability and dispersibility within the PSF substance, which endowed the membrane with long-acting hydrophilicity and UV responsiveness. Given the UV responsiveness that is introduced by PLA-TiO2, UV-assisted strategies (UV-F and UV-C) were designed to further mitigate membrane fouling. The fouling analysis indicated that both reversible fouling and irreversible fouling were reduced in the UV-C process, signifying the synergistic effect between photocatalysis and hydraulics in membrane fouling mitigation. The enhanced membrane performance and the efficient preparation process highlight the potential of PLA-TiO2 in membrane modifications.

Asymmetric Porous Membranes with Improving Mass Transfer for Proton Exchange Membrane Water Electrolysis (PEMWE)

Hydrogen is a promising and efficient energy source that can replace fossil fuels. Hydrogen can be obtained from various raw materials, including water. Recently, among various hydrogen production methods, high purity of hydrogen gas can be obtained by hydroelectricity. It also focused on water electrolysis, where efficient and continuous production of hydrogen is possible. Moreover, in terms of efficient and continuous production of hydrogen and environmental effects, PEMWE (Proton Exchange Membrane Water Electrolysis) has been evaluated as the most inspiring technology for producing high purity hydrogen of renewable energy and has the strength to discharge only oxygen by-products without hazards. These days, PEMWE research is surging as demand for hydrogen-based energy increases. Therefore, considerable research has recently been completed on membrane development for PEMWE. Currently, the PFSA (Perfluorosulfonic acid) polymer is used in PEMWE systems. A previous study reported that the thinner the PFSA membrane used for PEMWE, the lower the resistance of the MEA (Membrane Electrode Assembly), resulting in improved single-cell performance. Nevertheless, the single cell operates using a thick electrolyte membrane considering the safety aspects of the PEMWE system. Applying thick electrolytic membranes to PEMWE systems improves physical and chemical durability, but increasing the thickness of the MEA increases the resistance and mass transfer resistance, which degrades the performance of PEMWE. To compensate for these limitations, Previous studies have been conducted to reduce the resistance by modifying the catalyst structure constituting the MEA, but any case hasn't been reported to modify the structure of the membrane for PEMWE.Therefore, in this study, an asymmetric membrane was prepared to improve the performance of the PEMWE single cell by applying a porous structure into a thick membrane to ensure high durability. Research on asymmetric membranes has been conducted in energy fields such as vanadium redox flow batteries, fuel cells, and lithium-ion batteries. As a result of applying an asymmetric membrane to each energy research, it has been reported that the doping amount of the electrolyte increases due to the strengthening of the capillary force according to the porous structure, and accordingly, the ionic conductivity increases, thereby improving the performance of the cell. Besides, studies are showing that the diffusion rate of water and ions increases, and the internal resistance decreases due to the structure of the dense layer and the porous layer.In this study, to apply the performance improvement effect of the previous study to the electrolyte membrane for electrolysis, we referred the porous structure to confirm the performance of the PEMWE single cell. The porous layer of the asymmetric membrane was prepared using a solvent/non-solvent evaporation method. The solvent of the Nafion dispersion solution is alcohol, and the non-solvent is ortho-dichlorobenzene (ODB). The porous surface was prepared using the difference in boiling point and density between the solvent/non-solvent. Through the SEM analysis, the porous layer on the surface of the asymmetric membrane and dense layer on the bottom was observed. The Uniform round micropores distributed on the entire surface of the porous layer, which was below 10 μm. A cross-sectional view showed that the thickness of the asymmetric membrane is 175 ~ 180 μm. As a result of an EIS analysis, the asymmetric membrane showed a tendency to have lower ohmic and mass transfer resistance than the Nafion 117 membrane of the same thickness. Through the evaluation of a single cell performed under 80 ℃ temperature conditions, Nafion 117 was 1.5 A/cm2 and the asymmetric membrane was 2.5 A/cm2, about 1.67 times higher than Nafion117. The results of PEMWE single cell measurement confirmed that the porous structure of the asymmetric membrane improved the material transfer efficiency of the membrane, thus lowering the material transfer resistance, thereby improving the PEMWE performance.

PTFE-assisted immobilization of Pluronic F127 in PVDF hollow fiber membranes with enhanced hydrophilicity through nonsolvent-thermally induced phase separation method

The use of amphiphilic copolymer Pluronic F127 as an additive has shown effectiveness in fabricating polyethersulfone (PES) membranes with excellent antifouling properties due to its roles in enhancing pore structure and surface hydrophilicity. However, F127 was found to be unstable in polyvinylidene fluoride (PVDF) membranes as its hydrophilic modifying function was deactivated over time. In present work, we developed a novel approach to immobilize F127 in PVDF hollow fiber membranes using polytetrafluoroethylene (PTFE) particles as a binding agent through the combined nonsolvent and thermally induced phase separation (N-TIPS) method. The results suggest that the hydrophobic segment of F127 could adsorb firmly onto PTFE with the hydrophilic segments protruding outwards. The dual-functions of F127 were observed in pore formation and surface hydrophilization for PVDF membranes. The water contact angle of PVDF/PTFE/F127 membranes decreased from 102 ± 4° to 76 ± 3° compared with membranes without additives. The resultant membranes possess a pure water permeability (PWP) of 869 ± 39 L m−2h−1bar−1 with a mean pore size of 0.09 ± 0.01 μm and an outstanding tensile strength of 7.0 ± 0.3 MPa, suggesting the potential of N-TIPS method for tuning the membrane pore structure and hydrophilicity by using multifunctional additives.

Enhanced performances of chlorinated polyvinyl chloride (CPVC) ultrafiltration membranes by styrene-maleic anhydride copolymer

To enhance the performances of the CPVC ultrafiltration membranes, herein, styrene-maleic anhydride copolymer (SMA), an amphiphilic copolymer, was used to blend with CPVC to adjust the microstructures of membranes. The pure CPVC and SMA/CPVC composite ultrafiltration membranes were prepared by a non-solvent-induced phase inversion process. It has been proved that SMA and CPVC were partially compatible according to the rheological behavior of casting solution, DSC, FT-IR and SEM. SMA changed the phase separation mechanism and the pore structure of the composite membranes, and significantly increased the porosity. According to the results of ATR-FTIR, EDS and XPS analysis, intact anhydride groups existed on the surface of the composite membranes, which enhanced the permeability of membranes. The SMA/CPVC composite ultrafiltration membranes with 2 wt% SMA exhibited superior pure water flux (459.85 L/m2·h), protein rejection (97.2%) and permeability flux (140.69 L/m2·h) compared with the neat CPVC membrane (248.97 L/m2·h, 74.5%, 74.14 L/m2·h, respectively) at 0.1 MPa. Moreover, the flux recovery ratio increased from 55.32% to 92.68% and irreversible fouling index decreased from 42.51% to 5.00%. Importantly, the antifouling mechanism of the SMA/CPVC ultrafiltration membrane was discussed in detail.

Harvesting of Microcystis aeruginosa using membrane filtration: Influence of pore structure on fouling kinetics, algogenic organic matter retention and cake formation

Different membrane pore structures can affect filtration characteristics and membrane fouling during membrane harvesting of algae suspensions. In this study, four membrane materials with different pore structures (MC-5, PC-3, PVDF-5, and PVDF-100KDa) were employed to filter Microcystis aeruginosa suspensions to compare their filtration characteristics, retention of algogenic organic matter and membrane fouling. The correlation between membrane performance and pore structure characteristics, such as pore size, porosity, surface free energy, zeta potential, and surface pore area, were analyzed by a redundancy analysis method. The results revealed that PVDF-100KDa had the lowest deionized water flux compared with the microfiltration membranes due to its smaller pore size, and its high retention of organic matter aggravated membrane fouling. In addition, the track-etched single-pore PC-3 membrane exhibited fast flux decline and the highest cake layer resistance. PVDF-5 had strong adsorption capacity for aromatic protein-like compounds, which can increase irreversible fouling. Overall, MC-5 exhibited the best average flux and better flux recovery with a lower retention of organic matter and the maximum roughness observed by optical coherence tomography. For further insight, a conceptual model was proposed, which clarifies the effect of pore structure on fouling kinetics, algogenic organic matter retention and cake formation and thus provides valuable guidance for the development of membrane harvesting of algae suspensions.

Validity of Three-Dimensional Tortuous Pore Structure and Fouling of Hemoconcentration Capillary Membrane Using the Tortuous Pore Diffusion Model and Scanning Probe Microscopy.

Hemoconcentration membranes used in cardiopulmonary bypass require a pore structure design with high pure water permeability, which does not allow excessive protein adsorption and useful protein loss. However, studies on hemoconcentration membranes have not been conducted yet. The purpose of this study was to analyze three-dimensional pore structures and protein fouling before and after blood contact with capillary membranes using the tortuous pore diffusion model and a scanning probe microscope system. We examined two commercially available capillary membranes of similar polymer composition that are successfully used in hemoconcentration clinically. Assuming the conditions of actual use in cardiopulmonary bypass, bovine blood was perfused inside the lumens of these membranes. Pure water permeability before and after bovine blood perfusion was measured using dead-end filtration. The scanning probe microscopy system was used for analysis. High-resolution three-dimensional pore structures on the inner surface of the membranes were observed before blood contact. On the other hand, many pore structures after blood contact could not be observed due to protein fouling. The pore diameters calculated by the tortuous pore diffusion model and scanning probe microscopy were mostly similar and could be validated reciprocally. Achievable pure water permeabilities showed no difference, despite protein fouling on the pore inlets (membrane surface). In addition, low values of albumin sieving coefficient are attributable to protein fouling that occurs on the membrane surface. Therefore, it is essential to design the membrane structure that provides the appropriate control of fouling. The characteristics of the hemoconcentration membranes examined in this study are suitable for clinical use.

Correlating the membrane surface energy to the organic fouling and wetting of membrane distillation at elevated temperature

Membrane fouling is an inevitable process but could be mitigated by understanding its fouling mechanism. In this work, organic fouling phenomena of direct contact membrane distillation (DCMD) on membrane with different surface properties were examined under high salinity and elevated temperature conditions. Membranes with different surface energies and pore structures showed different fouling phenomenon by the hydrophilic/amphiphilic polymer. Surface energy studies showed that molecular interaction between the organic solutes and Polytetrafluoroethylene (PTFE) membrane were strong enough to form the segregated or films like structure on the membrane. On the other hand, the weaker interactions between the Polyvinylidene fluoride (PVDF) membrane induced aggregated/precipitated form of foulants. The flux declination trend is very much depending on the characteristic of the foulants. The aggregated foulants could easily precipitate on the membrane surface to produce loose fouling layer that reduced the flux. However, the smaller precipitate could block the pores and gave significant flux declination. The effort to make the surface become more hydrophilic could reduce the fouling propensity of bovine serum albumin, however the hydrophilic PVDF layer was susceptible to higher wetting potential at elevated temperature. Increasing the surface hydrophobicity could alleviate the molecular interactions but its potential to interact via hydrophobic interactions could be an unwanted phenomenon. Therefore, studying the surface energy as well as pore structure of membrane is crucial to understand the organic fouling behaviour of DCMD at elevated temperature.

Topological analysis of single-stranded DNA with an alpha-hederin nanopore

Nanopores have been emerged as a powerful tool for analyzing the structural information and interactional properties of a range of biomolecules. The spatial resolution of nanopore is determined by the diameter and effective thickness of its constriction region, but the presence of vestibule or stem structure in protein-based nanopore could negatively affect the sensitivity of the nanopore when applied for genome sequencing and topological analysis of DNA. Recently, alpha-hederin (Ah) has been reported to form a sub-nanometer scale pore structure in lipid membrane. With the simple structure and extremely small effective thickness, the Ah nanopore was shown to discriminate four different types of nucleotides. However, identification of a certain nucleotide in a strand of DNA, which is essential for genome sequencing, remains challenging. Here, we investigated the resolving capability of Ah nanopore to discriminate few nucleotides in a strand of single-stranded DNA, and the factors determining the sensitivity of Ah nanopore. The Ah nanopore was shown to be able to identify as few as three adenosine nucleotides in a strand of poly cytidine, in which the dwell time of the additional current blockade that represents the adenosine residue was in good agreement with their physical length. We also found that the lateral tension and chain pressure generated around the nanopore were influenced by pore's diameter and played as a dependent variables to determine the geometry of nanopore's constriction as well as the spatial resolution of the Ah nanopore.

Effect of membrane pore structure on fouling behavior of glycoconjugate vaccines

Sterile filtration can be difficult when processing large glycoconjugate vaccines. The objective of this work was to evaluate the performance of three commercial 0.2 μm nominal pore size sterilizing grade membranes with very different morphology: Millipore Durapore® (homogeneous), Millipore Express® (asymmetric), and Sartopore® Platinum (dual layer) during sterile filtration of a glycoconjugate vaccine provided by Pfizer. The location of deposited glycoconjugate within the filters was examined by confocal microscopy. The greatest capacity was obtained with the asymmetric membrane due to its high permeability, while the lowest capacity was found with the two-layer membrane in which the fouling occurred at the entrance to the 0.2 μm layer. The pressure profiles during constant flux filtration were analyzed using a modified intermediate pore blockage model accounting for the fouled and unfouled regions within the filter, providing additional insights into the effects of membrane morphology on the fouling characteristics.

Three-Dimensional Porous Alginate Fiber Membrane Reinforced PEO-Based Solid Polymer Electrolyte for Safe and High-Performance Lithium Ion Batteries

The rational design and optimization of solid polymer electrolytes (SPEs) are critical for the application of safety and high efficiency lithium ion batteries (LIBs). Herein, we synthesized a novel poly(ethylene oxide) (PEO)-based SPE (PEO@AF SPE) with a cross-linking network by the introduction of alginate fiber (AF) membranes. Depending on the high-strength supporting AF skeleton and the cross-linking network formed by hydrogen bonds between the PEO matrix and AF skeleton, the obtained PEO@AF SPE exhibits an excellent tensile strength of 3.71 MPa, favorable heat resistance (close to 120 °C), and wide electrochemical stability window (5.2 V vs Li/Li+). Meanwhile, the abundant oxygen-containing groups in alginate macromolecular and the three-dimensional (3D) porous structure of the AF membrane can greatly increase Li+ anchor points and provide more Li+ migration pathways, leading to the enhancement of Li+ conduction and interfacial stability between the SPE and Li anode. Furthermore, the assembled LiFePO4/PEO@AF SPE/Li cells also exhibit satisfactory electrochemical performance. These results reveal that PEO incorporating with AFs can boost the mechanical strength, thermostability, and electrochemical properties of the SPE simultaneously. Furthermore, one will expect that the newly designed PEO@AF SPE with cross-linked networks thus provides the possibility for future applications of safety and high-performance LIBs.

On the influence of pore connectivity on performance of membrane filters

Abstract

Development of polyethersulfone (PES)/reduced graphene oxide nanocomposite nanofiltration membrane

Polyethersulfone (PES) is a polymeric material that is commonly used due to its chemical resistance, high mechanical strength, and thermal stability. The improvement of PES hydrophilicity and anti-fouling properties can be facilitated by mixing additives into the polymer casting solution. This study involved the preparation and characterization of PES/pluronic F108/chitosan/reduced graphene oxide (rGO) nanocomposite nanofiltration membrane. The modified PES membrane was developed by employing the phase inversion method via immersion precipitation. The effect of varying concentration of rGO nanocomposite ranging from 0.05 to 0.20 wt% in the fabricated membrane was evaluated in terms of membrane pure water permeation (PWP), salt rejection, morphology, and hydrophilicity. Images obtained from scanning electron microscopy (SEM) showed increasing rGO nanocomposite concentration in the casting solution, resulted in the increase in membrane sub layer thickness, hydrophilicity, salt rejection, and improvement in the membrane pore structure. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of the hydrophilic functional group and chemical compound in the prepared membrane. PES with 0.20 wt% of rGO nanocomposite obtained the highest PWP at 28.64 (L/m2h) at 5 bar pressure, whereas the highest rejections of monovalent and multivalent salt were obtained by PES with 0.15 wt% rGO nanocomposite with 75% and 89% rejections, respectively at 5 bar pressure. This study shows that the utilization of rGO nanocomposite as an additive in the PES casting solution can enhance nanofiltration membrane performance and morphological structure.

Transport and Electrochemical Characteristics of CJMCED Homogeneous Cation Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions.

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na2SO4, and CaCl2 solutions, permeability in respect to the NaCl and CaCl2 diffusion, transport numbers, current–voltage curves (CVC), and the difference in the pH (ΔpH) of the NaCl solution at the desalination compartment output and input are examined for these membranes in comparison with a well-studied commercial Neosepta CMX cation-exchange membrane produced by Astom Corporation, Japan. It is found that the conductivity, CVC (at relatively low voltages), and water splitting rate (characterized by ΔpH) for both CJMCED membranes are rather close to these characteristics for the CMX membrane. However, the diffusion permeability of the CJMCED membranes is significantly higher than that of the CMX membrane. This is due to the essentially more porous structure of the CJMCED membranes; the latter reduces the counterion permselectivity of these membranes, while allowing much easier transport of large ions, such as anthocyanins present in natural dyes of fruit and berry juices. The new membranes are promising for use in electrodialysis demineralization of brackish water and natural food solutions.

Effects of Particles Diffusion on Membrane Filters Performance

Membrane filtration fouling is a very complex process and is determined by many properties such as the membrane internal morphology, membrane pore structure, flow rate and contaminant properties. In a very slow filtration process or during the late stage of filtration, when the flow rate is naturally low and Péclet number is small, particle diffusion is essential and cannot be neglected, while in typical filtration models, especially in moderate and fast filtration process, the main contribution stems from the particle advection. The objectives of this study is to formulate mathematical models that can (i) investigate how filtration process varies under possible effects of particles diffusion; and (ii) describe how membrane morphology evolves and investigate the filtration performance during the filtration process. We also compare the results with the case that diffusion is less important and make a prediction about what kind of membrane filter pore structure should be employed to achieve a particular optimum filtration performance. According to our results, the filtrate and efficiency of particle separation are found to be under the trade-off relationship, and the selection of the membrane properties depends on the requirement of the filtration.

Phase Inversion-Induced Porous Polybenzimidazole Fuel Cell Membranes: An Efficient Architecture for High-Temperature Water-Free Proton Transport.

To cope with the demand for cleaner alternative energy, polymer electrolyte membrane fuel cells (PEMFCs) have received significant research attention owing to their high-power density, high fuel efficiency, and low polluting by-product. However, the water requirement of these cells has necessitated research on systems that do not require water and/or use other mediums with higher boiling points. In this work, a highly porous meta-polybenzimidazole (m-PBI) membrane was fabricated through the non-solvent induced phase inversion technique and thermal cross-linking for high-temperature PEMFC (HT-PEMFC) applications. Standard non-thermally treated porous membranes are susceptible to phosphoric acid (PA) even at low concentrations and are unsuitable as polymer electrolyte membranes (PEMs). With the porous structure of m-PBI membranes, higher PA uptake and minimal swelling, which is controlled via cross-linking, was achieved. In addition, the membranes exhibited partial asymmetrical morphology and are directly applicable to fuel cell systems without any further modifications. Membranes with insufficient cross-linking resulted in an unstable performance in HT-PEMFC environments. By optimizing thermal treatment, a high-performance membrane with limited swelling and improved proton conductivity was achieved. Finally, the m-PBI membrane exhibited enhanced acid retention, proton conductivity, and fuel cell performance.

Improved permeability and biofouling resistance of microfiltration membranes via quaternary ammonium and zwitterion dual-functionalized diblock copolymers

In order to improve permeability and biofouling resistance of microfiltration (MF) membranes, quaternary ammonium and zwitterion dual-functionalized diblock polyelectrolyte copolymers, poly(dimethylaminoethyl methacrylate-butylammonium bromide)-b-poly(sulfobetaine methacrylate) (PDB-b-PSB) prepared via RAFT polymerization, were immobilized on commercial poly(vinylidene fluoride) (PVDF) MF membrane surface via using a versatile and facile mussel-inspired method to fabricate hierarchical copolymer brushes. Hierarchical PDB-b-PSB brushes contained bottom passive anti-adhesive zwitterionic PSB layer and upper active biocidal quaternary ammonium PDB layer. The surface chemical composition and morphology characterizations of pure and modified membranes demonstrated that PDB-b-PSB copolymers were successfully grafted to the dopamine-modified membrane surface via thiol mediated Michael addition reaction, which did not significantly change the membrane pore structure. However, the initial contact angle of PDB-b-PSB modified membrane (M/PDB-b-PSB) was changed from 128° for pure membrane (M/pure) to 43.2° and became 0° within 10 s, indicating the enhanced hydrophilicity. More importantly, the M/PDB-b-PSB membrane exhibited active biocidal effects against E. coli and S. aureus with inhibition rates over 98% and the E. coli and S. aureus suspension fluxes of M/PDB-b-PSB membranes were 1.61 times and 1.35 times higher than those of M/pure membranes. The M/PDB-b-PSB membrane had excellent anti-biofouling property with a better water flux recovery rate of 72%, which was 30% higher than that of the M/pure membrane. Moreover, PDB-b-PSB brushes showed a good immobilization stability. Therefore, the approach of poly(dopamine)-assisted fabrication of anti-biofouling MF membranes with quaternary ammonium and zwitterion dual-functionalized diblock copolymers had a prospect application in membrane-based separation technology and water purification.

Microstructure evolution and enhanced permeation of SiC membranes derived from allylhydridopolycarbosilane

The evolution of the physicochemical properties of allylhydridopolycarbosilane (AHPCS) was systematically investigated via DLS, TG, FTIR, XRD, and EDS. AHPCS-derived membranes were prepared by coating AHPCS sols onto porous substrates, which was then followed by pyrolysis at 300–800 °C. The pre-crosslinking by thermal curing significantly increased the colloidal sol size of AHPCS in toluene solutions, which effectively reduced penetration into substrates and enhanced the gas permeation. Furthermore, the pore structure of AHPCS-derived membranes could be precisely tailored by the pyrolysis temperatures, and the results indicated that the structure of membranes could be roughly classified into one of three types: a dense polymer structure, a loose transitional structure, and a denser ceramic structure (here, the term ‘dense/denser’ refers to the small/smaller pore structure, while the ‘loose’ refers to the large pore structure). AHPCS-derived membranes prepared at 300–800 °C under a N2 flow displayed superior H2 permeance of (0.2–5) × 10−6 mol/(m2 s Pa) at 200 °C with good H2/N2 selectivity of 12–56. Ceramic SiC membranes prepared at 700 °C showed an attractive H2 permeance of (2–4) × 10−6 mol (m2 s Pa)−1 at 200 °C with H2/N2 selectivity of 16–22, H2/SF6 selectivity higher than 10,000, and N2/SF6 selectivity higher than 800. Moreover, the structure of the ceramic SiC membranes was highly stable with good oxidation resistance at 500 °C under air. AHPCS membranes prepared at 300–800 °C had different pore structures that exhibited a high level of quality and a variety of permeation properties that could provide many options for membrane materials over a wide range of applications.

The morphology of polyethylene (PE) separator for lithium-ion battery tuned by the extracting process

Abstract Thermally induced phase separation (TIPS) is used to prepare polyethylene (PE) micro-porous membrane, consisting of melt blending, fast cooling, stretching and extracting process, which determine the pore-structure of the PE membrane. In this study, we tried to extract PE/liquid paraffin (LP) oil membrane to obtain PE porous membrane by n-hexane (n-PE) and dichloromethane (d-PE). The n-PE membrane would shrink by 10% for extractant volatilizing, less than 15% of the d-PE membrane after the extraction. These PE membranes were applied into symmetrical cells and LiCoO2/Li cells. As a result, the LiCoO2/Li cell based on n-PE separator exhibited better capacity retention (98%) than d-PE separator (91%) after 80 cycles at a current density of 1C rate for higher ionic conductivity. And the LiCoO2/Li cell with d-PE separator had higher capacity at 2C and 3C, it could be attributed to stronger interaction between solvent and wall of d-PE separator with the smaller and curved pore. In addition, the method that electrochemical impedance spectroscopy (EIS) technique carried out with cyclic voltammetry (CV) and charge-discharge curves is successfully applied to monitor the variety of impedance during the cycles, which is helpful to explore the mechanism of capacity attenuation.