Preparation Of Composite Membranes Research Articles

The Influence of Non-Charged Sidechains on the Performance of Meta-Polybenzimidazole Membranes in Vanadium Redox Flow Batteries

The global goal to combat climate change is growing year by year, as for example indicated by the latest climate conference by the United Nations, COP26. Hereby, one of the main goals concerns the transition from fossil fuels to more renewable energy means. In doing so, the importance of highly efficient energy storage technologies, such as supercapacitors, Li-ion batteries and/or redox flow batteries that both store and release energy on a short-, mid- and long-term scale, grows alongside it1. Among storage technologies, redox flow batteries (RFBs) are considered as promising candidates for mid-term storage (daily discharge for 2-12 h) due to their unique characteristic of a decoupled energy storage and power output2. To enable the incorporation of these systems into society further and thus smoothen the transition towards renewable energy technologies, highly efficient and low cost membranes in terms of efficiency and durability are needed, that will simultaneously improve the efficiency and reduce the cost of energy storage.One of the membrane types for vanadium redox flow battery (VRFB) applications that gained the interest of industry and the scientific community are of the polybenzimidazole (PBI) type. Although these materials possess excellent chemical stability and vanadium barrier properties, they suffer from a poor proton conductivity compared to commercial standards such as Nafion® 212. Several strategies were proposed to tackle this issue, ranging from the preparation of composite membranes with a thin PBI skin layer3, alkaline pretreatments that improve the swelling characteristics of the PBI film4 and chemical modifications to attach ionic conducting groups on the polymer backbone, thus directly improving the conductivity5. This latter approach showed that a highly conductive PBI membrane could be obtained by the addition of sidechains containing charged moieties such as sulfonic acid5. However, this improved conductivity comes at a price, specifically, a decrease in its vanadium barrier properties due to a significant crossover of vanadium ions, thus losing one of the main benefits of PBI type membranes5.The work presented herein describes the preparation of multiple PBI derivatives containing small and readily available non-charged sidechains, such as alkylated or benzylated PBI. Herein, it was envisaged that the addition of non-charged sidechains to the PBI backbone could increase the free volume of the membrane and thus enable the incorporation of electrolyte into the film without significantly affecting its repelling effect for vanadium ions. With this in mind, the influence of these non-charged sidechains on the ex-situ properties under VRFB conditions was studied in terms of dimensional swelling, acid uptake, vanadium barrier properties and mechanical strength. Hereby, key differences in the behavior of the membranes were observed between each individual type of functionalization, such as swelling, uptake and composition in acidic media. Subsequently, the correlation between the ex-situ properties of the PBI derivatives and in-situ VRFB cycling performance was studied to further understand their significance. Through this process, valuable knowledge was obtained that showed a clear correlation between the ex-situ properties and the observed in-situ area specific resistance, energy efficiency and capacity fading of the various materials, with the best material outperforming Nafion® 212 in terms of energy efficiency by 1% at a current density of 200 mA∙cm2, a current density regime that is normally dominated by cation exchange membranes due to their low resistance. Thereby proving that even a small modification of the PBI backbone can have a significant influence on the performance in a VRFB cell. Yuan, Z.; Duan, Y.; Zhang, H.; Li, X.; Zhang, H.; Vankelecom, I., Advanced porous membranes with ultra-high selectivity and stability for vanadium flow batteries. Energy & Environmental Science 2016, 9 (2), 441-447. Chae, I. S.; Luo, T.; Moon, G. H.; Ogieglo, W.; Kang, Y. S.; Wessling, M., Ultra-High Proton/Vanadium Selectivity for Hydrophobic Polymer Membranes with Intrinsic Nanopores for Redox Flow Battery. Advanced Energy Materials 2016, 6 (16), 1600517. Gubler, L.; Vonlanthen, D.; Schneider, A.; Oldenburg, F. J., Composite Membranes Containing a Porous Separator and a Polybenzimidazole Thin Film for Vanadium Redox Flow Batteries. Journal of The Electrochemical Society 2020, 167 (10), 100502. Noh, C.; Serhiichuk, D.; Malikah, N.; Kwon, Y.; Henkensmeier, D., Optimizing the performance of meta-polybenzimidazole membranes in vanadium redox flow batteries by adding an alkaline pre-swelling step. Chemical Engineering Journal 2020, 126574. Yan, X.; Dong, Z.; Di, M.; Hu, L.; Zhang, C.; Pan, Y.; Zhang, N.; Jiang, X.; Wu, X.; Wang, J.; He, G., A highly proton-conductive and vanadium-rejected long-side-chain sulfonated polybenzimidazole membrane for redox flow battery. Journal of Membrane Science 2020, 596, 117616.

Novel bifunctional fillers (ATP/P–CNOs) for sulfonated poly(aryl ether sulfone) matrix for improved power output and durability of H2/O2 fuel cell at low humidity

The preparation of novel composite proton exchange membranes (PEMs) with homogeneous structures and efficient proton-conducting sites is of great importance for the development of PEM fuel cells. In this work, a double-filler of adenosine triphosphate (ATP) and phosphorylated carbon nano-onions (P–CNOs) is incorporated into sulfonated poly(aryl ether sulfone) (SPAES) by simple solution mixing to design a bionic proton-conduction pathways for high-performance PEMs. A series of uniformly distributed, dense and flexible SPAES/ATP/P–CNOs membranes are prepared and characterized for their membrane morphology, water uptake, dimensional stability, electrochemical properties and durability. Both the ATP and P–CNOs fillers can provide abundant proton conducting sites through hydrogen-bonding networks and acid-base pairs, thus improving the membrane stability and proton conductivity. Thanks to the formation of ionic interaction between ATP/P–CNOs and their interaction with SPAES substrates, the composite membranes demonstrate higher ATP retention, better dimensional-mechanical-chemical stability, higher proton conductivity and power output than the pristine and single-filler SPAES membranes. The SPAES/ATP/P–CNOs-2 membrane displays high proton conductivity (196 mS/cm at 90 °C in water and 33 mS/cm at 80 °C/51% relative humidity, RH) and power output (752 mW/cm2 at 80 °C/100% RH and 302 mW/cm2 at 80 °C/50% RH) in a H2/O2 fuel cell. It also experiences the minimal cell performance loss and lowest hydrogen crossover during 6 days of operation at 60% RH. The proposed ATP/P–CNOs channel approach can provide a reference for the development of multi-component composite high-efficiency PEMs for fuel cells.

Preparation and characterization of novel thin film composite forward osmosis membrane with halloysite nanotube interlayer

In this study, the electrospun polyacrylonitrile (ePAN) fiber mats were used as support layer and natural mineral-halloysite nanotubes (HNTs) was used to construct the interlayer. Polydopamine modification was utilized to enhance the hydrophilicity of ePAN substrates and dispersibility of HNTs. The mHNTs interlayer effectively minified the surface pore size of substrates providing a better interface for interfacial polymerization forming an integrated and thin PA selective layers. Compared to the unmodified membranes, the water flux of the optimized membrane with mHNTs interlayer about 61.60% and 79.70% higher and the reverse salt flux of which was 38.95% and 45.08% lower in AL-FS mode and AL-DS mode respectively. These results suggested that introducing halloysite nanotube interlayer is an effective, and low-cost way to fabricate high-performance FO membrane. ● Highly accessible and low-cost halloysite nanotubes (HNTs) were utilized to construct interlayers on electrospun nanofiber substrates. ● A high-performance thin film composite forward osmosis membrane was successfully prepared. ● HNTs interlayer showed benefits in generation of polyamide selective layers in interfacial polymerization. ● High water flux and low reverse salt flux were observed synchronously.

Proportion-dependent osteogenic activity of electrospun nano-hydroxyapatite/polylactic acid fiber membrane in vitro and in vivo

The effect of proportion on the physicochemical and osteogenic properties of electrospun nano-hydroxyapatite/polylactic acid (nHAP/PLA) fiber membrane was investigated from 0/100 to 20/80 (nHAP/PLA mass ratio), aiming to optimise the proportion and integrate mechanical support, biodegradability, cell infiltration and osteogenic activity for better bone repair. The results showed the incorporated nHAP increased the hydrophilicity of the fiber surface, and 6–10 wt% nHAP/PLA membrane showed the enhanced modulus in the direction perpendicular to membrane plane. Biological experiments demonstrated the nHAP proportion-dependent osteogenic activity of nHAP/PLA membranes. The addition of 6–10 wt% nHAP in the fiber membrane significantly promoted cell proliferation and differentiation. In vivo experiments of stacked implantation of the membrane displayed multilayer growth in the pure PLA group owing to the hydrophobicity of PLA and single-layer growth in the nHAP/PLA group because the hydrophilicity of the nHAP/PLA membrane improved the adhesion of the layers. The addition of 6–10 wt% nHAP/PLA also promoted cell recruitment and infiltration and increased osteogenesis, with enhancements of 41% in bone tissue volume/total tissue volume and 37% in bone mineral density. Our study provides helpful support for the preparation of composite electrospun membranes with improved osteogenic activity by optimising the organic–inorganic proportion.

Preparation of Rosin-Based Composite Membranes and Study of Their Dencichine Adsorption Properties.

In this work, rosin-based composite membranes (RCMs) were developed as selective sorbents for the preparation of dencichine for the first time. The rosin-based polymer microspheres (RPMs) were synthesized using 4-ethylpyridine as a functional monomer and ethylene glycol maleic rosinate acrylate as a crosslinking. RCMs were prepared by spinning the RPMs onto the membranes by electrostatic spinning technology. The optimization of various parameters that affect RCMs was carried out, such as the ratio concentration and voltage intensity of electrospinning membrane. The RCMs were characterized by SEM, TGA and FT-IR. The performances of RCMs were assessed, which included adsorption isotherms, selective recognition and adsorption kinetics. The adsorption of dencichine on RCMs followed pseudo-second-order and adapted Langmuir–Freundlich isotherm model. As for the RCMs, the fast adsorption stage appeared within the first 45 min, and the experimental maximum adsorption capacity was 1.056 mg/g, which is much higher than the previous dencichine adsorbents reported in the literature. The initial decomposition temperature of RCMs is 297 °C, the tensile strength is 2.15 MPa and the elongation at break is 215.1%. The RCMs have good thermal stability and mechanical properties. These results indicated that RCMs are a tremendously promising adsorbent for enriching and purifying dencichine from the notoginseng extracts.

A dual regulation strategy for MXene-based composite membrane to achieve photocatalytic self-cleaning properties and multi-functional applications

The development of two-dimensional (2D) membrane materials is limited by their relatively low antifouling performance. The high oxidation activity of photocatalytic technology can degrade the contaminants depositing on the membrane, which is expected to solve the problem of membrane fouling. Here, we reported a dual regulation strategy to construct a composite membrane, including chitosan modified MXene nanosheets as separation layer as well as g-C3N4 photocatalyst blended PVDF membrane as support layer. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used to verify the successful preparation of the dual interface composite membrane. Experimental results showed that the novel composite membrane exhibited high water permeability as well as achieved excellent rejection of anionic dyes and heavy metal ions (Congo red: over 98 % and Cr6+: 85.4%). Owing to photocatalytic activity, the composite membrane almost completely removed rhodamine B and tetracycline hydrochloride, and its self-cleaning ability improved the anti-fouling performance. Based on density functional theory, we further confirmed that the strong photocatalytic activity of the composite membrane was attributed to the efficient charge transfer between the photocatalytic support layer and the MXene separation layer. This work not only deepened the study of 2D-based materials in membrane preparation, but also provided a new dual regulation strategy to enhance multi-pollutants removal by composite membranes in wastewater treatment.

Covalent organic framework membrane on electrospun polyvinylidene fluoride substrate with a hydrophilic intermediate layer

Generally, electrospun membranes have high mechanical strength, high porosity and low permeation resistance. Although covalent organic frameworks (COFs) have attracted great interest as advanced membrane materials, few works disclosed that the COFs composite membranes were synthesized on electrospun substrates. In this work, the electrospun polyvinylidene fluoride (PVDF) membranes were used as substrates for the preparation of COF composite membranes with graphene oxide and oxidized carbon nanotubes (GO-OCNTs) as an intermediate layer. The COF/GO-OCNTs/PVDF composite membranes were prepared by suction filtering the GO-OCNTs intermediate layer on the electrospun substrate, and then interfacial polymerization of COF layer. After adding the intermediate layer, the water permeance and dye retention rate of the composite COF membrane are both improved. By exploring the reaction parameters in the interfacial polymerization process, the optimized membrane shows that the rejection rate of Coomassle brilliant blue G250 (BBG-250) is about 97.1%, and the water permeability achieves 96.7 L m−2 h−1 bar−1. In addition, the COF/GO-OCNTs/PVDF composite membrane exhibits excellent chemical and mechanical stability. The long-term filtration experiment of the composite membrane shows good water permeation stability. This work provides a method to prepare dense and defect-free COF films on electrospun substrates.

The Intrinsic Parameters of the Polyamide Nanofilm in Thin-Film Composite Reverse Osmosis (TFC-RO) Membranes: The Impact of Monomer Concentration.

The realistic resistance zone of water and salt molecules to transport across a TFC-RO membrane is the topmost polyamide nanofilm. The existence of hollow voids in the fully aromatic polyamide (PA) film gives its surface ridge-and-valley morphologies, which confuses the comprehensions of the definition of the PA thickness. The hollow voids, however, neither participate in salt–water separation nor hinder water penetrating. In this paper, the influence of intrinsic thickness (single wall thickness) of the PA layer on water permeability was studied by adjusting the concentration of reacting monomers. It confirms that the true permeation resistance of water molecules originates from the intrinsic thickness portion of the membrane. The experimental results show that the water permeability constant decreases from 3.15 ± 0.02 to 2.74 ± 0.10 L·m−2·h−1·bar−1 when the intrinsic thickness of the membrane increases by 9 nm. The defects on the film surface generate when the higher concentration of MPD is matched with the relatively low concentration of TMC. In addition, the role of MPD and TMC in the micro-structure of the PA membrane was discussed, which may provide a new way for the preparation of high permeability and high selectivity composite reverse osmosis membranes.

Preparation and Properties of Thin-Film Composite Forward Osmosis Membranes Supported by Cellulose Triacetate Porous Substrate via a Nonsolvent-Thermally Induced Phase Separation Process.

A porous substrate plays an important role in constructing a thin-film composite forward osmosis (TFC-FO) membrane. To date, the morphology and performance of TFC-FO membranes are greatly limited by porous substrates, which are commonly fabricated by non-solvent induced phase separation (NIPS) or thermally induced phase separation (TIPS) processes. Herein, a novel TFC-FO membrane has been successfully fabricated by using cellulose triacetate (CTA) porous substrates, which are prepared using a nonsolvent-thermally induced phase separation (N-TIPS) process. The pore structure, permeability, and mechanical properties of CTA porous substrate are carefully investigated via N-TIPS process (CTAN-TIPS). As compared with those via NIPS and TIPS processes, the CTAN-TIPS substrate shows a smooth surface and a cross section combining interconnected pores and finger-like macropores, resulting in the largest water flux and best mechanical property. After interfacial polymerization, the obtained TFC-FO membranes are characterized in terms of their morphology and intrinsic transport properties. It is found that the TFC-FO membrane supported by CTAN-TIPS substrate presents a thin polyamide film full of nodular and worm-like structure, which endows the FO membrane with high water permeability and selectivity. Moreover, the TFC-FO membrane supported by CTAN-TIPS substrate displays a low internal concentration polarization effect. This work proposes a new insight into preparing TFC-FO membrane with good overall performance.

Preparation and properties of composite membranes of fully fluorinated nanofibrous electrospun mat impregnated with highly sulfonated polysulfone: Effect of thermal treatment on the mat and the membranes thereof

To prepare highly sulfonated/fully fluorinated nanofibrous composites, sulfonated polysulfone with 70% degree of sulfonation and fully fluorinated poly(aryl ether) are synthesized as components. Nucleophilic aromatic substitution reaction is applied for polymerization. Then, the composite membrane with thickness of 60 μm and 30 wt% electrospun nanofibers is prepared via impregnation of the fully fluorinated mat by a suitable solution of the sulfonated polymer. In the next step, two treated composite samples with thicknesses of 60 and 20 μm containing 20 wt% of treated electrospun nanofibers are also prepared by impregnation. A simple thermal treatment on fully fluorinated mat is used to obtain the latter composites. The thermal crosslinking make the handling of the thin mat possible. Fourier transform infrared spectroscopy, solubility assessment, and gel content measurement are used to confirm thermal crosslinking. The properties of three developed composites are studied to investigate the presence of fluorinated electrospun nanofibers, thermal treatment effectiveness, and nature of the thin membrane structure. The remarkable tensile strength of 87.52 MPa is attained for the thin membrane. Moreover, the conductivity value of 0.146 S/cm at 30 °C with an activation energy of 10.22 kJ/mol in this sample is motivating.

Liquid–liquid interface induced PDMS‐PTFE composite membrane for ethanol perm‐selective pervaporation

AbstractPervaporation has great potential in the separation of many significant mixtures. However, excessive penetration of separation layer into the substrate pores enhances the transport resistance of solvent molecules, which impedes the development of pervaporation membrane. In this study, a facile floating‐on‐water (FOW) method was used to prepare poly(dimethylsiloxane) (PDMS)/polytetrafluoroethylene (PTFE) composite membranes. The formation of separation layer and preparation of composite membrane were step‐by‐step completed through this liquid–liquid interface induced method. The PDMS layer thickness could be precisely regulated from 0.5 to 8 μm. Moreover, the pore penetration could be controlled by optimizing pre‐crosslinking density, crosslinking time on water and polymer solution volume. The obtained PDMS/PTFE composite membrane exhibited a high flux of 2016 g·m−2·h−1 with the separation factor of 12 when separating ethanol from a 5 wt% ethanol/water mixture. The performance of the membrane could be stable for over 200 h, exhibiting great potential in ethanol perm‐selective pervaporation.

Preparation and Characterization of a Thin-Film Composite Membrane Modified by MXene Nano-Sheets.

MXene nano-sheets were introduced into a thin-film composite membrane (TFC) to reduce the mass transfer resistance (concentration polarization) and improve the membrane performance. The process entailed dissolving the MXene nano-sheets in a membrane casting solution using the blending method and introducing them into the porous support layer to prepare a modified thin-film composite forward osmosis (TFC-FO) membrane. The results showed that the water contact angle decreased by about 16%, indicating that the hydrophilicity was strengthened, and the O/N ratio of the active selective layer decreased by 13%, indicating an increased degree of crosslinking, thereby demonstrating that the introduction of MXene nano-sheets changed the properties of the membrane and played a positive role in its physicochemical properties. In contrast to the unmodified TFC-FO membrane, the modified membrane had a slightly higher reverse solute flux, while its water flux increased by about 80%. Its specific reverse osmosis flux was also significantly optimized (only 0.63 g/L). In conclusion, adding MXene nanosheets to TFC-FO membranes led to the modified membranes with better mass transfer, lessened internal concentration polarization (ICP), and better osmotic separation.

Preparation, structure and properties of soy protein and silk fibroin composite nanofiber membrane by jet spinning

<p indent=0mm>It is a hot topic in science nowadays and of great practical significance for developing abundant green natural resources and their applications in the research of biomedicine and tissue engineering. This article successfully prepared the biocompatible and biodegradable soy protein and silk fibroin composite nanofiber membrane by spinning technique. The apparent morphologies, structural changes and interactions of the two materials were characterized by scanning electron microscopy, Raman and Fourier transform infrared spectroscopy and X-ray diffraction. Differential scanning calorimetry and thermogravimetric analysis were used to investigate the blending properties of the two phases. The water retention, <italic>in vitro</italic> degradation, and cytocompatibility of the composite films were also evaluated. The results showed mainly hydrogen bond interactions between silk fibroin and soy protein molecular chains, which had thermodynamic compatibility and showed good morphology and thermal properties of nanofibers. With the increase of soybean protein content, the <italic>β</italic>-sheet content of the composite nanofiber membrane increases gradually. At the same time, the glass transition temperature decreases, the specific heat capacity increases a little more, and the water retention ability increases as well as the enzymatic degradation speed. Simultaneously, compared with pure silk fibroin, soy protein/silk fibroin composite nanofiber membrane can provide a better environment for cell adhesion and proliferation, which can be used as a wound dressing and drug delivery system. Especially, the composite fiber membrane containing 60% soy protein showed the strongest cell activity. This study provides a new view for preparing natural materials such as silk fibroin and soy protein and supplies the experimental and theoretical basis for the wide applications of green natural resources.

SYNTHESIS AND CHARACTERIZATION OF MAGNETIC NANOPARTICLES EMBEDDED ON IONIC POLYMER BY CHEMICAL REDUCTION METHOD

Magnetite nanoparticles (Fe3O4 NPs) are prepared using chemical reduction method. This is a simple, economical, nontoxic, facile, clean, and environment friendly process. Preparation of composite polymeric membrane of polyvinyl alcohol (PVA)/Fe3O4 has been performed using dry phase inversion technique for different medical/filtration applications. PVA coatings using magnetite NPs are focused to passivate the surface and decrease agglomeration and also reduce module biomedical absorption and most of the times increase dispersion stability. Therefore, research on PVA coatings on magnetite NPs are in trend now a days, as they are of high charge density that makes them stable in dispersion by electrostatic repulsion. The prepared samples (Fe3O4 NPs) and PVA/Fe3O4 composite membrane have been analyzed for their different properties by using X-ray direction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis) and thermogravimetric Analysis (TGA).

Preparation of Polymer Composite Selective Permeable Membrane with Graphene Oxide and Application for Chemical Protective Clothing

Chemical warfare agents (CWA) can poison people through the skin and cause injury, and the use of chemical protective clothing (CPC) is an important way to protect personnel from injury. CPC performance strongly depends on chemical protective materials, and satisfactory protective materials must meet various requirements, including protective performance, physiological comfort, mechanical performance, and cost effectiveness. Here, low-cost materials were used to prepare PVDF sodium sulfonate composite membranes with different contents of modified graphene oxide (GO-SSS). Their tensile properties, contact angle, permeability, and selectivity were tested and analyzed. The results show that when the addition ratio of GO-SSS to the bare membrane is 0.5%, the composite membrane has desirable permeation selectivity of water vapor/CWA simulant vapor and desirable mechanical properties. Hence, our sodium sulfonate composite membrane of PVDF with GO-SSS is an ideal material for potential applications in CPC.

Preparation of superhydrophobic PVDF composite membrane via catechol/polyamine co-deposition and Ag nanoparticles in-situ growth for membrane distillation

Membrane distillation (MD) has gained widespread attention in desalination and wastewater treatment. However, membrane fouling and membrane wetting seriously hinder its further development and industrial application. This work provides a method for preparing superhydrophobic modified membranes for MD through mussel-inspired coating, in-situ growth of nanoparticles and modification of low surface energy substances. The copolymerization of catechol and polyethyleneimine produced a poly(catechol/polyamine) layer rich in catechol groups and amino groups, which realized the in-situ reduction of silver nanoparticles and constructed a micro-nano rough structure. The resulting superhydrophobic modified membrane with an average roughness of 314.78 nm has a static water contact angle of 151.6 ± 2.5° and a sliding angle of 9.6°. The superhydrophobic membrane showed a membrane flux increase of more than 20% compared with the pristine PVDF and exhibited stable membrane flux and high salt rejection (>99.9%) when processing saline feeds containing surfactants, oily substances, organic pollutants and high concentration salts, indicating the excellent anti-wetting and anti-fouling properties. The superhydrophobic modified membrane prepared in this study improves the adaptability of the MD process and provides a promising candidate for membrane modification methods for MD.

One-Step Water-Induced Phase Separation Simultaneously Triggering Polymer Solidification and Polyelectrolyte Complexation for Porous Ultrafiltration Membranes.

Functional additives have been widely utilized for the membrane structure modulation and performance improvement during the nonsolvent-induced phase separation process, but the resulted membranes easily suffer from additives' inhomogeneous dispersity and compatibility with the polymer matrix. Herein, a facile and robust strategy, i.e., one-step water-induced phase separation, was proposed for the preparation of polyelectrolytes-contained composite membranes. Polyanion (dopamine modified polyacrylic acid) and polycation (quaternized chitosan paired with bis(trifluoromethane-sulfonyl)imide) were first premixed in dimethyl sulfoxide and used as polyelectrolyte additives in a polysulfone (PSF) solution, and then a uniform PSF-based casting solution was readily obtained. During the solvent-water exchange process, polymer solidification and polyelectrolyte complexation were simultaneously triggered, in situ generating a polyelectrolyte complex fixed within the membrane matrix. Ultrafiltration membranes with hierarchical structures were notably tailored through altering the concentration, molecular weight, and type of polyelectrolytes. The obtained membrane exhibited a water flux of 672 L·m-2·h-1, three times over the raw PSF membrane, while almost maintaining high bovine serum albumin (BSA) rejection. This work paves a straightforward and convenient path for the preparation of composite membranes with tunable architecture and properties.

An ultrapermeable thin film composite membrane supported by “green” nanofibrous polyimide substrate for polar aprotic organic solvent recovery

The preparation of polymeric-based thin film composite (TFC) membrane with high permeance and superior solvent resistance in organic solvent nanofiltration (OSN) applications always involves the consumption of toxic chemicals or high energy, which does not meet the requirements of green chemistry. In this work, intrinsic insoluble polyimide (PI) nanofiber substrates were obtained by a two-step method including electrospinning of poly (amic acid) synthesized by polycondensation reaction between various monomers and subsequent thermal imidization, and the optimized one with low thermal imidization temperature was employed as substrate for TFC membrane in strong polar aprotic solvents recovery, therefore achieving the green process. The effects of different dianhydride and diamine monomers and different thermal imidization temperatures on the solvent resistance and microscopic morphology of nanofiber substrates are also studied. The optimized monomers in this work contribute to a low-temperature imidization of PI nanofiber substrate. The solvent permeance of corresponding TFC OSN membrane with the insoluble PI nanofiber substrate reaches up to 11.2 L m −2 h −1 bar −1 with 99.7% rejection in rose bengal/DMF system, and good long-term stability. This work provides potential guidelines for developing next-generation OSN membranes under a green process. • Insoluble polyimide (PI) nanofibrous substrate was prepared facilely with low-temperature thermal imidization. • A green modification without toxic chemical solvent involved is applied. • PI nanofibrous substrate can withstand strong polar aprotic solvents for more than three months. • The high porosity and interconnected pores endow substrate superior solvent permeance. • TFC membrane exhibits outstanding OSN performance and long-term stability.

Ultrathin cyclodextrin nanofilm composite membranes for efficient separation of xylene isomers

Molecule separation membranes with high flux and precise sieving are promising for discriminating xylene isomers. However, the thick separation layer (>300 nm) and dense inner structure with wide pore size distribution generally restrict the further development. Here, we demonstrate the preparation of novel thin-film composite membranes with sub-10 nm cyclodextrin (CD) nanofilms that are cross-linked on thin vermiculite (Vr) lamellar layer through electrostatic atomization-assisted interfacial polymerization technology. The regular Vr layer provides smooth and hydrophilic platform for synthesizing ultrathin and defect-free CD nanofilms. The as-prepared composite membranes achieve precise separation for xylene isomers and benzene derivatives based on size sieving effect using the intrinsic cavities in CDs. Meanwhile, the ultrathin CD nanofilms and regular Vr layer jointly contribute to fast molecule transfer. Specifically, TFC membrane with β-CDs nanofilm attains separation factor (SF) of 6.7 and 6.1 for p-xylene/m-xylene (PX/MX) and p-xylene/o-xylene (PX/OX), respectively, with the PX permeance of 7.9 and 7.8 L m−2 h−1 bar−1. Moreover, the SF for cyclohexane/1,3,5-triisopropyl benzene reaches as high as 46.8 by membrane with α-CD nanofilm. In addition, these TFC membranes exhibit favorable structural and operational stabilities, providing insight into practical separation applications.

Preparation of Sodalite and Faujasite Clay Composite Membranes and Their Utilization in the Decontamination of Dye Effluents.

The present work describes the deposition of two zeolite films, sodalite and faujasite, by the hydrothermal method to tune the mesopores of clay support, which are prepared from a widely available clay depot from the central region of Morocco (Midelt). The clay supports were prepared by a powder metallurgy method from different granulometries with activated carbon as a porosity agent, using uniaxial compression followed by a sintering process. The 160 µm ≤ Φ ≤ 250 µm support showed the highest water flux compared to the supports made from smaller granulometries with a minimum water flux of 1405 L.m−2·h−1 after a working time of 2 h and 90 min. This support was chosen for the deposition of sodalite (SOM) and faujasite (FAM) zeolite membranes. The X-ray diffraction of sodalite and faujasite showed that they were well crystallized, and the obtained spectra corresponded well with the sought phases. Such findings were confirmed by the SEM analysis, which showed that SOM was crystalized as fine particles while the FAM micrographs showed the existence of crystals with an average size ranging from 0.53 µm to 1.8 µm with a bipyramidal shape and a square or Cubo octahedral base. Nitrogen adsorption analysis showed that the pore sizes of the supports got narrowed to 2.28 nm after deposition of sodalite and faujasite. The efficiencies of SOM and FAM membranes were evaluated by filtration tests of solutions containing methyl orange (MO) using a flow loop, which were developed for dead-end filtration. The retention of methylene orange (MO) followed the order: SOM > FAM > 160 µm ≤ Φ ≤ 250 µm clay support with 55%, 48% and 35%, respectively. Size exclusion was the predominant mechanism of filtration of MO through SOM, FAM, and the support. However, the charge repulsion between the surface of the membrane and the negatively charged MO have not been ruled out. The point of zero charge (pzc) of the clay support, SOM and FAM membrane were pHpzc = 9.4, pHpzc = 10.6, and pHpzc = 11.4, respectively. Filtrations of MO were carried out between pH = 5.5 and pH = 6.5, which indicated that the surface of the membranes was positively charged while MO was negatively charged. The interaction of MO with the membranes might have happened through its vertical geometry.