Organic Solvent Nanofiltration Membranes Research Articles

Hollow Fiber Membrane for Organic Solvent Nanofiltration: A Mini Review.

Organic solvents take up 80% of the total chemicals used in pharmaceutical and related industries, while their reuse rate is less than 50%. Traditional solvent treatment methods such as distillation and evaporation have many disadvantages such as high cost, environmental unfriendliness, and difficulty in recovering heat-sensitive, high-value molecules. Organic solvent nanofiltration (OSN) has been a prevalent research topic for the separation and purification of organic solvent systems since the beginning of this century with the benefits of no-phase change, high operational flexibility, low cost, as well as environmental friendliness. Especially, hollow fiber (HF) OSN membranes have gained a lot of attention due to their high packing density and easy scale-up as compared with flat-sheet OSN membranes. This paper critically reviewed the recent research progress in the preparation of HF OSN membranes with high performance, including different materials, preparation methods, and modification treatments. This paper also predicts the future direction of HF OSN membrane development.

Machine learning based prediction and optimization of thin film nanocomposite membranes for organic solvent nanofiltration

In this study, machine learning was used to form prediction models for thin film nanocomposite (TFN) organic solvent nanofiltration (OSN) membrane performance evaluation in terms of relative permeability (RP) and relative selectivity (RS). Twenty references including 9252 data points were collected to form four different models: linear, support vector machine (SVM), boosted tree (BT), and artificial neural network (ANN). Among the four models, BT exhibited optimal prediction accuracy in terms of root mean square error (RMSE) and coefficient of determination (R2) values for membrane RP (RMSE: 0.295, R2: 0.918) and RS (RMSE: 0.053, R2: 0.849) performance prediction. Parameter contribution analysis indicated that nanoparticle loading, amine concentration, chloride concentration, water contact angle, solvent viscosity, and molar volume are the main parameters influencing RP performance. For RS performance, nanoparticle loading, amine concentration, chloride concentration, and solute molecular weight play important roles. Partial dependence analysis indicated that the optimal conditions for TFN-OSN membrane fabrication are nanoparticle loading less than 5 wt%, the amine concentration around 2 wt%, and the chloride concentration around 0.15 wt%. In addition, membrane with super-hydrophilic or super-hydrophobic surface property exhibited higher RP performance based on different feed solvent types. Overall, this work introduces new ways both for TFN-OSN membrane performance prediction and for higher performance membrane design and development.

Polybenzimidazole (PBI) membranes cross-linked with various cross-linkers and impregnated with 4-sulfocalix [4]arene (SCA4) for organic solvent nanofiltration (OSN)

The chemical, pharmaceutical, and edible oil industries have employed enormous amounts of organic solvents to produce medicines, chemicals, and other goods. In order to recycle these valuable organic solvents, organic solvent nanofiltration (OSN) is crucial. However, choosing the optimal cross-linker is vital for producing membranes with improved performance and chemical resistance. In this study, integrally skinned polybenzimidazole (PBI) flat membranes for OSN were studied through a covalent modification employing α, α′-dibromo-p-xylene (DBX), α, α′-dichloro-p-xylene (DCX) or trimesoyl chloride (TMC), followed by ionic impregnation with 4-sulfocalix [4]arene (SCA4). The nucleophilic-electrophilic reactions between PBI and cross-linkers and the ionic interactions among SCA4, PBI and cross-linkers were investigated and elucidated. Due to the two-fold modifications, the resultant PBI membranes show enhanced molecular sieving capabilities and chemical stability. Especially, the membranes modified with DBX and DCX, and then SCA4 infiltration demonstrate a wide range of stability in harsh organic solvents such as n-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc). They also possess impressive rejections against low molecular weight (Mw) dyes, reconfirming their superiority in terms of structural and chemical stability to PBI for practical OSN uses. However, the dye rejection is still influenced by the physical characteristics of the solvents and dyes as well as the interactions among the solute, solvent, and membrane. This work may provide a workable plan to design membranes with precise molecular sieving capabilities for OSN.

Crosslinked polyethersulfone membranes for organic solvent nanofiltration in polar aprotic and halogenated solvents

Organic solvent nanofiltration is a promising and more sustainable alternative to classic separation processes in multiple industries; however, proposed materials for polymeric membranes with high solvent stability mostly utilize unique or expensive polymers, or are fabricated by complex methods. Herein, a facile method is presented to fabricate crosslinked polyethersulfone membranes with remarkable stability in halogenated and polar aprotic solvents. After preparing the membranes by the conventional non-solvent-induced phase inversion process, a multidentate aromatic amine embedded in the polysulfone underwent diazotization/dediazonization to effectively crosslink the polymer matrix. Membrane performance was easily adjusted from ultra-to nanofiltration via the polymer fraction. The performance of the crosslinked polyethersulfone nanofiltration is similar to the state-of-the-art solvent stable membranes. A weeklong filtration experiment in dimethylformamide and chloroform underlines the membranes' excellent stability. Overall, the range of solvent stability and state-of-the-art performance, combined with high accessibility and scalability, make the presented membranes an ideal platform material.

Extraction of monophenols and fractionation of depolymerized lignin oil with nanofiltration membranes

Organic solvent nanofiltration membranes were employed to fractionate birch derived reductive catalytic fractionated (RCF) lignin oil. This lignin oil is highly depolymerized, with most, if not all chemical compounds lighter than 3 kDa. Sixteen commercially available membranes were investigated for the fractionation, in combination with methanol and ethyl acetate as solvents. Membrane performances were quantified using Gaussian fits of gel permeation chromatograms and separation factor calculations. The separation factor was found to be primarily based on affinities instead of size-exclusion. The silicon-based membranes from Borsig (Germany) and PuraMem S600 from Evonik (UK) proved best at separating lignin into different functional fractions, showing monomer separation factors up to 7.4 and providing a permeate fraction with 88 % phenolic monomer purity. These membranes were further examined in batch diafiltration and two-stage filtration. This increased the separation factor from 7.4 to 25.4, and the monomer purity of the permeate to 95 %, proving that membrane purification of the lignin-derived monophenols is technically feasible.

Analyzing transport in ceramic membranes for organic solvent nanofiltration using Maxwell-Stefan theory

Ceramic membranes are highly promising for application in organic solvent nanofiltration (OSN). Unfortunately, the governing molecular transport mechanisms are not yet fully understood. To study the importance of different transport mechanisms, we analyze transport through these membranes using Maxwell-Stefan theory. We show that the total flux is dominated by the viscous contribution, when using Poiseuille’s law. Cross-coupling of the order of magnitude observed in liquids, leads to changes in retention of up to 20%. Finally, it was shown that non-ideal thermodynamics in the external liquid phase can explain changes from positive to negative retention when using the same solute in different solvents. This work opens perspectives to choose simpler mass transfer models for process modelling, as well as provides physical insight into which mass transfer mechanisms are important in OSN with ceramic membranes.

Robust polyamide-PTFE hollow fibre membranes for harsh organic solvent nanofiltration

Polymeric membranes have been extensively studied for organic solvent nanofiltration (OSN) but many fail to show sufficient chemical resistance in strong solvents like dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This study focuses on harnessing the outstanding chemical resistance of polytetrafluoroethylene (PTFE), to develop polyamide-PTFE thin film composite (TFC) membranes that are resistant to such aprotic solvents. A defect-free polyamide thin film layer was successfully synthesized on the microfiltration PTFE hollow fibre substrates, overcoming challenges such as large and uneven pore size, and hydrophobicity of the PTFE substrates. A simple polydopamine (PDA) coating was carried out to improve the substrate’s hydrophilicity prior to the polyamide synthesis via interfacial polymerization (IP). Polyethyleneimine (PEI) and trimesoyl chloride (TMC) were used as the monomers and a two-time IP method was employed to obtain a defect-free polyamide coating. The synthesized membranes showed high acetonitrile (ACN) and DMF permeabilities of 7.94 and 3.70 lm−2h−1bar−1, respectively, with acid fuchsin (585 Da) rejections of > 90 %. The molecular weight cut-off (MWCO) of the membranes could be further reduced to ∼300 Da by the addition of piperazine (PIP) monomers. The membranes also showed excellent stability and performance in a 72-hour OSN test performed in DMF indicating their great potential in effective molecular separation in harsh solvents. This study demonstrates how a simple modification and coating technique can transform commercially available microfiltration PTFE hollow fibres into durable and high value OSN membranes.

Solvent-resistant polyimide aerogel film as ultrapermeable support for thin-film composite and covalent organic framework nanofiltration membranes

Organic solvent nanofiltration (OSN) membranes require robust selective layers and support materials. In this study, polyamide and polyester thin-film composites (TFCs) and covalent organic frameworks (COFs) were fabricated as selective layers on a polyimide aerogel support. The ultrapermeable support was stable in various organic solvents including harsh polar aprotic solvents such as N,N-dimethylformamide (DMF), dimethylsulfoxide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone for more than six months. The support enabled fabricating both amorphous and crystalline selective layers at both room and higher temperatures. Moreover, the polyimide aerogel support had 85% porosity, facilitating high solvent flux. The compatibility of the selective layers and support was excellent, and as low molecular weight cutoff values (MWCO) as 356 and as high as 591 g mol−1 were obtained in methanol at 10 bar for the COFs and polyester TFC membranes, respectively. Both experimental MWCO and permeance values of the COF membrane agreed with those predicted using the pore flow model. The effect of the operating temperature on the OSN performance was examined in DMF at 20 and 100 °C. Both membranes demonstrated constant permeance and rejection for more than nine days of continuous filtration.

Anti-fouling membranes for organic solvent nanofiltration (OSN) and organic solvent ultrafiltration (OSU): graft modified polybenzimidazole (PBI)

Fouling is one of the major obstacles to successful membrane-based separations. In aqueous systems, fouling is well characterised and fouling reduction techniques are established. However, in organic solvents, membrane fouling is not well understood. In this work we manufactured anti-fouling organic solvent stable polybenzimidazole (PBI) membranes by graft modifying the surface with linear poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Graft modification provided an effective method of reducing fouling. However, the anti-fouling properties were dependent on the interactions between the modifying polymer and the solvent. In water, the hydrophilic PEG graft modifiers had favourable modifier-water interactions and provided an anti-fouling steric layer on the surface of the membrane. However, hydrophobic PPG graft modifiers had unfavourable modifier-water interactions and provided no anti-fouling properties. Conversely, in polar organic solvents, graft modification with PPG showed superior modifier-solvent interactions, and superior anti-fouling properties, relative to graft modification with the same molecular weight PEG. In non-polar solvents, both the PEG and PPG modifiers had unfavourable modifier-solvent interactions and provided minimal anti-fouling properties. The anti-fouling properties after graft modification were closely correlated to the hydrodynamic diameter of the grafting polymer in solution, and the selection of an optimal grafting polymer for manufacturing anti-fouling OSN and OSU membranes is significantly solvent dependant.

Nanocomposite membranes for organic solvent nanofiltration: Recent advances, challenges, and prospects

Organic solvent nanofiltration (OSN) is an emerging technology for the separation of organic solvents that are relevant to the petrochemical, pharmaceutical, food and fine chemical industries. The separation performance of OSN membranes has continued to push the boundary up through advanced membrane fabrication techniques and novel materials for fabricating the membranes. Despite the many advantages, OSN membranes still face such challenges as low solvent permeability and durability in harsh organic solvent conditions. To overcome these limitations, attempts have been made to incorporate nanomaterial fillers into OSN membranes to improve their overall performance. This review analyzes the potential and use of nanomaterials for OSN membranes, including covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal oxides (MOs) and carbon-based materials (CBMs). Recent advances in the state-of-the-art nano-based OSN membranes, in the form of thin-film nanocomposite (TFN) membranes and mixed matrix membranes (MMMs), are reviewed. Moreover, the separation mechanisms of OSN with nano-based membranes are discussed. The challenges faced by these OSN membranes are also elaborated, and recommendations for further research in this field are provided.

Intercalated 2D nanowires network cooperating with its entanglement in tuneable GO membrane nanochannels for ultrafast organic solvent nanofiltration

Organic solvent nanofiltration (OSN) as an emerging membrane separation technology has received substantial attentions recently. However, high permeability and selectivity simultaneously remains a momentous challenge for OSN mainly limited by the trade-off between permeance and selectivity. Here, ultralong and flexible polymeric nanowires (PWs) with positive charge were used to construct highly entangled PWs network fabricating interlayered GO composite membrane for OSN. The membrane exhibits a unique configuration with alternating stacking of highly entangled nanowires network and ultrathin GO layers. Meanwhile, the alternating layers become interlinked closely due to the strong electrostatic interactions between the positively charged nanowires and negatively GO layers. It could endow composite membrane with excellent stability in solvent. Unique membrane separation channels, constructed by close-knit interlaced PWs network and GO interlayer structure, allow a high flux of various solvents through the membrane and excellent rejection for small molecules. Solvent permeance of the optimized membrane could reach 91.3 L/m2·h with rejection of above 90% for Congo Red in methanol. The designed GO composite membrane is promising to practical application in OSN field, and it may also be useful for aqueous applications in separation and precise screening process.

Interlayered thin-film nanocomposite membrane with synergetic effect of COFs interlayer and GQDs incorporation for organic solvent nanofiltration

The separation performance of current organic solvent nanofiltration (OSN) membranes are still not satisfied. In this work, an ultra-thin TpHz covalent organic frameworks (COFs) interlayer was in situ constructed in advance on polyimide substrate, then an ultra-thin polyamide separation layer incorporated with amino-functionalized graphene quantum dots (af-GQDs) was constructed via interfacial polymerization (IP). A high performance interlayered thin-film nanocomposite (iTFN) OSN membrane with integrally covalent bonding structure, ultra-thin and ultra-smooth surface was obtained after post crosslinking and activation. The effect of ultra-low concentrations for the polyamide reaction monomers, the COFs monomer Tp and the doped af-GQDs nanoparticle reveals that they could help to form a very thin (7–8 nm in thickness) and defect-free skin layer with very smooth surface (about 2.7 nm in roughness). The iTFN OSN membrane shows excellent solvent permeance and solute selectivity, with an ethanol permeance reaching 97.6 L m−2 h−1 MPa−1 and an RDB rejection higher than 99%. After a 180 h long-term filtration with 100 mg L−1 RB/DMF solution, it remained an RB rejection of higher than 99%, demonstrating its superior resistance to strong polar solvent. Our work paves a unique way for the fabrication of novel OSN membrane with both in situ constructed nanomaterials interlayer and nanomaterials incorporated in skin layer.

Highly stable epoxy-crosslinked polybenzimidazole membranes for organic solvent nanofiltration under strongly basic conditions

Organic solvent nanofiltration (OSN) often needs to be conducted under extreme conditions in the chemical and food industries. In this work, we fabricated polybenzimidazole (PBI)-based OSN membranes that possess excellent stability under strongly basic conditions at pH 13. Two crosslinked PBI membranes were prepared by treating pristine PBI membranes with two epoxy-containing crosslinkers. Various permeation and characterization tests were performed to investigate the resistance of the membranes to solvents and basic environments. Both crosslinked membranes displayed reasonable permeance in pure solvents at room temperature under 10 bar operating pressure, along with a sharp molecular discrimination performance in ethanol environments. The crosslinked PBI membranes were found to be stable and did not completely lose their separation properties at high pH, although the effective pore size of the membranes increased presumably due to swelling. The separation performance of the membranes was found to be reversible between filtrations of neutral and basic aqueous solutions. Therefore, our crosslinked PBI membranes, which display exceptional stability, hold great potential for applications in OSN under basic conditions.

Preparation of microporous organic solvent nanofiltration (OSN) composite membrane from a novel tris-phenol monomer

As an emerging membrane separation technology, organic solvent nanofiltration (OSN) has shown great application potential in the field of pharmaceutical and chemical industries referring to organic media. Herein, we prepared a novel microporous thin-film composite (TFC) OSN membrane with superior perm-selective performances, which was fabricated by applying 4,4′,4″-trihydroxytriphenylmethane (Tris-Phenol) to react with trimesoyl chloride (TMC) by interfacial polymerization (IP) technique. The rigid, non-planar and multifunctional nature of Tris-Phenol endowed the polyarylate nanofilm with enhanced microporosity. Of note, the prepared composite membrane showed good selectivity to small organic solutes with molecular weight cut-off (MWCO) as low as ∼295 Da, meanwhile had medium methanol permeance up to 5.86 LMH/bar, by the help of surfactant dodecyl trimethyl ammonium chloridea (DTAC) during the IP reaction. The experiments showed that the Tris-Phenol membrane exhibited extraordinary long-term operation stability. In addition, the Tris-Phenol membrane could achieve separation of solutes with similar molecular weights but different charges. This research well illustrated the novel IP monomer design strategy to fabricate new TFC OSN membrane with high perm-selectivity.

Thin-Film Composite Membranes with a Carbon Nanotube Interlayer for Organic Solvent Nanofiltration.

Compared to the traditional chemical-crosslinking-based polymer, the porous polytetrafluoroethylene (PTFE) substrate is considered to be an excellent support for the fabrication of thin-film composite (TFC) organic solvent nanofiltration (OSN) membranes. However, the low surface energy and chemical inertness of PTFE membranes presented major challenges for fabricating a polyamide active layer on its surface via interfacial polymerization (IP). In this study, a triple-layered TFC OSN membrane was fabricated via IP, which consisted of a PA top layer on a carbon nanotube (CNT) interlayer covering the macroporous PTFE substrate. The defect-free formation and cross-linking degree of the PA layer can be improved by controlling the CNT deposition amount to achieve a good OSN performance. This new TFC OSN membrane exhibited a high dye rejection (the rejection of Bright blue B > 97%) and a moderate and stable methanol permeated flux of approximately 8.0 L m−2 h−1 bar−1. Moreover, this TFC OSN membrane also exhibited an excellent solvent resistance to various organic solvents and long-term stability during a continuous OSN process.

A facile crosslinking method for polybenzimidazole membranes toward enhanced organic solvent nanofiltration performance

Herein, a facile method for crosslinking polybenzimidazole membranes applied in organic solvent nanofiltration (OSN) using an aqueous potassium permanganate (KMnO4) solution is presented. The membranes were crosslinked under mild water-based conditions at room temperature for less than 4 h. The crosslinked polybenzimidazole OSN membrane exhibited superior separation performance and enhanced stability in various solvents, including dimethylformamide and N-methyl-2-pyrrolidone. The crosslinked membranes exhibited greater than 90% rejection rate for dyes with molecular weights in the range of 327 to 1017 Da, and they were compatible with various common organic solvents such as ethanol, isopropyl alcohol, acetone, and dimethylformamide. Furthermore, no significant change in the membrane performance was observed when polar and nonpolar solvents were used in filtration experiments.

Polyoxometalate-modified halloysite nanotubes-based thin-film nanocomposite membrane for efficient organic solvent nanofiltration

Polyoxometalate-modified halloysite nanotubes (POM@MHNTs) were synthesized and doped into the polyamide (PA) matrix by interfacial polymerization to prepare doped POM@MHNTs thin-film nanocomposite (TFN) membranes for organic solvent nanofiltration (OSN). Likewise, thin-film composite (TFC) and TFN membranes doped with HNTs were fabricated. It is worth noting that the methanol flux of the TFN can be efficiently enhanced by tuning the contents of POM@MHNTs. The as-synthesized optimal sample (TFN-0.10) exhibits superior methanol flux of TFN-0.10 membrane of 14.80 L m−2 h−1 bar−1 (1.76 times of that of undoped TFC membrane and 1.12 times of that of doped HNTs membrane (TFN-HNTs-0.10). These are mainly due to the tubular structure of POM@MHNTs providing additional solvent transfer channels and the ridge-valley morphology of the membrane surface increasing the contact area between the membrane and the solvent. Meanwhile, the POM@MHNTs nanohybrids are similarly electrostatically attracted by the amide groups on the polyamide chains produced by interfacial polymerization, improving the compatibility of POM@MHNTs with polyamide membranes. TFN-0.10 OSN membrane showed stable chemical properties in medium polar organic (methanol, ethanol, THF), acid polar organic (acetonitrile), and strong polar organic (DMF) solvents. Prepared TFN OSN membranes exhibited strong long-term operation capability and organic solvent resistance after 80 °C DMF immersion for 7 days with inconspicuous separation performance changes. This work offers the prospect of using organic-inorganic hybrid modified nanomaterials to improve OSN performance.

Unraveling the influence of dissolved gases on permeate flux in organic solvent nanofiltration – Experimental analysis

The first step in quantifying the performance of organic solvent nanofiltration membranes are usually lab-scale experiments with respect to flux and rejection. The necessary pressurization of the feed is either realized mechanically by a high-pressure pump or by means of a pressurized inert gas. While the latter option is most frequently applied, the gas may dissolve in the feed mixture and permeate through the membrane, affecting the transport of the other components. This potential effect is commonly neglected, inherently assuming that the gas solubility is negligible. The current study provides a systematic experimental investigation and analysis of the impact of dissolved gases on solvent flux for a hydrophilic DuraMem membrane, with gas solubilities assessed through PC-SAFT. The results prove that a gas with low solubility has a negligible effect on the solvent flux. In contrast, an increasing gas solubility may result in significant gas flux through the membrane with a considerable effect on the solvent flux. Furthermore, the correlation of the solvent flux with the gas solubility in the feed mixture is strongly non-linear. Therefore, gas solubility is recommended to be critically evaluated when conducting OSN experiments, specifically considering the final application. In that context, the permeation of dissolved gas has to be actively accounted for in OSN experiments for gas–liquid systems.

Leaf-veins-inspired nickel phosphate nanotubes-reduced graphene oxide composite membranes for ultrafast organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes provide extraordinary opportunities for environment friendly and cost-competitive solvent recovery in petrochemical and pharmaceutical purifications. Currently, membranes that based on two-dimensional (2D) materials are extremely attractive in ultrafast molecular separations owing to the atomic thickness and remarkable physicochemical properties of the 2D nanosheets. Inspired by the structures and functions of vessel element that transport water in leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) ultrathin laminar membrane is successfully prepared for ultrafast organic solvent nanofiltration. The in-situ synthetic NPTs can not only contribute to the size-dependent ultrafast molecular separation of the rGO membrane by providing additional molecular transport pathways as well as enlarging the interlayer space of the rGO layer, but also enhance the stability of the resultant membrane. The optimum membrane exhibits a methanol permeance of 670 L m −2 h −1 bar −1 and a high rejection toward molecules greater than 2 nm (MWCO: 650 Da). More importantly, the NPTs-rGO membrane shows promising anti-swelling property under OSN operating conditions. Inspired by leaf veins, this strategy provides insight into designing high-performance lamellar membranes with tubular-channel network, which may promote the fabrication and application of lamellar membranes in OSN. • Inspired by leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) composite was applied to develop organic solvent nanofiltration (OSN) membrane. • The OSN performance of the resultant membrane was markedly improved. • The NPTs in the membrane could create tubular transport pathways for solvent. • The resultant NPTs-rGO membrane has superior anti-swelling stability and mechanical strength.

TFC organic solvent nanofiltration membrane fabricated by a novel HDPE membrane support covered by manganese dioxide /tannic acid-Fe3+layers

BackgroundIt is of great importance to select an ultrafiltration (UF) support with outstanding solvent stability to fabricate thin film composite (TFC) organic solvent nanofiltration (OSN) membranes. MethodsHigh density polyethylene (HDPE)-polystyrene (PS)-styrene-ethylene-butylene-styrene (SEBS) blends were prepared through the incorporation of different SEBS weight percentages. Next, HDPE membranes were made via extracting the dispersed phase from the HDPE/PS/SEBS blends using THF. Then, the membrane with the optimum properties was selected as the support for preparing the TFC membranes. Accordingly, the support was first contacted with KMnO4 solution, by which MnO2 nanoparticles (NPs) were generated on the support surface. The membrane surface was then contacted with tannic acid (TA) and FeCl3 aqueous solutions consecutively to form a uniform TA-Fe3+ layer. Eventually, the PA layer was formed on the membrane surface through contacting with m-phenylenediamine aqueous solution and trimesoyl chloride/n-hexane solution consecutively. Significant FindingsThe TFC membrane exhibited extraordinary dyes rejection and good methanol permeance in OSN applications. Moreover, DMF activation process was conducted on the TFC membrane, after which both the dye rejection performance and methanol permeance were enhanced. Moreover, it is worth pointing out that the membrane provided an excellent solvent stability after dipping in DMF after 100 days.