Selective Layer Thickness Research Articles

Regulating interfacial polymerization via constructed 2D metal-organic framework interlayers for fabricating nanofiltration membranes with enhanced performance

Interlayered thin-film nanocomposite (TFN) membranes have been proven to achieve enhanced water permeance for desalination applications, while those lacking effective control over the construction of interlayers were prone to unsatisfactory permselectivity. In this study, a high-performance TFN membrane was constructed via interfacial polymerization on a Metal-Organic Frameworks (MOFs)-interlayered polyethersulfone substrate. Regulating the thickness of the MOFs (copper-tetrakis(4-carboxyphenyl) porphyrin, Cu-TCPP) interlayer could effectively tailor the structural parameters (effective filtration area, selective layer thickness, and pore size) and physicochemical properties of the membrane. A resistance-in-series model was applied to analyze the hydraulic resistance distribution and the specific value of the intrinsic solution permeability of each layer of the TFN membranes. Results showed that the interlayer with a proper deposition density of MOFs nanosheets could simultaneously increase the cross-linking degree by adsorbing the PIP monomers and reduce the thickness of the PA layer to enhance the intrinsic permeability. The optimal membrane with a thin PA film (20 nm) displayed an excellent water permeance of 32.7 L·m−2·h−1·bar−1 and an ultrahigh NaCl/Na2SO4 selectivity of 271.7. Moreover, the membrane demonstrated remarkable stability during 120 h filtration. This work provides a promising strategy for fabricating TFN membranes with higher selectivity and enhanced comprehensive performance.

Ultrathin-film composite (uTFC) membranes based on amorphous perfluoropolymers for liquid separations

Thin-film composite membranes based on ∼100 nm cross-linked polyamides (PAs) are state-of-the-art membranes for liquid separations such as desalination. However, the PA layer shows poor antifouling properties and instability in chlorine solutions. Herein, we show for the first time that glassy amorphous perfluoropolymers (PFPs, such as Teflon AF and Hyflon AD) can be fabricated into ultrathin film composite (uTFC) membranes with a selective layer of <20 nm for desalination. Increasing the polymer concentration in the coating solutions from 0.05 mass% to 0.3 mass% increases the selective layer thickness from 9 to 25 nm. When Teflon AF2400 was fabricated into 16-nm selective layers on various porous supports, the water permeance decreases from 0.37 LMH/bar for PES10k to 0.07 LMH/bar for PES1k, and the Na2SO4 rejection increases from 86.6% to 95.2%. While the water permeance is lower than the commercial PA-based NF membranes, the rejection in these PFP-based membranes is comparable. The effect of the porous support on the water permeance can be ascribed to the geometric restriction and satisfactorily described using an empirical model. Interestingly, the membranes also exhibit good Na+/Li+ separation performance and stable performance for organic solvent nanofiltration, showcasing the versatility of the PFP-based uTFC membranes for various liquid separations.

Characterizing phenol mass transfer coefficients of composite extractive membranes with different PDMS thicknesses by electrochemical impedance spectroscopy

The extractive membrane is typically composed of a selective layer prepared by polydimethysiloxane (PDMS) and a highly porous substrate. A thin and defect-free PDMS selective layer is critical for the extractive membrane. The extractive membrane performance is predominantly evaluated by its organic mass transfer efficiency, which needs to conduct a time-consuming aqueous-aqueous extractive test. Herein, we proposed a novel, rapid, and sensitive method to characterize the organic mass transfer efficiency of extractive membranes. In this paper, PDMS-coated nanofibrous composite membranes with controllable thickness were prepared by electrospinning. The mass transfer efficiency of as-developed membranes was characterized by electrochemical impedance spectroscopy (EIS). A straightforward relationship between the membrane impedance, the thickness of selective layer and the mass transfer rate of phenol was obtained. A theoretical equation suggesting a linear relationship between the transfer efficiency and membrane resistance was proposed, which was confirmed by the experimental data. Moreover, aniline, as another contaminant was selected to validate the effectiveness and universality of this method. Therefore, EIS can be promisingly utilized for valid predication of the organic mass transfer performances of extractive membranes without time-consuming running of extraction experiments.

Ultra-permeable intercalated metal-induced microporous polymer nano-dots rooted smart membrane for environmental remediation

Energy efficient CO2 separation using ultrathin smart membranes must possess efficient permeation performance, higher surface area and hydrostatic stability at industrially relevant high pressures. However, ultrathin membranes are susceptible to lower surface area, plasticization and swelling which reduces the performance at higher pressure under humidified conditions. This paper evaluates the routes for the potential intercalated effect of metal-induced microporous polymers (MMPs) dots into a cellulose-based polymer matrix to enhance promising properties, including the surface area, CO2 permeation performance, plasticization resistance and hydrostatic stability of ultrathin smart membranes at high pressure. The MMP dots-rooted smart membrane demonstrated 55 nm thickness of ultrathin selective layer with a higher surface of 220 cm2. The enhancement of CO2 permeability from 14.1 to 108.9 Barrer and CO2/CH4 ideal selectivity from 11.8 to 31.1 was observed due to the integration of MMP dots into the cellulose polymer. This result could be due to enhancement of nitrogen lone pair electron interactions with CO2 followed by amines group which improved the CO2 adsorption on the membrane surface. The MMP dots-rooted membrane demonstrated plasticization resistance up to 26 bar pressure, as compared to a pristine polymer membrane which is a percentage increase of 160% under humidified conditions. The resulting ultrathin smart membrane exhibited stable performance for a duration of 200 h under humidified conditions which confirmed the higher hydrostatic stability of the membrane. These findings confirmed the potential of MMP dots materials for the development of an industrial scale CO2 separation process using intercalated membranes.

Modification of Thin Film Composite PVA/PAN Membranes for Pervaporation Using Aluminosilicate Nanoparticles.

The effect of the modification of the polyvinyl alcohol (PVA) selective layer of thin film composite (TFC) membranes by aluminosilicate (Al2O3·SiO2) nanoparticles on the structure and pervaporation performance was studied. For the first time, PVA-Al2O3·SiO2/polyacrylonitrile (PAN) thin film nanocomposite (TFN) membranes for pervaporation separation of ethanol/water mixture were developed via the formation of the selective layer in dynamic mode. Selective layers of PVA/PAN and PVA-Al2O3·SiO2/PAN membranes were formed via filtration of PVA aqueous solutions or PVA-Al2O3·SiO2 aqueous dispersions through the ultrafiltration PAN membrane for 10 min at 0.3 MPa in dead-end mode. Average particle size and zeta potential of aluminosilicate nanoparticles in PVA aqueous solution were analyzed using the dynamic light scattering technique. Structure and surface properties of membranes were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle measurements. Membrane performance was investigated in pervaporation dehydration of ethanol/water mixtures in the broad concentration range. It was found that flux of TFN membranes decreased with addition of Al2O3·SiO2 nanoparticles into the selective layer due to the increase in selective layer thickness. However, ethanol/water separation factor of TFN membranes was found to be significantly higher compared to the reference TFC membrane in the whole range of studied ethanol/water feed mixtures with different concentrations, which is attributed to the increase in membrane hydrophilicity. It was found that developed PVA-Al2O3·SiO2/PAN TFN membranes were more stable in the dehydration of ethanol in the whole range of investigated concentrations as well as at different temperatures of the feed mixtures (25 °C, 35 °C, 50 °C) compared to the reference membrane which is due to the additional cross-linking of the selective layer by formation hydrogen and donor-acceptor bonds between aluminosilicate nanoparticles and PVA macromolecules.

Development of high‐flux aciduric ultra‐thin nanofibrous pervaporation composite membrane for acetic acid dehydration

AbstractAcetic acid is an essential intermediate chemical in industry. Traditional inorganic membrane cannot meet the demand of high‐efficient dehydration and polymeric membrane is restricted by its low organic solution resistance. In this work, a novel aciduric pervaporation composite membrane was successfully generated by fabricating an ultrathin polysulfonamide (PSA) layer on the polyacrylonitrile (PAN) nanofibrous substrate via interfacial polymerization (IP) method. Through the optimization of fabrication process including selecting the suitable structure of diamine (taking three types aliphatic amines as candidates), optimizing the concentration of two phase solutions, the resultant thin‐film nanofibrous composite (TFNC) membrane was fabricated by using aliphatic amine triethylenetetramine (TETA: 3.0 wt%) and 1, 3‐benzenedisulfonyl chloride (BDSC: 1.0 wt%) as IP monomers and the network structure with suitable sieving size was constructed. The ultrathin aciduric PSA selective layer (thickness: 104 ± 15 nm) endowed the TFNC membrane with excellent separation efficiency. For dehydrating 70 wt% acetic acid aqueous solution at 60°C, PSA‐3.0‐1.0/PAN TFNC membrane exhibited competitive separation efficiency and great acid stability. It possessed extremely high permeate flux (15,321 g/m2 h) with stable separation factor (109). For long‐term acid dehydration evaluation, PSA/PAN membrane showed great stability during 7 days pervaporation. This work took advantage of traditional IP method for designing a novel pervaporation membrane with aciduric chemical structure, suggested an effective and facile approach to develop novel pervaporation membranes for harsh environment separation.

Ultra-pure hydrogen production via ammonia decomposition in a catalytic membrane reactor

In this work two alternatives are presented for increasing the purity of hydrogen produced in a membrane reactor for ammonia decomposition. It is experimentally demonstrated that either increasing the thickness of the membrane selective layer or using a small purification unit in the permeate of the membranes, ultra-pure hydrogen can be produced. Specifically, the results show that increasing the membrane thickness above 6 μm ultra-pure hydrogen can be obtained at pressures below 5 bar. A cheaper solution, however, consists in the use of an adsorption bed downstream the membrane reactor. In this way, ultra-pure hydrogen can be achieved with higher reactor pressures, lower temperatures and thinner membranes, which result in lower reactor costs. A possible process diagram is also reported showing that the regeneration of the adsorption bed can be done by exploiting the heat available in the system and thus introducing no additional heat sources.

Ultra-thin microporous membranes based on macrocyclic pillar[n]arene for efficient organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a green, environmentally friendly and sustainable separation technology. High-performance OSN membranes are expected to play a critical role in the field of chemical separation involving organic solvents. However, traditional OSN membranes suffer from the constraints on perm-selectivity. Herein, we introduced macrocyclic molecules with intrinsic angstrom-size cavity, pillar[n]arene (P[n]a, n = 5, 6), as a novel aqueous monomer to react with trimesoyl chloride (TMC) to prepare highly perm-selective thin-film composite (TFC) OSN membranes through interfacial polymerization. The prepared TFC-P[n]a membranes exhibit ultra-thin selective layer thickness of sub-10 nm and possess permanent intrinsic microporous structure, which endows the membrane with high perm-selectivity. Especially, the TFC-P[6]a membrane exhibits a high methanol permeance (8.10 L m−2 h−1 bar−1) and a low molecular weight cut-off (MWCO) of 300 g mol−1. In addition, the prepared TFC-P[n]a membranes exhibit molecule sieving function and could discriminate molecules with similar molecular weights but different shapes. Our work provides an insight of material design for the preparation of next-generation high-performance organic solvent nanofiltration membranes.

Hydrophobic Ag-Containing Polyoctylmethylsiloxane-Based Membranes for Ethylene/Ethane Separation in Gas-Liquid Membrane Contactor.

The application of gas-liquid membrane contactors for ethane-ethylene separation seems to offer a good alternative to conventional energy-intensive processes. This work aims to develop new hydrophobic composite membranes with active ethylene carriers and to demonstrate their potential for ethylene/ethane separation in gas-liquid membrane contactors. For the first time, hybrid membrane materials based on polyoctylmethylsiloxane (POMS) and silver tetrafluoroborate, with a Si:Ag ratio of 10:0.11 and 10:2.2, have been obtained. This technique allowed us to obtain POMS-based membranes with silver nanoparticles (8 nm), which are dispersed in the polymer matrix. The dispersion of silver in the POMS matrix is confirmed by the data IR-spectroscopy, wide-angle X-ray diffraction, and X-ray fluorescence analyses. These membranes combine the hydrophobicity of POMS and the selectivity of silver ions toward ethylene. It was shown that ethylene sorption at 600 mbar rises from 0.89 cm3(STP)/g to 3.212 cm3(STP)/g with an increase of Ag content in POMS from 0 to 9 wt%. Moreover, the membrane acquires an increased sorption affinity for ethylene. The ethylene/ethane sorption selectivity of POMS is 0.64; for the membrane with 9 wt% silver nanoparticles, the ethylene/ethane sorption selectivity was 2.46. Based on the hybrid material, POMS-Ag, composite membranes were developed on a polyvinylidene fluoride (PVDF) porous support, with a selective layer thickness of 5–10 µm. The transport properties of the membranes were studied by separating a binary mixture of ethylene/ethane at 20/80% vol. It has been shown that the addition of silver nanoparticles to the POMS matrix leads to a decrease in the ethylene permeability, but ethylene/ethane selectivity increases from 0.9 (POMS) to 1.3 (9 wt% Ag). It was noted that when the POMS-Ag membrane is exposed to the gas mixture flow for 3 h, the selectivity increases to 1.3 (0.5 wt% Ag) and 2.3 (9 wt% Ag) due to an increase in ethylene permeability. Testing of the obtained membranes in a gas-liquid contactor showed that the introduction of silver into the POMS matrix makes it possible to intensify the process of ethylene mass transfer by more than 1.5 times.

Development of dynamic PVA/PAN membranes for pervaporation: Correlation between kinetics of gel layer formation, preparation conditions, and separation performance

Thin film composite (TFC) membranes possessing polyvinyl alcohol (PVA) selective layer and polyacrylonitrile membrane-support were developed via dynamic mode technique based on concentration polarization phenomenon. The effect of the molecular weight cut-off (MWCO) of membrane-support, concentration of PVA solution and filtration mode on the gel layer formation was studied via the analysis of kinetic curves of flux and PVA rejection in ultrafiltration. The effects of concentrations of PVA, glutaraldehyde (GA) and hydrochloric acid (HA), filtration time, and transmembrane pressure (TMP) on the structure and pervaporation (PV) performance of TFC membranes for ethanol dehydration were investigated. It was found that an increase in PVA concentration, duration of filtration and TMP results in an increase in the TFC membrane selective layer thickness. It was shown that pervaporation permeate flux decreased when TFC membranes were prepared using higher PVA concentration and longer time of PVA filtration. The pervaporative permeate flux through TFC membranes passed through the maximum at TMP of 3 bar, then became practically stable for membranes prepared at TMP in the range of 4-8 bar. It was attributed to the formation of microdefects of the selective layer due to the compaction-relaxation behavior of membrane support during selective layer formation at elevated pressures. It was also shown that the dependence of PV separation factor on the duration of PVA solution filtration passes through the maximum which is consistent with the time of the stable gel-layer formation calculated from the kinetic curves. The found optimal conditions for preparation of TFC dynamic membranes were following: dead-end ultrafiltration mode, the component concentrations in the solution — 1.0 wt.% PVA, 0.06 wt.% GA, 0.5 wt.% HA, using the simultaneous application technique (SimAT) with the filtration time — 10 min and TMP — 3 bar.

Ultra-Highly permeable loose nanofiltration membrane containing PG/PEI/Fe3+ ternary coating for efficient dye/salt separation

Loose nanofiltration membrane (LNM) with high separation toward dye/salt and high permeability is a promising candidate for resource recovery of textile wastewater. In this study, to prepare a high permeable LNM, a ternary coating system containing a small polyphenol molecule named pyrogallol (PG), polyethylenimine (PEI) and Fe3+ ion was co-deposited on the hydrolyzed polyacrylonitrile substrate via regulating the competition reactions between coordination bond (COB) and covalent bond (CB). The membrane formation mechanism, morphology, surface properties, and separation performance of dye/salts were investigated by characterizations and filtration experiments. The characterization results indicated that the addition of Fe3+ limited the CB formation between PG and PEI via Michael addition and Schiff base reaction, due to its strong coordination ability toward PG and PEI via COB with –OH and –NH- groups, further reducing the selective layer thickness and improving the membrane permeance as a result. The content of PEI and Fe3+ in ternary coating solution obviously affected membrane morphology and hydrophilicity, thus influencing the permeance. More importantly, The LNM-5 exhibited an ultrahigh water permeability of 141.5 LHM·bar−1, high rejection of Congo Red (CR, 99.5%) and Alcian blue 8GX (ALBL, 99.7%) as well as high transmission of salts (98.8% for NaCl, 97.3% for Na2SO4, respectively.), which performed much better than many reported state-of-the-art LNMs prepared by different methods. Even under 60 g/L salt content, high rejection of CR (99.1%) and high pass of salts (98.8% for Na2SO4) could be still maintained. Furthermore, the LNM-5 had a superior antifouling performance and long-term stability during filtration (22 h) of dye/salt mixture. This work indicated that small polyphenol/PEI/Fe3+ trinity coating could be used as a promising alternative in practical applications, realizing excellent molecular separation towards sustainable textile wastewater remediation.

Modeling and optimization of metal-organic frameworks membranes for reverse osmosis with artificial neural networks

Metal-organic frameworks (MOFs) have recently attracted tremendous attention as membrane materials for desalination owing to their diversified structures, permselectivity, and tunable functionalities. However, the structure-performance relationship of MOF membranes still has not been elucidated. Herein, artificial neural networks (ANN) were developed to form prediction model of MOF thin film nanocomposite (TFN) membrane performances in reverse osmosis applications. Key parameters including MOF size, MOF pore diameter, MOF loading, selective layer thickness, salt concentration, and pressure were collected from literature to predict the water permeability and salt rejection. 5-fold cross-validation and hyperparameter tuning method were employed to acquire a better performing model. When the node structure was 6–9–9–8–2 with the learning rate of 0.001, the developed ANN model attained a remarkable prediction R2 of 90.62%. By introducing mean impact value algorithm into the model, the feature importance of each factor on the membrane performance was also calculated. Rather than the MOF loading and size, proper control of selective layer thickness and MOF pore diameter was key to breaking the permeability-selectivity tradeoff. Finally, ANN proved its ability to predict the membrane performance for water purification and further provide guidance for MOF-based membrane design, or even other TFN membrane design.

Gas separation performance and physical aging of tubular thin-film composite carbon molecular sieve membranes based on a polyimide of intrinsic microporosity precursor

We present a study on the fabrication of tubular thin-film composite CMS membranes based on an intrinsically microporous polyimide of intrinsic microporosity (PIM-PI), PIM-6FDA-OH. Besides the inherent structural similarity between the PIM-PI and CMS membranes (i.e. microporosity with pores <20 Å), the unique feature of the chosen precursor is its ability to undergo a thermal rearrangement (TR) reaction which constitutes an additional mechanism of microporosity evolution in addition to the pyrolysis process. By using Raman spectroscopy and in-situ thermal spectroscopic ellipsometry we tracked the structural TR- and pyrolysis-related evolution in CMS films as thin as 100 nm. Our study revealed a pronounced acceleration of the microstructure collapse (densification) due to physical aging that occurred in ultra-thin films. These, and our previous findings, suggest that excessive reductions in selective layer thickness in microporous amorphous materials, such as PIMs or CMS, may not be beneficial to obtaining highly efficient membranes. Instead, we have shown that excellent and stable separation properties could be achieved by PIM-PI-derived CMS membranes with thicker, ∼3 μm, selective layers (e.g. CO2, H2 permeances of >200 GPU, with CO2/CH4, CO2/N2, and O2/N2 selectivities of 43.0, 41.0, and 7.5, respectively) even after 3 months of aging.

Facile suppression of intensified plasticization in glassy polymer thin films towards scalable composite membranes for propylene/propane separation

Membrane-based propylene/propane (C3H6/C3H8) separation has the potential to significantly reduce the extremely high energy consumption in the conventional distillation process. However, no large-scale commercialization case currently exists despite decades of remarkable advancements in membrane materials. This challenge can potentially be attributed to a lack of understanding of the close relationship between material properties and membrane configurations, including confinement-driven transitions in polymer dynamics from the bulk to thin films (<1 μm). We first report design aspects of thin-film composite (TFC) membranes for C3H6/C3H8 separation based on a cost-effective, versatile, and scalable fabrication method. An unprecedented acceleration in C3 hydrocarbon-induced plasticization is observed in TFC membranes as the selective layer thickness decreases, causing anomalous gas transport properties and poor mixed-gas selectivities, which deviate from those of bulk membranes. To overcome this issue, a plasticization resistant (PR) layer is additionally coated onto the TFC membranes. Advanced thin-film characterization techniques, including quartz crystal microbalance (QCM) and nanomechanical analyses, demonstrate effective suppression of intensified plasticization in glassy polymer thin films by introducing a PR layer. Ultimately, the PR layer-coated TFC membranes exhibited excellent mixed-gas C3H6/C3H8 separation performances close to industrial requirements, which can be further extended to prepare large-area TFC membranes by roll-to-roll processes.

Spray-coated tough thin film composite membrane for pervaporation desalination

Water flux of pervaporation (PV) desalination membranes can be increased by reducing thickness of the selective layer and/or reducing the resistance of the support layer. However, low resistant support layer typically has large surface pores that requires a thick selective layer to avoid fracture. To solve this problem, we used poly(acrylic acid-co-2-acrylamido-2-methyl propane sulfonic acid) (P(AA-AMPS)) to crosslink PVA to improve the mechanical property of the coating layer. The PVA layer was deposited on to a highly porous PTFE substrate via spray-coating. By optimizing the spray-coating conditions, a thin and defect-free P(AA-AMPS) crosslinked PVA/PTFE composite membrane with a selective layer thickness of 1.1 μm was prepared. The water flux of the composite membrane reached to 256.6 ± 31.3 kg/(m2 h) at 75 °C with a NaCl rejection rate over 99.9% when desalinating a 3.5 wt.% NaCl solution. The membrane flux is higher than all reported PV desalination membranes.

New hydrophilic carbon molecular sieve membranes for bioethanol dehydration via pervaporation

Tubular supported carbon molecular sieve membranes (CMSMs) with high hydrophilicity and perm-selectivities for water suitable for ethanol dehydration were developed from a Novolac oligomer phenolic resin as precursor. Alpha alumina supported CMSMs resulted in 1.69 times higher surface roughness than zirconia supports. The higher surface roughness resulted in 48% higher selective layer thickness. According to pervaporation results, water permeance decreased by the increase in selective layer thickness and mole based selectivity of water- ethanol was enhanced. The oligomer with 3982 g/mol molecular weight enabled membrane to reach high selectivity with one-layer coating. Performance of the membranes are compared with literature data in terms of mole-based selectivity vs. water permeance. CMSMs could be a potential substitution for traditional ethanol dehydration methods with offering higher performance and as a result reducing the final price of bioethanol to be used as a sustainable energy source.

Scalable dual-layer PVDF loose nanofiltration hollow fiber membranes for treating textile wastewater

A dual-layer (DL) PVDF loose nanofiltration (NF) hollow fiber membrane (HFM) with desirable properties was designed via phase inversion process using a continuous online-coating device. By fine-tuning dope formulation and fiber formation, the PVDF coating layer with NF separation capabilities was formed on the shell side of porous matrix-reinforced hollow fiber support while making fiber continuously. The effects of several parameters (e.g., LiCl content, co-solvent ratio (i.e., DMAc:THF) and air-bath distance (evaporation time)) on structures and properties were investigated to manipulate membrane MWCO. It was found that the introduction of volatile co-solvent and the control of evaporation time helped to significantly reduce the PVDF selective layer's thickness. The structure along with performance of the HFM demonstrated the DL ultrafiltration (UF) HFM could be successfully converted into NF HFM only by adjusting the parameters in the production system. After optimizing both phase inversion parameters and coating conditions, the resultant loose NF HFM presented a low MWCO of 1530 Da and a high pure water flux (PWF) of 14.2 L·m−2·h−1·bar−1. Meanwhile, the HFM showed competitive dyes rejection (i.e., 99.9% for Rose bengal and Eriochrome black T, 96.5% for Methylene blue) and low NaCl rejection (3.2%). Furthermore, the prepared membrane also presented good stability and high flux recovery during a continuous NF process. This work provided a simple and economical strategy for engineering scalable loose NF HFM for dye purification.

Collagen Fibril-Assembled Skin-Simulated Membrane for Continuous Molecular Separation.

A skin-simulated thin-film-composite membrane was fabricated using a vacuum-assisted interfacial polymerization method. A negatively charged surface-selective layer on a polyacrylonitrile (PAN) substrate was cross-linked using trimesoyl chloride to form polyamide and polyester with a three-layer structure that was similar to skin. The loading of collagen fibrils assembled on the membrane surface was varied, and a selective layer was obtained, of which the thickness, morphology, and hydrophilicity can be manipulated. The optimal membrane decorated with 0.5 mg of collagen fibril had a selective layer thickness of around 130 nm with pure water permeability up to 84.7 LMH bar-1. Furthermore, the membrane exhibited impressive rejections toward dyes (Congo red with a molecular weight of 696.68 Da: 99.6%, reactive blue 19 with a molecular weight of 626.54 Da: 99.8%, and Coomassie blueG-250 with a molecular weight of 854.02 Da: 98.6%) while high permeations of Na2SO4 and NaCl were achieved. This facile strategy provides a useful guideline for constructing bionic membranes through biomaterials.

High-performance loose nanofiltration membrane prepared with assembly of covalently cross-linked polyethyleneimine-based polyelectrolytes for textile wastewater treatment

• High-flux loose NF membrane prepared by assembly of branched PEI and PEI-PO 3 Na. • Cross-linkable PEI and PEI-PO 3 Na enable the good stability of the membrane. • Chelatable phosphonate groups in PEI-PO 3 Na lower the membrane scaling tendency. • Membrane properties are optimizable by varying Mw of PEI-PO 3 Na. • Great potential for actual textile wastewater treatment is expected. Conventional nanofiltration membrane with high rejections to both dyes and inorganic salts are not suitable for the treatment of the textile wastewater. Herein, novel loose nanofiltration membranes were fabricated by the assembly of polyethyleneimine (PEI) and phosphorylated PEI (PEI-PO 3 Na) coupled with glutaraldehyde crosslinking. The PEI-based polyelectrolytes with branched structures and plentiful amine crosslinking sites enabled the formation of a highly permeable and robust selective layer. Meanwhile, the introduced phosphonate groups endowed the membrane with anti-fouling and anti-scaling properties owing to their surface hydrophilicity and chelation ability. By varying the molecular weight of PEI-PO 3 Na, the surface properties, pore size, and selective layer thickness and corresponding performances of the resultant PEI-PO 3 Na/PEI membranes can be successfully manipulated. The PEI-PO 3 Na 10 k/PEI membrane showed a high permeability (24.2 LMH/bar), high Victoria blue BO (99.5%) but low NaCl rejection (10.1%), demonstrating the best dye/salt fractionation performance. While PEI-PO 3 Na 70 k/PEI membrane exhibited the highest chroma and chemical oxygen demand (COD) removal rates, and the best anti-fouling ability for the textile wastewater treatment. The PEI-PO 3 Na/PEI membrane also exhibited good stability in various pH, and relatively low scaling propensity. This work provides a facile and convenient method for fabricating high-performance loose NF membranes for the practical textile wastewater treatment.

Pressure effect during the formation of a selective layer on the structure and performance of dynamic composite membranes for pervaporation

Composite membranes for pervaporation were prepared by forming a selective layer based on cross-linked polyvinyl alcohol (PVA) on the porous membrane-substrate surface in the dynamic mode (via PVA solution ultrafiltration). It was found that the pressure growth results in increasing the thickness of the composite membrane selective layer. Composite membrane contact angle, flux, water content in permeate in ethanol/water (mass ratio 90/10) pervaporation were revealed to have maximum values at 3–4 atm depending on the PVA concentration in the feed solution. It was shown that the revealed dependence of the contact angle, selectivity, and permeability on the pressure of the selective layer formation is due to the compaction of the polymer matrix-substrate under the action of the transmembrane pressure and its relaxation after pressure release. When using elevated pressures (more than 3–4 atm), the relaxation of the polymer matrix causes the microdefect to form as a result of deformation of the selective layer.