Ultrahigh Permeability Research Articles

Low-pressure highly permeable polyester loose nanofiltration membranes tailored by natural carbohydrates for effective dye/salt fractionation

With the continuous pressure of water contamination caused by textile industry, loose nanofiltration (LNF) membranes prepared by green materials with an extraordinary water permeability are highly desirable for the recovery and purification of dyes and salts. In this work, low-pressure LNF membranes with ultrahigh permeability were fabricated via one-step interfacial polymerization (IP), in which inexpensive natural carbohydrate-derived sugars with large size and low reactivity were utilized as aqueous monomers to design selective layer. A systematic characterization by chemical analysis and optical microscopy demonstrated that the formed polyester film features not only loosen the structure, but also results in a hydrophilic and negatively charged surface. The optimized sucrose-based membrane (Su0.6/TMC0.1) with an excellent water permeability of 52.4 LMH bar−1 was found to have a high rejection of dyes and a high transmission of salts. In addition, the sugar-based membrane manifested an excellent anti-fouling performance and long-term stability. Furthermore, the non-optimized Gl0.6/TMC0.1 and Ra0.6/TMC0.1 membranes also shown a high water permeability, while maintaining a competitive dye/salt separation performance, which confirmed the universal applicability of the membrane design principle. Therefore, the proposed new strategy for preparing next-generation LNF membranes can contribute towards the textile wastewater treatment.

Ultrahigh permeance metal coated porous graphene membranes with tunable gas selectivities

<h2>Summary</h2> Membranes play an important role in gas separation on account of their low cost, energy efficiency, and durability. Gas-separation membranes, however, are subject to permeability-selectivity trade-off, i.e., atomically thin 2D materials such as porous graphene can provide ultrahigh permeances in the range of ∼10⁵–10⁷ GPU but suffer from low gas selectivity. Here, we show a new concept to enhance the selectivity of graphene-based membranes by employing adsorptive separation for binary gas mixtures. The deposition of "microislands" of Pd and Ni on the porous double-layer graphene support allowed us to selectively target H₂ in He/H₂ and CO₂ in H₂/CO₂ mixtures, respectively, thus enabling efficient separation of He and also leading to the highest H₂/CO₂ separation factor of 26 within the ∼10⁵ GPU permeance range. Moreover, the selective targeting of individual gases in a membrane setting through adsorptive separation at room temperature can be a promising alternative for economical gas separation.

Ultrahigh permeance metal coated porous graphene membranes with tunable gas selectivities

Ultrahigh permeance metal coated porous graphene membranes with tunable gas selectivities

One-Step Fabrication of a Micro/Nanosphere-Coordinated Dual Stimulus-Responsive Nanofibrous Membrane for Intelligent Antifouling and Ultrahigh Permeability of Viscous Water-in-Oil Emulsions.

Membrane fouling is a major challenge for long-term oil/water separation. The incomplete degradation of organic pollutants or membrane damage exists in the common methods of membrane regeneration. Herein, a dual-responsive nanofibrous membrane with high water-in-oil emulsion separation efficiency and smart cleaning properties is reported, which shows complete restoration of its original separation performance. The pH-responsive and upper critical solution temperature (UCST)-type thermoresponsive nanofibrous membrane with a micro/nanosphere structure was developed via a one-step-blending electrospinning strategy. The membrane displays high hydrophobicity/oleophilicity at pH 7 and 25 °C and hydrophilicity/oleophobicity at pH 3 and 55 °C. As a result, it exhibits an ultrahigh permeability of 60528.76 L m-2 h-1 bar-1 and a separation efficiency of 99.5% for water-in-D5 emulsions at room temperature (25 °C). Moreover, the contaminated membranes could be easily reclaimed by being rinsed with warm acidic water (pH 3 and 55 °C). The membrane maintained high separation performance after being used for multiple cycles, indicating its scalable application for purifying emulsified oil. This study provides a facial method of constructing membranes with multiscale hierarchical structures and a new idea for the design of recyclable oil/water separation membranes.

Multifunctional strain-controlled graphdiyne membrane for gas separation: a theoretical study

ABSTRACT Graphdiyne (GDY) membrane with intrinsic pore has potential for gas separation. Here we report a multistage gas separation of H2/CO2/N2/CH4 gas mixture through graphdiyne by applying tensile strain using molecular dynamics simulation. The results indicate that gas permeability is remarkably enhanced through tensile strain. H2 molecules have always been able to penetrate GDY membrane, while all CH4 molecules are blocked during the progress of tensile strain up to ultimate strain. An ultrahigh H2 permeance of ∼106 GPU (gas permeation unit) and H2 selectivity towards CO2/N2/CH4 was obtained, which is larger than the acceptable value in industrial applications. As the tensile strain is between 7.5% and 10% (ϵx )–15%(ϵy ), the membrane adopted in this work can be utilised for separating CO2 from CO2/N2/CH4 mixture. When the strain level is beyond 10% (ϵx )–15% (ϵy ), the strained GDY can be served as a CH4 upgrading membrane. The ultrahigh gas permeance is ascribed to the ultrathin membrane and high-density pore, and the size sieving effect of GDY membrane with small pores is responsible for the excellent gas selectivity. The results suggest that these two-dimensional membranes with intrinsic pores could serve as the ideal multifunctional size-selective membrane for gas separation towards different separation requirements.

Highly Permeable Polyamide Nanofiltration Membrane Mediated by an Upscalable Wet-Laid EVOH Nanofibrous Scaffold.

For energy-saving purposes, the pursuit of ultrahigh permeance nanofiltration membranes without sacrificing selectivity is never-ending in desalination, wastewater treatment, and industrial product separation. Herein, we reported a novel facile route to engineer a highly porous and superhydrophilic nanofibrous substrate to mediate the interfacial polymerization between trimesoyl chloride and piperazine, generating an ultrathin PA active layer (∼13 nm) with a hierarchical crumpled surface. The wet laying process and subsequent plasma treatment endowed a rougher and more hydrophilic surface for ethylene vinyl alcohol copolymer (EVOH) nanofibers in the thin compact nanofibrous scaffold (∼9 μm) with a mean pore size of 210 nm, radically different from the nanofibrous membrane by other methods. Nanofibrous scaffold with these features provide abundant thin-thick alternative continuous water layers between nanofibers and organic phase, facilitating the formation of the abovementioned PA layer. As a result, an ultrahigh permeance of 42.25 L·m-2 h-1 bar-1 and a reasonably high rejection of 95.97% to 1000 ppm Na2SO4 feed solution were obtained, superior to most state-of-the-art NF membranes reported so far. Our work provides an easy and scalable method to fabricate advanced PA NF membranes with outstanding performance, highlighting its great potential in liquid separation.

Amidoxime-functionalized polymer of intrinsic microporosity (AOPIM-1)-based thin film composite membranes with ultrahigh permeance for organic solvent nanofiltration

Advanced organic solvent nanofiltration (OSN) membranes with high permeance and stability are highly needed in petrochemical and pharmaceutical industries. Recently, polymers of intrinsic microporosity (PIMs) have attracted significant attention for the development of advanced membranes, because of their high porosity and solution processability. In this study, a thin film composite membrane based on an amidoxime-functionalized PIM (AOPIM-1) was prepared by spin coating followed by solvent activation. The activation approach could dramatically improve the solvent permeance of the membrane without compromising its rejection performance. The changes in porosity of the AOPIM-1 layer before and after activation were confirmed by positron annihilation Doppler spectroscopy. The optimum membrane exhibited an impressively high ethanol permeance of 15.5 L m−2 h−1 bar−1, nearly one orders of magnitude higher than that of Starmem240 (a commercial polyimide-based OSN membrane) with a comparable rejection of Rose Bengal (MW 1017 Da). In addition, the present membrane exhibited outstanding stability in polar solvents and a remarkably high rejection of active pharmaceutical ingredients (vitamin B12) from ethanol. This work could provide a new avenue for developing highly permeable OSN membranes and is expected to stimulate the use of PIM membranes in OSN applications.

A facile and green route to fabricate fiber-reinforced membrane for removing oil from water and extracting water under slick oil

Except the good separation performance, the membranes used for oil-water mixture separation should be fabricated with as little wastewater produced as possible. Thus, we proposed a green tactic--water vapor induced phase inversion to prepare the high-strength and superhydrophilic/underwater superoleophobic nonwoven fabric-based cotton/PA6/PAN membranes which is based on the polymer/solvent/nonsolvent ternary system analysis. Differing from adding additives in polymer solution or coagulation bath, above proposed strategy has an “subtractive effect” with the advantages of constructing three-dimensional porous structure and greatly reducing the organic wastewater produced during preparation process. Moreover, the obtained cotton/PA6/PAN membranes exhibited unexpected performances for separating oil-in-water emulsions. An ultrahigh permeation flux of up to 478,000 L m−2 h−1 bar−1 with a separation efficiency of > 99.9% was obtained under the driving pressure of 1.6 KPa, which was one order of magnitude higher than the conventional separation membranes with similar properties. In addition, it is surprising that the cotton/PA6/PAN membranes can also extract water from the slick oil/water immiscible mixture. Therefore, it is expected that the cotton/PA6/PAN membranes can be used in practical oily wastewater purification.

Dynamically Tunable Ultrathin Protein Membranes for Controlled Molecular Separation.

Developing the ultrathin membranes for high-performance separation still faces the challenge of both high permeance and selectivity. Herein, a large-area protein membrane was fabricated by the interfacial self-assembly of bovine serum albumin (BSA) and surfactants at the oil/water interface of emulsions. Benefiting from the ultrathin thickness and unique protein-surrounded tortuous channels, the membrane displays ultrahigh permeation flux and selective sieving capability for various molecules ranging from small dye molecules to proteins based on a dual filtration mechanism. More importantly, the rejection precision can also be reversibly regulated by the folding/unfolding transition of proteins to control the effective pore size of transport channels, even under a pressure-driven condition. This dynamically tunable ultrathin protein membrane combines the advantages of high permeance, selectivity, controllability, recyclability, and mechanical stability, which may create new opportunities for advanced applications in extended fields.

Durable and chemical resistant ultra-permeable nanofiltration membrane for the separation of textile wastewater

It is highly challenging to prepare durable and chemical resistant ultra-permeable membranes that can quickly separate small organic molecules like dye or inorganic salt in the complex textile wastewater industry. Here, side-chain sulfonated poly(ether ether ketone) (SPEEK) was synthesized and prepared the poly(ether ether ketone) (PEEK) - SPEEK nanofiltration (NF) membrane by a simple dipping coating and heat treatment. Single component filtration tests of the optimized membrane showed ultrahigh pure water flux (126 Lm−2 h−1 bar−1) and relatively low NaCl rejection (6.7%). Moreover, the negatively charged membrane exhibited excellent rejection of 98.8% toward Congo red (CR). The pure water flux was about 9 folds than that of commercial NF270 with comparable solutes rejection. The separation tests of CR and NaCl mixed solution at optimized conditions exhibited ultra-high permeation flux (34 Lm−2 h−1 bar−1), satisfactory dye (98.8%)/salt (< 10%) rejection and the separation performance remained stable after 10 cycles. Finally, the contaminated membrane was washed with ethanol, the permeation flux and the CR rejection remained constant after several cycles, while the commercial NF1 membrane exhibited serious swelling only within one cycle. The prepared membrane exhibited good organic solvents resistance and antifouling properties. Thus, this work confirmed the PEEK-SPEEK NF membrane showed great potential in the sustainable treatment of textile wastewater.

Positively charged ultrafiltration membranes fabricated via graft polymerization combined with crosslinking and branching for textile wastewater treatment

2-methacryloyloxy ethyl trimethylammonium chloride (DMC) was successfully grafted with 2-hydroxyethyl methacrylate (HEMA) as branching agent and N, N'-methylenebisacrylamide (MBAA) as crosslinker onto the surface of hydrolyzed polyacrylonitrile (HPAN) ultrafiltration membrane with high density via ceric ion (Ce4+)-induced graft polymerization. The successful graft polymerizations were confirmed by characterization of attenuated total reflectance spectrophotometer, X-ray photoelectron spectroscopy, scanning electron microscope and atomic-force microscopy. The obtained membranes showed surface positive charges and favorable hydrophilicity, which resulted in an ultrahigh permeability, distinguished rejection for positively charged dyes (>99%) and almost no retention for divalent salts (<4%), as well as excellent stability in multiple cycles of filtration. This work provided an efficient and facile approach to tailor the structure and properties of ultrafiltration membranes.

Second interfacial polymerization of thin‐film composite hollow fibers with amine‐cyclodextrins for pervaporation dehydration

AbstractHigh performance thin‐film composite (TFC) hollow fiber membranes have been developed for pervaporation dehydration by second interfacial polymerization (SIP) modification with three kinds of amine‐functionalized β‐cyclodextrin (amine‐CDs), which were synthesized by modifying β‐CD with ammonia, ethylenediamine (EDA), and tris(2‐aminoethyl)amine, respectively. The chemical properties of amine‐CDs and SIP‐modified TFC membranes were characterized by various techniques. The effects of amine‐CD type and SIP parameters (pH or concentration of CD‐EDA solution) were studied systematically to acquire the optimized selective layer of TFC membranes for ethanol dehydration. Among all SIP‐modified TFC membranes, the one with SIP by 2 wt% CD‐EDA aqueous solution (pH = 2) exhibited the most outstanding separation performance with a ultrahigh permeation flux (3,018.0 ± 12.0 g/m2 hr) and permeate concentration (98.7 ± 0.2 wt% water) at 50°C (equivalent to separation factor of 415), contributed by the effectively incorporated CD with rich hydrophilic functional groups and intrinsic nanocavities facilitating the passage of water molecules.

Graphene oxide membranes with stable porous structure for ultrafast water transport.

The robustness of carbon nanomaterials and their potential for ultrahigh permeability has drawn substantial interest for separation processes. However, graphene oxide membranes (GOms) have demonstrated limited viability due to instabilities in their microstructure that lead to failure under cross-flow conditions and applied hydraulic pressure. Here we present a highly stable and ultrapermeable zeolitic imidazolate framework-8 (ZIF-8)-nanocrystal-hybridized GOm that is prepared by ice templating and subsequent in situ crystallization of ZIF-8 at the nanosheet edges. The selective growth of ZIF-8 in the microporous defects enlarges the interlayer spacings while also imparting mechanical integrity to the laminate framework, thus producing a stable microstructure capable of maintaining a water permeability of 60 l m-2 h-1 bar-1 (30-fold higher than GOm) for 180 h. Furthermore, the mitigation of microporous defects via ZIF-8 growth increased the permselectivity of methyl blue molecules sixfold. Low-field nuclear magnetic resonance was employed to characterize the porous structure of our membranes and confirm the tailored growth of ZIF-8. Our technique for tuning the membrane microstructure opens opportunities for developing next-generation nanofiltration membranes.

Trilayer Interlinked Graphene Oxide Membrane for Wearable Hemodialyzer.

2D nanomaterials have long been considered for development of high permeability membranes. However, current processes have yet to yield a viable membrane for practical use due to the lack of scalability and substantial performance improvements over existing membranes. Herein, an ultrathin graphene oxide (GO) membrane with a permeability of 1562 mL h-1 mmHg-1 m-2, two orders of magnitude higher than the existing nanofiltration membranes, and a tight molecular weight cut-off is presented. To build such a membrane, a new process involving self-assembly and optimization of GO nanoplatelet physicochemical properties is developed. The process produces a highly organized mosaic of nanoplatelets enabling ultra-high permeability and selectivity. An adjustable molecular interlinker between the layers enables absolute nanometer-scale size cut-offs. These characteristics promise significant improvements to many nanoparticle and biological separation applications. In this work, the performance of the membrane in blood dialysis scenarios is evaluated. Urea and cytochrome-c sieving coefficients of 0.5 and 0.4 are achieved while retaining 99% of albumin. Hemolysis, complement activation, and coagulation studies exhibit a performance on par or superior to the existing dialysis membrane materials.

Engineering Janus CNTs/OCS composite membrane at air/water interface for excellent dye molecules screening

• A Janus composite membrane has been fabricated through interfacial self-assembled. • The CNTs side can inhibit the dyes accumulation and concentration polarization. • The interpenetrating network can weaken the Laplace pressure from the CNTs side. • The permeance has far exceeded most of the separation membranes reported up date. Two-dimensional (2D) membrane with ultrahigh permeability and precise sieving performance is highly desired. Herein, we have constructed a Janus composite membrane, which is integrated with carbon nanotubes (CNTs) and oxidized carbon spheres (OCS) modified with polyetherimide (PEI), through an interfacial self-assembly process. The designed Janus CNTs/OCS@PEI composite membrane has asymmetric micromorphology and wettability. The hydrophobic side is functioned as an active layer to inhibit concentration polarization during separation process. The superhydrophilic side can allow partial CNTs to stretch into its interior and form an interpenetrating network, which can weaken the Laplace pressure arising from the hydrophobic side. Hence, this membrane has the ability to reject various dye molecules, such as congo red (permeance flux of 3110.2 ± 285 L m −2 h −1 bar −1 and efficiency about 98.8%), which has transcended the majority of the separation membranes previously reported. Furthermore, this membrane can withstand physical damage and chemical corrosion that has presented stable rejection performance for dye molecules. This intriguing work would open the door to developing novel Janus materials to satisfy the water resources requirements of real-world applications.

Construction of graphene oxide membrane through non-covalent cross-linking by sulfonated cyclodextrin for ultra-permeable butanol dehydration

Two-dimensional (2D) lamellar graphene oxide (GO) membranes represent promising porous materials in alcohol dehydration. The separation performance can be manipulated by the physicochemical properties of interlayer channels. The relatively low flux and poor stability of GO-based membranes in aqueous environment are the major drawbacks. Herein, we intercalated a supramolecular compound, sulfobutyl-β-cyclodextrin (SCD), into the interlayer pores/channels of GO membranes. The sulfonic acid groups on SCD molecules are able to cross-link adjacent GO nanosheets throughnon-covalent interactions. The GO-SCD membranes possess excellent water affinity due to the presence of high hydrophilic sulfonic acid groups. For the n-butanol dehydration, the GO-SCD/PTFE membranes with well-defined interlayer pores exhibited ultrahigh permeation flux of 12955 g m-2 h-1 and separation factor of 1299 under 80 oC. The membranes remained stable in 144 h separation performance evaluation test and exhibited obviously enhanced thermal stability.

Vein-supported porous membranes with enhanced superhydrophilicity and mechanical strength for oil-water separation

Oil fouling is a major obstacle for the efficient and reliable oil-water separation of mesh-based membrane processes. Innovations in membrane materials and preparation processes are therefore needed to develop anti-oil-adhesion strategies. This study reports a series of vein-supported porous membranes (VPMs) fabricated by casting polyacrylonitrile (PAN) on veins through non-solvent induced phase separation, confirmed by FTIR, SEM and XRD characterizations, and applied as an effective oil-water separation membrane. Benefiting from the combination of tubular-like vein and hydrophilic PAN, the resultant VPM demonstrates a fine-tunable morphology and superhydrophilicity, extremely boosting underwater superoleophobicty, mechanical strength and superior performance for oil/water separation to various oily mixtures/emulsions, showing underwater oil contact angles over 157° and nearly zero underwater oil adhesion. In oil-water mixture separation process, a separation efficiency of > 99% and ultrahigh permeation flux of 9592 LMH can be achieved under gravity conditions using VPM-2 (casting with 2 wt% PAN). For oil-water emulsion separation, a highest flux of 3011 LMH and trace oil concentration <10 ppm in the filtrate was generated using VPM-9 (casting with 9 wt% PAN) under a low external pressure of 3 kPa. The VPM-2 membrane is further carried out a 40-h cycling separation, showing a constantly stable water flux of ~6000 LMH. The developed VPMs open a bright path to use biomaterials for design and fabrication of novel oil-water separation membrane.

Solid-Vapor Interface Engineered Covalent Organic Framework Membranes for Molecular Separation.

Covalent organic frameworks (COFs) with intrinsic, tunable, and uniform pores are potent building blocks for separation membranes, yet poor processing ability and long processing time remain grand challenges. Herein, we report an engineered solid-vapor interface to fabricate a highly crystalline two-dimensional COF membrane with a thickness of 120 nm in 9 h, which is 8 times faster than that in the reported literature. Due to the ultrathin nature and ordered pores, the membrane exhibited an ultrahigh permeance (water, ∼411 L m-2 h-1 bar-1 and acetonitrile, ∼583 L m-2 h-1 bar-1) and excellent rejection of dye molecules larger than 1.4 nm (>98%). The membrane exhibited long-term operation which confirmed its outstanding stability. Our solid-vapor interfacial polymerization method may evolve into a generic platform to fabricate COFs and other organic framework membranes.

Ultrathin Cellulose Voronoi-Nanonet Membranes Enable High-Flux and Energy-Saving Water Purification.

Creating a desirable porous membrane with high-flux and energy-saving properties for the purification of water containing submicron-sized contaminants, especially pathogenic microbes, is of great significance, yet a great challenge. Herein, we demonstrate a facile methodology to construct an innovative membrane with continuous cellulose Voronoi-nanonet structures via nonsolvent-induced phase separation. This approach enables cellulose Voronoi nanonets to tightly weld with electrospun nanofibrous substrates by controlling the solvent-nonsolvent mutual diffusion process. The resultant membranes exhibit integrated properties of small pore size (0.23 μm), high porosity (90.7%), good interconnectivity, and ultrathin thickness (∼600 nm, 2 orders of magnitude thinner than the conventional microfiltration membrane). As a result, the prepared membranes can effectively intercept submicron particles (∼0.3 μm) with robust rejection efficiency (>99.80%) and ultrahigh permeation flux (maximum of 8834 L m-2 h-1) under an extremely low driving pressure (≤20 kPa). More importantly, prominent bacterial rejection efficiency with a log reduction value (LRV) of 8.0 (overcoming the previous limitation of LRV <7) and outstanding antifouling function are also achieved for the membranes. The successful fabrication of such a versatile membrane may provide new insights into the development of next-generation high-performance separation materials for various applications.

Phosphonium Modification Leads to Ultrapermeable Antibacterial Polyamide Composite Membranes with Unreduced Thickness.

Water transport rate in network membranes is inversely correlated to thickness, thus superior permeance is achievable with ultrathin membranes prepared by complicated methods circumventing nanofilm weakness and defects. Conferring ultrahigh permeance to easily prepared thicker membranes remains challenging. Here, a tetrakis(hydroxymethyl) phosphonium chloride (THPC) monomer is discovered that enables straightforward modification of polyamide composite membranes. Water permeance of the modified membrane is ≈6 times improved, give rising to permeability (permeance × thickness) one magnitude higher than state-of-the-art polymer nanofiltration membranes. Meanwhile, the membrane exhibits good rejection (RNa2SO4 = 98%) and antibacterial properties under crossflow conditions. THPC modification not only improves membrane hydrophilicity, but also creates additional angstrom-scale channels in polyamide membranes for unimpeded transport of water. This unique mechanism provides a paradigm shift in facile preparation of ultrapermeable membranes with unreduced thickness for clean water and desalination.