High Permeation Flux Research Articles

Non-metallic cation and anion co-doped perovskite oxide ceramic membranes for high-efficiency oxygen permeation at low temperatures

Insufficient structural stability and limited lattice oxygen mobility at low temperatures seriously limit the application of perovskite-type oxides in mixed ionic-electronic conducting oxygen-permeable membranes. Engineering the crystal structure and oxygen vacancies by ion doping is an effective strategy to enhance both structural stability and lattice oxygen mobility. Different from conventional metal ion doping, we report that the co-doping of the classical SrCoO3-δ by the non-metallic cation P5+ and the anion Cl− stabilizes the cubic perovskite structure and allows low temperature oxygen permeation due to improved lattice oxygen mobility. In detail, P doped at the Co site transforms the crystal structure from the hexagonal phase to the cubic phase, and Cl doped at the oxygen site weakens the metal-oxygen bond, which significantly enhances the lattice oxygen mobility. Optimal doping concentrations were found to be SrCo0.95P0.05O3-δCl0.05 (SCP5Cl5). Furthermore, by constructing an asymmetric membrane with a sandwich structure, the oxygen permeation flux of the SCP5Cl5 ceramic membrane was up to 1.10 mL min−1 cm−2 at 873 K, which provides an effective strategy for developing oxygen-permeable membranes with high permeation flux at low temperatures.

Carbon-Doped TiO2 Nanofiltration Membranes Prepared by Interfacial Reaction of Glycerol with TiCl4 Vapor.

In the pursuit of developing advanced nanofiltration membranes with high permeation flux for organic solvents, a TiO2 nanofilm was synthesized via a vapor-liquid interfacial reaction on a flat-sheet α-Al2O3 ceramic support. This process involves the reaction of glycerol, an organic precursor with a structure featuring 1,2-diol and 1,3-diol groups, with TiCl4 vapor to form organometallic hybrid films. Subsequent calcination in air at 250 °C transforms these hybrid films into carbon-doped titanium oxide nanofilms. The unique structure of glycerol plays a crucial role in determining the properties of the resulting nanopores, which exhibit high solvent permeance and effective solute rejection. The synthesized carbon-doped TiO2 nanofiltration membranes demonstrated impressive performance, achieving a pure methanol permeability as high as 90.9 L·m-2·h -1·bar-1. Moreover, these membranes exhibited a rejection rate of 93.2% for Congo Red in a methanol solution, underscoring their efficacy in separating solutes from solvents. The rigidity of the nanopores within these nanofilms, when supported on ceramic materials, confers high chemical stability even in the presence of polar solvents. This robustness makes the carbon-doped TiO2 nanofilms suitable for applications in the purification and recovery of organic solvents.

Co-doped Zr-UiO-66-NH2@carboxylated cellulose nanocrystals/PAN membrane for oil/water separation with photocatalysis-PMS synergistic self-cleaning and antibacterial activity

The development of superwetting membranes is a promising approach for separating emulsified oily wastewater. However, challenges such as low flux without external pressure and membrane fouling have hindered membrane performance. Herein, we fabricated a novel nanofibrous membrane by grafting Co-doped Zr-UiO-66-NH2 (UiO(Zr/Co)) nanoparticles onto carboxylated cellulose nanocrystals (CCNC)-polyacrylonitrile (PAN) mixed matrix electrospinning membrane via chemical bonds through EDC/NHS reaction. CCNC served a dual purpose by enhancing membrane hydrophilicity and providing connection points for UiO(Zr/Co). The as-prepared UiO(Zr/Co)@CCNC/PAN exhibited superhydrophilic/underwater superoleophobic and anti-fouling properties. The membrane demonstrated excellent demulsification and gravity-driven separation capabilities for various oil-in-water emulsions, with superior permeation flux (1588–2557 L m−2 h−1) and separation efficiency (above 99 %). Furthermore, UiO (Zr/Co)@CCNC/PAN could activate peroxomonosulfate (PMS) under visible light to remove both high viscous crude oil-fouling and bio-fouling, exhibiting impressive photocatalytic self-cleaning and antibacterial activity. The generation of reactive radicals (O2−, OH and SO4−) and non-radical (1O2) species in UiO(Zr/Co)@CCNC/PAN+PMS system through multiple pathways was confirmed. Additionally, the band structure of UiO(Zr/Co) and synergistic photocatalytic-PMS activation mechanism were investigated. This work provides new insights into the design and fabrication of MOF modified superwetting nanofibrous membrane with inherent bonding, high permeation flux, anti-fouling and self-cleaning properties.

Low chemical-expansion and self-catalytic nickel-substituted strontium cobaltite perovskite four-channel hollow fibre membrane for partial oxidation of methane

In membrane reactors, the thermo-mechanical stability of the membrane determines the operability of the reaction, while the permeability and catalytic performance dictate the reaction process. A high chemical expansion coefficient can exacerbate the mismatch in the thermal expansion behaviour between the two sides of the membrane, potentially resulting in fracture. The low permeability and slow catalytic activity can slow the reaction process and result in an unsatisfactory product composition. Here, a Ba0.5Sr0.5Co0.7Fe0.2Ni0.1O3-δ (BSCFN) four-channel hollow fibre membrane with a low chemical-expansion and high oxygen permeation flux has been successfully fabricated by phase inversion and a one-step thermal process (OSTP). Reaction sintering during the OSTP forms an NiO in-situ exsolution phase on the membrane surface, and A-site stoichiometry excess occurs, improves the oxygen permeation flux, and provides the membrane with self-catalytic ability during the partial oxidation of methane (POM) reactions. Consequently, the BSCFN membrane shows excellent performance; exhibiting an oxygen flux of 11.75 mL cm−2·min−1 at 900 °C. Furthermore, the self-catalytic BSCFN membrane has a good hydrogen production of 10.1 mL cm−2·min−1 during the POM process, which is 7.5 times higher than that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes (1.87 mL cm−2·min−1). This offers a viable strategy for the development of membrane reactor applications.

A novel multifunctional photocatalytic membrane based on β-FeOOH for oily wastewater purification

In order to deal with the environmental pollution caused by complex oily wastewater, it is necessary to develop filtration membrane materials. However, significant challenges such as poor effect of emulsion separation, limited functionality, and susceptibility to membrane fouling require urgent resolution. Here, we successfully prepared a β-hydroxyl iron oxide/polydopamine-polyethylenimine/polyacrylonitrile (β-FeOOH/PDA-PEI/PAN) nanofiber membrane for treatment of complex wastewater by growing PDA-PEI on a blow-spinning PAN nanofiber membrane and decorating the membrane with β-FeOOH. The porous structure and the large number of hydrophilic groups greatly increase the hydrophilicity of the membrane and give the membrane high permeation fluxes (11531.26 L m−2 h−1) for surfactant-free kerosene-in-water emulsion. The loaded β-FeOOH nanorods increase the roughness of the membrane surface, which enhances the underwater superoleophobic ability of the membrane, and promotes the demulsification of the emulsion and makes it have high separation efficiency of 99.48 % for surfactant-stabilized kerosene-in-water emulsion. In addition, the β-FeOOH/PDA-PEI/PAN also exhibited high organic dye removal efficiency (99.38 %) due to the presence of β-FeOOH. The synergistic effect of low oil adhesion and photocatalysis enhances the antifouling and self-cleaning performances of the material. Significantly, the multifunctional membrane also shows exceptional oil/water separation ability and good stability. The presented synergistic strategy of β-FeOOH/PDA-PEI/PAN membrane materials represents a prospective candidate for the treatment of complex wastewater.

Hydrophilic PVDF emulsion separation membranes prepared using TA/APTES as a non-solvent: Effect of lithium chloride hydrate additive content

Currently, surfactant-containing oil–water emulsions are the more difficult part of oily wastewater to treat because of their small droplet size and stable oil–water interface. Membrane separation technology is commonly used for emulsion separation due to its surface wettability and adjustable pore size. Here, tannic acid (TA) and 3-aminopropyltriethoxysilane prepolymerization solutions are used as the exchange solvents, allowing growth on the surface and inside of polyvinylidene difluoride (PVDF). Among them, the content of lithium chloride (LCM) hydrate modulates the range and amount of growth. In the pressure range of 0.1–0.7 bar, the modified hydrophilic PVDF-TA/LCM-2 membranes exhibit high pure water permeation fluxes and emulsion separation efficiencies that can be adapted to different separation conditions. At 0.2 bar, the PVDF-TA/LCM-2 achieves pure water permeate flux and emulsion separation fluxes of 1860 and 648 L m-2 h−1 bar−1, and an emulsion separation efficiency of 99.5 %. In addition, for different kinds of oil-in-water emulsions, the high separation fluxes and high separation efficiencies indicate that PVDF-TA/LCM-2has good emulsion separation performance.

Hydrogen-Rich Syngas Production in a Ce0.9Zr0.05Y0.05O2−δ/Ag and Molten Carbonates Membrane Reactor

This study proposes a new dense membrane for selectively separating CO2 and O2 at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce0.9Zr0.05Y0.05O2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO2/N2 and O2/N2 permselectivity and a high permeation flux under different CO2 concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO2 valorization via the oxy-CO2 reforming of methane, wherein both CO2 and O2 permeated gases were effectively utilized to produce hydrogen-rich syngas (H2 + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver.

Incorporation of Graphene Oxide Quantum Dots in Gradient Layers of Polyethersulphone Nanofiltration Membranes for Nitrate Rejection from Aqueous Solution.

Graphene oxide quantum dots (GOQDs) have been widely used to prepare nanofiltration membranes due to the merits of excellent dispersity, ultrasmall size, and unique properties related to graphene. In this study, we first prepared the polyethersulphone-based nanofiltration (PES-NF) membrane via an interfacial polymerization process using a piperazine and m-phenylenediamine mixed solution as the aqueous phase. Then GOQDs were incorporated into the top-down gradient structured layers (i.e., ultrathin layer, interlayer, and substrate membrane layer) of the nanofiltration membrane, and subsequently the effect of GOQD addition on the nitrate rejection was evaluated. Compared with the pristine PES-NF membrane without the incorporation of GOQDs, the fabricated NF membrane (GOQD/PES-NF-2) incorporating GOQDs at both the ultrathin layer and interlayer exhibits more remarkable performances (an acceptable permeation flux of 52.2 L m-1 h-1 and excellent nitrate rejection of 96.3% at 0.6 MPa), the permeation flux of this membrane increases by nearly 2.4 times, and its nitrate rejection also shows a slight enhancement (∼7.6%) compared with those of PES-NF. Remarkably, at the operating pressure much lower than that required by reverse osmosis membranes, the GOQD/PES-NF-2 membrane possesses an equivalent monovalent ion rejection to reverse osmosis membranes but a higher permeation flux. Furthermore, the result of a 7 day continuous stability test validates the excellent durability of the GOQD/PES-NF-2 membrane, and its antifouling and chlorine resistance performances also outperform those of the PES-NF membrane.

Advanced absorption-storage water molecules strategy reinforces antifouling property for stable oil/water emulsions separation

Constructing membranes with extraordinary resistance to oil contamination under high permeation flux is a considerable challenge. Herein, an advanced absorption-storage water molecules strategy is proposed for constructing the robust hydration layers to achieve effective anti-oil fouling and stable oily wastewater purification. Specifically, metal–organic framework (MOF, UiO-66-NH2) nanoparticles with powerful water-absorbing characteristics are preferentially adsorbed to collect water in oil/surfactant/water systems. Combining excellent water retention, the micro-/ nano-networks formed by attapulgite (APT) could store the water molecules captured by MOF. The synergistic effect of the water-absorbing/water-retaining interactions between the MOF and APT created robust hydration layers defense barriers, which enhanced the resistance of membrane to oil contamination. Furthermore, the abundant hydrophilic groups (e.g., –OH, –NH2 and –CONH2) of chitosan (CS) further improved the membrane surface hydrophilic coverage, permeability and hydration ability. As a result, the developed CS/APT@MOF composite membrane exhibited significant anti-oil fouling capability and realized superior purification property towards various oil-in-water emulsions stabilized by surfactants. The CS/APT@MOF composite membrane demonstrated outstanding oil repellency (flux recovery ratio > 99.6 %, total flux decline ratio < 3.8 %) over 10 cycles under large permeability (>660 L m-2h−1 bar−1). Meanwhile, the constructed CS/APT@MOF composite membrane exhibited stable separation cycle capability (10 cycles) and continuous purification performance (60 min) for different oil/water emulsions. Therefore, this advanced strategy based on absorption-storage water molecules to construct robust hydration layers provides a promising insight for the development of superior antifouling and operationally stable oil/water emulsions separation membranes.

High-performance COFs composite nanofiltration membrane fabricated by organobase catalyst

Covalent Organic Frameworks (COFs) composite nanofiltration (NF) membrane has high permeation flux and rejection. However, the reaction rate of COFs is relatively slow. Adding acid catalyst is a common method to shorten reaction time. However, the dissatisfactory synthesis rate will lead to irregular structure of COFs materials. In this work, it is the first time to use organobase as a catalyst to prepare COFs composite membrane. The COFs structure will be optimized and the membrane performance can be enhanced. The prepared TpPa-PIP membrane compared with acid catalyzed TpPa-HAc membrane has better permeability, permeance of 89 L m−2·h−1·bar−1 and CR rejection of 99.54 %. This improvement is because of the TpPa-PIP intermediate made slower reaction speed that improves the overall regularity and crystallinity of COFs. Therefore, it is better method for broadening the application of organobase-catalyzed in preparing membranes.

Tolterodine Tartrate Loaded Cationic Elastic Liposomes for Transdermal Delivery: In Vitro, Ex Vivo, and In Vivo Evaluations.

Tolterodine tartrate (TOTA) is a first-line therapy to treat overactive urinary bladder (OAB). Oral delivery causes high hepatic clearance, xerostomia, headache, constipation, and blurred vision. We addressed Hansen solubility parameter (HSP) and Design Expert oriented optimized cationic elastic liposomes for transdermal application. The experimental solubility was conducted in HSPiP predicted excipients to tailor formulations using surfactants, stearylamine, ethanol, and phosphatidylcholine (PC). These were evaluated for formulation characteristics. The optimized OTEL1 and OTEL1-G (gel) were compared against the drug solution (DS) and liposomes. In vitro and ex vivo studies were accomplished to investigate the insights into the mechanistic understanding of TOTA release and permeation ability. Finally, confocal laser scanning microscopy (CLSM) supported ex vivo results. HSP values of TOTA were closely related to tween-80, stearylamine, and human's skin. The size (153nm), %EE (87.6%), and PDI (0.25) values of OTEL1 were in good agreement to the predicted values (161nm, 80.4%, and 0.31) with high desirability (0.963). Spherical and smooth OTEL1 (including OTEL1-G and liposomes) vesicles followed non-Fickian drug release as compared to DS (Fickian) as evidence with n > 0.5 (Korsmeyer and Peppas coefficient). OTEL1 (containing lipid and surfactant as 90mg and 13.8mg, respectively) exhibited 2.6 and 1.8-folds higher permeation flux than DS and liposomes, respectively. Biocompatible cationic OTEL1 was safe and non-hemolytic. OTEL1 was promised as a lead vesicular approach and an alternative to conventional oral therapy to treat OAB in children and advanced age patients.

Highly adhesive bioinspired membrane for efficient oil/water separation by optimization of synergistic effects of hierarchical structure and superhydrophobic modification

Superwetting membranes have good prospective for treatment of oil-containing wastewaters. However, development of highly adhesive superhydrophobic membranes with efficient oil-water separation performance remains a great challenge that needs to be addressed urgently. Herein, highly adhesive membrane surface with hierarchical structure were fabricated by in-situ TEOS hydrolysis and fluorinated modification. The interface bonding force between polyvinylidene fluoride (PVDF) and silica nanoparticles (SiO2 NPs) was increased through the dopamine self-polymerization and adhesion. The hierarchical structure was obtained by simultaneously adjusting TEOS and ammonia contents. The three-dimensional hierarchical membrane structure which is similar to that of a rose petal was shown by SEM analysis. The obtained membrane showed a water contact angle of 158 ± 2°, while the oil contact angle approaches 0°. In-situ grown multi-scale SiO2 NPs, perfluorooctyltriethoxysilane (FAS) brushes and dopamine can form a stable hierarchical surface which sustained superhydrophobicity/superoleophilicity when immersed in aqueous solutions at different pH values. Meanwhile, FAS brushes can serve as steric obstacles to efficiently repel water droplets during oil/water separation. The fabricated membrane possesses a high permeation flux and excellent separation properties (> 98%). In addition, this highly adhesive coating modification and hierarchical design can be widely applied on the surfaces of different materials, giving an attractive potential application prospect, such as oil/water separation, antifouling surface, and superwetting materials.

Bio-inspired super-wetting coatings constructed from interfacial mineralization of rare earth phosphate for oil/water separation applications

The oil fouling problem of lipophilic polymer matrix causes severe decline of separation performance, becoming one of the most serious challenges for oil/water separation. A chemical-stable and mechanical-strong anti-fouling coating is highly emerged. Herein, to achieve anti-fouling performance on diverse polymer substrates, a biomimic super-wetting coating is fabricated by interfacial mineralization of lanthanum phosphate (LaPO4). The strong interaction between ions makes LaPO4 very stable against acid, base, oil and mechanical impact, while the dense charges on the surface of LaPO4 attract water molecules and create a hydration layer to repulse oil under water. The membranes and meshes modified by such mineralized coating exhibit good separation efficiency (>99 %) and high permeation flux for oil-in-water emulsions and oil/water mixtures, respectively. In addition, notable cyclic flux recovery ability was fulfilled by water rinsing. The fabrication of such mineralized coating is easily operated through solution process and no harmful byproducts will be generated. Basically, the low-cost and eco-friendly mineralized coating is promising for oily water treatment in the practical complicated environment.

Bilayer cellulosic FO membrane developed by polydopamine and nanochitosan through layer by layer coating process

A highly efficient bilayer cellulose acetate forward osmosis (FO) membrane was developed using polydopamine (PDA) and chitosan nanoparticles (CsNP) through layer by layer coating process and characterized using DLS, FESEM, AFM, EDX, and static contact angle. The use of CsNP and PDA led to an improvement in chemical properties, surface hydrophilicity, and structural parameter. The experimental tests for both RO and FO experiments were carried out to calculate structural parameter (it decreased from 0.59 mm for neat CA to 0.37 mm for CA-PDA/CsNP2) of membranes. Also, the salt rejection and water permeability of membranes were tested in RO mode using 40 mM NaCl, while the water flux and reverse salt flux of membranes were analyzed in FO test. The CA-PDA/CsNP2 membrane with 0.6 wt.% of CsNP in the coating solution not only showed a high water permeation flux about 21.23 LMH for 2 mM NaCl but also decreased its reverse salt flux from 7.08 to 4.52 gMH. According to the fouling test results, the normalized water flux of the neat membrane declined from 1 to about 0.65 while it was higher than 0.85 for CA-PDA/CsNP2 which represents an improvement in the antifouling property. This improvement was mainly due to an increase in the hydrophilicity of the coated membrane and the electrostatic repulsion among the foulant and surface of CA-PDA/CsNP2. The results showed that the fabricated CA-PDA/CsNP2 membrane shows a high potential application in the FO process and is more competitive than other existing FO membranes.

Bio-Inspired Underwater Superoleophobic Aramid Nanofiber-Based Aerogel Membranes for Highly Efficient Removal of Emulsified Oils and Organic Dyes.

Effective elimination of insoluble emulsified oils and soluble organic dyes has received extensively attention in wastewater treatment. In this work, a chitosan and polydopamine @ aramid nanofibers (CS&PDA@ANFs) aerogel membrane was fabricated through an integration methodology consisting of phase inversion and successive deposition of PDA and CS. The as-prepared aerogel membrane possessed a satisfactory three-dimensional interpenetrating network architecture with high porosity and desirable mechanical property. Furthermore, due to the synergistic effect of hydrophilic CS and PDA, the resultant membrane exhibited good superhydrophilicity and underwater superoleophobicity associated with favorable oil resistance/antioil fouling properties. The combination of the interconnected porous structures and super wettability endowed the aerogel membranes with desirable oil-in-water emulsion separation performance. Particularly, an extremely high permeation flux (3729 L/m2/h) and a rejection rate (99.3%) were achieved for the CS&PDA@ANFs membrane. Moreover, diverse dyes could be also adsorbed by the resultant membrane, and the equilibrium adsorption capacity of cationic dye malachite green could reach 36 mg/g, with a high rejection rate over 97%. This study indicated that the CS&PDA@ANFs aerogel membrane held great promise for practical applications in complex wastewater remediation.

Faveolate cell-engineered and multi-heterostructured flexible ceramic nanofibrous membranes with confined coalescent nanochannels enable sustainable oily water remediation

Oily wastewater, resulting from oil recovery, petrochemical industries, or accidents, poses a significant threat to the aquatic environment. Membrane separation technology can offer unprecedented opportunities for highly efficient water remediation but at the cost of poor permeability and serious oil fouling. Here, we report a faveolate nanofibrous membrane through the steric growth of bismuth oxybromide-bismuth oxyiodide nanoflakes on the TiO2/polypyrrole nanofibers. The spatially faveolate cells create highly covered confined spaces that efficiently capture and coalesce nanosized oil droplets, thus achieving substantial selectivity for micron porous membranes. The faveolate membranes are capable of efficiently separating various oil-in-water emulsions, particularly nanoscale surfactant-stabilized emulsions with a high permeation flux of 6075 L m-2h−1 and a good separation efficiency of 99.95 %. Moreover, the membranes with multi-heterostructure act as efficient photocatalysts, giving rise to visible light-induced sufficient fouling-tolerant property with nearly zero irreversible oil fouling. This study could provide a novel strategy for developing a new generation of membranes with high performance and long service lifetime for oily sewage remediation.

Revealing the role of interlayer spacing in radioactive-ion sieving of functionalized graphene membranes

Functionalization of graphene enables precise control over interlayer spacing during film formation, thereby enhancing the separation efficiency of radioactive ions in graphene membranes. However, the systematic impact of interlayer spacing of graphene membranes on radioactive-ion separation remains unexplored. This study aims to elucidate how interlayer spacing in functionalized graphene membranes affects the separation of radioactive ions. Utilizing polyamidoxime (PAO) to modify graphene oxide, we controlled the interlayer spacing of graphene membranes. Experimental results indicate that tuning interlayer spacing enables control of the permeation flux of radioactive ions (UO22+ 1.01 × 10−5–8.32 × 10−5 mol/m2·h, and K+ remains stable at 3.60 × 10−4 mol/m2·h), and the K+/UO22+ separation factors up to 36.2 at an interlayer spacing of 8.8 Å. Using density functional theory and molecular dynamics simulations, we discovered that the effective separation is mainly determined via interlayer spacing and the quantity of introduced functional groups, explaining the anomalous high permeation flux of target ions at low interlayer spacing (4.3 Å). This study deepens our comprehension of interlayer spacing within nanoconfined spaces for ion separation and recovery via graphene membranes, offering valuable insights for the design and synthesis of high-performance nanomembrane materials.

Room temperature aqueous synthesis of defect-engineered MOF-801 membrane towards efficient nanofiltration

Room temperature (RT) aqueous preparation of MOF membranes is of significant interest in meeting the demands of sustainability. Nevertheless, there remains no report on RT aqueous synthesis of water-stable high-valence MOF membranes to date. In this study, we developed a one-step RT protocol for fabricating defect-engineered MOF-801 membrane in aqueous media. Owing to enhanced structural hydrophilicity and enlarged micropore size, water was enabled to diffuse through the membrane with higher permeation flux. Obtained membrane exhibited exceptional dye rejection rate (CR:99.75 %, MB:99.69 % and MG:99.41 %) and unprecedented water flux (CR:77.33 L m−2 h−1·bar−1, MB:71.43 L m−2 h−1·bar−1 and MG:81.28 L m−2 h−1·bar−1), which were superior to state-of-the-art 3D pure MOF membranes. Our protocol paves a promising way towards sustainable production of water-stable MOF membranes under mild conditions.

Analysis of the gas transport resistance of CO2 and CH4 through ultra-thin DD3R zeolite membrane

Ultra-thin DD3R zeolite membranes exhibit excellent separation properties for CO2 capture from natural gas, as well as the lower transmembrane resistance. However, the interfacial transport of permeation gas in such systems may dominate the whole separation process. In this work, we employed external force non-equilibrium molecular dynamic (EF-NEMD) simulation to predict the single-component permeabilities of CO2 and CH4 through a defect-free DD3R zeolite membrane at different pressured drops. By explicitly including the gas transport from bulk phase to zeolitic channels, the predicted results of EF-NEMD simulation showed good agreements with the reported experimental data. The contribution of interfacial resistance over the total transport resistance (Rinter/Rtotal) was further evaluated for the membranes with different thicknesses under temperatures between 273 K and 373 K. The results revealed a decrease in Rinter/Rtotal with increasing membrane thickness, leading to a reduction in CO2/CH4 selectivity, and the critical thickness (Rinter/Rtotal < 0.01) was determined to be approximately 300 nm at pressure of 1.0 MPa and temperature of 298 K. Similarly, the Rinter/Rtotal decreased with increasing temperature due to the augmentation in molecule kinetic energy. Furthermore, it was confirmed that the gas adsorption effect could expand the effective size of eight membered ring (8-MR) channels in DD3R zeolite membrane, thereby decreasing the CO2/CH4 selectivity, despite higher permeation fluxes. The above discoveries essentially benefit the design of the ultra-thin DD3R zeolite membrane through an understanding of CO2 and CH4 transport behaviors.

Tuning the interlayer spacing of graphene oxide membrane via surfactant intercalation for ultrafast nanofiltration

A facile method has been developed to fabricate lamellar composite graphene oxide (CGO) membranes by incorporating positively charged surfactants – cetyltrimethylammonium bromide (CTAB). The interlayer spacing of GO nanosheets was regulated by the sum of both vertical and horizontal alignment of CTAB on the GO surface via electrostatic interaction. The CTAB intercalated GO membrane exhibited an internal layer spacing of 16.97 Å compared to 8.26 Å for the GO membrane. The obtained CGO lamellar membrane with well-defined nanochannels showed ultrafast pure water flux of ∼1112 L h−1 m−2 bar−1 and an excellent separation efficiency of >99 % towards negatively charged organic dye molecules at a high permeation flux of ∼932 L h−1 m−2 bar−1, which was nearly 2.5-fold enhancement compared with that of the pristine GO membrane (∼400 L h−1 m−2 bar−1). The electrostatic and π–π interaction forces between the CGO membrane and organic dye molecules played a major role in the overall dye separation mechanism. Furthermore, the CGO membrane demonstrated excellent stability with no loss in separation performance (>96 % organic molecules rejection) after exposure to various pH solutions and deionized water (DI) water. The current work provides a straightforward approach for the formation of highly tunable and stable CTAB-intercalated GO membranes for ultrafast molecular separation.