Separation Performance Of Membranes Research Articles

C-axis oriented ZIF-95 sheets intermixed with polyimide matrix with enhanced gas separation performance

The fabrication of mixed matrix membranes (MMMs) by intermixing suitable fillers with organic polymers is an effective strategy to surmount the well-known trade-off effect between gas permeability and selectivity, which can promote separation performance of membranes to a great extent. Two-dimensional (2D) metal-organic frameworks (MOFs) are considered as potential fillers for strengthening the separation performance of MMMs as they possess high aspect ratio and distinctive chemical characteristics. However, it remains challenging in engineering the morphology of the MOFs with desired pore structure and high aspect ratio. In this study, we firstly prepare c-axis oriented ZIF-95 sheets with lateral dimension exceeding 22 μm and thickness of around 3 μm by the solvothermal method. And then the ZIF-95 sheets are incorporated into the polyimide (PI) matrix to fabricate highly c-axis oriented ZIF-95@PI MMMs (denoted as COZIF-95@PI MMMs thereafter). Attributing to the straight permeation channel of ZIF-95 (3.6 Å) for gas permeation as well as its high compatibility with polyimide substrates, the COZIF-95@PI MMMs show a high gas separation capability. At 373 K and 100 kPa for the COZIF-95@PI MMM with 40 wt% loading, the mixture separation factors of H2/CH4 and H2/CO2 are 134 and 58, respectively, and the H2 permeability exceeds 967 barrer, which is hopeful for the separation and purification of hydrogen.

Mechanism for regulation of a forward osmosis membrane by the SA/UiO-66-NH2 composite interlayer and the resulting lithium ion concentration performance

The traditional thin-film composite (TFC) forward osmosis (FO) membrane has problems such as poor water permeability and low lithium concentration selectivity because the separation layer is too thick and has many defect pores. In this study, a thin and dense separation layer was obtained by constructing a sodium alginate (SA)/UiO-66-NH2 interlayer to control the attachment amount and diffusion rate of m-phenylenediamine (MPD), which enhanced the performance of the membrane. This paper studies the effect and mechanism of the interlayer on the structure and separation performance of the FO membrane, and explores the lithium ion concentration performance of the interlayer membrane. According to the results, based on the strong interaction between the interlayer and MPD, the equilibrium concentration of MPD available for interfacial polymerization was increased and the diffusion rate of MPD was slowed, resulting in the generation of a thin and dense separation layer. Since the interlayer restricted the escape of bubbles formed in the interfacial polymerization, the separation layer showed a leaf-like structure with increased filtration area and water storage space. Due to the reduced thickness of the separation layer and its leaf-like structures, the water flux increased significantly, and the water flux of the interlayer membrane was 47.9% greater than that of the original membrane. Drawing upon the heightened density of the separation layer and secondary separation of the interlayer, the reverse solute flux was lowered by 37.4%. The interlayer membrane exhibited efficient Li+ rejection (R>93%) and the concentration ratio of Li+ was close to its theoretical concentration ratio at 1.46 ± 0.03.

Hybridizing zeolite MFI nanosheets with PTMSP membranes for enhanced butane isomer separations

Hybridizing zeolite nanosheets with a high aspect ratio has the potential to improve the gas separation performance of polymeric materials due to their good mechanical strength, thermal stability, and well-defined microporous structure. However, the use of zeolite-nanosheet-based mixed matrix membranes (MMMs) has been limited, and their effects on polymeric materials have not been studied thoroughly. In this study, zeolite MFI nanosheets were directly synthesized and introduced into PTMSP polymer using the shear-coating method. This resulted in a horizontally aligned structure with preferentially b-oriented zeolite MFI fillers. The straight b-channels of zeolite MFI facilitated fast gas permeation, while the high aspect ratio increased the tortuosity for non-permeable gases. The elastic modulus of the composite increased from 306 MPa to 2069 MPa as the zeolite MFI nanosheet content was increased to 50 wt%. The membrane was thermally stable up to 285 °C due to the protection provided by the zeolite MFI filler, which prevented thermal degradation by oxygen. The gas separation performance was improved, with a butane isomer selectivity of 7.3 and a permeability of 5400 barrer, a 20% increase from the neat PTMSP membrane. The selectivity was well preserved even in the binary mixture of butane isomers gas permeation test at 1 bar, while the neat PTMSP membrane showed a dramatic decrease in selectivity under this condition. The compatibility between the nanosheets and the polymer is expected to be important in achieving high separation performance of the composite membrane, as can be inferred from the large difference between the performance predicted by the modified Cussler model and the actual performance.

Evaluation of Surface Properties and Separation Performance of NF and RO Membranes for Phthalates Removal

Many studies indicated that phthalates, a common plasticizer, lurk silently in water bodies and can potentially harm living organisms. Therefore, removing phthalates from water sources prior to consumption is crucial. This study aims to evaluate the performance of several commercial nanofiltrations (NF) (i.e., NF3 and Duracid) and reverse osmosis (RO) membranes (i.e., SW30XLE and BW30) in removing phthalates from simulated solutions and further correlate the intrinsic properties of membranes (e.g., surface chemistry, morphology, and hydrophilicity) with the phthalates removal. Two types of phthalates, i.e., dibutyl phthalate (DBP) and butyl benzyl phthalate (BBP), were used in this work, and the effects of pH (ranging from 3 to 10) on the membrane performance were studied. The experimental findings showed that the NF3 membrane could yield the best DBP (92.5-98.8%) and BBP rejection (88.7-91.7%) regardless of pH, and these excellent results are in good agreement with the surface properties of the membrane, i.e., low water contact angle (hydrophilicity) and appropriate pore size. Moreover, the NF3 membrane with a lower polyamide cross-linking degree also exhibited significantly higher water flux compared to the RO membranes. Further investigation indicated that the surface of the NF3 membrane was severely covered by foulants after 4-h filtration of DBP solution compared to the BBP solution. This could be attributed to the high concentration of DBP presented in the feed solution owing to its high-water solubility (13 ppm) compared to BBP (2.69 ppm). Further research is still needed to study the effect of other compounds (e.g., dissolved ions and organic/inorganic matters that might be present in water) on the performance of membranes in removing phthalates.

Improved SSZ-13 thin membranes fabricated by seeded-gel approach for efficient CO2 capture

High-quality standard oil synthetic zeolite-13 (SSZ-13) membranes with thickness only ∼1.0 µm were prepared on tubular supports by the new seeded-gel approach. Seeded-gel approach is simpler than the normal secondary-growth one since adding seeds in the gel is simpler than seeding on the support surface. The synthesis time was greatly reduced from 3.0 to 1.0 d after synthesis modification of gel aging and seed sizes. Low temperature ozone calcination was used for the removal of the organic structural directing agent. The best SSZ-13 membrane displayed CO2 permeances of 1.3×10–6 and 1.5×10–6 mol∙m–2∙s–1∙Pa–1 and CO2/CH4 and CO2/N2 selectivities of 125 and 27 for equimolar CO2/CH4 and CO2/N2 mixtures at 0.2 MPa pressure drop and 298 K, respectively. Separation performance of the membrane in the two binary mixtures is higher than that of most zeolite membranes. Three SSZ-13 membranes were reproducibly prepared on tubular supports by seeded-gel approach and the standard deviation ratios of CO2 permeance and CO2/CH4 selectivity are 12.5% and 7%, respectively. It suggests that this new synthesis approach is creditable. The effects of temperature and pressure on separation performance of the thin SSZ-13 membranes were studied in the two binary mixtures. The tubular SSZ-13 membranes displayed great potentials for CO2 capture from natural gas, biogas and flue gas.

Experimental and modeling study on interfacial morphology of ZIF-67/Pebax-2533 mixed matrix membranes for CO2 separation applications

This work focuses on the influence of interfacial morphology on separation performance of mixed matrix membranes (MMMs). For this purpose, high CO2 separation performance MMMs were fabricated, in which the cobalt-based zeolite imidazole framework (ZIF-67) was merged into the poly(ether-block-amide) (Pebax-2533). Moreover, a novel model-based method was applied to estimate the gas permeability through matrix and ZIF-67 and characterize the interfacial morphology via the molecular probing technique. The experimental gas separation results exhibited that the CO2 permeability improved from 63.8 Barrer (neat membrane) to 190.5 Barrer (16 wt.% of ZIF-67). Also, the CO2/N2 and CO2/CH4 ideal selectivities increased from 25.3 to 11.4 to 39.7 and 22.5, respectively, at 25 °C and 4 bar. The validity of the suggested model was appraised, which revealed good accordance between the predicted gas permeabilities and experimental measurements with%AARDs of 0.49, 0.42, and 0.35% for CO2, CH4, and N2 gases, respectively. The model results confirmed the presence of a chain dilution interface around the ZIF-67 nanoparticles and agglomeration of ZIFs at high loading. In addition, the gas permeability from nanoparticles and the interface layer were determined by optimizing two characterization parameters, viz., the correction factor for the gas permeability from the interface (β) and filler pores (γ). It was found that for both CO2 and N2, β and γ increased and decreased, respectively, by increasing the ZIF-67 loading. In fact, the gases preferred to permeate through the diluted interfacial layer rather than trying to pass through small ZIF-67 pores.

Research progress on the substrate for metal–organic framework (MOF) membrane growth for separation

During the last decade, metal–organic frameworks (MOFs) have been applied in various fields due to their unique chemical and functional advantages. One of the widespread research hotspots is MOF-based membranes for separations, specifically continuous defect-free MOF membranes, which are usually grown on porous substrates. The substrate not only serves as the MOF layer support but also has a great influence on the membrane fabrication process and the final separation performance of the resultant membrane. In this review, we mainly introduce the progress focused on the substrates for MOF membranes fabrication. The substrate modifications and seeding methods aimed at synthesizing high-quality MOF membranes are also summarized systematically.

Internal Concentration Polarization in the Polyamide Active Layer of Thin-Film Composite Membranes.

A free-standing polyamide (PA) film is fabricated via in situ release from a thin-film composite (TFC) membrane achieved through the removal of the polysulfone support. The structure parameter S of the PA film is measured to be 24.2 ± 12.6 μm, which is about 87-fold of its film thickness. A significant decline in water flux of the PA film from an ideal forward osmosis membrane is observed. We find that the decline is predominantly influenced by the internal concentration polarization (ICP) of the PA film based on our experimental measurements and theoretical calculations. We propose that the asymmetric hollow structures of the PA layer with dense crusts and cavities may be the underlying cause of the occurrence of the ICP. More importantly, the structure parameter of the PA film can be reduced and its ICP effect can be mitigated by tuning its structures with fewer and shorter cavities. Our results for the first time provide experimental evidence to prove that the PA layer of the TFC membrane has the ICP effect, which could potentially provide fundamental insights into the influence of structural properties of PA on the membrane separation performance.

Ag@BiOBr/PVDF photocatalytic membrane for remarkable BSA anti-fouling performance and insight of mechanism

Membrane technologies offer great potential in desalination and wastewater treatment. However, the serious issue of membrane fouling results in the unsatisfactory sustainability and reusability for treating wastewater containing high level of organic foulants. In this work, a photocatalytic membrane reactor system combining Ag@BiOBr photocatalyst and polyvinylidene fluoride (PVDF) ultrafiltration with remarkable anti-fouling property was constructed. The integrated Ag@BiOBr/PVDF photocatalytic ultrafiltration membranes were prepared by blending Ag@BiOBr nanoparticles (NPs) into PVDF membrane via phase inversion method. The membrane separation performance and fouling resistance were studied in a cross-flow ultrafiltration system using bovine serum albumin (BSA) as the model foulants. Compared with the pristine PVDF membrane, the hydrophilicity and surface smoothness of composite membranes were promoted by photocatalyst-incorporation, the Ag@BiOBr/PVDF membrane with the optimal Ag@BiOBr blending content of 2.0 wt% achieved both enhanced water flux and higher BSA rejection efficiency. More importantly, the mechanism of anti-fouling and self-cleaning performances were further studied, the photocatalysis process based on Ag@BiOBr/PVDF membrane effectively decomposed the BSA foulant into broken protein with induced change of carbonyl, ionic bond and hydrogen bond contents in BSA foulants via the active radicals, weakened the intermolecular force of BSA foulants to prevent membrane pore blockage. Meanwhile, the broken protein peptide chains with more negative charges could result in the strength of electrostatic repulsive forces between BSA molecules and membrane. As a result, the BSA foulant could be stably removed in the Ag@BiOBr/PVDF photocatalytic ultrafiltration system under visible light irradiation, achieving the excellent anti-fouling performance by preventing the membrane pore blockage and foulant adhesion. We believe the Ag@BiOBr/PVDF photocatalytic membrane presented in this study will be one example among many photocatalyst-membrane combinations that can be further pursued for organic pollutants removal. In particular, we expect the theoretical support can present a great opportunity to design novel photocatalytic membranes with sustainable anti-fouling performance.

The antifouling and separation performance of an ultrafiltration membrane derived from a novel amphiphilic copolymer containing a crown ether

Amphiphilic copolymers have attracted extensive attention for the preparation of ultrafiltration (UF) membranes processed with high separation and antifouling performances. Herein, hydrophilic crown ether (dibenzo-18-crown-6-ether, DE) units were introduced into poly(p-terphenyl, isatin) (PDTI) based on a polycondensation reaction via superacid-catalysis. The copolymers showed good thermal stability and membrane-forming properties, and the UF membranes fabricated by NIPS exhibited excellent separation performance. The content of the hydrophilic DE significantly influenced the morphology structure of the UF membranes. The cross-section structure of the membranes gradually converted from finger-like pores to loose sponge pores during delayed phase separation. The water flux of membranes ascended from 130.9 LMH bar−1 to 286.6 LMH bar−1 while the BSA rejection rate decreased from 99.4% to 90.8% as the DE content increased from 10% to 30%. These changes were associated with an enhanced surface porosity, larger surface pore diameter, and thinner top layer. Moreover, increasing the DE content in the copolymer greatly improved the antifouling performance due to greater hydrophilicity. Upon increasing the molar ratio of DE to p-terphenyl from 1: 9 to 3: 7, the flux recovery rate of the membranes surged from 58.5% to 91.5% and remained >80.2% after three fouling-cleaning cycles. In addition, the surface segregation of the hydrophilic DE segment in the copolymer was confirmed by the higher oxygen element content of the UF membrane on the top surface (18.62%) than that of the polymer (13.97%). Therefore, the amphiphilic copolymer containing a crown ether synthesized by a one-pot polycondensation reaction provides an effective way for the preparation and property adjustment of UF membranes.

Molecular Simulation for Guiding the Design and Optimization of Mixed Matrix Membranes (MMMs) in the Pervaporation Process

Molecular simulation has been used extensively in the study of pervaporation membranes as a new economical and environmentally friendly research method. In this paper, A-SiO2/PDMS-PTFE mixed matrix membranes (MMMs) were prepared by molecular-simulation-guided experiments to achieve the separation of dimethyl carbonate/methanol (DMC/MeOH)) azeotropes. The interaction energy, X-ray diffraction pattern mean square displacement, and density field between PDMS and inorganic particles were analyzed by molecular dynamics simulations. The dissolution and diffusion processes of the DMC/MeOH azeotropes system in the MMM were simulated, and the surface-silylated silica (A-SiO2) with relatively better performance was screened. Based on the simulation results, A-SiO2/PDMS-PTFE MMMs were prepared by the coblending method, and the pervaporation separation performance of MMM membranes for DMC/MeOH azeotropes with different A-SiO2 loadings was investigated. When the A-SiO2 loading was 15 wt %, the separation factor of DMC/MeOH azeotropes at 50 °C was 4.74 and the flux was 1178 g m-2 h-1, which was consistent with the expected results of the simulation. The MMMs showed good stability in pervaporation over a period of up to 120 h. This study demonstrates that molecular simulations can provide a viable means for pretest screening and validation of experimental mechanisms, and to a certain extent, guide the design and optimization of pervaporation membranes.

Coordination enhancement of hydrogen and helium recovery in polybenzimidazole-based carbon molecular sieve membranes

Tailoring the microporous architecture of the precursors facilitates the gas separation performance in carbon molecular sieve (CMS) membranes. Herein, we report a facile strategy to tune the gas separation performance of CMS membranes through coordination between rare earth and imidazoles in the hierarchical triptycene-based polybenzimidazole (TPBI) precursor. By optimizing the pyrolysis condition and rare earth doping level, the resulting CMS membranes exhibited unprecedented H2 and He permeabilities and high gas selectivities, and the TPBI-Yb0.67@700 CMS membrane exhibited a 3-fold increase in H2 permeability and a 2-fold increase in H2/CO2 selectivity compared to the TPBI-CMS@700 CMS membrane. It was demonstrated by the solution/diffusion coefficients and microporosity analysis that the enhancement of gas separation performance originated from the more pronounced hierarchically slit-like micropore structure, as well as the boosted diffusion and sorption selectivities. The TPBI-Yb0.67@700 membrane displayed a H2 permeability of 8648 Barrer and a mixed-gas H2/CO2 selectivity of 14.5 at 150 °C, far exceeding the experimental CMS upper bound.

Improving CO2 separation performance of PVAm membrane by the addition of polyethylenimine-functionalized halloysite nanotubes

Mixed matrix composite membranes (MMCMs) integrate the merits of inorganic and organic materials, but the tortuous transport passageways bring about large transfer mass resistance for gas transport. Herein, we prepared polyethylenimine-functionalized halloysite nanotubes (PEI-HNTs) by the electrostatic self-assembly of positively charged polyethylenimine and negatively charged halloysite nanotubes. Blending as-obtained PEI-HNTs with polyvinylamine (PVAm), MMCMs were prepared by casting above mixed solution on the top of ultrafiltration polysulfone (PSf) support. PEI-HNTs had good miscibility with PVAm due to hydrogen bonding. MMCMs (1 wt% PEI-HNTs loading) exhibited exceptional separation performance (CO2 permeance: 179 GPU; CO2/N2 selectivity: 127.9), respectively, which were 1.4 and 2.3 times that of MMCMs embedding with 1 wt% HNTs. Noticeably, its value was beyond those of MMCMs incorporating with reported hollow tubular filler as well as other shape filler. This is due to the fact that PEI on the surfaces of HNTs provides a lot of amine carriers, which facilitate CO2 transport. More importantly, the transport passageways are continuous, thus presumably reducing the CO2 transfer resistance compared to other shape inorganic material filled-MMMs. Besides, resultant MMCMs revealed desirable stability for over 360 h, with a CO2/N2 mixture as feed gas. Remarkably, it maintained superior gas separation performance (CO2 permeance of 126 GPU; CO2/N2 selectivity of 88.6) under the acidic conditions.

Nanocomposite substrate-supported nanofiltration membrane for efficient treatment of rare earth wastewater

The incorporation of nanomaterials into the selective layer of nanofiltration membranes can effectively enhance membrane performance. However, the agglomeration of nanoparticles inevitably leads to defects in the membrane PA layer. To address this issue, this paper reports a novel nanocomposite substrate-supported thin-film composite (TFC) nanofiltration membrane with good stability and excellent separation performance. Inorganic two-dimensional O–MoS2 nanosheets were embedded into a polysulfone (PSF) substrate by a non-solvent-induced phase transition method. The PSF/O–MoS2 nanocomposite was used as a support for the interfacial polymerization between piperazine and tricarbonyl chloride. The pore morphology of the nanocomposites changed dramatically as the O–MoS2 content increased. With the optimal content of O–MoS2 in substrates was 0.06 wt%, the pore structure of the substrate changed from a larger irregular bubble pore structure to a finger-like pore structure. The nanocomposite matrix-supported TFC membrane exhibited 1.7 times higher water flux and better salt removal compared to the control membrane. Meanwhile, the obtained nanofiltration membranes showed excellent separation performance in treating simulated rare earth wastewater (P507) containing surfactants with a desalination rate of 97.08%. The desalination rate also reached 95% in a 24- h performance test on real rare earth wastewater (50-fold dilution), demonstrating its great potential for industrial applications. This work also highlights that modification of substrates with functional nanomaterials can provide a versatile approach to enhance the separation performance and stability of TFC membranes.

A novel glue attachment approach for precise anchoring of hydrophilic EGCG to enhance the separation performance and antifouling properties of PVDF membranes

A novel glue attachment approach was proposed to form a durable hydration layer on a hydrophobic PVDF hollow fiber membrane (PVDF HFM) surface to improve its hydrophilicity and antifouling ability during wastewater filtration. The functional glue was synthesized from reclaimed styrene butadiene rubber (SBR) and a hydroxyl group was created with an epoxidation reaction (ESBR). The hydrophilic epigallocatechin-s-gallate (EGCG) was then precisely anchored via hydrogen bonding with multiple phenolic hydroxyl groups in the ESBR without penetrating into the inner matrix of the PVDF to prevent flux decline. The hydrophilicity of the PVDF membrane increased drastically and the water contact angle decreased from 62.7° to 45.1° with only a 25% decline in the pure water flux. Furthermore, due to precise anchoring of the EGCG, the modified EGCG-ESBR/PVDF membrane showed a higher pure water flux (110.6 L m−2h−1) and much higher BSA and oil (kerosene) rejection rates (approximately 94.5% and 99.5%, respectively) compared to membranes directly coated with EGCG (EGCG-PVDF). Moreover, the modified membrane also showed higher water flux recovery after multiple filtration cycles. This promising and efficient hydrophilic modification suggests great potential for application of the eco-friendly material in wastewater treatment.

Enhancing the C3 separation performances of polycrystalline ZIF-8 membranes by additive-assisted secondary growth

Polycrystalline zeolitic-imidazolate framework-8 (ZIF-8) membranes have shown very promising for propylene/propane (C3) separation. Though high-performance ZIF-8 membranes have been prepared by various synthesis methods, secondary growth method offers unique advantages due to its decoupling of a seeding step and a growth step, leading to membranes with better microstructures, thereby not only better separation performances but also higher reproducibility. However, there are only a few reports on ZIF-8 membranes with ultra-high C3 separation factors (i.e., >200) that are made by secondary growth method. Here, we report polycrystalline ZIF-8 membranes by a secondary growth method modified with an addition of 1,4-butanediol (Bdiol). The membranes showed significantly improved C3 separation factors up to ∼283 as compared to those prepared without modification. It was found that adding Bdiol in the secondary growth solution improved the microstructures of the ZIF-8 membranes, thereby enhancing their C3 separation performances. Furthermore, the presence of Bdiol in the growth solution enabled formation of well-intergrown ZIF-8 membranes even with a low linker-to-metal ratio (∼16), otherwise not possible to form ZIF-8 membranes. Interestingly, the resulting membranes showed a plate-like morphology with the highest separation factor of ∼283 among those prepared. All membranes in this work exhibited enhanced C3 separation performances as compared to those synthesized without modification.

Improved pervaporation dehydration performance of alginate composite membranes by embedding organo-montmorillonite

In this work, two different montmorillonite (MMT) nanoclays were incorporated in sodium alginate (Alg) solution for fabrication of hybrid membrane for pervaporative separation of aqueous isopropanol solution. Sodium-MMT (Na-MMT) was modified to organo-montmorillonite (O-MMT) using cationic surfactant dialkyldimethyl ammonium chloride (DDAC). The influence of incorporating MMTs on the membrane properties and separation performance was investigated. Intercalating of DDA+ on Na-MMT tailored the chemical structure and morphology of the MMTs. Integrating of MMTs modified the physicochemical properties of the membranes. The membrane morphology shows the homogeneous dispersion of MMTs in athe Alg matrix. Positron annihilation lifetime spectroscopy analysis revealed a tuned microstructure of the membranes. Swelling measurements showed better compatibility of O-MMT than the Na-MMT with the Alg matrix. As a result, AlgO-MMT had better separation performance than the AlgNa-MMT with permeation flux of 4764 g∙m−2∙h−1 and water concentration in permeate of 99.99 wt% on dehydrating 70 wt% IPA/water aqueous solution at 25 °C. Owing to the favorable compatibility between the polymer and filler, AlgO-MMT membrane demonstrated stability at different pervaporation operating conditions and long-term use. Our results demonstrated that the properties and separation performance of Alg membrane can be enhanced through incorporation of O-MMTs.

Ester-crosslinked polymers of intrinsic microporosity membranes with enhanced plasticization resistance for CO2 separation

Polymers of intrinsic microporosity (PIMs) have seen a growing role in gas separation membranes. Further exploitation of gas separation performance of PIM membranes and overcoming their persistent challenge of plasticization are urgently demanded. To address these issues, exemplified PIM-1 is synthesized and hydrolyzed to form carboxylated PIM-COOH polymers, followed by esterification using propylene glycol to prepare monoesterified PIM, which is finally thermally ester-crosslinked at various temperatures and time. The 300 °C-8 h treated membranes exhibit a CO2 permeability of 7421 Barrer, with a CO2/CH4 and CO2/N2 selectivity of 11.5 and 19.2, respectively, considerably exceeding the 2008 Robeson upper bounds. Furthermore, the crosslinked membranes demonstrate significantly enhanced CO2 plasticization resistance up to 42 bar, compared with uncrosslinked ones. It is the first time of reporting ester-crosslinking of carboxylated PIM-1 with both higher gas permeability and selectivity than PIM-1, using a much milder crosslinking temperature than other techniques, such as decarboxylated crosslinking. The design principle of this work paves the way for preparing high-performance and plasticization-resistant PIM membranes with promises for energy-efficient gas separations.

Highly selective and permeable SSZ-13 zeolite membranes synthesized by a facile in-situ approach for CO2/CH4 separation

High-quality tubular SSZ-13 zeolite membranes were fabricated by a facile in-situ approach for the first time. The in-situ approach requires only a single hydrothermal step for membrane growth, which is much simpler than the normal multi-step secondary-growth approach with seed preparation and seeding steps. The proper aging time and relatively high synthesis temperature provide sufficient nuclei for SSZ-13 growth, which further facilitates the in-situ formation of continuous membranes on the substrates. Three SSZ-13 zeolite membranes fabricated by the simple in-situ approach displayed ultrahigh average selectivity of (233 ± 46) and high average carbon dioxide permeance of (1220 ± 100) × 10−9 mol (m2 s Pa)−1 [∼3660 ± 300 Gas Permeation Unit (GPU), 1 GPU = 3.348 × 10−10 mol/(m2 s Pa)] at 298 K in the CO2/CH4 (50/50 in mol) mixture. The overall separation performance of the current membranes exceeded that of most reported zeolite membranes in the CO2/CH4 mixture. It indicated that the current in-situ synthesis approach had good reproducibility. The typical membrane also showed excellent separation performance in the CO2/N2 mixture toward the carbon capture from flue gas. The long-term stability of this membrane was investigated in the humidified CO2/CH4 mixture with a relative humidity close to 100%. This simple in-situ approach is suitable to prepare other zeolite membranes for gas separation after improving the gel nucleation.

Designing an energy-efficient multi-stage selective electrodialysis process based on high-performance materials for lithium extraction

Membrane technologies demonstrate great promise for treating salt lake brines with high Mg/Li mass ratios. However, current coupled membrane processes suffer from many obstacles, including poor membrane separation performance, high energy consumption, noncontinuous processes, large space occupation, and process complexity. Herein, we designed the multi-stage selective electrodialysis (S-ED) process with high-performance monovalent cation exchange membranes (MCEMs) to treat simulated penetration water from a one-stage nanofiltration (NF) process. The mussel-inspired gallic acid/polyethyleneimine assembled membrane (M-GA/PEI) with specific architecture and charge properties demonstrated better separation performance than CSO (a commercial MCEM) during the multi-stage S-ED process. The first-stage and second-stage S-ED processes with high-performance M-GA/PEI showed lower energy consumption (0.029–0.039 kWh·mol−1Li and 0.011–0.014 kWh·mol−1Li, respectively) than those with CSO and other processes with commercial MCEMs for lithium extraction (0.040–3.795 kWh·mol−1Li). This indicated that M-GA/PEI could be deployed as a substitute for commercial MCEMs to reduce the operation costs. This study provides new insights into the design of a multi-stage coupled membrane process (one-stage NF + first-stage S-ED + second-stage S-ED) based on high-performance materials for energy-efficient lithium extraction from salt lake brines towards a sustainable energy-water nexus.