Performance Of Mixed Matrix Membranes Research Articles

Zeolite/polyimide mixed-matrix membranes with enhanced natural gas purification performance: Importance of filler structural integrity

Mixed-matrix formulation is a promising method to overcome permeability-selectivity trade-off of polymers with incorporation of fillers with well-defined nanopores. The filler properties play a key role in determining the performance of mixed-matrix membrane (MMM). In this work, for the first time, we explored the critical effect of filler structural integrity on separation performance of MMM. Typically, micron as-synthesized, submicron as-synthesized and submicron ground SAPO-34 zeolites were incorporated into 6FDA-DAM polyimide, respectively. The interface compatibility between two phases was ensured by (3-aminopropyl) trimethoxysilane (APTMS) modification on SAPO-34 fillers. It was found that the directly synthesized micron and submicron fillers contributed to enhance the CO2/CH4 separation performance whereas the submicron ground filler lowered the CO2 permeability. Notably, incorporating 30 wt% micron as-synthesized SAPO-34 into 6FDA-DAM enhanced the CO2 permeability by 68% and CO2/CH4 by 37%, surpassing the performance upper-bound. Moreover, the hydrogen bonding between the filler and polymer matrix endowed the membrane with outstanding plasticization resistance with CO2 partial pressure up to 20 bar. Adsorption isotherms and Maxwell model prediction revealed that the filler transport properties could be significantly affected by commonly-used methods of reducing the filler size. A decreased structural integrity was identified in the sequence of micron as-synthesized, submicron as-synthesized and submicron ground fillers. This work highlights the importance of a careful balance between structural integrity and crystal size of filler, and reliable routes to obtain nanofillers with desirable structural integrity as pursuing high-performing MMM toward practical application.

Investigation of the effect of functionalized carbon nanotube and graphene oxide in guar gum‐based mixed matrix membrane for gas separation application

AbstractThe present study deals with preparing mixed matrix membranes (MMMs), a new polysaccharide‐based natural polymer used as a matrix with functionalized carbon nanotubes (FCNTs) and graphene oxide (GO) used as an inorganic filler. This work identified the effect of the inorganic fillers (FCNTs or GO) with naturally occurring polymer for gas separation. The incorporation of fillers improves the gas separation performance of MMMs. In GG/FCNTs MMMs, the selectivities of CO2/N2 and CO2/H2 were enhanced by 55.24% and 57.89%, respectively. Moreover, in GG/GO MMMs, the selectivities of CO2/N2 and CO2/H2 were improved by 99.50% and 50%, respectively. The membrane was characterized by scanning electron microscopy (SEM) and Fourier‐transform infrared spectroscopy (FTIR). The SEM analysis of GG/GO MMMs reveals layered structure, and GG/FCNTs MMMs create passages to transport gases. The Universal testing machine (UTM) is used to analyze the mechanical properties of pristine and modified membranes.

Improved CO2 separation performance of mixed matrix membranes via expanded layer double hydroxides and methanol post-treatment

Two-dimensional (2D) nanosheets (NSs) have shown significant promise as nanofillers in mixed-matrix membranes (MMMs) for overcoming the trade–off between permeability and selectivity. However, the effective regulation of the interlayer spacing of 2D NSs on the separation performance of MMMs remains a challenge. In this study, we adjusted the interlayer spacing of 2D NSs by intercalating layered double hydroxide (LDH) with different anions. The LDH NSs were embedded in a commercial polyether–block–amide (PEBAX 1657) to form MMMs for CO2 separation. The results of our study indicated that increasing the interlayer spacing and intercalated carboxyl groups of the LDH NSs facilitated the fast permeation of CO2 through the membranes. The prepared PEBAX/LDH MMMs (P–LDH series) exhibited promising CO2 permeability, accompanied by good CO2/N2 and CO2/CH4 selectivities. In addition, we demonstrated that methanol enabled the microstructure optimization of the prepared PEBAX/LDH MMMs. The synergistic effects of the intercalated LDH NSs and methanol post–treatment were studied to improve CO2 separation. The prepared MMMs were subjected to scanning electron microscopy (SEM), X-ray diffraction (XRD), FTIR, thermogravimetric analysis (TG), time-lag, positron annihilation lifetime spectroscopy (PALS), and mechanical tests. Methanol-treated MMMs (M–P–LDH series) showed significantly improved CO2 permeability, outstanding CO2/N2 selectivity, and excellent stability for long-term operation under harsh conditions, surpassing Robeson's 2008 upper-bound limit.

Surface-modified silicalite-1-filled PDMS membranes for pervaporation dehydration of trichloroethylene.

In this study, the impact of silane coupling agents, namely 3-aminopropyltrimethoxysilane (APTMS), trimethylchlorosilane (TMCS), and 1,1,3,3-tetramethyldisilazane (TMDS), on the hydrophobicity of silicalite-1 zeolite was investigated to enhance the pervaporation separation performance of mixed matrix membranes (MMMs) for trichloroethylene (TCE). The hydrophobicity of TMCS@silicalite-1 and TMDS@silicalite-1 particles exhibited significant improvement, as evidenced by the increase in water contact angle from 96.1° to 101.9° and 109.1°, respectively. Conversely, the water contact angle of APTMS@silicalite-1 particles decreased to 85.2°. Silane-modified silicalite-1 particles were incorporated into polydimethylsiloxane (PDMS) to prepare mixed matrix membranes (MMMs), resulting in a significant enhancement in the adsorption selectivity of trichloroethylene (TCE) on membranes containing TMCS@silicalite-1 and TMDS@silicalite-1 particles. The experimental findings demonstrated that the PDMS membrane with a TMDS@silicalite-1 particle loading of 40 wt% exhibited the most favorable pervaporation performance. Under the conditions of a temperature of 30 °C, a flow rate of 100 mL min-1, and a vacuum degree of 30 kPa, the separation factor and total flux of a 3 × 10-7 wt% TCE aqueous solution were found to be 139 and 242 g m-2 h-1, respectively. In comparison to the unmodified silicalite-1/PDMS, the separation factor exhibited a 44% increase, while the TCE flux increased by 16%. Similarly, when compared to the pure PDMS membrane, the separation factor showed an 83% increase, and the TCE flux increased by 20%. These findings provide evidence that the hydrophobic modification of inorganic fillers can significantly enhance the separation performance of PDMS membranes for TCE.

Introducing defect-engineering 2D layered MOF nanosheets into Pebax matrix for CO2/CH4 separation

The layered Ni-MOF nanosheets (Ni-NS) with defective structure were used as fillers to prepare mixed matrix membranes (MMMs) for CO2 separation. In this work, the defect structure of Ni-MOF nanosheets was manipulated by adjusting the molar ratio of metal source to organic linker (RM/L), and the influence of defects at the Ni-MOF nanocrystal on the gas separation performance of MMMs was investigated. The characterization of filler and membranes showed that Ni-MOF nanosheets with defective structure could improve the gas separation performance mainly through the enlarged pore size and the increased adsorption sites. Compared with the Ni-NS-2 with complete crystal structure, the Ni-NS-8 with defective structure showed better interfacial compatibility with poly(ether-block-amide) (Pebax® MH 1657) matrix. The Pebax/Ni-NS-8-6 MMM showed the best CO2/CH4 separation performance. The CO2 permeability and CO2/CH4 selectivity were 436.1 Barrer and 33.1, which were 115% and 18% higher than those of pure Pebax membrane, respectively. The results showed that defect-engineering in MOF nanocrystals was an important strategy to optimize the gas separation performance of 2D MOF-based MMMs.

Aminosilane-Functionalized Zeolite Y in Pebax Mixed Matrix Hollow Fiber Membranes for CO2/CH4 Separation

Due to their interfacial defects between inorganic fillers and polymer matrices, research into mixed matrix membranes (MMMs) is challenging. In the application of CO2 separation, these defects can potentially jeopardize the performance of membranes. In this study, aminosilane functionalization is employed to improve the nano-sized zeolite Y (ZeY) particle dispersion and adhesion in polyether block amide (Pebax). The performance of CO2/CH4 separation of Pebax mixed matrix composite hollow fiber membranes, incorporated with ZeY and aminosilane-modified zeolite Y (Mo-ZeY), is investigated. The addition of the zeolite filler at a small loading at 5 wt.% has a positive impact on both gas permeability and separation factor. Due to the CO2-facilitated transport effect, the performance of MMMs is further improved by the amino-functional groups modified on the ZeY. When 5 wt.% of Mo-ZeY is incorporated, the gas permeability and CO2/CH4 separation factor of the Pebax membrane are enhanced by over 100% and 35%, respectively.

Constructing multi-dimensional transport pathways by mixed-dimensional fillers in membranes for efficient CO2 separation

Mixed matrix membranes (MMMs) with mixed-dimensional fillers can take simultaneously advantages of the different-dimensional materials, and they hold the potential in exhibiting excellent CO2 separation performance. In this study, the mixed-dimensional fillers of NiCo-layered double hydroxide-decorated polypyrrole nanotubes (PNT@NiCo-LDH) were synthesized and incorporated into Pebax MH 1657 (Pebax) matrix to fabricate MMMs for efficient CO2 separation. PNT@NiCo-LDH played a vital role in MMMs. PNT@NiCo-LDH can take the advantages of the tubular structure of PNT, the lamellar structure of LDH, the hollow nanocage structure of NiCo-LDH, constructing 1D/2D/3D CO2 transport pathways in MMMs, respectively. Thus, the construction of multi-dimensional (1D/2D/3D) CO2 transport pathways could synergistically improve CO2 separation performance of MMMs. Besides, the CO2-affinity groups (amino groups and hydroxyl groups) and bimetallic sites (Ni and Co) on PNT@NiCo-LDH effectively accelerated CO2 selective transport in MMMs, increasing CO2/CH4 selectivity. Therefore, the as-prepared MMMs exhibited an excellent CO2 separation performance. The Pebax/PNT@NiCo-LDH-5 MMM showed the optimum CO2 permeability of 513 ± 10 Barrer and CO2/CH4 separation factor of 39 ± 0.5. This work implied that the construction of multi-dimensional CO2 pathways by mixed-dimensional fillers were an effective strategy for efficient CO2 separation in MMMs.

The effect of filler loading and APTES treatment on the performance of PSf/SBA-15 mixed matrix membranes

Abstract The fabrication of mixed matrix membranes (MMMs) is of particular importance due to their advantages over neat membranes. The performance of MMMs is a function of the type and fraction of the nanoparticles in the membrane. Moreover, the proper interaction of the polymer and nanoparticles affects the MMMs performance. In this study polysulfone (PSf)/SBA-15 mesoporous silicas MMMs were prepared and their performance was evaluated for CO2/CH4 gas separation. SBA-15 mesoporous silicas were previously synthesized and functionalized with 3-aminopropyltriethoxysilane by post-synthesis treatment. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, N2 adsorption–desorption, and Brunauer–Emmett–Teller analysis was applied to examine the functional groups, morphology, and textural properties of the unmodified and modified mesoporous silica in the prepared membrane, respectively. The effects of modified and unmodified SBA-15 particle loading were investigated for the gas separation performance of PSf/SBA-15 membranes. The experimental results illustrate that a higher modified mesoporous silica loading leads to an increase in gas permeance and gas pair selectivity. The highest increase in permeability and selectivity was related to the incorporation of S2 and AP-S2 into the PSf matrix, respectively.

Breakthroughs on tailoring membrane materials for ethanol recovery by pervaporation

• Mixed matrix membranes (MMMs) with well-designed membrane structures may provide both high permeability and membrane selectivity to break trade-off effect due to the better control over physi-/chemical micro-environment and cavity/pore size as well as size distribution. • Fillers should be orderly arranged in polymer matrix and form continuous transport channels for ethanol to full play the synergistic effect of polymer and fillers. • Building firm bonding interactions between filler and polymer is one of the most promising methods to strengthen the PV performance of MMMs. • The development of bioinspired materials and structures provides enlightening ideas for the construction of ethanol perm-selective membranes. Bioethanol, as a clean and renewable fuel, has gained increasing attention due to its major environmental benefits. Pervaporation (PV) is a promising and competitive technique for the recovery of ethanol from bioethanol fermentation systems due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. The main challenge for the industrial application of ethanol perm-selective membranes is to break the trade-off effect between permeability and selectivity. As membrane is the heart of the pervaporation separation process, this article attempts to provide a comprehensive survey on the breakthroughs of ethanol perm-selective PV membranes from the perspectives of tailoring membrane materials to enhance PV separation performance. The research and development of polymeric and organic/inorganic hybrid membranes are reviewed to explore the fundamental structure-property-performance relationships. It is found that mixed matrix membranes with well-designed membrane structures offer the hope of better control overphysi-/chemical micro-environment and cavity/pore size as well as size distribution, which may provide both high permeability and membrane selectivity to break the trade-off effect. The tentative perspective on the possible future directions of ethanol perm-selective membranes is also briefly discussed, which may provide some insights in developing a new generation of high-performance PV membranes for ethanol recovery.

Nanoengineered ZIF fillers for mixed matrix membranes with enhanced CO2/CH4 selectivity

Zeolitic-imidazolate frameworks (ZIFs) are considered as promising nanoporous solids for the development of membranes with exceptional gas separation properties. In this work, we show how molecular-scale modifications can lead to ZIF variants, which can greatly enhance the CO2/CH4 separation performance of mixed-matrix membranes (MMMs) when used as additives. First the permeabilities of CO2 and CH4 in ZIF-8 are estimated with the help of molecular simulations. Based on these results and a macroscopic model, the performance of MMMs with ZIF-8 as fillers is deduced. The validity of this approach is confirmed through experiments by developing flat-sheet ZIF-8 based nanocomposite membranes with two typical polymers (rubbery Pebax® MH1657 and glassy 6FDA-DAM) having different permeability properties. In a subsequent step, we design computationally new ZIF crystals, by changing the original metal, organic linker and functional group of ZIF-8, and the CO2/CH4 separation performance of MMMs with the new ZIF variants is predicted. Our results reveal that some of these MMMs exhibit an unprecedented CO2/CH4 separation performance, which surpasses any reported MMM and is directly attributed to the enhanced sieving capacity of the modified ZIF fillers. In conclusion, this work highlights the effectiveness of ZIF nanoengineering as a means to develop highly selective CO2 membranes.

Visualization of the gas permeation in core–shell MOF/Polyimide mixed matrix membranes and structural optimization based on finite element equivalent simulation

Core-shell MOFs recently have suggested the greater potential on gas separation of mixed matrix membranes (MMMs) than the single MOFs. In this work, two core–shell MOFs (ZIF-67@ZIF-8 (ZIF-67@8) and ZIF-8@ZIF-67 (ZIF-8@67)) with adverse structure were specially designed to explore what structure is more conducive to gas separation of MMMs. Moreover, a simplified equivalent simulation based on electrical conductivity of Maxwell model was adopted to predict the gas permeability and the internal gas permeation behavior for core–shell MOF based MMMs. The simulation exhibited the better predicted results than the Felske model and revealed the gas transport pathway. As a result, ZIF-67@8 based MMM with the shell-dependent transport and a thin interlayer had the highest H2 permeability of 224 Barrer and H2/CH4 separation factor of 76.7, which are 180% and 24% higher than neat PI, respectively. Finally, core–shell MOFs based MMMs also showed the lower temperature dependence of permeation for N2 and CH4 compared to pure PI. This work provides a unique method to investigate how core–shell structure affects the gas separation performance of MMMs, especially for equivalent simulation, which not only is proved to play as an efficient tool to predict the gas permeability, but also exhibits a great potential on investigation of gas transport pathway for the further structural optimization.

Fabrication of polydimethylsiloxane mixed matrix membranes for recovery of ethylene glycol butyl ether from water by pervaporation

Due to its wide application as a solvent or cleaning agent in automotive paints and other coatings industries, the separation and recovery of ethylene glycol butyl ether (EB) from wastewater played a key role in reducing emissions in industries such as automotive coatings. To achieve the efficient separation of EB by pervaporation process, three different types of nanomaterials were first used as additives to construct the mixed matrix membranes (MMMs) for pervaporation using polydimethylsiloxane (PDMS) as the polymer material. The addition of three nanomaterials could improve the affinity of the resulting MMMs toward EB and accelerate the diffusion process of EB in MMMs, thus eventually enhancing the separation performance of the resulting membranes. When three nanomaterials seriously agglomerated in polymeric materials, the improvement of the EB diffusion in MMMs decreased. Moreover, the diffusion of EB molecules in the MMMs containing nanomaterials was still lower than that of water molecules due to the insufficient capturing of EB, and the diffusion selectivity of the resulting MMMs for EB was less than 1. The surface modification for nanomaterials by grafting polyethylene glycol (PEG) could enhance the affinity between PEG-grafted nanomaterials and EB molecules, which simultaneously improved the swelling performance of MMMs and the diffusion process of EB in MMMs. Owing to the stronger affinity between the PEG2000-grafted nanomaterials containing more ether groups and EB molecules, PDMS incorporated with PEG2000-grafted nanomaterials exhibited the best membrane flux (730 g m−2 h−1) and selectivity (30), which was twice that of the commercial membrane. Furthermore, the PDMS incorporated with PEG2000-grafted nanomaterials maintained excellent and stable performance for separating EB during pervaporation for 20 h, while the separation performance of the commercial membrane decreased significantly after 12 h of pervaporation experiments. Therefore, the MMMs fabricated in this work are promising candidates for the separation and recovering the ether solvents through membrane technology.

Controlled Covalent Functionalization of ZIF-90 for Selective CO2 Capture & Separation.

Mixed Matrix Membranes (MMM) with enhanced selectivity and permeability are preferred for gas separations. The porous metal-organic frameworks (MOFs) materials incorporated in them play a crucial part in improving the performance of MMM. In this study, Zeolitic imidazolate frameworks (ZIF-90) are selected to fabricate Polyetherimide (PEI) MMMs owing to their lucrative structural and chemical properties. This work reports new controlled post-synthetic modifications of ZIF-90 (50-PSM-ZIF-90) with ethanolamine to control the diffusion and uptake of CO2. Physical and chemical properties of ZIF-90, such as stability and presence of aldehyde functionality in the imidazolate linker, allow for easy modulation of the ZIF-90 pores and window size to tune the gas transport properties across ZIF-90-based membranes. Effects of these materials were investigated on the performance of MMMs and compared with pure PEI membranes. Performance of the MMMs was evaluated in terms of permeability of different gases and selective separation of CO2 and H2 gas. Results presented that the permeability of all membranes was in the following order, i.e., P(H2) > P(CO2) > P(O2) > P(CH4) > P(C2H6) > P(C3H8) > P(N2), demonstrating that kinetic gas diffusion is the predominant gas transport mode in these membranes. Among all the membranes, permeability of pure PEI membrane was highest for all gases due to the uniform porous morphology. The pure PEI membrane showed highest permeability of H2, which is 486.5 Barrer, followed by 49 Barrer for O2, 29 Barrer for N2, 142 Barrer for CO2, 41 Barrer for CH4, 40 Barrer for C2H6 and 39.6 Barrer for C3H8. Results also confirm the superiority of controlled PSM-ZIF-90-PEI membrane over the pure PEI and ZIF-90-PEI membranes in CO2 and H2 separation performance. The 50-PSM-ZIF-90 PEI membrane exhibited a 20% increase in CO2 separation from methane and a 26% increase over nitrogen compared to the ZIF-90-PEI membrane. The 50-PSM-ZIF-90 PEI membrane showed 15% more H2/O2 separation and 9% more H2/CH4 separation than ZIF-90 PEI membrane. Overall, this study represents the role of controlled PSM in enhancing the property of new materials like ZIF and its application in MMMs fabrication to develop a promising approach for the CO2 capture and separation.

Phenolic resin regulated interface of ZIF-8 based mixed matrix membrane for enhanced gas separation

The performance of mixed matrix membranes (MMMs) is significantly determined by the inherent structure and composition of incorporated nanofillers. In this work, the core-shell ZIF-8@RF nanofillers were prepared through a kinetically-controlled growth of zeolitic imidazolate framework-8 (ZIF-8) and polymerization of resorcinol and formaldehyde (RF), followed by being incorporated into the glassy 6FDA-Durene and rubbery Pebax 1657 via a physical blending approach to form MMMs. Benefiting from the enhanced interfacial compatibility, CO2 affinity, and the intrinsic characteristics of porous ZIF-8, the resultant MMMs demonstrated outstanding performance for CO2/CH4 separation. The CO2 permeability and CO2/CH4 selectivity of the ZIF-8@RF/6FDA-Durene (ZIF-8@RF/Pebax 1657) MMMs increased up to 1332.1/363 Barrer and 28.6/29.6, corresponding to an improvement of 65.4/116.3% of the CO2 permeability and 49.7/53.4% of the CO2/CH4 selectivity compared to the pristine membrane. Meanwhile, CO2/CH4 selectivity of ZIF-8@RF MMMs increases by up to 33.0% and 28.1% in comparison to the ZIF-8 without RF layer MMMs, respectively. More importantly, both MMMs can maintain their extraordinary separation performance after stabilized in the existence of moisture. These results demonstrate that the separation performance of the MMMs was remarkably improved with the addition of ZIF-8@RF.

Synthesis of novel Al2O3 nanoparticle organic hybrid materials for enhancing the CO2-separation performance of prepared Al2O3-NOHMs/Pebax mixed matrix membrane

In this study, a novel liquid-like nanoparticle organic hybrid materials (NOHMs) is synthesized, in which Al2O3 was used as core, called as Al2O3-NOHMs, and it has been used for the first time to improve the performance of mixed matrix membranes (MMMs) for CO2 capture. In addition, the Al2O3-NOHMs with core/corona/canopy structure observed by TEM possess unique enthalpy effect and entropy effect, which can break through the trade-off effect of membrane separation process. According to gas separation permeation tests, the Al2O3-NOHMs/Pebax mixed matrix membranes with 2 wt% Al2O3-NOHMs showed higher CO2 permeability of 137.15 Barrer and CO2/N2 selectivity of 77.8 compared with neat Pebax membranes, and surpassed 2008 Robeson upper bound. Hence, this novel NOHMs is a very promising alternative to prepare MMMs for CO2 capture.

CO2 separation of fluorinated 6FDA-based polyimides, performance-improved ZIF-incorporated mixed matrix membranes and gas permeability model evaluations

In this study, we compare a newly introduced high free volume fluorinated 6FDA-polyimide, namely 6FDA-bisP, with excellent gas separation properties (CO2 permeability, PCO2 of 35.3 Barrer; CO2/CH4 selectivity, αCO2/CH4 of 25.5) to the well-investigated, lower free volume 6FDA-ODA (PCO2 = 25.9 Barrer; αCO2/CH4 = 20.6). Their gas separation performances were improved in the form of mixed matrix membranes (MMMs) with size sieving zeolitic imidazolate framework (ZIF-8, particle range of <160 nm) addition between 5 and 20 wt% loadings. XRD, BET, FTIR, TGA, DSC, SEM, and TEM were used to characterize the nanoparticles and MMMs. Solid density was obtained from He pycnometry analysis (pressurized cycle test between 2 and 20 bar at 20 °C) to calculate the free fractional volume (FFV). Using an equimolar CO2 and CH4 mixture, gas separation performance was evaluated at a constant 5 bar, at 25 °C. The optimum loading was achieved at 15 wt% for 6FDA-bisP with MMM performance of PCO2 = 81.2 Barrer and αCO2/CH4 = 35.0, whereas 10 wt% for 6FDA-ODA (PCO2 = 42.2 Barrer; αCO2/CH4 = 44.8). The MMMs showed superior performances than the currently relevant polymers in industrial separation processes. Four different gas permeability models: Maxwell, Maxwell-Wagner-Sillar, Higuchi and Lewis Nielsen, were utilized to analyze the obtained data.

Toluene/water separation using MCM-41/ PEBA mixed matrix membrane via pervaporation process

Pervaporation (PV) process with the mixed matrix membrane (MMM) is a feasible and cost-effective alternative to conventional volatile organic compounds (VOC) removal methods. In this study, the mesoporous silicate MCM-41 was synthesized by a new and rapid sol-gel method and incorporated into the polyether-block-amide (PEBA-2533) polymer network. Prepared MMM and MCM-41 were characterized by XRD, FESEM, TEM, AFM, TGA, DSC, FTIR, contact angle, and mechanical analyses. Effect of MCM-41 calcination on the performance of MMM for toluene/water solution separation was studied using a PV setup. Experiments were conducted to determine the effects of MCM-41 loading, feed concentration, and feed temperature on total flux, component flux, separation factor, and pervaporation separation index (PSI). For a 300 ppm toluene aqueous solution at 30 °C, the separation factor, from 44.4 to 203.7 (358.7% increment), and toluene flux, from 3.9 to 10.5 g m−2 h−1 (163.8% increment), were improved by using 7.5% uncalcined MCM-41 loading. The PSI value of this sample was attained at 67290 g m−2 h−1, which was 412% higher than that of a neat PEBA membrane (13142 g m−2 h−1).

Boosting the permeation of ultrafiltration membranes by covalent organic frameworks nanofillers: Nanofibers doing better than nanoparticles

Mixed matrix membranes (MMMs) have attracted everlasting attentions, as their large permeance and high selectivity can be accessible synchronously. Herein, we show that covalent organic framework (COF) nanofibers serving as the nanofillers are doing better than COF nanoparticles in boosting the separation performance of MMMs. The nanofibers and the nanoparticles are synthesized and doped into polysulfone matrices to prepare MMMs. The high porosity and relative hydrophilicity of TpPa nanofibers and nanoparticles enable rapid exchange of solvent and nonsolvent during the process of nonsolvent induced phase separation, thus leading to instantaneous demixing. Furthermore, compared with TpPa nanoparticles possessing small and irregular shapes, the one-dimensional structure of TpPa nanofibers weakens the entanglement of the surrounding polysulfone linear chains, resulting in much pronounced instantaneous demixing. In contrast with the nanoparticle-incorporated membranes, the porosity of nanofiber-incorporated membranes is significantly improved. The resultant nanofiber-incorporated membrane demonstrates a high water permeance of 424.4 L m−2 h−1 bar−1, along with a BSA rejection rate of 94.3%. This work clearly reveals that porous one-dimensional structures such as COF nanofibers are highly promising in the preparation of high-performance MMMs.

Preparation of Pebax 1657/MAF-7 Mixed Matrix Membranes with Enhanced CO2/N2 Separation by Active Site of Triazole Ligand.

Fillers play a critical role in the performance of mixed matrix membranes (MMMs). Microporous metal azolate frameworks (MAFs) are a subclass material of metal–organic frameworks (MOFs). Due to the uncoordinated nitrogen of the organic ligands, MAF-7 (SOD-[Zn(mtz)2], Hmtz = 3-methyl-1,2,4-triazole, window: d = 0.34 nm) shows excellent CO2 adsorption performance. In this work, Pebax 1657/MAF-7 MMMs were prepared by a sample solution casting method with MAF-7 particles as fillers for the first time. By means of X-ray diffraction (XRD), scanning electron microscope (SEM), infrared radiation (IR), and thermogravimetry (TG), the compositional and structural properties of the mixed matrix membrane with different filler content were analyzed. The results show that the compatibility of MAF-7 and Pebax is good with a filler content of 5 wt.%. The pure gas testing showed that mixed matrix membrane has a high ideal CO2/N2 selectivity of 124.84 together with a better CO2 permeability of 76.15 Barrer with the optimized filler content of 5 wt.%. The obtained membrane showed 323.04% enhancement in selectivity of CO2/N2 and 27.74% increase in the permeability of CO2 compared to the pristine membrane at 25 °C and 3 bar. The excellent separation performance may be due to the ligands that can afford a Lewis base active site for CO2 binding with the uniform dispersion of MAF-7 particles in Pebax and the favorable interface compatibility. The obtained membrane overcomes the Robeson’s upper bound in 2008 for CO2/N2 separation. This work provides a new strategy by utilizing MAFs as fillers with triazole ligand to enhance the gas separation performance of mixed matrix membranes.

CO2 separation performance for PIM based mixed matrix membranes embedded by superbase ionic liquids

• Superbase ionic liquid [HDBU][Im] has high affinity towards ZIF-67 and PIM-1. • The addition of [HDBU][Im]@ZIF-67 improves CO 2 separation performance of MMMs. • Reducing temperature increases the CO 2 selectivity by enhancing the CO 2 solubility. Mixed matrix membranes (MMMs) have drawn much interest in CO 2 separation due to their excellent separation performance, mechanical property, and desirable processability. However, obtaining highly compatible MMMs is a great challenge and is vital to avoid the loss of the separation selectivity of the MMMs. In this work, superbase ionic liquid (1,8-diazabicyclo[5,4,0]undec-7-ene imidazole ([HDBU][Im])) was used as a wetting agent to increase the interfacial compatibility between ZIF-67 and PIM-1, hence improving the membrane gas separation. [HDBU][Im] embeding into the MMMs could efficiently enhance the compatibility and diminish the interfacial voids. Furthermore, incorporating 5 wt% [HDBU][Im]@ZIF-67 nanocomposite into the PIM-1 matrix improves the gas permeability and CO 2 selectivity. The separation performances under the different temperatures were also conducted and showed that reducing temperature slightly decreases the gas permeability but significantly increases the CO 2 /CH 4 selectivity via enhancing the CO 2 solubility. The permeation active energies, diffusivities and solubilities were obtained to explain the gas permeate mechanism.