Performance Of Mixed Matrix Membranes Research Articles

Investigating the impact of metal ion variations in terephthalate metal–organic frameworks on the organic solvent nanofiltration performance of mixed matrix membranes

Nano-fillers integrated into mixed matrix membranes (MMMs) present promising alternatives for organic solvent nanofiltration (OSN). In this work, our objective is to enhance OSN performance by incorporating terephthalate metal-organic frameworks (M-BDC, where M = Zr or Cu) into a P84 matrix to fabricate M-BDC/P84 composite MMMs. This work focuses on the influence of metal cluster variation on particle size, pore size distribution, and specific surface area of M-BDC, while systematically investigating the impact of M-BDC addition on OSN performance and underlying separation mechanisms. The synthesized membranes underwent comprehensive characterization using SEM, XRD, ATR-FTIR, contact angle, zeta potential, and thermogravimetric analysis. Significantly, all MMMs exhibited superior permeance and methyl blue (MB) rejection compared to P84 membranes. This enhancement is attributed to the improved interfacial contact between M-BDC and P84, as well as their effective dispersion within the membrane matrix. Interestingly, comparative analysis between Cu-BDC/P84 and Zr-BDC/P84 MMMs revealed the latter's superior permeance, attributed to its larger pore size and surface area. The resulting MMMs demonstrated outstanding MB rejection (>96.7%) with ethanol permeance of 21.5 and 19.0 LMH/Bar for Zr-BDC/P84 and Cu-BDC/P84 MMMs, respectively. Furthermore, the stable performance of M-BDC-based MMMs during prolonged MB/ethanol operation underscores their potential significance in the field of OSN, providing valuable insights for future membrane design and application.

Enhancing butanol separation efficiency in pervaporation with ZIF-8 porous liquid infused mixed matrix membranes

Separating butanol/water mixtures via distillation is notably energy-intensive and costly, highlighting the urgent need for more efficient alternatives. This study introduces a novel approach using mixed matrix membranes (MMMs) infused with Zeolitic Imidazolate Framework-8 (ZIF-8) transformed into its porous liquid (PL) form, aimed at enhancing the separation efficiency of butanol/water mixtures through pervaporation (PV). We selected ZIF-8 for its hydrophobic nature and high surface area, which are critical for improving both flux and selectivity in membrane-based separation processes. The study details the synthesis of ZIF-8-PL, its characterization through techniques such as Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and the fabrication of the MMMs. Our results demonstrate that ZIF-8-PL-based membranes at 55°C with a 30 wt% PL loading significantly enhance biobutanol-selective PV efficiency. Specifically, these membranes show an improvement in flux of approximately 102% and an increase in separation factor by 64% when compared to unmodified polydimethylsiloxane (PDMS) membranes. This significant enhancement highlights the effectiveness of PL-based fillers in advancing MMM performance for biofuel separation, providing a promising route to optimize energy efficiency and cost-effectiveness in industrial scale applications.

Comparison of the effect of topology type and linker composition of zeolitic imidazolate framework fillers on the performance of mixed matrix membranes in CO2/N2 separation

Mixed matrix membranes (MMMs) combine the high separation performance of porous materials with the processibility of polymers and so possess potential for carbon capture from CO2-containing gas streams. Zeolitic imidazolate frameworks (ZIFs) are promising candidates as molecular-sieve fillers in MMMs due to their tunability and ease of synthesis. We have compared four ZIFs, all as nanoparticles of similar sizes (ca. 400 nm), as MMM fillers, to investigate the effects of ZIF structure and chemistry on MMM performance of pure gas (CO2, N2) permeation under the same conditions. The chosen ZIFs include two that exhibit strong CO2 adsorption (hybrid ZIF-7/COK-17 and ZIF-94) and two that have higher pore volumes but weaker CO2 interactions (ZIF-8 and a hybrid ZIF-11/ZIF-71). The hybrid ZIF-7/COK-17 and ZIF-94 are structurally related to ZIF-7 (rhombohedral sod topology) and ZIF-8 (cubic sod), respectively, via partial or complete substitution of benzimidazole or 2-methylimidazole by 4,5-dichloroimidazole or 4-methyl-5-imidazolecarboxaldehyde, while the hybrid ZIF-11/ZIF-71 has the rho topology but the same composition as the ZIF-7/COK-17 hybrid. In the first part of the comparative study, MMMs based on two types of commercial polymers, Matrimid®5218 and PEBAX-MH1657, were prepared containing the ZIF-7/COK-17 hybrid and also with ZIF-94. ZIF-94 shows much better compatibility with the polymers, forming homogeneous dispersions at all loadings attempted (≤35 % wt%) whereas the hybrid shows inhomogeneity above 12 wt% in each case. At 12 wt% loading, both fillers show an increase in CO2 permeability at 1.2 bar and 293 K compared to the pure membrane (in PEBAX, this increases from 49.5 to 60 and 68 Barrer) which is the result of increased solubility compensating for decreased diffusivity, and this improvement in permeability continues to increase at the higher levels of loading possible with ZIF-94. ZIF-7/COK-17 in PEBAX show higher selectivity, achieving a calculated CO2/N2 selectivity up to 70. Further investigation of CO2 and N2 permeation on MMMs with the four ZIFs at 12 wt% in PEBAX-MH1657 showed a clear distinction between the ZIF-94 and ZIF-7/COK-17 MMMs (which show higher membrane solubilities but lower diffusivities) compared to ZIF-8 and ZIF-11/ZIF-71 MMMs. At the loading chosen, the CO2 permeability increase achieved by the four ZIFs over PEBAX-MH1657 increases in the order ZIF-11/-71, ZIF-7-COK-17 (ca. 60 Barrer) < ZIF-94 (68) < ZIF-8 (81), reflecting the complex interplay between CO2 solubility (increasing with interaction strength) and diffusivity (increasing with available cage and window size). The calculated CO2/N2 selectivity is highest for the hybrid ZIF-7/COK-17 membrane (70), which is attributed to molecular sieving effects in the rhombohedral sod structure

Nanocomposite membranes comprising covalent organic framework and polymer of intrinsic microporosity for efficient CO2 separation

The fabrication of new mixed-matrix membranes (MMMs) with superior gas permeability and selectivity are highly sought for industrial development of membrane separation technology for CO2 capture. This study reports improvement in CO2 permeability and selectivity by employing porous covalent organic framework (COF-TpPa-1). Herein, we report a novel PIM-1 doped with COF-TpPa-1 in various concentrations ranging from 0 to 10 wt% to prepare COF-TpPa-1/PIM-1 MMMs. Good compatibility between COF-TpPa-1 particles and PIM-1 matrix rendered an ideal interfacial morphology. The MMMs composed of 7 wt% COF-TpPa-1 exhibit a CO2 permeability of 6336 Barrer with an enhancement of 104 % compared to pristine sample and CO2/N2 ideal selectivity 20.1 among five tested compositions. The CO2 permeability of COF-TpPa-1 7 wt% doped membrane was 88 % more than pristine PIM-1 after 30 days aging, while CO2/N2 selectivity was well maintained, coupled with excellent anti-plasticization and mixed-gas separation properties. The overall gas separation performance of MMMs exceeds the Robeson Upper bound (2008) for CO2/N2 and O2/N2. The measured experimental permeability exhibited excellent agreement with the Singh thermal conductivity model at low loading (<5 wt%). This work provides a potential approach to fabricate PIM-1-based high performance MMMs with COF fillers for efficient CO2 separation.

Orientation of two-dimensional materials mf-BN in Pebax mixed matrix membranes by magnetic fields for enhancing CO2/N2 separation performance

Two-dimensional materials possess a high aspect ratio and excellent spatial utilization, making them potential filler for the fabrication of mixed matrix membranes (MMMs). However, the disordered arrangement of two-dimensional materials can negatively impact membrane performance. In this study, hexagonal boron nitride (h-BN) two-dimensional material loaded with polyethyleneimine (PEI) and magnetic material Fe3O4 was prepared. The filler (mf-BN) was incorporated into Pebax-1657, and the orientation of mf-BN in the MMM was controlled using a magnetic field. Horizontally and vertically oriented mf-BN/Pebax MMMs were successfully prepared and subjected to gas separation tests. The results demonstrate that oriented MMMs exhibit superior performance compared to non-oriented ones. When the mf-BN loading is 20 wt%, the CO2/N2 selectivity for horizontally and vertically oriented MMMs respectively reaches 83.9 and 76.8. The CO2 permeability increases to 114.7 and 139.8 Barrer, respectively. The magnetic field orientation of filler presents a promising approach for further enhancing the performance of MMMs.

Synergistic improvement in gas separation performance of MMMs by porogenic action and strong molecular forces of ZIF-93

In the present study, ZIF-93 metal–organic frameworks were prepared. N2 adsorption tests revealed that the particle size, specific surface area, and pore size of ZIF-93 were 30 nm–45 nm, 869.40 m2/g, and 0.36 nm, respectively. Pebax-based mixed matrix membranes (MMMs) were prepared using ZIF-93 as the filler. The pore diameters of ZIF-93 lied between the kinetic diameters of CO2 and N2; thus, its pore structure provided a fast transfer channel for CO2 and increased the permeability of the membrane. Further, X-ray diffraction showed that the membrane became denser upon introducing ZIF-93 because of the formation of a bridging structure between the Pebax molecular chains and ZIF-93. A denser stacking by moving the Pebax molecular chains closer to each other effectively bettered the CO2 selectivity of the mixed matrix membrane. The test results showed that when the ZIF-93 loading was 10 wt%, the CO2 permeability was 84.85 barrer and the CO2/N2 selectivity was 65.76 at 0.4 MPa, which are 51.57 % and 65.50 % higher than those of the pure Pebax membrane, respectively. When the feed pressure was increased to 0.8 MPa, the CO2 permeability was 94.5 barrer and the CO2/N2 selectivity is 87.5, which are 51.57 % and 65.50 % higher compared with those of the pure Pebax membrane, in order. The membrane performance significantly exceeded that of the 2008 Robeson curve.

Boosting CO2 transport in mixed matrix membranes by chitosan-MOF networks

The chitosan (CS)-grafted UiO-66-NH2 (U6N) (CSGUN) was synthesized and incorporated into Pebax matrix to fabricate mixed matrix membranes (MMMs) for boosting CO2 transport. The excellent CO2 separation performance was exhibited for MMMs due to the following reasons: U6N with the suitable porosity and abundant CO2 transport carriers can provide a unique “expressway” for CO2 to boost CO2 transport through MMMs. The grafting CS in CSGUN can connect Pebax (regular roads) and U6N (expressway), acting as an “on-ramp” between them to enrich CO2 and guide CO2 through U6N in an orderly manner. Thus, the constructed “on-ramp” and “expressway” in MMMs can improve CO2 separation performance. Furthermore, the CS-MOF networks were formed in MMMs through using CS molecular chains to connect U6N for enhancing CO2 separation performance of MMMs. Therefore, Pebax/CSGUN MMMs exhibited the excellent CO2 separation performance with the CO2 permeability of 558 ± 7 Barrer and the CO2/CH4 selectivity of 37.5 ± 0.7. The study indicated that MMMs with CS-MOF bridged networks had great potential for boosting CO2 transport by combining “expressways” and “on-ramp”.

Optimum content of incorporated nanomaterials: Characterizations and performance of mixed matrix membranes a review

Environmental concerns about chemical and biological pollution of water are of alarming proportions. Therefore, various polymeric membranes with improved mechanical and physico-chemical qualities for water treatment were developed using mixed matrix membranes (MMMs) or nanoparticles (NPs) embedded with the membranes. However, the problem of fouling and consequent higher operating and membrane replacement costs are barriers to the use of membrane technology. Therefore, a deeper comprehension of membrane fouling is not only essential for finding solutions but also a crucial factor in the development of membrane technology. The conventional blending modification would result in a large number of nanoparticles in the polymer matrix. In reality, the aggregation of nanoparticles in composite membranes is a considerable issue and would result in unfavorable changes to the features of the membrane (e.g. decreased water flux, weakened mechanical strength). In this review, it was looked into the effect of an optimal concentration of the hydrophilic nanoparticle additions to avoid the aggregation of nanoparticles in composite membranes and the reduced of using high amounts of valuable and costly nanoparticles in the membranes production and to obtain better results. The influence of the additives, such as (carbon nanotubes (CNTs), silica (SiO2), titanium dioxide (TiO2), zinc oxide (ZnO), aluminum oxide (Al2O3), and graphene oxide (GO), etc.) was investigated.

Graphene-Oxide-Modified Metal-Organic Frameworks Embedded in Mixed-Matrix Membranes for Highly Efficient CO2/N2 Separation.

MOF-74 (metal-organic framework) is utilized as a filler in mixed-matrix membranes (MMMs) to improve gas selectivity due to its unique one-dimensional hexagonal channels and high-density open metal sites (OMSs), which exhibit a strong affinity for CO2 molecules. Reducing the agglomeration of nanoparticles and improving the compatibility with the matrix can effectively avoid the existence of non-selective voids to improve the gas separation efficiency. We propose a novel, layer-by-layer modification strategy for MOF-74 with graphene oxide. Two-dimensional graphene oxide nanosheets as a supporting skeleton creatively improve the dispersion uniformity of MOFs in MMMs, enhance their interfacial compatibility, and thus optimize the selective gas permeability. Additionally, they extended the gas diffusion paths, thereby augmenting the dissolution selectivity. Compared with doping with a single component, the use of a GO skeleton to disperse MOF-74 into Pebax®1657 (Polyether Block Amide) achieved a significant improvement in terms of the gas separation effect. The CO2/N2 selectivity of Pebax®1657-MOF-74 (Ni)@GO membrane with a filler concentration of 10 wt% was 76.96, 197.2% higher than the pristine commercial membrane Pebax®1657. Our results highlight an effective way to improve the selective gas separation performance of MMMs by functionalizing the MOF supported by layered GO. As an efficient strategy for developing porous MOF-based gas separation membranes, this method holds particular promise for manufacturing advanced carbon dioxide separation membranes and also concentrates on improving CO2 capture with new membrane technologies, a key step in reducing greenhouse gas emissions through carbon capture and storage.

Fluorinated Metal–Organic Framework–Polymer Mixed Matrix Membrane with Tunable Hydrophobic Channel for Efficient Pervaporation of Butanol/Water

The permeability–selectivity trade‐off of membrane is a major challenge limiting the development of pervaporation (PV) technology. Rational design of high‐performance mixed matrix membranes (MMMs) has the potential to break off the trade‐off. Herein, a solvent‐assisted linker exchange‐based strategy is reported to introduce fluoroalkyl into metal–organic framework‐808 (MOF‐808). The pore size of fluorinated MOF‐808 can be adjusted with fluoroalkyl of different chain length (like trifluoromethyl and pentafluoropropyl). Then, the fluorinated MOF‐808/polyether block amide (PEBA) MMMs are prepared for the PV of n‐butanol/water. Compared with pristine PEBA membrane, 20 wt% 3F‐MOF‐808(P)/PEBA MMMs (3F = ‐CF3 group; P = postmodification method) exhibit 69% increase in permeation flux and 33% increase in separation factor in the PV of 2.5 wt% n‐butanol aqueous solutions at 70 °C. Based on Grand Canonical Monte Carlo and molecular dynamics simulations, fluorinated MOF‐808 shows better butanol affinity (pull effect) and stronger water repulsion ability (push effect). And the “push–pull effect” between fluorinated MOF‐808 with butanol/water is helpful to enhance the PV performance of MMMs. The application of “push–pull effect” provides a new strategy for the rational design of high‐performance MMMs, which is of great significance for the in‐depth research and application of PV technology.

Mixed matrix membranes with intrinsic microporous/UiO-66 post-synthesis modifications with no defects for efficient CO2/N2 separation

Mixed matrix membranes (MMMs) based on metal–organic frameworks (MOFs) are expected to realize efficient separation of CO2. However, interfacial compatibility issues between MOFs and polymer matrices limit their performance. In this work, a post-synthesis modification (PSM) strategy was adopted to convert UiO-66 into porous liquids (PLs). MMMs were prepared by incorporating PLs into PIM-1 matrix. The PLs have a liquid-like behavior and can be evenly scattered in PIM-1 matrix to form an interface without defect. The SEM morphology analysis further certified that MMMs had no interface defect and PLs had brilliant compatibility with the polymer film. In addition, the CO2-philic ether bonds of the EO fragments enable the MMMs to have superior CO2 selective separation. Compared with pure PIM-1, the highest CO2 permeability was improved by 158.0 % and 62.5 % was the increase in CO2/N2 selectivity, arriving at 7211.7 Barrer and 26.0, respectively. Meanwhile, the overall separation performance of MMMs for CO2/N2 exceeds the 2008 Robson upper limit, showing outstanding gas separation performance.

Stability of Filled PDMS Pervaporation Membranes in Bio-Ethanol Recovery from a Real Fermentation Broth.

Mixed matrix membranes (MMMs) have shown great potential in pervaporation (PV). As for many novel membrane materials however, lab-scale testing often involves synthetic feed solutions composed of mixed pure components, overlooking the possibly complex interactions and effects caused by the numerous other components in a real PV feed. This work studies the performance of MMMs with two different types of fillers, a core-shell material consisting of ZIF-8 coated on mesoporous silica and a hollow sphere of silicalite-1, in the PV of a real fermented wheat/hay straw hydrolysate broth for the production of bio-ethanol. All membranes, including a reference unfilled PDMS, show a declining permeability over time. Interestingly, the unfilled PDMS membrane maintains a stable separation factor, whereas the filled PDMS membranes rapidly lose selectivity to levels below that of the reference PDMS membrane. A membrane autopsy using XRD and SEM-EDX revealed an almost complete degradation of the crystalline ZIF-8 in the MMMs. Reference experiments with ZIF-8 nanoparticles in the fermentation broth demonstrated the influence of the broth on the ZIF-8 particles. However, the observed effects from the membrane autopsy could not exactly be replicated, likely due to distinct differences in conditions between the in-situ pervaporation process and the ex-situ reference experiments. These findings raise significant questions regarding the potential applicability of MOF-filled MMMs in real-feed pervaporation processes and, potentially, in harsh condition membrane separations in general. This study clearly confirms the importance of testing membranes in realistic conditions.

High CO2 adsorption of ultra-small Zr-MOF nanocrystals synthesized by modulation method boosts the CO2/CH4 separation performance of mixed-matrix membranes

The separation performance of mixed matrix membranes (MMMs) is greatly impacted by both the inherent structure of porous fillers and the interfacial compatibility between the filler and matrix. Here, ultra-small Zr-MOFs (UiO-66-mod and NH2-UiO-66-mod) with more defect sites were synthesized through a simple sodium formate modulation strategy. Then, these modulated Zr-MOFs were used as porous fillers in combination with polyetherimide (PEI) to construct a high-quality mixed matrix membrane for efficient CO2 separation. The modulated Zr-MOF not only exposed more defect sites, which significantly enhanced the CO2 adsorption capacity but also exhibited high dispersion in the PEI matrix due to strong interfacial forces, avoiding non-selective voids. The 10-UiO-66-mod-PEI and 10-NH2-UiO-66-mod-PEI membranes developed here showed admirable CO2/CH4 separation performance (CO2 permeability of around 400 and 440 Barrer, CO2/CH4 selectivity of ∼33 and ∼47, respectively) much higher than that of non-modulated UiO-66-PEI membranes, surpassing the 2008 upper bound of MMMs. This work demonstrated that the proposed UiO-66-mod-PEI and NH2-UiO-66-mod-PEI MMMs could be potential candidates for an efficient CO2 capture process.

Tailoring filler/gas vs. filler/polymer interactions via optimizing Co/Zn ratio in bimetallic ZIFs and decorating on GO nanosheets for enhanced CO2 separation

Despite numerous efforts devoted to enhancing the gas separation performance of mixed matrix membranes (MMMs), there still remain challenges in effectively embedding nanofillers into the polymer matrix due to the improper interactions between filler and polymer/gas molecules. Concerning that, synthesizing filler with well-structured physical and chemical properties and endowing its synergistic effects with a 2D filler has been considered a promising idea. Herein, five series of bimetallic ZIFs with various Co/Zn ratios were synthesized and embedded within the Pebax-1657 matrix to investigate the exact influence of metal ratio on the separation performance of MMMs. The results revealed that the Co60Zn40ZIF has the highest Co content that does not induce early chain rigidification, and enhances permeability and selectivity by 41.93 % and 93.65 % at 7.5 wt% loading, respectively. Furthermore, by hybridizing the optimized bimetal ZIF with GO, a substantial enhancement in selectivity was achieved, elevated by 250.37 % (compared to neat Pebax-1657) at the 7.5 % loading of GO@ZIF. The integration of the strategies applied to synthesizing bimetal ZIF with fine-tuned pores on the GO nanosheets exceeded the Robeson upper bond and yielded an exemplary separation index, which may offer enormous prospects for future research on multi-metallic composited MOF fillers.

Introducing pyrazole-based MOF to polymer of intrinsic microporosity for mixed matrix membranes with enhanced CO2/CH4 separation performance

The performance of mixed matrix membranes (MMMs) substantively depends on the intrinsic structure and composition of the introduced nanofillers. In this work, pyrazole-based metal-organic frameworks (termed as MOF-303) were introduced into polymer of intrinsic microporosity (PIM-1) through a physical blending approach. Thanks to the well CO2-philic capability, high porosity, and appropriate pore structure of the incorporated MOF-303, the obtained MMMs exhibited remarkable separation performance. The improved CO2 permeability and well-maintained CO2/CH4 selectivity were achieved. Specifically, MMMs introducing 30 wt% MOF-303 loading exhibited a CO2/CH4 selectivity of 27.6 and a high-CO2 permeability of 7528.2 Barrer, which were 2.2 and 1.9 times greater than those of the unfilled PIM-1 membranes, respectively. Furthermore, a 33-h continuous separation test verified the excellent stability of the manufactured MMMs. More importantly, the MMMs showed significant resistance against physical aging, retaining up to 92.8% of their original CO2 permeability after 150 days, compared to just 33.0% for control PIM-1 over the same period. Meanwhile, the plasticization resistance of the MMMs was reinforced compared to the unfilled PIM-1 membrane. This study potentially provides a novel approach for the rational design of MMMs in CO2 separation applications.

Investigation of ZIF‐8, amine‐modified ZIF‐8 and polysulfone based mixed matrix membranes for CO2/CH4 separation

AbstractMembrane separation is one of the techniques used for biogas upgradation. Mixed matrix membranes (MMMs) are currently being explored to overcome the trade‐off of selectivity‐permeability inherent in polymer membranes used for gas separation. A significant challenge associated with MMMs is the poor polymer‐metal–organic framework (MOF) filler interfacial compatibility, reducing the selectivity or permeability of gas. To address this issue, the present study focuses on the effect of the amine functionalization of ZIF‐8 to enhance the CO2 gas permeation without reducing the CO2/CH4 selectivity. MMMs were fabricated using unmodified ZIF‐8 and amine‐modified ZIF‐8 nanofillers dispersed in polysulfone at 5, 10, and 15 wt% loadings. MMMs were characterized by FTIR, DSC, TGA, and FESEM. X‐ray diffraction and FTIR analysis was conducted to verify the amine modification of ZIF‐8. Further, the performance of MMMs was tested with pure gasses (CO2 and CH4) and a model mixture of CO2 and CH4. In the mixed gas permeation test, the 10 wt% ZIF‐8 MMM exhibited the highest CO2 permeability of 25.4 Barrers, while 15 wt% NH2‐ZIF‐8 MMM exhibited the highest selectivity of 13.5. Notably, the ZIF‐8 MMMs demonstrated a 148% increase in CO2/CH4 selectivity, whereas the NH2‐ZIF‐8 MMMs exhibited a 155% increase compared to the pure polysulfone membrane.

Effect of TiO2 concentration in PVDF-TiO2-PVP mixed matrix membrane performance using ultrafiltration process

This study investigated how the addition of hydrophilic TiO2 to a porous asymmetric polyvinylidene fluoride (PVDF) Ultrafiltration (UF) membrane altered its properties and performance. The hydrophilicity and flux of PVDF and polyvinylpyrrolidone (PVP) combinations will be lower, and TiO2 will significantly impact raising those values. By mixing titanium dioxide (TiO2) nanoparticles with a pore-forming agent in a dope solution, PVDF-TiO2-PVP membranes were prepared via non-solvent-induced phase inversion method. Experiments using PVDF membranes with varying concentrations of TiO2 (0, 0.25, 0.5, 1, 1.5, and 2% wt) were applied to evaluate pure water flux and Bovine Serum Albumin (BSA) flux. The functional group composition of membranes was investigated by Fourier transform infrared spectroscopy. The wettability of porous membranes was determined by measuring contact angles. Results demonstrated that membranes constructed from PVDF/PVP/TiO2 with a lower loading of TiO2 nanoparticles had a smaller mean pore size, more apertures inside the membrane, and better membrane hydrophilicity. The highest flux of pure water (121 L/m2h) was achieved by the PVDF-TiO2-PVP mixed-matrix membrane at a TiO2 concentration of 2 wt%.

Effect of Thermally Reduced Graphene on the Characteristics and Performance of Polysulfone Mixed Matrix Ultrafiltration Membranes

Ultrafiltration (UF) polymeric membranes are widely used in water treatment and support desalination and gas separation membranes. In this article, we enhance the performance of Polysulfone (PSF) mixed matrix membranes (MMMs) by dispersing different concentrations of thermally reduced graphene (TRG) nanofillers. The UF PSF-TRG MMMs were fabricated via the phase inversion process, and the impact of TRG loading on the characteristics of the membrane, including hydrophilicity, porosity, roughness, and morphology, were analyzed using a contact angle measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM), and dynamic mechanical analysis. Incorporating TRG into the PSF matrix led to favorable effects in the instantaneous de-mixing during phase inversion, increasing the porosity and hydrophilicity of MMMs and improving the mechanical properties of the membranes. Moreover, membrane performance was examined to remove dispersed oil from oil–water emulsion and support air-dehumidification membranes. MMM performance in terms of flux and oil rejection was superior to the control PSF membrane. Incorporating 0.25% TRG into PSF resulted in a 70% water flux increase and higher oil rejection compared to the control PSF membrane. As a support for air-dehumidification membranes, the MMM also demonstrated enhanced humidity reduction and an over 20% increase in water vapor permeance over the control PSF membrane. These results indicate that the PSF-TRG MMMs are an excellent candidate for reliable oil–water separation and as a support for air-dehumidification membranes.

Mixed-matrix membranes composed of dopamine modified covalent organic framework and PIM-1 for efficient CO2/N2 separation

Due to the good compatibility and adjustable porous structure, covalent organic frameworks (COFs) gradually become one favorable filler to fabricate mixed matrix membranes (MMMs) used for efficient CO2 separation. In this study, TPB-TMDP-COF (TD-COF) with high porosity and long-range ordered structure was chosen to improve the CO2/N2 separation performance of the PIM-1 membrane. Meanwhile, the dopamine modified TD-COF was facilely prepared and incorporated into PIM-1 to fabricate MMMs considering the aperture adjustment and CO2-philic channel decoration. The MMMs composed of 3 wt% TD-COF shows a CO2 permeability of 8427.1 Barrer and a CO2/N2 ideal selectivity of 16.9 among three tested compositions. In comparison, the PIM-1 based MMMs that contains 3 wt% PDA@TD-COF exhibits a maximum CO2 permeability of 9750.6 Barrer and a CO2/N2 ideal selectivity of 26.4 at 1 bar and 30 oC, which are 82.0% and 54.3% higher than the pure PIM-1 membrane, respectively, far exceeding the known upper bound reported for CO2/N2 separation. Furthermore, the significant improvement of MMMs performance can be ascribed to the intensified gas diffusion due to long-range ordered channels of TD-COFs and the improved CO2 dissolution caused by more CO2 affinity sites of dopamine. In addition, the PDA@TD-COF/PIM-1 MMMs displayed decent plasticization resistance and long-term operational stability, indicating the great potential in industrial application.

PEO-based mixed matrix membranes containing N-doped microporous carbon microparticles for enhanced CO2/N2 separation

As a promising strategy to reduce greenhouse gas emissions, carbon dioxide capture from industrial and power plants has been proposed. Due to its advantages of low consumption and a modest environmental impact, membrane technology has been widely used in the gas separation process. Advanced porous fillers can be successfully added into the polymer matrix to create mixed matrix membranes (MMMs) with simple processing and applicable gas separation performance. The high porosity and stability of microporous carbon materials make them desirable for use in the gas separation process. Herein, N-doped microporous carbon microparticles (NMCP) were successfully synthesized and incorporated into UV crosslinked polyethylene oxide (XLPEO) matrix membranes. Fast CO2 transport channels are created in MMMs by rationally constructing NMCP fillers with ultra-micropores (∼0.53 nm), high-content heteroatoms (N, 13.94%), and two-dimensional morphology. The relationship between the structure of the NMCP samples and the gas separation performance of MMMs was discussed. Additionally, tests were conducted on the effects of NMCP loading, operating conditions, and long-term stability of NMCP/XLPEO membranes. NMCP/XLPEO membranes with a 2.5 wt% NMCP loading displayed a CO2 permeability of 606 Barrer and a CO2/N2 selectivity of 56.4, approaching the 2019 upper bound. This work offers a novel perspective to build fast gas transport channels in porous carbon-based MMMs for carbon capture.