Comparison between ZIF-67 and ZIF-8 in Pebax® MH-1657 mixed matrix membranes for CO2 separation

Study of mixed matrix membranes with in situ synthesized zeolite imidazolate frameworks (ZIF-8, ZIF-67) in polyethersulfone polymer for CO2/CH4 separation

Biogas, produced from anaerobic digestion, is a sustainable and renewable energy source. To upgrade biogas to Bio-CNG, CO2 must be removed from the raw mixture. Membrane separation is an economical process for the removal of CO2, and mixed matrix membranes (MMMs) are being explored for CO2/CH4 separation. MMMs are fabricated using techniques such as in situ techniques to overcome research gaps, such as in filler agglomeration and filler-polymer interfaces. In this work, MMMs were fabricated using the in situ growth of ZIF-8 and ZIF-67 in polyethersulfone (PES) and compared with traditional filler dispersion of ZIF-8 and ZIF-67. The fabricated MMMs were characterized and tested for gas permeation using a model biogas. Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FESEM) analysis were conducted to confirm in situ synthesis of ZIF-8 and ZIF-67. CO2 permeability of in situ ZIF-8 and ZIF-67-based MMMs have enhanced to 84.5 Barrer and 78.8 Barrer, respectively, compared to pure PES membrane, which is around 25 Barrer. Similarly, ZIF-8 and ZIF-67-based traditional MMMs have shown an increase in the CO2 permeability of 75.6 Barrer and 68 Barrer, respectively. Additionally, the selectivity for CO2/CH4 separation increased for some of the prepared MMMs, demonstrating the effectiveness of the in situ fabrication method.

Micro and Nanoporous Membrane Platforms for Carbon Neutrality: Membrane Gas Separation Prospects

Recently, carbon neutrality has been promoted as a potentially practical solution to global CO2 emissions and increasing energy-consumption challenges. Many attempts have been made to remove CO2 from the environment to address climate change and rising sea levels owing to anthropogenic CO2 emissions. Herein, membrane technology is proposed as a suitable solution for carbon neutrality. This review aims to comprehensively evaluate the currently available scientific research on membranes for carbon capture, focusing on innovative microporous material membranes used for CO2 separation and considering their material, chemical, and physical characteristics and permeability factors. Membranes from such materials comprise metal-organic frameworks, zeolites, silica, porous organic frameworks, and microporous polymers. The critical obstacles related to membrane design, growth, and CO2 capture and usage processes are summarized to establish novel membranes and strategies and accelerate their scaleup.

Enhancement strategies of poly(ether-block-amide) copolymer membranes for CO2 separation: A review

Poly(ether-block-amide) (Pebax) membranes have become the preferred CO2 separation membrane because of their excellent CO2 affinity and robust mechanical resistance. Nevertheless, their development must be considered to overcome the typical obstacles in polymeric membranes, including the perm-selectivity trade-off, plasticization, and physical aging. This article discusses the recent enhancement strategies as a guideline for designing and developing Pebax membranes. Five strategies were developed in the past few years to improve Pebax gas transport properties, including crosslinking, mobile carrier attachment, polymer blending, filler incorporation, and the hybrid technique. Among them, filler incorporation and the hybrid technique were most favorable for boosting CO2/N2 and CO2/CH4 separation performance with a trade-off-free profile. On the other hand, modified Pebax membranes must deal with two latent issues, mechanical strength loss, and perm-selectivity off-balance. Therefore, exploring novel materials with unique structures and surface properties will be promising for further research. In addition, seeking eco-friendly additives has become worthwhile for establishing Pebax membrane sustainable development for gas separation.

Enhancing Hydrogen Sulfide Detection at Room Temperature Using ZIF-67-Chitosan Membrane

Developing new materials for energy and environment-related applications is a critical research field. In this context, organic and metal-organic framework (MOF) materials are a promising solution for sensing hazardous gases and saving energy. Herein, a flexible membrane of the zeolitic imidazole framework (ZIF-67) mixed with a conductivity-controlled chitosan polymer was fabricated for detecting hydrogen sulfide (H₂S) gas at room temperature (RT). The developed sensing device remarkably enhances the detection signal of 15 ppm of H₂S gas at RT (23 °C). The response recorded is significantly higher than previously reported values. The optimization of the membrane doping percentage achieved exemplary results with respect to long-term stability, repeatability, and selectivity of the target gas among an array of several gases. The fabricated gas sensor has a fast response and a recovery time of 39 s and 142 s, respectively, for 15 ppm of H₂S gas at RT. While the developed sensing device operates at RT and uses low bias voltage (0.5 V), the requirement for an additional heating element has been eliminated and the necessity for external energy is minimized. These novel features of the developed sensing device could be utilized for the real-time detection of harmful gases for a healthy and clean environment.

Hybrid Benzimidazole-Dichloroimidazole Zeolitic Imidazolate Frameworks Based on ZIF-7 and Their Application in Mixed Matrix Membranes for CO2/N2 Separation

Mixed-linker zeolitic imidazolate frameworks (ZIFs) with the sodalite (sod) topology type and based on ZIF-7 have been prepared by direct synthesis from the mixtures of benzimidazole (BzIm) and 4,5-dichloroimidazole (dcIm). Incorporation of dcIm into the ZIF-7 structure gives ZIF-7/COK-17 hybrids with rhombohedral symmetry that do not show the "open-to-closed form" structural transition upon solvent removal exhibited by ZIF-7. They show Type I isotherms for low molecular weight gases and high affinity for CO₂ even at low partial pressures. Synthesis under mild conditions gives ZIF nanoparticles (250-400 nm) suitable for incorporation into mixed matrix membranes (MMMs): these were prepared with both glassy (Matrimid) and rubbery (PEBAX 1657) polymers. Permeation tests at 298 K and 1.2 bar reveal that the incorporation of Zn(BzIm_0.55dcIm_0.45)₂ nanoparticles at up to ca. 12 wt % gives defect-free membranes with enhanced CO₂ permeability in both polymer matrices, with retention of selectivity (Matrimid) or with an enhancement in selectivity that is most pronounced for the smaller nanoparticles (PEBAX). The membrane with the best performance exhibits a selectivity of ca. 200 for CO₂/N₂ (a 4-fold increase compared to the pure polymer) and a CO₂ permeability of 64 Barrer. At the relatively low loadings investigated, the MMMs' performance obeys the Maxwell model, and the intrinsic property of diffusivity of the ZIFs can be extracted as a result.

Synthesis and Characterization of ZIF-67 Mixed Matrix Nanobiocatalysis for CO2 Adsorption Performance

In this study, ZIF-67-based mixed matrix membrane was synthesized with a solution casting method using tetrahydrofuran as the solvent. The as-synthesized ZIF-67 was characterized using PXRD, TGA, ATR-FTIR, and BET analysis for the surface area measurements. The minimum 3 wt% loading of ZIF-67 was incorporated within a hydrophobic polymer to evaluate the CO2 adsorption performance of ZIF-67. The stability of ZIF-67 in pure water and inorganic solvents was investigated. The maximum CO2 adsorption of the ZIF-67 mixed-matrix membrane (MMM) was 0.5 mmol/g at 273 K, which is higher than that of the pure polymer. The fabricated ZIF-67-based mixed-matrix membrane showed higher CO2 capture even at lower MOF loading using THF. The current study highly recommends the combination of hydrophobic polysulfone and a water-stable ZIF-67 for CO2 capture from wet flue gases.

Carbonic Anhydrase-Mimicking Supramolecular Nanoassemblies for Developing Carbon Capture Membranes

As a ubiquitous family of enzymes with high performance in converting carbon dioxide (CO₂) into bicarbonate, carbonic anhydrases (CAs) sparked enormous attention for carbon capture. Nevertheless, the high cost and operational instability of CAs hamper their practical relevance, and the utility of CAs is mainly limited to aqueous applications where CO₂-to-bicarbonate conversion is possible. Taking advantage of the chemical motif that endows CA-like active sites (metal-coordinated histidine), here we introduce a new line of high-performance gas separation membranes with CO₂-philic behavior. We first self-assembled a histidine-based bolaamphiphile (His-Bola) molecule in the aqueous phase and coordinated the resulting entities with divalent zinc. Optimizing the supramolecular synthesis conditions ensured that the resultant nanoparticles (His-NPs) exhibit high CO₂ affinity and catalytic activity. We then exploited the His-NPs as nanofillers to enhance the separation performance of Pebax MH 1657. The hydrogen-bonding interactions allowed the dispersion of His-NPs within the polymer matrix uniformly, as confirmed by microscopic, spectroscopic, and thermal analyses. The imidazole and amine functionalities of His-NPs enhanced the solubility of CO₂ molecules in the polymer matrix. The CA-mimic active sites of His-NPs nanozymes, on the other hand, catalyzed the reversible hydration of CO₂ molecules in humid conditions, facilitating their transport across the membranes. The resulting nanocomposite membranes displayed excellent CO₂ separation performance, with a high level of stability. At a filling ratio as low as 3 wt %, we achieved a CO₂ permeability of >145 Barrer and a CO₂/N₂ selectivity of >95 with retained performance under humid continuous gas feeds. The bio-inspired approach presented in this work offers a promising platform for designing durable and highly selective CO₂ capture membranes.

Hybrid Ce-Fe2O3/ZIF-67 Photoanode with Efficient Photoelectrochemical Water Oxidation Performance

Surface states and slow water oxidation kinetics greatly limit the photoelectrochemical (PEC) water oxidation performance of Fe₂O₃. To solve the above problems, coupling Fe₂O₃ with a passivation layer and an oxygen evolution cocatalyst, respectively, is the common method. Though this method may improve its PEC performance, this also results in a low charge-transfer efficiency caused by the interface resistance between Fe₂O₃ and the modification materials (passivation layer and oxygen evolution cocatalyst). Therefore, it is important to identify a multifunctional modifier material to reduce the interfacial resistance due to the presence of multiple different materials. In this work, we introduced a thin cobalt-based metal-organic framework layer (ZIF-67) as a dual-functional material that acted as both a passivation layer and a water oxidation cocatalyst for a photoanode based on Ce-Fe₂O₃ nanorod arrays. The ZIF-67 layer inhibited charge carrier recombination by passivating the surface states. The PEC performance was improved due to the rich Co²⁺ photogenerated hole-capture sites, which facilitated charge transfer and separation. As expected, the Ce-Fe₂O₃/ZIF-67 photoanode exhibited superior water oxidation performance, with a photocurrent of 2.07 mA cm^-2 at 1.23 V_RHE, which is 1.74 times higher than that of the Ce-Fe₂O₃ photoanode. The onset potential was negatively shifted by 71 mV. This study provides basic insights and a strategy for reducing interfacial resistance in hybrid materials.

Cadmium ion removal from aqueous media using banana peel biochar/Fe3O4/ZIF-67

In the present study, banana peel waste was used as a suitable source for biochar production. The banana peel biochar (BPB) was modified using Fe₃O₄ magnetic and ZIF-67 nanoparticles. The modification of the BPB surface (4.70 m²/g) with Fe₃O₄ and Fe₃O₄/ZIF-67 significantly increased the specific surface of the nanocomposites (BPB/Fe₃O₄: 78.83 m²/g, and BPB/Fe₃O₄/ZIF-67: 1212.40 m²/g). The effect of pH, temperature, contact time, adsorbent dose, and concentration of Cd²⁺ on the efficiency of the Cd²⁺ adsorption was explored. Maximum adsorption efficiencies for BPB (97.76%), BPB/Fe₃O₄ (97.52%), and BPB/Fe₃O₄/ZIF-67 (99.14%) were obtained at pH 6, Cd²⁺ concentration of 10 mg/L, times of 80 min, 50 min, and 40 min, and adsorbent doses of 2 g/L, 1.5 g/L, and 1 g/L, respectively. Thermodynamic measurements indicated that the process is spontaneous and exothermic. The maximum capacity of Cd²⁺ adsorption using BPB, BPB/Fe₃O₄, and BPB/Fe₃O₄/ZIF-67 were obtained 20.63 mg/g, 30.33 mg/g, and 50.78 mg/g, respectively. The Cd²⁺ adsorption using magnetic nanocomposites followed the pseudo-first-order kinetic model. The results showed that studied adsorbents especially BPB/Fe₃O₄/ZIF-67 have a good ability to adsorb-desorb Cd²⁺ and clean an effluent containing pollutants.

Immobilization of D-allulose 3-epimerase into magnetic metal-organic framework nanoparticles for efficient biocatalysis

D-allulose is a rare low-calorie sugar that has many fundamental biological functions. D-allulose 3-epimerase from Agrobacterium tumefaciens (AT-DAEase) catalyzes the conversion of D-fructose to D-allulose. The enzyme has attracted considerable attention because of its mild catalytic properties. However, the bioconversion efficiency and reusability of AT-DAEase limit its industrial application. Magnetic metal-organic frameworks (MOFs) have uniform pore sizes and large surface areas and can facilitate mass transport and enhance the capacity for enzyme immobilization. Here, we successfully encapsulated cobalt-type AT-DAEase into the cobalt-based magnetic MOF ZIF-67@Fe₃O₄ using a self-assembly strategy. We confirmed the immobilization of enzyme AT-DAEase and characterized the enzymatic properties of the MOF-immobilized AT-DAEase@ZIF-67@Fe₃O₄. The AT-DAEase@ZIF-67@Fe₃O₄ nanoparticles had higher catalytic activity (65.1 U mg^-1) and bioconversion ratio (38.1%) than the free AT-DAEase. The optimal conditions for maximum enzyme activity of the AT-DAEase@ZIF-67@Fe₃O₄ nanoparticles were 55 °C and pH 8.0, which were significantly higher than those of the free AT-DAEase (50 °C and pH 7.5). The AT-DAEase@ZIF-67@Fe₃O₄ nanoparticles displayed significantly improved thermal stability and excellent recycling performance, with 80% retention of enzyme activity at a temperature range of 45-70 °C and > 45% of its initial activity after eight cycles of enzyme use. The AT-DAEase@ZIF-67@Fe₃O₄ nanoparticles have great potential for large-scale industrial preparation of D-allulose by immobilizing cobalt-type AT-DAEase into magnetic MOF ZIF-67@Fe₃O₄.

The Effect of Solution Casting Temperature and Ultrasound Treatment on PEBAX MH-1657/ZIF-8 Mixed Matrix Membranes Morphology and Performance

Approximately two-thirds of anthropogenic emissions causing global warming are from carbon dioxide. Carbon capture is essential, with membranes proving to be a low cost and energy-efficient solution to alternative technologies. In particular, mixed matrix membranes (MMMs) can have higher permeability and selectivity than pure polymer membranes. The fabrication conditions affect the formation of defects within the membranes. In this work, MMMs were created using a PEBAX MH-1657 polymer and a ZIF-8 filler. The effect of casting plate temperature, varying from −5 °C to 50 °C, and the effect of ultrasound treatment time (80–400 min) and method (filler solution only, filler and polymer combined solution only and filler solution followed by combined solution) were investigated, aiming to reduce defect formations hence improving the performance of the MMMs. SEM images and permeation tests using pure CO2 and N2 gas, replicating flue gas for carbon capture, were used to investigate and compare the membranes morphology and performance. The results indicated that the MMMs maintained their permeabilities and selectivities at all tested casting temperatures. However, the neat PEBAX membranes demonstrated increased phase separation of the polyamide and polyether oxide phases at higher temperatures, causing a reduction in permeability due to the higher crystallinity degree, confirmed by DSC experiment. The MMMs fabricated at low ultrasound times displayed a large amount of aggregation with large particle size causing channeling. At high ultrasound times, a well-dispersed filler with small filler diameters was observed, providing a high membrane performance. Overall, defect-free membranes were successfully fabricated, leading to improved performance, with the best membrane resulting from the longest ultrasound time reaching the Robeson bound upper limits.

Effect of process parameters over carbon-based ZIF-62 nano-rooted membrane for environmental pollutants separation

The paper evaluates the routes towards the evaluation of membranes using ZIF-62 metal organic framework (MOF) nano-hybrid dots for environmental remediation. Optimization of interaction of operating parameters over the rooted membrane is challenging issue. Subsequently, the interaction of operating parameters including temperature, pressure and CO₂ gas concentration over the resultant rooted membranes are evaluated and optimized using response surface methodology for environmental remediation. In addition, the stability and effect of hydrocarbons on the performance of the resulting membrane during the gas mixture separation are evaluated at optimum conditions to meet the industrial requirements. The characterization results verified the fabrication of the ZIF-62 MOF rooted composite membrane. The permeation results demonstrated that the CO₂ permeability and CO₂/CH₄ selectivity of the composite membrane was increased from 15.8 to 84.8 Barrer and 12.2 to 35.3 upon integration of ZIF-62 nano-glass into cellulose acetate (CA) polymer. Subsequently, the optimum conditions have been found at a temperature of 30 °C, the pressure of 12.6 bar and CO₂ feed concentration of 53.3 vol%. These optimum conditions revealed the highest CO₂ permeability, CH₄ permeability and CO₂/CH₄ separation factor of 47.9 Barrer, 0.2 Barrer and 26.8. The presence of hydrocarbons in gas mixture dropped the CO₂ permeability of 56.5% and separation factor of 46.4% during 206 h of testing. The separation performance of the composite membrane remained stable without the presence of hydrocarbons for 206 h.

Mixed Dimensional Nanostructure (UiO-66-Decorated MWCNT) as a Nanofiller in Mixed-Matrix Membranes for Enhanced CO2 /CH4 Separation

Mixed-matrix membranes (MMMs) with combination of two distinct dimensional nanofillers (such as 1D-3D, 2D-3D, or 3D-3D, etc.) have drawn special attention for gas separation applications due to their concerted effects on gas permeation and mechanical properties. An amine-functionalized 1D multiwalled carbon nanotube (NH₂ -MWCNT) with exceptional mechanical strength and rapid gas transport was crosslinked with an amine-functionalized 3D metal-organic framework (UiO-66-NH₂ ) with high CO₂ affinity in a Schiff base reaction. The resultant crosslinked mixed-dimensional nanostructure was used as a nanofiller in a polysulfone (PSf) polymer matrix to explore the underlying synergy between 1D and 3D nanostructures on the gas separation performance of MMMs. Cross-sectional scanning electron microscopy and mapping revealed the homogenous dispersion of UiO-66@MWCNT in the polymer matrix. The MMM containing 5.0 wt. % UiO-66@MWCNT demonstrated a superior permeability 8.3 Barrer as compared to the 4.2 Barrer of pure PSf membrane for CO₂ . Moreover, the selectivity (CO₂ /CH₄ ) of this MMM was enhanced to 39.5 from the 28.0 observed for pure PSf under similar conditions of pressure and temperature.

Recent Advances in Polymer-Inorganic Mixed Matrix Membranes for CO2 Separation

Since the second industrial revolution, the use of fossil fuels has been powering the advance of human society. However, the surge in carbon dioxide (CO2) emissions has raised unsettling concerns about global warming and its consequences. Membrane separation technologies have emerged as one of the major carbon reduction approaches because they are less energy-intensive and more environmentally friendly compared to other separation techniques. Compared to pure polymeric membranes, mixed matrix membranes (MMMs) that encompass both a polymeric matrix and molecular sieving fillers have received tremendous attention, as they have the potential to combine the advantages of both polymers and molecular sieves, while cancelling out each other's drawbacks. In this review, we will discuss recent advances in the development of MMMs for CO2 separation. We will discuss general mechanisms of CO2 separation in an MMM, and then compare the performances of MMMs that are based on zeolite, MOF, metal oxide nanoparticles and nanocarbons, with an emphasis on the materials' preparation methods and their chemistries. As the field is advancing fast, we will particularly focus on examples from the last 5 years, in order to provide the most up-to-date overview in this area.

Pebax Mixed-Matrix Membrane with Highly Dispersed ZIF-8@CNTs to Enhance CO2/N2 Separation

In this work, zeolitic imidazolate frameworks (ZIF-8) and carboxylated carbon nanotubes (CNTs) were compounded to prepare a kebab-like one-dimensional linear composite, ZIF-8@CNTs. The mixed-matrix membrane (MMM) for separating carbon dioxide is prepared by embedding it into the polymer matrix Pebax-1657. The results indicated the successful synthesis of the ZIF-8@CNT composite. The combination of ZIF-8 and carboxylated CNTs avoided the aggregation of ZIF-8 in the polymer, increased the free volume of the MMM, and enhanced the CO₂ adsorption performance and CO₂/N₂ separation performance. In addition, the interaction between CNTs and ZIF-8 provided a fast transport channel for CO₂ molecules and improved the mechanical properties of the MMM. The 5 wt % ZIF-8@CNT MMM showed the best separation performance with a CO₂ permeability of 225.5 Barrer and a CO₂/N₂ selectivity of 48.9, which exceeded the Robeson upper limit in 2008. The combination of high permeability and selectivity made Pebax/ZIF-8@CNT MMMs promising for industrial CO₂ separation applications.

Prediction of the phenol removal capacity from water by adsorption on activated carbon

High-performance sulfonated polysulfone (SPSf) mixed-matrix membranes (MMMs) were fabricated via a nonsolvent-induced phase separation (NIPS) method using zeolitic imidazolate frameworks-67 (ZIF-67) as a crosslinker. Acid-base crosslinking occurred between the sulfonic acid groups of SPSf and the tertiary amine groups of the embedded ZIF-67, which improved the dispersion of ZIF-67 and simultaneously improved the membrane strzcture and permselectivity. The dispersion of ZIF-67 in the MMMs and the acid-base crosslinking reaction were verified by energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The pore structure analysis of MMMs indicated that filling ZIF-67 into SPSf enhanced the average surface pore sizes, surface porosities and more micropore in cross-sections. The crossflow filtrations showed the MMMs have higher pure water fluxes (57 to 111 L m^-2 h^-1) than the SPSf membrane (55 L m^-2 h^-1) but also higher bovine serum albumin (BSA) rejection rate of 93.9-95.8%, a model protein foulant. The MMMs showed a higher water contact angle than the SPSf membrane due to the addition of hydrophobic ZIF-67 and acid-base crosslinking, and also maintained high thermal stability evidenced by the thermogravimetric analysis (TGA) results. At the optimal ZIF-67 concentration of 0.3 wt%, the water flux of the SPSf-Z67-0.3 membrane was 82 L m^-2 h^-1 with a high BSA rejection rate of 95.3% at 0.1 MPa and better antifouling performance (FRR = 70%).

Carbon Dioxide Enrichment PEBAX/MOF Composite Membrane for CO2 Separation

Zeolitic imidazole framework (ZIF-8) was incorporated into poly(ether-block-amide) (Pebax-1657) in differing ratios to prepare mixed matrix membranes (MMMs) for gas separation. As ZIF-8 loading is increased, gas separation selectivity also gradually increases. For economic considerations, the proportion of the increase in selectivity to the amount of MOF loaded per unit was calculated. The results show that mixing 5% MOF gives the best unit performance. With this, a variety of MOFs (UiO-66, UiO-66-NH₂, A520, MIL-68(Al) and MIL-100(Fe)) were mixed with PEBAX at 5 loading to prepare MMMs. In this work, metal-organic frameworks (MOFs) were processed using the dry-free method, where in the synthesized MOF was not dried prior to incorporation. The gas separation performance test carried out shows the highest separation performance was exhibited by P-UiO-66, wherein the CO₂/N₂ gas selectivity was 85.94, and the permeability was 189.77 (Barrer), which was higher than Robeson’s Upper bound in 2008, and obtained a high permeability and selectivity among mixed matrix membranes. In the preparation of high quality MMMs for gas separation, details regarding the interface phenomenon were assessed.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part II: Gas Separation Properties toward Fluorinated Greenhouse Gases

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32= 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.

High performance polyvinylidene fluoride (PVDF) mixed matrix membrane (MMM) doped by various zeolite imidazolate frameworks

Zeolitic imidazolate framework (ZIF-8) in three particle sizes (40, 70 and 100 nm) was prepared through both solvothermal and hydrothermal methods and employed to decorate polyvinylidene fluoride (PVDF). The finger-like macro-voids, sponge-like poly-porous morphology and surface roughness of prepared membranes were characterized by SEM and AFM microscopy. The FTIR spectrum and XPS analysis bear out the chemical component. ZIF-8 has the characteristics of higher porosity and appropriate pore size, which is a condition for improving the permeability and pollution resistance of the modified membrane. Results indicated that different ZIF-8s have different enhancement effects on PVDF MMM. 100 nm ZIF-8 membrane possessed pure water flux (PWF) of 350 L m−2h−1, which was 10 times more than the bare membrane (30 L m−2h−1), and OVA flux recovery ration (FRR%) is 98%. 40 nm ZIF-8 membrane owned BSA FRR% of 98.4%. The 70 nm ZIF-8 showed the best mechanical properties. The dynamic contact angles of UP-Z70 ranged from 104.5° to 62.5° within 180 s. Furthermore, pore size distribution, molecular weight cut-off (MWCO) and porosity were also researched to evaluate the MMM. The dislodge of Reactive Black KN-B, Reactive Red 3BS and Reactive Brilliant Blue KN-R dyes by MMM were studied under different dye concentrations and transmembrane pressures. The membrane can provide selective separation methods for dyes and Reactive Brilliant Blue KN-R up to 99%. Overall, the permeability, hydrophilicy, anti-fouling performance and wastewater treatment of modified membranes were regulated by the ZIF-8 in a steerable blending reaction modification process.