Preparation Of Mixed Matrix Membranes Research Articles

Mixed matrix membranes with highly dispersed MOF nanoparticles for improved gas separation

• IPD is used to modify ZIF-8 nanoparticles by a simple coordination interaction. • IPD@ZIF-8 nanoparticles exhibit excellent dispersity in various solvents. • H 2 /CH 4 selectivity of PI/IPD@ZIF-8 MMM with 45 wt% loading is increased by 46.6%. • The CO 2 plasticization resistance of PI/IPD@ZIF-8 MMMs is improved from 21 to 30 bar. Metal organic frameworks (MOFs) are ideal fillers for preparing mixed matrix membranes (MMMs) because of their molecular sieving property. However, MOF nanoparticles are not easy to be dispersed, which limits their application in MMMs with high MOFs loading. In this study, highly dispersed ZIF-8 nanoparticles with diameter of around 50 nm were prepared by coating isophthalic dihydrazide (IPD) molecular layer onto their surfaces via coordination interaction (abbre. IPD@ZIF-8). Benefiting from the highly stable and highly dispersed IPD@ZIF-8 solution, MMMs with high nanoparticles loading content and excellent uniformity are achieved. The modification of IPD on the surface of ZIF-8 nanoparticles greatly enhances the interfacial affinity between ZIF-8 as filler and 6FDA-Durene polyimide (PI) as polymer matrix under the interaction of strong hydrogen bond between them. Gas permeation results reveal that the H 2 permeability of IPD@ZIF-8 mixed PI (PI/IPD@ZIF-8) MMM with 45 wt% loading content is up to 8000 Barrer and the corresponding ideal selectivities of H 2 /CH 4 and H 2 /N 2 gas pairs are 15.1 and 13.0, which increase by 46.6% and 32.7%, respectively, comparing to those of ZIF-8 mixed PI (PI/ZIF-8) MMMs. The comprehensive separation performance of PI/IPD@ZIF-8 MMMs surpasses the 2008 Robeson’s upper bounds. The surface modification of IPD enhances the CO 2 plasticization resistance property of PI/IPD@ZIF-8 MMMs from 21 bar to 30 bar. This study provides a facile and easy-operated strategy for the surface modification of MOF nanoparticles, and opens up a new way for the preparation of MMMs with high filler loading and good quality.

Preparation of mixed matrix membranes made up of polysulfone and MIL-53(Al) nanoparticles as promising membranes for separation of aqueous dye solutions

• A mixed matrix membrane was fabricated via the addition of MIL-53 (Al) into the Polysulfone membrane. • Different compositions of the membranes were prepared via an asymmetric structure. • The membranes contained a dense layer and an open cellular spongy morphology. • The prepared membranes showed a significant dye rejection performance. Polysulfone-MIL-53(Al) mixed matrix membranes were fabricated by using the VIPS-NIPS technique, in which 1,4-Dioxane was used as the co-solvent. MIL-53(Al) nanoparticles were used in this study owing to their small pore sizes, high hydrophilicity and superior water stability. Hence, different membrane compositions with various MIL-53(Al) contents were prepared so that a membrane with superior performance for dye rejection application and high flux can be achieved. The performance of the fabricated membranes was investigated for rejection of various dyes in aqueous solutions including Reactive Red (RR), Direct Yellow (DY), Methyl Green (MG), and Crystal Violet (CV), based on which a great separation performance (dye rejections of 99.8, 99.5, 99.2, 98.8 and 97.1 for RR, MG, DY, CV and MB, respectively) and an excellent water flux (4.8 L/m 2 .h.bar) were provided by the membrane containing 0.06 wt% MIL-53(Al).

Mixed-Matrix Membrane Fabrication for Water Treatment.

In recent years, technology for the fabrication of mixed-matrix membranes has received significant research interest due to the widespread use of mixed-matrix membranes (MMMs) for various separation processes, as well as biomedical applications. MMMs possess a wide range of properties, including selectivity, good permeability of desired liquid or gas, antifouling behavior, and desired mechanical strength, which makes them preferable for research nowadays. However, these properties of MMMs are due to their tailored and designed structure, which is possible due to a fabrication process with controlled fabrication parameters and a choice of appropriate materials, such as a polymer matrix with dispersed nanoparticulates based on a typical application. Therefore, several conventional fabrication methods such as a phase-inversion process, interfacial polymerization, co-casting, coating, electrospinning, etc., have been implemented for MMM preparation, and there is a drive for continuous modification of advanced, easy, and economic MMM fabrication technology for industrial-, small-, and bulk-scale production. This review focuses on different MMM fabrication processes and the importance of various parameter controls and membrane efficiency, as well as tackling membrane fouling with the use of nanomaterials in MMMs. Finally, future challenges and outlooks are highlighted.

A comprehensive modeling approach for determining the role and nature of interfacial morphology in mixed matrix membranes

In this study, a new algorithm was developed to mathematically insight into the interfacial morphology in mixed matrix membranes (MMMs) by only using related experimental permeation data to a maximum loading of particles used in MMM preparation. According to this algorithm, the maximum possible interphase thickness is determined based on the size and the maximum used loading of particles in membrane fabrication. The benefits of this approach are determining the optimal characteristic parameters of the surrounded particles including interphase thickness, effective permeability of interphase, and porous particles (if applicable) affected by the blockage, with no arbitrary assumption to them. The validity of the proposed modeling approach was evaluated using 154 data points related to experimental permeability data of 13 series MMMs. Comparing the results obtained by using related experimental data to maximum used particle loading and all loading levels revealed that the sensitivity of the modified Maxwell model to the number of applied experimental data points is negligible. The predictions indicate that the maximum average absolute relative error (AARE) is 9%. Using modified GPG and modified Higuchi models instead of the modified Maxwell model in the proposed modeling approach showed that this algorithm is not sensitive to the type of model.

Polymerizable metal-organic frameworks for the preparation of mixed matrix membranes with enhanced interfacial compatibility

SummaryThe preparation of flawless and defect-free mixed matrix membranes (MMMs) comprising metal-organic framework (MOF) and polymer is often difficult owing to the poor MOF/polymer interface compatibility. Herein, we present the synthesis of an important family of pillared-layered MOFs with polymerizable moieties based on the parent structure [Zn2L2P]n [L = vinyl containing benzenedicarboxylic acid linkers; P = 4,4′-bipyridine (bipy)]. The crystalline structures of polymerizable MOFs were analyzed using single-crystal X-ray crystallography. The presence of reactive double bonds in MOFs was verified by the successful thiol-ene click reaction with sulfhydryl compounds. The subsequent copolymerization of polymerizable MOFs with organic monomers produced mixed matrix membranes with enhanced MOF/polymer interfacial adhesion that enabled good separation efficiency of CO2 from flue gas. This strategy provides a stimulating platform to the preparation of highly efficient MMMs that are capable of mitigating energy consumption and environment issues.

Mixed matrix membranes based on NH2-MIL-53 (Al) and 6FDA-ODA polyimide for CO2 separation: Effect of the processing route on improving MOF-polymer interfacial interaction

This work compares the effect of two different fabrication routes on the gas separation performance of mixed matrix membranes (MMM). Flat-sheet symmetric membranes based on 6FDA-ODA as the matrix and 10–20 wt% metal–organic frameworks (MOF) MIL-53 (Al) and NH2-MIL-53 (Al) as fillers were fabricated via two approaches. In approach A, the MOF was incorporated at the early stage of the polyimide synthesis and the 6FDA-ODA polymerization reaction took place in the presence of MOF, while approach B followed the traditional solution mixing technique of MMM preparation. From the samples produced, XRD, N2 adsorption at 77 K, ATR-FTIR, FEG-SEM, TGA-DTG, DMA and density measurements were used to characterize the MOF structure and the membrane properties. Then, single and mixed gas separation performances were evaluated for CO2, CH4 and N2 at 2 and 5.5 bar and 35 °C. As a result of better interfacial interactions between NH2-MIL-53 (Al) and polyimide via hydrogen bonding, the MMM-A series showed excellent dispersion in the polymer matrix compared to MMM-B. At 10 wt% NH2-MIL-53, the membrane prepared by approach A showed 100% improvement in CO2/CH4 mixed gas separation factor (50:50 vol% CO2:CH4 at 35 °C and 5.5 bar) compared to that of neat 6FDA-ODA, which is 27% better than the membrane prepared by approach B. Better interfacial compatibility also improved the thermal and mechanical properties of the MMM, which confirms the efficiency of this approach for the NH2-MIL-53 (Al)/6FDA-ODA system. On the other hand, unfunctionalized MIL-53 (Al) MMM showed no difference between approach A and B in improving the gas separation performance.

Effect of new metal–organic framework (zeolitic imidazolate framework [ZIF-12]) in mixed matrix membranes on structure, morphology, and gas separation properties

Abstract In our study, the synthesis of zeolitic imidazolate framework (ZIF-12) crystals and the preparation of mixed matrix membranes (MMMs) with various ZIF-12 loadings were targeted. The characterization of ZIF-12 and MMMs were carried out by Fourier transform infrared spectroscopy analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and thermomechanical analysis. The performance of MMMs was measured by the ability of binary gas separation. Commercial polyetherimide (PEI-Ultem® 1000) polymer was used as the polymer matrix. The solution casting method was utilized to obtain dense MMMs. In the SEM images of ZIF-12 particles, the particles with a rhombic dodecahedron structure were identified. From SEM images, it was observed that the distribution of ZIF-12 particles in the MMMs was homogeneous and no agglomeration was present. Gas permeability experiments of MMMs were measured for H2, CO2, and CH4 gases at steady state, at 4 bar and 35 °C by constant volume-variable pressure method. PEI/ZIF-12-30 wt% MMM exhibited high permeability and ideal selectivity values for H2/CH4 and CO2/CH4 were P H 2 / CH 4 = 331.41 ${P}_{{\text{H}}_{2}/{\text{CH}}_{4}}=331.41$ and P CO 2 / CH 4 = 53.75 ${P}_{{\text{CO}}_{2}/{\text{CH}}_{4}}=53.75$ gas pair.

Enhanced Gas Separation Performance by Embedding Submicron Poly(ethylene glycol) Capsules into Polyetherimide Membrane

Recently, hollow filler as an emerging concept is attracting more attention in preparation of mixed matrix membranes (MMMs). Herein, poly(ethylene glycol) microcapsules (PMC) are synthesized via distillation precipitation polymerization and embedded into the polyetherimide (Ultem®1000) matrix to fabricate MMMs for CO2 capture. The PMC exhibits a preferential hollow structure within the Ultem matrix to furnish highways within membrane, and thus achieve high gas permeability. Meanwhile, the favorable affinity of poly(ethylene glycol) (PEG) microcapsule with ether oxygen group (EO) towards CO2 enhances the CO2 solubility selectivity. Such integration of physical and chemical microenvironments in the as-designed PEG microcapsule affords highly enhanced CO2 separation performance. Compared to pristine Ultem®1000, the membrane with 2.5 wt% PMC loading exhibits 310% increment in CO2 permeability and 22% increment in CO2/N2 selectivity, which shows the promising prospects of designing PEG-containing microcapsules as the filler of MMMs for CO2 capture.

Modification of polyethersulfone membrane using MWCNT-NH2 nanoparticles and its application in the separation of azeotropic solutions by means of pervaporation.

In this study, functionalized multi-walled carbon nanotubes (MWCNT-NH2) were synthesized as an additive for the preparation of mixed matrix membranes (MMMs) and then were investigated by FTIR and FE-SEM techniques. Polyether sulfone (PES) polymeric membrane modified with functionalized MWCNT-NH2 carbon nanotubes was prepared by phase inversion method. The effect of MWCNT-NH2 on the morphology and property of the PES membrane was evaluated using scanning electron microscopy. The flux, enrichment factor and swelling properties of modified membranes were also used to investigate the membranes performance. The results showed that the flux and enrichment factor in modified PES membrane containing 5 wt.% of functionalized MWCNT-NH2 carbon nanotubes were obtained 1.2 L.m-2h-1 and 3.3, respectively. The influence of methanol concentration on the flux and enrichment factor was investigated. The results corroborated that the flux didn’t change significantly, while the enrichment factor was decreased.

Intensification of helium separation from CH4 and N2 by size-reduced Cu-BTC particles in Matrimid matrix

Preparation of mixed matrix membranes (MMMs) with appropriate separation efficiency requires tenacious interfacial affinity between filler particles and polymer matrix. In this work, Cu-BTC particles with two structures of size-reduced and needle were successfully synthesized via the three-layer synthesis approach and combined with Matrimid to prepare MMMs for helium separation. Extensive characterization of particles (XRD, SEM, TGA, FTIR and N2 sorption) and membranes (SEM, TGA, DSC and density-FFV measurements) were performed to gain insight in the membranes separation behavior.Then gas separation performance of membranes were examined for the single gases He, CH4 and N2 and the gas mixtures He/CH4 and He/N2. The combination of MOFs with Matrimid resulted in an increase in Tg, density and degradation behavior of MMMs indicating a good compatibility between the fillers and polymer, however this development is more pronounced for reduced particles. The MMMs containing size-reduced MOF had premiere gas separation performance in comparison with the needle particles and overcame the 1991 Robeson upper bond.The MMM at 40 wt% loading exhibited the best efficiency with Hepermeability of 66.4Barrer which is about three times more than pure Matrimid. In addition, the improvements in He/CH4 and He/N2ideal selectivities were 181 and 169%, respectively. Mixed gas permeability measurements showed that helium permeability values and also selectivities decreased slightly compared to single gas data due to the competitive effects between large gases of CH4 and N2 with small helium.

Gas transport properties of mixed matrix membranes based on thermally rearranged poly(hydroxyimide)s filled with inorganic porous particles

In this study, we explore the use of two kinds of inorganic sieves, microporous MFI zeolite and mesoporous MCM-41 silica, as fillers to enhance the gas transport characteristics of thermally rearranged (TR) poly(hydroxyimides) (HPI). To the best of our knowledge, this is the first report on the use of these fillers to modify properties of TR HPIs, except for our previous research on MCM-41 filled HPIs based on BPADA dianhydride. In this work, 6FDA-HAB and BPADA-HAB varying in gas permeability and properties were selected as matrices for preparation of mixed matrix membranes (MMM) with the aim of studying the effect of both the kind of filler and a matrix on thermal rearrangement and properties of the resultant TR-MMMs. In addition to pure gas permeability measurements, HPIs and MMMs were examined by WAXD, SEM, TGA, DMA, and tensile tests before and after thermal rearrangement. For all MMM precursors, the permeability increased in proportion to the filler loading (e.g. by 1.2–4.4 times for O2) while selectivity remained virtually the same. The same effect of improved permeability and maintained selectivity was observed for the series of TR-MMMs; for example, TR-MMM based on 6FDA and filled with 7 wt% of MCM-41 exhibited 6.7 fold higher O2 permeability over its filled precursor. The permeation properties of the filled membranes showed a strong dependence on both the kind of matrix and filler. The addition of MCM-41 particles to BPADA-HAB increased permeability more than the incorporation of the similar amount of MFI ones, while the contrary was true for 6FDA-HAB. The best result, comprising the position on the upper bound for He/N2, has been achieved for 6FDA-HAB filled with 25 wt% of MFI, whereas its TR analogue showed the highest 20.4 fold permeability improvement.

Fabrication and characterization of polyvinyl chloride mixed matrix membranes containing high aspect ratio anatase titania and hydrous manganese oxide nanoparticle for efficient removal of heavy metal ions: Competitive removal study

AbstractIn this study, novel polyvinyl chloride (PVC) ultrafiltration mixed matrix membranes (MMMs) containing high aspect ratio anatase titania (ANT) and hydrous manganese oxide (HMO) nanoparticles were synthesized in order to decontaminate cadmium and copper metal ions. ANT and HMO nanoparticles with various loadings in a range of 5‐15 were used in the casting solution of MMMs. The characterization of fabricated MMMs was carried out with respect to the structural morphology, hydrophilicity, and composition by scanning electron microscopy (SEM), water contact angle, and Fourier transform infrared spectroscopy (FTIR), respectively. With an increase in the nanoparticle loadings, the change in other membrane characteristics such as mean pore size, pure water flux, and porosity were also evaluated. The results revealed that the mean pore size and water flux increased at a higher loading of ANT and HMO nanoparticles, while the contact angle and porosity of the membranes showed reverse trends. Moreover, the higher flux of pure water was obtained for PVC‐ANT MMMs compared to PVC‐HMO MMMs because of the larger mean pore size, higher porosity, and hydrophilicity of PVC‐ANT MMMs. In this study, the decontamination of cadmium and copper metal ions in single and binary systems of heavy metals was investigated and the effect of Mn2+ (as an interfering ion) was also studied. The evaluation of the metal ion removal data demonstrated that the affinity sequence of both the PVC‐ANT‐15 and PVC‐HMO‐15 MMMs for heavy metal removal was Cu2+ > Cd2+ > Mn2+ in the single and binary systems. It was found through ultrafiltration (UF) experiments that PVC‐ANT MMM was the most efficient membrane in the elimination of heavy metals due to the superior ANT adsorption capacity. However, the overall findings disclosed that both ANT and HMO nanoparticles are suitable candidates for the preparation of MMMs used in cadmium and copper decontamination from aqueous solutions.

Fabrication of pebax-1657-based mixed-matrix membranes incorporating N-doped few-layer graphene for carbon dioxide capture enhancement

In this study, an environmentally friendly method was developed to fabricate N-doped few-layer graphene (N-FLG)/Pebax mixed-matrix membranes (MMMs) for CO2 capture. A supermixer was introduced to ensure homogeneity of the N-FLG in the Pebax solution, and a highly efficient method of N-FLG/Pebax MMM preparation was achieved. The membrane structures were analyzed by SEM, while the N-FLG morphology was examined by SEM, AFM, XPS and EDX. A detailed molecular simulation was applied to mimic and predict the behavior of and interaction between membranes and gas molecules. Through the simulation, an independent analysis of transport-related characteristics, such as diffusivity, solubility and permeability, was achieved. In addition, the simulation indicated that the affinity of N-FLG for CO2 molecules improves the CO2 capture performance, that the membranes are solubility-dependent when prepared with low contents of N-FLG and that the effect of diffusivity increases as the addition of N-GO increases above 5 wt%. The simulation results were highly correlated with the experimental results, while the experimental gas permeability results showed that the optimal performance of N-FLG/Pebax MMM was obtained with the addition of 4 wt% N-FLG, providing CO2 permeability and CO2/N2 selectivity of 239.8 Barrer and 95.5, respectively. Pebax-1657-based MMMs incorporating N-FLG nanosheets fabricated by an environmentally friendly method can therefore be considered a promising material for CO2 capture applications.

Removal of polycyclic aromatic hydrocarbons from aqueous media with polysulfone/MCM-41 mixed matrix membranes

This work describes the synthesis and characterization of the MCM-41-NH2 mesoporous material from the use of amorphous silica extracted from rice husk ash (RHA), as well as the preparation of mixed matrix membranes (MMMs) using the mesoporous material as filler material to be used in the remediation of the polycyclic aromatic hydrocarbons (PAHs). The MCM-41-NH2 was synthesized by the hydrothermal method and the MMMs by solvent casting. The hydrothermal method was efficient in the synthesis of the amorphous condensed silica framework, typical of mesoporous materials of the M41S family, with high surface area. The casting method was efficient for the preparation of the MMMs, which showed a good dispersion of the mesoparticles incorporated, small-angle ordering and a small increase in the Tg values of the MMMs with the incorporation of the MCM-41-NH2. The transport properties were influenced by the incorporation of the MCM-41-NH2 into polysulfone acrylate (PSf-Ac). The obtained MMMs exhibited PAH permeation, retention, and removal values ranged from 1.66-6.70%, 93.30–98.34%, and 36.57–78.89%, respectively. Consequently, the MMMs present potential to remediate PAH from aqueous media.

Tuning of Nano-Based Materials for Embedding Into Low-Permeability Polyimides for a Featured Gas Separation

Several concepts of membranes have emerged, aiming at the enhancement of separation performance, as well as some other physicochemical properties, of the existing membrane materials. One of these concepts is the well-known mixed matrix membranes (MMMs), which combine the features of inorganic (e.g., zeolites, metal–organic frameworks, graphene, and carbon-based materials) and polymeric (e.g., polyimides, polymers of intrinsic microporosity, polysulfone, and cellulose acetate) materials. To date, it is likely that such a concept has been widely explored and developed toward low-permeability polyimides for gas separation, such as oxydianiline (ODA), tetracarboxylic dianhydride–diaminophenylindane (BTDA-DAPI), m-phenylenediamine (m-PDA), and hydroxybenzoic acid (HBA). When dealing with the gas separation performance of polyimide-based MMMs, these membranes tend to display some deficiency according to the poor polyimide–filler compatibility, which has promoted the tuning of chemical properties of those filling materials. This approach has indeed enhanced the polymer–filler interfaces, providing synergic MMMs with superior gas separation performance. Herein, the goal of this review paper is to give a critical overview of the current insights in fabricating MMMs based on chemically modified filling nanomaterials and low-permeability polyimides for selective gas separation. Special interest has been paid to the chemical modification protocols of the fillers (including good filler dispersion) and thus the relevant experimental results provoked by such approaches. Moreover, some principles, as well as the main drawbacks, occurring during the MMM preparation are also given.

Preliminary Fractional Factorial Design (FFD) study using incorporation of Graphene Oxide in PVC in mixed matrix membrane to enhance CO2/CH4 separation

Mixed matrix membranes (MMMs) comprising of where polyvinyl chloride (PVC) and graphene oxide (GO) were employed in the membrane fabrication in order to improve the membrane characteristics. In this study of gas separation using mixed matrix membrane, gases such as CO2 and CH4 were used. The objectives of this research were to synthesize and develop MMMs PVC/GO, and also to carry out screening to determine best factors condition for membrane to function at high selectivity. The development of MMMs PVC/GO was based on 5 factors. Based on the screening tests, the run which was made up of factors PVC 20%, GO 4%, 1 bar of pressure during gas permeation, NMP solvent, and immersion time of 300s, shows to have the highest selectivity at 26.09 which was above the upper bound lines in the Robeson’s Upper bound plot. Fractional Factorial Design (FFD) was applied to study the minimalization of influenced factors during MMMs preparation. Based on the FFD run, the R-squared (R2) was

Porous covalent triazine piperazine polymer (CTPP)/PEBAX mixed matrix membranes for CO2/N2 and CO2/CH4 separations

Mixed Matrix Membranes (MMMs) made from a porous covalent triazine piperazine polymer (CTPP) as filler embedded in poly ether-block-amide (PEBAX® 1657) were studied for the separation of CO2/N2 and CO2/CH4 gas systems. At a loading rate of 0.025 wt%, significant improvement was achieved for both CO2 permeability (from 53 to 73 barrer) and selectivity (from 51 to 79 for CO2/N2 and from 17 to 25 for CO2/CH4) that were measured at 293 K and 3 bars. Results of FTIR, DSC, WAXS, and SEM revealed a strong interaction between CTPP and PEBAX due to the high density of hydrogen bonding in CTPP, which led to chain rigidification of PEBAX at very low loading rate compared to other literature reported systems. On the other hand, CTPP contains rich nitrogen in the framework, which favourites the adsorption of CO2 more than N2 and CH4. Hence, although the chain rigidification decreased the CO2 adsorption sites in PEBAX matrix, the intrinsic porosity and high surface area of CTPP compensated the diffusivity and solubility which in turn improved the overall permeability and selectivity at a very low loading rate. CTPP is highly stable in acid, base, and high temperature up to 400 °C. Hence, this novel type material is a very promising filler for preparation of mixed matrix membranes for the separation of CO2/N2 and CO2/CH4 systems.

Preparation of mixed-matrix membranes from metal organic framework (MIL-53) and poly (vinylidene fluoride) for use in determination of sulfonylurea herbicides in aqueous environments by high performance liquid chromatography

Novel mixed-matrix membranes (MMM) were prepared from metal-organic frameworks (MOF) (MIL-53) and poly (vinylidene fluoride) (PVDF), viz MIL-53–PVDF MMM, for the simultaneous dispersion membrane extraction (DME) of seven sulfonylurea herbicides (SUs) in aqueous environments followed by high performance liquid chromatography (HPLC) determination. The MIL-53–PVDF MMM was well characterized and major factors influencing DME performances were systematically investigated including membrane type, MOF dosage, eluent type, solution pH, extraction/elution time and salinity, etc. Under optimal conditions, the MIL-53–PVDF MMM based DME coupled with HPLC exhibited excellent linearity within 0.03–10 μg L−1 for chlorimuronethyl and 0.01–10 μg L−1 for other six SUs individual. High enrichment factor of 250 was obtained, as well as low detection limits and quantification limits ranged from 3.75 to 10.30 ng L−1 and 12.49–34.30 ng L−1, respectively. Furthermore, the method attained high recoveries of 77.20–111.00% at three spiking levels of SUs, with relative standard deviations of 1.28–14.67% in tap water, seawater and surface water samples. Additionally, the MMM was readily separated from water and well regenerated, and could keep about 80% recovery after 25 cycles. Compared to that reported extraction materials, the MIL-53–PVDF MMM possessed the advantages of high enrichment ability, excellent reusability, good practicality and easy separation, indicating it was a promising alternative for the enrichment of SUs from aqueous environments.

Improving ZIF-8 stability in the preparation process of polyimide-based organic solvent nanofiltration membrane

Recently, Zeolitic imidazolate framework-8 (ZIF-8) has drawn considerable attention in preparing mixed matrix membranes (MMMs) because of high specific surface area and unique pore structure. However, the structure degradation of ZIF-8 was found in the preparation process of a polyimide (PI)-based MMM due to the protonation effect in an acid environment of polyamide acid (PAA) solution. Herein, a novel strategy was proposed to overcome this obstacle by transferring the coordinating linkers of ZIF-8 structure into carbon skeleton via direct carbonization. As expected, the unique framework of carbonized ZIF-8 (CZIF-8) was fully retained in MMM preparation process. Meanwhile, CZIF-8 provided preferential flow paths for the solvents because of improved porosity and enhanced sorption capacity for the MMMs. As a result, the 10 wt% CZIF-8/PI MMM exhibited a high rejection of >90% to congo red (MW of 696 g mol−1) and outstanding permeances of 16.52, 4.05 and 2.08 L m−2 h−1 bar−1 in water, ethanol and isopropanol, respectively. This method indicates the feasibility of the proposed strategy and effectively enables the ZIF-8 stability for practical applications in an acid environment.

Polymer engineering by blending PIM-1 and 6FDA-DAM for ZIF-8 containing mixed matrix membranes applied to CO2 separations

The preparation of mixed matrix membranes (MMMs) for post-combustion CO2 capture and biogas upgrading from PIM-1 (10–90 wt%)/6FDA-DAM heterogeneous blends with ZIF-8 as filler (3–20 wt% with regard to the polymer blend) is described. The heterogeneity of the blend, considered here as an advantage for the dispersion of the filler within the MMMs, has been confirmed by the existence of a single glass transition temperature, consistent with that of 6FDA-DAM. The segregation between the two polymeric phases and the filler dispersion has been studied by Raman spectroscopy, SEM microscopy and EDX analysis. Increasing the amount of PIM-1 in the blend makes the d-spacing of the polymer chains higher and increases gas permeability. When embedding filler nanoparticles of ZIF-8, a better compatibility with 6FDA-DAM than with PIM-1 is observed. The filler locates near the interphase between polymers helping its dispersion. The use of small loadings of ZIF-8 enhances the gas separation performance of the MMMs in terms of permeability and selectivity for 50/50 CO2/CH4 and 10/90 CO2/N2 mixtures. The best performing membranes are the blends PIM-1/6FDA-DAM 10/90 (w/w) with 10 wt% of ZIF-8, showing a CO2 permeability of 2891 Barrer, a CO2/CH4 selectivity of 26.6 and 2802 Barrer of CO2 with a CO2/N2 selectivity of 18.1. Importantly, the CO2, N2 and CH4 permeabilities of the pure polymeric blends can be predicted using both the logarithmic and the Maxwell models. A new coupled Maxwell model has also been developed able to calculate the flow through the blends containing ZIF-8 and to predict the gas separation properties of the filler itself.