Permeability Of Mixed Matrix Membranes Research Articles

Description of non-ideal effects in composite membranes by a new theoretical approach

In present study, a theoretical model is introduced to calculate the gas permeability of mixed matrix membranes (MMMs) containing porous fillers. This model is based on analogy of gas permeation in MMMs with tensile modulus in composites. The representative parameters of MMM morphologies such as polymer chains tightening around the filler (β<1), unselective channel formation (β>1) and polymer chains penetrating into filler pores (0≤α≤1) which leads to the filler pore blocking are all included in the model. Furthermore, the interphase thickness (t) which is a critical parameter of MMMs participates in calculation equation along with the other parameters. To validate the proposed model, an experimental study with poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend as polymer matrix and zeolite 4A and NH2-MOF-199 as fillers is performed. The obtained gas permeability data of constructed MMMs and some of the literature data are employed to be fitted with the proposed model. The details of the existence morphologies of MMMs can be described by earning the mentioned parameters ranges. Therefore, by this model, by having a measure of t, the gas permeation of MMM can be achieved accompany with details of the related morphologies. All the theoretical investigations are done utilizing one equation which contains all parameters simultaneously.

Shape engineering for improved gas separation: Computation-driven insights on harnessing platonic particles in mixed-matrix membranes

Recently, there has been a growing focus on the significance of mixed matrix membranes (MMMs) in the domain of gas separation processes. It is well known that, the integration of structurally diverse porous materials into a polymeric matrix intensifies the influence of filler structural sensitivity during the performance evaluation of MMMs. In this study, a computational approach utilizing voxel-based finite element method (FEM) was employed for a systematic investigation of the impact of Platonic shapes used as fillers on the criteria that dictate the design of optimal membranes. The assessment of single gas transport in MMMs containing randomly distributed fillers has confirmed that filler particles with varying sphericity, but the same volume, can significantly influence the effective permeability of MMMs. A reduction in filler particle sphericity, such as in the case of a tetrahedral structure compared to a spherical one, results in a substantial enhancement of effective permeability, primarily due to the introduction of more interconnected pathways. This effect becomes increasingly pronounced at higher filler loading fractions and filler-to-polymer ratios. Furthermore, binary gas transport assessments of MMMs established that filler particle shapes have a considerable influence over the optimal filler–matrix combination, particularly in the context of phase gas transport compatibility, aimed at achieving maximal selectivity in gas mixtures. Filler particles with lower sphericity yield a higher maximum selectivity; however, this is achieved with a partially higher filler-to-polymer permeability for faster gas flow compared to spherical filler particles. This research offers valuable insights for the strategic enhancement of permeability and selectivity in MMMs through the integration of structurally diverse porous materials.

Study of the physicochemical and transport performance of neat Matrimid 5218 membrane with nanoparticles: A molecular dynamics simulation

Our study employed Molecular dynamics (MD) simulations using BIOVIA Materials Studio 2021 software programs to analyze neat and mixed matrix membranes (MMMs) for their solubility behaviour, thermodynamics, mechanical properties, and separation properties. The d-space, followed by the Matrimid 5218 (MAT) membranes’ amorphous state, was enhanced by adding particles to their structure. Furthermore, Calix[4]arene (CA) particles lead to improved membrane physicochemical properties, such as fractional free volume (FFV), glass transition temperature (Tg), Young's Modulus (E), shear modulus (G), and bulk modulus (B), which are indicators of improved thermal resistance and transport capacity. Besides, the N2, CH4, and CO2 gases’ transport properties and performance of membrane structures were analyzed in terms of their diffusivity, solubility, permeability, and selective behaviours. Based on MC simulations, increasing pressure results in a significant increase in gas adsorption, and CO2 is more readily absorbed than N2 or CH4, thanks to the robust interaction between the CO2 molecule and membrane structures. There were significant improvements in the CO2 permeability of MMMs filled with 0.75% CA particles compared to the neat MAT. Moreover, the MMMs were found to have improved selectivity in CO2/N2 and CO2/CH4 in comparison with neat membranes. Lastly, the measuring results of transport properties indicated that the MAT-CA (0.75%) membrane is proper for industrial applications, including the treatment of natural gas.

Gas permeation model for mixed matrix membranes: the new renovated Maxwell model

ABSTRACT The accurate prediction of gas separation properties of mixed matrix membranes (MMMs) is essential to eliminate the tedious experimental work. In this work, a new model is proposed to predict the gas permeability of MMMs, considering the role of interface voids between the polymer matrix and inorganic fillers. The new model is developed based on an analogy with a model derived for thermal conduction through the particulate composites using effective medium theory. The new model is validated using the gas permeability data of four sets of MMMs containing spherical micro- or nano-fillers reported in the literature. The results show an excellent agreement between new model predictions and gas permeability experimental data with deviations lower than 10% in comparison with the other models (29–43%). In addition, the value of the thickness of the interface voids layer for MMMs, which is difficult to directly determine by experimental methods, is correctly predicted using the new model. Therefore, a new theoretical model named as renovated Maxwell model considering the effect of filler/polymer interface voids is developed to accurately predict the gas permeability of MMMs.

Computational Investigation of Dual Filler-Incorporated Polymer Membranes for Efficient CO2 and H2 Separation: MOF/COF/Polymer Mixed Matrix Membranes.

Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H2, N2, CH4, and CO2 permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO2/N2, CO2/CH4, H2/N2, H2/CH4, and H2/CO2. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (≥104 barrer) but low selectivity (≤2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H2 purification and CO2 capture applications.

Carbon nanotubes grown on ZIF-L(Zn@Co) surface improved CO2 permeability of mixed matrix membranes

Increasing CO2 permeability via tailoring CO2 diffusivity and selective absorption represents a critical endeavor toward achieving efficient CO2 separation. Herein, hierarchical structures composed of carbon nanotubes in-situ grown on carbonized ZIF-L (Zn@Co) (C-ZIF) were developed as nanofillers in a Pebax polymer to fabricate mixed matrix membranes (MMMs) with high CO2 permeability. The high volatility of zinc ions facilitated formation of a porous matrix in ZIF-L (Zn@Co) carbonization, while cobalt ions catalyzed in-situ growth of carbon nanotubes on C-ZIF surfaces due to their high carbon solubility at elevated temperatures (≥600 °C). This hierarchically structured C-ZIF with nanotubes increased perturbation of molecular chains of polymer membrane and thus improved its gas diffusivity toward CO2, evidenced by the decreased glassy transition temperature and crystallinity of MMMs with 10% C-ZIF-700 loadings. Meanwhile, C-ZIF facilitated transformation of saturated Me–N4 to unsaturated Me–N2 and imidazole-N to pyridine-N, thus providing abundant active sites for CO2 adsorption. Taken together, a largely increased CO2 permeability (161.3 Barrer) of MMMs with 10 wt% C-ZIF-700 was observed with a CO2/N2 selectivity of 51.4, representing a 62.1% increase compared to that of pure Pebax membrane (99.5 Barrer). This study demonstrates that carbonized-ZIF with hierarchical nanostructures may offer a great potential in constructing high-performance MMMs for various gas separations.

Ultrathin Ni-Co nanosheets with disparate-CO2-affinity nanodomains in membranes to improve gas separation

One of the biggest challenges of Pebax-based membranes is how to simultaneously achieve high CO2 permeability and selectivity. Hence, mixed matrix membranes (MMMs) were designed and fabricated by incorporating the ultrathin Ni-Co nanosheet (Ni-Co-NS) fillers into Pebax® MH 1657 (Pebax) matrix to improve CO2 separation performance. The ultrathin Ni-Co-NS fillers had disparate-CO2-affinity nanodomains and were endowed with three main functions in the Pebax/Ni-Co-NS MMMs: i) First, Ni and Co metals constituted CO2-philic and non-CO2-philic nanodomains, respectively, because the two metals had disparate CO2 adsorption enthalpy. CO2-philic nanodomains rendered a high affinity capacity, whereas non-CO2-philic nanodomains rendered low-friction diffusion. Thus, a combination of the disparate-CO2-affinity nanodomains significantly facilitated CO2 transport. ii) Second, the pore size of the nanosheets decreased from 0.79 nm to 0.49 nm by introducing the second Co metal into Ni-NS, and the decreased pores size contributed to strengthen CO2/CH4 selectivity. iii) Third, the uniform nanopores of Ni-Co-NS that paralleled to the gas concentration gradient constituted high-speed CO2 transport channels, which was conducive to improving CO2 permeability of MMMs. Therefore, CO2 separation performance of MMMs was remarkably improved by Ni-Co-NS fillers. Pebax/Ni-Co-NS MMMs with the content of 5 wt% Ni-Co-NS fillers showed the highest CO2 permeability of 483 ± 11 Barrer and CO2/CH4 selectivity of 39 ± 1.1. It implies that the introduction of nanosheets with two different metals is an effective method to fabricate MMMs with an excellent CO2 separation performance.

Evaluation of CO2 separation performance with enhanced features of materials – Pebax® 2533 mixed matrix membranes containing ZIF-8-PEI@[P(3)HIm][Tf2N

Zeolitic imidazolate framework (ZIF-8) was functionalized by polyethyleneimine (PEI) and subsequently decorated with ionic liquid (IL) – [P(3)HIm][Tf2N]. ZIF-8-PEI@IL/Pebax® 2533 mixed matrix membranes (MMMs) were fabricated to enhance the CO2 capture performance of Pebax membranes. The amino groups and IL in ZIF-8-PEI improved the gas separation performance of the MMMs due to the additional CO2 transporting pathways by using the reversible reaction with amino groups and the high affinity between IL and CO2. The modified ZIF-8 particles demonstrated enhanced interfacial interactions and compatibility between fillers and polymer matrix due to the presence of amino groups and IL, confirmed by the enhanced gas separation performance, improved elongation at break, and tensile strength of MMMs. Comparing with the pristine membranes, CO2 permeability of MMMs containing 15 wt% ZIF-8-PEI@IL increased by 123% to 285 Barrer, and the CO2/N2 and CO2/CH4 ideal selectivity increased from 17 and 12 to 76 and 25, respectively.

Preparation of polybenzimidazole‐based mixed matrix membranes containing modified‐COK‐12 mesoporous silica and evaluation of the mixed‐gas separation performance

AbstractThis work reports the preparation and characterization of mixed matrix membranes (MMMs) based on mesoporous ordered COK‐12 silica modified with 3‐aminopropyltrimethoxysilane as filler, and a series of polybenzimidazoles with different main‐chain structure as polymer matrix. Polybenzimidazoles (PBIs) were prepared from 3,3′‐diaminobenzidine and several dicarboxylic acids with different chemical structure. The physicochemical studies, as well as thermal, structural, and morphological properties of MMMs were determined by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction (XRD), and scanning electron microscopy. In addition, gas permeability properties of MMMs were tested by using a gas mixture of CO2/CH4 at different upstream pressures. Results indicated that thermal stability of PBI above 400°C is kept even after the addition of the modified COK‐12 silica. The d‐spacing of the PBI membranes determined by XRD was slightly increased with the addition of the modified COK‐12 silica particles. The permeability tests carried out at operating pressures of 50 and 150 psi showed that the addition of amino‐modified COK‐12 silica particles improved significantly the CO2 permeability of MMMs with respect to the pristine PBI. At the same time, the selectivity values were also enhanced, which in some cases were found to be more than double compared to the respective pristine membrane. The contribution of the modified COK‐12 silica on the gas transport properties was more promising in MMMs comprising PBIs with less rigid backbone chemical structure.

Mixed Matrix Membranes Based on Torlon® and ZIF-8 for High-Temperature, Size-Selective Gas Separations.

Torlon® is a thermally and plasticization-resistant polyamide imide characterized by low gas permeability at room temperature. In this work, we aimed at improving the polymer performance in the thermally-enhanced He/CO2 and H2/CO2 separations, by compounding Torlon® with a highly permeable filler, ZIF-8, to fabricate Mixed Matrix Membranes (MMMs). The effect of filler loading, gas size, and temperature on the MMMs permeability, diffusivity, and selectivity was investigated. The He permeability increased by a factor of 3, while the He/CO2 selectivity decreased by a factor of 2, when adding 25 wt % of ZIF-8 at 65 °C to Torlon®; similar trends were observed for the case of H2. The MMMs permeability and size-selectivity were both enhanced by temperature. The behavior of MMMs is intermediate between the pure polymer and pure filler ones, and can be described with models for composites, indicating that such materials have a good polymer/filler adhesion and their performance could be tailored by acting on the formulation. The behavior observed is in line with previous investigations on MMMs based on glassy polymers and ZIF-8, in similar conditions, and indicates that ZIF-8 can be used as a polymer additive when the permeability is a controlling aspect, with a proper choice of loading and operative temperature.

Tailoring the separation performance of ZIF-based mixed matrix membranes by MOF-matrix interfacial compatibilization

Controlling the metal-organic framework (MOF)-matrix interface is a useful strategy to improve the gas separation performance of mixed matrix membranes (MMMs). Although polymer blending has been investigated to enhance MMM performances, its true strength, i.e., aligning polymer and additive chemistries to improve interfacial compatibility and ultimately the separation performance, is only poorly investigated. In this work we demonstrate how controlling interfacial chemistries by polymer blending is an effective tool to tune the membrane performance. Three isoreticular zeolitic imidazolate frameworks (ZIFs) and two matrix polymers (Matrimid and polybenzimidazole oPBI (PBI)) were used to prepare the MMMs. The ZIF linker functionality strongly determined the extent of the effect of PBI addition in the MMMs. For both the hydrophobic ZIF-7 and ZIF-8-based MMMs, PBI compatibilized the MOF-matrix interface and increased the CO2/N2 separation factor while slightly decreasing the permeability. Contrarily, the separation performance of the hydrophilic ZIF-90 MMM was not affected by PBI incorporation. Additionally, the MMM permeability followed the trend of the ZIF pore geometries and linker flexibilities. These results proved that MOF-matrix interfacial compatibility can effectively be controlled by polymer blending and that the extent of control is determined by a subtle balance between the MOF linker functionality and matrix chemistry.

PIM-based mixed-matrix membranes containing MOF-801/ionic liquid nanocomposites for enhanced CO2 separation performance

In this work, we fabricated PIM-based mixed matrix membranes (MMMs) containing MOF-801/ionic liquid nanocomposites to enhance CO2 separation performance of pure polymer membranes. All membranes and MOF-801/ionic liquid nanocomposites were prepared by solution casting method and wet impregnation, respectively. The samples were analyzed by SEM, XRD, FTIR, TGA and Nitrogen adsorption-desorption measurements. The nanocomposites are composed of metal-organic framework (MOF) MOF-801 and ionic liquid (IL) adsorption capacity. MOF-801 can well control the dispersion of IL in the polymer matrix, which is conducive to exposing more active sites in the nanocomposites to improve the CO2 adsorption selectivity of MOF-801/ionic liquid nanocomposites. At the same time, the porous structure of nanocomposites also enhances the gas adsorption and diffusion, thereby improving the gas separation performance. Compared with pure PIM-1 membranes, the CO2 permeability and CO2/N2 selectivity of IL@MOF/PIM-5% MMMs was increased by 129% and 45% (CO2 = 9420 Barrer, CO2/N2 = 29）, respectively. Compared with MOF-801/PIM-1 MMMs, the permeability of CO2 decreased slightly but the selectivity of CO2/N2 increased from 27 to 29. The aging test showed that the CO2 permeability of MMMs could remain above 70% after 90 days. The anti-plasticization performance of MMMs has also been significantly improved. The CO2 separation performance of IL@MOF/PIM-5% MMMs significantly exceeded the 2008 Robeson upper bound, showing excellent gas separation performance and working stability.

Constructing Strong Interfacial Interactions under Mild Conditions in MOF-Incorporated Mixed Matrix Membranes for Gas Separation.

Although mixed matrix membranes (MMM) possess remarkably improved gas separation performance compared to traditional polymeric membranes, membrane stability including CO2 plasticization and aging is still a serious issue due to the existence of interfacial defects. In this work, we report an efficient and less destructive route to cross-link the MOFs/polyimide (PI) MMM, where amine group-functionalized MOF (NH2-UiO-66) nanoparticles are thermally cross-linked with a carboxylic acid-functionalized PI (COOH-PI) matrix to form an amide bond at the interface at 150 °C under vacuum condition. Such a chemical cross-linking strategy conducted at a relatively mild condition improves membrane stability greatly while ensuring that the membrane structure is not destroyed. The resulting cross-linked MMM achieves enhanced mechanical strength with higher Young's modulus than a pristine polymer membrane. The CO2 antiplasticization pressure of the MMM after cross-linking is enhanced by 200% from ∼10 to >30 bar and the CO2 permeability of MMM only drops slightly from 995 to 735 Barrer after 450 days. At the same time, the separation performance of H2/CH4 gas pair surpasses the 2008 upper bound and that of CO2/CH4 gas pair nearly approaches the 2008 upper bound. The cross-linking strategy used herein provides a feasible and effective route for improving membrane stability and membrane performance in the MMM system for gas separation.

Gas Permeation Model of Mixed-Matrix Membranes with Embedded Impermeable Cuboid Nanoparticles.

In the packaging industry, the barrier property of packaging materials is of paramount importance. The enhancement of barrier properties of materials can be achieved by adding impermeable nanoparticles into thin polymeric films, known as mixed-matrix membranes (MMMs). Three-dimensional numerical simulations were performed to study the barrier property of these MMMs and to estimate the effective membrane gas permeability. Results show that horizontally-aligned thin cuboid nanoparticles offer far superior barrier properties than spherical nanoparticles for an identical solid volume fraction. Maxwell’s model predicts very well the relative permeability of spherical and cubic nanoparticles over a wide range of the solid volume fraction. However, Maxwell’s model shows an increasingly poor prediction of the relative permeability of MMM as the aspect ratio of cuboid nanoparticles tends to zero or infinity. An artificial neural network (ANN) model was developed successfully to predict the relative permeability of MMMs as a function of the relative thickness and the relative projected area of the embedded nanoparticles. However, since an ANN model does not provide an explicit form of the relation of the relative permeability with the physical characteristics of the MMM, a new model based on multivariable regression analysis is introduced to represent the relative permeability in a MMM with impermeable cuboid nanoparticles. The new model possesses a simple explicit form and can predict, very well, the relative permeability over an extensive range of the solid volume fraction and aspect ratio, compared with many existing models.

Enhanced CO2 selectivity of mixed matrix membranes with carbonized Zn/Co zeolitic imidazolate frameworks

In order to efficiently separate CO2, Zn/Co zeolitic imidazolate framework (Zn/Co-ZIF) nanoparticles were carbonized and then loaded in situ into PEBAX polymer to enhance CO2 permeability and selectivity of mixed matrix membranes (MMMs), simultaneously. Positron annihilation lifetime spectroscopy (PALS), gas adsorption apparatus, and FTIR were used to characterize Zn/Co-ZIF carbonized at 600 °C for various hours and MMMs. It was found that carbonized Zn/Co-ZIF obtained local defective structures with abundant carbon and nitrogen active sites, CO2 adsorption capacity of Zn/Co-ZIF carbonized at 600 °C for 24 h increased by 1.87 times to 2.64 mmol/g. With the increasing of carbonization time, CO2 permeability of MMMs firstly decreased and then increased, while selectivity showed the opposite tendency. CO2 permeability of PEBAX-8H membrane loaded with Zn/Co-ZIF carbonized at 600 °C for 8 h increased by 15% to 102.5 ± 3.0 barrers, and selectivity of CO2/N2, CO2/CH4 and CO2/H2 increased by 45%, 43% and 18% to 52.1, 16.4 and 9.4, respectively.

Metal-organic framework MOF-801/PIM-1 mixed-matrix membranes for enhanced CO2/N2 separation performance

This work mainly studies the CO2 separation performance of a new type mixed-matrix membranes (MMMs) based on MOF-801 as the microporous filler and PIM-1 as the polymer matrix. MMMs was successfully formed via simple casting/solvent evaporation approach at room temperature. The samples were systematically characterized by SEM, XRD, TGA and FTIR, the permeability-selectivity of MMMs to CO2, O2 and N2 was studied by gas permeability test. The experimental results show that the uniform dispersion of the CO2-philic MOF-801 filler provides a channel for the rapid and selective transport of CO2, so the MOF-801/PIM-1 MMMs revealed much higher CO2 permeability and CO2/N2 ideal selectivity (CO2 = 9686 Barrer, CO2/N2 = 27, all selectivity in the paper is ideal) than pure polymer membrane. After 90-days aging test, the CO2 permeability of MMMs remains above 70%, which reflects its good anti-aging performance. After 120 h continuous gas permeability test, it also shows good long-term working stability. The experimental results show that the good gas separation performance of MMMsexceeds the Robeson upper bound (2008), showing good application prospect for practical greenhouse gas CO2 separation.

Molecular sieving mixed matrix membranes embodying nano-fillers with extremely narrow pore-openings

Polysulfone-based mixed matrix membranes (MMMs) embodying metal-organic framework ZIF-11 with extremely narrow pore-openings (~3.0 Å of aperture windows) as the nano-fillers were fabricated and applied in CO2/CH4 separation for natural gas upgrading. The proper dispersion of ZIF-11 nano-fillers, below a threshold loading, led to defect-free free-standing membranes. The CO2/CH4 separation factor and CO2 permeability of MMMs with filler loading of 24 wt% showed a 43.5% and 99.5% of increment compared with the pure polysulfone (PSF) membrane, respectively. Adsorption/diffusion coefficients and the corresponding selectivities of gases for ZIF-11/PSF MMMs were quantitatively determined. Importantly, the diffusion coefficient of CO2 of MMMs with 24 wt% of ZIF-11 nanoparticles increased by 48.8% compared with that of the pure polymer membrane, but the diffusion coefficient of CH4 decreased by 42.7%. Accordingly, the CO2/CH4 diffusion selectivity increased by 160%, indicating that the restricted aperture windows of ZIF-11 permit CO2 to pass through but imped CH4. A clear molecular sieving process was realized in MMMs with ZIF-11 nano-fillers.

The Potential of Lipid-polymer Nanoparticle as Epigenetic and ROS Control Approaches for COPD

The fabrication of mixed matrix membranes (MMMs), with a view to using them for gas separation applications, such as the capturing and separating carbon dioxide, oxygen, or nitrogen from air, and natural gas separation, has been thoroughly explored. Here we report on MMMs containing surface-modified non-porous pearl-necklace nanoparticles (P-NP), which were synthesized by connecting together approximately six spherical nanoparticles. The gas permeability of MMMs containing P-NPs increased with increasing P-NP concentration, and the increase was associated with the formation of micro- and meso-pores, which were confirmed using the nitrogen-adsorption/desorption and 129Xe NMR measurements. The permeabilities of an MMM containing 50 wt% P-NP for CO2, O2, N2, and CH4 were 15200, 2850, 916, and 1340 Barrer, respectively. This MMM also had a CO2/N2 selectivity of 16.6, CO2/CH4 selectivity of 11.4 and O2/N2 selectivity of 3.1. The gas permeation data of the resulting MMM was above the 2008 Robeson upper bound line for CO2/N2, CO2/CH4, and O2/N2 gas pairs. This strategy, using anisotropic nanoparticles with a large gas permeable space, has the potential to be applied to the fabrication of MMMs for gas separation.

Mixed matrix membranes incorporated with sonication-assisted ZIF-8 nanofillers for hazardous wastewater treatment

Mixed matrix membranes (MMMs) provide a unique pathway to treat hazardous industrial effluents. MMMs containing zeolitic imidazolate framework-8 (ZIF-8) as filler in polydimethoxysilane (PDMS) matrix were synthesized. ZIF-8 was prepared using a modified recipe and characterized by different techniques to evaluate its morphology, thermal stability, surface area, pore volume, and other characteristics. The performance of membranes was evaluated for their application in industrial dye-stuff wastewater treatment and solvent-resistant nanofiltration. The results demonstrated that increase in the percentage of ZIF-8 loading in PDMS led to simultaneous increase in the solvent permeability as well as solute rejection from wastewater. The permeability of MMMs increased up to 32% as compared with neat PDMS membrane. The organic dye rejection was achieved more than 87% with MMMs incorporated with 20% loading of nanofillers. Rejection of MMMs was 22% higher than that of unfilled PDMS membrane due to the effect of reduced polymer swelling and size exclusion of the nanofillers. Membrane swelling tests with toluene and isopropanol demonstrated that nanofiller amount has inverse relation with membrane swelling, which implied that nanofillers were in good interaction with polymer and allowed defect free membranes with higher solute rejections and reduced membrane swelling.

Using lantern Zn/Co-ZIF nanoparticles to provide channels for CO2 permeation through PEO-based MMMs

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.