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

Mixed matrix membranes for selective gas separation of H2/CH4 and CO2/CH4 via fabricating high-performing double-ligand ZIF-8 with cellulose acetate-based polymer

ZIF-8-based mixed matrix membranes are most used for selective gas separation due to their obvious molecular sieving properties. However, their application remains challenging due to their incompatibility with polymer matrix. In this study, we introduced the AZIF-8 nanoparticles synthesized via partial substitution of 2-methyl imidazole (2-Mim) ligand by 3-amino-1, 2, 4-triazole (Atz) to finely tune the aperture and increase gas separation performance of MMMs. The integration of Atz ligand significantly enhances particle dispersion and compatibility with polymer. Different ligand substitution times and loadings were applied to investigate the gas separation performance. The experimental results reveal that the Atz modified ZIF-8 (AZIF-8) blended CA MMMs with 1 wt% loading showed the high separation activity. The A8ZIF-8/CA (A8 = 8 h) is able to achieve high H2 and CO2 permeability values of 183.5 and 135.0 Barrer, respectively, with ideal selectivity of 49.1 and 36.1 for H2/CH4 and CO2/CH4, respectively, under the 0.4 MPa feed pressure. Remarkably, the gas separation activity of Atz modified ZIF-8 MMMs lies very close to the Robeson upper bound 2008, signifying the effectiveness of the reported modification strategy.

Covalent Organic Frameworks for Membrane Separation

Membranes with switchable wettability, solvent resistance, and toughness have emerged as promising materials for separation applications. However, challenges like limited mechanical strength, poor chemical stability, and structural defects during membrane fabrication hinder their widespread adoption. Covalent organic frameworks (COFs), crystalline materials constructed from organic molecules connected by covalent bonds, offer a promising solution due to their high porosity, stability, and customizable properties. The ordered structures and customizable functionality provide COFs with a lightweight framework, large surface area, and tunable pore sizes, which have attracted increasing attention for their applications in membrane separations. Recent research has extensively explored the preparation strategies of COF membranes and their applications in various separation processes. This review uniquely delves into the influence of various COF membrane fabrication techniques, including interfacial polymerization, layer-by-layer assembly, and in situ growth, on membrane thickness and performance. It comprehensively explores the design strategies and potential applications of these methods, with a particular focus on gas separation, oil/water separation, and organic solvent nanofiltration. Furthermore, future opportunities, challenges within this field, and potential directions for future development are proposed.

Graphene-modified MIL-125-NH2 mixed matrix membranes for efficient H2 and CH4 purification

This study investigates the performance of the mixed matrix membranes (MMMs) incorporating hybrid fillers of metal-organic framework (MIL-125-NH2) and graphene nanosheets (GNs) for enhanced methane (CH₄) and hydrogen (H₂) separation in the purification sector. The physico-chemical properties of the MMMs were evaluated by SEM, XRD, FTIR, AFM, TGA, DTG, and Brunauer-Emmett-Teller. The permeability and selectivity of the MMMs were determined using different single gases (CO2, N2, H2, and CH4) at various temperatures (20-60 °C). Optimization of fabrication parameters resulted in a significant improvement in porosity and roughness of the fabricated MMMs. The permeabilities of the MOF/PES membrane are 20.3 (CO2), 23.9 (N2), 32.2 (CH4), and 24.1 (H2) x 104 Barrer, while incorporating 0.05 wt% of GNs into the MOF/PES membrane improved the permeability by 36 % (CO2), 41 % (N2), 31 % (CH4), and 370 % (H2). In addition, the H2/CO2 and H2/N2 selectivities of the MMMs significantly increased up to 4 and 3.3, with an improvements of 236 % and 230 %, respectively, compared to the MOF/PES membrane. Furthermore, the CH4/CO2 and CH4/N2 selectivities of the MMMs decreased by 4 %. Therefore, a hybrid filler (10 wt % of MIL-125-NH2 and 0.05 wt % of GNs is highly recommended to improve the permeability and selectivity of the PES membrane, expanding its potential applications in CH4 and H2 purification.

Research on reliability index and failure probability of inherent defect insurance from the insurance perspective

With the continuous improvement of people 's living standards, people have put forward higher requirements for the safety and comfort of housing. Therefore, Inherent Defect Insurance, a financial method to guarantee the quality of construction projects, has also emerged. At present, China 's Inherent Defect Insurance has been gradually promoted, but its claim mechanism has not been analyzed and studied. From the perspective of construction engineering, this paper first makes a bibliometric analysis of the influencing factors of insurance claims that may be caused by construction engineering quality through VOSViewers, and the evaluation index system of inherent defects is constructed. Then, according to the influencing factors, the PSO-LSSVR model is adopted to fit the performance function of the inherent defects. Finally, based on the reliability design principle of engineering structure, the reliability index and failure probability of Inherent Defect Insurance are derived from the performance function of inherent defects. This paper also analyzes its application in insurance practice and determines the relationship between the number of insurance underwriting policies and the initial reserve of insurance at a certain risk level. This paper studies the probability of Inherent Defect Insurance by constructing the reliability model of inherent defect risks in construction quality, and analyzes the anti-risk ability of insurance companies from the perspective of claim, which provides scientific analysis methods and theoretical basis for the scientific decision-making of insurance companies.

Ultrasmall Functionalized UiO-66 Nanoparticle/Polymer Pebax 1657 Thin-Film Nanocomposite Membranes for Optimal CO2 Separation

Ultrasmall 4 to 6 nm nanoparticles of the metal-organic framework (MOF) UiO-66 (University of Oslo-66) were successfully prepared and embedded into the polymer Pebax 1657 to fabricate thin-film nanocomposite (TFN) membranes for CO2/N2 and CO2/CH4 separations. Furthermore, it has been demonstrated that ligand functionalization with amino (-NH2) and nitro (-NO2) groups significantly enhances the gas separation performance of the membranes. For CO2/N2 separation, 7.5 wt % UiO-66-NH2 nanoparticles provided a 53% improvement in CO2 permeance over the pristine membrane (from 181 to 277 GPU). Regarding the CO2/N2 selectivity, the membranes prepared with 5 wt % UiO-66-NO2 nanoparticles provided an increment of 17% over the membrane without the MOF (from 43.5 to 51.0). However, the CO2 permeance of this membrane dropped to 155 GPU. The addition of 10 wt % ZIF-94 particles with an average particle size of ∼45 nm into the 5 wt % UiO-66-NO2 membrane allowed to increase the CO2 permeance to 192 GPU while maintaining the CO2/N2 selectivity at ca. 51 due to the synergistic interaction between the MOFs and the polymer matrix provided by the hydrophilic nature of ZIF-94. In the case of CO2/CH4 separation, the 7.5 wt % UiO-66-NH2 membrane exhibited the best performance with an increase of the CO2 permeance from 201 to 245 GPU.

Durable and recyclable MOF@polycaprolactone mixed-matrix membranes with hierarchical porosity for wastewater treatment

With the fast-growing global water crisis, the development of novel technologies for water remediation and reuse is crucial. Industrial wastewater especially contains various toxic pollutants that pose an additional threat to the environment; thus, efficient removal of such contaminants can ensure safe reprocessing of industrial wastewater, thereby alleviating the demand for fresh water. Herein, we describe a novel and efficient approach for preparing porous polycaprolactone (PCL) membranes with a hierarchical architecture via a simple solvent/non-solvent methodology. A mixed-matrix membrane (MMM) was further constructed utilizing an amine-functionalized metal-organic framework as the sorbent filler nanoparticles and PCL as the polymer support matrix (MOF@PCL) for wastewater treatment applications. The MOF@PCL MMM demonstrated homogeneous morphology as well as exceptional performance towards the removal of both cationic (methylene blue, MB) and anionic (methyl orange, MO) organic dyes, where the maximum adsorption capacities reached 309 mg g-1 and 208 mg g-1, respectively. Kinetic and thermodynamic investigations revealed that the adsorption process was endothermic with a fast intraparticle diffusion rate constant. The MOF@PCL MMM also displayed excellent mechanical stability and recyclability, where the removal efficiency was maintained after 10 cycles.

Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

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

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

Polyvinyl alcohol and aminated cellulose nanocrystal membranes with improved interfacial compatibility for environmental applications

Biogas up-gradation is a useful method to control CO₂ emission and enhance the green process. The demand for renewable sources is increasing due to the depletion of fossil fuels. Thin-film nanocomposites functionalized with tunable molecular-sieving nanomaterials have been employed to tailor membranes with enhanced permeability and selectivity. In this work, the cellulose nanocrystals as a filler in the polyvinyl alcohol matrix are prepared to achieve high-performance facilitated transport membranes for CO₂ capture. Considering the mechanical stability, interfacial compatibility and high moisture uptake of the filler, the main objective of this work was to develop a novel aminated CNC (Am-CNC)/polyvinyl alcohol nanocomposite membrane for biogas upgrading. The hydroxyl groups (O-H) on the reducing end of the cellulose nanocrystals were replaced by amino groups (N-H₂). It was discovered through Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) that adding Am-CNCs in PVA membranes shows an increment in the CO₂ removal and effectively upgrades the biogas. The effect of change in concentration of Am-CNC and feed pressure was investigated. The results showed that with increasing Am-CNC concentration up to 1.5 wt%, the thickness of the selective membrane layer increased from 0.95 to 1.9 μm with a decrease in the moisture uptake from 85.04 to 58.84%. However, the best CO₂ permeance and selectivity were achieved at 0.306 m³/m².bar.h (STP) and 33.55, respectively. Furthermore, there was a more than two-fold decrease in CO₂ permeance and a 27% decrease in the CO₂/CH₄ selectivity when the feed pressure increased from 5 to 15 bar. It was revealed that PVA/Am-CNC membrane is high performing for the biogas upgradation.

Pebax® 2533/PVDF thin film mixed matrix membranes containing MIL-101 (Fe)/GO composite for CO2 capture

MIL-101 (Fe) and MIL-GO composites were successfully synthesized and used as fillers for the preparation of Pebax® 2533/PVDF thin film MMMs for CO2/N2 separation. The defect-free Pebax® 2533/PVDF thin film MMMs were fabricated by casting the Pebax solution containing fillers on the PVDF support. The presence of GO nanosheets in the reaction solution did not destroy the crystal structure of MIL-101 (Fe). However, the BET surface area and total pore volume of MIL-GO decreased dramatically, comparing with MIL-101 (Fe). The incorporation of MIL-GO-2 into Pebax matrix simultaneously increased the CO2 permeability and the CO2/N2 ideal selectivity of Pebax® 2533/PVDF thin film MMMs mainly owing to the porous structure of MIL-GO-2, and the tortuous diffusion pathways created by GO nanosheets. MMMs containing 9.1 wt% MIL-GO-2 exhibited the highest CO2 permeability equal to 303 barrer (1 barrer = 10-10 cm3 (STP) cm cm-2 s-1 cmHg-1) and the highest CO2/N2 ideal selectivity equal to 24. Pebax-based MMMs containing composite fillers showed higher gas separation performance than the Pebax-based MMMs containing single filler (GO or MOFs). Therefore, the synthesis and utilization of 3D@2D composite filler demonstrated great potential in the preparation of high-performance MMMs for gas separation processes.

In Situ Synthesis of Multivariate Zeolitic Imidazolate Frameworks for C2 H4 /C2 H6 Kinetic Separation

Herein, a new approach for the in situ synthesis of zeolitic imidazolate framework (ZIF) nanoparticles with triple ligands, referred to as Sogang ZIF-8 (SZIF-8), is reported for enhanced C₂ H₄ /C₂ H₆ kinetic separation. SZIF-8 consists of tetrahedral zinc metals coordinated with tri-butyl amine (TBA), 2,4-dimethylimidazole (DIm), and 2-methylimidazole (MIm). SZIF-8(x) with different DIm contents in x (up to 23.2 mol%) are synthesized in situ because TBA preferably deprotonates DIm ligands due to the much lower pK_a of DIm over MIm, allowing for the Zn-DIm coordination. The Zn-DIm coordination reduces the window size of ZIF-8 with suppressed linker flipping motion due to bulky DIm ligands and simultaneously enhances the interfacial interaction between 6FDA-DAM polyimide (6FDA) and SZIF-8 via electron donor-acceptor interactions. Consequently, 6FDA/SZIF-8(13) mixed matrix membrane exhibits an excellent C₂ H₄ permeability of 60.3 Barrer and C₂ H₄ /C₂ H₆ selectivity of 4.5. The temperature-dependent transport characterization reveals that such excellent C₂ H₄ /C₂ H₆ kinetic separation is attained by the enhancement in size discrimination-based energetic selectivity. Our hybrid multi-ligand approach can offer a useful tool for the fine-tuning of molecular structures and textural properties of other metal organic frameworks.

Optimization of a MOF Blended with Modified Polyimide Membrane for High-Performance Gas Separation

The preparation, characterization and gas separation properties of mixed matrix membranes (MMMs) were obtained from polyimide capped with ionic liquid and blended with metal-organic frameworks (MOFs). The synthesized MOF was amine functionalized to produce UiO-66-NH₂, and its amino group has a higher affinity for CO₂. Mixed matrix membranes exhibited good membrane forming ability, heat resistance and mechanical properties. The polyimide membrane exclusively capped by ionic liquid exhibited good permselectivity of 74.1 for CO₂/CH₄, which was 6.2 times that of the pure polyimide membrane. It is worth noting that MMM blended with UiO-66-NH₂ demonstrated the highest ideal selectivity for CO₂/CH₄ (95.1) with a CO₂ permeability of 7.61 Barrer, which is close to the 2008 Robeson upper bound. The addition of UiO-66-NH₂ and ionic liquid enhanced the permselectivity of MMMs, which may be one of the promising technologies for high performance CO₂/CH₄ gas separation.