Improved CO2/N2 separation performance of Pebax composite membrane containing polyethyleneimine functionalized ZIF-8

Metal-Organic-Frameworks Based Mixed-Matrix Membranes for CO2 Separation: An Applicable-Conceptual Approach

A promising class of porous crystalline materials, metal-organic frameworks (MOFs), have recently emerged as a potential material in fabricating mixed matrix membranes (MMMs) for gas separation applications. Their unique chemistry and structural versatility offer substantial advantages over conventional fillers. This review gives an in-depth exploration of MOF chemistry, focusing on strategies to manipulate their adsorption behavior to enhance separation properties. We scrutinize the impact of various MOF-based MMM components, including polymer matrix, MOFs fillers and polymer/filler interface, on the overall gas separation performance. This involves a detailed analysis of key parameters associated with MMM preparation. Additionally, we offer a comprehensive overview of the determining factors in MOF-based MMM development for gas separation, including MOF structure, synthesis, and chemistry. Moreover, the most advances in modification strategies of MOF for CO2 separation, such as a wide variety of hybrid MOFs will be outlined, which opens the door to an improved CO2 separation process. Finally, the gas transport mechanisms of MMMs are thoroughly discussed to understand the factors affecting the gas permeation through the polymer matrix, MOFs and interface between them.

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

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

Highly dispersive PEI-modified CDs@ZIF-L dual-emitting fluorescent sensor for detecting metal ions

The leaf-like zeolitic imidazolate framework (ZIF-L) is a promising porous nanomaterial that has attracted increasing attention as an ideal host material to encapsulate functional fluorescent nanoparticles for designing fluorescent sensors. However, owing to the large particle size, gravity readily facilitates the precipitation of the ZIF-L from the aqueous solution, and thus lead to imperfect experimental results. Herein, we report a simple and rapid synthetic method which uses the polyethyleneimine (PEI)-modified ZIF-L as a host to solve the precipitation problem and construct a dual-emitting system that combines its fluorescence with carbon dots (CDs). Furthermore, CDs@ZIF-L/PEI with dual-emitting centres could be utilised as a ratio fluorescence sensor to detect Hg2+ ions. The sensor exhibited excellent dispersibility and good selectivity for sensing Hg2+ ions, with a limit of detection (LOD) of 14.5 nM. Furthermore, experimental results reveal that the CDs@ZIF-L/PEI fluorescent sensor could be effectively dispersed into agarose and less polar organic solvents such as DMF, MeOH, EtOH and CH3CN, expanding the application scope of the fluorescent sensor.

Improved CO2/N2 separation performance of Pebax-1074 blend membranes containing poly(ethylene glycol)

Developing blend membrane material is one feasible and effective route for improving the gas separation efficiency and commercial attractiveness of membrane technologies. Here, free-standing membranes were prepared by casting method using Pebax-1074 as continuous polymer matrix and poly(ethylene glycol) (PEG) as dispersive organic fillers. The morphology, surface functional groups, microstructure and thermal stability of the membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry, respectively. The effects of preparation variables including average molecular weight and dosage of PEG on the microstructure, morphology and properties of the blend membranes were investigated. In addition, the effects of operation conditions including permeation temperature and permeation pressure on the gas separation performance of the blend membranes were also examined. The results showed that the addition of PEG can obviously modify the structure-properties and significantly improve the separation performance of resultant membranes. Under the conditions of 30°C and 0.25 MPa, the optimal CO2 permeability and CO2/N2 selectivity respectively reached to 124.3Barrer and 115.8 for the blend membranes made by PEG600 with a content of 20% in Pebax-1074 matrix. In brief, the as-prepared blend membranes are proved to be promising for CO2/N2 separation application.

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.

Pebax-Based Composite Membranes with High Transport Properties Enhanced by ZIF-8 for CO2 Separation

A series of mixed matrix membranes containing poly (ether-block-amide) Pebax 1657 as matrix and polyethylene glycol (PEG) and Zeolitic Imidazolate Framework-8 (ZIF-8) as additives, were prepared and tested for CO₂ separation. The membranes were prepared by solvent evaporation method and were characterized by TGA, DSC, SEM, and gas permeation measurements. The effects of PEG and its molecular weight, and the percentage of ZIF-8 into Pebax matrix were investigated. The results showed that the addition of PEG to Pebax/ZIF-8 blends avoid the agglomeration of ZIF-8 particles. A synergic effect between PEG and ZIF was particularly observed for high ZIF-8 content, because the initial permeability of pristine Pebax was multiplied by three (from 54 to 161 Barrers) while keeping the CO₂ selectivity (α_CO2/N2 = 61, α_CO2/CH4 = 12 and α_CO2/O2 = 23). Finally, the mechanism of CO₂ transport is essentially governed by the solubility of CO₂ into the membranes. Therefore, this new Pebax/PEG/ZIF-8 system seems to be a promising approach to develop new selective membranes for CO₂ with high permeability.

Mixed-Matrix Membranes Based on Polyetherimide, Metal–Organic Framework and Ionic Liquid: Influence of the Composition and Morphology on Gas Transport Properties

In this work, membranes based on polyetherimide (PEI), a ZIF-8 metal–organic framework and 1-ethyl-methylimidazolium tetrafluoroborate ionic liquid (IL) were prepared. IL and ZIF-8 contents amounting to 7 wt% and 25 wt%, respectively, were investigated. CO₂, He and H₂ transport properties of PEI/IL/ZIF-8 membranes were compared to those obtained for the respective PEI/ZIF-8 and PEI/IL systems. Membranes’ gas permeability and selectivity are discussed as a function of the membrane composition and morphology, and they were assessed in relation to existing experimental and theoretical data from the literature. Promising gas transport properties were obtained using the appropriate combination of ZIF-8 and IL amounts in the PEI matrix. Indeed, an increase in the CO₂ permeability coefficient by a factor of around 7.5 and the He and H₂ permeability coefficients by a factor of around 4 was achieved by adding 7 wt% IL and 10 wt% ZIF-8 to the PEI matrix. Moreover, diffusion was evidenced as a governing factor in the studied membrane series.

A simple and versatile synthesis strategy of hollow MOFs for CO2 separation and catalysis

A novel single-solvent-interfacial strategy is proposed to synthesize hollow MOFs, fabricated at the two-phase interface originated from the self-deliquescence of hydration water in the metallic precursors and the solvents with low water solubility. The as-fabricated HMOFs with hierarchically porous structures exhibit significant enhancement in CO₂ separation and catalysis.

Polymeric composite membranes in carbon dioxide capture process: a review

Carbon dioxide (CO₂) emission to the atmosphere is the prime cause of certain environmental issues like global warming and climate change, in the present day scenario. Capturing CO₂ from various stationary industrial emission sources is one of the initial steps to control the aforementioned problems. For this concern, a variety of resources, such as liquid absorbents, solid adsorbents, and membranes, have been utilized for CO₂ capturing from various emission sources. Focused on membrane-based CO₂ capture, polymeric membranes with composite structure (polymeric composite membrane) offer a better performance in CO₂ capturing process than other membranes, due to the composite structure it offers higher gas flux and less material usage, thus facile to use high performed expensive material for membrane fabrication and achieved good efficacy in CO₂ capture. This compressive review delivers the utilization of different polymeric composite membranes in CO₂ capturing applications. Further, the types of polymeric materials used and the different physicochemical modifications of those membrane materials and their CO₂ capturing ability are briefly discussed in the text. In conclusion, the current status and possible perspective ways to improve the CO₂ capture process in industrial CO₂ gas separation applications are described in this review.

Highly dispersive AuNCs/ChOx@ZIF-8/PEI nanocomplexes for fluorescent detection of cholesterol in human serum

Gold nanoclusters (AuNCs) are widely used in the fluorescence detection of biomolecules in human serum due to their good fluorescence properties, low toxicity, and better biocompatibility. However, the weak fluorescence intensity of AuNCs limits the fluorescence detection of molecules within a wide concentration range. It is reported that coating AuNCs in ZIF-8 with adjustable pore size can effectively improve the fluorescence intensity of AuNCs and broaden the detection range. And the AuNCs wrapped in the gaps of ZIF-8 can prevent the fluorescence quenching caused by the aggregation of AuNCs. However, ZIF-8 has high crystallinity, poor dispersion, and easy deposition, which reduces the fluorescence stability of the detection system and affects the detection. Based on the above research, the highly hydrophilic polymer PEI was modified to the surface of ZIF-8, and a kind of nanocomposite material AuNCs/ChOx@ZIF-8/PEI was obtained by co-encapsulating AuNCs prepared with glutathione as a ligand and cholesterol oxidase (ChOx) into ZIF-8 modified with PEI. The composite material emits strong red light at 650 nm under the excitation of 395-nm light, and the system can sensitively detect cholesterol (Chol) in human serum. Compared with other materials, the PEI-modified composite has better solubility and stability, so the detection effect of Chol is better. Encapsulation of ChOx in the ZIF-8 shell can protect the enzyme and increase the local concentration of ChOx, thereby speeding up the reaction rate. Compared with free AuNCs/ChOx, the quenching rate of AuNCs/ChOx@ZIF-8/PEI system is doubled. Secondly, the addition of Fe²⁺ to the detection process results in higher quenching rate and detection sensitivity. The system can detect Chol in the concentration range 0.1-2.4 μM, with a detection limit of 0.073 μM. The determination is a fast and sensitive strategy. In addition, the practicability of this assay in the detection of Chol in human serum has been verified. Due to its selectivity and sensitivity, it has potential application value in clinical diagnosis.

A Highly Permeable Mixed Matrix Membrane Containing a Vertically Aligned Metal-Organic Framework for CO2 Separation

Delicately regulating the distribution morphology of a filler is an effective strategy to promote the separation performance of mixed matrix membranes (MMMs). Herein, we describe a highly permeable metal-organic framework (MOF)-based MMM comprising vertically aligned ZIF-8 (V-ZIF-8) and polysulfone (PSF). The V-ZIF-8 is distributed uniformly within the PSF matrix. With this unique distribution morphology of ZIF-8, the shortest gas transport pathways are formed in the membrane. Meanwhile, the molecular-sieving pores of ZIF-8 can allow CO₂ to pass through and crowding out N₂. The obtained V-ZIF-8/PSF membrane shows a high CO₂ permeability of 89.7 Barrer and a CO₂/N₂ selectivity of 30.0 that is stable over a period of 50 h. The CO₂ permeability is enhanced about 11.8 times than that of the pure PSF membrane. The results prove that the vertically aligned distribution morphology of an MOF in a polymer matrix is an effective method to improve the separation performance of a membrane, providing a new concept for designing more advanced membranes.

Thin Film Mixed Matrix Hollow Fiber Membrane Fabricated by Incorporation of Amine Functionalized Metal-Organic Framework for CO2/N2 Separation

Membrane separation technology can used to capture carbon dioxide from flue gas. However, plenty of research has been focused on the flat sheet mixed matrix membrane rather than the mixed matrix thin film hollow fiber membranes. In this work, mixed matrix thin film hollow fiber membranes were fabricated by incorporating amine functionalized UiO-66 nanoparticles into the Pebax® 2533 thin selective layer on the polypropylene (PP) hollow fiber supports via dip-coating process. The attenuated total reflection-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping analysis, and thermal analysis (TGA-DTA) were used to characterize the synthesized UiO-66-NH2 nanoparticles. The morphology, surface chemistry, and the gas separation performance of the fabricated Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes were characterized by using SEM, ATR-FTIR, and gas permeance measurements, respectively. It was found that the surface morphology of the prepared membranes was influenced by the incorporation of UiO-66 nanoparticles. The CO2 permeance increased along with an increase of UiO-66 nanoparticles content in the prepared membranes, while the CO2/N2 ideal gas selectively firstly increased then decreased due to the aggregation of UiO-66 nanoparticles. The Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes containing 10 wt% UiO-66 nanoparticles exhibited the CO2 permeance of 26 GPU and CO2/N2 selectivity of 37.

Enhanced Gas Separation Prowess Using Functionalized Lignin-Free Lignocellulosic Biomass/Polysulfone Composite Membranes

Delignified lignocellulosic biomass was functionalized with amine groups. Then, the pretreated lignin-free date pits cellulose and the amine-functionalized-date pits cellulose (0–5 wt%) were incorporated into a polysulfone polymer matrix to fabricate composite membranes. The amine groups give additional hydrogen bonding to those existing from the hydroxyl groups in the date pits cellulose. The approach gives an efficient avenue to enhance the CO₂ molecules’ transport pathways through the membrane matrix. The interactions between phases were investigated via Fourier transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), whereas pure gases (CO₂ and N₂) were used to evaluate the gas separation performances. Additionally, the thermal and mechanical properties of the fabricated composites were tested. The pure polysulfone membrane achieved an optimum separation performance at 4 Bar. The optimum separation performance for the composite membranes is achieved at 2 wt%. About 32% and 33% increments of the ideal CO₂/N₂ selectivity is achieved for the lignin-free date pits cellulose composite membrane and the amine-functionalized-date pits cellulose composite membrane, respectively.