UiO-66-polyether block amide mixed matrix membranes for CO2 separation

Pushing Rubbery Polymer Membranes To Be Economic for CO2 Separation: Embedment with Ti3C2Tx MXene Nanosheets

Sustainable and energy-efficient molecular separation requires membranes with high gas permeability and selectivity. This work reports excellent CO₂ separation performance of self-standing and thin-film mixed matrix membranes (MMMs) fabricated by embedding 2D Ti₃C₂T_x MXene nanosheets in Pebax-1657. The CO₂/N₂ and CO₂/H₂ separation performances of the free-standing membranes are above Robeson's upper bounds, and the performances of the thin-film composite (TFC) membranes are in the target area for cost-efficient CO₂ capture. Characterization and molecular dynamics simulation results suggest that the superior performances of the Pebax-Ti₃C₂T_x membranes are due to the formation of hydrogen bonds between Ti₃C₂T_x and Pebax chains, leading to the creation of the well-formed galleries of Ti₃C₂T_x nanosheets in the hard segments of the Pebax. The interfacial interactions and selective Ti₃C₂T_x nanochannels enable fast and selective CO₂ transport. Enhancement of the transport properties of Pebax-2533 and polyurethane when embedded with Ti₃C₂T_x further supports these findings. The ease of fabrication and high separation performance of the new TFC membranes point to their great potential for energy-efficient CO₂ separation with the low cost of $29/ton separated CO₂.

MOF-Polymer Hybrid Materials: From Simple Composites to Tailored Architectures

Metal-organic frameworks (MOFs) are inherently crystalline, brittle porous solids. Conversely, polymers are flexible, malleable, and processable solids that are used for a broad range of commonly used technologies. The stark differences between the nature of MOFs and polymers has motivated efforts to hybridize crystalline MOFs and flexible polymers to produce composites that retain the desired properties of these disparate materials. Importantly, studies have shown that MOFs can be used to influence polymer structure, and polymers can be used to modulate MOF growth and characteristics. In this Review, we highlight the development and recent advances in the synthesis of MOF-polymer mixed-matrix membranes (MMMs) and applications of these MMMs in gas and liquid separations and purifications, including aqueous applications such as dye removal, toxic heavy metal sequestration, and desalination. Other elegant ways of synthesizing MOF-polymer hybrid materials, such as grafting polymers to and from MOFs, polymerization of polymers within MOFs, using polymers to template MOFs, and the bottom-up synthesis of polyMOFs and polyMOPs are also discussed. This review highlights recent papers in the advancement of MOF-polymer hybrid materials, as well as seminal reports that significantly advanced the field.

Metal-organic framework UiO-66 membranes

Metal-organic frameworks (MOFs) have emerged as a class of promising membrane materials. UiO-66 is a prototypical and stable MOF material with a number of analogues. In this article, we review five approaches for fabricating UiO-66 polycrystalline membranes including in situ synthesis, secondary synthesis, biphase synthesis, gas-phase deposition and electrochemical deposition, as well as their applications in gas separation, pervaporation, nanofiltration and ion separation. On this basis, we propose possible methods for scalable synthesis of UiO-66 membranes and their potential separation applications in the future.

Zirconium based porous coordination polymer (PCP) bearing organocatalytic ligand: A promising dual catalytic center for ultrasonic heterocycle synthesis

Herein, the efficient role of ultrasonic irradiation both in synthesis of Zr based porous coordination polymer (Zr-PCP) nanoparticles and boosting its catalytic activity, towards the benzimidazoles synthesis is represented. We use an amine based ligand (amino-terephthalate) for PCP and we exhibit that it can have a synergistic catalytic activity. In this work, a unique nano-engineering of cooperative and synergistic catalytic activity of zirconium, as a Lewis acid, and aminophenylene, as an organocatalyst, in the synthesis of heterocycles is presented for the synthesis of benzimidazole from cascade reaction of phenylene diamine with aldehyde at ambient temperature. Zr and amine groups of the Zr-PCP are active catalytic sites which in combination with the ultrasonic irradiation leads to a high selectivity and rapid catalytic production of benzylimidazoles. N₂ adsorption-desorption along with BJH analyses confirm the microporosity of the catalyst and recyclability shows that the catalyst is green and sustainable heterogeneous microporous catalyst.

Polydopamine-Modified Metal-Organic Framework Membrane with Enhanced Selectivity for Carbon Capture

In this work, a versatile postmodification strategy based polydopamine (PDA) grafting is reported for improving CO₂ separation performance of MOF membranes. Owning to the strong bioadhesion, PDA can be deposited on the UiO-66 membrane through a simple and mild process. Since PDA impregnation in invalid nanometer-sized pinholes and grain boundaries of the MOF membrane suppress nonselective gas transports, the modified PDA/UiO-66 membrane exhibits significantly enhanced CO₂/N₂ and CO₂/CH₄ selectivities of 51.6 and 28.9, respectively, which are 2-3 times higher than the reported MOF membranes with similar permeance. Meanwhile, because PDA modification do not change UiO-66 intrinsic pores and membrane thickness is submicrometer-sized, the CO₂ permeance is 2-3 orders of magnitude larger than those membranes with similar selectivity, up to 3.7 × 10^-7 mol m^-2 s^-1 Pa^-1 (1115 GPU). Moreover, the PDA/UiO-66 membrane with good reproducibility has excellent long-term stability for CO₂ capture under moist condition in 36 h measurement period.

Mixed-Matrix Composite Membranes Based on UiO-66-Derived MOFs for CO2 Separation

We demonstrated a novel mixed-matrix composite membrane (MMCM) based on acrylated polyurethane (APU) and UiO-66 nanoparticles to separate CO₂/N₂ mixture. UiO-66 and functionalized UiO-66 including NH₂-UiO-66 and glycidyl methacrylate (GMA)-UiO-66 were loaded into APU/2-hydroxyethyl methacrylate (APUH) matrix at variable concentrations between 3 and 30 wt %. APUH/GMA-UiO-66 MMCMs exhibited strong adhesion with a support layer of polyester/polysulfone, which was not deteriorated after immersion in water for a long time (20 days). Incorporation of UiO-66 and its functionalized forms increased simultaneously permeability and CO₂/N₂ selectivity, which were indeed superior in comparison with those of MMCMs reported previously. GMA-UiO-66-filled MMCM displayed a CO₂ permeance of 14.5 Barrer and a CO₂/N₂ selectivity of 53 at a critical concentration (25 wt %). This attractive separation performance of APUH/UiO-66 offered an exciting platform for the development of composite membranes for sustainable CO₂ separations.

CO2-philic moderate selective layer mixed matrix membranes containing surface functionalized NaX towards highly-efficient CO2 capture

A functional moderate selective layer mixed matrix membrane (F-MSL-MMM) is a promising candidate to obtain superior separation of industrial gases, compared to commonly mixed matrix membranes. In this work, highly permeable and selective F-MSL-MMMs consisting of a moderate Pebax layer filled with functionalized NaX nano-zeolite over a microstructure PES support layer with the desired operating stability were prepared to investigate the effect of –COOH surface functionalization on the NaX nano-zeolites and to achieve the efficient separation of CO₂/N₂, CO₂/CH₄ and CH₄/N₂ gas mixtures. It was found that modification of the nano-zeolite had significant effects on the morphology and gas separation performance of the F-MSL-MMMs. The incorporation of NaX–COOH nano-zeolites into the polymeric matrix showed superior dispersion, capabilities and interactions over unmodified zeolite without any defects. In addition, based on gas permeation results at various filler loadings and feed pressures, different trends were observed for the permeability and selectivity of the F-MSL-MMMs. Combination of NaX up to 1.5% into the moderate selective layer enhanced the CO₂ permeability (187.76 barrer) and CO₂/N₂ (288.86), CO₂/CH₄ (57.41) and N₂/CH₄ (5.03) selectivities at 6 bar.

A functional moderate selective layer mixed matrix membrane (F-MSL-MMM) is a promising candidate to obtain superior separation of industrial gases, compared to commonly mixed matrix membranes.

Enhanced Polymer Crystallinity in Mixed-Matrix Membranes Induced by Metal-Organic Framework Nanosheets for Efficient CO2 Capture

The design and fabrication of novel mixed-matrix membranes (MMMs) with simultaneously enhanced gas permeability and selectivity are highly sought for the industrial deployment of membrane technology for large-scale CO₂ capture and storage. Conventional isotropic bulky particle fillers often exhibit limited interfacial compatibility that eventually leads to significant selectivity loss in MMMs. Here, we report the incorporation of chemically stable metal-organic framework (MOF) nanosheets into a highly permeable polymer matrix to prepare defect-free MMMs. MOF nanosheets are homogeneously dispersed within the polymer matrix, owing to their high aspect ratios that improve the polymer-filler integration. The strong hydrogen bonding and π-π interactions between the two components not only enhance the interfacial compatibility but also favor the efficient polymer chain packing along the surface of MOF nanosheets, leading to enhanced polymer crystallinity as well as size-sieving capability of the membranes. The as-prepared MMMs demonstrate high CO₂-selective separation performance, good antipressure, and antiaging abilities, thus offering new opportunities in developing advanced membranes for industrial gas separation applications.

Advanced Porous Materials in Mixed Matrix Membranes

Membrane technology has gained great interest in industrial separation processing over the past few decades owing to its high energy efficiency, small capital investment, environmentally benign characteristics, and the continuous operation process. Among various types of membranes, mixed matrix membranes (MMMs) combining the merits of the polymer matrix and inorganic/organic fillers have been extensively investigated. With the rapid development of chemistry and materials science, recent studies have shifted toward the design and application of advanced porous materials as promising fillers to boost the separation performance of MMMs. Here, first a comprehensive overview is provided on the choices of advanced porous materials recently adopted in MMMs, including metal-organic frameworks, porous organic frameworks, and porous molecular compounds. Novel trends in MMMs induced by these advanced porous fillers are discussed in detail, followed by a summary of applying these MMMs for gas and liquid separations. Finally, a concise conclusion and current challenges toward the industrial implementation of MMMs are outlined, hoping to provide guidance for the design of high-performance membranes to meet the urgent needs of clean energy and environmental sustainability.

Performance of Mixed Matrix Membranes Containing Porous Two-Dimensional (2D) and Three-Dimensional (3D) Fillers for CO₂ Separation: A Review

Application of conventional polymeric membranes in CO₂ separation processes are limited by the existing trade-off between permeability and selectivity represented by the renowned upper bound. Addition of porous nanofillers in polymeric membranes is a promising approach to transcend the upper bound, owing to their superior separation capabilities. Porous nanofillers entice increased attention over nonporous counterparts due to their inherent CO₂ uptake capacities and secondary transport pathways when added to polymer matrices. Infinite possibilities of tuning the porous architecture of these nanofillers also facilitate simultaneous enhancement of permeability, selectivity and stability features of the membrane conveniently heading in the direction towards industrial realization. This review focuses on presenting a complete synopsis of inherent capacities of several porous nanofillers, like metal organic frameworks (MOFs), Zeolites, and porous organic frameworks (POFs) and the effects on their addition to polymeric membranes. Gas permeation performances of select hybrids with these three-dimensional (3D) fillers and porous nanosheets have been summarized and discussed with respect to each type. Consequently, the benefits and shortcomings of each class of materials have been outlined and future research directions concerning the hybrids with 3D fillers have been suggested.

Ultraselective Pebax Membranes Enabled by Templated Microphase Separation

Block copolymer materials have been considered as promising candidates to fabricate gas separation membranes. This microphase separation affects the polymer chain packing density and molecular separation efficiency. Here, we demonstrate a method to template microphase separation within a thin composite Pebax membrane, through the controllable self-assembly of one-dimensional halloysite nanotubes (HNTs) within the thin film via the solution-casting technique. Crystallization of the polyamide component is induced at the HNT surface, guiding subsequent crystal growth around the tubular structure. The resultant composite membrane possesses an ultrahigh selectivity (up to 290) for the CO₂/N₂ gas pair, together with a moderate CO₂ permeability (80.4 barrer), being the highest selectivity recorded for Pebax-based membranes, and it easily surpasses the Robeson upper bound. The templated microphase separation concept is further demonstrated with the nanocomposite hollow fiber gas separation membranes, showing its effectiveness of promoting gas selectivity.