Amino-functionalized NUS-8 nanosheets as fillers in PIM-1 mixed matrix membranes for CO2 separations

A phase-transition ionic liquid endows COF-based mixed matrix membranes with efficient CO2 separation

The interfacial compatibility of COF-based MMMs was significantly enhanced through the incorporation of thermoresponsive phase-transition ionic liquids. The IL@DAAQ-COF was synthesized in situ, with the ionic liquid (IL) playing a key role in modulating the COF channel and enhancing the CO2 affinity. The resulting membrane exhibited a CO2 permeability of 17 449 Barrer and a CO2/N2 selectivity of 27.2, surpassing the 2019 Jansen/McKeown upper bound.

A review of metal-organic frameworks and polymers in mixed matrix membranes for CO2 capture

Polymeric membranes offer an appealing solution for sustainable CO2 capture, with potential for large-scale deployment. However, balancing high permeability and selectivity is an inherent challenge for pristine membranes. To address this challenge, the development of mixed matrix membranes (MMMs) is a promising strategy. MMMs are obtained by carefully integrating porous nano-fillers into polymeric matrices, enabling the simultaneous enhancement of selectivity and permeability. In particular, metal-organic frameworks (MOFs) have gained recognition as MMM fillers for CO2 capture. Here, a review of the current state, recent advancements, and challenges in the fabrication and engineering of MMMs with MOFs for selective CO2 capture is proposed. Key considerations and promising research directions to fully exploit the gas separation potential of MOF-based MMMs in CO2 capture applications are highlighted.

Membranes of Polymer of Intrinsic Microporosity PIM-1 for Gas Separation: Modification Strategies and Meta-Analysis

Polymers of intrinsic microporosity (PIMs) have received considerable attention for making high-performance membranes for carbon dioxide separation over the last two decades, owing to their highly permeable porous structures. However, challenges regarding its relatively low selectivity, physical aging, and plasticisation impede relevant industrial adoptions for gas separation. To address these issues, several strategies including chain modification, post-modification, blending with other polymers, and the addition of fillers, have been developed and explored. PIM-1 is the most investigated PIMs, and hence here we review the state-of-the-arts of the modification strategies of PIM-1 critically and discuss the progress achieved for addressing the aforementioned challenges via meta-analysis. Additionally, the development of PIM-1-based thin film composite membranes is commented as well, shedding light on their potential in industrial gas separation. We hope that the review can be a timely snapshot of the relevant state-of-the-arts of PIMs guiding future design and optimisation of PIMs-based membranes for enhanced performance towards a higher technology readiness level for practical applications.

Solution Processable Metal-Organic Frameworks: Synthesis Strategy and Applications

Metal-organic frameworks (MOFs), constructed by inorganic secondary building units with organic linkers via reticular chemistry, inherently suffer from poor solution processability due to their insoluble nature, resulting from their extensive crystalline networks and structural rigidity. The ubiquitous occurrence of precipitation and agglomeration of MOFs upon formation poses a significant obstacle to the scale-up production of MOF-based monolith, aerogels, membranes, and electronic devices, thus restricting their practical applications in various scenarios. To address the previously mentioned challenge, significant strides have been achieved over the past decade in the development of various strategies aimed at preparing solution-processable MOF systems. In this review, the latest advance in the synthetic strategies for the construction of solution-processable MOFs, including direct dispersion in ionic liquids, surface modification, controllable calcination, and bottom-up synthesis, is comprehensively summarized. The respective advantages and disadvantages of each method are discussed. Additionally, the intriguing applications of solution-processable MOF systems in the fields of liquid adsorbent, molecular capture, sensing, and separation are systematically discussed. Finally, the challenges and opportunities about the continued advancement of solution-processable MOFs and their potential applications are outlooked.

Phage Display Against 2D Metal-Organic Nanosheets as a New Route to Highly Selective Biomolecular Recognition Surfaces

Peptides are important biomarkers for various diseases, however distinguishing specific amino-acid sequences using artificial receptors remains a major challenge in biomedical sensing. This study introduces a new approach for creating highly selective recognition surfaces using phage display biopanning against metal-organic nanosheets (MONs). Three MONs (ZIF-7, ZIF-7-NH2, and Hf-BTB-NH2) are added to a solution containing every possible combination of seven-residue peptides attached to bacteriophage hosts. The highest affinity peptides for each MON are isolated through successive bio-panning rounds. Comparison of the surface properties of the MONs and high-affinity peptides provide useful insights into the relative importance of electrostatic, hydrophobic, and co-ordination bonding interactions in each system, aiding the design of future MONs. Coating of the Hf-BTB-NH2 MONs onto a quartz crystal microbalance (QCM) produced a five-fold higher signal for phage with the on-target peptide sequence compared to those with generic sequences. Surface plasmon resonance (SPR) studies produce a 4600-fold higher equilibrium dissociation constant (KD) for on-target sequences and are comparable to those of antibodies (KD = 4 x 10-10 m). It is anticipated that insights from the biopanning approach, combined with the highly tunable nature of MONs, will lead to a new generation of highly selective recognition surfaces for use in biomedical sensors.

Recent Advances of Carbon Capture in Metal-Organic Frameworks: A Comprehensive Review

The excessive emission of greenhouse gases, which leads to global warming and alarms the world, has triggered a global campaign for carbon neutrality. Carbon capture and sequestration (CCS) technology has aroused wide research interest as a versatile emission mitigation technology. Metal-organic frameworks (MOFs), as a new class of high-performance adsorbents, hold great potential for CO2 capture from large point sources and ambient air due to their ultra-high specific surface area as well as pore structure. In recent years, MOFs have made great progress in the field of CO2 capture and separation, and have published a number of important results, which have greatly promoted the development of MOF materials for practical carbon capture applications. This review summarizes the most recent advanced research on MOF materials for carbon capture in various application scenarios over the past six years. The strategies for enhancing CO2 selective adsorption and separation of MOFs are described in detail, along with the development of MOF-based composites. Moreover, this review also systematically summarizes the highly concerned issues of MOF materials in practical applications of carbon capture. Finally, future research on CO2 capture by MOF materials is prospected.

Zinc triazolate oxalate CALF-20 with platelet morphology and its PEBAX-based mixed matrix membranes for CO2/N2 separation

CALF-20, [Zn2(1,2,4-triazolate)2(oxalate)] shows remarkable performance in post-combustion carbon capture, even under humid conditions1 but its reported crystal morphology hinders its applicability in mixed matrix membranes (MMMs). Here, a route to its preparation as platelets a few tens of nm thick is reported. These were incorporated into a PEBAX MH1567 polymer matrix and the resultant MMMs display improvement in CO2 permeability and CO2/N2 selectivity.

A metal-organic framework signaling probe-mediated immunosensor for the economical and rapid determination of enrofloxacin in milk

Ensuring the safety of animal-derived foods requires the reliable and swift identification of enrofloxacin residues to monitor the presence of antibiotics. In this regard, we synthesized, tuned, and investigated the optical properties of a bimetallic metal-organic framework (Ce/Zr-UiO 66). The investigation was facilitated by employing a polydopamine-coated pipette tip with high adsorption efficiency, serving as an immunoreactive carrier. Subsequently, an immunofunctionalized variant of Ce/Zr-UiO 66, referred to as Ce/Zr-UiO 66@ Bovine serum albumin-enrofloxacin, was developed as an optical probe for the rapid and sensitive identification of enrofloxacin across a variety of samples. The method can accurately detect enrofloxacin at concentrations as low as 0.12 ng/mL, with a determination time of under 15 min; furthermore, it demonstrates exceptional efficacy when applied to food, environmental, and clinical samples. The implementation of this methodology offers a valuable means for cost-effective, rapid, and on-site enrofloxacin determination.

Recent advancements in polyurethane-based membranes for gas separation

Gas separation membranes are critical in a variety of environmental research and industrial applications. These membranes are designed to selectively allow some gases to flow while blocking others, allowing for the separation and purification of gases for a variety of applications. Therefore, the demand for fast and energy-efficient gas separation techniques is of central interest for many chemical and energy production diligences due to the intensified levels of greenhouse and industrial gases. This encourages the researchers to innovate techniques for capturing and separating these gases, including membrane separation techniques. Polymeric membranes play a significant role in gas separations by capturing gases from the fuel combustion process, purifying chemical raw material used for plastic production, and isolating pure and noncombustible gases. Polyurethane-based membrane technology offers an excellent knack for gas separation applications and has also been considered more energy-efficient than conventional phase change separation methodologies. This review article reveals a thorough delineation of the current developments and efforts made for PU membranes. It further explains its uses for the separation of valuable gases such as carbon dioxide (CO2), hydrogen (H2), nitrogen (N2), methane (CH4), or a mixture of gases from a variety of gas spillages. Polyurethane (PU) is an excellent choice of material and a leading candidate for producing gas-separating membranes because of its outstanding chemical chemistry, good mechanical abilities, higher permeability, and variable microstructure. The presence of PU improves several characteristics of gas-separating membranes. Selectivity and separation efficiency of PU-centered membranes are enhanced through modifications such as blending with other polymers, use of nanoparticles (silica, metal oxides, alumina, zeolite), and interpenetrating polymer networks (IPNs) formation. This manuscript critically analyzes the various gas transport methods and selection criteria for the fabrication of PU membranes. It also covers the challenges facing the development of PU-membrane-based separation procedures.

Synergistic enhancement of CO2/N2 separation performance via Ce-MOF-infused chitosan mixed matrix membrane

Reticular chemistry, exemplified by metal-organic frameworks (MOFs), has proven invaluable in creating porous materials with finely tuned structures to address critical global energy and environmental challenges. In this context, the need for efficient carbon dioxide (CO2) capture and utilization has taken center stage. One promising approach involves the integration of MOFs into polymer matrix to develop mixed matrix membranes (MMMs). In this work, cerium-based MOFs (Ce-MOF) were selected due to their robust CO2 capture capabilities, while chitosan (CS) was chosen as the polymer matrix due to its reasonably good selectivity and balanced CO2 permeance for the development of MMMs for CO2/N2 (20/80 vol%) separation. A comprehensive suite of analytical techniques, including FTIR, XRD, FESEM, XPS, TGA, EDX, FETEM, and BET, was applied for precise characterization of both the MOF and MMMs. Various operational parameters, such as Ce-MOF content and temperature, were systematically explored to investigate the CO2 capture efficiency of the synthesized MMMs. The results revealed that the optimized Ce-MOF-embedded CS MMMs consistently outperformed the bare CS membranes.

CO2-Philic Nanocomposite Polymer Matrix Incorporated with MXene Nanosheets for Ultraefficient CO2 Capture

The incorporation of two-dimensional (2D) functional nanosheets in polymeric membranes is a promising material strategy to overcome their inherent performance trade-off behavior. Herein, we report a novel nanocomposite membrane design by incorporating MXene, a 2D sheet-like nanoarchitecture known for its advantageous lamellar morphology and surface functionalities, into a cross-linked polyether block amide (Pebax)/poly(ethylene glycol) methyl ether acrylate (PEGMEA) blend matrix, which delivered exceptional CO2/N2 and CO2/H2 separation performances that are critical to industrial CO2 capture applications. The finely dispersed Ti3C2Tx nanosheets in the blend polymer matrix led to an expansion of the free volume within the resultant mixed matrix membrane (MMM), giving rise to a substantially enhanced CO2 permeability of up to 1264.6 barrer, which is 102% higher than that of the pristine polymer. Moreover, these MXene-incorporated MMMs exhibited preferential sorption for CO2 over light gases, which contributed to an exceptional CO2/N2 and CO2/H2 selectivity (64.3 and 19.2, respectively) even at a small loading of only 1 wt %, allowing the overall performance to not only surpass the latest upper bounds but also exceed many previously reported high-performance nanosheet-based nanocomposite membranes. Long-term performance tests have also demonstrated the good stability of these membranes. This composite membrane design strategy reveals the remarkable potential of combining a blend copolymer matrix with ultrathin MXene nanosheets to achieve superior gas separation performance for environmentally important gas separations.

Ultrafast Ion Transfer of Metal-Organic Framework Interface for Highly Efficient Energy Storage

Flexible supercapacitors are favorable for wearable electronics. However, their high-rate capability and mechanical properties are limited because of unsatisfactory ion transfer kinetics and interfacial modulus mismatch inside devices. Here, we develop a metal-organic framework interface with superior electrical and mechanical properties for supercapacitors. The interfacial mechanism facilitates ultrafast ion transfer with an energy barrier reduction of 43% compared with that of conventional transmembrane transport. It delivers high specific capacity at a wide rate range and exhibits ultrastability beyond 30000 charge-discharge cycles. Furthermore, meliorative modulus mismatch benefited from ultrathin interface design that improves mechanical properties of flexible supercapacitors. It delivers a stable energy supply under various mechanical conditions like bending and twisting status and displays ultrastable mechanical properties with performance retention of 95.5% after 10 000 bending cycles. The research paves the way for interfacial engineering for ultrastable electrochemical devices.

Penetrant-induced plasticization in microporous polymer membranes

Penetrant-induced plasticization has prevented the industrial deployment of many polymers for membrane-based gas separations. With the advent of microporous polymers, new structural design features and unprecedented property sets are now accessible under controlled laboratory conditions, but property sets can often deteriorate due to plasticization. Therefore, a critical understanding of the origins of plasticization in microporous polymers and the development of strategies to mitigate this effect are needed to advance this area of research. Herein, an integrative discussion is provided on seminal plasticization theory and gas transport models, and these theories and models are compared to an exhaustive database of plasticization characteristics of microporous polymers. Correlations between specific polymer properties and plasticization behavior are presented, including analyses of plasticization pressures from pure-gas permeation tests and mixed-gas permeation tests for pure polymers and composite films. Finally, an evaluation of common and current state-of-the-art strategies to mitigate plasticization is provided along with suggestions for future directions of fundamental and applied research on the topic.

Membrane Separation Technology in Direct Air Capture

Direct air capture (DAC) is an emerging negative CO2 emission technology that aims to introduce a feasible method for CO2 capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO2 concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO2 concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers' further work in the field of m-DAC.

Advancements in Gas Separation for Energy Applications: Exploring the Potential of Polymer Membranes with Intrinsic Microporosity (PIM)

Membrane-based Polymers of Intrinsic Microporosity (PIMs) are promising candidates for energy-efficient industrial gas separations, especially for the separation of carbon dioxide over methane (CO2/CH4) and carbon dioxide over nitrogen (CO2/N2) for natural gas/biogas upgrading and carbon capture from flue gases, respectively. Compared to other separation techniques, membrane separations offer potential energy and cost savings. Ultra-permeable PIM-based polymers are currently leading the trade-off between permeability and selectivity for gas separations, particularly in CO2/CH4 and CO2/N2. These membranes show a significant improvement in performance and fall within a linear correlation on benchmark Robeson plots, which are parallel to, but significantly above, the CO2/CH4 and CO2/N2 Robeson upper bounds. This improvement is expected to enhance the credibility of polymer membranes for CO2 separations and stimulate further research in polymer science and applied engineering to develop membrane systems for these CO2 separations, which are critical to energy and environmental sustainability. This review aims to highlight the state-of-the-art strategies employed to enhance gas separation performances in PIM-based membranes while also mitigating aging effects. These strategies include chemical post-modification, crosslinking, UV and thermal treatment of PIM, as well as the incorporation of nanofillers in the polymeric matrix.

Heteroatom-doped noble carbon-tailored mixed matrix membranes with ultrapermeability for efficient CO2 separation

Membranes with ultrapermeability for CO2 are desired for future large-scale carbon capture projects, because of their excellent separative productivity and economic efficiency. Herein, we demonstrate that a membrane with ultrapermeability for CO2 can be constructed by combining N/O para-doped noble carbons, C2NxO1-x, with high-permeability polymer PIM-1. The optimal PIM-1/C2NxO1-x membranes exhibit superior CO2 permeability (22110 Barrer) with a CO2/N2 selectivity of 15.5, and an unprecedented CO2 permeability of 37272 Barrer can be obtained after a PEG activation treatment, far surpassing the 2008 upper bound. Both broad experiments and molecular dynamics simulations reveal that the numerous ordered polar channels of C2NxO1-x and their excellent compatibility with PIM-1 are responsible for the superior CO2 separation performance of the membrane. Although this is the first study on C2N-type gas separation membranes, the outstanding results indicate that noble carbon building blocks may pave a new avenue to advance high-performance CO2 separation membranes.

Metal-Organic Framework Coated Devices for Gas Sensing

The demand for monitoring chemical and physical information surrounding, air quality, and disease diagnosis has propelled the development of devices for gas sensing that are capable of translating external stimuli into detectable signals. Metal-organic frameworks (MOFs), possessing particular physiochemical properties with designability in topology, specific surface area, pore size and/or geometry, potential functionalization, and host-guest interactions, reveal excellent development promises for manufacturing a variety of MOF-coated sensing devices for multitudinous applications including gas sensing. The past years have witnessed tremendous progress on the preparation of MOF-coated gas sensors with superior sensing performance, especially high sensitivity and selectivity. Although limited reviews have summarized different transduction mechanisms and applications of MOF-coated sensors, reviews summarizing the latest progress of MOF-coated devices under different working principles would be a good complement. Herein, we summarize the latest advances of several classes of MOF-based devices for gas sensing, i.e., chemiresistive sensors, capacitors, field-effect transistors (FETs) or Kelvin probes (KPs), electrochemical, and quartz crystal microbalance (QCM)-based sensors. The surface chemistry and structural characteristics were carefully associated with the sensing behaviors of relevant MOF-coated sensors. Finally, challenges and future prospects for long-term development and potentially practical application of MOF-coated sensing devices are pointed out.

Membrane-based carbon capture: Recent progress, challenges, and their role in achieving the sustainable development goals

The rapid growth in the consumption of fossil fuels resulted in climate change and severe health issues. Among the different proposed methods to control climate change, carbon capture technologies are the best choice in the current stage. In this study, the various membrane technologies used for carbon capture and their impact on achieving sustainable development goals (SDGs) are discussed. Membrane-based carbon capture processes in pre-combustion and post-combustion, which are known as membrane gas separation (MGS) and membrane contactor (MC), respectively, along with the process of fabrication and the different limitations that hinder their performances are discussed. Additionally, the 17 SDGs, where each representing a crucial topic in the current global task of a sustainable future, that are impacted by membrane-based carbon capture technologies are discussed. Membrane-based carbon capture technologies showed to have mixed impacts on different SDGs, varying in intensity and usefulness. It was found that the membrane-based carbon capture technologies had mostly influenced SDG 7 by enhancement in the zero-emission production, SDG 9 by providing 38-42% cost savings compared to liquid absorption, SDG 3 through reducing pollution and particulate matter emissions by 23%, and SDG 13, with SDG 13 being the most positively influenced by membrane-based carbon capture technologies, as they significantly reduce the CO₂ emissions and have high CO₂ capture yields (80-90%), thus supporting the objectives of SDG 13 in combatting climate change.

Putting Forward NUS-8-CO2H/PIM-1 as a Mixed Matrix Membrane for CO2 Capture

Mixed matrix membranes (MMMs) composed of NUS-8 metal-organic framework (MOF) nanosheets dispersed into a polymer of intrinsic microporosity 1 (PIM-1) polymer matrix are known to be promising candidates for CO₂/N₂ separation because of a solubility-driven separation mechanism. In this work, we predict that a chemical functionalization of the organic linker of NUS-8 by a CO₂-philic function confers an even better separation performance to the resulting MMM. Our simulations revealed that the NUS-8-CO₂H/PIM-1 composite exhibits a 3-fold increase in CO₂/N₂ selectivity versus the NUS-8/PIM-1 analogue while achieving a high CO₂ permeability (6700 barrer). We demonstrated that this improved level of performance is due to an increase both in the total MOF/polymer interfacial pore volume and in the CO₂-affinity due to the chemical functionalization. These results suggest that an appropriate choice of chemical functionalization of a MOF is a promising strategy to improve gas separation performances for MMM composites that exhibit a solubility-driven separation mechanism.