Synthesis and characterization of ZIF-69 membranes and separation for CO2/CO mixture

Leveraging Diffusion Kinetics to Reverse Propane/Propylene Adsorption in Zeolitic Imidazolate Framework-8

The separation challenge posed by propylene/propane mixtures arises from their nearly identical molecular sizes and physicochemical properties. Metal-organic frameworks (MOFs) have demonstrated potential in addressing this challenge through the precision tailoring of pore sizes and surface chemistry. However, introducing modifications at the molecular level remains a considerable hurdle. This work presents an approach to reversibly tune the propylene/propane adsorption preference in zeolitic imidazolate framework-8 (ZIF-8) by manipulating the particle size and gas flow rate. Systematically increasing the ZIF-8 crystals from 9 to 224 μm restricts propane diffusion, thereby reversing its preferential adsorption over propylene. Furthermore, raising the gas flow rate of mixed propylene/propane shifts the rate-determining breakthrough step from thermodynamic equilibrium to kinetics, again reversing the adsorption preference in a particular ZIF-8 sample. We propose "dynamic selectivity (Sd(t))" as a concept that incorporates both thermodynamic and kinetic factors to elucidate these unexpected findings. Moreover, the driving force equation, grounded on the concept of Sd(t), has improved the precision and stability of the computational simulation for fixed-bed adsorption processes. This work underscores the potential of diffusion-based modulation, implemented through manageable external changes, as a viable strategy to optimize separation performance in porous adsorbent materials.

Aqueous Pb(II) Removal Using ZIF-60: Adsorption Studies, Response Surface Methodology and Machine Learning Predictions

Zeolitic imidazolate frameworks (ZIFs) are increasingly gaining attention in many application fields due to their outstanding porosity and thermal stability, among other exceptional characteristics. However, in the domain of water purification via adsorption, scientists have mainly focused on ZIF-8 and, to a lesser extent, ZIF-67. The performance of other ZIFs as water decontaminants is yet to be explored. Hence, this study applied ZIF-60 for the removal of lead from aqueous solutions; this is the first time ZIF-60 has been used in any water treatment adsorption study. The synthesized ZIF-60 was subjected to characterization using FTIR, XRD and TGA. A multivariate approach was used to investigate the effect of adsorption parameters on lead removal and the findings revealed that ZIF-60 dose and lead concentration are the most significant factors affecting the response (i.e., lead removal efficiency). Further, response surface methodology-based regression models were generated. To further explore the adsorption performance of ZIF-60 in removing lead from contaminated water samples, adsorption kinetics, isotherm and thermodynamic investigations were conducted. The findings revealed that the obtained data were well-fitted by the Avrami and pseudo-first-order kinetic models, suggesting that the process is complex. The maximum adsorption capacity (q_max) was predicted to be 1905 mg/g. Thermodynamic studies revealed an endothermic and spontaneous adsorption process. Finally, the experimental data were aggregated and used for machine learning predictions using several algorithms. The model generated by the random forest algorithm proved to be the most effective on the basis of its significant correlation coefficient and minimal root mean square error (RMSE).

Recent advance in biomass membranes: Fabrication, functional regulation, and antimicrobial applications

Both inorganic and polymeric membranes have been widely applied for antimicrobial applications. However, these membranes exhibit low biocompatibility, weak biodegradability, and potential toxicity to human being and environment. Biomass materials serve as excellent candidates for fabricating functional membranes to address these problems due to their unique physical, chemical, and biological properties. Here we present recent progress in the fabrication, functional regulation, and antimicrobial applications of various biomass-based membranes. We first introduce the types of biomass membranes and their fabrication methods, including the phase inversion, vacuum filtration, electrospinning, layer-by-layer self-assembly, and coating. Then, the strategies on functional regulation of biomass membranes by adding 0D, 1D, and 2D nanomaterials are presented and analyzed. In addition, antibacterial, antifungal, and antiviral applications of biomass-based functional membranes are summarized. Finally, potential development aspects of biomass membranes are discussed and prospected. This comprehensive review is valuable for guiding the design, synthesis, structural/functional tailoring, and sustainable utilization of biomass membranes.

Sintering Metal-Organic Framework Gels for Application as Structural Adhesives

Metal-organic frameworks (MOFs)/coordination polymers are promising materials for gas separation, fuel storage, catalysis, and biopharmaceuticals. However, most applied research on MOFs is limited to these functional materials thus far. This study focuses on the potential of MOFs as structural adhesives. A sintering technique is applied to a zeolitic imidazolate framework-67 (ZIF-67) gel that enables the joining of Cu substrates, resulting in a shear strength of over 30 MPa, which is comparable to that of conventional structural adhesives. Additionally, systematic experiments are performed to evaluate the effects of temperature and pressure on adhesion, indicating that the removal of excess 2-methylimidazole and the by-product (acetic acid) from the sintered material by vaporization results in a microstructure composed of large spherical ZIF-67 crystals that are densely aggregated, which is essential for achieving a high shear strength.

Direct Sintering Behavior of Metal Organic Frameworks/Coordination Polymers

In this study, we investigate the sintering behavior and mechanisms of metal-organic frameworks/coordination polymers (CPs) through physical and microstructural characterization of [Zn(HPO₄)(H₂PO₄)₂]·2H₂Im (ZPI; a melting CP, Im = imidazole) and ZIF-8 (a non-melting CP). By performing simple compaction and subsequent sintering, a bulk body of CPs was obtained without losing the macroscopic crystallinity. The sintering behavior was found to be dependent on the temperature, heating rate, and physical properties of the CPs and, in particular, their meltability. During sintering, shrinkage occurred in both the CPs, but the observed shrinkage rate of the ZPI was in the 10-20% range, whereas that of the ZIF-8 was less than 1%. Additionally, the sintering mechanisms of the ZPI and ZIF-8 varied between low and high temperatures, and in the case of ZPI, localized melting between the primary particles was the dominant mechanism on the high-temperature side. However, substantial shrinkage did not correspond to an increase in density; on the contrary, a decrease in the apparent density of ZPI was observed as the sintering temperature was increased. The sintering technique is well established and commercially available; thus, the results obtained in this study can be utilized for optimizing the manufacturing conditions of melting CPs.

Porous Adsorption Materials for Carbon Dioxide Capture in Industrial Flue Gas

Due to the intensification of the greenhouse effect and the emphasis on the utilization of CO₂ resources, the enrichment and separation of CO₂ have become a current research focus in the environment and energy. Compared with other technologies, pressure swing adsorption has the advantages of low cost and high efficiency and has been widely used. The design and preparation of high-efficiency adsorbents is the core of the pressure swing adsorption technology. Therefore, high-performance porous CO₂ adsorption materials have attracted increasing attention. Porous adsorption materials with high specific surface area, high CO₂ adsorption capacity, low regeneration energy, good cycle performance, and moisture resistance have been focused on. This article summarizes the optimization of CO₂ adsorption by porous adsorption materials and then applies them to the field of CO₂ adsorption. The internal laws between the pore structure, surface chemistry, and CO₂ adsorption performance of porous adsorbent materials are discussed. Further development requirements and research focus on porous adsorbent materials for CO₂ treatment in industrial waste gas are prospected. The structural design of porous carbon adsorption materials is still the current research focus. With the requirements of applications and environmental conditions, the integrity, mechanical strength and water resistance of high-performance materials need to be met.

Robust ultrathin nanoporous MOF membrane with intra-crystalline defects for fast water transport

Rational design of high-performance stable metal–organic framework (MOF) membranes is challenging, especially for the sustainable treatment of hypersaline waters to address critical global environmental issues. Herein, a molecular-level intra-crystalline defect strategy combined with a selective layer thinning protocol is proposed to fabricate robust ultrathin missing-linker UiO-66 (ML-UiO-66) membrane to enable fast water permeation. Besides almost complete salt rejection, high and stable water flux is achieved even under long-term pervaporation operation in hash environments, which effectively addresses challenging stability issues. Then, detailed structural characterizations are employed to identify the type, chemical functionality, and density of intra-crystalline missing-linker defects. Moreover, molecular dynamics simulations shed light on the positive atomistic role of these defects, which are responsible for substantially enhancing structural hydrophilicity and enlarging pore window, consequently allowing ultra-fast water transport via a lower-energy-barrier pathway across three-dimensional sub-nanochannels during pervaporation. Unlike common unfavorable defect effects, the present positive intra-crystalline defect engineering concept at the molecular level is expected to pave a promising way toward not only rational design of next-generation MOF membranes with enhanced permeation performance, but additional water treatment applications.

The development of highly water-permeable membranes is key for the treatment of high salinity waters. Here the authors enhance the water permeability of a metal-organic framework nanoporous membrane via an intra-crystalline defect engineering strategy.

Recent advancement in bimetallic metal organic frameworks (M’MOFs): Synthetic challenges and applications

Metal-organic frameworks (MOFs) is a burgeoning research field and has received increasing interest in recent years due to their inherent advantages of inorganic metal ions, range of organic linkers, tunable...

High Degradation of Methylene Blue Using a New Nanocomposite Based on Zeolitic Imidazolate Framework-8

The development of broad-spectrum ultraviolet- and visible-light photocatalysts constitutes one of the most significant challenges in the field of photocatalytic pollutant removal. Here, the efficiency of the directly prepared nitrogen-doped quantum zeolitic imidazolate framework (ZIF)-8-dot catalyst for the photocatalytic degradation of the methylene blue dye was reported. The prepared catalysts were characterized using Brunauer-Emmett-Teller, X-ray diffraction, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy techniques. Under sunlight irradiation, the 1% nitrogen-doped quantum-ZIF-8-dot catalyst showed 75% photodegradation in half an hour and ≈93% photodegradation after 3 hours compared to ≈87% for the ZIF-8 metal-organic framework. The high performance of the 1% nitrogen-doped quantum-ZIF-8-dot catalyst was attributed to the synergism between the catalyst components, upconverted fluorescence property of nitrogen-doped quantum dots, and charge (electrons-holes) separation. The reactive radical test revealed that the hydroxyl radical was dominant. The step-scheme heterojunction mechanism for photocatalytic degradation was also deduced. The kinetic study through the photocatalytic isotherms revealed that the pseudo-first-order kinetic model can describe the reaction mechanism.

Recent advances in simulating gas permeation through MOF membranes

In the last two decades, metal organic frameworks (MOFs) have gained increasing attention in membrane-based gas separations due to their tunable structural properties. Computational methods play a critical role in providing molecular-level information about the membrane properties and identifying the most promising MOF membranes for various gas separations. In this review, we discuss the current state-of-the-art in molecular modeling methods to simulate gas permeation through MOF membranes and review the recent advancements. We finally address current opportunities and challenges of simulating gas permeation through MOF membranes to guide the development of high-performance MOF membranes in the future.

Ultrafast Synthesis of Silica-Based Molecular Sieve Membranes in Dielectric Barrier Discharge at Low Temperature and Atmospheric Pressure

Microporous silica membranes have shown promise as potential candidates for energy-efficient chemical separation. Herein, we report the ultrafast synthesis of silica membranes, on the order of minutes, in atmospheric-pressure, low-temperature plasma. Direct deposition in the discharge region of atmospheric-pressure plasma enables the immediate formation of a thin silica layer on a porous substrate. The plasma-deposited layer had a thickness of ∼13 nm and was confined to the immediate surface of the substrate. With an increase in deposition temperature, we observed an increase in the inorganic nature of the plasma-deposited layer and simultaneous improvement in the membrane performance. Consequently, the resulting membranes exhibited outstanding permeance for small-sized gas molecules, such as H₂ (>10^-6 mol m^-2 s^-1 Pa^-1), with a high H₂/SF₆ permeance ratio of ∼6300, providing a nonthermal alternative for the fabrication of silica-based membranes.

CO2 capture using membrane contactors: a systematic literature review

With fossil fuel being the major source of energy, CO2 emission levels need to be reduced to a minimal amount namely from anthropogenic sources. Energy consumption is expected to rise by 48% in the next 30 years, and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis. Nonetheless, exploring CO2 capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post- and pre-combustion of CO2. A systematic review of the literature has been conducted to analyse and assess CO2 removal using membrane contactors for capturing techniques in industrial processes. The review began with a total of 2650 papers, which were obtained from three major databases, and then were excluded down to a final number of 525 papers following a defined set of criteria. The results showed that the use of hollow fibre membranes have demonstrated popularity, as well as the use of amine solvents for CO2 removal. This current systematic review in CO2 removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work. This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO2.

Synthesis and Characterization of Hybrid Metal Zeolitic Imidazolate Framework Membrane for Efficient H2/CO2 Gas Separation

In this paper, we propose mixed metal ions in the node of the zeolitic imidazolate framework (ZIF) structure. The hybrid metal ZIF is formed for the gas separation of hydrogen and carbon dioxide. In the first stage, the nanoparticles were prepared as a coating on a substrate, and acting as secondary growing nuclei. The hybrid metal ZIF structures were characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). N₂ adsorption–desorption isotherms determined surface area, and scanning electron microscopy (SEM) was used to observe the microstructure and surface morphology. The hybrid metal ZIF-8-67 powder had the largest surface area (1260.40 m² g⁻¹), and the nanoparticles (100 nm) could be fully dense-coated on the substrate to benefit the subsequent membrane growth. In the second stage, we prepared the hybrid metal ZIF-8-67 membrane on the pre-seeding substrate with mixed metal nanoparticles of cobalt and zinc, by the microwave hydrothermal method. Cobalt ions were identified in the tetrahedral coordination through UV–Vis, and the membrane structure and morphology were determined by XRD and SEM. Finally, a gas permeation analyzer (GPA) was used to determine the gas separation performance of the hybrid metal ZIF-8-67 membrane. We successfully introduced zinc ions and cobalt ions into the ZIF structure, where cobalt had a strong interaction with CO₂. Therefore, GPA analysis showed an excellent H₂/CO₂ separation factor due to lower CO₂ permeability. The CO₂ permeance was ~0.65 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹, and the separation factors for H₂/CO₂ and H₂/N₂ were 9.2 and 2.9, respectively. Our results demonstrate that the hybrid metal ZIF-8-67 membrane has a superior H₂/CO₂ separation factor, which can be attributed to its very high specific surface area and structure. Based on the above, hybrid metal ZIF-8-67 membranes are expected to be applied in hydrogen or carbon dioxide gas separation and purification.

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

Metal-organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn-Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H₂/CO₂ separation ability of bMOF-200. We examine the H₂/CO₂ separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H₂/CO₂ separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H₂ and CO₂ and a significantly improved H₂/CO₂ separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H₂/CO₂ separations.

Accelerated lithium-ion conduction in covalent organic frameworks

We design a porous separator that consists of a covalent organic framework (COF), the ionic conductivity of which is 8 times higher than that of the most well-established separator of lithium-ion batteries. Moreover, the effective ionic conductivity is even higher than that of the corresponding pure liquid electrolyte.

MOF-Based Membranes for Gas Separations

Metal-organic frameworks (MOFs) represent the largest known class of porous crystalline materials ever synthesized. Their narrow pore windows and nearly unlimited structural and chemical features have made these materials of significant interest for membrane-based gas separations. In this comprehensive review, we discuss opportunities and challenges related to the formation of pure MOF films and mixed-matrix membranes (MMMs). Common and emerging separation applications are identified, and membrane transport theory for MOFs is described and contextualized relative to the governing principles that describe transport in polymers. Additionally, cross-cutting research opportunities using advanced metrologies and computational techniques are reviewed. To quantify membrane performance, we introduce a simple membrane performance score that has been tabulated for all of the literature data compiled in this review. These data are reported on upper bound plots, revealing classes of MOF materials that consistently demonstrate promising separation performance. Recommendations are provided with the intent of identifying the most promising materials and directions for the field in terms of fundamental science and eventual deployment of MOF materials for commercial membrane-based gas separations.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Separation Selectivity of CH4/CO2 Gas Mixtures in the ZIF-8 Membrane Explored by Dynamic Monte Carlo Simulations

Here we report a series of nonequilibrium dynamic Monte Carlo simulations combined with dual control volume (DCV-DMC) to explore the separation selectivity of CH₄/CO₂ gas mixtures in the ZIF-8 membrane with a thickness of up to about 20 nm. Meanwhile, an improved DCV-DMC approach coupled with the corresponding potential map (PM-DCV-DMC) is further developed to speed up the computational efficiency of conventional DCV-DMC simulations. Our simulation results provide the molecular-level density and selectivity profiles along the permeation direction of both CH₄ and CO₂ molecules in the ZIF-8 membrane, indicating that the parts near membrane surfaces at both ends play a key role in determining the separation selectivity. All densities initially show a sharp increase in the individual maximum within the first outermost unit cell at the feed side and follow a long fluctuating decrease process. Accordingly, the corresponding selectivity profiles initially display a long fluctuating increase in the individual maximum and follow a sharp decrease near the membrane surface at the permeation side. Furthermore, the effects of feed composition, temperature, and pressure on the relevant separation selectivity are also discussed in detail, where the temperature has a greater influence on the separation selectivity than the feed composition and pressure. More importantly, the predicted separation selectivities from our PM-DCV-DMC simulations are well consistent with previous experimental results.

In-situ preparation of hollow cellulose nanocrystals/zeolitic imidazolate framework hybrid microspheres derived from Pickering emulsion

In situ interfacial growth of nanoparticles induced by a Pickering emulsion is recognized as a practical method for the fabrication of hollow composites. Herein, hybrid hollow microspheres were prepared using cellulose nanocrystals (CNCs) emulsified water-dodecane system as a template. The hybrid microspheres were composed of zeolitic imidazolate framework-8 (ZIF-8) shells and CNCs surface-layers. ZIF-8 crystals formed and grew at the oil-water interface with a low ligand/metal ion molar ratio. The composite microspheres owned rich porous structure with a high surface area of 1240 m² g^-1 and performed obvious hydrophilicity owing to the role of CNCs layers. The two characters offered CNCs/ZIF-8 composite materials with very prominent adsorption capacity towards dyes (1060.2 mg g^-1 for malachite green). Carbonization of CNCs/ZIF-8 composite materials afford ZIF-8 based materials more effective removal of methylene blue from water under sunlight, owing to the photocatalytic role of ZnO remained in carbonized product. This research paves the way to realize a variety of hollow CNCs/ZIFs hybrid materials for different application purposes.

Thermodynamic Evidence of Structural Transformations in CO2-Loaded Metal-Organic Framework Zn(MeIm)2 from Heat Capacity Measurements

Metal-organic frameworks are a class of porous compounds with potential applications in molecular sieving, gas sequestration, and catalysis. One family of MOFs, zeolitic imidizolate frameworks (ZIFs), is of particular interest for carbon dioxide sequestration. We have previously reported the heat capacity of the sodalite topology of the zinc 2-methylimidazolate framework (ZIF-8), and in this Article we present the first low-temperature heat capacity measurements of ZIF-8 with various amounts of sorbed CO₂. Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO₂ per mol of ZIF-8. Samples with at least 0.56 mol of CO₂ per mol of ZIF-8 display a large, broad anomaly from 70 to 220 K with a shoulder on the low-temperature side, suggesting sorption-induced structural transitions. We attribute the broad anomaly partially to a gate-opening transition, with the remainder resulting from CO₂ rearrangement and/or lattice expansion. The measurements also reveal a subtle anomaly from 0 to 70 K in all samples that does not exist in the sorbate-free material, which likely reflects new vibrational modes resulting from sorbate/ZIF-8 interactions. These results provide the first thermodynamic evidence of structural transitions induced by CO₂ sorption in the ZIF-8 framework.

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

The hydrogen, carbon dioxide, and carbon monoxide gas adsorption and storage capacity of lithium-decorated cyclopropane ring systems were examined with quantum chemical calculations at density functional theory, DFT M06-2X functional using 6-31G(d) and cc-pVDZ basis sets. To examine the reliability of M06-2X DFT functional, a few representative systems are also examined with complete basis set CBS-QB3 method and CCSD-aug-cc-pVTZ level of theory. The cyclopropane systems can bind to one Li⁺ ion; however, the corresponding the methylated systems can bind with two Li⁺ ions. The cyclopropane systems can adsorb six hydrogen molecules with an average binding energy of 3.8 kcal/mol. The binding free energy (ΔG) values suggest that the hydrogen adsorption process is feasible at 273.15 K. The calculation of desorption energies indicates the recyclable property of gas adsorbed complexes. The same number of CO₂ and CO gas molecules can also be adsorbed with an average binding energy of -14.4 kcal/mol and -10.7 kcal/mol, respectively. The carbon dioxide showed ~3-4 kcal/mol better binding energy as compared to carbon monoxide and hence such designed systems can function as a potential candidate for the separation of these flue gas molecules. The nature of interactions in complexes was examined with atoms in molecules analysis revealed the electrostatic nature for the interaction of Li⁺ ion with cyclopropane rings. The chemical hardness and electrophilicity calculations showed that the gas adsorbed complexes are rigid and therefore robust as gas storage materials.

Computational Analysis of Linker Defective Metal-Organic Frameworks for Membrane Separation Applications

Intracrystalline defects in metal-organic frameworks (MOFs) are known to have crucial roles in dictating their material properties. In this work, computational simulations were used to induce linker vacancy defects in MOF membranes and to investigate their influence on H₂/CH₄ separation. Linker defective structures were created for the 228 candidate MOFs, and their separation performances were compared between the defective and the nondefective structures. Our results show that the existence of linker vacancy defects can lead to significant performance changes in the MOF membranes, and more importantly, the ranking of the best materials can differ with the defects present. This suggests the importance of taking into account the potential for defects when it comes to materials design for various membrane separation applications.

Mesoporous Metal-Organic Frameworks: Synthetic Strategies and Emerging Applications

Metal-organic frameworks (MOFs) have attracted much attention over the past two decades due to their highly promising applications not only in the fields of gas storage, separation, catalysis, drug delivery, and sensors, but also in relatively new fields such as electric, magnetic, and optical materials resulting from their extremely high surface areas, open channels and large pore cavities compared with traditional porous materials like carbon and inorganic zeolites. Particularly, MOFs involving pores within the mesoscopic scale possess unique textural properties, leading to a series of research in the design and applications of mesoporous MOFs. Unlike previous Reviews, apart from focusing on recent advances in the synthetic routes, unique characteristics and applications of mesoporous MOFs, this Review also mentions the derivatives, composites, and hierarchical MOF-based systems that contain mesoporosity, and technical boundaries and challenges brought by the drawbacks of mesoporosity. Moreover, this Review subsequently reveals promising perspectives of how recently discovered approaches to different morphologies of MOFs (not necessarily entirely mesoporous) and their corresponding performances can be extended to minimize the shortcomings of mesoporosity, thus providing a wider and brighter scope of future research into mesoporous MOFs, but not just limited to the finite progress in the target substances alone.

Locating the binding domains in a highly selective mixed matrix membrane via synchrotron IR microspectroscopy

The location of binding domains in a new CO₂ selective mixed matrix membrane has been established via in situ synchrotron IR microspectroscopy.

Preparation of a pure ZIF-67 membrane by self-conversion of cobalt carbonate hydroxide nanowires for H2 separation

A self-conversion strategy was adopted for the first time to achieve a pure ZIF-67 membrane on a porous alumina tube for H₂ separation.

Mapping the Functional Tortuosity and Spatiotemporal Heterogeneity of Porous Polymer Membranes with Super-Resolution Nanoparticle Tracking

As particles flow through porous media, they follow complex pathways and experience heterogeneous environments that are challenging to characterize. Tortuosity is often used as a parameter to characterize the complexity of pathways in porous materials and is useful in understanding hindered mass transport in industrial filtration and mass separation processes. However, conventional calculations of tortuosity provide only average values under static conditions; they are insensitive to the intrinsic heterogeneity of porous media and do not account for potential effects of operating conditions. Here, we employ a high-throughput nanoparticle tracking method which enables the observation of actual particle trajectories in polymer membranes under relevant operating conditions. Our results indicate that tortuosity is not simply a structural material property but is instead a functional property that depends on flow rate and particle size. We also resolved the spatiotemporal heterogeneity of flowing particles in these porous media. The distributions of tortuosity and of local residence/retention times were surprisingly broad, exhibiting heavy tails representing a population of highly tortuous trajectories and local regions with anomalously long residence times. Interestingly, local tortuosity and residence times were directly correlated, suggesting the presence of highly confining regions that cause more meandering trajectories and longer retention times. The comprehensive information about tortuosity and spatiotemporal heterogeneity provided by these methods will advance the understanding of complex mass transport and assist rational design and synthesis of porous materials.

Microstructural Engineering and Architectural Design of Metal-Organic Framework Membranes

In the past decade, a huge development in rational design, synthesis, and application of molecular sieve membranes, which typically included zeolites, metal-organic frameworks (MOFs), and graphene oxides, has been witnessed. Owing to high flexibility in both pore apertures and functionality, MOFs in the form of membranes have offered unprecedented opportunities for energy-efficient gas separations. Reports on the fabrication of well-intergrown MOF membranes first appeared in 2009. Since then there has been tremendous growth in this area along with an exponential increase of MOF-membrane-related publications. In order to compete with other separation and purification technologies, like cryogenic distillation, pressure swing adsorption, and chemical absorption, separation performance (including permeability, selectivity, and long-term stability) of molecular sieve membranes must be further improved in an attempt to reach an economically attractive region. Therefore, microstructural engineering and architectural design of MOF membranes at mesoscopic and microscopic levels become indispensable. This review summarizes some intriguing research that may potentially contribute to large-scale applications of MOF membranes in the future.