Selective Hydrogen Isotope Separation via Breathing Transition in MIL-53(Al)

Facile mechanochemical synthesis of MIL-53 and its isoreticular analogues with a glance at reaction reversibility

MIL-53 represents one of the most notable metal-organic frameworks given its unique structural flexibility and remarkable thermal stability. In this study, a shaker-type ball milling method has been developed into a facile and generalizable synthetic strategy to access a family of MIL-53 type materials under ambient conditions. During the explorations of [M(OH)(fumarate)] (M = Al, Ga, and In), we report a positive correlation between the metal-ligand (M-L) bond reversibility and the size of resultant crystallites under the mechanochemical process. The more kinetically labile the M-L bond is, the larger the afforded crystallite size is.

Sulfur defect induced Cd0.3Zn0.7S in-situ anchoring on metal organic framework for enhanced photothermal catalytic CO2 reduction to prepare proportionally adjustable syngas

The rapid recombination of interfacial charges is considered to be the main obstacle limiting the photocatalytic CO2 reduction. Thus, it is a challenge to research an accurate and stable charge transfer control strategy. MIL-53 (Al)-S/Cd0.3Zn0.7S (MAS/CZS-0.3) photocatalysts with chemically bonded interfaces were constructed by in-situ electrostatic assembly of sulfur defect Cd0.3Zn0.7S (CZS-0.3) on the surface of MIL-53 (Al) (MAW), which enhanced interfacial coupling and accelerated electron transfer efficiency. An adjustable proportion of syngas (H2/CO) was prepared by photothermal catalytic CO2 reduction at micro-interface. and the optimal yield of CO (66.10 μmol∙g-1∙h-1) and H2 (71.0 μmol∙g-1∙h-1) was realized by the MAS/CZS-0.3 photocatalyst. The improved activity was due to the photogenerated electrons migrated from CZS-0.3 to the adsorption active sites of MAS, which strengthened the adsorption and activation of CO2 on MAS. The photothermal catalytic CO2 reduction to CO follows the pathway of CO2→*COOH → CO and CO2→*HCO3-→CO. This work provided a reference for the research, characterization, and application of in-situ anchoring of metal organic frameworks in photothermal catalytic CO2 reduction, and provided a green path for the supply of Syngas in industry.

Shape-Memory Effect Enabled by Ligand Substitution and CO2 Affinity in a Flexible SIFSIX Coordination Network

We report that linker ligand substitution involving just one atom induces a shape-memory effect in a flexible coordination network. Specifically, whereas SIFSIX-23-Cu, [Cu(SiF6 )(L)2 ]n , (L=1,4-bis(1-imidazolyl)benzene, SiF6 2- =SIFSIX) has been previously reported to exhibit reversible switching between closed and open phases, the activated phase of SIFSIX-23-CuN , [Cu(SiF6 )(LN )2 ]n (LN =2,5-bis(1-imidazolyl)pyridine), transformed to a kinetically stable porous phase with strong affinity for CO2 . As-synthesized SIFSIX-23-CuN , α, transformed to less open, γ, and closed, β, phases during activation. β did not adsorb N2 (77 K), rather it reverted to α induced by CO2 at 195, 273 and 298 K. CO2 desorption resulted in α', a shape-memory phase which subsequently exhibited type-I isotherms for N2 (77 K) and CO2 as well as strong performance for separation of CO2 /N2 (15/85) at 298 K and 1 bar driven by strong binding (Qst =45-51 kJ/mol) and excellent CO2 /N2 selectivity (up to 700). Interestingly, α' reverted to β after re-solvation/desolvation. Molecular simulations and density functional theory (DFT) calculations provide insight into the properties of SIFSIX-23-CuN .

Recent Progress in Functional Nanomaterials towards the Storage, Separation, and Removal of Tritium

Tritium is a sustainable next-generation prime fuel for generating nuclear energy through fusion reactions to fulfill the increasing global energy demand. Owing to the scarcity-high demand tradeoff, tritium must be bred inside a fusion reactor to ensure sustainability and must therefore be separated from its isotopes (protium and deuterium) in pure form, stored safely, and supplied on demand. Existing multistage isotope separation technologies exhibit low separation efficiency and require intensive energy inputs and large capital investments. Furthermore, tritium-contaminated heavy water constitutes a major fraction of nuclear waste, and accidents like the one at Fukushima Daiichi leave behind thousands of tons of diluted tritiated water, whose removal is beneficial from an environmental point of view. In this review, the recent progress and main research trends in hydrogen isotope storage and separation by focusing on the use of metal hydride (e.g., intermetallic, and high-entropy alloys), porous (e.g., zeolites and metal organic frameworks (MOFs)), and 2-D layered (e.g., graphene, hexagonal boron nitride (h-BN), and MXenes) materials to separate and store tritium based on their diverse functionalities are discussed. Finally, the challenges and future directions for implementing tritium storage and separation are summarized in the reviewed materials.

Computational NMR investigation of mixed-metal (Al,Sc)-MIL-53 and its phase transitions

Compositionally complex metal-organic frameworks (MOFs) have properties that depend on local structure that is often difficult to characterise. In this paper a density functional theory (DFT) computational study of mixed-metal (Al,Sc)-MIL-53, a flexible MOF with several different forms, was used to calculate the relative energetics of these forms and to predict NMR parameters that can be used to evaluate whether solid-state NMR spectroscopy can be used to differentiate, identify and characterise the forms adopted by mixed-metal MOFs of different composition. The NMR parameters can also be correlated with structural features in the different forms, giving fundamental insight into the nature and origin of the interactions that affect nuclear spins. Given the complexity of advanced NMR experiments required, and the potential need for expensive and difficult isotopic enrichment, the computational work is invaluable in predicting which experiments and approaches are likely to give the most information on the disorder, local structure and pore forms of these mixed-metal MOFs.

A squarate-pillared titanium oxide quantum sieve towards practical hydrogen isotope separation

Separating deuterium from hydrogen isotope mixtures is of vital importance to develop nuclear energy industry, as well as other isotope-related advanced technologies. As one of the most promising alternatives to conventional techniques for deuterium purification, kinetic quantum sieving using porous materials has shown a great potential to address this challenging objective. From the knowledge gained in this field; it becomes clear that a quantum sieve encompassing a wide range of practical features in addition to its separation performance is highly demanded to approach the industrial level. Here, the rational design of an ultra-microporous squarate pillared titanium oxide hybrid framework has been achieved, of which we report the comprehensive assessment towards practical deuterium separation. The material not only displays a good performance combining high selectivity and volumetric uptake, reversible adsorption-desorption cycles, and facile regeneration in adsorptive sieving of deuterium, but also features a cost-effective green scalable synthesis using chemical feedstock, and a good stability (thermal, chemical, mechanical and radiolytic) under various working conditions. Our findings provide an overall assessment of the material for hydrogen isotope purification and the results represent a step forward towards next generation practical materials for quantum sieving of important gas isotopes.

Active Separation of Water Isotopologues by Local Molecular Motion in Microporous Framework Materials

Around 10-15 % of the world's energy consumption is accounted for by the separation and purification of chemicals. Among them is the enrichment and separation of isotopologues which are an essential aspect of modern chemistry. In their recent work, Su et al. demonstrate the separation of water isotopologues by responsive dynamic pore windows in a microporous coordination polymer with unprecedented selectivity based on an elegant mechanism.

H2/D2 Separation Using UTSA-16@CAU-10-H@γ-AlOOH Composites as the Stationary Phase in Gas Chromatography via the Additive Effects of Kinetic Sieving and Chemical Affinity Quantum Sieving

In this work, CAU-10-H@γ-AlOOH is prepared, and then UTSA-16 is loaded on CAU-10-H@γ-AlOOH to obtain UTSA-16@CAU-10-H@γ-AlOOH. Using the as-prepared composites as stationary materials by cryogenic gas chromatography at 77 K, while CAU-10-H@γ-AlOOH achieves the complete separation of ortho-H₂ (o-H₂) and D₂ with a resolution R of 1.66 and a separation time t of 9.52 min, UTSA-16@CAU-10-H@γ-AlOOH achieves higher efficiency separation of hydrogen isotopes in a shorter separation time (4.56 min) with R = 1.7. Molecular simulation results show that CAU-10-H has both chemical affinity quantum sieving and kinetic sieving effects for H₂/D₂ at 77 K, and UTSA-16 can only exert the kinetic sieving effect. UTSA-16's load on CAU-10-H@γ-AlOOH weakens the adsorption of hydrogen isotopes, and the presence of Co²⁺ in UTSA-16 promotes the conversion of para-H₂ to ortho-H₂. In gas chromatography, H₂ was preferentially desorbed from the system due to strong D₂ adsorption caused by the chemical affinity quantum sieving effect and faster H₂ diffusion caused by the kinetic sieving effect. These additive effects achieved efficient hydrogen isotope separation at 77 K.

H2/D2 separation in gas chromatography through a MOF-on-MOF strategy using γ-AlOOH@Al(OH)(1,4-NDC)@ZIF-67 as the stationary phase via additive effects of chemical affinity quantum sieving and kinetic sieving

The reaction of porous γ-Al₂O₃ particles acting as both a sacrificial template and an aluminum source with 1,4-naphthalene diacid (H₂NDC) resulted in the formation of γ-AlOOH@Al(OH)(1,4-NDC) composites, in which ZIF-67 was then loaded by the in situ crystallization method, leading to the formation of γ-AlOOH@Al(OH)(1,4-NDC)@ZIF-67 composites. The deliberately designed composite was used to separate H₂/D₂ at 77 K in a 1 m chromatographic column. The results demonstrated that the optimized composite can achieve the effective separation of H₂/D₂ in gas chromatography due to the additive effects of kinetic sieving and chemical affinity quantum sieving of Al(OH)(1,4-NDC) and ZIF-67. By optimizing chromatographic separation conditions, the resolution R reached 2.02 with the separation time t = 7.72 min. The composite also showed satisfactory repeatability and reproducibility.

High Efficiency of Na- and Ca-Exchanged Chabazites in D2/H2 Separation by Quantum Sieving

Quantum sieving is a promising approach for separation of hydrogen isotopes using porous solids as sorbents at cryogenic temperatures (<77 K). In the present work, we characterized the properties of two aluminum-rich chabazites: Na-CHA and Ca-CHA (Si/Al = 2.1). The single-gas D₂ and H₂ adsorption isotherms were measured, and the thermodynamic selectivities were determined through coadsorption experiments in the temperature range 38-77 K. We found that at 38 K, Na-CHA shows a selectivity of 25.8 at a loading of 10.6 mmol·g^-1. At the same temperature, Ca-CHA has slightly lower selectivity (18.3), but its uptake (12.9 mmol·g^-1) is higher than that for Na-CHA. Comparison with the literature shows that the obtained values of selectivity are among the highest reported so far. This property combined with robustness and availability on the industrial scale of Al-rich chabazites makes them very promising materials for separation of hydrogen isotopes by quantum sieving.

Thermodynamic Separation of Hydrogen Isotopes Using Hofmann-Type Metal-Organic Frameworks with High-Density Open Metal Sites

Hydrogen isotope separation with nanoporous materials is a very challenging yet promising approach. To overcome the limitation of the conventional isotope separation strategy, quantum sieving-based separation using nanoporous materials has been investigated recently. In this study, to see the thermodynamic deuterium separation phenomena attributed to the chemical affinity quantum sieving effect, we examine Hofmann-type metal-organic frameworks (MOFs), Co(pyz)[M(CN)₄] (pyz = pyrazine, M = Pd²⁺, Pt²⁺, and Ni²⁺), which have microporosity (4.0 × 3.9 Ų) and an extraordinarily high density of open metal sites (∼9 mmol/cm³). Owing to the preferential adsorption of D₂ over H₂ at strongly binding open metal sites, the Hofmann-type MOF, Co(pyz)[Pd(CN)₄] exhibited a high selectivity (S_D2/H2) of 21.7 as well as a large D₂ uptake of 10 mmol/g at 25 K. This is the first study of Hofmann-type MOFs to report high selectivity and capacity, both of which are important parameters for the practical application of porous materials toward isotope separation.

High-Throughput Computational Exploration of MOFs with Open Cu Sites for Adsorptive Separation of Hydrogen Isotopes

Effective separation of hydrogen isotopes still remains one of the extremely challenging tasks in industry. Compared to the present methods that are energy- and cost-intensive, quantum sieving technology based on nanostructured materials offers a more efficient alternative approach, where metal-organic frameworks (MOFs) featuring open metal sites (OMS) can serve as an ideal platform. Herein, a combination of periodic density functional theory (DFT) with dispersive correction and high-throughput molecular simulation was employed from thermodynamic viewpoints to explore the D₂/H₂ separation properties of 929 experimental MOFs bearing a copper-paddlewheel unit. The DFT calculations showed that there is a negligible rotational energy barrier for the molecule adsorbed at the OMS, and the movement of the Cu atoms along the Cu-Cu axis vector almost has no influence on the interaction energy. On the basis of the DFT results, a new force field with a proposed cutoff scheme was developed to accurately describe the strong isotope-OMS interaction. Under practical conditions (40 K and 1.0 bar), large-scale computational material screening demonstrated that the OMS interaction plays a more important role in highly selective materials and ignoring such interactions can lead to completely wrong identification of the most promising materials. Using the adsorption selectivity and adsorbent performance score as evaluation metrics, this work demonstrated that the materials with sql topology notably outperform many benchmark adsorbents reported so far.

Lipidomic and Membrane Mechanical Signatures in Triple-Negative Breast Cancer: Scope for Membrane-Based Theranostics

Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer associated with poor prognosis, higher grade, and a high rate of metastatic occurrence. Limited therapeutic interventions and the compounding issue of drug resistance in triple-negative breast cancer warrants the discovery of novel therapeutic targets and diagnostic modules. To this view, in addition to proteins, lipids also regulate cellular functions via the formation of membranes that modulate membrane protein function, diffusion, and their localization; thus, orchestrating signaling hot spots enriched in specific lipids/proteins on cell membranes. Lipid deregulation in cancer leads to reprogramming of the membrane dynamics and functions impacting cell proliferation, metabolism, and metastasis, providing exciting starting points for developing lipid-based approaches for treating TNBC. In this review, we provide a detailed account of specific lipidic changes in breast cancer, link the altered lipidome with membrane structure and mechanical properties, and describe how these are linked to subsequent downstream functions implicit in cancer progression, metastasis, and chemoresistance. At the fundamental level, we discuss how the lipid-centric findings in TNBC are providing cues for developing lipid-inspired theranostic strategies while bridging existing gaps in our understanding of the functional involvement of lipid membranes in cancer.

Isotope-selective pore opening in a flexible metal-organic framework

Flexible metal-organic frameworks that show reversible guest-induced phase transitions between closed and open pore phases have enormous potential for highly selective, energy-efficient gas separations. Here, we present the gate-opening process of DUT-8(Ni) that selectively responds to D₂, whereas no response is observed for H₂ and HD. In situ neutron diffraction directly reveals this pressure-dependent phase transition. Low-temperature thermal desorption spectroscopy measurements indicate an outstanding D₂-over-H₂ selectivity of 11.6 at 23.3 K, with high D₂ uptake. First-principles calculations coupled with statistical thermodynamics predict the isotope-selective gate opening, rationalized by pronounced nuclear quantum effects. Simulations suggest DUT-8(Ni) to remain closed in the presence of HT, while it also opens for DT and T₂, demonstrating gate opening as a highly effective approach for isotopolog separation.

Flexible metal-organic frameworks for gas storage and separation

Flexible metal-organic frameworks (MOFs) have gradually attracted much attention due to their reversible structural changes and flexible structural responses. The basic research of flexible MOFs is to study their dynamic responses under different external stimuli and translate the responses into applications. Most research studies on flexible MOFs focus on gas storage and separation, but lack a systematic summary. Here, we review the development of flexible MOFs, the structural transformation under the external effects of temperature, pressure, and guest molecules, and their applications in gas storage and separation. Microporous MOFs with flexible structures provide unique opportunities for fine-tuning their performance because the pore shape and size can be controlled by external stimuli. The characteristics of breathing phenomena and large specific surface area make flexible MOFs suitable candidates for gas storage and separation. Finally, the application prospects of flexible MOFs are reported.

Evaluation of the Adsorption-Accessible Surface Area of MIL-53(Al) using Cannabinoids in a Closed System

Cannabinoids are important industrial analytes commonly assayed with high-pressure liquid chromatography (HPLC). In this study, we evaluate the suitability of MIL-53(Al), a commercially available metal-organic framework (MOF), as a stationary phase for cannabinoid separations. The suitability of an MOF for a given separation is hypothesized to be limited by the ability of a given molecule to enter the pore of the MOF. To evaluate the extent of possible adsorptive interactions between cannabinoids and the interior surface area of MIL-53(Al), the radii of gyration (R_g) and solvent-accessible surface areas were calculated for three cannabinoids, namely, cannabidiol, cannabinol, and Δ9-tetrahydrocannabinol, as well as the MOF. These values were used to calculate the theoretical adsorption capacity of the MOF, using four competing adsorption models. The R_g of cannabinoids (4.1 Å) is larger than one MOF pore aperture dimension (4.0 × 5.0 Å). The adsorption capacity was measured by relating a decrease in the cannabinoid concentration in acetonitrile when exposed to 100 mg of MOF. The cannabinoid uptake by the MOF was estimated using the relative standard deviation (RSD) of the soaking solution assay, as the decomposition-corrected RSD as uptake (DCRU). The DCRU was calculated as 0.007 ± 0.004 μg_cannabinoids/mg_MOF. These findings indicate that most of the MOF surface area was inaccessible for adsorption by cannabinoids due to size-exclusion effects. The implication of this work is that the suitability of an MOF for adsorptive separations, such as liquid chromatography, must have an upper limit for the size of the analyte. Additionally, MOFs may generally be more suitable for separations in the gas phase, where adsorbates are not hindered by the presence of a solvation shell.

Generation of Strong Basicity in Metal-Organic Frameworks: How Do Coordination Solvents Matter?

Solid strong bases with an ordered pore structure (OPS-SSBs) have attracted much attention because of their high catalytic activity and shape selectivity as heterogeneous catalysts in various reactions. Nevertheless, high temperatures are required to fabricate OPS-SSBs by using traditional methods. Herein, we report for the first time that the coordination solvents affect basicity generation in metal-organic frameworks (MOFs) greatly and that strong basicity can be formed at comparatively low temperatures. A typical MOF, MIL-53, was employed, and three different solvents, namely, water, methanol, and N,N-dimethylformamide (DMF), were coordinated, respectively, by means of solvent exchange. Thermogravimetry-mass spectrometer analysis shows that the conversion temperature of base precursor KNO₃ is quite different on MIL-53 coordinated with different solvents. The conversion of KNO₃ to basic sites takes place at 350, 300, and 250 °C on MIL-53 coordinated with water, methanol, and DMF, respectively. It is fascinating to observe the generation temperature of strongly basic sites at 250 °C, which is noticeably lower than that on various supports, such as mesoporous silica SBA-15 (600 °C), zeolite Y (700 °C), and metal oxide ZrO₂ (730 °C). This is due to the redox interaction between coordination solvents and KNO₃, leading to a significant decrease in the temperature for KNO₃ conversion. Consequently, OPS-SSBs were prepared successfully with an ordered pore structure and strong basicity. The obtained OPS-SSBs show good shape selectivity in Knoevenagel condensation of aromatic aldehydes with different active methylene compounds. Moreover, these solid bases are highly active in the synthesis of dimethyl carbonate through transesterification reaction. This work might open up a new avenue for the fabrication of various functional materials at low temperatures through redox interactions.

Encapsulation of AgInS2/GaSx core/shell quantum dots in In-fumarate metal–organic frameworks for stability enhancement

Silver indium sulfide/gallium sulfide (AgInS2/GaSx) core/shell quantum dots (QDs), among the cadmium-free alternatives that possess a narrow band-edge emission, have attracted immense attention in recent years. However, the insufficient stability...

Reversible tuning of luminescence and magnetism in a structurally flexible erbium–anilato MOF

By combining 3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (H₂trz₂An) with NIR-emitting Er^III ions, two different 3D neutral polymorphic frameworks (1a and 1b), differing in the number of uncoordinated water molecules, formulated as [Er₂(trz₂An)₃(H₂O)₄]_n·xH₂O (x = 10, a; x = 7, b), have been obtained. The structure of 1a shows layers with (6,3) topology forming six-membered rings with distorted hexagonal cavities along the bc plane. These 2D layers are interconnected through the N4 atoms of the two pendant arms of the trz₂An linkers, leading to a 3D framework, where neighboring layers are eclipsed along the a axis, with hexagonal channels filled with water molecules. In 1b, layers with (6,3) topology in the [101] plane are present, each Er^III ion being connected to three other Er^III ions through bis-bidentate trz₂An linkers, forming rectangular six-membered cavities. 1a and 1b are multifunctional materials showing coexistence of NIR emission and field-induced slow relaxation of the magnetization. Remarkably, 1a is a flexible MOF, showing a reversible structural phase transition involving shrinkage/expansion from a distorted hexagonal 2D framework to a distorted 3,6-brickwall rectangular 3D structure in [Er₂(trz₂An)₃(H₂O)₂]_n·2H₂O (1a_des). This transition is triggered by a dehydration/hydration process under mild conditions (vacuum/heating to 360 K). The partially dehydrated compound shows a sizeable change in the emission properties and an improvement of the magnetic blocking temperature with respect to the hydrated compound, mainly related to the loss of one water coordination molecule. Theoretical calculations support the experimental findings, indicating that the slight improvement observed in the magnetic properties has its origin in the change of the ligand field around the Er^III ion due to the loss of a water molecule.

Tuning of luminescent and SIM properties is herein reported, in a novel flexible 3D anilato-based Er^III-MOF, displaying reversible shrinkage/expansion from a distorted hexagonal to a 3,6-brickwall rectangular structure.

Structural resolution and mechanistic insight into hydrogen adsorption in flexible ZIF-7

Flexible metal-organic frameworks offer a route towards high useable hydrogen storage capacities with minimal swings in pressure and temperature via step-shaped adsorption and desorption profiles. Yet, the understanding of hydrogen-induced flexibility in candidate storage materials remains incomplete. Here, we investigate the hydrogen storage properties of a quintessential flexible metal-organic framework, ZIF-7. We use high-pressure isothermal hydrogen adsorption measurements to identify the pressure-temperature conditions of the hydrogen-induced structural transition in ZIF-7. The material displays narrow hysteresis and has a shallow adsorption slope between 100 K and 125 K. To gain mechanistic insight into the cause of the phase transition correlating with stepped adsorption and desorption, we conduct powder neutron diffraction measurements of the D2 gas-dosed structures at conditions across the phase change. Rietveld refinements of the powder neutron diffraction patterns yield the structures of activated ZIF-7 and of the gas-dosed material in the dense and open phases. The structure of the activated phase of ZIF-7 is corroborated by the structure of the activated phase of the Cd congener, CdIF-13, which we report here for the first time based on single crystal X-ray diffraction measurements. Subsequent Rietveld refinements of the powder patterns for the gas-dosed structure reveal that the primary D2 adsorption sites in the dense phase form D2-arene interactions between adjacent ligands in a sandwich-like adsorption motif. These sites are prevalent in both the dense and the open structure for ZIF-7, and we hypothesize that they play an important role in templating the structure of the open phase. We discuss the implications of our findings for future approaches to rationally tune step-shaped adsorption in ZIF-7, its congeners, and flexible porous adsorbents in general. Lastly, important to the application of flexible frameworks, we show that pelletization of ZIF-7 produces minimal variation in performance.

Tetraethylthiuram disulphide alleviates pulmonary fibrosis through modulating transforming growth factor-β signalling

Idiopathic pulmonary fibrosis (IPF) induces significant morbidity and mortality, for which there are limited therapeutic options available. Here, we found that tetraethylthiuram disulphide (disulfiram, DSF), a derivative of thiuram, used in the treatment of alcohol abuse, has an inhibitory effect on bleomycin (BLM)-induced pulmonary fibrosis via the attenuation of the fibroblast-to-myofibroblast transition, migration, and proliferation of fibroblasts. Furthermore, DSF inhibited the activation of primary pulmonary fibroblasts and fibroblast cell line under transforming growth factor-β 1 (TGF-β1) challenge. Mechanistically, the anti-fibrotic effect of DSF on fibroblasts depends on the inhibition of TGF-β signalling. We further determined that DSF interrupts the interaction between SMAD3 and TGF-β receptor Ι (TBR Ι), and identified that DSF directly binds with SMAD3, in which Trp326, Thr330, and Cys332 of SMAD3 are critical binding sites for DSF. Collectively, our results reveal a powerful anti-fibrotic function of DSF in pulmonary fibrosis through the inhibition of TGF-β/SMAD signalling in pulmonary fibroblasts, indicating that DSF is a promising therapeutic candidate for IPF.

Exploiting the Specific Isotope-Selective Adsorption of Metal-Organic Framework for Hydrogen Isotope Separation

Adsorptive separation using narrow-micropore adsorbents has demonstrated the potential to separate hydrogen isotopes. In this work, we employed an isotope-responsive separation using cobalt formate. A D₂-responsive third sorption step was revealed, and consequently, a noticeable difference was observed in the uptakes of D₂ and H₂. This may have resulted from the additional space created for D₂ due to its dense packing, as DFT calculations revealed that cobalt formate possesses 2.26 kJ/mol higher binding strength for D₂ than for H₂. The exploitation of this D₂-responsive third sorption step renders a promising separation performance, with a D₂/H₂ selectivity of up to 44 at 25 K/1 bar. Lastly, cobalt formate was synthesized on a gram scale here, which makes it a prospect for commercialization.

Elucidation of Diffusivity of Hydrogen Isotopes in Flexible MOFs by Quasi-Elastic Neutron Scattering

Kinetic-quantum-sieving-assisted H₂ :D₂ separation in flexible porous materials is more effective than the currently used energy-intensive cryogenic distillation and girdle-sulfide processes for isotope separation. It is believed that material flexibility results in a pore-breathing phenomenon under the influence of external stimuli, which helps in adjusting the pore size and gives rise to the optimum quantum-sieving phenomenon at each stage of gas separation. However, only a few studies have investigated kinetic-quantum-sieving-assisted isotope separation using flexible porous materials. In addition, no reports are available on the microscopic observation of isotopic molecular transportation during the separation process under dynamic transition. Here, the experimental observation of a significantly faster diffusion of deuterium than hydrogen in a flexible pore structure, even at high temperatures, through quasi-elastic neutron scattering, is reported. Unlike rigid structures, the extracted diffusion dynamics of hydrogen isotopes within flexible frameworks show that the diffusion difference between the isotopes increases with an increase in temperature. Owing to this unique inverse trend, a new strategy is suggested for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal-organic framework system.

High-Efficiency Separation of n-Hexane by a Dynamic Metal-Organic Framework with Reduced Energy Consumption

The separation of n-alkanes from their branched isomers is vitally important to improve octane rating of gasoline. To facilitate mass transfer, adsorptive separation is usually operated under high temperatures in industry, which require considerable energy. Herein, we present a kind of dynamic pillar-layered MOF that exhibits self-adjustable structure and pore space, a behavior induced by guest molecules. A combination of the flexibility of the framework with the commensurate adsorption for n-hexane results in exceptional performance in separating hexane isomers. More significantly, lower temperature prompts the guest molecules to open the dynamic pores, which may provide a new perspective for optimized separation performance at lower temperatures with less energy consumption.

Porous flexible frameworks: origins of flexibility and applications

Porous crystalline frameworks including zeolites, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs) have attracted great research interest in recent years. In addition to their assembly in the solid-state being fundamentally interesting and aesthetically pleasing, their potential applications have now pervaded in different areas of chemistry, biology and materials science. When framework materials are endowed with 'flexibility', they exhibit some properties (e.g., stimuli-induced pore breathing and reversible phase transformations) that are distinct from their rigid counterparts. Benefiting from flexibility and porosity, these framework materials have shown promise in applications that include separation of toxic chemicals, isotopes and hydrocarbons, sensing, and targeted delivery of chemicals. While flexibility in MOFs has been widely appreciated, recent developments of COFs and HOFs have established that flexibility is not just limited to MOFs. In fact, zeolites-that are considered rigid when compared with MOFs-are also known to exhibit dynamic modes. Despite flexibility may be conceived as being detrimental to the formation and stability of periodic structures, the landscape of flexible framework structures continues to expand with discovery of new materials with promising applications. In this review, we make an account of different flexible framework materials based on their framework types with a more focus on recent examples and delve into the origin of flexibility in each case. This systematic analysis of different flexibility types based on their origins enables understanding of structure-property relationships, which should help guide future development of flexible framework materials based on appropriate monomer design and tailoring their properties by bottom-up approach. In essence, this review provides a summary of different flexibility types extant to framework materials and critical analysis of importance of flexibility in emerging applications.

Rational strategies for proton-conductive metal-organic frameworks

Since the transition of energy platforms, proton-conducting materials have played a significant role in broad applications for electrochemical devices. In particular, solid-state proton conductors (SSPCs) are emerging as the electrolyte in fuel cells (FC), a promising power generation technology, because of their high performance and safety for operating in a wide range of temperatures. In recent years, proton-conductive porous metal-organic frameworks (MOFs) exhibiting high proton-conducting properties (>10-2 S cm-1) have been extensively investigated due to their potential application in solid-state electrolytes. Their structural designability, crystallinity, and porosity are beneficial to fabricate a new type of proton conductor, providing a comprehensive conduction mechanism. For the proton-conductive MOFs, each component, such as the metal centres, organic linkers, and pore space, is manipulated by a judicious predesign strategy or post-synthetic modification to improve the mobile proton concentration with an efficient conducting pathway. In this review, we highlight rational design strategies for highly proton-conductive MOFs in terms of MOF components, with representative examples from recent years. Subsequently, we discuss the challenges and future directions for the design of proton-conductive MOFs.

Selectivity for water isotopologues within metal organic nanotubes

Through a combination of many analytical approaches, we show that a metal organic nanotube (UMON) displays selectivity for H₂O over all types of heavy water (D₂O, HDO, HTO). Water adsorption experiments combined with vibrational and radiochemical analyses reveal significant differences in uptake and suggest that surface adsorption processes may be a key driver in water uptake for this material.

Water adsorption experiments combined with vibrational and radiochemical analyses reveal significant differences in uptake of H₂O over D₂O, HDO, and HTO within metal organic nanotubes.

The state of the field: from inception to commercialization of metal–organic frameworks

We provide a brief overview of the state of the MOF field from their inception to their synthesis, potential applications, and finally, to their commercialization.

Dynamic metal-organic frameworks for the separation of hydrogen isotopes

Reversible structural transformation upon exposure to external stimuli can lead to breathing effect or gate-opening phenomena for dynamic metal-organic frameworks (MOFs), which endow them with excellent gas separation performance. The separation of hydrogen isotopes remains a huge challenge due to their nearly identical physical and chemical properties. The unique feature of dynamic MOFs, especially structural transition triggered by isotopes or by temperature, maximally enhances kinetic quantum sieving and contributes to the highly selective separation of hydrogen isotopes. Herein, we present some examples for the separation of hydrogen isotopes based on dynamic frameworks, and we expect to attract increasing attention to this research field.

New force field for GCMC simulations of D2/H2 quantum sieving in pure silica zeolites

We report a study on adsorption and coadsorption of H₂ and D₂ in FAU, MFI and CHA pure silica zeolites having different pore sizes and shapes. Adsorption capacities, selectivities, enthalpies and entropies are determined by combining experiments and GCMC simulations. We show that the force fields available in the literature cannot predict the adsorption equilibria below 77 K with sufficient accuracy. Here we propose a new force field adjusted by using our experimental data obtained for the pure silica MFI zeolite at 65 K and 77 K. With this new force field, it is possible to predict the adsorption and coadsorption equilibria on the three zeolite structures in a temperature range between 47 and 77 K with satisfactory precision. We corroborate that the step appearing on the single adsorption isotherms in CHA is the result of a molecular rearrangement of the adsorbed phase due to the apparition of a new adsorption site characterized by weaker interactions of H₂ with the adsorbent. We conclude that the quantum sieving of H₂ and D₂ not only depends on the pore size but also on the pore shape, in particular, at high loading when the confinement effects become important.

Specific Isotope-Responsive Breathing Transition in Flexible Metal-Organic Frameworks

An isotope-selective responsive system based on molecular recognition in porous materials has potential for the storage and purification of isotopic mixtures but is considered unachievable because of the almost identical physicochemical properties of the isotopes. Herein, a unique isotope-responsive breathing transition of the flexible metal-organic framework (MOF), MIL-53(Al), which can selectively recognize and respond to only D₂ molecules through a secondary breathing transition, is reported. This novel phenomenon is examined using in situ neutron diffraction experiments under the same conditions for H₂ and D₂ sorption experiments. This work can guide the development of a novel isotope-selective recognition system and provide opportunities to fabricate flexible MOF systems for energy-efficient purification of the isotopic mixture.

An Expandable Hydrogen-Bonded Organic Framework Characterized by Three-Dimensional Electron Diffraction

A molecular crystal of a 2-D hydrogen-bonded organic framework (HOF) undergoes an unusual structural transformation after solvent removal from the crystal pores during activation. The conformationally flexible host molecule, ABTPA, adapts its molecular conformation during activation to initiate a framework expansion. The microcrystalline activated phase was characterized by three-dimensional electron diffraction (3D ED), which revealed that ABTPA uses out-of-plane anthracene units as adaptive structural anchors. These units change orientation to generate an expanded, lower density framework material in the activated structure. The porous HOF, ABTPA-2, has robust dynamic porosity (SA_BET = 1183 m² g^-1) and exhibits negative area thermal expansion. We use crystal structure prediction (CSP) to understand the underlying energetics behind the structural transformation and discuss the challenges facing CSP for such flexible molecules.

A Promising Alternative for Sustainable and Highly Efficient Solar-Driven Deuterium Evolution at Room Temperature by Photocatalytic D2 O Splitting

Motivated by energy shortages and in view of current efforts to develop clean, renewable energy sources based on fusion, a solar-driven strategy has been developed for deuterium evolution. Deuterium is a critical resource for many aspects. However, the limited natural abundance of deuterium and the complexity of established technologies, such as quantum sieving (QS) for deuterium production under extreme conditions, pose challenges. The new method has the potential for robust and sustainable deuterium evolution, enabling deuterium production at a high rate of 9.745 mmol g^-1  h^-1 . The activity, thermodynamic, and kinetic characteristics are also investigated and compared between photocatalytic heavy water (D₂ O) splitting and water (H₂ O) splitting. This study opens a new avenue to discover promising photocatalytic deuterium generation systems for advanced solar energy utilization and deuterium enrichment.

Enhanced quantum sieving of hydrogen isotopes via molecular rearrangement of the adsorbed phase in chabazite

Coadsorption experiments reveal an unexpected increase of the D2/H2 selectivity with loading in pure silica chabazite at 47 K. This effect is correlated with the appearance of a step in the adsorption isotherms of H2 and D2. Grand canonical Monte Carlo simulations show that this phenomenon is related to a molecular rearrangement of the adsorbed phase induced by its strong confinement. In the case of a H2 and D2 mixture, this rearrangement favors the adsorption of D2 having a smaller size due to quantum effects.

Exploiting Dynamic Opening of Apertures in a Partially Fluorinated MOF for Enhancing H2 Desorption Temperature and Isotope Separation

Deuterium has been recognized as an irreplaceable element in industrial and scientific research. However, hydrogen isotope separation still remains a huge challenge due to the identical physicochemical properties of the isotopes. In this paper, a partially fluorinated metal-organic framework (MOF) with copper, a so-called FMOFCu, was investigated to determine the separation efficiency and capacity of the framework for deuterium extraction from a hydrogen isotope mixture. The unique structure of this porous material consists of a trimodal pore system with large tubular cavities connected through a smaller cavity with bottleneck apertures with a size of 3.6 Å plus a third hidden cavity connected by an even smaller aperture of 2.5 Å. Depending on the temperature, these two apertures show a gate-opening effect and the cavities get successively accessible for hydrogen with increasing temperature. Thermal desorption spectroscopy (TDS) measurements indicate that the locally flexible MOF can separate D₂ from anisotope mixture efficiently, with a selectivity of 14 at 25 K and 4 at 77 K.

Metal-organic framework crystal-glass composites

The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO₂ adsorption capacity.

The formation of composite materials has been widely exploited to alter the chemical and physical properties of their components. Here the authors form metal–organic framework (MOF) crystal–glass composites in which a MOF glass matrix stabilises the open pore structure of MIL-53, leading to enhanced CO₂ adsorption.

Molecular Sieves for the Separation of Hydrogen Isotopes

Stable molecular hydrogen isotopes, D₂ and T₂, are both scarce and essential in several energy, industrial, and large-scale fundamental research applications. Due to the chemical similarity of these isotopes, their extraction and purification from hydrogen has relied for decades on expensive and energy-demanding processes. However, factoring in the phenomenon of quantum sieving could provide a new route for these separations. In this work, we have explored how to separate hydrogen isotopes by adsorption taking these quantum effects into account. To this end, we have conducted adsorption measurements to test our deuterium model and performed a widespread computational screening over 210 pure-silica zeolites for D₂/H₂ and T₂/H₂ separations. Based on low-coverage adsorption properties, a reduced set of zeolites have been singled out and their performance in terms of adsorption capacity, selectivity, and dynamic behavior have been assessed. Overall, the BCT-type zeolite clearly stands out for highly selective separations of both D₂ and T₂ over H₂, achieving the highest reported selectivities at cryogenic temperatures. We also identified other interesting zeolites for the separation of hydrogen isotopes that offer an alternative way to tackle similar isotopic separations by an aimed selection or design of porous materials.