Rational design of a robust aluminum metal-organic framework for multi-purpose water-sorption-driven heat allocations

Engineered Nanoporous Frameworks for Adsorption Cooling Applications

The energy demand for traditional vapor-compressed technology for space cooling continues to soar year after year due to global warming and the increasing human population's need to improve living and working conditions. Thus, there is a growing demand for eco-friendly technologies that use sustainable or waste energy resources. This review discusses the properties of various refrigerants used for adsorption cooling applications followed by a brief discussion on the thermodynamic cycle. Next, sorbents traditionally used for cooling are reviewed to emphasize the need for advanced capture materials with superior properties to improve refrigerant sorption. The remainder of the review focus on studies using engineered nanoporous frameworks (ENFs) with various refrigerants for adsorption cooling applications. The effects of the various factors that play a role in ENF-refrigerant pair selection, including pore structure/dimension/shape, morphology, open-metal sites, pore chemistry and possible presence of defects, are reviewed. Next, in-depth insights into the sorbent-refrigerant interaction, and pore filling mechanism gained through a combination of characterization techniques and computational modeling are discussed. Finally, we outline the challenges and opportunities related to using ENFs for adsorption cooling applications and provide our views on the future of this technology.

Avoiding pitfalls in molecular simulation of vapor sorption: Example of propane and isobutane in metal-organic frameworks for adsorption cooling applications

This study introduces recommendations for conducting molecular simulations of vapor adsorption, with an emphasis on enhancing the accuracy, reproducibility, and comparability of results. The first aspect we address is consistency in the implementation of some details of typical molecular models, including tail corrections and cutoff distances, due to their significant influence on generated data. We highlight the importance of explicitly calculating the saturation pressures at relevant temperatures using methods such as Gibbs ensemble Monte Carlo simulations and illustrate some pitfalls in extrapolating saturation pressures using this method. For grand canonical Monte Carlo (GCMC) simulations, the input fugacity is usually calculated using an equation of state, which often requires the critical parameters of the fluid. We show the importance of using critical parameters derived from the simulation with the same model to ensure internal consistency between the simulated explicit adsorbate phase and the implicit bulk phase in GCMC. We show the advantages of presenting isotherms on a relative pressure scale to facilitate easier comparison among models and with experiment. Extending these guidelines to a practical case study, we evaluate the performance of various isoreticular metal-organic frameworks (MOFs) in adsorption cooling applications. This includes examining the advantages of using propane and isobutane as working fluids and identifying MOFs with a superior performance.

Progress and perspectives of sorption-based atmospheric water harvesting for sustainable water generation: Materials, devices, and systems

Establishing alternative methods for freshwater production is imperative to effectively alleviate global water scarcity, particularly in land-locked arid regions. In this context, extracting water from the ubiquitous atmospheric moisture is an ingenious strategy for decentralized freshwater production. Sorption-based atmospheric water harvesting (SAWH) shows strong potential for supplying liquid water in a portable and sustainable way even in desert environments. Herein, the latest progress in SAWH technology in terms of materials, devices, and systems is reviewed. Recent advances in sorbent materials with improved water uptake capacity and accelerated sorption-desorption kinetics, including physical sorbents, polymeric hydrogels, composite sorbents, and ionic solutions, are discussed. The thermal designs of SAWH devices for improving energy utilization efficiency, heat transfer, and mass transport are evaluated, and the development of representative SAWH prototypes is clarified in a chronological order. Thereafter, state-of-the-art operation patterns of SAWH systems, incorporating intermittent, daytime continuous and 24-hour continuous patterns, are examined. Furthermore, current challenges and future research goals of this cutting-edge field are outlined. This review highlights the irreplaceable role of heat and mass transfer enhancement and facile structural improvement for constructing high-yield water harvesters.

Breathing Metal-Organic Frameworks Supported by an Arsenic-Bridged 4,4'-Bipyridine Ligand

Bent ligands bridged by heteroatoms have drawn significant interest as supramolecular coordination architectures. Traditionally, divalent group 16 elements are preferred over trivalent group 15 elements because of the anticipated steric hindrance. In this study, we explore metal-organic frameworks (MOFs) based on dipyridinoarsoles (DPAs), 4,4'-bipyridines bridged with an arsenic atom. An MOF with methyl-substituted DPA collapsed upon solvent removal, whereas that with phenyl-substituted DPA demonstrated breathing behavior due to guest molecule adsorption/desorption. In contrast, MOFs using the phosphorus analogue dipyridinophosphole exhibit inferior adsorption and lack breathing behavior. This is the first study to investigate the interplay among substituents, bridging elements, and dynamic behavior in MOFs using bent group 15 ligands.

When Polymorphism in Metal-Organic Frameworks Enables Water Sorption Profile Tunability for Enhancing Heat Allocation and Water Harvesting Performance

The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- µ-OH-connected corner-sharing AlO4(OH)2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers, and cis-µ-OH-connected corner-sharing AlO4(OH)2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc has a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P0 ≈ 0.5 in MIL-53-muc, to P/P0 ≈ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo reveal that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations show that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60 °C, outperforming benchmark sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air.

Advanced Material Design and Engineering for Water-Based Evaporative Cooling

Water-based evaporative cooling is emerging as a promising technology to provide sustainable and low-cost cold to alleviate the rising global cooling demand. Given the significant and fast progress made in recent years, this review aims to provide a timely overview on the state-of-the-art material design and engineering in water-based evaporative cooling. The fundamental mechanisms and major components of three water-based evaporative cooling processes are introduced, including direct evaporative cooling, cyclic sorption-driven liquid water evaporative cooling (CSD-LWEC), and atmospheric water harvesting-based evaporative cooling (AWH-EC). The distinctive requirements on the sorbent materials in CSD-LWEC and AWH-EC are highlighted, which helps synthesize the literature information on the advanced material design and engineering for the purpose of improving cooling performance. The challenges and future outlooks on further improving the water-based evaporative cooling performance are also provided.

Tunable Low-Pressure Water Adsorption in Stable Multivariate Metal-Organic Frameworks for Boosting Water-Based Ultralow-Temperature-Driven Refrigeration

The green water-based adsorption refrigeration is considered as a promising strategy to realize near-zero-carbon cooling applications. Although many metal-organic frameworks (MOFs) have been developed as water adsorbents, their cooling performance are commonly limited by the insufficient water uptakes below P/P0 = 0.2. Herein, the development of multivariate MOFs (MTV-MOFs) is reported to highly modulate and boost the low-pressure water uptake for improving coefficient of performance (COP) for refrigeration. Through ligand exchange in the pristine MIL-125-NH2 , a series of MTV-MOFs with bare nitrogen sites are designed and synthesized. The resulting MIL-125-NH2 /MD-5% exhibits the significantly improved water uptake of 0.39 g g-1 at 298 K and P/P0 = 0.2, which is three times higher than MIL-125-NH2 (0.12 g g-1 ) and comparable to some benchmark materials including KMF-1 (0.4 g g-1 ) and MIP-200 (0.36 g g-1 ). Combined with its low-temperature regeneration, fast sorption kinetics and high stability, MIL-125-NH2 /MD-5% achieves one of the highest COP values (0.8) and working capacities (0.24 g g-1 ) for refrig-2 under an ultralow-driven temperature of 65 °C, which are higher than some best-performing MOFs such as MIP-200 (0.74 and 0.11 g g-1 ) and KMF-2 (0.62 and 0.16 g g-1 ), making it among the best adsorbents for efficient ultralow-temperature-driven refrigeration.

Confined Water Cluster Formation in Water Harvesting by Metal-Organic Frameworks: CAU-10-H versus CAU-10-CH3

Several metal-organic frameworks (MOFs) excel in harvesting water from the air or as heat pumps as they show a steep increase in water uptake at 10-30 % relative humidity (RH%). A precise understanding of which structural characteristics govern such behavior is lacking. Herein, CAU-10-H and CAU-10-CH3 are studied with H, CH3 corresponding to the functions grafted to the organic linker. CAU-10-H shows a steep water uptake ≈18 RH% of interest for water harvesting, yet the subtle replacement of H by CH3 in the organic linker drastically changes the water adsorption behavior to less steep water uptake at much higher humidity values. The materials' structural deformation and water ordering during adsorption with in situ sum-frequency generation, in situ X-ray diffraction, and molecular simulations are unraveled. In CAU-10-H, an energetically favorable water cluster is formed in the hydrophobic pore, tethered via H-bonds to the framework μOH groups, while for CAU-10-CH3, such a favorable cluster cannot form. By relating the findings to the features of water adsorption isotherms of a series of MOFs, it is concluded that favorable water adsorption occurs when sites of intermediate hydrophilicity are present in a hydrophobic structure, and the formation of energetically favorable water clusters is possible.

Separation of High-Purity C2H2 from Binary C2H2/CO2 Using Robust Al-Based MOFs Comprising Nitrogen-Containing Heterocyclic Dicarboxylate

In this study, three nitrogen-containing aluminum-based metal-organic frameworks (Al-MOFs), namely, CAU-10pydc, MOF-303, and KMF-1, were investigated for the efficient separation of a C2H2/CO2 gas mixture. Among these three Al-MOFs, KMF-1 demonstrated the highest selectivity for C2H2/CO2 separation (6.31), primarily owing to its superior C2H2 uptake (7.90 mmol g-1) and lower CO2 uptake (2.82 mmol g-1) compared to that of the other two Al-MOFs. Dynamic breakthrough experiments, using an equimolar binary C2H2/CO2 gas mixture, demonstrated that KMF-1 achieved the highest separation performance. It yielded 3.42 mmol g-1 of high-purity C2H2 (>99.95%) through a straightforward desorption process under He purging at 298 K and 1 bar. To gain insights into the distinctive characteristics of the pore surfaces of structurally similar CAU-10pydc and KMF-1, we conducted computational simulations using canonical Monte Carlo and dispersion-corrected density functional theory methods. These simulations revealed that the secondary amine (C2N-H) groups in KMF-1 played a more significant role in differentiating between C2H2 and CO2 compared to that of the N atoms in CAU-10pydc and MOF-303. Consequently, KMF-1 emerged as a promising adsorbent for the separation of high-purity C2H2 from binary C2H2/CO2 gas mixtures.

Shaping the Water-Harvesting Behavior of Metal-Organic Frameworks Aided by Fine-Tuned GPT Models

We construct a data set of metal-organic framework (MOF) linkers and employ a fine-tuned GPT assistant to propose MOF linker designs by mutating and modifying the existing linker structures. This strategy allows the GPT model to learn the intricate language of chemistry in molecular representations, thereby achieving an enhanced accuracy in generating linker structures compared with its base models. Aiming to highlight the significance of linker design strategies in advancing the discovery of water-harvesting MOFs, we conducted a systematic MOF variant expansion upon state-of-the-art MOF-303 utilizing a multidimensional approach that integrates linker extension with multivariate tuning strategies. We synthesized a series of isoreticular aluminum MOFs, termed Long-Arm MOFs (LAMOF-1 to LAMOF-10), featuring linkers that bear various combinations of heteroatoms in their five-membered ring moiety, replacing pyrazole with either thiophene, furan, or thiazole rings or a combination of two. Beyond their consistent and robust architecture, as demonstrated by permanent porosity and thermal stability, the LAMOF series offers a generalizable synthesis strategy. Importantly, these 10 LAMOFs establish new benchmarks for water uptake (up to 0.64 g g-1) and operational humidity ranges (between 13 and 53%), thereby expanding the diversity of water-harvesting MOFs.

Atmospheric-moisture-induced polyacrylate hydrogels for hybrid passive cooling

Heat stress is being exacerbated by global warming, jeopardizing human and social sustainability. As a result, reliable and energy-efficient cooling methods are highly sought-after. Here, we report a polyacrylate film fabricated by self-moisture-absorbing hygroscopic hydrogel for efficient hybrid passive cooling. Using one of the lowest-cost industrial materials (e.g., sodium polyacrylate), we demonstrate radiative cooling by reducing solar heating with high solar reflectance (0.93) while maximizing thermal emission with high mid-infrared emittance (0.99). Importantly, the manufacturing process utilizes only atmospheric moisture and requires no additional chemicals or energy consumption, making it a completely green process. Under sunlight illumination of 800 W m-2, the surface temperature of the film was reduced by 5 °C under a partly cloudy sky observed at Buffalo, NY. Combined with its hygroscopic feature, this film can simultaneously introduce evaporative cooling that is independent of access to the clear sky. The hybrid passive cooling approach is projected to decrease global carbon emissions by 118.4 billion kg/year compared to current air-conditioning facilities powered by electricity. Given its low-cost raw materials and excellent molding feature, the film can be manufactured through simple and cost-effective roll-to-roll processes, making it suitable for future building construction and personal thermal management needs.

Incorporation of multiple supramolecular binding sites into a robust MOF for benchmark one-step ethylene purification

One-step adsorption separation of C2H4 from ternary C2 hydrocarbon mixtures remains an important and challenging goal for petrochemical industry. Current physisorbents either suffer from unsatisfied separation performance, poor stability, or are difficult to scale up. Herein, we report a strategy of constructing multiple supramolecular binding sites in a robust and scalable MOF (Al-PyDC) for highly efficient one-step C2H4 purification from ternary mixtures. Owing to suitable pore confinement with multiple supramolecular binding sites, Al-PyDC exhibits one of the highest C2H2 and C2H6 uptakes and selectivities over C2H4 at ambient conditions. The gas binding sites have been visualized by single-crystal X-ray diffraction studies, unveiling that the low-polarity pore surfaces with abundant electronegative N/O sites provide stronger multiple supramolecular interactions with C2H2 and C2H6 over C2H4. Breakthrough experiments showed that polymer-grade C2H4 can be separated from ternary mixtures with a maximum productivity of 1.61 mmol g-1. This material can be prepared from two simple reagents using a green synthesis method with water as the sole solvent, and its synthesis can be easily scaled to multikilogram batches. Al-PyDC achieves an effective combination of benchmark separation performance, high stability/recyclability, green synthesis and easy scalability to address major challenges for industrial one-step C2H4 purification.

Improvement of water adsorption performance of UiO-66 by post-synthetic modification

Post-synthetic modification can be used for structural replacement or functional modification of materials after they have been formed or assembled. It can effectively combine various modification methods for metal-organic frameworks (MOFs) such as defect control, replacement of metal sites, or functionalization of ligands. In this work, organic ligands that incorporate N-functionalities or amino groups were introduced into defective UiO-66 through post-synthetic ligand exchange (PSE) to improve its water adsorption performance. Parameters such as water adsorption capacity, half adsorption value (α), and Henry constant KH were used to characterize the water adsorption performance. After PSE, new ligands in different molar ratios entered the skeleton of UiO-66. The N sites or amino groups on the ligands provided new sites for the adsorption of water molecules. The water adsorption capacity and hydrophilicity of all samples were significantly superior to those of LD-UiO-66, which had almost no defects. H-UiO-66-PyDC samples exhibited the highest ligand replacement ratio and a significant enhancement of water adsorption performance. Compared to the unchanged H-UiO-66, the water uptake of H-UiO-66-PyDC increased from 0.08 g g-1 to 0.23 g g-1 at P/P0 = 0.30 and α decreased from 0.36 to 0.28. After 20 water adsorption/desorption tests, the water uptake of all samples did not decrease, showing excellent cycling stability. These results suggest that the combination of defect modulation and PSE is a potential tool to make UiO-66 more appropriate for applications based on reversible adsorption.

Reticular Chemistry in Its Chiral Form: Axially Chiral Zr(IV)-Spiro Metal-Organic Framework as a Case Study

The interplay of primary organic ligands and inorganic secondary building units (SBUs) has led to a continual boom of reticular chemistry, particularly metal-organic frameworks (MOFs). Subtle variations of organic ligands can have a significant impact on the ultimate structural topology and consequently, the material's function. However, the role of ligand chirality in reticular chemistry has rarely been explored. In this work, we report the organic ligand chirality-controlled synthesis of two zirconium-based MOFs (Spiro-1 and Spiro-3) with distinct topological structures as well as a temperature-controlled formation of a kinetically stable phase (Spiro-4) based on the carboxylate-functionalized inherently axially chiral 1,1'-spirobiindane-7,7'-phosphoric acid ligand. Specifically, Spiro-1 is a homochiral framework comprising only enantiopure S-spiro ligands and has a unique 4,8-connected sjt topology with large 3D interconnected cavities, while Spiro-3 contains equal amounts of S- and R-spiro ligands, resulting in a racemic framework of 6,12-connected edge-transitive alb topology with narrow channels. Interestingly, the kinetic product Spiro-4 obtained with racemic spiro ligands is built of both hexa- and nona-nuclear zirconium clusters acting as 9- and 6-connected nodes, respectively, giving rise to a newly discovered azs net. Notably, the preinstalled highly hydrophilic phosphoric acid groups combined with large cavity, high porosity, and outstanding chemical stability endow Spiro-1 with remarkable water vapor sorption performance, whereas Spiro-3 and Spiro-4 show poor performances due to inappropriate pore systems and structural fragility upon the water adsorption/desorption process. This work highlights the important role of ligand chirality in manipulating the framework topology and function and would further enrich the development of reticular chemistry.

Design of Pore Properties of an Al-Based Metal-Organic Framework for the Separation of an Ethane/Ethylene Gas Mixture via Ethane-Selective Adsorption

A series of Al-based isomorphs (CAU-10H, MIL-160, KMF-1, and CAU-10pydc) were synthesized using isophthalic acid (ipa), 2,5-furandicarboxylic acid (fdc), 2,5-pyrrole dicarboxylic acid (pyrdc), and 3,5-pyridinedicarboxylic acid (pydc), respectively. These isomorphs were systematically investigated to identify the best adsorbent for effectively separating C₂H₆/C₂H₄. All CAU-10 isomorphs exhibited preferential adsorption of C₂H₆ over that of C₂H₄ in mixture. CAU-10pydc exhibited the best C₂H₆/C₂H₄ selectivity (1.68) and the highest C₂H₆ uptake (3.97 mmol g^-1) at 298 K and 1 bar. In the breakthrough experiment using CAU-10pydc, 1/1 (v/v) and 1/15 (v/v) C₂H₆/C₂H₄ gas mixtures were successfully separated into high-purity C₂H₄ (>99.95%), with remarkable productivities of 14.0 L_STP kg^-1 and 32.0 L_STP kg^-1, respectively, at 298 K. Molecular simulations revealed that the exceptional separation performance of CAU-10pydc originated from the increased porosity and reduced electron density of the pyridine ring of pydc, leading to a relatively larger decrease in π-π interactions with C₂H₄ than in the C-H···π interactions with C₂H₆. This study demonstrates that the pore size and geometry of the CAU-10 platform are modulated by the inclusion of heteroatom-containing benzene dicarboxylate or heterocyclic rings of dicarboxylate-based organic linkers, thereby fine-tuning the C₂H₆/C₂H₄ separation ability. CAU-10pydc was determined to be an optimum adsorbent for this challenging separation.

Fe-MOF with U-Shaped Channels for C2H2/CO2 and C2H2/C2H4 Separation

The development of high-performance adsorbents is critical for the low-energy separation of acetylene. Herein, we synthesized an Fe-MOF (MOF, metal-organic framework) with U-shaped channels. The adsorption isotherms of C₂H₂, C₂H₄, and CO₂ show that the adsorption capacity of acetylene is significantly larger than that of the other two gases. Meanwhile, the actual separation performance was verified by breakthrough experiments, indicating the potential to separate C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures at normal temperatures. Grand Canonical Monte Carlo (GCMC) simulation demonstrates that the framework with U-shaped channels interacts more strongly with C₂H₂ than with C₂H₄ and CO₂. The high C₂H₂ uptake and low adsorption enthalpy highlight Fe-MOF as a promising candidate for C₂H₂/CO₂ separation with a low regeneration energy.

Metal-Organic Frameworks for Greenhouse Gas Applications

Using petrol to supply energy for a car or burning coal to heat a building generates plenty of greenhouse gas (GHG) emissions, including carbon dioxide (CO₂ ), water vapor (H₂ O), methane (CH₄ ), nitrous oxide (N₂ O), ozone (O₃ ), fluorinated gases. These up-and-coming metal-organic frameworks (MOFs) are structurally endowed with rigid inorganic nodes and versatile organic linkers, which have been extensively used in the GHG-related applications to improve the lives and protect the environment. Porous MOF materials and their derivatives have been demonstrated to be competitive and promising candidates for GHG separation, storage and conversions as they shows facile preparation, large porosity, adjustable nanostructure, abundant topology, and tunable physicochemical property. Enormous progress has been made in GHG storage and separation intrinsically stemmed from the different interaction between guest molecule and host framework from MOF itself in the recent five years. Meanwhile, the use of porous MOF materials to transform GHG and the influence of external conditions on the adsorption performance of MOFs for GHG are also enclosed. In this review, it is also highlighted that the existing challenges and future directions are discussed and envisioned in the rational design, facile synthesis and comprehensive utilization of MOFs and their derivatives for practical applications.

Novel strategies for the formulation and processing of aluminum metal-organic framework-based sensing systems toward environmental monitoring of metal ions

Aluminum is a relatively inexpensive and abundant metal for the mass production of metal-organic frameworks (MOFs). Aluminum-based MOFs (Al-MOFs) have drawn a good deal of research interest due to their unique properties for diverse applications (e.g., excellent chemical and structural stability). This review has been organized to highlight the current progress achieved in the synthesis/functionalization of Al-MOF materials with the special emphasis on their sensing application, especially toward metal ion pollutants in the liquid phase. To learn more about the utility of Al-MOF-based sensing systems, their performances have been evaluated for diverse metallic components in reference to many other types of sensing systems (in terms of the key quality assurance (QA) criteria such as limit of detection (LOD)). Finally, the challenges and outlook for Al-MOF-based sensing systems are discussed to help expand their real-world applications.

Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure

In this study, the ability of the highly scalable metal-organic framework (MOF) CALF-20 to adsorb polar and non-polar gases at low pressure was investigated using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results from the simulated adsorption isotherms revealed that the highest loading was achieved for SO₂ and Cl₂, while the lowest loading was found for F₂ molecules. The analysis of interaction energies indicated that SO₂ molecules were able to form the strongest adsorbent-adsorbate interactions and had a tight molecular packing due to their polarity and angular structure. Additionally, Cl₂ gas was found to be highly adsorbed due to its large van der Waals surface and strong chemical affinity in CALF-20 pores. MD simulations showed that SO₂ and Cl₂ had the lowest mobility inside CALF-20 pores. The values of the Henry coefficient and isosteric heat of adsorption confirmed that CALF-20 could selectively adsorb SO₂ and Cl₂. Based on the results, it was concluded that CALF-20 is a suitable adsorbent for SO₂ and Cl₂ but not for F₂. This research emphasizes the importance of molecular size, geometry, and polarity in determining the suitability of a porous material as an adsorbent for specific adsorbates.

High-yield, green and scalable methods for producing MOF-303 for water harvesting from desert air

Metal-organic frameworks (MOFs) are excellent candidates for water harvesting from desert air. MOF-303 (Al(OH)(PZDC), where PZDC is 1-H-pyrazole-3,5-dicarboxylate), a robust and water-stable MOF, is a particularly promising water-harvesting sorbent that can take up water at low relative humidity and release it under mild heating. Accordingly, development of a facile, high-yield synthesis method for its production at scale is highly desirable. Here we report detailed protocols for the green, water-based preparation of MOF-303 on both gram and kilogram scales. Specifically, four synthetic methods (solvothermal, reflux, vessel and microwave), involving different equipment requirements, are presented to guarantee general accessibility. Typically, the solvothermal method takes ~24 h to synthesize MOF-303, while the reflux and vessel methods can reduce the time to 4-8 h. With the microwave-assisted method, the reaction time can be further reduced to just 5 min. In addition, we provide guidance on the characterization of MOF-303, as well as water-harvesting MOFs in general, to ensure high quality of the product in terms of its purity, crystallinity, porosity and water uptake. Furthermore, to address the need for future commercialization of this material, we demonstrate that our protocol can be employed to produce 3.5 kg per batch with a yield of 91%. MOF-303 synthesized at this large scale shows similar crystallinity and water uptake capacity compared to the respective material produced at a small scale. Our synthetic procedure is green and water-based, and can produce the MOF within hours.

An Amine-Functionalized Ultramicroporous Metal-Organic Framework for Postcombustion CO2 Capture

Among the most promising methods by which to capture CO₂ from flue gas, the emission of which has accelerated global warming, is energy-efficient physisorption using metal-organic framework (MOF) adsorbents. Here, we present a novel cuprous-based ultramicroporous MOF, Cu(adci)-2 (adci^- = 2-amino-4,5-dicyanoimidazolate), which was rationally synthesized by combining two strategies to design MOF physisorbents for enhanced CO₂ capturing, i.e., aromatic amine functionalization and the introduction of ultramicroporosity (pore size <7 Å). Synchrotron powder X-ray diffraction and a Rietveld analysis reveal that the Cu(adci)-2 structure has one-dimensional square-shaped channels, in each of which all affiliated ligands, specifically NH₂ groups at the 2-position of the imidazolate ring, have the same orientation, with a pair of NH₂ groups therefore facing each other on opposite sides of the channel walls. While Cu(adci)-2 exhibits a high CO₂ adsorption capacity (2.01 mmol g^-1 at 298 K and 15 kPa) but a low zero-coverage isosteric heat of adsorption (27.5 kJ mol^-1), breakthrough experiments under dry and 60% relative humidity conditions show that its CO₂ capture ability is retained even in the presence of high amounts of moisture. In a Monte Carlo simulation and a radial distribution analysis, the preferential CO₂ binding site of Cu(adci)-2 was predicted to be between two ligands, forming a sandwich-like structure and implying that its CO₂ adsorption properties originate from the enhancement of Lewis base-acid and London dispersion interactions due to the amino groups and ultramicroporosity, respectively.

New Insight into Sorption Cycling Stability of Three Al-Based MOF Materials in Water Vapour

Three porous aluminium benzene-1,3,5-tricarboxylates MIL-96(Al), MIL-100(Al) and MIL-110(Al) materials were studied for their hydrothermal stability. The 40-cycles water vapour sorption experiments for the three samples were performed by varying the temperature between 40 and 140 °C at 75% relative humidity to simulate working conditions for materials used in water sorption-based low-T heat storage and reallocation applications. The materials were characterized by powder X-ray diffraction, N₂ physisorption, and Nuclear Magnetic Resonance and Infrared spectroscopies before and after the cycling tests. The results showed that the structure of MIL-110(Al) lost its crystallinity and porosity under the tested conditions, while MIL-96(Al) and MIL-100(Al) exhibited excellent hydrothermal stability. The selection of structures, which comprise the same type of metal and ligand, enabled us to attribute the differences in stability primarily to the known variances in secondary building units and the shielding of potential water coordination sites due to the differences in pore accessibility for water molecules. Additionally, our results revealed that water adsorption and desorption at tested conditions (T, RH) is very slow for all three materials, being most pronounced for the MIL-100(Al) structure.

Immobilization of Lewis Basic Nitrogen Sites into a Chemically Stable Metal-Organic Framework for Benchmark Water-Sorption-Driven Heat Allocations

Developing efficient and stable water adsorbents for adsorption-driven heat transfer technology still remains a challenge due to the lack of efficient strategies to enhance low-pressure water uptakes. The authors herein demonstrate that the immobilization of Lewis basic nitrogen sites into metal-organic frameworks (MOFs) can improve water uptake and target benchmark coefficient of performances (COPs) for cooling and heating. They present the water sorption properties of a chemically stable MOF (termed as Zr-adip), designed by incorporating hydrophilic nitrogen sites into the adsorbent MIP-200. Zr-adip exhibits S-shaped sorption isotherms with an extremely high water uptake of 0.43 g g-1  at 303 K and P/P0  = 0.25, higher than MIP-200 (0.39 g g-1 ), KMF-1 (0.39 g g-1 ) and MOF-303 (0.38 g g-1 ). Theoretical calculations reveal that the incorporated N sites can serve as secondary adsorption sites to moderately interact with water, providing more binding sites to strengthen the water binding affinity. Zr-adip achieves exceptionally high COPs of 0.79 (cooling) and 1.75 (heating) with a low driving temperature of 70 °C, outperforming MIP-200 (0.78 and 1.53) and KMF-1 (0.75 and 1.74). Combined with its ultrahigh stability, excellent cycling performance, and easy regeneration, Zr-adip represents one of the best water adsorbents for adsorption-driven cooling and heating.

Hygroscopic holey graphene aerogel fibers enable highly efficient moisture capture, heat allocation and microwave absorption

Aerogel fibers have been recognized as the rising star in the fields of thermal insulation and wearable textiles. Yet, the lack of functionalization in aerogel fibers limits their applications. Herein, we report hygroscopic holey graphene aerogel fibers (LiCl@HGAFs) with integrated functionalities of highly efficient moisture capture, heat allocation, and microwave absorption. LiCl@HGAFs realize the water sorption capacity over 4.15 g g⁻¹, due to the high surface area and high water uptake kinetics. Moreover, the sorbent can be regenerated through both photo-thermal and electro-thermal approaches. Along with the water sorption and desorption, LiCl@HGAFs experience an efficient heat transfer process, with a heat storage capacity of 6.93 kJ g⁻¹. The coefficient of performance in the heating and cooling mode can reach 1.72 and 0.70, respectively. Notably, with the entrapped water, LiCl@HGAFs exhibit broad microwave absorption with a bandwidth of 9.69 GHz, good impedance matching, and a high attenuation constant of 585. In light of these findings, the multifunctional LiCl@HGAFs open an avenue for applications in water harvest, heat allocation, and microwave absorption. This strategy also suggests the possibility to functionalize aerogel fibers towards even broader applications.

Functionalization of aerogel fibers, characterized by high porosity and low thermal conductivity, to obtain multifunctional materials is highly desirable. Here the authors report hygroscopic holey graphene aerogel fibers hosting LiCl salt, enabling moisture capture, heat allocation, and microwave absorption performance.

Ultralow-temperature-driven water-based sorption refrigeration enabled by low-cost zeolite-like porous aluminophosphate

Thermally driven water-based sorption refrigeration is considered a promising strategy to realize near-zero-carbon cooling applications by addressing the urgent global climate challenge caused by conventional chlorofluorocarbon (CFC) refrigerants. However, developing cost-effective and high-performance water-sorption porous materials driven by low-temperature thermal energy is still a significant challenge. Here, we propose a zeolite-like aluminophosphate with SFO topology (EMM-8) for water-sorption-driven refrigeration. The EMM-8 is characterized by 12-membered ring channels with large accessible pore volume and exhibits high water uptake of 0.28 g·g-1 at P/P0 = 0.2, low-temperature regeneration of 65 °C, fast adsorption kinetics, remarkable hydrothermal stability, and scalable fabrication. Importantly, the water-sorption-based chiller with EMM-8 shows the potential of achieving a record coefficient of performance (COP) of 0.85 at an ultralow-driven temperature of 63 °C. The working performance makes EMM-8 a practical alternative to realize high-efficient ultra-low-temperature-driven refrigeration.

Metal-Organic Frameworks for Ammonia-Based Thermal Energy Storage

Recently, the application of metal-organic frameworks (MOFs) in thermal energy storage has attracted increasing research interests. MOF-ammonia working pairs have been proposed for controlling/sensing the air quality, while no work has yet been reported on the immense potential of MOFs for thermal energy storage up till now. Herein, the feasibility of thermal energy storage using seven MOF-ammonia working pairs is experimentally assessed. From ammonia sorption stability and sorption thermodynamics results, it is found that MIL-101(Cr) exhibits both high ammonia sorption stability and the largest sorption capacity of ≈0.76 g g^-1 . Compared with MIL-101(Cr)-water working pair, MIL-101(Cr)-ammonia working pair improves the sorption capacity by over three times with evaporation temperature lower than 8.4 °C. Due to stable ammonia sorption stability and negligible hysteresis, MIL-101(Cr) and ZIF-8(Zn) are tested at condensation/evaporation temperature of 30 °C/10 °C. The thermal energy storage density (reaching over 1200 kJ kg^-1 ) and coefficient of performance of MIL-101(Cr)-based system are both higher than ZIF-8(Zn)-based one due to larger average isosteric enthalpy and cycle sorption capacity. This experimental work paves the way for developing the high efficient and stable thermal energy storage system with MOF-ammonia working pairs especially for critical conditions with low evaporation temperature and high condensation temperature.

An improved water-harvesting cycle

[Figure: see text].

Efficient C2H2/CO2 Separation in Ultramicroporous Metal-Organic Frameworks with Record C2H2 Storage Density

Physical separation of C₂H₂ from CO₂ on metal-organic frameworks (MOFs) has received substantial research interest due to the advantages of simplicity, security, and energy efficiency. However, that C₂H₂ and CO₂ exhibit very close physical properties makes their separation exceptionally challenging. Previous work appeared to mostly focused on introducing open metal sites that aims to enhance the C₂H₂ affinity at desired sites, whereas the reticular manipulation of organic components has rarely been investigated. In this work, by reticulating preselected amino and hydroxy functionalities into isostructural ultramicroporous chiral MOFs-Ni₂(l-asp)₂(bpy) (MOF-NH₂) and Ni₂(l-mal)₂(bpy) (MOF-OH)-we targeted efficient C₂H₂ uptake and C₂H₂/CO₂ separation, which outperforms most benchmark materials. Explicitly, MOF-OH adsorbs substantial amount of C₂H₂ with record storage density of 0.81 g mL^-1 at ambient conditions, which even exceeds the solid density of C₂H₂ at 189 K. In addition, MOF-OH gave IAST selectivity of 25 toward equimolar mixture of C₂H₂/CO₂, which is nearly twice higher than that of MOF-NH₂. Notably, the adsorption enthalpies for C₂H₂ at zero converge in both MOFs are remarkably low (17.5 kJ mol^-1 for MOF-OH and 16.7 kJ mol^-1 for MOF-NH₂), which to our knowledge are the lowest among efficient rigid C₂H₂ sorbents. The efficiencies of both MOFs for the separation of C₂H₂/CO₂ are validated by multicycle breakthrough experiments. DFT calculations provide molecular-level insight over the adsorption/separation mechanism. Moreover, MOF-OH can survive in boiling water for at least 1 week and can be easily scaled up to kilograms eco-friendly and economically, which is very crucial for potential industrial implementation.

Metal- and halide-free, solid-state polymeric water vapor sorbents for efficient water-sorption-driven cooling and atmospheric water harvesting

Metal- and halide-free, solid-state water vapor sorbents are highly desirable for water-sorption-based applications, because most of the solid sorbents suffer from low water sorption capacity caused by their rigid porosity, while the liquid sorbents are limited by their fluidity and strong corrosivity, which is caused by the halide ions. Herein, we report a novel type of highly efficient and benign polymeric sorbent, which contains no metal or halide, and has an expandable solid state when wet. A group of sorbents are synthesized by polymerizing and crosslinking the metal-free quaternary ammonium monomers followed by an ion-exchange process to replace chloride anions with benign-anions, including acetate, oxalate, and citrate. They show significantly reduced corrosivity and improved water sorption capacity. Importantly, the water sorption capacity of the acetate paired hydrogel is among the best of the literature reported hygroscopic polymers in their pure form, even though the hydrogel is crosslinked. The hydrogel-based sorbents are further used for water-sorption-driven cooling and atmospheric water harvesting applications, which show improved coefficient of performance (COP) and high freshwater production rate, respectively. The results of this work would inspire more research interest in developing better water sorbents and potentially broaden the application horizon of water-sorption-based processes towards the water-energy nexus.

Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X-Ray Diffraction Protocol

Structurally characterizing new materials is tremendously challenging, especially when single crystal structures are hardly available which is often the case for covalent organic frameworks. Yet, knowledge of the atomic structure is key to establish structure-function relations and enable functional material design. Herein, a new protocol is proposed to unambiguously predict the structure of poorly crystalline materials through a likelihood ordering based on the X-ray diffraction (XRD) pattern. Key of the procedure is the broad set of structures generated from a limited number of building blocks and topologies, which is submitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements, yielding unparalleled agreement with experimental powder XRD patterns. The proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, a crucial step to design next generation functional materials.