Structural Diversity and Dimensionality of Three Cu(II)-dpds-C5O5 2- Coordination Polymers Controlled by the Coordination Sphere of Cu(II) Centers and the Coordination Modes of C5O5 2- (dpds = 4,4'-Dipyridyldisulfide)

Three supramolecular architectures, [Cu2(dpds)2(C5O5)2(H2O)4]·3H2O (1), [Cu(dpds)(C5O5)]·3H2O (2), and [Cu2(dpds)2(C5O5)2]·9H2O·C2H5OH (3) (dpds = 4,4'-dipyridyldisulfide and C5O5 2- (croconate) = dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), have been synthesized and structurally characterized. Compound 1 contains two crystallographically independent Cu(II) ions, which are both distorted octahedral geometry with elongation along the croconate- and H2O-bound axial positions and bonded with two N atoms of two dpds, two O atoms of one C5O5 2-, and two H2O molecules. Two crystallographically independent dpds ligands, both adopting the bis-monodentate bridging mode, connect two Cu(II) ions to form a one-dimensional zigzag chain-like coordination polymer. In 2 and 3, there are two and three crystallographically independent Cu(II) ions, respectively, which are all distorted octahedral geometries with elongation along the croconate-bound axial positions six-coordinated and bonded with two N atoms of two dpds ligands in cis- or/and trans-forms and four O atoms of two C5O5 2- ligands. The dpds ligands in 2 and 3 all adopt the bis-monodentate bridging mode, and the C5O5 2- ligands act as bridging ligands with bridging bis-bidentate through three C5O5 2- oxygen atoms in 2 and bridging bis-bidentate through four adjacent C5O5 2- oxygen atoms in 3, respectively, linking the Cu(II) ions to generate a two-dimensional layered and a three-dimensional metal-organic framework, respectively. The structural diversity and dimensionality observed in 1-3 may be attributed to the cis- or/and trans-coordination sphere of Cu(II) centers with two dpds ligands and the coordination modes of croconate ligands. Thermal stability and in situ temperature-dependent structural variations of 1-3 have been verified by thermogravimetric analysis and powder X-ray diffraction measurements. Compounds 1 and 3 both exhibit water vapor capture behaviors with hysteresis isotherms.

Enhanced water stability of MOFs via multiple hydrogen bonds and their application in water harvesting

A mechanism based on multiple hydrogen bonds was proposed to describe the great water stability of some hydrated Cu paddle-wheel-based MOFs, which was demonstrated through density functional theory (DFT) calculations and single-crystal X-ray diffraction (SCXRD) of water-loaded MOFs. This mechanism endowed Cu-TDPAT with exceptional water stability and outstanding atmospheric water harvesting capability.

How Can the Filler-Polymer Interaction in Mixed Matrix Membranes Be Enhanced?

Mixed matrix membranes (MMMs) constitute a type of molecular separation membranes in which a nanomaterial type filler is dispersed in a given polymer to enhance its selective permeation ability. The key issue in MMMs is the establishing of a proper filler-polymer interaction to avoid non-selective transport paths while increasing permeability but also to improve other membrane properties such as aging and plasticization. Along the pass years several strategies have been applied to enhance the physicochemical interaction between the fillers (e. g. silicas, zeolites, porous coordination polymers, carbonaceous materials, etc.) and the membrane polymers: increase of external surface area, priming, use of intrinsically more compatible fillers, in situ synthesis of filler, in situ polymerization, polymer side-chain modification and post-synthetic modification of filler.

Isoreticular Curves: A Theory of Capillary Condensation To Model Water Sorption within Microporous Sorbents

Metal-organic frameworks have gained traction as leading materials for water sorption applications due to precise chemical tunability of their well-ordered pores. These applications include atmospheric water capture, heat pumps, desiccation, desalination, humidity control, and thermal batteries. However, the relationships between the framework pore structure and the measurable water sorption properties, namely critical relative humidity for condensation, maximal capacity, and pore size or temperature for the onset of hysteresis, have not been clearly delineated. Herein, we precisely formulate these relationships by application of the theory of capillary condensation and macroscopic thermodynamic models to a large data set of MOF water isotherms. These relationships include a concept termed isoreticular curves that relates the critical pressure for pore condensation (α), gravimetric capacity (Qmax), and hydrophilicity (the Gibbs free energy for binding water, ΔG) as Qmax = a1(ΔG/ln α)2 + a2(ΔG/ln α), with constants a1 and a2 dependent upon the density and volume occupied by the linker and secondary building unit, and framework topology. Through this analysis, we propose guidelines for the maximization of sorption capacity at a given relative humidity with minimal hysteresis and discuss the theoretical limits for capacity at low relative humidity. This model provides an explanation for the lack of high-capacity frameworks at low relative humidity, as increasing pore size also causes an increase in relative humidity. We propose a loose upper bound of Qmax = -0.25(1/ln α)2 - 1.75(1/ln α) for the limit of maximal capacity at a given relative humidity in the dry regime. These guidelines are consequential for the design of new materials for water sorption applications.

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.

Engineering Porosity and Functionality in a Robust Twofold Interpenetrated Bismuth-Based MOF: Toward a Porous, Stable, and Photoactive Material

Defect engineering in metal-organic frameworks (MOFs) has gained worldwide research traction, as it offers tools to tune the properties of MOFs. Herein, we report a novel 2-fold interpenetrated Bi-based MOF made of a tritopic flexible organic linker, followed by missing-linker defect engineering. This procedure creates a gradually augmented micro- and mesoporosity in the parent (originally nonporous) network. The resulting MOFs can tolerate a remarkable extent of linker vacancy (with absence of up to 60% of linkers per Bi node) created by altering the crystal-growth rate as a function of synthesis temperature and duration. Owing to the enhanced porosity and availability of the uncoordinated Lewis acidic Bi sites, the defect-engineered MOFs manifested improved surface areas, augmented CO2 and water vapor uptake, and catalytic activity. Parallel to this, the impact of defect engineering on the optoelectronic properties of these MOFs has also been studied, offering avenues for new applications.

Amino-Functionalizing Ce-Based MOF UiO-66 for Enhanced CO2 Adsorption and Selectivity

Metal-organic frameworks (MOF) hold great promise for CO2 adsorption due to their high surface areas, tunable pore sizes, and the ability to modify their chemical properties to enhance CO2 affinity. MOFs tagged with functional groups either at linker or metal sites have shown improved CO2 uptake capacity and selectivity. This study focuses on investigating the potential of selective CO2 adsorption using amino functionalization of linker forming Ce-UiO-66. The physicochemical properties and characteristics of MOFs to determine the degree of amino functionalization and structural stability were examined using powder X-ray diffraction (PXRD), Fourier transformer infra-red (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and N2 porosimetry and specific surface area (BET). This work unveils a novel array of results on CO2, N2 and water vapour adsorption on Ce-UiO-66-NH2. The amino-functionalized Ce-UiO-66-NH2 shows 63 % higher CO2 uptake and 84 % higher CO2/N2 selectivity at 273 K and 1 bar over Ce-UiO-66. Ce-UiO-66-NH2 also shows excellent structural stability after gas and vapour sorption making Ce-UiO-66-NH2 potential adsorbent for CO2 capture.

Molecular driving forces for water adsorption in MOF-808: A comparative analysis with UiO-66

Metal-organic frameworks (MOFs), with their unique porous structures and versatile functionality, have emerged as promising materials for the adsorption, separation, and storage of diverse molecular species. In this study, we investigate water adsorption in MOF-808, a prototypical MOF that shares the same secondary building unit (SBU) as UiO-66, and elucidate how differences in topology and connectivity between the two MOFs influence the adsorption mechanism. To this end, molecular dynamics simulations were performed to calculate several thermodynamic and dynamical properties of water in MOF-808 as a function of relative humidity (RH), from the initial adsorption step to full pore filling. At low RH, the μ3-OH groups of the SBUs form hydrogen bonds with the initial water molecules entering the pores, which triggers the filling of these pores before the μ3-OH groups in other pores become engaged in hydrogen bonding with water molecules. Our analyses indicate that the pores of MOF-808 become filled by water sequentially as the RH increases. A similar mechanism has been reported for water adsorption in UiO-66. Despite this similarity, our study highlights distinct thermodynamic properties and framework characteristics that influence the adsorption process differently in MOF-808 and UiO-66.

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.

Metal-Organic Frameworks for Water Harvesting and Concurrent Carbon Capture: A Review for Hygroscopic Materials

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure-performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal-organic frameworks (MOFs) for their excellent performance in water and CO2 adsorption, and representative role of micro- and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO2 adsorption are reviewed. This review summarizes recent advances in water-harvesting porous materials with special attention on MOFs and expects to direct researchers' attention into the topic of concurrent water harvesting and carbon capture as a future challenge.

Hydrovoltaic Electricity Generator with Hygroscopic Materials: A Review and New Perspective

The global energy crisis caused by the overconsumption of nonrenewable fuels has prompted researchers to develop alternative strategies for producing electrical energy. In this review, a fascinating strategy that simply utilizes water, an abundant natural substance throughout the globe and even in air as moisture, as a power source is introduced. The concept of the hydrovoltaic electricity generator (HEG) proposed herein involves generating an electrical potential gradient by exposing the two ends of the HEG device to dissimilar physicochemical environments, which leads to the production of an electrical current through the active material. HEGs, with a large variety of viable active materials, have much potential for expansion toward diverse applications including permanent and/or emergency power sources. In this review, representative HEGs that generate electricity by the mechanisms of diffusion, streaming, and capacitance as case studies for building a fundamental understanding of the electricity generation process are discussed. In particular, by comparing the use and absence of hygroscopic materials, HEG mechanism studies to establish active material design principles are meticulously elucidated. The review with future perspectives on electrode design using conducting nanomaterials, considerations for high performance device construction, and potential impacts of the HEG technology in improving the livelihoods are reviewed.

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.

Chiral Reticular Chemistry: A Tailored Approach Crafting Highly Porous and Hydrolytically Robust Metal-Organic Frameworks for Intelligent Humidity Control

Control of humidity within confined spaces is critical for maintaining air quality and human well-being, with implications for environments ranging from international space stations and pharmacies to granaries and cultural relic preservation sites. However, existing techniques rely on energy-intensive electrically driven equipment or complex temperature and humidity control (THC) systems, resulting in imprecision and inconvenience. The development of innovative techniques and materials capable of simultaneously meeting the stringent requirements of practical applications holds the key to creating intelligent and energy-efficient humidity control devices. In this study, we introduce chiral reticular chemistry as a tailored synthetic approach, targeting a highly porous hea topological framework characterized by intrinsic interpenetrating pore architecture. This groundbreaking design successfully circumvents the traditional compromise between the pore volume and hydrolytic stability. Our metal-organic framework (MOF) exhibits an extraordinary working capacity, setting a new record at 1.35 g g-1 within the relative humidity (RH) range of 40-60%, without exhibiting hysteresis. Consequently, it emerges as a state-of-the-art candidate for intelligent humidity regulation within confined spaces. Utilizing single-crystal X-ray measurements and molecular simulations, we unequivocally elucidate the mechanism of water clustering and pore filling, underscoring the pivotal role of the linker functionality in governing the water seeding process. Our findings represent a significant advancement in the field, paving the way for the development of highly efficient humidity control technologies and offering promising solutions for diverse real-world scenarios.

Connectivity Analysis of Adsorption Sites in Metal-Organic Frameworks for Facilitated Water Adsorption

Metal-organic frameworks (MOFs) have recently drawn considerable attention as promising adsorbents to harvest atmospheric water. To achieve an efficient harvesting process, seeking MOFs that demonstrate sharp condensation behavior is the key. Given that the clustering of water molecules in MOFs should be driven by not only MOF-water interactions but also water-water interactions, the spatial arrangement of water adsorption sites in a MOF is therefore crucial. Specifically, this study demonstrates the critical role of continuous adsorption channels (CACs) in MOFs. Such CACs will enable water molecules to stay in proximity and in a continuous manner, thus promoting the formation of hydrogen bonds and, consequently, the clustering of water molecules. We have developed an automatic algorithm to detect CACs based on the energy grid of host-guest interactions and applied the algorithm to more than 2000 diverse structures. The results show that more than 80% of the studied MOFs displaying water condensation at 298 K and 20% relative humidity predicted by Monte Carlo simulations indeed have CACs. The developments herein are anticipated to largely facilitate the future discovery of optimal adsorbents for water harvesting or water-adsorption-related applications in general. A Python-based code for detecting CACs in porous materials is also provided along with this article to employ this approach.

Sorption-Based Atmospheric Water Harvesting: Materials, Components, Systems, and Applications

Freshwater scarcity is a global challenge posing threats to the lives and daily activities of humankind such that two-thirds of the global population currently experience water shortages. Atmospheric water, irrespective of geographical location, is considered as an alternative water source. Sorption-based atmospheric water harvesting (SAWH) has recently emerged as an efficient strategy for decentralized water production. SAWH thus opens up a self-sustaining source of freshwater that can potentially support the global population for various applications. In this review, the state-of-the-art of SAWH, considering its operation principle, thermodynamic analysis, energy assessment, materials, components, different designs, productivity improvement, scale-up, and application for drinking water, is first extensively explored. Thereafter, the practical integration and potential application of SAWH, beyond drinking water, for wide range of utilities in agriculture, fuel/electricity production, thermal management in building services, electronic devices, and textile are comprehensively discussed. The various strategies to reduce human reliance on natural water resources by integrating SAWH into existing technologies, particularly in underdeveloped countries, in order to satisfy the interconnected needs for food, energy, and water are also examined. This study further highlights the urgent need and future research directions to intensify the design and development of hybrid-SAWH systems for sustainability and diverse applications.

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.

MIL-101(Cr)@QCM and MIL-101(Cr)@IDE as Sorbent-Based Humidity Sensors for Indoor Air Monitoring

MIL-101(Cr) films were deposited on the quartz crystal microbalance and interdigitated electrode transductors as humidity sensors. Both devices combine high sensitivity with fast response/recovery times, good repeatability, long-term stability, favorable selectivity versus toluene alongside a dual mode behavior in the optimal domain of humidity for indoor air.

High-Concentration Self-Assembly of Zirconium- and Hafnium-Based Metal-Organic Materials

Metal-organic frameworks (MOFs) are crystalline, porous solids constructed from organic linkers and inorganic nodes that are promising for applications in chemical separations, gas storage, and catalysis, among many others. However, a major roadblock to the widespread implementation of MOFs, including highly tunable and hydrolytically stable Zr- and Hf-based frameworks, is their benchtop-scalable synthesis, as MOFs are typically prepared under highly dilute (≤0.01 M) solvothermal conditions. This necessitates the use of liters of organic solvent to prepare only a few grams of MOF. Herein, we demonstrate that Zr- and Hf-based frameworks (eight examples) can self-assemble at much higher reaction concentrations than are typically utilized, up to 1.00 M in many cases. Combining stoichiometric amounts of Zr or Hf precursors with organic linkers at high concentrations yields highly crystalline and porous MOFs, as confirmed by powder X-ray diffraction (PXRD) and 77 K N2 surface area measurements. Furthermore, the use of well-defined pivalate-capped cluster precursors avoids the formation of ordered defects and impurities that arise from standard metal chloride salts. These clusters also introduce pivalate defects that increase the exterior hydrophobicity of several MOFs, as confirmed by water contact angle measurements. Overall, our findings challenge the standard assumption that MOFs must be prepared under highly dilute solvothermal conditions for optimal results, paving the way for their scalable and user-friendly synthesis in the laboratory.

Carbon monoxide separation: past, present and future

Large amounts of carbon monoxide are produced by industrial processes such as biomass gasification and steel manufacturing. The CO present in vent streams is often burnt, this produces a large amount of CO2, e.g., oxidation of CO from metallurgic flue gasses is solely responsible for 2.7% of manmade CO2 emissions. The separation of N2 from CO due to their very similar physical properties is very challenging, meaning that numerous energy-intensive steps are required for CO separation, making the CO separation from many process streams uneconomical in spite of CO being a valuable building block in the production of major chemicals through C1 chemistry and the production of linear hydrocarbons by the Fischer-Tropsch process. The development of suitable processes for the separation of carbon monoxide has both industrial and environmental significance. Especially since CO is a main product of electrocatalytic CO2 reduction, an emerging sustainable technology to enable carbon neutrality. This technology also requires an energy-efficient separation process. Therefore, there is a great need to develop energy efficient CO separation processes adequate for these different process streams. As such the urgency of separating carbon monoxide is gaining greater recognition, with research in the field becoming more and more crucial. This review details the principles on which CO separation is based and provides an overview of currently commercialised CO separation processes and their limitations. Adsorption is identified as a technology with the potential for CO separation with high selectivity and energy efficiency. We review the research efforts, mainly seen in the last decades, in developing new materials for CO separation via ad/bsorption and membrane technology. We have geared our review to both traditional CO sources and emerging CO sources, including CO production from CO2 conversion. To that end, a variety of emerging processes as potential CO2-to-CO technologies are discussed and, specifically, the need for CO capture after electrochemical CO2 reduction is highlighted, which is still underexposed in the available literature. Altogether, we aim to highlight the knowledge gaps that could guide future research to improve CO separation performance for industrial implementation.

Monolithic Zirconium-Based Metal-Organic Frameworks for Energy-Efficient Water Adsorption Applications

Space cooling and heating, ventilation, and air conditioning (HVAC) accounts for roughly 10% of global electricity use and are responsible for ca. 1.13 gigatonnes of CO₂ emissions annually. Adsorbent-based HVAC technologies have long been touted as an energy-efficient alternative to traditional refrigeration systems. However, thus far, no suitable adsorbents have been developed which overcome the drawbacks associated with traditional sorbent materials such as silica gels and zeolites. Metal-organic frameworks (MOFs) offer order-of-magnitude improvements in water adsorption and regeneration energy requirements. However, the deployment of MOFs in HVAC applications has been hampered by issues related to MOF powder processing. Herein, three high-density, shaped, monolithic MOFs (UiO-66, UiO-66-NH₂ , and Zr-fumarate) with exceptional volumetric gas/vapor uptake are developed-solving previous issues in MOF-HVAC deployment. The monolithic structures across the mesoporous range are visualized using small-angle X-ray scattering and lattice-gas models, giving accurate predictions of adsorption characteristics of the monolithic materials. It is also demonstrated that a fragile MOF such as Zr-fumarate can be synthesized in monolithic form with a bulk density of 0.76 gcm^-3 without losing any adsorption performance, having a coefficient of performance (COP) of 0.71 with a low regeneration temperature (≤ 100 °C).

Modelling toluene sorption in ionic liquid/metal organic framework composite materials

Toluene is a prevalent pollutant in indoor environments and its removal is essential to maintain a healthy environment. Adsorption is one of the best alternatives for organic vapours removal, specially at low indoor concentrations. Metal Organic Frameworks (MOFs) and Ionic Liquids (ILs) are potential materials for this mean. In this work, the synthesis and application of IL/MOF composite materials for toluene removal is reported. Loading [BMIM][CH₃COO] ionic liquid into MIL101 porous structure improves parent materials affinity towards toluene capture by two orders of magnitude (as Henry's constants, attesting to their synergy). MIL101(Cr) and absorption in [BMIM][CH₃COO] IL is best described by Henry's Law, while the Langmuir adsorption model predicts toluene adsorption on [BMIM][CH₃COO]/MIL101(Cr) better than Freundlich and Toth equations. Diffusional and kinetics models revealed that toluene diffusion is the rate limiting step for pristine MIL101. Kinetic and diffusion rates were systematically improved upon the incorporation of the ionic liquid due to shorter toluene hops with the adsorbed IL and the increased hydrophobicity in the composites making the sorption more favourable. This study provides a systematic analysis and modelling of the toluene capture process in IL/MOF composites aiding a better understanding of the sorption process in these novel materials.

Water-Harvesting Metal-Organic Frameworks with Gigantic Al24 Units and their Deconstruction into Molecular Clusters

In contrast to the vast Al-oxo molecular cluster chemistry, Al-based building units for metal-organic framework (MOF) construction are limited in structural diversity and complexity. Synthesis of single crystalline MOFs based on this "hard" metal is further complicated by the poor reversibility of the Al-organic coordination linkages. Here, a strategy to employ two kinds of linkages with distinct strength-strong Al-carboxylate linkage and weak Cu-pyrazol N linkage-gives FDM-91 (FDM=Fudan Materials) with gigantic Al₂₄ -based units. After replacing the weak moieties with organic linkers post-synthetically, two new stable MOFs with exceptional water harvesting capacity (up to 0.53 g g^-1 ) and outstanding cycling performance are developed. Linkage-selective dissociation of FDM-91 further leads to the isolation of the Al₂₄ molecular clusters. The versatile chemistry performed here to reinforce or deconstruct MOFs provides a new way to make important extended and discrete structures.

MOF/MWCNT-Nanocomposite Manipulates High Selectivity to Gas via Different Adsorption Sites with Varying Electron Affinity: A Study in Methane Detection in Parts-per-Billion

Metal-organic frameworks (MOFs) present specific adsorption sites with varying electron affinity which are uniquely conducive to selective gas sensing but are typically large-band-gap insulators. On the contrary, multiwall carbon nanotubes (MWCNTs) exhibit superior mesoscopic transport exploiting strong electron correlations among sub-bands below and above the Fermi level at room temperature. We synergize them in a new class of nanocomposites based on zeolitic imidazolate framework-8 (ZIF-8) and report selective sensing of CH₄ in ∼10 parts-per-billion (ppb) with a determined limit of detection of ∼0.22 ppb, hitherto unprecedented. The observed selectivity to CH₄ over non-polar CO₂, polar volatile organic compounds, and moisture has roots in competing electron-sharing mechanisms at its different adsorption sites. This important result provides a significant reference to guide future MOF-related composite research to achieve the best sensing performance. On molecular adsorption, MWCNTs facilitate electrical transport via manipulating the ZIF-8 band gap to show a p-type semiconductor behavior with lower activation energy to induce a measurable resistance change. Excellent repeatability and reversibility are shown. A carbon-engineered MOF composite has the potential to actuate similar selective response to low reactive gases via carrier manipulation in the energy band gap.

Defect-induced tuning of polarity-dependent adsorption in hydrophobic-hydrophilic UiO-66

Structural defects in metal-organic frameworks can be exploited to tune material properties. In the case of UiO-66 material, they may change its nature from hydrophobic to hydrophilic and therefore affect the mechanism of adsorption of polar and non-polar molecules. In this work, we focused on understanding this mechanism during adsorption of molecules with different dipole moments, using the standard volumetric adsorption measurements, IR spectroscopy, DFT + D calculations, and Monte Carlo calculations. Average occupation profiles showed that polar and nonpolar molecules change their preferences for adsorption sites. Hence, defects in the structure can be used to tune the adsorption properties of the MOF as well as to control the position of the adsorbates within the micropores of UiO-66.

Recent developments in MOF and MOF based composite as potential adsorbents for removal of aqueous environmental contaminants

With the growth of globalization which has been the primary cause of water pollution, it is utmost necessary for us living being to have access to clean water for the purpose of drinking, washing and various other useful applications. With the purpose of future security and to restore our ecological balance, it is essential to give much significance towards the removal of unwanted toxic contaminants from our water resources. In this regard adsorptive removal of toxic pollutants from wastewater with porous adsorbent is regarded as one of the most promising way for water decontamination process. Metal organic frameworks (MOFs) comprising of uniformly arranged pores, abundant active sites and containing an easily tunable structure has aroused as a promising material for adsorbent to remove the unwanted contaminants from water sources. The adsorption of pollutants by the different MOFs surface are driven by various interactions including π-π, acid-base, electrostatic and H-bonding etc. On the other hand, the removal of various contaminants by MOFs is influenced by various factors including pH, temperature and initial concentration. In this review we will specifically discuss the adsorptive removal of different organic and inorganic pollutants present in our water systems with the use of MOFs as adsorbent along with the various factors and interaction mechanism manipulating the adsorption behaviour.

Synthesis and Characterization of the Metal–Organic Framework CIM-80 for Organic Compounds Adsorption

Metal–organic frameworks (MOF) are a new type of porous materials that have great potential for adsorption of voltaic organic compounds (VOCs). These types of materials composed of metal ions and organic ligands are easy to synthesize, have high surface areas, their surface chemistry can be adjusted to the desired application, and they can also have good chemical and thermal stability. Therefore, this work focuses on the synthesis of a highly hydrophobic MOF material called CIM-80, a porous material that is made up of the Al³⁺ cation and the mesaconate linker. This MOF has a B.E.T. of approximately 800 m²/g and has potential applications for the adsorption of hydrophobic organic compounds. However, its synthesis is expensive and very dirty. Therefore, we have studied the synthesis conditions necessary to achieve high synthesis yields (85%) and materials with high crystallinity and accessible porosity. To achieve these results, we have used urea as a mild deprotonation reagent and modulator as an alternative to NaOH, which is traditionally used for the synthesis of this MOF. Once the synthesis of this material was controlled, its adsorption/desorption behavior of water and organic compounds such as toluene, cyclohexane and m-xylene was studied by means of vapor adsorption isotherms. The results show the hydrophobic character of the material and the greater affinity the material has toward aliphatic compounds than toward aromatic ones, with toluene being the most adsorbed compound, followed by cyclohexane and m-xylene.

Porous Colloidal Nanoparticles as Injectable Multimodal Contrast Agents for Enhanced Geophysical Sensing

Injecting fluids into underground geologic structures is crucial for the development of long-term strategies for managing captured carbon and facilitating sustainable energy extraction operations. We have previously reported that the injection of metal-organic frameworks (MOFs) into the subsurface can enhance seismic monitoring tools to track fluids and map complex structures, reduce risk, and verify containment in carbon storage reservoirs because of their absorption capacity of low-frequency seismic waves. Here, we demonstrate that water-based Cr/Zn/Zr MOF colloidal suspensions (nanofluids) are multimodal geophysical contrast agents that enhance near-wellbore logging tools. Based on experimental fluid-only measurements, MIL-101(Cr), ZIF-8, and UiO-66 nanofluids have distinct complex conductivity and/or low-field nuclear magnetic resonance (NMR) signatures that are relevant to field-deployed technologies, implying the potential to enhance near-wellbore monitoring of CO2 injection and associated processes with downhole logging tools. Small- and wide-angle X-ray scattering characterization of ∼0.5 wt % MIL-101(Cr) suspensions confirmed phase stability and provided insight into the fractal nature of colloidal nanoparticles. Finally, low-field (2 MHz) NMR measurements of MIL-101(Cr) nanofluid injection into a prototypical Berea sandstone demonstrate how paramagnetic high-surface area MOFs may dominate the relaxation times of hydrogen-bearing fluids in porous geologic matrices, enhancing the mapping of near-surface and near-wellbore transport pathways and advancing sustainable subsurface energy technologies.

Homochiral Eu3+@MOF Composite for the Enantioselective Detection and Separation of (R/S)-Ornidazole

The development of homochiral materials for the enantioselective detection and separation of chiral drugs is in high demand for the pharmaceutical industry. Herein, an anionic homochiral metal-organic framework (HMOF) with in situ generated [Me₂NH₂]⁺ counterions, {[Me₂NH₂]₂[Zn₂(d-L)₂(HCO₂)(OH)]·5H₂O}_n (HMOF-1), was synthesized using a d-camphorate-derived enantiopure dicarboxylate ligand, 4,4'-[[(1R,3S)-1,2,2-trimethylcyclopentane-1,3-dicarbonyl]bis(azanediyl)]dibenzoic acid (d-H₂L) via a simple solvothermal method. Interestingly, HMOF-1 could be used as a parent framework to encapsulate Eu³⁺ cations via an ion-exchange process, yielding an Eu³⁺@HMOF-1 composite with dual-luminescent centers. The obtained Eu³⁺@HMOF-1 has high chemical stability and good luminescence stability in water. Importantly, Eu³⁺@HMOF-1 exhibits enhanced enantioselectivity and sensitivity in the detection of an important chiral nitroimidazole antibiotic, (R/S)-ornidazole (ONZ) in comparison to HMOF-1 under the same aqueous conditions. The enantiomeric excess (ee) value of the ONZ enantiomers can be accurately determined by the ratio of dual emission from the ligand and Eu³⁺. In addition, Eu³⁺@HMOF-1 shows the enantioselective separation of racemic ONZ enantiomers with an ee value of 86.6%. This work provides a simple strategy for the preparation of Ln^III-incorporated HMOF composite materials for the simultaneous enantioselective detection and separation of chiral drugs.

Atmospheric Water Harvesting by Large-Scale Radiative Cooling Cellulose-Based Fabric

Atmospheric water harvesting (AWH) has received tremendous interest because of population growth, limited freshwater resources, and water pollution. However, key challenges remain in developing efficient, flexible, and lightweight AWH materials with scalability. Here, we demonstrated a radiative cooling fabric for AWH via its hierarchically structured cellulose network and hybrid sorption-dewing mechanisms. With 8.3% solar absorption and ∼0.9 infrared (IR) emissivity, the material can drop up to 7.5 °C below ambient temperature without energy consumption via radiative cooling. Water adsorption onto the hydrophilic functional groups of cellulose is dominated by sorption at low relative humidity (RH) and dewing at high RH. The cellulose network provides desirable mechanical properties with entangled high-aspect-ratio fibers over tens of adsorption-extraction cycles. In the field test, the cellulose sample exhibited water uptake of 1.29 kg/kg at 80% RH during the night. The profusion of radiative cooling fabric features desirable cost effectiveness and allows fast deployment into large-scale AWH applications.

Ethylene dimethacrylate used as an NH3 adsorbent with high adsorption capacity and selectivity

NH₃ molecularly imprinted polymers (NH₃-MIPs) were synthesized that could successfully separate and recover NH₃ during sludge aerobic composting; however, increased toluene usage during the adsorbent preparation incurred a high cost and severe environmental risks. The purpose of this study was to reduce toluene usage by optimizing the reagent composition of NH₃-MIPs, based on maintaining a high NH₃ adsorption capacity and selectivity. Five adsorbent groups, including NH₃-MIPs, and NH₃-Ethylene dimethacrylate adsorbents (NH₃-EGDMA) with 0%, 75%, 90%, and 100% toluene reduction efficiencies, were prepared and tested for their adsorption performance. The results showed that NH₃-EGDMA with 75% toluene reduction not only had a high NH₃ adsorption capacity (104.42 mg g^-1) but also had a high separation factor for NH₃/methyl sulfide (3121) and NH₃/dimethyl disulfide (4597). The adsorption mechanism was identified as a chemical force between NH₃ and NH₃-EGDMA with a 75% toluene reduction using the analysis of the kinetic model. This study significantly reduces NH₃ adsorbent cost as well as harm to the environment during the adsorbent preparation, which was beneficial to the popularization and application of this NH₃ adsorbent.

Finding the Sweet Spot of Photocatalysis─A Case Study Using Bipyridine-Based CTFs

Covalent triazine frameworks (CTFs) are a class of porous organic polymers that continuously attract growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic framework structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far. Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows us to tailor the physicochemical features of the CTF materials, including the nitrogen content, the apparent specific surface area, and optoelectronic properties. Based on a comprehensive analytical investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as the specific surface area, band gap, charge separation, and surface wettability with water. The entirety of these parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER). The material with the optimal balance between optoelectronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol/(h·g) under visible light irradiation and in the presence of a platinum cocatalyst.

Validation of two contrasting capturing mechanisms for gaseous formaldehyde between two different types of strong metal-organic framework adsorbents

In this research, the adsorption behavior of formaldehyde (FA) onto two types of metal-organic frameworks (MOFs: MOF-199 [M199] and UiO-66-NH₂ [U6N]) is investigated against changes in the key process variables (e.g., FA partial pressure (0.5-10 Pa), temperature (30-120 °C), and relative humidity (RH: 0%, 50%, and 100%)). The results revealed that the FA adsorption behavior onto both MOFs is exothermic in nature. Besides, their relative dominance for FA uptake varies interactively with the changes in RH and FA partial pressure levels. As the FA levels increase in dry conditions, their breakthrough volumes (BTV (100% BT)) exhibit contrasting trends: The values of U6N decreased noticeably from 5232 and 3792 L·atm·g^-1, while those of M199 increased from 4152 to 5772 L·atm·g^-1. The superiority of U6N over M199 in the lower FA level (at<5 Pa) is supported by the Lewis acid-base interactions with amine groups (U6N) in line with kinetic/isotherm studies. Such superiority is also persistent at higher (10 Pa) FA level under all humid conditions in line with its higher moisture stability. However, in dry conditions, the reversal of relative dominance in which M199 exhibits enhanced efficacy for 10 Pa FA uptake (relative to U6N) should reflect its breathing effects with the potent role of pore-diffusion mechanism. This study offers valuable insights into the construction of tunable adsorbents with enhanced adsorptivity toward key targets.

Dissecting the effects of water guest adsorption and framework breathing on the AlO4(OH)2 centres of metal-organic framework MIL-53 (Al) by solid state NMR and structural analysis

The relationship between the adsorption of water on MIL-53 (Al) MOF, the structural phase of MIL-53 (Al), and the quadrupole coupling constant of ²⁷Al framework aluminium atom (QCC) of the MOF AlO₄(OH)₂ centres (Al-sites) has been investigated by combining solid-state ²⁷Al MAS NMR spectroscopy with XRD analysis and DFT calculations. It is established that ²⁷Al QCC is primarily sensitive to water adsorption to the Al-sites and by a minor extent to the framework contraction/expansion interconversions. We thus conclude that the ²⁷Al MAS NMR method is sensitive enough to differentiate the effects of pore contractions and water adsorption to Al-sites basing on the changes of the QCC value.

Non-injective gas sensor arrays: identifying undetectable composition changes

Metal-organic frameworks (MOFs) are nanoporous materials with good prospects as recognition elements for gas sensors owing to their adsorptive sensitivity and selectivity. A gravimetric, MOF-based sensor functions by measuring the mass of gas adsorbed in a MOF. Changes in the gas composition are expected to produce detectable changes in the mass of gas adsorbed in the MOF. In practical settings, multiple components of the gas adsorb into the MOF and contribute to the sensor response. As a result, there are typically many distinct gas compositions that produce the same single-sensor response. The response vector of a gas sensor array places multiple constraints on the gas composition. Still, if the number of degrees of freedom in the gas composition is greater than the number of MOFs in the sensor array, the map from gas compositions to response vectors will be non-injective (many-to-one). Here, we outline a mathematical method to determine undetectable changes in gas composition to which non-injective gas sensor arrays are unresponsive. This is important for understanding their limitations and vulnerabilities. We focus on gravimetric, MOF-based gas sensor arrays. Our method relies on a mixed-gas adsorption model in the MOFs comprising the sensor array, which gives the mass of gas adsorbed in each MOF as a function of the gas composition. The singular value decomposition of the Jacobian matrix of the adsorption model uncovers (i) the unresponsive directions and (ii) the responsive directions, ranked by sensitivity, in gas composition space. We illustrate the identification of unresponsive subspaces and ranked responsive directions for gas sensor arrays based on Co-MOF-74 and HKUST-1 aimed at quantitative sensing of CH₄/N₂/CO₂/C₂H₆mixtures relevant to natural gas sensing.

Large breathing effect induced by water sorption in a remarkably stable nonporous cyanide-bridged coordination polymer

While metal-organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)]2[Mo(CN)8]} n (1Mn; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known - the cyanide. The sorption performance of {[Mn(imH)]2[Mo(CN)8]} n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H2O by 1Mn switches the EPR signal intensity of the MnII centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [MoIV(CN)8]4- photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character (e.g. photomagnetism and long-range magnetic ordering).

High Proton Conductivity in Nafion/Ni-MOF Composite Membranes Promoted by Ligand Exchange under Ambient Conditions

Metal-organic frameworks (MOFs) have appeared to be promising competitive candidates as crystalline porous materials for proton conduction. Explorations of the method of preparation of proton conductive MOFs and the proton transfer mechanism have enabled them to attract widespread attention, and tremendous efforts have been made to improve the proton conductivity of MOFs. On the basis of our previous work, we explicitly propose that ligand exchange can upgrade the proton conduction performance of MOFs. Using MOF-azo as the precursor, the proton conductivities of exchange products MOF-bpy and MOF-bpe increase by 3.5- and 2.8-fold, respectively. After the MOFs had been doped into the Nafion matrix to prepare composite membranes, the proton conduction performance of composite membranes filled with subproducts (2.6 × 10^-2 and 1.95 × 10^-2 S cm^-1) is significantly better than that of a composite membrane filled with a parent product (1.12 × 10^-2 S cm^-1) under ambient conditions (without heating or humidifying). The ligand exchange strategy presented herein demonstrates great promise for the development of high-proton conductivity MOFs and MOF composites with expanded future applications.

Enhanced ammonia adsorption and separation by a molecularly imprinted polymer after acid hydrolysis of its ester crosslinker

While ammonia (NH₃) is one of the primary hazardous emissions from sludge aerobic composting plants, it has the potential to be recycled as an energy source or nitrogen fertilizer. Recently, an NH₃ molecularly imprinted polymer (NH₃-MIP) was developed that efficiently separated NH₃ from other compounds, but its adsorption capacity required improvement. This study improved both NH₃ adsorption capacity and separation of the NH₃-MIP using acid hydrolysis optimization. NH₃ adsorption capacity increased 13-fold and remained between 5.59 and 7.84 mmol·g^-1 during simulated sludge aerobic composting. Separation factors for NH₃/methyl sulfide (DMS) (i.e. NH₃ adsorption capacity/DMS adsorption capacity) and NH₃/dimethyl disulfide both increased more than 15-fold. Results showed that hydrolysis of the ester crosslinker, ethylene glycol dimethacrylate, on the NH₃-MIPs produced chemical adsorption sites (‒COOH and epoxides) and increased hydrogen bonds (‒COOH and alcohol hydroxyl), which promoted NH₃ adsorption and separation. It is expected that this will be a beneficial strategy for elimination of odors and NH₃ recovery during sludge aerobic composting.

Metal-Dependent and Selective Crystallization of CAU-10 and MIL-53 Frameworks through Linker Nitration

The reaction of the V-shaped linker molecule 5-hydroxyisophthalic acid (H2 L0 ), with Al or Ga nitrate under almost identical reaction conditions leads to the nitration of the linker and subsequent formation of metal-organic frameworks (MOFs) with CAU-10 or MIL-53 type structure of composition [Al(OH)(L)], denoted as Al-CAU-10-L0, 2, 4, 6 or [Ga(OH)(L)], denoted as Ga-MIL-53-L2 . The Al-MOF contains the original linker L0 as well as three different nitration products (L2 , L4 and L4/6 ), whereas the Ga-MOF mainly incorporates the linker L2 . The compositions were deduced by 1 H NMR spectroscopy and confirmed by Rietveld refinement. In situ and ex situ studies were carried out to follow the nitration and crystallization, as well as the composition of the MOFs. The crystal structures were refined against powder X-ray diffraction (PXRD) data. As anticipated, the use of the V-shaped linker results in the formation of the CAU-10 type structure in the Al-MOF. Unexpectedly, the Ga-MOF crystallizes in a MIL-53 type structure, which is usually observed with linear or slightly bent linker molecules. To study the structure directing effect of the in situ nitrated linker, pure 2-nitrobenzene-1,3-dicarboxylic acid (m-H2 BDC-NO2 ) was employed which exclusively led to the formation of [Ga(OH)(C8 H3 NO6 )] (Ga-MIL-53-m-BDC-NO2 ), which is isoreticular to Ga-MIL-53-L2 . Density Functional Theory (DFT) calculations confirmed the higher stability of Ga-MIL-53-L2 compared to Ga-CAU-10-L2 and grand canonical Monte Carlo simulations (GCMC) are in agreement with the observed water adsorption isotherms of Ga-MIL-53-L2 .