Metal-Organic Frameworks for Water Harvesting from Air

Emissive Substoichiometric Covalent Organic Frameworks for Water Sensing and Harvesting

Emissive covalent organic frameworks (COFs) have recently emerged as next-generation porous materials with attractive properties such as tunable topology, porosity, and inherent photoluminescence. Among the different types of COFs, substoichiometric frameworks (so-called Type III COFs) are especially attractive due to the possibility of not only generating unusual topology and complex pore architectures but also facilitating the introduction of well-defined functional groups at precise locations for desired functions. Herein, the first example of a highly emissive (PLQY 6.8%) substoichiometric 2D-COF (COF-SMU-1) featuring free uncondensed aldehyde groups is reported. In particular, COF-SMU-1 features a dual-pore architecture with an overall bex net topology, tunable emission in various organic solvents, and distinct colorimetric changes in the presence of water. To gain further insights into its photoluminescence properties, the charge transfer, excimer emission, and excited state exciton dynamics of COF-SMU-1 are investigated using femtosecond transient absorption spectroscopy in different organic solvents. Additionally, highly enhanced atmospheric water-harvesting properties of COF-SMU-1 are revealed using FT-IR and water sorption studies.The findings will not only lead to in-depth understanding of structure-property relationships in emissive COFs but also open new opportunities for designing COFs for potential applications in solid-state lighting and water harvesting.

Self-recovering passive cooling utilizing endothermic reaction of NH4NO3/H2O driven by water sorption for photovoltaic cell

Power efficiency of photovoltaic cell is significantly affected by the cell temperature. Here, a self-recovering passive cooling unit is developed. The water-saturated zeolite 13X is coated on the back side of photovoltaic cell, and ammonium nitrate is dispersed as a layer to form a thin film. When heat is supplied, water is desorbed from zeolite 13X (latent cooling), and dissolves ammonium nitrate to induce endothermic reaction cooling. It is a reversible process that recovers itself at night. The unit works on the basis that the water sorption performance of porous materials is inversely proportional to temperature, and the solubility of endothermic reaction pairs increases proportionally with temperature. The average temperature of photovoltaic cell can be reduced by 15.1 °C, and the cooling energy density reaches 2,876 kJ/kg with average cooling power of 403 W/m². We show that highly efficient passive cooling comprising inexpensive materials for photovoltaic cell could be achieved.

3D Solar Evaporation Enhancement by Superhydrophilic Copper Foam Inverted Cone and Graphene Oxide Functionalization Synergistic Cooperation

Solar evaporation has become a promising and sustainable technique for harvesting freshwater from seawater and wastewater. However, the applicability and efficacy of solar evaporation need further improvement to achieve high production closer to theoretical limits in compact systems. A 3D (three-dimensional) hierarchical inverted conical solar evaporation is developed, which consists of a 3D copper foam skeleton cone decorated with micro-/nano-structures functionalized with graphene oxide, fabricated via easy and scalable wet oxidation, impregnation, and drying at room temperature. The proposed configuration empowers high-efficiency solar absorption, continuous liquid film spreading and transport, enhanced interfacial local evaporation, and rapid vapor diffusion through the pores. More notably, the 3D conical evaporator realizes thermal localization at the skeleton interface and allows evaporation to occur along the complete structure with unimpeded liquid and vapor rapid diffusion. The solar-thermal evaporation efficiency under 1-Sun is as high as 93% with a maximum evaporation rate per unit area of 1.71 kg·m^-2 ·h^-1 . This work highlights the benefits of synergistic cooperation of an easily scalable 3D hierarchical functiomicro-/nano-structured copper foam skeletons and functionalized graphene oxide for high-efficient solar evaporation of interest to numerous applications.

Covalent Organic Frameworks for Atmospheric Water Harvesting

Atmospheric water harvesting using reticular materials is an innovation that has the potential to change the world. Using covalent organic frameworks (COFs) for capturing water holds great promise because COFs are metal-free, stable under working conditions, and their structure can be intentionally designed to meet the requirements for this application. To promote the chemistry and use of COFs for atmospheric water harvesting, important features for synthesizing suitable water-harvesting COFs are discussed. The achievements of using COFs as water harvesters are then highlighted, showing how the water harvesting properties are related to the structural design. Finally, perspectives and research directions for further studies in COF chemistry are provided.

An overview of atmospheric water harvesting methods, the inevitable path of the future in water supply

Although science has made great strides in recent years, access to fresh water remains a major challenge for humanity due to water shortage for two-thirds of the world's population. Limited access to fresh water becomes more difficult due to the lack of natural resources of water. Many of these resources are also contaminated by human activities. Many attempts have been made to harvest water from the atmosphere, and condensation systems have received much attention. One of the challenges in generation systems is the high consumption energy of the cooling feed, despite the generation of large amounts of water from the atmosphere. As other airborne contaminants condense with water vapor, the water after harvesting needs to be treated, which adds to construction and maintenance costs. Also, the need for high relative humidity in condensation systems has led scientists to find ways of atmospheric water harvesting at low relative humidity and use renewable energy sources. Sorption systems can absorb atmospheric water without the need for an energy supply and spontaneously. Desiccants such as silica gel and zeolite, due to their high affinity for water, can absorb water vapor in the air through physical or physicochemical bonding, but all of these have slow adsorption kinetics. Therefore, it takes a long time for the water harvesting cycle or they are not able to absorb water at low relative humidity, and others need a lot of energy for the water desorption phase. Metal-Organic Frameworks (MOF) are porous materials that, due to their special structure, are considered the most promising material for atmospheric water harvesting at low relative humidity. MOF-303 has been identified as the most efficient material to date and can harvest 0.7 liters of water per kilogram of MOF-303 at 10% RH and 27 °C. MOFs can harvest atmospheric water even in desert areas using only solar energy, and the water produced is drinkable and does not need to be treated. In this review, systems and methods of atmospheric water harvesting will be studied and compared and then the mechanism of adsorption and desorption in sorption systems will be discussed in detail.

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.

Isomer of NU-1000 with a Blocking c-pore Exhibits High Water-Vapor Uptake Capacity and Greatly Enhanced Cycle Stability

Chemically and hydrolytically stable metal-organic frameworks (MOFs) have shown great potential for many water-adsorption-related applications. However, MOFs with large pores that show high water-uptake capacity and high hydrolytic and mechanical cycle stability are rare. Through a deliberate adjustment of the linker of a typical zirconium-based MOF (Zr-MOF) (NU-1000), a new isomer of NU-1000 with blocked c-pores, but large mesopores was successfully synthesized. This new isomer, ISO-NU-1000, exhibits excellent water stability, one of the highest water vapor uptake capacities, and excellent cycle stability, making it a promising candidate for water-vapor-sorption-based applications such as water-adsorption-driven heat transfer. We find that the high water-cycling stability of ISO-NU-1000 is traceable to its blocking c-pore that hinders the hydrolysis of node-coordinating formate in the c-pore area and thereby prevents the introduction of node aqua and terminal hydroxo ligands. With the absence of these ligands and their ability to hydrogen-bond to channel-located water molecules, the strength of guest (water)/host (MOF) interactions is diminished and the absolute magnitude of the capillary force exerted by water during its evacuation from MOF channels is attenuated. The attenuation leaves the MOF capable of resisting pore collapse, capacity loss, and crystallinity loss during repetitive evaporative removal (and re-introduction) of water from pores.

Pore Environment Optimization of Microporous Metal-Organic Frameworks with Huddled Pyrazine Pillars for C2H2/CO2 Separation

Metal-organic frameworks (MOFs) have been proven promising in addressing many critical issues related to gas separation and purification. However, it remains a great challenge to optimize the pore environment of MOFs for purification of specific gas mixtures. Herein, we report the rational construction of three isostructural microporous MOFs with the 4,4',4"-tricarboxyltriphenylamine (H₃TCA) ligand, unusual hexaprismane Ni₆O₆ cluster, and functionalized pyrazine pillars [PYZ-x, x = -H (DZU-10), -NH₂ (DZU-11), and -OH (DZU-12)], where the building blocks of Ni₆O₆ clusters and huddled pyrazine pillars are reported in porous MOFs for the first time. These building blocks have enabled the resulting materials to exhibit good chemical stability and variable pore chemistry, which thus contribute to distinct performances toward C₂H₂/CO₂ separation. Both single-component isotherms and dynamic column breakthrough experiments demonstrate that DZU-11 with the PYZ-NH₂ pillar outperforms its hydrogen and hydroxy analogues. Density functional theory calculations reveal that the higher C₂H₂ affinity of DZU-11 over CO₂ is attributed to multiple electrostatic interactions between C₂H₂ and the framework, including strong C≡C···H-N (2.80 Å) interactions. This work highlights the potential of pore environment optimization to construct smart MOF adsorbents for some challenging gas separations.

Carbon-Carbon Linked Organic Frameworks: An Explicit Summary and Analysis

Organic frameworks with carbon-carbon (CC) linkage are an important class of materials owing to their outstanding chemical stability and extended π-electron delocalization resulting in unique optoelectronic properties. In the first part of this review article, the design principles for the bottom-up synthesis of 2D and 3D sp/sp² CC linked organic frameworks are summarized. Representative reaction methodologies, such as Knoevenagel condensation, Aldol condensation, Horner-Wadsworth-Emmons reaction, Wittig reaction, and coupling reactions (Ullmann, Suzuki, Heck, Yamamoto, etc.) are included. This is discussed in the context of their reaction mechanism, reaction dynamics, and whether and why resulting in an amorphous or crystalline product. This is followed by a discussion of different state-of-the art bottom-up synthesis methodologies, like solvothermal, interfacial, and solid-state synthesis. In the second part, the structure-property relationships in CC linked organic frameworks with representative examples of organocatalysis, photo(electro)catalysis, energy storage and conversion, magnetism, and molecular storage and separation are analyzed. The importance of linkage type, building blocks, topology, and crystallinity of the framework material in connection with the structure-property relationship is highlighted. Finally, brief concluding remarks are presented based on the key development of bottom-up synthetic methods and provide perspectives for future development in this field.

Synergistically Enabling Fast-Cycling and High-Yield Atmospheric Water Harvesting with Plasma-Treated Magnetic Flower-Like Porous Carbons

Sorption-based atmospheric water harvesting (AWH) offers a promising solution to the water scarcity in arid regions. However, majority of the existing AWH sorbents are suffering from rather poor water productivity due to their slow water adsorption-desorption cycling capability especially when they are applied in high packing thickness. Herein, an oxygen plasma-treated magnetic flower-like porous carbon (P-MFPC) with large open surfaces, abundant surface oxygen-containing moieties, and excellent localized magnetic induction heating (LMIH) capacity is developed. These merits, together with the use of air-blowing-assisted water adsorption and LMIH-driven water desorption strategy, synergistically allow P-MFPC with 2 cm of packing thickness to complete a AWH cycling in 20 min and deliver a record 4.5 L_H2O kg^-1 day^-1 of water productivity at 30% relative humidity. Synergistically enabling such an ultrafast AWH cycling at high sorbent packing thickness provides a promising way for the scalable high-yield AWH with compact AWH systems.

Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes. Conductive two-dimensional (2D) materials with robust structural skeletons and/or functionalized surfaces can form stabilizing interactions with MOF components, enabling the fabrication of MOF nanocomposites with tunable pore characteristics. Graphene and its functional derivatives are the largest class of 2D materials and possess remarkable compositional versatility, structural diversity, and controllable surface chemistry. Here, we critically review current knowledge concerning the growth, structure, and properties of graphene derivatives, MOFs, and their graphene@MOF composites as well as the associated structure-property-performance relationships. Synthetic strategies for preparing graphene@MOF composites and tuning their properties are also comprehensively reviewed together with their applications in gas storage/separation, water purification, catalysis (organo-, electro-, and photocatalysis), and electrochemical energy storage and conversion. Current challenges in the development of graphene@MOF hybrids and their practical applications are addressed, revealing areas for future investigation. We hope that this review will inspire further exploration of new graphene@MOF hybrids for energy, electronic, biomedical, and photocatalysis applications as well as studies on previously unreported properties of known hybrids to reveal potential "diamonds in the rough".

A Highly Stable Ortho-Ketoenamine Covalent Organic Framework with Balanced Hydrophilic and Hydrophobic Sites for Atmospheric Water Harvesting

Atmospheric moisture is a sustainable clean water source that can solve the shortage of fresh water in arid areas. Herein a 2D covalent organic framework (COF-ok) was reported as a promising porous sorbent for solar-driven atmospheric water harvesting. COF-ok with ortho-ketoenamine linkage was extremely stable in harsh environment, including in boiling water, strong acids and bases. Because of the balanced hydrophilic and hydrophobic sites in channels, COF-ok showed a high water uptake of 0.33 g g^-1 at a low relative humidity of 34 % featuring a characteristic S-shaped water sorption isotherm with low regeneration temperature (∼45 °C) and excellent cyclic stability. A laboratory-scale water harvesting system could collect water of 161 g kg^-1 under sunlight.

Fluorine extraction from organofluorine molecules to make fluorinated clusters in yttrium MOFs

A new rare earth based two-dimensional coordination network and a three-dimensional metal-organic framework (MOF) have been synthesized using bicinchoninic acid (BCA) and yttrium(iii) ions. Yttrium dimer nodes are formed in the absence of a modulator, resulting in a 2D layered coordination network (Y-BCA-2D). The presence of fluorinating agents, e.g., 2-fluorobenzoic acid (2-FBA), 2,6-difluorobenzoic acid (2,6-DFBA), and perfluorohexanoic acid (PFHxA) result in μ₃-F bridged metal hexaclusters (Y₆F₈) that form a three-dimensional MOF (Y-BCA-3D). It was found that Y³⁺ can break highly stable C-F bonds in aromatic and aliphatic fluorinated compounds. Single-crystal X-ray diffraction (SC-XRD) shows the presence of fluorine in the metal cluster which was confirmed by energy dispersive X-ray spectroscopy (EDS). High resolution X-ray photoelectron spectroscopy (XPS) and ¹⁹F Nuclear Magnetic Resonance (NMR) also verify the presence of metal-fluorine bonds in the cluster. The Y-BCA-3D MOF selectively adsorbs CO₂ but not N₂.

Photonic crystals umbrella for thermal desalination: simulation study

For sustainable water desalination, there is a worldwide push towards solar thermal desalination with the objective to limit the amount of consumed energy in other desalination technologies and maximize the resulting freshwater from saline water. Here, we demonstrate a photonic crystals solar umbrella that covers the saline water surface, demanding to absorb all the incident electromagnetic wave and remit it as greater wavelengths in the range of mid-infrared (MIR) to be highly absorbed and localized close to the water surface. The temperature of the saline water with a refractive index of 1.3326 is reached to [Formula: see text] after one hour of illumination with the incident power intensity equal 680 [Formula: see text]. Hence, by adding one-dimensional PCs the surface temperature is reached [Formula: see text]. Also, by adding 2D PCs to allow the vapor to flow up through the pores of the structure with the diameter of the pore equal to 500 nm, the surface temperature is reached [Formula: see text] after three hour of illumination. Thus, the effective use of electromagnetic waves and warmth localization at the surface of saline water is accomplished by radiative coupling with the effect of 2D PCs. We design the considered structure by using COMSOL multiphysics which based on the finite element method (FEM).

A convenient catalytic method for preparation of new tetrahydropyrido[2,3-d]pyrimidines via a cooperative vinylogous anomeric based oxidation

In this study, a novel functionalized metal-organic frameworks MIL-125(Ti)-N(CH₂PO₃H₂)₂ was designed and synthesized via post-modification methodology. Then, MIL-125(Ti)-N(CH₂PO₃H₂)₂ as a mesoporous catalyst was applied for the synthesis of a wide range of novel tetrahydropyrido[2,3-d]pyrimidines as bioactive candidate compounds by one-pot condensation reaction of 3-(1-methyl-1H-pyrrol-2-yl)-3-oxopropanenitrile, 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and aromatic aldehydes at 100 °C under solvent-free condition. Interestingly, the preparation of tetrahydropyrido[2,3-d]pyrimidine was achieved via vinylogous anomeric based oxidation mechanism with a high yield and short reaction time.

Mapping short-range order at the nanoscale in metal-organic framework and inorganic glass composites

Characterization of nanoscale changes in the atomic structure of amorphous materials is a profound challenge. Established X-ray and neutron total scattering methods typically provide sufficient signal quality only over macroscopic volumes. Pair distribution function analysis using electron scattering (ePDF) in the scanning transmission electron microscope (STEM) has emerged as a method of probing nanovolumes of these materials, but inorganic glasses as well as metal-organic frameworks (MOFs) and many other materials containing organic components are characteristically prone to irreversible changes after limited electron beam exposures. This beam sensitivity requires 'low-dose' data acquisition to probe inorganic glasses, amorphous and glassy MOFs, and MOF composites. Here, we use STEM-ePDF applied at low electron fluences (10 e^- Å^-2) combined with unsupervised machine learning methods to map changes in the short-range order with ca. 5 nm spatial resolution in a composite material consisting of a zeolitic imidazolate framework glass a_gZIF-62 and a 0.67([Na₂O]_0.9[P₂O₅])-0.33([AlO_3/2][AlF₃]_1.5) inorganic glass. STEM-ePDF enables separation of MOF and inorganic glass domains from atomic structure differences alone, showing abrupt changes in atomic structure at interfaces with interatomic correlation distances seen in X-ray PDF preserved at the nanoscale. These findings underline that the average bulk amorphous structure is retained at the nanoscale in the growing family of MOF glasses and composites, a previously untested assumption in PDF analyses crucial for future non-crystalline nanostructure engineering.

Simultaneous atmospheric water production and 24-hour power generation enabled by moisture-induced energy harvesting

Water and electricity scarcity are two global challenges, especially in arid and remote areas. Harnessing ubiquitous moisture and sunlight for water and power generation is a sustainable route to address these challenges. Herein, we report a moisture-induced energy harvesting strategy to realize efficient sorption-based atmospheric water harvesting (SAWH) and 24-hour thermoelectric power generation (TEPG) by synergistically utilizing moisture-induced sorption/desorption heats of SAWH, solar energy in the daytime and radiative cooling in the nighttime. Notably, the synergistic effects significantly improve all-day thermoelectric power density (~346%) and accelerate atmospheric water harvesting compared with conventional designs. We further demonstrate moisture-induced energy harvesting for a hybrid SAWH-TEPG device, exhibiting high water production of 750 g m-2, together with impressive thermoelectric power density up to 685 mW m-2 in the daytime and 21 mW m-2 in the nighttime. Our work provides a promising approach to realizing sustainable water production and power generation at anytime and anywhere.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Hydrogen production from the air

Green hydrogen produced by water splitting using renewable energy is the most promising energy carrier of the low-carbon economy. However, the geographic mismatch between renewables distribution and freshwater availability poses a significant challenge to its production. Here, we demonstrate a method of direct hydrogen production from the air, namely, in situ capture of freshwater from the atmosphere using hygroscopic electrolyte and electrolysis powered by solar or wind with a current density up to 574 mA cm⁻². A prototype of such has been established and operated for 12 consecutive days with a stable performance at a Faradaic efficiency around 95%. This so-called direct air electrolysis (DAE) module can work under a bone-dry environment with a relative humidity of 4%, overcoming water supply issues and producing green hydrogen sustainably with minimal impact to the environment. The DAE modules can be easily scaled to provide hydrogen to remote, (semi-) arid, and scattered areas.

While obtaining H₂ from water splitting offers a promising strategy for renewable fuel production, current technologies rely on liquid freshwater. Here, authors use a hygroscopic electrolyte to achieve electrocatalytic water vapor splitting driven by renewable resources without liquid water.

Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates

The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from the ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake by salt-based sorbents makes them attractive for AWH, especially in arid environments. However, they often have relatively high desorption heat, rendering water release an energy-intensive process. A  LiCl-incorporating polyacrylamide hydrogel (PAM-LiCl) capable of effective moisture harvesting from arid environments is proposed. The interactions between the hydrophilic hydrogel network and the captured water generate more free and weakly bonded water, significantly lowering the desorption heat compared with conventional neat salt sorbents. Benefiting from the affinity for swelling of the polymer backbones, the developed PAM-LiCl achieves a high water uptake of ≈1.1 g g^-1 at 20% RH with fast sorption kinetics of ≈0.008 g g^-1  min^-1  and further demonstrates a daily water yield up to ≈7 g g^-1 at this condition. These findings provide a new pathway for the synthesis of materials with efficient water absorption/desorption properties, to reach energy-efficient water release for AWH in arid climates.

Prospects for Simultaneously Capturing Carbon Dioxide and Harvesting Water from Air

Mitigation of anthropogenic climate change is expected to require large-scale deployment of carbon dioxide removal strategies. Prominent among these strategies is direct air capture with sequestration (DACS), which encompasses the removal and long-term storage of atmospheric CO₂  by purely engineered means. Because it does not require arable land or copious amounts of freshwater, DACS is already attractive in the context of sustainable development, but opportunities to improve its sustainability still exist. Leveraging differences in the chemistry of CO₂  and water adsorption within porous solids, here, the prospect of simultaneously removing water alongside CO₂  in direct air capture operations is investigated. In many cases, the co-adsorbed water can be desorbed separately from chemisorbed CO₂  molecules, enabling efficient harvesting of water from air. Depending upon the material employed and process conditions, the desorbed water can be of sufficiently high purity for industrial, agricultural, or potable use and can thus improve regional water security. Additionally, the recovered water can offset a portion of the costs associated with DACS. In this Perspective, molecular- and process-level insights are combined to identify routes toward realizing this nascent yet enticing concept.

Magnetic Stuffed Bun-Structured Metal-Organic Framework Monoliths with Noncompromised Accessible Pores and Highly Efficient Recycling Capability

Development of industrially favorable metal-organic framework (MOF) monoliths is of paramount importance for their real-world applications. However, MOF monoliths prepared with the existing MOF shaping methods usually have seriously compromised accessible pores and suffer from inefficient and energy-intensive recycling, thereby greatly limiting their practical applications. We herein present a magnetic stuffed bun-structured MOF (mSBM) bead consisting of highly porous poly(vinyl alcohol) wraps stuffed with a binder-free powder mixture of UiO-66 and Fe₃O₄ nanoparticles. Such a unique structure and composition of the mSBM not only make its MOF component have a well-reserved crystal structure, surface area, and porosity and the corresponding accessible pores but also impart it with excellent localized magnetic induction heating (LMIH) capability that enables the sufficient heating and highly efficient recycling of the mSBM. These merits of mSBMs are further exemplified by assessing their atmospheric water adsorption and LMIH-driven water desorption performance. The mSBMs exhibit well-reserved atmospheric water adsorption capacities, up to 100% LMIH-driven water desorption, excellent reusability, and durability toward the practical applications. Our current work, therefore, demonstrates a new MOF shaping strategy to produce MOF monoliths with well-defined shapes, noncompromised accessible pores, and highly efficient recycling capabilities, paving a bright avenue to accelerate the practical applications of MOF monoliths.

Environmentally adaptive MOF-based device enables continuous self-optimizing atmospheric water harvesting

Harvesting water vapor from desert, arid environments by metal-organic framework (MOF) based devices to deliver clean liquid water is critically dependent on environment and climate conditions. However, reported devices have yet been developed to adapt in real-time to such conditions during their operation, which severely limits water production efficiency and unnecessarily increases power consumption. Herein, we report and detail a mode of water harvesting operation, termed ‘adaptive water harvesting’, from which a MOF-based device is proven capable of adapting the adsorption and desorption phases of its water harvesting cycle to weather fluctuations throughout a given day, week, and month such that its water production efficiency is continuously optimized. In performance evaluation experiments in a desert, arid climate (17–32% relative humidity), the adaptive water harvesting device achieves a 169% increase in water production (3.5 L_H2O kg_MOF⁻¹ d⁻¹) when compared to the best-performing, reported active device (0.7–1.3 L_H2O kg_MOF⁻¹ d⁻¹ at 10–32% relative humidity), a lower power consumption (1.67–5.25 kWh L_H2O⁻¹), and saves time by requiring nearly 1.5 cycles less than a counterpart active device. Furthermore, the produced water meets the national drinking standards of a potential technology-adopting country.

Atmospheric water harvesting by MOF-based devices is critically dependent on weather conditions. Here, the authors report a MOF-based adaptive water harvesting system capable of adapting its cycles to temperature and relative humidity fluctuations throughout the day, continuously optimizing water production.

Partially Ordered Lanthanide Carboxylates with a Highly Adaptable 1D Polymeric Structure

A new family of 14 isostructural [Ln(piv)₃(en)]_∞ lanthanide pivalate (piv⁻, 2,2-dimethylpropanoate) complexes with ethylenediamine (en) was synthesized by a topology-preserving transformation from 1D coordination polymers [Ln(piv)₃]_∞. The crystal structures of the compounds were determined by single-crystal and powder X-ray diffraction, which demonstrated that despite the regular ligand arrangement within the chains, the latter are intricately packed within the partially ordered crystal, as only two of four ligands are strictly bound by the translational symmetry. The peculiarities of the lanthanide coordination environment were explored by total X-ray scattering with pair distribution function analysis. Periodic DFT calculations revealed the chain stabilization by intrachain H-bonds and weak interchain interactions. Noticeably, the energy difference was infinitesimally small even between the two considered extreme variants of ordered packing, which is in line with the disturbed packing order of the chains. The luminescent properties of Eu and Tb complexes were investigated in order to prove the energy transfer between lanthanide ions within the heterometallic complex. This opens up the prospect of creating new materials for optical applications. The heterometallic compound Eu_0.05Tb_0.95(piv)₃(en) was synthesized, and was found to demonstrate temperature-dependent luminescence with a linear dependence of the thermometric parameter I(Eu)/I(Tb) within the temperature range from −80 °C to 80 °C, and had a maximum relative sensitivity value of 0.2%/K.

Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water

Metal-based oxoanions are potentially toxic pollutants that can cause serious water pollution. Therefore, the segregation of such species has recently received significant research attention. Even though several adsorbents have been employed for effective management of chemicals, their limited microporous nature along with non-monolithic applicability has thwarted their large-scale real-time application. Herein, we developed a unique anion exchangeable hybrid composite aerogel material (IPcomp-6), integrating a stable cationic metal-organic polyhedron with a hierarchically porous metal-organic gel. The composite scavenger demonstrated a highly selective and very fast segregation efficiency for various hazardous oxoanions such as, HAsO₄ ^2- , SeO₄ ^2- , ReO₄ ^- , CrO₄ ^2- , MnO₄ ^- , in water, in the presence of 100-fold excess of other coexisting anions. The material was able to selectively eliminate trace HAsO₄ ^2- even at low concentration to well below the As^V limit in drinking water defined by WHO.

High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels

Solar-driven, sorption-based atmospheric water harvesting (AWH) offers a cost-effective solution to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption-desorption cycles per day is crucial for increasing water production rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents' slow water adsorption-desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ~1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal conductivity. A rapid-cycling water harvester based on nanoporous carbon derived from metal-organic frameworks can produce 0.18 L kg_carbon^-1 h^-1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.

Acetylenedicarboxylate as a linker in the engineering of coordination polymers and metal-organic frameworks: challenges and potential

Despite its simplicity as a short and rod-like linear linker, acetylenedicarboxylate (ADC) has for a long time been somewhat overlooked in the engineering of coordination polymers (CPs) and especially in the construction of porous metal-organic frameworks (MOFs). This situation seems to be stemming from the thermosensitivity of the free acid (H₂ADC) precursor and its dicarboxylate, which makes the synthesis of their CP- and MOF-derivatives, as well as the evacuation of guest molecules from their pores, challenging. However, an increasing number of publications dealing with the synthesis, structural characterization and properties of ADC-based CPs and MOFs, disclose ways to tackle this obstacle. In this regard, using mostly room temperature solution synthesis or mechanochemical synthesis, and very rarely solvothermal synthesis, the ADC linker has successfully been used to form one-, two-, and three-dimensional CPs with metal cations from almost all groups of the periodic table of the elements, whereby its carboxylate groups adopt mainly all types of known coordination modes. ADC-based CPs feature properties, including negative thermal expansion, formation of non-centrosymmetric networks, long-range magnetic ordering, and solid-state polymerization. The first ADC-based microporous MOFs were obtained with Ce(IV), Hf(IV) and Zr(IV), in which the presence of the -CC- triple-bond within their backbone results in high hydrophilicity, high CO₂ adsorption capacity and enthalpy, as well as the uptake of halogen vapors. This discloses the potential of ADC-MOFs for gas storage/separation and water adsorption-based applications. Furthermore, H₂ADC/ADC was discovered to undergo facile in situ hydrohalogenation to yield halogen-functionalized fumarate-based CPs/MOFs. This review surveys investigations on ADC-based coordination polymers and metal-organic frameworks, and is intended to stimulate interest on this linker in chemists working in the fields of crystal chemistry or materials science.

Macroporous Hydrogel for High-Performance Atmospheric Water Harvesting

Simple, low-cost, and high-performance atmospheric water harvesting (AWH) still remains challenging in the context of global water shortage. Here, we present a simple and low-cost macroporous hydrogel for high-performance AWH to address this challenge. We employed an innovative strategy of pore foaming and vacuum drying to rationally fabricate a macroporous hydrogel. The hydrogel is endowed with a macroporous structure and a high specific surface area, enabling sufficient contact of the inner sorbent with outside air and high-performance AWH. The experiments demonstrate that macroporous hydrogels can achieve high-performance AWH with a broad range of sorption humidity [relative humidity (RH) from 100% to even lower than 20%], high water sorption capacity (highest 433.72% of hydrogel's own weight at ∼98% RH, 25 °C within 60 h), rapid vapor capturing (the sorption efficiency is as high as 0.32 g g^-1 h^-1 in the first 3 h at 90% RH, 25 °C), unique durability, low desorption temperature (∼50 °C, lowest), and high water-releasing rate (release 99.38% of the sorbed water under 500 W m^-2 light for 6 h). The results show that this macroporous hydrogel can sorb water more than 193.46% of its own weight overnight (13 h) at a RH of ∼90%, 25 °C and release as high as 99.38% of the sorbed water via the photothermal effect. It is estimated that the daily water yield can reach up to approximately 2.56 kg kg^-1 day^-1 in real outdoor conditions, enabling daily minimum water consumption of an adult. Our simple, affordable, and easy-to-scale-up macroporous hydrogel can not only unleash the unlimited possibilities for large-scale and high-performance AWH but also offer promising opportunities for functional materials, soft matter, flexible electronics, tissue engineering, and biomedical applications.

Photoresponsive Metal-Organic Frameworks as Adjustable Scaffolds in Reticular Chemistry

The easy and remote switching of light makes this stimulus an ideal candidate for a large number of applications, among which the preparation of photoresponsive materials stands out. The interest of several scientists in this area in order to achieve improved functionalities has increase parallel to the growth of the structural complexity of these materials. Thus, metal-organic frameworks (MOFs) turned out to be ideal scaffolds for light-responsive ligands. This review is focused on the integration of photoresponsive organic ligands inside MOF crystalline arrays to prepare enhanced functional materials. Besides the summary of the preparation, properties and applications of these materials, an overview of the future outlook of this research area is provided.

Mechanically interlocked molecules in metal-organic frameworks

Mechanically interlocked molecules (MIMs) have great potential in the development of molecular machinery due to their intercomponent dynamics. The incorporation of these molecules in a condensed phase makes it possible to take advantage of the control of the motion of the components at the macroscopic level. Metal-organic frameworks (MOFs) are postulated as ideal supports for intertwined molecules. This review covers the chemistry of the mechanical bond incorporated into metal-organic frameworks from the seminal studies to the latest published advances. We first describe some fundamental concepts of MIMs and MOFs. Next, we summarize the advances in the incorporation of rotaxanes and catenanes inside MOF matrices. Finally, we conclude by showing the study of the rotaxane dynamics in MOFs and the operation of some stimuli-responsive MIMs within MOFs. In addition to emphasising some selected examples, we offer a critical opinion on the state of the art of this research field, remarking the key points on which the future of these systems should be focused.

Seasonal atmospheric water harvesting yield and water quality using electric-powered desiccant and compressor dehumidifiers

Atmospheric water harvesting (AWH) is an emerging technology for decentralized water supply and is proving to be viable for use in emergencies, military deployment, and sustainable industries. The atmosphere is a freshwater reservoir that contains 12,900 km³ of water, 6-fold more than the volume of global rivers. Dehumidification water harvesting technologies can be powered by solar, wind, or electric sources. Compressor/refrigerant-based dehumidifiers operate via dew point condensation and provide a cold surface upon which water vapor can condense. Conversely, desiccant-based technologies saturate water vapor using a sorbent that is then heated, and the supersaturated water vapor condenses on a surface when interacting with cooler ambient process air. This work compares productivity, energy consumption, efficiency, cost and quality of water produced of two water-harvesting mechanisms. Electric-powered compressor and desiccant dehumidifiers were operated outdoors for more than one year in the arid southwestern USA, where temperatures ranged from 3.1 to 43.7 °C and relative humidity (RH) ranged from 6 to 85%. The compressor system harvested >2-fold more water than the desiccant system when average RH during the run cycle was >30%, average temperature was >20 °C, and average dew point temperature was >5 °C. Desiccant systems performed more favorably when average RH during the run cycle was <30%, average temperature was <20 °C, and average dew point temperature was <5 °C. Water collected by compressor-based technologies had conductivity up to 180 μS/cm, turbidity up to 190 NTU, and aluminum, iron and manganese near or above the US EPA secondary drinking water standard. Dissolved organic carbon (DOC) averaged <2 mg C/L but ranged up to 12 mg C/L. Water collected by desiccant-based technologies had significantly lower conductivity, metals, and turbidity, and DOC was always <6 mg/L. Aldehydes such as formaldehyde and acetaldehyde and carboxylic acids such as formic acid and acetic acid were primary contributors to DOC. The differences in harvested water quality were attributed to differences in the condensation method between compressor and desiccant AWH technologies. Multiple strategies could be employed to prevent these volatile organic compounds (VOCs) from contributing to DOC in harvested water, such as pretreating air to remove VOCs or post-treating DOC in harvested liquid water.

Construction and application of base-stable MOFs: a critical review

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials constructed from organic ligands and metal ions/clusters. Owing to their unique advantages, they have attracted more and more attention in recent years and numerous studies have revealed their great potential in various applications. Many important applications of MOFs inevitably involve harsh alkaline operational environments. To achieve high performance and long cycling life in these applications, high stability of MOFs against bases is necessary. Therefore, the construction of base-stable MOFs has become a critical research direction in the MOF field. This review gives a historic summary of the development of base-stable MOFs in the last few years. The key factors that can determine the robustness of MOFs under basic conditions are analyzed. We also demonstrate the exciting achievements that have been made by utilizing base-stable MOFs in different applications. In the end, we discuss major challenges for the further development of base-stable MOFs. Some possible methods to address these problems are presented.

Structure Tuning of Hafnium Metal–Organic Frameworks through a Mixed Solvent Approach

The recent development of water-stable metal–organic frameworks (MOFs) has significantly broadened the application scope of this emerging type of porous material. Structure tuning of hafnium MOFs is less studied compared with zirconium MOFs. In this work, we report the synthesis of a mesoporous hafnium MOF, csq-MOF-1, through finely tuning the solvent mixture ratio. The successful synthesis of csq-MOF-1 also relies on the linker flexibility as linker bending and a symmetry decrease were observed in this framework as compared to its structural isomer NPF-300 (Hf). The mesoporous feature and permanent porosity were determined by the N2 adsorption at 77 K. Such a hierarchical pore feature is expected to enable a variety of applications through encapsulation of large functional molecules. The synthetic strategy of utilizing a mixed solvent and flexible linker is expected to inspire the development of new hafnium MOFs with diverse topological structures.

Aggregation-Induced Luminescence Based UiO-66: Highly Selective Fast-Response Styrene Detection

One of the main pollutants in indoor air is volatile organic compounds (VOCs), which can cause great harm to human health. So the development of a VOC detection technology is of great significance. In this work, a tetraphenylethylene-functionalized UiO-66 based on aggregation-induced emission was successfully prepared. The UiO-66-TBPE structure exhibits the characteristic blue emission of TBPE ligands under UV excitation and can be used as a luminescence sensor for fast and efficient detection of VOCs. More importantly, UiO-66-TBPE has a high fluorescence sensing selectivity in p-xylene and styrene vapor. To further improve the practical performance, we combined UiO-66-TBPE with the polymer polyacrylate (PA) to obtain a flexible hybrid membrane with fast detection performance for styrene vapor within the 30 s. The deeper sensing mechanism of p-xylene and styrene inducing different fluorescence enhancement and fluorescence quenching is explained by a combination of modern characterization techniques and computer simulation. Finally, we applied UiO-66-TBPE/PA to leather and still maintained a good sensing performance. It provides a potential way for the application of fluorescent metal-organic frameworks (MOFs) to detect VOCs in daily life.

Metal-Organic Frameworks Can Photocatalytically Split Water-Why Not?

The opinion is provided about the stability and photocatalytic capability of metal-organic frameworks in photocatalytic overall water splitting.

Linker Functionalization Strategy for Water Adsorption in Metal-Organic Frameworks

Water adsorption in metal-organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be -12.7 Kcal/mol for the -OSO₃H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm³/cm³ for all candidates, classifying them among the top performing materials for water harvesting.