Design and applications of water-stable metal-organic frameworks: status and challenges

Au Deposition Enhanced Fenton-like Chemistry within a Metal-Organic Framework

Chemodynamic therapy (CDT), which regulates oxidative stress in tumor tissues, has emerged as a promising alternative. However, the efficiency of MOF-based Fenton catalysts for CDT still needs improvement. This study presents a strategy to improve the Fenton catalytic performance of ZnCo-ZIF by depositing Au nanoparticles on its surface. Monodisperse ZnCo-ZIF particles (≤200 nm) were prepared by optimizing the Zn/Co ratio, and Au deposition enhanced electron transfer between Au and Co, increasing the charge density around Co atoms. This resulted in a 2.28-fold improvement in Fenton activity under acidic conditions and mild near-infrared (NIR) light. Loading the system with the natural product naringin (NA) molecule further demonstrated synergistic anticancer effects in vitro. This work offers insights into enhancing MOF-based catalysts for cancer therapy.

Fluorinated metal-organic frameworks: hydrophobic nanospaces with high fluorine density and proton conductivity

The current work revealed the relationship between the fluorine density of organic-based porous materials and water dynamics (proton conduction) in the hydrophobic nanospace. In detail, by focusing on UiO-66 with structural durability at high temperature/humidity based on strong Zr-O bonds, we prepared UiO-66-CF3 and UiO-66-(CF3)2 with different fluorine densities. The activation energies for proton conduction of UiO-66-CF3 (0.91 eV) and UiO-66-(CF3)2 (1.38 eV) were significantly larger than that in UiO-66 (0.47 eV) depending on their fluorine density. Introducing fluorine into organic-based porous materials allowed the hydrophobic nanospace to interact with protons, yielding a larger energy for proton conduction (activation energy). The fluorine density and activation energy were proportional. We clarified that the activation energy of proton conduction increased proportionally with the fluorine density in the nanospace. This indicated the possibility that the state of proton/water in the nanospace could be freely controlled by the fluorine density.

Water-Stable MIL-MOFs Developed Through a Novel Sacrifice-Protection Strategy Inspired by Butterfly Wings' Scales for Long-Term Turn-On Fluorescence Sensing of H2S

Metal-organic frameworks, which are the desired candidates for biosensing application due to their tunable properties, are significantly hindered by their rapid degradation in aqueous solutions, as well as the loss of their inherent fluorescence. Most studies aim to improve the hydrophobicity of materials by modifying their contact angle, thereby enhancing water stability. However, water droplets poorly adhere to the surface of hydrophobic materials, limiting their application for direct contact and detection in aqueous environments. Drawing inspiration from the sacrificial protection mechanism of butterfly wings used to evade predation and entanglement, a universal approach is successfully developed to protect water-sensitive MIL-MOFs from water molecule attack while preserving good hydrophilicity. Using the organic ligand 2,2'-bipyridine-5,5'-dicarboxylic acid (bpydc) as sacrificial protection scales, the MIL-125-NH2-bpydc demonstrated broad pH structural stability (pH 2-12) and fluorescence stability increased by 10.17 time in aqueous solutions, achieving the highest performance in MILMOFs. The MIL-125-NH2-bpydc is biocompatible enabling it to perform long-term fluorescence imaging in living cells and zebrafish, further detecting hydrogen sulfide (H2S) in the aqueous and biological systems via turn-on fluorescence emission. This study offers a novel and universal sacrifice-protection strategy for the design and development of the luminescent biocompatible MOFs tailored for biosensing applications.

Porous MIL, ZIF, and UiO metal-organic frameworks for adsorption of pharmaceuticals and personal care products

Pharmaceuticals and personal care products (PPCPs) are a newly identified category of emerging global pollutants often found in aquatic systems. Efficient removal of these pollutants from the water/wastewater is currently problematic because of their low biodegradability and high hydrophilicity, as well as their distinct physicochemical features and lower concentrations. Materials of Institut Lavoisier (MIL), Zeolitic imidazolate framework (ZIF), and University of Oslo (UiO) are highly engineered metal-organic frameworks (MOFs) composed of unique components necessary for the formation of crystals with exceptional porosity, large surface areas, large pore sizes, crystalline structures, tunable properties, excellent chemical and thermal stability for environmental remediation. This study provides detailed and combined applications of UiOs, MILs, and ZIFs as adsorbents for capturing the new class of emerging pollutants (PPCPs) from the liquid phase. MOFs as ideal candidates for PPCP decontamination were discussed, followed by the MOF porosity and factors that affect MOF stability. Various synthetic approaches for MILs, ZIFs, and UiOs were discussed, as well as their corresponding pros and cons. An in-depth performance of these three MOFs for adsorptive removal of PPCPs from the liquid phase was discussed, assessing the state-of-the-art for specific applications and the effectiveness of UiOs, MILs, and ZIFs as adsorbents for PPCP decontamination . The unique performance garnered from the study provided a way forward/potential for real-life/practical applications of these sorbents and insight into corresponding mechanisms and synergistic relationships. To foster the advancement of the field, viable shortcomings and strengths associated with these novel classes of MOFs, treatment options, and knowledge gaps to explore specific research directives for large-scale or industrial-scale applications were highlighted.

High-Performance Overall Water Splitting Dominated by Direct Ligand-to-Cluster Photoexcitation in Metal-Organic Frameworks

Expanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single-phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible-light-responsive OWS photocatalysis dominated by direct ligand-to-cluster charge transfer (LCCT) within metal-organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g-1 h-1 for H2 and O2 evolution, surpassing all previously documented MOF-based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well-optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

A Hydrolytically Stable Metal-Organic Framework for Simultaneous Desulfurization and Dehydration of Wet Flue Gas

Metal-organic frameworks (MOFs) have great prospects as adsorbents for industrial gas purification, but often suffer from issues of water stability and competitive water adsorption. Herein, we present a hydrolytically stable MOF that could selectively capture and recover trace SO2 from flue gas, and exhibits remarkable recyclability in the breakthrough experiments under wet flue-gas conditions, due to its excellent resistance to the corrosion of SO2 and the water-derived capillary forces. More strikingly, its SO2 capture efficiency is barely influenced by the increasing humidity, even if the pore filling with water is reached. Mechanistic studies demonstrate that the delicate pore structure with diverse pore dimensions and chemistry leads to different adsorption kinetics and thermodynamics as well as segregated adsorption domains of SO2 and H2O. Significantly, this non-competitive adsorption mechanism enables simultaneous desulfurization and dehydration by a single adsorbent, opening an avenue toward cost-effective and simplified processing flowcharts for flue gas purification.

Infection Diagnostics Enabled by Selective Adsorption of Breath-Based Biomarkers in Zr-Based Metal-Organic Frameworks

Exhaled breath contains trace levels of volatile organic compounds (VOCs) that can reveal information about metabolic processes or pathogens in the body. These molecules can be used for medical diagnosis, but capturing and accurately measuring them is a significant challenge in chemical separations. A highly selective nanoporous sorbent can be used to capture target molecules from a breath sample and preconcentrate them for use in a detector. In this work, we present a combined predictive modeling-experimental validation study in which five Zr-based metal-organic frameworks (MOFs) were identified and tested. These MOFs display good selectivity for a variety of VOCs known to be indicators of viral infections such as influenza and COVID-19. We first used molecular simulation to identify promising MOF candidates that were subsequently synthesized and tested for recovery of a variety of VOCs (toluene, propanal, butanone, octane, acetaldehyde) at concentrations of 20 ppm in humid nitrogen. We show that MOF-818, PCN-777, and UiO-66 have particularly good selectivity for the target molecules in the presence of humidity. These three MOFs each recover around 40-60% of the targets (with the exception of acetaldehyde) at up to 95% relative humidity. MOF-818 recovers 63% of butanone and 60% of toluene at 80% relative humidity. Recovery for acetaldehyde is lower across all MOFs at high humidity, but notably, MOF-808 recovers 90% of acetaldehyde at 60% humidity.

The Road Ahead for Metal-Organic Frameworks: Current Landscape, Challenges and Future Prospects

This perspective highlights the transformative potential of Metal-Organic Frameworks (MOFs) in environmental and healthcare sectors. It discusses work that has advanced beyond technology readiness levels of >4 including applications in capture, storage, and conversion of gases to value added products. This work showcases efforts in the most salient applications of MOFs which have been performed at a great cadence, enabled by the federal government, large companies, and startups to commercialize these technologies despite facing significant challenges. This article also forecasts the role of nanoscale MOFs in healthcare, including strides toward personalized medicine, advocating for their use in custom-tailored drug delivery systems. Finally we underscore the potential acceleration in MOF research and development through the integration of machine learning and AI, positioning MOFs as versatile tools poised to address global sustainability and health challenges.

Recent Progress in Enzyme Immobilization to Metal-Organic Frameworks to Enhance the CO2 Conversion Efficiency

Climate change and the energy crisis, driven by excessive CO2 emissions, have emerged as pressing global challenges. The conversion of CO2 into high-value chemicals not only mitigates atmospheric CO2 levels but also optimizes carbon resource utilization. Enzyme-catalyzed carbon technology offers a green and efficient approach to CO2 conversion. However, free enzymes are prone to inactivation and denaturation under reaction conditions, which limit their practical applications. Metal-organic frameworks (MOFs) serve as effective carriers for enzyme immobilization, offering porous crystalline structures that enhance enzyme stability. Moreover, their high specific surface area facilitates strong gas adsorption, making enzyme@MOF composites particularly advantageous for CO2 catalytic conversion. In this paper, we review the synthesis technologies and the application of enzyme@MOFs in CO2 catalytic conversion. Furthermore, the strategies, including the enhancement of CO2 utilization, coenzyme regeneration efficiency, and substrate mass transfer efficiency, are also discussed to further improve the efficiency of enzyme@MOFs in CO2 conversion. The aim of this review is to present innovative ideas for future research and to highlight the potential applications of enzyme@MOFs in achieving efficient CO2 conversion.

Chrome-free leather processing based on amine pendant metal-organic frameworks and dialdehyde with enhanced dye affinity

To overcome the stringent regulations in the usage of chromium salts and dye-rich effluent let out by the tanning industry, a sustainable way of leather processing has been demonstrated utilizing amine pendant metal-organic frameworks (MOF) UiO-66-NH2 along with glyoxal. It was found that an offer of 8% (w/w) MOF along with 6% (w/w) glyoxal increased the shrinkage temperature of the leathers to 89 ± 2 °C with exhaustion of MOF up to 84.3 ± 1.5%. The presence of cationic amine sites in the MOF aided in the fixation of anionic post-tanning agents and improved the adsorption of dyes from 74.3 ± 2.5% in the case of conventional leather to 91.8 ± 1.7% for experimental leather. In comparison to chrome-tanned leather, the experimental leathers were rated the highest in terms of dye fastness concerning rubbing action and against perspiration, showcasing the washable properties and better affinity and irreversible binding of dyes to the leather matrix. Mechanism studies through XPS spectroscopy revealed the interaction between the acidic amino acids of collagen and free zirconium metal sites and the imine linkage between amine pendants of MOF and basic amino acids of collagen protein. Further, the BOD5/COD ratio of 0.36 confirmed the better treatability of the wastewater emanating from the proposed process making it a sustainable tanning system. Thus, the combination of amine pendant MOFs with dialdehyde can be a promising strategy for the development of robust chrome-free leathers with excellent functional properties.

Incorporation of enzyme-mimic species in porous materials for the construction of porous biomimetic catalysts

The unique catalytic properties of natural enzymes have inspired chemists to develop biomimetic catalyst platforms for the intention of retaining the unique functions and solving the application limitations of enzymes, such as high costs, instability and unrecyclable ability. Porous materials possess unique advantages for the construction of biomimetic catalysts, such as high surface areas, thermal stability, permanent porosity and tunability. These characteristics make them ideal porous matrices for the construction of biomimetic catalysts by immobilizing enzyme-mimic active sites inside porous materials. The developed porous biomimetic catalysts demonstrate high activity, selectivity and stability. In this feature article, we categorize and discuss the recently developed strategies for introducing enzyme-mimic active species inside porous materials, which are based on the type of employed porous materials, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), molecular sieves, porous metal silicate (PMS) materials and porous carbon materials. The advantages and limitations of these porous materials-based biomimetic catalysts are discussed, and the challenges and future directions in this field are also highlighted.

HKUST-1 in-situ loaded ultrastable covalently crosslinked agarose aerogel with solvothermal for highly efficient removal of methylene blue

A new HKUST-1@covalently crosslinked agarose aerogel (HKUST-1@CCAGA) was synthesized for the highly effective elimination of Methylene Blue (MB). Firstly, the covalently crosslinked agarose aerogel (CCAGA) was obtained by hydrothermal crosslinking reaction with epichlorohydrin (ECH) as crosslinker, which remained stabilized under hydrothermal and solvothermal conditions. Then, HKUST-1 was made to bind to CCAGA by in situ solvothermal assays, and the HKUST-1 loading rate reached 47.4 % based on thermogravimetric data and calculated using the cross over method. Meanwhile, the SEM exhibited the complete 3D honeycomb structure of CCAGA, and HKUST-1 particles uniformly distributed on its layers. Additionally, the specific surface area of HKUST-1@CCAGA can reached 648.59 m2·g-1. The HKUST-1@CCAGA composite was utilized for MB removal, achieving a high adsorption capacity of 424.30 mg·g-1 at pH 8. The adsorption of MB was also maintained at 80 % after 5 cycles of the experiment. The composite aerogel exhibits good recyclability and has excellent adsorption capacity.

Domingues N, Pougin MJ, Smit B, Hosta-Rigau L, Oostenbrink C. Stability Assessment in Aqueous and Organic Solvents of Metal-Organic Framework PCN 333 Nanoparticles through a Combination of Physicochemical Characterization and Computational Simulations

Mesoporous metal-organic frameworks (MOFs) have been recognized as powerful platforms for drug delivery, especially for biomolecules. Unfortunately, the application of MOFs is restricted due to their relatively poor stability in aqueous media, which is crucial for drug delivery applications. An exception is the porous coordination network (PCN)-series (e.g., PCN-333 and PCN-332), a series of MOFs with outstanding stability in aqueous media at the pH range from 3 to 9. In this study, we fabricate PCN-333 nanoparticles (nPCN) and investigate their stability in different solvents, including water, ethanol, and methanol. Surprisingly, the experimental characterizations in terms of X-ray diffraction, Brunauer-Emmett-Teller (BET), and scanning electron microscopy demonstrated that nPCN is not as stable in water as previously reported. Specifically, the crystalline structure of nPCN lost its typical octahedral shape and even decomposed into an irregular amorphous form when exposed to water for only 2 h, but not when ethanol and methanol were used. Meanwhile, the porosity of nPCN substantially diminished while being exposed to water, as demonstrated by the BET measurement. With the assistance of computational simulations, the mechanism behind the collapse of PCN-333 is illuminated. By molecular dynamics simulation and umbrella sampling, we elucidate that the degradation of PCN-333 occurs by hydrolysis, wherein polar solvent molecules initiate the attack and subsequent breakage of the metal-ligand reversible coordination bonds.

Highly enhanced chloramphenicol adsorption performance of MIL-53-NH2(Al)-derived porous carbons modified with tannic acid

The worldwide demand for antibiotics has experienced a notable surge, propelled by the repercussions of the COVID-19 pandemic and advancements in the global healthcare sector. A prominent challenge confronting humanity is the unregulated release of antibiotic-laden wastewater into the environment, posing significant threats to public health. The adoption of affordable carbon-based adsorbents emerges as a promising strategy for mitigating the contamination of antibiotic wastewater. Here, we report the synthesis of novel porous carbons (MPC) through a direct pyrolysis of MIL-53-NH2(Al) and tannic acid (TANA) under N2 atmosphere at 800 °C for 4 h. The effect of TANA amount ratios (0%-20%, wt wt-1) on porous carbon structure and adsorption performance was investigated. Results showed that TANA modification resulted in decreased surface area (1,600 m2 g-1-949 m2 g-1) and pore volume (2.3 cm3 g-1-1.7 cm3 g-1), but supplied hydroxyl functional groups. Adsorption kinetic, intraparticle diffusion, and isotherm were examined, indicating the best fit of Elovich and Langmuir models. 10%-TANA-MPC obtained an ultrahigh adsorption capacity of 564.4 mg g-1, which was approximately 2.1 times higher than that of unmodified porous carbon. 10%-TANA-MPC could be easily recycled up to 5 times, and after reuse, this adsorbent still remained highly stable in morphology and surface area. The contribution of H bonding, pore-filling, electrostatic and π-π interactions to chloramphenicol adsorption was clarified. It is recommended that TANA-modified MIL-53-NH2(Al)-derived porous carbons act as a potential adsorbent for removal of pollutants effectively.

Metal Effect on the Proton Conduction of Three Isostructural Metal-Organic Frameworks and Pseudo-Capacitance Behavior of the Cobalt Analogue

Three isostructural transition metal-organic frameworks, [M(bta)0.5(bpt)(H2O)2]·2H2O (M = Co (1), Ni (2), Zn (3), H4bta = 1,2,4,5-benzenetetracarboxylic acid, bpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole), were successfully constructed using different metal cations. These frameworks exhibit a three-dimensional network structure with multiple coordinated and lattice water molecules within the framework, contributing to high stability and a rich hydrogen-bond network. Proton conduction studies revealed that, at 333 K and 98% relative humidity, the proton conductivities (σ) of MOFs 1-3 reached 1.42 × 10-2, 1.02 × 10-2, and 6.82 × 10-3 S cm-1, respectively. Compared to the proton conductivity of the initial ligands, the σ values of the complexes increased by 2 orders of magnitude, with the activation energies decreasing from 0.36 to 0.18 eV for 1, 0.09 eV for 2, and 0.12 eV for 3. An in-depth analysis of the correlation between different metal centers and proton conduction performance indicated that the varying coordination abilities of the metal cations and the water absorption capacities of the frameworks might account for the differences in conductivity. Additionally, the potential of 1 as a supercapacitor electrode material was assessed. 1 exhibited a specific capacitance of 61.13 F g-1 at a current density of 0.5 A g-1, with a capacitance retention of 82.4% after 5000 cycles, making it a promising candidate for energy storage applications.

Leveraging Isoreticular Principle to Elucidate the Key Role of Inherent Hydrogen-Bonding Anchoring Sites in Enhancing Water Sorption Cyclability of Zr(IV) Metal-Organic Frameworks

Water adsorption/desorption cyclability of porous materials is a prerequisite for diverse applications, including atmospheric water harvesting (AWH), humidity autocontrol (HAC), heat pumps and chillers, and hydrolytic catalysis. However, unambiguous molecular insights into the correlation between underlying building blocks and the cyclability are still highly elusive. In this work, by taking advantage of the well-established isoreticular synthetic principle in Zr(IV) metal-organic frameworks (Zr-MOFs), we show that the inherent density of hydrogen atoms in the organic skeleton can play a key role in regulating the water sorption cyclability of MOFs. The ease of isoreticular practice of Zr-MOFs enables the successful syntheses of two pairs of isostructural Zr-MOFs (NU-901 and NU-903, NU-950 and SJTU-9) from pyrene- or benzene-cored carboxylate linkers, which feature scu and sqc topological nets, respectively. NU-901 and NU-950 comprised of pyrene skeletons carrying more hydrogen-bonding anchoring sites show distinctly inferior cyclability as compared with NU-903 and SJTU-9 built of benzene units. Single-crystal X-ray crystallography analysis of the hydrated structure clearly unveils the water molecule-involved interactions with the hydrogen-bonding donors of benzene moieties. Remarkably, NU-903 and SJTU-9 isomers exhibit outstanding water vapor sorption capacities as well as working capacities at the desired humidity range with potential implementations covering indoor humidity control and water harvesting. Our findings uncover the importance of hydrogen-bonding anchoring site engineering of organic scaffold in manipulating the framework durability toward water sorption cycle and will also likely facilitate the rational design and development of highly robust porous materials.

Metal-Organic Framework Stability in Water and Harsh Environments from Data-Driven Models Trained on the Diverse WS24 Data Set

Metal-organic frameworks (MOFs) are porous materials with applications in gas separations and catalysis, but a lack of water stability often limits their practical use given the ubiquity of water. Consequently, it is useful to predict whether a MOF is water-stable before investing time and resources into synthesis. Existing heuristics for designing water-stable MOFs lack generality and limit the diversity of explored chemistry due to narrowly defined criteria. Machine learning (ML) models offer the promise to improve the generality of predictions but require data. In an improvement on previous efforts, we enlarge the available training data for MOF water stability prediction by over 400%, adding 911 MOFs with water stability labels assigned through semiautomated manuscript analysis to curate the new data set WS24. The additional data are shown to improve ML model performance (test ROC-AUC > 0.8) over diverse chemistry for the prediction of both water stability and stability in harsher acidic conditions. We illustrate how the expanded data set and models can be used with a previously developed activation stability model in combination with genetic algorithms to quickly screen ∼10,000 MOFs from a space of hundreds of thousands for candidates with multivariate stability (upon activation, in water, and in acid). We uncover metal- and geometry-specific design rules for robust MOFs. The data set and ML models developed in this work, which we disseminate through an easy-to-use web interface, are expected to contribute toward the accelerated discovery of novel, water-stable MOFs for applications such as direct air gas capture and water treatment.

Design of Multivariate Biological Metal-Organic Frameworks: Toward Mimicking Active Sites of Enzymes

Mimicking enzymatic processes carried out by natural enzymes, which are highly efficient biocatalysts with key roles in living organisms, attracts much interest but constitutes a synthetic challenge. Biological metal-organic frameworks (bioMOFs) are potential candidates to be enzyme catalysis mimics, as they offer the possibility to combine biometals and biomolecules into open-framework porous structures capable of simulating the catalytic pockets of enzymes. In this work, we first study the catalase activity of a previously reported bioMOF, derived from the amino acid L-serine, with formula {CaIICuII6[(S,S)-serimox]3(OH)2(H2O)} · 39H2O (1) (serimox = bis[(S)-serine]oxalyl diamide), which is indeed capable to mimic catalase enzymes, in charge of preventing cell oxidative damage by decomposing, efficiently, hydrogen peroxide to water and oxygen (2H2O2 → 2 H2O + O2). With these results in hand, we then prepared a new multivariate bioMOF (MTV-bioMOF) that combines two different types of bioligands derived from L-serine and L-histidine amino acids with formula CaIICuII6[(S,S)-serimox]2[(S,S)-hismox]1(OH)2(H2O)}·27H2O (2) (hismox = bis[(S)-histidine]oxalyl diamide ligand). MTV-bioMOF 2 outperforms 1 degrading hydrogen peroxide, confirming the importance of the amino acid residue from the histidine amino acid acting as a nucleophile in the catalase degradation mechanism. Despite displaying a more modest catalytic behavior than other reported MOF composites, in which the catalase enzyme is immobilized inside the MOF, this work represents the first example of a MOF in which an attempt is made to replicate the active center of the catalase enzyme with its constituent elements and is capable of moderate catalytic activity.

Separable Metal-Organic Framework-Based Materials for the Adsorption of Emerging Contaminants

Thousands of chemicals have been released into the environment in recent decades. The presence of emerging contaminants (ECs) in water has emerged as a pressing concern. Adsorption is a viable solution for the removal of ECs. Metal-organic frameworks (MOFs) have shown great potential as efficient adsorbents, but their dispersed powder form limits their practical applications. Recently, researchers have developed various separable MOF-based adsorbents to improve their recyclability. The purpose of this review is to summarize the latest developments in the construction of separable MOF-based adsorbents and their applications in adsorbing ECs. The construction strategies for separable MOFs are classified into four categories: magnetic MOFs, MOF-fiber composites, MOF gels, and binder-assisted shaping. Typical emerging contaminants include pesticides, pharmaceuticals and personal care products, and endocrine-disrupting compounds. The adsorption performance of different materials is evaluated based on the results of static and dynamic adsorption experiments. Additionally, the regeneration methods of MOF-based adsorbents are discussed in detail to facilitate effective recycling and reuse. Finally, challenges and potential future research opportunities are proposed, including reducing performance losses during the shaping process, developing assessment systems based on dynamic purification and real polluted water, optimizing regeneration methods, designing multifunctional MOFs, and low-cost, large-scale synthesis of MOFs.

Nanoscale and chiral metal-organic frameworks for asymmetric reactions in water: bridging Lewis acid catalysis and biological systems

Nowadays, stereoselective control over the sheer variety of chemical transformations benefits from the multipotency of chiral Lewis acids. Their use under biocompatible conditions has long posed a challenge because profuse amounts of biogenic nucleophiles readily deactivate them. To bridge the gap between chiral Lewis acid catalysis and biocompatible chemistry, the conversion of UiO(BPY)-type nanosized metal-organic frameworks (NMOFs) into chiral variants was herein exemplified. The combination of an elongated 2,2'-bipyridyl linker and scandium salt with a hydrophobic anion proved essential to implement traits such as robustness, biocompatibility, and catalytic activity. The catalyst could construct sufficiently hydrophobic environments sequestered within the framework, catalyzing asymmetric ring-opening reactions of meso-epoxide with low catalyst loading to afford β-amino acid alcohols in high yield (up to >99%) with high enantioselectivity (up to 88%). Most impressively, it exhibited a tolerance to the ex vivo poisoning of chiral Lewis acid catalysis by biogenic nucleophiles in sharp contrast to conventional water-compatible Lewis acids.

Enabling C2H2/CO2 Separation Under Humid Conditions with a Methylated Copper MOF

As a unique subclass of metal-organic frameworks (MOFs), MOFs with open metal site (OMS) are demonstrated efficient gas separation performance through pi complexation with unsaturated hydrocarbons. However, their practical application faces the challenge of humidity that causes structure degradation and completive binding at the OMS. In this work, the effect of linker methylation of a copper MOF (BUT-155) on the C2H2/CO2 separation performance under humid condition is evaluated. The water adsorption isotherm, adsorption kinetics, and breakthrough under dry and humid conditions are performed. The BUT-155 with methylated linker exhibits lower water uptake and adsorption kinetics under humid condition (RH = 20%), in comparison with HKUST-1. Therefore, the C2H2/CO2 separation performance of BUT-155 is much less affected by water, especially under higher gas flow rate. Moreover, the dynamic C2H2/CO2 separation performance of BUT-155 can maintain five breakthrough cycles under humid conditions (RH = 20% and RH = 80%) without obvious performance degradation.

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.

Remediation of multifarious metal ions and molecular docking assessment for pathogenic microbe disinfection in aqueous solution by waste-derived Ca-MOF

The present study demonstrates an eco-friendly and cost-effective synthesis of calcium terephthalate metal-organic frameworks (Ca-MOF). The Ca-MOF were composed of metal ions (Ca2+) and organic ligands (terephthalic acid; TPA); the former was obtained from egg shells, and the latter was obtained from processing waste plastic bottles. Detailed characterization using standard techniques confirmed the synthesis of Ca-MOF with an average particle size of 461.9 ± 15 nm. The synthesized Ca-MOF was screened for its ability to remove multiple metal ions from an aqueous solution. Based on the maximum sorption capacity, Pb2+, Cd2+, and Cu2+ ions were selected for individual parametric batch studies. The obtained results were interpreted using standard isotherms and kinetic models. The maximum sorption capacity (qm) obtained from the Langmuir model was found to be 644.07 ± 47, 391.4 ± 26, and 260.5 ± 14 mg g-1 for Pb2+, Cd2+, and Cu2+, respectively. Moreover, Ca-MOF also showed an excellent ability to remove all three metal ions simultaneously from a mixed solution. The metal nodes and bonded TPA from Ca-MOF were dissociated by the acid dissolution method, which protonated and isolated TPA for reuse. Further, the crystal structure of Ca-MOF was prepared and docked with protein targets of selected pathogenic water-borne microbes, which showed its disinfection potential. Overall, multiple metal sorption capability, regeneration studies, and broad-spectrum antimicrobial activity confirmed the versatility of synthesized Ca-MOF for industrial wastewater treatment.

Spatial Heterogeneity and Strong Coupling of FeII /FeIII in an Individual Metal-Organic Framework Nanoparticle for Efficient CO2 Photoreduction

The synthesis and characterization of an FeII /FeIII metal-organic framework (MOF) nanocrystal with spatial heterogeneity that arises from the non-uniform distribution of different valence states is disclosed. The FeII /FeIII -Ni Prussian blue analog (PBA) delivers superior photocatalytic performance in the selective CO2 reduction reaction thanks to the strong FeII /FeIII coupling, with CO yield up to 12.27 mmol g-1 h-1 and 90.6% selectivity under visible-light irradiation. Density functional theory calculation and experimental studies prove that the spatial heterogeneity of FeII /FeIII in the individual MOF nanocrystal not only directs and expedites the charge transfer within a catalyst particle but also creates the heterogeneity of catalytically-active Ni sites for efficient CO2 photoreduction. The current findings add to a growing literature of materials with compositional heterogeneity and provide a reference for future research.

Non-CO2 greenhouse gas separation using advanced porous materials

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.

Water-stable metal-organic frameworks (MOFs): rational construction and carbon dioxide capture

Metal-organic frameworks (MOFs) are considered to be a promising porous material due to their excellent porosity and chemical tailorability. However, due to the relatively weak strength of coordination bonds, the stability (e.g., water stability) of MOFs is usually poor, which severely inhibits their practical applications. To prepare water-stable MOFs, several important strategies such as increasing the bonding strength of building units and introducing hydrophobic units have been proposed, and many MOFs with excellent water stability have been prepared. Carbon dioxide not only causes a range of climate and health problems but also is a by-product of some important chemicals (e.g., natural gas). Due to their excellent adsorption performances, MOFs are considered as a promising adsorbent that can capture carbon dioxide efficiently and energetically, and many water-stable MOFs have been used to capture carbon dioxide in various scenarios, including flue gas decarbonization, direct air capture, and purified crude natural gas. In this review, we first introduce the design and synthesis of water-stable MOFs and then describe their applications in carbon dioxide capture, and finally provide some personal comments on the challenges facing these areas.

Advances in metal-organic frameworks for water remediation applications

Rapid industrialization and agricultural development have resulted in the accumulation of a variety of harmful contaminants in water resources. Thus, various approaches such as adsorption, photocatalytic degradation and methods for sensing water contaminants have been developed to solve the problem of water pollution. Metal-organic frameworks (MOFs) are a class of coordination networks comprising organic-inorganic hybrid porous materials having organic ligands attached to inorganic metal ions/clusters via coordination bonds. MOFs represent an emerging class of materials for application in water remediation owing to their versatile structural and chemical characteristics, such as well-ordered porous structures, large specific surface area, structural diversity, and tunable sites. The present review is focused on recent advances in various MOFs for application in water remediation via the adsorption and photocatalytic degradation of water contaminants. The sensing of water pollutants using MOFs via different approaches, such as luminescence, electrochemical, colorimetric, and surface-enhanced Raman spectroscopic techniques, is also discussed. The high porosity and chemical tunability of MOFs are the main driving forces for their widespread applications, which have huge potential for their commercial use.

Recent advances in metal-organic framework (MOF)-based agricultural sensors for metal ions: a review

Metal ions have great significance for agricultural development, food safety, and human health. In turn, there exists an imperative need for the development of novel, sensitive, and reliable sensing techniques for various metal ions. Agricultural sensors for the diagnosis of both agricultural safety and nutritional health can establish quality and safety traceability systems of both agro-products and food to guarantee human health, even life safety. Metal-organic frameworks (MOFs) are utilized widely for the design of diversified sensors due to their distinctive structural characteristics and extraordinary optical and electrical properties. To serve agricultural sensors better, this review is dedicated to providing a brief overview of the synthesis of MOFs, the modification of MOFs, the fabrication of MOF-based film electrodes, the applications of MOF-based agricultural sensors for metal ions, which are centered on electrochemical sensors and optical sensors, and current challenges of MOF-based agricultural sensors. In addition, this review also provides potential future opportunities for the development and practical application of agricultural sensors.

Hot-Pressing Metal Covalent Organic Frameworks as Personal Protection Films

Effective personal protection is crucial for controlling infectious disease spread. However, commonly used personal protective materials such as disposable masks lack antibacterial/antiviral function and may lead to cross infection. Herein, a polyethylene glycol-assisted solvent-free strategy is proposed to rapidly synthesize a series of the donor-acceptor metal-covalent organic frameworks (MCOFs) (i.e., GZHMU-2, JNM-1, and JNM-2) under air atmosphere and henceforth extend it via in situ hot-pressing process to prepare MCOFs based films with photocatalytic disinfect ability. Best of them, the newly designed GZHMU-2 has a wide absorption spectrum (200 to 1500 nm) and can efficiently produce reactive oxygen species under sunlight irradiation, achieving excellent photocatalytic disinfection performance. After in situ hot-pressing as a film material, the obtained GZHMU-2/NMF can effectively kill E. coli (99.99%), S. aureus (99%), and H1N1 (92.5%), meanwhile possessing good reusability. Noteworthy, the long-term use of a GZHMU-2/NWF-based mask has verified no damage to the living body by measuring the expression of mouse blood routine, lung tissue, and inflammatory factors at the in-vivo level.

Multilevel-Regulated Metal-Organic Framework Platform Integrating Pore Space Partition and Open-Metal Sites for Enhanced CO2 Photoreduction to CO with Nearly 100% Selectivity

Rational design and regulation of atomically precise photocatalysts are essential for constructing efficient photocatalytic systems tunable at both the atomic and molecular levels. Herein, we propose a platform-based strategy capable of integrating both pore space partition (PSP) and open-metal sites (OMSs) as foundational features for constructing high-performance photocatalysts. We demonstrate the first structural prototype obtained from this strategy: pore-partitioned NiTCPE-pstp (TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene, pstp = partitioned stp topology). Nonpartitioned NiTCPE-stp is constructed from six-connected [Ni3(μ3-OH)(COO)6] trimer and TCPE linker to form 1D hexagonal channels with six coplanar OMSs directed at channel centers. After introducing triangular pore-partitioning ligands, half of the OMSs were retained, while the other half were used for PSP, leading to unprecedented microenvironment regulation of the pore structure. The resulting material integrates multiple advanced properties, including robustness, wider absorption range, enhanced electronic conductivity, and high CO2 adsorption, all of which are highly desirable for photocatalytic applications. Remarkably, NiTCPE-pstp exhibits excellent CO2 photoreduction activity with a high CO generation rate of 3353.6 μmol g-1 h-1 and nearly 100% selectivity. Theoretical and experimental studies show that the introduction of partitioning ligands not only optimizes the electronic structure to promote the separation and transfer of photogenerated carriers but also reduces the energy barrier for the formation of *COOH intermediates while promoting CO2 activation and CO desorption. This work is believed to be the first example to integrate PSP strategies and OMSs within metal-organic framework (MOF) photocatalysts, which provides new insight as well as new structural prototype for the design and performance optimization of MOF-based photocatalysts.

Selective cycloaddition of ethylene oxide to CO2 within the confined space of an amino acid-based metal-organic framework

Host-guest chemistry within the confined space of metal-organic frameworks (MOFs) offers an almost unlimited myriad of possibilities, hardly accessible with other materials. Here we report the synthesis and physical characterization, with atomic resolution by single-crystal X-ray diffraction, of a novel water-stable tridimensional MOF, derived from the amino acid S-methyl-L-cysteine, {SrZn6[(S,S)-Mecysmox]3(OH)2(H2O)}·9H2O (1), and its application as a robust and efficient solid catalyst for the cycloaddition reaction of ethylene/propylene oxide with CO2 to afford ethylene/propylene carbonate with yields of up to 95% and selectivity of up to 100%. These results nicely illustrate the great potential of MOFs to be game changers for the selective synthesis of industrially relevant products, representing a powerful alternative to the current heterogeneous catalysts.

A Water-Stable Cationic SIFSIX MOF for Luminescent Probing of Cr2 O7 2- via Single-Crystal to Single-Crystal Transformation

The sensing and monitoring of toxic oxo-anion contaminants in water are of significant importance to biological and environmental systems. A rare hydro-stable SIFSIX metal-organic framework, SiF6 @MOF-1, {[Cu(L)2 (H2 O)2 ]·(SiF6 )(H2 O)}n , with exchangeable SiF6 2- anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr2 O7 2- oxo-anion in an aqueous medium having high sensitivity, selectivity, and recyclability through fluorescence quenching phenomena. More importantly, the recognition and ion exchange mechanism is unveiled through the rarely explored single-crystal-to-single crystal (SC-SC) fashion with well-resolved structures. A thorough SC-SC study with interfering anions (Cl- , F- , I- , NO3 - , HCO3 - , SO4 2- , SCN- , IO3 - ) revealed no such transformations to take place, as per line with quenching studies. Density functional theory calculations revealed that despite a lesser binding affinity, Cr2 O7 2- shows strong orbital mixing and large driving forces for electron transfer than SiF6 2- , and thus enlightens the fluorescence quenching mechanism. This work inaugurates the usage of a SIFSIX MOF toward sensing application domain under aqueous medium where hydrolytic stability is a prime concern for their plausible implementation as sensor materials.

Studying Fluorescence Sensing of Acetone and Tryptophan and Antibacterial Properties Based on Zinc-Based Triple Interpenetrating Metal-Organic Skeletons

Two triple interpenetrating Zn(II)-based MOFs were studied in this paper. Named [Zn6(1,4-bpeb)4(IPA)6(H2O)]n (MOF-1) and {[Zn3(1,4-bpeb)1.5(DDBA)3]n·2DMF} (MOF-2), {1,4-bpeb = 1,4-bis [2-(4-pyridy1) ethenyl]benze, IPA = Isophthalic acid, DDBA = 3,3'-Azodibenzoic acid}, they were synthesized by the hydrothermal method and were characterized and stability tested. The results showed that MOF-1 had good acid-base stability and solvent stability. Furthermore, MOF-1 had excellent green fluorescence and with different phenomena in different solvents, which was almost completely quenched in acetone. Based on this phenomenon, an acetone sensing test was carried out, where the detection limit of acetone was calculated to be 0.00365% (volume ratio). Excitingly, the MOF-1 could also be used as a proportional fluorescent probe to specifically detect tryptophan, with a calculated detection limit of 34.84 μM. Furthermore, the mechanism was explained through energy transfer and competitive absorption (fluorescence resonance energy transfer (FRET)) and internal filtration effect (IFE). For antibacterial purposes, the minimum inhibitory concentrations of MOF-1 against Escherichia coli and Staphylococcus aureus were 19.52 µg/mL and 39.06 µg/mL, respectively, and the minimum inhibitory concentrations of MOF-2 against Escherichia coli and Staphylococcus aureus were 68.36 µg/mL and 136.72 µg/mL, respectively.

Understanding and controlling the nucleation and growth of metal-organic frameworks

Metal-organic frameworks offer a diverse landscape of building blocks to design high performance materials for implications in almost every major industry. With this diversity stems complex crystallization mechanisms with various pathways and intermediates. Crystallization studies have been key to the advancement of countless biological and synthetic systems, with MOFs being no exception. This review provides an overview of the current theories and fundamental chemistry used to decipher MOF crystallization. We then discuss how intrinsic and extrinsic synthetic parameters can be used as tools to modulate the crystallization pathway to produce MOF crystals with finely tuned physical and chemical properties. Experimental and computational methods are provided to guide the probing of MOF crystal formation on the molecular and bulk scale. Lastly, we summarize the recent major advances in the field and our outlook on the exciting future of MOF crystallization.

Water-Stable Fluorous Metal-Organic Frameworks with Open Metal Sites and Amine Groups for Efficient Urea Electrocatalytic Oxidation

Urea oxidation reaction (UOR) is one of the promising alternative anodic reactions to water oxidation that has attracted extensive attention in green hydrogen production. The application of specifically designed electrocatalysts capable of declining energy consumption and environmental consequences is one of the major challenges in this field. Therefore, the goal is to achieve a resistant, low-cost, and environmentally friendly electrocatalyst. Herein, a water-stable fluorinated Cu(II) metalorganic framework (MOF) {[Cu2 (L)(H2 O)2 ]·(5DMF)(4H2 O)}n (Cu-FMOF-NH2 ; H4 L = 3,5-bis(2,4-dicarboxylic acid)-4-(trifluoromethyl)aniline) is developed utilizing an angular tetracarboxylic acid ligand that incorporates both trifluoromethyl (-CF3 ) and amine (-NH2 ) groups. The tailored structure of Cu-FMOF-NH2 where linkers are connected by fluoride bridges and surrounded by dicopper nodes reveals a 4,24T1 topology. When employed as electrocatalyst, Cu-FMOF-NH2 requires only 1.31 V versus reversible hydrogen electrode (RHE) to deliver 10 mA cm-2 current density in 1.0 m KOH with 0.33 m urea electrolyte and delivered an even higher current density (50 mA cm-2 ) at 1.47 V versus RHE. This performance is superior to several reported catalysts including commercial RuO2 catalyst with overpotential of 1.52 V versus RHE. This investigation opens new opportunities to develop and utilize pristine MOFs as a potential electrocatalyst for various catalytic reactions.

Cobalt Species-Loaded MOFs as Chemiluminescent Catalysts for Monitoring Carbendazim

The application of active metal-based nanoscale catalysts as signal enhancers for chemiluminescent immunoassay (CLIA) is restricted by poor thermodynamic stability and ease of aggregation. For the present exploration, zirconium-based MOFs UiO-66-NH2 were adopted as supports to load cobalt species by an impregnation-reduction approach. Cobalt species were uniformly distributed in the framework architecture of the MOF materials. The prepared cobalt-loaded MOF hybrids, noted as UiO-66-NH2/Co, display superior chemiluminescence (CL) catalytic activity owing to the introduction of cobalt catalytic centers. The CL catalytic capability of UiO-66-NH2/Co hybrids is about 18 times of that of free cobalt ions at the same cobalt amount. The results of mechanism exploration manifest that the hybrids are capable of accelerating the decay of hydrogen peroxide and promoting the yield of reactive oxygen species. Based on their remarkable CL catalytic capability, a CLIA approach was proposed to monitor carbendazim by adopting the hybrids as signal probes, which showed the merits of high sensitivity and satisfactory selectivity. Carbendazim was quantitated within a concentration range of 0.05 to 60 ng mL-1, with a detection limit of 19.8 pg mL-1. The results for monitoring spiked samples verify the acceptable practicality of the proposed CLIA approach.

Ag2(0) dimers within a thioether-functionalized MOF catalyze the CO2 to CH4 hydrogenation reaction

Ultrasmall silver clusters in reduced state are difficult to synthesize since silver atoms tend to rapidly aggregate into bigger entities. Here, we show that dimers of reduced silver (Ag₂) are formed within the framework of a metal-organic framework provided with thioether arms in their walls (methioMOF), after reduction with NaBH₄ of the corresponding Ag⁺-methioMOF precursor. The resulting Ag₂-methioMOF catalyzes the methanation reaction of carbon dioxide (CO₂ to CH₄ hydrogenation reaction) under mild reaction conditions (1 atm CO₂, 4 atm H₂, 140 °C), with production rates much higher than Ag on alumina and even comparable to the state-of-the-art Ru on alumina catalyst (Ru-Al₂O₃) under these reaction conditions, according to literature results.

Unveiling Unexpected Modulator-CO2 Dynamics within a Zirconium Metal-Organic Framework

Carbon capture, storage, and utilization (CCSU) represents an opportunity to mitigate carbon emissions that drive global anthropogenic climate change. Promising materials for CCSU through gas adsorption have been developed by leveraging the porosity, stability, and tunability of extended crystalline coordination polymers called metal-organic frameworks (MOFs). While the development of these frameworks has yielded highly effective CO₂ sorbents, an in-depth understanding of the properties of MOF pores that lead to the most efficient uptake during sorption would benefit the rational design of more efficient CCSU materials. Though previous investigations of gas-pore interactions often assumed that the internal pore environment was static, discovery of more dynamic behavior represents an opportunity for precise sorbent engineering. Herein, we report a multifaceted in situ analysis following the adsorption of CO₂ in MOF-808 variants with different capping agents (formate, acetate, and trifluoroacetate: FA, AA, and TFA, respectively). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis paired with multivariate analysis tools and in situ powder X-ray diffraction revealed unexpected CO₂ interactions at the node associated with dynamic behavior of node-capping modulators in the pores of MOF-808, which had previously been assumed to be static. MOF-808-TFA displays two binding modes, resulting in higher binding affinity for CO₂. Computational analyses further support these dynamic observations. The beneficial role of these structural dynamics could play an essential role in building a deeper understanding of CO₂ binding in MOFs.

Exploring the Role of Amino Acid-Derived Multivariate Metal-Organic Frameworks as Catalysts in Hemiketalization Reactions

Understanding the host-guest chemistry in MOFs represents a research field with outstanding potential to develop in a rational manner novel porous materials with improved performances in fields such as heterogeneous catalysis. Herein, we report a family of three isoreticular MOFs derived from amino acids and study the influence of the number and nature of functional groups decorating the channels as a catalyst in hemiketalization reactions. In particular, a multivariate (MTV) MOF 3, prepared by using equal percentages of amino acids L-serine and L-mecysteine, in comparison to single-component ("traditional") MOFs, derived from either L-serine or L-mecysteine (MOFs 1 and 2), exhibits the most efficient catalytic conversions for the hemiketalization of different aldehydes and ketalization of cyclohexanone. On the basis of the experimental data reported, the good catalytic performance of MTV-MOF 3 is attributed to the intrinsic heterogeneity of MTV-MOFs. These results highlight the potential of MTV-MOFs as strong candidates to mimic natural nonacidic enzymes, such as glycosidases, and to unveil novel catalytic mechanisms not so easily accessible with other microporous materials.

Low-concentration CO2 capture using metal-organic frameworks - current status and future perspectives

The ever-increasing atmospheric CO₂ level is considered to be the major cause of climate change. Although the move away from fossil fuel-based energy generation to sustainable energy sources would significantly reduce the release of CO₂ into the atmosphere, it will most probably take time to be fully implemented on a global scale. On the other hand, capturing CO₂ from emission sources or directly from the atmosphere are robust approaches that can reduce the atmospheric CO₂ concentration in a relatively short time. Here, we provide a perspective on the recent development of metal-organic framework (MOF)-based solid sorbents that have been investigated for application in CO₂ capture from low-concentration (<10 000 ppm) CO₂ sources. We summarized the different sorbent engineering approaches adopted by researchers, both from the sorbent development and processing viewpoints. We also discuss the immediate challenges of using MOF-based CO₂ sorbents for low-concentration CO₂ capture. MOF-based materials, with tuneable pore properties and tailorable surface chemistry, and ease of handling, certainly deserve continued development into low-cost, efficient CO₂ sorbents for low-concentration CO₂ capture.

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework

Developing practical storage technologies for acetylene (C₂ H₂ ) is important but challenging because C₂ H₂ is useful but explosive. Here, a novel metal-organic framework (MOF) (FJI-H36) with adaptive channels was prepared. It can effectively capture C₂ H₂ (159.9 cm³  cm^-3 ) at 1 atm and 298 K, possessing a record-high storage density (561 g L^-1 ) but a very low adsorption enthalpy (28 kJ mol^-1 ) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C₂ H₂ can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C₂ H₂ . Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C₂ H₂ . This will provide a useful strategy for developing practical and efficient adsorbents for C₂ H₂ storage.

A porous cobalt(II)-organic framework exhibiting high room temperature proton conductivity and field-induced slow magnetic relaxation

A two-dimensional (2D) cobalt(II) metal-organic framework (MOF) constructed by a ditopic organic ligand, formulated as {[Co(Hbic)(H₂O)]·4H₂O}_n (1) (H₂bic = 1H-benzimidazole-5-carboxylic acid), was hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction shows that the distorted octahedral Co²⁺ ions, as coordination nodes, are bridged to form 2D honeycomb networks, which are further organized into a 3D supramolecular porous framework through multiple hydrogen bonds and interlayer π-π interactions. Dynamic crystallography experiments reveal the anisotropic thermal expansion behavior of the lattice, suggesting a flexible hydrogen-bonded 3D framework. Interestingly, hydrogen-bonded (H₂O)₄ tetramers were found to be located in porous channels, yielding 1D proton transport pathways. As a result, the compound exhibited a high room-temperature proton conductivity of 1.6 × 10^-4 S cm^-1 under a relative humidity of 95% through a Grotthuss mechanism. Magnetic investigations combined with theoretical calculations reveal giant easy-plane magnetic anisotropy of the distorted octahedral Co²⁺ ions with the experimental and computed D values being 87.1 and 109.3 cm^-1, respectively. In addition, the compound exhibits field-induced slow magnetic relaxation behavior at low temperatures with an effective energy barrier of U_eff = 45.2 cm^-1. Thus, the observed electrical and magnetic properties indicate a rare proton conducting SIM-MOF. The foregoing results provide a unique bifunctional cobalt(II) framework material and suggest a promising way to achieve magnetic and electrical properties using a supramolecular framework platform.

(Multivariate)-Metal-Organic Framework for Highly Efficient Antibiotic Capture from Aquatic Environmental Matrices

Contamination of aquatic environments by pharmaceuticals used by modern societies has become a serious threat to human beings. Among them, antibiotics are of particular concern due to the risk of creating drug-resistant bacteria and, thus, developing efficient protocols for the capture of this particular type of drug is mandatory. Herein, we report a family of three isoreticular MOFs, derived from natural amino acids, that exhibit high efficiency in the removal of a mixture of four distinct families of antibiotics, such as fluoroquinolones, penicillins, lincomycins, and cephalosporins, as solid-phase extraction (SPE) sorbents. In particular, a multivariate (MTV)-MOF, prepared using equal percentages of amino acids l-serine and l-methionine, also exhibits outstanding recyclability, surpassing the benchmark material activated carbon. The good removal performance of the MTV-MOF was rationalized by means of single-crystal X-ray diffraction. These results highlight the situation of MOFs as a real and promising alternative for the capture of antibiotics from environmental matrices, especially wastewater streams.

Room-temperature synthesis of nanometric and luminescent silver-MOFs

Three silver-MOFs were prepared using an optimized, room-temperature methodology starting from AgNO₃ and dicarboxylate ligands in water/ethanol yielding Ag ₂ BDC, Ag ₂ NDC (UAM-1), and Ag ₂ TDC (UAM-2) at 38%-48% (BDC, benzenedicarboxylate; NDC, 1,8-naphthalene-dicarboxylate; TDC, p-terphenyl-4,4″-dicarboxylate). They were characterized by PXRD/FT-IR/TGA/photoluminescence spectroscopy, and the former two by SEM. These materials started decomposing at 330°C, while showing stability. The crystal structure of UAM-1 was determined by PXRD, DFT calculations, and Rietveld refinement. In general, the structure was 3D, with the largest Ag-O bond interlinking 2D layers. The FT-IR spectra revealed 1450 and 1680 bands (cm^-1) of asymmetrically stretching aniso-/iso-bidentate -COO in coordination with 2/3-Ag atoms, accompanied by Ag-O bands at 780-740 cm^-1, all demonstrating the network formation. XRD and SEM showed nanometric-scale crystals in Ag₂BDC, and UAM-1 developed micrometric single-stranded/agglomerated fibrillar particles of varying nanometric widths. Luminescence spectroscopy showed emission by Ag₂BDC, which was attributed to ligand-to-metal or ligand-to-metal-metal transitions, suggesting energy transfer due to the short distance between adjacent BDC molecules. UAM-1 and UAM-2 did not show luminescence emission attributable to ligand-to-metal transition; rather, they presented only UV emission. The stabilities of Ag₂BDC and UAM-1 were evaluated in PBS/DMEM/DMEM+FBS media by XRD, which showed that they lost their crystallinity, resulting in AgCl due to soft-soft (Pearson's principle) affinity.