Isoreticular chemistry within metal–organic frameworks for gas storage and separation

Construction of a series of pH stable Ca-based MOFs, their CO2 adsorption and catalytic activity

In this study, three different solvent systems have been employed to investigate the effect of reaction parameters on the synthesis of four alkaline earth metal-based MOFs namely [Ca(0.5 1,4-phenyl diacetic acid)2(H2O)DMF]∞ (Ca-MOF-1), [Ca(1,4-naphthalene dicarboxylate)DMF]∞ (Ca-MOF-2), [Ca2(0.5 1,2,4,5-benzene tetracarboxylate)2(H2O)3DMF]∞ (Ca-MOF-3) and [Ca2(2,6-naphthalene dicarboxylate)2(H2O)6]∞ (Ca-MOF-4). The crystal structures of these four MOFs have been resolved through single crystal X-ray analysis and the bulk phase purity of these MOFs was assessed using PXRD and FT-IR analysis. To check the stability of these MOFs, thermogravimetric analysis (TGA) was carried out. To analyze the robustness of these MOFs, the PXRD of the samples was also collected at different pH levels. These MOFs were further explored as Lewis acid catalysts for the alcoholysis of epoxides and the activity of these catalysts depend on the open metal sites present in the MOFs. The catalytic activity follows the order: Ca-MOF-2 > Ca-MOF-4 > Ca-MOF-1 > Ca-MOF-3. The activity was also checked with various epoxide substrates using Ca-MOF-2. Density functional theory (DFT) calculations also support this trend with the help of the thermodynamic feasibility of epoxide binding, considering model MOF structures. The weak interaction between the epoxide oxygen and the metal centre of the most stable MOF structure has also been clarified by computational studies.

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

Recent Advances in Pristine Iron Triad Metal-Organic Framework Cathodes for Alkali Metal-Ion Batteries

Pristine iron triad metal-organic frameworks (MOFs), i.e., Fe-MOFs, Co-MOFs, Ni-MOFs, and heterometallic iron triad MOFs, are utilized as versatile and promising cathodes for alkali metal-ion batteries, owing to their distinctive structure characteristics, including modifiable and designable composition, multi-electron redox-active sites, exceptional porosity, and stable construction facilitating rapid ion diffusion. Notably, pristine iron triad MOFs cathodes have recently achieved significant milestones in electrochemical energy storage due to their exceptional electrochemical properties. Here, the recent advances in pristine iron triad MOFs cathodes for alkali metal-ion batteries are summarized. The redox reaction mechanisms and essential strategies to boost the electrochemical behaviors in associated electrochemical energy storage devices are also explored. Furthermore, insights into the future prospects related to pristine iron triad MOFs cathodes for lithium-ion, sodium-ion, and potassium-ion batteries are also delivered.

Network topology diversification of porous organic salts

Hydrogen-bonded organic frameworks (HOFs) are porous organic materials constructed via hydrogen bonds. HOFs have solubility in specific high-polar organic solvents. Therefore, HOFs can be returned to their components and can be reconstructed, which indicates their high recyclability. Network topologies, which are the frameworks of porous structures, control the pore sizes and shapes of HOFs. Therefore, they strongly affect the functions of porous materials. However, hydrogen bonds are usually weak interactions, and the design of the intended network topology in HOFs from their components has been challenging. Porous organic salts (POSs) are an important class of HOFs, are hierarchically constructed via strong charge-assisted hydrogen bonds between sulfonic acids and amines, and therefore are expected to have high designability of the porous structure. However, the network topology of POSs has been limited to only dia-topology. Here, we combined tetrasulfonic acid with the adamantane core (4,4',4'',4'''-(adamantane-1,3,5,7-tetrayl)tetrabenzenesulfonic acid; AdPS) and triphenylmethylamines with modified substituents in para-positions of benzene rings (TPMA-X, X = F, methyl (Me), Cl, Br, I). We changed the steric hindrance between the adamantane and substituents (X) in TPMA-X and obtained not only the common dia-topology for POSs but also rare sod-topology, and lon- and uni-topologies that are formed for the first time in HOFs. Changing template molecules under preparation helped in successfully isolating the porous structures of AdPS/TPMA-Me with dia-, lon-, and sod-topologies which exhibited different gas adsorption properties. Therefore, for the first time, we demonstrated that the steric design of HOF components facilitated the formation, diversification, and control of the network topologies and functions of HOFs.

A dual-responsive RhB-doped MOF probe for simultaneous recognition of Cu2+ and Fe3

Based on the dual response of RhB@UiO-67 (1:6) to Cu2+ and Fe3+, a proportional fluorescent probe with (I392/I581) as the output signal was developed to recognize Cu2+ and Fe3+. Developing highly sensitive and selective trace metal ions probes is crucial to human health and ecological sustainability. In this work, a series of ratio fluorescent probes (RhB@UiO-67) were successfully synthesized using a one-pot method to enable fluorescence sensing of Cu2+ and Fe3+ at low concentrations. The proportional fluorescent probe RhB@UiO-67 (1:6) exhibited simultaneous quenching of Cu2+ and Fe3+, which was found to be of interest. Furthermore, the limits of detection (LODs) for Cu2+ and Fe3+ were determined to be 2.76 μM and 0.76 μM, respectively, for RhB@UiO-67 (1:6). These values were significantly superior to those reported for previous sensors, indicating the probe's effectiveness in detecting Cu2+ and Fe3+ in an ethanol medium. Additionally, RhB@UiO-67 (1:6) demonstrated exceptional immunity and reproducibility towards Cu2+ and Fe3+. The observed fluorescence quenching of Cu2+ and Fe3+ was primarily attributed to the mechanisms of fluorescence resonance energy transfer (FRET), photoinduced electron transfer (PET), and competitive absorption (CA). This work establishes a valuable foundation for the future study and utilization of Cu2+ and Fe3+ sensing technologies.

Stimulus-Induced Dynamic Behavior Regulation of Flexible Crystals through the Tuning of Module Rigidity

Introducing dynamic behavior into periodic frameworks has borne fruit in the form of flexible porous crystals. The detailed molecular design of frameworks in order to control their collective dynamics is of particular interest, for example, to achieve stimulus-induced behavior. Herein, by varying the degree of rigidity of ditopic pillar linkers, two isostructural flexible metal-organic frameworks (MOFs) with common rigid supermolecular building bilayers were constructed. The subtle substitution of single (in bibenzyl-4,4'-dicarboxylic acid; H2BBDC) with double (in 4,4'-stilbenedicarboxylic acid; H2SDC) C-C bonds in pillared linkers led to markedly different flexible behavior of these two MOFs. Upon the removal of guest molecules, both frameworks clearly show reversible single-crystal-to-single-crystal transformations involving the cis-trans conformation change and a resulting swing of the corresponding pillar linkers, which gives rise to Flex-Cd-MOF-1a and Flex-Cd-MOF-2a, respectively. Strikingly, a more favorable gas-induced dynamic behavior in Flex-Cd-MOF-2a was verified in detail by stepwise C3H6/C3H8 sorption isotherms and the corresponding in situ powder X-ray diffraction experiments. These insights are strongly supported by molecular modeling studies on the sorption mechanism that explores the sorption landscape. Furthermore, a consistency between the macroscopic elasticity and microscopic flexibility of Flex-Cd-MOF-2 was observed. This work fuels a growing interest in developing MOFs with desired chemomechanical functions and presents detailed insights into the origins of flexible MOFs.

Deep learning and big data mining for Metal-Organic frameworks with high performance for simultaneous desulfurization and carbon capture

Carbon capture and desulfurization of flue gases are crucial for the achievement of carbon neutrality and sustainable development. In this work, the "one-step" adsorption technology with high-performance metal-organic frameworks (MOFs) was proposed to simultaneously capture the SO2 and CO2. Four machine learning algorithms were used to predict the performance indicators (NCO2+SO2, SCO2+SO2/N2, and TSN) of MOFs, with Multi-Layer Perceptron Regression (MLPR) showing better performance (R2 = 0.93). To address sparse data of MOF chemical descriptors, we introduced the Deep Factorization Machines (DeepFM) model, outperforming MLPR with a higher R2 of 0.95. Then, sensitivity analysis was employed to find that the adsorption heat and porosity were the key factors for SO2 and CO2 capture performance of MOF, while the influence of open alkali metal sites also stood out. Furthermore, we established a kinetic model to batch simulate the breakthrough curves of TOP 1000 MOFs to investigate their dynamic adsorption separation performance for SO2/CO2/N2. The TOP 20 MOFs screened by the dynamic performance highly overlap with those screened by the static performance, with 76 % containing open alkali metal sites. This integrated approach of computational screening, machine learning, and dynamic analysis significantly advances the development of efficient MOF adsorbents for flue gas treatment.

Metal-Organic Framework Based Sensors for Benzene Vapor

Sensing of benzene vapor is a hot spot due to the volatile drastic carcinogen even at trace concentration. However, achieving convenient and rapid detection is still a challenge. As a sort of functional porous material, metal-organic frameworks (MOFs) have been developed as detection sensors by adsorbing benzene vapor and converting it into other signals (fluorescence intensity/wavelength, chemiresistive, weight or color, etc.). Supramolecular interaction between benzene molecules and the host framework, aperture size/shape and structural flexibility are influential factors in the performance of MOF-based sensors. Therefore, enhancing the host-guest interactions between the host framework and benzene molecules, or regulating the diffusion rate of benzene molecules by changing the aperture size/shape and flexibility of the host framework to enhance the detection signal are effective strategies for constructing MOF-based sensors. This concept highlights several types of MOF-based sensors for the detection of benzene vapor.

Interface Engineering-Modulated Nanoscale Bimetallic CoFe-MIL-88A In-Situ-Grown on 2D V2CTx MXene for Electrocatalytic Nitrogen Reduction

The electrochemical nitrogen reduction reaction (eNRR) provides a sustainable green development route for the nitrogen-neutral cycle. In this work, bimetallic CoFe-MIL-88A with two active sites (Fe, Co) were immobilized on a 2D V2CTx MXene surface by in situ growth method to achieve the purpose of the control interface. A large number of heterostructures are formed between small CoFe-MIL-88A and V2CTx, which regulate the electron transfer between the catalyst interfaces. The adsorption and activation of nitrogen on the active sites were enhanced, and the NRR reaction kinetics was accelerated. CoFe-MIL-88A is tightly arranged on V2CTx, which makes CoFe-MIL-88A/V2CTx have better hydrophobicity and can significantly inhibit the hydrogen evolution reaction. The synergistic effect of multicatalytic active sites and multi-interface structure of CoFe-MIL-88A/V2CTx MXene is propitious to nitrogen efficiently and stably to convert into ammonia under environmental conditions with superior selectivity and good catalytic activity. The NH3 yield rate is 29.47 μg h-1 mgcat-1 at -0.3 V vs RHE, and the Faradaic efficiency (FE) is 28.86% at -0.1 V vs RHE. The catalytic mechanism was verified to conform to the distal pathway. This work will provide a new way to develop an MXene-based electrocatalyst for eNRR.

Controlling the Uptake and Release of Semiochemicals in Channel-Type Metal-Organic Frameworks Through Pore Expansion

Semiochemicals can be used to manipulate insect behaviour for sustainable pest management strategies, but their high volatility is a major issue for their practical implementation. Inclusion of these molecules within porous materials is a potential solution to this issue, as it can allow for a slower and more controlled release. In this work, we demonstrate that a series of Zr(IV) and Al(III) metal-organic frameworks (MOFs) with channel-type pores enable controlled release of three semiochemicals over 100 days by pore size design, with the uptake and rate of release highly dependent on the pore size. Insight from grand canonical Monte Carlo simulations indicates that this is due to weaker MOF-guest interactions per guest molecule as the pore size increases. These MOFs are all stable post-release and can be reloaded to show near-identical re-release profiles. These results provide valuable insight on the diffusion behaviour of volatile guests in MOFs, and for the further development of porous materials for sustainable agriculture applications.

Enhanced photoreduction efficiency of Cr(VI) driven by visible light in a new Zr-based metal-organic framework modified by hydroxyl groups

While metal-organic framework (MOF) photocatalysts have demonstrated a unique Cr(VI) photoreduction capability in recent decades, their performance is still insufficient for practical applications because of their low Cr(VI) uptake and poor visible light response. To cope with these drawbacks, a new OH-modified Zr-based MOF, termed HCMUE-1, was successfully prepared via a solvothermal method in this work. The complete characterization of HCMUE-1 was performed through various techniques, including powder X-ray diffraction (PXRD), Raman spectroscopy, Fourier transform infrared (FT-IR), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), scanning electron microscopy combined with energy-dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). The obtained data exhibited the excellent Cr(VI) photoreduction efficiency of HCMUE-1, reaching up to 98% after 90 min and almost 100% after 120 min under visible light illumination in a low acidic medium. Noteworthily, HCMUE-1 retained the same Cr(VI) removal rate for at least seven cycles without considerable loss. Further experimental investigations demonstrated that the structural stability and surface morphology of HCMUE-1 were retained after photoreduction. Moreover, the photocatalytic reduction mechanism of Cr(VI) to Cr(III) was interpreted through a series of systematic experimental measurements. These results indicate that HCMUE-1 possesses potential as an efficient photocatalyst for reducing toxic Cr(VI) species from wastewater in real-life conditions.

Influence of Humidity on Layer-by-Layer Growth and Structure in Coordination Networks

Metal-organic frameworks (MOFs) are promising materials because of their high designability of pores and functionalities. Especially, MOF thin films and their properties have been investigated toward applications in nanodevices. Typically, MOF thin films are fabricated by using a bottom-up method such as layer-by-layer (LbL) growth in air. Because the water molecules can coordinate and be replaced with organic linkers during synthesis, humidity conditions will be expected to influence the LbL growth processes. In this study, we fabricated MOF thin films composed of Zn2+, tetrakis-(4-carboxyphenyl)-porphyrin (TCPP), and 4,4'-bipyridyl (bpy) at 10 and 40% relative humidity (RH) conditions. Then, we investigated the humidity effects on chemical compositions of TCPP and bpy, periodic structure, orientation, and surface morphology. At high RH, coordination replacement of water with the organic linkers becomes more competitive than that at low RH, resulting in a different TCPP/bpy composition ratio between the two RH conditions. Also, more frequent coordination replacements of water with the organic linkers at high RH led to the formation of phases other than that observed at low RH, loss of growth orientation, and rough surface. The findings clarified the importance of controlling the RH condition during LbL growth to obtain the desired coordination networks.

Cobalt MOF-Based Porous Carbonaceous Spheres for Multimodal Soft Actuator Exhibiting Intricate Biomimetic Motions

The advancement of active electrode materials is essential to meet the demand for multifaceted soft robotic interactions. In this study, a new type of porous carbonaceous sphere (PCS) for a multimodal soft actuator capable of both magnetoactive and electro-ionic responses is reported. The PCS, derived from the simultaneous oxidative and reductive breakdown of specially designed cobalt-based metal-organic frameworks (Co-MOFs) with varying metal-to-ligand ratios, exhibits a high specific surface area of 529 m2 g-1 and a saturated magnetization of 142.7 Am2 kg-1. The size of the PCS can be controlled through the Ostwald ripening mechanism, while the porous structure can be regulated by adjusting the metal-to-ligand mol ratio. Its exceptional compatibility with poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) enables the creation of uniform electrode, crucial for producing soft actuators that work in both magnetic and electrical fields. Operated at an ultralow voltage of 1 V, the PCS-based actuator generates a blocking force of 47.5 mN and exhibits significant bending deflection even at an oscillation frequency of 10 Hz. Employing this simultaneous multimodal actuation ensures the dynamic and complex motions of a balancing bird robot and a dynamic eagle robot. This advancement marks a significant step toward the realization of more dynamic and versatile soft robotic systems.

Expanding the Reticular Chemistry Building Block Library toward Highly Connected Nets: Ultraporous MOFs Based on 18-Connected Ternary, Trigonal Prismatic Superpolyhedra

The chemistry of metal-organic frameworks (MOFs) continues to expand rapidly, providing materials with diverse structures and properties. The reticular chemistry approach, where well-defined structural building blocks are combined together to form crystalline open framework solids, has greatly accelerated the discovery of new and important materials. However, its full potential toward the rational design of MOFs relies on the availability of highly connected building blocks because these greatly reduce the number of possible structures. Toward this, building blocks with connectivity greater than 12 are highly desirable but extremely rare. We report here the discovery of novel 18-connected, trigonal prismatic, ternary building blocks (tbb's) and their assembly into unique MOFs, denoted as Fe-tbb-MOF-x (x: 1, 2, 3), with hierarchical micro- and mesoporosity. The remarkable tbb is an 18-c supertrigonal prism, with three points of extension at each corner, consisting of triangular (3-c) and rectangular (4-c) carboxylate-based organic linkers and trigonal prismatic [Fe3(μ3-Ο)(-COO)6]+ clusters. The tbb's are linked together by an 18-c cluster made of 4-c ligands and a crystallographically distinct Fe3(μ3-Ο) trimer, forming overall a 3-D (3,4,4,6,6)-c five nodal net. The hierarchical, highly porous nature of Fe-tbb-MOF-x (x: 1, 2, 3) was confirmed by recording detailed sorption isotherms of Ar, CH4, and CO2 at 87, 112, and 195 K, respectively, revealing an ultrahigh BET area (4263-4847 m2 g-1) and pore volume (1.95-2.29 cm3 g-1). Because of the observed ultrahigh porosities, the H2 and CH4 storage properties of Fe-tbb-MOF-x were investigated, revealing well-balanced high gravimetric and volumetric deliverable capacities for cryoadsorptive H2 storage (11.6 wt %/41.4 g L-1, 77 K/100 bar-160 K/5 bar), as well as CH4 storage at near ambient temperatures (367 mg g-1/160 cm3 STP cm-3, 5-100 bar at 298 K), placing these materials among the top performing MOFs. The present work opens new directions to apply reticular chemistry for the construction of novel MOFs with tunable porosities based on contracted or expanded tbb analogues.

Continuous-Flow Catalysis Using Phosphine-Metal Complexes on Porous Polymers: Designing Ligands, Pores, and Reactors

Continuous-flow syntheses using immobilized catalysts can offer efficient chemical processes with easy separation and purification. Porous polymers have gained significant interests for their applications to catalytic systems in the field of organic chemistry. The porous polymers are recognized for their large surface area, high chemical stability, facile modulation of surface chemistry, and cost-effectiveness. It is crucial to immobilize transition-metal catalysts due to their difficult separation and high toxicity. Supported phosphine ligands represent a noteworthy system for the effective immobilization of metal catalysts and modulation of catalytic properties. Researchers have been actively pursuing strategies involving phosphine-metal complexes supported on porous polymers, aiming for high activities, durabilities, selectivities, and applicability to continuous-flow systems. This review provides a concise overview of phosphine-metal complexes supported on porous polymers for continuous-flow catalytic reactions. Polymer catalysts are categorized based on pore sizes, including micro-, meso-, and macroporous polymers. The characteristics of these porous polymers are explored concerning their efficiency in immobilized catalysis and continuous-flow systems.

Strategies to Improve Electrical Conductivity in Metal-Organic Frameworks: A Comparative Study

Metal-organic frameworks (MOFs), formed by the combination of both inorganic and organic components, have attracted special attention for their tunable porous structures, chemical and functional diversities, and enormous applications in gas storage, catalysis, sensing, etc. Recently, electronic applications of MOFs like electrocatalysis, supercapacitors, batteries, electrochemical sensing, etc., have become a major research topic in MOF chemistry. However, the low electrical conductivity of most MOFs represents a major handicap in the development of these emerging applications. To overcome these limitations, different strategies have been developed to enhance electrical conductivity of MOFs for their implementation in electronic devices. In this review, we outline all these strategies employed to increase the electronic conduction in both intrinsically (framework-modulated) and extrinsically (guests-modulated) conducting MOFs.

Fe-Co-Based Metal-Organic Frameworks as Peroxidase Mimics for Sensitive Colorimetric Detection and Efficient Degradation of Aflatoxin B1

Building multifunctional platforms for integrating the detection and control of hazards has great significance in food safety and environment protection. Herein, bimetallic Fe-Co-based metal-organic frameworks (Fe-Co-MOFs) peroxidase mimics are prepared and applied to develop a bifunctional platform for the synergetic sensitive detection and controllable degradation of aflatoxin B1 (AFB1). On the one hand, Fe-Co-MOFs with excellent peroxidase-like activity are combined with target-induced catalyzed hairpin assembly (CHA) to construct a colorimetric aptasensor for the detection of AFB1. Specifically, the binding of aptamer with AFB1 releases the prelocked Trigger to initiate the CHA cycle between hairpin H2-modified Fe-Co-MOFs and hairpin H1-tethered magnetic nanoparticles to form complexes. After magnetic separation, the colorimetric signal of the supernatant in the presence of TMB and H2O2 is inversely proportional to the target contents. Under optimal conditions, this biosensor enables the analysis of AFB1 with a limit of detection of 6.44 pg/mL, and high selectivity and satisfactory recovery in real samples are obtained. On the other hand, Fe-Co-MOFs with remarkable Fenton-like catalytic degradation performance for organic contaminants are further used for the detoxification of AFB1 after colorimetric detection. The AFB1 is almost completely removed within 120 min. Overall, the introduction of CHA improves the sensing sensitivity; efficient postcolorimetric-detection degradation of AFB1 reduces the secondary contamination and risk to the experimental environment and operators. This strategy is expected to provide ideas for designing other multifunctional platforms to integrate the detection and degradation of various hazards.

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Design and application of dual-emission metal-organic framework-based ratiometric fluorescence sensors

Metal-organic frameworks (MOFs) are novel inorganic-organic hybridized crystals with a wide range of applications. In the last twenty years, fluorescence sensing based on MOFs has attracted much attention. MOFs can exhibit luminescence from metal nodes, ligands or introduced guests, which provides an excellent fluorescence response in sensing. However, single-signal emitting MOFs are susceptible to interference from concentration, environment, and excitation intensity, resulting in poor accuracy. To overcome the shortcomings, dual-emission MOF-based ratiometric fluorescence sensors have been proposed and rapidly developed. In this review, we first introduce the luminescence mechanisms, synthetic methods, and detection mechanisms of dual-emission MOFs, highlight the strategies for constructing ratiometric fluorescence sensors based on dual-emission MOFs, and classify them into three categories: intrinsic dual-emission and single-emission MOFs with luminescent guests, and non-emission MOFs with other luminescent materials. Then, we summarize the recent advances in dual-emission MOF-based ratiometric fluorescence sensors in various analytical industries. Finally, we discuss the current challenges and prospects for the future development of these sensors.

Deep Learning Enabled SERS Identification of Gaseous Molecules on Flexible Plasmonic MOF Nanowire Films

Through the capture of a target molecule at the metal surface with a highly confined electromagnetic field induced by surface plasmon, surface enhanced Raman spectroscopy (SERS) emerges as a spectral analysis technology with high sensitivity. However, accurate SERS identification of a gaseous molecule with low density and high velocity is still a challenge due to its difficulty in capture. In this work, a flexible paper-based plasmonic metal-organic framework (MOF) film consisting of Ag nanowires@ZIF-8 (AgNWs@ZIF-8) is fabricated for SERS detection of gaseous molecules. Benefiting from its micronanopores generated by the nanowire network and ZIF-8 shell, the effective capture of the gaseous molecule is achieved, and its SERS spectrum is obtained in this paper-based flexible plasmonic MOF nanowire film. With optimal structure parameters, spectra of gaseous 4-aminothiophenol, 4-mercaptophenol, and dithiohydroquinone demonstrate that this film has good SERS performance, which could maintain obvious Raman signals within 30 days during reproducible detection. To realize SERS identification of gaseous molecules, deep learning is performed based on the SERS spectra of the mixed gaseous analyte obtained in this flexible porous film. The results point out that an artificial neural network algorithm could identify gaseous aldehydes (gaseous biomarker of colorectal cancer) in simulated exhaled breath with high accuracy at 93.7%. The integration of the flexible paper-based film sensors with deep learning offers a promising new approach for noninvasive colorectal cancer screening. Our work explores SERS applications in gaseous analyte detection and has broad potential in clinical medicine, food safety, environmental monitoring, etc.

Finely Tuning Metal Ion Valences of [Fe3-xMx(μ3-OH)(Carboxyl)6(pyridyl)2] Cluster-Based ant-MOFs for Highly Improved CO2 Capture Performances

Solvothermal reactions of different trinuclear precursors and 5-(pyridin-4-yl)isophthalic acid (H2L) successfully led to four anionic ant topological MOFs as Fe3-xMx(μ3-OH)(CH3COO)2(L)2·(DMA+)·DMF [M = Mn(II), Fe(II), Co(II), x = 0, 1, 2 and 3], namely, NJTU-Bai79 [NJTU-Bai = Nanjing Tech University Bai's group, Mn3(μ3-OH)], NJTU-Bai80 [Fe2Mn(μ3-OH)], NJTU-Bai81 [Fe3(μ3-OH)], and NJTU-Bai82 [Fe2Co(μ3-OH)], which possess the narrow pores (2.5-6.0 Å). NJTU-Bai80-82 is able to be tuned to the neutral derivatives [NJTU-Bai80-82(-ox), ox = oxidized] with M2+ ions oxidized to M3+ ones in the air and the OH- ions coordinated on M3+ ions. Very interestingly, selective CO2/N2 adsorptions of NJTU-Bai80-82(-ox) are significantly enhanced with the CO2 adsorption uptakes more than about 6 times that of NJTU-Bai79. GCMC simulations further revealed that neutral NJTU-Bai80-82(-ox) supplies more open frameworks around the -CH3 groups at separate spaces to the CO2 gas molecules with relatively more pores available to them after the removal of counterions. For the first time, finely tuning metal ion valences of metal clusters of ionic MOFs and making them from electrostatic to neutral were adopted for greatly improving their CO2 capture properties, and it would provide another promising strategy for the exploration of high-performance CO2 capture materials.

Reproductive and whole-body toxicity of Ag-doped and -undoped ZIF-8 nanoparticles and the building blocks: An Artemia-based comparative bioassay

The present research assessed, for the first time, toxicity of ZIF-8 (1 mg/L) and the building blocks (0.1 mg/L Zn2+ and 0.4 mg/L 2-methylimidazole (2-MIm)), besides that of AgNPs@ZIF-8 (0.25, 0.5, and 1 mg/L) and AgNO3 (0.1 mg/L) to aquatic organisms. Two consecutive generations (F0 & F1) of Artemia salina were exposed to these chemicals. All of the chemical treatments considerably caused mortality in F0, especially AgNPs@ZIF-8 and AgNO3, whereas F1 displayed notable tolerance and survived comparable to the control group, except in the case of AgNO3 treatment. Similarly, growth indices (weight, mainly in ZIF-8, Zn2+, and 2-MIm; length, in Ag-doped ZIF-8 and AgNO3) were significantly retarded in F0 and especially F1 of all treatments, and 2-MIm caused the greatest length retardation in F0. AgNPs@ZIF-8 (0.5 and 1 mg/L), 2-MIm, and AgNO3 postponed the ovary emergence in about 40%-60% of the exposed F0, and ZIF-8 delayed this phenomenon in some individuals of F0 and F1 up to 6 days. This temporal disturbance was also observed in time to first brood of almost all experimental F0 and F1 groups, with being over 80% of F1 exposed to ZIF-8, 2-MIm, and Zn2+, as well as about 50% of F0 treated with 2-MIm, and Zn2+. The highest neonate number was recorded for F0 and F1 exposed to AgNO3 and Zn2+, while ZIF-8 and, importantly, 2-MIm decreased the reproductivity to the lowest levels in both generations. Generally, the reproductive frequency was significantly decreased in all F0 and F1 treatments, especially 2-MIm, ZIF-8, AgNPs@ZIF-8 (0.25 & 1 mg/L). This study highlighted the neglected importance of 2-MIm in assessing overall toxicity of ZIF-8, and even other organic ligands of MOFs, and also filled a gap in the literature by investigating the potential effect of additives such as AgNPs on the toxicity of ZIF-8 and other MOFs.

Synthesis and activation of pH-sensitive metal-organic framework Sr(BDC)∞ for oral drug delivery

Metal-organic frameworks (MOFs) are widely used in the biomedical industry. In this study, we developed a new method for obtaining a metal-organic structure of strontium and terephthalic acid, Sr(BDC), and an alternative activation method for removing DMF from the pores. Sr(BDC) MOFs were successfully prepared and characterized by XRD, FTIR, TGA, and SEM. The importance of the activation steps was confirmed by TGA, which showed that the Sr(BDC)(DMF) sample can contain up to a quarter of the solvent (DMF) before activation. In our study, IR spectroscopy confirmed the possibility of removing DMF by ethanol treatment from the Sr-BDC crystals. A comparative analysis of the effect of the activation method on the specific surface and pore size of Sr-BDC and its sorption properties using the model drug doxorubicin showed that due to the undeveloped surface of the Sr-(BDC)(DMF) sample, it is not possible to obtain an adsorption isotherm and determine the pore size distribution, thus showing the importance of the activation step. Cytotoxicity and apoptosis assays were carried out to study the biological activity of MOFs, and we observed relatively low toxicity in the tested concentration range after 48 h, with over 92% cell survival for Sr(BDC)(DMF) and Sr(BDC)(260 °C), with a decrease only in the highest concentration (800 mg L-1). Similar results were observed in our apoptosis assays, as they revealed low apoptotic population generation of 2.52%, 3.23%, and 2.77% for Sr(BDC)(DMF), Sr(BDC) and Sr(BDC)(260 °C), respectively. Overall, the findings indicate that ethanol-activated Sr(BDC) shows potential as a safe and effective material for drug delivery.

Three-Dimensional Hydrogen-Bonded Porous Metal-Organic Framework for Natural Gas Separation with High Selectivity

A 3D hydrogen-bonded metal-organic framework, [Cu(apc)2]n (TJU-Dan-5, Hapc = 2-aminopyrimidine-5-carboxylic acid), was synthesized via a solvothermal reaction. The activated TJU-Dan-5 with permanent porosity exhibits a moderate uptake of 1.52 wt% of hydrogen gas at 77 K. The appropriate BET surface areas and decoration of the internal polar pore surfaces with groups that form extensive hydrogen bonds offer a more favorable environment for selective C2H6 adsorption, with a predicted selectivity for C2H6/CH4 of around 101 in C2H6/CH4 (5:95, v/v) mixtures at 273 K under 100 kPa. The molecular model calculation demonstrates a C-H···π interaction and a van der Waals host-guest interaction of C2H6 with the pore walls. This work provides a strategy for the construction of 3D hydrogen-bonded MOFs, which may have great potential in the purification of natural gas.

In-based coordination polymer-derived carbon nanoribbons with abundant CoP nanoparticles in carbon nanotubes for water oxidation

The sluggish oxygen evolution reaction (OER) in overall electrocatalytic water splitting poses a significant challenge in hydrogen production. A series of transition metal phosphides are emerging as promising electrocatalysts, effectively modulating the charge distribution of surrounding atoms for OER. In this study, a highly efficient OER electrocatalyst (CoP-CNR-CNT) was successfully synthesized through the pyrolysis and phosphatization of a Co-doped In-based coordination polymer, specifically InOF-25. This process resulted in evenly dispersed CoP nanoparticles encapsulated in coordination polymer-derived carbon nanoribbons. The synthesized CoP-CNR-CNT demonstrated a competitive OER activity with a smaller overpotential (η10) of 295.7 mV at 10 mA cm-2 and a satisfactory long-term stability compared to the state-of-the-art RuO2 (η10 = 353.7 mV). The high OER activity and stability can be attributed to the high conductivity of the carbon network, the abundance of CoP particles, and the intricate nanostructure of nanoribbons/nanotubes. This work provides valuable insights into the rational design and facile preparation of efficient non-precious metal-based OER electrocatalysts from inorganic-organic coordination polymers, with potential applications in various energy conversion and storage systems.

MOF-GRU: A MOFid-Aided Deep Learning Model for Predicting the Gas Separation Performance of Metal-Organic Frameworks

The remarkable versatility of metal-organic frameworks (MOFs) stems from their rich chemical information, leading to numerous successful applications. However, identifying optimal MOFs for specific tasks necessitates a thorough assessment of their chemical attributes. Conventional machine learning approaches for MOF prediction have relied on intricate chemical and structural details, hampering rapid evaluations. Drawing inspiration from recent advancements exemplified by Snurr et al., wherein a text string was used to represent a MOF (MOFid), we introduce a MOFid-aided deep learning model, named the MOF-GRU model. This model, founded on natural language processing principles and utilizing the gated recurrent unit architecture, leverages the serialized text string representation of metal-organic frameworks (MOFs) to forecast gas separation performance. Through a focused study on CH4/N2 separation, we substantiate the efficacy of this approach. Comparative assessments against traditional machine learning techniques underscore our model's superior predictive accuracy and its capacity to handle extensive data sets adeptly. The MOF-GRU model remarkably uncovers latent structure-performance relationships with only MOF sequences, obviating the necessity for intricate three-dimensional (3D) structural information. Overall, this model's judicious design empowers efficient data utilization, thereby hastening the discovery of high-performance materials tailored for gas separation applications.

Metal-organic framework-derived metal oxides for resistive gas sensing: a review

Gas sensors with exceptional sensitivity and selectivity are vital in the real-time surveillance of noxious and harmful gases. Despite this, traditional gas sensing materials still face a number of challenges, such as poor selectivity, insufficient detection limits, and short lifespan. Metal oxides, which are derived from metal-organic framework materials (MOFs), have been widely used in the field of gas sensors because they have a high surface area and large pore volume. Incorporating metal oxides derived from MOFs into gas sensors can improve their sensitivity and selectivity, thus opening up new possibilities for the development of innovative, high-performance gas sensors. This article examines the gas sensing process of metal oxide semiconductors (MOS), evaluates the advances made in the research of different structures of MOF-derived metal oxides in resistive gas sensors, and provides information on their potential applications and future advancements.

Developing Mixed Matrix Membranes with Good CO2 Separation Performance Based on PEG-Modified UiO-66 MOF and 6FDA-Durene Polyimide

The use of mixed matrix membranes (MMMs) comprising metal-organic frameworks (MOFs) for the separation of CO2 from flue gas has gained recognition as an effective strategy for enhancing gas separation efficiency. When incorporating porous materials like MOFs into a polymeric matrix to create MMMs, the combined characteristics of each constituent typically manifest. Nevertheless, the inadequate dispersion of an inorganic MOF filler within an organic polymer matrix can compromise the compatibility between the filler and matrix. In this context, the aspiration is to develop an MMM that not only exhibits optimal interfacial compatibility between the polymer and filler but also delivers superior gas separation performance, specifically in the efficient extraction of CO2 from flue gas. In this study, we introduce a modification technique involving the grafting of poly(ethylene glycol) diglycidyl ether (PEGDE) onto a UiO-66-NH2 MOF filler (referred to as PEG-MOF), aimed at enhancing its compatibility with the 6FDA-durene matrix. Moreover, the inherent CO2-philic nature of PEGDE is anticipated to enhance the selectivity of CO2 over N2 and CH4. The resultant MMM, incorporating 10 wt% of PEG-MOF loading, exhibits a CO2 permeability of 1671.00 Barrer and a CO2/CH4 selectivity of 22.40. Notably, these values surpass the upper bound reported by Robeson in 2008.

Electrochromism in Isoreticular Metal-Organic Framework Thin Films with Record High Coloration Efficiency

The power of isoreticular chemistry has been widely exploited to engineer metal-organic frameworks (MOFs) with fascinating molecular sieving and storage properties but is underexplored for designing MOFs with tunable optoelectronic properties. Herein, three dipyrazole-terminated XDIs (X = PM (pyromellitic), N (naphthalene), or P (perylene); DI = diimide) with different lengths and electronic properties are prepared and employed as linkers for the construction of an isoreticular series of Zn-XDI MOFs with distinct electrochromism. The MOFs are grown on fluorine-doped tin oxide (FTO) as high-quality crystalline thin films and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Due to the constituting electronically isolated XDI linkers, each member of the isoreticular thin film series exhibits two reversible one-electron redox events, each at a distinct electrochemical potential. The orientation of the MOFs as thin films as well as their isoreticular nature results in identical cation-coupled electron hopping transport rates in all three materials, as demonstrated by comparable apparent electron diffusion coefficients, Deapp. Upon electrochemical reduction to either the [XDI]•- or [XDI]2- state, each MOF undergoes characteristic changes in its optical properties as a function of linker length and redox state of the linker. Operando spectroelectrochemistry measurements reveal that Zn-PDI@FTO (PDI = perylene diimide) thin films exhibit a record high coloration efficiency of 941 cm2 C-1 at 746 nm, which is attributed to the maximized Faradaic transformations at each electronically isolated PDI unit. The electrochromic response of the thin film is retained to more than 99% over 100 reduction-oxidation cycles, demonstrating the applicability of the presented materials.

Series of Cadmium-Organic Frameworks Based on Mixed Flexible and Rigid Ligands: Single-Crystal-to-Single-Crystal Transformations, Sorption, and Luminescence Properties

Here, we present a series of Cd(II) coordination polymers containing two types of ligands: sterically rigid terephthalate derivatives (bdc-NO22- and bdc-Br2-) and flexible bis(2-methylimidazolyl)propane (bmip). The combination of two types of ligands is used to obtain and characterize compounds by single crystal and powder X-ray diffraction, FT-IR, elemental analysis, and TGA. Guest exchange results in structural transformations. 2-fold interpenetrated 1·DMF and 2·DMF rapidly undergo to 4-fold interpenetrated 1·Et2O, 1·EtOH, and 1·H2O, or 2·Et2O, respectively. Also, changes in the coordinating numbers and length of the N,N'-donor bmip ligand were observed according to single crystal X-ray analysis. Activated guest-free compounds [Cd(bdc-NO2)(bmip)] (1) and [Cd(bdc-Br)(bmip)] (2) are shown to be porous with a BET surface area of 103 and 283 m2·g-1, respectively. Moreover, both compounds demonstrate gate-opening behavior of ethylene adsorption isotherms at low pressures (<1 bar) and highly selective adsorption of benzene over cyclohexane or lower alcohols. Also, both compounds demonstrate a strong dependence of the maximum of the photoluminescence emission on an excitation wavelength. As a result, the photoluminescence color changes from white to red and from blue to red through green and yellow for compounds 1 and 2, respectively, with excitation wavelength changing from 360 to 540 nm.

Photo-Fenton degradation of tetracycline antibiotic over MIL-101(Cr)/FeOOH nanocomposite as stable and efficient visible light responsive photocatalyst

Designing an inexpensive, easily synthesized, stable and efficient photocatalyst is a major challenge in photocatalysis area, especially when photo-reaction is performed in aquatic medium to degrade organic pollutants. To this aim, nano-sized MIL-101(Cr) (MIL = Materials Institute Lavoisier), as chemically tolerant metal-organic framework (MOF), was simply prepared via HF-free hydrothermal synthesis procedure. In order to decorate amorphous FeOOH quantum dots (QDs) on the surface of this MOF, various amounts of FeOOH QDs (i.e., 5, 10, 15 and 20 wt%) were synthesized in the presence of MIL-101(Cr) to prepare MIL-101(Cr)/FeOOH(x%) nanocomposites. Decoration of such iron oxide quantum dots on the surface of MIL-101(Cr) and investigation of its activity in photo-Fenton degradation of tetracycline (TC) antibiotic is reported here for the first time. Among the synthesized nanocomposites, MIL-101(Cr)/FeOOH(15%) demonstrated superior photo-Fenton activity in degradation of TC (80%) at short reaction time under optimum reaction condition using the energy-efficient white LED lamps as visible light source. It was observed that the synergy between any component of this photo-Fenton system such as nanocomposite, hydrogen peroxide and visible light is the main reason for enhancement of TC removal over time. Also, neither MIL-101(Cr) nor FeOOH QDs exhibited poor degradation efficiency, which implies the positive role of the coupling of these materials. Furthermore, the stability and recoverability of MIL-101(Cr)/FeOOH(15%) nanocomposite was investigated in four photo-Fenton cycles, which no significant decrease in TC degradation performance was observed.

Highly Efficient Cauliflower-like Palladium-Loaded Porous MOF as a Robust Material for the Degradation of Organic Dyes

A series of porous MOF materials, viz., Pdx@IRMOF-9 (x = 2, 5, and 10%) were synthesized by loading varying concentrations of Pd(II) on IRMOF-9. The synthesized MOF materials were characterized by ltravioletisible (UV-Vis) spectroscopy, Fourier transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), Brunauer-Emmett-Teller (BET), and scanning electron microscopy (SEM) analyses. UV, FT-IR, and PXRD data of Pd(II)@IRMOF-9 were found to be in line with those of IRMOF-9, which suggests that the structure of the IRMOF-9 remained intact upon Pd(II) loading. Surface morphology of IRMOF-9 showed sheet-like structures, and upon incorporation of Pd(II) to IRMOF-9, porous cauliflower-shaped MOFs were obtained. The SEM area mapping of Pd10%@IRMOF-9 confirmed the homogeneous dispersion of Pd(II) on IRMOF-9. BET measurements suggested an increase in the surface area as well as pore size upon incorporation of Pd(II) on IRMOF-9. Due to high porosity and high petal density, Pd10%@IRMOF-9 demonstrated degradation of seven organic dyes, namely, orange G, methylene blue, methyl orange, congo red , methyl red, rhodamine 6G, and neutral red. It showed excellent results with >90% dye degradation efficiency in case of cationic, anionic as well as neutral dyes. Degradation of organic dyes followed the pseudo-first-order kinetics. Kinetic parameters, KM and Vmax, were calculated using the double reciprocal Lineweaver-Burk plot and were found to be 13.2 μM and 26.68 × 10-8 M min-1, respectively. Recyclability studies of heterogeneous Pd10%@IRMOF-9 demonstrated the degradation of CR dye for five consecutive cycles without significant loss of its catalytic activity. Herein, a robust and efficient material for the degradation of organic dyes has been developed and demonstrated.

Metal-Organic Frameworks for Phthalate Capture

Indoor air contamination by phthalate ester (PAE) derivatives has become a significant concern since traces of PAEs can cause endocrine disruption, among other health issues. PAE abatement from the environment is thus mandatory to further ensure a good quality of indoor air. Herein, we explored the physisorption-based capture of volatile PAEs by metal-organic frameworks (MOFs). A high-throughput computational screening approach was first applied on databases compiling more than 20,000 MOF structures in order to identify the best MOFs for adsorbing traces of dimethyl phthalate (DMP), considered as a representative molecule of the family of PAE contaminants. Among the 20 top candidates, MOF-74(Ni), which combines substantial DMP uptake at the 10 ppm concentration level (∼0.20 g g-1) with high adsorption enthalpy at infinite dilution (-ΔHads(DMP),0 = 109.9 kJ mol-1), was revealed as an excellent porous material to capture airborne DMP. This prediction was validated by further experiments: gravimetric sorption isotherms were carried out on MOF-74(Ni), replacing DMP by dimethyl maleate (DMM), a molecule with a higher vapor pressure and indeed easier to manipulate compared to DMP while mimicking the adsorption behavior of DMP by MOFs, as evidenced by Monte Carlo calculations. Notably, saturation of DMM by MOF-74(Ni) (∼0.35 g g-1 at 343 K) occurs at very low equivalent concentration of the sorbate, i.e., 15 ppm, while half of the DMM molecules remain trapped in the MOF pores, even by heating the system up to 473 K under vacuum. This computational-experimental study reveals for the first time the potential of MOFs for the capture of phthalate ester contaminants as vapors of key importance to address indoor air quality issues.

Porous crystalline materials for memories and neuromorphic computing systems

Porous crystalline materials usually include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs) and zeolites, which exhibit exceptional porosity and structural/composition designability, promoting the increasing attention in memory and neuromorphic computing systems in the last decade. From both the perspective of materials and devices, it is crucial to provide a comprehensive and timely summary of the applications of porous crystalline materials in memory and neuromorphic computing systems to guide future research endeavors. Moreover, the utilization of porous crystalline materials in electronics necessitates a shift from powder synthesis to high-quality film preparation to ensure high device performance. This review highlights the strategies for preparing porous crystalline materials films and discusses their advancements in memory and neuromorphic electronics. It also provides a detailed comparative analysis and presents the existing challenges and future research directions, which can attract the experts from various fields (e.g., materials scientists, chemists, and engineers) with the aim of promoting the applications of porous crystalline materials in memory and neuromorphic computing systems.

Luminescent Metal-Organic Framework for the Selective Detection of Aldehydes

The detection of toxic, hazardous chemical species is an important task because they pose serious risks to either the environment or human health. Luminescent metal-organic frameworks (LMOFs) as alternative sensors offer rapid and sensitive detection of chemical species. Interactions between chemical species and LMOFs result in changes in the photoluminescence (PL) profile of the LMOFs which can be readily detected using a simple fluorometer. Herein, we report the use of a robust, Zn-based LMOF, [Zn5(μ3-OH)2(adtb)2(H2O)5·5 DMA] (Zn-adtb, LMOF-341), for the selective detection of benzaldehyde. Upon exposure to benzaldehyde, Zn-adtb experiences significant luminescent quenching, as characterized through PL experiments. Photoluminescent titration experiments reveal that LMOF-341 has a detection limit of 64 ppm and a Ksv value of 179 M-1 for benzaldehyde. Furthermore, we study the guest-host interactions that occur between LMOF-341 and benzaldehyde through in situ Fourier transform infrared and computational modeling employing density functional theory. The results show that benzaldehyde interacts more strongly with LMOF-341 compared to formaldehyde and propionaldehyde. Our combined studies also reveal that the mechanism of luminescence quenching originates from an electron-transfer process.

Two-Dimensional Conjugated Metal-Organic Frameworks with Large Pore Apertures and High Surface Areas for NO2 Selective Chemiresistive Sensing

The emergence of two-dimensional conjugated metal-organic frameworks (2D c-MOFs) with pronounced electrical properties (e.g., high conductivity) has provided a novel platform for efficient energy storage, sensing, and electrocatalysis. Nevertheless, the limited availability of suitable ligands restricts the number of available types of 2D c-MOFs, especially those with large pore apertures and high surface areas are rare. Herein, we develop two new 2D c-MOFs (HIOTP-M, M=Ni, Cu) employing a large p-π conjugated ligand of hexaamino-triphenyleno[2,3-b:6,7-b':10,11-b'']tris[1,4]benzodioxin (HAOTP). Among the reported 2D c-MOFs, HIOTP-Ni exhibits the largest pore size of 3.3 nm and one of the highest surface areas (up to 1300 m2  g-1 ). As an exemplary application, HIOTP-Ni has been used as a chemiresistive sensing material and displays high selective response (405 %) and a rapid response (1.69 min) towards 10 ppm NO2 gas. This work demonstrates significant correlation linking the pore aperture of 2D c-MOFs to their sensing performance.

Anisotropic flexibility and rigidification in a TPE-based Zr-MOFs with scu topology

Tetraphenylethylene (TPE)-based ligands are appealing for constructing metal-organic frameworks (MOFs) with new functions and responsiveness. Here, we report a non-interpenetrated TPE-based scu Zr-MOF with anisotropic flexibility, that is, Zr-TCPE (H4TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), remaining two anisotropic pockets. The framework flexibility is further anisotropically rigidified by installing linkers individually at specific pockets. By individually installing dicarboxylic acid L1 or L2 at pocket A or B, the framework flexibility along the b-axis or c-axis is rigidified, and the intermolecular or intramolecular motions of organic ligands are restricted, respectively. Synergistically, with dual linker installation, the flexibility is completely rigidified with the restriction of ligand motion, resulting in MOFs with enhanced stability and improved separation ability. Furthermore, in situ observation of the flipping of the phenyl ring and its rigidification process is made by 2H solid-state NMR. The anisotropic rigidification of flexibility in scu Zr-MOFs guides the directional control of ligand motion for designing stimuli-responsive emitting or efficient separation materials.

Metal-mediated tunability of MOF-based optical modulators

We report on the design of 1D MOFs based on a nopinane-annelated organic ligand and Co(II) or Ni(II), the variation of which allows tuning the optical modulation bandwidth. Structural and time-resolved analysis revealed the optical modulation mechanism, the rates and its endurance, thereby enriching the list of sustainable MOFs for tunable optical modulators.

Catalytic Application of Functionalized Bimetallic-Organic Frameworks with Phosphorous Acid Tags in the Synthesis of Pyrazolo[4,3-e]pyridines

Combining two different metals for the synthesis of a metal-organic framework (MOF) is a smart strategy for the architecture of new porous materials. Herein, a bimetal-organic framework (bimetal-MOFs) based on Fe and Co metals was synthesized. Then, phosphorous acid tags were decorated on bimetal-MOFs via a postmodification method as a new porous acidic functionalized catalyst. This catalyst was used for the synthesis of pyrazolo[4,3-e]pyridine derivatives as suitable drug candidates. The present study provides new insights into the architecture of novel porous heterogeneous catalysts based on a bimetal-organic framework (bimetal-MOFs). The type of final structures of catalyst and pyrazolo[4,3-e]pyridine derivatives were determined using different techniques such as fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), SEM-elemental mapping, N₂ adsorption-desorption isotherm, Barrett-Joyner-Halenda (BJH), thermogravimetry/differential thermal analysis (TG/DTA), ¹H NMR, and ¹³C NMR.

Preparation of MOF-derived ZnO/Co3O4 nanocages and their sensing performance toward H2S

We report a type of micro-electro-mechanical system (MEMS) H₂S gas sensors with excellent sensing performance at the ppb level (lowest detection limit is 5 ppb). The sensors were fabricated with ZnO/Co₃O₄ sensing materials derived from Zn/Co-MOFs by annealing at a suitable temperature of 500 °C. ZnO/Co₃O₄-500 exhibits the highest response when exposed to 10 ppb H₂S gas at 120 °C, and the response/recovery times are 10 s/21 s. Moreover, it exhibits outstanding selectivity, long-term stability (retained 95% response after 45 days), and moisture resistance (only a minor fluctuation of 2% even at 90% RH). This can be ascribed to the fact that ZnO/Co₃O₄-500 has regular morphology, abundant oxygen vacancies (52.8%) and high specific surface area (96.5 m² g^-1). This work provides not only a high performance H₂S MEMS gas sensor but also a systematic study of the effect of the annealing temperature on the sensing performance of ZnO/Co₃O₄ sensing materials derived from bimetal organic frameworks.

DigiMOF: A Database of Metal-Organic Framework Synthesis Information Generated via Text Mining

The vastness of materials space, particularly that which is concerned with metal-organic frameworks (MOFs), creates the critical problem of performing efficient identification of promising materials for specific applications. Although high-throughput computational approaches, including the use of machine learning, have been useful in rapid screening and rational design of MOFs, they tend to neglect descriptors related to their synthesis. One way to improve the efficiency of MOF discovery is to data-mine published MOF papers to extract the materials informatics knowledge contained within journal articles. Here, by adapting the chemistry-aware natural language processing tool, ChemDataExtractor (CDE), we generated an open-source database of MOFs focused on their synthetic properties: the DigiMOF database. Using the CDE web scraping package alongside the Cambridge Structural Database (CSD) MOF subset, we automatically downloaded 43,281 unique MOF journal articles, extracted 15,501 unique MOF materials, and text-mined over 52,680 associated properties including the synthesis method, solvent, organic linker, metal precursor, and topology. Additionally, we developed an alternative data extraction technique to obtain and transform the chemical names assigned to each CSD entry in order to determine linker types for each structure in the CSD MOF subset. This data enabled us to match MOFs to a list of known linkers provided by Tokyo Chemical Industry UK Ltd. (TCI) and analyze the cost of these important chemicals. This centralized, structured database reveals the MOF synthetic data embedded within thousands of MOF publications and contains further topology, metal type, accessible surface area, largest cavity diameter, pore limiting diameter, open metal sites, and density calculations for all 3D MOFs in the CSD MOF subset. The DigiMOF database and associated software are publicly available for other researchers to rapidly search for MOFs with specific properties, conduct further analysis of alternative MOF production pathways, and create additional parsers to search for additional desirable properties.

Cathodic deposition of MOF films: mechanism and applications

Metal-organic framework (MOF) thin films could be used for ion/molecular sieving, sensing, catalysis, and energy storage, but thus far no large-scale applications are known. One of the reasons is the lack of convenient and controllable fabrication methods. This work reviews the cathodic deposition of MOF films, which has advantages (e.g., simple operations, mild conditions, and controllable MOF film thickness/morphology) over other reported techniques. Accordingly, we discuss the mechanism of the cathodic deposition of MOF films which consists of the electrochemically triggered deprotonation of organic linkers and the formation of inorganic building blocks. Thereafter, the main applications of cathodically deposited MOF films are introduced with the aim of showing this technique's wide-ranging applications. Finally, we give the remaining issues and outlooks of the cathodic deposition of MOF films to drive its future development.

Calculation of Self, Corrected, and Transport Diffusivities of Isopropyl Alcohol in UiO-66

The UiO-6x family of metal-organic frameworks has been extensively studied for applications in chemical warfare agent (CWA) capture and destruction. An understanding of intrinsic transport phenomena, such as diffusion, is key to understanding experimental results and designing effective materials for CWA capture. However, the relatively large size of CWAs and their simulants makes diffusion in the small-pored pristine UiO-66 very slow and hence impractical to study directly with direct molecular simulations because of the time scales required. We used isopropanol (IPA) as a surrogate for CWAs to investigate the fundamental diffusion mechanisms of a polar molecule within pristine UiO-66. IPA can form hydrogen bonds with the μ3-OH groups bound to the metal oxide clusters in UiO-66, similar to some CWAs, and can be studied by direct molecular dynamics simulations. We report self, corrected, and transport diffusivities of IPA in pristine UiO-66 as a function of loading. Our calculations highlight the importance of the accurate modeling of the hydrogen bonding interactions on diffusivities, with about an order of magnitude decrease in diffusion coefficients when the hydrogen bonding between IPA and the μ3-OH groups is included. We found that a fraction of the IPA molecules have very low mobility during the course of a simulation, while a small fraction are highly mobile, exhibiting mean square displacements far greater than the ensemble average.

Rapid detection of the biomarker for cystinuria by a metal-organic framework fluorescent sensor

Arginine (Arg) is considered a valuable biomarker for various diseases, including cystinuria, and its concentration level holds significant implications for human health. To achieve the purposes of food evaluation and clinical diagnosis, it is imperative to develop a rapid and facile method for selective and sensitive determination of Arg. In this work, a novel fluorescent material (Ag/Eu/CDs@UiO-66) was synthesized by encapsulating carbon dots (CDs), Eu³⁺ and Ag ⁺ into UiO-66. This material can serve as a ratiometric fluorescent probe for detecting Arg. It exhibits a high sensitivity with a detection limit of 0.74 μM and a relatively broad linear range from 0-300 μM. After dispersing the composite Ag/Eu/CDs@UiO-66 in an Arg solution, the red emission of Eu³⁺ center at 613 nm was significantly enhanced, while the characteristic peak of CDs center at 440 nm remained unchanged. Therefore, a ratio fluorescence probe could be constructed based on the peak height ratio of the two emission peaks to achieve selective detection of Arg. In addition, the remarkable ratiometric luminescence response induced by Arg results in a significant color transition from blue to red under UV-lamp for Ag/Eu/CDs@UiO-66, which was convenient for visual analysis.

Highly Tunable MOF Luminophores Featuring Anthracene Directed Assembly and Fluorescence Regulation

Metal-organic frameworks (MOFs) have been recognized as a potential platform for the development of tunable luminophores owing to their highly modulable structures and components. Herein, two MOF luminophores based on Cd(II) ions, 1,3,5-tri(4-pyridinyl)benzene (TPB), and 1,4-dicarboxybenzene (H₂BDC) were constructed. The directed assembly of the metal ions and organic linkers results in [Cd₂(BDC)₂(TPB)(H₂O)]·x(solvent) (MOF-1) featuring TPB-based blue fluorescence centered at 425 nm. By introducing anthracene as the structure directing agent (SDA) for assembly regulation, [Cd₂(BDC)(TPB)₂(NO₃)₂]·x(solvent) (MOF-2) was obtained, which reveals anthracene feeding-dependent high tunable emission in the 517-650 nm range. Detailed components, photophysical properties, and structural characteristics investigations of MOF-2 indicate the TPB and NO₃^- interactions as the origin of its redshifted emission compared with that of MOF-1. Furthermore, the fluorescence of MOF-2 was found to be regulatable by the anthracene feeding based on the SDA-determined crystallinity of the crystalline sample. All these results provided a unique example of the structural and fluorescence regulation of MOF luminophores.

Bismuth Coordination Polymers with Fluorinated Linkers: Aqueous Stability, Bivolatility, and Adsorptive Behavior

Bismuth metal-organic frameworks and coordination polymers (CP) are challenging to synthesize, given the poor solubility of bismuth precursors and asymmetric and labile ligation of Bi³⁺ due to its intrinsic lone pair. Here, we synthesize and structurally characterize three Bi³⁺-CPs, exploiting a tetrafluoroterephtalate (F₄BDC) linker to determine the effect of high acidity on these synthesis and coordination challenges. Single-crystal X-ray diffraction characterization showed that pi-pi stacking of linkers directs framework arrangement and generally deters open porosity in the three structures, respectively featuring Bi chains (Bi _chain -F ₄ BDC), Bi dimers (Bi ₂ -F ₄ BDC) linked into chains, and Bi tetramers (Bi ₄ -F ₄ BDC). Powder X-ray diffraction and microscopic imaging show the high purity and stability of these compounds in water. Naphthalenedisulfonate (NDS) was used as a mineralizer in the synthesis of (Bi _chain -F ₄ BDC) and (Bi ₄ -F ₄ BDC), and studies of its role in assembly pathways yielded two additional structures featuring mixed NDS and F₄BDC, respectively, linking monomer and octamer Bi nodes, and confirmed that F₄BDC is the preferred (less labile) linker. Methylene blue (MB) adsorption studies show differing efficacies of the three Bi-F₄BDC phases, attributed to surface characteristics of the preferential growth facets, while generally most effective adsorption is attributed to the hydrophobicity of fluorinated ligands. Finally, thermogravimetric analysis of all three Bi-F₄BDC phases indicates simultaneous ligand degradation and in situ formation of volatile Bi compounds, which could be exploited in the chemical vapor deposition of Bi-containing thin films.

Highly Stable Fe/Co-TPY-MIL-88(NH2) Metal-Organic Framework (MOF) in Enzymatic Cascade Reactions for Chemiluminescence-Based Detection of Extracellular Vesicles

Metal-Organic Frameworks (MOFs) can deliver many advantages when acting as enzyme mimics to assist with signal amplification in molecular detection: they have abundant active catalytic sites per unit volume of the material; their structures and elemental compositions are highly tunable, and their high specific surface area and porous property can assist with target separation and enrichment. In the present work, we have demonstrated that, by adding the pore partition agent, 2,4,6-tris(4-pyridyl)pyridine (TPY) during synthesis of the bimetallic Fe/Co-MIL-88(NH₂) MOF to block the open metal sites, a highly porous MOF of Fe/Co-TPY-MIL-88(NH₂) can be produced. This material also exhibits high stability in basic solutions and biofluids and possesses high peroxidase-mimicking activity, which can be utilized to produce long-lasting chemiluminescence (CL) from luminol and H₂O₂. Moreover, acting as the peroxidase-mimic, the Fe/Co-TPY-MIL-88(NH₂) MOF can form the enzymatic cascade with glucose oxidase (GOx) for biomarker detection. When applied to detect extracellular vesicles (EVs), the MOF material and GOx are brought to the proximity on the EVs through two surface proteins, which triggers the enzyme cascade to produce high CL from glucose and luminol. EVs within the concentration range of 5 × 10⁵ to 4 × 10⁷ particles/mL can be detected with an LOD of 1 × 10⁵ particles/mL, and the method can be used to analyze EV contents in human serum without sample preparation and EV purification. Overall, our work demonstrates that the high versatility and tunability of the MOF structures could bring in significant benefits to biosensing and enable ultrasensitive detection of biomarkers with judicious material designs.