Multi-Emission Carbon Dots Combining Turn-On Sensing and Fluorescence Quenching Exhibit Ultrahigh Selectivity for Mercury in Real Water Samples.

Mercury is a ubiquitous heavy-metal pollutant and poses serious ecological and human-health risks. There is an ever-growing demand for rapid, sensitive, and selective detection of mercury in natural waters, particularly for regions lacking infrastructure specialized for mercury analysis. Here, we show that a sensor based on multi-emission carbon dots (M-CDs) exhibits ultrahigh sensing selectivity toward Hg(II) in complex environmental matrices, tested in the presence of a range of environmentally relevant metal/metalloid ions as well as natural and artificial ligands, using various real water samples. By incorporating structural features of calcein and folic acid that enable tunable emissions, the M-CDs couple an emission enhancement at 432 nm and a simultaneous reduction at 521 nm, with the intensity ratio linearly related to the Hg(II) concentration up to 1200 µg/L, independent of matrix compositions. The M-CDs have a detection limit of 5.6 µg/L, a response time of 1 min, and a spike recovery of 94 ± 3.7%. The intensified emission is attributed to proton transfer and aggregation-induced emission enhancement, whereas the quenching is due to proton and electron transfer. These findings also have important implications for mercury identification in other complex matrices for routine, screening-level food safety and health management practices.

Portably and Visually Sensing Cytisine through Smartphone Scanning Based on a Post-Modified Luminescence Center Strategy in Zinc-Organic Frameworks.

Cytisine (CTS) is a useful medicine for treating nervous disorders and smoking addiction, and exploring a convenient method to detect CTS is of great significance for long-term/home medication to avoid the risk of poisoning, but it is full of challenges. Here, a modified metal-organic framework sensor Tb@Zn-TDA-80 with dual emission centers was prepared using a post-modified luminescence center strategy. The obtained Tb@Zn-TDA-80 can serve as a CTS sensor with high sensitivity and selectivity. To achieve portable detection, Tb@Zn-TDA-80 was further fabricated as a membrane sensor, M-Tb@Zn-TDA-80, which displayed an obvious CTS-responsive color change by simply dropping a CTS solution onto its surface. Benefiting from this unique functionality, M-Tb@Zn-TDA-80 successfully realized the visual detection and quantitative monitoring of CTS in the range of 5.26-52.6 mM by simply scanning the color with a smartphone. The results of nuclear magnetic resonance spectroscopy and theoretical computation illustrated that the high sensing efficiency of Tb@Zn-TDA-80 for CTS was attributed to the N-H⋅⋅⋅π and π⋅⋅⋅π interactions between the ligand and CTS. And luminescence quenching may result from the intramolecular charge transfer. This study provides a convenient method for ensuring long-term medication safety at home.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks.

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

A Strong-Acid-Resistant [Th6 ] Cluster-Based Framework for Effectively and Size-Selectively Catalyzing Reductive Amination of Aldehydes with N,N-Dimethylformamide.

Utilization of N,N-dimethylformamide (DMF) as an amine source and reductant for synthesizing tertiary amines is a promising way to replace the substrates formaldehyde and dimethylamine, and it is desirable to seek porous acid-resistant catalysts for heterogeneous catalysis of this reaction. Herein, a robust metal-organic framework (MOF) {[Th6 O4 (OH)4 (H2 O)6 (BCP)3 ]⋅10 DMF}n (1) containing stacked nanocages with a diameter of 1.55 nm was constructed. Compound 1 can maintain its single-crystal structure even kept in air at 400 °C for 3 h, and in DMF or water at 200 °C for 7 days. Density functional theory (DFT) calculations suggested that the high interaction energy between the [Th6 O4 (OH)4 (H2 O)6 ]12+ clusters and ligands was responsible for the excellent stability of 1. Catalytic investigations revealed that 1 can effectively and size-selectively catalyze the reductive amination of aldehydes with DMF, and it can be reused at least five times without obvious loss in catalytic activity.

Luminescent Sensor with High Sensitivity and Selectivity for Amikacin Detection in a Serum using a Unique Gallium-Organic Framework.

Amikacin is a widely used antibiotic in the treatment of Gram-negative bacteria, but high concentrations of amikacin can cause cochlear nerve damage. Therefore, accurate and quick detection of the concentration of amikacin is desired and important. In this work, we have synthesized a new gallium-organic framework {[(CH3)2(NH2)Ga(PPTA)]·0.5DMF}n (1) (H4PPTA = 4,4',4″,4″'-(1-4-phenlene-bis(pyridine-4,2,6-triyl)) with good solvent and pH stabilities. A structure analysis reveals that 1 is a twofold interpenetrated framework exhibiting a large 1D square aperture with a size of 10.8 Å × 14 Å. The experimental results show that 1 can be used as a stable, fast, and recyclable luminescent probe for the detection of amikacin in aqueous solution and serum. The limit of detection is 2.9 × 10-7 mol/L, which is lower than the harmful concentration of amikacin in human serum. This is the first example of a metal-organic framework used for luminescence sensing of amikacin.

Recyclable Luminescent Sensor for Detecting Creatinine Based on a Lanthanide-Organic Framework.

Creatinine is an important clinical marker for human health, but detecting it by a luminescent sensor based on metal-organic frameworks is rarely investigated. In this work, we synthesized a new lanthanide-organic framework {[Tb(L)(CH3COO)(H2O)]·0.5DMF}n (1) (H2L = 3,5-bis(4'-carboxy-phenyl)1,2,4-triazole) with good solvent and acid/alkaline stabilities. Experimental results indicate that 1 can be used in the detection of creatinine in an aqueous solution with a wide linear detection range from 3.27 to 371 µM, and the detection limit can reach 1.7 × 10-6 M based on the 3σ method, which is less than the pathogenic concentration in a real environment. In addition, this luminescent sensor can also monitor the concentration changes of creatinine in diluted serum solutions and can be recycled at least five times, suggesting that it has a potential application for clinical monitoring.

Selectively Regulating Lewis Acid-Base Sites in Metal-Organic Frameworks for Achieving Turn-On/Off of the Catalytic Activity in Different CO2 Reactions.

Regulating Lewis acid-base sites in catalysts to investigate their influence in the chemical fixation of CO2 is significant but challenging. A metal-organic framework (MOF) with open metal Co sites, {(NH2 Me2 )[Co3 (µ3 -OH)(BTB)2 (H2 O)]⋅9 H2 O⋅5 DMF}n (1), was obtained and the results of the catalytic investigation show that 1 can catalyze cycloaddition of CO2 and aziridines to give 99 % yield. The efficiency of the cyclization of CO2 with propargyl amines is only 32 %. To improve the catalytic ability of 1, ligand XN with Lewis base sites was introduced into 1 and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF 2 ({(NH2 Me2 )[Co3 (µ3 -OH)(NHMe2 )(BTB)2 (XN)]⋅8 H2 O⋅4 DMF}n ). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from 2 treated with acid solution support this conclusion. This work illuminates a MOF-construction strategy that produces efficient catalysts for CO2 conversion.

Efficient Cycloaddition of CO2 and Aziridines Activated by a Quadruple-Interpenetrated Indium-Organic Framework as a Recyclable Catalyst.

On the basis of the global warming effect, it is of great significance to convert CO2 into the high value-added products oxazolidinones, but investigations on main-group-based metal-organic frameworks (MOFs) as heterogeneous catalysts still have not been reported so far. In this work, a quadruple-interpenetrated porous indium-based MOF, {[NH2(CH3)2][In(CPT)2]·3CH3CN·3DMA}n (1), is constructed from the organic ligand 3,5-bis(4'-carboxyphenyl)-1,2,4-triazole through solvothermal reactions, and N2 adsorption proves that the framework has a high Brunauer-Emmett-Teller surface areas with 2024 m2/g. The catalytic research on CO2 conversion reveals that compound 1 has high reactivity for the cycloaddition of CO2 with aziridines, and the product 3-ethyl-5-phenyloxazolidin-2-one can be obtained with a yield of 99% under mild conditions. In addition, 1 exhibits excellent activity for different kinds of substrates and can be reused at least five cycles without any significant deactivation, suggesting that 1 is a potential candidate for the chemical conversion of CO2 and aziridines. Mechanistic explorations indicate that the high efficiency of 1 is attributed to the indium center in the framework as a Lewis acid site, and the large porosity can enrich substrates. Importantly, 1 behaved as the first main-group MOF-based catalyst in the reported coupling reaction of CO2 with aziridines.

Anchoring Ag(I) into Nitro-Functionalized Metal-Organic Frameworks: Effectively Catalyzing Cycloaddition of CO2 with Propargylic Alcohols under Mild Conditions.

Carboxylative cyclization of propargylic alcohols with CO2 is significant in synthetic chemistry, but harsh conditions are often needed according to reported results. Herein, a new stable nitro-functionalized metal-organic framework (MOF) of {[Co3(L)2(bpy)4(H2O)2]·DMF·H2O·bpy}n (1) was fabricated through the solvothermal reaction, which exhibited excellent stability in acid and basic solutions. Owing to the porous structure, unsaturated metal sites, and uncoordinated 4,4'-bpy ligands, 1 can serve as an excellent platform for catalytic applications. Hence, Ag(I) ions were incorporated in 1 through a postsynthetic method, and the as-synthesized Ag-1 catalyst with low metal loading (0.64 mol %) displayed excellent catalytic performance in the chemical fixation of CO2 with alkynols under room temperature and atmospheric pressure. The results of 1H NMR analyses further confirmed that Ag-1 can efficiently activate hydroxyl groups and promote the reaction. Moreover, the turnover frequency (TOF) of the Ag-1 catalyst can reach 262 h-1 in a short period of time, which is a high TOF value among the state-of-the-art MOF-based catalysts for catalyzing cycloaddition of CO2 with propargylic alcohols.

A Facile Strategy for Constructing a Carbon-Particle-Modified Metal-Organic Framework for Enhancing the Efficiency of CO2 Electroreduction into Formate.

Electrocatalytic reduction of CO2 by metal-organic frameworks (MOFs) has been widely investigated, but insufficient conductivity limits application. Herein, a porous 3D In-MOF {(Me2 NH2 )[In(BCP)]⋅2 DMF}n (V11) with good stability was constructed with two types of channels (1.6 and 1.2 nm diameter). V11 exhibits moderate catalytic activity in CO2 electroreduction with 76.0 % of Faradaic efficiency for formate (FEHCOO- ). Methylene blue molecules of suitable size and pyrolysis temperature were introduced and transformed into carbon particles (CPs) after calcination. The performance of the obtained CPs@V11 is significantly improved both in FEHCOO- (from 76.0 % to 90.1 %) and current density (2.2 times). Control experiments show that introduced CPs serve as accelerant to promote the charges and mass transfer in framework, and benefit to sufficiently expose active sites. This strategy can also work on other In-MOFs, demonstrating the universality of this method for electroreduction of CO2 .

Dual-Selective Catalysis in Dephosphorylation Tuned by Hf6-Containing Metal-Organic Frameworks Mimicking Phosphatase.

Selective dephosphorylation is full of great challenges in the field of biomimetic catalysis. To mimic the active sites of protein phosphatase, Hf-OH-Hf motif-containing metal-organic frameworks (MOFs) were obtained and structurally characterized, which are assembled from [Hf48Ni6] cubic nanocages and exhibit good stability in various solvents and acid/base solutions. Catalytic investigations suggest as-synthesized Hf-Ni and Hf-Ni-NH 2 display accurate type-selectivity (selectively catalyzed P-O rather than S-O or C-O bonds) and position-selectivity (selectively catalyzed phosphomonoesters over phosphodiesters) for the hydrolysis of phosphoesters. Reaction kinetic studies further revealed the high activity of the catalytic sites in these catalysts, and the unique catalytic selectivity and high activity are comparable to phosphatase. Additionally, these MOF catalysts possess good recursivity and hypotoxicity. Control experiments (including Hf- and Zr-based isomorphous MOFs) and theoretical calculations indicate that both triplet nickel and Hf6 clusters play significant roles in the unique binding site and favorable binding energy. To our knowledge, this is the first example of selective dephosphorylation through MOF catalysts as mimic enzymes, which paves a potential way for the development of specific therapeutic MOFs.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks.

Cyclization of propargylamines with CO2 to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique CuI /CuII mixed valence copper-based framework {[(CuI 6 I5 )Cu3 II L6 (DMA)3 ](NO3 )⋅9DMA}n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO2 , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO2 without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between CuI /CuII and uncoordinated amino groups promotes highly efficient and green conversion of CO2 . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO2 source.

Recyclable Luminescence Sensor for Dinotefuran in Water by Stable Cadmium-Organic Framework.

Due to the widespread use of dinotefuran around the world, its impact on food and environmental safety has aroused great concern, and the establishment of a rapid and convenient approach for dinotefuran detection is necessary but challenging. Herein, we synthesized a unique three-dimensional framework {[(CH3)2NH2]2[Cd3(BCP)2]·10H2O·3.5DMF}n (1). Single-crystal X-ray analysis indicates that 1 possesses a 4,8-connected anion framework that corresponds to alb topology, with a one-dimensional rectangular channel along the c-axis with the size of 4 Å × 10 Å. Compound 1 displays satisfactory solvent and thermal stability. Luminescent investigations reveal that 1 can selectively detect dinotefuran by fluorescence quenching among other pesticides, displaying excellent anti-interference performance with common ions in water. Importantly, the limit of detection is as low as 2.09 ppm, which is far below the residual concentration of the U.S. food standard. A fluorescence quenching mechanism study shows that there exists competitive energy absorption and static quenching processes. To our knowledge, 1 is the first MOF-based fluorescence probe for dinotefuran detection.

Photocatalytic Hydrogen Evolution Based on Cobalt-Organic Framework with High Water Vapor Adsorption.

Photocatalytic hydrogen evolution is desired to effectively alleviate the serious crisis of energy and the environment, and the utilization of low-cost photocatalysts, especially cobalt-based MOF catalysts, is meaningful, but rarely investigated. Herein, through a self-assembly strategy, we synthesized a Co clusters-based MOF (Co3-XL) by the ligand N,N'-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole), containing abundant carbonyl O atoms in the channels of the 3D skeleton, and a large porosity of 50.7%. The as-synthesized MOF can be stable in the pH range of 3-10 and shows a narrow band gap of 1.82 eV. Furthermore, its maximum amount of water absorption can reach 192 cm3/g. Under irradiation of simulated solar light, the rate of hydrogen evolution is 23.05 µmol·h-1·g-1 among 12 h with the presence of co-catalyst Pt and photosensitizer RhB. The reaction mechanism has been probed by the transient photocurrent response and steady-state photoluminescence spectra. Therefore, as a narrow band gap photocatalyst, the cobalt clusters-based MOF (Co3-XL) has potential applications for hydrogen evolution from water.

Bimetallic Lanthanide-Organic Framework Membranes as a Self-Calibrating Luminescent Sensor for Rapidly Detecting Antibiotics in Water.

Rapid, facile, and reliable recognition of different antibiotics by self-calibrating luminescent sensors are important for practical requirements. Herein, we design and synthesize a series of Eu1-xTbx-MOF using a flexible ligand H4L (5,5'-(propane-1,3-diylbis(oxy))di-isophthalic acid). With changing reactant time, submicrometer bimetallic SMOF-10-10h with homogeneous morphology was achieved and further fabricated MOF-based membrane combining with polymer materials. A luminescent study indicated that the bimetallic SMOF-10-10h membrane possesses a legible emission peak for Eu3+ and Tb3+ ions, which can act as a self-calibrating luminescent probe for efficiently sensing different antibiotics within a certain concentration range through two-dimensional (2D) readouts based on the emission intensity ratio. Our work first reports an inexpensive and convenience bimetallic MOF-based membrane as a luminescent sensor with self-calibrating to detect various antibiotics, which makes it a potential luminescent sensor for beneficial application.

Highly Sensitive and Selective Luminescence Sensor Based on Two-Fold Interpenetrated MOFs for Detecting Glutamate in Serum.

Glutamate is a biomarker for many nervous system diseases, and sensitively detecting glutamate is meaningful in the clinic. Therefore, a unique 3D framework of Cd-MOF (1) is synthesized and characterized. A single-crystal X-ray study reveals that it is a two-fold interpenetration (4,4)-connected framework with a PtS topology, where a large 1D rhombic channel with a size of 8 × 14 Å exists and the total potential void volume can reach 62%. Luminescence results demonstrate that 1 has good luminescence stability and can sensitively detect glutamate in water with a detection limit of 1.15 × 10-7 mol/L, which makes it the most sensitive MOF-based luminescence sensor of glutamate to date. More importantly, it also can serve as a luminescence sensor to detect glutamate in serum, and the quenching concentration needs to be only 43.1 µmol/L, which is much lower than the harmful level of glutamate (400 µmol/L) in glioma patients' blood. Compound 1 can be used at least five cycles. These results show that 1 has a potential application in monitoring glutamate in clinical scenarios.

MOFs-Based Catalysts Supported Chemical Conversion of CO2.

The dramatic increase in atmospheric carbon dioxide (CO2) concentrations has attracted human attention and many strategies about converting CO2 into high-value chemicals have been put forward. Metal-organic frameworks (MOFs), as a class of versatile materials, have been widely used in CO2 capture and chemical conversion, due to their unique porosity, multiple active centers and good stability and recyclability. Herein, we focused on the processes of chemical conversion of CO2 by MOFs-based catalysts, including the coupling reactions of epoxides, aziridines or alkyne molecules, CO2 hydrogenation, and other CO2 conversion reactions. The synthesized methods and high catalytic activity of MOFs-based materials were also analyzed systematically. Finally, a brief perspective on feasible strategies is presented to improve the catalytic activity of novel MOFs-based materials and explore the new CO2 conversion reactions.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks.

Transformation of CO2 based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO2 . In fact, it is the formation of new covalent bonds between CO2 and substrate molecules that successfully result in CO2 solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO2 conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO2 , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Luminescent Detection of Colchicine by a Unique Indium-Organic Framework in Water with High Sensitivity.

Colchicine is highly toxic to creatures, and sensitively detecting colchicines is of profound significance in the pharmaceutical, clinical, food, and breeding industries. We herein designed and constructed a unique luminescent indium-organic framework {[(CH3)2NH2][In(L)]·9DMF}n (V105) via an in situ ligand-mediated method, which possesses a 2-fold interpenetrated 3D anionic framework. Due to the large channels that exist in the framework with the size of 12 Å × 14 Å, V105 can rapidly remove harmful cationic dyes from water in a few minutes. Importantly, luminescent experiments demonstrate that V105 can selectively detect colchicine with high sensitivity in water, and the limit of detection can reach 1.0 × 10-7 M. To our knowledge, this is the first example of a metal-organic framework-based luminescent sensor for detecting colchicine.

Stable Lanthanide-Organic Framework as a Luminescent Probe To Detect Both Histidine and Aspartic Acid in Water.

A three-dimensional metal-organic framework (MOF) {[Eu(L)(H2O)2]·DMF} n (1) (H3L = 2'-nitro-3,4',5-biphenyl tricarboxylic acid) was obtained by hydrothermal methods and was characterized in detail. Compound 1 contains [Eu2] binuclear units, and [Eu2] units are further linked by H3L, forming a three-dimensional structure. Stability tests suggest that compound 1 exhibits high solvent, pH, and thermal stability. Besides, we also explored the influence of pH values in the luminescence emission of 1 which shows that pH has a negligible effect on the luminescence intensity with the range of pH = 3-11. Importantly, luminescent investigations reveal that 1 can selectively detect aspartic acid or histidine among 14 amino acids with good regenerability in water. Meanwhile, the concentration of aspartic acid can be quantitatively determined. We also discuss the mechanism of luminescence quenching and enhancement in detail. Importantly, this Eu-MOF provides a MOF-based luminescence sensor to detect two amino acids for the first time.