Unprecedented Ultralow Detection Limit of Amines using a Thiadiazole-Functionalized Zr(IV)-Based Metal–Organic Framework

A dual emitting CsPbBr3/Eu-BDC composite as a ratiometric photoluminescent turn-on probe for aliphatic amine sensing

The impressive photoluminescence properties of all inorganic cesium lead halide perovskite quantum dots (PeQDs) make them highly intriguing for fluorescence chemosensor applications. Herein, a ratiometric dual emitting perovskite-based sensor was designed by synthesizing fluorescent CsPbBr3 PeQDs in situ within a matrix of Eu-BDC (Eu(III) benzene-1,4-dicarboxylate). The results presented here establish the suggested sensor's quick and selective turn-on PL response to volatile primary aliphatic amine derivatives. In the presence of amines, the designed CsPbBr3/Eu-BDC sensor exhibits an enhancement of the PL signal of CsPbBr3 at 518 nm and the Eu-BDC signal at 615 nm served as a standard for constructing the ratiometric sensing system. Thereby, a visual color change from red to green was observed with the incremental addition of methylamine to the probe. A low detection limit of 0.083 ppm was determined for methylamine. In both the solution and vapor phases, this ratiometric sensor responds to a variety of primary aliphatic amines with very quick and strong fluorescence. Moreover, the sensor was effectively used for monitoring meat spoilage owing to the emission of biogenic amine vapor from meat products.

Packaged europium/fluorescein-based hydrogen bond organic framework as ratiometric fluorescent probe for visual real-time monitoring of seafood freshness

The freshness of sea food has always been the focus of attention from consumers, and food-safety issues are in urgent need of efficient approaches. A HOF-based ratiometric fluorescence probe (HOF-FITC/Eu) featuring superior amine-response, offers the real-time and visual detection of seafood freshness. Via intermolecular hydrogen bond interaction to form hydrogen-bonded organic frameworks (HOFs), which serve as a structural basis for the conjugate loading of pH-sensitive fluorescein (5-FITC) and coordination doping of lanthanide Eu3+. Amine vapors stimulate the dual-wavelength (525 nm and 616 nm) characteristic fluorescence of HOF-FITC/Eu with an inverse trend, resulting in an increase of the ratio of I525 to I616 accompanied by a distinct color transition from red to green. Prepared HOF-FITC/Eu featuring sensitive red-green color change characteristics of amine response are readily dripped into composite films of filter paper through integrated smartphone and 254 nm UV lamp as mobile observation devices to on-site monitor the freshness of raw fish and shrimp samples. The intelligent food probe HOF-FITC/Eu opens a novel material assembly type for fluorescence sensing and a potential pathway for other functional materials in the field of investigational food.

Hydrophobic functionalization of a metal-organic framework as an ammonia visual sensing material under high humidity conditions

Since exhaled ammonia (NH3) is one of the metabolic markers of liver and kidney diseases, ammonia visual sensing materials in humid environments have received extensive attention and investigation. Herein, through a tailor-made pore environment provided by metal-organic framework (MOF) materials (CH3-Cu(BDC)), we achieved NH3 anti-interference sensing with apparent color changing under humid conditions. With methyl (CH3-) functionalization, CH3-Cu(BDC) demonstrated a strong response for trace ammonia and showed high selectivity under a humid environment. Grand canonical Monte Carlo (GCMC) simulations indicated that CH3-Cu(BDC) showed stronger attraction towards NH3 molecules than H2O. Benefiting from the target changing coordination environment, CH3-Cu(BDC) showed a rapid response and simple analysis properties for patients' exhaled air. The strategy used in this study not only provides a demonstration case for NH3 colorimetric sensing with high humidity and anti-interference but also introduces a new method for painless and quick exhaled breath analysis for diagnosis of patients with kidney and liver diseases.

Selective Detection of Primary Aromatic Amines through Enhanced Luminescence of a 2D + 2D Inclined Polycatenated Microporous Nitro-Functionalized Metal-Organic Framework

Detection and sensing of amines through enhanced fluorescence emission are always challenging in aqueous solution. The range of different Lewis basicities, shapes, and sizes as well as the different structural arrangements of amines is responsible for their less specificity in aqueous solution. Here, we have designed a highly fluorescent emissive 2D + 2D → 3D inclined polycatenated NO2-functionalized flexible metal-organic framework (MOF) for selective segregation of electron-rich aromatic primary amines from electron-deficient amines in aqueous solution, showing different emission behaviors. The inclined polycatenated 2D + 2D → 3D MOF having an asymmetric unit {[Cd(dim)(2-nta)(H2O)](H2O)(MeOH)}n (1) has been synthesized by a slow diffusion process and characterized thoroughly by single-crystal and powder X-ray diffraction (PXRD) as well as other physicochemical methods. The desolvated species of 1 (Ref. MOF) is found to be stable and has been characterized by PXRD and adsorption study. The fluorescence profile of the Ref. MOF shows selective enhancement in the presence of electron-rich primary aromatic amines, while the same shows quenching for electron-deficient amines in aqueous solution. The Ref. MOF reported here consists of flexible space between two 2D layers that is responsible for different orientations for different analyte primary aromatic amines (PAAs) with different sizes. The above findings are also supported by time-resolved fluorescence spectroscopy. The respective fluorescence enhancement and quenching have been explained by the interaction between the CB of the host MOF and LUMO of guest amines. Therefore, this work presents an operable method for the sensing of PAAs using a single compound, which is a polycatenated MOF.

A two-dimensional metal-organic framework assembled from scandium-based cages for the selective capture of sulfur hexafluoride

Herein, we report the synthesis of a two-dimensional metal-organic framework (MOF), assembled from octahedral metal-organic cages featuring phenanthroline-based carboxylate linkers and μ3-oxo-centered trinuclear Sc(III) inorganic building blocks. We study the performance of this MOF towards the capture of sulfur hexafluoride (SF6). On account of its structural features and porous nature, this MOF displays an SF6 uptake capacity of 0.92 mmol g-1 at 0.1 bar and an isosteric heat of adsorption of about 30.7 kJ mol-1 for SF6, illustrating its potential application for the selective capture of SF6 from N2. In addition, we study the adsorptive binding mechanism of SF6 and N2 inside this MOF via molecular simulations.

Chromaticity sensor for discriminatory identification of aliphatic and aromatic primary amines based on conformational changes of polyacetylene

The design and construction of suitable sensors that can selectively recognize chemically similar substances such as aliphatic and aromatic amines remain challenging. In this work, we reported a poly(phenylacetylene) bearing two aldehyde pendants as the color indicator for discriminative identification of amines. Reversible Schiff-base reaction of the aldehyde group with the amine resulted in a conformational transition of the polyacetylene backbone from cis-cisoid to cis-transoid, which further achieved a colorimetric change. Thirteen aliphatic amines and aromatic amines had been studied. Compared with aromatic amines, aliphatic amines generally caused the polyene backbone to display perceivable colorimetric change. Steric and electronic effect played a significant role in the colorimetric response. In addition, external environment, including amine content, polymer concentration, and temperature, had influence on the sensitivity of this colorimetric indicator system. The amines-induced colorimetric variation was further demonstrated by the CIELAB color space. Moreover, the colorimetric sensor exhibited excellent reversibility and recyclability.

Rare Earth -MOFs: From Synthesis to Their Deployment for Amine-Sensing Application in Aqueous Media

The pursuit of developing sensors, characterized by their fluorescence-intensity enhancement or "turn-on" behavior, for accurately detecting noxious small molecules, such as amines, at minimal levels remains a significant challenge. Metal-organic frameworks (MOFs) have emerged as promising candidates as sensors as a result of their diverse structural features and tunable properties. This study introduces the rational synthesis of a new highly coordinated (6,12)-connected rare earth (RE) alb-MOF-3, by combining the nonanuclear 12-connected hexagonal prismatic building units, [RE9(μ3-O)2(μ3-X)12(OH)2(H2O)7(O2C-)12], with the 6-connected rigid trigonal prismatic extended triptycene ligand. The resulting Y-alb-MOF-3 material is distinguished by its high microporosity and Brunauer-Emmett-Teller surface area of approximately 1282 m2/g, which offers notable hydrolytic stability. Remarkably, it demonstrates selective detection capabilities for primary aliphatic amines in aqueous media, as evidenced by fluorescence turn-on behavior and photoluminescence (PL) titration measurements. This work emphasizes the potential of MOFs as sensors in advancing their selectivity and sensitivity toward various analytes.

A Drop-and-Drain Method for Convenient and Efficient Fabrication of MOF/Fiber Composites

The fabrication of flexible composites by integrating metal-organic frameworks (MOFs) with flexible substrates is a critical strategy for developing advanced materials with excellent feasibility and processability. These flexible MOF-based composites play a particularly important role in the separation and purification processes. However, several drawbacks remain challenge to overcome such as long processing time, high-cost, complicated processes, or harsh reaction conditions. In this paper, a convenient and efficient method is reported for fabricating MOF/fiber composites using a simple drop-and-drain (D&D) process. By exploiting the electrostatic interactions between the positively charged MOF particles and negatively charged fiber-based flexible substrates, a uniform coating of MOF on flexible fibers are achieved. This is accomplished by allowing the MOF ink to drop and drain through a substrate using a custom-made Teflon cell. Additionally, the D&D method enables the production of multiple layers of composites in a single-step process. UiO-66 and ZIF-8 submicroparticles and various substrates such as cotton-pad, cotton-fabric, nylon-fabric, PET-fabric, and filter-paper are employed to create flexible MOF/fiber composites. These composites demonstrate outstanding capacities for capturing negatively charged organic dyes, including methyl orange and indigo carmine. Furthermore, the MOF/fiber composites can be reused for dye capture after a simple washing process.

Fluorescence sensing and device fabrication with luminescent metal-organic frameworks

Metal-organic frameworks (MOFs) are a novel class of hybrid porous multi-functional materials consisting of metal ions/clusters and organic ligands. MOFs have exclusive benefits due to their tunable structure and diverse properties. Luminescent MOFs (LMOFs) exhibit both porosity and light emission. They display abundant host and guest responses, making them conducive to sensing. Currently, LMOF sensing research is gaining more depth, with attention given to their device and practical applications. This work reviews recent advancements and device applications of LMOFs as chemical sensors toward ions, volatile organic compounds, biomolecules, and environmental toxins. Furthermore, the detection mechanism and the correlation between material properties and structure are elaborated. This analysis serves as a valuable reference for the preparation and efficient application of targeted LMOFs.

Simultaneous Detection and Decontamination of Dichromate Ions: The Fluorescence Response and Photocatalysis of Thiadiazole-Modified Zr-Metal-Organic Frameworks

The simultaneous analysis and removal of highly toxic hexavalent chromium (Cr (VI)) in contaminated water via an easy method remain a serious task. Based on the guidance of bibliometric analysis, a thiadiazole ligand-modified zirconium metal-organic framework (Zr-MOF) heralds a new and simple approach to Cr (VI) treatment. The concentration can be determined by fluorescence quenching with a low detection limit of 1.4 μM and a high quenching constant of 6.88 × 103 M-1. For the sensing mechanism, the fluorescence intensity of the Zr-MOF decreased rapidly due to the competition of Cr (VI) with the Zr-MOF for absorption excitation energy and the induction of Zr-MOF aggregation. The analysis system also displayed satisfactory stability and applicability. Apart from sensing application, Zr-MOF can convert Cr (VI) to Cr (III), and the reduction rate constant was 0.004 min-1 under irradiation. Therefore, the bifunctional Zr-MOF provided a potential application method for controlling the pollution caused by Cr (VI) in wastewater.

Metal Ion-controlled Growth of Different Metal-Organic Framework Micro/nanostructures for Enhanced Supercapacitor Performance

We report a metal ion-modulated effective strategy to achieve different metal-organic framework (MOF) micro/nanostructures using different metal precursors like CoCl2  ⋅ 6H2 O, CoCl2  ⋅ 6H2 O and NiCl2  ⋅ 6H2 O, and NiCl2  ⋅ 6H2 O with pyridine-3,5-dicarboxylate (3,5-pdc). The structural characterizations confirm that different morphological structures, hollow microsphere, hierarchical nanoflower, and solid nanosphere are for Co-(3,5-pdc), Co0.19 Ni0.81 -(3,5-pdc), and Ni-(3,5-pdc), respectively. These different MOF micro/nanostructures correlate with the coordination ability of Co and Ni with 3,5-pdc. Benefitting from the synergistic effect of the alloying metal nodes of Co and Ni producing rapid and rich redox reactions and the hierarchical nanoflower with higher surface area enabling excellent ion kinetics, the Co0.19 Ni0.81 -(3,5-pdc) exhibits higher specific capacitance of 515 F g-1 /273 C g-1 at 0.5 A g-1 than that of Ni-(3,5-pdc) (290 F g-1 /153.7 C g-1 ) and Co-(3,5-pdc) (132 F g-1 /67 C g-1 ), good rate capability and cycling stability. Moreover, the asymmetric supercapacitor device (Co0.19 Ni0.81 -(3,5-pdc)//AC) assembled from Co0.19 Ni0.81 -(3,5-pdc) and activated carbon (AC) achieves a maximum energy density of 42.6 Wh kg-1 at a power density of 277.3 W kg-1 .

Pyrazine Functionalization in Eu-MOF for Exclusive Ratiometric Luminescence Sensing of PO43

Single-emission luminescence sensors are less than satisfactory for complex systems due to their susceptibility to environmental disturbances. Lanthanum-based metal-organic frameworks (Ln-MOFs) with highly stable ratiometric dual-emission are regarded as promising luminescence probes owing to their fascinating ligand-to-metal energy transfer behaviors (also known as the antenna effect). Herein, we report the synthesis of a pair of isostructural europium-based MOFs (termed JNU-219 and JNU-220) by utilizing two X-shaped tetracarboxylate linkers, 4,4',4″,4‴-benzene-2,3,5,6-tetrayl-tetrabenzoate (BTEB) and 4,4',4″,4‴-pyrazine-2,3,5,6-tetrayl-tetrabenzoate (BTTB). Both JNU-219 and JNU-220 present the characteristic red luminescence of Eu3+, yet the pyrazine functionalization of the BTTB linker renders JNU-220 with significantly increased luminescence emission, almost 30 times that of JNU-219. As a result, the detection limit of JNU-220 for the ratiometric luminescence sensing of PO43- was determined to be as low as 0.22 μM, which is far superior to those of other reported MOF materials. Additionally, we demonstrate the excellent stability and reusability of JNU-220, further verifying its potential as a robust ratiometric luminescence probe.

An Ir(III) cyclometalate-functionalized molecularly imprinted polymer: photophysics, photochemistry and chemosensory applications

A luminescent trimethylamine (TMA) sensor, PTMA-Ir, has been designed and synthesized through immobilizing a phosphorescent iridium(III) complex on a TMA-imprinted polymer. Detailed study shows that the quenching of phosphorescence of PTMA-Ir can serve as a reporter for the binding of TMA on the imprinting sites, thus providing a sensitive, selective, and rapid detection of TMA in both aqueous solutions and gaseous states. Loading PTMA-Ir on filter paper produced a deposition T-Ir, the phosphorescence of which is quenched within 5 s upon exposure to TMA vapor with detection limits of 9.0 ± 0.1 ppm under argon and 15.0 ± 0.1 ppm in an air atmosphere. This work provided an effective method for establishing an imprinting polymer-immobilized luminescent amine sensor.

A Nitro-Modified Luminescent Hydrogen-Bonded Organic Framework for Non-Contact and High-Contrast Sensing of Aromatic Amines

The global demand for intelligent sensing of aromatic amines has consistently increased due to concerns about health and the environment. Efforts to improve material design and understand mechanisms have been made, but highly efficient non-contact sensing with host-guest structures remains a challenge. Herein, we report the first example of non-contact, high-contrast sensing of aromatic amines in a hydrogen-bonded organic framework (HOF) based on a nitro-modified stereo building block. Direct observation of binding interactions of trapped amines is achieved, leading to charge separation-induced emission quenching between host and guests. Non-contact sensing of aniline and diphenylamine is realized with quenching efficiencies up to 91.7 % and 97.0 %, which shows potential for versatile applications. This work provides an inspiring avenue to engineer multifunctional HOFs via co-crystal preparations, thus enriching applications of porous materials with explicit mechanisms.

Linker engineering toward near-infrared-I emissive metal-organic frameworks for amine detection

Herein, organic linker-based near-infrared-I (NIR-I) emissive metal-organic frameworks (MOFs), with a maximum emission peak at 741 nm, were synthesized via linker engineering. By integration of stronger acceptor and donor groups into one linker, a significant bathochromic-shift is realized. This MOF exhibits great selectivity and sensitivity for aniline and p-phenylenediamine detection. This finding provides new insights into the rational design of NIR-MOFs for sensing and related applications.

Linker Engineering for Reactive Oxygen Species Generation Efficiency in Ultra-Stable Nickel-Based Metal-Organic Frameworks

Interfacial charge transfer on the surface of heterogeneous photocatalysts dictates the efficiency of reactive oxygen species (ROS) generation and therefore the efficiency of aerobic oxidation reactions. Reticular chemistry in metal-organic frameworks (MOFs) allows for the rational design of donor-acceptor pairs to optimize interfacial charge-transfer kinetics. Herein, we report a series of isostructural fcu-topology Ni8-MOFs (termed JNU-212, JNU-213, JNU-214, and JNU-215) with linearly bridged bipyrazoles as organic linkers. These crystalline Ni8-MOFs can maintain their structural integrity in 7 M NaOH at 100 °C for 24 h. Experimental studies reveal that linker engineering by tuning the electron-accepting capacity of the pyrazole-bridging units renders these Ni8-MOFs with significantly improved charge separation and transfer efficiency under visible-light irradiation. Among them, the one containing a benzoselenadiazole unit (JNU-214) exhibits the best photocatalytic performance in the aerobic oxidation of benzylamines with a conversion rate of 99% in 24 h. Recycling experiments were carried out to confirm the stability and reusability of JNU-214 as a robust heterogeneous catalyst. Significantly, the systematic modulation of the electron-accepting capacity of the bridging units in donor-acceptor-donor MOFs provides a new pathway to develop viable noble-metal-free heterogeneous photocatalysts for aerobic oxidation reactions.

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection

The development of nanoscaled luminescent metal-organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu- and csq-type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH2 -substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

Engineering Metal-Organic Frameworks with Tunable Colors for High-Performance Wireless Communication

Metal-organic frameworks (MOFs) have emerged as excellent platforms possessing tunable and controllable optical behaviors that are essential in high-speed and multichannel data transmission in optical wireless communications (OWCs). Here, we demonstrate a novel approach to achieving a tunable wide modulation bandwidth and high net data rate by engineering a combination of organic linkers and metal clusters in MOFs. More specifically, two organic linkers of different emission colors, but equal molecular length and connectivity, are successfully coordinated by zirconium and hafnium oxy-hydroxy clusters to form the desired MOF structures. The precise change in the interactions between these different organic linkers and metal clusters enables control over fluorescence efficiency and excited state lifetime, leading to a tunable modulation bandwidth from 62.1 to 150.0 MHz and a net data rate from 303 to 363 Mb/s. The fabricated color converter MOFs display outstanding performance that competes, and in some instances surpasses, those of conventional materials commonly used in light converter devices. Moreover, these MOFs show high practicality in color-pure wavelength-division multiplexing (WDM), which significantly improved the data transmission link capacity and security by the contemporary combining of two different data signals in the same path. This work highlights the potential of engineered MOFs as a game-changer in OWCs, with significant implications for future high-speed and secure data transmission.

Polyaromatic hydrocarbons (PAHs) in the water environment: A review on toxicity, microbial biodegradation, systematic biological advancements, and environmental fate

Polycyclic aromatic hydrocarbons (PAHs) are considered a major class of organic contaminants or pollutants, which are poisonous, mutagenic, genotoxic, and/or carcinogenic. Due to their ubiquitous occurrence and recalcitrance, PAHs-related pollution possesses significant public health and environmental concerns. Increasing the understanding of PAHs' negative impacts on ecosystems and human health has encouraged more researchers to focus on eliminating these pollutants from the environment. Nutrients available in the aqueous phase, the amount and type of microbes in the culture, and the PAHs' nature and molecular characteristics are the common factors influencing the microbial breakdown of PAHs. In recent decades, microbial community analyses, biochemical pathways, enzyme systems, gene organization, and genetic regulation related to PAH degradation have been intensively researched. Although xenobiotic-degrading microbes have a lot of potential for restoring the damaged ecosystems in a cost-effective and efficient manner, their role and strength to eliminate the refractory PAH compounds using innovative technologies are still to be explored. Recent analytical biochemistry and genetically engineered technologies have aided in improving the effectiveness of PAHs' breakdown by microorganisms, creating and developing advanced bioremediation techniques. Optimizing the key characteristics like the adsorption, bioavailability, and mass transfer of PAH boosts the microorganisms' bioremediation performance, especially in the natural aquatic water bodies. This review's primary goal is to provide an understanding of recent information about how PAHs are degraded and/or transformed in the aquatic environment by halophilic archaea, bacteria, algae, and fungi. Furthermore, the removal mechanisms of PAH in the marine/aquatic environment are discussed in terms of the recent systemic advancements in microbial degradation methodologies. The review outputs would assist in facilitating the development of new insights into PAH bioremediation.

Benzothiazole-based novel fluorescence probe sensing 1, 3-diaminopropane

Amines are extensively present in biological systems and are abundantly used in research, industries and agriculture. Systematic detection and quantification of certain amines can help us in food quality control and diagnosis of many diseases. A Schiff base probe HL was designed and successfully synthesized. It was proposed as a sensor for the exclusive detection of 1, 3- diaminopropane through turn-on fluorescence response in a variety of solvents including water. Micromolar limits of detection was achieved in all these solvents. Mechanism of detection was proposed by investigating mass spectrometric and NMR results. These were corroborated with DFT/TD-DFT calculations. Spiking experiments performed in various real water samples revealed the potential of the sensor to be used in day-to-day applications. Paper strip experiments demonstrated the suitability of the probe for real-life applications.

Solvothermal synthesis and device fabrication of a Eu3+-based metal-organic framework as a turn-on and blue-shift fluorescence sensor toward Cr3+, Al3+ and Ga3

A novel three-dimensional Eu³⁺-based metal-organic framework with the formula {[(CH₃)₂NH₂][Eu(BTDI)]·H₂O·DMF}_n (JXUST-25) was prepared by solvothermal method based on Eu³⁺ and 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H₄BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu³⁺ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr³⁺, Al³⁺ and Ga³⁺ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr³⁺, Al³⁺ and Ga³⁺ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M³⁺ ions may be caused by the host-guest interaction and the absorbance caused enhancement mechanism.

Tunable Photoinduced Charge Transfer at the Interface between Benzoselenadiazole-Based MOF Linkers and Thermally Activated Delayed Fluorescence Chromophore

Structural modifications to molecular systems that lead to the control of photon emission processes at the interfaces between photoactive materials play a key role in the development of fluorescence sensors, X-ray imaging scintillators, and organic light-emitting diodes (OLEDs). In this work, two donor-acceptor systems were used to explore and reveal the effects of slight changes in chemical structure on interfacial excited-state transfer processes. A thermally activated delayed fluorescence (TADF) molecule was chosen as the molecular acceptor. Meanwhile, two benzoselenadiazole-core MOF linker precursors, Ac-SDZ and SDZ, with the presence and absence of a C≡C bridge, respectively, were carefully chosen as energy and/or electron-donor moieties. We found that the SDZ -TADF donor-acceptor system exhibited efficient energy transfer, as evidenced by steady-state and time-resolved laser spectroscopy. Furthermore, our results demonstrated that the Ac-SDZ-TADF system exhibited both interfacial energy and electron transfer processes. Femtosecond-mid-IR (fs-mid-IR) transient absorption measurements revealed that the electron transfer process takes place on the picosecond timescale. Time-dependent density functional theory (TD-DFT) calculations confirmed that photoinduced electron transfer occurred in this system and demonstrated that it takes place from C≡C in Ac-SDZ to the central unit of the TADF molecule. This work provides a straightforward way to modulate and tune excited-state energy/charge transfer processes at donor-acceptor interfaces.

Boric Acid Functional Fluorescent Covalent-Organic Framework for Sensitive and Selective Visualization of CH3Hg. ACS Appl Mater Interfaces 2023;15:9524-9532. [PMID: 36757912 DOI: 10.1021/acsami.2c23302]

Methylmercury (CH3Hg+) recognition remains a challenging and imperative task due to its high toxicity and wide existence in the ecosystem. Herein, a novel fluorescent covalent-organic framework containing a boric acid functional group (COF-BA) was prepared by a postmodification strategy for CH3Hg+ detection. COF-BA served as a sensing platform for CH3Hg+ with fluorescence static quenching accompanied by fluorescence color changing from intense blue to colorless, and the detection limit was determined as 1.68 μM in a relatively narrow concentration range. COF-BA also exhibited superior selectivity toward CH3Hg+ detection. Furthermore, the spiked and recovery test in real water samples showed its efficient detection practicality. The detection mechanism of COF-BA toward CH3Hg+ was investigated. The recognitive boric acid group in COF-BA was first replaced by CH3Hg+. Then, the quinoline structure that served to limit the rotation of the imine bond was disrupted, leading to dramatic fluorescence quenching. The boric acid functional COF fluorescent probe can be a promising sensing platform for the detection of methylmercury and also provides new ideas for the construction of new fluorescent COF materials.

Naked-Eye Optical Recognition of Ammonia Vapor and Melamine in Water Using a Fluorophore Appended Polymer Matrix

The generation of solid-state emitters is a challenge due to the intrinsic aggregation-caused quenching feature of the fluorophores. A conformationally twisted pyridyl π-conjugate as a solid-state emitter is appended with well-known and inexpensive poly(methylmethacrylate) [PMMA] to afford a handy, portable, and reusable solid-state emitting polymer matrix. Entrapment of the probe is noticed through non-covalent interactions, resulting in a green-emitting platform. It quickly accepts a proton upon acid vapor exposure and switches emission from green to red with a significant 107 nm redshift. This shift is reversible with red to green emissions while exposed to base vapor. Thus, polymer-blended, homogeneous red-emitting pyridyl salt is employed as potential material to detect various basic vapors optically. Among different bases, naked-eye detection of essential analytes such as ammonia vapor and melamine shows potential demands. Hence, we have established an easy detection of ammonia vapor and aqueous melamine as low as 2.5 and 0.126 ppm, respectively, using this solid-state emitter that displays an emission color change with an enhancement of emission intensity even in an aqueous solution.

Computational Quantification of the Zwitterionic/Quinoid Ratio of Phenolate Dyes for Their Solvatochromic Prediction

Solvatochromic dyes are utilized in various chemical and biological media as chemical sensors. Unfortunately, there is no simple way to predict the type of solvatochromism based on the structure of the dye alone, which restricts their design and synthesis. The most important family of solvatochromic sensors, pyridinium phenolate dyes, has the strongest solvatochromism. Using a natural population analysis (NPA) of the natural bond orbitals (NBO) of the phenolate group in the frontier molecular orbitals, it is possible to calculate the relative polarity of the ground state and excited state and, thus to develop a model that can predict the three types of solvatochromism observed for this family: negative, positive, and inverted. This methodology has been applied to thirteen representative examples from the literature. Our results demonstrate that the difference in the electron density of the phenolate moiety in the frontier molecular orbitals is a simple and inexpensive theoretical indicator for calculating the relative polarity of the ground and excited states of a representative library of pyridinium phenolate sensors, and thus predicting their solvatochromism. Comparing the results with the bond length alternation (BLA) and bond order alternation (BOA) indices showed that the NPA/NBO method is a better way to predict solvatochromic behavior.

Rational Pore Design of a Cage-like Metal-Organic Framework for Efficient C2H2/CO2 Separation

Considering the importance of C₂H₂ in industry, it is of great significance to develop porous materials for efficient C₂H₂/CO₂ separation. Besides the high selectivity, the C₂H₂ adsorption capacity is another vital factor in C₂H₂/CO₂ separation. However, the "trade-off" between these two factors is still perplexing. Rational pore design of metal-organic frameworks (MOFs) has been proven to be an effective way to solve the above problem. In this work, we have appropriately combined three kinds of strategies in the design of the MOF (FJI-H33), i.e., the introduction of open metal sites, construction of cage-like cavities, and adjustment of moderate pore size. As anticipated, FJI-H33 exhibits both outstanding C₂H₂ adsorption capacity and high C₂H₂/CO₂ selectivity. At 298 K and 100 kPa, the C₂H₂ storage capacity of FJI-H33 is 154 cm³/g, while the CO₂ uptake is only 80 cm³/g. The ideal adsorbed solution theory (IAST) selectivity of C₂H₂/CO₂ (50:50) is calculated as high as 15.5 at 298 K. More importantly, the excellent practical separation performance was verified by breakthrough experiments. In addition, the calculation of adsorption sites and relevant energy by density functional theory (DFT) provides a good explanation for the excellent separation performance and pore design strategy.

Highly Luminescent MOF and Its In Situ Fabricated Sustainable Corn Starch Gel Composite as a Fluoro-Switchable Reversible Sensor Triggered by Antibiotics and Oxo-Anions

Frequent use of antibiotics and the growth of industry lead to the pollution of several natural resources which is one of the major consequences for fatality to human health. Exploration of smart sensing materials is highly anticipated for ultrasensitive detection of those hazardous organics. The robust porous hydrogen bonded network encompassing a free-NH₂ moiety, Zn(II)-based metal-organic framework (MOF) (1), is used for the selective detection of antibiotics and toxic oxo-anions at the ppb level. The framework is able to detect the electronically dissimilar antibiotic sulfadiazine and nitrofurazone via fluorescence "turn-on" and "turn-off" processes, respectively. The antibiotic-triggered reversible fluoro-switching phenomena (fluorescence "on-off-on") are also observed by using the fluorimetric method. An extensive theoretical investigation was performed to establish the fluoro-switching response of 1, triggered by a class of antibiotics and also the sensing of oxo-anions. This investigation reveals that the interchange of the HOMO-LUMO energy levels of fluorophore and analytes is responsible for such a fluoro-switchable sensing activity. Sensor 1 showed the versatile detection ability which is reflected by the detection of a carcinogenic nitro-group-containing drug "roxarsone". In view of the sustainable environment along with quick-responsive merit of 1, an in situ MOF gel composite (1@CS; CS = corn starch) is prepared using 1 and CS due to its useful potential features such as biocompatibility, toxicologically innocuous, good flexibility, and low commercial price. The MOF composite exhibited visual detection of the above analytes as well as antibiotic-triggered reversible fluoro-switchable colorimetric "on-off-on" response. Therefore, 1@CS represents a promising smart sensing material for monitoring of the antibiotics and oxo-anions, particularly appropriate for the real-field analysis of carcinogenic drug molecule "roxarsone" in food specimens.

Unique Fluorescence Turn-On and Turn-Off-On Responses to Acids by a Carbazole-Based Metal-Organic Framework and Theoretical Studies

Distinct from predominately known fluorescence quenching (turn-off) detection, turn-on response to hazardous substances by luminescent metal-organic frameworks (LMOFs) could greatly avoid signal loss and susceptibility to environmental stimulus. However, such detection rarely occurs and lacks theoretical elucidations. Here, we present the first example of unique turn-on and unprecedented turn-off-on responses to a variety of acids by a stable 12-connected hexanuclear Y(III)-cluster-based LMOF material─JLU-MOF111, featuring the nondefault pcu topology. Benefiting from the "pocket" structures formed by the carbazole-containing ligands, JLU-MOF111 can sense multiple inorganic and organic acids via different degrees of fluorescence turn-on behaviors. Particularly, turn-on sensing of HNO₃, HCl, HBr, and TFA is hypersensitive with LODs as low as the ppb level. Theoretical calculations confirm weak interactions in acid-ligand complexes, which lead to constrained rotations of benzene moieties of the ligands when the complexes decay from excited states. These account for the turn-on response through reduced nonradiative energy consumption that competes with emissive decay. The turn-off-on response to 4-NBA and 3,5-DNBA involves an excited-state electron transfer process that dominates the turn-off stage and prohibited nonradiative decay that competes with the intrinsic emission of the ligand and dominates the turn-on stage. This work has a guiding significance for the full-scale understanding of turn-on and turn-off-on sensing performance in LMOF materials and beyond.

Fluorescence turn on amine detection in a cationic covalent organic framework

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and have shown great potential for various applications. When functionalized with suitable emission sites, guest uptake via the ionic moieties of iCOFs can cause a significant change in luminescence, making them excellent candidates for chemosensors. In here, we present a luminescence sensor in the form of an ionic covalent organic framework (TGH⁺•PD) composed of guanidinium and phenanthroline moieties for the detection of ammonia and primary aliphatic amines. TGH⁺•PD exhibits strong emission enhancement in the presence of selective primary amines due to the suppression of intramolecular charge transfer (ICT) with an ultra-low detection limit of 1.2 × 10^‒7 M for ammonia. The presence of ionic moieties makes TGH⁺•PD highly dispersible in water, while deprotonation of the guanidinium moiety by amines restricts its ICT process and signals their presence by enhanced fluorescence emission. The presence of ordered pore walls introduces size selectivity among analyte molecules, and the iCOF has been successfully used to monitor meat products that release biogenic amine vapors upon decomposition due to improper storage.

Ionic covalent organic frameworks (iCOFs) are new examples of porous materials and show great potential for various applications. Here, the authors demonstrate functionalization of an iCOFs with suitable emission sites and application as chemosensor for amine detection with high sensitivity which can be used to monitor meat spoilage.

Rapid and Specific Enhanced Luminescent Switch of Aniline Gas by MOFs Assembled from a Planar Binuclear Cadmium(II) Metalloligand

Due to the low vapor pressure of aniline, it is challenging to develop a specific rapid fluorescence detection material for low concentrations of aniline gas, which is suspected to result in carcinogenicity when people are exposed by ingestion, inhalation, and skin contact. Herein, the easy-preparing Schiff base ligands were employed to construct the binuclear cadmium(II) compounds featuring a good plane and fine luminescent property, and then, the end groups were changed, making the compounds metalloligands to further build the 3D metal-organic frameworks (MOFs), named MECS-2. It is found that MECS-2 can achieve specific luminescent enhancement response for aniline gas. Furthermore, a large-scale MECS-2a film could be easily prepared by electrospinning nanoMECS-2, which presents the highly efficient and visual detection for aniline gas with the luminescent enhancement effect up to 20 times and good repeatability. Our work provides a good example for the efficient construction of MOF-based films with the fluorescence detection function for organic aromatic gases.

Non-Calcined Layer-Pillared Mn0.5Zn0.5 Bimetallic-Organic Framework as a Promising Electrocatalyst for Oxygen Evolution Reaction

Electrocatalytic generation of oxygen is of great significance for sustainable, clean, and efficient energy production. Multiple electron transfer in oxygen evolution reaction (OER) and its slow kinetics represent a serious hedge for efficient water splitting, requiring the design and development of advanced electrocatalysts with porous structures, high surface areas, abundant electroactive sites, and low overpotentials. These requisites are common for metal-organic frameworks (MOFs) and derived materials that are promising electrocatalysts for OER. The present work reports on the synthesis and full characterization of a heteroleptic 3D MOF, [Zn₂(μ₄-odba)₂(μ-bpdh)]_n·nDMF (Zn-MUM-1), assembled from 4,4'-oxydibenzoic acid and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh). Besides, a series of heterometallic MnZn-MUM-1 frameworks (abbreviated as Mn_0.5Zn_0.5-MUM-1, Mn_0.66Zn_0.33-MUM-1, and Mn_0.33Zn_0.66-MUM-1) was also prepared, characterized, and used for the fabrication of working electrodes based on Ni foam (NF), followed by their exploration in OER. These noble-metal-free and robust electrocatalysts are stable and do not require pyrolysis or calcination while exhibiting better electrocatalytic performance than the parent Zn-MUM-1/NF electrode. The experimental results show that the Mn_0.5Zn_0.5-MUM-1/NF electrocatalyst features the best OER activity with a low overpotential (253 mV at 10 mA cm^-2) and Tafel slope (73 mV dec^-1) as well as significant stability after 72 h or 6000 cycles. These excellent results are explained by a synergic effect of two different metals present in the Mn-Zn MOF as well as improved charge and ion transfer, conductivity, and stability characteristics. The present study thus widens the application of heterometallic MOFs as prospective and highly efficient electrocatalysts for OER.

Three-pole wheel paddle luminescent metal organic frameworks (LMOFs) based on the oxygen substituted triazine tricarboxylic acid ligand: recognition and detection of small drug molecules and aromatic amine molecules

Luminescent metal organic frameworks (LMOFs) are considered to be a type of promising optical sensing material due to their designable and tunable functions, and stable pore structures. Therefore, the preparation of LMOFs has become a research hotspot in recent years. As we know, triazine carboxylic acid ligands are conducive for constructing LMOF materials due to their large π electron conjugated system. In this work, two crystalline materials [Cd₃(TCPT)₂]·0.5DMF·4H₂O (1) and (H₃O)[Zn₂(TCPT)(μ₂-OH)₂]·0.5DMF·3H₂O (2) were obtained by the reaction of the triazine carboxylic acid ligand 2,4,6-tris(4-carboxyphenoxy)-1,3,5-triazine (H₃TCPT), as an extended carboxylate arm, and d¹⁰ transition metal salts. Their structures were determined by single crystal X-ray diffraction and characterized by infrared spectroscopy (IR), ultraviolet visible spectroscopy (UV-vis), fluorescence spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG). The experimental results showed that complexes 1 and 2 show excellent fluorescent emission behavior. Thus, we explored their fluorescence sensing properties. To our delight, the results showed that they both had the ability to sense small organic drug molecules and aromatic amine molecules containing o-phenylenediamine (OPD), m-phenylenediamine (MPD) and p-phenylenediamine (PPD). In general, the practical applications of a MOF material are usually limited because of the relatively harsh synthesis methods. In this aspect, we studied the synthesis method in detail to obtain the optimal reaction conditions for the large-scale synthesis of 1 and 2. The preparation of the two LMOF materials only required about 3 hours of heating time and they could be prepared on a large scale, which is significant for the practical applications of LMOFs.

Hydrogen-bonding and "π-π" interaction promoted solution-processable mixed matrix membranes for aromatic amines detection

Detection of hazardous compounds can alleviate risk to human health. However, it remains a challenge to develop easy-to-use testing tools for carcinogenic aromatic amines. Herein, we presented a conjugated molecule-based aniline detector, mixed matrix membranes (MMMs), through the solution-processable strategy. The pentacene-based dispersed phase is achieved using the state-of-the-art ionic liquids (ILs) as the continuous phase, based on which MMMs are easily manufactured by a solution process. Moreover, molecular dynamics (MD) simulations and quantum mechanical calculations suggested that hydrogen bonding and π-π interaction between ILs cations and pentacene could promote the dissolution. These prepared MMMs can offer easy-operation and on-site detection of carcinogenic primary aromatic amines with eye-readable fluorescence signal. This work provides a paradigm for the design of a portable testing device for various hazardous compounds.

Role of Lewis Acid Metal Centers in Metal–Organic Frameworks for Ultrafast Reduction of 4-Nitrophenol

Metal–Organic Frameworks (MOFs) can be a good alternative to conventional catalysts because they are non-toxic and can be selective without compromising efficiency. Nano MOFs such as UiO-66 have proven themselves to be competitive in the catalytic family. In this study, we report the excellent catalytic behavior of UiO-66 MOF in the reduction of a model reaction: 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) over MOF-5 (Zn-BDC) and MIL-101 (Fe-BDC). Nano UiO-66 crystals were synthesized by a hydrothermal process and characterized by Powder X-ray Diffraction, Diffused Reflectance UV-Vis spectroscopy, Scanning Electron Microscopy, and Transmission Electron Microscopy. The catalysts’ performance during the hydrogenation reduction reaction from 4-NP to 4-AP was investigated in the presence of a reducer, NaBH4. The UiO-66 nano crystals exhibited excellent catalytic behavior owing to its large surface area and Lewis acidic nature at the metal nodes. Furthermore, UiO-66 showed excellent recyclability behavior, verified during repeated consecutive use in a sequence. The catalyst yielded similar catalytic behavior during the reduction of nitrophenols at each cycle, which is a novel finding.

Metal-Organic Framework-Based Selective Molecular Recognition of Organic Amines and Fixation of CO2 into Cyclic Carbonates

Synthesis and structural depiction of two new metal-organic frameworks (MOFs), namely, [{Zn(L)(oba)}·4H₂O]_α (Zn-MOF-1) and [{Cd_1/2(L)_1/2(nipa)_1/2(H₂O)_1/2}·(DMF)_1/2(H₂O)]_α (Cd-MOF-2) (where L = N²,N⁶-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide, 4,4'-H₂oba = 4,4'-oxybisbenzoic acid, and 5-H₂nipa = 5-nitroisophthalic acid) are reported. Both Zn-MOF-1 and Cd-MOF-2 have been prepared by reacting ligand L and coligand 4,4'-H₂oba or 5-H₂nipa with the respective dihydrates of Zn(OAc)₂ and Cd(OAc)₂ (OAc = acetate). Crystal structure X-ray analysis discloses that Zn-MOF-1 displays an overall 2D → 3D interpenetrated framework structure. The topological analysis by ToposPro suggests a (4)-connected uninodal sql topology with a point symbol of {4⁴·6²} having 2D + 2D parallel polycatenation. However, crystal packing of Cd-MOF-2 adapted a porous framework architecture and was topologically simplified as (3,4)-connected binodal 2D net. In addition, both Zn-MOF-1 and Cd-MOF-2 were proved to be multifunctional materials for the recognition of organic amines and in the fixation of CO₂ to cyclic carbonates. Remarkably, Zn-MOF-1 and Cd-MOF-2 showed very good fluorescence stability in aqueous media and have shown 98 and 97% quenching efficiencies, respectively, for 4-aminobenzoic acid (4-ABA), among all of the researched amines. The mechanistic study of organic amines recognition proposed that fluorescence quenching happened mainly through hydrogen-bonding and π-π stacking interactions. Additionally, cycloaddition of CO₂ to epoxide in the presence of Zn-MOF-1 and Cd-MOF-2 afforded up to 96% of cyclic carbonate within 24 h. Both Zn-MOF-1 and Cd-MOF-2 exhibited recyclability for up to five cycles without noticing an appreciable loss in their sensing or catalytic efficiency.

Subtle Ligand Spacer Change in 2D Metal-Organic Framework Sheets for Dual Turn-On/Turn-Off Sensing of Acetylacetone and Turn-On Sensing of Water in Organic Solvents

Metal-organic framework (MOF)-based sensors for the detection of various analyte molecules has been a subject of absolute importance. However, most of these sensors rely on the turn-off (quenching) transduction response, while those reporting turn-on response are very rare. In this article, we have synthesized two new MOF-based sensors, {[Zn₂(oxdz)₂(tpbn)]·14H₂O}_n (1) and {[Zn₂(oxdz)₂(tpxn)]·10H₂O·2C₂H₅OH}_n (2), via the self-assembly of Zn(II) metal ions, a fluorogenic oxdz^2- linker, and bis(tridentate) ligands (tpbn and tpxn) under ambient conditions. Their formation from such a self-assembly process has been evaluated on the basis of the geometry around the five-coordinated Zn(II), preferential meridional binding of the bis(tridentate) ligands, and diverse binding of the carboxylate groups in oxdz^2-. Although 1 and 2 are isostructural, a difference in the transduction mechanism for the sensing of acetylacetone in organic solvents (turn-on for 1 and turn-off for 2) is observed and can be attributed to the spacer in the bis(tridentate) ligands. We have demonstrated the competing effect of the nonradiative interactions and photoinduced electron transfer toward the sensing mechanism. The results are well-supported by the Fourier transform infrared spectroscopy study, intensity versus concentration plots, spectral overlap measurements, time-resolved fluorescence studies, and MM2 and density functional theory calculations. Furthermore, we have showcased the utilization of 1 for the sensing of trace amounts of water in organic solvents.

Recent Progress in Metal-Organic Framework Based Fluorescent Sensors for Hazardous Materials Detection

Population growth and industrial development have exacerbated environmental pollution of both land and aquatic environments with toxic and harmful materials. Luminescence-based chemical sensors crafted for specific hazardous substances operate on host-guest interactions, leading to the detection of target molecules down to the nanomolar range. Particularly, the luminescence-based sensors constructed on the basis of metal-organic frameworks (MOFs) are of increasing interest, as they can not only compensate for the shortcomings of traditional detection techniques, but also can provide more sensitive detection for analytes. Recent years have seen MOFs-based fluorescent sensors show outstanding advantages in the field of hazardous substance identification and detection. Here, we critically discuss the application of MOFs for the detection of a broad scope of hazardous substances, including hazardous gases, heavy metal ions, radioactive ions, antibiotics, pesticides, nitro-explosives, and some harmful solvents as well as luminous and sensing mechanisms of MOF-based fluorescent sensors. The outlook and several crucial issues of this area are also discussed, with the expectation that it may help arouse widespread attention on exploring fluorescent MOFs (LMOFs) in potential sensing applications.

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

Energy Transfer in Metal-Organic Frameworks for Fluorescence Sensing

The development of materials with outstanding performance for sensitive and selective detection of multiple analytes is essential for the development of human health and society. Luminescent metal-organic frameworks (LMOFs) have controllable surface and pore sizes and excellent optical properties. Therefore, a variety of LMOF-based sensors with diverse detection functions can be easily designed and applied. Furthermore, the introduction of energy transfer (ET) into LMOFs (ET-LMOFs) could provide a richer design concept and a much more sensitive and accurate sensing performance. In this review, we focus on the recent five years of advances in ET-LMOF-based sensing materials, with an emphasis on photochemical and photophysical mechanisms. We discuss in detail possible energy transfer processes within a MOF structure or between MOFs and guest materials. Finally, the possible sensing applications of the ET-LMOF-based sensors are highlighted.

Bimetallic Cd/Zr-UiO-66 material as a turn-on/off probe for As5+/Fe3+ in organic media

In this work, a series of bimetallic Cd/Zr-UiO-66 materials were successfully synthesized for fluorescence sensing toward traces of As⁵⁺ and Fe³⁺ via a one-pot method. Interestingly, the obtained bimetallic Cd/Zr-UiO-66 (1:9) can be served as turn-on probe for As⁵⁺ as well as turn-off probe for Fe³⁺. The LODs of Cd/Zr-UiO-66 (1:9) toward As⁵⁺ and Fe³⁺ were calculated to be 5.4 μM and 4.3 μM, respectively, indicating its effective sensing properties for As⁵⁺ and Fe³⁺ in methanol media. Moreover, even in the presence of other potentially interfering toxic metal ions such as As³⁺, Cd²⁺ and Pb²⁺, Cd/Zr-UiO-66 (1:9) still presented good anti-interference abilities. Additionally, the removal efficiency of Cd/Zr-UiO-66 (1:9) toward As⁵⁺ was higher than 70% when the initial As⁵⁺ was lower than 50 mg/L. The fluorescence quenching of Fe³⁺ were mainly due to the competitive absorption of excitation source and RET, while the ACE mechanism was mostly responsible for the enhancement of As⁵⁺. More importantly, this job might pave the way for future researches and applications on sensing As⁵⁺ and Fe³⁺.

ZIF-8@GMP-Tb nanocomplex for ratiometric fluorescent detection of alkaline phosphatase activity

Luminescent metal-organic frameworks (LMOFs) and their functional materials with unique characteristics can provide the basis for the construction of new analytical techniques, which can meet the continuous demand for various fields. In this work, guanosine monophosphate (GMP), terbium ion (Tb³⁺) and zeolitic imidazolate framework-8 (ZIF-8) are self-assembled to form a ZIF-8@GMP-Tb nanocomplex, which can be utilized as a ratiometric fluorescent probe to monitor alkaline phosphatase (ALP) activity. Specifically, with adding ALP, the fluorescence intensity at 547 nm (one of the characteristic emission peaks of Tb³⁺) obviously decreased. Meanwhile, the conjugated structure of GMP increased the fluorescence of ZIF-8 (located at 330 nm). The possible mechanism was proposed through the characterization of the materials. Based on the variation of the emission peaks at 330 and 547 nm, the ratiometric fluorescent sensor of ALP has a linear range of 0.25-20 U/L. Moreover, applying this sensing system to the detection of ALP in the human serum sample and ALP inhibitor investigation possesses satisfactory results. This work provides a new perspective for the utilization of ZIF-8 and lanthanide ions in manufacturing simple and sensitive sensors.