Selective sensing of CrVI and FeIII ions in aqueous solution by an exceptionally stable TbIII-organic framework with an AIE-active ligand

We herein report a new lanthanide metal-organic framework (MOF) that exhibits excellent chemical stability, especially in the aqueous solution over a wide pH range from 1 to 14. In contrast to many reported lanthanide MOFs, this Tb-based MOF emits cyan fluorescence inherited from the integrated AIE-active ligand, rather than Ln³⁺ ions. More remarkably, its fluorescence signal features a highly selective and sensitive “turn-off” response toward CrO₄²⁻, Cr₂O₇²⁻ and Fe³⁺ ions, highlighted with the low detection limits down to 68.18, 69.85 and 138.8 ppm, respectively. Thus, the exceptional structural stability and sensing performance render this material able to be a superior luminescent sensor for heavy metal ions in wastewater.     

Post-Synthetic Modification of Zr-based Metal-Organic Frameworks with Imidazole: Variable Optical Behavior and Sensing

UiO-66-NH₂-IM, a fluorescent metal-organic framework (MOF), was synthesized by post-synthetic modification of UiO-66-NH₂ with 2-imidazole carboxaldehyde via a Schiff base reaction. It was examined using various characterization techniques (PXRD, FTIR, NMR, SEM, TGA, UV-Vis DRS, and photoluminescence spectroscopy). The emissive feature of UiO-66-NH₂-IM was utilized to detect volatile organic compounds (VOCs), metal ions, and anions, such as acetone, Fe³⁺, and carbonate (CO₃²⁻). Acetone turns off the high luminescence of UiO-66-NH₂-IM in DMSO, with the limit of detection (LOD) being 3.6 ppm. Similarly, Fe³⁺ in an aqueous medium is detected at LOD=0.67 μM (0.04 ppm) via quenching. On the contrary, CO₃²⁻ in an aqueous medium significantly enhances the luminescence of UiO-66-NH₂-IM, which is detected with extremely high sensitivity (LOD=1.16 μM, i. e., 0.07 ppm). Large Stern-Volmer constant, K_sv, and low LOD values indicate excellent sensitivity of the post-synthetic MOF. Experimental data supported by density functional theory (DFT) calculations discern photo-induced electron transfer (PET), resonance energy transfer (RET), inner filter effect (IFE), or proton abstraction as putative sensing mechanisms. NMR and computational studies propose a proton abstraction mechanism for luminescence enhancement with CO₃²⁻. Moreover, the optical behavior of the post-synthetic material toward analytes is recyclable.     

Enhanced Performance of CNT‐doped Imine Based Receptors as Fe(III) Sensor Using Potentiometry and Voltammetry

A highly sensitive and selective potentiometric and voltammteric assay for the detection of Fe³⁺ using (E)‐3‐((2‐(2‐(2‐aminoethylamino) ethylamino) ethylimino)methyl)‐4H‐chromen‐4‐one (IFE(III)) ionophore was developed. To demonstrate the ion‐to‐electron transfer ability of MWCNT, these were incorporated in the ion‐selective membrane and response characteristics of Fe³⁺ electrode was compared with those of the traditional ion selective electrode. The electrode showed an improved Nernstian slope, lower detection limit, response time of less than 5 s and working in a pH range of 3.0 to 8.0. Differential pulse voltammetric studies were performed for IFE(III)‐Fe³⁺ complex in DMSO solvent medium at glassy carbon (GC) electrode. A linear relationship between the cathodic peak current and concentration of Fe³⁺ was observed in the range of 1.6×10^?5 to 4.4×10^?5 mol/L with a detection limit of 5.2×10^?8 mol/L. The electrode shows remarkable selectivity for Fe³⁺ ions over alkali, alkaline earth, transition and heavy metal ions. The optimized electrode was successfully applied for the determination of Fe³⁺ ion in different real‐life samples using potentiometric technique. Theoretical calculations were used to support the complexation behavior of Fe³⁺ with IFE(III).     

A Water‐Stable Terbium(III)–Organic Framework as a Chemosensor for Inorganic Ions,Nitro‐Containing Compounds and Antibiotics in Aqueous Solutions

Effective detection of organic/inorganic pollutants, such as antibiotics, nitro‐compounds, excessive Fe³⁺ and MnO₄^?, is crucial for human health and environmental protection. Here, a new terbium(III)–organic framework, namely [Tb(TATAB)(H₂O)]?2H₂O ( Tb‐MOF , H₃TATAB=4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐m‐aminobenzoic acid), was assembled and characterized. The Tb‐MOF exhibits a water‐stable 3D bnn framework. Due to the existence of competitive absorption, Tb‐MOF has a high selectivity for detecting Fe³⁺, MnO₄^?, 4‐nirophenol and nitroimidazole (ronidazole, metronidazole, dimetridazole, ornidazole) in aqueous through luminescent quenching. The results suggest that Tb‐MOF is a simple and reliable reagent with multiple sensor responses in practical applications. To the best of our knowledge, this work represents the first Tb^III‐based MOF as an efficient fluorescent sensor for detecting metal ions, inorganic anions, nitro‐compounds, and antibiotics simultaneously.     

Selective Sensing of Fe3+ and Al3+ Ions and Detection of 2,4,6‐Trinitrophenol by a Water‐Stable Terbium‐Based Metal–Organic Framework

A water‐stable luminescent terbium‐based metal–organic framework (MOF), {[Tb(L₁)_1.5(H₂O)] ? 3 H₂O}_n (Tb‐MOF), with rod‐shaped secondary building units (SBUs) and honeycomb‐type tubular channels has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. The high green emission intensity and the microporous nature of the Tb‐MOF indicate that it can potentially be used as a luminescent sensor. In this work, we show that Tb‐MOF can selectively sense Fe³⁺ and Al³⁺ ions from mixed metal ions in water through different detection mechanisms. In addition, it also exhibits high sensitivity for 2,4,6‐trinitrophenol (TNP) in the presence of other nitro aromatic compounds in aqueous solution by luminescence quenching experiments.     

The Role of Bi3+ in Promoting and Stabilizing Iron Oxo Clusters in Strong Acid

Metal oxo clusters and metal oxides assemble and precipitate from water in processes that depend on pH, temperature, and concentration. Other parameters that influence the structure, composition, and nuclearity of “molecular” and bulk metal oxides are poorly understood, and have thus not been exploited. Herein, we show that Bi³⁺ drives the formation of aqueous Fe³⁺ clusters, usurping the role of pH. We isolated and structurally characterized a Bi/Fe cluster, Fe₃BiO₂(CCl₃COO)₈(THF)(H₂O)₂, and demonstrated its conversion into an iron Keggin ion capped by six Bi³⁺ irons ( Bi₆Fe₁₃ ). The reaction pathway was documented by X‐ray scattering and mass spectrometry. Opposing the expected trend, increased cluster nuclearity required a pH decrease instead of a pH increase. We attribute this anomalous behavior of Bi/Fe(aq) solutions to Bi³⁺, which drives hydrolysis and condensation. Likewise, Bi³⁺ stabilizes metal oxo clusters and metal oxides in strongly acidic conditions, which is important in applications such as water oxidation for energy storage.     

Dye@MOF composites(RhB@1): Highly sensitive dual emission sensor for the detection of pesticides,Fe3+ and ascorbate acid

With the rapid development of economy, industrial and agricultural pollutants have caused great damage to the ecological environment and the normal development of organisms, posing a serious threat to global public health. Therefore, rapid and sensitive detection of pollutants is very important for environmental safety and people’s health. A stable multi-response fluorescence sensor(RhB@1) with dual emission characteristics was constructed by embedding Rh B guest molecules in Zn-MOF using a simp...     

Anthrone-spirolactam and quinoline hybrid based sensor for selective fluorescent detection of Fe3+ ions

The synthesis of a novel, and highly selective Fe³⁺ ion sensor based on anthrone-spirolactam and its quinoline hybrid ligand is reported. The designed ligand displayed selective detection of Fe³⁺ ions with enhanced fluorescence emission. The complexation of Fe³⁺ ion led to a red shift of 32 nm from 420 nm to 452 nm, and a several fold increase in intensity with fluorescent green emission. The complexation (detection) of Fe³⁺ ions with ligand resulted in chelation enhanced fluorescence and intramolecular charge transfer through the inhibition of C=N isomerization. This hybrid sensor shows high sensitivity and selectivity, spontaneous response, and works on a wide pH range a minimum detection limit of 6.83 × 10⁻⁸ M. Importantly, the sensor works through the fluorescence turn-on mechanism that overcomes the paramagnetic effect of Fe³⁺ ions. The binding mechanism between the ligand and the Fe³⁺ ions was established from the Job's plot method, optical studies, Fourier transfor infrared spectroscopy, NMR titration, fluorescence life-time studies, and density functional theory optimization. The sensor displayed excellent results in the quantification of Fe³⁺ ions from real water samples. Furthermore, due to its biocompatibility nature, fluorescent spotting of Fe³⁺ ions in live cells revealed its bioimaging applications.     

Enhanced Separation of Potassium Ions by Spontaneous K+‐Induced Self‐Assembly of a Novel Metal–Organic Framework and Excess Specific Cation–π Interactions

A novel metal–organic framework (MOF) was fabricated by spontaneous K⁺‐induced supramolecular self‐assembly with the embedded tripodal ligand units. When the 3D ligand was loaded onto Fe₃O₄@mSiO₂ core‐shell nanoparticles, it could effectively separate K⁺ ions from a mixture of Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions through nanoparticle‐assisted MOF crystallization into a Fe₃O₄@mSiO₂@MOF hybrid material. Excess potassium ions could be extracted because of the specific cation–π interaction between K⁺ and the aromatic cavity of the MOF, leading to enhanced separation efficiency and suggesting a new application for MOFs.     

A Recyclable bi‐functional Luminescent Zinc (II) metal–organic framework as highly selective and sensitive sensing probe for nitroaromatic explosives and Fe3+ ions

By introducing carboxyl tag to the aromatic ligands system and borrowing the organic template open framework idea, a stable fluorescent Zn metal–organic framework was successfully prepared through a rigid ligand H₆L (3,5‐bis‐(3‐carboxyphenoxy)benzoic acid) under hydrothermal conditions. The selectivity and sensitivity of the Zn‐MOF to metal ions and nitro‐aromatic compounds (NACs) were investigated by fluorescence quenching. And the Zn‐MOF showed a high sensibility of nitro‐aromatic compounds (NACs) and Fe³⁺ ions, especially for 4‐(4‐nitropheny lazo) resorcinol (NPLR). More importantly, the detection limit of the Zn‐MOF for detecting NPLR solution was found to be 1.71 ppb. Moreover, this sensor is remarkable recyclable and is promisingly applied for rapid, on‐site and sensing of explosive residuals.     

A threefold interpenetrating two‐dimensional zinc(II) coordination polymer: synthesis,crystal structure and selective luminescence sensing properties

The Fe³⁺ ion is the most important element in environmental systems and plays a fundamental role in biological processes. Iron deficiency can result in diseases and highly selective and sensitive detection of trace Fe³⁺ has become a hot topic. A novel two‐dimensional Zn^II coordination framework, poly[[μ‐4,4′‐bis(2‐methylimidazol‐1‐yl)diphenyl ether‐κ²N³:N^3′](μ‐4,4′‐sulfonyldibenzoato‐κ²O:O′)zinc(II)], [Zn(C₁₄H₈O₆S)(C₂₀H₁₈N₄O)]_n or [Zn(SDBA)(BMIOPE)]_n, (I), where H₂SDBA is 4,4′‐sulfonyldibenzoic acid and BMIOPE is 4,4′‐bis(2‐methylimidazol‐1‐yl)diphenyl ether, has been prepared and characterized by IR, elemental analysis, thermal analysis and X‐ray diffraction analysis, the latter showing that the coordination polymer exhibits a threefold interpenetrating two‐dimensional 4⁴‐ sql network. In addition, it displays a highly selective and sensitive sensing for Fe³⁺ ions in aqueous solution.     

Synthesis of a conjugated polymer for sensing ferric/ferrous cations based on dual responses

A conjugated polymer (PPETE-RB) with poly[p-(phenylene ethynylene)-alt-(thienylene-ethynylene)] (PPETE) as the backbone with pendant rhodamine B (RB) groups in the close-ring spirolactam form was synthesized. With long spacer between backbone and pedant groups as well as long solubilizing side chains, the polymer possesses good solubility in most organic solvents and relatively large molecular weight. The fluorescence of the conjugated polymer in THF exhibited selective dual responses upon adding Fe³⁺/Fe²⁺ but negligible response upon other cations. The emission around 481 nm (excited at 360 nm) decreased and that around 571 nm (excited at 520 nm) emerged and increased when increasing the concentration of iron ions. The responses to Fe³⁺ and Fe²⁺ are very similar. The limits of detection were found to fall in between 6 μM and 8 μM. The mechanism study showed that the quenching around 481 nm was due to the inner filter effect (IFE) between the Fe³⁺/Fe²⁺ and PPETE-RB; while that enhancement around 571 nm could be attributed to the formation of fluorescent ring-open structure from nonfluorescent spirolactam of pedant RB group upon Fe³⁺/Fe²⁺. Such dual and opposite responses provided more reliable information than single response for sensing applications.     

Piperazine-based new sensor: selective ratiometric sensing of Fe3+, logic gate construction and cell imaging

Newly designed and synthesised chemosensor 1 selectively recognises Fe³⁺ ions in CHCl₃–MeOH (1:1, v/v) by showing ratiometric change in emission and green colouration of the solution under the exposure of UV light. The ensemble 1·Fe³⁺ selectively detects F^?  ions over other halides and the phenomenon is useful to construct combinatorial logic gate. Furthermore, the probe 1 can be used for in vitro detection of Fe³⁺ in human cervical cancer (HeLa) cells.     

A water-stable lanthanide-coordination polymer with free Lewis site for fluorescent sensing of Fe3+

A Tb³⁺ based coordination polymer (NKU-115) with free N sites was successfully constructed, featuring strong green light emission and selective quenching response toward Fe³⁺ in aqueous solution.     

A S2O32−‐Enhanced Fluorogenic Chemosensor for Fe3+ in Aqueous Media Based on a Boron–Fluorine Derivative

A fluorescent “turn‐on” probe for Fe³⁺ was investigated in an aqueous system based on a boron 2‐(2′‐pyridyl) imidazole complex (BOPIM‐dma). BOPIM‐dma shows weak or no fluorescence in polar solvents due to twisted intramolecular charge transfer, but the addition of Fe³⁺ to BOPIM‐dma leads to fluorescence switch‐on responses. The binding is highly selective to Fe³⁺ over other metal ions, indicating that BOPIM‐dma is a chemodosimeter for Fe³⁺. Furthermore, the existence of S₂O₃²⁻ could much enhance and stabilize the emission significantly, indicating that the BOPIM‐dma/Fe³⁺/S₂O₃²⁻ complexes are a strong fluorescence system, and can be used as a sensitive detector for Fe³⁺, with the limit of detection of 6.0 × 10⁻⁷ mol L⁻¹.     

A Selective Colorimetric and Fluorescent Chemodosimeter for Fe(III) Ion Based on Hydrolysis of Schiff Base

An efficient colorimetric and fluorescent chemodosimeter for Fe³⁺ ions has been developed. The visual and fluorescent behaviors of the receptor toward various metal ions were investigated. The receptor shows exclusive response toward Fe³⁺ ions and also distinguishes Fe³⁺ from other cations by color change and unusual fluorescence enhancement in aqueous solution (DMSO/H₂O = 4/1, v/v). Thus, the receptor can be used as a colorimetric and fluorescent sensor for the determination of Fe³⁺ ion. The visual color detection limit and the fluorescence detection limit of the receptor towards Fe³⁺ are (1.42 ± 0.01) × 10^‐6 M and (7.57 ± 0.04) × 10^‐8 M, respectively. The fluorescence microscopy experiments showed that the receptor is efficient for detection of Fe³⁺ in vitro, developing a good image of the biological organelles. The sensing mechanism is proven to be a hydrolysis process     

Mixed‐Metal MIL‐100(Sc,M) (M=Al,Cr, Fe) for Lewis Acid Catalysis and Tandem CC Bond Formation and Alcohol Oxidation

The trivalent metal cations Al³⁺, Cr³⁺, and Fe³⁺ were each introduced, together with Sc³⁺, into MIL‐100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X‐ray diffraction (PXRD) and solid‐state NMR, UV/Vis, and X‐ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL‐100 samples were prepared in which part of the Fe is present as α‐Fe₂O₃ nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed‐metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed‐metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α‐Fe₂O₃ nanoparticles were also active Lewis acid species, although less active than Sc³⁺ in trimer sites. The incorporation of Fe³⁺ into MIL‐100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc³⁺ and Fe³⁺. A procedure for using these mixed‐metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.     

A novel nano‐size lanthanum metal–organic framework based on 5‐amino‐isophthalic acid and phenylenediamine: Photoluminescence study and sensing applications

In this paper, a novel lanthanum metal–organic framework La‐MOF was prepared via hydrothermal and reflux methods. The La‐MOF was achieved through the reaction of a 5‐amino‐isophthalic acid with 1, 2‐phenylenediamine and lanthanum chloride. The prepared La‐MOF structure was confirmed by XRD, mass spectrometry, IR, UV–Vis and elemental analysis, whereas the size, and morphology was examined by FE‐SEM/EDX and HR‐TEM. The results indicated that the La‐MOF prepared via both methods have the same structure and composition. Meanwhile, the MOF yield, reaction time, morphology, physiochemical and sensing properties were highly depended on the used preparation method. The photoluminescence (PL) study was carried out for the La‐MOF, and the results showed that La‐MOF exhibits strong emission at 558 nm after excitation at 369 nm. Moreover, the PL data indicating that the La‐MOF has highly selective sensing properties for iron (III) competing with different metal ions. The Stern‐Völmer graph shows a linear calibration curve which achieved over a concentration range 1.0–500 μM of Fe³⁺ with a correlation coefficient, detection, and quantitation limits 0.998, 1.35 μM and 4.08 μM, respectively. According to the remarkable quenching of the PL intensity of La‐MOF using various concentrations of Fe³⁺, it was successfully used as a sensor for Fe³⁺detecting in different water resources (pure and waste) samples. The quenching mechanism was studied and it has a dynamic type and due to efficient energy transfer between the La‐MOF and Fe³⁺.     

Photo-Physical Properties of a New Norfloxacin-Containing Polymer for Protons and Fe3+ Sensing

A novel norlfoxacin-containing fluorescent polymer was synthesized via copolymerization of two derivatives of norfloxacin and methylmetacrylate (MMA). It could emit blue fluorescence in both the solution and film states. Fluorescence characteristics of the polymer as a function of pH were investigated in aqueous solution. The polymer solution showed weaker fluorescence between pH 5-9. When the pH of the solution was higher than 9 or lower than 5, stronger fluorescence could be seen. Responses of metal cations (Mn^{2 +}, Fe^{3 +}, Co^{2 +}, Ni^{2 +}, Cu^{2 +} and Zn^{2 +}) to the fluorescence intensity of this polymer were obtained that only Fe^{3 +} could quench efficiently the fluorescence intensity of the polymer in solution and film state. The results suggested the possibility that this newly synthesized compound might work as a polymeric sensor responding to water polluted by protons and Fe^{3 +}.     

Salicylaldimine‐functionalized poly(m‐phenyleneethynylene) as turn‐on chemosensor for ferric ion

A new turn on fluorescent probe for ferric ion based on poly(m‐phenyleneethynylene salicylaldimine) ( PPE‐IM ) has been developed. The preparation of PPE‐IM involves post‐polymerization functionalization of the corresponding polymeric amine, PPE‐AM , via the condensation with salicylaldehyde. The degree of polymerization of both PPE‐IM and PPE‐IM is 17 with polydispersity index of 1.5. In aqueous solution, the polymeric PPE‐IM is highly stable unlike its small molecule analog which is gradually hydrolyzed. The weak fluorescence of initial PPE ‐ IM (λ_em = 470) is greatly enhanced by 300 folds upon the addition of Fe³⁺. The ¹H NMR reveals that the fluorescence enhancement is caused by Fe³⁺‐induced hydrolysis of the imine group. The sensing system shows a detection limit of 0.14 μM of Fe³⁺. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1155–1161