A Multi‐responsive Regenerable Europium–Organic Framework Luminescent Sensor for Fe3+, CrVI Anions,and Picric Acid

A novel luminescent microporous lanthanide metal–organic framework (Ln‐MOF) based on a urea‐containing ligand has been successfully assembled. Structural analysis revealed that the framework features two types of 1D channels, with urea N?H bonds projecting into the pores. Luminescence studies have revealed that the Ln‐MOF exhibits high sensitivity, good selectivity, and a fast luminescence quenching response towards Fe³⁺, Cr^VI anions, and picric acid. In particular, in the detection of Cr₂O₇^2? and picric acid, the Ln‐MOF can be simply and quickly regenerated, thus exhibiting excellent recyclability. To the best of our knowledge, this is the first example of a multi‐responsive luminescent Ln‐MOF sensor for Fe³⁺, Cr^VI anions, and picric acid based on a urea derivative. This Ln‐MOF may potentially be used as a multi‐responsive regenerable luminescent sensor for the quantitative detection of toxic and harmful substances.     

Interpreted Recognition Process: A Highly Sensitive and Selective Luminescence Chemosensor

A luminescence‐sensing process based on coordination compound [H₂N(CH₃)₂]₃[Tb(dipic)₃] was developed. It shows fast response (within 1 min), high selectivity, and is ultrasensitive to detect Fe³⁺ or Cr³⁺ in aqueous solution and living cells (K_SV values are calculated to be 3.6×10⁴ L mol^?1 for Fe³⁺ and 1.9×10⁴ L mol^?1 for Cr³⁺). The whole recognition process has been witnessed through electrospray ionization mass spectrometry (ESI‐MS) analysis, and the ligand‐transfer‐induced luminescence‐quenching mechanism is interpreted. This work contributes to extend the potential applications of lanthanide coordination compounds (LnCCs) in the fields of biological and environmental technologies.     

Systematic Investigation of High‐Sensitivity Luminescent Sensing for Polyoxometalates and Iron(III) by MOFs Assembled with a New Resorcin[4]arene‐Functionalized Tetracarboxylate

A new family of resorcin[4]arene‐based metal–organic frameworks (MOFs), namely, [Eu(HL)(DMF)(H₂O)₂] ? 3 H₂O ( 1 ), [Tb(HL)(DMF)(H₂O)₂] 3 H₂O ( 2 ), [Cd₄(L)₂(DMF)₄(H₂O)₂] 3 H₂O ( 3 ) and [Zn₃(HL)₂(H₂O)₂] 2 DMF ? 7 H₂O ( 4 ), have been constructed from a new resorcin[4]arene‐functionalized tetracarboxylic acid (H₄L=2,8,14,20‐tetra‐ethyl‐6,12,18,24‐tetra‐methoxy‐4,10,16,22‐tetra‐carboxy‐methoxy‐calix[4]arene). Isostructural 1 and 2 exhibit charming 1D motifs built with the cup‐like HL^3? anions and rare earth cations. Compounds 3 and 4 show a unique sandwich‐based 2D layer and a fascinating 3D framework, respectively. Remarkably, compounds 1 and 2 display intensive red and green emissions triggered by the efficient antenna effect of organic ligands under UV light. More importantly, systematic luminescence studies demonstrate that Ln‐MOFs 1 and 2 , as efficient multifunctional fluorescent materials, show highly selective and sensitive sensing of Fe³⁺, polyoxometalates (POMs), and acetone, which represents a rare example of a sensor for quantitatively detecting three different types of analytes. This is also an exceedingly rare example of Fe³⁺ and POMs detection in aqueous solutions employing resorcin[4]arene‐based luminescent Ln‐MOFs. Furthermore, the possible mechanism of the sensing properties is deduced.     

A Water Stable CdII‐based Metal‐Organic Framework as a Multifunctional Sensor for Selective Detection of Cu2+ and Cr2O72– Ions

A water stable tetrazolate‐containing metal‐organic framework, [Cd₂(L)(OH)(H₂O)₂]_n ( 1 ) [H₃L = 5‐(4‐(tetrazol‐5‐yl)phenyl)isophthalic acid], was synthesized under solvothermal conditions and structurally characterized. Compound 1 displays a three dimensional porous network with one dimensional tubular channels based on trinuclear cluster [Cd₃(μ₃‐OH)N₄C] units. Notably, 1 exhibits highly sensitive response to Cu²⁺ and Cr₂O₇^2– through luminescence quenching effects with the detection limit of 0.666 ppm for Cu²⁺ and 0.846 ppm for Cr₂O₇^2–, respectively. The possible mechanism of the luminescence quenching was discussed in detail.     

Luminescence‐Functionalized Metal–Organic Frameworks Based on a Ruthenium(II) Complex: A Signal Amplification Strategy for Electrogenerated Chemiluminescence Immunosensors

Novel luminescence‐functionalized metal–organic frameworks (MOFs) with superior electrogenerated chemiluminescence (ECL) properties were synthesized based on zinc ions as the central ions and tris(4,4′‐dicarboxylicacid‐2,2′‐bipyridyl)ruthenium(II) dichloride ([Ru(dcbpy)₃]²⁺) as the ligands. For potential applications, the synthesized MOFs were used to fabricate a “signal‐on” ECL immunosensor for the detection of N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP). As expected, enhanced ECL signals were obtained through a simple fabrication strategy because luminescence‐functionalized MOFs not only effectively increased the loading of [Ru(dcbpy)₃]²⁺, but also served as a loading platform in the ECL immunosensor. Furthermore, the proposed ECL immunosensor had a wide linear range from 5 pg mL^?1 to 25 ng mL^?1 and a relatively low detection limit of 1.67 pg mL^?1 (signal/noise=3). The results indicated that luminescence‐functionalized MOFs provided a novel amplification strategy in the construction of ECL immunosensors and might have great prospects for application in bioanalysis.     

Combining field‐amplified sample stacking with moving reaction boundary electrophoresis on a paper chip for the preconcentration and separation of metal ions

A common drawback of paper‐based separation devices is their poor detection limit. In this study, we combined field‐amplified sample stacking with moving reaction boundary electrophoresis on a paper chip with six array channels for the parallel separation and concentration of multiple samples. With a new hyphenated technique, the brown I₂ from the Fe³⁺/I⁻ oxidation–reduction reaction emerged near the boundary between the dilute ethylene diamine tetraacetic acid and potassium iodide and highly concentrated KCl solutions. For the separation and concentration of three components, Cr³⁺, Cu²⁺, and Fe³⁺, the Fe³⁺ detection limit was improved at least 266‐fold by comparing the hyphenated technique with moving reaction boundary electrophoresis. The detection limit of Fe³⁺ was found to be as low as 0.34 ng (20 μM) on the paper chip. We also demonstrated the analysis of a real sample of four metal ions, with detection limits as follows: 0.16 μg Cr³⁺, 1.5 μg Ni²⁺, 0.64 μg Cu²⁺, and 1.5 μg Co²⁺. The synergy of field‐amplified sample stacking and moving reaction boundary electrophoresis in the micron paper‐based array channels dramatically improved the detection limit and throughput of paper‐based electrophoresis.     

两个基于Cd(Ⅱ)金属有机骨架化合物在金属离子和有机分子发光传感中的应用

合成了2个镉（Ⅱ）金属有机骨架化合物{[Cd（L）（fma）]·0.5H₂O}_n（1）和{[Cd（L）_0.5（sdb）]·DMF}_n（2）（L=E,E-2,5-二己氧基-1,4-双（2-乙烯-吡啶基）苯,H₂fma=延胡酸,H₂sdb=4,4''-磺酰基二苯甲酸）,研究了它们在金属离子和有机分子的发光传感中的应用。结果表明,Fe³⁺对配位聚合物1和2的发光强度有明显的猝灭作用。此外,聚合物1和2还对水杨醛具有明显的猝灭能力。     

A new luminescent anionic metal–organic framework based on heterometallic zinc(II)–barium(II) for selective detection of Fe3+ and Cu2+ ions in aqueous solution

Over the past two decades, the development of novel inorganic–organic hybrid porous crystalline materials or metal–organic frameworks (MOFs) using crystal engineering has provoked significant interest due to their potential applications as functional materials. In this context, luminescent MOFs as fluorescence sensors have recently received significant attention for the sensing of ionic species and small molecules. In this work, a new luminescent heterometallic zinc(II)–barium(II)‐based anionic metal–organic framework, namely poly[imidazolium [triaqua(μ₆‐benzene‐1,3,5‐tricarboxylato)bariumtrizinc] tetrahydrate], {(C₃H₄N₂)[BaZn₃(C₉H₃O₆)₃(H₂O)₃]·4H₂O}_n ( 1 ), was synthesized under hydrothermal conditions and characterized. Compound 1 presents a three‐dimensional framework with an unprecedented (3,5)‐connected topology of the point symbol (3.9²).(3³.4².5.9³.10), and exhibits `turn‐off' luminescence responses for the Cu²⁺ and Fe³⁺ ions in aqueous solution based on significantly different quenching mechanisms.     

A EuIII‐MOF with Bis(2‐carboxyethyl)isocyanurate for Luminescence Sensing of Fe3+ and SCN– Ions

The water‐stable 3D lanthanide‐organic framework (Ln‐MOF) {[Eu(bci)(H₂O)] · 2H₂O}_n ( 1 ) [H₂bci = bis(2‐carboxyethyl)isocyanurate] was synthesized under hydrothermal conditions. Compound 1 ‐ Eu exhibits a 3D open‐framework connected by Eu–(μ‐O)₂–Eu chains and bci ligands. Meanwhile, 1 ‐ Eu exhibits highly efficient luminescent sensing for environmentally relevant Fe³⁺ and SCN^– ions through luminescence quenching. These results indicated that it could be utilized as a multi‐responsive luminescence sensor.     

Syntheses,Structures and Luminescence Sensing Properties of Two Cd(II) MOFs Constructed from Mixed Ligands

Hydrothermally reaction of Cd(NO₃)₂·4H₂O, pimelic acid (H₂Pim) mixed with two N-containing ligands of 1,2-bis(2-methyl-imidazol-1-ylmethyl)benzene (1,2-mbix) or 1,3-bis(2-methyl-imidazol-1-ylmethyl)benzene (1,3-mbix) gave rise to two new Cd(II) MOFs, [Cd(Pim)(1,2-mbix)] (1) and [Cd(Pim)(1,3-mbix)]·H₂O (2). Both MOFs were structurally characterized by IR and UV–Vis spectra, single-crystal and powder X-ray diffraction, thermogravimetric analyses. MOF 1 shows a fourfold interpenetrating dia network. Differently, MOF 2 shows a 2D?→?3D interdigitated architecture base on the 6³ hcb layer when 1,2-mbix was replaced by 1,3-mbix. The luminescent properties of 1 and 2 have been investigated. Furthermore, the luminescent quenching experiments suggest both MOFs exhibit good selectivity and sensitivity to detect Fe³⁺ and Cr₂O₇^2? in water.

     

3D Cadmium(II)‐Based Coordination Polymer Constructed from V‐Shaped Semirigid Ligand: Selective Detection of Oxoanion Pollutants CrO42–, Cr2O72–, MnO4– in Water

A new coordination polymer (CP), namely, [Cd(HL)(4,4′‐bipy)] ( 1 ) (H₃L = 4‐(5‐carboxy‐pyridine‐3‐yloxy)‐phthalic acid, 4,4′‐bipy = 4,4′‐bipyridine), was synthesized employing a V‐shaped asymmetric tricarboxylic acid ligand under hydrothermal condition. Single‐crystal X‐ray diffraction analysis indicates that compound 1 exhibits a novel three‐dimensional (3D) framework with (3, 5)‐connected (6³)(6⁹ · 8) topology. Meanwhile, it shows high selectivity and sensitivity for oxoanion pollutants CrO₄^2–, Cr₂O₇^2–, and MnO₄^– anions in aqueous solutions with detection limits of 4.12 × 10^–6 M, 1.75 × 10^–6 M, and 6.47 × 10^–7 M, respectively. The high selectivity and low detection limit indicate that the compound is promising functional luminescence probe for CrO₄^2–, Cr₂O₇^2–, and MnO₄^–. The mechanisms of the quenching effect and sensing properties were discussed in detail.     

Removal of chromate from aqueous solution by reduction with nanoscale Fe–Al layered double hydroxide

Nanoscale layered double hydroxides of Fe^II and Al^III (Fe–Al LDH) have been applied for removal of chromate (Cr^VI) from aqueous solution. Given the reaction stoichiometry, Cr^VI was completely reduced to Cr^III and coprecipitated with Fe^III and Al^III oxyhydroxides. The extent of Cr^VI removal decreased with increasing initial pH and decreasing molar ratio of Cr^VI/structural Fe^II in the LDH. The chromate reduction rate at different initial concentrations of Cr^VI was well described by the pseudo-second-order model with reaction rate constant ranging from 197.4 to 13.53 (mmol min)^?1. Initial pH and substitution of various amounts of Fe^III in the LDH structure had little effect on the reaction rate. Backtransformation of Cr^III to Cr^VI by birnessite Mn oxide (δ-MnO₂) after 40 days of reaction was less than 1% of the initial Cr (as Cr^III solid), indicating high stability of the final reaction products and high efficiency of nanoscale Fe–Al LDHs for removal of chromate from aqueous solution.     

CdII‐Organic Frameworks Fabricated with a N‐Rich Ligand and Flexible Dicarboxylates: Structural Diversity and Multi‐Responsive Luminescent Sensing for Toxic Anions and Ethylenediamine

Three metal‐organic frameworks {[Cd( L )(glu)]?3 H₂O}_∞ ( 1 ), {[Cd₂( L )₂(adi)₂]?5 H₂O}_∞ ( 2 ) and {[Cd( L )(sub)]?3 H₂O?DMA }_∞ ( 3 ) ( L =pyridine‐3,5‐bis(5‐azabenzimidazole), H₂glu=glutaric acid, H₂adi=adipic acid and H₂sub=suberic acid) were obtained under solvothermal conditions. Complex 1 shows a 2D (4,4) network constructing of Cd₂‐glu and Cd‐ L chains. Complex 2 presents a 2‐fold interpenetrating 3D framework with pcu topology. Complex 3 is a 3D framework with cds topology. Three complexes with versatile structures were obtained by changing aliphatic dicarboxylate ligands with different lengths based on a N‐rich ligand. Moreover, the fluorescence measurements indicate that complex 1 is a good multifunctional chemosensor for the detection of Cr₂O₇^2? and MnO₄^? anions by fluorescence quenching effect, and ethylenediamine by fluorescence enhancement effect, with detection limits of 1.196 ppm, 0.551 ppm and 64.572 ppm, respectively. Both complexes 2 and 3 can selectively sense Cr₂O₇^2? anion with detection limits of 1.126 ppm for 2 and 0.831 ppm for 3 by a fluorescence quenching effect.     

Turn‐on fluorogenic and chromogenic detection of cations in complete water media with poly(N‐vinyl pyrrolidone) bearing rhodamine B derivatives as polymeric chemosensor

A hydrophobic organic monomer GRBE with a polymerizable methacrylester moiety had been synthesized by reaction of rhodamine B‐ethanediamine with glycidyl methacrylate. A water‐soluble polymeric chemosensor poly(VP‐GRBE) had been prepared via copolymerization with a hydrophilic comonomer (vinylpyrrolidone) and GRBE, which was able to sense environmentally poisonous cations in completely aqueous media. The chemosensor was a derivative of rhodamine B, which behaved as a fluorescent and chromogenic sensor toward various heavy cations, particularly Cr³⁺, Fe³⁺, and Hg²⁺. Titration curves of Cr³⁺, Fe³⁺, and Hg²⁺ were constructed using rapid, cheap, and widely available technique of fluorescence spectroscopies. The detection limits for Cr³⁺, Fe³⁺, or Hg²⁺ ions were found to be 2.20 × 10^?12, 2.39 × 10^?12, and 1.11 × 10^?12 mol/l in the same medium, respectively. Moreover, a colorimetric response from the polymeric chemosensor permitted the detection of Cr³⁺, Hg²⁺, or Fe³⁺ by “naked eye” because of the development of a pink or brown yellow color when Cr³⁺, Hg²⁺, or Fe³⁺ cations interacted with the copolymer in aqueous media. Copyright © 2015 John Wiley & Sons, Ltd.     

Ratiometric Fluorescent Chemosensor for Selective Detection Cr3+ based on Carbazole and Benzimidazole

A novel Cr³⁺‐selective ratiometric fluorescent chemosensor 1‐substitued‐2‐carbazoleylbenzoimidazole ( L ) based on benzimidazole and carbazole was synthesized and characterized by nuclear magnetic resonance (¹H/¹³C NMR), Fourier transform infrared spectrometry (FTIR), and mass spectroscopy. L could selectively detect Cr³⁺ over other metal ions by UV–vis absorption and fluorescence emission spectroscopic methods in CH₃CN. L showed ratiometric fluorescent recognition of Cr³⁺; the fluorescent responses could be observed by naked eye under a UV lamp. The binding stoichiometry ratio of the L –Cr³⁺ complex was found to be 1:1 according to Job’s plot and MALDI‐TOF MS analysis. The results of DFT calculation supported this conclusion.     

Unfolding the Role of Building Units of MOFs with Mechanistic Insight Towards Selective Metal Ions Detection in Water**

The potential emergence of fluorescence-based techniques has propelled research towards developing probes that can sense trace metal ions specifically. Although luminescent metal-organic frameworks (MOFs) are well suited for this application, the role of building blocks towards detection is not fully understood. In this work, a systematic screening by varying number of Lewis basic (pyridyl-N atoms) sites is carried out in a series of isostructural, robust UiO-67 MOFs, and targeting a model metal ion-Fe³⁺. All the three fluorescent MOFs are seen to present quenching response towards Fe³⁺ ions in water. However, UiO-67@N exhibits highly selective and sensitive response, whereas emission of both UiO-67 and UiO-67@NN is quenched by several metal ions. Detailed experimental and theoretical mechanistic investigation is carried out in addition to demonstration of UiO-67@N being able to sense trace amount of Fe³⁺ ions in synthetic biological water sample. Further, UiO-67@N based mixed-matrix membrane (MMM) has been prepared and employed to mimic the real time Fe³⁺ ions detection in water.     

Selective recognition of Fe3+ and Cr3+ in aqueous medium via fluorescence quenching of graphene quantum dots

Graphene quantum dots (GQDs) have been prepared from graphene oxide (GO) and characterized by standard analytical techniques. The size of the prepared GQDs ranges from 2-10?nm. Aqueous dispersion of GQDs exhibited excitation-dependent emission behavior. Emission intensity of the aqueous dispersion found stable for the examined duration of about four months. GQDs exhibited selective recognition of Fe³⁺ and Cr³⁺ out of various common ions such as alkali, alkaline-earth and transition metal ions in aqueous medium through fluorescence quenching. The lower limit of detection of Fe³⁺ is 1?µM and that of Cr³⁺ is 4?µM.     

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.     

A serial of 2D Co-Zn isomorphous metal–organic frameworks for photodegradation and luminescent detection properties

A series of 2D isomorphous MOFs [M (HBTC)(BMIOPE)·DMF·H₂O]_n (M = Zn ( 1 ), Zn_0.7Co_0.3 ( 2 ), Zn_0.5Co_0.5 ( 3 ), Zn_0.3Co_0.7 ( 4 ), Co ( 5 ), H₃BTC = 1,3,5-benzenetricarboxylic acid, BMIOPE = 4,4′-bis(2-methylimidazol-1-yl)diphenyl ether) were synthesized to investigate the correction between the center metal ions and the photocatalytic behaviors. The photocatalytic results show that with the increase of Co²⁺ content, the photodegradation properties are continuously improved from 1 to 5 , which fully indicate that only changing metal ions could regulate the photodegradation properties. In detail, 1 is an inactive photocatalyst to degrade methylene blue (MB), while 5 exhibits preeminent photocatalytic properties under visible light irradiation. Moreover, 1 shows good selective sensing toward Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution. To the best of our knowledge, 1 is the first MOF example for the optical detection of Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution.