Highly selective detection of Fe3+, Cd2+ and CH2Cl2 based on a fluorescent Zn-MOF with azine-decorated pores

A Bifunctional Three-Dimensional Zn(II) Metal-Organic Framework with Strong Luminescence and Adsorption Cr(VI) Properties

The mixed ligand 3-amino-1,2,4-triazole (Hatz) and terephthalic acid (H2pta) reacted with Zn(NO3)2·6H2O to synthesize a three-dimensional binuclear Zn(II) metal-organic framework: {[Zn2·(atz)2·(pta)]·3H2O}n (3D-Zn-MOF). This 3D-Zn-MOF has two different types of pores (4.5 × 4.5 Å2, 5.7 × 5.7 Å2). The crystalline 3D-Zn-MOF could be prepared into nanomaterials (3D-N-Zn-MOF) with particles of approximately 100 nm by a cell fragmentation apparatus. Compared with the solid-state luminescence of Hatz and H2pta, it was found that 3D-N-Zn-MOF exhibited strong luminescence performance and significant red-shift phenomenon. Due to the decrease in electronegativity and rigidity of ligands, as well as the effect of ligand metal charge transfer (LMCT), the fluorescence lifetime and quantum yield of 3D-ZN-N-MOF were 2.7241 ns and 3.02%, respectively. The maximum experimental adsorption capacity of 3D-N-Zn-MOF could reach 125.52 mg/g, which was superior to the majority of MOF adsorbents under the optimal adsorption conditions (25 °C, pH = 7, and the adsorbent concentration is 0.2000 g/L). The thermodynamic analysis of adsorption showed that the adsorption of Cr(VI) by 3D-N-Zn-MOF was a spontaneous (△G < 0) and exothermic (△H < 0) process. It could be found that 3D-N-Zn-MOF was a bifunctional material with potential applications by comprehensive analysis of the fluorescence and adsorption Cr(VI) performance.

Rapid Detection of Cd2+ Ions in the Aqueous Medium Using a Highly Sensitive and Selective Turn-On Fluorescent Chemosensor

Herein, a novel optical chemosensor, (CM1 = 2, 6-di((E)-benzylidene)-4-methylcyclohexan-1-one), was designed/synthesized and characterized by ¹H-NMR and FT-IR spectroscopy. The experimental observations indicated that CM1 is an efficient and selective chemosensor towards Cd²⁺, even in the presence of other metal ions, such as Mn²⁺, Cu²⁺, Co^2+, Ce³⁺, K⁺, Hg²⁺,^, and Zn²⁺ in the aqueous medium. The newly synthesized chemosensor, CM1, showed a significant change in the fluorescence emission spectrum upon coordination with Cd²⁺. The formation of the Cd²⁺ complex with CM1 was confirmed from the fluorometric response. The 1:2 combination of Cd²⁺ with CM1 was found optimum for the desired optical properties, which was confirmed through fluorescent titration, Job's plot, and DFT calculation. Moreover, CM1 showed high sensitivity towards Cd²⁺ with a very low detection limit (19.25 nM). Additionally, the CM1 was recovered and recycled by the addition of EDTA solution that combines with Cd²⁺ ion and, hence, frees up the chemosensor.

Zinc(II) Carboxylate Coordination Polymers with Versatile Applications

This review considers the applications of Zn(II) carboxylate-based coordination polymers (Zn-CBCPs), such as sensors, catalysts, species with potential in infections and cancers treatment, as well as storage and drug-carrier materials. The nature of organic luminophores, especially both the rigid carboxylate and the ancillary N-donor bridging ligand, together with the alignment in Zn-CBCPs and their intermolecular interaction modulate the luminescence properties and allow the sensing of a variety of inorganic and organic pollutants. The ability of Zn(II) to act as a good Lewis acid allowed the involvement of Zn-CBCPs either in dye elimination from wastewater through photocatalysis or in pathogenic microorganism or tumor inhibition. In addition, the pores developed inside of the network provided the possibility for some species to store gaseous or liquid molecules, as well as to deliver some drugs for improved treatment.

Amine/hydrazone functionalized Cd(II)/Zn(II) metal-organic framework for ultrafast sensitive detection of hazardous 2,4,6-trinitrophenol in water

Amine/hydrazone functionalized dual ligand Cd(II)/Zn(II) based metal-organic frameworks (MOFs) denoted as CdMOF- and ZnMOF-NH₂, respectively were synthesized via a simple conventional high-yield reflux method using low-cost and readily available starting materials, i.e., a Schiff base linker, 4-pyridylcarboxaldehydeisonicotinoylhydrazone (L₁) and 2-aminoterephthalic acid (H₂ata) linker. Crystallographic and thermogravimetric studies confirmed the formation of MOFs with good crystallinity and thermal stability. Photoluminescence studies point out that both MOFs can be used efficiently for fast sensing of 2,4,6-trinitrophenol (TNP) in water with noticeable turn-off quenching response. Their limits of detection (LODs) for TNP were 7 ppb and 10 ppb, respectively with enhanced selectivity toward TNP (over other nitro explosives) as verified by competitive nitro explosive tests. Density functional theory calculations and spectral overlap were used to assess the sensing mechanism. These MOF-based fluorescent sensing systems for TNP are demonstrated to have easy recoverability and high sensitivity.

A Luminescent Cu(II)-MOF with Lewis Basic Schiff Base Sites for the Highly Selective and Sensitive Detection of Fe3+ Ions and Nitrobenzene

A Schiff base functionalized Cu(II)-based metal-organic framework (MOF) denoted as Cu-L, was developed via a solvothermal method using low-cost starting material, i.e., Schiff base linker, 4,4'-(hydrazine-1,2-diylidenedimethylylidene)dibenzoic acid (L). Good crystallinity and thermal stability of synthesized Cu-L was confirmed by the crystallographic and thermogravimetric studies. An excellent photoluminescent properties of Cu-L ensure their suitability for the ultrafast detection of Fe³⁺ ions and nitrobenzene via a turn-off quenching response. The remarkable sensitivity of Cu-L towards Fe³⁺ ions and nitrobenzene was certified by the low limit of detection (LOD) of 47 ppb and 0.004 ppm, respectively. With incorporated free azine groups, this MOF could selectively capture Fe³⁺ ions and nitrobenzene in aqueous solution. The plausible mechanistic pathway for the quenching in the fluorescence intensity of the Cu-L in the presence of Fe³⁺ ions and nitrobenzene have been explained in detail through the density functional theory calculations, photo-induced electron transfer (PET), fluorescence resonance energy transfer (FRET), and competitive energy adsorption. This present study open a new avenue to synthesize novel crystalline MOF-based sensing materials from cheap Schiff base linkers for fast sensing of toxic pollutants.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Schiff Base-functionalized Metal-organic Frameworks for Selective Sensing of Chromate and Dichromate in Water

In this research, Zn- or Cd-based metal-organic frameworks (coded ZnMOF-1 and CdMOF-1) containing benzene-1,4-dicarboxylic acid (H₂bdc) and pyridyl-based Schiff base (4-pyridylcarboxaldehydeisonicotinoylhydrazone (L)) dual ligands were successfully assembled via a conventional solvothermal method. The photoluminescence quenching response of ZnMOF-1 and CdMOF-1 and their sensing sensitivity and selectivity towards various inorganic anions were evaluated in aqueous media. Crystallographic and thermogravimetric studies confirm the formation of both MOFs with good crystallinity and thermal stability. Photoluminescence studies also verify the selectivity of ZnMOF-1 and CdMOF-1 for efficient sensing of inorganic oxyanions (like chromate/dichromate: CrO₄^2- and Cr₂O₇^2-). Further, it was noted that only chromate/dichromate (CrO₄^2-/Cr₂O₇^2-) anions showed a significant turn-off quenching effect while other anions (like F^-, Br^-, I^-, Cl^-, ClO₄^-, SCN^-, SO₄^2-, NO₃^-, and NO₂^-) have a low/negligible effect on the photoluminescence intensity of both MOFs. The limit of detection (LOD) of chromate/dichromate by ZnMOF-1 and CdMOF-1 was 9.79/10.94 µM and 2.68/1.48 µM, respectively. A probable mechanism for turn-off quenching response towards chromate and dichromate anions could be attributed to the spectral overlap of both excitation and emission spectra of ZnMOF-1/CdMOF-1 with the absorption spectra of chromate/dichromate anions. As a result, the energy transfer from ZnMOF-1 or CdMOF-1 to the target chromate and dichromate anions decreased fluorescence intensity (i.e., fluorescence quenching effect).

Design of a Sensitive Fluorescent Zn-Based Metal-Organic Framework Sensor for Cimetidine Monitoring in Biological and Pharmaceutical Samples

A new highly fluorescent zinc-organic framework [Zn₂(btca)(DMSO)₂]_n (Zn-MOF) was prepared via in situ ligand formation by the solvothermal reaction of Zn(NO₃)₂·6H₂O and pyromellitic dianhydride (PMDA) in DMSO solvent. During the solvothermal reaction, PMDA was gradually hydrolyzed to a pyromellitic acid, 1,2,4,5-benzene tetracarboxylic acid (H₄btca), to provide a tetracarboxylic acid as a linker in the reaction medium. Single-crystal X-ray diffraction analysis exhibits a 3D porous structure with open tetragonal channels running along the crystallographic c-axis. The Zn-MOF was explored as an on-mode fluorescent sensor for tracing cimetidine in biological fluids and pharmaceutical samples in the presence of interfering species. The results show a quick response in a short time range. The characteristics of this sensor were investigated by field-emission scanning electron microscopy, dynamic light scattering, energy-dispersive X-ray analysis, powder X-ray diffraction, Fourier transform infrared and UV-vis spectroscopy as well as thermogravimetric, and elemental analyses.

Novel NBN-Embedded Polymers and Their Application as Fluorescent Probes in Fe3+ and Cr3+ Detection

The isosteric replacement of C═C by B–N units in conjugated organic systems has recently attracted tremendous interest due to its desirable optical, electronic and sensory properties. Compared with BN-, NBN- and BNB-doped polycyclic aromatic hydrocarbons, NBN-embedded polymers are poised to expand the diversity and functionality of olefin polymers, but this new class of materials remain underexplored. Herein, a series of polymers with BNB-doped π-system as a pendant group were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization from NBN-containing vinyl monomers, which was prepared via intermolecular dehydration reaction between boronic acid and diamine moieties in one pot. Poly{2-(4-Vinylphenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborinine} (P1), poly{N-(4-(1H-naphtho[1,8-de][1,3,2]diazaborinin-2(3H)-yl)phenyl)acrylamide} (P2) and poly{N-(4-(1H-benzo[d][1,3,2]diazaborol-2(3H)-yl)phenyl)acrylamide} (P3) were successfully synthesized. Their structure, photophysical properties and application in metal ion detection were investigated. Three polymers exhibit obvious solvatochromic fluorescence. As fluorescent sensors for the detection of Fe³⁺ and Cr³⁺, P1 and P2 show excellent selectivity and sensitivity. The limit of detection (LOD) achieved by Fe³⁺ is 7.30 nM, and the LOD achieved by Cr³⁺ is 14.69 nM, which indicates the great potential of these NBN-embedded polymers as metal fluorescence sensors.

Stimuli-Responsive Zinc (II) Coordination Polymers: A Novel Platform for Supramolecular Chromic Smart Tools

The unique role of the zinc (II) cation prompted us to cut a cross-section of the large and complex topic of the stimuli-responsive coordination polymers (CPs). Due to its flexible coordination environment and geometries, easiness of coordination-decoordination equilibria, "optically innocent" ability to "clip" the ligands in emissive architectures, non-toxicity and sustainability, the zinc (II) cation is a good candidate for building supramolecular smart tools. The review summarizes the recent achievements of zinc-based CPs as stimuli-responsive materials able to provide a chromic response. An overview of the past five years has been organised, encompassing 1, 2 and 3D responsive zinc-based CPs; specifically zinc-based metallorganic frameworks and zinc-based nanosized polymeric probes. The most relevant examples were collected following a consequential and progressive approach, referring to the structure-responsiveness relationship, the sensing mechanisms, the analytes and/or parameters detected. Finally, applications of highly bioengineered Zn-CPs for advanced imaging technique have been discussed.

Recent progress in the development of MOF-based optical sensors for Fe3

Fe(iii) is a common pollutant released into our ecosystem from various industrial and anthropogenic activities which when in excess interferes with human health. A plethora of sensors based on various designs and working principles are being continuously synthesized and improvised for its facile detection. In the present review, we have provided a brief overview of the developments made in the field of metal organic framework (MOF) based optical sensors for Fe3+. MOFs have exponentially emerged in the field of research due to their high porosity, modular construction and easy tunability. These inorganic-organic hybrid porous materials are being essentially promoted as optical sensors because of their unique photophysical properties and potential sensing applications.

Applications of MOFs as Luminescent Sensors for Environmental Pollutants

The environmental pollution has become a serious issue because the pollutants can cause permanent damage to the DNA, nervous system, and circulating system, resulting in various incurable diseases, such as organ failure, malformation, angiocardiopathy, and cancer. The effective detection of environmental pollutants is urgently needed to keep them far away from daily life. Among the reported pollutant sensors, luminescent metal-organic frameworks (LMOFs) with tunable structures have attracted remarkable attention to detect the pollutants because of their excellent selectivity, sensitivity, and recyclability. Although lots of metal-organic framework (MOF)-based luminescent sensors have been summarized and discussed in previous reviews, the detection of environmental pollutants, especially radioactive ions and heavy metal ions, still have not been systematically presented. Here, the sensing mechanisms and construction principles of luminescent MOFs are discussed, and the state-of-the-art MOF-based luminescent sensors of environmental pollutants, including pesticides, antibiotics, explosives, VOCs, toxic gas, toxic small molecules, radioactive ions, and heavy metal ions are highlighted. This comprehensive review may further guide the development of luminescent MOFs and promote their practical applications for sensing environmental pollutants.

Design of turn-on luminescent sensor based on nanostructured molecularly imprinted polymer-coated zirconium metal-organic framework for selective detection of chloramphenicol residues in milk and honey

Herein, an optical sensor based on nanostructured molecularly imprinted polymer (MIP) coated on a luminescent zirconium metal-organic framework (MIP/Zr-LMOF) is introduced, and its performance is investigated for the fluorescent determination of chloramphenicol (CAP) antibiotic residues in milk and honey. To fabricate the sensor, the surface of Zr-LMOF is modified with MIP in the presence of CAP template, resulting in the introduction of recognition sites for antibiotic molecules. The porous structure of Zr-LMOF with specific binding sites for CAP recognition benefiting from coated MIP leads to selective and sensitive detection of antibiotic. The probe yields a linear range for detection of CAP in trace concentrations (0.16-161.56 µg.L^-1) and provides a detection limit of 0.013 µg.L^-1. Acceptable recoveries are achieved for antibiotic in real samples, which are consistent with that obtained from liquid chromatography-tandem mass spectrometry (LC-MS/MS), confirm the favorable performance of sensor for accurate determination of CAP in practical applications.

A study of , a water-stable zinc-based metal–organic framework as a highly selective and sensitive fluorescent sensor in the detection of Al3+ and Fe3+ ions

A unique Zn-MOF (GUPT-2) with excellent fluorescence characteristics, which have a highly selective fluorescent probe for Al³⁺ and Fe³⁺ ions in a pure water system based on the ESIPT process with the LOD values 0.446 and 0.269 μM, respectively.

Amino group decorated coordination polymers for enhanced detection of folic acid

A series of fluorescent coordination polymers (CPs) {[Cd₂(CH₃-bpeb)₂(BDC)₂] CP1, (BDC)_0.5/(NH₂-BDC)_0.5-CP1, (BDC)_0.34/(NH₂-BDC)_0.66-CP1, (BDC)_0.25/(NH₂-BDC)_0.75-CP1, (BDC)_0.2/(NH₂-BDC)_0.8-CP1, (NH₂-BDC)-CP1} were prepared from conjugated ligand 4,4'-((2-methyl-1,4-phenylene)bis(ethene-2,1-diyl))bipyridine (CH₃-bpeb), terephthalic acid (BDC), aminoterephthalic acid (NH₂-BDC) and CdSO₄ under solvothermal conditions. The fluorescence of aqueous suspensions of these CPs was quenched by folic acid (FA) in a concentration dependent manner. The efficiency of quenching increasing with an increased proportion of NH₂-BDC ligand in the CP with (NH₂-BDC)-CP1 exhibiting a low detection limit of 1.7 × 10^-7 M.