Fabrication of a Luminescence-Silent System Based on a Post-Synthetic Modification Cd-MOFs: A Highly Selective and Sensitive Turn-on Luminescent Probe for Ascorbic Acid Detection

High-sensitively fluorescent switch-type sensing for Ag+ and halide anions of 2D Cd-based network constructed with logic gates

Effective detection of the concentration of Ag+ ions in bactericidal fluid is one of the necessary conditions for their effective utilization for sterilization. A novel 2D Cd(II) coordination polymer (CP1), named as [Cd(HDPN)(4,4'-bbpy)]·2H2O, was hydrothermally synthesized using 5-(2',4'-dicarboxylphenyl) nicotic acid (H3DPN) and 4,4'-bis(imidazolyl)biphenyl (4,4'-bbpy). The structure analysis discovered that CP1 possessed a 2D network structure of dinuclear inorganic building blocks. Fluorescence sensing discovered that CP1 could high-sensitively detect Ag+, tetracycline, nitrobenzene and pyrimethanil and the lowest limit of detection (LOD) were 1.44 × 10-8M, 2.15 × 10-8M, 8.09 × 10-8M, and 2.54 × 10-7M, respectively. It is worth noting that the quenching occurs after the addition of Ag+ to the aqueous solution of CP1, and then it gradually recovers when one of the halide anions (X- = Cl-, Br- and I-) is added, forming a unique "on-off-on" fluorescence sensor for Ag+ and constructing a simple logic gate. The fluorescence sensing mechanism of CP1 was investigated using ultraviolet-visible spectroscopy, PXRD, XPS, and DFT methods. The research indicates that CP1 is anticipated to serve as an excellent multifunctional fluorescence sensor, especially as a switch-type sensor for Ag+ and the halide anions.

MOFs as versatile scaffolds to explore environmental contaminants based on their luminescence bustle

Metal-Organic Frameworks (MOFs) with luminescent properties hold significant promise for environmental remediation. This review critically examines recent research on these materials design, synthesis, and applications, mainly focusing on their role in combating environmental pollutants. Through a comprehensive analysis of metal ions, ligands, and framework compositions, the review discusses the importance of tailored design and synthesis approaches in achieving desired luminescent characteristics. Key findings highlight the effectiveness of luminous MOFs as fluorescent sensors for a wide range of contaminants, including heavy metals, reactive species, antibiotics, and explosives. Considering all this, the review discusses future research needs and opportunities in the field of luminous MOFs. It emphasizes the importance of developing multifunctional materials, refining design methodologies, exploring sensing mechanisms, and ensuring environmental compatibility, scalability, and affordability. By providing insights into the current state of research and outlining future directions, this review is a valuable resource for researchers seeking to address environmental challenges using MOF-based solutions.

Orange peel-derived carbon dots/Cu-MOF nanohybrid for fluorescence determination of l-ascorbic acid and Fe3. Anal Chim Acta 2024;1287:342066. [PMID: 38182373 DOI: 10.1016/j.aca.2023.342066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Recycling and reuse of biomass waste in synthesis of nanomaterials have recently received much attention as an effective solution for environmental protection and sustainable development. Herein, nitrogen-doped carbon dots (N-CDs) with blue emission were synthesized from the orange peels as a precursor through a simple hydrothermal method and then, modified with ethylenediamine tetraacetic acid (N-CD@EDTA). The N-CD@EDTA was embedded as a fluorophore in Cu-based metal-organic framework (MOF-199) structure (N-CD@EDTA/MOF-199) to construct fluorescence sensor toward l-ascorbic acid (L-AA) determination. The N-CD@EDTA/MOF-199 nanohybrid significantly and selectively turned on toward L-AA determination during the fluorimetric experiments. Under optimal conditions, the probe showed a suitable linear response in the concentration range of 10 nM-100 μM with a low limit of detection (LOD) of 8.6 nM and high sensitivity of 0.201 μM-1. The possible mechanism of recognition and adsorption, including the reduction of Cu 2+ nodes in the MOF-199 structure in the presence of L-AA and the release of trapped N-CD@EDTA into the solution, was explored. Moreover, the N-CD@EDTA/MOF-199/L-AA (100 μM) system was further applied as a fluorescent "on-off" sensor for Fe3+ determination with a LOD of 1.15 μM. The proposed probe was successfully used in orange juice and water samples to determine L-AA and Fe3+ with satisfactory recovery, which displays the promising capability of sensor in real samples. The recoveries obtained by suggested method are consistent with that obtained from high performance liquid chromatography (HPLC) and atomic absorption spectroscopy which confirm the favorable characteristic of the sensor for accurate determination of L-AA and Fe3+ in practical applications.

Highly efficient determination of trace ascorbic acid in vitamin C tablets by boronate affinity-modified magnetic metal-organic frameworks

Ascorbic acid (AA) plays an important role in many life processes. The chronic nutritional deficiency of AA will lead to the symptoms of scurvy. Therefore, the sensitive quantitative detection of AA is most important in the pharmaceutical analysis, food industry and diagnostic application. In this study, a dual-functional magnetic metal-organic frameworks (Fe3O4@SiO2@UiO-PBA) nanoparticles was synthesized by modifying phenylboronic acid to the surface of magnetic UiO-66-NH2 via postsynthetic modification for selectively and sensitively florescent detection of AA. Due to the abundant amino groups and grafted phenylboronic acid, the proposed nanoparticles have the dual properties of hydrophilicity and boronate affinity. Under optimum conditions, the obtained Fe3O4@SiO2@UiO-PBA nanoparticles can detect AA within 30 s, and has a good linear relationship with the concentration of AA in the range of 5.0-60 μM with a detection limit of 2.5 μM (S/N = 3). In addition, the prepared Fe3O4@SiO2@UiO-PBA nanoparticles showed excellent selectivity and great potential application in the highly efficient determination of trace AA in vitamin C tablets. These results indicated that a convenient method was proposed to develop fluorescent probes for rapid and sensitive detection of trace AA in real samples.

Multivariate metal-organic frameworks generated through post-synthetic modification: impact and future directions

Reticular chemistry has proven to be invaluable over time, thanks to the structural versatility, and tailored porosity observed in structures like metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and metal-organic polyhedra (MOPs). Despite the wide array of ligands and metals available for synthesizing MOFs, they are still somewhat constrained by the reliance on de novo conditions and the focus on generating MOFs with single ligand and metal. To surpass these limitations, researchers have established strategies to generate multivariate (MTV) MOF structures incorporating more than one ligand/metal into the crystal lattice. MTV-MOFs have demonstrated enhanced properties by virtue of the additional functionalities incorporated within their structures. One approach to developing MTV-MOFs is through post-synthetic modification (PSM), where new functionalities are introduced after the initial synthesis, thereby achieving the enhanced properties of MTV-MOFs even in cases where the new functionalities are incompatible with MOF synthesis.

A Ratiometric Fluorescent Probe Based on RhB Functionalized Tb-MOFs for the Continuous Visual Detection of Fe3+ and AA

In this study, a red-green dual-emitting fluorescent composite (RhB@MOFs) was constructed by introducing the red-emitting organic fluorescent dye rhodamine B (RhB) into metal-organic frameworks (Tb-MOFs). The sample can be used as a ratiometric fluorescent probe, which not only avoids errors caused by instrument and environmental instability but also has multiple applications in detection. The results indicated that the RhB@MOFs exhibited a turned-off response toward Fe3+ and a turned-on response for the continuous detection of ascorbic acid (AA). This ratiometric fluorescent probe possessed high sensitivity and excellent selectivity in the continuous determination of Fe3+ and AA. It is worth mentioning that remarkable fluorescence change could be clearly observed by the naked eye under a UV lamp, which is more convenient in applications. In addition, the mechanisms of Fe3+- and AA-induced fluorescence quench and recovery are discussed in detail. This ratiometric probe displayed outstanding recognition of heavy metal ions and biomolecules, providing potential applications for water quality monitoring and biomolecule determination.

Multifunctional Cd-CP for fluorescence sensing of Cr(VI), MnO4-, acetylacetone and ascorbic acid in aqueous solutions

The development of multifunctional fluorescent chemosensors for the detection of multiple targets remains challenging but of great importance. In this paper, one novel coordination polymer (CP), denoted as [Cd₂(edda)(phen)₂]∙H₂O (compound 1, H₄edda = 5,5' (ethane-1,2-diylbis(oxy)) diisophthalic acid, phen = 1,10-phenanthroline) is successfully designed and prepared under hydrothermal conditions. Structural analysis indicates that compound 1 possesses a one-dimensional (1D) double chain structure, then self-assembles into a three-dimensional (3D) supramolecular framework via π…π interactions between phen molecules. Interestingly, compound 1 is found to be tolerant in wide range of acidic to alkaline aqueous solutions (pH = 2-13). Fluorescent spectral investigations reveal that compound 1 exhibits highly selective and sensitive fluorescence responses toward MnO₄^-, Cr(VI) ions, acetylacetone (acac) and ascorbic acid (AA) by fluorescence quenching in the aqueous phase. The detection limits are in the very low range, reaching μM level for the detection of MnO₄^-, Cr(VI) ions, nM for AA and ppm for acac detection. The distinguished multi-responsive performance suggests compound 1 to be a potential multifunctional probe. Furthermore, the possible quenching mechanisms have also been systematically investigated in this work.

Tandem Förster resonance energy transfer induced visual ratiometric fluorescence sensing of tetracyclines based on zeolitic imidazolate framework-8 incorporated with carbon dots and safranine T

With increasing TC concentration, tandem FRET1 from CDs to TC, then FRET2 from TC to safranine T were occurred. TC could be easily recognized by naked eye. Besides, we could perform on-site detection of TC with the help of a mobile phone.

Two porous three-dimensional (3D) metal–organic frameworks based on diverse metal clusters: selective sensing of Fe3+ and Cr2O72−

Using a rigid 3,5-di(2′,5′-dicarboxylphenyl)benzoic acid, two porous 3D MOFs have been synthesized and characterized, and the luminescent properties have been studied.

Post-synthetic modification within MOFs: a valuable strategy for modulating their ferroelectric performance

It is a great route designing new MOF ferroelectrics to enrich the scope of ferroelectrics or improving the ferroelectric performance to enhance the opportunity of applications through the strategy of post-synthetic modification (PSM).

Isomers of Terpyridine as Ligands in Coordination Polymers and Networks Containing Zinc(II) and Cadmium(II)

The use of divergent 4,2′:6′,4″- and 3,2′:6′,3″-terpyridine ligands as linkers and/or nodes in extended coordination assemblies has gained in popularity over the last decade. However, there is also a range of coordination polymers which feature 2,2′:6′,2″-terpyridine metal-binding domains. Of the remaining 45 isomers of terpyridine, few have been utilized in extended coordination arrays. Here, we provide an overview of coordination polymers and networks containing isomers of terpyridine and either zinc(II) and cadmium(II). Although the motivation for investigations of many of these systems is their luminescent behavior, we have chosen to focus mainly on structural details, and we assess to what extent assemblies are reproducible. We also consider cases where there is structural evidence for competitive product formation. A point that emerges is the lack of systematic investigations.

Turn-On Fluorescence Enantioselective Sensing of Hydroxyl Carboxylic Enantiomers by Metal-Organic Framework Nanosheets with a Homochiral Tetracarboxylate of Cyclohexane Diamide

Two-dimensional (2D) metal-organic frameworks (MOFs) have attracted growing interest due to excellent performance in gas separation, energy conversion and storage, catalysis, and sensing, but their homochirality and exfoliation as well as related enantioselective catalysis and sensing remain a stage of pending exploration owing to the scarcity of homochiral MOFs and intrinsic aggregation of nanosheets. Herein, a homochiral 2D MOF (HMOF-3) with polymeric chirality, good thermostability, and solvent stability is designed and constructed by a homochiral organic ligand 5,5'-((1R,2R)-cyclohexane dicarbonyl bis(azanediyl)) diisophthalic acid (R,R-CHCAIP), a ditopic coligand 4,4'-bipyridine, and Zn salts. Remarkably, HMOF-3 can be exfoliated via solvent-assisted sonication to achieve 2D HMOF-3 nanosheets (HMOF-3-NS), which exhibit a sensitive turn-on effect with the fluorescence enhancement up to 63.5 times in the presence of R/S-mandelic acid, d/l-tartaric acid, d/l-lactic acid, d/l-alanine, and d/l-tryptophan. More importantly, the high surface area, polymeric chirality environment, and highly accessible functional sites on the surface of HMOF-3 nanosheets enable close contact with probed enantiomers, leading to highly enantioselective and sensitive sensing. The turn-on mechanism of host-guest-assisted electronic transfer is confirmed by DFT calculation and the relative experiment. This work highlights the promise of homochiral 2D MOF nanosheets for enantioselective sensing applications.

Terpyridine-Based 3D Metal-Organic-Frameworks: A Structure-Property Correlation

Design, synthesis, and applications of metal-organic frameworks (MOFs) are among the most salient fields of research in modern inorganic and materials chemistry. As the structure and physical properties of MOFs are mostly dependent on the organic linkers or ligands, the choice of ligand system is of utmost importance in the design of MOFs. One such crucial organic linker/ligand is terpyridine (tpy), which can adopt various coordination modes to generate an enormous number of metal-organic frameworks. These frameworks generally carry physicochemical characteristics induced by the π-electron-rich (basically N-electron-rich moiety) terpyridines. In this minireview, the construction of 3D MOFs associated with symmetrical terpyridines is discussed. These ligands can be easily derivatized at the lateral phenyl (4'-phenyl) position and incorporate additional organic functionalities. These functionalities lead to some different binding modes and form higher dimensional (3D) frameworks. Therefore, these 3D MOFs can carry multiple features along with the characteristics of terpyridines. Some properties of these MOFs, like photophysical, chemical selectivity, photocatalytic degradation, proton conductivity, and magnetism, etc. have also been discussed and correlated with their frameworks.

Stimuli -triggered fluoro-switching in metal-organic frameworks: applications and outlook

The design and synthesis of efficient sensor materials with fast-responsive and ultrasensitive detection ability is critical to monitor ecological safety, supervise human health, control industrial wastes, and govern food quality among others. Metal-organic frameworks (MOFs) or coordination polymers (CPs) are a new class of porous crystalline materials that have emerged in several potential applications in last two decades. In particular, applications of MOFs as sensory scaffolds for the detection of hazardous pollutants have attracted researchers due to their fabulous structural characteristics and wide range of pore environment tunability. Among several transducer procedures, the luminescence detection of a particular analyte is immensely desirable as it is easy to handle and cost effective, where visual changes in physicochemical attributes can be comprehended via a quick naked eye detection. The porous nature of MOFs facilitates the pre-concentration of target analytes within the pore structure and provides superior host-guest interaction with good detection limits when compared to conventional materials. To this end, guest-induced fluorescence switching in sensory MOFs with good recyclability and unique detectable fingerprints are of particular importance to benefit futuristic monitoring aptitudes and promises environmental remediation. In this review, we present the latest literature based on the analyte-responsive modulation of fluorescence intensity in MOFs towards the detection of target pollutants and discuss the underlying sensing mechanism, which can assist in developing new useful nano-scale devices and sensors.

Two Cd(ii)-based metal–organic frameworks for the highly effective detection of Fe3+ ions and levofloxacin in aqueous media

Two new Cd(ii)-MOFs are hydrothermally synthesized and can be applied as dual-response sensors to identify Fe3+ and levofloxacin (LVX) with high selectivity, sensitivity and excellent reusability.

Efficient luminescence sensing in two lanthanide metal–organic frameworks with rich uncoordinated Lewis basic sites

Two novel Ln-MOFs containing uncoordinated Lewis basic sites for sensitive detection of Fe3+ ions and nitrobenzene through fluorescence quenching.

Luminescence response mode and chemical sensing mechanism for lanthanide-functionalized metal–organic framework hybrids

This comprehensive review systematically summarizes the luminescence response mode and chemical sensing mechanism for lanthanide-functionalized MOF hybrids (abbreviated as LnFMOFH).

Porous and Nonporous Coordination Polymers Induced by Pseudohalide Ions for Luminescence and Gas Sorption

The three-dimensional (3D) coordination polymers [Cd(tpmd)(NCX)₂]_n [X = O (1), S (2), and BH₃ (3); tpmd = N,N,N',N'-tetrakis(pyridin-4-yl)methanediamine] have been determined to display their network structures through coordinated anionic ligands. Polymers 1 and 2 show nonporous structures, whereas polymer 3 shows a porous coordination framework. On the basis of the Cd(II) network structures, the 3D coordination polymer [Zn(tpmd)(NCBH₃)₂]_n·nMeOH (4) was self-assembled. In the cases of polymers 1 and 2, pseudohalide ions acted to form nonporous network structures; however, in polymers 3 and 4, NCBH₃^- helps to construct porous network structures. Polymers 1-4 show strong ultraviolet luminescence emissions, depending on the pseudohalide ions present, compared to the tpmd ligands. Interestingly, coordination polymers 3 and 4 that possess NCBH₃^- ions exhibit high porosities and gas sorption properties. The polymers appeared to absorb N₂, H₂, CO₂, and CH₄. In the case of polymer 4, the structure is almost identical with that of polymer 3, except for the Cd(II) ion. However, polymer 4 has a larger void volume and higher gas absorption ability for N₂ gas than polymer 3. For the sorption of gases, polymers 3 and 4 showed similar behaviors.

Two cadmium(II) coordination polymers as multi-functional luminescent sensors for the detection of Cr(VI) anions, dichloronitroaniline pesticide, and nitrofuran antibiotic in aqueous media

Two ternary cadmium(II) coordination polymers, with the formulas being {[Cd(tptc)_0.5(bpz)(H₂O)]·0.5H₂O}_n (CP 1), and [Cd(tptc)_0.5(bpy)]_n (CP 2), were designed through mixed ligands strategy. Benefiting from the excellent chemical stability and luminescent property, two Cd(II) CPs possessing efficient multi-functional fluorescent responses toward Cr(VI) anions, 2,6-dichloro-4-nitroaniline pesticide, and nitrofuran antibiotic in aqueous media with high sensitivity, selectivity, and excellent recyclable behaviors with the detection limits (LODs) are 235 ppb for CrO₄^2- anion, 343 ppb for Cr₂O₇^2- anion, 112 ppb for DCN pesticide, 62 ppb for NFT antibiotic for CP 1, and 173 ppb for CrO₄^2- anion, 270 ppb for Cr₂O₇^2- anion, 638 ppb for DCN pesticide, 184 ppb for NFT antibiotic for CP 2, respectively. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photoinduced electron transfer (PET).

Smartphone assisted colorimetric and fluorescent triple-channel signal sensor for ascorbic acid assay based on oxidase-like CoOOH nanoflakes

Ascorbic acid (AA) is an important diet-derived antioxidant to human body. Thus, efficient and accurate detection of AA is of considerable significance in food analysis. Herein, smartphone assisted colorimetric and fluorescent triple-channel signal sensor has been developed for AA monitoring based on oxidase-like CoOOH nanoflakes. CoOOH nanoflakes can efficiently catalyze the oxidation of p-phenylenediamine (p-PD) into reddish brown p-PDox. The carbon dots (C-dots) are further introduced, of which the fluorescence can be quenched by p-PDox. However, in the presence of AA, the CoOOH nanoflakes is reduced and thus collapsed. As a result, the oxidation of p-PD is restrained, and thus the fluorescence of C-dots keeps strong. Based on AA induced light color, low absorbance, and strong fluorescence, triple-channel signal sensor has been proposed for AA determination. The AA assay shows a dynamic response range from 0.5 to 10 μM with a detection limit of 0.09 μM. The method assay allows detection of AA in real samples such as fruit juices. Combination with portable smartphone, the developed sensor is potential for AA determination in resource-poor settings.

Crystal structures and the ferroelectric properties of homochiral metal-organic frameworks constructed from a single chiral ligand

MOFs have proven to be promising candidates for designing ferroelectric materials. Herein, two new homochiral MOFs, Co-MOF-1 and Co-MOF-2, have been synthesized using the chiral ligand, HL (HL = phenyl-((pyridin-4-ylmethyl)-amino)-acetic acid), and Co(NO₃)₂·6H₂O. Co-MOF-1 was obtained via a two-step synthetic route involving a hydrogel to Zn-MOF conversion and a dissolution-recrystallization process. Co-MOF-2 was directly synthesized by a coordination reaction between chiral ligand, HL, and Co(NO₃)₂·6H₂O under hydrothermal conditions. We investigate the correlation between the ferroelectric properties of the samples and their crystal structures. The ferroelectric properties of Co-MOF-1 and Co-MOF-2 are drastically different. Indeed, Co-MOF-2 shows an obvious hysteretic behavior, while a clear electric hysteresis loop was not observed for Co-MOF-1. These significant disparities may be attributed to the different molecular dipole moments in Co-MOF-1 and Co-MOF-2. The different octahedral coordination units in the molecular structures of the Co-MOFs may alter the dipole moments of the molecules, resulting in the absence of a hysteresis loop for Co-MOF-1.

An unusual high-frequency ferroelectric obtained via the post-synthetic modification of a metal-organic framework

Ferroelectrics as crucial functional materials have attracted much interest since ferroelectricity was discovered in 1920. Herein, an unusual high-frequency ferroelectric, (CH3)2NH·HCl@Cd-MOF, was successfully obtained through a dual-step synthetic methodology. A chiral porous Cd-MOF with a channel size of 6.8 × 6.8 Å was synthesized via self-assembly of chiral Schiff-base ligands and Cd2+ ions. Subsequently, polarizable (CH3)2NH·HCl was introduced into the channels of the Cd-MOF and hence the host-guest system (CH3)2NH·HCl@Cd-MOF was formed. The as-synthesized (CH3)2NH·HCl@Cd-MOF displays obvious ferroelectricity at a high frequency of 1 kHz. Such a high-frequency ferroelectric is extremely rare among MOF-based ferroelectric materials, and the high-frequency ferroelectricity means that (CH3)2NH·HCl@Cd-MOF has potential for use in ferroelectric memories. The results again demonstrate that post-synthetic modification is a promising approach for achieving rational and precise design of ferroelectric materials.

Intriguing pH-modulated Luminescence Chameleon System based on Postsynthetic Modified Dual-emitting Eu3+@Mn-MOF and Its Application for Histidine Chemosensor

Due to the disruption by other nonanalyte factors, single-emission probes have been limited in complicated detecting systems. In this work, a pH-modulated luminescence chameleon system based on lanthanide-based MOF (Eu³⁺@Mn-MOF), with stable structure and miraculous dual-emitting fluorescent properties, was synthesized by a postsynthetic modification (PSM) strategy of a simple hydrothermal and agitation method. Amazingly, not only can the Eu³⁺@Mn-MOF emit a broad emission at 500 nm attributed to the ligand-based fluorescence emission but it can also exhibit the characteristic emission of Eu³⁺ ions responding to the antenna effect. Moreover, the Eu³⁺@Mn-MOF displays an interesting luminescence color transition between acidic and basic solutions. Inspired by this phenomenon, a pH-modulated luminescence chameleon system was first constructed and employed to detect histidine, a kind of basic amino acid for a variety of biological matters, causing a unique fluorescence signal of the ratio-dependent color to change from yellow to light pink which differs from the color change of other water-soluble amino acids. Therefore, Eu³⁺@Mn-MOF can be as a practical pH-modulated luminescence chameleon system chemsensor for sensing histidine with low detection limit, high sensitivity, and rapid sensing time. In conclusion, the postsynthetic modified Eu³⁺@Mn-MOF has outstanding applications in the fields of chemical detection and human health.