Ultrasound-Assisted Synthesis of Luminescent Micro- and Nanocrystalline Eu-Based MOFs as Luminescent Probes for Heavy Metal Ions

Synthesis and applications of luminescent metal organic frameworks (MOFs) for sensing dipicolinic acid in biological and water samples: a review

The detection of trace quantities of 2,6-dipicolinic acid (DPA) in real-world samples is crucial for early disease diagnosis and routine health monitoring. Metal-organic frameworks (MOFs), recognized for their diverse structural architectures, have emerged as advanced multifunctional hybrid materials. One of the most notable properties of MOFs is their luminescence (L), which can arise from structural ligands, guest molecules, and emissive metal ions. Luminescent MOFs have shown significant promise as platforms for sensor design. This review highlights the application of luminescent MOFs in the detection of DPA in biological and aqueous environments. It provides a comprehensive discussion of the various detection strategies employed in luminescent MOF-based DPA sensors. Additionally, it explores the origins of L in MOFs, their synthesis, and the mechanisms underlying their sensing capabilities. The article also addresses key challenges and limitations in this field, offering practical insights for the development of efficient luminescent MOFs for DPA detection.

Microcrystalline Luminescent (Eu1-xLnx)2bdc3·nH2O (Ln = La, Gd, Lu) Antenna MOFs: Effect of Dopant Content on Structure, Particle Morphology, and Luminescent Properties

In this work, three series of micro-sized heterometallic europium-containing terephthalate MOFs, (Eu1-xLnx)2bdc3·nH2O (Ln = La, Gd, Lu), are synthesized via an ultrasound-assisted method in an aqueous medium. La3+ and Gd3+-doped terephthalates are isostructural to Eu2bdc3·4H2O. Lu3+-doped compounds are isostructural to Eu2bdc3·4H2O with Lu contents lower than 95 at.%. The compounds that are isostructural to Lu2bdc3·2.5H2O are formed at higher Lu3+ concentrations for the (Eu1-xLux)2bdc3·nH2O series. All materials consist of micrometer-sized particles. The particle shape is determined by the crystalline phase. All the synthesized samples demonstrate an "antenna" effect: a bright-red emission corresponding to the 5D0-7FJ transitions of Eu3+ ions is observed upon 310 nm excitation into the singlet electronic excited state of terephthalate ions. The fine structure of the emission spectra is determined by the crystalline phase due to the different local symmetries of the Eu3+ ions in the different kinds of crystalline structures. The photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are equal to 11 ± 2% and 0.44 ± 0.01 ms, respectively, for the Ln2bdc3·4H2O structures. For the (Eu1-xLux)2bdc3·2.5H2O compounds, significant increases in the photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are observed, reaching 23% and 1.62 ms, respectively.

A gas-selective Zn-MOF exhibits selective sensing of Fe3+ ions by doping with Tb3

Here, a new Zn2+ metal organic framework, {[Me2NH2][Zn2(L)(DTZ)]·2DMF·3H2O}n (Zn-MOF), has been synthesized with low-symmetric carboxylic acid ligand 2,6 bis(2',5'-dicarboxyphenyl)pyridine (H4L) as the main ligand and 3,5-diamino-1,2,4-riazole (DTZ) containing an electron-rich N atom as an auxiliary ligand. Because of its high structural stability and adsorption properties, it can be used to efficiently separate CO2/CH4 and C2H2/CH4. In addition, Tb@Zn-MOF was obtained by doping with Tb3+ to partially replace Zn2+. A study of its luminescence sensing performance demonstrated that Tb@Zn-MOF showed intense luminescence properties and can be used for the directional detection of Fe3+ in aqueous solution. Furthermore, PXRD analysis, UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) were also used to study possible luminescence sensing mechanisms. The recognition mechanism for Fe3+ ions is believed to be caused by electron transfer.

Metal-Organic Frameworks (MOFs)-Based Sensors for the Detection of Heavy Metals: A Review

Metal-organic-frameworks (MOFs) have emerged as promising candidates in different scientific disciplines owing to their intriguing characteristics. Their unique structural properties, including large surface area to volume ratio with multi-functionalities and ultra-high porosity, tunability, uniformity, and easy derivation and fabrication, render them effective materials for sensing applications. The detection of heavy metals in different environmental matrices using various MOF-based sensors is in practice. They include luminescent, electrochemical, electrochemiluminescent, colorimetric, and surface-enhanced Raman scattering, are of great interest. This review elaborates on selected synthetic methods for the fabrication of MOF-based sensors, modification routes for tailoring and enhancing the desired properties, basic characterization techniques, and their limitations in the detection of heavy metals. Also, it emphasizes the use of various types of MOF-based sensors alternatively for the detection of different heavy metals such as Fe(III), Cr(III), Hg(II), Cd(II), and Pb(II) in addition to a normal metal Al(III). A collection of recent references is provided for researchers interested in such applications. Results from the literature have been summarized in tables which give an easy comparison and will help to develop efficient materials.

Recent progress of metal-organic frameworks as sensors in (bio)analytical fields: towards real-world applications

The deployment of metal-organic frameworks (MOFs) in a plethora of analytical and bioanalytical applications is a growing research area. Their unique properties such as high but tunable porosity, well-defined channels or pores, and ease of post-synthetic modification to incorporate additional functional units make them ideal candidates for sensing applications. This is possible because the interaction of analytes with a MOF often results in a change in its structure, eventually leading to a modification of the intrinsic physicochemical properties of the MOF which is then transduced into a measurable signal. The high porosity allows for the adsorption of analytes very efficiently, while the tunable pore sizes/nature and/or installation of specific recognition groups allow modulating the affinity towards different classes of compounds, which in turn lead to good sensor sensitivity and selectivity, respectively. Some figures are given to illustrate the potential of MOF-based sensors in the most relevant application fields, and future challenges and opportunities to their possible translation from academia (i.e., laboratory testing of MOF sensing properties) to industry (i.e., real-world analytical sensor devices) are critically discussed.

Heterometallic Europium(III)–Lutetium(III) Terephthalates as Bright Luminescent Antenna MOFs

A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (Eu_xLu_1−x)₂bdc₃·nH₂O, was synthesized using a direct reaction in a water solution. At the Eu³⁺ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (Eu_xLu_1−x)₂bdc₃ and (Eu_xLu_1−x)₂bdc₃·4H₂O crystalline phases, where the Ln₂bdc₃·4H₂O crystalline phase was enriched by europium(III) ions. At an Eu³⁺ concentration of more than 40 at %, only one crystalline phase was formed: (Eu_xLu_1−x)₂bdc₃·4H₂O. All MOFs containing Eu³⁺ exhibited sensitization of bright Eu³⁺-centered luminescence upon the 280 nm excitation into a ¹ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu^{3+ 5}D₀-⁷F_J (J = 0–4) significantly depended on the Eu³⁺ concentration. The luminescence quantum yield of Eu³⁺ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu³⁺ due to the absence of Eu-Eu energy migration and the presence of the Ln₂bdc₃ crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln₂bdc₃·4H₂O.

A red luminescent europium metal organic framework (Eu-MOF) integrated with a paper strip using smartphone visual detection for determination of folic acid in pharmaceutical formulations

Integration of smartphone with visual-based paper strip as a low-cost, fast, and reliable probe for semi-quantitative analysis of folic acid.