Two new luminescent ternary Cd(II)-MOFs by regulation of aromatic dicarboxylate ligands used as efficient dual-responsive sensors for toxic metal ions in water

Detection and Sorption of Heavy Metal Ions in Aqueous Media by a Fluorescent Zr(IV) Metal-Organic Framework Functionalized with 2-Picolylamine Receptor Groups

Increasing global environmental pollution due to heavy metal ions raises the importance of research on new multifunctional materials for simultaneous detection and removal of these contaminants from water resources. In this study, we report a microporous 8-connected Zr⁴⁺ metal-organic framework (MOF) based on a terephthalate ligand decorated with a chelating 2-picolylamine side group (dMOR-2), which shows highly efficient fluorescence sensing and sorption of heavy metal cations. We demonstrate by detailed fluorescence studies the ability of a water-dispersible composite of dMOR-2 with polyvinylpyrrolidone for real-time detection of Cu²⁺, Pb²⁺, and Hg²⁺ in aqueous media. The limits of detection were found to be below 2 ppb for these species, while the system's performance is not affected by the presence of other potentially competitive ions. In addition, sorption studies showed that a composite of dMOR-2 with calcium alginate (dMOR-2@CaA) is an excellent sorbent for Pb²⁺ and Cu²⁺ ions with capacities of 376 ± 15 and 117 ± 4 mg per gram of dMOR-2@CaA, respectively, while displaying the capability for simultaneous removal of various heavy metal ions in low initial concentrations and in the presence of large excesses of other cationic species. Structural and spectroscopic studies with model ligands analogous to our material's receptor unit showed chelation to the 2-picolylamine moiety to be the main binding mode of metal ions to dMOR-2. Overall, dMOR-2 is shown to represent a rare example of a MOF, which combines sensitive fluorescence detection and high sorption capacity for heavy metal ions.

Amine-substituent induced highly selective and rapid "turn-on" detection of carcinogenic 1,4-dioxane from purely aqueous and vapour phase with novel post-synthetically modified d10-MOFs

Herein, an amine decorated Cd(II) metal-organic framework (MOF) with a uninodal 6-c topology was synthesized as a suitable platform for facile post-synthetic modification (PSM). The as-synthesized parent d¹⁰-MOF (1) with free -NH₂ centers, when functionalized with two different carbonyl substituents (1-naphthaldehyde and benzophenone) of varying conjugation, produces two novel luminescent MOFs (LMOFs) viz.PSM-1 and PSM-2. The judicious incorporation of carbonyl substituents into the skeleton of 1 was rationalized via ESI-MS, ¹H-NMR, FT-IR and PXRD analyses. Interestingly, both PSM-1 and PSM-2 show 'turn-on' luminescent behaviour in the presence of 1,4-dioxane with the limit of detection (LOD) as 1.079 ppm and 2.487 ppm, respectively, with prompt response time (∼55 s & ∼58 s, respectively). The inhibition of PET is comprehended to be the prime reason for luminescence enhancement upon interaction with the targeted analyte which was further validated from DFT calculations. In continuation, the PSM-MOFs were equally responsive towards 1,4-dioxane in several complex environmental matrices and cosmetic products. Additionally, vapor phase detection of 1,4-dioxane using PSM-MOFs has also been demonstrated as an additional advantage ensuring propagation of future research endeavour.

Copper doped terbium metal organic framework as emitter for sensitive electrochemiluminescence detection of CYFRA 21-1

Lanthanide metal organic frameworks (L-MOFs) are emerging as promising electrochemiluminescence (ECL) emitters for bioanalysis. This work proposed a copper doped terbium MOF as a luminescent tag for construction of a "signal-on" ECL immunosensing method. The Tb-Cu-PA MOF was prepared using Tb³⁺ and Cu²⁺ ions as metal linkers and m-phthalic acid as bridge ligand, and exhibited strong ECL emission with K₂S₂O₈ as a coreactant. The immunosensor was prepared by immobilizing capture antibody on Pd nanoparticles modified Ni-Co layered double hydroxide (Pd-ZIF-67@LDH) nanoboxes, which showed strong electrocatalytic activity toward the reduction of S₂O₈^2- for amplifying the ECL signal. Upon the sandwich-typed immunoreactions, Tb-Cu-PA MOF labeled antibody was introduced onto the immunosensor for sensitive ECL detection of target protein. Using cytokeratin 19 fragment 21-1 (CYFRA21-1), a representative lung cancer biomarker, as target model, the ECL immunosensing method showed a linear range of 0.01-100 ng/mL and a detection limit of 2.6 pg/mL (S/N = 3). This immunosensing strategy highlighted the advances of using luminescent and electroactive MOFs in the developments of highly efficient immunosensors for bioanalysis.

Progress in Metal-Organic Frameworks Facilitated Mercury Detection and Removal

Metal Organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. MOFs were reported in particular for the detection/removal of environmental contaminants, such as heavy metal ions, toxic anions, hazardous gases, explosives, etc. Among heavy metal ions, mercury has been noted as a global hazard because of its high toxicity in the elemental (Hg0), divalent cationic (Hg2+), and methyl mercury (CH3Hg+) forms. To secure the environment and living organisms, many countries have imposed stringent regulations to monitor mercury at all costs. Regarding the detection/removal requirements of mercury, researchers have proposed and reported all kinds of MOFs-based luminescent/non-luminescent probes towards mercury. This review provides valuable information about the MOFs which have been engaged in detection and removal of elemental mercury and Hg2+ ions. Moreover, the involved mechanisms or adsorption isotherms related to sensors or removal studies are clarified for the readers. Finally, advantages and limitations of MOFs in mercury detection/removal are described together with future scopes.

A newly-constructed hydrolytically stable Co(ii) coordination polymer showing dual responsive fluorescence sensing of pH and Cu2+

A novel CP (1), showing distinct dual responsive fluorescence sensing of pH in three continuous stages as well as efficient and selective sensing of Cu²⁺.

Two new NiII and ZnII metal-organic frameworks of glutarate and 1,4-bis[(2-methyl-1H-imidazol-1-yl)methyl]benzene ligands: syntheses, structures and luminescence sensing properties

Two new metal-organic frameworks (MOFs), namely, three-dimensional poly[diaquabis{μ₂-1,4-bis[(2-methyl-1H-imidazol-1-yl)methyl]benzene}bis(μ₂-glutarato)dinickel(II)] monohydrate], {[Ni₂(C₅H₆O₄)₂(C₁₆H₁₈N₄)₂(H₂O)₂]·H₂O}_n or {[Ni₂(Glu)₂(1,4-mbix)₂(H₂O)₂]·H₂O}_n, (I), and two-dimensional poly[[{μ₂-1,4-bis[(2-methyl-1H-imidazol-1-yl)methyl]benzene}(μ₂-glutarato)zinc(II)] tetrahydrate], {[Zn(C₅H₆O₄)(C₁₆H₁₈N₄)]·4H₂O}_n or {[Zn(Glu)(1,4-mbix)]·4H₂O}_n (II), have been synthesized hydrothermally using glutarate (Glu^2-) mixed with 1,4-bis[(2-methyl-1H-imidazol-1-yl)methyl]benzene (1,4-mbix), and characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopy, powder X-ray diffraction, and thermogravimetric and photoluminescence analyses. Ni^II MOF (I) shows a 4-connected 3D framework with point symbol 6⁶, but is not a typical dia network. Zn^II MOF (II) displays a two-dimensional 4⁴-sql network with one-dimensional water chains penetrating the grids along the c direction. The solid-state photoluminescence analysis of (II) was performed at room temperature and the MOF exhibits highly selective sensing toward Fe³⁺ and Cr₂O₇^2- ions in aqueous solution.

A dual-responsive luminescent sensor based on a water-stable Cd(ii)-MOF for the highly selective and sensitive detection of acetylacetone and Cr2O72− in aqueous solutions

Two water-stable cadmium(ii) MOFs were synthesized and characterized. 1 is the first dual-function Cd(ii)-MOF luminescent sensor for sensing acetylacetone and Cr₂O₇²⁻ in aqueous solution with high sensitivity and selectivity and good recyclability.