2D Cd(II)–Lanthanide(III) Heterometallic–Organic Frameworks Based on Metalloligands for Tunable Luminescence and Highly Selective, Sensitive, and Recyclable Detection of Nitrobenzene

Advance Progress on Luminescent Sensing of Nitroaromatics by Crystalline Lanthanide-Organic Complexes

Water environment pollution is becoming an increasingly serious issue due to industrial pollutants with the rapid development of modern industry. Among many pollutants, the toxic and explosive nitroaromatics are used extensively in the chemical industry, resulting in environmental pollution of soil and groundwater. Therefore, the detection of nitroaromatics is of great significance to environmental monitoring, citizen life and homeland security. Lanthanide-organic complexes with controllable structural features and excellent optical performance have been rationally designed and successfully prepared and used as lanthanide-based sensors for the detection of nitroaromatics. This review will focus on crystalline luminescent lanthanide-organic sensing materials with different dimensional structures, including the 0D discrete structure, 1D and 2D coordination polymers and the 3D framework. Large numbers of studies have shown that several nitroaromatics could be detected by crystalline lanthanide-organic-complex-based sensors, for instance, nitrobenzene (NB), nitrophenol (4-NP or 2-NP), trinitrophenol (TNP) and so on. The various fluorescence detection mechanisms were summarized and sorted out in the review, which might help researchers or readers to comprehensively understand the mechanism of the fluorescence detection of nitroaromatics and provide a theoretical basis for the rational design of new crystalline lanthanide-organic complex-based sensors.

A facile strategy of using MoS2 quantum dots for fluorescence-based targeted detection of nitrobenzene

We present a simple approach for producing photoluminescent MoS₂ quantum dots (QDs) using commercial MoS₂ powder as a precursor along with NaOH and isopropanol. The synthesis method is particularly easy and environmentally friendly. The successful intercalation of Na⁺ ions into MoS₂ layers and subsequent oxidative cutting reaction leads to the formation of luminescent MoS₂ QDs. The present work, for the first time, shows the formation of MoS₂ QDs without any additional energy source. The as-synthesized MoS₂ QDs were characterized using microscopy and spectroscopy. The QDs have a few layer thicknesses and a narrow size distribution with an average diameter of ∼3.8 nm. Nitrobenzene (NB), an industrial chemical, is both toxic to human health and dangerously explosive. The present MoS₂ QDs can be used as an effective photoluminescent probe, and a new turn-off sensor for NB detection. The selective quenching was operated via multiple mechanisms; electron transfer between the nitro group and MoS₂ QDs through dynamic quenching and the primary inner filter effect (IFE). The quenching has a linear relationship with NB concentrations from 0.5 μM to 11 μM, with a calculated detection limit of 50 nM.

Multicomponent Anti-Kasha's Rule Emission from Nanotubular Metal-Organic Frameworks for Selective Detection of Small Molecules

The peak photoluminescence (PL) of conventional fluorophores is independent of the excitation wavelength (called Kasha's rule), while the search of metal-organic framework materials with the so-called anti-Kasha's rule emission remains very limited. Herein, we report the observation of anti-Kasha's rule emission in a multicomponent PL three-dimensional nanotubular metal-organic framework (abbr. MOF-NT), [Zn(μ-L)(μ-bix)]_n·0.33nH₂O [H₂L = biphenyl-3,5-dicarboxylic acid; bix = 1,4-bis(imidazole-1-ylmethyl)benzene]. The MOF-NT crystalline sample represents a notable example of strong excitation-dependent fluorescence from the ultraviolet to the visible spectral region. Moreover, by virtue of electronic flexibility and high PL efficiency, MOF-NT shows a discriminative PL response between isomeric nitroaromatic compounds. The work demonstrated the intrinsic anti-Kasha's rule emission in the crystalline-state MOF materials, providing new visions for the development of advanced solid-state emissive materials.

Ultrasensitive fluorescence detection of norfloxacin in aqueous medium employing a 2D Zn(ii)-based coordination polymer

A 2D fluorescent coordination polymer, {[Zn(L)0.5(mip)] 1.75H2O}n (1), was successfully assembled. 1 was developed as an ultrasensitive fluorescent probe for the sensing of norfloxacin (NOR) in water.

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.

A multi-functional two-dimensional Zn(ii)-organic framework for selective carbon dioxide adsorption, sensing of nitrobenzene and Cr2O72−

A novel two-dimensional coordination polymer {[(CH3)2NH2][Zn2(L)2]·DMF}n was synthesized. It exhibits good selective adsorption for CO2; moreover, it shows high selectivity and sensitivity for NB and Cr2O72− ions.

Luminescent metal–organic frameworks as chemical sensors based on “mechanism–response”: a review

The comprehensive review systematically summarizes the recent developments in the study of LMOFs as chemical sensors based on “mechanism–response”.

A series of lanthanide–quinoxaline-2,3(1H,4H)-dione complexes containing 1D chiral Ln2O3 (Ln = Eu, Tb, Sm, Dy) chains: luminescent properties and response to small molecules

A series of isostructural lanthanide–quinoxaline-2,3(1H,4H)-dione containing 1D chiral chains shows high sensing effect toward the small solvent molecules, in which tertiary butanol was an excellent sensitizer, while tetrahydrofuran was a highly quenching species.

Boosting CO2 adsorption and selectivity in metal–organic frameworks of MIL-96(Al) via second metal Ca coordination

Aluminum trimesate-based MOF (MIL-96-(Al)) has attracted intense attention due to its high chemical stability and strong CO₂ adsorption capacity. In this study, CO₂ capture and selectivity of MIL-96-Al was further improved by the coordination of the second metal Ca. To this end, a series of MIL-96(Al)–Ca were hydrothermally synthesised by a one-pot method, varying the molar ratio of Ca²⁺/Al³⁺. It is shown that the variation of Ca²⁺/Al³⁺ ratio results in significant changes in crystal shape and size. The shape varies from the hexagonal rods capped in the ends by a hexagonal pyramid in MIL-96(Al) without Ca to the thin hexagonal disks in MIL-96(Al)–Ca4 (the highest Ca content). Adsorption studies reveal that the CO₂ adsorption on MIL-96(Al)–Ca1 and MIL-96(Al)–Ca2 at pressures up to 950 kPa is vastly improved due to the enhanced pore volumes compared to MIL-96(Al). The CO₂ uptake on these materials measured in the above sequence is 10.22, 9.38 and 8.09 mmol g⁻¹, respectively. However, the CO₂ uptake reduces to 5.26 mmol g⁻¹ on MIL-96(Al)–Ca4. Compared with MIL-96(Al)–Ca1, the N₂ adsorption in MIL-96(Al)–Ca4 is significantly reduced by 90% at similar operational conditions. At 100 and 28.8 kPa, the selectivity of MIL-96(Al)–Ca4 to CO₂/N₂ reaches up to 67 and 841.42, respectively, which is equivalent to 5 and 26 times the selectivity of MIL-96(Al). The present findings highlight that MIL-96(Al) with second metal Ca coordination is a potential candidate as an alternative CO₂ adsorbent for practical applications.

MIL-96(Al)–Ca1 shows the highest CO₂ adsorption capacity; while MIL-96(Al)–Ca4 displays a distinguished morphology with the highest selectivity of CO₂/N₂.

A water-stable EuIII-based MOF as a dual-emission luminescent sensor for discriminative detection of nitroaromatic pollutants

This work reports a water-stable Eu^III-based MOF as the first MOF sensor for detecting nitroaromatic compounds discriminatively by ratiometric methods.

A 3D pillared-layer metal–organic framework with fluorescence property for detection of nitroaromatic explosives

A novel pillared-layer Cd-MOF was synthesized as luminescent sensor for detection of nitroaromatic explosives with highly selective and recyclable properties. The study also shows that the photoinduced electron transfer and resonance energy transfer were possible mechanisms of fluorescence quenching.

Lanthanide-MOFs constructed from mixed dicarboxylate ligands as selective multi-responsive luminescent sensors

Five novel Ln-MOFs associated with the mixed ligands of 4-(pyridin-3-yloxy)-phthalic acid (H₂ppda) and terephthalic acid (H₂bdc), namely, [Ln(ppda)(bdc)_0.5(C₂H₅OH)(H₂O)]_n (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) were synthesized under the solvothermal conditions. Compounds 1-5 exhibit the isostructural 2D layered structures. The solid-state luminescence properties of compounds 1, 2, 4 and 5 were investigated in detail. It was found that compound 4 not only detected nitrobenzene derivatives-based explosives with high selectivity, sensitivity, and recyclability, but also served as an excellent selective sensing material for Fe³⁺ ion and Cr₂O₇^2- ion. In particular, it is worth noting that the detection limit of TNP can reach 3.0 × 10^-8 M. It was found that the free oxygen atoms of the ether bond, which function as the Lewis basic sites in Ln-MOFs, might interact with metal ions. In addition, the sensing mechanisms of 4 for different analytes were explored further.

Two novel lanthanide(III) organic frameworks based on a biphenyltetracarboxylate ligand: synthesis, structure and magnetic and luminescence properties

Two new two-dimensional lanthanide coordination polymers, namely poly[[tetra-μ₂-acetato-tetraaquabis(μ₄-biphenyl-3,3',5,5'-tetracarboxylato)tetrakis(dimethylacetamide)tetraterbium(III)] pentahydrate], {[Tb₄(C₁₆H₆O₈)₂(C₂H₃O₂)₄(C₄H₉NO)₄(H₂O)₄]·5H₂O}_n, (1), and poly[[tetra-μ₂-acetato-tetraaquabis(μ₅-biphenyl-3,3',5,5'-tetracarboxylato)tetrakis(dimethylacetamide)tetraeuropium(III)] tetrahydrate], {[Eu₄(C₁₆H₆O₈)₂(C₂H₃O₂)₄(C₄H₉NO)₄(H₂O)₄]·4H₂O}_n, (2), have been synthesized from biphenyl-3,3',5,5'-tetracarboxylic acid (H₄bpt) and Ln(NO₃)₃·6H₂O (Ln = Tb and Eu) under solvothermal conditions. Single-crystal X-ray structure analysis shows that the two compounds are isostructural and crystallize in the monoclinic P2₁/n space group. The crystal structures are constructed from bpt^4- ligands (as linkers) and {Ln₂(μ₂-CH₃COO)₂} building units (as nodes), which topological analysis shows to be a (4,6)-connected network with sql topology. Compounds (1) and (2) have been characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and fluorescence analysis in the solid state. In addition, a magnetic investigation shows the presence of antiferromagnetic interactions in compound (1).

Mg1−xCoxLi2(3,5-pdcH)2(DMF)2 (x = 0, 0.285, 0.575, 1): a series of heterometallic coordination polymers doped with magnetic Co2+ ions

Presented is a series of Mg_1−xCo_xLi-HCPs with the turn-on effect of anti-ferromagnetic properties upon the doping of high-spin Co²⁺ ions at Mg²⁺ sites.

Highly selective luminescence sensing for the detection of nitrobenzene and Fe3+ by new Cd(ii)-based MOFs

Herein, three Cd(ii)-based MOFs were assembled, and the complex 3 showed a high selectivity in the detection of nitrobenzene and Fe³⁺.

Design and application of a fluorogenic receptor for selective sensing of cations, small neutral molecules, and anions

An unprecedented single multi-analyte fluorogenic receptor, a sodium salt of N-(methyl-2-thiophenyl)-tyrosine (NaHTyrthio), is reported for the selective sensing of cations (Cu²⁺), small neutral molecules (nitrobenzene and aniline) and anions (F⁻) by variable spectral responses.

Novel double layer lanthanide metal–organic networks for sensing applications

Two isostructural lanthanide-based 2D coordination polymers were synthesized under hydrothermal conditions and fully characterized. The obtained compounds display notable sensing ability for p-phenylenediamine, benzidine, and acetone analytes.

A 3D metal–organic framework with dual-aerial-octahedral trinucleate building units: synthesis, structure and fluorescence sensing properties

JLNU-2 can be used to detect nitrobenzene with high selectivity, sensitivity, anti-interference ability and recyclability through tracing the fluorescence quenching behaviour.

A new three-dimensional zinc-based metal-organic framework as a fluorescent sensor for detection of cadmium ion and nitrobenzene

In this study, a novel three-dimensional zinc-based metal-organic framework (Zn-MOF), i.e., {Zn₂(L)₂(DMF)₂H₂O}_n (L = 2,5-bis(phenylamino)-1,4-benzenedicarboxylic acid) was designed and developed under solvothermal condition. As a proof-of-principle, a π-conjugated framework of carboxylate ligand capable of "bottom up" synthesis was integrated with metal ion to construct a novel MOF for sensing applications. As expected, the synthesized Zn-MOF exhibited fluorescence enhancement for cadmium ion (Cd²⁺) and sensing of nitrobenzene (NB) through fluorescence quenching. The detection limits were calculated to be 0.12 μM for Cd²⁺ and 1.19 μg mL^-1 for NB based on signal-to-noise ratio of 3:1. Moreover, various techniques and density functional theory investigations verified that the possible sensing mechanisms for Cd²⁺ and NB included ion exchange and photoinduced electron transfer, respectively. Finally, their practical applications on real samples also demonstrated that the Zn-MOF-based sensor can be effectively utilized for detection and imaging of Cd²⁺ present in the real water samples and living cells. This study may inspire future research and design of target fluorescent MOFs with specific functions.

A twofold interpenetrating three-dimensional heterometallic metal–organic framework with pcu topology based on 2-methylbiphenyl-4,4′-dicarboxylic acid

The 2-methylbiphenyl-4,4′-dicarboxylate (mbpdc2−) ligand has versatile coordination modes and can be used to construct multinuclear structures. Despite this, reports of the synthesis of coordination complexes involving this ligand are scarce. The title compound, poly[[triaquadi-μ3-hydroxido-hexakis(μ4-2-methylbiphenyl-4,4′-dicarboxylato)calcium(II)hexazinc(II)] monohydrate], {[CaZn6(C15H10O4)6(OH)2(H2O)3]·H2O} n , has been prepared by the hydrothermal assembly of Zn(NO3)2·6H2O, CaCl2 and 2-methylbiphenyl-4,4′-dicarboxylic acid. Two ZnII atoms adopt a four-coordinated distorted tetrahedral geometry by bonding to three O atoms from three different 2-methylbiphenyl-4,4′-dicarboxylate (mbpdc2−) dianionic ligands and one bridging hydroxide O atom. For the remaining ZnII atom, a five-coordinate environment is completed half the time by one carboxylate O atom, and then the same carboxylate O atom and an aqua O atom are present the other half of the time, giving a six-coordinate environment. The CaII atom is coordinated by six O atoms to give an octahedral coordination geometry. The supramolecular secondary building unit (SBU) is a hamburger-like heptanuclear unit (Zn6CaO30) and these units are interconnected through mbpdc2− carboxylate groups to generate a three-dimensional framework with the pcu topology. The single net leaves voids that are filled by mutual interpenetration of an independent equivalent framework in a twofold interpenetrating architecture. The title compound shows thermal stability up to 673 K. The excitation and luminescence data showed the emission of a bright-blue fluorescence.

Water-stable Eu-MOF fluorescent sensors for trivalent metal ions and nitrobenzene

We have synthesized two functionalized Eu-MOFs and found that the MOFs are promising luminescent probes for selectively sensing metal ions (Fe³⁺and Cr³⁺) and nitrobenzene.

Lanthanide doped coordination polymers with tunable afterglow based on phosphorescence energy transfer

Lanthanide ion doped coordination polymers (CPs) exhibit an unusual red/green afterglow with long photoemission lifetimes (10.54 ms for Eu³⁺ and 57.66 ms for Tb³⁺) due to the phosphorescence energy transfer at room temperature.

A series of Mg–Zn heterometallic coordination polymers: synthesis, characterization, and fluorescence sensing for Fe3+, CS2, and nitroaromatic compounds

Herein, three luminescent Mg–Zn coordination polymers were constructed, which demonstrated high fluorescence sensing of Fe³⁺, CS₂, and nitro explosive compounds.