Design and preparation of a multi-responsive Cd-based fluorescent coordination polymer for smart sensing of nitrobenzene and ornidazole

The improper utilization of nitrobenzene (NB) and ornidazole (ORN) has resulted in irreversible effects on the environment. By combining experimental investigation, density functional theory (DFT) calculations, and machine learning, an effective green strategy for detecting NB and ORN in aqueous solutions can be developed. In this study, a one-dimensional Cd-based coordination polymer (Cd-HCIA-3) was designed and synthesized using 5-((4-carboxybenzyl)oxy)isophthalic acid and rigid 2,2'-bipyridine under solvothermal reaction conditions. Cd-HCIA-3 exhibits excellent fluorescence properties and stability in aqueous solutions. DFT calculations were performed to predict the fluorescence sensing performance of Cd-HCIA-3, revealing that photoinduced electron transfer is the key mechanism for inducing fluorescence quenching in the presence of NB and ORN, with weak molecular interactions promoting electron transfer. Fluorescence sensing experiments were conducted to verify the DFT results, showing that Cd-HCIA-3 can selectively detect NB and ORN in aqueous solutions with limits of detection of 7.22 × 10-8 and 1.31 × 10-7 mol/L, respectively. This study's findings provide valuable insights into the design and synthesis of fluorescent coordination polymers for target analytes.

A 2-fold interpenetrating 3D pillar-layered MOF for the gas separation and detection of metal ions

A 2-fold interpenetrating 3D pillar-layered MOF, which was assembled from a mixed-linker and paddle-wheel cluster, was successfully synthesized. It possesses good thermal and water stability as well as high selectivity for C2H6 over CH4 and CO2 over N2 under ambient conditions, which was further proved by breakthrough experiments. Moreover, this porous material exhibits good detection of Cu2+, [Co(NH3)6]3+ and Fe3+ in an aqueous solution.

A Dy(III) Coordination Polymer Material as a Dual-Functional Fluorescent Sensor for the Selective Detection of Inorganic Pollutants

A Dy(III) coordination polymer (CP), [Dy(spasds)(H2O)2]n (1) (Na2Hspasds = 5-(4-sulfophenylazo)salicylic disodium salt), has been synthesized using a hydrothermal method and characterized. 1 features a 2D layered structure, where the spasda3- anions act as pentadentate ligands, adopting carboxylate, sulfonate and phenolate groups to bridge with four Dy centers in η3-μ1: μ2, η2-μ1: μ1, and monodentate coordination modes, respectively. It possesses a unique (4,4)-connected net with a Schläfli symbol of {44·62}{4}2. The luminescence study revealed that 1 exhibited a broad fluorescent emission band at 392 nm. Moreover, the visual blue color has been confirmed by the CIE plot. 1 can serve as a dual-functional luminescent sensor toward Fe3+ and MnO4- through the luminescence quenching effect, with limits of detection (LODs) of 9.30 × 10-7 and 1.19 × 10-6 M, respectively. The LODs are relatively low in comparison with those of the reported CP-based sensors for Fe3+ and MnO4-. In addition, 1 also has high selectivity and remarkable anti-interference ability, as well as good recyclability for at least five cycles. Furthermore, the potential application of the sensor for the detection of Fe3+ and MnO4- was studied through simulated wastewater samples with different concentrations. The possible sensing mechanisms were investigated using Ultraviolet-Visible (UV-Vis) absorption spectroscopy and density functional theory (DFT) calculations. The results revealed that the luminescence turn-off effects toward Fe3+ and MnO4- were caused by competitive absorption and photoinduced electron transfer (PET), and competitive absorption and inner filter effect (IFE), respectively.

A Eu-MOF-Based Fluorescent Sensing Probe for the Detection of Tryptophan and Cu2+ in Aqueous Solutions

Abnormal tryptophan (Trp) metabolism can be used as an important indicator of chronic hepatitis, paranoia, Parkinson's disease and other diseases. Deficiency or excessive accumulation of Cu2+ can cause diseases such as Wilson's disease and Alzheimer's disease. Eu-based metal-organic framework (Eu-MOF) was successfully prepared for fluorescence sensing of Trp and Cu2+ in an aqueous solution (pH = 7.4). Eu-MOF showed high selectivity and sensitivity for Trp and Cu2+ with detection limits of 0.22 µM and 0.09 µM and Ksv of 6.17 × 103 M- 1 and 2.37 × 104 M- 1 respectively. Trp and Cu2+ had overlapped UV absorption spectra with that of Eu-MOF and competed for the excitation light source. Trp also attenuated the antennae effect of organic ligands on Eu-MOF, thus quenching the red fluorescence of Eu-MOF. This study provides insights into the application of MOFs in bioanalysis and diagnostics.

A Tb3+ ion encapsulated anionic indium-organic framework as logical probe for distinguishing quenching Fe3+ and Cu2+ ions

We successfully synthesized a stable anionic microporous metal-organic framework (MOF) HDU-1 ([Me2NH2]2In2[(TATAB)4(DMF)4](DMF)4(H2O)4) and constructed a fluorescent probe Tb@HDU-1 by an exchange strategy. Because of its suspension distinct fluorescent response of Tb(III) characteristic transition and ligand emission, the Tb@HDU-1 can be used as fluorescent probe for sensing towards Fe3+ and Cu2+ ions. It is surprising that Tb@HDU-1 is used as a ratiometric fluorescent probe for Cu2+ ions while only single peak detection for Fe3+ ions, which describes a particular rare example of a sensor based on Ln-MOFs to distinguish quenching Fe3+ and Cu2+ ions. Hence we designed a molecular logic gate device for making the distinction of Fe3+ and Cu2+ ions more clearly and appropriately. In addition, the different quenching effect between Fe3+ and Cu2+ ions may be ascribed to the differences of competitive absorption and interaction between frameworks and metal ions.

A highly efficient lanthanide coordination polymer luminescent material for the multi-task detection of environmental pollutants

It is challenging to explore novel-structure lanthanide coordination polymers (Ln-CPs) for sensing environmental pollutants. Herein, we designed and synthesized an organic bridging linker 3-(carboxymethoxy)-1-(carboxymethyl) pyrazole-4-carboxylic acid (H3ccpc), and then successfully prepared and characterized a novel Ln-CP, namely [Tb2(ccpc)2(H2O)6]·1.5H2O (ccpcTb). Structural analysis indicates that ccpcTb exhibits a two-dimensional structure, in which Tb ions are in an eight-coordinated environment. The photoluminescence performance of ccpcTb was discussed in detail. The ccpcTb displays bright green luminescence and behaves as a multi-responsive luminescent sensor toward Fe3+ ions, Cr2O72- ions and 2,4,6-trinitrophenol with high selectivity and low detection limits. Furthermore, the possible luminescence sensing mechanisms have been addressed in detail. The luminescence quenching mechanism of sensing Fe3+ and Cr2O72- is attributed to the energy competitive absorption, while that of sensing TNP is due to the synergistic effect of energy competitive absorption and photo-induced electron transfer.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

Two-Dimensional Lanthanide Metal-Organic Frameworks as a Platform for Sensing Pollutant and Nitrophenols Reduction

The discharge of harmful and toxic pollutants in water is destroying the ecosystem balance and human being health at an alarming rate. Therefore, the detection and removal of water pollutants by using stable and efficient materials are significant but challenging. Herein, three novel lanthanide metal-organic frameworks (Ln-MOFs), [La(L)(DMF)2(H2O)2]·H2O (LCUH-104), [Nd(L)(DMF)2(H2O)2]·H2O (LCUH-105), and [Pr(L)(DMF)2(H2O)2]·H2O (LCUH-106) [H3L = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid (H3TZI)] were solvothermally constructed and structurally characterized. In the three Ln-MOFs, dinuclear metallic clusters {Ln2} were connected by deprotonated tetrazol-containing dicarboxylate TZI3- to obtain a 2D layered framework with a point symbol of {42·84}·{46}. Their excellent chemical and thermal stabilities were beneficial to carry out fluorescence sensing and achieve the catalytic nitrophenols (NPs) reduction. Especially, the incorporation of the nitrogen-rich tetrazole ring into their 2D layered frameworks enables the fabrication of Pd nanocatalysts (Pd NPs@LCUH-104/105/106) and have dramatically enhanced catalytic activity by using the unique metal-support interactions between three Ln-MOFs and the encapsulating palladium nanoparticles (Pd NPs). Specifically, the reduction of NPs (2-NP, 3-NP, and 4-NP) in aqueous solution by Pd NPs@LCUH-104 exhibits exceptional conversion efficiency, remarkable rate constants (k), and outstanding cycling stability. The catalytic rate of Pd NPs@LCUH-104 for 4-NP is nearly 8.5 times more than that of Pd/C (wt 5%) and its turnover frequency value is 0.051 s-1, which indicate its excellent catalytic activity. Meanwhile, LCUH-105, as a multifunctional fluorescence sensor, exhibited excellent fluorescence detection of norfloxacin (NFX) (turn on) and Cr2O72- (turn off) with high selectivity and sensitivity at a low concentration, and the corresponding fluorescence enhancement/quenching mechanism has also been systematically investigated through various detection means and theoretical calculations.

Zinc(II)-Based Ring-and-Rod Coordination Layer as an Excitation-Wavelength-dependent Dual-Emissive Chemosensor for Discriminating Fe3+, Cr3+, and Al3+ in Water

The reactions of Zn(NO3)2, 3,6-bis(pyridin-3-yl)-9H-carbazole (bpycz), and 2,5-dihydroxyterephthalic acid (H4dhbdc) or 2-bromoterephthalic acid (Br-1,4-H2bdc) under hydro(solvo)thermal conditions yielded corresponding coordination polymers (CPs) {[Zn(H2dhbdc)(bpycz)]•0.5H2O}n (1) and [Zn(Br-1,4-bdc)(bpycz)]•2DMAc•H2O (2), respectively, with high thermal stability approaching 350 °C. CP 1 adopts a ring-and-rod layer structure, which is topologically described as a 4-connected net with the point symbol of 2•65. Two layers are interpenetrated in parallel interlocking mode to form a double 2D → 2D polyrotaxane entanglement with extra-framework void space of 19.6%. CP 2 has a non-interpenetrating ring-and-rod layer structure of 4-connected 2•65 net topology, with extra-framework void space of 16.6%. Thermally activated 1 and 2 revealed CO2 uptakes of 101.1 and 98.6 cm3 g-1, respectively, at P/P0 = 1 and 195 K. X-ray powder diffraction (XRPD) patterns confirmed that 1 and 2 both possessed high chemical stability in H2O, CH3OH, acetone, and DMF, and framework stability during gas adsorption-desorption. The H2O suspension of 1 displayed excitation-dependent dual-emissive properties, appearing at 432 nm upon excitation at 300 nm and at 528 nm upon excitation at 365 nm. Of note, 1 was capable of detection of Fe3+, Cr3+, and Al3+ ions in H2O, showing good anti-interference ability, excellent selectivity, and high sensitivity. More interesting, the dual-emissive properties make 1 to be an excellent luminescence chemosensor to screen Fe3+, Cr3+, and Al3+ from a pool of metal ions in H2O upon excitation at 300 nm via luminescence quenching effect and then discriminate Fe3+, Cr3+, and Al3+ upon excitation at 365 nm via luminescence quenching, unaltered, and enhancement responses, respectively. On the other hand, the H2O suspension of 2 demonstrated an excitation-independent emission appearing at around 430 nm, which could be utilized to sensitively detect Fe3+ and Cr3+ ions with good anti-interference ability and excellent selectivity via luminescence quenching effect. Further, 1 and 2 were recyclability and possessed cycling stability. The plausible sensing mechanisms for 1 and 2 toward Fe3+, Cr3+, and Al3+ were also explored in detail.

Green Ultrasound-Assisted Synthesis of Rare-Earth-Based MOFs

Rare-earth (RE)-based metal organic frameworks (MOFs) are quickly gaining popularity as flexible functional materials in a variety of technological fields. These MOFs are useful for more than just conventional uses like gas sensors and catalyst materials; in fact, they also show significant promise in emerging technologies including photovoltaics, optical, and biomedical applications. Using yttrium and europium as ionic host centres and dopants, respectively, and 1,3,5-benzenetricarboxylic acid (H3-BTC) as an organic linker, we describe a simple and green approach for the fabrication of RE-MOFs. Specifically, Y-BTCs and Eu-doped Y-BTCs MOFs have been synthesised in a single step using an eco-friendly method that makes use of ultrasound technology. To establish a correlation between the morphological and structural properties and reaction conditions, a range of distinct reaction periods has been employed for the synthetic processes. Detailed analyses of the synthesised samples through powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR) have confirmed the phase formation. Furthermore, thermal analyses such as thermogravimetric analysis (TGA) have been employed to evaluate the thermal stability and structural modifications of the Y-BTC and Eu-doped Y-BTC samples. Finally, the luminescent properties of the synthesised samples doped with Eu3+ have been assessed, providing an evaluation of their characteristics. As a proof of concept, an Eu-doped Y-BTC sample has been applied for the sensing of nitrobenzene as a molecule test of nitro derivatives.

Selective Supramolecular Recognition of Nitroaromatics by a Fluorescent Metal-Organic Cage Based on a Pyridine-Decorated Dibenzodiaza-Crown Macrocyclic Co(II) Complex

Two isomorphous fluorescent (FL) lantern-shaped metal-organic cages 1 and 2 were prepared by coordination-directed self-assembly of Co(II) centers with a new aza-crown macrocyclic ligand bearing pyridine pendant arms (L_py). The cage structures were determined using single-crystal X-ray diffraction analysis, thermogravimetric, elemental microanalysis, FT-IR spectroscopy, and powder X-ray diffraction. The crystal structures of 1 and 2 show that anions (Cl^- in 1 and Br^- in 2) are encapsulated within the cage cavity. 1 and 2 bear two coordinated water molecules that are directed inside the cages, surrounded by the eight pyridine rings at the "bottom" and the "roof" of the cage. These hydrogen bond donors, π systems, and the cationic nature of the cages enable 1 and 2 to encapsulate the anions. FL experiments revealed that 1 could detect nitroaromatic compounds by exhibiting selective and sensitive fluorescence quenching toward p-nitroaniline (PNA), recommending a limit of detection of 4.24 ppm. Moreover, the addition of 50 μL of PNA and o-nitrophenol to the ethanolic suspension of 1 led to a significant large FL red shift, namely, 87 and 24 nm, respectively, which were significantly higher than the corresponding values observed in the presence of other nitroaromatic compounds. The titration of the ethanolic suspension of 1, with various concentrations of PNA (>12 μM) demonstrated a concentration-dependent emission red shift. Hence, the efficient FL quenching of 1 was capable of distinguishing the dinitrobenzene isomers. Meanwhile, the observed red shift (10 nm) and quenching of this emission band under the influence of a trace amount of o- and p-nitrophenol isomers also showed that 1 could discriminate between o- and p-nitrophenol. Replacement of the chlorido with a bromido ligand in 1 generated cage 2 which was a more electron-donating cage than 1. The FL experiments showed that 2 was partially more sensitive and less selective toward NACs than 1.

Green carbon-carbon homocoupling of terminal alkynes by a silica supported Cu(II)-hydrazone coordination compound

A Cu(II) complex, [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH (1), was obtained by the reaction of Cu(NO₃)₂·3H₂O and H2L in methanol solvent (H2L is (E)-4-amino-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide). H2L and compound 1 were characterized by various spectroscopic analyses and the molecular structure of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was determined by single-crystal X-ray analysis. The results indicated the product is a mononuclear Cu(II) complex and contains a free NH₂ functional group on the structure of the ligand. [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was used for the preparation of a heterogeneous catalyst by supporting it on functionalized silica gel. The heterogeneous catalyst (Si-Cu) was prepared by an amidification reaction of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH with functionalized silica gel. The resulting silica-supported catalyst (Si-Cu) was characterized by TGA, FT-IR, EPR, DRS, EDS, XRD, SEM and XPS analyses. Si-Cu was employed in a carbon-carbon coupling reaction and the effects of the amount of Si-Cu and temperature were investigated in the catalytic coupling. The structure of one of the products of the catalytic reactions (C₁₆H₂₂O₂, CP1) was determined by single-crystal X-ray analysis, which proved the formation of a C-C bond and the production of di-acetylene by homocoupling of terminal alkyne. This catalytic system is stable and it can be reused for a coupling reaction without a significant change in its catalytic activity.

A Water-Stable Zn-MOF Used as Multiresponsive Luminescent Probe for Sensing Fe3+/Cu2+, Trinitrophenol and Colchicine in Aqueous Medium

A water-stable Zn-MOF was constructed based on H₂PBA and 1, 10-phenanthroline under solvothermal conditions. The compound exhibited a 3D (2,3,8)-connected (4³)₂(4⁶.6⁶.8¹⁵.12)(8) topology framework. The crystal structure and phase purity of the compound was verified by single crystal X-ray diffraction. Subsequently, some studies on the morphology, structure, and luminescent properties were carried out. The results showed that this compound could be used as a versatile chemosensor for Fe³⁺/Cu²⁺, trinitrophenol and colchicine via a luminescence quenching effect in an aqueous medium.

Design of "turn-off" luminescent Ln-MOFs for sensitive detection of cyanide anions

Two novel 2D lanthanide metal-organic frameworks (Ln-MOFs), namely {[Eu₂(DBTA)₃(DMF)₂]·DMF}_n (1) and {[Tb₂(DBTA)₃(DMF)₂]·DMF}_n (2) (H₂DBTA = 2,5-dibromoterephthalic acid), have been successfully synthesized by the solvothermal method. Single-crystal X-ray diffraction results proved that the complexes possess the same topological structure of a (4²·6)₂(4²·8⁴)(4⁷·6³)₂-connected net. The recognition of CN^- from interfering anions with a low detection limit by "turn-off" luminescence makes them promising candidates for the highly selective and sensitive detection of the cyanide ion. The Ln-MOFs 1 and 2 exhibit excellent chemical sensing properties for CN^- with efficiency, selectivity, and excellent performance in various mixed anions. The evaluation parameters, including the quenching constant and detection limit, have been investigated to obtain the detection performance for CN^-.

Integrating a Luminescent Porous Aromatic Framework into Indicator Papers for Facile, Rapid, and Selective Detection of Nitro Compounds

Porous aromatic framework materials with high stability, sensitivity, and selectivity have great potential to provide new sensors for optoelectronic/fluorescent probe devices. In this work, a luminescent porous aromatic framework material (LNU-23) was synthesized via the palladium-catalyzed Suzuki cross-coupling reaction of tetrabromopyrene and 1,2-bisphenyldiborate pinacol ester. The resulting PAF solid exhibited strong fluorescence emission with a quantum yield of 18.31%, showing excellent light and heat stability. Because the lowest unoccupied molecular orbital (LUMO) of LNU-23 was higher than that of the nitro compounds, there was an energy transfer from the excited LNU-23 to the analyte, leading to the selective fluorescence quenching with a limit of detection (LOD) ≈ 1.47 × 10⁻⁵ M. After integrating the luminescent PAF powder on the paper by a simple dipping method, the indicator papers revealed a fast fluorescence response to gaseous nitrobenzene within 10 s, which shows great potential in outdoor fluorescence detection of nitro compounds.

Design of an antenna effect Eu(III)-based metal-organic framework for highly selective sensing of Fe3

Highly selective sensing of Fe³⁺ is very important due to its great effect on biological systems. A novel ligand [1,1':4',1'':4'',1''':4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H₄qptca) was designed and successfully obtained for the first time via three steps in high total yields according to the absorption spectrum of Fe³⁺. The europium(III)-based metal-organic framework derived from H₄qptca, {[Eu(qptca)_1/2(H₂qptca)_1/2(H₂O)₂]·DMF}_n (referred to as SLX-1), was then synthesized and used as a water-stable and highly selective luminescent sensor for Fe³⁺ in aqueous solution with a comparable detection limit using Ln-MOF probes (6.45 μM) through the antenna effect of SLX-1. Furthermore, the luminescence quenching mechanism was also proposed as a competitive absorption mechanism.

A Eu(iii) metal–organic framework based on anthracenyl and alkynyl conjugation as a fluorescence probe for the selective monitoring of Fe3+ and TNP

In this work, a luminescent metal–organic framework (Eu-MOF {[Eu₆L₆(μ₃-OH)₈(H₂O)₃]₈·H₂O}_n) was constructed by a solvothermal method with a linear organic ligand L (10-[(2-amino-4-carboxyl-phenyl)ethynyl]anthracene-9-carboxylic acid) based on anthracene and alkyne groups and using Eu³⁺ as the metal center. The MOF exhibits a stable UiO-66 crystal structure, and a six-core cluster twelve-linked secondary structural unit was successfully synthesized using 2-fluorobenzoic acid as a modulator, forming a classical fcu topology. Moreover, it exhibits good chemical stability. Interestingly, Eu-MOF exhibited high selectivity and sensitive fluorescence burst properties towards Fe³⁺ ions and 2,4,6-trinitrophenol (TNP) in DMF solution. For Fe³⁺, the K_SV value is 5.06 × 10⁵ M⁻¹ and the LOD value is 5.1 × 10⁻⁷ M. For TNP, the K_SV value is 1.92 × 10⁴ M⁻¹ and the LOD value is 1.93 × 10⁻⁶ M. In addition, Eu-MOF showed good anti-interference ability and fast response. This work provides an excellent fluorescent sensor for the detection of Fe³⁺ and 2,4,6-trinitrophenol (TNP) residues in contaminants.

In this work, Eu-MOF has been synthesized and has excellent luminescence recognition ability for Fe³⁺ and TNP with good selectivity and high sensitivity via luminescence quenching.

Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72

Luminescent Ln-MOFs (Eu0.075Tb0.925-MOF) were successfully synthesised through the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and the ligand pyromellitic acid. The product was characterised by X-ray diffraction (XRD), TG analysis, EM, X-ray photoelectron spectroscopy (XPS), and luminescence properties, and results show that the synthesised material Eu0.075Tb0.925-MOF has a selective ratio-based fluorescence response to Fe3+ or Cr2O72-. On the basis of the internal filtering effect, the fluorescence detection experiment shows that as the concentration of Fe3+ or Cr2O72- increases, the intensity of the characteristic emission peak at 544 nm of Tb3+ decreases, and the intensity of the characteristic emission peak at 653 nm of Eu3+ increases in Eu0.075Tb0.925-MOF. The fluorescence intensity ratio (I653/I544) has a good linear relationship with the target concentration. The detection linear range for Fe3+ or Cr2O72- is 10-100 μM/L, and the detection limits are 2.71 × 10-7 and 8.72 × 10-7 M, respectively. Compared with the sensor material with a single fluorescence emission, the synthesised material has a higher anti-interference ability. The synthesised Eu0.075Tb0.925-MOF can be used as a highly selective and recyclable sensing material for Fe3+ or Cr2O72-. This material should be an excellent candidate for multifunctional sensors.

Multifunctional Zn-Ln (Ln = Eu and Tb) heterometallic metal-organic frameworks with highly efficient I2 capture, dye adsorption, luminescence sensing and white-light emission

A new family of isostructural 3d-4f heterometallic metal-organic frameworks (HMOFs), [Zn₃Eu_xTb_2-x(TZI)₄(DMA)₅(H₂O)₃]·4DMA [x = 0 (1), 0.3 (2), 0.6 (3), 0.9 (4), 1 (5), 1.2 (6), 1.5 (7), 1.8 (8), 2 (9)], has been synthesized using the 5-(4-(tetrazol-5-yl) phenyl)isophthalic acid (H₃TZI) ligand, Ln^III ions and Zn^II ions under solvothermal conditions. All HMOFs exhibit a (3,3,4,5,5)-connected 6³·6³(4²·6²·8²)(4·6⁵·8)(4·6⁶·8³) topology, which features three different types of motifs: one is a mononuclear Zn^II ion and the other two motifs are binuclear [Zn(COO)₃Ln] clusters. The adsorption experiments indicate that Zn₃Tb₂ (1) could efficiently remove almost all I₂ from cyclohexane solution after 12 h and also showed better adsorption towards neutral red (NR) dye (adsorption: only the Zn₃Tb₂ (1) was taken as one representative). Simultaneously, the luminescence sensing showed that Zn₃Tb₂ (1) and Zn₃Eu₂ (9) have excellent response and sensitivity towards pollutants such as Fe³⁺ ions and 2,4,6-trinitrophenol (TNP) with high selectivity and a fairly low limit of detection through luminescence quenching effect. Moreover, seven trimetallic-doped HMOFs 2-8 analogues of Zn₃Ln₂ (single) HMOFs were designed and prepared, showing different changes of luminescent color. More interestingly, Zn₃Eu_1.5Tb_0.5 (7) with white-light emission was fabricated by doping relative concentrations of Eu³⁺ and Tb³⁺ ions. To the best of our knowledge, Zn₃Eu_1.5Tb_0.5 (7) represents a novel kind of heterometallic Zn₃Ln₂ HMOFs with white-light emission. It could be deduced that the excellent characteristics, namely strong typical luminescence emission of Zn^II and Ln^III ions, microporous channels, active open metal sites (tetra-coordinated Zn^II-metal sites), and uncoordinated carboxylate O atoms and uncoordinated tetrazolate N atoms, made the above HMOFs an ideal platform for adsorption, luminescence sensing, and white-light emission. More significantly, these HMOFs are the first reported Zn-Ln heterometallic materials with the H₃TZI ligand.

Highly Fluorescent Cadmium Based Metal-Organic Frameworks for Rapid Detection of Antibiotic Residues, Fe3+ and Cr2O72- Ions

Here, two novel 3D Cd(II)-MOFs, [Cd₃·L·(BTB)₂·2DMF] and [(Cd₃O₂)·L·BTC] (denoted as CUST-532 and CUST-533, L = 9,10-bis(N-benzimidazolyl)-anthracene, BTB = 1,3,5-tris(4-carboxyphenyl) benzene, BTC = 1,3,5-benzenetricarboxylic acid, CUST = Changchun University of Science and Technology), were synthesized by solvothermal conditions. Both CUST-532 and CUST-533 are 3D (3,8)-c topological nets with the same point symbol of {4³}₂{4⁶·6¹⁸·8⁴}. PXRD and TGA analyses prove that CUST-532 and CUST-533 have good structural stability and thermal stability. On the basis of the high fluorescence characteristics, the results of fluorescence sensing experiments show that CUST-532 and CUST-533 can be used as multifunctional chemical sensors to achieve rapid fluorescence quenching response to antibiotic residues, Fe³⁺ and Cr₂O₇^2- ions at a much lower concentration. Furthermore, the possible mechanisms of fluorescence quenching in the sensing process were systematically studied by PXRD, UV-vis, fluorescence decay lifetime, and density functional theory.

Covalent-coordination tandem functionalization of a metal-organic framework (UiO-66) as a hybrid probe for luminescence detection of trans,trans-muconic acid as a biomarker of benzene and Fe3

By means of post-synthetic treatment on the UiO-66 derivative with -SO3H, a novel luminescent hybrid material named Tb3+@UiO-66-SO3H has been prepared simply and efficiently. Given its wonderful luminescence properties like intense green emission, a long lifetime, a robust structure and photostability, it is further developed as a fluorescent probe for the sensing of trans,trans-muconic acid (tt-MA, a biomarker of benzene) and Fe3+, which are closely related to human health. Notably, Tb3+@UiO-66-SO3H shows an outstanding recognition ability for Fe3+ among common cations with a low detection limit (0.11 μM, 0.006 ppm). More importantly, Tb3+@UiO-66-SO3H can realize highly sensitive and selective detection of tt-MA (detection limit, 0.58 μM, 0.083 ppm). Besides, this rapid response probe is facilely prepared, non-toxic and reusable, showing the potential of Tb3+@UiO-66-SO3H in the practical monitoring of tt-MA and Fe3+.

Multidimensional Ln-Aminophthalate Photoluminescent Coordination Polymers

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach. One- and two-dimensional (1D and 2D) LnCPs were prepared from 5-aminoisophthalic acid and Sm³⁺/Tb³⁺ using hydrothermal and/or microwave-assisted synthesis. The unprecedented LnCPs were characterized by single-crystal X-ray diffraction (SCRXD), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), and their photoluminescence (PL) properties were studied in the solid state, at room temperature, using the CPs as powders and encapsulated in poly(methyl methacrylate (PMMA) films, envisaging the potential preparation of devices for sensing. The materials revealed interesting PL properties that depend on the dimensionality, metal ion, co-ligand used and water content.

A Facile One-Pot Approach to the Synthesis of Gd-Eu Based Metal-Organic Frameworks and Applications to Sensing of Fe3+ and Cr2O72- Ions

Gadolinium metal-organic frameworks (Gd-MOFs) and Eu-doped Gd-MOFs have been synthesized through a one-pot green approach using commercially available reagents. The 1,4-benzenedicarboxylic acid (H2-BDC) and 2,6-naphthalenedicarboxylic acid (H2-NDC) were chosen as ditopic organic linkers to build the 3D structure of the network. The Gd-MOFs were characterized using powder X-ray diffraction (XRD), FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM) and N2 adsorption-desorption analysis. The Gd-MOF structures were attributed comparing the XRD patterns, supported by the FT-IR spectra, with data reported in the literature for Ln-MOFs of similar lanthanide ionic radius. FE-SEM characterization points to the effect of the duration of the synthesis to a more crystalline and organized structure, with grain dimensions increasing upon increasing reaction time. The total surface area of the MOFs has been determined from the application of the Brunauer-Emmett-Teller method. The study allowed us to correlate the processing conditions and ditopic linker dimension to the network surface area. Both Gd-MOF and Eu-doped Gd-MOF have been tested for sensing of the inorganic ions such as Fe3+ and Cr2O72-.

An excellent water-stable 3D Zn-MOF with 8-fold interpenetrated diamondoid topology showing “turn-on/turn-off” luminescent detection of Al3+ and SNT in aqueous media

An excellent water-stable 3D Zn-MOF with 8-fold interpenetrated diamondoid topology acts as a bi-responsive chemical sensor for “turn-on” and “turn-off” luminescent detection of Al3+ and SNT in aqueous media, respectively.