A rare earth metal-organic framework material, a preparation method and application thereof

Abstract

The application provides a rare earth metal-organic framework material, a preparation method and application thereof, relates to the field of fluorescent detection technology, and the general formula of the material is {[Ln4(THBA)2(H2O)5]·4H2O} n , wherein Ln is Eu 3+ , or Tb 3+ ; THBA is a deprotonated [1,1',4',1''-triphenyl] 2',3,3',5,5',5''-hexacarboxylic acid ligand; the material belongs to a triclinic system, the space group is P 1, has a three-dimensional porous framework structure, and each Ln 3+ ion is in an octahedral coordination; n is greater than or equal to 1, and n is an integer. The material not only shows high sensitivity, high selectivity and rapid response detection capability for harmful substances malachite green, but also successfully realizes conversion from a powder material to a portable device, and has wide application prospects in the fields of environmental monitoring, food safety and information encryption.

Description

Technical Field

[0001] This invention relates to the field of detection technology, and in particular to a rare earth metal-organic framework material, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of hybrid porous materials composed of metal ions or clusters and organic linkers. Over the past few decades, these materials have attracted considerable research attention due to their defining characteristics, such as extremely high specific surface area, structural tunability, and designable pore environments. This makes them superior to many traditional porous materials. Among the various MOF families, materials doped with lanthanides (Ln-MOFs) are considered particularly promising luminescent materials. This prominence is attributed to the unique photophysical properties of lanthanides, including large Stokes shifts, sharp characteristic emission lines, and long emission lifetimes. The "antenna effect" is considered a key advantage of lanthanide metal-organic frameworks (Ln-MOFs) as luminescent materials, where organic ligands efficiently absorb light energy and transfer it to lanthanide ions, resulting in enhanced luminescence. This inherent luminescent property readily interacts with guest molecules, thus lanthanide metal-organic framework materials (Ln-MOFs) exhibit great application potential as fluorescence sensors. The ability to tailor their structure by selecting specific metal ions and multifunctional organic linkers enables the rational design of sensors with high selectivity and sensitivity to a wide range of analytes. From ions and small molecules to biological macromolecules.

[0003] With increasing public concern about environmental pollution and biosafety threats, the demand for sensing materials capable of detecting hazardous substances is constantly growing across various sectors. Malachite green (MG), as a synthetic material, has historically been widely used in aquaculture as a bactericide and antiparasitic agent due to its low cost and significant bactericidal effect. However, because MG and its metabolite, white malachite green, are highly toxic, carcinogenic, and mutagenic, posing a serious threat to human health, many countries currently strictly prohibit or severely restrict their use. Furthermore, because this substance persists in aquatic environments and bioaccumulates in the food chain, it is necessary to develop rapid, sensitive, and on-site detection methods to monitor its illegal use and environmental residues.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a rare-earth metal-organic framework material, its preparation method, and its applications. This material not only exhibits high sensitivity, high selectivity, and rapid response in detecting the harmful substance malachite green, but also successfully realizes the transformation from powder material to portable devices, showing broad application prospects in environmental monitoring, food safety, and information encryption.

[0006] In order to achieve the objective of this invention, the following technical solution is adopted:

[0007] This invention provides a rare earth metal-organic framework material, the general formula of which is: {[Ln4(THBA)2(H2O)5]·4H2O} n Where Ln is Eu 3+ or Tb 3+ ;

[0008] THBA is a deprotonated [1,1',4',1''-terphenyl]-2',3,3',5,5',5''-hexacarboxylic acid ligand;

[0009] The material belongs to the triclinic crystal system, space group [missing information]. P 1. It has a three-dimensional porous frame structure, each Eu 3+ or Tb 3+ All ions are octagonal in configuration;

[0010] n≥1, and n is an integer.

[0011] Furthermore, the three-dimensional porous framework structure is formed by connecting binuclear lanthanide clusters as nodes through THBA ligands, and the porosity of the three-dimensional porous framework structure is 7.7%.

[0012] This invention also provides a method for preparing the above-mentioned rare earth metal-organic framework material, comprising the following steps:

[0013] S1. H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid solution were reacted to obtain colorless needle-like crystals;

[0014] S2. Place the colorless needle-like crystals in a mixed solvent composed of N,N-dimethylformamide and deionized water, and transfer them to a reaction vessel;

[0015] S3. The reaction vessel is lined with polytetrafluoroethylene for the reaction, and then the reaction temperature is adjusted to room temperature to obtain product crystals.

[0016] S4. The product is crystallized, filtered, washed with DMF, and dried under vacuum to obtain the final product.

[0017] Furthermore, the molar ratio of H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid in S1 is (1-3):(2-4):(2-4).

[0018] Furthermore, the molar ratio of H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid in S1 is 1:2:2.

[0019] Furthermore, the volume ratio of N,N-dimethylformamide to deionized water in S2 is 1:(3-5).

[0020] Furthermore, the volume ratio of N,N-dimethylformamide to deionized water in S2 is 1:4.

[0021] Furthermore, in S3, the reaction temperature for using polytetrafluoroethylene as a liner is 145°C, and the reaction time is 72 hours.

[0022] The present invention also provides a sensing membrane, which is made by mixing the above-mentioned rare earth metal-organic framework material with polymethyl methacrylate in N,N-dimethylformamide.

[0023] Furthermore, the mass ratio of rare earth metal-organic framework material to polymethyl methacrylate in N,N-dimethylformamide is 1:10.

[0024] The present invention also provides an invisible anti-counterfeiting ink, which is made by mixing the above-mentioned rare earth metal-organic framework material with a mixture of ethanol and ethylene glycol.

[0025] Furthermore, ethanol and ethylene glycol are mixed at a volume ratio of 1:5.

[0026] The present invention also provides a fluorescence sensor comprising the above-mentioned rare earth metal-organic framework material.

[0027] This invention also provides the application of the above-mentioned rare earth metal-organic framework materials in the preparation of chemical sensing materials, or in the visible light fluorescence detection of MG and DPA.

[0028] The present invention has the following technical effects:

[0029] The material of this invention possesses a robust three-dimensional porous framework structure and an eight-coordinate configuration, endowing it with excellent thermal and chemical stability and ensuring its reliability in complex real-world environments. This structure can effectively transfer the energy absorbed by the ligands to rare-earth ions through the "antenna effect," exciting strong and sharp characteristic fluorescence from europium (red light) and terbium (green light) ions, laying the foundation for high-contrast fluorescence sensing and visualization applications. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1Example 1: Characterization of the finished product, wherein (a) is an asymmetric unit of europium-based metal-organic framework (Eu-MOF); (b) is an Eu... 3+ (c) Schematic diagram of the coordination geometry of the ions; (d) Schematic diagram of the coordination mode of Eu-MOF; (e) Schematic diagram of the two-dimensional structure of Eu-MOF; (f) Schematic diagram of the three-dimensional structure of Eu-MOF;

[0032] Figure 2 PXRD spectra of Tb-MOF and Eu-MOF, where (a) is the PXRD spectrum of Tb-MOF; and (b) is the PXRD spectrum of Eu-MOF.

[0033] Figure 3 Thermogravimetric maps of Tb-MOF and Eu-MOF;

[0034] Figure 4 PXRD spectra of Eu-MOF after immersion in solutions with different solvents and pH values, where (a) is the PXRD spectrum of Eu-MOF after immersion in solutions with different solvents; and (b) is the PXRD spectrum of Eu-MOF after immersion in solutions with different pH values.

[0035] Figure 5 PXRD spectra of Tb-MOF after soaking in solutions with different solvents and pH values, where (a) is the PXRD spectrum of Tb-MOF after soaking in different solvents; (b) is the PXRD spectrum of Tb-MOF after soaking in solutions with different pH values.

[0036] Figure 6 The luminescence intensity and anti-interference performance of Eu-MOF after the addition of different small molecules, where (a) is the luminescence intensity of Eu-MOF after the addition of different small molecules; (b) is the anti-interference performance of Eu-MOF after the addition of different small molecules.

[0037] Figure 7 The fluorescence changes and linear fitting of Eu-MOF and Tb-MOF with the addition of MG molecules are shown in (a) for the fluorescence change of Eu-MOF, (b) for the linear fitting of Eu-MOF, (c) for the fluorescence change of Tb-MOF, and (d) for the linear fitting of Tb-MOF.

[0038] Figure 8 The time response and cyclic performance of Eu-MOF are shown in (a) and (b) respectively.

[0039] Figure 9XRD and infrared spectra of Eu-MOF after five cycles of MG, where (a) is the XRD spectrum of Eu-MOF after five cycles of MG; and (b) is the infrared spectrum of Eu-MOF after five cycles of MG.

[0040] Figure 10 Comparison of fluorescence film luminescence, where (a) is Eu-MOF fluorescent film; (b) is Eu-MOF@MG fluorescent film; (c) is Eu-MOF@DPA fluorescent film; (d) is Tb-MOF fluorescent film; (e) is Tb-MOF@MG fluorescent film; and (f) is Tb-MOF@MG fluorescent film.

[0041] Figure 11 The luminescence behavior of fluorescent products, wherein (a) is an invisible ink pen mark; (b) is an ink pen holder; (c) is the luminescence behavior of a syringe under sunlight; (d) is the luminescence behavior of an invisible ink pen mark under ultraviolet light irradiation; (e) is the luminescence behavior of an ink pen holder; and (f) is the luminescence behavior of a syringe under ultraviolet light irradiation. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] In a first aspect, the present invention provides a rare earth metal-organic framework material, the general formula of which is: {[Ln4(THBA)2(H2O)5]·4H2O} n Where Ln is Eu 3+ or Tb 3+ ;

[0044] THBA is a deprotonated [1,1',4',1''-terphenyl]-2',3,3',5,5',5''-hexacarboxylic acid ligand;

[0045] The material belongs to the triclinic crystal system, space group [missing information]. P 1. It has a three-dimensional porous frame structure, with each Eu... 3+ or Tb 3+ All ions are octagonal in configuration;

[0046] n≥1, and n is an integer.

[0047] In some embodiments, the three-dimensional porous framework structure is formed by connecting binuclear lanthanide clusters as nodes via THBA ligands, and the porosity of the three-dimensional porous framework structure is 7.7%.

[0048] A three-dimensional porous framework was constructed using rigid, multidentate-coordinated H6THBA organic ligands and lanthanide ions. This structure provides the basis for the "antenna effect": the ligands effectively absorb ultraviolet light and efficiently transfer energy to rare earth ions, exciting the latter to produce strong and pure characteristic fluorescence.

[0049] Triclinic crystal system P A space group and an eight-coordinate three-dimensional network composed of binuclear cluster nodes and rigid ligands together form a robust framework structure. This allows the material's internal porosity (7.7%) to be maintained under varying thermal and chemical environments, which is key to its potential for practical applications. The material produces a high-intensity, sharply shaped red (Eu) color. 3+ ) or green (Tb 3+ The material exhibits characteristic fluorescence and a high signal-to-noise ratio, making it highly suitable for fluorescence sensing and visualization applications. This three-dimensional framework structure endows the material with excellent thermal and chemical stability, enabling it to withstand high temperatures and various organic solvents, as well as acidic and alkaline solutions with different pH values, ensuring its reliability for long-term use in complex real-world environments.

[0050] Secondly, the present invention also provides a method for preparing the above-mentioned rare earth metal-organic framework material, comprising the following steps:

[0051] S1. H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid solution were reacted to obtain colorless needle-like crystals;

[0052] S2. Place the colorless needle-like crystals in a mixed solvent composed of N,N-dimethylformamide and deionized water, and transfer them to a reaction vessel;

[0053] S3. The reaction vessel is lined with polytetrafluoroethylene for the reaction, and then the reaction temperature is adjusted to room temperature to obtain product crystals.

[0054] S4. The product is crystallized, filtered, washed with DMF, and dried under vacuum to obtain the final product.

[0055] In some embodiments, the molar ratio of H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid in S1 is (1-3):(2-4):(2-4).

[0056] In some embodiments, the molar ratio of H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid in S1 is 1:2:2.

[0057] In some embodiments, the volume ratio of N,N-dimethylformamide to deionized water in S2 is 1:(3-5).

[0058] In some embodiments, the volume ratio of N,N-dimethylformamide to deionized water in S2 is 1:4.

[0059] A solvothermal method was employed, providing an ideal environment for slow and orderly crystal growth at a specific temperature (145°C) and time (72 h), ensuring high crystallinity and phase purity of the product. The molar ratio of key reactants (H6THBA, Ln salt, and o-fluorobenzoic acid) and the volume ratio of the mixed solvent (DMF / H2O) were determined. O-fluorobenzoic acid acts as a modulator, competitively coordinating the metal centers, promoting the formation of a specific crystal structure, and preventing precipitation, thereby obtaining high-quality needle-like single crystals.

[0060] This method is simple to operate, has well-defined conditions, and achieves high yield. It can stably and repeatedly prepare high-purity Ln-MOF crystals with consistent structures, laying the foundation for large-scale preparation. Furthermore, the obtained materials are single-crystal materials, which is beneficial for structural analysis and performance studies. The powder samples also exhibit good phase purity, ensuring the consistency of subsequent sensing performance.

[0061] Thirdly, the present invention provides a sensing membrane made of the above-mentioned rare earth metal-organic framework material and polymethyl methacrylate mixed with N,N-dimethylformamide.

[0062] In some embodiments, the rare earth metal-organic framework material and polymethyl methacrylate are in a mass ratio of 1:10 in N,N-dimethylformamide.

[0063] Fourthly, the present invention provides an invisible anti-counterfeiting ink, which is made by mixing the above-mentioned rare earth metal-organic framework material with a mixture of ethanol and ethylene glycol.

[0064] In some embodiments, ethanol and ethylene glycol are mixed at a volume ratio of 1:5.

[0065] Fifthly, the present invention provides a fluorescence sensor comprising the above-mentioned rare earth metal-organic framework material.

[0066] By combining powdered Ln-MOFs with a polymer matrix (PMMA) to create flexible sensing films, coating them onto the surface of LED chips, or dispersing them in alcohol solvents to create invisible inks, the intrinsic fluorescence properties of the materials are essentially endowed to different physical forms and carriers. When these devices come into contact with analytes (such as MG) or are excited by ultraviolet light, the fluorescence quenching or emission characteristics of the materials are manifested at the macroscopic device level, thereby achieving detection or anti-counterfeiting functions.

[0067] This represents a successful leap from laboratory powder samples to portable, naked-eye observable devices. The sensing film and LED beads enable rapid on-site detection. The developed device can not only detect malachite green, but its invisible ink properties can also be extended to advanced anti-counterfeiting markings and information encryption, achieving a "write-and-hide, UV-visible" effect with a wide range of applications.

[0068] In a sixth aspect, the present invention provides the application of the above-mentioned rare earth metal-organic framework materials in the preparation of chemical sensing materials, or in the visible light fluorescence detection of MG and DPA.

[0069] The following is a detailed explanation using specific embodiments:

[0070] Example 1:

[0071] Colorless needle-like crystals were obtained by a solvothermal reaction of H6THBA (25 mg, 0.05 mmol), Eu(NO3)3·6H2O (45 mg, 0.1 mmol) and o-fluorobenzoic acid powder (100 mg, 0.1 mmol).

[0072] 71 mmol of the compound was placed in 5 mL of a mixed solvent of N,N-dimethylformamide (DMF) and deionized water (volume ratio 1:4), and then transferred to a 25 mL stainless steel reactor. Polytetrafluoroethylene (PTFE) was used as a liner, and the reaction was carried out at 145°C for 72 hours, followed by slow cooling in an oven to room temperature. The crystalline product was filtered, washed with DMF, and dried under vacuum, designated as Eu-MOF, with a yield of 67%.

[0073] Fourier spectroscopy: FT-IR (KBr, v / cm -1 ): 3891(w), 3745(w), 3612(w), 3522(w),2793(w), 1651(m), 1603(s), 1541(s), 1442(s), 1395(s), 1252(m), 1150(w), 1115(w), 1019(w), 943(w), 834(m), 775(m), 736(m), 587(w), 521(w).

[0074] Example 2:

[0075] Colorless needle-like crystals were obtained by a solvothermal reaction of H6THBA (25 mg, 0.05 mmol), Tb(NO3)3·6H2O (45 mg, 0.1 mmol) and o-fluorobenzoic acid powder (100 mg, 0.1 mmol).

[0076] 71 mmol of the compound was placed in 5 mL of a mixed solvent of N,N-dimethylformamide (DMF) and deionized water (volume ratio 1:4), and then transferred to a 25 mL stainless steel reactor. Polytetrafluoroethylene (PTFE) was used as a liner, and the reaction was carried out at 145°C for 72 hours, followed by slow cooling in an oven to room temperature. The crystalline product was filtered, washed with DMF, and dried under vacuum, designated as Tb-MOF, with a yield of 69%.

[0077] Fourier spectroscopy: FT-IR (KBr, v / cm 1 ): 3892(w), 3746(w), 3613(w), 3525(w),2799(w), 1654(m), 1605(s), 1546(s), 1448(s), 1393(s), 1254(m), 1149(w), 1115(w), 1016(w), 947(w), 833(m), 775(m), 739(m), 582(w), 524(w).

[0078] Experimental Example 1: Characterization of the structures of Eu-MOF and Tb-MOF

[0079] Based on single-crystal X-ray diffraction analysis and PXRD patterns, both Eu-MOF and Tb-MOF were identified as isomorphic crystals belonging to the triclinic crystal system. This study selected niobium-based metal-organic frameworks (Eu-MOF) as a typical example for structural analysis. This material... P Crystallization in space group 1 ( Figure 1 (a) Its niobium-based metal-organic framework's asymmetric unit structure consists of four crystallographically independent Eu(III) ions, two deprotonated hexacarboxylic acid ligands, five coordinated water molecules, and four lattice water molecules. Each Eu... 3+ The ion coordinates with two coordinated water molecules and six ligand-derived oxygen atoms, with each of the two carboxyl groups of the ligands contributing two oxygen atoms and the other two carboxyl groups each contributing one oxygen atom. This forms an eight-coordinate structure. The Eu value was calculated using the SHAPE program. 3+ The ion coordination geometry exhibits a double-reinforced triangular prism structure, possessing a J50-coordination configuration. Figure 1 (b)). The bond length of the coordinate bond Eu 3+ The bond lengths with O atoms range from 2.289 Å to 2.520 Å. A unique coordination mode was observed when the HBA ligand interacts with Eu... 3+ Ion binding, specifically manifested by the HBA ligand, half of which is a carboxylic acid group, binding via (μ-η) 1 η 1) Chelation pattern and Eu 3+ Ions bind together, while the other half binds through (μ-η). 1 η 1 The coordination is achieved through a double-tooth bridging mode, as shown in the coordination mode below. Figure 1 As shown in (c). During the structural construction, two Eu... 3+ The ions are bridged by a carboxylate group on the central benzene ring. An HBA ligand, followed by another ligand, binds to these two metal ions, forming an infinitely extending one-dimensional metal chain. These metal chains are interconnected and extend through ligands, thus constructing a two-dimensional structure parallel to the ab plane. Figure 1 (d)). These similar two-dimensional planes are further connected by ligands and extend along the three-dimensional direction to form an infinitely extending three-dimensional porous framework structure. Figure 1 (e) PLATON software calculated its porosity to be 7%.

[0080] The phase purity of the Ln-MOF powder samples was characterized using X-ray powder diffraction. Figure 2 The results showed that the PXRD diffraction peak pattern of the synthesized sample was consistent with the simulation results. Furthermore, to investigate the thermal stability of lanthanide metal-organic frameworks (Ln-MOFs), thermogravimetric analysis (TGA) under a nitrogen (N) atmosphere was used to study the thermal stability of the materials from room temperature to 1000 °C. The thermal stability differences between tungsten-based metal-organic frameworks (Tb-MOFs) and tungsten-europium metal-organic frameworks (Eu-MOFs) were also investigated in the experiment. They are isomorphic crystals with similar thermal decomposition curves. As shown in the thermogravimetric analysis (TG) curves, the sample mass showed a continuous decreasing trend with increasing temperature. When the temperature reached approximately 100 °C, the sample began to exhibit a 7.4% weight loss, which may be due to the escape of free water molecules in the channels and the detachment of coordinated water molecules in the framework. Figure 3 When the temperature reaches approximately 600°C, significant weight loss occurs, indicating that the framework structure of the MOFs almost completely collapses. This demonstrates that Eu-MOFs and Tb-MOFs possess good thermal stability and can maintain their structural integrity over a relatively high temperature range.

[0081] Experiment Example 2: Stability Verification

[0082] Eu-MOFs were immersed in water and ethanol and treated with N,N-dimethylformamide (DMF), cyclohexane, acetonitrile, and dichloromethane solutions for 24 hours, respectively. PXRD analysis showed that they remained in a pure phase state. Figure 4 (a)). These results fully demonstrate the excellent solvent stability of europium-based metal-organic frameworks (Eu-MOFs). Eu-MOFs were then immersed in aqueous solutions with pH values ​​ranging from 2 to 12 for 24 hours, followed by PXRD measurements ( Figure 4 (b) The obtained PXRD pattern is highly consistent with the simulation data. Furthermore, solvent stability and pH stability tests were performed on Tb-MOF. Through the above procedures, we arrive at the same conclusion as before: this material can maintain its structural integrity under different solvent and acid / alkali conditions. Figure 5 This indicates that lanthanide MOFs (Eu-MOF) and Tb-MOF also exhibit good stability in acidic and alkaline solutions.

[0083] Experiment Example 3: Performance Testing of Rare Earth Metal-Organic Framework Materials

[0084] The Eu-MOF sample was thoroughly ground and prepared into a 0.5 mg·mL⁻¹ solution. -1 An aqueous solution was sonicated for 30 minutes to form a stable suspension. To investigate the fluorescence sensing properties of europium-based metal-organic frameworks (Eu-MOF) for small molecule analytes, 5 μL of common small molecule analytes were selected for the experiment, including uric acid (UA), gallic acid (GA), fatty acids (FA), homovanillic acid (HVA), and dopamine (DA). Maleic acid (MA), niacin (NA), ascorbic acid (AOA), and malachite green (MG) were also included. These analytes were added to the prepared suspensions, and the fluorescence emission spectra of the mixed systems were detected at an excitation wavelength of 344 nm. After adding the small molecule analytes to the Eu-MOF aqueous suspension, the detection results showed that ( Figure 6 (a)). Except for malachite green (MG), which exhibited significant quenching, the other analytes had relatively weak effects on the fluorescence emission of the Eu-MOF suspension. These results indicate that Eu-MOF has good selectivity for MG.

[0085] To quantitatively evaluate the sensing ability of Eu-MOF for MG and to investigate its limit of detection, a fluorescence titration experiment was performed. Figure 7 (a) When different concentrations of MG solution were added to the prepared Eu-MOF solution, the fluorescence intensity of Eu-MOF continuously decreased. A good linear relationship was observed between concentration and fluorescence intensity as the molar concentration of MG increased. Therefore, the limit of detection (LOD) of MG was estimated to be 0.139 μM ( Figure 7 (b) The result was calculated using the formula 3σ / k (where σ represents the standard deviation and k represents the slope of the calibration curve). The LOD (minimum inhibitory dose) of Eu-MOF for MG was significantly lower than the infectious dose of bacterial endotoxin to humans (1 μg / kg). Considering whether isomorphic crystals have the same sensing effect against the same recognition agent, a cross-experiment was conducted based on this focus, in which two crystals were tested as targets for each other. The analyte was used as the analytical substance. At the same time, a luminescence sensing experiment was conducted on Tb-MOF for MG, and it was found that this crystal showed good concentration gradient relationship with MG. Figure 7 (c)); good linear correlation was obtained by fitting experimental data, and the detection limit was as low as 0.089 μM ( Figure 7 (d) The results show that the detection limit of the material studied is lower than that of the reference sample, further confirming that the synthesized crystal has broad application prospects.

[0086] The specificity of Eu-MOF was further investigated on MG, and its specific fluorescence response in the presence of other small molecule analytes was explored in detail. To further investigate the effect of interfering substances, the concentration of the interfering substances was set to the same level as that of MG. As shown in the figure, the experimental results show that even in the presence of equimolar amounts of other small molecule analytes, MG still induces fluorescence quenching of Eu-MOF. This demonstrates the characteristics of Eu-MOF. This method exhibits excellent anti-interference ability in MG fluorescence quenching sensing. Figure 6 (b) Therefore, it can serve as a highly selective probe for MG detection in complex matrices. Recyclability is recognized as one of the key indicators for evaluating the practicality of fluorescent sensors. Therefore, the recyclability of Eu-MOF as a fluorescent probe for MG was studied. After MG sensing was completed, Eu-MOF was thoroughly washed with a water-ethanol-water solvent system until the supernatant was clear. Subsequently, the washed powder was subjected to multiple rounds of centrifugation and drying, and finally redispersed in an aqueous solution. The results showed that the obtained fluorescence emission spectrum and intensity ratio were basically the same as the original spectrum. After repeating the process, the changes in fluorescence intensity in five consecutive Eu-MOF detection cycles were as follows: The migration data to MG has been recorded ( Figure 8 (b) The data clearly show that Eu-MOF exhibits excellent cycling performance, and the entire sensing process is stable and reversible, indicating that this composite material has broad application prospects.

[0087] The time-sensitivity of Eu-MOF to MG was investigated using an excitation wavelength of 344 nm. Experimental results showed that complete quenching occurred after 10 seconds, indicating that Eu-MOF possesses fast response performance. Figure 8 (a) It is generally accepted in academia that the fluorescence sensing mechanism of lanthanide metal-organic frameworks (Ln-MOFs) is based on the antenna enhancement effect, and the process involves three steps: initial light absorption by the organic ligand, subsequent ligand-metal energy transfer (LMET), and Ln... 3+ The final luminescence of the ions. Ln 3+ The emission energy mainly originates from photoexcited organic ligands; therefore, the spectral characteristics of the organic ligands and the efficiency of lanthanide organometallic compounds (LMETs) significantly influence the emission energy of Ln. 3+The emission intensity of ions is crucial. To further investigate the quenching sensing mechanism behind the fluorescence response of Eu-MOF to MG, PXRD analysis was performed on Eu-MOF samples after five MG sensing cycles. The results showed that the PXRD patterns were highly consistent with those obtained before sensing. Figure 9 (a)). These test results demonstrate the excellent structural stability of Eu-MOF and further reveal that framework collapse is not the mechanism of Eu-MOF fluorescence quenching. A comparison of FTIR spectra before and after the addition of MG showed no significant changes ( Figure 9 (b) indicates that no coordination reaction or new chemical bond formation occurred between Eu-MOFs, and the behavior of MG during the reaction process. Subsequent analysis of the UV absorption spectrum of MG showed that MG has a strong absorption peak in the wavelength range of 375-475 nm, which highly overlaps with the excitation wavelength range of Eu-MOFs. This suggests the possible existence of a competitive absorption mechanism.

[0088] Experiment Example 4: Device Manufacturing

[0089] Hybrid sensing film: Rare earth metal-organic frameworks (Ln-MOFs) and polymethyl methacrylate (PMMA) were mixed in DMF to obtain a uniform dispersion. The dispersion was coated onto a glass substrate, and after cooling, a fluorescent film was obtained. The above steps were repeated to add analytes to lanthanum metal-organic frameworks (LnMOFs) to prepare fluorescent films; simultaneously, by adding a recognition agent and following the above steps, a recognized fluorescent film was prepared. (The last sentence appears to be a repetition of the previous one and can be omitted.) Figure 10 (b) and (d)). Compared with the former, no significant difference was observed under sunlight, but a strong quenching phenomenon was observed under ultraviolet radiation. Figure 10 (a) and (c)

[0090] LED light beads: After grinding the crystals, they were uniformly mixed with nail polish and then coated onto the surface of the LED lamp to prepare a lanthanum metal-organic framework (Ln-MOF) coated LED lamp. Significant changes before and after analyte addition were clearly visible under natural light and 365 nm ultraviolet light. The recognition performance of the LED lamp was similar to that of the Tb / Eu@PMMA hybrid sensing film. Figure 10 (e) and (f)).

[0091] A mixture of Ln-MOFs with ethanol and ethylene glycol was prepared. Utilizing the volatility of ethanol and the viscosity of ethylene glycol, an Ln-MOF ink with excellent volatility and viscosity was prepared. The prepared ink was then filled into a hollow pen refill. When writing with the custom-made MOF ink pen, it was invisible in sunlight but emitted characteristic lanthanide ion luminescence under 365 nm ultraviolet light. Figure 11These findings suggest that MOF ink pens have potential applications in concealing anti-counterfeiting marks and encrypting information.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a rare earth metal-organic framework material, characterized in that, S1. H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid solution were reacted to obtain colorless needle-like crystals; S2. Place the colorless needle-like crystals in a mixed solvent composed of N,N-dimethylformamide and deionized water, and transfer them to a reaction vessel; S3. The reaction vessel is lined with polytetrafluoroethylene for the reaction, and then the reaction temperature is adjusted to room temperature to obtain product crystals. S4. The product is crystallized, filtered, washed with DMF, and dried under vacuum to obtain the final product. The general formula of the material is: {[Ln4(THBA)2(H2O)5]·4H2O} n Ln is Eu 3+ or Tb 3+ ; THBA is a deprotonated [1,1',4',1''-terphenyl]-2',3,3',5,5',5''-hexacarboxylic acid ligand; The material belongs to the triclinic crystal system, space group [missing information]. P 1. It has a three-dimensional porous frame structure, each Eu 3+ or Tb 3+ All ions are octagonal in configuration; n≥1, and n is an integer; The molar ratio of H6THBA ligand, Ln(NO3)3·H2O and o-fluorobenzoic acid in S1 is (1-3):(2-4):(2-4); In S3, the reaction temperature for using polytetrafluoroethylene as a liner is 145°C, and the reaction time is 72 hours.

2. The method for preparing rare earth metal-organic framework materials according to claim 1, characterized in that, The three-dimensional porous framework structure is formed by connecting binuclear lanthanide clusters as nodes through THBA ligands, and the porosity of the three-dimensional porous framework structure is 7.7%.

3. The method for preparing rare earth metal-organic framework materials according to claim 1, characterized in that, The volume ratio of N,N-dimethylformamide to deionized water in S2 is 1:(3-5).

Images