A metal-organic framework material for detecting copper ions, its preparation method and application

Abstract

This invention discloses a metal-organic framework (MOF) material for detecting copper ions, its preparation method, and its application, relating to the field of nanomaterials technology. The MOF material, for the first time, uses 3-(pyridin-4-yl)benzoic acid as an organic ligand to react with terbium ions (Tb). 3+ Stable three-dimensional porous Tb-PBA MOFs materials were formed through solvothermal coordination. The chemical structure and optical properties of the Tb-PBA MOFs materials were characterized using various techniques. After a series of condition optimizations, the Tb-PBA MOFs could be uniformly dispersed in water and emitted bright and stable green fluorescence. Testing showed that the Tb-PBA MOFs exhibited good adhesion to copper ions (Cu). 2+ This invention exhibits a remarkable fluorescence quenching response, demonstrating rapid, sensitive, and selective detection capabilities for copper ions. The preparation method is simple, the material exhibits good stability, and it has broad application prospects in environmental monitoring and biosensing.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and more specifically, to a metal-organic framework material for detecting copper ions, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of porous crystalline materials formed by the coordination of metal ions or metal clusters with organic ligands, exhibiting a highly ordered topological network structure. These materials, with their extremely high specific surface area, tunable pore size, and surface chemical properties, have shown significant potential in catalysis, gas storage, separation, and chemical sensing. Particularly in fluorescence sensing applications, MOFs are considered an ideal platform for constructing high-performance fluorescent probes due to their designable structure and tunable function. The MOF material itself or its supported luminescent centers can serve as signal response units. When the target analyte interacts with the framework channels or surface, the material's fluorescence properties (such as intensity, emission wavelength, or lifetime) often change significantly, thereby achieving highly sensitive and selective detection of the target analyte.

[0003] Among numerous luminescent MOF materials, rare earth terbium (Tb) stands out. 3+ MOFs based on Tb³ exhibit particularly outstanding performance. These materials not only possess the structural advantages of MOFs but also have properties derived from Tb³. + The characteristic line emission spectrum of the ion features sharp peaks and a large Stokes shift, effectively avoiding broadband background interference and significantly improving the accuracy and resolution of the detection signal. Furthermore, its unique "antenna effect" enables the organic ligand to efficiently absorb light energy and transfer it to Tb. 3+ At the center, the luminescence signal is amplified, overcoming the limitation of the low absorption coefficient of rare earth ions. These properties give terbium-based MOFs significant advantages in constructing highly sensitive and selective fluorescent probes.

[0004] Copper is an important industrial metal widely used in metallurgy, electronics, and chemical industries, but its emissions may lead to the accumulation of copper ions (Cu) in the environment. 2+ The accumulation of Cu. 2+ As a heavy metal pollutant, Cu can accumulate in organisms through the food chain. Excessive intake can damage the liver, kidneys, and nervous system, and even cause various diseases. Therefore, it is crucial to achieve effective control of Cu in the environment and within organisms. 2+ Rapid, sensitive, and selective detection is of great significance for environmental protection, food safety, and clinical diagnosis.

[0005] Currently Cu 2+Conventional detection methods mainly include atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). While these methods offer high accuracy and low detection limits, they typically rely on large instruments, are complex to operate, and are costly, making them unsuitable for on-site, real-time monitoring. Therefore, developing novel sensing technologies that are easy to operate, have rapid response, are cost-effective, and suitable for real-time online detection has become an important research direction in this field. Sensing strategies based on fluorescent MOF materials, due to their high sensitivity, good selectivity, and ability to enable visual detection, offer promising prospects for developing next-generation Cu... 2+ Rapid detection methods offer promising solutions. Summary of the Invention

[0006] The present invention aims to provide a metal-organic framework material for detecting copper ions, its preparation method, and its application. A novel terbium-based metal-organic framework (Tb-PBA MOFs) was prepared by using terbium salts and 3-(pyridin-4-yl)benzoic acid as the metal source and organic acid, respectively. The green fluorescence of Tb-PBA MOFs can be quenched by copper ions, and the change in copper ion concentration is highly correlated with the change in fluorescence intensity. Utilizing these characteristics, this work will be applied to the rapid detection of copper ions.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a metal-organic framework material for detecting copper ions, which uses terbium salt and 3-(pyridin-4-yl)benzoic acid as metal source and organic ligand, respectively, to coordinate and form a stable three-dimensional porous crystalline metal-organic framework (Tb-PBA MOFs) material.

[0008] Secondly, the present invention provides a method for preparing a metal-organic framework material, which includes the following steps: forming a metal-organic framework material by hydrothermal reaction using terbium salt, 3-(pyridin-4-yl)benzoic acid and alkaline solution.

[0009] Thirdly, the present invention provides a method for detecting copper ions, comprising the following steps: uniformly dispersing the metal-organic framework in deionized water to form a stable suspension; adding a buffer solution to the suspension to form a mixed solution; mixing the mixed solution and the test solution in a certain proportion; detecting the change in fluorescence intensity in the system using a multifunctional microplate reader; and calculating the concentration of copper ions in the test solution based on a pre-established standard working curve of fluorescence intensity versus copper ion concentration.

[0010] The present invention has the following beneficial effects: This invention synthesizes green fluorescent Tb-PBA MOFs via terbium salts and 3-(pyridin-4-yl)benzoic acid. The preparation method is simple, easy to operate, and low in cost. This fluorescent metal-organic framework can be quenched by copper ions as a fluorescent probe, thus enabling rapid, sensitive, and highly specific recognition of copper ions. It overcomes the shortcomings of existing metal ion detection methods, such as long detection time, cumbersome procedures, and high costs. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 The images show the solutions of products prepared using different synthetic raw materials according to the operation method of Example 1 of the present invention, under 365nm ultraviolet light irradiation. Figure 2 The images and corresponding feature signals of Tb-PBA MOFs obtained by scanning electron microscope (A) and infrared spectrometer (B) in Example 1 of this invention are shown. Figure 3 The fluorescence excitation and emission spectra of Tb-PBA MOFs prepared in Example 1 of this invention, as scanned by a fluorescence spectrometer; Figure 4 The X-ray diffraction pattern (XRD) and X-ray photoelectron spectroscopy (XPS) of the Tb-PBA MOFs prepared in Example 1 of this invention are shown in Figure 1. Figure 5 The graph shows the linear relationship between the Tb-PBA MOFs prepared in Example 1 of this invention and the detection of copper ions. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0014] The following provides a detailed description of a metal-organic framework material for detecting copper ions, its preparation method, and its application.

[0015] In a first aspect, the present invention provides a metal-organic framework material for detecting copper ions, which uses terbium salt and 3-(pyridin-4-yl)benzoic acid as metal source and organic ligand, respectively, to coordinate and form a stable three-dimensional porous crystalline metal-organic framework (Tb-PBA MOFs) material.

[0016] The molar ratio of the terbium salt to 3-(pyridin-4-yl)benzoic acid is (1-3):(1-10), for example, it can be 1:10, 1:8, 1:6, 1:4, 1:2 or 3:4, or any other value within the range of (1-3):(1-10), preferably 1:4.

[0017] In some embodiments, the terbium salt is at least one of terbium chloride hexahydrate, terbium nitrate hexahydrate, or terbium sulfate octahydrate.

[0018] Specifically, the fluorescent Tb-PBA MOFs have a particle size of 5-20 μm, exhibit green fluorescence in deionized water, and have an excitation wavelength of 230-330 nm and an emission wavelength of 475-630 nm.

[0019] Preferably, the maximum excitation wavelength is 310 nm and the maximum emission wavelength is 548 nm.

[0020] Secondly, the present invention provides a method for preparing a metal-organic framework material, comprising the following steps: dissolving terbium salt and 3-(pyridin-4-yl)benzoic acid separately by thorough shaking with deionized water; mixing the two solutions evenly in proportion, adding alkaline solution and carrying out a hydrothermal reaction; and obtaining the metal-organic framework material after washing, centrifugation and drying after the reaction is completed.

[0021] In some embodiments, the alkali solution is sodium hydroxide with a concentration of 1-2 mol / L, preferably 2 mol / L, and the amount of alkali solution added is 10-75 μL, for example, 10 μL, 25 μL, 50 μL or 75 μL, or any other value in the range of 10-75 μL, preferably 50 μL.

[0022] It should be noted that the amount of alkali solution added is 10-75 μL per 10 ml of mixed solution.

[0023] In some embodiments, the hydrothermal reactor includes, but is not limited to, a polytetrafluoroethylene reactor or a round-bottom flask condenser reflux device.

[0024] In some embodiments, the temperature of the hydrothermal reaction is 100-140°C, preferably 120°C, and the reaction time is 0-9h, for example, it can be 0h, 1h, 3h, 6h or 9h, or any other value within the range of 0-9h, preferably 6h.

[0025] It should be noted that the mixed solution obtained after the solvent reaction can be used directly for detection, or it can be washed with water and dried. The dried Tb-PBA MOFs powder can be stored at room temperature and taken out when needed.

[0026] Some embodiments of the present invention also provide the application of the above-described fluorescent metal-organic framework in the detection of copper ions.

[0027] This invention discovers that copper ions can quench the fluorescence of Tb-PBA MOFs prepared according to the embodiments of this invention. Concentration gradient detection with different concentrations of copper ions revealed that Tb-PBA MOFs exhibit specific selectivity and high sensitivity to copper ions. The linear range for copper ion detection is 50-500 μmol / L, and the detection limit is 1.45 μmol / L.

[0028] Specifically, in some embodiments, the metal-organic framework is uniformly dispersed in deionized water as a fluorescent probe to form a stable suspension; a buffer solution is added to the suspension to form a mixed solution; the mixed solution and the test solution are mixed in a 96-well plate in a certain proportion; the change in fluorescence intensity in the system is detected using a multifunctional microplate reader; and the concentration of copper ions in the test solution is calculated based on a pre-established standard working curve of fluorescence intensity versus copper ion concentration.

[0029] Furthermore, the fluorescence detection is performed at an excitation wavelength of 310 nm, detecting the fluorescence intensity of the solution at the emission peak of 548 nm. Preferably, the detection standard system is 200 μL, using 4-hydroxyethylpiperazine ethanesulfonic acid (HEPES) as a buffer. In the fluorescent metal-organic framework system, 100 μL of Tb-PBA MOFs is added to 100 μL of the detection solution.

[0030] In some embodiments, the buffer solution is 4-hydroxyethylpiperazine ethanesulfonic acid with a concentration of 10-100 mmol / L and a pH of 6.0-8.0.

[0031] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0032] Example 1 This embodiment 1 provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by ultrasonic treatment at a molar ratio of 1:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was ultrasonically mixed thoroughly. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and ultrasonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0033] Structural characterization of Tb-PBA MOFs: The high-resolution scanning electron microscope image and infrared spectrum of the Tb-PBA MOFs prepared in this embodiment are shown below. Figure 1 and 2 As shown, by Figure 2 As can be seen, the Tb-PBA MOFs prepared in this embodiment are clearly observed under scanning electron microscopy, and are approximately cuboid in shape. Statistically, the particle size of Tb-PBA MOFs is mainly concentrated in the range of 5-20 μm, with an average particle size of approximately 8 μm.

[0034] Based on the infrared spectrum of Tb-PBA MOFs ( Figure 1 ), observed 1397 and 1544 cm -1 The signals observed correspond to the C=C and C=N bonds of the pyridine ring. The 1314, 1694, and 3461 cm⁻¹ values ​​observed in the infrared spectrum of 3-(pyridin-4-yl)benzoic acid, which were not observed, correspond to the CO, C=O, and OH bonds of the carboxylic acid. Therefore, it can be determined that the terbium salt and 3-(pyridin-4-yl)benzoic acid, or the carboxyl group of the organic ligand and the terbium ion, form a metal-organic framework structure with an antenna-like structure.

[0035] The blank Tb-PBA MOFs to be used for copper ion detection were detected by fluorescence spectroscopy. The excitation wavelength of the Tb-PBA MOFs was 310 nm, and the maximum emission wavelength was 548 nm. The peak shape was clean and sharp, and green fluorescence was observed.

[0036] Example 2 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:10. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0037] Example 3 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:2. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask and stirred, then refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed in 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0038] Example 4 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 3:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask and stirred, then refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed in 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0039] Example 5 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:1. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0040] Example 6 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted raw materials, the solid was redispersed in 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0041] Example 7 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 1 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0042] Example 8 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 3 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0043] Example 9 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 50 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask and stirred, then refluxed at 120 °C for 9 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0044] Example 10 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 10 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed in 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0045] Example 11 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 25 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask with a stir bar and refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0046] Example 12 This embodiment provides a method for preparing a terbium-based metal-organic framework for detecting copper ions, comprising the following steps: First, the terbium salt and 3-(pyridin-4-yl)benzoic acid were completely dissolved in 20 mL of deionized water by sonication at a molar ratio of 1:4. 75 μL of 2 mol / L sodium hydroxide solution was added to every 10 mL of the mixture, and the mixture was sonicated until homogeneous. The reactants were transferred to a round-bottom flask and stirred, then refluxed at 120 °C for 6 h. After cooling to room temperature, the resulting solution was centrifuged at 4500 rpm to remove the liquid. To remove unreacted reactants, the solid was redispersed with 30 mL of deionized water and sonicated. After repeated washing and centrifugation, the prepared Tb-PBA MOFs were vacuum dried to completely remove the solvent. Finally, the powder was stored at room temperature for later use.

[0047] Experimental Example 1 An equal amount of Tb-PBA MOFs prepared in Example 1 were dissolved in deionized water, and the fluorescence spectra of the Tb-PBA MOFs were measured under excitation with light at wavelengths of 290-330 nm. Figure 3 As shown.

[0048] Depend on Figure 3 The excitation spectrum reveals that Tb-PBA MOFs exhibit a strong excitation response in the wavelength range of 230–330 nm, with the excitation peak located at approximately 310 nm, indicating that the optimal excitation wavelength for this material is 310 nm. Under 310 nm photoexcitation, its emission spectrum exhibits Tb³ + Characteristic sharp emission peaks, with the main peak located at approximately 548 nm, corresponding to... 5 D4→ 7 The F5 level transition was observed, along with weaker characteristic emission peaks near 490 nm, 585 nm, and 620 nm, corresponding to... 5 D4→ 7 F6 5 D4→7 F4 and 5 D4→ 7 F3 transition. The above results show that the Tb-PBA MOFs prepared in Example 1 have typical terbium-based metal-organic framework fluorescence characteristics. Under 310 nm excitation, they can produce strong green fluorescence emission centered at 548 nm with a sharp peak and high fluorescence intensity, demonstrating good fluorescence luminescence performance, which provides an optical basis for their subsequent application in copper ion detection.

[0049] Experimental Example 2 An equal amount of Tb-PBA MOFs prepared in Example 1 were dissolved in deionized water, and their diffraction patterns and photoelectron spectroscopy were detected by X-ray diffraction. Figure 4 As shown.

[0050] Depend on Figure 4 The XRD pattern in -A shows that the sample exhibits multiple sharp and high-intensity characteristic diffraction peaks in the low-angle region (2θ < 30°), with regular peak shapes and low background noise, indicating that Tb-PBA MOFs possess good crystallinity and an ordered crystal structure, consistent with the typical XRD characteristics of metal-organic framework materials. Figure 4 XPS full spectrum analysis in -B further verified the elemental composition of the material. The spectrum clearly showed characteristic signal peaks for C 1s (~285 eV), O 1s (~531 eV), N 1s (~400 eV), and Tb 3d (~1240 eV and 1276 eV), corresponding to carbon, oxygen, nitrogen, and terbium ions in the ligand 3-(pyridin-4-yl)benzoic acid, respectively. This confirmed the successful coordination assembly of the ligand and metal ions in the Tb-PBA MOFs, and the elemental composition was completely consistent with the designed metal-organic framework structure. These results collectively demonstrate that Example 1 successfully prepared a well-crystallized Tb-PBA MOF material with accurate elemental composition.

[0051] Experimental Example 3 The detection of copper ions in samples was performed using a simple mixture of a green fluorescent metal-organic framework (MOF) and a test solution containing copper ions. Using 4-hydroxyethylpiperazine ethanesulfonic acid (HEPES) (10 mM, pH 7.1) as a buffer, 100 μL of test solutions containing copper ions of different concentrations were added to a 96-well plate, followed by 100 μL of a Tb-PBA MOF suspension to prepare a 200 μL test solution. The effect of different concentrations of copper ions on the fluorescence signal of the Tb-PBA MOF probe was detected using a multi-mode microplate reader (final concentrations: 0, 50, 100, 200, 300, 400, and 500 μM). The fluorescence of Tb-PBA MOFs was measured at an excitation wavelength of 310 nm and an emission wavelength of 548 nm, and the fluorescence intensity was taken as F0. The fluorescence signal with added copper ions was also measured, and the fluorescence intensity was expressed as F. The difference was calculated, and the percentage of the difference in F0 was then determined. The experiment was repeated three times, and the average result was taken as the quenching rate. A linear regression equation was used to fit the final concentration of the target substance and the quenching rate of the metal-organic framework.

[0052] The response of Tb-PBA MOFs to different concentrations of copper ions was studied using a multi-functional microplate reader. The results are as follows: Figure 5 As shown, the fluorescence quenching degree of Tb-PBA MOFs increases with increasing copper ion concentration. The linear detection curve of its relative fluorescence intensity can be expressed as (F0-F) / F0 = 0.58374 lg[concentration] - 0.81072, with a correlation coefficient R² = 0.99. The constructed linear range for copper ion detection is 50–500 μM. Calculations using the triple signal-to-noise ratio method yielded a detection limit of 1.45 μM. These results demonstrate that the Tb-PBA MOFs fluorescent probe prepared according to this invention can be used to analyze and detect copper ion content in actual samples.

[0053] This invention primarily establishes a method for preparing green fluorescent metal-organic frameworks (Tb-PBA MOFs) and their application in copper ion detection. The preparation and application methods of Tb-PBA MOFs are simple, easy to operate, low-cost, environmentally friendly, and suitable for mass production. Finally, the methods proposed in this invention exhibit good selectivity, high sensitivity, a wide detection range, and simple operation, making them significant for the widespread application of monitoring pollutants in environmental samples.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A metal-organic framework material for detecting copper ions, characterized in that, The metal-organic framework has a three-dimensional porous crystal structure comprising a terbium salt and 3-(pyridin-4-yl)benzoic acid, wherein the molar ratio of the terbium salt to 3-(pyridin-4-yl)benzoic acid is (1-3):(1-10).

2. The metal-organic framework material for detecting copper ions according to claim 1, characterized in that, The terbium salt is at least one of terbium chloride hexahydrate, terbium nitrate hexahydrate, or terbium sulfate octahydrate.

3. The metal-organic framework material for detecting copper ions according to claim 1, characterized in that, The particle size of the metal-organic framework material is 5-20 μm.

4. A metal-organic framework material for detecting copper ions according to claim 1, characterized in that, The metal-organic framework material has an excitation wavelength of 230-330 nm and an emission wavelength of 475-630 nm in water.

5. A method for preparing a metal-organic framework material as described in any one of claims 1-4, characterized in that, The process includes the following steps: dissolving terbium salt and 3-(pyridin-4-yl)benzoic acid separately in deionized water by thorough shaking; mixing the two solutions in a specific ratio, adding alkaline solution, and then carrying out a hydrothermal reaction; after the reaction is completed, washing, centrifuging, and drying are performed to obtain the metal-organic framework material.

6. The method for preparing a metal-organic framework material according to claim 5, characterized in that, The alkaline solution is sodium hydroxide with a concentration of 1-2 mol / L, and the amount of alkaline solution added is 10-75 μL.

7. The method for preparing a metal-organic framework material according to claim 5, characterized in that, The hydrothermal reactor is a polytetrafluoroethylene reaction vessel or a round-bottom flask condenser and reflux device. And / or, the temperature of the hydrothermal reaction is 100-140℃, and the reaction time is 0-9h.

8. A method for detecting copper ions, characterized in that, Using the metal-organic framework material as described in any one of claims 1-4 as a fluorescent probe, the method includes the following steps: uniformly dispersing the metal-organic framework in deionized water to form a stable suspension; adding a buffer solution to the suspension to form a mixed solution; mixing the mixed solution and the test solution in a certain proportion; detecting the change in fluorescence intensity in the system using a multifunctional microplate reader; and calculating the concentration of copper ions in the test solution based on a pre-established standard working curve of fluorescence intensity versus copper ion concentration.

9. The method for detecting copper ions according to claim 8, characterized in that, The buffer solution is 4-hydroxyethylpiperazine ethanesulfonic acid with a concentration of 10-100 mmol / L and a pH of 6.0-8.

0.

10. The method for detecting copper ions according to claim 8, characterized in that, The linear range for copper ion detection by the method is 50-500 μmol / L, and the detection limit is 1.45 μmol / L.

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