An Eu-NH2BDC / OX MOF material, its preparation method and application

Abstract

This invention relates to an Eu-NH2BDC / OX MOF material, its preparation method, and its applications, belonging to the field of fluorescent materials technology. Using 2-fluorobenzoic acid as a core cluster structure directing agent and oxalic acid and 2-aminoterephthalic acid as organic ligands, this invention synthesizes an Eu-NH2BDC / OX MOF material based on a dual-ligand strategy. The material is applied as a sulfur dioxide ratio fluorescence sensor, for the detection of sulfur dioxide and its derivatives in food, and for the development of fluorescent test strips for sulfur dioxide and its derivatives. This material exhibits dual-wavelength emission characteristics, with the emission color varying with SO3. 2‑ The concentration change transitions from red to blue, making it easy to observe with the naked eye. It exhibits rapid response, high stability, and high sensitivity; as a sulfur dioxide ratio fluorescence sensor, it can detect SO3. 2‑ The high sensitivity and interference resistance of the detection method meet the accuracy requirements of food safety testing; the fluorescent test strip prepared with Eu-NH2BDC / OX MOF material is simple and rapid to use. This invention enables the visual and rapid detection of sulfur dioxide and its derivatives, and has application value and market potential.

Description

Technical Field

[0001] This invention belongs to the field of fluorescent materials technology, specifically relating to an Eu-NH2BDC / OX MOF material, its preparation method, and its application. Background Technology

[0002] Sulfur dioxide and its derivatives (sulfites / bisulfites / sulfur dioxide) are commonly used to protect food and beverages from oxidation, browning, and microbial reactions. However, high concentrations of SO3... 2- SO3 poses a threat to human health and food safety. In most countries, SO3 is present in pharmaceuticals and food. 2- The threshold level for SO2 is strictly limited; according to the standards published by the World Health Organization's expert committee, its acceptable intake (ADI) limit is 0.7 mg / kg. Therefore, developing effective methods for SO2 detection and quantification is of great significance for food safety and quality control.

[0003] Fluorescence analysis has received increasing attention in the detection of sulfur dioxide in recent years due to its advantages such as fast response speed, strong anti-interference ability, high sensitivity and convenient operation.

[0004] Lanthanide-based metal-organic frameworks (Ln-MOFs) fluorescent probes are suitable for the fluorescence detection of various substances. Existing techniques utilize 2-fluorobenzoic acid as a cluster-directing agent, designing and using the organic ligand 2-aminoterephthalic acid, along with europium rare-earth salts, to synthesize the hexanuclear cluster rare-earth metal-organic framework material Eu-BDC-NH2 via a clustering preparation strategy, achieving SO2 detection. However, Ln-MOFs synthesized from 2-fluorobenzoic acid (2-FBA) exhibit low thermal stability, remaining stable only below 500℃. Furthermore, the introduction of only a single organic ligand results in low responsiveness to the detected substances, with a detection limit of 0.65 mg / L, low luminescence efficiency, poor sensitivity, and poor anti-interference properties.

[0005] Therefore, developing a dual-ligand strategy to synthesize Eu-NH2BDC / OX MOF material to achieve rapid response, high stability, and high sensitivity to sulfur dioxide and its derivatives, and its application as a sulfur dioxide ratio fluorescence sensor, has important research significance and application value. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies, and its primary objective is to provide an Eu-NH2BDC / OX MOF material. The Eu-NH2BDC / OX MOF material provided by this invention uses 2-fluorobenzoic acid as a core cluster structure directing agent and oxalic acid and 2-aminoterephthalic acid as organic ligands. Based on this dual-ligand strategy, a Eu-NH2BDC / OX MOF material that not only specifically recognizes sulfur dioxide and its derivatives but also exhibits good stability was synthesized.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned Eu-NH2BDC / OX MOF material.

[0008] Another object of the present invention is to protect the application of the above-mentioned Eu-NH2BDC / OX MOF material as a sulfur dioxide ratio fluorescence sensor.

[0009] Another object of the present invention is to protect the application of the above-mentioned Eu-NH2BDC / OX MOF material in the detection of sulfur dioxide and its derivatives.

[0010] Another object of the present invention is to protect a method for fluorescent detection of sulfur dioxide and its derivatives.

[0011] Another object of the present invention is to protect the application of the above-mentioned Eu-NH2BDC / OX MOF material in the preparation of test paper for sulfur dioxide and its derivatives.

[0012] Another object of the present invention is to protect a fluorescent test strip for sulfur dioxide and its derivatives.

[0013] Another object of the present invention is to provide a method for preparing the fluorescent test paper of sulfur dioxide and its derivatives.

[0014] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0015] This invention protects a method for preparing Eu-NH2BDC / OX MOF material, comprising the following steps:

[0016] The Eu-NH2BDC / OX MOF material was prepared by hydrothermal reaction of europium salt, oxalic acid, 2-aminoterephthalic acid, and 2-fluorobenzoic acid in DMF-nitric acid-water mixture at 115-125℃ for 20-30 h.

[0017] The molar ratio of europium salt, oxalic acid, 2-aminoterephthalic acid, and 2-fluorobenzoic acid is (4-5):(1-3):(3-3.5):(40-50).

[0018] This invention uses 2-fluorobenzoic acid (2-FBA) as a core cluster structure directing agent and oxalic acid (H2OA) and 2-aminoterephthalic acid (H2BDC-NH2) as organic ligands. Based on the above dual-ligand strategy, a Eu-NH2BDC / OX MOF material that can not only specifically recognize sulfur dioxide and its derivatives but also has good stability was synthesized.

[0019] Eu 3+ The ligand is chelated by the -COOH group, which increases the rigidity of the backbone and enhances the fluorescence properties. Eu 3+ With its high coordination number and flexible and varied structure, Eu-NH2BDC / OX has a three-dimensional rigid structure formed by the interaction of Eu and ligands, which gives it good thermal stability and allows it to exist relatively stably up to 800℃.

[0020] Oxalic acid (H₂OA) is a rigid organic ligand; its -COOH group participates in coordination and linkage with metal centers, forming extended structures from 0 to 3D. It also exhibits a more flexible framework and coordination mode, capable of linking metal ions into high-dimensional frameworks. Using oxalic acid as a synthesis regulator can modulate crystal growth, resulting in Eu-NH₂BDC / OXMOF with good crystallinity without affecting the material's structure and composition.

[0021] More preferably, in the preparation method of the Eu-NH2BDC / OX MOF material, the hydrothermal reaction is carried out at 120°C for 24 hours.

[0022] Preferably, the concentration of HNO3 is 3-4 mol / L.

[0023] More preferably, the concentration of HNO3 is 3.5 mol / L.

[0024] Preferably, the volume ratio of DMF to water is 1:7 to 1:8. More preferably, the volume ratio of DMF to water is 1:7.8.

[0025] Preferably, the europium salt is europium nitrate.

[0026] This invention protects the Eu-NH2BDC / OX MOF material prepared according to the above preparation method.

[0027] This invention protects the application of the above-mentioned Eu-NH2BDC / OX MOF material as a sulfur dioxide ratio fluorescence sensor.

[0028] This invention protects the application of the above-mentioned Eu-NH2BDC / OX MOF material in the detection of sulfur dioxide and its derivatives.

[0029] This invention protects a method for fluorescence detection of sulfur dioxide and its derivatives, using the above-mentioned Eu-NH2BDC / OXMOF material as a sulfur dioxide ratio fluorescence sensor.

[0030] Specifically, the method includes the following steps:

[0031] The test solution was added to the Eu-NH2BDC / OX MOF material dispersion to obtain a mixed solution, the pH was adjusted to 7-11, and the fluorescence spectrophotometry was used for detection.

[0032] Fluorescence detection conditions: λex: 300nm, λem: 450nm / 615nm, voltage: 400V, slit width: 5nm, scan speed: 3000nm / min.

[0033] Preferably, the pH value is adjusted to 10.

[0034] Preferably, the method uses sodium sulfite to prepare a standard solution, and the amount of the standard solution added is 0.4–0.8 mL, wherein the standard solution contains SO3. 2- The concentration ranges from 5 to 50 μg / mL, and the detection limit is 0.25 mg / kg.

[0035] Preferably, the method uses the concentration of sodium sulfite as the x-axis and I as the y-axis. 450 / I 615 Plot a standard curve for the ordinate, with an r value of 0.9939.

[0036] Preferably, the dispersant of the Eu-NH2BDC / OX MOF material dispersion is one of methanol, ethanol, acetonitrile, isopropanol or N,N-dimethylformamide.

[0037] Preferably, the detection volume of the Eu-NH2BDC / OX MOF material dispersion is 1-3 mL, more preferably 1.5 mL; the concentration is 0.3-1 mg / mL, and more preferably 0.5 mg / mL.

[0038] Preferably, the method for preparing the sample solution includes the following steps: the sample to be tested is mixed with the extractant and then extracted by ultrasonication, and the supernatant is taken after separation; the extractant is selected from a sodium hydroxide or potassium hydroxide solution with a concentration of 0.1% to 1%.

[0039] Preferably, the concentration of the extract is 0.5%.

[0040] Preferably, the extraction time is 20 to 40 minutes, more preferably 30 minutes.

[0041] Preferably, the sample to be tested is a candied fruit, selected from at least one of candied dates, raisins, preserved plums, and dried mangoes.

[0042] Preferably, the amount of the sample to be tested and the extract is 1-10g: 5-15mL, more preferably 5g: 10mL.

[0043] This invention protects the application of the above-mentioned Eu-NH2BDC / OX MOF material in the preparation of test paper for sulfur dioxide and its derivatives.

[0044] This invention protects a fluorescent test strip for sulfur dioxide and its derivatives, the test strip containing the Eu-NH2BDC / OX MOF material.

[0045] This invention protects a method for preparing the above-mentioned fluorescent test strip, comprising the following steps:

[0046] Glass fibers were soaked in a dispersion of Eu-NH2BDC / OX MOF material and dried to obtain the fluorescent test paper.

[0047] Specifically, the Eu-NH2BDC / OX MOF material dispersion is prepared by dispersing the Eu-NH2BDC / OX MOF material in an alcohol solvent, wherein the dispersion is ultrasonic dispersion, and the alcohol solvent is selected from at least one of methanol, ethanol, and propanol.

[0048] Specifically, the soaking is performed with ultrasonic assistance for 5 to 20 minutes.

[0049] Preferably, in the above-mentioned method for preparing fluorescent test strips, the amount of alcohol solvent added is 1 mL, and the amount of Eu-NH2BDC / OX MOF added is 1 mg.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. This invention synthesizes an Eu-NH2BDC / OX MOF material that can specifically recognize sulfur dioxide and its derivatives, and has good stability and cyclicability within 800℃, using 2-fluorobenzoic acid as a core cluster structure directing agent and oxalic acid and 2-aminoterephthalic acid as organic ligands. It exhibits rapid response, high stability and high sensitivity to sulfur dioxide and its derivatives.

[0052] 2. This invention uses Eu-NH2BDC / OX MOF material as a sulfur dioxide fluorescence ratio sensor, and achieves quantitative detection of sulfur dioxide and its derivatives in candied foods such as jujubes, raisins, preserved plums, and dried mangoes by fluorescence spectrophotometry. It has low detection limit and high recovery rate, with a detection limit of 0.25 mg / kg and a recovery rate of 87.28% to 106.3%.

[0053] 3. This invention prepares fluorescent test strips for sulfur dioxide and its derivatives using Eu-NH2BDC / OX MOF material. The changes in fluorescence intensity can be observed with the naked eye and the strips have good stability. The strips are simple and fast to use in practice, and the color develops in 30 seconds. Attached Figure Description

[0054] Figure (1) shows the preparation process of Eu-NH2BDC / OX material.

[0055] Figure (2) Schematic diagram of the fluorescence reaction process.

[0056] Figure (3) SEM image of Eu-NH2BDC / OX material.

[0057] Figure (4) TEM image of Eu-NH2BDC / OX material.

[0058] Figure (5) Particle size distribution of Eu-NH2BDC / OX material.

[0059] Figure (6) EDS spectrum of Eu-NH2BDC / OX material.

[0060] Figure (7) EDS diagram of C, N, O and Eu on the surface of Eu-NH2BDC / OX material.

[0061] Figure (8) Infrared spectrum of Eu-NH2BDC / OX material.

[0062] Figure (9) Thermogravimetric curve of Eu-NH2BDC / OX powder.

[0063] Figure (10) XRD pattern of Eu-NH2BDC / OX material.

[0064] Figure (11) XPS spectra of Eu-NH2BDC / OX material: N1s (a), Eu3d (b), C1s (c), total spectrum (d).

[0065] Figure (12) shows the UV-Vis absorption spectrum of the Eu-NH2BDC / OX material.

[0066] Figure (13) Excitation and emission spectra of Eu-NH2BDC / OX and emission spectrum of Eu-NH2BDC. Figure (14) Effect of solvent type on fluorescence intensity of the system.

[0067] Figure (15) shows the effect of the amount of material solution used on the fluorescence intensity of the system.

[0068] Figure (16) shows the effect of sodium sulfite solution dosage on the fluorescence intensity of the system.

[0069] Figure (17) shows the effect of pH on the fluorescence intensity of the system.

[0070] Figure (18) shows the fluorescence intensity changes of Eu-NH2BDC / OX dissolved in anhydrous ethanol after storage at 4°C for 3 days under 275 nm excitation.

[0071] Figure (19) shows the changes in sodium sulfite solution after multiple tests on Eu-NH2BDC / OX material.

[0072] Figure (20) shows the effect of different interfering ions on the detection results of the system.

[0073] Figure (21) Fluorescence spectrum and standard curve of Eu-NH2BDC / OX material for detecting sodium sulfite from 0 to 50 μg / ml.

[0074] Figure (22) shows the linear relationship between different concentrations of sodium sulfite and the green value detected by Eu-NH2BDC / OX. Figure (23) shows the CIE colorimetric diagram of sodium sulfite detected by Eu-NH2BDC / OX material.

[0075] Figure (24) shows the RGB values ​​and the standard curve of sodium sulfite concentration. Detailed Implementation

[0076] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0077] Embodiments 1 to 3 of the present invention include the following:

[0078] Example 1: Preparation and Application of a Sulfur Dioxide Ratio Fluorescence Sensor - Preparation of a Sulfur Dioxide Ratio Fluorescence Sensor

[0079] (1) Synthesis of Eu-NH2BDC / OX MOF (diaminoterephthalic acid to oxalic acid ratio is 0.33:0.166 = 2:1)

[0080] Accurately weigh 223 mg europium nitrate hexahydrate, 59.8 mg 2-aminoterephthalic acid, 21.415 mg oxalic acid (the amount of oxalic acid dihydrate), and 604.8 mg 2-fluorobenzoic acid. Dissolve them in 7.8 mL of DMF. Then add 1 mL of H₂O and 0.6 mL of HNO₃ (the DMF is used to dilute HNO₃ to 3.5 mol / L). Seal the solution in a 25 mL reactor and react at 120 °C for 24 hours, then cool to room temperature. The product needs to be washed three times with DMF and ethanol to remove excess ligands and metal ions. Finally, dry at 40 °C for 12 hours for later use.Figure 1 ).

[0081] (2) Characterization methods for Eu-NH2BDC / OX materials

[0082] The surface morphology of Eu-NH2BDC / OX MOF was determined using scanning electron microscopy (SEM). Figure 2 ) and transmission electron microscopy (TEM) Figure 3 , 4 )observe; Figure 5 The particle size distribution of Eu-NH2BDC / OX MOF is shown; the elemental composition and content of the micro-area of ​​Eu-NH2BDC / OX material were determined by energy dispersive spectroscopy (EDS). Figure 6 , 7 The analysis was performed using Fourier transform infrared spectroscopy (FTIR); the surface chemical properties of the material were analyzed using Fourier transform infrared spectroscopy (FTIR). Figure 8 Thermogravimetric analysis (TGA) was used to analyze and explore the thermal stability of Eu-NH2BDC / OX MOF materials. Figure 9 ).

[0083] (3) Characterization Experiment Results - Morphology Analysis

[0084] SEM testing of Eu-NH2BDC / OX MOF ( Figure 3 The prepared Eu-NH2BDC / OX MOF powder was dispersed in an ethanol solution. Figure 3 As can be seen, the crystals of Eu-NH2BDC / OX MOF are relatively regular polyhedral in shape, with clear shape and size, and a certain degree of granularity. The particle size is approximately 54.5±15.8 nm, which is significantly smaller than that of Eu-NH2BDC, thus exhibiting superior stability and solubility. Figure 3 , 4 5).

[0085] This further demonstrates the successful preparation of Eu-NH2BDC / OX MOF materials, with the impurity phases formed during the preparation process likely being the main reason for the presence of a small number of spherical particles on the crystal surface. Therefore, the dual-ligand strategy achieves dual emission, specific recognition, and rapid response to sulfur dioxide and its derivatives, as well as the modulation of MOF size and morphology.

[0086] Meanwhile, based on the EDS energy dispersive spectroscopy data of the Eu-NH2BDC / OX MOF material ( Figure 6 Not only can the signal peaks of C, N, and O elements be observed, but also those of Eu can be observed. 3+ Elemental signal peaks prove Eu 3+ The successful introduction into the system demonstrates the successful preparation of Eu-NH2BDC / OX MOF materials.

[0087] Table 1. C, O, Zr, and Eu content measured by EDS.

[0088]

[0089] To further investigate the actual distribution of C, N, O, and Eu elements on the surface of Eu-NH2BDC material, EDS mapping was used to characterize the surface of Eu-NH2BDC / OX MOF. Figure 7 As can be seen from the EDS diagram, the four elements C, N, O and Eu are uniformly distributed on the surface of each Eu-NH2BDC / OX MOF, which reflects the successful preparation of Eu-NH2BDC / OX MOF material (Table 1).

[0090] (4) Characterization of experimental results - Infrared spectroscopy analysis

[0091] The FT-IR spectra of Eu-NH2BDC / OX MOF and oxalic acid were compared. Figure 8 ), and it was found that carbonyl groups react with rare earth ions (oxalic acid has a concentration of 1700 cm⁻¹). -1 Eu-NH2BDC / OX is 1640cm -1 The coordination of ) was significantly low. At 740cm -1 A new band appears at this location, which is the region where Eu-O bonds occur, corresponding to a new pattern. This is due to the formation of Eu carboxylic acid bonds under the coordination of oxalic acid. Eu-NH2BDC / OX MOF at 1320 cm⁻¹ -1 Another displacement was also observed, corresponding to the stretching of the CO bonds. Furthermore, the OCO band shifted from 722 cm⁻¹. -1 (Oxalic acid) was transferred to 802 cm⁻¹ -1 (Eu-NH2BDC / OX) is part of the binding site, further supporting the chelation of the carboxylic acid group with the metal site.

[0092] On the other hand, oxalic acid has a CC (1380cm). -1 It remains unchanged in all FT-IR spectra. 3+ The ligands are chelated with -COOH groups, which increases the rigidity of the skeleton and enhances the fluorescence properties. Furthermore, comparing the infrared spectra of Eu-NH2BDC / OX MOF with those of oxalic acid and H2BDC-NH2 reveals significant changes in the position and intensity of the bands, indicating that Eu... 3+ It has a coordination relationship with the ligand, that is, it forms a coordination compound.

[0093] (5) Characterization of experimental results - thermogravimetric analysis

[0094] In practical applications, the structural stability of MOFs is very important. Lanthanide (III) ions are characterized by high coordination numbers and flexible and varied structures, thus exhibiting significant thermal stability.

[0095] Depend on Figure 9 The weight loss of Eu-NH2BDC / OX MOF is 10% from 40 to 336℃, which is likely due to the volatilization of water and DMF molecules from the surface and pores of the Eu-NH2BDC / OX MOF crystal. From 336 to 397℃, the weight loss is 20.2%, corresponding to the release of two lattice water molecules and four coordinated water molecules. From 397 to 600℃, the weight loss is estimated to be due to the collapse of the main framework. The figure shows that the three-dimensional rigid structure formed by the interaction of Ln and ligands in Eu-NH2BDC / OX gives it good thermal stability, allowing it to exist relatively stably up to 800℃.

[0096] (6) Characterization of experimental results - X-ray diffraction

[0097] Using oxalic acid as a synthesis regulator can modulate crystal growth, resulting in Eu-NH2BDC / OX MOF with good crystallinity without affecting the material's structure and composition. The results are as follows (…). Figure 10 As shown in the figure, distinct spikes can be observed at 12.86°, 14.34°, and 19.02°. These three peaks show slight shifts compared to their corresponding standard simulated peaks (CCD number: 2061887), indicating their isomorphic skeleton topology. PXRD confirms the structural stability of Eu-NH2BDC / OX during the sensing process, ruling out the possibility of structural collapse during the sensing experiment.

[0098] (7) Characterization of experimental results - X-ray photoelectron spectroscopy

[0099] X-ray photoelectron spectroscopy (XPS) can be used with MOFs to elucidate the identity of elements and their chemical states, such as their coordination environments. To further verify Eu... 3+ To determine whether it was actually introduced into the system, XPS characterization was performed on Eu-NH2BDC / OX to observe the bonding situation of each element.

[0100] The results are as follows Figure 11As shown, a distinct 3d peak of Eu is visible, confirming the presence of Eu. Eu, N, O, and C elements were observed in the Eu-NH2BDC / OX MOF. Three peaks of 284.78, 285.98, and 288.58 eV were observed in the C1s phase, which can be attributed to O=C-OH, C=O, and NC=O, respectively. Separate peaks of Eu 3d in Eu-NH2BDC / OX are shown at 1164.78, 1154.38, 1135.08, and 1124.78 eV, and these peaks are related to Eu 3d3 and Eu 3d5.

[0101] Example 2: Preparation and Application of a Sulfur Dioxide Ratio Fluorescence Sensor - Fluorescence Detection of Sulfur Dioxide and its Derivatives

[0102] (1) Preparation of the main solution

[0103] Sodium sulfite standard solution: Dilute the Na2SO3 standard (concentration of 100 μg / mL) to a Na2SO3 stock solution with a concentration range of 5–50 μg / mL and place it in a 50 mL volumetric flask.

[0104] (2) Calculation of sulfur dioxide residue

[0105]

[0106] Where X is the sulfur dioxide content (mg / kg); V 提取 V is the volume of ultrapure water used during sample extraction (mL); C is the SO2 concentration (μg / mL) calculated from the standard curve; V 定容 That is the constant volume (mL) of the reaction; M 称量 It is the actual sample mass (g) weighed; V 吸取 This is the volume (mL) of the sample extract taken.

[0107] (3) Fluorescence detection conditions

[0108] λex: 300nm, λem: 450nm / 615nm. Voltage: 400V. Slit width: 5nm. Scan speed: 3000nm / min.

[0109] (4) Fluorescence spectrophotometry detection process

[0110] Weigh a certain amount of Eu-NH2BDC / OX MOF, add an appropriate amount of detection dispersant to prepare a 0.5 mg / mL material solution, add sodium sulfite standard solution to adjust the pH to 7-11, and bring the volume to 5 mL. After sonication for 5 min, perform the detection. The entire experimental procedure is as follows: Figure 2 As shown.

[0111] (5) Preparation of actual samples

[0112] Accurately weigh 5.00g each of the candied dates, raisins, preserved plums, and dried mangoes that have been cut into small pieces with scissors using a balance. Add 10mL of 0.5% sodium hydroxide solution, sonicate for 30min, centrifuge (8000r / min) for 5min, and take 1.0mL of the supernatant to dilute with deionized water to 10mL for later use.

[0113] The obtained diluted solution was tested according to method (4).

[0114] (6) Fluorescence performance analysis

[0115] UV-Vis absorption: Sodium sulfite and H₂OA have absorption peaks at 226 nm and 232 nm, respectively. Figure 12 Sodium sulfite and Eu-NH2BDC / OX MOF have an effective overlap in the UV-vis absorption range, indicating that there is competitive absorption of the light source between sodium sulfite and Eu-NH2BDC / OX MOF.

[0116] The fluorescence excitation and emission spectra of Eu-NH2BDC / OX MOF and the fluorescence emission spectrum of Eu-NH2BDC were recorded outdoors, as follows: Figure 13 As shown. The excitation spectrum measured at EM=615nm shows a relatively broad absorption band centered at 260nm for Eu-NH2BDC / OX MOF at 596nm (…). 5 D0→ 7 F2) and 615nm 5 D0→ 7 There is typical red light emission at F2), consistent with Eu. 3+ The f-f electron transfer indicates an antenna effect, whereby the ligand absorbs energy and it is then conducted to the lanthanide ion. Furthermore, the excitation spectra of Eu-NH₂BDC / OX MOF and Eu-NH₂BDC are the same, while the fluorescence spectra of Eu-NH₂BDC are significantly different. 3+ The higher emission level is speculated to be due to the introduction of oxalic acid, which further sensitizes its luminescence.

[0117] Specifically, H2BDC-NH2 acts as an "antenna" molecule. When excited by ultraviolet light, Eu-NH2BDC / OX MOF exhibits an "antenna effect," absorbing energy through H2BDC-NH2 and transferring it to the central Eu. 3+ Eu 3+ The luminescence is sensitized, thus exhibiting characteristic Eu. 3+ Emission, due to the emission peak of H2BDC-NH2 at 450nm and Eu 3+ Corresponding to 5 D0→ 7The excitation peaks of the F2 level transition highly overlap, at which point fluorescence resonance energy transfer occurs. Figure 13 ).

[0118] Numerous exposed selective recognition sites are located on the surface and internal channels of the Eu-NH2BDC / OX MOF crystal, which become more sensitive when SO3 is introduced. 2- Subsequently, it specifically interacts with H2BDC-NH2 at the site to form a stable 1:1 charge-transfer complex, which can lead to charge transfer and thus hinder the transfer of H2BDC-NH2 to Eu. 3+ The ligand-to-metal charge transfer (LMCT) process occurs when H2BDC-NH2 reacts with Eu. 3+ The FRET between them was cut off, Eu 3+ The fluorescence intensity decreased while the fluorescence intensity of H2BDC-NH2 increased, I 450 / I 615 Increase.

[0119] (7) Optimization of detection conditions - solvent types

[0120] To effectively detect sulfur dioxide and its derivatives, the effect of solvent on fluorescence intensity was investigated. Six commonly used solvents—methanol, ethanol, acetonitrile, isopropanol, and N,N-dimethylformamide (DMF)—were selected for solvent effect studies. Figure 14 ).

[0121] Emission spectra of Eu-NH2BDC / OX MOF suspensions excited at 300 nm in five solvents showed that different solvents significantly affected the luminescence intensity of Eu-NH2BDC / OX MOF. The order of luminescence intensity in different solvents was: DMF, ethanol, isopropanol, methanol, and acetonitrile. The results indicate that ethanol is the optimal Eu-NH2BDC / OX MOF solvent for detecting sulfur dioxide and its derivatives because it has a high Ig content. 450 / I 615 Furthermore, ethanol has relatively low toxicity compared to other solvents of choice.

[0122] (8) Optimization of testing conditions - material usage

[0123] The amount of Eu-NH2BDC / OX MOF material used is a crucial factor affecting the fluorescence intensity of the system during the reaction. To minimize waste of Eu-NH2BDC / OX MOF material, the volume of the Eu-NH2BDC / OX material solution should be as small as possible while achieving optimal fluorescence intensity. Different volumes of Eu-NH2BDC / OX MOF material will result in different fluorescence intensities. If the amount of Eu-NH2BDC-OX MOF material solution does not achieve the strongest fluorescence intensity, the reaction will be incomplete.

[0124] This study conducted a series of experiments on material volumes of 1, 1.5, 2, 2.5, and 3 mL, and the results are as follows: Figure 15 The results showed that the fluorescence intensity of the system was strongest when the material volume was 1.5 mL. Therefore, subsequent experiments selected 1.5 mL (RSD = 0.085%) as the optimal volume of Eu-NH2BDC / OX MOF material solution.

[0125] (9) Optimization of detection conditions - dosage of sodium sulfite solution

[0126] The amount of sodium sulfite used is a crucial factor affecting the fluorescence intensity of the Eu-NH2BDC / OX MOF system during the experimental reaction, thus requiring optimization. This study conducted a series of volume experiments with 15ug / mL sodium sulfite solutions of 0.1, 0.3, 0.5, 0.7, and 0.9 mL, which were then diluted to 5 mL with anhydrous ethanol, and their fluorescence intensity was measured.

[0127] like Figure 16 The results showed that the fluorescence intensity of the system was strongest when 0.5 mL of sodium sulfite solution was added. Therefore, 0.5 mL (RSD = 0.02%) was selected as the optimal amount of sodium sulfite solution for subsequent experiments.

[0128] (10) Optimization of detection conditions - pH

[0129] Reports indicate that acid modifiers (such as trifluoroacetic acid, hydrochloric acid, and formic acid) can be used to improve the crystallinity of metal oxides in solvothermal reactions. Free sulfate ions can be released into HSO3 at different pH values. - SO3 2- It converts between the three forms of sulfur dioxide.

[0130] pH value is an important factor affecting the application of probes. Experimental studies investigated the detection of SO3 using an Eu-NH2BDC / OX probe within a pH range of 2–9. 2- fluorescence ratio (I 450 / I 615 When the pH value is 4 to 9 ( Figure 17When ), the fluorescence ratio of the probe (I) 450 / I 615 A pH value less than 1 indicates that the probe remains stable over a wide pH range. This can be improved by adding SO3. 2- The fluorescence ratio of the probe (I 450 / I 615 The pH value rapidly increases to a peak at 10, indicating that the probe can reliably detect SO3. 2- Moreover, from Figure 17 It can be seen that the fluorescence intensity of the Eu-NH2BDC / OXMOF system is strongest at pH=10. Therefore, pH 10 was chosen as the most suitable pH for subsequent experiments.

[0131] (11) Optimization of detection conditions - stability experiment

[0132] The stability of Eu-NH2BDC / OX MOF materials is crucial in experiments, significantly impacting the final results. To investigate the stability of Eu-NH2BDC / OX MOF materials, this study conducted a series of stability tests on sulfur dioxide detection using Eu-NH2BDC / OX MOF materials at different time points. As shown in the figure, good detection performance was observed within 72 hours (RSD < 2.05%). The good stability of Eu-NH2BDC / OX MOF may be attributed to the... 3+ The three-dimensional rigid structure generated by the interaction with ligands laid the foundation for subsequent testing.

[0133] After being placed in an ethanol solution for 96 hours, the fluorescence intensity of the Eu-NH2BDC / OX MOF system decreased to approximately 60% of its initial fluorescence intensity. This is because, after 96 hours of exposure to ethanol, the fluorescence intensity of Eu-NH2BDC / OX-SO3... 2- The rate of aggregation and degradation increased, resulting in a loss of nearly 40% of the initial fluorescence within 24 hours. Strong red fluorescence, good structural stability, and fluorescence stability demonstrate the feasibility of the synthesized Eu-NH2BDC / OX MOF as a fluorescent probe in aqueous media. Figure 18 ).

[0134] (12) Optimization of detection conditions - cyclic experiment and interference experiment

[0135] In practical applications, easily recoverable sensors are also important. Recovery tests were conducted on a suspension containing sodium sulfite (Eu-NH2BDC / OX MOF), involving centrifugation under ultrasonic conditions and multiple washes with ethanol. After the 5th cycle (RSD < 3.60%), the framework remained intact. Simultaneously, the quenching efficiency remained above 90% for each cycle. Figure 19The results showed that Eu-NH2BDC / OX MOF exhibits high cyclicity and stability in the detection of sodium sulfite in ethanol medium.

[0136] Considering the complexity of actual samples, this study selected different metal ions as interfering ions to analyze the anti-interference ability of the probe. Under optimal detection conditions, a certain amount of Na2SO3 solution (15 μg / mL) and interfering substance (HPO4) were added to the ethanol solution of the probe, respectively. 2- HCO3 - P2O7 2- S 2- Cl - The concentration was 150 μg / mL and Br - I - F - SO4 2- The concentration of the solution was 300 μg / mL, and the anti-interference ability of the probe for the detection of sulfur dioxide and its derivatives was analyzed.

[0137] Depend on Figure 20 It can be seen that even when interfering substances are introduced at concentrations 10 to 20 times higher than Na₂SO₃, their impact on the fluorescence signal is minimal. These results demonstrate that Eu-NH₂BDC / OX MOF is an excellent luminescent sensor with superior anti-interference performance, high sensitivity, and recyclability, suitable for analyzing sulfur dioxide residues in real-world samples.

[0138] (13) Optimization of detection conditions - characteristics of analysis methods

[0139] Based on the above results, anhydrous ethanol was selected as the dispersant for the Eu-NH2BDC / OX MOF material, and the sensing performance of Eu-NH2BDC / OX MOF for detecting sulfur dioxide and its derivatives was studied using 300 nm as the excitation wavelength. The ratio of the emission intensity of Eu-NH2BDC / OX MOF to I... 450 / I 615 The concentration increased significantly with the addition of sodium sulfite aqueous solution. Figure 21 This is very consistent with the first-order exponential equation.

[0140] Within the range of 5-50 μg / mL, the intensity changes linearly. 450 / I 615 The equation is 0.1179x + 2.3043c, where c is the concentration of sodium sulfite, r is 0.9939, and the detection limit is 0.25 mg / kg. This indicates that Eu-NH2BDC / OX MOF material can be used as an excellent sensing material for high-precision quantitative detection of sulfur dioxide and its derivatives in candied fruit.

[0141] The above results indicate that Eu-NH2BDC / OX MOF materials can be used to detect SO3 in aqueous phases. 2- ion.

[0142] To obtain a more obvious visual detection effect, RGB curves were plotted based on the differences in fluorescence intensity caused by changes in sodium sulfite concentration. A good linear relationship was found between the two (r = 0.9883). Figure 22 As shown in the figure. The above results indicate that the Eu-NH2BDC / OX MOF ratiometric fluorescence sensor exhibits a wide range of color changes during the reaction with the analyte.

[0143] When excited at 300 nm, the emission peak of Eu-NH2BDC / OX MOF is at 615 nm, and the blue emission peak at 450 nm increases with SO3. 2- The concentration increased significantly from 5 μg / mL to 50 μg / mL, while the red emission peak at 615 nm gradually decreased. The corresponding CIE chromaticity diagram was calculated based on the emission spectrum, and the CIE value also decreased with increasing SO3 concentration. 2- The content increased from (0.45, 0.20) to (0.17, 0.06), and the corresponding point position also changed from the initial red area to the final blue area. Figure 23 ).

[0144] (14) Detection of actual samples

[0145] To verify the practicality of the method, four samples were weighed: preserved plum, mango, grape, and jujube. The actual samples were processed according to the above (5) and then tested. The test was repeated 3 times. Under the best experimental conditions, two concentration levels (15 μg / mL and 20 μg / mL) were spiked and recovered simultaneously, and the spiked recovery rate was calculated to verify the accuracy of the method.

[0146] The results are shown in Table 2. The recoveries of the four groups of samples ranged from 87.28% to 106.3%, and the relative standard deviations of the recoveries ranged from 1.03% to 9.29%. This detection method has good accuracy, and the recoveries and precision meet the quality control requirements for routine experimental analysis. The detection results for dried mango and jujube were lower than the national standard requirement of 350 mg / kg, while those for grapes and preserved plums exceeded the national allowable range.

[0147] The samples were analyzed according to the national standard method, and the Eu-NH₂BDC / OX MOF fluorescence spectrophotometric method was validated. The relative deviations of the parallel sample results all met the precision requirements of the acid-base titration method, Method 1, of GB5009.34-2022 "National Food Safety Standard - Determination of Sulfur Dioxide in Food". The absolute difference between two independent determinations obtained under repeated conditions did not exceed 10% of the arithmetic mean. The sample's 2.68% ≥ RSD ≥ 1.03% indicates that the Eu-NH₂BDC / OX MOF method has good precision. Statistical analysis of the results from the two methods showed a significant difference (P>0.05), indicating that the established method yielded accurate results.

[0148] Table 2. Results of actual candied fruit food testing and spiked recovery experiments (n=3)

[0149]

[0150] Example 3: Preparation and Application of a Sulfur Dioxide Ratio Fluorescence Sensor - Fluorescent Test Paper for Sulfur Dioxide and its Derivatives

[0151] Preparation of Eu-NH2BDC / OX MOF ratio probe test strips: Eu-NH2BDC / OX MOF ethanol solution (1 mg / ml) was ultrasonically dispersed to obtain a uniform and stable suspension. Glass fibers were immersed in the solution and ultrasonicated for another 10 min. The glass fibers were then removed and dried in an oven to obtain test strips that show red light under ultraviolet light.

[0152] A series of sulfur dioxide and its derivative test strips were prepared according to the above method. Sodium sulfite solutions with concentrations of 0, 10, 20, 30, 40, and 50 μg / mL were simultaneously added to the test strips for detection. The fluorescence intensity was observed under ultraviolet light in a dark environment. The time from the addition of the sodium sulfite solution to the appearance of color change was approximately 30 seconds, and the color change stabilized and stopped deepening after about 1 minute. The experiment showed that the concentration of sodium sulfite solution had a certain influence on the fluorescence intensity of Eu-NH2BDC / OX MOF; the higher the concentration of sodium sulfite, the higher the fluorescence intensity of Eu-NH2BDC / OX MOF material under ultraviolet light irradiation. The RGB values ​​of the same sites on each test strip were extracted, and the ratio of their RGB values ​​to concentration was calculated to create a linear curve, as shown in the figure. Figure 24 As shown, the linear relationship is good, r = 0.9978, indicating that the sulfur dioxide test paper has been successfully prepared and has the characteristics of being visual, simple and fast.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing Eu-NH2BDC / OX MOF material, characterized in that, Includes the following steps: The Eu-NH2BDC / OX MOF material was prepared by hydrothermal reaction of europium salt, oxalic acid, 2-aminoterephthalic acid, and 2-fluorobenzoic acid in DMF-nitric acid-water mixture at 115-125℃ for 20-30 hours. The molar ratio of europium salt, oxalic acid, 2-aminoterephthalic acid, and 2-fluorobenzoic acid is (4~5):(1~3):(3~3.5):(40~50).

2. An Eu-NH2BDC / OX MOF material, characterized in that, It is prepared by the preparation method described in claim 1.

3. The application of the Eu-NH2BDC / OX MOF material of claim 2 as a sulfur dioxide ratio fluorescence sensor.

4. The application of the Eu-NH2BDC / OX MOF material of claim 2 in the detection of sulfur dioxide, sulfite, and bisulfite in preserved fruit.

5. A method for fluorescent detection of sulfur dioxide, sulfite, and bisulfite, characterized in that, The Eu-NH2BDC / OX MOF material described in claim 2 is used as a sulfur dioxide ratio fluorescence sensor.

6. The method according to claim 5, characterized in that, Includes the following steps: The test solution was added to the Eu-NH2BDC / OX MOF material dispersion to obtain a mixed solution, the pH was adjusted to 7-11, and the solution was detected by fluorescence spectrophotometry. Fluorescence detection conditions: λex: 300 nm, λem: 450 nm / 615 nm, voltage: 400 V, slit width: 5 nm, scan rate: 3000 nm / min.

7. The method according to claim 6, characterized in that, The dispersant in the Eu-NH2BDC / OX MOF material dispersion is one of methanol, ethanol, acetonitrile, isopropanol, or N,N-dimethylformamide.

8. The application of the Eu-NH2BDC / OX MOF material of claim 2 in the preparation of test paper for sulfur dioxide, sulfite, and bisulfite.

9. A fluorescent test strip for detecting sulfur dioxide, sulfite, and bisulfite, characterized in that, The fluorescent test strip contains the Eu-NH2BDC / OX MOF material as described in claim 2.

10. A method for preparing the fluorescent test paper for sulfur dioxide, sulfite, and bisulfite as described in claim 9, characterized in that, Includes the following steps: Glass fibers were soaked in a dispersion of Eu-NH2BDC / OX MOF material and dried to obtain the fluorescent test paper.

Images