A pyrazole carboxylic acid rare earth MOF luminescent material and its preparation and application

Abstract

The present invention discloses a pyrazole carboxylic acid rare earth MOF luminescent material and its preparation and application, belonging to the technical field of sensor materials. The luminescent material is prepared by a solvothermal method by mixing 3-carboxymethoxy-1-carboxymethylpyrazole-4-carboxylic acid as an organic ligand with a terbium salt. The chemical expression is {[Tb2(ccpc)2(H2O)6]·1.5H2O} n , each asymmetric unit contains 2 Tb 3+ ions, 2 3-carboxymethoxy-1-carboxymethylpyrazole-4-carboxylates, 6 coordinated water molecules and 1.5 lattice water molecules. The MOF material can efficiently emit strong green light under light excitation of 265nm wavelength, with a quantum efficiency of 77.5%. When used for TNP sensing, the fluorescence quenching constant is 61119L / mol and the detection limit is 0.28μmol / L. The synthesis method of this material is simple, the performance is stable, and it has great potential application value in the field of fluorescence sensing.

Description

Technical Field

[0001] The invention relates to the technical field of sensing materials, and in particular to a pyrazolecarboxylic acid rare earth MOF luminescent material and a preparation method and application thereof. Background Art

[0002] With the rapid development of industrialization, many pollutants are also discharged into the existing living environment of human beings, and various toxic pollutants seriously threaten the ecosystem and human health. Nitroaromatic compounds, heavy metal ions and small organic molecules are all common pollutants. Although these substances occupy an important position in industrial production, they are highly toxic and difficult to degrade naturally. Therefore, rapid and selective detection of such compounds has become one of the most important topics.

[0003] Traditional detection methods such as inductively coupled plasma mass spectrometry, chromatography, atomic absorption spectroscopy, ion mobility spectrometry, etc., all have the disadvantages of complex operation, high cost and long time consumption. Fluorescence sensing has attracted much attention from researchers in this field due to its advantages such as fast response speed, simple operation and good stability.

[0004] Metal organic framework (MOF) is a new type of porous material formed by metal ions or metal clusters connected to organic ligands through coordination bonds. It has the characteristics of high porosity, large specific surface area, and rich structure. It has been widely used in catalysis, gas storage, adsorption, and chemical sensing. Among them, rare earth MOF materials have an "antenna effect". Organic ligands can absorb ultraviolet light and sensitize rare earth ions to emit light. Therefore, rare earth MOF materials have the advantages of pure chromaticity, long life, and large Stokes shift. It is precisely because rare earth MOF has excellent photoluminescence properties that it can provide an ideal fluorescent sensing material for detecting anions, cations, explosive molecules, etc.

[0005] For example, Zi-Ying Li et al. published a paper titled “A highly stable terbium metal-organic framework for efficient detection of picric acid in water. Chinese Chemical Letters 32 (2021) 3095–3098” that describes a highly stable fluorescent Tb-MOF (Tb 4 (paip) 6 1.2H 2O), the ligand paip used is 5-(1H-pyrazol-4-yl) isophthalate. The material shows obvious terbium characteristic green light under ultraviolet light excitation. Under the action of electron transfer quenching mechanism, the MOF material can be used to detect picric acid (2,4,6-trinitrophenol) in aqueous solution, and the fluorescence quenching constant can reach 2.012×10 4 L / mol, the detection limit can reach 1.3×10 -5 mol / L. Although this material also has high sensitivity and selectivity, its quantum efficiency is only 21.0%, and there is still room for improvement in terms of effect. The main reason for this problem is that when the ligand sensitizes the rare earth ions to emit light, only when the absorption coefficient of the ligand is large and its triplet energy matches the energy level of the rare earth ions, the luminescence quantum efficiency of the rare earth MOF material formed can be higher, the luminescence intensity can be greater, and its corresponding detection sensitivity is more accurate. In addition, the luminescence performance of the material is closely related to the structure of the rare earth MOF material. Therefore, by designing appropriate ligands, developing and researching novel high quantum efficiency photoluminescent rare earth MOF materials is the current research direction in this field.

[0006] Pyrazole carboxylic acid compounds have a high absorption coefficient in the ultraviolet region because they contain pyrazole aromatic conjugated rings, and they contain multiple coordination sites between pyrazole nitrogen and carboxyl oxygen, making them an ideal choice for constructing MOF materials. 3-Carboxymethoxy-1-carboxymethyl-4-pyrazole carboxylic acid contains two flexible carboxyl groups and one rigid carboxyl substituent, and its triplet energy is similar to that of Tb 3+ Based on the above considerations, if a new structure of rare earth MOF material is prepared using 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid and terbium salt as reactants, it is expected to achieve high quantum efficiency and provide a good choice for the development of sensing materials. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and provide a pyrazolecarboxylic acid rare earth MOF luminescent material and its preparation and application. The synthesis method of the material is simple, the performance is stable, and it has good potential application value in the field of fluorescence sensing.

[0008] In order to achieve the above technical objectives, the present invention is implemented by the following technical solutions: The present invention provides a pyrazole carboxylic acid rare earth MOF luminescent material, whose chemical formula is {[Tb 2 (ccpc) 2 (H 2 O) 6 ]·1.5H 2 O} n , which is a H 3Metal-organic framework materials containing Tb metal ions with ccpc as ligand, ccpc 3- It is a 3-carboxymethoxy-1-carboxymethyl-4-pyrazole carboxylic acid ligand anion; each asymmetric unit of the MOF material contains 2 Tb 3+ ions, 2 3-carboxymethoxy-1-carboxymethylpyrazole-4-carboxylates, 6 coordinated water molecules and 1.5 lattice water molecules. Its molecular structure is shown below:

[0009]

[0010] Furthermore, the MOF material belongs to the triclinic system, P-1 space group, and the unit cell parameters are: α=78.2750°, β=79.5600°, γ=72.4270°,

[0011] Furthermore, the asymmetric units of the MOF material are interconnected to form a two-dimensional layered structure.

[0012] The preparation method of the above-mentioned pyrazole carboxylic acid rare earth MOF luminescent material is as follows:

[0013] (1) dissolving 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid and terbium salt in a mixed solvent of water and DMF, and mixing by ultrasonication;

[0014] (2) placing the mixed solution in an oven for hydrothermal reaction, cooling to room temperature, filtering, washing, and drying to obtain a pyrazolecarboxylic acid rare earth MOF luminescent material.

[0015] Furthermore, in step (1), the molar ratio of terbium salt to 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid is 1 to 2:1.

[0016] Furthermore, in step (1), the terbium salt used is terbium nitrate hexahydrate or terbium chloride hexahydrate.

[0017] Furthermore, in step (1), the volume ratio of water to DMF in the mixed solvent is 1 to 4:1.

[0018] Furthermore, in step (2), the temperature of the hydrothermal reaction is 80-90° C., and the reaction time is 48-72 h.

[0019] The above-mentioned pyrazolecarboxylic acid rare earth MOF luminescent material can be used in the field of fluorescence sensing. Under ultraviolet light, the material emits the characteristic green light of Tb. Under 265nm light excitation conditions, the quantum efficiency reaches 77.5%. It has high selectivity and high sensitivity sensing for 2,4,6-trinitrophenol, the fluorescence quenching constant is 61119L / mol, and the detection limit is 0.28μmol / L.

[0020] The beneficial effects of the present invention are:

[0021] 1. The pyrazole carboxylic acid rare earth MOF luminescent material disclosed in the present application is based on 3-carboxymethoxy-1-carboxymethylpyrazole-4-carboxylic acid (H 3 The metal organic framework material is prepared by solvent thermal reaction after mixing ccpc) as an organic ligand with terbium salt. 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid has a high absorption coefficient in the ultraviolet region, and the triplet energy of the ligand is similar to that of Tb 3+ The energy level of Tb is well matched, so it can well sensitize Tb 3+ Luminescence, so that the quantum efficiency of the terbium pyrazolecarboxylate MOF material prepared in the present application can reach 77.5%;

[0022] 2. The pyrazole carboxylic acid rare earth MOF luminescent material disclosed in the present application can efficiently emit strong green light under light excitation of 265nm wavelength. When applied to the sensing of trinitrophenol, the fluorescence quenching constant is 61119L / mol, and the detection limit is as low as 0.28μmol / L, showing high selectivity and high sensitivity;

[0023] 3. The synthesis method of the pyrazolecarboxylic acid rare earth MOF luminescent material disclosed in this application is simple and the preparation conditions are mild. It has great potential application value in the field of fluorescence sensing and can also provide new ideas for the design of new fluorescence sensing materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the minimum asymmetric unit structure diagram of pyrazole carboxylic acid rare earth MOF luminescent material;

[0025] Figure 2 This is a SEM image of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1;

[0026] Figure 3 The powder XRD and single crystal simulated XRD patterns of the pyrazolecarboxylic acid rare earth MOF luminescent materials prepared in Examples 1 to 3;

[0027] Figure 4 This is the infrared spectrum of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1;

[0028] Figure 5 Thermogravimetric analysis spectrum of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1;

[0029] Figure 6 This is an emission spectrum of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1 under 265nm excitation light irradiation;

[0030] Figure 7The emission spectra of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1 in different nitroaromatic compound solutions;

[0031] Figure 8 This is a characteristic peak intensity diagram of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1 in different nitroaromatic compound solutions at 542 nm;

[0032] Fig. 9 This is a graph showing the emission spectrum changes of the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1 in 2,4,6-trinitrophenol solutions of different concentrations. DETAILED DESCRIPTION

[0033] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the essence of the present invention, modifications and substitutions made to the methods, steps or conditions of the present invention all fall within the scope of the present invention.

[0034] Example 1: Preparation of a pyrazole carboxylic acid rare earth MOF luminescent material

[0035] Weigh 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid (0.03mmol, 7.3mg) and terbium nitrate hexahydrate (0.03mmol, 13.6mg) into a glass bottle, add 3.5mL of distilled water and 1.0mL of N,N-dimethylformamide solution, and dissolve by ultrasonication; place the glass bottle in an oven and react at 90°C for 72h; after the reaction, the product is cooled to room temperature, filtered, washed with distilled water and ether, and dried to obtain 9.1mg of the product.

[0036] The structural formula of the ligand 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid is as follows:

[0037]

[0038] The obtained product was characterized by infrared spectroscopy (see Figure 4 ), the specific results are: 3249 (m), 1608 (w), 1566 (s), 1435 (m), 1383 (m), 1321 (m), 1190 (m), 1031 (m), 893 (w), 704 (w). At 3249cm -1 The broad peak at 1435 cm is caused by the stretching vibration of OH in water. -1 The absorption peak at 1608 cm represents the stretching vibration of the C=C bond. -1 and 1321cm -1 The absorption peaks at are attributed to the stretching vibrations of the C=O and CO bonds on the carboxyl group, respectively.

[0039] Example 2: Preparation of a pyrazole carboxylic acid rare earth MOF luminescent material

[0040] Weigh 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid (0.03mmol, 7.3mg) and terbium nitrate hexahydrate (0.03mmol, 13.6mg) into a glass bottle, add 3.5mL of distilled water and 1.0mL of N,N-dimethylformamide solution, and dissolve by ultrasonication; place the glass bottle in an oven and react at 80°C for 72h; after the reaction, the product is cooled to room temperature, filtered, washed with distilled water and ether, and dried to obtain 8.7mg of the product.

[0041] Example 3: Preparation of a pyrazole carboxylic acid rare earth MOF luminescent material

[0042] Weigh 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid (0.03mmol, 0.0073g) and terbium chloride hexahydrate (0.03mmol, 11.2mg) into a glass bottle, add 3.0mL of distilled water and 1.0mL of N,N-dimethylformamide solution, and dissolve by ultrasonication; place the glass bottle in an oven and react at 90°C for 72h; after the reaction, the product is cooled to room temperature, filtered, washed with distilled water and ether, and dried to obtain 8.9mg of the product.

[0043] Figure 1 The minimum asymmetric unit diagram of the pyrazole carboxylic acid rare earth MOF luminescent material, which is composed of 2 Tb 3+ ions, two completely deprotonated ligand anions (ccpc 3- ), 6 coordinated water molecules and 1.5 lattice water molecules, and the asymmetric units are interconnected to form a two-dimensional layered structure. 3+ The ions are all in an octahedral coordination mode, showing a dodecahedral coordination environment. The two H 3 The ccpc organic ligands adopt the same coordination mode for coordination.

[0044] Figure 2 This is a SEM image of the product obtained in Example 1. From the overall perspective, the sample presents a block crystal. When the side of each crystal is enlarged, it can be seen that each block crystal is composed of many sub-layers stacked together. This macroscopic morphology is consistent with the single crystal X-ray analysis results (two-dimensional layered structure).

[0045] Figure 3 The figures are comparison results of the powder XRD patterns and single crystal XRD patterns of the products prepared in Examples 1 to 3. It can be seen from the figures that the three examples prepare the same products with high phase purity.

[0046] Figure 5This is the thermogravimetric analysis spectrum of the product obtained in Example 1. After analysis, in a nitrogen environment, there is an obvious weight loss platform when the temperature rises to 320°C, and the weight loss rate is 14.57%, corresponding to the detachment of 6 coordinated water and 1.5 lattice water.

[0047] Figure 6 The emission spectrum of the pyrazole carboxylic acid rare earth MOF luminescent material prepared in Example 1 under the irradiation of the excitation light with a wavelength of 265 nm. The prepared complex exhibits strong green light under the excitation light with a wavelength of 265 nm, and the quantum efficiency reaches 77.5%. The emission spectrum shows that Tb 3+ The typical luminescence of ions, with emission peak positions at 488nm, 542nm, 581nm, 622nm and 649nm, is attributed to Tb 3+ Ion-electron energy levels 5 D 4 → 7 F j (J = 6, 5, 4, 3 and 2), the strongest characteristic peak is located at 5 D 4 → 7 F 5 of 542nm.

[0048] Related performance testing

[0049] The pyrazole carboxylic acid rare earth MOF luminescent material prepared in Example 1 was used to carry out a fluorescence sensing experiment on nitro aromatic compounds.

[0050] The pyrazole carboxylic acid rare earth MOF luminescent material prepared in Example 1 was ground into powder with a mortar, added to a methanol solution to obtain a 2 mg / mL suspension, and ultrasonically treated for 1 h to mix it evenly; 2 mL of the suspension was taken in a four-way cuvette, and its fluorescence emission spectrum was tested at room temperature and used as a blank control group, and then 1 mL of the suspension was taken and dispersed in 1 mL of a methanol solution containing 2 mmol / L of different nitroaromatic compounds (NACs), NACs including: 2,4,6-trinitrophenol (TNP), 2-nitrotoluene (2-NT), 3-nitrotoluene (3-NT), 4-nitrotoluene (4-NT), p-nitrophenol (PNP), 2,4-dinitrotoluene (2,4-DNT) and nitrobenzene (NB), after mixing evenly, the luminescence response was measured under the same conditions, and the results are as follows: Figure 7 As shown in the figure, different nitroaromatic compounds have different degrees of quenching effect on the fluorescence properties of pyrazolecarboxylic acid rare earth MOF luminescent materials. It is worth noting that 2,4,6-trinitrophenol has the most significant fluorescence quenching effect on pyrazolecarboxylic acid rare earth MOF luminescent materials, with a quenching efficiency of up to 98.26%.

[0051] When different nitroaromatic compounds quench the complex, the selectivity can be judged by the fluorescence quenching efficiency, and the quenching efficiency η=1-I / I 0 , where I 0 and I are the fluorescence intensities before and after adding the analyte solution. The calculated fluorescence quenching efficiency of different NACs on pyrazole carboxylic acid rare earth MOF luminescent materials:

[0052] serial number Nitroaromatic compounds Fluorescence quenching efficiency η / % 1 TNP 98.26 2 4-NT 22.71 3 2-NT 30.54 4 3-NT 29.84 5 PNP 33.16 6 NB 46.84 7 2,4-DNT 57.16

[0053] Among them, the fluorescence quenching rate of 2,4,6-trinitrophenol (TNP) on pyrazolecarboxylic acid rare earth MOF luminescent material is as high as 98.26%, which is highly selective.

[0054] From the above content, it can be seen that the pyrazolecarboxylic acid rare earth MOF luminescent material prepared in Example 1 has shown highly selective quenching of 2,4,6-trinitrophenol. Next, its linear relationship and detection limit are further determined by titration experiments.

[0055] (1) Take 2 mL of 2 mg / mL pyrazole carboxylic acid rare earth MOF luminescent material suspension in a four-way cuvette and gradually add 2 mmol / L TNP solution until the TNP concentration increases from 0 μmol / L to 180 μmol / L. The emission spectrum changes as shown in the figure. Fig. 9 As shown in the figure, when the TNP concentration reaches 180 μmol / L, the fluorescence intensity is almost completely quenched;

[0056] (2) Select the fluorescence intensity at 542 nm and the TNP concentration as the coordinate axes and draw the Stern-Volmer (SV) curve. Fig. 9 It can be seen that a good linear relationship is shown in the low concentration range of TNP from 0 to 50 μmol / L, and the correlation coefficient R 2 Reaching 0.9944, the slope of the linear equation is 61119L / mol; that is, the quenching constant K sv , K sv From equation I 0 / I=K sv [Q] + 1 is calculated, where I 0 and I are the fluorescence intensities before and after adding the analyte solution, respectively, and [Q] is the concentration of the analyte.

[0057] (3) The detection limit can be calculated according to the formula LOD = 3σ / K sv where σ is the standard deviation of fluorescence intensity of five blank samples at 542 nm wavelength, K sv is the slope of the linear equation corresponding to low concentration TNP. The detection limit obtained after calculation is 0.28 μmol / L, which further proves that the sensitivity of pyrazolecarboxylic acid rare earth MOF material in sensing TNP is very high.

[0058] The above shows and describes the basic principles, main features and advantages of the present invention. However, the above is only a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other implementation methods derived by any technician in the field without departing from the technical solution of the present invention should be included in the patent scope of the present invention.

Claims

1. A pyrazolecarboxylic acid rare earth MOF luminescent material, characterized in that: Its chemical formula is {[Tb2(ccpc)2(H2O)6]·1.5H2O} n , which is a metal organic framework material containing Tb metal ions with H3ccpc as ligand. 3- is a 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid ligand anion; Each asymmetric unit of the MOF material contains 2 Tb 3+ ions, 2 3-carboxymethoxy-1-carboxymethylpyrazole-4-carboxylates, 6 coordinated water molecules and 1.5 lattice water molecules; The molecular structure of the MOF material is shown below: The MOF material belongs to the triclinic system, P-1 space group, and the unit cell parameters are: α=78.2750°, β=79.5600°, γ=72.4270°, 2. The pyrazolecarboxylic acid rare earth MOF luminescent material according to claim 1, characterized in that: The asymmetric units of this MOF material are interconnected to form a two-dimensional layered structure.

3. The method for preparing the pyrazolecarboxylic acid rare earth MOF luminescent material according to any one of claims 1 to 2, characterized in that: The specific preparation steps are as follows: (1) dissolving 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid and terbium salt in a mixed solvent of water and DMF, and mixing by ultrasonication; (2) placing the mixed solution in an oven for hydrothermal reaction, cooling to room temperature, filtering, washing, and drying to obtain a pyrazolecarboxylic acid rare earth MOF luminescent material.

4. The method for preparing the pyrazolecarboxylic acid rare earth MOF luminescent material according to claim 3, characterized in that: In step (1), the molar ratio of terbium salt to 3-carboxymethoxy-1-carboxymethyl-4-pyrazolecarboxylic acid is 1 to 2:

1.

5. The method for preparing the pyrazolecarboxylic acid rare earth MOF luminescent material according to claim 3, characterized in that: In step (1), the terbium salt used is terbium nitrate hexahydrate or terbium chloride hexahydrate.

6. The method for preparing the pyrazolecarboxylic acid rare earth MOF luminescent material according to claim 3, characterized in that: In step (1), the volume ratio of water to DMF in the mixed solvent is 1 to 4:

1.

7. The method for preparing the pyrazolecarboxylic acid rare earth MOF luminescent material according to claim 3, characterized in that: In step (2), the temperature of the hydrothermal reaction is 80-90° C., and the reaction time is 48-72 hours.

8. Application of the pyrazolecarboxylic acid rare earth MOF luminescent material according to any one of claims 1 to 2 in the field of fluorescence sensing, characterized in that: Under ultraviolet light, the material emits the characteristic green light of Tb. Under 265nm light excitation conditions, it has high selectivity and high sensitivity for sensing 2,4,6-trinitrophenol, with a fluorescence quenching constant of 61119L / mol and a detection limit of 0.28μmol / L.

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