Praseodymium (III) metal organic framework crystalline material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of fluorescence sensing, in particular to a praseodymium (III) metal organic framework crystalline material and a preparation method and application thereof. According to the praseodymium (III) metal organic framework crystalline state material, Pr (III) is used as a central metal ion and forms eight coordination with eight oxygen atoms of six (4-CPCA) 2-ligands. And adjacent Pr (III) are connected through 4-CPCA < 2-> bridging to form a one-dimensional annular chain. And the one-dimensional chains are further bridged and topologically connected through a (4-CPCA) 2-ligand to form a three-dimensional structure. The praseodymium (III) metal organic framework crystalline material has good fluorescent property and stability, and can be applied to the field of fluorescence sensing.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorescence sensing, and particularly to praseodymium(III) metal-organic framework crystalline materials, their preparation methods and applications. Background Art

[0002] The excessive emission of pollutants in the environment has become a very serious international problem. Approximately 20% of diseases are related to heavy metal ions and organic pollutants, and excessive intake of some heavy metal ions will cause irreversible harm to the human body. Among them, silver and iron metals have special properties, such as being chemically active and having good water solubility. Therefore, developing methods for detecting trace silver ions and iron ions in food and environmental samples has become a current research hotspot. Currently, there are many methods for detecting heavy metal ions, such as spectrophotometry, inductively coupled plasma mass spectrometry, neutron activation analysis, and high performance liquid chromatography. However, these methods have disadvantages such as high cost, the need for large instruments and complex pretreatment, the consumption of a large amount of manpower and material resources, and the inability to perform on-site real-time detection. Therefore, it is necessary and urgent to develop a method with high sensitivity, rapidity, convenience and low cost.

[0003] Metal-Organic Frameworks (MOFs for short) are a class of crystalline porous materials with a periodic network structure formed by the self-assembly connection of inorganic metal centers (metal ions or metal clusters) and organic ligands. Due to their unique advantages such as high specific surface area, adjustable pore size, and construction of active sites, they can be widely used in fields such as gas adsorption and separation, catalysis, and optoelectronic devices. And when metal-organic frameworks are used as fluorescence sensors, they can express detection information through changes in optical signals, and have the advantages of strong selectivity, high sensitivity, simple operation, and rapidity. In recent years, they have been increasingly used in quantitative analysis and detection. Among them, rare earth complexes, as a branch, have many advantages. First, their emission spectra are narrow, which can reduce background interference and improve the accuracy of detection; second, rare earth coordination polymers have long-lived fluorescence, which gives them advantages in fields such as time-resolved and in-vivo analysis; and the fluorescence quantum yields of rare earth coordination polymers are relatively high, capable of generating relatively strong fluorescence signals; finally, under most conditions, rare earth coordination polymers have high chemical stability, enabling them to be applied to complex environments. These characteristics make rare earth complexes a hot research object in recent years. Nowadays, rare earth complexes can play a crucial role as fluorescence probes in the detection of metal ions, organic molecules, and antibiotics. Summary of the Invention

[0004] The present invention provides a praseodymium(III) metal-organic framework crystalline material, a preparation method thereof, and an application thereof. The pyridazine carboxylic acid derivative H2(4-CPCA) is selected as an organic ligand and coordinated with the rare earth metal praseodymium (Pr) to obtain a praseodymium(III) metal-organic framework crystalline material, and the chemical formula of a single molecule thereof is {Pr[H(4-CPCA)2]·5H2O} n , with Pr(III) as the central metal ion, respectively coordinating with 8 oxygen atoms of 6 (4-CPCA) 2- ligands to form an octahedral coordination. Adjacent Pr(III) are bridged by 4-CPCA 2- to form a one-dimensional cyclic chain. The one-dimensional chains are further bridged and topologically connected by the (4-CPCA) 2- ligand to form a three-dimensional structure, which has good fluorescence properties and stability and can be applied to the field of fluorescence sensing.

[0005] To solve the above technical problems, the present invention provides a praseodymium(III) metal-organic framework crystalline material, and the chemical formula of a single molecule of the praseodymium(III) metal-organic framework crystalline material is {Pr[H(4-CPCA)2]·5H2O} n .

[0006] The present invention also provides a preparation method of the above-mentioned praseodymium(III) metal-organic framework crystalline material, including the following steps: S1. Add a praseodymium salt and H2(4-CPCA) to an H2O solvent, mix evenly to obtain a mixed solution, adjust the pH value of the mixed solution to 4.2-5.3, and perform a constant-temperature reaction to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, and sequentially wash, filter, and dry the crystallization product to obtain a praseodymium(III) metal-organic framework crystalline material.

[0007] According to the preparation method of the praseodymium(III) metal-organic framework crystalline material provided by the present invention, the praseodymium salt in S1 is any one of PrCl3·7H2O or Pr(NO3)3·6H2O, the temperature condition of the constant-temperature reaction is 110 °C, and the time condition of the constant-temperature reaction is 72 h.

[0008] According to the preparation method of the praseodymium(III) metal-organic framework crystalline material provided by the present invention, the H2(4-CPCA) in S1 is 1-(4-carboxyphenyl-4-oxopyridazine)-3-carboxylic acid, and the structural formula of the H2(4-CPCA) is: .

[0009] According to the preparation method of the praseodymium(III) metal-organic framework crystalline material provided by the present invention, the molar ratio of the praseodymium salt to H2(4-CPCA) in S1 is 0.05 - 0.1 mmol : 0.05 - 0.1 mmol, and the volume of the H2O solvent is 4 mL.

[0010] According to the preparation method of the praseodymium(III) metal-organic framework crystalline material provided by the present invention, the solution used to adjust the pH value of the mixed solution in S1 is sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 0.3 mol / L.

[0011] According to the preparation method of the praseodymium(III) metal-organic framework crystalline material provided by the present invention, the filtration in S2 is vacuum filtration, the drying temperature is 60 °C, and the drying time is 3 h.

[0012] The present invention also provides an application of the above-mentioned praseodymium(III) metal-organic framework crystalline material, and the praseodymium(III) metal-organic framework crystalline material is applied to fluorescence sensing.

[0013] The present invention has the following advantages compared with the prior art: In the present invention, the praseodymium(III) metal-organic framework crystalline material is prepared by a one-pot thermal method. The praseodymium(III) metal-organic framework crystalline material uses Pr(III) as the central metal ion and is respectively coordinated with 8 oxygen atoms of 6 (4-CPCA) 2- ligands to form an octahedral coordination. Adjacent Pr(III) are bridged by 4-CPCA 2- to form a one-dimensional ring chain. The one-dimensional chains are further bridged and topologically connected by (4-CPCA) 2- ligands to form a three-dimensional structure. Due to the good fluorescence properties and stability of the praseodymium(III) metal-organic framework crystalline material, it can be applied to the field of fluorescence sensing. Description of the Drawings

[0014] Figure 1 is the single molecule diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 2 is the one-dimensional ring chain diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 3 is the three-dimensional framework diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 4 is the IR diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 5 is the XRD diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 6 is the solid-state fluorescence spectrum diagram of the praseodymium(III) metal-organic framework crystalline material; Figure 7is the fluorescence emission intensity of the suspension of praseodymium(III) metal-organic framework crystalline materials in different solvents; Figure 8 is the fluorescence spectrum of praseodymium(III) metal-organic framework crystalline materials after adding different volumes of Fe 3+ solution (0.1 mmol / L); Figure 9 is the linear fitting graph of the fluorescence change value of praseodymium(III) metal-organic framework crystalline materials in Fe 3+ solution; Figure 10 is the fluorescence spectrum of praseodymium(III) metal-organic framework crystalline materials after adding different volumes of Ag + solution (0.1 mmol / L); Figure 11 is the linear fitting graph of the fluorescence change value of praseodymium(III) metal-organic framework crystalline materials in Ag + solution. Specific Embodiments

[0015] Example 1 This example provides a preparation method of praseodymium(III) metal-organic framework crystalline materials.

[0016] S1. Add 0.1 mmol of PrCl3·7H2O and 0.1 mmol of H2(4-CPCA) into a glass scintillation vial containing 4 mL of H2O, mix evenly to obtain a mixed solution, adjust the pH value of the mixed solution to 4.2 with a 0.3 mol / L sodium hydroxide solution, and carry out a solvothermal constant-temperature reaction on the mixed solution at 110 °C for 72 h to obtain a reaction product; wherein, H2(4-CPCA) is 1-(4-carboxyphenyl-4-oxo-pyridazine)-3-carboxylic acid, and the structural formula of the H2(4-CPCA) is: ; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, rinse the crystallization product with deionized water, then carry out vacuum filtration to obtain dark green block crystals, place the crystals in an oven at 60 °C for constant-temperature drying for 3 h to obtain Product 1, namely praseodymium(III) metal-organic framework crystalline materials, and the yield is about 84.6%.

[0017] Figure 1 is the single molecule diagram of Product 1, Figure 2 is the one-dimensional ring chain diagram of Product 1, Figure 3 is the three-dimensional framework diagram of Product 1. According to Figures 1 - 3 it can be known that the molecular formula of the product is {Pr[H(4-CPCA)2]·5H2O} n , namely praseodymium(III) metal-organic framework crystalline materials.

[0018] It can be seen from Figures 1 - 3 that the praseodymium(III) metal-organic framework crystalline material prepared in this example uses Pr 3+ as the central metal ion, and forms an octahedral coordination with 8 oxygen atoms of 6 (4-CPCA) 2- ligands respectively. Adjacent Pr(III) are bridged by 4-CPCA 2- to form a one-dimensional chain structure. The one-dimensional chains are further bridged by (4-CPCA) 2- ligands to form a three-dimensional structure. The metal-organic framework {Pr[H(4-CPCA)2]·5H2O} n crystallizes in the space group C2 / c and belongs to the monoclinic system. Its asymmetric structural unit includes 1 Pr 3+ , and 2 deprotonated H2(4-CPCA) ligand molecules. The central metal ion Pr(III) ion forms an octahedral coordination with 8 oxygen atoms of 6 (4-CPCA) 2- ligands. Among them, 4 coordinated O atoms come from the carboxyl and carbonyl groups in two ligands (O3, O4, O3#1 and O4#2) of chelating coordination, and the other 4 coordinated oxygen atoms come from the carboxyl groups in four ligands (O1, O5, O1 and O5) of chelating coordination. Along the a-axis direction, adjacent Pr 3+ are bridged by 4-CPCA 2- to form a one-dimensional chain structure. The one-dimensional chains are further bridged by (4-CPCA) 2- ligands to form a three-dimensional structure.

[0019] Due to its good fluorescence properties and good stability, it can be applied to the field of fluorescence sensing.

[0020] Example 2 This example provides a preparation method of a praseodymium(III) metal-organic framework crystalline material.

[0021] S1. Add 0.05 mmol of Pr(NO3)3·6H2O and 0.05 mmol of H2(4-CPCA) to a glass scintillation vial containing 4 mL of H2O, mix well to obtain a mixed solution, adjust the pH value of the mixed solution to 4.8 with a 0.3 mol / L sodium hydroxide solution, and carry out a solvothermal constant-temperature reaction on the mixed solution at 110 °C for 72 h to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, rinse the crystallization product with deionized water, then carry out vacuum filtration to obtain dark green block-shaped crystals, and place the crystals in an oven at 60 °C for constant-temperature drying for 3 h to obtain the product praseodymium(III) metal-organic framework crystalline material, and the yield is about 82.2%.

[0022] Example 3 This example provides a method for preparing a praseodymium(III) metal-organic framework crystalline material.

[0023] S1. Add 0.06 mmol of PrCl3·7H2O and 0.06 mmol of H2(4-CPCA) to a glass scintillation vial containing 4 mL of H2O, mix well to obtain a mixed solution, adjust the pH value of the mixed solution to 4.9 with a 0.3 mol / L sodium hydroxide solution, and carry out a solvothermal constant-temperature reaction on the mixed solution at 110 °C for 72 h to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, rinse the crystallization product with deionized water, then carry out vacuum filtration to obtain dark green block-shaped crystals, place the crystals in an oven at 60 °C for constant-temperature drying for 3 h to obtain the product praseodymium(III) metal-organic framework crystalline material, and the yield is about 82.8%.

[0024] Example 4 This example provides a method for preparing a praseodymium(III) metal-organic framework crystalline material.

[0025] S1. Add 0.09 mmol of Pr(NO3)3·6H2O and 0.09 mmol of H2(4-CPCA) to a glass scintillation vial containing 4 mL of H2O solvent, mix well to obtain a mixed solution, adjust the pH value of the mixed solution to 5.2 with a 0.3 mol / L sodium hydroxide solution, and carry out a solvothermal constant-temperature reaction on the mixed solution at 110 °C for 72 h to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, rinse the crystallization product with deionized water, then carry out vacuum filtration to obtain dark green block-shaped crystals, place the crystals in an oven at 60 °C for constant-temperature drying for 3 h to obtain the product praseodymium(III) metal-organic framework crystalline material, and the yield is about 83.6%.

[0026] Example 5 This example provides a method for preparing a praseodymium(III) metal-organic framework crystalline material.

[0027] S1. Add 0.08 mmol of PrCl3·7H2O and 0.08 mmol of H2(4-CPCA) to a glass scintillation vial containing 4 mL of H2O solvent, mix well to obtain a mixed solution, adjust the pH value of the mixed solution to 5.3 with a 0.3 mol / L sodium hydroxide solution, and carry out a solvothermal constant-temperature reaction on the mixed solution at 110 °C for drying for 72 h to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product. Rinse the crystallization product with deionized water, then perform vacuum filtration to obtain dark green massive crystals. Place the crystals in an oven at 60 °C and keep them at a constant temperature for 3 h to obtain the product praseodymium(III) metal-organic framework crystalline material, with a yield of approximately 82.4%.

[0028] Example 6 Take the final product 1 prepared in Example 1, namely the praseodymium(III) metal-organic framework crystalline material, for characterization.

[0029] (1) Determination of the crystal structure of the praseodymium(III) metal-organic framework crystalline material Select a single crystal with a size of 0.11×0.11×0.11 under a microscope and perform X-ray diffraction experiments at room temperature.

[0030] Collect diffraction data on a Bruker-ApexП X-ray single crystal diffractometer, using Mo-Kα radiation (λ = 0.71073 Å) monochromatized by a graphite monochromator, and collect diffraction points in the ω-2θ scanning mode. All data are corrected by factors and empirical absorption. The crystal structure is solved by a direct method using a program, and hydrogen atoms are determined by difference Fourier synthesis and fixed at the calculated optimal positions. Using the OLEX2 program, a full matrix least squares refinement based on all non-hydrogen atoms and their anisotropic thermal parameters was carried out. The main crystallographic determination data of the praseodymium(III) metal-organic framework crystalline material are shown in Tables 1 and 2, and the important bond length and bond angle data of the praseodymium(III) metal-organic framework crystalline material are shown in Table 2. The crystal structure is as Figure 1 shown, and its one-dimensional ring chain is as Figure 2 shown, and the three-dimensional structure is as Figure 3 shown.

[0031] Table 1

[0032] Table 2

[0033] Symmetry codes: # 1 1-x, +y, 3 / 2-z; # 2 3 / 2-x, 3 / 2-y, 1-z; # 3 -1 / 2+x, 3 / 2-y, 1 / 2+z; # 4 -1 / 2+x, 1 / 2+y, +z; # 5 3 / 2-x, 1 / 2+y, 3 / 2-z; In Table 1, a, b, and c represent the edge lengths of the crystal in the three crystal axis directions, and α, β, and γ represent the angles between the three axes a and b, a and c, and b and c, respectively; Zis the number of molecules contained in the unit cell; the diffraction index range of the restraint factor is (h, k, l); F(000) is the number of electrons in the unit cell; Final 1 R indices [I>2σ(I)] are the residual factor R values for observable diffraction points; R is the non-weighted goodness-of-fit factor; R1 and wR2 are both weighted goodness-of-fit factors; Pr1 in the first row of Table 2 refers to Pr atom 1 in the single crystal of the Pr(III) metal-organic framework crystalline material, O1 1 refers to the symmetry atom 1 of O atom 1 in the single crystal of the Pr(III) metal-organic framework crystalline material, Pr1-O1 1 represents the bond length between Pr atom 1 and the symmetry atom 1 of O atom 1, and its bond length is 2.432±12, where 12 is the standard deviation; O1 1 -Pr1-O1 represents the bond angle between the symmetry atom 1 of O atom 1, Pr atom 1 and O atom 1, and its bond angle is 77.86±6; (2) Infrared (IR) spectrum characterization Figure 3 is the IR spectrum of the Pr(III) metal-organic framework crystalline material and H2(4-CPCA). The sample infrared spectrum collection data is 500~4000 cm -1 , using KBr pressing tablets, and it can be seen from Figure 4 that the two peaks between 1507~1598 cm -1 are the stretching vibration peaks of the benzene ring, and the stretching vibration peak of the O-H bond in water molecules is at 3600 cm -1 , and the stretching vibration peak of the carbonyl group is at 1654 cm -1 .

[0034] (3) Phase purity characterization of the Pr(III) metal-organic framework crystalline material The powder XRD characterization results of the Pr(III) metal-organic framework crystalline material using a Bruker / D8Advance X-ray diffractometer show that it has reliable phase purity, which provides a guarantee for its use as a fluorescence probe to detect excessive organic pollutants, pesticides, and heavy metal ions in the environment, as Figure 5 shown.

[0035] Fluorescence sensing performance of the Pr(III) metal-organic framework crystalline material Using an Edinburgh instruments / FLS 1000 fluorescence spectrometer, the solid fluorescence performance of the Pr(III) metal-organic framework crystalline material was tested. The Pr(III) metal-organic framework crystalline material has a strong fluorescence emission peak at 430 nm with an excitation wavelength of 360 nm, as Figure 6 shown.

[0036] Weigh 2.0 mg of the powdered sample of praseodymium(III) metal-organic framework crystalline material after sufficient grinding and place it separately in 7 kinds of 3 mL organic solvents. After ultrasonic treatment for half an hour and standing for one hour, take the supernatant and place it in a cuvette. At an excitation wavelength of 254 nm, measure its fluorescence emission intensity in suspensions with ethanol (EtOH), acetonitrile (ACN), N,N'-dimethylacetamide (DMA), N,N'-dimethylformamide (DMF), N,N-diethylformamide (DEF), 2,2'-dihydroxydiethylamine (DEA), and water as solvents (see Figure 7 ). As can be seen from Figure 7 , the praseodymium(III) metal-organic framework crystalline material has the strongest fluorescence intensity in ethanol solvent and the lowest fluorescence intensity in DEF solvent.

[0037] The photoluminescence (PL) properties of the praseodymium(III) metal-organic framework crystalline material were studied at room temperature, and fluorescence sensing experiments were carried out in an ethanol suspension. Immerse 2 mg of the powdered sample of the praseodymium(III) metal-organic framework crystalline material in 4 mL of ethanol to dissolve it, and then obtain a stable suspension after ultrasonic treatment for 20 min. Prepare suspension solutions of metal cations such as 0.01 mol / L Na + , K + , Pb 2+ , Cd 2+ , Zn 2+ , Mn 2+ , Ba 2+ , Hg 2+ , Ca 2+ , Co 2+ , Ag + , Ni 2+ , Cu 2+ , Eu 3+ , Sm 3+ , Nd 3+ , Gd 3+ , Pr 3+ , Dy 3+ , La 3+ , Ho 3+ , Lu 3+ etc. for qualitative research. Each time, add 3 μL of the above-prepared metal cation suspension solution with a concentration of 0.01 mol / L for quantitative titration research, and record and collect the fluorescence spectra under excitation at a wavelength of 254 nm.

[0038] At an excitation wavelength of 360 nm, the corresponding fluorescence emission intensity of the praseodymium(III) metal-organic framework crystalline material is as shown in Figure 6 . By comparing the changes in the luminescence intensity caused by each metal ion, a fluorescence quenching effect occurs with the addition of Fe 3+ , and with the addition of Ag+ The addition results in an enhanced fluorescence effect.

[0039] To study the ability of praseodymium(III) metal-organic framework crystalline materials as fluorescent probes for detecting Fe 3+ and Ag + based on the obtained experimental data for further analysis, Figure 8 Figure [0000229] shows the fluorescence spectra of praseodymium(III) metal-organic framework crystalline materials after adding different volumes of Fe 3+ solution (0.1 mmol / L). Figure 9 Figure [0000230] is the linear fitting graph of the fluorescence change value of praseodymium(III) metal-organic framework crystalline materials in Fe 3+ solution. It can be seen from Figure 8 and Figure 9 that the fluorescence intensity of praseodymium(III) metal-organic framework crystalline materials at 510 nm wavelength decreases with the increase of Fe 3+ ion concentration and shows a good linear relationship in a certain concentration range (R 2 = 0.99454).

[0040] Figure 10 Figure [0000233] shows the fluorescence spectra of praseodymium(III) metal-organic framework crystalline materials after adding different volumes of Ag + solution (0.1 mmol / L). With the increase of Ag + concentration, the fluorescence intensity of the coordination polymer gradually increases. Figure 11 Figure [0000236] is the linear fitting graph of the fluorescence change value of praseodymium(III) metal-organic framework crystalline materials in Ag + solution. Fitting by the Stern-Volmer equation (I0 - I) / I = K sv φ (I0 and I are the fluorescence intensities before and after adding Ag + respectively, φ is the volume fraction of Ag + , and Ksv is the quenching constant), the linear correlation coefficient R 2 = 0.96959.

[0041] The limit of detection (LOD) is also an important indicator to measure the fluorescence detection ability. The limit of detection (LOD) can be calculated by the formula 3σ / K sv (where σ is the standard deviation value of the fluorescence intensity of 11 blank experiments of the test complex without adding any ions). Calculated from the limit of detection formula: the limit of detection of praseodymium(III) metal-organic framework crystalline materials for Fe 3+ is: 2.61×10 -6 mol·L -1 , and the limit of detection for Ag + is: 5.53×10 -6 mol·L -1。Compared with other fluorescence sensors of coordination polymers, the praseodymium(III) metal-organic framework crystalline material has a lower detection limit and a wider linear detection range.

[0042] As described above, it is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any simple modification, change, and equivalent change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A praseodymium(III) metal-organic framework crystalline material, characterized in that, The single-molecule chemical formula of the praseodymium(III) metal-organic framework crystalline material is {Pr[H(4-CPCA)2]·5H2O} n .

2. A preparation method of the praseodymium (III) metal-organic framework crystalline material as described in claim 1, characterized in that, It includes the following steps: S1. Add praseodymium salt and H2(4-CPCA) into H2O, mix evenly to obtain a mixed solution, adjust the pH value of the mixed solution to 4.2 - 5.3, carry out a constant-temperature reaction to obtain a reaction product; S2. Cool the reaction product obtained in S1 for crystallization to obtain a crystal product, and sequentially wash, filter and dry the crystallization product to obtain a praseodymium(III) metal-organic framework crystalline material.

3. The preparation method of the praseodymium (III) metal-organic framework crystalline material according to claim 2, wherein The praseodymium salt described in S1 is any one of PrCl3·7H2O or Pr(NO3)3·6H2O, the temperature condition of the constant-temperature reaction is 110 °C, and the time condition of the constant-temperature reaction is 72 h.

4. The preparation method of the praseodymium (III) metal-organic framework crystalline material according to claim 2, wherein H2(4-CPCA) described in S1 is 1-(4-carboxyphenyl-4-oxo-pyridazine)-3-carboxylic acid, and the structural formula of H2(4-CPCA) is: 。 5. The preparation method of the praseodymium (III) metal-organic framework crystalline material according to claim 2, wherein, The molar ratio of the praseodymium salt and H2(4-CPCA) described in S1 is 0.05 - 0.1 mmol: 0.05 - 0.1 mmol, and the volume of H2O is 4 mL.

6. The preparation method of the praseodymium (III) metal-organic framework crystalline material according to claim 2, wherein The solution used to adjust the pH value of the mixed solution in S1 is a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 0.3 mol / L.

7. The preparation method of the praseodymium(III) metal-organic framework crystalline material according to claim 2, characterized in that, The filtration in S2 is vacuum filtration, the drying temperature is 60 °C, and the drying time is 3 h.

8. Use of the praseodymium (III) metal-organic framework crystalline material as described in claim 1, characterized in that, The praseodymium(III) metal-organic framework crystalline material is applied to fluorescence sensing.

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