Rare earth metal europium framework and its preparation method and application for turn-on detection of cadmium ions and synergistic turn-off response to copper ions and glutamic acid

Abstract

The present invention relates to the field of fluorescence sensing technology, and particularly to a rare earth metal europium framework, a preparation method thereof, and an application for turn-on detection of cadmium ions and synergistic turn-off response to copper ions and glutamic acid. The rare earth metal europium framework of the present invention is prepared by a one-pot solvothermal reaction. The rare earth metal europium framework is a europium(III) coordination polymer, and the chemical formula of the europium(III) coordination polymer is [Eu(bppc)3(H2O)4]·5H2O, and its molecular formula is C 42 H 24 EuN 15 O 15 . This preparation method has the advantages of simple process, convenient operation, high yield, and good reproducibility. The rare earth metal europium framework prepared by the present invention has good fluorescence properties, shows high selectivity and high sensitivity to glutamic acid, and can effectively detect glutamic acid through the fluorescence quenching phenomenon.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorescence sensing, and particularly to a rare earth metal europium skeleton, a preparation method thereof, and an application for the turn-on detection of cadmium ions and the synergistic turn-off response to copper ions and glutamic acid. Background Art

[0002] Amino acids are crucial for maintaining normal physiological functions of humans, of great significance to human life and health, and play important roles in the ecosystem and industrial development, affecting human life, the natural environment, and social progress in all aspects. Glutamic acid, as a key amino acid, plays important roles in biology, ecology, industry, and the environment. It is not only an important raw material for protein synthesis but also serves as the main excitatory neurotransmitter in the central nervous system, participating in physiological processes such as learning and memory. Microorganisms in the soil can utilize glutamic acid to decompose organic substances, release nutrients required for plant growth, promote the growth and development of plants, and thus maintain the stability of the ecosystem. Glutamic acid is the main component of monosodium glutamate, which can significantly enhance the flavor of food, participate in drug synthesis, and be used to treat certain diseases. Glutamic acid can be decomposed by microorganisms in the natural environment, participate in the material cycle, and reduce the environmental pressure of waste to a certain extent. At the same time, the reasonable use of glutamic acid-related products, such as amino acid fertilizers, can reduce the use of chemical fertilizers and is beneficial to environmental protection.

[0003] Excessive glutamic acid can also bring many hazards. In terms of human health, excessive intake of glutamic acid may disrupt the excitatory-inhibitory balance of the nervous system, over-stimulate nerve cells, and cause discomfort symptoms such as headache, dizziness, and fatigue. Long-term excessive intake may also be related to nervous system diseases such as Alzheimer's disease and Parkinson's disease. For people with allergic constitutions, excessive glutamic acid may also trigger allergic reactions such as skin itching, redness, and shortness of breath. In the ecological environment, if a large amount of glutamic acid-containing waste is directly discharged without treatment, it may lead to water eutrophication, excessive growth of algae, and damage to the aquatic ecological balance. Therefore, establishing an effective glutamic acid detection method is crucial for protecting the ecosystem and human health.

[0004] Metal elements show differential concentration distribution characteristics in different geological regions of the world. Some metals play important roles in maintaining ecological balance and promoting biological growth, while heavy metals pose serious threats to the health of animals, plants, and humans. In particular, it is worth noting that transition metal ions (including but not limited to Cr 7 ⁺, Cr 5 ⁺, Hg²⁺, Fe²⁺, Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, etc.) can induce oxidative stress reactions in the body, leading to increased lipid peroxidation, DNA damage, and damage to the functions of the kidney / reproductive / central nervous system. Among them, Cd²⁺ and Cr 4⁺Classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). For divalent metal ions commonly present in the drinking water system, even at low concentrations, they can still cause chronic pathological changes. Taking Cu²⁺ as an example, according to the drinking water standard of the US Environmental Protection Agency (EPA), its safety threshold is limited to 1.3 ppm. Exceeding this limit will cause potential damage to the respiratory system, gastrointestinal tract and blood system. This toxicity mechanism is closely related to the accumulation characteristics and redox activity of metal ions in organisms. Based on the bioaccumulation characteristics of the above heavy metal ions and the low-concentration toxicity mechanism, developing a highly sensitive analytical method with a detection limit of ppb level to achieve accurate identification and quantitative analysis of target metal ions has become the core technical link in the field of environmental monitoring. The establishment of this detection system not only provides data support for pollutant source tracing, but also lays a methodological foundation for the construction of an ecological risk early warning system.

[0005] Currently, the methods for amino acid and ion detection mainly include high performance liquid chromatography (HPLC), enzymatic method, electrochemical analysis method and spectrophotometry, etc. These methods have the disadvantages of expensive equipment, professional personnel, cumbersome sample pretreatment, high cost, harsh storage conditions, poor sensitivity and selectivity, and are easily interfered by colored substances or substances that can react with reagents. Fluorescent sensing technology has been studied due to its characteristics of high sensitivity, easy operation, rapid response, high selectivity and low cost. Currently, many coordination polymers for amino acid and metal ion detection have been developed. However, most of the reported probe molecules are based on transition metal complexes. Although lanthanide metal complexes have unique advantages such as narrow emission spectra, high optical stability and biodegradability, due to the high coordination number of lanthanide metal ions, relatively few studies have been conducted on them. Therefore, the construction of fluorescent probes based on rare earth complexes is still an important focus of current research. Based on fluorescent sensing, using lanthanide metal complexes for amino acid and metal ion detection has the advantages of high sensitivity, good selectivity, rapid detection and relatively simple detection process, and can also remain stable in a wide range of pH and temperature. This innovative strategy has greatly promoted the development of amino acid and ion detection technologies. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a rare earth metal europium framework, its preparation method and its application for the turn-on detection of cadmium ions and the turn-off response to copper ions and glutamic acid in view of the deficiencies of the above-mentioned prior art. Its coordination polymer is [Eu(bppc)3(H2O)4]·5H2O. This coordination polymer has a mononuclear structure with europium(III) as the center, forming a nine-coordinate structure. Strong hydrogen bond interactions are formed between the oxygen atoms of the coordinated water molecules and the carboxyl oxygen atoms of the ligands to connect adjacent europium(III) to form a one-dimensional Z-shaped chain structure. The one-dimensional chains are then connected into a two-dimensional supramolecular structure through π…π interactions between the side pyrazine rings.

[0007] The present invention provides a rare earth metal europium framework, and the chemical expression of the rare earth metal europium framework is [Eu(bppc)3(H2O)4]·5H2O, where the ligand bppc - is deprotonated Hbppc, and the Hbppc is 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid. The single molecular formula of the rare earth metal europium framework is C 42 H 24 EuN 15 O 15 。

[0008] The present invention provides a preparation method of the above rare earth metal europium framework, comprising the following steps:

[0009] S1. Dissolve 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid and europium metal salt in deionized water to obtain a mixed solution, add a NaOH solution to adjust the pH value of the mixed solution, and then obtain a reaction product through a solvothermal reaction;

[0010] S2. Wait for the reaction product obtained in S1 to naturally cool and crystallize, and then obtain the rare earth metal europium framework through washing and drying.

[0011] According to the preparation method provided by the present invention, the europium metal salt in S1 is Eu(NO3)3 . 6H2O.

[0012] According to the preparation method provided by the present invention, the molar ratio of 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid to europium metal salt in S1 is 0.1-0.15 mmol: 0.05-0.1 mmol.

[0013] According to the preparation method provided by the present invention, the pH value of the mixed solution in S1 is 6-6.5.

[0014] According to the preparation method provided by the present invention, the temperature of the hydrothermal reaction in S1 is 180 °C, the heating rate of the temperature in the hydrothermal reaction is 4-6 °C / h, the solvothermal reaction is carried out in a sealed reaction kettle, and the time of the solvothermal reaction is 4-5 d.

[0015] According to the preparation method provided by the present invention, the drying condition in S2 is: drying in a constant temperature drying oven at 80 °C for 2 h.

[0016] The present invention also provides an application of the above rare earth metal europium framework for the detection of cadmium ions and the synergistic closing response to copper ions and glutamic acid. The rare earth metal europium framework can effectively detect the contents of L-glutamic acid, Cu 2+ and Cd 2+ in water.

[0017] The present invention has the following advantages compared with the prior art:

[0018] The rare earth metal europium framework of the present invention is prepared by a one-pot solvothermal reaction. The rare earth metal europium framework is a europium(III) coordination polymer, and the chemical formula of the europium(III) coordination polymer is [Eu(bppc)3(H2O)4]·5H2O, and its molecular formula is C 42 H 24 EuN 15 O 15 , and this preparation method has the advantages of simple process, convenient operation, high yield and good reproducibility.

[0019] The rare earth metal europium framework prepared by the present invention has good fluorescence properties, can detect cadmium ions and respond synergistically with copper ions and glutamic acid to turn off, shows high selectivity and high sensitivity to glutamic acid, and can effectively detect glutamic acid through the fluorescence quenching phenomenon, as well as the content of Cu 2+ and Cd 2+ in water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the coordination environment diagram of europium(III) in the europium(III) coordination polymer;

[0021] Figure 2 is the one-dimensional structure diagram of the europium(III) coordination polymer;

[0022] Figure 3 is the two-dimensional structure diagram of the europium(III) coordination polymer;

[0023] Figure 4 is the powder X-ray diffraction pattern of the europium(III) coordination polymer;

[0024] Figure 5 is the fluorescence lifetime diagram of the europium(III) coordination polymer;

[0025] Figure 6 is the emission spectrum diagram of the europium(III) coordination polymer in different amino acids;

[0026] Figure 7 is the intensity comparison diagram of the europium(III) coordination polymer in different amino acids;

[0027] Figure 8 is the emission spectrum diagram of the europium(III) coordination polymer in different glutamic acid concentrations;

[0028] Figure 9 is the linear fitting diagram of the europium(III) coordination polymer in different glutamic acid concentrations.

[0029] Figure 10It is the emission spectrum diagram of europium(III) coordination polymer in different ions;

[0030] Figure 11 It is the intensity comparison diagram of europium(III) coordination polymer in different ions;

[0031] Figure 12 It is the emission spectrum diagram of europium(III) coordination polymer in different concentrations of Cu 2+ ;

[0032] Figure 13 It is the emission spectrum diagram of europium(III) coordination polymer in different concentrations of Cu 2+ ;

[0033] Figure 14 It is the emission spectrum diagram of europium(III) coordination polymer in different concentrations of Cd 2+ ;

[0034] Figure 15 It is the emission spectrum diagram of europium(III) coordination polymer in different concentrations of Cd 2+ ; Specific embodiments

[0035] Example 1

[0036] This example provides a preparation method of a rare earth metal europium skeleton, and the specific steps are as follows:

[0037] S1. Dissolve 0.1 mmol of ligand 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid (Hbppc) and 0.1 mmol of metal salt Eu(NO3)3 . ·6H2O in 10 mL of deionized water to obtain a mixed solution. Add NaOH solution to adjust the pH value of the mixed solution to 6, then transfer the mixed solution to a high-pressure reaction kettle, and heat the temperature in the high-pressure reaction kettle to 180 °C at a heating rate of 4 °C / h for a total of 4 d for hydrothermal reaction to obtain a reaction product;

[0038] The structural formula of Hbppc is:

[0039]

[0040] S2. Wait for the reaction product obtained in S1 to cool and crystallize naturally, then wash it with absolute ethanol and filter it under reduced pressure to obtain a white crystal powder. Place it in an oven at 80 °C for 2 h for drying to obtain a rare earth metal europium skeleton [Eu(bppc)3(H2O)4]·5H2O, and the yield is 35%.

[0041] Example 2

[0042] This embodiment provides a method for preparing a rare earth metal europium framework, and the specific steps are as follows:

[0043] S1. Dissolve 0.15 mmol of the ligand 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid and 0.1 mmol of the metal salt Eu(NO3)3 . 6H2O in 10 mL of deionized water to obtain a mixed solution. Add NaOH solution to adjust the pH value of the mixed solution to 6.2, and then transfer the mixed solution to a high-pressure reaction kettle. After the temperature in the high-pressure reaction kettle is raised to 180 °C at a heating rate of 4 °C / h, carry out a solvothermal reaction for 4 days to obtain a reaction product;

[0044] S2. Wait for the reaction product obtained in S1 to cool and crystallize naturally, then wash it with absolute ethanol and filter it under reduced pressure to obtain a white crystal powder. Place it in an oven at 80 °C and dry it at a constant temperature for 2 h to obtain a rare earth metal europium framework, europium(III) coordination polymer [Eu(bppc)3(H2O)4]·5H2O, with a yield of 42.3%.

[0045] Example 3

[0046] This embodiment provides a method for preparing a rare earth metal europium framework, and the specific steps are as follows:

[0047] S1. Dissolve 0.10 mmol of the ligand 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid and 0.05 mmol of the metal salt Eu(NO3)3 . 6H2O in 10 mL of deionized water to obtain a mixed solution. Add NaOH solution to adjust the pH value of the mixed solution to 6.5, and then transfer the mixed solution to a high-pressure reaction kettle. After the temperature in the high-pressure reaction kettle is raised to 180 °C at a heating rate of 5 °C / h, carry out a solvothermal reaction for 5 days to obtain a reaction product;

[0048] S2. Wait for the reaction product obtained in S1 to cool and crystallize naturally, then wash it with absolute ethanol and filter it under reduced pressure to obtain a white crystal powder. Place it in an oven at 60 °C and dry it at a constant temperature for 3 h to obtain a rare earth metal europium framework, europium(III) coordination polymer [Eu(bppc)3(H2O)4]·5H2O, with a yield of 59.2%.

[0049] Example 4

[0050] This comparative example provides a method for preparing a rare earth metal europium framework, and the specific steps are as follows:

[0051] S1. Dissolve 0.15 mmol of the ligand 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid and 0.05 mmol of the metal salt Eu(NO3)3. 6H2O was dissolved in 10 mL of deionized water to obtain a mixed solution. The pH value of the mixed solution was adjusted to 6.5 by adding NaOH solution. Then the mixed solution was transferred to a high-pressure reaction kettle. After the temperature in the high-pressure reaction kettle was raised to 180 °C at a heating rate of 5 °C / h, a solvothermal reaction was carried out for 5 days to obtain a reaction product.

[0052] S2. After the reaction product obtained in S1 was naturally cooled and crystallized, it was washed with absolute ethanol and filtered under reduced pressure to obtain a white crystal powder. It was placed in an oven at 80 °C and dried at a constant temperature for 2 h to obtain a rare earth metal europium framework, europium(III) coordination polymer [Eu(bppc)3(H2O)4]·5H2O, with a yield of 48.8%.

[0053] Example 5

[0054] The europium(III) coordination polymer prepared in Example 3 was further characterized, and the process was as follows:

[0055] (1) Determination of the crystal structure of the rare earth metal europium framework

[0056] Single crystals of the coordination polymer with a clean, smooth surface, no concave surface, and no cracks were selected. At a temperature of 293(2) K, a BRDUKER SMART APEX-II CCD X-ray single crystal diffractometer was used, and graphite-monochromated Mo-Kα (wavelength 0.71073 Å) radiation was used to collect diffraction data in a ω-φ scanning mode. All data were corrected by empirical absorption, and the crystal structure was solved by the direct method. The anisotropic parameters and the coordinates of all non-hydrogen atoms were refined by the least squares method. The F2 was refined using the SHELXTL-97 program, and the hydrogen atom coordinates were obtained by theoretical calculation methods.

[0057] The detailed crystal determination data are shown in Table 1, the important bond length and bond angle data are shown in Table 2, and the crystal structure is shown in Figures 1 to 3 .

[0058] Table 1 Main crystallographic data of europium(III) coordination polymerization

[0059]

[0060] Among them, R1 = ∑(||Fo| - |Fc||) / ∑|Fo|, wR2 = [∑w(Fo 2 - |Fc 2 ) 2 / ∑w(Fo) 2 1 / 2 ;

[0061] Table 2 Important bond lengths (Å) and bond angles (°) of europium(III) coordination polymer​

[0062]

[0063] In Table 1, a, b, and c represent the edge lengths of the crystal in the three crystallographic axis directions, and α, β, and γ represent the angles between the three axes of a and b, a and c, and b and c, respectively; Z is 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; Θ is the Θ angle range for data collection; Final R indices I >2σ( I )] is the residual factor R value for observable diffraction points; R is the non-weighted consistency factor; R1 and wR2 are both weighted consistency factors;

[0064] Eu1 in the first row of Table 2 refers to Eu atom 1 in the europium(III) coordination polymer single crystal, O5 refers to O atom 5 in the europium(III) coordination polymer single crystal, and Eu1-O5 represents the bond length between Eu atom 1 and O atom 5, and its bond length is 2.398 ± 4, where 4 is the standard deviation;

[0065] O(5)-Eu(1)-O(9) represents the bond angle between O atom 5, Eu atom 1, and O atom 9, and its bond angle is 135.86 ± 15;

[0066] The other data in the table can be obtained by analogy.

[0067] The europium(III) coordination polymer takes europium(III) as the center to form a nine-coordinate structure, and forms a one-dimensional Z-shaped chain structure through hydrogen bonds between the carboxyl oxygen atoms of the ligand and the oxygen atoms of the coordinated water molecules. The Z-shaped chain structure further undergoes π…π interactions between the side pyrazine rings.

[0068] (2) Phase purity characterization of the rare earth metal europium skeleton

[0069] The powder of the europium(III) coordination polymer was characterized by XRD using the instrument Bruker / D8Advance. The characterization results are shown in Figure 4 , and it can be seen that it has reliable phase purity, providing a guarantee for its fluorescence sensing application.

[0070] (2) Fluorescence lifetime characterization of the rare earth metal europium skeleton

[0071] The fluorescence lifetime of the europium(III) coordination polymer was characterized using the instrument Hitachi FLS-1000. The characterization results are shown in Figure 5 , and it can be seen that it has a relatively high fluorescence lifetime, providing a support guarantee for its fluorescence sensing application.

[0072] Example 6

[0073] Weigh 2 mg of the ground europium(III) coordination polymer prepared in Example 3, immerse it in 1 mL of different amino acid solutions (amino acids: glycine, L-isoleucine, L-serine, L-alanine, L-cysteine, L-tryptophan, L-arginine, and L-glutamic acid) with a concentration of 0.01 mol / L and 4 mL of ultrapure water. After ultrasonic treatment, let it stand still, and take its clear supernatant for luminescence study at room temperature.

[0074] At an excitation wavelength of 325 nm, the emission intensities of the europium(III) coordination polymer in different amino acids were measured and repeated three times as parallel experiments. It can be seen that when L-glutamic acid is present, the luminescence intensity of the complex decreases significantly. This phenomenon indicates that the europium(III) coordination polymer has an obvious fluorescence quenching phenomenon for L-glutamic acid. Therefore, L-glutamic acid can be effectively detected by fluorescence quenching. The results are as Figure 6 and Figure 7 shown.

[0075] Example 7

[0076] Weigh 2 mg of the ground europium(III) coordination polymer prepared in Example 3, immerse it in a mixed solution of 0.01 moL / L of different volumes of L-glutamic acid solution and deionized water. After ultrasonic treatment, let it stand still, and take its clear supernatant for luminescence study at room temperature.

[0077] At an excitation wavelength of 325 nm, the emission intensities of the europium(III) coordination polymer with different L-glutamic acid concentrations added were measured and repeated three times as parallel experiments. The results are as Figure 8 shown. The numerical values of the above different emission intensities were subjected to fitting analysis and calculation. The obtained fitting graph has a good linear relationship (R 2 > 0.9). The results are as Figure 9 shown. By calculating with the formula for the detection limit, it is obtained that the europium(III) coordination polymer can detect the minimum L-glutamic acid concentration of 4.29 μM (0.63 mg / L).

[0078] Example 8

[0079] Weigh 20 mg of the ground europium(III) coordination polymer prepared in Example 3, immerse it in 1 mL of different metal solutions (Ag + , Li + , Na + , Cu 2+ , Co 2+ , Ni 2+ , Ga2+ , Ba 2+ , Mg 2+ , Hg 2+ , Zn 2+ ,Cd 2+ , Mn 2+ and Pb 2+ ), and in 4 mL of ultrapure water. After ultrasonic treatment, it was allowed to stand, and the clear supernatant was taken for luminescence studies at room temperature.

[0080] At an excitation wavelength of 325 nm, the emission intensities of the europium(III) coordination polymer in different amino acids were measured and repeated three times as parallel experiments. It was found that when Cu 2+ was present, the luminescence intensity of the complex decreased significantly. When Cd 2+ was present, the luminescence intensity of the complex increased significantly. This phenomenon indicates that the europium(III) coordination polymer has an obvious fluorescence quenching effect on Cu 2+ and an obvious fluorescence enhancement effect on Cd 2+ . Therefore, L-glutamic acid can be effectively detected by fluorescence quenching. The results are as shown in Figure 10 and Figure 11 .

[0081] Example 9

[0082] Weigh 2 mg of the ground europium(III) coordination polymer prepared in Example 3 and immerse it in a mixed solution of 0.01 moL / L, different volumes of Cu 2+ or Cd 2+ and deionized water. After ultrasonic treatment, it was allowed to stand, and the clear supernatant was taken for luminescence studies at room temperature.

[0083] At an excitation wavelength of 325 nm, the emission intensities of the europium(III) coordination polymer with different Cu 2+ or Cd 2+ concentrations were measured and repeated three times as parallel experiments. The results are as shown in Figure 12 , Figure 13 . The numerical values of the above different emission intensities were subjected to fitting analysis and calculation, and the obtained fitting graph had a good linear relationship (R 2 > 0.9). The results are as shown in Figure 14 , Figure 15 .

[0084] By calculating through the formula of the detection limit, it was found that the europium(III) coordination polymer could detect the minimum Cu 2+ or Cd 2+ concentrations of 0.64 μM and 10.51 μM, respectively.

[0085] Therefore, it can be obtained that the europium(III) coordination polymer prepared by the present invention can effectively detect the contents of L-glutamic acid, Cu 2+ and Cd 2+ in water.

[0086] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments based on the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A rare earth metal europium skeleton, characterized in that, The chemical formula of the rare earth metal europium framework is [Eu(bppc)3(H2O)4]·5H2O, where the ligand bppc - is the deprotonated Hbppc, and the Hbppc is 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid. The single molecular formula of the rare earth metal europium framework is C 42 H 24 EuN 15 O 15 . The unit cell parameters of the rare earth metal europium framework are a = 19.312(2) Å, b = 11.7539(13) Å, c = 40.358(5) Å, α = 90(3)°, β = 99.110(2)°, and γ = 90(3)°. The space group of the rare earth metal europium framework is C2 / c, and the crystal system of the rare earth metal europium framework is monoclinic system.

2. A method for preparing a rare earth metal europium skeleton as described in claim 1, characterized in that, It includes the following steps: S1. Dissolve 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid and europium metal salt in deionized water to obtain a mixed solution. Add NaOH solution to adjust the pH value of the mixed solution to 6-6.5, and then obtain a reaction product through a solvothermal reaction; S2. Wait for the reaction product obtained in S1 to cool and crystallize naturally, and then obtain a rare earth metal europium framework through washing and drying.

3. The preparation method of the rare earth metal europium skeleton according to claim 2, characterized in that, The europium metal salt described in S1 is Eu(NO3)3 . 6H2O.

4. The preparation method of the rare earth metal europium skeleton according to claim 2, wherein, In S1, the molar ratio of 2,6-bis(2-pyrazinyl)pyridine-4-carboxylic acid to europium metal salt is 0.1-0.15 mmol: 0.05-0.1 mmol.

5. The preparation method of the rare earth metal europium skeleton according to claim 2, characterized in that, In S1, the temperature of the hydrothermal reaction is 180 °C, the heating rate of the temperature in the hydrothermal reaction is 4-6 °C / h, the solvothermal reaction is carried out in a sealed reaction kettle, and the time of the solvothermal reaction is 4-5 d.

6. The preparation method of the rare earth metal europium skeleton according to claim 2, characterized in that, The drying condition in S2 is: drying in a constant temperature drying oven at 80 °C for 2 h.

7. An application of the rare earth metal europium framework as described in claim 1 for the turn-on detection of cadmium ions and the synergistic turn-off response to copper ions and glutamic acid, characterized in that, The rare earth metal europium framework can effectively detect the contents of L-glutamic acid, Cu 2+ and Cd 2+ in water.

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