Preparation method and application of fluorescent copper nanocluster based on 2-mercaptopyridine

Abstract

The invention belongs to the technical field of preparation of metal nanoclusters, and discloses a preparation method and application of fluorescent copper nanoclusters based on 2-mercaptopyridine, and the preparation method comprises the following steps: S1, preparing a reaction solution; s2, putting the prepared copper sulfate solution and PVP-30 solution into a round-bottom flask to obtain a primary mixed solution; s3, adding a 2-mercaptopyridine solution and a 16M hydrazine hydrate solution into the preliminary mixed solution, and stirring; and S4, taking out the magnet when the color of the solution is bright yellow, observing that the solution emits strong red fluorescence under the irradiation of ultraviolet equipment, taking out the reaction solution, and storing the reaction solution in a plastic pipe at normal temperature to obtain the fluorescent copper nanocluster based on 2-mercaptopyridine. The method is easy and convenient to operate and low in cost, and efficient preparation of the fluorescent copper nanocluster is achieved by controlling reaction conditions and selecting proper ligands.

Description

Technical Field

[0001] The invention relates to the technical field of metal nanocluster preparation, and in particular to a preparation method and application of fluorescent copper nanocluster based on 2-mercaptopyridine. Background Art

[0002] Metal nanoclusters refer to multi-nuclear metal aggregates based on ligand protection, which are usually between one and two nanometers in size, and between single atoms and nanoparticles in size. As a new type of ultra-small molecular aggregates, metal nanoclusters not only have structures and compositions that can be accurately determined at the atomic level, but also have a variety of physical and chemical properties due to their variable structures and quantum size effects. Compared with single metal coordination compounds and nanoparticles, metal clusters have more complex and variable structures and compositions, which are controllable, as well as rich material properties and easier to describe. In recent years, metal nanoclusters have become a research hotspot that has attracted widespread attention from researchers in multiple disciplines such as physics, chemistry, materials science, and computing. Compared with precious metals such as gold, silver, and platinum, nanoclusters synthesized with copper as the main material have very low preparation costs and are more widely used. In addition, the variable chemical valence states of copper atoms and the diversity of ligand types have also laid a theoretical basis for the construction of various copper nanoclusters, and also resulted in the rich properties and related applications of copper nanoclusters. Such development potential makes copper nanoclusters of exploratory significance in both basic research and applied science.

[0003] Currently, Co based on fluorescent nanoclusters 2+ The detection method mainly relies on the cluster and Co 2+ However, traditional methods often have problems such as low sensitivity, poor selectivity or complex operation, which are difficult to meet the needs of practical applications. Therefore, the development of an efficient, sensitive and easy-to-operate Co2+ detection method has important scientific significance and application value. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a preparation method and application of fluorescent copper nanoclusters based on 2-mercaptopyridine. The present invention successfully prepares a fluorescent copper nanocluster based on 2-mercaptopyridine using copper sulfate, PVP-30, 2-mercaptopyridine, and hydrazine hydrate solution as raw materials, and successfully uses it in the detection of Co2+. The fluorescent copper nanocluster sensor based on 2-mercaptopyridine can realize the accurate detection of trace heavy metal ions and organic molecules in the sample, with high sensitivity and good selectivity. At the same time, the preparation method of the sensor is simple, and it is expected to provide useful reference and inspiration for the design and preparation of other nanosensors.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine comprises the following steps:

[0007] S1. Preparation of reaction solution:

[0008] Prepare 1-30 mM copper sulfate solution, 0.5-2.0 mM PVP-30 solution, 0-16 M hydrazine hydrate solution, and 10-300 mM 2-mercaptopyridine solution;

[0009] S2. The prepared copper sulfate solution and PVP-30 solution in a mass ratio of 2:2 are placed in a 50 ml round-bottom flask, and stirred with a magnet in a magnetic stirrer for 8 to 13 minutes at room temperature to fully mix the copper sulfate solution and the PVP-30 solution to obtain a preliminary mixed solution;

[0010] S3. Add 2-mercaptopyridine solution and hydrazine hydrate solution in a ratio of 1:1 by mass to the preliminary mixed solution at intervals of 5 to 15 minutes and stir in a magnetic stirrer for 1 to 10 hours;

[0011] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of an ultraviolet device, it is observed that the solution emits strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0012] Preferably, in S1, the 2-mercaptopyridine solution with a concentration of 10 to 300 mM is prepared with a sodium hydroxide solution with a concentration of 1 M.

[0013] Preferably, in S1, the concentration of the copper sulfate solution is selected to be 10 mM.

[0014] Preferably, in S1, the concentration of the PVP-30 solution is 1 mM.

[0015] Preferably, in S1, the concentration of the 2-mercaptopyridine solution is selected to be 150 mM.

[0016] Preferably, in S1, the concentration of the hydrazine hydrate solution is selected to be 16M.

[0017] Preferably, in S3, the time interval is selected to be 10 minutes.

[0018] Preferably, in S3, the stirring time of the magnetic stirrer is 7 hours.

[0019] Preferably, the ultraviolet device in S4 is a 365nm ultraviolet lamp.

[0020] Application of 2-mercaptopyridine-based fluorescent copper nanoclusters prepared according to the preparation method in the detection of Co2+.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The invention is simple to operate and low in cost. By controlling the reaction conditions and selecting a suitable ligand, the fluorescent copper nanoclusters are efficiently prepared. The fluorescent copper nanocluster sensor based on 2-mercaptopyridine can accurately detect trace heavy metal ions and organic molecules in the sample. At the same time, the preparation method of the fluorescent copper nanocluster sensor based on 2-mercaptopyridine is simple, highly sensitive, and has good selectivity and wide application.

[0023] The present invention has found through creative labor that the best technical effect can be achieved when the order of adding reactants is copper sulfate solution, PVP solution, 2-mercaptopyridine solution, and hydrazine hydrate solution, and other orders cannot prepare better 2-mercaptopyridine fluorescent copper nanoclusters.

[0024] 3. By optimizing the coordination structure of 2-mercaptopyridine and copper ions, the fluorescent copper nanoclusters prepared by the present invention are more sensitive to Co2+. This high sensitivity enables accurate detection of Co2+ even at low concentrations, meeting the needs of high-sensitivity detection in the fields of environmental monitoring, food safety, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a flow chart of the preparation steps of fluorescent copper nanoclusters based on 2-mercaptopyridine;

[0026] Figure 2 The fluorescence spectrum diagram of the effect of reaction time on the reaction product after adding hydrazine hydrate solution;

[0027] Figure 3 The fluorescence spectra of the effects of different concentrations of copper sulfate solutions on the reaction products;

[0028] Figure 4 The fluorescence spectra of the effects of different concentrations of 2-mercaptopyridine solutions on the reaction products;

[0029] Figure 5 The fluorescence spectra of the effects of different concentrations of PVP-30 solutions on the reaction products;

[0030] Figure 6 The fluorescence spectra of the effects of different concentrations of hydrazine hydrate solutions on the reaction products;

[0031] Figure 7 It is the fluorescence spectra of the product solution at different volume concentrations;

[0032] Figure 8 is the fluorescence bar graph of the salt tolerance of the reaction products;

[0033] Fig. 9It is the fluorescence bar graph of the acid and alkali resistance of the reaction product;

[0034] Fig.10 The fluorescence bar graph of the stability of the reaction products in different organic solutions;

[0035] Fig.11 Fluorescence spectra of ion and molecule detection of product solution after 3h and 7h of reaction (a is a fluorescence spectra of hydroxylamine hydrochloride, lysine, etc. detected after 3h of reaction; b is a fluorescence spectra of potassium chloride, barium chloride, etc. detected after 3h of reaction; c is a fluorescence spectra of magnesium sulfate, sodium sulfate, etc. detected after 3h of reaction; d is a fluorescence spectra of hydroxylamine hydrochloride, lysine, etc. detected after 7h of reaction; e is a fluorescence spectra of potassium chloride, barium chloride, etc. detected after 7h of reaction; f is a fluorescence spectra of magnesium sulfate, sodium sulfate, etc. detected after 7h of reaction);

[0036] Fig.12 Fluorescence histograms for detecting ions and molecules in the product solutions after 3h and 7h of reaction (a is a fluorescence histogram for detecting hydroxylamine hydrochloride, lysine, etc. after 3h of reaction; b is a fluorescence histogram for detecting potassium chloride, barium chloride, etc. after 3h of reaction; c is a fluorescence histogram for detecting hydroxylamine hydrochloride, lysine, etc. after 7h of reaction; d is a fluorescence histogram for detecting potassium chloride, barium chloride, etc. after 7h of reaction);

[0037] Fig.13 The fluorescence spectra of the reaction products at different concentrations of Co2+ quenching degree;

[0038] Fig.14 It is the linear spectrum of the quenching degree of the reaction product at different concentrations of Co2+;

[0039] Fig.15 is the UV spectrum (a is PVP; b is the sample with PVP; c is 2-mercaptopyridine; d is the sample without PVP);

[0040] Fig.16 is the infrared spectrum (a is PVP; b is the sample with PVP; c is 2-mercaptopyridine; d is the sample without PVP);

[0041] Fig.17 This is the experimental phenomenon of the product obtained from the reaction solution of Example 1 of the present invention;

[0042] Fig.18 This is the experimental phenomenon of the product obtained from the reaction solution of Comparative Example 1 of the present invention;

[0043] Fig.19 This is the experimental phenomenon of the product obtained from the reaction solution of Comparative Example 2 of the present invention;

[0044] Fig. 20This is the experimental phenomenon of the product obtained from the reaction solution of Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] The present invention adopts a reaction mechanism to synthesize metal nano clusters through coordination, that is, the functional groups in the template or ligand molecule form coordination with metal ions to form metal-ligand complexes.

[0047] See also Figures 1 to 20 , the present invention provides a technical solution:

[0048] mM is the abbreviation of mole per liter (mol / L), which means the concentration unit is molar concentration. In chemistry and biology, the mole is the international unit for measuring the amount of a substance, and the molar concentration refers to the number of moles of a substance contained in a unit volume (liter). Therefore, mM means the number of moles of a substance contained in each liter of solution is millimole (1 millimole is equal to 0.001 mole). mM is often used to describe low concentration solutions, such as the concentration of enzymes, substrates or other chemicals in biochemical experiments.

[0049] Example 1

[0050] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine:

[0051] S1. Preparation of reaction solution:

[0052] Prepare 10 mM copper sulfate solution, 1 mM PVP-30 solution, 16 M hydrazine hydrate solution, and 150 mM 2-mercaptopyridine solution;

[0053] S2. Put the prepared 2 ml copper sulfate solution and 2 ml PVP-30 solution into a 50 ml round-bottom flask, stir with a magnet in a magnetic stirrer for 10 min at room temperature to fully mix the copper sulfate solution and PVP-30 solution to obtain a preliminary mixed solution;

[0054] S3. At a time interval of 10 min, 1 ml of 2-mercaptopyridine solution and 1 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 7 h;

[0055] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0056] Example 2

[0057] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine:

[0058] S1. Preparation of reaction solution:

[0059] Prepare 8 mM copper sulfate solution, 0.8 mM PVP-30 solution, 14 M hydrazine hydrate solution, and 145 mM 2-mercaptopyridine solution;

[0060] S2. The prepared 4 ml copper sulfate solution and 4 ml PVP-30 solution were placed in a 50 ml round-bottom flask, respectively, and stirred with a magnet in a magnetic stirrer for 9 min at room temperature to fully mix the copper sulfate solution and the PVP-30 solution to obtain a preliminary mixed solution;

[0061] S3. At a time interval of 5 min, 2 ml of 2-mercaptopyridine solution and 2 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 5 h;

[0062] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0063] Example 3

[0064] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine:

[0065] S1. Preparation of reaction solution:

[0066] Prepare 30 mM copper sulfate solution, 2.0 mM PVP-30 solution, 16 M hydrazine hydrate solution, and 300 mM 2-mercaptopyridine solution;

[0067] S2. The prepared 2 ml copper sulfate solution and 2 ml PVP-30 solution were placed in a 50 ml round-bottom flask and stirred with a magnet in a magnetic stirrer for 13 min at room temperature to fully mix the copper sulfate solution and PVP-30 solution to obtain a preliminary mixed solution;

[0068] S3. At a time interval of 15 min, 1 ml of 2-mercaptopyridine solution and 1 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 10 h;

[0069] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0070] Example 4

[0071] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine:

[0072] S1. Preparation of reaction solution:

[0073] Prepare 1 mM copper sulfate solution, 0.5 mM PVP-30 solution, 0 M hydrazine hydrate solution, and 10 mM 2-mercaptopyridine solution;

[0074] S2. The prepared 6 ml copper sulfate solution and 6 ml PVP-30 solution were placed in a 50 ml round-bottom flask and stirred with a magnet in a magnetic stirrer for 8 min at room temperature to fully mix the copper sulfate solution and PVP-30 solution to obtain a preliminary mixed solution;

[0075] S3. At a time interval of 5 min, 3 ml of 2-mercaptopyridine solution and 3 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 1 h;

[0076] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0077] Example 5

[0078] A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine:

[0079] S1. Preparation of reaction solution:

[0080] Prepare 9 mM copper sulfate solution, 1.1 mM PVP-30 solution, 9 M hydrazine hydrate solution, and 152 mM 2-mercaptopyridine solution;

[0081] S2. Place 4 ml of the prepared copper sulfate solution and 4 ml of the PVP-30 solution in a 50 ml round-bottom flask and stir with a magnet in a magnetic stirrer for 11 min at room temperature to fully mix the copper sulfate solution and the PVP-30 solution to obtain a preliminary mixed solution;

[0082] S3. At a time interval of 15 min, 2 ml of 2-mercaptopyridine solution and 2 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 5 h;

[0083] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0084] Comparative Example 1

[0085] S1. Preparation of reaction solution:

[0086] Prepare 10 mM copper sulfate solution, 1 mM PVP-30 solution, 16 M hydrazine hydrate solution, and 150 mM 2-mercaptopyridine solution;

[0087] S2. The prepared 2 ml copper sulfate solution and 1 ml 2-mercaptopyridine solution were placed in a 50 ml round-bottom flask and stirred with a magnet in a magnetic stirrer for 10 min at room temperature to fully mix the copper sulfate solution and 2-mercaptopyridine solution to obtain a preliminary mixed solution;

[0088] S3. At a time interval of 10 min, 2 ml of PVP-30 solution and 1 ml of hydrazine hydrate solution were added to the preliminary mixture and stirred for 7 h;

[0089] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0090] Comparative Example 2

[0091] S1. Preparation of reaction solution:

[0092] Prepare 10 mM copper sulfate solution, 1 mM PVP-30 solution, 16 M hydrazine hydrate solution, and 150 mM 2-mercaptopyridine solution;

[0093] S2. Put the prepared 2 ml copper sulfate solution and 2 ml PVP-30 solution into a 50 ml round-bottom flask, stir with a magnet in a magnetic stirrer for 10 min at room temperature to fully mix the copper sulfate solution and PVP-30 solution to obtain a preliminary mixed solution;

[0094] S3. At a time interval of 10 min, 1 ml of hydrazine hydrate solution and 1 ml of 2-mercaptopyridine solution were added to the preliminary mixture and stirred for 7 h;

[0095] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0096] Comparative Example 3

[0097] S1. Preparation of reaction solution:

[0098] Prepare 10 mM copper sulfate solution, 1 mM PVP-30 solution, 16 M hydrazine hydrate solution, and 150 mM 2-mercaptopyridine solution;

[0099] S2. The prepared 2 ml copper sulfate solution and 1 ml hydrazine hydrate solution were placed in a 50 ml round-bottom flask and stirred with a magnet in a magnetic stirrer for 10 min at room temperature to fully mix the copper sulfate solution and the hydrazine hydrate solution to obtain a preliminary mixed solution;

[0100] S3. At a time interval of 10 min, 2 ml of PVP-30 solution and 1 ml of 2-mercaptopyridine solution were added to the preliminary mixture and stirred for 7 h;

[0101] S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of a 365 nm ultraviolet lamp, the solution is observed to emit strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

[0102] Performance testing and result analysis:

[0103] By selecting different addition orders of the reactants in Example 1 and Comparative Examples 1 to 3, the results are shown in Table 1 below:

[0104] Table 1

[0105]

[0106] The experimental results show that the best experimental conditions are when the reactants are copper sulfate solution, PVP-30 solution, 2-mercaptopyridine solution and hydrazine hydrate solution in the order of reaction.

[0107] 1. Optimization of reaction time

[0108] Under the condition that the reaction sequence is the best choice and the reaction time is 7 hours after the last solution is added, the time interval for adding the reactants is optimized. The effect of adding the solutions involved in the reaction at different time intervals on the reaction products is explored. The addition time intervals are 5 minutes, 10 minutes and 15 minutes. Finally, the obtained reaction product solution is detected by F-4600 fluorescence spectrophotometer.

[0109] When the reaction sequence, the time interval for adding the reactant solutions, the concentration of the copper sulfate solution, the concentration of the 2-mercaptopyridine solution, and the concentration of the PVP solution are optimal, the effect of the reaction time after adding the last solution on the reaction product is explored. The reaction time gradient is 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 h. Finally, the obtained reaction product solution is detected by the F-4600 fluorescence spectrophotometer, and the final result is as follows Figure 2 As shown in the figure, it is found that adding the reactants for too long will affect the fluorescence intensity of the reaction products. The reason may be that PVP prevents the aggregation of copper nanoclusters, making the size of the generated nanoclusters too small, thus affecting the fluorescence value. The one with the strongest fluorescence value is selected through the fluorescence spectrum, and the time interval for adding the reactant solution is 10 minutes. Figure 2 It was found that the longer the reaction time after adding 2-mercaptopyridine solution, the stronger the fluorescence intensity of the product. The reason may be that the copper nanoclusters formed by copper ions and 2-mercaptopyridine did not react completely when the reaction time was short. The one with the strongest fluorescence value was selected through the fluorescence spectrum, that is, the reaction time was 10h.

[0110] 2. Optimization of copper sulfate concentration

[0111] When the reaction sequence and the time interval for adding the reactant solutions are optimal, and the reaction time after adding the last solution is 7 hours, the effects of different concentrations of copper sulfate solutions on the reaction products are investigated. The concentration gradient of the copper sulfate solution is 1, 3, 5, 7, 10, 25 and 30 mM. Finally, the obtained reaction product solution is detected by F-4600 fluorescence spectrophotometer. The results are as follows Figure 3 As shown, it was found that the fluorescence value was very low when the concentration of copper sulfate solution was 1mM, and the reason may be that almost no copper nanoclusters were produced; although the fluorescence value was weak when the concentration was 3mM, it was found that the fluorescence spectrum had an obvious upward trend, indicating that the nanoclusters had been partially synthesized; when the concentration was 5-10mM, it was found that the difference in fluorescence values ​​was not large, and the one with the strongest fluorescence value was selected through the fluorescence spectrum, that is, the concentration of 10mM; when the concentration was greater than 10mM, it was found that the fluorescence value of the reaction product solution decreased, and the reason may be that the copper sulfate concentration was too high and the PVP content was too low, and PVP failed to prevent partial agglomeration of copper nanoclusters, thereby generating large-sized nanoparticles.

[0112] 3. Optimization of 2-mercaptopyridine solution concentration

[0113] When the reaction sequence, the time interval for adding the reactant solution and the concentration of the copper sulfate solution are optimal, and the reaction time after adding the last solution is 7 hours, the effects of different concentrations of 2-mercaptopyridine solution on the reaction product are investigated. The concentration gradient of 2-mercaptopyridine solution is 10, 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275 and 300 mM. Finally, the obtained reaction product solution is detected by F-4600 fluorescence spectrophotometer. The results are as follows Figure 4 As shown, it was found that the fluorescence value of the 2-mercaptopyridine solution was low when the concentration was 10 mM, which may be caused by too few synthesized copper nanoclusters; when the concentration was between 25 and 300 mM, the difference in fluorescence values ​​was not large, and the one with the highest fluorescence value was selected through the fluorescence spectrum, that is, the concentration was 150 mM.

[0114] 4. Optimization of PVP solution concentration

[0115] When the reaction sequence, the time interval for adding the reactant solution, the concentration of the copper sulfate solution and the concentration of the 2-mercaptopyridine solution were optimal, and the reaction time after adding the last solution was 7 hours, the effect of different concentrations of PVP solution on the reaction product was investigated. The concentration gradient of the PVP solution was 0.5, 1.0, 1.5 and 2.0 mM. Finally, the obtained reaction product solution was detected by F-4600 fluorescence spectrophotometer. The results are as follows Figure 5 As shown, it was found that no matter how high the PVP concentration was, it had little effect on the fluorescence value of the product solution. However, considering the solubility of PVP and other factors, the PVP concentration was selected to be 1.0 mM.

[0116] 5. Optimization of hydrazine hydrate concentration

[0117] When the reaction sequence, the time interval for adding the reactant solution, the concentration of the copper sulfate solution, the concentration of the 2-mercaptopyridine solution, and the concentration of the PVP solution are optimal, and the reaction time after adding the last solution is 7 hours, the effects of different concentrations of hydrazine hydrate solution on the reaction product are investigated. The concentration gradient of the hydrazine hydrate solution is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 M. Finally, the obtained reaction product solution is detected by an F-4600 fluorescence spectrophotometer, and the results are as follows Figure 6 As shown, it was found that the reaction product solution also had fluorescence even without the addition of hydrazine hydrate solution, so it is possible to choose not to add hydrazine hydrate during the experiment.

[0118] 6. Optimization of reaction stock solution concentration

[0119] When the reaction sequence, the time interval for adding the reactant solution, the concentration of the copper sulfate solution, the concentration of the 2-mercaptopyridine solution, and the concentration of the PVP solution are optimal, and the reaction time after adding the last solution is 7 hours, the fluorescence of the product solution at different volume concentrations is investigated. The volume concentration gradient of the product solution is 2.5%, 5%, 10%, 20%, 25%, 33.3%, 50%, and 100%. Finally, the reaction product solutions of different concentrations are detected by the F-4600 fluorescence spectrophotometer. The results are as follows Figure 7 As shown, it was found that when the volume concentration of the product solution was between 20% and 100%, the fluorescence value of the solution showed an upward trend, so the volume concentration of the solution was selected to be 20%.

[0120] 7. Test results of salt resistance, acid and alkali resistance and stability in different organic solutions

[0121] The obtained 2-mercaptopyridine-based fluorescent copper nanoclusters were detected by observing Figure 8 It was found that the concentration of sodium chloride solution had no effect on the copper nanoclusters, indicating that the product has good salt tolerance. Fig. 9 It was found that the fluorescence intensity of copper nanoclusters was affected when the pH was less than 4, which might be caused by the destruction of the cluster structure by the acid; when the pH was greater than 4, it had no effect on the reaction product. This shows that copper nanoclusters have good alkali resistance; they are not stable in acids with a pH less than 4, but are more stable in acids with a pH greater than 4. Fig.10 It was found that acrylic acid, tetrahydrofuran, formaldehyde and N,N-dimethylformamide can partially quench the fluorescence of copper nanoclusters, among which formaldehyde has the strongest quenching effect. Dimethyl sulfoxide, acetonitrile, ethanol and diethanolamine have no effect on copper nanoclusters.

[0122] 8. Liquid-phase fluorescent copper nanoclusters for ion and molecular detection of Co2+

[0123] By observation Fig.11 and Fig.12It was found that ascorbic acid, hydroxylamine hydrochloride, methionine, valine, glycine, glutamic acid, lysine, serine, histidine, threonine, barium chloride, cobalt chloride, zirconium chloride, potassium chloride, calcium chloride, magnesium sulfate, sodium sulfate, ammonium sulfate, mercuric sulfate, sodium sulfite, sodium persulfate, potassium persulfate, sodium nitrite, potassium carbonate, sodium carbonate, sodium bromide, potassium bromide, sodium iodide, hydrogen peroxide, dipotassium hydrogen phosphate, potassium thiocyanide and silver nitrate had no effect on the fluorescence of copper nanoclusters. Cadmium chloride can slightly enhance its fluorescence; iron sulfate, troxerutin, minocycline hydrochloride and cobalt chloride can quench the fluorescence of copper nanoclusters, among which cobalt chloride has a better quenching degree when the reaction product synthesis time is 3h and 7h. The reaction product of ferric sulfate with a synthesis time of 3 hours was completely quenched. The reason for this phenomenon may be that too few copper nanoclusters were synthesized at 3 hours, and the cluster structure was destroyed by the acid dissolved in ferric sulfate. The fluorescence quenching degree of the reaction product with a synthesis time of 7 hours was not strong. The reason for this phenomenon may be that enough copper nanoclusters were synthesized at 7 hours, but the acid dissolved in ferric sulfate destroyed some of the cluster structures, causing fluorescence quenching. The quenching degree of troxerutin and minocycline hydrochloride was not strong for the reaction products of 3 hours or 7 hours.

[0124] 9. Results of Co2+ linearity experiment using liquid phase fluorescent copper nanoclusters for Co2+ detection

[0125] By observation Fig.13 It was found that the fluorescence of the product can be quenched starting from a cobalt ion concentration of 0.1 μM, indicating that the presence of cobalt ions destroyed the copper nanoclusters, causing the fluorescence to decrease rapidly, and the selectivity for cobalt ions was strong. Fig.14 It was found that the linear equation for the quenching of copper nanoclusters by cobalt ions was Y=245-28.69X, R2=0.98729.

[0126] 10. Ultraviolet and infrared detection

[0127] By observation Fig.15 The UV spectrum analysis shows that the reason for the absorption peak of copper nanoclusters is 2-mercaptopyridine. Fig.16 Infrared spectra show that -SH disappears at 2500cm-1 for copper nanoclusters synthesized without PVP, while -SH still exists at 2500cm-1 for copper nanoclusters synthesized with PVP. It can be seen that -SH in copper nanoclusters synthesized without PVP is completely reacted, while -SH in copper nanoclusters synthesized with PVP is not completely reacted. 2960cm-1 is the antisymmetric stretching vibration peak of CH, 3500cm-1 is the stretching vibration peak of NH, 1640cm-1 is the stretching vibration peak of C=O, and 1440cm-1 is the stretching vibration peak of CN.

[0128] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine, It is characterized in that The following steps are involved: S1. Preparation of reaction solution: Prepare 1-30 mM copper sulfate solution, 0.5-2.0 mM PVP-30 solution, 0-16 M hydrazine hydrate solution, and 10-300 mM 2-mercaptopyridine solution; S2. The prepared copper sulfate solution and PVP-30 solution in a mass ratio of 2:2 are placed in a 50 ml round-bottom flask, and stirred with a magnet in a magnetic stirrer for 8 to 13 minutes at room temperature to fully mix the copper sulfate solution and the PVP-30 solution to obtain a preliminary mixed solution; S3. Add 2-mercaptopyridine solution and hydrazine hydrate solution in a ratio of 1:1 by mass to the preliminary mixed solution at intervals of 5 to 15 minutes and stir in a magnetic stirrer for 1 to 10 hours; S4. When the solution turns bright yellow, the magnet is taken out. Under the irradiation of an ultraviolet device, it is observed that the solution emits strong red fluorescence. The reaction solution is taken out and stored in a plastic tube at room temperature to obtain fluorescent copper nanoclusters based on 2-mercaptopyridine.

2. A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S1, a 2-mercaptopyridine solution having a concentration of 10 to 300 mM is prepared with a sodium hydroxide solution having a concentration of 1 M.

3. A method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S1, the concentration of the copper sulfate solution is selected to be 10 mM.

4. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S1, the concentration of the PVP-30 solution was selected to be 1 mM.

5. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S1, the concentration of the 2-mercaptopyridine solution is selected to be 150 mM.

6. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S1, the concentration of the hydrazine hydrate solution is selected to be 16M.

7. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S3, the time interval is selected as 10 minutes.

8. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that In S3, the stirring time of the magnetic stirrer is 7 h.

9. The method for preparing fluorescent copper nanoclusters based on 2-mercaptopyridine according to claim 1, It is characterized in that The UV device in S4 is a 365nm UV lamp.

10. A fluorescent copper nanocluster based on 2-mercaptopyridine prepared by the preparation method according to any one of claims 1 to 9 in Co 2+ application in detection.

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