A method for preparing nano-copper powder

Abstract

The application discloses a preparation method of nano copper powder and belongs to the technical field of nano copper powder preparation. The method comprises the following steps: S1, preparing a mercaptopropionic acid-ethanol solution; S2, preparing surface carboxylated quantum dots; S3, preparing an enzyme solution; S4, preparing an enzyme solution in which surface carboxyl groups are converted into active esters; S5, preparing a surface carboxylated quantum dot solution; S6, preparing a quantum dot-biomolecule mixture; S7, preparing a copper salt solution and adjusting the pH to 5-6; and S8, preparing nano copper powder. In the method, copper ions in the copper salt solution are reduced into copper atoms by the quantum dot-biomolecule mixture to prepare the nano copper powder. The prepared nano copper powder can accurately control the nucleation rate and quantity of the nano copper powder, and has low preparation cost and high preparation efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nano copper powder preparation, and particularly relates to a preparation method of nano copper powder. BACKGROUND

[0002] Nano copper powder refers to powder material composed of pure copper elements and having nano-level particle size, and has the characteristics of large specific surface area, high surface activity, low melting point, good sintering performance and good electrical conductivity, and is widely applied to fields of high-efficiency catalyst, conductive material, electromagnetic shielding and drug additive material.

[0003] At present, the preparation methods of nano copper powder include physical method and chemical method, wherein the physical method has the problems of relatively high cost of preparation equipment and relatively low preparation efficiency, and the chemical method has the problem that the preparation rate and quantity of nano copper powder are difficult to control.

[0004] In view of this, a preparation method of nano copper powder is designed to solve the above problems. SUMMARY

[0005] To solve the problems in the above background, the application provides a preparation method of nano copper powder, which has the characteristics of being able to accurately control the nucleation rate and quantity of nano copper powder, low preparation cost and high preparation efficiency.

[0006] To achieve the above purpose, the application provides the following technical scheme: a preparation method of nano copper powder, comprising the following steps:

[0007] S1: take mercaptopropionic acid and ethanol into a container, stir and accelerate mixing at room temperature, and prepare a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L;

[0008] S2: take the mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir and accelerate coordination reaction at room temperature for 2-3 h, centrifuge and wash after the reaction is completed, and prepare carboxylated quantum dots on the surface;

[0009] S3: take glucose oxidase into a phosphate buffer solution, stir and accelerate mixing at room temperature, and prepare an enzyme solution with a concentration of 0.01 mol / L;

[0010] S4: take the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution into a container, activate for 30-60 min, and prepare an enzyme solution in which the surface carboxyl group is converted into an active ester after the reaction is completed;

[0011] S5: take the carboxylated quantum dots and the phosphate buffer solution into a container, stir and accelerate mixing at room temperature, and prepare a carboxylated quantum dot solution;

[0012] S6: Take the enzyme solution of surface carboxyl group conversion to active ester and the surface carboxylated quantum dot solution into the container, stir at room temperature to accelerate the covalent connection reaction for 2-4h, centrifuge, wash, and prepare the quantum dot-biomolecule mixture;

[0013] S7: Take copper sulfate and deionized water into the container, stir at room temperature to accelerate mixing, prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6;

[0014] S8: Add the quantum dot-biomolecule mixture and the copper salt solution into the container, and add an ascorbic acid solution with a concentration of 0.01-0.05 mol / L, and place the container in a light condition, the copper salt solution dissociates free-moving copper ions, which are adsorbed by glucose oxidase, and the quantum dots absorb light energy to generate electron-hole pairs, and the electrons are transferred to the glucose oxidase to reduce the copper ions into copper atoms, which polymerize to form crystal nuclei, and the crystal nuclei continue to grow to form nano-copper powder, centrifuge, wash, and dry to prepare the nano-copper powder.

[0015] Further, in the step S2, the adding amount of the mercaptopropionic acid-ethanol solution and the CdSe / ZnS quantum dot solution is 0.8 mL and 10 mL, respectively.

[0016] Further, in the step S2, the specific steps of centrifugation include:

[0017] Take a pipette, and move the surface carboxylated quantum dot solution into the centrifuge tube through the pipette;

[0018] Take ethanol with a volume ratio of 1:1 to the surface carboxylated quantum dot solution, and add it into the centrifuge tube, and shake uniformly to accelerate mixing, thereby reducing the solubility of the quantum dots in the solution and making them precipitate;

[0019] Place the centrifuge tube into the centrifuge, and centrifuge at a speed of 8000-1000 rpm for 15-20 min;

[0020] After centrifugation, the centrifuge tube contains supernatant containing impurities and precipitated quantum dots, take a pipette, and suck out the supernatant containing impurities through the pipette, and the centrifugation is completed.

[0021] Further, in the step S2, the specific steps of washing include:

[0022] Take out the centrifuge tube containing the precipitated quantum dots, take ethanol, and add it into the centrifuge tube, and the ethanol covers the precipitated quantum dots, and shake uniformly to disperse the precipitated quantum dots in the ethanol;

[0023] Place the centrifuge tube into the centrifuge, and centrifuge at a speed of 8000-1000 rpm;

[0024] After centrifugation, the centrifuge tube is filled with the supernatant containing impurities and the re-precipitated quantum dots, a pipette is taken, and the supernatant containing impurities is sucked out through the pipette, and one washing is completed;

[0025] The above washing step is repeated 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed.

[0026] Further, in the step S4, the added amount of the enzyme solution and the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution is 10 mg and 0.5 mL, respectively.

[0027] Further, in the step S6, the added amount of the enzyme solution for converting the surface carboxyl group into an active ester and the surface carboxylated quantum dot solution is 2 mL and 2 mL, respectively.

[0028] Further, in the step S8, the added amount of the quantum dot-biomolecule mixture, the copper salt solution and the ascorbic acid solution is 2 mL, 2 mL and 1 mL, respectively.

[0029] Further, in the step S8, the light irradiation condition is simulated by ultraviolet lamp irradiation, the light wavelength is 365 nm, the light intensity is 10-20 mW / cm², and the light temperature is 25-30°C.

[0030] Further, in the steps S6 and S8, the centrifugation and washing steps are the same as S2.

[0031] Further, in the step S8, the drying temperature is 40-45°C, and the drying time is 6-12 h.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1. The present application can prepare nano-copper powder by reducing copper ions in the copper salt solution into copper atoms through the quantum dot-biomolecule mixture, and the prepared nano-copper powder can accurately control the nucleation rate and quantity of the nano-copper powder, has low preparation cost and high preparation efficiency.

[0034] 2. The quantum dots have good chemical stability, which can ensure the continuous and stable preparation process, and are beneficial to the formation of nano-copper powder with uniform size and regular morphology.

[0035] 3. The high fluorescence quantum yield of the quantum dots can realize the preparation tracking of the nano-copper powder as a fluorescent marker, so as to timely adjust the light irradiation condition, optimize the preparation process, and improve the finished product quality of the nano-copper powder. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The flow chart of the method of the present application;

[0037] Figure 2 A centrifugal flow chart of the present application;

[0038] Figure 3 A washing flow chart of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0040] Referring to the drawings Figure 1 The present application provides the following technical solutions: a preparation method of nano copper powder, comprising the following steps:

[0041] S1: take mercaptopropionic acid and ethanol into a container, stir to accelerate mixing at room temperature, and prepare a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L;

[0042] S2: take the mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir to accelerate coordination reaction at room temperature for 2-3 h, centrifuge, wash, and prepare surface carboxylated quantum dots after the reaction is completed;

[0043] In this embodiment, 0 mL, 0.5 mL, 0.8 mL, 1 mL and 1.5 mL of mercaptopropionic acid-ethanol solution and 10 mL of CdSe / ZnS quantum dot solution are used to perform the above operation respectively, and surface carboxylated quantum dots are prepared;

[0044] Referring to the drawings Figure 2 The specific steps of centrifugation include:

[0045] Take a pipette, and move the surface carboxylated quantum dot solution into a centrifuge tube through the pipette;

[0046] Take ethanol with a volume ratio of 1:1 to the surface carboxylated quantum dot solution, and add it into the centrifuge tube, and shake uniformly to accelerate mixing, so as to reduce the solubility of the quantum dots in the solution and make them precipitate;

[0047] Put the centrifuge tube into a centrifuge, and centrifuge at a centrifugal speed of 8000-1000 rpm;

[0048] After centrifugation, the centrifuge tube contains supernatant containing impurities and precipitated quantum dots, take a pipette, and suck out the supernatant containing impurities through the pipette, and the centrifugation is completed;

[0049] Referring to the drawings Figure 3 The specific steps of washing include:

[0050] Take out the centrifuge tube containing the precipitated quantum dots, take ethanol and add it into the centrifuge tube, cover the precipitated quantum dots with ethanol, and shake uniformly to disperse the precipitated quantum dots in ethanol;

[0051] Put the centrifuge tube into the centrifuge and centrifuge at a speed of 8000-1000 rpm;

[0052] After centrifugation, the centrifuge tube contains supernatant containing impurities and re-precipitated quantum dots, take a pipette, and suck out the supernatant containing impurities through the pipette, and complete the first washing;

[0053] Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed;

[0054] Detect the fluorescence intensity of the quantum dots by fluorescence spectrometer, and the results show that the fluorescence intensity on the surface of the quantum dots gradually decreases with the increase of the mercaptopropionic acid-ethanol solution;

[0055] Detect the number of carboxyl groups on the quantum dots by infrared spectroscopy, and the results show that the number of carboxyl groups on the surface of the quantum dots gradually increases with the increase of the mercaptopropionic acid-ethanol solution;

[0056] But 0.8 mL of mercaptopropionic acid-ethanol solution and 10 mL of CdSe / ZnS quantum dot solution are used for the above operation, and the surface carboxylated quantum dots are prepared, which not only better maintain the fluorescence performance of the quantum dots, but also better meet the covalent connection requirements with biomolecules;

[0057] S3: Take glucose oxidase and add it into the phosphate buffer solution, stir to accelerate mixing at room temperature, and prepare an enzyme solution with a concentration of 0.01 mol / L;

[0058] S4: Take the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution and add them into the container, activate the reaction for 30-60 min, and prepare an enzyme solution with active ester converted from the surface carboxyl group after the reaction is completed;

[0059] In this embodiment, 10 mg of enzyme solution and 0 mL, 0.1 mL, 0.3 mL, 0.5 mL, and 1 mL of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution are used for the above operation respectively, and an enzyme solution with active ester converted from the surface carboxyl group is prepared;

[0060] The SDS-PAGE electrophoresis analysis of the enzyme solution shows that the amount of glucose oxidase on the quantum dots increases obviously with the increase of the amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride solution, but the enzyme activity decreases obviously when the amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride solution is 1 mL, which indicates that the excessive 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride solution damages the structure of glucose oxidase and affects the enzyme activity;

[0061] That is, 10 mg of enzyme solution and 0.5 mL of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride solution are optimal;

[0062] S5: The surface carboxylated quantum dots and the phosphate buffer solution are taken into a container, and stirring is performed at room temperature to accelerate mixing, so as to prepare a surface carboxylated quantum dot solution;

[0063] S6: The enzyme solution with the surface carboxyl group converted into an active ester and the surface carboxylated quantum dot solution are taken into a container, and stirring is performed at room temperature to accelerate the covalent bonding reaction for 2-4 h. After the reaction is completed, centrifugation and washing are performed, so as to prepare a quantum dot-biomolecule mixture;

[0064] In this embodiment, 1 mL of enzyme solution and 1 mL of quantum dot solution, 1 mL of enzyme solution and 3 mL of quantum dot solution, 3 mL of enzyme solution and 1 mL of quantum dot solution, and 2 mL of enzyme solution and 2 mL of quantum dot solution are respectively subjected to the above operation, so as to prepare a quantum dot-biomolecule mixture;

[0065] Referring to FIG. 2, the specific steps of centrifugation include the following steps: Figure 2 A pipette is taken, and the quantum dot-biomolecule mixture solution is transferred into a centrifuge tube by the pipette;

[0066] Ethanol with a volume ratio of 1:1 to the quantum dot-biomolecule mixture solution is taken and added into the centrifuge tube, and uniform shaking is performed to accelerate mixing, so as to reduce the solubility of the quantum dot-biomolecule mixture in the solution and make it precipitate;

[0067] The centrifuge tube is placed into a centrifuge, and centrifugation is performed at a centrifugal speed of 8000-1000 rpm;

[0068] After centrifugation, the centrifuge tube contains supernatant containing impurities and precipitated quantum dot-biomolecule mixture. A pipette is taken, and the supernatant containing impurities is sucked out by the pipette, and the centrifugation is completed;

[0069] Referring to FIG. 3, the specific steps of washing include the following steps:

[0070] Figure 3

[0071] ​​Take out the centrifuge tube containing the precipitated quantum dot-biomolecule mixture, add ethanol into the centrifuge tube, cover the precipitated quantum dot-biomolecule mixture with ethanol, and shake uniformly to disperse the precipitated quantum dot-biomolecule mixture in ethanol;

[0072] Put the centrifuge tube into the centrifuge and centrifuge at a speed of 8000-1000 rmp;

[0073] After centrifugation, the centrifuge tube contains supernatant containing impurities and re-precipitated quantum dot-biomolecule mixture, take a pipette, and suck out the supernatant containing impurities through the pipette, and complete the washing once;

[0074] Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dot-biomolecule mixture are completely removed;

[0075] The results of ultraviolet-visible spectroscopy and fluorescence spectroscopy analysis show that the glucose oxidase content of the quantum dot-biomolecule mixture increases with the increase of the enzyme solution;

[0076] The results of enzyme activity detection show that the glucose oxidase activity of the quantum dot-biomolecule mixture increases with the increase of the enzyme solution, but there is free glucose oxidase when the amount of enzyme solution is 3 mL;

[0077] That is, 2 mL of enzyme solution and 2 mL of quantum dot solution are optimal;

[0078] S7: Take copper sulfate and deionized water into a container, stir to accelerate mixing at room temperature, prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6;

[0079] S8: Add the quantum dot-biomolecule mixture and the copper salt solution into the container, and at the same time, add an ascorbic acid solution with a concentration of 0.01-0.05 mol / L, and put the container into a light condition. The copper salt solution dissociates free-moving copper ions, which are adsorbed by glucose oxidase. The quantum dots absorb light energy to generate electron-hole pairs, and the electrons are transferred to glucose oxidase, reducing copper ions to copper atoms. The copper atoms polymerize to form crystal nuclei, and with the continuous growth of the crystal nuclei, nano-copper powder is formed. After centrifugation, washing, and drying, nano-copper powder is prepared;

[0080] In this example, 1 mL of quantum dot-biomolecule mixture, 1 mL of copper salt solution, and 0.5 mL of ascorbic acid solution, 1 mL of quantum dot-biomolecule mixture, 3 mL of copper salt solution, and 1.5 mL of ascorbic acid solution, 3 mL of quantum dot-biomolecule mixture, 1 mL of copper salt solution, and 0.5 mL of ascorbic acid solution, and 2 mL of quantum dot-biomolecule mixture, 2 mL of copper salt solution, and 1 mL of ascorbic acid solution are used to prepare nano-copper powder by the above operation;

[0081] The lighting conditions are simulated by ultraviolet light irradiation, with a wavelength of 365nm, a light intensity of 10-20mW / cm², and a light temperature of 25-30℃;

[0082] See attached Figure 2 The specific steps of centrifugation include:

[0083] Take a pipette and transfer the solution containing nano-copper powder into a centrifuge tube;

[0084] Take ethanol in a volume ratio of 1:1 to the solution containing nano-copper powder, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of nano-copper powder in the solution, and cause it to precipitate;

[0085] Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm;

[0086] After centrifugation, the centrifuge tube is filled with the supernatant containing impurities and the precipitated nano-copper powder. Take a pipette and suck out the supernatant containing impurities through the pipette. The centrifugation is completed.

[0087] See attached Figure 3 The specific steps of washing include:

[0088] Take out the centrifuge tube containing the precipitated nano-copper powder, add ethanol to the centrifuge tube, cover the precipitated nano-copper powder with ethanol, and shake it at a constant speed to disperse the precipitated nano-copper powder in the ethanol;

[0089] Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm;

[0090] After centrifugation, the centrifuge tube is filled with the supernatant containing impurities and the reprecipitated nano-copper powder. Take a pipette and suck out the supernatant containing impurities through the pipette, and the washing is completed in one step.

[0091] Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated nano-copper powder are completely removed;

[0092] Dry in a vacuum drying oven at a temperature of 40-45°C for 6-12 hours.

[0093] The results of observation by transmission electron microscope show that the nano copper powder prepared from 1 mL quantum dot-biomolecule mixture, 1 mL copper salt solution and 0.5 mL ascorbic acid solution has large particle size and uneven distribution, and obvious agglomeration phenomenon, and the yield is about 30%; the nano copper powder prepared from 1 mL quantum dot-biomolecule mixture, 3 mL copper salt solution and 1.5 mL ascorbic acid solution has reduced particle size and uneven distribution, and improved dispersibility, and the yield is 50% because of the increase of copper salt and ascorbic acid, which promotes the reduction of copper ions; the nano copper powder prepared from 3 mL quantum dot-biomolecule mixture, 1 mL copper salt solution and 0.5 mL ascorbic acid solution has small particle size and good dispersibility, and the yield is about 20% because of the excess of quantum dot-biomolecule mixture, which provides more nucleation sites for the nucleation and growth of copper atoms; the nano copper powder prepared from 2 mL quantum dot-biomolecule mixture, 2 mL copper salt solution and 1 mL ascorbic acid solution has uniform particle size and good dispersibility, and the yield is about 60%;

[0094] That is, 2 mL quantum dot-biomolecule mixture, 2 mL copper salt solution and 1 mL ascorbic acid solution are the best.

[0095] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nano-copper powder, characterized in that, The method comprises the following steps: S1: take mercaptopropionic acid and ethanol into a container, stir to accelerate mixing at room temperature, and prepare a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L; S2: take the mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir to accelerate coordination reaction at room temperature for 2-3 hours, centrifuge, wash, and prepare a surface carboxylated quantum dot solution; S3: take glucose oxidase into a phosphate buffer solution, stir to accelerate mixing at room temperature, and prepare an enzyme solution with a concentration of 0.01 mol / L; S4: take the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution into a container, activate for 30-60 minutes, and prepare an enzyme solution with surface carboxyl groups converted into active esters; S5: take the surface carboxylated quantum dot solution and the phosphate buffer solution into a container, stir to accelerate mixing at room temperature, and prepare a surface carboxylated quantum dot solution; S6: take the enzyme solution with surface carboxyl groups converted into active esters and the surface carboxylated quantum dot solution into a container, stir to accelerate covalent connection reaction at room temperature for 2-4 hours, centrifuge, wash, and prepare a quantum dot-biomolecule mixture; S7: take copper sulfate and deionized water into a container, stir to accelerate mixing at room temperature, prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6; S8: add the quantum dot-biomolecule mixture and the copper salt solution into a container, add ascorbic acid solution with a concentration of 0.01-0.05 mol / L, and place the container in a light condition; the copper salt solution dissociates free-moving copper ions, which are adsorbed by the glucose oxidase; the quantum dots absorb light energy to generate electron-hole pairs, and the electrons are transferred to the glucose oxidase to reduce the copper ions into copper atoms; the copper atoms polymerize to form crystal nuclei, and the crystal nuclei continuously grow to form nano copper powder; centrifuge, wash, and dry to prepare the nano copper powder.

2. The method according to claim 1, wherein: In the step S2, the mercaptopropionic acid-ethanol solution and the CdSe / ZnS quantum dot solution are added in amounts of 0.8 mL and 10 mL, respectively.

3. The method according to claim 1, wherein the method is characterized by: In the step S2, the specific steps of centrifugation include: take a pipette, and use the pipette to transfer the surface carboxylated quantum dot solution into a centrifuge tube; take ethanol with a volume ratio of 1:1 to the surface carboxylated quantum dot solution, add the ethanol into the centrifuge tube, and shake uniformly to accelerate mixing, so as to reduce the solubility of the quantum dots in the solution and make the quantum dots precipitate; place the centrifuge tube into a centrifuge, and centrifuge at a speed of 8000-1000 rmp for 15-20 minutes; after centrifugation, the centrifuge tube contains supernatant containing impurities and precipitated quantum dots, take a pipette, and use the pipette to suck out the supernatant containing impurities, and the centrifugation is completed.

4. The method for preparing nano copper powder according to claim 3, wherein: In the step S2, the specific steps of washing include: take out the centrifuge tube containing the precipitated quantum dots, add ethanol into the centrifuge tube, and shake uniformly to make the precipitated quantum dots disperse in the ethanol; place the centrifuge tube into a centrifuge, and centrifuge at a speed of 8000-1000 rmp; After centrifugation, the centrifuge tube is filled with supernatant containing impurities and re-precipitated quantum dots, a pipette is taken, and the supernatant containing impurities is sucked out through the pipette, and one washing is completed; The above washing step is repeated 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed.

5. The method for preparing nano copper powder according to claim 1, wherein: In the step S4, the added amount of enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution is 10 mg and 0.5 mL respectively.

6. The method according to claim 1, wherein the method is characterized by: In the step S6, the added amount of enzyme solution for converting surface carboxyl to active ester and surface carboxylated quantum dot solution is 2 mL and 2 mL respectively.

7. The method according to claim 1, wherein the method is characterized by: In the step S8, the added amount of quantum dot-biomolecule mixture, copper salt solution and ascorbic acid solution is 2 mL, 2 mL and 1 mL respectively.

8. The method according to claim 1, wherein the method is characterized by: In the step S8, the light irradiation condition is simulated by ultraviolet lamp irradiation, the wavelength of light irradiation is 365 nm, the light intensity is 10-20 mW / cm², and the light irradiation temperature is 25-30°C.

9. The method according to claim 1, wherein the method is characterized by: In the steps S6 and S8, the steps of centrifugation and washing are the same as S2.

10. The method according to claim 1, wherein the method is characterized by: In the step S8, the drying temperature is 40-45°C, and the drying time is 6-12 h.

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