A method for preparing nano-silver antioxidant particles using mulberry leaf extract

Abstract

A method for preparing nano-silver antioxidant particles using mulberry leaf extract belongs to the field of nano-material technology preparation. In this invention, mulberry leaf extract and silver nitrate are used as raw materials. Through three steps: raw material pretreatment, mediated synthesis of nano-silver antioxidant particles, and separation and purification of nano-silver antioxidant particles, nano-silver antioxidant particles are obtained. At the same time, the application of nano-silver antioxidant particles in the removal of DPPH free radicals is explored, providing a theoretical basis for the preparation of nano-silver antioxidant particles. The method of this invention uses mulberry leaf extract as the main raw material for synthesizing nano-silver antioxidant particles, with lower costs, achieving the high-value application of biomass resources. Moreover, the process conditions are simple, the equipment is simple, the operation is convenient, the energy consumption is less, and no steps such as ultrasonic treatment are required, making it suitable for large-scale production. The synthesized nano-silver antioxidant particles have a stable structure and a small average particle size, which is 10 - 40 nm, have certain antioxidant ability, meet market demand, and have practical significance and economic value.

Description

Technical Field

[0001] The invention belongs to the field of nanomaterial technology preparation, and specifically relates to a method for achieving green synthesis of nanosilver antioxidant particles by using mulberry leaf extract and silver nitrate as raw materials through a synergistic reaction of citric acid and anhydrous ethanol. Background Art

[0002] Silver nanoparticles (AgNPs) are one of the most commercially available nanomaterials. Due to their unique properties, such as small size and large surface area, as well as excellent antioxidant and antibacterial properties, they are widely used in medical, food, cosmetic, and environmental fields. Therefore, the preparation methods and physical and chemical properties of silver nanoparticles have attracted much attention and are of great significance. Currently, there are many methods for synthesizing silver nanoparticles, mainly three of which are physical, chemical, and biological methods. The physical method is a method in which large silver particles are crushed into nanometer-sized silver particles. However, it has high equipment requirements, high operating costs, and heavy energy requirements. The chemical method is a method in which silver ions are reduced to silver particles. The solvent is water or an organic solvent, and the main components are metal precursors, reducing agents, and stabilizers. However, the yield is low, the reagents and by-products are highly toxic, and there are serious environmental pollution problems. The biological method is a method in which nanoparticles are prepared from natural sources and products or microorganisms. It has the advantages of low raw material costs, high efficiency, mild reaction conditions, high yield, solubility, and high stability. Compared with the above three methods, biological methods are gradually being used in the field of nanomaterial preparation due to their excellent properties such as environmental friendliness, greenness and energy saving, and are becoming an important branch of nanotechnology.

[0003] Existing methods for the green synthesis of silver nanoparticles, such as the "Green Synthesis Method for Preparing Silver Nanoparticles Using Ferulic Acid from Plant Extracts" with the application number 202210768877.X published on September 20, 2022, disclose the following method: Dissolve the mixture of silver oxide and ferulic acid in ultrapure water, with the mass ratio of the mixture being 2 - 20:1. React under ultrasonic conditions where the random amplitude bar is rod numbers Φ2 - 15, the ultrasonic crushing power ratio is 10 - 90%, and the ultrasonic crushing time is 5 - 20 min. After the reaction is completed, centrifuge at a rotational speed of 2000 - 5000 g for 8 - 12 min to precipitate the unreacted substances, and collect the supernatant to obtain silver nanoparticles. Disperse the precipitate with fresh ultrapure water and then perform ultrasonic crushing again, followed by centrifugation to obtain the precipitate and supernatant. Repeat the dispersion, ultrasonic crushing, and centrifugation operations on the precipitate three times, and combine all the supernatants to obtain silver nanoparticles with a spherical structure, having an average particle size of 35 - 80 nm. The method of this patent has the following deficiencies: (1) Ferulic acid has few sources and high costs, and the raw material source is difficult, which increases the production cost. (2) The mixture of silver oxide and ferulic acid undergoes multiple steps such as ultrasonic crushing and centrifugation, with cumbersome operation steps and high equipment energy consumption, resulting in high production costs and being not conducive to promotion. (3) The obtained silver nanoparticle particles are liquid rather than solid and have a spherical structure with a size of 35 - 80 nm. The relatively large particle size of the silver nanoparticles results in a small specific surface area and low functional performance. The liquid state is not conducive to storage, increasing the storage site, transportation, and management costs, and increasing the difficulty of technology promotion. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing silver nanoparticle antioxidant particles using mulberry leaf extract, aiming at the deficiencies of the existing methods for synthesizing silver nanoparticle antioxidant particles. This method has the characteristics of wide raw material sources, low cost, mild reaction conditions, simple process conditions, simple equipment, convenient operation, less energy consumption, and does not require ultrasonic treatment. It is suitable for large-scale production, and the prepared silver nanoparticle antioxidant particles have a stable structure and a small average particle size of 10 - 40 nm, having a certain antioxidant effect, and having broad market prospects and economic value.

[0005] The mechanism of the present invention is as follows: Mulberry leaf extract contains natural active substances such as alkaloids, flavonoids, polysaccharides, aldehydes, ketones, and carboxylic acids. Microacid-controlled alcohol catalysis induces the structural modification of silver nanoparticles, and can reduce silver ions to nanoparticles at normal temperature and pressure. These active substances act as reducing agents, chelating agents, capping agents during the synthesis process, and attach to the surface of the silver nanoparticles as stabilizers to prevent particle aggregation. Microacid-controlled alcohol catalysis-induced modification makes the synthesized silver nanoparticle antioxidant particles have better performance and a stable structure.

[0006] The technical solution for achieving the invention purpose is: a method for preparing nano-silver antioxidant particles using mulberry leaf extract. Taking mulberry leaf extract and silver nitrate as raw materials, through three simple processes of raw material pretreatment, mediated synthesis of nano-silver antioxidant particles, and separation and purification of nano-silver antioxidant particles, nano-silver antioxidant particles are obtained, and their application as antioxidants in the removal of DPPH free radicals. The specific steps of the method are as follows:

[0007] (1) Raw material pretreatment

[0008] The mulberry leaves are washed, dried and ground to obtain mulberry leaf powder. The mulberry leaf powder is stirred and mixed with deionized water at a solid-liquid ratio of 1:10 - 200 g / mL. After hydrothermal reaction and filtration, centrifugation is carried out at a speed of 2000 - 10000 r / min for 10 - 40 min. The centrifugal supernatant and centrifugal residue are collected respectively. The upper centrifugal supernatant is freeze-dried to obtain mulberry leaf extract.

[0009] (2) Mediated synthesis of nano-silver antioxidant particles

[0010] After the completion of step (1), 0.1 - 2 g of silver nitrate and 0.1 - 5 g of mulberry leaf extract are weighed and placed in a beaker respectively. The mass ratio of the mixture is 1:0.1 - 8 g / g. It is dissolved in a solution containing citric acid at a concentration of 0 - 5 g / L and anhydrous ethanol with a volume fraction of 0 - 90% to obtain a mixed solution with a solid-liquid ratio of 1:5 - 50 g / mL. Stirring reaction is continuously carried out at a reaction temperature of 20 - 80 °C for 20 - 240 min to mediate the synthesis of nano-silver antioxidant particles.

[0011] (3) Separation and purification of nano-silver antioxidant particles

[0012] After the completion of step (2), the mixed solution is allowed to stand at room temperature in the dark for 12 - 48 h, and centrifuged at a speed of 2000 - 10000 r / min for 10 - 40 min. The centrifugal supernatant and centrifugal residue are collected respectively. The upper centrifugal supernatant containing part of the unreacted mulberry leaf extract can be placed in a container for recycling. The filter residue, namely nano-silver antioxidant particles, is dried at a temperature of 60 - 200 °C for 1 - 6 h, and ground to separate and purify the nano-silver antioxidant particles with a particle size of 10 - 50 nm. The yield of nano-silver antioxidant particles is calculated to be 281.70 - 409.60 mg / g.

[0013] (4) Application of nano-silver antioxidant particles in the scavenging of DPPH free radicals

[0014] First, dissolve the nano-silver antioxidant particles obtained in step (3) in absolute ethanol to obtain an AgNPs dispersion with a concentration of 0.1 - 10 mg / mL. Weigh the drug DPPH and dissolve it in absolute ethanol to obtain a DPPH solution with a concentration of 0.0001 - 0.007 mg / mL. Secondly, take the AgNPs dispersion and the DPPH solution to form a mixed solution with a ratio of 1:10 - 50 mL / mL, and carry out ultrasonic reaction in the dark for 10 - 60 min. Then, centrifuge at a rotational speed of 1000 - 6000 rpm for 10 - 60 min and take the supernatant to be detected by a UV spectrophotometer (UV-1900) with a detection wavelength of 450 - 560λ, and record the absorbance as A 样 (0 - 1); If the above mixed solution does not react, carry out centrifugation and detection directly, and record the absorbance as A 空 (0 - 1); Similarly, take the same volume of absolute ethanol to replace the AgNPs dispersion to form a mixed solution for direct detection, and record the absorbance as A 参 Finally, calculate the DPPH radical scavenging rate according to the function relation formula (1), and analyze that the DPPH radical scavenging rate of nano-silver is 0.55 - 86.83%; DPPH scavenging rate % = (A 参 - A 样 ) / A 空 * 100% Formula (1).

[0015] After the present invention adopts the above technical solutions, the main effects are as follows:

[0016] (1) The raw material of the present invention is mulberry leaf extract. Mulberry leaves are rich in natural active substances such as alkaloids, flavonoids, polysaccharides, aldehydes, ketones, and carboxylic acids, which meet the requirements for the green synthesis of nano-silver. At the same time, as a medicine and food homology substance, mulberry leaves are widely planted in various regions of our country, and there are many waste and inferior mulberry leaves every year. The raw material source is wide and the production cost is low.

[0017] (2) The present invention uses mulberry leaf extract to prepare nano-silver antioxidant particles. The active substances in mulberry leaf extract act as reducing agents, chelating agents, and capping agents during the synthesis process. They can reduce silver ions to silver nanoparticles at normal temperature and pressure, and adhere to the surface of the silver nanoparticles as stabilizers to prevent particle aggregation. Micro-acid controlled alcohol catalytic induction modification makes the synthesized nano-silver antioxidant particles have better performance and a stable spherical structure. The yield of nano-silver antioxidant particles is as high as 281.70 - 409.60 mg / g.

[0018] (3)The present invention uses mulberry leaf extract and silver nitrate as raw materials, and the preparation steps only require three steps. The method has simple steps, mild reaction conditions, simple process conditions, simple equipment, easy operation, less energy consumption, is green and environmentally friendly without pollution, and does not require ultrasonic and freeze-drying. It is suitable for large-scale production. The prepared silver nanocomposite antioxidant particles have a stable structure, a small average particle size of 10-40 nm, have a certain antioxidant effect, and have broad market prospects and economic value. Description of the Drawings

[0019] Figure 1 It is a physical picture and scanning electron microscope picture (SEM) of the silver nanocomposite antioxidant particles prepared in Example 1.

[0020] Figure 2 It is the X-ray diffraction pattern (XRD) of the silver nanocomposite antioxidant particles prepared in Example 1.

[0021] Figure 3 It is the thermogravimetric analysis pattern (TG) of the silver nanocomposite antioxidant particles prepared in Example 1. Embodiment

[0022] The present invention will be further described in detail below in conjunction with specific embodiments: Example 1:

[0023] A method for preparing silver nanocomposite antioxidant particles using mulberry leaf extract is as follows:

[0024] (1) Pretreatment of raw materials

[0025] The mulberry leaves are washed, dried and ground to obtain mulberry leaf powder. The mulberry leaf powder and deionized water are stirred and mixed at a material-liquid ratio of 1:20 g / mL, subjected to hydrothermal reaction and filtration, centrifuged at 4000 r / min for 20 min, and the centrifuged supernatant and centrifuged residue are collected respectively. The upper centrifuged supernatant is freeze-dried to obtain mulberry leaf extract.

[0026] (2) Mediated synthesis of silver nanocomposite antioxidant particles

[0027] After the completion of the first step, 0.5 g of silver nitrate and 1.2 g of mulberry leaf extract are weighed and placed in a beaker respectively, and the mass ratio of the mixture is 1:2.5 g / g. It is dissolved in a solution containing 0.5 g / L of citric acid and 25% by volume of absolute ethanol to obtain a mixed solution with a material-liquid ratio of 1:14.29 g / mL, and continuously stirred and reacted at a reaction temperature of 40 °C for 80 min to mediate the synthesis of silver nanocomposite antioxidant particles.

[0028] (3) Separation and purification of silver nanocomposite antioxidant particles

[0029] After the completion of step (2), the mixed solution is allowed to stand at room temperature in the dark for 18 h, centrifuged at 4000 rpm for 20 min, and the centrifuged supernatant and centrifuged residue are collected respectively. The upper centrifuged supernatant containing partially unreacted mulberry leaf extract can be placed in a container for recycling. The filter residue, namely the nano-silver antioxidant particles, is dried at 150 °C for 2 h, ground, separated and purified to obtain the nano-silver antioxidant particles with a particle size of 10 - 50 nm, and the yield of the nano-silver antioxidant particles is calculated to be 387.89 mg / g.

[0030] (4) Application of nano-silver antioxidant particles as an antioxidant in the removal of DPPH free radicals

[0031] First, the nano-silver antioxidant particles obtained in step (3) are dissolved in absolute ethanol to obtain an AgNPs dispersion with a concentration of 1 mg / mL, and the drug DPPH is weighed and dissolved in absolute ethanol to obtain a DPPH solution with a concentration of 0.0017 mg / mL. Secondly, an AgNPs dispersion and a DPPH solution are taken to form a mixed solution with a ratio of 1:29 mL / mL, and ultrasonic reaction is carried out in the dark for 30 min. Then, it is centrifuged at a rotation speed of 4000 r / min for 8 min, and the supernatant is taken and sent to a UV-visible spectrophotometer (UV-1900) with a detection wavelength of 517λ for detection, and the absorbance A is recorded. 样 is 0.0152; the above mixed solution is centrifuged and detected without reaction, and the absorbance A is recorded. 空 is 0.0206; similarly, the same volume of absolute ethanol is taken to replace the AgNPs dispersion to form a mixed solution for direct detection, and the absorbance A is recorded. 参 is 0.0253; finally, the DPPH free radical scavenging rate is calculated according to the functional relationship formula (1), and the DPPH free radical scavenging rate of nano-silver is analyzed to be 48.64%. Example 2:

[0032] A method for preparing nano-silver antioxidant particles using mulberry leaf extract is the same as that in Example 1, wherein:

[0033] In step (1), the material-liquid ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, and the centrifugation time is 20 min.

[0034] In step (2), a mixture of 0.5 g of silver nitrate and 1 g of mulberry leaf extract, with a mass ratio of 1:2 g / g, the citric acid concentration in the solution is 0.5 g / L, the volume fraction of water ethanol is 45%, the material-liquid ratio of the mixture mass to the solution volume is 1:20 g / mL, the reaction temperature is 50 °C, and the reaction time is 90 min.

[0035] In step (3), it is left standing at room temperature in the dark for 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, and the drying time is 2 h; the yield of the prepared nano-silver antioxidant particles is weighed on an electronic balance to be 344.07 mg / g.

[0036] In step (4), 0.3 mL of a 1 mg / mL AgNPs dispersion solution and 8.7 mL of a 0.017 mg / mL DPPH solution are used, the mixing ratio of the mixed solution is 1:29 mL / mL, the ultrasonic reaction time in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength of the ultraviolet spectrophotometer (UV-1900) is 517λ, A 空 = 0.0242, A 样 = 0.0194, A 参 = 0.0262, and the DPPH scavenging rate is calculated to be 28.10%. Example 3:

[0037] A method for preparing nano-silver antioxidant particles using mulberry leaf extract is the same as in Example 1, wherein:

[0038] In step (1), the material-liquid ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, and the centrifugation time is 20 min.

[0039] In step (2), a mixture of 0.5 g of silver nitrate and 1.25 g of mulberry leaf extract, with a mass ratio of 1:2.5 g / g, the concentration of citric acid in the solution is 0.5 g / L, the volume fraction of water ethanol is 15%, the material-liquid ratio of the mixture mass to the solution volume is 1:14.29 g / mL, the reaction temperature is 50 °C, and the reaction time is 90 min.

[0040] In step (3), it is left standing at room temperature in the dark for 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, and the drying time is 2 h; the yield of the prepared nano-silver antioxidant particles is weighed on an electronic balance to be 357.66 mg / g.

[0041] In step (4), 0.3 mL of a 1 mg / mL AgNPs dispersion solution and 8.7 mL of a 0.017 mg / mL DPPH solution are used, the mixing ratio of the mixed solution is 1:29 mL / mL, the ultrasonic reaction time in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength of the ultraviolet spectrophotometer (UV-1900) is 517λ, A 空 = 0.0339, A 样 = 0.0286, A 参= 0.0373, and the calculated DPPH scavenging rate is 24.78%.

[0042] Experimental results

[0043] 1. Influence of different mass ratios on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0044] 2. Influence of different solid-liquid ratios on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0045] Serial number Dosage of mulberry leaf extract (g) Dosage of silver nitrate (g) Ratio of material to liquid (g / mL) <![CDATA[A 空 > <![CDATA[A 样 > <![CDATA[A 参 > Yield (mg / g) DPPH scavenging rate (%) 1 1 0.5 1:10 0.0236 0.0223 0.0262 40.68 16.53 2 1 0.5 1:13.33 0.0211 0.0184 0.0262 38.16 36.97 3 1 0.5 1:16.67 0.02 0.0177 0.0262 36.35 42.50 4 1 0.5 1:20 0.0242 0.0194 0.0262 34.41 28.10 5 1 0.5 1:23.33 0.0239 0.0219 0.0262 34.61 17.99

[0046] 3. Influence of different citric acid concentrations on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0047] 4. Influence of different reaction temperatures on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0048] 5. Influence of different reaction time ratios on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0049] 6. Influence of different volumes of absolute ethanol on the yield of nano-silver antioxidant particles and DPPH radical scavenging rate

[0050] 7. Application of nano-silver antioxidant particles in DPPH radical scavenging

[0051] 8. Particle size test of nano-silver antioxidant particles

[0052] From the above experiments, it is known that: In this invention, nano-silver antioxidant particles are prepared using mulberry leaf extract. When the ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the mass of silver nitrate is 0.5 g, the mass of mulberry leaf extract is 1.25 g, the mass ratio of the mixture is 1:2.5 g / g, the citric acid concentration is 0.5 g / L, the volume fraction of absolute ethanol is 25%, the solid-liquid ratio of the mixed solution is 1:14.29 g / mL, the reaction temperature is 40 °C, the reaction time is 80 min, the standing time at room temperature in the dark is 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, the drying time is 2 h, the yield of nano-silver antioxidant particles is 387.89 mg / g, the concentration of AgNPs dispersion is 1 mg / mL, the concentration of DPPH solution is 0.0017 mg / mL, the ratio of the two mixed solutions is 1:29 mL / mL, the ultrasonic reaction time in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength is 517λ, the absorbance A 样 is 0.0152, the absorbance A 空 is 0.0206, the absorbance A 参is 0.0253, and the DPPH free radical scavenging rate is 48.64%; the production raw materials are widely sourced and low in cost. The production process has simple steps, simple process conditions, simple equipment, mild reaction conditions, easy operation, less energy consumption, and is green and pollution-free. It does not require ultrasonic treatment and freeze-drying, etc. It is suitable for large-scale production. Moreover, the prepared silver nano antioxidant particles have a stable structure and a small average particle size, which is 10 - 40 nm, have a certain antioxidant effect, and have broad market prospects and economic value.

Claims

1. A method for preparing nano-silver antioxidant particles using mulberry leaf extract, characterized in that, It includes the following steps: (1) Pretreatment of raw materials The mulberry leaves are washed, dried and ground to obtain mulberry leaf powder. The mulberry leaf powder is stirred and mixed with deionized water at a solid-liquid ratio of 1:10-200 g / mL, subjected to hydrothermal reaction and filtration, and centrifuged at a speed of 2000-10000 r / min for 10-40 min. The centrifuged supernatant and centrifuged residue are collected respectively. The upper centrifuged supernatant is freeze-dried to obtain mulberry leaf extract; (2) Mediated synthesis of nano-silver antioxidant particles After the completion of step (1), 0.1-2 g of silver nitrate and 0.1-5 g of mulberry leaf extract are weighed and placed in a beaker respectively. The mass ratio of the mixture is 1:0.1-8 g / g. It is dissolved in an anhydrous ethanol solution containing citric acid at a concentration of 0-5 g / L and a volume fraction of 0-90%, and a mixed solution with a solid-liquid ratio of 1:5-50 g / mL is obtained. The reaction is continuously stirred at a reaction temperature of 20-80 °C for 20-240 min to mediate the synthesis of nano-silver antioxidant particles; (3) Separation and purification of nano-silver antioxidant particles After the completion of step (2), the mixed solution is allowed to stand at room temperature in the dark for 12-48 h, centrifuged at a speed of 2000-10000 rpm for 10-40 min. The centrifuged supernatant and centrifuged residue are collected respectively. The upper centrifuged supernatant contains partially unreacted mulberry leaf extract and silver ions, which can be placed in a container for recycling. The filter residue is nano-silver antioxidant particles, which are dried at a temperature of 60-200 °C for 1-6 h, ground and separated and purified to obtain nano-silver antioxidant particles with a particle size of 10-50 nm. The yield of nano-silver antioxidant particles is calculated to be 281.70-409.60 mg / g.

2. A method for preparing nano-silver antioxidant particles using mulberry leaf extract according to claim 1, wherein: In step (1), the solid-liquid ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, and the centrifugation time is 20 min; In step (2), a mixture of 0.5 g of silver nitrate and 1.25 g of mulberry leaf extract, with a mass ratio of 1:2.5 g / g, the citric acid concentration in the solution is 0.5 g / L, the volume fraction of water ethanol is 25%, the mass of the mixture and the volume of the solution have a solid-liquid ratio of 1:14.29 g / mL, the reaction temperature is 40 °C, and the reaction time is 80 min; In step (3), it is allowed to stand at room temperature in the dark for 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, and the drying time is 2 h; The yield of the prepared nano-silver antioxidant particles is weighed on an electronic balance to be 387.89 mg / g.

3. A method for preparing nano-silver antioxidant particles using mulberry leaf extract according to claim 1, wherein: In step (1), the solid-liquid ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, and the centrifugation time is 20 min; In step (2), a mixture of 0.5 g of silver nitrate and 1 g of mulberry leaf extract, with a mass ratio of 1:2 g / g, the concentration of citric acid in the solution is 0.5 g / L, the volume fraction of water ethanol is 45%, the ratio of the mass of the mixture to the volume of the solution is 1:20 g / mL, the reaction temperature is 50 °C, and the reaction time is 90 min; In step (3), it is left to stand at room temperature in the dark for 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, and the drying time is 2 h; the yield of the prepared silver nano-antioxidant particles is weighed on an electronic balance to be 344.07 mg / g.

4. A method for preparing silver nano-antioxidant particles using mulberry leaf extract according to claim 1, characterized in that: In step (1), the ratio of mulberry leaf powder to deionized water is 1:20 g / mL, the centrifugation speed is 4000 r / min, and the centrifugation time is 20 min; In step (2), a mixture of 0.5 g of silver nitrate and 1.25 g of mulberry leaf extract, with a mass ratio of 1:2.5 g / g, the concentration of citric acid in the solution is 0.5 g / L, the volume fraction of water ethanol is 15%, the ratio of the mass of the mixture to the volume of the solution is 1:14.29 g / mL, the reaction temperature is 50 °C, and the reaction time is 90 min; In step (3), it is left to stand at room temperature in the dark for 18 h, the centrifugation speed is 4000 r / min, the centrifugation time is 20 min, the drying temperature is 150 °C, and the drying time is 2 h; the yield of the prepared silver nano-antioxidant particles is weighed on an electronic balance to be 357.66 mg / g.

5. Use of the nano-silver antioxidant particles according to claim 1 in DPPH free radical scavenging, characterized in that, It includes the following steps: The application method is as follows: First, dissolve the silver nano-antioxidant particles in absolute ethanol to obtain an AgNPs dispersion solution with a concentration of 0.01 - 10 mg / mL, and weigh the drug DPPH and dissolve it in absolute ethanol to obtain a DPPH solution with a concentration of 0.0001 - 0.007 mg / mL; Secondly, take the AgNPs dispersion solution and the DPPH solution to form a mixed solution with a ratio of 1:10 - 50 mL / mL, and react under ultrasonic irradiation in the dark for 10 - 60 min; Then, centrifuge at a speed of 1000 - 6000 rpm for 5 - 60 min and take the supernatant to be detected by an ultraviolet spectrophotometer with a detection wavelength of 450 - 560 λ, and record the absorbance as A sample; The above mixed solution is centrifuged and detected without reaction, and the absorbance is recorded as A blank; Similarly, take the same volume of absolute ethanol to replace the AgNPs dispersion solution to form a mixed solution and directly detect it, and record the absorbance as A reference; Finally, calculate the DPPH free radical scavenging rate according to the following functional relationship, and analyze that the DPPH free radical scavenging rate of the silver nano-antioxidant particles is 0.55 - 86.83%; DPPH scavenging rate % = (A reference - A sample) / A blank * 100%.

6. The application of the silver nano-antioxidant particles according to claim 5 as an antioxidant in the removal of DPPH free radicals, characterized in that: 0.3 mL of AgNPs dispersion with a concentration of 1 mg / mL, 8.7 mL of DPPH solution with a concentration of 0.017 mg / mL, the mixing ratio of the mixture is 1:29 mL / mL, the reaction time of ultrasonic irradiation in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength of the ultraviolet spectrophotometer is 517λ, A blank = 0.0206, A sample = 0.0152, A reference = 0.0253, and the calculated DPPH scavenging rate % is 48.64%.

7. The application of the nano-silver antioxidant particles as claimed in claim 5 in the removal of DPPH free radicals, characterized in that: 0.3 mL of AgNPs dispersion with a concentration of 1 mg / mL, 8.7 mL of DPPH solution with a concentration of 0.017 mg / mL, the mixing ratio of the mixture is 1:29 mL / mL, the reaction time of ultrasonic irradiation in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength of the ultraviolet spectrophotometer is 517λ, A blank = 0.0242, A sample = 0.0194, A reference = 0.0262, and the calculated DPPH scavenging rate % is 28.10%.

8. The application of the nano-silver antioxidant particles as claimed in claim 5 in the removal of DPPH free radicals, characterized in that: 0.3 mL of AgNPs dispersion with a concentration of 1 mg / mL, 8.7 mL of DPPH solution with a concentration of 0.017 mg / mL, the mixing ratio of the mixture is 1:29 mL / mL, the reaction time of ultrasonic irradiation in the dark is 30 min, the centrifugation speed is 4000 r / min, the centrifugation time is 8 min, the detection wavelength of the ultraviolet spectrophotometer is 517λ, A blank = 0.0339, A sample = 0.0286, A reference = 0.0373, and the calculated DPPH scavenging rate % is 24.78%.

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