Green synthesis method for preparing micron spherical silver powder from green soybean pod extract

Abstract

The invention discloses a green synthesis method for preparing micron spherical silver powder from green soybean pod extract. The green soybean pod extract is used as a reducing agent, and silver nitrate is used as a silver source. The preparation method comprises the following steps: cleaning, drying and crushing green soybean pods, putting the crushed green soybean pods into a round-bottom flask, connecting a reflux condensing tube, adding deionized water in a ratio of 1: 10, heating to boil, and keeping a reflux state for 1-3 hours; and after the reflux is finished, cooling the extracting solution, filtering to remove filter residues to obtain a green soybean pod crude extracting solution, carrying out ion exchange resin chromatography and water elution on the crude extracting solution to obtain a green soybean pod eluent, and carrying out vacuum concentration and drying to obtain the green soybean pod extract. Adding a dispersing agent into the silver nitrate solution, adjusting the pH value to 7, and then adding the mixed solution into the green soybean pod extract solution to obtain a mixed solution; and the mixed solution is magnetically stirred for 10 min, and then the micron spherical silver powder is obtained through high-speed centrifugation, xenon lamp irradiation, azeotropic distillation, washing and drying. The micron spherical silver powder prepared through the method is high in sphericity degree, good in fluidity and high in purity.

Description

Technical Field

[0001] This invention belongs to the field of micro- and nanomaterial preparation technology, specifically relating to a green synthesis method for preparing micron-sized spherical silver powder from extracts of soybean pods. Background Technology

[0002] With the rapid development of modern technology, micron-sized silver powder has shown great application potential in many fields. Due to its high specific surface area and active surface, it possesses excellent electrical conductivity, thermal conductivity, and antibacterial properties, playing an important role in electronics, optoelectronics, biomedicine, and materials science. Although traditional physicochemical synthesis methods can produce products that meet certain requirements, they also have many problems.

[0003] On the one hand, traditional physicochemical synthesis processes have significant environmental pollution problems: the production process easily generates wastewater containing high concentrations of silver ions, unreacted chemical waste liquid, and toxic byproducts, which not only pose potential risks to the health of operators, but also pollute the air and water, failing to meet environmental protection requirements.

[0004] On the other hand, the cost bottleneck of traditional synthesis processes is prominent: some processes rely on special reaction conditions such as high temperature and high pressure, or require the use of expensive equipment and high-purity raw materials, resulting in high production costs of micron silver powder, which limits its large-scale production and wider application scenarios.

[0005] Green synthesis aims to prepare silver powder using a more environmentally friendly, mild, and low-cost method, minimizing negative environmental impacts while reducing resource consumption and costs during production. Therefore, developing a green synthesis method to produce micron-sized spherical silver powder with high sphericity, particle dispersion, and narrow distribution is a pressing issue in this field. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a green synthesis method for preparing micron-sized spherical silver powder from edamame pod extract. The present invention is a green synthesis method for preparing micron-sized spherical silver powder with controllable particle size, narrow distribution, and high sphericity using edamame pod extract as a reducing agent.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A green synthesis method for preparing micron-sized spherical silver powder from soybean pod extract includes the following steps: Add a dispersant to the silver nitrate solution and adjust the pH to neutral to obtain mixture A; Add mixture A to the green soybean pod extract solution and mix well to obtain mixture B; A catalyst was added to the mixture B, and the reaction was carried out by irradiation with a xenon lamp to obtain mixture C; The mixture C is subjected to solid-liquid separation, and the separated solid substances are washed to obtain the washing product; Polyols were added to the washing product, and then the product was treated by magnetic stirring. After the magnetic stirring was completed, solid-liquid separation was performed, and the separated solid product was vacuum dried to obtain micron-sized spherical silver powder.

[0008] Preferably, the concentration of the silver nitrate solution is 0.1 mol / L to 0.5 mol / L, and the amount of dispersant added is 5 wt.% to 16 wt.% of the mass of silver nitrate.

[0009] Preferably, the dispersant is gelatin, gum arabic, PVP, PVA, PEG, sodium citrate, or Tween-80.

[0010] Preferably, the solvent for the edamame pod extract solution is deionized water, the mass ratio of edamame pod extract to silver nitrate solution is 1:(0.68~5.7), and the mixture A and the edamame pod extract solution are mixed in equal volume ratios at a mixing temperature of 32~38℃.

[0011] Preferably, the catalyst is an alcohol dehydrogenase.

[0012] Preferably, the amount of catalyst added is 0.5 wt.% to 5 wt.% of the mass of silver nitrate in the silver nitrate solution.

[0013] Preferably, when using a xenon lamp for irradiation, the power of the xenon lamp is 290-310W, the wavelength is 200-400nm, and the time is 29-31min.

[0014] Preferably, when a polyol is added to the washing product and then treated by magnetic stirring: The volume ratio of washing product to polyol was 1:(1~3), the magnetic stirring speed was 400~700 r / min, the temperature was 90℃~150℃, and the time was 1~3 h; The polyol is glycerol, 1,2-propylene glycol, 1,3-propylene glycol, or 1,4-butanediol.

[0015] Preferably, the preparation method of the green soybean pod extract includes: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2 The following fragments; The fragments were mixed with deionized water at a mass ratio of 1:(9~11), the mixture was heated to 325~335℃, and the extract was obtained by reflux condensation. Then, the extract was cooled and separated into solid and liquid components to obtain crude extract of green soybean pods. The crude extract of green soybean pods was subjected to ion exchange resin chromatography and eluted with water several times to obtain the eluent of green soybean pods. The eluent of the green soybean pods was concentrated under reduced pressure at a vacuum of 0.08~0.09 MPa and dried for 10-14 hours to obtain the green soybean pod extract.

[0016] The present invention also provides a micron-sized spherical silver powder, which is obtained by the green synthesis method described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, a green synthesis method for preparing micron-sized spherical silver powder from edamame pod extract involves adding a dispersant to a silver nitrate solution, adjusting the pH to neutral, and then adding the solution to the edamame pod extract to obtain a mixture. The mixture is then subjected to magnetic stirring, catalyst addition, xenon lamp irradiation, high-speed centrifugation, azeotropic distillation, washing, and drying to obtain micron-sized spherical silver powder. Xenon lamp irradiation creates a uniform energy field in the reaction system, causing the reduction rate of silver ions in each region to tend to be uniform, avoiding preferential growth in one direction, guiding silver atoms to be isotropically deposited on the crystal nucleus surface, and accelerating the reaction rate with the catalyst, forming a large number of crystal nuclei, achieving controllable particle size and high sphericity. Simultaneously, xenon lamp irradiation can regulate the surface charge of the silver powder, and combined with azeotropic distillation to remove water molecules from the system, it avoids hard agglomeration caused by hydrogen bonds and van der Waals forces on the silver powder surface. Attached Figure Description

[0018] Figure 1 This is an SEM image of the micron-sized spherical silver powder prepared in Example 1 of the present invention.

[0019] Figure 2 This is an SEM image of the micron-sized spherical silver powder prepared in Example 2 of the present invention.

[0020] Figure 3 The image shows the X-ray diffraction pattern of the micron-sized spherical silver powder prepared in Example 3 of this invention.

[0021] Figure 4 The particle size distribution diagram of the micron-sized spherical silver powder prepared in Example 4 of this invention is obtained by a particle size distribution calculation tool.

[0022] Figure 5 The particle size distribution diagram of the micron-sized spherical silver powder prepared in Example 5 of the present invention is obtained by a particle size distribution calculation tool.

[0023] Figure 6 This is a SEM image of the micron-sized spherical silver powder prepared in Comparative Example 1 of this invention.

[0024] Figure 7 This is a SEM image of the micron-sized spherical silver powder prepared in Comparative Example 2 of this invention.

[0025] Figure 8 This is a SEM image of the micron-sized spherical silver powder prepared in Comparative Example 3 of this invention.

[0026] Figure 9 This is a SEM image of the micron-sized spherical silver powder prepared in Comparative Example 4 of this invention.

[0027] Figure 10 This is a flowchart of a green synthesis method for preparing micron-sized spherical silver powder from soybean pod extract in an embodiment of the present invention. Detailed Implementation

[0028] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0029] See Figure 10 The present invention discloses a green synthesis method for preparing micron-sized spherical silver powder from soybean pod extract, comprising the following steps: Step one: This invention uses a combination of reflux condensation and ion exchange resin chromatography to prepare green soybean pod extract. Specifically, the preparation process of the green soybean pod extract is as follows: Green soybean pods are washed with deionized water, dried, and then pulverized into 0.5 cm particles. 2 The following fragments were prepared. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:(9~11) (the ratio in the following examples is 1:10). The round-bottom flask was connected to a reflux condenser, and the deionized water was heated to 330±5℃ to boil. The rising water vapor was cooled in the condenser and then refluxed back into the flask, maintaining reflux for 1~3 h. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, and a crude extract of green soybean pods was obtained. The crude extract of green soybean pods was subjected to ion exchange resin chromatography, eluted several times with water (generally 3~5 times is sufficient) to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08~0.09 MPa and dried for 10-12 h to obtain the green soybean pod extract.

[0030] Step 2, Preparation of micron-sized spherical silver powder: 5 wt.%~16 wt.% (relative to the mass of silver nitrate) of dispersant was added to 100 mL of a 0.1 mol / L~0.5 mol / L silver nitrate solution, and the pH was adjusted to 7 to obtain mixture A. The dispersant used was one of gelatin, gum arabic, PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), PEG (polyethylene glycol), sodium citrate, and Tween-80. Mixture A was then added to 100 mL of a *Echinopsis pilosula* pod extract solution (solvent: deionized water) with a mass ratio of silver nitrate of 1:(0.68~5.7), and magnetically stirred at a speed of 500±10 r / min for 30-35 min at a temperature of 35±3℃. After adding the catalyst, a mixture was obtained by irradiation with a xenon lamp. The catalyst was alcohol dehydrogenase, with a mass of 0.5 wt.%~5 wt.% (relative to the mass of silver nitrate). The xenon lamp irradiation was performed at a power of 300±10W, a wavelength of 200~400 nm, and a time of 29-31 min. The mixture was centrifuged at 8000±10 r / min for 2-4 min to separate the solid and liquid phases. After solid-liquid separation, the mixture was washed three times with deionized water to obtain the washing product. During each wash, the mixture was ultrasonically cleaned for 4-6 min at 35±3℃. A certain amount of polyol was added to the washing product, and the mixture was magnetically stirred on a magnetic stirrer until the liquid level was below half. Specifically, the volume ratio of the washing product to the polyol was 1:(1~3), the magnetic stirring speed was 400~700 r / min, the temperature was 90℃~150℃, and the time was 1~3 h. The mixture was centrifuged again at 8000±10 r / min for 2-4 min, and the excess polyol was discarded. The centrifuged product was dried in a vacuum drying oven at 80±2℃ for 10-12 h to obtain micron-sized spherical silver powder. Since hydrogen bonds in water can exacerbate powder aggregation, any non-toxic polyol with a boiling point higher than water can be used. High-boiling-point, non-toxic polyol azeotropic reactions can effectively remove most water molecules; therefore, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, or 1,4-butanediol are suitable polyols.

[0031] In the above scheme, the value before “±” is the set value (or nominal value) of the corresponding parameter, and the value before “±” is the deviation value of the corresponding parameter. In the following embodiments, only the set value (or nominal value) of the corresponding parameter is given. It can be understood that the relevant parameters in the following embodiments are within the range of the above set value (or nominal value) ± deviation value, and the technical solution is feasible.

[0032] Example 1: This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1 hour. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0033] Step 2: Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 1.2 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 30 min at 35℃. Add 0.5 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 200 nm xenon lamp for 30 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Add 1:1 glycerol to the washing product and stir on a magnetic stirrer at 90℃ and 400 r / min for 1 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 12 h to obtain micron-sized spherical silver powder.

[0034] SEM images of the micron-sized spherical silver powder obtained in this embodiment, taken using a GeminiSEM500 scanning electron microscope, are shown below. Figure 1 As shown, the agglomeration coefficient of the micron-sized spherical silver powder obtained in this embodiment is 1.0, the sphericity is 88%, and the Span value is 0.93. Therefore, the micron-sized spherical silver powder obtained in this embodiment has high dispersibility, high sphericity, and narrow particle size distribution.

[0035] Example 2: This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1.5 h. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract of green soybean pods was subjected to ion exchange resin chromatography, eluted four times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.09 MPa and dried for 10 h to obtain the green soybean pod extract.

[0036] Step 2: Add 0.3 g of PVP to 100 mL of 0.2 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 6.8 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 33 min at 35℃. Add 1 wt.% of alcohol dehydrogenase catalyst and irradiate with a 300 W, 200 nm xenon lamp for 29 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 2 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain the washing product, with ultrasonic cleaning for 4 min at 35℃ between each wash. Add 1:1.5 glycerol to the washing product and stir on a magnetic stirrer at 100℃ and 500 r / min for 1.5 h until the liquid level is below half. Centrifuge again at 8000 r / min for 2 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven for 12 h to obtain micron-sized spherical silver powder.

[0037] SEM images of the micron-sized spherical silver powder obtained in this embodiment, taken using a GeminiSEM500 scanning electron microscope, are shown below. Figure 2 As shown, the agglomeration coefficient of the micron-sized spherical silver powder obtained in this embodiment is 1.0, the sphericity is 89%, and the Span value is 0.88. Therefore, the micron-sized spherical silver powder obtained in this embodiment has high dispersion, high sphericity, and narrow particle size distribution.

[0038] Example 3: This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 2 hours. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract of green soybean pods was subjected to ion exchange resin chromatography, eluted five times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.09 MPa and dried for 11 hours to obtain the green soybean pod extract.

[0039] Step 2: Add 0.4 g of PVA to 100 mL of 0.3 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 15.3 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 35 min at 35°C. Add 2 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 250 nm xenon lamp for 31 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 4 min to separate the solid and liquid phases. Wash three times with deionized water to obtain the washing product, with ultrasonic cleaning for 6 min at 35°C between each wash. Add 1:2 glycerol to the washing product and stir at 110°C and 450 r / min on a magnetic stirrer for 1.5 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 12 h to obtain micron-sized spherical silver powder.

[0040] like Figure 3 As shown, the micron-sized spherical silver powder obtained in this embodiment was tested using a Bruker D8 X-ray diffractometer, and the Ag purity was 99.98%, proving that the product is silver and has a very high purity.

[0041] Example 4: This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 2.5 h. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract of green soybean pods was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 h to obtain the green soybean pod extract.

[0042] Step 2: Add 0.5 g of PEG to 100 mL of 0.4 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 27.2 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 30 min at 35℃. Add 3 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 400 nm xenon lamp for 30 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Add glycerol in a 1:2.5 ratio to the washing product and stir on a magnetic stirrer at 130℃ and 500 r / min for 2.5 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 11 h to obtain micron-sized spherical silver powder.

[0043] like Figure 4 As shown, the average particle size of the micron-sized spherical silver powder obtained in this embodiment was 550.41 nm, as measured using Nano Measurer 1.2 software.

[0044] Example 5: This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 3 hours. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.09 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0045] Step 2: Add 0.5 g of gum arabic to 100 mL of 0.5 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 46 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 30 min at 35℃. Add 5 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 400 nm xenon lamp for 30 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Add 1:3 glycerol to the washing product and stir on a magnetic stirrer at 150℃ and 600 r / min for 3 h until the liquid level is below half. Centrifuge again at 8000 r / min for 4 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 10 h to obtain micron-sized spherical silver powder.

[0046] like Figure 5 As shown, the average particle size of the micron-sized spherical silver powder obtained in this embodiment was 629.86 nm, as measured using Nano Measurer 1.2 software.

[0047] Comparative Example 1: The difference from Example 1 is that the temperature of the magnetic stirring during the reaction is increased to 75°C.

[0048] This comparison will present a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1 hour. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0049] Step 2: Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 1.2 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 30 min at 75 ℃. Add 0.5 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 200 nm xenon lamp for 30 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35 ℃ between each wash. Add 1:1 glycerol to the washing product and stir on a magnetic stirrer at 90 ℃ and 400 r / min for 1 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 12 h to obtain micron-sized spherical silver powder.

[0050] The SEM image of the micron-sized spherical silver powder obtained in this comparative example, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 6 As shown, the sphericity of the micron-sized spherical silver powder obtained in this comparative example is 37%, and the average particle size is 36 μm. Therefore, the sphericity of the micron-sized spherical silver powder obtained in this comparative example is poor and the particle size is too large.

[0051] Comparative Example 2: The difference from Example 1 is that no catalyst is added.

[0052] This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1 hour. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0053] Step 2: Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 1.2 g of edamame pod extract and magnetically stir at 500 r / min for 30 min at 35℃. Irradiate with a 300 W, 200 nm xenon lamp for 30 min to obtain the final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Add 1:1 glycerol to the washing product and stir on a magnetic stirrer at 90℃ and 400 r / min for 1 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min and discard the excess glycerol. The centrifuged product was dried in an 80°C vacuum drying oven for 12 h to obtain micron-sized spherical silver powder.

[0054] The SEM image of the micron-sized spherical silver powder obtained in this comparative example, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 7 As shown, the agglomeration coefficient of the micron-sized spherical silver powder obtained in this comparative example is 2.4, the sphericity is 62%, and the Span value is 1.2. Therefore, the micron-sized spherical silver powder obtained in this comparative example has poor sphericity and poor dispersibility.

[0055] Comparative Example 3: The difference from Example 1 is that the dispersant was reduced by 3 wt.%.

[0056] This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1 hour. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0057] Step 2: Add 0.05 g of gelatin to 100 mL of 0.1 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 1.2 g of *Echinops latifolius* pod extract and magnetically stir at 500 r / min for 30 min at 35℃. Add 0.5 wt.% alcohol dehydrogenase catalyst and irradiate with a 300 W, 200 nm xenon lamp for 30 min to obtain a final mixture. Centrifuge the mixture at 8000 r / min for 3 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain a washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Add 1:1 glycerol to the washing product and stir on a magnetic stirrer at 90℃ and 400 r / min for 1 h until the liquid level is below half. Centrifuge again at 8000 r / min for 3 min, and discard excess glycerol. Place the centrifuged product in an 80℃ vacuum drying oven and dry for 12 h to obtain micron-sized spherical silver powder.

[0058] The SEM image of the micron-sized spherical silver powder obtained in this comparative example, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 8 As shown, the sphericity of the micron-sized spherical silver powder obtained in this comparative example is 34%, and the average particle size is 3.8 μm. Therefore, the sphericity of the micron-sized spherical silver powder obtained in this comparative example is poor and the particle size is too large.

[0059] Comparative Example 4: The difference from Example 1 is that the xenon lamp irradiation step is not performed.

[0060] This embodiment will provide a method for preparing micron-sized spherical silver powder, specifically including the following steps: Step 1: Wash the green soybean pods with deionized water, dry them, and then crush them into 0.5 cm pieces. 2The following fragments were collected. The fragments were placed in a round-bottom flask, and deionized water was added at a mass ratio of 1:10. The round-bottom flask was connected to a reflux condenser, and the water was heated to 330°C until boiling. The rising steam entered the condenser and was cooled, then refluxed back into the flask, maintaining reflux for 1 hour. After reflux, the extract was cooled, then centrifuged, filtered to remove the residue, yielding a crude extract of green soybean pods. The crude extract was subjected to ion exchange resin chromatography, eluted three times with water to obtain the green soybean pod eluent. The green soybean pod eluent was concentrated under reduced pressure at 0.08 MPa and dried for 12 hours to obtain the green soybean pod extract.

[0061] Step 2: Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate solution and adjust the pH to 7 to obtain mixture A. Then add mixture A to 100 mL of a solution containing 1.2 g of *Echinops latifolius* pod extract and magnetically stir at 500 rpm for 30 min at 35°C. Add 0.5 wt.% alcohol dehydrogenase catalyst to obtain the final mixture. Centrifuge the mixture at 8000 rpm for 3 min to separate the solid and liquid phases. Wash the mixture three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35°C between each wash. Add 1:1 glycerol to the washing product and stir on a magnetic stirrer at 400 rpm for 1 h until the liquid level is below half. Centrifuge again at 8000 rpm for 3 min and discard the excess glycerol. The centrifuged product was dried in an 80°C vacuum drying oven for 12 h to obtain micron-sized spherical silver powder.

[0062] The SEM image of the micron-sized spherical silver powder obtained in this comparative example, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 9 As shown, the sphericity of the micron-sized spherical silver powder obtained in this comparative example is 28%, and the average particle size is 3.8 μm. Therefore, the micron-sized spherical silver powder obtained in this comparative example is severely deformed and has an excessively large particle size.

[0063] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A green synthesis of microspherical silver powder from green pod extract characterized in that, The method comprises the following steps: adding a dispersing agent into a silver nitrate solution and adjusting the pH to neutral to obtain a mixed solution A; adding the mixed solution A into a solution of green velvet bean pod extract and mixing uniformly to obtain a mixed solution B; adding a catalyst into the mixed solution B and performing a reaction by using a xenon lamp to obtain a mixed solution C; performing solid-liquid separation on the mixed solution C and washing the separated solid substance to obtain a washing product; adding a polyhydric alcohol into the washing product and then performing a treatment by magnetic stirring, after the magnetic stirring is completed, performing solid-liquid separation, and vacuum drying the separated solid product to obtain micron spherical silver powder.

2. A green synthesis process for the preparation of microspherical silver powder from green bean pods as claimed in claim 1, wherein, The concentration of the silver nitrate solution is 0.1 mol / L-0.5 mol / L, and the adding amount of the dispersing agent is 5 wt.%-16 wt.% of the mass of the silver nitrate.

3. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, The dispersing agent is gelatin, gum arabic, PVP, PVA, PEG, sodium citrate or Tween-80.

4. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, The solvent of the solution of green velvet bean pod extract is deionized water, the mass ratio of the green velvet bean pod extract to the silver nitrate in the silver nitrate solution is 1:(0.68-5.7), the mixed solution A and the solution of green velvet bean pod extract are mixed in an equal volume ratio, and the mixing temperature is 32-38℃.

5. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, The catalyst is ethanol dehydrogenase.

6. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, The adding amount of the catalyst is 0.5 wt.%-5 wt.% of the mass of the silver nitrate in the silver nitrate solution.

7. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, When the reaction is performed by using a xenon lamp, the power of the xenon lamp is 290-310 W, the wavelength is 200-400 nm, and the time is 29-31 min.

8. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, When the polyhydric alcohol is added into the washing product and then a treatment is performed by magnetic stirring: the volume ratio of the washing product to the polyhydric alcohol is 1:(1-3), the rotating speed of the magnetic stirring is 400-700 r / min, the temperature is 90℃-150℃, and the time is 1-3 h; wherein the polyhydric alcohol is glycerol, 1,2 propylene glycol, 1,3 propylene glycol or 1,4 butanediol.

9. A green synthesis of microspherical silver powder from green bean pod extract according to claim 1, characterized in that, The preparation method of the green velvet bean pod extract comprises the following steps: The green pods were washed with deionized water, dried and comminuted to 0.5 cm 2 The following pieces; mixing the crushed pieces and deionized water in a mass ratio of 1:(9-11), heating the mixture to 325-335℃, obtaining an extract by using a condensation reflux method, and then cooling and performing solid-liquid separation to obtain a green velvet bean pod crude extract; performing ion exchange resin chromatography on the green velvet bean pod crude extract and washing with water for several times to obtain a green velvet bean pod eluent; performing vacuum concentration and drying on the green velvet bean pod eluent under a vacuum degree of 0.08-0.09 MPa for 10-14 h to obtain a green velvet bean pod extract.

10. A microspheroidal silver powder, characterized by, The micron spherical silver powder is obtained by the green synthesis method in any one of claims 1-9.

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