Method for green synthesis of nano spherical silver powder from black bean and natto extract

Abstract

The invention belongs to the technical field of nano material preparation, and discloses a method for green synthesis of nano spherical silver powder from black bean and natto extracts, which comprises the following steps: adding a sodium borohydride solution into a first silver nitrate solution, and magnetically stirring to obtain a yellow seed crystal solution; a dispersing agent is added into the second silver nitrate solution, then the pH is adjusted to 3.8-4.2, and a mixed solution A is obtained; adding the mixed solution A into the black bean and natto extract solution, and uniformly mixing to obtain a growth solution; adding the seed crystal solution into the growth solution, and stirring to obtain a mixed solution B; adding a catalyst into the mixed solution B, and carrying out electric field induction, solid-liquid separation and washing to obtain a washing product; and polyhydric alcohol is added into the washing product, then treatment is conducted through magnetic stirring, after magnetic stirring is completed, solid-liquid separation is conducted, a solid product obtained through separation is subjected to vacuum drying, and the nanometer spherical silver powder is obtained. The nanometer spherical silver powder prepared through the method is controllable in particle size, narrow in distribution, high in sphericity degree and high in purity.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for the green synthesis of nano-spherical silver powder from black bean and natto extract. Background Technology

[0002] Due to its unique microstructure, spherical silver nanoparticles possess high specific surface area, high surface activity, excellent conductivity, and broad-spectrum antibacterial properties, making them a key functional material in high-end manufacturing and biomedicine. In the electronics industry, they serve as the core conductive phase in electronic pastes, used in MLCC (Multilayer Ceramic Capacitor) internal electrodes, solar cell silver grid lines, and flexible electronic conductive coatings, requiring uniform particle size, high sphericity, and good dispersibility. In the biomedical field, they can be used as a core component of antibacterial dressings and targeted drug delivery carriers, with clear requirements for low toxicity and biocompatibility. Furthermore, in catalysis and new energy fields, the morphology and size of spherical silver nanoparticles directly determine their catalytic activity and stability.

[0003] Currently, the preparation methods for nano-spherical silver powder are mainly divided into physical methods (such as spray pyrolysis and vacuum evaporation condensation) and chemical methods (such as chemical reduction and microemulsion methods). While physical methods can produce high-purity silver powder, they suffer from drawbacks such as high energy consumption, easy product agglomeration, and difficulty in particle size control, making them unsuitable for low-cost, large-scale production. Chemical methods are currently the mainstream technology, relying on chemical reducing agents (such as sodium borohydride, ascorbic acid, and glucose) to reduce silver ions to elemental silver. However, they have significant technical challenges: First, poor environmental friendliness: traditional chemical reducing agents (such as sodium borohydride) are highly toxic and volatile, easily leaving harmful impurities after the reaction, requiring complex post-processing, which not only increases production costs but also easily causes water pollution. Although ascorbic acid is relatively less toxic... The chemical reduction method has several drawbacks. First, it has low efficiency, but its aqueous solution stability is poor, making it difficult to precisely control reaction conditions and resulting in a wide product particle size distribution. Second, the product performance is insufficient: chemical reduction is prone to local overgrowth of silver nuclei due to fluctuations in local reducing agent concentration, forming irregular morphologies such as ellipsoids and spindles. Furthermore, due to their high surface energy, nanoparticles are prone to agglomeration through van der Waals forces and hydrogen bonds, making it difficult to meet the dispersibility requirements of high-end electronic pastes. Third, it is highly dependent on resources: traditional chemical reducing agents are mostly derived from fossil resources. With increasingly stringent global environmental policies, renewable and low-pollution green preparation paths have become an inevitable trend in the industry.

[0004] Green synthesis, as an upgrade of chemical methods, focuses on replacing chemical reducing agents with natural bio-based reducing agents, aligning with the concept of sustainable development. Its advantages lie in the fact that the reducing agents are derived from renewable biological resources, leaving no toxic residues and exhibiting good biocompatibility. Furthermore, some bioactive components possess both reducing and dispersing functions, enabling simultaneous silver ion reduction and particle dispersion, thus simplifying the preparation process. Current research has used green tea extracts and ginkgo leaf extracts to prepare nano-silver powder, but these methods suffer from low reduction efficiency, poor product sphericity, and a narrow controllable particle size range. The core reason is the unstable structure of active reducing components in existing plant extracts (such as tea polyphenols), making it difficult to precisely control the silver ion reduction rate and the silver nucleus growth pathway. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a green method for synthesizing nano-spherical silver powder from black bean and natto extract. This invention can prepare nano-spherical silver powder with controllable particle size, narrow distribution, high sphericity, and high purity, and belongs to the category of green synthesis methods.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for the green synthesis of nano-spherical silver powder from black bean and natto extract includes the following steps: Sodium borohydride solution was added to the first silver nitrate solution and the mixture was magnetically stirred to obtain a yellow seed solution. Add a dispersant to the second silver nitrate solution, and then adjust the pH to 3.8-4.2 to obtain mixture A; Add the mixture A to the black bean and natto extract solution and mix well to obtain the growth solution; The seed solution was added to the growth solution and stirred to obtain mixture B; A catalyst was added to mixture B and an electric field was applied. After the electric field was applied, solid-liquid separation was performed. The separated solid product was washed to obtain the washed 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 nano-spherical silver powder.

[0007] Preferably, the concentration of the sodium borohydride solution is 0.04-0.06 mol / L, and the concentration of the first silver nitrate solution is 0.1 mol / L to 0.5 mol / L; the first silver nitrate solution and the sodium borohydride solution are mixed in equal volumes; When adding sodium borohydride solution to the first silver nitrate solution and magnetically stirring to obtain a yellow seed crystal solution, the magnetic stirring speed is 490-510 r / min, the stirring time is 4-6 min, and the temperature is 32-38℃.

[0008] Preferably, the dispersant is one of gelatin, gum arabic, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium citrate, and Tween-80. The concentration of the second silver nitrate solution is 0.1 mol / L to 0.5 mol / L, and the mass of the dispersant is 5 wt.% to 16 wt.% of the mass of silver nitrate in the second silver nitrate solution.

[0009] Preferably, the mass ratio of black bean natto extract in the black bean natto extract solution to silver nitrate in the second silver nitrate solution is 1:(2.4~6.5). Mixture A with an equal volume of black bean and natto extract solution. After adding mixture A to the black bean and natto extract solution, magnetic stirring is performed at 490-510 r / min for 4-6 min at a temperature of 32-38℃.

[0010] Preferably, the seed solution is added to the growth solution and magnetically stirred at a speed of 490-510 r / min for 19-21 min and a temperature of 32-38℃.

[0011] Preferably, the catalyst is alcohol dehydrogenase, and the amount of alcohol dehydrogenase added is 0.5 wt.% to 5 wt.% of the mass of silver nitrate in the second silver nitrate solution.

[0012] Preferably, a catalyst is added to the mixture B, and an electric field is induced using an electric field generator, the electric field voltage of which is 5~15 V.

[0013] 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.

[0014] Preferably, the preparation method of the black bean natto extract includes: Black soybeans and natto are washed with deionized water, dried, and ground into powder to obtain black soybean and natto powder. Adding deionized water to black bean natto powder yields mixture A, wherein the mass ratio of black bean natto powder to deionized water is 1:(4~6). Mixture A was subjected to microwave extraction. The parameters for microwave extraction included: microwave power of 300 W to 500 W, extraction time of 30 min to 90 min, and extraction temperature of 30℃ to 60℃. After microwave extraction, the residue was removed by filtration, and the filtrate was concentrated under reduced pressure at a vacuum degree of 0.08~0.09 MPa and dried for 10-12 hours to obtain black bean natto extract.

[0015] The present invention also provides a nanosphere silver powder, which is obtained by the green synthesis method of black bean natto extract as described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a green method for synthesizing nano-spherical silver powder from black bean and natto extract. The method uses black bean and natto extract as a reducing agent, employs a seed crystal method to reduce silver ions, pre-determines the number of crystal nuclei, and ensures that subsequent growth occurs around these existing nuclei. Furthermore, the method utilizes electric field induction and catalysts to regulate the reaction rate, particularly for positively charged Ag. + This generates a directional driving force, causing Ag to diffuse uniformly along the direction of the electric field into the reaction region, avoiding local concentration fluctuations and ensuring that all crystal nuclei are in contact with the reaction zone. + Consistent concentration, synchronized growth, and controllable particle size are achieved. The powder's dispersibility is enhanced through electrostatic repulsion. Micron-sized spherical silver powder is obtained using azeotropic distillation, eliminating hard agglomerations of water molecules formed on the particle surface due to hydrogen bonds and van der Waals forces. This results in the green synthesis of nano-spherical silver powder with controllable particle size, high sphericity, and narrow particle size distribution. Attached Figure Description

[0017] Figure 1 This is a SEM image of the nanosphere silver powder prepared in Example 1 of the present invention.

[0018] Figure 2 This is a SEM image of the nanosphere silver powder prepared in Example 2 of the present invention.

[0019] Figure 3 The image shows the X-ray diffraction pattern of the nanosphere silver powder prepared in Example 3 of this invention.

[0020] Figure 4 The particle size distribution diagram of the nanosphere silver powder prepared in Example 4 of this invention is obtained by a particle size distribution calculation tool.

[0021] Figure 5 The particle size distribution diagram of the nanosphere silver powder prepared in Example 5 of this invention is obtained by a particle size distribution calculation tool.

[0022] Figure 6 This is a SEM image of the nanosphere silver powder prepared in Comparative Example 1 of this invention.

[0023] Figure 7 This is a SEM image of the nanosphere silver powder prepared in Comparative Example 2 of this invention.

[0024] Figure 8This is a SEM image of the nanosphere silver powder prepared in Comparative Example 3 of this invention.

[0025] Figure 9 This is a SEM image of the nanosphere silver powder prepared in Comparative Example 4 of this invention.

[0026] Figure 10 This is a flowchart of the method for green synthesis of nano-spherical silver powder from black bean and natto extract according to the present invention. Detailed Implementation

[0027] 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.

[0028] Reference Figure 10 The present invention discloses a method for the green synthesis of nano-spherical silver powder from black bean and natto extract, comprising the following steps: Step 1: This invention uses microwave extraction and vacuum concentration to obtain an extract from black soybeans and natto. Specifically, the preparation process of the black soybean and natto extract is as follows: First, the black soybeans and natto are washed with deionized water, dried, and ground into powder to obtain black soybean and natto powder. Deionized water is added to the black soybean and natto powder at a mass ratio of 1:(4~6) to obtain mixture A. Mixture A is placed in a microwave extraction device, and extraction is performed at a microwave power of 300 W~500 W, an extraction time of 30 min~90 min, and a temperature of 30℃~60℃. After extraction, the residue is removed by filtration, and the filtrate is concentrated under vacuum of 0.08~0.09 MPa and dried for 10-12 hours to obtain the black soybean and natto extract.

[0029] Step 2, Preparation of spherical silver powder: Add 100 mL of a 0.04-0.06 mol / L sodium borohydride aqueous solution to 100 mL of a 0.1 mol / L-0.5 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution). Stir magnetically to obtain a yellow seed solution. The magnetic stirring speed is 500±10 r / min, the stirring time is 4-6 min, and the temperature is 35±3℃. Take 5 wt.%~16 wt.% (relative to the mass of silver nitrate in the second silver nitrate solution) of dispersant, wherein the dispersant is one of gelatin, gum arabic, PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), PEG (polyethylene glycol), sodium citrate, and Tween-80. The dispersant was added to 100 mL of a 0.1 mol / L~0.5 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), and the pH was adjusted to 4.0±0.2. Then, the entire solution was added to 100 mL of a black bean and natto extract solution (the solvent used in the black bean and natto extract solution was deionized water, and the mass ratio of black bean and natto extract to silver nitrate in the second silver nitrate solution was 1:(2.4~6.5)) to form the growth solution. Magnetic stirring was then performed at a speed of 500±10 r / min, a stirring time of 4-6 min, and a temperature of 35±3℃. The seed crystal solution was then added to the growth solution and magnetically stirred to obtain mixture B, with a stirring speed of 500±10 r / min, a stirring time of 19-21 min, and a temperature of 35±3℃. After adding the catalyst to mixture B, an electric field is induced using an electric field generator. The catalyst can be alcohol dehydrogenase, with a mass of 0.5 wt.%~5 wt.% of the mass of silver nitrate in the second silver nitrate solution. The electric field voltage induced by the electric field is 5~15 V. After the reaction, centrifuge at 8000±10 r / min for 2-4 min to separate the solid and liquid. Wash the product with deionized water 3-5 times to obtain the washing product. During each wash, ultrasonically clean the product for 4-6 min at 35±3℃. Add a certain amount of polyol to the washing product and stir it on a magnetic stirrer until the liquid level is less than half. The volume ratio of the washing product to the polyol is 1:(1~3). The magnetic stirring speed is 400~700 r / min, the temperature is 90℃~200℃, and the time is 1~3 h. Centrifuge again for 2-4 min at 8000±10 r / min, discard excess polyol, and obtain the centrifuged product. Place the centrifuged product in a vacuum drying oven at 80±2℃ and dry for 10-12 h to obtain nano-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 azeotropes can effectively remove most water molecules; therefore, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, or 1,4-butanediol are suitable polyols.

[0030] 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.

[0031] Example 1: This embodiment will provide a method for preparing nano-spherical silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 300 W microwave power for 60 min at 50℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 h to obtain the black soybean and natto extract.

[0032] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35 ℃ to obtain a yellow seed solution. Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the entire solution to 100 mL of an aqueous solution containing 4.1 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35 ℃. Add the seed solution to the growth solution and magnetically stir to obtain mixture B at 500 r / min for 20 min at 35 ℃. After adding alcohol dehydrogenase catalyst (0.5 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, an electric field generator (5 V) was used to induce the reaction, which accelerated the reaction process. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solids were then washed three times with deionized water, with ultrasonic cleaning at 35℃ for 5 min between each wash. Glycerol was added to the washing product at a volume ratio of 1:1, and the mixture was stirred at 90℃ and 400 r / min for 1 h until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and excess glycerol was discarded. The centrifuged product was dried in an 80℃ vacuum drying oven for 12 h to obtain nano-spherical silver powder.

[0033] SEM images of the nanosphere silver powder of this embodiment, taken using a GeminiSEM500 scanning electron microscope, are shown below. Figure 1 As shown, the agglomeration coefficient of the nano-spherical silver powder obtained in this embodiment is 1.4, the sphericity is 74%, and the particle size distribution Span value is 1.3. Therefore, the nano-spherical silver powder obtained in this embodiment has high dispersibility, high sphericity, and narrow particle size distribution. Example 2: This embodiment will provide a method for preparing nano-spherical silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:4 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 400 W microwave power for 50 min at 30℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.09 MPa, and dry for 11 h to obtain D-pineol.

[0034] Step 2: Add 100 ml of 0.05 mol / L sodium borohydride aqueous solution to 100 ml of 0.2 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35℃ to obtain a yellow seed solution. Add 0.4 g of PVP to 100 mL of 0.2 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of an aqueous solution containing 10.2 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35℃. Add the seed solution to the growth solution and magnetically stir to obtain mixture B at 500 r / min for 20 min at 35℃. After adding alcohol dehydrogenase catalyst (1 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, and using an electric field generator to induce an electric field at 8 V, the reaction process was accelerated. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solid was then washed three times with deionized water to obtain the washing product, with ultrasonic cleaning at 35 °C for 5 min between each wash. Glycerol was added to the washing product at a volume ratio of 1:2, and the mixture was stirred at 100 °C and 400 r / min on a magnetic stirrer for 1.5 h until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and the excess glycerol was discarded. The centrifuged product was then dried in an 80 °C vacuum drying oven for 12 h to obtain nano-spherical silver powder.

[0035] SEM images of the nanosphere silver powder of this embodiment, taken using a GeminiSEM500 scanning electron microscope, are shown below. Figure 2 As shown, the agglomeration coefficient of the nano-spherical silver powder obtained in this embodiment is 1.5, the sphericity is 72%, and the Span value is 1.2. Therefore, the nano-spherical silver powder obtained in this embodiment has high dispersibility, high sphericity, and narrow particle size distribution.

[0036] Example 3: This embodiment will provide a method for preparing nano-spherical silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:6 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 500 W microwave power for 50 min at 40℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 10 h to obtain D-pineol.

[0037] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.3 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35℃ to obtain a yellow seed solution. Add 0.5 g of PVA to 100 mL of 0.3 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of 1.0 mol / L D-pineol aqueous solution as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35℃. The seed solution is then added to the growth solution and magnetically stirred to obtain mixture B at 500 r / min for 20 min at 35℃. After adding alcohol dehydrogenase catalyst (2 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, and using an electric field generator to induce an electric field at 10 V, the reaction process was accelerated. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solid was then washed three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35 ℃ between each wash. Glycerol was added to the washing product at a volume ratio of 1:3, and the mixture was magnetically stirred at 500 r / min for 2 h at 120 ℃ until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and the excess glycerol was discarded. The centrifuged product was then dried in a vacuum drying oven at 80 ℃ for 12 h to obtain nano-spherical silver powder.

[0038] like Figure 3 As shown, the nanosphere silver powder of this embodiment was tested using a Bruker D8 X-ray diffractometer, and the silver purity was 99.96%, proving that the product is silver and has a very high purity.

[0039] Example 4: This embodiment will provide a method for preparing nano-spherical silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 400 W microwave power for 70 min at 45℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 h to obtain the black soybean and natto extract.

[0040] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.4 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35 ℃ to obtain a yellow seed solution. Add 0.6 g of PEG to 100 mL of 0.4 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of an aqueous solution containing 27 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35 ℃. Add the seed solution to the growth solution and magnetically stir to obtain mixture B at 500 r / min for 20 min at 35 ℃. After adding alcohol dehydrogenase catalyst (0.3 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, an electric field generator was used to induce the reaction, which accelerated the reaction process. The electric field voltage was 12V. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solid was then washed three times with deionized water to obtain the washing product. During each wash, the product was ultrasonically cleaned for 5 min at 35℃. Glycerol was added to the washing product at a volume ratio of 1:1.5, and the mixture was stirred on a magnetic stirrer at 150℃ and 450 r / min for 2 h until the liquid level was below half. The mixture was centrifuged again at 8000 r / min for 3 min, and the excess glycerol was discarded. The centrifuged product was dried in a vacuum drying oven at 80℃ for 12 h to obtain nano-spherical silver powder.

[0041] like Figure 4As shown, the average particle size of the nanosphere silver powder in this embodiment was 80.20 nm, as measured using Nano Measurer 1.2 software.

[0042] Example 5: This embodiment will provide a method for preparing nano-spherical silver powder, specifically including the following steps: Step one: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 450 W microwave power for 65 min at 55℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.09 MPa, and dry for 10 h to obtain D-pineol.

[0043] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.5 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35℃ to obtain a yellow seed solution. Add 0.7 g of sodium citrate to 100 mL of 0.5 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of an aqueous solution containing 51 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35℃. The seed solution is then added to the growth solution and magnetically stirred to obtain mixture B at 500 r / min for 20 min at 35℃. After adding alcohol dehydrogenase catalyst (0.5 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, and using an electric field generator to induce an electric field at 15V, the reaction process was accelerated. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solid was then washed three times with deionized water to obtain the washing product, with ultrasonic cleaning for 5 min at 35℃ between each wash. Glycerol was added to the washing product at a volume ratio of 1:2.5, and the mixture was stirred on a magnetic stirrer at 150℃ and 650 r / min for 2 h until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and the excess glycerol was discarded. The centrifuged product was dried in a vacuum drying oven at 80℃ for 12 h to obtain nano-spherical silver powder.

[0044] like Figure 5 As shown, the average particle size of the nanosphere silver powder in this embodiment was 84.33 nm, as measured using Nano Measurer 1.2 software.

[0045] Comparative Example 1: The difference from Example 1 is that the solution pH is changed from 4 to 7.

[0046] This comparative example will provide a method for preparing nanosphere silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 300 W microwave power for 60 min at 50℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 h to obtain the black soybean and natto extract.

[0047] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35 ℃ to obtain a yellow seed solution. Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 7, and then add the mixture to 100 mL of an aqueous solution containing 4.1 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35 ℃. The seed solution is then added to the growth solution and magnetically stirred to obtain mixture B at 500 r / min for 20 min at 35 ℃. After adding alcohol dehydrogenase catalyst (0.5 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, an electric field generator (5 V) was used to induce the reaction, which accelerated the reaction process. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solids were then washed three times with deionized water, with ultrasonic cleaning at 35℃ for 5 min between each wash. Glycerol was added to the washed product at a volume ratio of 1:1, and the mixture was stirred at 90℃ and 400 r / min for 1 h until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and excess glycerol was discarded. The centrifuged product was dried in an 80℃ vacuum drying oven for 12 h to obtain nano-spherical silver powder.

[0048] The SEM image of the comparative example of nanosphere silver powder, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 6As shown, the sphericity of the nano-spherical silver powder obtained in this comparative example is 48%, and the average particle size is 1.2 μm. Therefore, the sphericity of the nano-spherical silver powder obtained in this comparative example is poor and the particle size is too large.

[0049] Comparative Example 2: The difference from Example 1 is that no catalyst is added.

[0050] This comparative example will provide a method for preparing nanosphere silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 300 W microwave power for 60 minutes at 50℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 hours to obtain the black soybean and natto extract.

[0051] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35℃ to obtain a yellow seed solution. Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of an aqueous solution containing 4.1 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35℃. The seed solution is then added to the growth solution and magnetically stirred to obtain mixture B at 500 r / min for 20 min at 35℃. An electric field generator is used for induction, which accelerates the reaction process; the electric field voltage is 5 V. After the reaction was completed, the product was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The product was then washed three times with deionized water, with ultrasonic cleaning for 5 min at 35℃ between each wash. Glycerol was added to the washing product at a volume ratio of 1:1, and the mixture was stirred at 400 r / min on a magnetic stirrer at 90℃ for 1 h until the liquid level was below half. The product was then centrifuged again at 8000 r / min for 3 min, and excess glycerol was discarded. The centrifuged product was then dried in a vacuum drying oven at 80℃ for 12 h to obtain nano-spherical silver powder.

[0052] The SEM image of the comparative example of nanosphere silver powder, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 7As shown, the sphericity of the nano-spherical silver powder obtained in this comparative example is 53%, and the average particle size is 1.1 μm. Therefore, the sphericity of the nano-spherical silver powder obtained in this comparative example is poor and the particle size is too large.

[0053] Comparative Example 3: The difference from Example 1 is that 20 wt.% of dispersant was added.

[0054] This comparative example will provide a method for preparing nanosphere silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 300 W microwave power for 60 min at 50℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 h to obtain the black soybean and natto extract.

[0055] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35 ℃ to obtain a yellow seed solution. Add 0.34 g of gelatin to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the entire solution to 100 mL of an aqueous solution containing 4.1 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35 ℃. Add the seed solution to the growth solution and magnetically stir at 500 r / min for 20 min at 35 ℃ to obtain mixture B. After adding alcohol dehydrogenase catalyst (0.5 wt.% of the mass of silver nitrate in the second silver nitrate solution) to mixture B, an electric field generator was used to induce the reaction, which accelerated the reaction process. The electric field voltage was 5 V. After the reaction, the mixture was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The solid was then washed three times with deionized water to obtain the washing product. During each wash, the product was ultrasonically cleaned for 5 min at 35 °C. Glycerol was added to the washing product at a volume ratio of 1:1, and the mixture was magnetically stirred at 400 r / min for 1 h at 90 °C until the liquid level was below half. The mixture was then centrifuged again at 8000 r / min for 3 min, and the excess glycerol was discarded. The centrifuged product was dried in a vacuum drying oven at 80 °C for 12 h to obtain nano-spherical silver powder.

[0056] The SEM image of the comparative example of nanosphere silver powder, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 8 As shown, the agglomeration coefficient of the nano-spherical silver powder obtained in this comparative example is 1.8, the sphericity is 64%, and the Span value is 2.1. Therefore, the nano-spherical silver powder obtained in this comparative example has a large particle size distribution and poor dispersibility.

[0057] Comparative Example 4: The difference from Example 1 is that the electric field induction step is not performed.

[0058] This comparative example will provide a method for preparing nanosphere silver powder, specifically including the following steps: Step 1: First, wash the black soybeans and natto three times, dry them, and grind them into powder to obtain black soybean and natto powder. Add deionized water to the black soybean and natto powder at a mass ratio of 1:5 to obtain mixture A. Place mixture A in a microwave extraction device and extract using 300 W microwave power for 60 min at 50℃. After extraction, filter to remove the residue, concentrate the filtrate under reduced pressure at 0.08 MPa, and dry for 12 h to obtain the black soybean and natto extract.

[0059] Step 2: Add 100 mL of 0.05 mol / L sodium borohydride aqueous solution to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the first silver nitrate solution), and magnetically stir at 500 r / min for 5 min at 35℃ to obtain a yellow seed solution. Add 0.15 g of gelatin to 100 mL of 0.1 mol / L silver nitrate aqueous solution (i.e., the second silver nitrate solution), adjust the pH to 4, and then add the mixture to 100 mL of an aqueous solution containing 4.1 g of black bean natto extract as the growth solution. Magnetic stirring is then performed at 500 r / min for 5 min at 35℃. Add the seed solution to the growth solution and magnetically stir to obtain mixture B at 500 r / min for 20 min at 35℃. Add alcohol dehydrogenase catalyst to mixture B (the amount added is 0.5 wt.% of the mass of silver nitrate in the second silver nitrate solution). After the reaction was completed, the product was centrifuged at 8000 r / min for 3 min to separate the solid and liquid phases. The product was then washed three times with deionized water, with ultrasonic cleaning for 5 min at 35℃ between each wash. Glycerol was added to the washing product at a volume ratio of 1:1, and the mixture was stirred at 400 r / min on a magnetic stirrer at 90℃ for 1 h until the liquid level was below half. The product was then centrifuged again at 8000 r / min for 3 min, and excess glycerol was discarded. The centrifuged product was then dried in a vacuum drying oven at 80℃ for 12 h to obtain nano-spherical silver powder.

[0060] The SEM image of the comparative example of nanosphere silver powder, taken using a GeminiSEM500 scanning electron microscope, is shown below. Figure 9 As shown, the sphericity of the nano-spherical silver powder obtained in this comparative example is 56%, and the average particle size is 0.8 μm. Therefore, the sphericity of the nano-spherical silver powder obtained in this comparative example is poor and the particle size is too large.

[0061] The spherical silver powder prepared in the embodiments of the present invention can be widely used in the fields of microelectronics, catalysis, medical antibacterial, and sensors.

[0062] 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.

[0063] 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 scope of protection of the claims of the present invention.

Claims

1. A method for green synthesis of nanospherical silver powder from black bean natto extract, characterized by, The process comprises the following steps: A yellow seed solution is obtained by adding a sodium borohydride solution to the first silver nitrate solution and stirring magnetically; A dispersant is added to the second silver nitrate solution, and then the pH is adjusted to 3.8-4.2 to obtain a mixed solution A; The mixed solution A is added to the black bean natto extract solution and mixed uniformly to obtain a growth solution; The seed solution is added to the growth solution and stirred to obtain a mixed solution B; A catalyst is added to the mixed solution B, and an electric field is induced, and then solid-liquid separation is performed after the electric field induction, and the separated solid product is washed to obtain a washed product; Polyhydric alcohol is added to the washed product, and then the product is treated by magnetic stirring, and after the magnetic stirring is completed, solid-liquid separation is performed, and the separated solid product is vacuum dried to obtain a nanometer spherical silver powder.

2. The method of claim 1, wherein the green synthesized nanosilver powder is prepared from black bean natto extract. The concentration of the sodium borohydride solution is 0.04-0.06 mol / L, and the concentration of the first silver nitrate solution is 0.1 mol / L-0.5 mol / L; the first silver nitrate solution and the sodium borohydride solution are mixed in equal volumes. When the yellow seed solution is obtained by adding a sodium borohydride solution to the first silver nitrate solution and stirring magnetically, the magnetic stirring speed is 490-510 r / min, the stirring time is 4-6 min, and the temperature is 32-38℃.

3. The method of claim 1, wherein the green synthesized nanosilver powder is prepared from black bean natto extract. The dispersant is one of gelatin, gum arabic, polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, sodium citrate and Tween-80, the concentration of the second silver nitrate solution is 0.1 mol / L-0.5 mol / L, and the mass of the dispersant is 5wt.%-16wt.% of the mass of silver nitrate in the second silver nitrate solution.

4. The method of claim 1, wherein the green synthesized nanosilver powder is prepared from black bean natto extract. The mass ratio of black bean natto extract in the black bean natto extract solution to silver nitrate in the second silver nitrate solution is 1:(2.4-6.5). The mixed solution A and the black bean natto extract solution are mixed in equal volumes, and after the mixed solution A is added to the black bean natto extract solution, magnetic stirring is performed, wherein the speed is 490-510 r / min, the stirring time is 4-6 min, and the temperature is 32-38℃.

5. The method of claim 1, wherein the green synthesized nanosilver powder is prepared from black bean natto extract. The seed solution is added to the growth solution and stirred magnetically, the magnetic stirring speed is 490-510 r / min, the stirring time is 19-21 min, and the temperature is 32-38℃.

6. The method of claim 1, wherein the green synthesized nanosilver powder is prepared from black bean natto extract. The catalyst is ethanol dehydrogenase, and the amount of ethanol dehydrogenase added is 0.5wt.%-5wt.% of the mass of silver nitrate in the second silver nitrate solution.

7. The method of claim 1, wherein the green synthesized nanosilver powder is extracted from black bean natto. The catalyst is added to the mixed solution B, and an electric field is induced by using an electric field generator, and the electric field voltage of the electric field generator is 5-15 V.

8. The method of claim 1, wherein the green synthesized nanosilver powder is extracted from black bean natto. When polyhydric alcohol is added to the washed product and the product is treated by magnetic stirring: The volume ratio of the washed product to polyhydric alcohol is 1:(1-3), the speed of magnetic stirring is 400-700 r / min, the temperature is 90℃-150℃, and the time is 1-3 h; The polyhydric alcohol is glycerol, 1,2 propanediol, 1,3 propanediol or 1,4 butanediol.

9. The method for green synthesis of nano-spherical silver powder from black bean and natto extract according to claim 1, characterized in that, The preparation method of the black bean natto extract comprises the following steps: The black bean natto is washed with deionized water, dried and ground to obtain black bean natto powder; The black bean natto powder is added with deionized water to obtain a mixture A, wherein the mass ratio of the black bean natto powder to the deionized water is 1:(4-6); The mixture A is subjected to microwave extraction, and the microwave extraction parameters include that the microwave power is 300 W-500 W, the extraction time is 30 min-90 min, and the extraction temperature is 30°C-60°C. After the microwave extraction is completed, the filter residue is removed by filtration, the filtrate is concentrated under reduced pressure with a vacuum degree of 0.08-0.09 MPa, and dried for 10-12 h to obtain a black bean natto extract.

10. A nanospherical silver powder, characterized by, The nanospherical silver powder is obtained by the method for green synthesis of nanospherical silver powder according to any one of claims 1-9. The nanospherical silver powder is obtained by the method for green synthesis of nanospherical silver powder according to any one of claims 1-9.

Images