Nano silver powder and preparation method thereof

Abstract

The invention relates to the technical field of nano material preparation, in particular to nano silver powder and a preparation method thereof. The preparation method comprises the steps that primary silver powder and a protease solution are mixed and subjected to solid-liquid separation; the silver powder obtained through separation is subjected to acid etching treatment through a first etching solution, a second etching solution and a third etching solution in sequence, and then drying is conducted; the first etching liquid is selected from one or more of malic acid, 2-ethyl-butyric acid and glutamic acid; the second etching liquid is selected from one or more of ascorbic acid, citric acid and oxalic acid; the third etching liquid is selected from one or more of phytic acid, tartaric acid, lactic acid and caffeic acid. According to the method, the nano silver powder is prepared through multi-step etching, the technological process is simple, the preparation efficiency is high, the etching process is free of cyanide / strong acid, green and environmentally friendly, and the nano silver powder obtained through the method is high in dispersity, concentrated in particle size distribution and regular in morphology and can be widely applied to the industries of medical treatment, sensors, integrated circuit automobiles and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer material preparation, and particularly relates to a kind of nano silver powder and its preparation method. BACKGROUND

[0002] With the rapid development of current microelectronic technology, nano silver powder is widely used in electronic materials, photosensitive materials, catalysts, medicines and antibacterial materials and many other fields due to its unique surface effect and quantum size effect. The preparation technology of nano silver powder mainly includes physical method and chemical method. The physical method has complex preparation process and high preparation cost, and the prepared ultra-fine silver powder cannot meet the application requirements of conductive paste, so the chemical method is more common. Liquid phase reduction process is simple and has low equipment cost, so it is the most widely used method in current industrial large-scale production. However, there are still some technical problems in the preparation of nano silver powder by liquid phase reduction method, such as complex reaction system, uneven particle size and morphology of powder, and even the need for special equipment, which to some extent limits the practical application of nano silver material synthesis method.

[0003] When most of the current technologies use liquid phase reduction method to prepare nano silver powder, the concentration, temperature, pH and reaction time of the reactants need to be controlled at the same time. Since the concentration of the solution changes as the reaction proceeds, the particle size distribution of the obtained silver powder is not concentrated, and the morphology is not uniform. The invention CN202411687636.8 prepares nano silver particles in the first dispersion liquid, then adds a second dispersant in the reducing bottom liquid, and combines the use of surface modification coating solution to adjust the particle size and dispersity of the silver powder. This method has a complex process, harsh reaction conditions, and high requirements for equipment, which is difficult to realize large-scale production. The obtained powder has obvious agglomeration, which reduces the sintering activity of the silver powder. SUMMARY

[0004] To solve the above technical problems, the present application provides a kind of nano silver powder and its preparation method. The present application uses multi-step etching to prepare nano silver powder, which has simple process flow, high preparation efficiency, no cyanide / strong acid in etching process, and is green and environmentally friendly. The nano silver powder obtained by the method has high dispersity, concentrated particle size distribution and regular morphology, and can be widely used in medical, sensor, integrated circuit and automobile industries.

[0005] In a first aspect, the present application provides a preparation method of nano silver powder, comprising: mixing and treating primary silver powder with a protease solution, then performing solid-liquid separation; sequentially performing acid etching treatment on the separated silver powder with a first etching solution, a second etching solution and a third etching solution, and then drying; the first etching solution is selected from a solution of one or more of malic acid, 2-ethyl-butanoic acid and glutamic acid; the second etching solution is selected from a solution of one or more of ascorbic acid, citric acid and oxalic acid; and the third etching solution is selected from a solution of one or more of phytic acid, tartaric acid, lactic acid and coffee acid. The green process for preparing high-purity nano silver powder of the present application cooperatively prepares nano silver powder through biological enzyme pretreatment and gradient weak acid etching. The process flow of the method is simple, environmentally friendly and high in powder preparation efficiency. The obtained particles have a relatively smooth appearance, no obvious thorn-like protrusions, a spherical shape and good dispersibility, and no obvious agglomeration, and are suitable for the fields of electronic conductive paste, antibacterial materials and the like.

[0006] As preferred, the protease solution is selected from a solution of one or more of subtilisin, papain, bromelain and corn protease, and is preferably a subtilisin solution; the mass fraction of the protease solution is 0.5% to 6%, and is preferably 1 to 2.5%; the pH of the protease solution is 6.0 to 7.5, and is preferably 7.0; and the mass ratio of the silver powder to the protease solution is 1:5 to 20, and the treatment temperature is 30 to 35℃. In the present application, the specific protease treatment can better remove organic impurities on the surface of the primary silver powder, and the conditions are mild, which is conducive to realizing uniform etching while reducing impurity interference, providing a better basis for subsequent acid etching treatment, and helping to further improve the shape, surface and dispersing effect of the silver powder.

[0007] Further preferably, the first etching solution is a solution of malic acid and / or glutamic acid, and is preferably a malic acid solution. The acidity of malic acid is moderate, which further reduces over-etching.

[0008] Preferably, the mass fraction of the first etching solution is 1% to 3%, and is preferably 1.5% to 2.5%, and the etching temperature is 30 to 50℃, and is preferably 35 to 45℃.

[0009] Preferably, the mass ratio of the silver powder to the first etching solution is 1:10 to 15, and is preferably 1:10 to 12. In the present application, the optimized first etching solution can better treat silver powder particles and surfaces with little damage, optimize particle size distribution and improve morphology, and is conducive to subsequent treatment. In the preferred concentration and temperature range, the first etching rate is moderate and easy to control, which can more effectively etch without excessively dissolving the target nano particles, better realize the preliminary treatment of the silver powder and be conducive to subsequent treatment.

[0010] Further preferably, the second etching solution is a solution of ascorbic acid and / or citric acid, preferably a solution of ascorbic acid. Ascorbic acid has moderate reducing property, and further optimizes the etching speed.

[0011] Preferably, the mass fraction of the second etching solution is 0.6% to 1%, preferably 0.7% to 0.9%, and the etching temperature is 30 to 35℃, preferably 32 to 34℃.

[0012] Preferably, the mass ratio of the silver powder to the second etching solution is 1:5 to 15, preferably 1:7 to 10. In the present application, the second etching solution can etch more finely, and under optimized conditions, can repair some defects in the etching process, thereby improving the sphericity of the particles. Meanwhile, under certain concentration and temperature, the particle treatment effect and size are further homogenized, and the damage to the nanoparticles is avoided.

[0013] Further preferably, the third etching solution is a solution of phytic acid and / or caffeic acid, preferably a solution of phytic acid. The phytic acid solution has mild acidity and slow etching speed, and has a phosphate group, which can reduce particle agglomeration while etching the silver powder.

[0014] Preferably, the mass fraction of the third etching solution is 0.2% to 0.6%, and the etching temperature is 20 to 25℃, preferably 23 to 25℃.

[0015] Preferably, the mass ratio of the silver powder to the third etching solution is 1:5 to 10, preferably 1:5 to 7. In the present application, the third etching solution further optimizes the fine etching, and protects the surface of the silver nanoparticles, which is beneficial to preventing agglomeration in the subsequent process and improving the dispersion stability of the product. Under optimized concentration and temperature treatment, the comprehensive performance of the silver nanoparticles is improved.

[0016] As a preferred embodiment, the method further comprises: using a plasma to bombard a high-purity silver target, ultrasonically dispersing the obtained silver powder in anhydrous ethanol, centrifuging to obtain wet silver powder, and performing supercritical CO2 drying on the wet silver powder to obtain primary silver powder. The primary silver powder prepared by the method of the present application can provide higher-quality raw materials for subsequent enzyme treatment and multi-step etching, which is beneficial to obtaining high-performance silver nanoparticles.

[0017] Further preferably, the argon plasma bombardment treatment is performed at a plasma power of 5 to 20kw, preferably 8 to 12kw, and a gas flow rate of 10 to 40mL / min, preferably 20 to 30mL / min. The supercritical CO2 drying is performed at a pressure of 8 to 10MPa, preferably 9 to 10MPa, and a temperature of 40 to 50℃, preferably 40 to 45℃. The effect is better under the preferred conditions.

[0018] Preferably, after the plasma bombardment treatment, nitrogen gas is filled into the chamber to normal pressure, and a scraper is used to scrape the silver powder on the cooling baffle into a sealed transfer container. In the embodiment of the present application, the cooling baffle is a liquid nitrogen-cooled oxygen-free copper plate.

[0019] Further preferably, the drying is microwave drying; preferably, the temperature of the microwave drying is 60-70℃, preferably 60-65℃; and the time is 10-15min, preferably 10-12min. This avoids particle agglomeration during the drying process and maintains the high dispersibility of the powder.

[0020] As a preferred embodiment, the preparation method comprises the following steps: 1) A high-purity silver target is bombarded by argon plasma in a vacuum chamber, and the silver powder is ultrasonically dispersed in anhydrous ethanol, then centrifuged and dried by supercritical CO2.

[0021] 2) The primary silver powder obtained in step 1) is mixed with a protease solution and shaken, and the supernatant is removed by centrifugation.

[0022] 3) The silver powder obtained in step 2) is added with the first etching solution, ultrasonically vibrated, and the supernatant is removed by centrifugation.

[0023] 4) The silver powder obtained in step 3) is added with the second etching solution, mechanically stirred, and the supernatant is removed by centrifugation.

[0024] 5) The silver powder obtained in step 4) is added with the third etching solution, ultrasonically vibrated, and the supernatant is removed by centrifugation.

[0025] 6) The silver powder obtained in step 5) is microwave dried.

[0026] The present application uses a multi-step etching method to prepare nano silver powder, which has a simple process flow, high preparation efficiency, and no cyanide / strong acid in the etching process, and is green and environmentally friendly. The nano silver powder obtained by this method has high dispersibility, concentrated particle size distribution, and regular morphology, and can be widely used in the medical, sensor, integrated circuit, and automobile industries.

[0027] Further preferably, the preparation method comprises the following steps: 1) A 4-5N high-purity silver target is bombarded by argon plasma in a vacuum chamber for 30-60min, then high-purity nitrogen gas is filled into the chamber to normal pressure, and the silver powder is ultrasonically dispersed in anhydrous ethanol for 25-35min, then the wet silver powder is obtained by centrifugation, and then the wet silver powder is dried by supercritical CO2 for 1.5-2.5h.

[0028] 2) Powder pretreatment: The dried silver powder is mixed with a pretreatment solution, shaken at a temperature of 30-35℃ for 1.5-2.5h, and the supernatant is removed by centrifugation.

[0029] 3) Add the first etching solution to the silver powder after centrifugation in step 2), and ultrasonic vibration for 8-12 min. Remove the supernatant by centrifugation, and repeat 1-3 times.

[0030] 4) Add the second etching solution to the silver powder obtained in step 3), and mechanical stirring for 15-25 min. Remove the supernatant by centrifugation, and repeat 0-3 times.

[0031] 5) Add the third etching solution to the silver powder obtained in step 4), and ultrasonic vibration for 25-35 min. Remove the supernatant by centrifugation, and repeat 1-3 times.

[0032] 6) Microwave dry the silver powder obtained in step 5) to obtain the nano-silver powder.

[0033] Preferably, in steps 3)-5), the power of ultrasonic vibration is 50-300 w; the rotating speed of mechanical stirring is 400-2000 r / min; and the repeated steps are from adding the etching solution to removing the supernatant. In steps 3)-5), the rotating speed for removing the supernatant by centrifugation is 3500-10000 r / min.

[0034] In some embodiments of the present application, the preparation method of the nano-silver powder comprises the following steps: 1) In a vacuum chamber, argon plasma is used to bombard high-purity silver target material (5N) for 30-60 min. After the plasma is turned off, high-purity nitrogen is filled into the chamber to normal pressure. The silver powder on the cooling baffle is scraped into a sealed transfer container with a scraper, and the silver powder is dispersed by ultrasonic vibration in anhydrous ethanol for 30 min. The wet silver powder is placed in a supercritical CO2 drying oven for 2 h, slowly released to normal pressure, and loose powder without hard agglomeration is obtained.

[0035] 2) Powder pretreatment: mix the dried silver powder in step 1) with a pretreatment solution, and oscillate at a certain temperature for 2 h. Remove the supernatant by centrifugation.

[0036] 3) Add the first etching solution to the silver powder after centrifugation in step 2), and ultrasonic vibration for 10 min. Then remove the supernatant by centrifugation, and repeat 3 times to remove the supernatant.

[0037] 4) Add a certain volume of the second etching solution to the silver powder after the first etching in step 3), and perform mechanical stirring to ensure sufficient etching. After 20 min, remove the supernatant by centrifugation.

[0038] 5) Add a certain volume of the third etching solution to the silver powder in step 4), and ultrasonic vibration for 30 min. Then repeat 3 times to remove the supernatant by high-speed centrifugation, and obtain the etched nano-silver powder.

[0039] 6) Microwave dry the silver powder obtained in step 5) to obtain the nano-silver powder with high dispersibility and concentrated particle size distribution.

[0040] In a second aspect, the present application provides the nano-silver powder prepared by the method. The nano-silver powder has a regular powder shape, no obvious protrusions on the surface, high sphericity, good dispersibility and no significant agglomeration. Preferably, the powder shape is spherical, the surface has no obvious protrusions and the dispersibility is high.

[0041] The present application has at least the following beneficial effects: the high-purity nano-silver powder preparation method provided by the present application uses a multi-step etching method to prepare nano-silver powder, uses biological enzymes as a pretreatment liquid to assist in the three-step weak acid etching of silver powder, does not require reduction and has a simple process and high production efficiency. The etching liquid can be recycled, greatly reducing production costs. Compared with the traditional strong acid etching system using nitric acid, no nitrogen compounds / cyanide are produced, and it is green and environmentally friendly. The particles prepared by the present application have a smooth appearance and no obvious thorn-like protrusions, and the shape is spherical. At the same time, the powder has high dispersibility and no significant agglomeration. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0043] Figure 1 The scanning electron microscope picture of the silver powder provided for Example 1 of the present application.

[0044] Figure 2 The scanning electron microscope picture of the silver powder provided for Example 2 of the present application.

[0045] Figure 3 The scanning electron microscope picture of the silver powder provided for Example 3 of the present application.

[0046] Figure 4 The scanning electron microscope picture of the silver powder provided for Example 4 of the present application.

[0047] Figure 5 The scanning electron microscope picture of the silver powder provided for Example 5 of the present application.

[0048] Figure 6 The scanning electron microscope picture of the silver powder provided for Comparative Example 1 of the present application.

[0049] Figure 7 The scanning electron microscope picture of the silver powder provided for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts should fall within the scope of the present application.

[0051] The endpoints of the ranges and any values described in the present disclosure are not limited to the precise values stated. The ranges and values should be interpreted as approximately between the stated values. For ranges, the endpoints are included, and the ranges are inclusive of the individual points within the range. For example, a range from 1 to 10 should be interpreted to include not only the endpoints 1 and 10, but also individual points such as 3, 5, and 7, as well as ranges such as 3 to 5, 5 to 7, and 7 to 9.

[0052] Unless specific techniques or conditions are indicated in the embodiments of the present application, the techniques or conditions described in the literature in the art, or according to the product instructions, are used. The devices, instruments, reagents, etc. used are conventional products that can be purchased through regular channels. The experimental reagents and raw materials involved are commercially available, and the reagents are analytical grade products.

[0053] Embodiment 1 The present embodiment provides a high-purity nano-silver powder and a preparation method thereof, comprising the following steps: 1) The high-purity silver target material (5N) is bombarded by argon plasma in a vacuum chamber for 35 min, the plasma power is 10 kw, the gas flow rate is 30 mL / min, the cooling baffle is an oxygen-free copper plate cooled by liquid nitrogen, after the reaction is completed, the plasma is turned off, high-purity nitrogen is filled into the chamber to normal pressure, the silver powder on the cooling baffle is scraped into a sealed transfer container with a scraper, the silver powder is ultrasonically dispersed in anhydrous ethanol for 30 min, the wet silver powder is placed in a supercritical CO2 drying oven for 2 h, the pressure in the drying oven is 9 MPa, the temperature is 40°C, the supercritical CO2 drying oven is turned off after drying, and the pressure is slowly released to normal pressure. The obtained primary silver powder is a loose powder without hard agglomeration; 2) 10 g of the dried primary silver powder is weighed, 100 g of a solution of subtilisin with a mass fraction of 1% and a pH of 7.0 is measured, and added to the primary silver powder. The mixture is treated by oscillation at 30°C for 2 h, and then ultrasonic vibration is performed at a power of 100 w. The silver powder is then centrifuged to remove the supernatant at a speed of 8000 r / min; 3) 100 g of a malic acid solution with a mass fraction of 1.5% is added to the centrifuged silver powder, and ultrasonic vibration is performed at a power of 100 w in a 40°C water bath for 10 min. The supernatant is then removed by centrifugation, and the above steps are repeated 3 times. The supernatant is removed by centrifugation at a speed of 6000 r / min; 4) 40 g of ascorbic acid solution with a mass fraction of 0.8% is added to the silver powder after the first step of etching, and mechanical stirring is performed at a speed of 800 r / min, and the etching temperature is 35°C; after 20 min, the supernatant is removed by centrifugation at a speed of 6000 r / min; 5) 50 g of phytic acid solution with a mass fraction of 0.3% is added to the silver powder in step 4), ultrasonic oscillation is performed for 30 min, the ultrasonic vibration power is 120 w, the etching temperature is 23°C, and the process is repeated 3 times; the supernatant is removed to obtain the etched nano-silver powder, and the supernatant is removed by centrifugation at a speed of 6000 r / min.

[0054] 6) The obtained silver powder is dried at 60°C for 10 min by microwave drying to obtain dried nano-silver powder.

[0055] The silver powder prepared in this example is subjected to property determination, and a certain mass of silver powder is analyzed by scanning electron microscopy to observe the powder morphology and dispersion. As shown in FIG. 1, it can be seen from the scanning electron microscopy results that the powder shape is regular and spherical, the surface has no obvious protrusions, and the dispersion degree is high. Figure 1

[0056] Example 2 This example provides a high-purity nano-silver powder and a preparation method thereof, which comprises the following steps: 1) A high-purity silver target (5N) is bombarded by argon plasma in a vacuum chamber for 45 min, the plasma power is 12 kw, the gas flow rate is 25 mL / min, and the cooling baffle is an oxygen-free copper plate cooled by liquid nitrogen; after the reaction is completed, high-purity nitrogen gas is filled into the chamber to normal pressure, a scraper is used to scrape the silver powder on the cooling baffle into a sealed transfer container, and the silver powder is dispersed by ultrasonic ethanol for 30 min; the wet silver powder is obtained by centrifugation, and then the wet silver powder is placed in a supercritical CO2 drying oven for 2 h; the pressure in the drying oven is 10 MPa, and the temperature is 40°C; after drying, the supercritical CO2 drying oven is closed, and the pressure is slowly released to normal pressure; the obtained primary silver powder is a loose powder without hard agglomeration; 2) 5 g of dried primary silver powder is weighed, 30 g of papain solution with a mass fraction of 1.5% and a pH of 6.5 is measured, and then added to the primary silver powder; the mixture is treated by oscillation at 30°C for 2 h, and then the silver powder is obtained by centrifugation at a speed of 7500 r / min; 3) 60 g of glutamic acid solution with a mass fraction of 2% is added to the centrifuged silver powder, and ultrasonic vibration is performed for 10 min in a 45°C water bath, and then the supernatant is removed by centrifugation at a speed of 7000 r / min; the process is repeated 3 times to remove the supernatant. ​4) 70g of 0.7% citric acid solution was added to the silver powder after the first etching, and mechanical stirring was carried out at a speed of 800r / min, and the etching temperature was 32℃. After 20min, the supernatant was removed by centrifugation at a speed of 7000r / min; 5) 30g of 0.4% coffee acid solution was added to the silver powder in step 4), and ultrasonic oscillation was carried out for 30min, and the etching temperature was 25℃. The above process was repeated for 3 times, and the supernatant was removed by centrifugation at a speed of 7000r / min, to obtain the etched nano-silver powder; 6) The obtained silver powder was dried at 65℃ for 10min by microwave drying, to obtain the dried nano-silver powder.

[0057] The silver powder prepared in this example was subjected to property determination, and a certain amount of silver powder was analyzed by scanning electron microscopy to observe the powder morphology and dispersion. As shown in Figure 2 the scanning electron microscopy results showed that the powder shape was relatively regular, the surface had no obvious protrusions, the sphericity was high, and the dispersion was good without significant agglomeration.

[0058] Example 3 This example provides a high-purity nano-silver powder and a preparation method thereof. The steps of this example are basically the same as those of Example 1, and the difference lies in that the pretreatment solution of step 2) is a papain solution. As shown in Figure 2 the scanning electron microscopy results showed that the powder shape was relatively regular, the surface had no obvious protrusions, the sphericity was high, and the dispersion was good without significant agglomeration.

[0059] Example 4 This example provides a high-purity nano-silver powder and a preparation method thereof. The steps of this example are basically the same as those of Example 1, and the difference lies in that the pretreatment solution of step 2) is a corn protease solution. As shown in Figure 4 the scanning electron microscopy results showed that the powder shape was relatively regular, the surface had no obvious protrusions, and the sphericity was high.

[0060] Example 5 This example provides a high-purity nano-silver powder and a preparation method thereof. The steps of this example are basically the same as those of Example 1, and the difference lies in that the first etching solution of step 3) is 2-ethyl-butanoic acid, the second etching solution of step 4) is oxalic acid, and the etching solution of step 5) is lactic acid. As shown in Figure 5 the scanning electron microscopy results showed that the powder shape was relatively regular, the surface had no obvious protrusions, and the sphericity was high.

[0061] Comparative Example 1 This comparative example provides a preparation method of nano-silver powder, and the steps are basically the same as those of Example 1, and the difference lies in that there is no silver powder pretreatment step of step 2). As shown in Figure 6As shown in the scanning electron microscope results, the powder has poor dispersibility and is aggregated.

[0062] Comparative Example 2 The present comparative example provides a method for preparing nano silver powder, and the steps are basically the same as those of Example 1, except that the three-step etching is not used, and there is no step 5) third etching link. Figure 7 As shown in the scanning electron microscope results, the powder has irregular shape, obvious surface protrusions, poor dispersibility and is aggregated.

[0063] The present embodiment utilizes multi-step etching to prepare nano silver powder, and the process flow is simple, the preparation efficiency is high, the etching process is free of cyanide / strong acid, and is green and environmentally friendly. The nano silver powder obtained based on this method has high dispersibility, concentrated particle size distribution and regular morphology, and can be widely used in the medical, sensor, integrated circuit and automobile industries.

[0064] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing nano silver powder, characterized by, The preparation method comprises the following steps: mixing the primary silver powder with a protease solution, and then performing solid-liquid separation; performing acid etching treatment on the separated silver powder with a first etching solution, a second etching solution and a third etching solution in sequence, and then drying; the first etching solution is selected from a solution of one or more of malic acid, 2-ethyl-butanoic acid and glutamic acid; the second etching solution is selected from a solution of one or more of ascorbic acid, citric acid and oxalic acid; and the third etching solution is selected from a solution of one or more of phytic acid, tartaric acid, lactic acid and coffee acid.

2. The production method according to claim 1, characterized by, The protease solution is selected from a solution of one or more of subtilisin, papain, bromelain and corn protease; the mass fraction of the protease solution is 0.5% to 6%; the pH of the protease solution is 6.0 to 7.5; the mass ratio of the silver powder to the protease solution is 1:5 to 20, and the treatment temperature is 30 to 35℃.

3. The production method according to claim 1 or 2, characterized by, The first etching solution is a solution of malic acid and / or glutamic acid; and / or, the mass fraction of the first etching solution is 1% to 3%, and the etching temperature is 30 to 50℃; and / or, the mass ratio of the silver powder to the first etching solution is 1:10 to 15.

4. The production method according to any one of claims 1 to 3, characterized by, The second etching solution is a solution of ascorbic acid and / or citric acid; and / or, the mass fraction of the second etching solution is 0.6% to 1%, and the etching temperature is 30 to 35℃; and / or, the mass ratio of the silver powder to the second etching solution is 1:5 to 15.

5. The production method according to any one of claims 1 to 4, characterized by, The third etching solution is a solution of phytic acid and / or coffee acid; and / or, the mass fraction of the third etching solution is 0.2% to 0.6%, and the etching temperature is 20 to 25℃; and / or, the mass ratio of the silver powder to the third etching solution is 1:5 to 10.

6. The method of any one of claims 1-5, wherein, The preparation method further comprises the following steps: performing argon plasma bombardment treatment on high-purity silver target material, and then performing ultrasonic dispersion of the obtained silver powder with anhydrous ethanol, centrifugation to obtain wet silver powder, and supercritical CO2 drying of the wet silver powder to obtain the primary silver powder.

7. The production method according to claim 6, wherein The argon plasma bombardment treatment is performed at a plasma power of 5 to 20 kw and a gas flow rate of 10 to 40 mL / min; the supercritical CO2 drying is performed at a pressure of 8 to 10 MPa and a temperature of 40 to 50℃.

8. The method of any one of claims 1-7, wherein, The drying is microwave drying, and the microwave drying is performed at a temperature of 60 to 70℃ and for a time of 10 to 15 min.

9. The method of any one of claims 1-8, wherein, The preparation method comprises the following steps: 1) performing argon plasma bombardment treatment on high-purity silver target material, performing ultrasonic dispersion of the silver powder with anhydrous ethanol, and then performing supercritical CO2 drying after centrifugation; 2) mixing the primary silver powder obtained in step 1) with a protease solution, and then performing oscillation and centrifugation to remove the supernatant; 3) adding the first etching solution to the silver powder obtained in step 2), performing ultrasonic vibration, and then performing centrifugation to remove the supernatant; 4) adding the second etching solution to the silver powder obtained in step 3), performing mechanical stirring, and then performing centrifugation to remove the supernatant; 5) adding the third etching solution to the silver powder obtained in step 4), performing ultrasonic vibration, and then performing centrifugation to remove the supernatant; 6) performing microwave drying on the silver powder obtained in step 5).

10. The nano-silver powder obtained by the preparation method in any one of claims 1 to 9.

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