Preparation method of nano silver solution

Abstract

The invention provides a method for preparing a nano silver solution, and belongs to the technical field of nano silver preparation. The method uses silver nitrate as a silver source, water as a reaction solvent, polyvinyl pyrrolidone as a first dispersant, and gum arabic as a second dispersant. After the silver source is preferentially encapsulated by the first dispersant, a mixed solution of a reducing agent and a second dispersant is poured at one time to prepare a nano silver solution. The invention adopts the synergistic effect of the first dispersant and the second dispersant to make the prepared nano silver particle size distribution more uniform, and can still remain stable after being placed for 30 days; by adjusting the pH value of the solution to be alkaline, it is ensured that the H ‑ The concentration of the reducing agent increases the reducing ability. This method has a rapid reaction, simple operation, no requirements for experimental conditions and equipment, etc., can be stably expanded to 25L, and the particle size does not change after long-term storage. It has highly stable dispersibility and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of nano materials, and in particular to a method for preparing a nano silver solution. Background Art

[0002] The physical and chemical properties of nanosilver change with the increase of nano size. The particle size of nanosilver is distributed between 1 and 100 nm, which is between molecules and solids. Due to its huge specific surface area, strong surface effect and small size effect, its surface activity is significantly enhanced. Due to its small size, it has good penetration and antibacterial ability and is widely used in the medical field.

[0003] At present, the preparation method of nanosilver is mainly chemical reduction method. Invention patent CN 102218541 A discloses a new large-scale preparation method of water-soluble nanosilver. This method requires dissolving silver salt and protective agent in water at 30-70°C with stirring, adjusting the pH value, and when the solution system is clear and transparent for 5-20 minutes, adding the reducing agent into the reaction system and stirring. This method requires controlling the temperature and adjusting the pH value, and the operation is complicated.

[0004] Invention patent CN 114160785 B discloses a method for preparing a nanosilver solution under controllable mild conditions. The patent uses ultrapure water as a solvent, silver nitrate as a silver source, sodium citrate as a protective agent, polyvinyl pyrrolidone as a dispersant, and a reducing agent of a certain concentration to prepare a nanosilver solution. The patent requires the additional addition of a protective agent to generate a stable nanosilver solution.

[0005] In view of this, it is necessary to design a method for preparing a nano silver solution to solve the above problems. Summary of the invention

[0006] In view of the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a nano silver solution. The method uses a silver nitrate solution as a silver source, polyvinyl pyrrolidone as a first dispersant, and gum arabic as a second dispersant; the first dispersant is used to preferentially encapsulate the silver source, the silver source solution and the first dispersant solution are mixed and stabilized at room temperature, and then the mixed solution of the reducing agent and the second dispersant is poured at one time to prepare a nano silver solution. The present invention uses two different dispersants, the synergistic effect of the first dispersant and the second dispersant, so that the prepared nano silver particle size distribution is more uniform, and it can remain stable after being placed for one month.

[0007] To achieve the above object, the present invention provides a method for preparing a nano silver solution, comprising mixing a silver source solution and a first dispersant solution at room temperature to stabilize the mixture, adjusting the pH value of the solution, adding a mixed solution of a reducing agent and a second dispersant at one time, and then stirring for 5-30 minutes; the method comprises the following steps:

[0008] S1, preparing 1.6-1.8 g / L silver nitrate solution as a silver source solution;

[0009] S2, preparing 0.4-0.5 g / L polyvinyl pyrrolidone solution as the first dispersant;

[0010] S3, preparing 0.4-0.5 g / L gum arabic solution as a second dispersant; preparing a reducing agent solution;

[0011] S4, adding the polyvinyl pyrrolidone solution prepared in step S2 to the silver nitrate solution prepared in step S1, stirring evenly to obtain solution A; adjusting the pH value of solution A to 7-8; mixing the gum arabic solution prepared in step S3 with the reducing agent solution, pouring the mixture into solution A at once, stirring, to obtain a nanosilver solution, wherein the particle size of the nanosilver in the nanosilver solution is 8-31 nm.

[0012] Furthermore, in step S4, the mass ratio of the polyvinyl pyrrolidone to the silver nitrate is 1:(7-8).

[0013] Furthermore, in step S4, the mass ratio of the gum arabic to the silver nitrate is 1:(7-8).

[0014] Furthermore, in step S4, the mass ratio of the reducing agent to the silver nitrate is 1:(5-6).

[0015] Furthermore, the reducing agent is one of sodium borohydride and ascorbic acid.

[0016] Furthermore, in step S4, the pH value is adjusted by using ammonia water with a volume fraction of 25-28%.

[0017] Furthermore, when a 2L reaction is carried out, the mass ratio of the dispersant used to the silver nitrate is 1:(3-4), and the mass of the dispersant is the total mass of the first dispersant and the second dispersant.

[0018] Furthermore, when the reaction is carried out for 25 L, the mass ratio of the dispersant to the silver nitrate is 1:(0.5-1), and the mass of the dispersant is the total mass of the first dispersant and the second dispersant.

[0019] Furthermore, the rotation speed of the magnetic stirrer used in the 2L reaction is 200-400 rpm; the rotation speed of the stirring paddle of the reactor used in the 25L reaction is 10-30 Hz.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention provides a method for preparing a nano silver solution, wherein a silver nitrate solution is used as a silver source, polyvinyl pyrrolidone is used as a first dispersant, and gum arabic is used as a second dispersant; the first dispersant is used to preferentially encapsulate the silver source, the silver source solution and the first dispersant solution are mixed and stabilized at room temperature, and then, a mixed solution of a reducing agent and a second dispersant is poured at one time to prepare a nano silver solution. Polyvinyl pyrrolidone is used as the first dispersant because it has a high molecular weight and has a better coating effect on nano silver, making the size more uniform; gum arabic is selected as the second dispersant because it has hydroxyl and carboxyl groups in its chain, which can increase the hydrophilicity of nano silver while dispersing, and the synergistic effect of the two allows the nano silver to be better dispersed in water, and will not agglomerate even if placed for a long time; the pH value of the solution is adjusted to 7-8 to ensure the concentration of H- in the solution, increase the reducing ability of the reducing agent, and prepare a more uniform nano silver.

[0022] 2. The method of the present invention has rapid reaction, simple operation, no requirements on experimental conditions, equipment, etc., can be stably expanded to 25L, and the particle size does not change after long-term storage. It has highly stable dispersibility and is suitable for large-scale industrial production. The present invention requires fewer types of agents, small dosages, is green and pollution-free, and meets the requirements of green production.

[0023] 3. The present invention uses two different dispersants, polyvinyl pyrrolidone as the first dispersant and gum arabic as the second dispersant. First, the silver source is pre-coated with polyvinyl pyrrolidone solution to improve the dispersibility of the nano silver solution; then, a mixed solution of the reducing agent and the second dispersant is added by pouring at one time, and the reaction is instantaneous, so that the nano silver grows synchronously, the particle size is smaller, and the size is more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a particle size distribution diagram of the nanosilver solution prepared in Example 1 of the present invention.

[0025] Figure 2 This is a physical picture of the nanosilver solution prepared in Example 1 of the present invention after being placed for 30 days.

[0026] Figure 3 This is a SEM image of the silver powder synthesized from the nanosilver solution prepared in Example 1 of the present invention.

[0027] Figure 4 This is a SEM image of the nanosilver solution prepared in Comparative Example 1 of the present invention.

[0028] Figure 5 This is a physical picture of the nanosilver solution prepared in Comparative Example 1 of the present invention.

[0029] Figure 6 This is the particle size distribution diagram of the nanosilver solution prepared in Comparative Example 2 of the present invention.

[0030] Figure 7 This is a comparison chart of the particle size distribution of the nanosilver solution prepared in Comparative Example 3 of the present invention and after being left for one day.

[0031] Figure 8 This is the particle size distribution diagram of the nanosilver solution prepared in Comparative Example 5 of the present invention.

[0032] Fig. 9 This is the particle size distribution diagram of the nanosilver solution prepared in Comparative Example 6 of the present invention.

[0033] Fig.10 This is a SEM image of the nanosilver solution prepared in Example 2 of the present invention.

[0034] Fig.11 This is the particle size distribution diagram of the nanosilver solution prepared in Example 2 of the present invention.

[0035] Fig.12 This is a comparison chart of the particle size distribution of the nanosilver solution prepared in Example 3 of the present invention and after being placed for 30 days.

[0036] Fig.13 This is a SEM image of the silver powder synthesized from the nanosilver solution prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0039] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0040] The invention provides a method for preparing a nano silver solution, comprising the steps of mixing a silver source solution and a first dispersant solution at room temperature to stabilize the mixture, adjusting the pH value of the solution, pouring a mixed solution of a reducing agent and a second dispersant into the mixture at one time, and stirring for 5-30 minutes. The method comprises the following steps:

[0041] S1, preparing 1.6-1.8 g / L silver nitrate solution as a silver source solution;

[0042] S2, preparing 0.4-0.5 g / L polyvinyl pyrrolidone solution as the first dispersant;

[0043] S3, preparing 0.4-0.5 g / L gum arabic solution as a second dispersant; preparing a reducing agent solution;

[0044] S4, adding the polyvinyl pyrrolidone solution prepared in step S2 to the silver nitrate solution prepared in step S1, stirring evenly to obtain solution A; adjusting the pH value of solution A to 7-8; mixing the gum arabic solution prepared in step S3 with the reducing agent solution, pouring the mixture into the solution at once, stirring, to obtain a nanosilver solution, wherein the particle size of the nanosilver in the nanosilver solution is 8-31 nm.

[0045] In step S4, the mass ratio of the polyvinyl pyrrolidone to the silver nitrate is 1:(7-8).

[0046] The mass ratio of the gum arabic to the silver nitrate is 1:(7-8).

[0047] The mass ratio of the reducing agent to the silver nitrate is 1:(5-6).

[0048] The reducing agent is one of sodium borohydride, ascorbic acid and sodium citrate.

[0049] The invention adopts sodium borohydride to reduce silver nitrate to prepare a nano silver solution, adopts polyvinyl pyrrolidone as a first dispersant to preferentially encapsulate a silver source, so that nano silver particles formed in an initial stage of a reaction can be more dispersed, and then a second dispersant, gum arabic, is added to ensure the dispersibility of the subsequent nano silver in a growth process and the affinity in an aqueous solution, so that the prepared nano silver solution can remain stable after being placed for a long time; the pH value of the solution is adjusted to be alkaline because NaBH4 is reduced with H- ions, and under acidic conditions, H + It will consume H-, sodium borohydride, and reduce the reducing ability of the reaction; choosing the one-time pouring method for instantaneous reaction can make nanosilver grow synchronously, with smaller particle size and more uniform size.

[0050] The preparation method of the nano silver solution provided by the present invention is described below in conjunction with specific examples.

[0051] Example 1

[0052] Example 1 provides a method for preparing a nano silver solution, wherein 99.9% silver nitrate is used as a silver source, polyvinyl pyrrolidone is used as a first dispersant, sodium borohydride is used as a reducing agent, a second dispersant is gum arabic, and a solvent is water. 200 ml of a 1.7 g / L silver nitrate solution is added to 1.4 L of pure water, and then 100 ml of a 0.47 g / L polyvinyl pyrrolidone solution is quickly added, and stirred evenly to obtain a solution A. The speed of the magnetic stirrer is 380 rpm, and the pH value of the solution A is adjusted to 7.5 with ammonia water. A mixture of 250 ml of a sodium borohydride solution with a concentration of 0.23 g / L and 100 ml of a gum arabic solution with a concentration of 0.47 g / L is added at one time, and after stirring for 10 minutes, a particle size D is obtained. 50 At 12.9nm, the nanosilver solution with narrow size distribution has the following results: Figure 1 As shown, the volume fraction of ammonia water is 25%-28%.

[0053] The mass ratio of polyvinyl pyrrolidone to silver nitrate is 1:7.23.

[0054] The mass ratio of gum arabic to silver nitrate is 1:7.23.

[0055] Then, the mass ratio of the total mass of the two dispersants to the mass of silver nitrate is 1:3.615.

[0056] The mass ratio of sodium borohydride to silver nitrate is 1:5.91.

[0057] Polyvinyl pyrrolidone is used as the first dispersant because of its high molecular weight, which has a better coating effect on nanosilver and makes the size more uniform; gum arabic is selected as the second dispersant because it has hydroxyl and carboxyl groups in its chain, which can increase the hydrophilicity of nanosilver while dispersing, so that nanosilver can be better dispersed in water and will not agglomerate even if left for a long time.

[0058] like Figure 2 The figure shows the nanosilver solution prepared in Example 1 after being placed for 30 days. It can be seen that after being placed for 30 days, the solution is still clear and transparent, and the particle size does not change and remains stable.

[0059] Preparation of silver powder: 150g of silver nitrate was dissolved in 400ml of water to prepare solution A, 84g of ascorbic acid was dissolved in 375ml of water to prepare solution B, and 12g of polyvinyl pyrrolidone was dissolved in 1L of water to prepare base solution C. After the base solutions were evenly mixed, the speed of the magnetic stirrer was 380rpm, and 6g of ascorbic acid was added. After continuing to dissolve, 30ml of the nanosilver solution prepared in Example 1 was added, and then solutions A and B were added simultaneously at a drip rate of 60ml / min. After the reaction was completed, the silver powder was washed and dried.

[0060] After drying, the silver powder synthesized from the nanosilver solution is obtained, and its SEM image is as follows: Figure 3 shown.

[0061] The test shows that the silver powder prepared by this nanosilver solution has a size distribution of about 700-800nm, good dispersibility, narrow particle size distribution, and a tap density of 4.28g / cm 3 The silver powder obtained in this embodiment was mixed with flaky silver powder and organic components to make a 4cm*1cm*0.4cm conductive silver strip, and the resistance test was performed. The test result was 1.36mΩ.

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that the first dispersant polyvinyl pyrrolidone is not added to preferentially encapsulate the silver source, as follows:

[0064] 99.9% silver nitrate was used as the silver source, sodium borohydride was used as the reducing agent, gum arabic was used as the dispersant, and water was used as the solvent. 200 ml of 1.7 g / L silver nitrate solution was added to 1 L of pure water and stirred evenly with a magnetic stirrer at a speed of 380 rpm. Then, the pH value of the solution was adjusted to 7.5 with ammonia water. 250 ml of 0.23 g / L sodium borohydride solution and 100 ml of 0.47 g / L gum arabic solution were poured into the mixture at once. After stirring for 10 minutes, a particle size of D 50 Nanosilver solution at 35.4nm.

[0065] Experiments show that if the silver source is not first encapsulated with polyvinyl pyrrolidone, but the dispersant is gradually added during the reaction formation process, the generated nanosilver will grow together, resulting in agglomeration, such as Figure 4 shown.

[0066] like Figure 5 The figure shows a physical picture of the nanosilver solution prepared in Comparative Example 1. It can be seen that the silver source is not preferentially encapsulated by a dispersant, making the prepared nanosilver solution turbid and having obvious agglomeration.

[0067] Comparative Example 2

[0068] Comparative Example 2 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that no second dispersant gum arabic is added to coat the subsequently generated nanosilver, as follows:

[0069] With 99.9% silver nitrate as the silver source, polyvinyl pyrrolidone as the dispersant, sodium borohydride as the reducing agent, and water as the solvent, 200 ml of 1.7 g / L silver nitrate solution is added to 1 L of pure water, and then 100 ml of 0.47 g / L polyvinyl pyrrolidone solution is quickly added, and stirred evenly with a magnetic stirrer at a speed of 380 rpm. Then, the pH value of the solution is adjusted to 7.5, and 250 ml of 0.23 g / L sodium borohydride solution is poured in at one time. After stirring for 10 minutes, a nano silver solution with a particle size of 20.7 nm is obtained.

[0070] Experiments show that after the silver source is preferentially coated with polyvinyl pyrrolidone, the silver nitrate is simultaneously reduced, but in the subsequent growth process of nanosilver, there is a lack of further coating with a dispersant, resulting in uneven size of the nanosilver. Figure 6 shown.

[0071] Comparative Example 3

[0072] Comparative Example 3 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that the first dispersant and the second dispersant are the same, both of which are polyvinyl pyrrolidone, as follows:

[0073] 99.9% silver nitrate is used as a silver source, polyvinyl pyrrolidone is used as a first dispersant, sodium borohydride is used as a reducing agent, polyvinyl pyrrolidone is still used as a second dispersant, and water is used as a solvent. 200 ml of a 1.7 g / L silver nitrate solution is added to 1 L of pure water, and 100 ml of a 0.47 g / L polyvinyl pyrrolidone solution is quickly added. After stirring evenly, the mixture is stirred evenly with a magnetic stirrer at a speed of 380 rpm. Then, the pH value of the solution is adjusted to 7.5, and a mixed solution of 250 ml of a sodium borohydride solution with a concentration of 0.23 g / L and 100 ml of a polyvinyl pyrrolidone solution with a concentration of 0.47 g / L is poured at one time. After stirring for 10 minutes, a nano silver solution with a particle size of 5.69 nm is obtained.

[0074] Experiments show that due to the high molecular weight and long chain length of polyvinyl pyrrolidone, the coating effect is better, the prepared nanosilver particles are smaller in size and have a narrower size distribution.

[0075] However, as shown in Table 1 and Figure 7 As shown, after the nanosilver solution prepared in Comparative Example 3 was placed for 1 day, D 10 From 3.95 to 17.5, D 50 From 5.69 to 26.6, D 90 The change from 9.13 to 64.4 indicates that the nanosilver solution is unstable and will aggregate together to form agglomerates, making it difficult to remain stable in aqueous solution.

[0076] Comparative Example 4

[0077] Comparative Example 4 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that the first dispersant and the second dispersant are the same, both are gum arabic, as follows:

[0078] 99.9% silver nitrate is used as the silver source, gum arabic is used as the first dispersant, sodium borohydride is used as the reducing agent, the second dispersant is still gum arabic, and the solvent is water. 200 ml of 1.7 g / L silver nitrate solution is added to 1 L of pure water, and 100 ml of 0.47 g / L polyvinyl pyrrolidone solution is quickly added. After stirring evenly, it is stirred evenly with a magnetic stirrer at a speed of 380 rpm. Then, the pH value of the solution is adjusted to 7.5, and a mixture of 250 ml of 0.23 g / L sodium borohydride solution and 100 ml of 0.47 g / L gum arabic solution is poured at one time. After stirring for 10 minutes, a nanosilver solution with a particle size of 31.2 nm is obtained.

[0079] It can be seen that it is difficult to control the entire growth process of nanosilver with a single gum arabic, resulting in the generated nanosilver being too large in size and unevenly distributed.

[0080] In summary, if polyvinyl pyrrolidone is not preferentially used to coat the surface of silver nitrate before the reaction, if coating is performed again during the subsequent reaction process, the nanosilver will grow together and lead to agglomeration.

[0081] Comparative Example 5

[0082] Comparative Example 5 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that the pH value of solution A is not adjusted, and the pH value of solution A is 5-6; the details are as follows:

[0083] 99.9% silver nitrate is used as the silver source, polyvinyl pyrrolidone is used as the first dispersant, sodium borohydride is used as the reducing agent, gum arabic is used as the second dispersant, and water is used as the solvent. 200 ml of 1.7 g / L silver nitrate solution is added to 1 L of pure water, and 100 ml of 0.47 g / L polyvinyl pyrrolidone solution is quickly added. The mixture is stirred with a magnetic stirrer at a speed of 380 rpm. After stirring evenly, 250 ml of 0.23 g / L sodium borohydride solution and 100 ml of 0.47 g / L gum arabic solution are poured into the mixture at one time. After stirring for 10 minutes, a nano silver solution with a particle size of 33.9 nm is obtained.

[0084] The experimental results show that: without adjusting the pH value, the reducing ability of sodium borohydride is not the strongest state, resulting in weak reducing ability, slow reaction speed, large size and uneven distribution, such as Figure 8 shown.

[0085] Comparative Example 6

[0086] Comparative Example 6 provides a method for preparing a nanosilver solution, which is mainly different from Example 1 in that the mixed solution of the reducing agent and the second dispersant is added dropwise at a drop rate of 25 ml / min; specifically as follows:

[0087] 99.9% silver nitrate is used as the silver source, gum arabic is used as the first dispersant, sodium borohydride is used as the reducing agent, the second dispersant is still gum arabic, and the solvent is water. 200 ml of 1.7 g / L silver nitrate solution is added to 1 L of pure water, and 100 ml of 0.47 g / L polyvinyl pyrrolidone solution is quickly added. The mixture is stirred with a magnetic stirrer at a speed of 380 rpm. After stirring evenly, the pH value of the solution is adjusted to 7.5. A mixed solution of 250 ml of 0.23 g / L sodium borohydride solution and 100 ml of 0.47 g / L gum arabic solution is dripped at a dripping rate of 25 ml / min. After stirring for 10 minutes, a nanosilver solution with a particle size of 72.7 nm is obtained.

[0088] The experimental results show that if the addition method is slow dripping instead of pouring all at once, the reaction rate is slow, resulting in larger nanosilver size and uneven distribution, such as Fig. 9 shown.

[0089] Example 2

[0090] Example 2 provides a method for preparing a nanosilver solution, which differs from Example 1 mainly in that the reducing agent sodium borohydride is replaced with ascorbic acid. The details are as follows:

[0091] 99.9% silver nitrate was used as the silver source, polyvinyl pyrrolidone was used as the first dispersant, ascorbic acid was used as the reducing agent, gum arabic was used as the second dispersant, and water was used as the solvent. 200 ml of 1.7 g / L silver nitrate solution was added to 1 L of pure water, and 100 ml of 0.47 g / L polyvinyl pyrrolidone solution was quickly added. The mixture was stirred with a magnetic stirrer at a speed of 380 rpm. After stirring evenly, the pH value of the solution was adjusted to 7.5. A mixture of 250 ml of 0.704 g / L ascorbic acid solution and 100 ml of 0.47 g / L gum arabic solution was poured in one go, and after stirring for 10 minutes, a particle size D was obtained. 50 In the 312nm nanosilver solution, the results are as follows Fig.10 and Fig.11 shown.

[0092] Example 3: (25L expansion reaction)

[0093] 99.9% silver nitrate was used as the silver source, polyvinyl pyrrolidone was used as the first dispersant, sodium borohydride was used as the reducing agent, gum arabic was used as the second dispersant, and water was used as the solvent. 2L of 1.7g / L silver nitrate solution was added to 14L of pure water, and 4L of 0.47g / L polyvinyl pyrrolidone solution was quickly added. The speed of the stirring paddle of the reactor was 25Hz. After stirring evenly, the pH value of the solution was adjusted to 7.5 with ammonia water, and a mixture of 2.5L of 0.23g / L sodium borohydride solution and 4L of 0.47g / L gum arabic solution was poured in one go. After stirring for 30min, a particle size D 50 In 12.6nm nanosilver solution.

[0094] The mass ratio of the total mass of the two dispersants to the mass of silver nitrate is 1:0.9.

[0095] The mass ratio of sodium borohydride to silver nitrate is 1:5.91.

[0096] After the obtained nanosilver solution was placed for 30 days, the results were as follows: Fig.12 As shown in Table 1. It can be seen that the stability of the nano silver solution is very high.

[0097] See also Fig.13 As shown, it is a SEM image of the silver powder prepared in Example 3. The size distribution is between 700-800nm. It can be seen that the preparation method of the nanosilver solution of the present invention was successfully expanded to 25L, and the prepared nanosilver solution remained clear and transparent after being placed for 30 days. The size distribution of the silver powder prepared by the nanosilver solution is between 700-800nm, with good dispersibility, narrow particle size distribution, and a tap density of 4.21g / cm 3 It can be seen that the preparation method has stable process and is suitable for industrial production.

[0098] The particle size distribution test results of the nanosilver solutions prepared in Examples 1-3 and Comparative Examples 1-6 are shown in Table 1:

[0099] Table 1

[0100]

[0101] In summary, the preparation method of the nano silver solution provided by the present invention uses silver nitrate solution as the silver source, polyvinyl pyrrolidone as the first dispersant, and gum arabic as the second dispersant; the first dispersant is used to preferentially encapsulate the silver source, the silver source solution and the first dispersant solution are mixed and stabilized at room temperature, and then the mixed solution of the reducing agent and the second dispersant is poured at one time to prepare the nano silver solution. Polyvinyl pyrrolidone is used as the first dispersant because it has a higher molecular weight and has a better coating effect on nano silver, making the size more uniform; the second dispersant is selected from gum arabic because it has hydroxyl and carboxyl groups in its chain, which can increase the hydrophilicity of nano silver while dispersing. The synergistic effect of the two allows the nano silver to be better dispersed in water and will not agglomerate even if placed for a long time; the pH value of the solution is adjusted to 7-8 to ensure that the H - The concentration of the reducing agent is increased to increase the reducing ability of the reducing agent, and the prepared nanosilver is more uniform; the method has rapid reaction, simple operation, no requirements on experimental conditions, equipment, etc., can be stably expanded to 25L, and the particle size does not change after long-term storage, has highly stable dispersibility, and is suitable for large-scale industrial production; the present invention requires fewer types of agents, small dosages, is green and pollution-free, and meets the requirements of green production.

[0102] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a nano silver solution, characterized in that: After the silver source solution and the first dispersant solution are mixed and stabilized at room temperature, the pH value of the solution is adjusted, and the mixed solution of the reducing agent and the second dispersant is poured in one go, and then stirred for 5-30 minutes; comprising the following steps: S1, preparing 1.6-1.8 g / L silver nitrate solution as a silver source solution; S2, preparing 0.4-0.5 g / L polyvinyl pyrrolidone solution as the first dispersant; S3, preparing 0.4-0.5 g / L gum arabic solution as a second dispersant; preparing a reducing agent solution; S4, adding the polyvinyl pyrrolidone solution prepared in step S2 to the silver nitrate solution prepared in step S1, stirring evenly to obtain solution A; adjusting the pH value of solution A to 7-8; mixing the gum arabic solution prepared in step S3 with the reducing agent solution, pouring the mixture into solution A at once, stirring, to obtain a nanosilver solution, wherein the particle size of the nanosilver in the nanosilver solution is 8-31 nm.

2. The method for preparing the nano silver solution according to claim 1, characterized in that: In step S4, the mass ratio of the polyvinyl pyrrolidone to the silver nitrate is 1:(7-8).

3. The method for preparing the nano silver solution according to claim 1, characterized in that: In step S4, the mass ratio of the gum arabic to the silver nitrate is 1:(7-8).

4. The method for preparing the nano silver solution according to claim 1, characterized in that: In step S4, the mass ratio of the reducing agent to the silver nitrate is 1:(5-6).

5. The method for preparing the nano silver solution according to claim 1, characterized in that: The reducing agent is one of sodium borohydride and ascorbic acid.

6. The method for preparing the nano silver solution according to claim 1, characterized in that: In step S4, the pH value is adjusted by using ammonia water with a volume fraction of 25%-28%.

7. The method for preparing the nano silver solution according to claim 1, characterized in that: When a 2L reaction is carried out, the mass ratio of the dispersant to silver nitrate used is 1:(3-4), and the mass of the dispersant is the total mass of the first dispersant and the second dispersant.

8. The method for preparing the nano silver solution according to claim 1, characterized in that: When the reaction is carried out at 25 L, the mass ratio of the dispersant to silver nitrate is 1:(0.5-1), and the mass of the dispersant is the total mass of the first dispersant and the second dispersant.

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