A method for preparing nanosilver

Abstract

The present invention relates to the technical field of nanosilver preparation and discloses a method for preparing nanosilver. The method comprises providing a base liquid containing nanosilver particle seed crystals, a dispersant, a gel material, and a solubilizing agent; adding a silver salt solution and a reducing agent solution to the base liquid in parallel, wherein the silver ions are reduced to elemental silver during the addition process; after the silver salt solution is added, a metal chelating agent is added to the reaction system for a full reaction; after the reaction, a slurry is obtained, and solid nanosilver is extracted from the slurry; the solubilizing agent is selected from at least one of sodium oleate, polysorbate 80, and propylene glycol. This method reduces the difficulty of separating and purifying the obtained nanosilver; and the entire preparation process is simple. The obtained nanosilver has a particle size between 200 and 500 nm and good monodispersity, and has broad application prospects in the field of conductive pastes.

Description

Technical Field

[0001] The present invention relates to the technical field of nanosilver preparation, and in particular to a method for preparing nanosilver. Background Art

[0002] Nano-micron silver powder has attracted widespread attention due to its unique physicochemical properties and broad application prospects. Among the many methods for preparing nano-micron silver powder, the gel method, as an efficient and well-controllable preparation technology, has gradually revealed its unique advantages. The basic principle of the gel method is a technique that converts a metal salt solution into a gel-like substance and then converts it into nano-micron particles under appropriate conditions. This method generally dissolves a silver salt (such as silver nitrate, silver chloride, etc.) in an appropriate solvent to form a uniform silver salt solution. Then, it is necessary to select a suitable solvent and dissolution conditions to ensure that the silver salt can be completely dissolved and form a stable solution. Therefore, it is necessary to add a gelling agent such as polyvinyl alcohol or polyacrylic acid, and then adjust the reaction conditions (such as pH value and temperature) to gradually convert the silver salt solution into a gel. The selection and dosage of the gelling agent are key factors affecting gel formation and performance. After the gel network is formed, a reducing agent is added to form nano-micron silver powder.

[0003] Although the gel method has significant advantages in preparing nano-micron silver powder, it still faces some challenges. For example, how to further improve the yield and preparation efficiency of nano-micron silver powder, how to control the size and morphology consistency of the particles, etc., still require in-depth research and exploration. In addition, the industrial application of the gel method also needs to solve the problems that may be encountered during the scale-up production process, such as equipment design and process optimization. At the same time, due to the high viscosity of the gel, its separation is difficult and the purification process is cumbersome. Such operations include solvent washing, centrifugation, filtration, etc. These operations not only increase the complexity of the process, but may also lead to the loss or contamination of the nano-micron silver powder.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing nanosilver, aiming to improve at least one of the problems mentioned in the background art.

[0006] The present invention is achieved in that:

[0007] The present invention provides a method for preparing nanosilver, comprising:

[0008] Providing a base liquid, which includes nano silver particle seed crystals, a dispersant, a gel material, and a solubilizer;

[0009] Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during which the silver ions are reduced to elemental silver. After the silver salt solution is added, a metal chelating agent is added to the reaction system for full reaction.

[0010] After the reaction is completed, a slurry is obtained, and solid nanosilver is extracted from the slurry;

[0011] In the base liquid, the particle size of the nanosilver particles is 20 to 50 nm, and the mass ratio of the nanosilver particles to the theoretical target nanosilver powder is 0.1% to 5.0%; the mass ratio of the dispersant to the theoretical target nanosilver powder is 1 to 3%, the mass ratio of the gel material to the theoretical target nanosilver powder is 1 to 3.5%, and the mass ratio of the solubilizer to the theoretical target nanosilver powder is 0.4 to 1%.

[0012] The solubilizer is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

[0013] In an optional embodiment, the method for extracting solid nanosilver from the slurry comprises:

[0014] Add surfactant to the slurry and mix well;

[0015] The solution was allowed to settle, the upper clear liquid was poured out, and the lower solid layer was washed and dried to obtain nanosilver.

[0016] In an optional embodiment, the invention further includes at least one of the following features (1) to (4):

[0017] (1) The surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid;

[0018] (2) The mass ratio of the added amount of surfactant to the theoretical target of generating nanosilver powder is 0.1% to 2%;

[0019] (3) adding a surfactant to the slurry and mixing it uniformly at a speed of 300 to 800 rpm for 2 to 6 minutes;

[0020] (4) The lower layer of solid is cleaned by using an ethanol solution.

[0021] In an optional embodiment, the metal chelating agent is selected from at least one of sodium ethylenediaminetetraacetate, aminotriacetic acid, and ethylenediaminetetraacetic acid;

[0022] Optionally, the dispersant is selected from at least one of polyvinyl pyrrolidone, gum arabic and gelatin, preferably polyvinyl pyrrolidone.

[0023] In an optional embodiment, at least one of the following features (1) to (3) is also included:

[0024] (1) The mass ratio of the added amount of the metal chelating agent to the theoretical target of generating nano-silver powder is 0.1% to 0.5%;

[0025] (2) The total mass of solute in the base solution is less than or equal to 5% of the theoretical mass of the synthesized silver powder;

[0026] (3) The concentration of the silver nanoparticle seeds in the base solution is 0.009-0.455% wt, the concentration of the dispersant is 0.09-0.273% wt, the concentration of the gel material is 0.09-0.315% wt, and the concentration of the solubilizer is 0.036-0.09% wt.

[0027] In an optional embodiment, the silver salt in the silver salt solution is selected from at least one of silver nitrate, and;

[0028] Optionally, the silver salt solution is silver nitrate, and the mass concentration of the silver nitrate is 8 to 30%;

[0029] Optionally, the parallel addition time of the silver salt solution and the reducing agent solution is set to T, in min, where T=(0.01-0.05) / C*60, where C is the mass concentration of the silver salt solution.

[0030] In an optional embodiment, the reducing agent in the reducing agent solution is selected from at least one of ascorbic acid, sodium ascorbate, glucose and sodium borohydride.

[0031] In an optional embodiment, the reaction time after adding the metal chelating agent is 30 to 90 seconds.

[0032] In an optional embodiment, the gel material is selected from at least one of gum arabic and gelatin;

[0033] Optionally, the gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin, by weight.

[0034] In an optional embodiment, the preparation method of the base liquid includes:

[0035] Silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution;

[0036] placing the mixed solution in an environment of 100 to 160° C. and aging for 25 to 35 minutes to obtain a seed solution containing nano-silver particle seed crystals;

[0037] mixing a dispersant, a gel material, a solubilizer and deionized water to obtain a dispersion;

[0038] mixing the seed solution and the dispersion solution to prepare a base solution;

[0039] Optionally, the silver salt is silver nitrate;

[0040] Optionally, in the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%;

[0041] Optionally, in the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, gel material and solubilizer in the dispersion does not exceed 0.5%.

[0042] The present invention has the following beneficial effects:

[0043] The preparation method provided by the embodiment of the present invention significantly reduces the proportion of gel compared to the existing gel method for preparing nanosilver. If only the proportion of gel is reduced, the resistance to the migration of silver ions will be reduced, making it difficult to prepare nano-scale silver particles. To address this problem, the present invention improves the dispersibility of silver ions in the reaction system by adding a small amount of dispersant to the reaction system, and adds a solubilizer. These solubilizers are in the form of oil droplets when added to the base liquid, making the base liquid present an emulsion state, forming a water-in-oil micro-interface; since the continued addition of silver salt in the later stage of the reaction is easy to combine with the previously grown silver ions due to electrostatic adsorption and other reasons, hard agglomeration is caused, which leads to an increase in the D100 of the particles. The present invention adds a metal chelating agent after the anion and reducing agent are added to bind small silver particles, passivate the surface of the small silver particles, and reduce their agglomeration. Therefore, by adding a small amount of dispersant and solubilizer to the reaction system and adding the metal chelating agent in the post-reaction stage, the present invention can avoid the problem of larger silver particle size caused by reducing the amount of gel used. The resulting silver particles have a particle size range of 200 to 500 nm and good particle size distribution uniformity. The preparation method provided by the present invention significantly reduces the viscosity of the reaction system due to the reduced amount of gel used, which can reduce the difficulty of separating and purifying the resulting nanosilver. The entire preparation process is simple. The resulting nanosilver particles have a particle size between 200 and 500 nm and good monodispersity, and have broad application prospects in the field of conductive pastes. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 This is a SEM image of the nanosilver prepared in Example 1;

[0046] Figure 2 This is a SEM image of the nanosilver prepared in Example 2;

[0047] Figure 3 This is the SEM image of the nanosilver prepared in Example 3. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0049] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0050] The following is a detailed description of a method for preparing nanosilver provided in an embodiment of the present invention.

[0051] An embodiment of the present invention provides a method for preparing nanosilver, comprising:

[0052] Providing a base liquid, wherein the base liquid includes nanosilver particle seed crystals, a dispersant, a gel material, and a solubilizer;

[0053] Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during which the silver ions are reduced to elemental silver, and after the silver salt solution is added, adding a metal chelating agent to the reaction system for full reaction;

[0054] After the reaction is completed, a slurry is obtained, and solid nanosilver is extracted from the slurry;

[0055] In the base liquid, the particle size of the nanosilver particles is 20 to 50 nm, and the mass ratio of the nanosilver particles to the theoretical target nanosilver powder is 0.1% to 5.0%; the mass ratio of the dispersant to the theoretical target nanosilver powder is 1 to 3%, the mass ratio of the gel material to the theoretical target nanosilver powder is 1 to 3.5%, and the mass ratio of the solubilizer to the theoretical target nanosilver powder is 0.4 to 1%.

[0056] The preparation method provided by the embodiment of the present invention significantly reduces the proportion of gel compared to the existing gel method for preparing nanosilver. If only the proportion of gel is reduced, the resistance to the migration of silver ions will be reduced, making it difficult to prepare nano-scale silver particles. To address this problem, the present invention improves the dispersibility of silver ions in the reaction system by adding a small amount of dispersant to the reaction system, and adds a solubilizer. These solubilizers are in the form of oil droplets when added to the base liquid, making the base liquid present an emulsion state, forming a water-in-oil micro-interface; since the continued addition of silver salt in the later stage of the reaction is easy to combine with the previously grown silver ions due to electrostatic adsorption and other reasons, hard agglomeration is caused, which leads to an increase in the D100 of the particles. The present application adds a metal chelating agent after the addition of anions and a reducing agent to bind small silver particles, passivate the surface of the small silver particles, and reduce their agglomeration. Therefore, by adding a small amount of dispersant and solubilizer to the reaction system and adding the metal chelating agent in the post-reaction stage, the present invention can avoid the problem of larger silver particle size caused by reducing the amount of gel used. The obtained silver particles have a particle size range of 200 to 500 nm and good particle size distribution uniformity. The preparation method provided by the present invention significantly reduces the viscosity of the reaction system due to the reduced amount of gel used, which can reduce the difficulty of separating and purifying the obtained nanosilver. The entire preparation process is simple.

[0057] Specifically, the preparation method is:

[0058] S1. Preparation of seed solution

[0059] Silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution;

[0060] The mixed solution is placed in an environment of 100-160° C. (e.g., 100° C., 120° C., 140° C., or 160° C.) and aged for 25-35 min (e.g., 25 min, 30 min, or 35 min) to react and generate 20-50 nm nanosilver particles, thereby obtaining a seed solution containing nanosilver particle seed crystals.

[0061] Optionally, the mass percentage of the nanosilver particle seeds in the prepared seed solution is 0.1-5% (eg, 0.1%, 0.635%, 3.15% or 5%).

[0062] To obtain a seed solution with a mass percentage of 0.1-5% of nanosilver particle seeds, optionally, in the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%.

[0063] Optionally, the silver salt is silver nitrate.

[0064] Furthermore, the mixed solution is prepared, for example, as follows:

[0065] A silver nitrate solution containing 0.1-0.5g of silver nitrate, 0.2-1.0g of oleylamine, and polyethylene glycol 2000 are added to a container and stirred to obtain 10g of a mixed solution. The mixed solution is heated and aged to obtain a seed solution containing 0.635-3.18% by weight of nanosilver particle seed crystals.

[0066] Optionally, the heating method is oil bath heating.

[0067] S2. Prepare dispersion

[0068] The dispersant, the gel material, the solubilizer and deionized water are mixed to obtain a dispersion.

[0069] Optionally, in the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, gel material and solubilizer in the dispersion does not exceed 0.5%.

[0070] Optionally, the dispersant is selected from at least one of polyvinylpyrrolidone (PVP), gum arabic and gelatin.

[0071] Optionally, the gel material is selected from at least one of gum arabic (HLB value 8) and gelatin (HLB value 9.8).

[0072] Optionally, the gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin, by weight.

[0073] Optionally, the solubilizer is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

[0074] S3. Prepare base liquid

[0075] The seed solution and the dispersion solution are mixed under stirring conditions of 350-450 rpm (eg, 350 rpm, 400 rpm, or 450 rpm), and stirred for 25-35 s (eg, 25 s, 30 s, or 35 s) to obtain a base solution.

[0076] Specifically, the seed solution and the dispersion solution are prepared according to the following ingredients: the concentration of the nanosilver particle seeds in the obtained base solution is 0.009-0.455% wt, the concentration of the dispersant is 0.09-0.273% wt, the concentration of the gel material is 0.09-0.315% wt, and the concentration of the solubilizer is 0.036-0.09% wt.

[0077] For example, 10 g of a seed solution containing 0.1-5% by mass of silver nanoparticle seeds and 100 g of the above dispersion are mixed to obtain a base solution, in which the mass fraction of the silver nanoparticle seeds is 0.009-0.455%.

[0078] S4. Reduction reaction

[0079] Dissolve the silver salt in deionized water to obtain a silver salt solution with a mass concentration of 10% to 30% (eg, 1%, 20% or 30%).

[0080] Optionally, the silver salt is selected from at least one of silver nitrate, silver nitrate, silver chloride and silver acetate;

[0081] The reducing agent is dissolved in deionized water to obtain a reducing agent solution with a concentration of 10% to 15% (eg, 10%, 12% or 15%).

[0082] Optionally, the reducing agent is selected from at least one of ascorbic acid, sodium ascorbate and glucose.

[0083] The silver salt solution and the reducing agent solution are injected into the bottom liquid in parallel through a peristaltic pump. During this process, the rotation speed of the reactor is increased to 550-650 rpm (eg, 550 rpm, 600 rpm or 650 rpm).

[0084] Preferably, the silver salt is silver nitrate, and the mass concentration of silver nitrate is 8-12% (e.g., 8%, 10% or 12%); during injection, the parallel addition time of the silver nitrate solution and the reducing agent solution is set to T, in min, T=(0.01-0.05) / C*60, for example, 0.01 / C*60, 0.03 / C*60 or 0.05 / C*60, where C is the mass concentration of the silver salt solution.

[0085] After the silver salt solution is added, the metal chelating agent is added immediately, and the reaction is continued for 30 to 90 seconds (eg, 30 seconds, 60 seconds, or 90 seconds) to terminate the reaction and obtain a slurry.

[0086] Optionally, the mass ratio of the added amount of the metal chelating agent to the theoretical target generated nano silver powder is 0.1% to 0.5% (eg, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%).

[0087] Optionally, the metal chelating agent is at least one of sodium edetate, aminotriacetic acid, and ethylenediaminetetraacetic acid (EDTA).

[0088] S5. Extraction of Nanosilver

[0089] Add a surfactant to the slurry, and continue stirring and mixing at a rotation speed of 300 to 800 rpm (eg, 300 rpm, 500 rpm, or 800 rpm) for 2 to 6 minutes (2 minutes, 4 minutes, or 6 minutes).

[0090] After stirring, the mixture is allowed to stand for at least 30 minutes to allow the nanosilver ions to settle in the reaction container. The supernatant in the container is discarded, and then an ethanol solution is added to the container to wash the nanosilver in the reaction container. After repeating the operation at least twice, the wet powder obtained by washing is placed in an oven at 30 to 40° C. (e.g., 30° C., 35° C., or 40° C.) and dried to obtain nano-scale silver powder.

[0091] Optionally, the surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid.

[0092] Optionally, the mass ratio of the added amount of the surfactant to the theoretically synthesized nano-silver powder is 0.1% to 2% (eg, 0.1%, 0.5%, 1%, 1.5% or 2%).

[0093] Because the slurry contains a low proportion of gel and has low viscosity, in this step, the surfactant stearic acid is added to the slurry, allowing the nanosilver produced by the reaction to settle smoothly to the bottom of the container. This process is simple to operate and allows for convenient separation of the nanosilver. After separation, the nanosilver can be purified by simply washing with an ethanol solution. This purification method is also simple and does not cause contamination or loss of the nanosilver.

[0094] It should be noted that in this step, if a surfactant is not added, it will be difficult to achieve automatic precipitation of the nanosilver. The nanosilver in the slurry can only be extracted by high-speed centrifugation, which will reduce the convenience.

[0095] Example 1

[0096] 0.5 g of silver nitrate was added to 1.0 g of oleylamine and 8.5 g of PEG 2000 solution, and the mixture was heated in a constant temperature oil bath at 120° C. for 30 min to obtain 10.0 g of brown seed solution containing nano-silver. The mass percentage of nano-silver seeds in the seed solution was 3.175%.

[0097] Weigh 15.8g of silver nitrate and 142.2g of deionized water, stir until completely dissolved, and obtain 158g of 10% silver nitrate solution, theoretically producing 10g of silver powder;

[0098] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a 10% reducing agent solution.

[0099] Weigh 0.2 g of dispersant PVP K30 powder, 0.15 g of gum arabic, 0.1 g of gelatin, and 0.05 g of sodium oleate, which together account for 5% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 2%, 1.5%, 1%, and 0.5%, respectively. Add 99.5 g of deionized water and stir until completely dissolved to obtain 100 g of a solution with a dispersant mass fraction of 0.2%. Disperse the solution by high-speed shearing in a disperser and mix thoroughly to obtain a dispersion.

[0100] At a rotation speed of 400 rpm, 10 g of the seed solution was added to the dispersion and stirred for 30 seconds to obtain a base solution. The mass fraction of the silver nanoparticle seed solution in the base solution was 0.289%.

[0101] The silver nitrate solution and the reducing agent solution were added to the bottom solution in parallel through a peristaltic pump, and the speed was increased to 600 rpm at the same time. The parallel addition time was set to 10 min.

[0102] After the silver nitrate solution is added, 0.05 g of metal chelating agent sodium ethylenediaminetetraacetate (sodium EDTA) is immediately added, which is 0.5% of the theoretical mass of the generated silver powder, and the reaction is continued for 1 min to obtain a slurry;

[0103] Add 0.5 g of surfactant long-chain stearic acid to the slurry, which is 5% of the theoretical mass of the generated silver powder, and continue stirring for 4 minutes;

[0104] After stirring, the mixture was allowed to stand for 30 minutes. After the nano-sized silver particles settled on their own, the supernatant was poured off. A 70% ethanol solution was added to the obtained solid for washing. The operation was repeated twice to obtain a wet powder. The wet powder was placed in a 35° C. oven to dry to obtain nano-sized silver powder.

[0105] Example 2

[0106] This embodiment is basically the same as the first embodiment, except that:

[0107] Weigh 0.1 g of dispersant PVP K30 powder, 0.2 g of gum arabic, 0.15 g of gelatin, and 0.05 g of sodium oleate, totaling 5% of the theoretical mass of the generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 1%, 2%, 1.5%, and 0.5%, respectively. Add 99.5 g of deionized water and stir until completely dissolved to obtain a solution with a dispersant mass fraction of 0.1%. Then, disperse it through a disperser at high shear speed and mix thoroughly to obtain a dispersion.

[0108] Example 3

[0109] This embodiment is basically the same as the first embodiment, except that:

[0110] Take 0.1 g of silver nitrate, add 0.2 g of oleylamine, and then add 9.7 g of PEG 2000 solution, heat and mature in a constant temperature oil bath at 120°C for 30 minutes to obtain 10.0 g of brown seed solution containing nano-micron silver for use, wherein the mass fraction of the nanosilver seed crystals is 0.635%;

[0111] Weigh 15.8g of silver nitrate and 142.2g of deionized water, stir until completely dissolved, and obtain 158g of 10% silver nitrate solution, theoretically producing 10g of silver powder;

[0112] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a 10% reducing agent solution.

[0113] Weigh 10.0 g of sodium ascorbate and 90.0 g of deionized water, stir until completely dissolved, and obtain 100 g of a 10% reducing agent solution.

[0114] Weigh 0.2 g of dispersant PVP K30 powder, 0.15 g of gum arabic, 0.1 g of gelatin, and 0.05 g of sodium oleate, which together account for 5% of the theoretical target of generating nano-silver powder, wherein PVP, gum arabic, gelatin, and sodium oleate account for 2%, 1.5%, 1%, and 0.5%, respectively, and then add 99.5 g of deionized water, stir until completely dissolved, and obtain 100 g of a solution with a dispersant mass fraction of 0.2%, and then disperse it through a disperser at high shearing speed and fully mix to obtain a dispersion;

[0115] At a rotation speed of 400 rpm, the seed solution was added to the dispersion solution and stirred for 30 seconds to obtain a base solution in which the mass fraction of the nanosilver particle seed crystals was 0.058%;

[0116] The silver nitrate solution and the reducing agent solution were added to the bottom solution in parallel through a peristaltic pump, and the speed was increased to 600 rpm at the same time. The parallel addition time was set to 10 min.

[0117] After the silver nitrate solution is added, 0.05 g of metal chelating agent sodium ethylenediaminetetraacetate (sodium EDTA) is immediately added, which is 0.5% of the theoretical mass of the generated silver powder, and the reaction is continued for 1 min to obtain a slurry;

[0118] Add 0.5 g of surfactant long-chain stearic acid to the slurry, which is 5% of the theoretical mass of the generated silver powder, and continue stirring for 4 minutes;

[0119] After stirring, the mixture was allowed to stand for 30 minutes. After the nano-silver ions settled by themselves, the supernatant was poured out. A 70% ethanol solution was added to the obtained solid for washing. The operation was repeated twice to obtain a wet powder. The wet powder was placed in a 35°C oven for drying to obtain nano-silver powder.

[0120] Example 4

[0121] This embodiment is substantially the same as embodiment 1, except that sodium EDTA is replaced by aminotriacetic acid as the metal chelating agent.

[0122] Example 5

[0123] This embodiment is basically the same as embodiment 1, except that the solubilizer is polysorbate 80 instead of sodium oleate.

[0124] Example 6

[0125] This embodiment is basically the same as the first embodiment, except that:

[0126] 0.0157 g of silver nitrate was added to 0.2 g of oleylamine and then 9.7853 g of PEG 2000 solution. The mixture was heated in a constant temperature oil bath at 120°C for 30 min to obtain 10.0 g of brown seed solution containing nano-silver. The mass percentage of nano-silver seeds in the seed solution was 0.1%.

[0127] Weigh 0.1 g of dispersant PVP K30 powder, 0.05 g of gum arabic, 0.05 g of gelatin, and 0.1 g of sodium oleate, which together account for 3% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 1%, 0.5%, 0.5%, and 1%, respectively. Add 99.7 g of deionized water and stir until completely dissolved to obtain 100 g of a solution with a dispersant mass fraction of 0.1%. Disperse the solution by high-speed shearing in a disperser and mix thoroughly to obtain a dispersion.

[0128] In the prepared base solution, the concentration of nano silver particle seeds is 0.009% wt, the concentration of dispersant is 0.09% wt, the concentration of gel material is 0.09% wt, and the concentration of solubilizer is 0.09% wt.

[0129] Example 7

[0130] This embodiment is basically the same as the first embodiment, except that:

[0131] 0.785 g of silver nitrate was added to 1.0 g of oleylamine and 8.215 g of PEG 2000 solution. The mixture was heated in a constant temperature oil bath at 120° C. for 30 min to obtain 10.0 g of a brown seed solution containing nano-silver. The mass percentage of the nano-silver seeds in the seed solution was 5%.

[0132] Weigh 0.3 g of dispersant PVP K30 powder, 0.1 g of gum arabic, 0.05 g of gelatin, and 0.04 g of sodium oleate, which together account for 4.9% of the theoretically generated silver powder, of which PVP, gum arabic, gelatin, and sodium oleate account for 3%, 1%, 0.5%, and 0.4%, respectively. Add 99.51 g of deionized water and stir until completely dissolved to obtain 100 g of a solution with a dispersant mass fraction of 0.2%. Disperse the solution by high-speed shearing in a disperser and mix thoroughly to obtain a dispersion.

[0133] In the prepared base solution, the concentration of the nanosilver particle seed crystals was 0.455% wt, the concentration of the dispersant was 0.273% wt, the concentration of the gel material was 0.137% wt, and the concentration of the solubilizer was 0.036% wt.

[0134] Comparative Example 1

[0135] This comparative example is substantially the same as Example 1, except that the dispersion does not include a dispersant.

[0136] Comparative Example 2

[0137] This comparative example is substantially the same as Example 1, except that sodium oleate is not included in the dispersion.

[0138] Comparative Example 3

[0139] This comparative example is substantially the same as Example 1, except that no metal chelating agent is added after the silver nitrate solution is added.

[0140] Comparative Example 4

[0141] This comparative example is basically the same as Example 1, except that the amount of sodium oleate added to the dispersion is too high, 0.15 g, and the mass ratio of the theoretical target nano-silver powder is 1.5%, which exceeds the range required by this application.

[0142] Experimental example

[0143] (1) Take the SEM images of the nanosilver prepared in each embodiment, as shown in FIG. Figures 1 to 3 As shown in the figure, it can be seen that the nanosilver prepared in each embodiment of the present application is all nano-scale, with good particle size distribution uniformity, good monodispersity, and almost no agglomeration.

[0144] (2) The particle sizes of the products obtained in each embodiment and comparative example were measured and recorded in Tables 1 and 2.

[0145] Table 1 Particle size of the products obtained in each embodiment

[0146]

[0147] Table 2 Particle size of the products obtained in each comparative example

[0148] Group Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Particle size μm 1.35 1.65 2.18 4.24

[0149] It can be seen from the particle size data in Table 1 and Table 2 that the particle size of the particles prepared in each embodiment is in the range of 200 to 500 nm.

[0150] Comparing Comparative Example 1 and Comparative Example 2 with Example 1, the particle sizes of Comparative Example 1 and Comparative Example 2 are obviously larger, exceeding the nanometer level, indicating that both the dispersant and the solubilizer are indispensable in the base liquid;

[0151] Comparing Comparative Example 3 with Example 1, the particle size of Comparative Example 3 is obviously larger, indicating that if the metal chelating agent is not added after the silver salt is dissolved and added, the particle size of the prepared particles will be larger;

[0152] Comparing Comparative Example 4 with Example 1, the average particle size of Comparative Example 4 is the largest, indicating that excessive addition of solubilizer in the base liquid will cause powder agglomeration, resulting in larger particle size.

[0153] In summary, the preparation method provided by the embodiments of the present invention significantly reduces the viscosity of the reaction system by reducing the amount of gel used, thereby reducing the difficulty of separating and purifying the resulting nanosilver. Furthermore, the entire preparation process is simple. The resulting nanosilver has an average particle size between 200 and 500 nm and good monodispersity, showing broad application prospects in the field of conductive pastes.

[0154] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing nano silver, characterized in that: include: Providing a base liquid, wherein the base liquid includes nanosilver particle seed crystals, a dispersant, a gel material, and a solubilizer; Adding a silver salt solution and a reducing agent solution to the base liquid in parallel, during which the silver ions are reduced to elemental silver, and after the silver salt solution is added, adding a metal chelating agent to the reaction system for full reaction, wherein the mass ratio of the metal chelating agent added to the theoretical target nano-silver powder is 0.1% to 0.5%; After the reaction is completed, a slurry is obtained, and a surfactant is added to the slurry and mixed; Allowing the solution to settle, pouring out the supernatant, washing the lower solid layer and drying it to obtain the nanosilver; In the base liquid, the particle size of the nanosilver particle seed is 20-50 nm, and the mass ratio of the nanosilver powder to the theoretical target is 0.1%-5.0%; the mass ratio of the dispersant to the theoretical target is 1-3%, the mass ratio of the gel material to the theoretical target is 1-3.5%, and the mass ratio of the solubilizer to the theoretical target is 0.4-1.0%. The solubilizer is selected from at least one of sodium oleate, polysorbate 80 and propylene glycol.

2. The preparation method according to claim 1, characterized in that Also includes at least one of the following features (1) to (4): (1) The surfactant is a long-chain carboxylic acid; optionally, the long-chain carboxylic acid is selected from at least one of stearic acid and lauric acid; (2) The mass ratio of the added amount of the surfactant to the theoretical target of generating nano silver powder is 0.1% to 2%; (3) adding a surfactant to the slurry and mixing the mixture at a speed of 300 to 800 rpm for 2 to 6 minutes; (4) The lower layer of solid is cleaned by using an ethanol solution.

3. The preparation method according to claim 1, characterized in that The metal chelating agent is selected from at least one of sodium ethylenediaminetetraacetate, aminotriacetic acid, and ethylenediaminetetraacetic acid.

4. The preparation method according to claim 1, characterized in that The dispersant is selected from at least one of polyvinyl pyrrolidone, gum arabic and gelatin.

5. The preparation method according to claim 1, characterized in that Also includes at least one of the following features (1) and (2): (1) The total mass of the solute in the base solution is less than or equal to 5% of the mass of the theoretically synthesized silver powder; (2) The concentration of the nanosilver particle seed crystals in the base liquid is 0.009-0.455%wt, the concentration of the dispersant is 0.09-0.273%wt, the concentration of the gel material is 0.09-0.315%wt, and the concentration of the solubilizer is 0.036-0.09%wt.

6. The preparation method according to claim 1, characterized in that The silver salt in the silver salt solution is silver nitrate, and the mass concentration of the silver nitrate is 8-30%.

7. The preparation method according to claim 6, characterized in that The parallel addition time of the silver salt solution and the reducing agent solution is set to T, in minutes, T=(0.01-0.05) / C*60, where C is the mass concentration of the silver salt solution.

8. The preparation method according to claim 1, characterized in that The reducing agent in the reducing agent solution is selected from at least one of ascorbic acid, sodium ascorbate, glucose and sodium borohydride.

9. The preparation method according to claim 1, characterized in that The reaction time after adding the metal chelating agent is 30 to 90 seconds.

10. The preparation method according to claim 1, characterized in that The gel material is selected from at least one of gum arabic and gelatin.

11. The preparation method according to claim 10, characterized in that: The gel material consists of 1.5 to 2 parts of gum arabic and 1 to 1.5 parts of gelatin by weight.

12. The preparation method according to claim 1, characterized in that The preparation method of the base liquid comprises: Silver salt, oleylamine and polyethylene glycol 2000 are mixed and stirred to obtain a mixed solution; placing the mixed solution in an environment of 100-160° C. and aging for 25-35 minutes to obtain a seed solution containing the nanosilver particle seed crystals; mixing the dispersant, the gel material, the solubilizer and deionized water to obtain a dispersion solution; The seed solution and the dispersion solution are mixed to prepare the base solution.

13. The preparation method according to claim 12, characterized in that The silver salt is silver nitrate.

14. The preparation method according to claim 12, characterized in that In the mixed solution, the mass percentage of silver ions is 0.1-5%, the mass percentage of oleylamine is 2-10%, and the mass percentage of polyethylene glycol 2000 is 85-97%.

15. The preparation method according to claim 12, characterized in that In the dispersion, the mass percentage of the dispersant is 0.1-0.3%, the mass percentage of the gel material is 0.1-0.35%, the mass percentage of the solubilizer is 0.04-0.1%, and the total mass percentage of the dispersant, the gel material and the solubilizer in the dispersion does not exceed 0.5%.

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