Process for the preparation of highly reactive silver nanoparticles

Abstract

The application discloses a preparation method of high-reactivity silver nanoparticles, and comprises the following steps: step 1, silver hydroxide is used as raw material to prepare silver oxide as a high-reactivity silver source; silver nitrate is reacted with sodium hydroxide aqueous solution to obtain silver hydroxide precipitate; after vacuum drying, the silver hydroxide is converted into silver oxide; step 2, the silver oxide is suspended in an alcohol solution, and a reaction promoter is added to perform the reaction while applying strong physical action to the reaction system; step 3, after the reaction is completed, the reaction system is cooled to room temperature, and then acetone is added; after condensation / separation treatment and drying, silver nanoparticle products are obtained. The application realizes high reactivity and product stability which cannot be achieved by traditional silver oxide. Especially through the synergistic effect of the coexistence of various alcohol structures and physical action and the promoter, the essential limitation of solid-liquid reaction is effectively overcome.

Description

Technical Field

[0001] This invention relates to a method for preparing silver nanoparticles, specifically a method for preparing silver nanoparticles with low-temperature reactivity, excellent high reactivity, and high stability using silver oxide as a raw material. Background Technology

[0002] Silver nanoparticles have attracted much attention due to their high reactivity and ease of sintering at relatively low temperatures, and are expected to become the heat-resistant connection material for next-generation power semiconductors. Currently, there are several processes for mass production of silver nanoparticles, which are mainly divided into two categories: (1) Vapor phase evaporation method: In a low vacuum environment, metal is vaporized by means of electron beams, and then condensed in an inert gas to obtain silver nanoparticles (representative patent: Japanese Patent No. 3452617). This process requires expensive vacuum equipment, the metal evaporation process has high energy consumption and low yield, making it difficult to achieve mass production and the overall production cost is extremely high. (2) Faraday method / sodium borohydride reduction method: Using metal ion aqueous solution as raw material, silver nanoparticles are prepared by reduction with strong reducing agents such as sodium borohydride. This method is named Faraday method / sodium borohydride reduction method after the developer (representative patent: Japanese Patent Application Publication No. 10-265812). The silver nanoparticles prepared by this method are dispersed in water. Since silver particles readily ionize with water, a dense protective layer is necessary. This requires the use of thiols to form metal-sulfur bonds or amine functional groups as binding groups. Furthermore, the protective layer must be removed under stringent desorption conditions during subsequent use. This presents two major problems: ① Harsh processing conditions: The reaction temperature must reach above 300℃, and a high-pressure sintering process is required; ② High concentration costs and difficulty in mass production: In high-concentration systems, nanoparticles easily agglomerate, limiting synthesis to low-concentration dilute solutions. Obtaining high-concentration products requires concentration through ultracentrifugation, reverse osmosis, and other methods, which are costly, ultimately hindering mass production and resulting in expensive finished products.

[0003] To address the aforementioned issues, the inventors developed a non-aqueous synthesis method using silver salts of fatty acids, silver acetate, and silver carbonate as silver sources. For example, JP3205793 discloses a method for synthesizing and separating nanoparticles in a metastable state by heating and decomposing silver salts of fatty acids under non-oxidizing conditions. This method can prepare highly reactive nanoparticles with a fatty acid-type surface, but it suffers from a narrow process window and high synthesis difficulty in the synthesis and nanostructuring of silver salts of fatty acids. Furthermore, JP4732645B9 describes a process for forming nanoparticles through an exchange reaction with a protecting group using silver carbonate as the silver source. However, because the silver source used is solid, its reactivity is low, and incomplete reaction is prone to occur, leading to product quality problems and increasing the risk of defective products. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing highly reactive silver nanoparticles, which aims to use a cheaper and more active silver source, combined with the unique characteristics of solid-liquid reactions, and through the combined effects of physical treatment, chemical promoters and alcohols, to significantly improve the reactivity and product stability in the preparation process of silver compounds.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing highly reactive silver nanoparticles includes the following steps: Step 1: Prepare silver oxide using silver hydroxide as a raw material, as a highly reactive silver source: react silver nitrate with an aqueous solution of sodium hydroxide to obtain silver hydroxide precipitate; after vacuum drying, it is converted into silver oxide; Step 2: Suspend silver oxide in an alcohol solution, add a reaction promoter, and heat the reaction while applying a strong physical action to the reaction system. Step 3: After the reaction is complete, cool to room temperature, add organic solvent, and after coagulation / separation and drying, obtain silver nanoparticle product.

[0006] Compared with the prior art, the beneficial effects of the present invention are: 1. To address the shortcomings of traditional processes, this invention has developed a novel synthesis process through continuous improvement and iterative development of JP3205793 and JP4732645B9, which can prepare silver nanoparticles with a core size of 1-40 nm. This process has higher production efficiency and the nanoparticles exhibit excellent surface structure reactivity.

[0007] 2. This invention addresses the core defects of JP4732645B9, improving upon the technical experience accumulated during the research and development of that patent. It not only solves the original process problems but also further enhances product performance. Specific innovative improvements are as follows: The silver source is replaced with silver oxide, eliminating the original inorganic silver salt raw materials such as silver carbonate and silver acetate. Using silver oxide as the silver source significantly reduces the reaction barrier. In the original silver carbonate system, the average proportion of unreacted raw materials reached 30%; after replacing it with silver oxide, the unreacted rate drops to below 10%. If combined with an emulsifier to apply enhanced physical shearing, the unreacted rate can be further reduced to within a few percent. The technological advancements brought about by this improvement are remarkable.

[0008] 3. Differentiated advantages from JP3205793 product: The nanoparticles prepared by this invention have protective group characteristics that are very different from those of JP3205793 product, and the two are not comparable; moreover, the silver nanoparticles prepared by this process have a thermal decomposition temperature that is more than 50°C lower than the former, which can realize low-temperature processing and mass production.

[0009] 4. Significantly optimized equipment costs and production capacity: Based on this invention, only one set of synthesis equipment costing tens of thousands of yen and with a reaction volume of a few liters is needed to achieve large-scale production of several kilograms of high-performance silver nanoparticles per day.

[0010] 5. This invention achieves high reactivity and product stability that are difficult to attain with traditional silver oxide. In particular, through the structural and physical interactions of multiple alcohols and the synergistic effect of the promoter, it effectively overcomes the inherent limitations of solid-liquid reactions. Attached Figure Description

[0011] Figure 1 It is to precipitate silver hydroxide.

[0012] Figure 2 It is a micron-sized fine powder of silver hydroxide.

[0013] Figure 3 It consists of silver nanoparticles.

[0014] Figure 4 Silver nanoparticles under a TEM microscope. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention provides a method for preparing highly reactive silver nanoparticles, the method comprising the following steps: Step 1: Prepare silver oxide using silver hydroxide as a raw material, serving as a highly reactive silver source: Silver oxide prepared from silver hydroxide (AgOH) obtained by reacting silver nitrate with an aqueous solution of sodium hydroxide has a smaller particle size and more surface defects than commercially available silver oxide, thus exhibiting higher reactivity. Hydrated silver oxide is typically unstable and expensive. Research has shown that adding an equal amount of aqueous sodium hydroxide solution to an aqueous solution of silver nitrate with a concentration of approximately 1 mol / L achieves quantitative and economical synthesis; subsequently, drying the product at a temperature below 80°C converts it into silver oxide. Figure 1 Furthermore, silver oxide needs to be thoroughly ground into micron-sized fine powder. Figure 2 ).

[0017] Step 2: Suspend silver oxide, which has been ground into micron-sized fine powder, in an alcohol solution, add a reaction promoter, and heat the reaction while applying a strong physical action to the reaction system. Control the mass-volume ratio of silver oxide to alcohol solution to be 1:1, and the reaction temperature to be below 130℃.

[0018] In this step, the reaction is a solid-phase (silver oxide) / liquid-phase (alcohol) reaction. Due to the low reactivity within the solid, at least one physical action is required, such as high-speed stirring, mortar grinding, ball milling, ultrasonic homogenization, pressure homogenization, or shear dispersion homogenization, to renew the reaction interface. This physical pulverization operation can be performed before or during the reaction. In this invention, a shear dispersion homogenizer is preferably used.

[0019] In this step, the reaction promoter (auxiliary agent) can be at least one of amines, carboxylic acids, hydrogen peroxide, peroxides, periodate, etc., preferably carboxylic acids, and the amount added is about 0 to 1% of the weight of silver oxide. It can also be reacted in a nitrogen atmosphere containing 1% ozone gas. By dissolving silver ions on the solid surface and regulating their coordination environment, the reaction rate can be improved.

[0020] In this step, the alcohol solution contains multiple alcohols with different carbon numbers and / or different degrees of saturation. Specifically, straight-chain saturated alcohols with 3 to 18 carbon chains (such as n-propanol to n-octadecyl alcohol), or one or more unsaturated alcohols such as allyl alcohol and propynyl alcohol can be used. These alcohols can be used alone or in combination (including combinations of different chain lengths and degrees of saturation, such as ethanol and allyl alcohol, methanol and propynyl alcohol, etc.). In this way, the solubility of the silver source, the stability of the intermediate, and the anti-agglomeration effect of the final product can be synergistically improved, achieving high yield and long-term storage stability, while also enabling the prepared silver nanoparticles to possess all the excellent properties of products prepared from a single alcohol.

[0021] Step 3: After the reaction is complete, cool to room temperature, add organic solvent, and after coagulation / separation and drying, obtain silver nanoparticle product ( Figures 3-4 ), wherein: the organic solvent is an organic solvent with a similar structure, such as acetone or butanone, preferably acetone.

[0022] The above method is characterized by: using silver oxide prepared from silver hydroxide as a silver source with higher reactivity; given that the reaction is a solid / liquid reaction, the reaction interface is renewed by enhancing physical action; at the same time, a reaction promoter is added to dissolve silver ions on the solid surface and regulate their coordination environment to improve the reaction rate; in addition, using a variety of alcohols with different chain lengths and saturations can further enhance the reactivity and product stability.

[0023] Example 1: Hydrated silver oxide precipitate was vacuum dried to obtain silver oxide. 0.01 mol of silver oxide was suspended in a mixed solvent of 10 mL n-propanol and 2 mL n-butanol. 0.001 mol of acetic acid was added, and the mixture was vigorously stirred using a shear-dispersing homogenizer, then heated to 200°C under reflux. When the temperature exceeded 120°C, it was then maintained at 200°C for 30 minutes. After the reaction was complete, the mixture was cooled to room temperature, and 500 mL of acetone was added. After coagulation / separation and drying, silver nanoparticles with a particle size between 1 and 40 nm were obtained, with a yield of 92%. The obtained product is stable in air for more than 3 months.

[0024] Comparative Example 1: Using commercially available silver oxide (in the same molar amount), with ethanol as the solvent alone, and without applying any external force, the reaction was allowed to stand. The yield was less than 1%, and almost no product was obtained.

[0025] Example 2: Hydrated silver oxide precipitate was vacuum dried to obtain silver oxide. 0.01 mol of silver oxide was suspended in a mixed solvent of 10 mL hexanol and 2 mL pentanol. After vigorous stirring in a homogenizer, the mixture was heated to 200°C under reflux. Self-heating was observed when the temperature exceeded 120°C, and the temperature was then maintained at 200°C for 30 minutes. After the reaction, the mixture was cooled to room temperature, and 500 mL of acetone was added. After coagulation / separation and drying, silver nanoparticles with a particle size between 1 and 40 nm were obtained, with a yield as high as 92%. The obtained product can be stably stored in air for more than 3 months. The silver nanoparticles prepared in this way were made into a slurry and applied to the sintering of semiconductor components, achieving good sintering bonding results.

[0026] Comparative Example 2: Using commercially available silver oxide (in equal molar amounts) as a raw material and n-pentanol as a solvent, the reaction was carried out by static standing without any external force applied. The yield was less than 1%, and almost no product was obtained.

[0027] The above description is merely an example to clearly illustrate the present invention and is not intended to limit the patent scope of the present invention. It is impossible to exhaustively list all embodiments here. All equivalent structural transformations made using the content of the technical solution of the present invention under the concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing highly reactive silver nanoparticles, characterized in that... The method includes the following steps: Step 1: Prepare silver oxide using silver hydroxide as a raw material, as a highly reactive silver source; Step 2: Suspend silver oxide in an alcohol solution, add a reaction promoter, and heat the reaction while applying a strong physical action to the reaction system. Step 3: After the reaction is complete, cool to room temperature, add organic solvent, and after coagulation / separation and drying, obtain silver nanoparticle product.

2. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... The specific steps of step 1 are as follows: silver nitrate is reacted with an aqueous solution of sodium hydroxide to obtain silver hydroxide precipitate; after vacuum drying, it is converted into silver oxide.

3. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... In step 2, the mass-to-volume ratio of silver oxide to alcohol solution is 1:1, and the reaction temperature is below 130°C.

4. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... In step 2, at least one physical action needs to be continuously applied, such as high-speed stirring, mortar grinding, ball milling, ultrasonic homogenization, pressure homogenization, or shear dispersion homogenization.

5. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... In step 2, the reaction promoter is selected from at least one of amines, carboxylic acids, peroxides, and periodates, or the reaction is carried out in a nitrogen atmosphere containing 1% ozone gas. The amount of reaction promoter added is 0 to 1% of the weight of silver oxide.

6. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... In step 2, the alcohol solution is one or more of a straight-chain saturated alcohol or an unsaturated alcohol with a carbon chain number of 3 to 18.

7. The method for preparing highly reactive silver nanoparticles according to claim 1, characterized in that... In step 3, the organic solvent is acetone or butanone.

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