Efficient and simple synthesis method of silver nanoparticles based on chemical reduction method

Abstract

The invention discloses an efficient and simple silver nanoparticle synthesis method based on a chemical reduction method, which comprises the following steps: (1) uniformly mixing an aqueous solution of soluble silver salt and an aqueous solution of a complexing agent to obtain a silver ion complex aqueous solution; (2) adding hydroxy carboxylate into the silver ion complex aqueous solution obtained in the step (1); (3) adjusting the pH value of the solution obtained in the step (2) to be alkaline, and reacting for 10-60 minutes at low temperature; (4) adjusting the pH value of the solution obtained in the step (3) to be neutral, heating to a high temperature, and reacting for 10-30 minutes; and (5) naturally cooling the material obtained in the step (4) to room temperature, and sequentially centrifuging, washing with deionized water, washing with ethanol and drying to obtain the silver nanoparticles. The prepared silver nanoparticles are excellent in performance in conductive ink, and the resistivity of a sintered coating is only 2-50 times that of bulk silver. The characteristic shows that the material has important application potential in the field of printed electronics and can be used for preparing high-performance flexible circuits and conductive coatings.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial preparation, and particularly relates to a high-efficiency and simple silver nanoparticle synthesis method based on a chemical reduction method. BACKGROUND

[0002] Silver nanoparticles (AgNPs) exhibit important application values in multiple fields due to their excellent physical and chemical properties, such as high specific surface area, excellent electrical conductivity and antibacterial properties. In the electronic industry, silver nanoparticles are widely used in the preparation of conductive ink and flexible electronic devices; in the biomedical field, their antibacterial and antiviral properties make them a research hotspot for drug delivery and wound healing materials; in the catalytic field, silver nanoparticles are used for environmental governance and energy conversion due to their high catalytic activity. In addition, with the rapid development of nanotechnology, the application of silver nanoparticles in optical sensors and surface-enhanced Raman scattering (SERS) has also attracted increasing attention. However, these applications have strict requirements for the size, morphology and dispersibility of silver nanoparticles, and therefore, how to efficiently and controllably prepare silver nanoparticles has become the focus of current research.

[0003] Currently, the preparation methods of silver nanoparticles mainly include physical method, chemical method and biological method. Physical methods such as evaporation-condensation method and laser ablation method can prepare high-purity particles, but the equipment is expensive and the yield is low, making it difficult to achieve large-scale production. Biological methods use microorganisms or plant extracts to reduce silver ions, which have the advantage of being green and environmentally friendly, but the reaction conditions are difficult to control, and the product batch difference is large, limiting its industrial application. In contrast, the chemical method, especially the chemical reduction method, has become the most commonly used preparation means in laboratories and industries due to its simple equipment, relatively low cost and easy control.

[0004] The basic principle of the chemical reduction method is to reduce silver ions (Ag + ) to silver atoms (Ag 0 ) by a reducing agent, and then aggregate into nanoparticles with the assistance of a stabilizer. Common reducing agents include sodium borohydride (NaBH4), hydrazine (N2H4), sodium citrate and vitamin C (ascorbic acid), while the stabilizer is usually polyvinylpyrrolidone (PVP), a surfactant (such as CTAB) or a polymer. The choice of these reagents directly affects the reaction rate, yield, and particle size and morphology. For example, sodium borohydride has strong reducing power and can quickly complete the reduction reaction, but its reaction is too violent and easily leads to excessive aggregation of particles, affecting dispersibility; hydrazine has moderate reducing power, but its toxicity is high and its use is limited; as a mild reducing agent, vitamin C is environmentally friendly, but its reduction efficiency is low and it is difficult to meet the demand for high yield. In terms of stabilizers, PVP prevents particle agglomeration through steric hindrance, but the selection of its amount and molecular weight needs to be optimized precisely, otherwise it may lead to uneven particle size distribution.

[0005] Although chemical reduction is widely used in silver nanoparticle preparation, there are still significant drawbacks in the prior art. First, the reaction efficiency is generally low. In traditional methods, the reduction of silver ions is often incomplete, leading to waste of raw materials and reduction of yield. For example, when sodium borohydride is used, although the reaction speed is fast, side reactions and particle aggregation reduce the proportion of effective products. Second, the complexity of the process increases the difficulty of operation. In order to achieve precise control of size and morphology, traditional methods usually require multi-step operations, such as stepwise addition of multiple reagents or adjustment of reaction conditions (temperature, pH value, stirring rate, etc.). These parameters are coupled with each other, and the optimization process is tedious and difficult to control independently, resulting in a wide particle size distribution (such as 10-50 nanometers), which cannot meet the needs of high-precision applications.

[0006] In addition, cost is an important factor limiting the large-scale production of silver nanoparticles. The use of expensive reducing agents (such as hydrazine) and stabilizers (such as high molecular weight PVP), as well as the complex process optimization process, significantly increases the production cost. In an industrial scenario, the use of multiple reagents not only increases the cost of raw materials, but also may introduce impurities, affecting the purity and performance of the product. If the process involves high temperature and high pressure conditions, it further increases energy consumption and equipment investment. For example, some methods require reactions in an autoclave, which not only increases the cost of equipment, but also prolongs the production cycle.

[0007] In view of these problems, researchers have made various improvement attempts. Green chemistry methods are a major research direction, such as using plant extracts (such as tea extract) as reducing agents, or using a single step method to simplify the process flow. However, these methods still face challenges: natural extracts have complex components, poor batch stability, and difficulty in achieving process repeatability; single-step methods, although simple to operate, often sacrifice the accuracy of size control, and the particle distribution is still not ideal. In addition, some studies introduce new stabilizers (such as functional polymers) or optimize reaction conditions to improve yield and quality, but these improvements often only address a particular problem and do not fully address the contradiction between efficiency, cost, and controllability.

[0008] In summary, the existing silver nanoparticle preparation technology still has deficiencies in reaction efficiency, process complexity, cost control, and size control, which limits its large-scale application in the fields of electronics, biomedicine, and catalysis. Therefore, it is urgent to develop a synthesis method that can achieve high yield, low cost, and precise size control under mild conditions. SUMMARY

[0009] The purpose of the present application is to overcome the defects of the prior art and provide a simple and efficient synthesis method for silver nanoparticles based on chemical reduction.

[0010] The technical solution of the present application is as follows:

[0011] A simple and efficient method for synthesizing silver nanoparticles based on chemical reduction method, comprising the following steps:

[0012] (1) mixing a water solution of soluble silver salt with a water solution of complexing agent to obtain a water solution of silver ion complex;

[0013] (2) adding a salt of hydroxyl carboxylic acid to the water solution of silver ion complex obtained in step (1);

[0014] (3) adjusting the pH of the material obtained in step (2) to 8.0-10.5 and reacting at 40-90℃ for 10-60 min;

[0015] (4) adjusting the pH of the material obtained in step (3) to 6.5-7.5 and reacting at 90-100℃ for 10-30 min;

[0016] (5) naturally cooling the material obtained in step (4) to room temperature, and sequentially performing centrifugation, deionized water washing, ethanol washing and drying to obtain the silver nanoparticles.

[0017] In a preferred embodiment of the present application, the soluble silver salt is selected from silver nitrate, silver acetate and silver chlorate.

[0018] In a preferred embodiment of the present application, the complexing agent is selected from ammonia, disodium ethylenediaminetetraacetate, triethanolamine, ethylenediamine and ethanolamine.

[0019] In a preferred embodiment of the present application, the salt of hydroxyl carboxylic acid is selected from potassium sodium tartrate, sodium citrate, sodium gluconate and sodium malate.

[0020] In a preferred embodiment of the present application, the soluble silver salt is silver nitrate, the complexing agent is ammonia or disodium ethylenediaminetetraacetate, and the salt of hydroxyl carboxylic acid is sodium citrate or sodium gluconate.

[0021] In a preferred embodiment of the present application, the pH in steps (3) and (4) is adjusted by NaOH or citric acid.

[0022] In a preferred embodiment of the present application, in the whole reaction system, the concentration of the soluble silver salt is 0.1-1 mol / L, the concentration of the complexing agent is 0.1-2 mol / L, and the concentration of the salt of hydroxyl carboxylic acid is 0.1-2 mol / L.

[0023] Further preferably, in the whole reaction system, the molar ratio of the complexing agent to Ag is 1-2:1, and the molar ratio of the salt of hydroxyl carboxylic acid to Ag is 0.5-2:1.

[0024] The silver nanoparticles prepared by the above-mentioned high-efficiency and simple silver nanoparticle synthesis method are applied to the preparation of silver conductive ink.

[0025] A silver conductive ink, raw materials of which include the silver nanoparticles prepared by the above-mentioned high-efficiency and simple silver nanoparticle synthesis method.

[0026] The present application has the following beneficial effects:

[0027] 1. By precisely controlling the reaction process in sections of pH, the present application improves the yield of silver nanoparticles to 44% to 97%, far exceeding the average level of traditional chemical reduction method. This is due to the efficient reduction of silver ions and the nucleation and growth process of particles, significantly improving the raw material utilization rate and production efficiency.

[0028] 2. By optimizing the pH value and reaction conditions, the present application can accurately control the particle size of silver nanoparticles in the range of 2 to 30 nanometers, with an average particle size of 5 to 10 nanometers and uniform distribution. This narrow particle size distribution feature makes it particularly suitable for applications sensitive to particle size, such as conductive ink and catalyst.

[0029] 3. The present application uses a single reducing agent and stabilizer (such as basic carbonate), avoiding the complexity of multi-reagent synergy in traditional methods, simplifying the operation steps, reducing the cost of reagents and the difficulty of process optimization. At the same time, the reaction is carried out under mild conditions of 60 to 100℃, without the need for high-pressure equipment, further reducing energy consumption and equipment investment.

[0030] 4. The present application discards the highly toxic reducing agent (such as hydrazine, sodium borohydride), uses green reagents and mild reaction conditions, reduces the potential harm to the environment and operating personnel, and meets the requirements of sustainable development.

[0031] 5. The silver nanoparticles prepared by the present application perform well in conductive ink, with the resistivity of the sintered coating being only 2 to 50 times that of bulk silver. This feature indicates that it has important application potential in the field of printed electronics and can be used to prepare high-performance flexible circuits and conductive coatings. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 TEM image (a) and particle size distribution diagram (b) of silver nanoparticles of Example 1 of the present application.

[0033] Figure 2 TEM image (a) and particle size distribution diagram (b) of silver nanoparticles of Example 2 of the present application.

[0034] Figure 3 TEM image (a) and particle size distribution diagram (b) of silver nanoparticles of Comparative Example 2 of the present application.

[0035] Figure 4TEM image (a) and particle size distribution (b) of silver nanoparticles of the present application comparative example 3. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are further described and explained in detail below by means of specific embodiments in conjunction with the accompanying drawings.

[0037] Example 1

[0038] (1) Dissolve 140.0 g of Na2EDTA·2H2O in 400 mL of deionized water, adjust the pH of the solution to 9.5, and continuously stir until the solution is clear to obtain solution A;

[0039] (2) Dissolve 51.0 g of silver nitrate in 50 mL of deionized water, continuously stir until the solution is clear, and add this concentrated solution to solution A, continuously stir until the solution is clear to obtain solution B (i.e. silver ion complex aqueous solution);

[0040] (3) Add 130.9 g of sodium gluconate to solution B, continuously stir until the solution is clear, and dilute to 500 mL to obtain solution C;

[0041] (4) Alkaline low temperature: adjust the pH of solution C to 9.5 with sodium hydroxide, react at 60°C for 30 min to obtain solution D;

[0042] (5) Neutral high temperature: adjust the pH of solution D to 6.5 with citric acid, react at 90°C for 30 min to obtain solution E;

[0043] (6) After solution E is naturally cooled to room temperature, it is washed with deionized water twice and ethanol once, and dried in a drying oven at 60°C for 1 h to obtain silver nanoparticles. The mass of the obtained silver nanoparticles is 30.9 g, the yield is 95.6%, the silver nanoparticles have a spherical morphology, the particle size distribution has a normal characteristic, the range is 3-13 nm, and the average particle size is 8.96 nm (as shown in FIG. 1). Figure 1

[0044] (7) Take 1 g of the prepared silver nanoparticles and add 1 mL of silver ion ink (KZ-Ag12, purchased from Kezhi Note Electronic Technology Co., Ltd., Chongqing), and stir uniformly to obtain silver conductive ink.

[0045] (8) Spread the silver conductive ink evenly on a glass sheet, place it in a 300°C oven for 1 h, and the final silver sintered coating has a resistivity of 15.7 μΩ·cm (9.8 times that of pure silver).

[0046] Example 2

[0047] ​(1) 5.6 mL of concentrated ammonia (28%) was added to 150 mL of deionized water, and the solution was stirred until it was clear, to obtain solution A;

[0048] (2) 6.8 g of silver nitrate was dissolved in 15 mL of deionized water, and the solution was stirred until it was clear, and the concentrated solution was added to solution A, and the solution was stirred until it was clear, to obtain solution B (i.e. silver ion complex aqueous solution);

[0049] (3) 6.19 g of sodium citrate was added to solution B, and the solution was stirred until it was clear, and the volume was adjusted to 200 mL to obtain solution C;

[0050] (4) Alkaline low temperature: the pH of solution C was adjusted to 8.0 with a citric acid solution (0.1 mol / L), and the solution was reacted at 70°C for 20 min to obtain solution D;

[0051] (5) Neutral high temperature: the pH of the above solution was adjusted to 7.5, and the solution was reacted at 100°C for 10 min;

[0052] (6) After solution E was naturally cooled to room temperature, it was washed with deionized water twice and ethanol once, and dried in a drying oven at 60°C for 1 h to obtain silver nanoparticles. The mass of the obtained silver nanoparticles was 4.1 g, the yield was 94.8%, the silver nanoparticles had a spherical morphology, the particle size distribution showed normal characteristics, the range was 2-16 nm, and the average particle size was 5.45 nm (as shown in Figure 2

[0053] (7) 1 g of the prepared silver nanoparticles was added to 1 mL of silver ion ink (KZ-Ag12, purchased from Kezhi Note Electronics Technology Co., Ltd.), and the mixture was stirred until it was uniform, to obtain silver conductive ink.

[0054] (8) The silver conductive ink was evenly spread on a glass sheet, and placed in a 300°C oven for 1 h. The final silver sintered coating had a resistivity of 67.8 μΩ·cm (42.3 times that of pure silver).

[0055] Comparative Examples 1-4

[0056] The TEM images of the silver nanoparticles obtained in Comparative Examples 2-3 are shown in Figure 3 and 4 respectively. The process was as in Examples 1 and 2. The test methods for all the comparative examples were the same as in Examples 1 and 2, and the specific process conditions and test results are shown in Table 1 below:

[0057] Table 1 Experimental conditions and results of Comparative Examples 1-4

[0058]

[0059] ​

[0060] It can be found from the above Comparative Examples 1 to 2 and Comparative Examples 3 to 4 that the temperature significantly affects the yield of silver nanoparticles, while the change of pH value has little effect thereon, the main reason being that the reduction ability of sodium citrate is enhanced with the increase of temperature, thus promoting the reduction reaction of silver ions and increasing the yield of silver nanoparticles.

[0061] It can be found from the above Comparative Examples 1 to 2 that with the increase of pH value (6.5→9.5), the particle size distribution range of silver nanoparticles becomes wider (2-6 nm→5-85 nm), the average particle size gradually increases (3.18→20.70 nm), and the particle size distribution gradually changes from single normal distribution to polydisperse abnormal distribution. Meanwhile, the alkaline environment induces obvious size differentiation and irregular morphology of the particles, which can be attributed to the difference in reduction kinetics of silver ions under alkaline conditions, the enhanced particle agglomeration effect and the enhanced reduction ability of sodium citrate. Therefore, the size and distribution of silver nanoparticles can be regulated by dynamically adjusting the pH and reaction temperature.

[0062] It can be found from the above Examples 1 to 2 and Comparative Examples 1 to 4 that the optimized synthesis process: the nucleation and growth processes of nanoparticles are optimized in stages. The nucleation density is controlled in the first stage (alkaline low temperature), and the particle growth is optimized in the second stage (neutral high temperature), so that silver nanoparticles with regular morphology and normal distribution of particle size can be obtained.

[0063] It can be found from the above Examples 1 to 2 and Comparative Examples 2 to 3 that the silver nanoparticles prepared in Examples 1 to 2 have regular morphology, uniform size and normal distribution, and the sintered coating resistivity of the silver conductive ink prepared therefrom is low; while the silver nanoparticles prepared in Comparative Example 3 have larger size distribution and average particle size, and in the sintering process of the silver conductive ink prepared therefrom, the packing density is reduced (porosity is increased), the sintering is uneven (neck connection is insufficient) and the percolation path is broken (contact points are reduced), thus the three synergistically increase the coating resistivity.

[0064] It can be found from the above Examples 1 to 2 and Comparative Example 2 that although the silver nanoparticles prepared in Comparative Example 2 have regular morphology, uniform size and normal distribution, the silver yield is low and the sintered coating resistivity of the silver conductive ink prepared therefrom is high, which is because although small particles are easy to form sintering necks, the neck size is limited by the original particle diameter, the narrow sintering neck increases the "bottleneck effect" of the electron transport path, and there can be more isolated island structures in the coating that are not completely connected, resulting in a decrease in the continuity of the conductive network.

[0065] The above merely describes preferred embodiments of the present application, and therefore cannot limit the scope of the present application, i.e. equivalent changes and modifications made according to the patent scope and content of the present application should still be within the scope of the present application.

Claims

1. A simple and efficient synthesis method of silver nanoparticles based on chemical reduction method, characterized in that: The method comprises the following steps: (1) mixing a water solution of soluble silver salt with a water solution of complexing agent to obtain a water solution of silver ion complex; (2) adding a salt of hydroxyl carboxylic acid to the water solution of silver ion complex obtained in step (1); (3) adjusting the pH of the material obtained in step (2) to 8.0-10.5 and reacting at 40-90℃ for 10-60 min; (4) adjusting the pH of the material obtained in step (3) to 6.5-7.5 and reacting at 90-100℃ for 10-30 min; (5) naturally cooling the material obtained in step (4) to room temperature, and then sequentially performing centrifugation, deionized water washing, ethanol washing and drying to obtain the silver nanoparticles.

2. The simple and efficient synthesis of silver nanoparticles as claimed in claim 1, wherein: The soluble silver salt is selected from silver nitrate, silver acetate and silver chlorate.

3. The simple and efficient synthesis of silver nanoparticles as claimed in claim 1, wherein: The complexing agent is selected from ammonia, disodium ethylenediaminetetraacetate, triethanolamine, ethylenediamine and ethanolamine.

4. The simple and efficient synthesis of silver nanoparticles as claimed in claim 1, wherein: The salt of hydroxyl carboxylic acid is selected from potassium sodium tartrate, sodium citrate, sodium gluconate and sodium malate.

5. The simple and efficient synthesis of silver nanoparticles as claimed in claim 1, wherein: The soluble silver salt is silver nitrate, the complexing agent is ammonia or disodium ethylenediaminetetraacetate, and the salt of hydroxyl carboxylic acid is sodium citrate or sodium gluconate.

6. The simple and efficient synthesis of silver nanoparticles as claimed in claim 1, wherein: NaOH or citric acid is used to adjust the pH in steps (3) and (4).

7. The efficient and simple synthesis method for silver nanoparticles according to any one of claims 1 to 6, characterized in that: In the whole reaction system, the concentration of the soluble silver salt is 0.1-1 mol / L, the concentration of the complexing agent is 0.1-2 mol / L, and the concentration of the salt of hydroxyl carboxylic acid is 0.1-2 mol / L.

8. The simple and efficient synthesis of silver nanoparticles as claimed in claim 7, wherein: In the whole reaction system, the molar ratio of the complexing agent to Ag is 1-2:1, and the molar ratio of the salt of hydroxyl carboxylic acid to Ag is 0.5-2:

1.

9. The silver nanoparticles prepared by the method for high-efficiency and simple synthesis of silver nanoparticles according to any one of claims 1 to 8 are used in the preparation of silver conductive ink.

10. A silver conductive ink characterized by: The raw materials comprise the silver nanoparticles prepared by the method for high-efficiency and simple synthesis of silver nanoparticles according to any one of claims 1 to 8.

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