Preparation method of controllable particle size nanosilver

Abstract

The application provides a controllable particle size nano-silver preparation method, comprising the following steps: preparing a silver ammonia solution, mixing the silver ammonia solution with a dispersing agent to prepare A liquid, the amount of the dispersing agent being determined based on the target nano-silver particle size; adding the A liquid into heated ethylene glycol maintained at a first preset temperature to generate nano-silver; and performing solid-liquid separation, washing and drying on the nano-silver to obtain nano-silver powder with the target particle size; wherein the first preset temperature is set to make the dispersing agent and the ethylene glycol jointly play a reduction role. Through a large number of experiments, it is found that the average particle size y of the nano-silver and the input amount parameter x of the dispersing agent conform to a functional relationship. In the case of a certain total silver amount, the silver atoms allocated to a single crystal nucleus become less, and a high concentration of the dispersing agent can inhibit the further growth of the crystal, so that nano-particles with a smaller particle size are obtained. By using the linear correlation model, the digital and accurate customization of the average particle size of the nano-silver can be realized within a certain range.

Description

Technical Field

[0001] This application relates to the field of novel silver powder preparation, and more specifically, to a method for preparing nano-silver with controllable particle size. Background Technology

[0002] As one of the most important precious metal nanomaterials, silver nanoparticles possess excellent conductivity, antibacterial activity, and catalytic properties, making them promising for applications in cutting-edge fields such as flexible electronics, conductive inks, biomedicine, and high-efficiency catalysts. It is well known that the performance of nanomaterials is strongly dependent on their size and morphology; for silver nanoparticles, precise control of particle size is crucial to their final application performance. For example, in electronic packaging, silver nanoparticles with specific small particle sizes are required to achieve low-temperature sintering; while in certain sensor and catalytic applications, particle sizes within a specific range are required to optimize performance. Therefore, developing a preparation technology capable of precisely controlling the particle size of silver nanoparticles has become a core issue driving its high-end applications.

[0003] In the electronics and microelectronics industry, nano-silver powder is a core raw material for preparing high-end conductive pastes and conductive inks. With the rapid development of flexible electronics, printed electronics, wearable devices, and the photovoltaic industry, the market demand for high-performance nano-silver powder capable of high-resolution printing and low-temperature or room-temperature sintering has surged. Its particle size and dispersibility directly determine the precision, conductivity, and reliability of conductive circuits, making it a key material for achieving miniaturization and flexibility of electronic devices. In the medical and biotechnology fields, the excellent broad-spectrum antibacterial properties and biocompatibility of nano-silver powder make it the preferred choice for high-end medical dressings, antibacterial textiles, surface coatings for medical devices, and drug carriers. The increasing global emphasis on health and hygiene continues to drive the expansion of the antibacterial nano-silver market, and precise particle size control is a core parameter for regulating its antibacterial efficiency and biosafety. In the fields of green energy and catalysis, nano-silver powder, as a highly efficient catalyst, plays an irreplaceable role in fuel cells, exhaust gas treatment, fine chemical synthesis, and environmental pollution control. Its catalytic activity and selectivity are highly dependent on particle size and morphology; precise particle size control provides the possibility for developing next-generation high-efficiency, low-cost catalysts.

[0004] Currently, chemical reduction is the most commonly used method for preparing nano-silver powder. However, existing technologies, especially those geared towards industrial production, still face significant challenges in achieving precise and reproducible control over particle size. First, the inherently high surface energy of silver particles makes them prone to aggregation and uncontrolled growth during synthesis, resulting in a wide particle size distribution, irregular morphology, and poor batch-to-batch consistency. Second, existing control methods are often relatively simple, with most relying on crude control through changes in single variables such as reducing agent concentration or reaction temperature, lacking coordinated and precise management of both nucleation and growth stages, leading to a narrow particle size control range and low precision. Furthermore, some methods employ strong reducing agents or extreme pH conditions, which, while yielding nanoparticles, easily introduce impurities, cause environmental pollution, or increase subsequent purification costs, failing to meet the requirements of green and sustainable industrial production. Summary of the Invention

[0005] This application provides a method for preparing silver nanoparticles with controllable particle size, which can produce silver nanoparticles with a specified particle size.

[0006] Specifically, this application is implemented through the following technical solution: This application provides a method for preparing silver nanoparticles with controllable particle size, comprising the following steps: S1. Prepare a silver ammonia solution and mix it with a dispersant to form solution A. The amount of the dispersant is determined based on the target silver nanoparticle size. S2. While heating ethylene glycol and maintaining it at a first preset temperature, liquid A is added to generate nano-silver. S3. Separate the solid and liquid phases of the nano-silver, wash and dry them to obtain nano-silver powder with the target particle size; The first preset temperature is set to allow the dispersant and ethylene glycol to work together to reduce the temperature.

[0007] Optionally, the first preset temperature is 178℃-182℃.

[0008] Optionally, in step S1, after preparing liquid A, the liquid A is heated to a second preset temperature; In step S2, after the ethylene glycol is heated to a third preset temperature and stabilized, the A liquid is added while the ethylene glycol is heated to a first preset temperature. The second preset temperature is less than the third preset temperature, and the third preset temperature is less than the first preset temperature.

[0009] Optionally, the second preset temperature is 55℃-65℃, and the third preset temperature is greater than or equal to 130℃ and less than 175℃.

[0010] Optionally, in step S2, liquid A is added at a first rate, wherein the temperature fluctuation of the reaction system does not exceed 10°C during the addition of liquid A; and / or After adding liquid A in step S2, continue stirring for a total reaction time of 25-35 minutes.

[0011] Optionally, in step S1, liquid A further includes water as a solvent; The amount of ethylene glycol used is 200% of the amount of water used in solution A.

[0012] Optionally, the dispersant includes one or more of polycarboxylate ethers, ammonium polyacrylate, sodium polyacrylate, and polyacrylic acid.

[0013] Optionally, the dispersant comprises 3%-16% of the total mass of the entire reaction system.

[0014] Optionally, step S3 includes: completing the solid-liquid separation by centrifugal concentration, and washing with water and ethanol alternately; After washing, the moistened nano-silver was freeze-dried.

[0015] This application provides a method for preparing silver nanoparticles with controllable particle size. The technical effects of the preparation method provided by this application include at least the following: At specific high temperatures, ethylene glycol is oxidized to glyoxal / glyoxylic acid, releasing electrons and exhibiting reducing properties. Simultaneously, this application discovered that the selected dispersants, such as polyacrylates, under high temperature and the alkaline environment provided by silver ammonia solution, exhibit strong coordination between electron-rich groups such as carboxylate groups on their molecular chains and silver ammonia complex ions. This coordination not only stabilizes the silver precursor, but more importantly, under high-temperature excitation, these functional groups can assist ethylene glycol in electron transfer, thus exhibiting a mild auxiliary reducing property. This mild reducing environment avoids the explosive and uncontrollable nucleation caused by strong reducing agents, providing a thermodynamic basis for precise particle size control.

[0016] This application, through extensive experiments, reveals that the average particle size y of silver nanoparticles follows a linear functional relationship with the dispersant dosage parameter x: y = -1.95x + 145.65. Increasing the dispersant concentration effectively increases the density of effective coating centers and auxiliary reduction points in the system. More dispersant leads to a greater number of initial crystal nuclei induced during nucleation. With a fixed total silver content, fewer silver atoms are allocated to each individual crystal nucleus, and the high concentration of dispersant inhibits further crystal growth, resulting in smaller nanoparticles. Using this linear correlation model, the average particle size of silver nanoparticles can be precisely customized digitally within a certain range. Attached Figure Description

[0017] Figure 1 These are SEM images of the nano-silver powder prepared in Example 1; Figure 2 These are SEM images of the silver nanopowder prepared in Example 2; Figure 3 These are SEM images of the silver nanopowder prepared in Example 3; Figure 4 Here are SEM images of the silver nanopowder prepared in Example 4; Figure 5 The image shows a SEM image of the silver powder prepared in Comparative Example 1. Figure 6 The image shows a SEM image of the silver powder prepared in Comparative Example 2. Figure 7 These are the ultraviolet spectrophotometer test data from Examples 1 to 4; Figure 8 It is a graph showing the fitted data of particle size and dispersant dosage. Detailed Implementation

[0018] The technical solution of the present invention will be explained in detail below with reference to several representative embodiments.

[0019] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available.

[0020] To address the problems in the background technology, this application provides a method for preparing silver nanoparticles with controllable particle size, comprising the following steps: S1. Prepare a silver ammonia solution and mix it with a dispersant to form solution A. The amount of dispersant is determined based on the target silver nanoparticle size. S2. While heating ethylene glycol and maintaining it at a first preset temperature, add solution A to generate silver nanoparticles. S3. Separate the solid and liquid components of the silver nanoparticles, wash and dry them to obtain silver nanoparticle powder of the target particle size. The first preset temperature is set to allow the dispersant and ethylene glycol to work together to reduce the silver nanoparticles. The silver ammonia solution here is prepared from saturated silver nitrate at room temperature, such as 25°C.

[0021] At specific high temperatures, such as 178℃-182℃, ethylene glycol is oxidized to glyoxal / glyoxylic acid and releases electrons, exhibiting reducing properties. Meanwhile, this application found that the selected dispersants, such as polyacrylates, have carboxylate (-COO-) groups as core active groups on their molecular chains. Under high temperature and the alkaline environment provided by silver ammonia solution, the oxygen atoms of the carboxylate group are electron-rich and can attract silver ammonia complex ions ([Ag(NH3)2)). + Slowly transfer electrons, transferring some Ag + Restored to Ag 0Atoms. Because the reducing power of carboxylate ions is weaker than that of ethylene glycol, the reduction reaction is mainly dominated by ethylene glycol. The auxiliary reducing effect of the dispersant only plays a role in the initial nucleation stage of the reaction, inducing the formation of a large number of uniform initial nuclei, without causing the explosive nucleation commonly seen with strong reducing agents.

[0022] refer to Figure 7 Through extensive experiments, this application has discovered that, under the experimental conditions of the embodiments of this application, the average particle size y of silver nanoparticles conforms to a linear functional relationship with the dispersant dosage parameter x: y = -1.95x + 145.65. This verifies that a linear correlation can be formed between the dispersant and the particle size. With a fixed total silver content, increasing the amount of dispersant will simultaneously increase the number of effective active sites in the system, i.e., the number of carboxylate ions. The more active sites there are, the more initial crystal nuclei are generated in the early stages of the reaction, and the fewer silver atoms can be allocated to each individual crystal nucleus; simultaneously, a higher concentration of dispersant provides stronger steric hindrance, more effectively inhibiting the growth of crystal nuclei. Since the number of active sites is linearly positively correlated with the amount of dispersant, and the nucleation and growth behavior of each active site is highly consistent, the average particle size of silver nanoparticles exhibits a strictly linearly negative correlation with the amount of dispersant. Using this linear correlation model, digitally precise customization of the average particle size of silver nanoparticles within the range of 50nm to 120nm can be achieved.

[0023] In one embodiment, the first preset temperature is 178°C-182°C. Preferably, it is 180°C, as this temperature range is the key window for activating the synergistic reducing activity of ethylene glycol and the dispersant. The high temperature of around 180°C ensures that the reduction reaction proceeds at a stable and continuous rate. If the temperature is too low, insufficient reducing power will lead to low conversion rate and uneven particle size; if the temperature is too high, the reaction will be too vigorous, easily producing precipitation or coarse crystals.

[0024] In one embodiment, in step S1, after preparing liquid A, the liquid A is heated to a second preset temperature; in step S2, after the ethylene glycol is heated to a third preset temperature and stabilized, the liquid A is added while the ethylene glycol is heated to a first preset temperature; wherein the second preset temperature is lower than the third preset temperature, and the third preset temperature is lower than the first preset temperature.

[0025] In another embodiment, the second preset temperature is 55°C-65°C, and the third preset temperature is greater than or equal to 130°C and less than 175°C.

[0026] In step S1, after preparing solution A, the solution A is heated to a second preset temperature, 55℃-65℃, preferably 60℃. In step S2, the ethylene glycol is heated to a third preset temperature, 130℃-175℃, preferably 150℃, and after stabilization, solution A is added while continuing to heat to the first preset temperature. Preparing the silver ammonia solution at room temperature reduces ammonia leakage and environmental pollution. Preheating to 60℃ improves its chemical activity and shortens the temperature rise lag time after entering the reaction substrate. Pumping solution A in while preheating the ethylene glycol substrate to 150℃ and continuing to heat it utilizes the system's heating inertia, allowing the reaction to start in dynamic thermal equilibrium, greatly reducing the uneven local nucleation caused by temperature shock. The heating method here can be an oil bath; controlling the oil bath temperature controls the overall temperature.

[0027] In one embodiment, in step S2, liquid A is added at a first rate, which is set such that the temperature fluctuation of the reaction system does not exceed 10°C during the addition of liquid A; and / or after adding liquid A in step S2, stirring is continued, with a total reaction time of 25-35 minutes. Rate-controlled feeding can be achieved by precisely controlling the feed rate using a peristaltic pump, ensuring minimal temperature fluctuation in the reaction system, ≤10°C. This constant temperature field is crucial for maintaining the consistency of the reduction reaction rate and is a physical prerequisite for ensuring that the particle size conforms to the linear fitting formula y=-1.95x+145.65. A reaction time of approximately 30 minutes ensures complete reduction of silver ions, improving the yield, while simultaneously allowing sufficient time for surface remodeling of the nanoparticles, resulting in a more regular spherical morphology and preventing impurities.

[0028] In one embodiment, in step S1, solution A further includes water as a solvent; the amount of ethylene glycol used is 200% of the amount of water used in solution A. If the amount is too low, the system is mainly water, the boiling point is insufficient, and it is difficult to maintain a stable high-temperature reaction window of 178-182°C, resulting in incomplete or uneven reduction reaction. If the amount is too high, the system is too viscous, the diffusion of substances is hindered, not only slowing down the reaction rate, but also causing uneven crystal nucleus formation and agglomeration, disrupting the precise control of particle size.

[0029] In one embodiment, the dispersant comprises one or more selected from polycarboxylate ethers, ammonium polyacrylate, sodium polyacrylate, and polyacrylic acid. These preferred dispersants exhibit excellent chemical stability and extremely strong functional group activity under high-temperature alkaline conditions.

[0030] In one embodiment, the dispersant comprises 3%-16% of the total mass of the reaction system. Within this range, the dispersant concentration exhibits a negative correlation with particle size, thus covering a wide range of application needs, from finely milled conductive inks to large-particle-size general shielding coatings.

[0031] In one embodiment, step S3 includes: solid-liquid separation by centrifugal concentration, followed by alternating washing with water and ethanol; and then freeze-drying the moistened nano-silver. Alternating washing effectively removes excess organic components and byproducts adhering to the particle surface. Freeze-drying is used because nano-silver powder is highly prone to hard agglomeration; during ordinary heating and drying, the capillary force generated by water evaporation forcibly pulls the particles together. Freeze-drying directly removes the solvent through ice crystal sublimation, maximizing the preservation of the dispersed state at the reaction endpoint and ensuring the fragility and excellent redispersibility of the finished powder.

[0032] Examples and Comparative Examples Example 1 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 50 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0033] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0034] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0035] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0036] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0037] Example 2 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 40 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0038] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0039] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0040] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0041] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0042] Example 3 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 30 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0043] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0044] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0045] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0046] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0047] Example 4 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 10 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0048] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0049] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0050] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0051] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0052] Comparative Example 1 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 5 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0053] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0054] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0055] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0056] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0057] Comparative Example 2 according to Figure 7 The calculation of particle size versus dispersant dosage using fitted data and graphs shows that if the target powder D50 is 110 nm, the dispersant dosage is approximately 18.3 g. Experiments were conducted based on this. 1) Solution preparation Solution A: At room temperature, dissolve silver nitrate in 50 ml of stirred aqueous solution until saturated. Add ammonia dropwise and wait for the solution to clarify to obtain a silver ammonia solution. Heat the solution to 60 degrees Celsius and add 18.3 g of sodium polyacrylate. After the temperature stabilizes and all solutes have dissolved, keep it at this temperature and allow it to stand.

[0058] Solution B: Place 100 ml of ethylene glycol in a flask, stir mechanically, and heat it in an oil bath to 150 degrees Celsius, then wait for the temperature to stabilize.

[0059] 2) Mixed reaction Set the oil bath temperature of solution B to 180 degrees Celsius and monitor the temperature. During the heating process, start pumping solution A in using a peristaltic pump. Stop heating when the temperature reaches 180 degrees Celsius, and control the total reaction time to 30 minutes.

[0060] 3) Centrifugal washing After the temperature drops to room temperature, dilute with water and concentrate by centrifugation. Wash with a mixture of water and ethanol alternately three times to remove the dispersant and ethylene glycol from the nano-silver.

[0061] Moistened silver nanoparticles were freeze-dried, then crushed and sieved to obtain well-dispersed silver nanoparticles.

[0062] Table 1. Silver powder data for the examples and comparative examples. Combination Figures 1 to 6 And Table 1, Figure 1 This is a SEM image of the nano-silver powder prepared in Example 1. Figure 2 This is a SEM image of the silver nanopowder prepared in Example 2. Figure 3 This is a SEM image of the silver nanopowder prepared in Example 3. Figure 4 This is a SEM image of the nano-silver powder prepared in Example 4. Figure 5 This is a SEM image of the silver powder prepared in Comparative Example 1. Figure 6 This is a SEM image of the silver powder prepared in Comparative Example 2. Comparative Example 1 is silver nanoparticles with a very small amount of dispersant added. Comparative Example 2 is based on... Figure 8 The calculation is based on the fitting data image of particle size and dispersant dosage. If the target powder D50 is 110nm, the dispersant dosage is approximately 18.3g. (Refer to Table 1...) Figure 6 and Figure 8 Based on this, an experiment was conducted. After the experiment, the D50 of the nanosilver was 109.8 nm, which is very close to the predicted data and conforms to the linear relationship of the fitting formula. Figure 8 It is a graph showing the fitted data of particle size and dispersant dosage.

[0063] like Figures 1 to 4This is a nano-silver powder prepared by the method of this application. The nano-silver powder has a narrow distribution, good dispersibility, and a smooth surface. Strong reducing agents, such as sodium borohydride and hydrazine hydrate, can cause instantaneous explosive nucleation, generating a large number of tiny crystal nuclei. These nuclei do not have enough time to rearrange their surface atoms, easily forming irregular morphologies and rough surfaces. In contrast, in this system, the reduction reaction proceeds at a stable and continuous rate, allowing sufficient time for the crystal nuclei to arrange their surface atoms in an orderly manner. Therefore, the generated nano-silver particles are regularly spherical with smooth surfaces. Figures 1 to 4 As shown in the figure. This further proves that the reducing environment of this system is mild, which is conducive to the precise control of particle size.

[0064] Combination Figure 7 ,in Figure 7 These are the ultraviolet spectrophotometer test data from Examples 1 to 4. The surface plasmon resonance effect of metallic silver nanoparticles causes them to exhibit characteristic absorption peaks in the ultraviolet-visible spectral region. The position of these absorption peaks is directly related to the particle size; that is, as the particle size increases, the absorption peak red-shifts towards longer wavelengths, a trend already confirmed by existing technology. The median particle size D measured by the laser particle size analyzer... 50 As the particle size increases from 53.2 nm to 120.9 nm, the characteristic peak position of its UV-Vis absorption spectrum simultaneously redshifts from 415 nm to 442 nm, exhibiting a monotonic redshift trend. This is consistent with the particle size-peak position correspondence revealed by existing technologies, proving that there is a good correspondence between the particle size and absorption peak position of the silver powder in this application. Combined with direct verification of the actual particle morphology by electron microscopy, it can be fully confirmed that the silver powder prepared in this application has controllable particle size, good dispersibility, and reliable consistency between spectral data and particle size data.

[0065] Combination Figure 5 Comparative Example 1 is a nano-silver powder with a very small amount of dispersant added. The very small amount of dispersant cannot effectively coat the nano-silver, and cannot limit the phase selectivity of silver crystal growth during the reaction process, resulting in the formation of a large number of rod-shaped nano-silver during the reaction. Statistical analysis showed that the particle size distribution of Comparative Example 1 was wider, and the particle size of Comparative Example 1 was more uneven, as can be seen from the SEM image.

[0066] It should be noted that the technical solutions or features described in the above embodiments can be combined or complemented each other without conflict. The scope of protection of this application is not limited to the precise structure described in the above embodiments; all modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing silver nanoparticles with controllable particle size, characterized in that, Includes the following steps: S1. Prepare a silver ammonia solution and mix it with a dispersant to form solution A. The amount of the dispersant is determined based on the target silver nanoparticle size. S2. While heating ethylene glycol and maintaining it at a first preset temperature, liquid A is added to generate nano-silver. S3. Separate the solid and liquid phases of the nano-silver, wash and dry them to obtain nano-silver powder with the target particle size; The first preset temperature is set to allow the dispersant and ethylene glycol to work together to reduce the temperature.

2. The method for preparing controllable particle size silver nanoparticles as described in claim 1, characterized in that, The first preset temperature is 178℃-182℃.

3. The method for preparing controllable particle size silver nanoparticles as described in claim 2, characterized in that, In step S1, after preparing liquid A, the liquid A is heated to a second preset temperature; In step S2, after the ethylene glycol is heated to a third preset temperature and stabilized, the A liquid is added while the ethylene glycol is heated to a first preset temperature. The second preset temperature is less than the third preset temperature, and the third preset temperature is less than the first preset temperature.

4. The method for preparing controllable particle size silver nanoparticles as described in claim 3, characterized in that, The second preset temperature is 55℃-65℃, and the third preset temperature is greater than or equal to 130℃ and less than 175℃.

5. The method for preparing controllable particle size silver nanoparticles as described in claim 3, characterized in that, In step S2, liquid A is added at a first rate, wherein the temperature fluctuation of the reaction system during the addition of liquid A does not exceed 10°C; and / or After adding liquid A in step S2, continue stirring for a total reaction time of 25-35 minutes.

6. The method for preparing controllable particle size silver nanoparticles as described in claim 1, characterized in that, In step S1, liquid A further includes water as a solvent; The amount of ethylene glycol used is 200% of the amount of water used in solution A.

7. The method for preparing controllable particle size silver nanoparticles as described in claim 1, characterized in that, The dispersant includes one or more of polycarboxylate ether, ammonium polyacrylate, sodium polyacrylate, and polyacrylic acid.

8. The method for preparing controllable particle size silver nanoparticles as described in claim 7, characterized in that, The dispersant accounts for 3%-16% of the total mass of the entire reaction system.

9. The method for preparing controllable particle size silver nanoparticles as described in claim 1, characterized in that, Step S3 includes: completing the solid-liquid separation by centrifugation concentration, and washing with water and ethanol alternately; After washing, the moistened nano-silver was freeze-dried.

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