Spherical silver nanoparticles and a method for preparing the same

Abstract

This invention provides spherical silver nanoparticles and their preparation method, belonging to the field of metal nanomaterial synthesis technology. By using a stepwise dropwise addition and controlling key parameters such as dropwise acceleration, reaction temperature, and reaction time, this invention achieves effective, stable, and controllable preparation of the average particle size and morphology of silver nanoparticles using the simplest raw material system. The prepared silver nanoparticles are spherical, offering advantages such as controllable morphology, simple process, and high product purity.

Description

Technical Field

[0001] This invention belongs to the field of metal nanomaterial synthesis technology, specifically relating to a spherical silver nanoparticle and its preparation method. Background Technology

[0002] Nanomaterials, due to their unique quantum size effect, small size effect, surface effect, and macroscopic quantum tunneling effect, show broad application prospects in optics, electronics, catalysis, and biomedicine. Among them, silver nanoparticles not only possess excellent conductivity and antibacterial properties but also have unique surface plasmon resonance characteristics, and are widely used in high-performance electronic pastes, flexible transparent conductive films, surface-enhanced Raman scattering substrates, and chemical catalysts.

[0003] In practical applications, the morphology and size of silver nanoparticles are key factors determining their final performance. Studies have shown that spherical or near-spherical silver nanoparticles, due to their isotropic geometry, offer significant advantages in achieving close packing, reducing sintering temperature, and realizing uniform optical response. For example, in electronic pastes, near-spherical silver nanoparticles help improve filling density and the uniformity of conductive pathways; in optical sensing, uniformly sized silver nanospheres can generate stable localized surface plasmon resonance signals. Therefore, developing a method for stably preparing spherical or near-spherical silver nanoparticles with regular morphology, uniform particle size, and good dispersibility has significant application value.

[0004] The synthesis of silver nanoparticles via polyol synthesis has become a research hotspot in the field of nanomaterial preparation due to its advantages such as simple process, relatively low cost, and high tunability of product morphology. The core principle of this method lies in utilizing the dual function of polyols (such as ethylene glycol) as solvents and reducing agents at high temperatures to reduce silver sources (such as silver nitrate) to silver atoms. Under the guidance of dispersants (such as polyvinylpyrrolidone, PVP), the nucleation and growth process of crystals is controlled, ultimately obtaining silver nanostructures with different morphologies and sizes. Studies have shown that by controlling reaction parameters, such as reaction temperature, precursor concentration, reaction time, and the type and dosage of control agents, the controllable preparation of various products, from zero-dimensional silver nanoparticles to one-dimensional silver nanorods and silver nanowires, can be achieved. For example, when potassium chloride is used as a control agent, one-dimensional silver nanorods tend to be generated; while when anhydrous sodium sulfate is used as a control agent, silver nanoparticles with particle sizes in the range of 200–500 nm can be obtained. In addition, the heating method and mixing state of the reaction system also have a significant impact on the uniformity and yield of the product. The introduction of new technologies such as continuous flow reactors further demonstrates the potential to improve synthesis efficiency and controllability.

[0005] Chinese patent application CN115945695A discloses a method for preparing silver nanoparticles using a polyol reduction method controlled by quinone compounds. This technical solution introduces quinone compounds as morphology modifiers to prepare silver nanomaterials with specific morphologies in a one-pot process. Specifically, a raw material solution is prepared by mixing quinone compounds, poly(N-vinylpyrrolidone), a silver source, additives, and a polyol compound in a specific ratio, followed by a reduction reaction at 110–180°C. The final product of this method is right-angled triangular bipyramidal silver nanoparticles and / or pentagonal silver nanorods. The advantages of this technical solution are its relatively simple operation, its attempt to solve the problem of difficult morphology control of silver nanomaterials by introducing quinone compounds, and its claimed high preparation efficiency.

[0006] However, the existing technical solutions described above still have the following main drawbacks: First, their target products are mainly right-angled triangular bipyramidal particles and pentagonal rods, limiting their applicability and controllability for the preparation of more widely used, uniformly sized spherical or near-spherical silver nanoparticles. Second, this method relies on quinone compounds as key morphology control agents, which may be costly or have certain biotoxicity, increasing raw material costs and the complexity of subsequent processing. Third, the reaction system contains many components with a wide ratio range, and precise control in actual operation to obtain highly monodisperse, uniformly sized silver nanoparticles remains a challenge. The product may contain multiple morphologies, affecting its purity and application performance.

[0007] Therefore, developing a simpler, lower-cost, and more easily scalable method for producing high-purity, uniformly sized silver nanoparticles remains a pressing technical problem to be solved in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this application achieves effective, stable, and controllable preparation of silver nanoparticles with the simplest raw material system by stepwise dropwise addition and control of key parameters.

[0009] The technical solution provided in this application is as follows: A method for preparing spherical silver nanoparticles includes the following steps: S1. Preparation of solution A: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare the first silver nitrate solution, add metal chloride salt solution to it, mix well, and sonicate. S2. Prepare solution B: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare a second silver nitrate solution, mix thoroughly, and sonicate. S3. Add the ethylene glycol solution of polyvinylpyrrolidone to the reaction vessel and heat it to the reaction temperature under stirring and reflux; quickly add solution A to the reaction vessel and react for 1-5 minutes. S4. Add solution B dropwise to the reaction vessel. After the addition is complete, turn off the stirring and continue the reaction for 1-5 minutes. S5. After the reaction is complete, the mother liquor is cooled to room temperature and centrifuged and washed to obtain the spherical silver nanoparticles.

[0010] Furthermore, the concentration of the first silver nitrate solution is 0.0025-0.05 g / mL.

[0011] In a preferred embodiment, the concentration of the first silver nitrate solution is 0.01-0.02 g / mL.

[0012] Furthermore, the metal chloride salt includes, but is not limited to, at least one of sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), strontium chloride (SrCl2), barium chloride (BaCl2), copper chloride (CuCl2), and ferric chloride (FeCl3).

[0013] In a preferred embodiment, the metal chloride salt is sodium chloride and / or potassium chloride.

[0014] Furthermore, the concentration of the metal chloride solution is 0.02-0.1 mol / L.

[0015] Furthermore, Ag in solution A + With Cl - The molar ratio is 3-20:1.

[0016] Furthermore, the volume ratio of the first silver nitrate solution to the metal chloride solution is 8-40:1-4.

[0017] Furthermore, the concentration of the second silver nitrate solution is 0.002-0.05 g / mL.

[0018] Furthermore, the ultrasonic frequency in S1 and S2 is 10-100Hz, the ultrasonic time is 2-40min, and the ultrasonic temperature is 25-50℃.

[0019] Furthermore, the average molecular weight of the polyvinylpyrrolidone is 3,500-1,300,000.

[0020] Furthermore, the concentration of the ethylene glycol solution of polyvinylpyrrolidone is 0.002-0.16 g / mL.

[0021] Furthermore, the reaction temperature in S3 is 90-150℃, preferably 90-120℃; the stirring speed is 100-600rpm, preferably 200-300rpm.

[0022] Furthermore, the dropping rate of liquid A is less than that of liquid B.

[0023] Furthermore, the dropping rate of solution A is 10-60 mL / min.

[0024] Furthermore, the dropping rate of solution B is 2-25 mL / min.

[0025] Furthermore, the centrifugal washing speed of S5 is 4000-12000 rpm.

[0026] Furthermore, the volume ratio of the first silver nitrate solution, the second silver nitrate solution, and the ethylene glycol solution of polyvinylpyrrolidone is 8-40:60-260:50-480.

[0027] A type of spherical silver nanoparticle, prepared by the aforementioned method, has a particle diameter distribution range of 30-1200 nm, preferably 30-660 nm, and more preferably 30-300 nm.

[0028] The beneficial effects of this invention are: (1) This application uses a step-by-step injection process, that is, firstly rapidly injecting liquid A to achieve explosive nucleation of crystal nuclei, and then precisely controlling the slow dripping acceleration rate of liquid B to regulate the crystal growth rate, combined with trace amounts of Cl - By leveraging the crystal-plane selective adsorption of polyvinylpyrrolidone (PVP) with a specific molecular weight and the steric hindrance effect, the optimal growth of silver nanoparticles was successfully achieved, yielding high-purity, near-spherical silver nanoparticles with uniform particle size and excellent dispersibility. This technique effectively suppresses the formation of byproducts such as silver nanowires and multi-branched structures, overcoming the technical bottlenecks of narrow morphology control windows and mixed product morphologies in traditional methods, and providing a new path for accurately constructing target morphologies.

[0029] (2) This application adopts a low-temperature (≤120℃) reaction system under normal pressure, which does not require inert atmosphere protection or complex high-temperature and high-pressure equipment. By optimizing the reaction kinetic conditions, the complexity of the process and energy consumption are significantly reduced. The synergistic design of step-injection process and mild reaction conditions not only simplifies the operation process, but also provides a technical basis for industrial continuous production.

[0030] (3) This application effectively removes residual PVP dispersant, inorganic salt byproducts and unreacted precursors from the reaction system by centrifugation and washing. The resulting spherical silver nanoparticles have a clean and residue-free surface with high surface purity. Attached Figure Description

[0031] Figure 1 SEM image of silver nanoparticles in Example 1.

[0032] Figure 2 SEM image of silver nanoparticles in Example 2.

[0033] Figure 3 SEM image of silver nanoparticles in Example 6.

[0034] Figure 4 SEM image of silver nanoparticles in Example 7.

[0035] Figure 5 SEM image of silver nanoparticles in Example 8.

[0036] Figure 6 SEM image of silver nanoparticles in Example 12. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0038] This application provides a method for preparing spherical silver nanoparticles, comprising the following steps: S1. Preparation of solution A: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare the first silver nitrate solution, add metal chloride salt solution to it, mix well, and sonicate. S2. Prepare solution B: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare a second silver nitrate solution, mix thoroughly, and sonicate. S3. Add the ethylene glycol solution of polyvinylpyrrolidone to the reaction vessel and heat it to the reaction temperature under stirring and reflux; quickly add solution A to the reaction vessel and react for 1-5 minutes. S4. Add solution B dropwise to the reaction vessel. After the addition is complete, turn off the stirring and continue the reaction for 1-5 minutes. S5. After the reaction is complete, the mother liquor is cooled to room temperature and centrifuged and washed to obtain the spherical silver nanoparticles.

[0039] In step S3, solution A is rapidly added, causing the high concentration of silver ions to be quickly reduced. This rapidly increases the supersaturation of the system beyond the critical value for homogeneous nucleation, resulting in a large number of crystal nuclei forming simultaneously within a short period. This ensures that all crystal nuclei are generated almost simultaneously, with very similar initial sizes. In step S4, solution B is slowly added dropwise, maintaining the concentration of silver ions in the reaction system below the growth critical value but above the nucleation critical value. This ensures that the reduced silver atoms only deposit on existing crystal seed nuclei and do not trigger new nucleation. The reaction time of 1-5 minutes is crucial for the formation and stabilization of the first batch of crystal nuclei. If solution B is added too early, the seed nuclei are not yet stable; if added too late, the seed nuclei may have already begun to aggregate or grow. Furthermore, if all the silver nitrate is added at once instead of in stages, nucleation will occur rapidly at the high concentration of silver nitrate in the initial stage of the reaction. However, as the reaction progresses, particles with extremely wide size distributions may be obtained, and even irregular morphologies such as rods or triangles may appear.

[0040] Furthermore, the concentration of the first silver nitrate solution is 0.0025-0.05 g / mL, preferably 0.005-0.04 g / mL, and more preferably 0.008-0.03 g / mL.

[0041] In a preferred embodiment, the concentration of the first silver nitrate solution is 0.01-0.02 g / mL.

[0042] Furthermore, the metal chloride salt includes, but is not limited to, at least one of sodium chloride (NaCl), potassium chloride (KCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), strontium chloride (SrCl2), barium chloride (BaCl2), copper chloride (CuCl2), and ferric chloride (FeCl3).

[0043] In a preferred embodiment, the metal chloride salt is sodium chloride and / or potassium chloride.

[0044] Furthermore, the concentration of the metal chloride solution is 0.02-0.1 mol / L, preferably 0.05-0.07 mol / L.

[0045] Furthermore, Ag in solution A + With Cl - The molar ratio is 3-20:1, preferably 10-15:1. If Cl - More free Ag + If the concentration is too low, the reduction reaction will be too slow, the nucleation period will be prolonged, which may lead to incomplete nucleation or the formation of particles that are too large or irregularly shaped; however, if Cl... - Too little S3 results in an excessively rapid reduction rate, leading to a massive, instantaneous production of silver atoms. This can cause explosive nucleation and disordered aggregation, resulting in a wide particle size distribution and even precipitation. Controlling the relative amounts of both S3 and S3 is crucial to minimizing the free Ag content. +Maintaining a suitable level promotes the slow and steady generation of silver atoms, creating conditions for the subsequent formation of uniform crystal nuclei.

[0046] In a preferred embodiment, Ag in liquid A + With Cl - The molar ratio is 8-15:1.

[0047] Furthermore, the volume ratio of the first silver nitrate solution to the metal chloride solution is 8-40:1-4.

[0048] Furthermore, the concentration of the second silver nitrate solution is 0.002-0.05 g / mL, preferably 0.005-0.02 g / mL.

[0049] In a preferred embodiment, the concentration of the second silver nitrate solution is 0.01-0.015 g / mL.

[0050] Furthermore, the ultrasonic frequency in S1 and S2 is 10-100Hz, the ultrasonic time is 2-40min, and the ultrasonic temperature is 25-50℃.

[0051] Preferably, the ultrasonic frequency in S1 and S2 is 10-50Hz, the ultrasonic time is 5-20min, and the ultrasonic temperature is 30-40℃.

[0052] Furthermore, the average molecular weight of the polyvinylpyrrolidone is 3,500-1,300,000.

[0053] Further, the concentration of the ethylene glycol solution of polyvinylpyrrolidone is 0.002-0.16 g / mL, preferably 0.01-0.05 g / mL, and more preferably 0.01-0.03 g / mL. Specifying the concentration range of polyvinylpyrrolidone is to balance its dual functions of steric stability and morphology guidance. If the concentration is too low, it cannot effectively coat the silver surface, easily leading to agglomeration or the formation of irregular morphologies such as nanowires; if the concentration is too high, it excessively inhibits crystal growth, resulting in excessively small particles, reduced yield, and difficulty in washing. (Combined with Ag) + / Cl - The molar ratio and specific reaction temperature can better synergistically promote uniform nucleation and isotropic growth, thereby obtaining monodisperse, high-purity spherical silver nanoparticles.

[0054] Furthermore, the reaction temperature in S3 is 90-150℃, preferably 90-120℃; the stirring speed is 100-600rpm, preferably 200-300rpm. If the reaction temperature is too low, the nucleation reaction is slow and asynchronous, resulting in Ag particles with uneven size and irregular morphology. However, if the temperature is too high, secondary nucleation is likely to occur, leading to smaller Ag particles with a bimodal distribution, or possibly cubic or linear morphologies.

[0055] Furthermore, the dropping rate of liquid A is less than that of liquid B.

[0056] Furthermore, the dropping rate of solution A is 10-60 mL / min, preferably 10-40 mL / min.

[0057] Furthermore, the dropping rate of solution B is 2-25 mL / min, preferably 5-20 mL / min.

[0058] Furthermore, the centrifugal washing speed of S5 is 4000-12000 rpm.

[0059] In one embodiment, the centrifugal washing process of S5 is as follows: take the mother liquor and anhydrous ethanol at a volume ratio of 1:1-3, centrifuge at 4000-12000 rpm for 10-30 min, pour out the supernatant, take the bottom precipitate, disperse it with anhydrous ethanol and centrifuge again, and repeat the operation 3-6 times.

[0060] Furthermore, the volume ratio of the first silver nitrate solution, the second silver nitrate solution, and the ethylene glycol solution of polyvinylpyrrolidone is 8-40:60-260:50-480.

[0061] A type of spherical silver nanoparticle, prepared by the aforementioned method, has a particle diameter distribution range of 30-1200 nm, preferably 30-660 nm, and more preferably 30-300 nm.

[0062] Example 1 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.1 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 9 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 1 mL of KCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 10 min at 20 Hz and 30°C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0063] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 0.7g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 60mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 10 minutes at a frequency of 20Hz and a temperature of 30℃ to ensure complete dissolution of the solid, thus obtaining Solution B.

[0064] S3. Weigh 1.5g of polyvinylpyrrolidone (average molecular weight 8000) using an electronic balance, mix it with 80mL of ethylene glycol, and heat it to 100℃ on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 200 rpm, and reflux to raise the temperature to 90℃. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (adding it all within about 1 minute), and react at 90℃ for 3 minutes.

[0065] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 3 minutes.

[0066] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 5 mL of the silver nanoparticle mother liquor and 5 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 8000 rpm for 20 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 10 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 5 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0067] Example 2 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.15 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 12 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 1 mL of KCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 12 min at 20 Hz and 30 °C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0068] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 0.7g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 60mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 12 minutes at a frequency of 20Hz and a temperature of 30℃ to ensure complete dissolution of the solid, thus obtaining Solution B.

[0069] S3. Weigh 2.0 g of polyvinylpyrrolidone (average molecular weight 10000) using an electronic balance, mix it with 90 mL of ethylene glycol, and heat it to 110 °C on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 200 rpm, and reflux to raise the temperature to 100 °C. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (completely adding it within about 1 minute), and react at 100 °C for 3 minutes.

[0070] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 4 minutes.

[0071] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 6 mL of the silver nanoparticle mother liquor and 6 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 10000 rpm for 15 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 10 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 5 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0072] Example 3 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.2 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 16 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 2 mL of NaCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 12 min at 20 Hz and 35°C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0073] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 1.5g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 125mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 12min at a frequency of 20Hz and a temperature of 35℃ to ensure complete dissolution of the solid, thus obtaining Solution B.

[0074] S3. Weigh 3.0 g of polyvinylpyrrolidone (average molecular weight 24000) using an electronic balance, mix it with 120 mL of ethylene glycol, and heat it to 110 °C on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 180 rpm, and reflux to raise the temperature to 100 °C. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (adding it all within about 1 minute), and react at 100 °C for 3 minutes.

[0075] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 4 minutes.

[0076] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 6 mL of the silver nanoparticle mother liquor and 6 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 8000 rpm for 20 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 12 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 5 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0077] Example 4 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.2 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 18 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 2 mL of NaCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 15 min at 20 Hz and 35°C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0078] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 1.75g ​​of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 150mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 15min at a frequency of 20Hz and a temperature of 35℃ to ensure complete dissolution of the solid, thus obtaining Solution B.

[0079] S3. Weigh 3.0 g of polyvinylpyrrolidone (average molecular weight 58,000) using an electronic balance, mix it with 120 mL of ethylene glycol, and heat it to 120 °C on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 200 rpm, and reflux to raise the temperature to 100 °C. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (adding it all within about 1 minute), and react at 100 °C for 3 minutes.

[0080] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 4 minutes.

[0081] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 5 mL of the silver nanoparticle mother liquor and 5 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 10000 rpm for 15 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 12 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 5 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0082] Example 5 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.4 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 35 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 4 mL of KCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 15 min at 20 Hz and 35°C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0083] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 3.0 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 250 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 15 min at a frequency of 20 Hz and a temperature of 35 °C to ensure complete dissolution of the solid, thus obtaining Solution B.

[0084] S3. Weigh 4.0 g of polyvinylpyrrolidone (average molecular weight 360,000) using an electronic balance, mix it with 350 mL of ethylene glycol, and heat it to 130 °C on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 220 rpm, and reflux to raise the temperature to 100 °C. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (adding it within about 1 minute), and react at 100 °C for 4 minutes.

[0085] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 4 minutes.

[0086] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 5 mL of the silver nanoparticle mother liquor and 5 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 10000 rpm for 15 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 12 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 5 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0087] Example 6 This embodiment provides a method for preparing spherical silver nanoparticles, including the following steps: S1. Preparation of Solution A: Under light-shielding conditions using tin foil, accurately weigh 0.4 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 36 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Then, accurately add 4 mL of KCl solution (0.0588 mol / L) and mix thoroughly. Sonicate the solution for 15 min at 20 Hz and 35°C to ensure complete dissolution of the solid, thus obtaining Solution A.

[0088] S2. Preparation of Solution B: Under light-shielding conditions using tin foil, accurately weigh 3.0 g of silver nitrate solid using an electronic balance and place it in a brown glass container. Add 250 mL of ethylene glycol and stir magnetically to dissolve the silver nitrate. Sonicate the solution for 10 min at a frequency of 20 Hz and a temperature of 30 °C to ensure complete dissolution of the solid, thus obtaining Solution B.

[0089] S3. Weigh 5.0 g of polyvinylpyrrolidone (average molecular weight 1,300,000) using an electronic balance, mix it with 350 mL of ethylene glycol, and heat it to 130 °C on a magnetic stirrer to ensure thorough mixing and dissolution, obtaining a clear solution. Add the ethylene glycol solution of polyvinylpyrrolidone to a brown three-necked flask, stir at 220 rpm, and reflux to raise the temperature to 100 °C. After the temperature stabilizes, quickly add solution A to the reaction flask using a pear-shaped funnel (completely adding it within about 1 minute), and react at 100 °C for 4 minutes.

[0090] S4. Using a pear-shaped funnel, slowly add solution B dropwise into the reaction flask, controlling the dropping rate to ensure the addition is completed within 12 minutes. After the addition is complete, turn off the stirring device and continue to keep the reaction at the desired temperature for 4 minutes.

[0091] S5. After the reaction is complete, allow the mother liquor to cool naturally to room temperature. Take a 15 mL polypropylene centrifuge tube, add 5 mL of the silver nanoparticle mother liquor and 5 mL of anhydrous ethanol, shake well to mix thoroughly, centrifuge at 11000 rpm for 12 min, pour off the supernatant, add anhydrous ethanol to the bottom precipitate to the 10 mL mark, and disperse the precipitate by sonication or shaking. Repeat the above centrifugation, pouring, and dispersion steps 6 times to thoroughly wash away residual polyvinylpyrrolidone, obtaining the spherical silver nanoparticles.

[0092] Example 7 The difference between this embodiment and Embodiment 1 is that the reaction temperature for S3-S4 is 120℃.

[0093] Example 8 The difference between this embodiment and Embodiment 1 is that the reaction temperature for S3-S4 is 150℃.

[0094] Example 9 The difference between this embodiment and Example 1 is that the concentration of KCl solution in S1 is 0.118 mol / L, i.e., Ag + / Cl - The molar ratio is 5.

[0095] Example 10 The difference between this embodiment and embodiment 1 is that the amount of PVP added in S3 is 4.5g.

[0096] Example 11 The difference between this embodiment and Embodiment 1 is that the rotational speed of S3 is 100 rpm.

[0097] Example 12 The difference between this embodiment and embodiment 1 is that in S3, solution A is added in 1.5 minutes, and in S4, solution B is added in 18 minutes.

[0098] Performance testing methods and results: I. Morphological analysis and dimensional uniformity: Appendix Figure 1 The image shows a SEM image of the silver nanoparticles from Example 1. As can be seen from the image, the silver nanoparticles prepared by the method in Example 1 have a size distribution range of 30-220 nm, a relatively uniform size distribution, and a spherical shape.

[0099] Appendix Figure 2 The image shows a SEM image of the silver nanoparticles from Example 2. As can be seen from the image, the silver nanoparticles prepared by the method in Example 2 have a size distribution range of 30-300 nm, a relatively uniform size distribution, and a spherical shape.

[0100] Appendix Figure 3 The image shows a SEM image of the silver nanoparticles from Example 6. As can be seen from the image, the silver nanoparticles prepared by the method in Example 6 have a size distribution range of 350-620 nm, a relatively uniform size distribution, and a spherical shape.

[0101] Appendix Figure 4 The image shows a SEM image of the silver nanoparticles from Example 7. As can be seen from the image, the silver nanoparticles prepared by the method in Example 7 have a size of 40-260 nm, a relatively uniform size distribution, and a spherical shape.

[0102] Appendix Figure 5 The image shows a SEM image of the silver nanoparticles from Example 8. As can be seen from the image, the silver nanoparticles prepared by the method in Example 8 have a size of 50-550 nm, a somewhat uneven size distribution, and are spherical and rod-shaped.

[0103] Appendix Figure 6 The image shows a SEM image of the silver nanoparticles from Example 12. As can be seen from the image, the silver nanoparticles prepared by the method in Example 12 have a size of 45-240 nm, a relatively uniform size distribution, and a spherical shape.

[0104] II. Product purity: Detected using XPS.

[0105] The test results are shown in Table 1.

[0106] Table 1

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0108] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing spherical silver nanoparticles, characterized in that, Includes the following steps: S1. Preparation of Solution A: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare the first silver nitrate solution, add a metal chloride salt solution to it, mix well, and sonicate. S2. Prepare solution B: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to prepare a second silver nitrate solution, mix thoroughly, and sonicate. S3. Add the ethylene glycol solution of polyvinylpyrrolidone to the reaction vessel and heat it to the reaction temperature under stirring and reflux; quickly add solution A to the reaction vessel and react for 1-5 minutes. S4. Add solution B dropwise to the reaction vessel. After the addition is complete, turn off the stirring and continue the reaction for 1-5 minutes. S5. After the reaction is complete, the mother liquor is cooled to room temperature and washed by centrifugation to obtain the spherical silver nanoparticles.

2. The preparation method according to claim 1, characterized in that, The concentration of the first silver nitrate solution is 0.0025-0.05 g / mL; the concentration of the metal chloride solution is 0.02-0.1 mol / L; and the volume ratio of the first silver nitrate solution to the metal chloride solution is 8-40:1-4.

3. The preparation method according to claim 1, characterized in that, Metal chloride salts include at least one of sodium chloride, potassium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, copper chloride, and ferric chloride.

4. The preparation method according to claim 1, characterized in that, The metal chloride salt is sodium chloride and / or potassium chloride; Ag in solution A + With Cl - The molar ratio is 3~20:

1.

5. The preparation method according to claim 2, characterized in that, The concentration of the second silver nitrate solution is 0.002-0.05 g / mL.

6. The preparation method according to claim 1, characterized in that, The average molecular weight of the polyvinylpyrrolidone is 3,500-1,300,000; the concentration of the ethylene glycol solution of the polyvinylpyrrolidone is 0.002-0.16 g / mL.

7. The preparation method according to claim 1, characterized in that, The reaction temperature in S3 is 90-150℃; the stirring speed is 100-600rpm.

8. The preparation method according to claim 1, characterized in that, The dropping rate of solution A is less than that of solution B; the dropping rate of solution A is 10-60 mL / min; the dropping rate of solution B is 2-25 mL / min.

9. The preparation method according to claim 5, characterized in that, The volume ratio of the first silver nitrate solution, the second silver nitrate solution, and the ethylene glycol solution of polyvinylpyrrolidone is 8-40:60-260:50-480.

10. A type of spherical silver nanoparticle, prepared by the preparation method according to any one of claims 1-9, characterized in that, The particle diameter ranges from 30 to 1200 nm.

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