A method for preparing nanoscale silver particles based on a nanoemulsion method

Abstract

This invention proposes a method for preparing nanoscale silver particles based on a nanoemulsion method. The method includes: mixing and emulsifying an aqueous solution of a silver complex with a nonionic surfactant and an organic solvent to obtain a silver nanoemulsion; similarly mixing and emulsifying an aqueous solution of a reducing agent with a nonionic surfactant and an organic solvent to obtain a reducing agent nanoemulsion; and mixing the silver nanoemulsion and the reducing agent emulsion and carrying out a reduction reaction to obtain the nanoscale metallic silver particles. This invention utilizes a specific silver complex system combined with nanoemulsion technology to achieve the controllable preparation of nanoscale silver particles. The resulting nanoscale silver particles have controllable particle size and morphology, good monodispersity, and are not prone to aggregation, and are expected to be widely used in many fields such as electronics, medicine, chemical industry, military, and aerospace.

Description

Technical Field

[0001] This invention relates to the field of precious metal manufacturing technology, and in particular to a method for preparing nanoscale silver particles based on nanoemulsion method. Background Technology

[0002] Nanomaterials, especially nanometals, exhibit unique photoelectric, catalytic, and magnetic properties due to their special structures, making them highly promising functional materials with great potential for application. Nanoscale silver, with its excellent conductivity, broad-spectrum antibacterial properties, and highly efficient catalytic activity, has wide applications in electronics, medicine, new energy, and other fields. Furthermore, its market size continues to expand, and with technological breakthroughs and application development, its development prospects are extremely broad.

[0003] Currently, how to prepare nanoparticles with controllable particle size and morphology, good monodispersity, and resistance to agglomeration to improve the various properties of nanomaterials has become a research hotspot. Traditional methods for preparing nanomaterials, such as vapor deposition and mechanical grinding, each have their drawbacks. Nanoparticles obtained by vapor deposition have large size dispersions (usually 1-200 nm) and are prone to aggregation, making subsequent preparation of stable dispersions extremely difficult; nanoparticles obtained by mechanical grinding are relatively large (usually >100 nm) and are also prone to aggregation.

[0004] Microemulsions have been used to prepare nanoscale metal particles. Since Boutonnet et al. first used this method to prepare monodisperse metal nanoparticles of 3-5 nm Pt and Pd in ​​1982, the method has developed rapidly. Currently, various nanoscale metal particles such as Fe, Co, Au, Ag, and Cu have been successfully prepared. For example, using n-pentanol as an auxiliary surfactant and n-heptane as the oil phase, a system constructed with a mixture of Tween 80 and Span 80 surfactants can prepare nano-copper; by adjusting parameters such as the ratio of water to surfactant, Fe nanoparticles of different sizes can also be prepared. However, this method is prone to phase separation during microemulsion preparation, and nanoparticles tend to agglomerate during storage and use, limiting its application in fields with extremely high purity requirements, such as high-precision electronic materials.

[0005] Nanoemulsions, as a spontaneously formed dispersion system composed of water, oil, surfactants, and co-surfactants, typically have droplet sizes ranging from 20 to 200 nm. Compared to microemulsions, they exhibit greater stability in large-scale preparation and are less prone to phase separation. This method requires no complex equipment and can be prepared through phase transitions, high-speed shearing, and ultrasonication, making it suitable for mass production. However, existing microemulsion methods for preparing silver nanoparticles often suffer from problems such as emulsion instability, incomplete silver ion reduction during the reaction, wide particle size distribution, and a tendency to agglomerate, severely impacting the quality and application performance of the silver nanoparticles. Therefore, there is an urgent need for a method to prepare nanoscale silver nanoparticles that can improve emulsion stability, effectively control particle size, and prevent agglomeration. Summary of the Invention

[0006] Based on the technical problems existing in the background art, this invention proposes a method for preparing nanoscale silver particles based on nanoemulsion method. By combining a specific silver complex system with nanoemulsion technology, the controllable preparation of nanoscale silver particles is achieved. The obtained nanoscale silver particles have controllable particle size and morphology, good monodispersity and are not easy to agglomerate, and are expected to be widely used in many fields such as electronics, medicine, chemical industry, military, and aerospace.

[0007] This invention proposes a method for preparing nanoscale silver particles based on a nanoemulsion method, comprising the following steps: S1. Mix and emulsify an aqueous solution of silver complex with a nonionic surfactant and an organic solvent to obtain a silver nanoemulsion; S2. The reducing agent aqueous solution is also mixed with nonionic surfactant and organic solvent and emulsified to obtain reducing agent nanoemulsion; S3. The silver nanoemulsion and reducing agent emulsion are mixed and a reduction reaction is carried out to obtain the nanoscale metallic silver particles.

[0008] In this invention, silver complexes and reducing agents are prepared into nanoemulsions. Specifically, silver is dissolved in an aqueous solution in the form of a complex. A nonionic surfactant is selected and premixed with an organic solvent and an aqueous solution. The nanoemulsion is formed by high-pressure homogenization or phase transition temperature method. The complex emulsion and the reducing agent emulsion are then mixed in a certain proportion. After sufficient reaction, the emulsion can be demulsified and collected to obtain metallic silver nanoparticles with controllable particle size and morphology, good monodispersity, and resistance to agglomeration. In this process, the nanoemulsion droplets are used as microreactors to restrict the growth space of the silver particles, thereby effectively controlling the particle size, preventing particle agglomeration, and realizing the preparation of nanoscale metallic silver particles with uniform particle size distribution.

[0009] Preferably, the aqueous solution of the silver complex comprises a silver salt, a halide, a complex, and water; Preferably, the silver salt is at least one of silver nitrate, silver fluoride, silver trifluoroacetate, silver trifluoromethanesulfonate, silver tetrafluoroborate, silver perchlorate, or silver acetate; the halide is at least one of sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, or potassium iodide; and the complex is at least one of sodium thiosulfate, ammonia, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, or ethylenediamine. Preferably, the molar ratio of the silver salt to the halide is 1:1-2, and the molar ratio of the silver salt to the complex is 1:2-4.

[0010] In this invention, a complex is introduced to form a complex ion with silver ions, which reduces the reactivity of silver ions and slows down the reduction reaction rate, thus helping to form silver particles with complete crystal shape and smaller particle size. At the same time, the aqueous solution of the silver complex contains a certain amount of halide anions. The halide anions can be a complexing agent for cations or a simple additive, which can play a growth guiding role in the subsequent nucleation of metallic silver nanoparticles.

[0011] Preferably, the reducing agent is at least one of ascorbic acid, sodium ascorbate, citric acid, sodium citrate, hydrazine hydrate, sodium borohydride, glucose, 37wt% formaldehyde aqueous solution, or hydroquinone.

[0012] Preferably, the nonionic surfactant is at least one of fatty alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, phenylalkyl alcohol polyoxyethylene ether, or isomeric alcohol polyoxyethylene ether.

[0013] Preferably, the organic solvent is at least one of C5-20 straight-chain alkanes, cyclohexane, toluene, o-xylene, m-xylene, p-xylene, or 1,3,5-trimethylbenzene.

[0014] In this invention, specific nonionic surfactants and oil phase solvents were selected to construct a kinetically stable nanoemulsion system, ensuring the uniformity of emulsion droplet size.

[0015] Preferably, in the silver nanoemulsion, the mass ratio of the silver complex aqueous solution to the nonionic surfactant and organic solvent is 1:0.1-2:1-20; in the reducing agent nanoemulsion, the mass ratio of the reducing agent aqueous solution to the surfactant and organic solvent is 1:0.1-2:1-20; and the molar ratio of the silver complex to the reducing agent is 1:2-10.

[0016] Preferably, when mixing the silver nanoemulsion and the reducing agent emulsion, an amphiphilic polymeric surfactant is also added; Preferably, the amphiphilic polymeric surfactant is obtained by imidizing dialdehyde polyethylene glycol with N,N-dimethylpropylene diamine, followed by quaternization with sodium bromoethylsulfonate. Preferably, the amount of the amphiphilic polymeric surfactant added is 0.5-5% of the silver nanoemulsion.

[0017] In this invention, the amphiphilic polymeric surfactant, as a class of polymeric organic compounds with an amphiphilic structure, has anionic groups of its sulfonate salt and cationic groups of its quaternary ammonium salt that can form electrostatic adsorption with silver complex and reducing agent, respectively. When used in the reaction of the two, it can ensure that the two can fully combine and react. At the same time, it can also effectively improve the surface activity of the surfactant and its hydrophilic-lipophilic balance, and participate in the formation of vesicles in nanoemulsions, regulate the polarity of the continuous phase water and the dispersed phase oil, thereby affecting the phase state and phase properties of the microemulsion components, ensuring the stability of the emulsion system, complete reduction of silver ions during the reaction, and precise control of the nanostructure of silver particles.

[0018] Preferably, the emulsification is performed by high-pressure homogenization or phase transition temperature method to form nanoemulsions; Preferably, the high-pressure homogenization method has a homogenization temperature of 20-40℃, a homogenization pressure of 40-130MPa, and a homogenization time of 1-10min.

[0019] In this invention, the high-pressure homogenization method or the phase transition temperature method can be used to prepare nanoemulsions with narrow particle size distribution and high stability, laying the foundation for the subsequent preparation of high-quality silver nanoparticles.

[0020] Preferably, the volume ratio of the silver nanoemulsion to the reducing agent emulsion is 1:9-9:1.

[0021] In this invention, since silver ions or silver complex ions are in a complex reaction system, and are affected by the steric hindrance effect of surfactants, complexing agents, and organic polymers, an excessive amount of reducing agent is added in order to ensure the final effective yield of silver powder particles.

[0022] In this invention, the mixing method can be that the reducing agent emulsion is added dropwise to the silver complex emulsion, the two emulsions are mixed rapidly, or the silver complex emulsion is added dropwise to the reducing agent emulsion. By adjusting the mixing method, mixing ratio and mixing time, the nucleation and growth process of metallic silver nanoparticles can be effectively controlled, and ultimately, large-scale production with no significant difference can be achieved.

[0023] The present invention also proposes a nanoscale silver particle, which is prepared by the above-described preparation method.

[0024] This invention prepares nanoemulsions from aqueous solutions of silver complexes and reducing agents, respectively. Utilizing the confinement effect of the emulsion droplets, the reaction is restricted to nanoscale droplets, effectively controlling the nucleation and growth processes. This solves the problems of easy agglomeration and uneven particle size distribution of silver nanoparticles in traditional methods. The introduction of the silver complex lowers the reduction potential of silver ions, slowing down the reaction rate and facilitating anisotropic crystal growth and particle size control. The method of this invention is simple, operates under mild conditions, and is highly controllable, producing small and uniformly distributed nanoscale silver particles with significant application value.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The dispersed phase cavity of the nanoemulsion serves as a microreactor, utilizing the numerous small spaces generated by the oil-in-water mixture to maintain the small reaction system required for the growth of nanomaterials, which is conducive to the stable and scaled-up production of metal nanoparticles.

[0026] (2) Nanoemulsion is a water-in-oil system, which can better load water-soluble reducing agents. After controlling the mixing operation of precursor emulsion and reducing agent emulsion, the nucleation and growth process of nanoparticles can be regulated. Attached Figure Description

[0027] Figure 1 The image shows a TEM image of the silver nanoemulsion described in Example 1. Figure 2 The particle size and polydispersity index of the silver nanoemulsion described in Example 1 under different homogenization pressures and homogenization times are shown. Figure 3 This is a TEM image of the nanoscale silver particles described in Example 1; Figure 4 This is a SEM image of the nanoscale silver particles described in Comparative Example 2. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0030] Example 1

[0031] This embodiment proposes a method for preparing nanoscale silver particles based on a nanoemulsion method, specifically including: (1) Preparation of silver nanoemulsion (high pressure homogenization method): 20 mmol of silver nitrate was dissolved completely in 16.5 mL of water to obtain a solution with a concentration of 17 wt%. Then, a 30 wt% potassium bromide aqueous solution was added until the silver was completely converted into a precipitate. 60 mmol of sodium thiosulfate was added, and the mixture was shaken and mixed at 700 rpm for 5 min to obtain an aqueous solution of the silver complex. 3.3g of fatty alcohol polyoxyethylene ether AEO3 was added to 109.6g of n-decane and stirred until completely dissolved. Then, the above-mentioned silver complex aqueous solution was added. After pre-homogenization at 11000rpm for 2min using a high-speed shear mill, the resulting crude emulsion was sent to a high-pressure homogenizer to break up the droplets and perform particle size homogenization. The homogenization temperature was 25℃, the homogenization pressure was 90MPa, and the homogenization time was 5min, resulting in a water-in-oil silver nanoemulsion. (2) Preparation of reducing agent emulsion (high pressure homogenization method): 100 mmol of sodium ascorbate was dissolved completely in 60 mL of water to obtain a reducing agent aqueous solution with a content of 25 wt%. 13.2g of fatty alcohol polyoxyethylene ether AEO3 was added to 438.4g of n-decane and stirred until completely dissolved. Then, the above-mentioned reducing agent aqueous solution was added. After pre-homogenization at 11000rpm for 2min using a high-speed shear mill, the resulting crude emulsion was sent to a high-pressure homogenizer to break up the droplets and perform particle size homogenization. The homogenization temperature was 25℃, the homogenization pressure was 100MPa, and the homogenization time was 5min, resulting in a water-in-oil reducing agent emulsion. (3) Preparation of silver nanoparticles The above-mentioned silver nanoemulsion was added to the reducing agent emulsion and stirred thoroughly for 30 minutes at a water bath temperature of 30°C and a stirring speed of 400 rpm. After stirring was stopped, a uniformly dispersed aqueous solution of nanoscale silver particles was obtained. After standing overnight at room temperature to allow the silver particles to settle completely, the supernatant was discarded, deionized water was added, the mixture was ultrasonically dispersed, centrifuged, and vacuum dried to obtain the silver nanoparticles.

[0032] Figure 1 The above is a TEM image of the silver nanoemulsion, with reference to... Figure 1 It can be seen that the droplets in the above silver nanoemulsion have a uniform spherical vesicle structure. Figure 2 The above silver nanoemulsions are shown to have emulsion particle size and polydispersity index (PDI) under different homogenization pressures. It can be seen that the controllable preparation of nanoscale silver particles can be achieved by controlling the homogenization parameters. Figure 3 The above-mentioned nanoscale silver particles are shown in the TEM image, with reference to... Figure 3It can be seen that the silver nanoparticles obtained in this embodiment are uniform in size, highly spherical, and well dispersed, with a diameter of about 8 nm and a polydispersity index of 0.08.

[0033] Example 2

[0034] This embodiment proposes a method for preparing nanoscale silver particles based on a nanoemulsion method, specifically including: (1) Preparation of silver nanoemulsion (phase transition temperature method): 20 mmol of silver nitrate was dissolved completely in 16.5 mL of water to obtain a solution with a concentration of 17 wt%. Then, a 30 wt% potassium bromide aqueous solution was added until the silver was completely converted into a precipitate. 60 mmol of sodium thiosulfate was added, and the mixture was shaken and mixed at 700 rpm for 5 min to obtain an aqueous solution of the silver complex. The above-mentioned silver complex aqueous solution was gradually added dropwise to a mixture containing 13.3g of fatty alcohol polyoxyethylene ether AEO3 and 106.7g of n-decane. After incubation at 80°C for 5 minutes at 700 rpm in a vortex mixer, the mixture was placed in a low-temperature reactor and rapidly cooled and allowed to stand to obtain a water-in-oil silver nanoemulsion. (2) Preparation of reducing agent emulsion (phase transition temperature method): 100 mmol of sodium ascorbate was dissolved completely in 60 mL of water to obtain a reducing agent aqueous solution with a content of 25 wt%. The above-mentioned reducing agent aqueous solution was gradually added dropwise to a mixture containing 53.2g of fatty alcohol polyoxyethylene ether AEO3 and 426.8g of n-decane. After incubation at 80°C for 5 minutes at 700 rpm in a vortex shaker, the mixture was placed in a low-temperature reactor and rapidly cooled and allowed to stand to obtain a water-in-oil reducing agent emulsion. (3) Preparation of silver nanoparticles The above-mentioned silver nanoemulsion was added to the reducing agent emulsion and stirred thoroughly for 30 minutes at a water bath temperature of 30°C and a stirring speed of 400 rpm. After stirring was stopped, a uniformly dispersed aqueous solution of nanoscale silver particles was obtained. After standing overnight at room temperature to allow the silver particles to settle completely, the supernatant was discarded, deionized water was added, the mixture was ultrasonically dispersed, centrifuged, and vacuum dried to obtain the silver nanoparticles.

[0035] The silver nanoparticles obtained in this embodiment are uniform in size, highly spherical, and well-dispersed, with a diameter of approximately 12 nm and a polydispersity index of 0.10.

[0036] Example 3

[0037] This embodiment proposes a method for preparing nanoscale silver particles based on a nanoemulsion method. Specifically, refer to Example 1, except that an amphiphilic polymeric surfactant is added in step (3). The amount of the amphiphilic polymeric surfactant is 3 wt% of the silver nanoemulsion, which is prepared by the following method: Dissolve dialdehyde polyethylene glycol in anhydrous ethanol, add 2.2 molar amounts of N,N-dimethylpropanediamine to dialdehyde polyethylene glycol at room temperature, heat to 80°C, stir for 3 hours, cool to room temperature, add 2 molar amounts of sodium bromoethylsulfonate to dialdehyde polyethylene glycol, heat to 50°C, stir for 6 hours, filter, wash, and dry to obtain the amphiphilic polymeric surfactant.

[0038] The silver nanoparticles obtained in this embodiment are uniform in size, highly spherical, and well-dispersed, with a diameter of approximately 6 nm and a polydispersity index of 0.02.

[0039] Comparative Example 1 This comparative example proposes a method for preparing nanoscale silver particles based on the emulsion method. Specifically, refer to Example 1, except that in step (1), the addition of a 30wt% potassium bromide aqueous solution until the silver is completely converted into precipitate is omitted.

[0040] The silver nanoparticles obtained in this comparative example have a size greater than 50 nm, poor size dispersion, and a polydispersity index exceeding 0.3.

[0041] Comparative Example 2 This comparative example proposes a method for preparing nanoscale silver particles based on the emulsion method. Specifically, refer to Example 1, except that step (2) is omitted, and in step (3), the above silver nanoemulsion is added to the reducing agent aqueous solution.

[0042] The silver nanoparticles obtained in this comparative example are nearly spherical with a size greater than 100 nm. (See...) Figure 4 SEM images.

[0043] Comparative Example 3 This comparative example proposes a method for preparing nanoscale silver particles based on emulsion method. Specifically, refer to Example 3, except that in step (3), the amphiphilic surfactant hexadecylhydroxypropyl betaine is added instead of the amphiphilic polymeric surfactant.

[0044] The silver nanoparticles obtained in this comparative example have a diameter of approximately 9 nm and a polydispersity index of 0.10.

[0045] As can be seen from the results of the above examples and comparative examples, the silver nanoparticles obtained by the present invention can maintain a particle size within 15 nm and a polydispersity index within 0.1, exhibiting excellent dispersion performance and high size uniformity. Furthermore, in Example 3, by using an amphiphilic polymeric surfactant, the polydispersity index can be further controlled within 0.05, thereby further improving the dispersion performance.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing nanoscale silver particles based on nanoemulsion method, characterized in that, Includes the following steps: S1. Mix and emulsify an aqueous solution of silver complex with a nonionic surfactant and an organic solvent to obtain a silver nanoemulsion; S2. The reducing agent aqueous solution is also mixed with nonionic surfactant and organic solvent and emulsified to obtain reducing agent nanoemulsion; S3. The silver nanoemulsion and reducing agent emulsion are mixed and a reduction reaction is carried out to obtain the nanoscale metallic silver particles.

2. The method for preparing nanoscale silver particles based on the nanoemulsion method according to claim 1, characterized in that, The aqueous solution of the silver complex comprises silver salt, halide, complex and water; Preferably, the silver salt is at least one of silver nitrate, silver fluoride, silver trifluoroacetate, silver trifluoromethanesulfonate, silver tetrafluoroborate, silver perchlorate, or silver acetate; the halide is at least one of sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, or potassium iodide; and the complex is at least one of sodium thiosulfate, ammonia, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, or ethylenediamine. Preferably, the molar ratio of the silver salt to the halide is 1:1-2, and the molar ratio of the silver salt to the complex is 1:2-4.

3. The method for preparing nanoscale silver particles based on the nanoemulsion method according to claim 1 or 2, characterized in that, The reducing agent is at least one of ascorbic acid, sodium ascorbate, citric acid, sodium citrate, hydrazine hydrate, sodium borohydride, glucose, 37wt% formaldehyde aqueous solution, or hydroquinone.

4. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-3, characterized in that, The nonionic surfactant is at least one of fatty alcohol polyoxyethylene ether, octylphenol polyoxyethylene ether, phenylalkyl alcohol polyoxyethylene ether, or isomeric alcohol polyoxyethylene ether.

5. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-4, characterized in that, The organic solvent is at least one of C5-20 straight-chain alkanes, cyclohexane, toluene, o-xylene, m-xylene, p-xylene, or 1,3,5-trimethylbenzene.

6. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-5, characterized in that, In the silver nanoemulsion, the mass ratio of the silver complex aqueous solution to the nonionic surfactant and organic solvent is 1:0.1-2:1-20; in the reducing agent nanoemulsion, the mass ratio of the reducing agent aqueous solution to the surfactant and organic solvent is 1:0.1-2:1-20; and the molar ratio of the silver complex to the reducing agent is 1:2-10.

7. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-6, characterized in that, When mixing the silver nanoemulsion and the reducing agent emulsion, an amphiphilic polymeric surfactant is also added. Preferably, the amphiphilic polymeric surfactant is obtained by imidizing dialdehyde polyethylene glycol with N,N-dimethylpropylene diamine, followed by quaternization with sodium bromoethylsulfonate. Preferably, the amount of the amphiphilic polymeric surfactant added is 0.5-5% of the silver nanoemulsion.

8. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-7, characterized in that, The emulsification is achieved by forming nanoemulsions through high-pressure homogenization or phase transition temperature method; Preferably, the high-pressure homogenization method has a homogenization temperature of 20-40℃, a homogenization pressure of 40-130MPa, and a homogenization time of 1-10min.

9. The method for preparing nanoscale silver particles based on the nanoemulsion method according to any one of claims 1-8, characterized in that, The volume ratio of the silver nanoemulsion to the reducing agent emulsion is 1:9-9:

1.

10. A type of nanoscale silver particle, characterized in that, It is prepared by the method described in any one of claims 1-9.

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