Preparation method of flower-shaped nano-silver particles

Abstract

The invention discloses a preparation method of flower-like nano-silver particles, which comprises the following steps: preparing a mixed aqueous solution of ascorbic acid and a surfactant, heating and stirring; preparing a silver nitrate aqueous solution, heating and stirring; and dropwise adding the silver nitrate aqueous solution into the mixed aqueous solution at the rate of 10-35 mL / min, and continuously reacting for 5-10 minutes after dropwise adding is finished, so as to obtain the flower-shaped nano-silver particles. The method is simple in process operation, the reaction is carried out in a water phase at normal pressure and medium temperature, ascorbic acid is used as a reducing agent, toxic solvents are avoided, complicated equipment (such as vacuum and laser) is not needed, the method is green and environment-friendly, and controllable growth of flower-like morphology is finally formed by controlling anisotropic growth of silver crystals; and flower-like nano-silver particles with uniform morphology and high purity are prepared under mild conditions by a one-step method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silver preparation, and particularly relates to a preparation method of flower-shaped silver nanoparticles. BACKGROUND

[0002] Silver nanoparticles have a wide application prospect in the fields of biomedicine, catalytic chemistry and photoelectric technology due to their excellent antibacterial performance, high catalytic activity, unique optical properties and good magnetic behavior. The performance thereof is strongly dependent on the geometric morphology and size of the particles, and therefore, controllable preparation of the morphology and size is the key to regulating the performance. At present, researchers have successfully prepared rod-shaped, cubic, filamentous, dendritic, polyhedral and triangular flake-shaped silver nanostructures.

[0003] Among the numerous morphologies, flower-shaped silver nanoparticles, as a kind of hierarchical structure with high anisotropy, have a larger specific surface area and abundant surface tips and edges compared with spherical or regular polyhedral nanoparticles. This unique structure enables a large number of electromagnetic field enhancement "hot spots" to be generated on the surface of a single particle, thereby serving as a high-performance surface enhanced Raman scattering (SERS) substrate and significantly improving the detection sensitivity. In addition, in the applications of catalysis, photoelectricity and antibiosis, the hierarchical morphology can expose more high-activity crystal faces and sites, which helps to improve the reaction efficiency and performance stability.

[0004] However, the controllable preparation of flower-shaped silver nanoparticles is still a technical difficulty in the field. The existing synthesis methods mainly rely on liquid or non-liquid phase chemical reduction method, which needs to introduce a variety of organic additives (such as surfactants, capping agents, structure directing agents, etc.) in the reaction system to guide the formation of flower-shaped structure. However, the complex organic additives make the synthesis and subsequent purification process cumbersome and difficult to completely remove. In contrast, although the present application also uses a surfactant, by optimizing the low-residue surfactant and strictly controlling the type and amount thereof, the structure is guided while avoiding the introduction of a complex additive system. This method not only simplifies the process, but also effectively reduces the surface organic residue, which is conducive to maintaining the intrinsic performance and application reliability of the silver nanoparticles. In addition, the growth kinetics of the flower-shaped structure is complex, and the nucleation and growth processes are difficult to accurately coordinate, resulting in the existing preparation methods generally having non-uniform product morphology, wide size distribution and poor batch repeatability.

[0005] In order to avoid the shortcomings of the chemical reduction method, methods such as microemulsion method, sol-gel method, photo-reduction method and laser ablation method have appeared. However, the microemulsion method needs to use a large amount of toxic organic solvents, which is not environmentally friendly; the sol-gel method has a long process flow, and the nanoparticles are prone to serious agglomeration during the drying process; and the photo-reduction method and laser ablation method have high requirements for equipment, complex operation and large energy consumption, which are difficult to realize low-cost and large-scale production and application. SUMMARY

[0006] The present application aims at solving the problems of the prior art and providing a green preparation method for accurately controlling the morphology of flower-shaped nanosilver particles in a mild, normal-pressure, aqueous phase system through simple operation.

[0007] The technical solution adopted by the present application is as follows: A preparation method of flower-shaped nanosilver particles, comprising the following steps: S1. preparing a mixed aqueous solution of ascorbic acid and a surfactant, heating and stirring; S2. preparing an aqueous silver nitrate solution, heating and stirring; S3. adding the aqueous silver nitrate solution of step S2 to the mixed aqueous solution of step S1 at a rate of 10-35 mL / min, continuing to react for 5-10 minutes after the addition is completed, to obtain flower-shaped nanosilver particles.

[0008] Further, the concentrations of ascorbic acid and silver nitrate in the present application are the same, both being 0.05-0.2 mol / L.

[0009] Further, the surfactant in the present application is selected from one or two of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and polyvinyl alcohol (PVA).

[0010] Further, the mass ratio of silver nitrate to surfactant in the present application is 1:2-1:6.

[0011] Further, the heating temperature in the present application is 40-50℃.

[0012] Further, the stirring rate in the present application is 200-400 rpm.

[0013] The present application also provides a flower-shaped nanosilver particle prepared by the method of the present application.

[0014] Further, the particle size of the flower-shaped nanosilver particle in the present application is 700 nm-6 μm, and a hierarchical petal-like structure is formed from the center to the periphery.

[0015] The present application has the following beneficial effects: 1. The reaction in the present application is carried out in an aqueous phase, at normal pressure and at a moderate temperature (40-50℃), using ascorbic acid as a reducing agent, avoiding the use of toxic solvents and the need for complex equipment (such as vacuum, laser), and being green and environmentally friendly, and the flow rate can be accurately controlled using a peristaltic pump, which is suitable for industrialized continuous or batch production.

[0016] 2、The process of the present application is simple to operate. By controlling the dropping rate to regulate the local concentration of Ag+ and the reduction rate, and combining the selective adsorption of surfactants on specific crystal planes, anisotropic growth of silver crystals is realized, and finally a hierarchical flower-like structure is formed. The dropping rate is the key to morphology control. When the dropping rate is lower than 10 mL / min, the silver atoms are generated too slowly, and spherical or near-spherical particles are easily formed. When the dropping rate is higher than 35 mL / min, the reaction is too violent, and particle agglomeration or irregular blocky structures are easily formed. Within the range of 10-35 mL / min, the anisotropic growth of silver crystals can be controlled to form flower-like morphology by the guiding effect of the surfactants in this ratio, and flower-like nano-silver particles with uniform morphology and clear structure are prepared in a one-step process under mild conditions.

[0017] 3、The flower-like nano-silver particles prepared by the present application have uniform morphology and high purity, and their unique structure endows them with potential applications in the fields of SERS and catalysis. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 SEM micro-morphology diagram of the flower-like nano-silver particles prepared in Example 1 of the present application; Figure 2 SEM micro-morphology diagram of the flower-like nano-silver particles prepared in Example 2 of the present application; Figure 3 SEM micro-morphology diagram of the flower-like nano-silver particles prepared in Example 3 of the present application; Figure 4 SEM micro-morphology diagram of the flower-like nano-silver particles prepared in Example 4 of the present application; Figure 5 SEM micro-morphology diagram of the flower-like nano-silver particles prepared in Example 5 of the present application; Figure 6 X-ray diffraction diagram of the flower-like nano-silver particles prepared in Example 5 of the present application; Figure 7 SEM micro-morphology diagram of the nano-silver particles prepared in Comparative Example 1 of the present application; Figure 8 SEM micro-morphology diagram of the nano-silver particles prepared in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0019] The content of the present application will be further described in detail below in combination with specific examples, but the protection scope of the present application is not limited to the examples. Example 1

[0020] A preparation method of flower-like nano-silver particles, comprising the following steps: S1. Prepare 10 mL of 0.05 mol / L ascorbic acid solution (containing PVP, m(AgNO3):m(PVP)=1:2), place it in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm until the PVP powder is completely dissolved; S2. Prepare 10 mL of 0.05 mol / L silver nitrate solution, place it in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm; S3. Using a peristaltic pump, add silver nitrate solution dropwise to the ascorbic acid mixture from step S1 at a rate of 10 mL / min. After the addition is complete, continue the reaction for 5 minutes to obtain the desired result. Figure 1 Flower-shaped silver nanoparticles. Figure 1 The typical flower-like structure formed at a drop rate of 10 mL / min is clearly shown, with the size of the flower-like silver nanoparticles being 1.25 μm. Example 2

[0021] A method for preparing flower-shaped silver nanoparticles includes the following steps: S1. Prepare 20 mL of 0.1 mol / L ascorbic acid solution (containing PVP, m(AgNO3):m(PVP)=1:3), place it in a water bath at 45℃ and heat it with magnetic stirring at a stirring speed of 300 rpm until the PVP powder is completely dissolved; S2. Prepare 20 mL of 0.1 mol / L silver nitrate solution, place it in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm; S3. Using a peristaltic pump, silver nitrate solution is added dropwise to the ascorbic acid mixture from step S1 at a rate of 15 mL / min. After the addition is complete, the reaction continues for 10 minutes to obtain the desired result. Figure 2 Flower-shaped silver nanoparticles. Figure 2 The uniform flower-like particles formed at a dropping rate of 15 mL / min are clearly shown, with the size of the flower-like silver nanoparticles being 1.56 μm. Example 3

[0022] A method for preparing flower-shaped silver nanoparticles includes the following steps: S1. Prepare 20 mL of 0.15 mol / L ascorbic acid solution (a mixture of PVP and PVA, m(AgNO3):m(mixture of PVP and PVA) = 1:3), wherein the mass ratio of PVP to PVA is 2:1. Place the solution in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm until the PVP and PVA powders are completely dissolved. S2. Prepare 20 mL of 0.15 mol / L silver nitrate solution, place it in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm; S3. Using a peristaltic pump, add silver nitrate solution dropwise to the ascorbic acid mixture from step S1 at a rate of 20 mL / min. After the addition is complete, continue the reaction for 10 minutes to obtain the desired result. Figure 3 Flower-shaped silver nanoparticles. Figure 3 The uniform flower-like particles formed at a dropping rate of 20 mL / min are clearly shown, with the size of the flower-like silver nanoparticles ranging from 0.7 to 1.43 μm. Example 4

[0023] A method for preparing flower-shaped silver nanoparticles includes the following steps: S1. Prepare 50 mL of 0.1 mol / L ascorbic acid solution (a mixture of PVP and PEG, m(AgNO3):m(a mixture of PVP and PVA) = 1:4), wherein the mass ratio of PVP to PEG is 2:1. Place the solution in a water bath at 50℃ and heat it with magnetic stirring at a stirring speed of 400 rpm until the PVP and PEG powders are completely dissolved. S2. Prepare 50 mL of 0.1 mol / L silver nitrate solution, place it in a water bath at 50℃ and heat it with magnetic stirring at a stirring speed of 400 rpm; S3. Using a peristaltic pump, add silver nitrate solution dropwise to the ascorbic acid mixture from step S1 at a rate of 30 mL / min. After the addition is complete, continue the reaction for 8 minutes to obtain the desired result. Figure 4 Flower-shaped silver nanoparticles. Figure 4 The typical flower-like structure formed at a dropping rate of 30 mL / min is clearly shown, with the size of the flower-like silver nanoparticles being 2.57 μm. Example 5

[0024] A method for preparing flower-shaped silver nanoparticles includes the following steps: S1. Prepare 100 mL of 0.2 mol / L ascorbic acid solution (containing PVP, m(AgNO3):m(PVP)=1:6), wherein the mass ratio of PVP to PEG is 2:1, and place it in a water bath at 40℃ for magnetic stirring and heating at a stirring speed of 200 rpm until the PVP powder is completely dissolved. S2. Prepare 100 mL of 0.2 mol / L silver nitrate solution, place it in a water bath at 40℃ and heat it with magnetic stirring at a stirring speed of 200 rpm; S3. The silver nitrate solution was added dropwise into the mixed ascorbic acid solution of step S1 using a peristaltic pump at a rate of 35 mL / min. After the addition was completed, the reaction was continued for 10 minutes to obtain flower-shaped silver nanoparticles. Figure 5 Figure 5 The typical flower-shaped structure formed at a dropwise rate of 35 mL / min is clearly shown. The flower-shaped silver nanoparticles have a size of 1.95-5.88 μm. Figure 6 The X-ray diffraction peaks of the nanoparticle characterization are consistent with the characteristic peak positions in the silver crystal standard card, indicating that the synthesized flower-shaped particles are pure-phase silver structures, confirming that the obtained product is a pure-phase silver crystal.

[0025] As can be seen from the results of the above examples, by controlling the dropwise rate of the ascorbic acid solution to control the reduction kinetics of Ag⁺, the generation rate of silver atoms is adjusted. Under the synergistic action of the ratio and PVP, PVA and PEG surfactants, the steric hindrance effect can selectively adsorb on the specific crystal face of the silver crystal, effectively controlling the anisotropic growth of the silver crystal. Finally, flower-shaped silver nanoparticles with hierarchical structure are successfully grown.

[0026] Comparative Example 1

[0027] The dropwise rate in Example 1 was changed to 5 mL / min, and the other conditions remained unchanged. The obtained product is shown in Figure 7 , which is mainly spherical particles and cannot form a flower-shaped structure. Because the dropwise rate is too slow to provide the kinetic conditions required to form a flower-shaped structure.

[0028] Comparative Example 2

[0029] The dropwise rate in Example 1 was changed to 50 mL / min, and the other conditions remained unchanged. The obtained product is shown in Figure 8 , which is an irregular block. Because the dropwise rate is too fast, the reaction is out of control and cannot form a uniform flower-shaped structure.

[0030] The above examples and comparative examples are used to illustrate the present application, but these examples are only exemplary and serve only to illustrate. On this basis, various substitutions and improvements can be made to the present application, which all fall within the scope of protection of the present application.​

Claims

1. A method for preparing flower-shaped silver nanoparticles, characterized in that, Includes the following steps: S1. Prepare a mixed aqueous solution of ascorbic acid and surfactant, heat and stir; S2. Prepare an aqueous solution of silver nitrate by heating and stirring; S3. Add the silver nitrate aqueous solution from step S2 dropwise to the mixed aqueous solution from step S1 at a rate of 10-35 mL / min. After the addition is complete, continue the reaction for 5-10 minutes to obtain flower-shaped silver nanoparticles.

2. The method according to claim 1, characterized in that, The concentrations of ascorbic acid and silver nitrate are the same, both ranging from 0.05 to 0.2 mol / L.

3. The method according to claim 1, characterized in that, The surfactant is selected from one or two of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyvinyl alcohol (PVA).

4. The method according to claim 1, characterized in that, The mass ratio of silver nitrate to surfactant is 1:2 to 1:

6.

5. The method according to claim 1, characterized in that, The heating temperature in steps S1 and S2 is 40~50℃.

6. The method according to claim 1, characterized in that, The stirring rate in steps S1 and S2 is 200~400 rpm.

7. A flower-shaped silver nanoparticle prepared by the method according to any one of claims 1 to 6.

8. The flower-shaped silver nanoparticles according to claim 7, characterized in that, Its particle size is 700nm~6μm, and it radiates from the center to form a hierarchical petal-like structure.

Images