Spherical monodisperse silver nanoparticles and a method for preparing the same

Abstract

The application provides a kind of spherical monodisperse nano silver particles and its preparation method, it relates to nanometer material technical field.The preparation method of spherical monodisperse nano silver particles provided by the application includes the following steps: mixing sodium citrate, tannic acid and water to obtain a mixed solution;after the mixed solution is heated to boiling, silver nitrate aqueous solution is added, the obtained reaction solution is heated to boiling again, and the oxidation-reduction reaction is carried out under boiling state to obtain spherical monodisperse nano silver particles;the time of the oxidation-reduction reaction is 40-60 min.In the application, sodium citrate and tannic acid are used as reducing agent to reduce silver nitrate, and by adjusting the temperature and reaction time of the reaction, nano silver particles with uniform morphology and good dispersibility can be obtained.The method has short reaction time, simple required instrument and equipment, low cost, low cost, simple preparation method, low toxicity of reactants, and is more green and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a spherical monodisperse silver nanoparticle and its preparation method. Background Technology

[0002] When particle size is reduced to the nanoscale, a series of unique physicochemical properties emerge. Since the rapid development of nanotechnology in commercial products, nanosilver has been one of the most commonly used nanomaterials in consumer goods. Due to its unique physicochemical properties, nanosilver is applied in various aspects of life.

[0003] Silver nanoparticles are highly sought after in the microelectronics industry due to their excellent electrical conductivity, low melting temperature, and high diffusion coefficient, and hold promise for applications in flexible electronic devices such as electronic and flat panel displays. Furthermore, silver nanoparticles exhibit antibacterial activity against a variety of microorganisms, making them one of the most promising materials in biomedical science.

[0004] Due to the widespread application and production of nanosilver, numerous methods for its preparation have been developed, such as template methods, microemulsion methods, and liquid-phase chemical reduction methods. However, nanosilver prepared by these methods still suffers from drawbacks such as uneven particle size and poor dispersibility. The preparation of nanomaterials is highly susceptible to the influence of reaction conditions, such as temperature, light irradiation, and the amount of reducing agent added. How to adjust these parameters to prepare nanosilver with uniform particle size and good dispersibility remains a crucial problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide spherical monodisperse silver nanoparticles and their preparation method. The silver nanoparticles prepared by this invention have good dispersibility, are all spherical, have uniform morphology, and are of uniform size.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing spherical monodisperse silver nanoparticles, comprising the following steps:

[0008] Sodium citrate, tannic acid, and water are mixed to obtain a mixed solution;

[0009] After heating the mixed solution to boiling, add silver nitrate aqueous solution, and heat the resulting reaction solution to boiling again. A redox reaction is carried out under boiling conditions to obtain spherical monodisperse silver nanoparticles.

[0010] The redox reaction takes 40–60 minutes.

[0011] Preferably, the molar ratio of sodium citrate to tannic acid in the mixed solution is 50:1;

[0012] The molar concentration of sodium citrate is 15 mmol / L.

[0013] Preferably, the concentration of the silver nitrate aqueous solution is 20–30 mmol / L.

[0014] Preferably, the molar ratio of silver nitrate in the sodium citrate and silver nitrate aqueous solution is 15-25:1.

[0015] Preferably, the temperature of the redox reaction is above 130°C.

[0016] Preferably, the redox reaction further includes: cooling the resulting reaction system to room temperature, and then washing and redissolving it sequentially.

[0017] Preferably, the washing is centrifugal washing; the washing solution used is ultrapure water;

[0018] The resolution is performed using ultrapure water.

[0019] The present invention provides spherical monodisperse silver nanoparticles prepared by the preparation method described above, with a particle size of 18-28 nm and a polydispersity index of less than 0.3.

[0020] This invention provides a method for preparing spherical monodisperse silver nanoparticles. The method uses sodium citrate and tannic acid as reducing agents to reduce silver nitrate. By adjusting the reaction temperature and time, uniformly shaped and well-dispersed silver nanoparticles can be obtained. This method has a short reaction time, requires simple and inexpensive equipment, is low in cost, and the preparation method is simple with low toxicity of the reactants, making it relatively green and environmentally friendly. Attached Figure Description

[0021] Figure 1 The UV-Vis spectrum of the spherical monodisperse silver nanoparticles prepared in Example 1;

[0022] Figure 2 Transmission electron microscope image of the spherical monodisperse silver nanoparticles prepared in Example 1;

[0023] Figure 3 The particle size distribution diagram of the spherical monodisperse silver nanoparticles prepared in Example 1 is shown.

[0024] Figure 4 Transmission electron microscope image of the product prepared for Comparative Example 1.

[0025] Figure 5 Transmission electron microscope image of the product prepared for Comparative Example 2. Detailed Implementation

[0026] This invention provides a method for preparing spherical monodisperse silver nanoparticles, comprising the following steps:

[0027] Sodium citrate, tannic acid, and water are mixed to obtain a mixed solution;

[0028] After heating the mixed solution to boiling, add silver nitrate aqueous solution, and heat the resulting reaction solution to boiling again. A redox reaction is carried out under boiling conditions to obtain spherical monodisperse silver nanoparticles.

[0029] The redox reaction takes 40–60 minutes.

[0030] This invention involves mixing sodium citrate, tannic acid, and water to obtain a mixed solution. In this invention, the preferred molar ratio of sodium citrate to tannic acid in the mixed solution is 50:1; the preferred molar concentration of sodium citrate is 15 mmol / L. In a specific embodiment of this invention, the sodium citrate is sodium citrate dihydrate. In this invention, the water is preferably ultrapure water.

[0031] In this invention, the mixing of sodium citrate, tannic acid, and water preferably comprises: dissolving sodium citrate in water, and then adding tannic acid. In this invention, the mixing is preferably performed using magnetic stirring. In this invention, the mixing is preferably carried out at room temperature.

[0032] After obtaining the mixed solution, the present invention heats the mixed solution to boiling, adds an aqueous solution of silver nitrate, and reheats the resulting reaction solution to boiling. A redox reaction is then carried out under boiling conditions to obtain spherical monodisperse silver nanoparticles. In this invention, the heating is preferably performed in an oil bath. In a specific embodiment of the present invention, the glycerol level in the oil bath is slightly higher than the level of the reaction solution in the round-bottom flask.

[0033] In this invention, the temperature at which the mixed solution is first heated to boiling is preferably above 135°C.

[0034] In this invention, the concentration of the silver nitrate aqueous solution is preferably 20-30 mmol / L, more preferably 25 mmol / L. In this invention, the preparation method of the silver nitrate aqueous solution preferably includes: dissolving 17 mg of silver nitrate in 4 mL of ultrapure water.

[0035] In this invention, the molar ratio of sodium citrate to silver nitrate in the aqueous solution is preferably 15 to 25:1, more preferably 20:1.

[0036] In this invention, the temperature of the redox reaction is preferably 130°C or higher, more preferably 130°C. Setting this temperature allows the reaction system to remain at boiling point while reducing energy consumption. In this invention, the redox reaction time is 40–60 min, preferably 40 min.

[0037] In this invention, the redox reaction is preferably carried out in a dark place.

[0038] In this invention, the redox reaction preferably further includes: cooling the resulting reaction system to room temperature, and then sequentially washing and redissolving. In this invention, the washing is preferably centrifugal washing; the washing solution is preferably ultrapure water. In this invention, the centrifugal washing speed is preferably 15000g; the single centrifugation time is preferably 20min. In this invention, the washing is preferably performed three times. Centrifugal washing in this invention allows for better separation of the product from the washing solution. In this invention, the redissolving is preferably performed using ultrapure water.

[0039] In this invention, the spherical monodisperse silver nanoparticles are preferably present in a state of dispersion in water.

[0040] This invention provides spherical monodisperse silver nanoparticles prepared by the preparation method described in the above technical solution. In this invention, the particle size of the spherical monodisperse silver nanoparticles is 18-28 nm; the polydispersity index of the spherical monodisperse silver nanoparticles is less than 0.3, preferably 0.2-0.3, and more preferably 0.225.

[0041] In this invention, the hydrated ionic radius of the spherical monodisperse silver nanoparticles is preferably 30-35 nm.

[0042] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. 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.

[0043] Example 1

[0044] Weigh 441 mg of sodium citrate dihydrate solid into a 250 mL round-bottom flask, then add 100 mL of ultrapure water into the round-bottom flask and stir magnetically at room temperature to dissolve it, thus obtaining a 15 mmol / L sodium citrate reaction solution.

[0045] Weigh 17 mg of silver nitrate solid and dissolve it in 4 mL of ultrapure water to obtain a silver nitrate solution with a concentration of 25 mmol / L.

[0046] Add 51 mg of tannic acid solid powder to the sodium citrate reaction solution, gently shake the round-bottom flask to disperse the powder adhering to the inner wall of the flask into the reaction solution, and the reaction solution changes from colorless and transparent to light yellow; place the round-bottom flask in a magnetically stirred oil bath, the level of glycerol in the oil bath should be slightly higher than the level of the reaction solution in the round-bottom flask, and be careful not to let the round-bottom flask touch the inner wall of the oil bath; set the heating temperature to 135℃, connect the serpentine condenser and introduce cooling water, and start stirring and heating under light-proof conditions;

[0047] When bubbles rise from the bottom of the round-bottom flask and large bubbles are generated from the center of the liquid surface outward, the mixture boils. At this point, immediately remove the condenser and quickly add 3 mL of 25 mmol / L silver nitrate solution at room temperature. The reaction solution will stop boiling. Then immediately reconnect the condenser and wait for the reaction solution to boil again. Adjust the temperature of the oil bath to 130°C and carry out the redox reaction in the dark for 40 minutes.

[0048] After the reaction is complete, close the oil bath, remove the round-bottom flask and the connected condenser together, and place it in a dark environment at room temperature. After it cools to room temperature, remove the serpentine condenser and clean the product.

[0049] After sonicating the round-bottom flask, the nanomaterials adhering to its wall dispersed in the solution. The solution in the round-bottom flask was transferred to a centrifuge tube. The centrifuge was set at 15000g and centrifuged for 20 minutes. After discarding the supernatant, ultrapure water was added and shaken well. The mixture was centrifuged again and washed three times. The final precipitate was dissolved in 5mL of ultrapure water to obtain a dispersion of silver nanoparticles, which was stored in a refrigerator at 4℃ protected from light.

[0050] The prepared silver nanoparticle dispersion was characterized using a UV-Vis spectrophotometer, a nanoparticle size analyzer, and an electron microscope. The UV-Vis spectrum was obtained by scanning wavelengths from 300 nm to 800 nm using a UV-Vis spectrophotometer. Figure 1 As shown, the ultraviolet characteristic peaks of the silver nanoparticles are stable, confirming that the obtained product is silver nanoparticles.

[0051] Particle size was measured using a high-resolution transmission electron microscope and a nanoparticle size analyzer (DLS), such as... Figures 2-3 As shown, the particle size of the silver nanoparticles was determined to be 18–28 nm, and the morphology was uniform.

[0052] The nano-silver particle dispersion prepared in this embodiment was ultrasonicated and its hydrated ionic radius was measured to be 33.9±13.5 nm using a nanoparticle size analyzer. Its polydispersity index was 0.225, which is less than 0.3, proving that the nano-silver particles have good dispersibility.

[0053] Comparative Example 1

[0054] The preparation method is basically the same as in Example 1, except that after adding silver nitrate solution, the reaction solution was not allowed to boil again, but the temperature of the oil bath was directly adjusted to 130°C and the oxidation-reduction reaction was carried out in the dark for 40 minutes.

[0055] This method does not provide sufficient heat for the reaction, hence the electron micrograph of the product ( Figure 4 The results show that most of the nanomaterials obtained are small-sized, non-uniform silver nanoparticles.

[0056] Comparative Example 2

[0057] The preparation method is basically the same as that in Example 1, except that the redox reaction time is adjusted to 30 minutes.

[0058] The heating time in this method is insufficient, according to the electron micrograph of the product ( Figure 5 As can be seen, the secondary reduction of small-diameter silver nanoparticles is still in progress, resulting in large particles of about 20 nm, while small particles around them have not yet fully reacted.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing spherical monodisperse silver nanoparticles, comprising the following steps: Sodium citrate, tannic acid, and water are mixed to obtain a mixed solution; After heating the mixed solution to boiling, add silver nitrate aqueous solution, and heat the resulting reaction solution to boiling again. Under boiling conditions, carry out redox reaction to obtain spherical monodisperse silver nanoparticles. The redox reaction takes 40-60 minutes; The molar ratio of sodium citrate to tannic acid in the mixed solution is 50:1; the molar concentration of sodium citrate is 15 mmol / L. The concentration of the silver nitrate aqueous solution is 20~30 mmol / L; The molar ratio of silver nitrate in the sodium citrate and silver nitrate aqueous solution is 15~25:

1.

2. The preparation method according to claim 1, characterized in that, The redox reaction is carried out at a temperature above 130°C.

3. The preparation method according to claim 1, characterized in that, The redox reaction is followed by: cooling the resulting reaction system to room temperature, and then washing and redissolving it sequentially.

4. The preparation method according to claim 3, characterized in that, The washing process is centrifugal washing; the washing solution used is ultrapure water. The resolution is performed using ultrapure water.

5. The spherical monodisperse silver nanoparticles prepared by the preparation method according to any one of claims 1 to 4 have a particle size of 18 to 28 nm and a polydispersity index of less than 0.3.

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