Nano silver solution with small and adjustable particle size and its preparation method

Abstract

The present invention provides a method for preparing a nano-silver solution with small and adjustable particle sizes. Using a silver nitrate solution as the silver source, sodium borohydride and tannic acid as co-reducing agents, and sodium citrate and polyvinylpyrrolidone as protective agents, a nano-silver solution with a narrow particle size distribution and small particle sizes is prepared, and it has good dispersibility. By adjusting the dosage ratio of the two reducing agents, the size of the nano-silver solution can be adjusted. Polyvinylpyrrolidone is used to pre-coat the silver source crystals, and a method of sharing a double reducing agent and a protective agent is adopted during the reduction process to enhance the dispersibility and stability of the nano-silver solution. The preparation cost of the present invention is low, the energy consumption is small, meeting the requirements of "green production"; the preparation conditions are mild, the operation is simple, and it is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and particularly relates to a nano-silver solution with small and adjustable particle size and a preparation method thereof. Background Art

[0002] Due to its unique physical and chemical properties, nano-silver has shown broad application prospects in multiple fields. Its main characteristics include extremely small particle size, high specific surface area, good electrical conductivity, and antibacterial properties. Due to the extremely small size of nano-silver particles, they can fully contact the surrounding environment, thus exerting strong biological activity and chemical reactivity; the high specific surface area enables nano-silver to have a larger reaction area, enhancing its interaction ability with other substances. In addition, nano-silver also has good electrical conductivity, making it widely used in fields such as electronic devices.

[0003] The commonly used synthesis method for nano-silver is the chemical reduction method, but the particle size usually cannot be concentratedly controlled within a range, the particle size distribution is relatively wide, and it is easy to agglomerate; therefore, a simple and easy-to-operate synthesis method is needed to solve the above problems.

[0004] In view of this, it is necessary to design an improved nano-silver solution with small and adjustable particle size and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] Aiming at the defects of the above-mentioned prior art, the purpose of the present invention is to provide a nano-silver solution with small and adjustable particle size and a preparation method thereof. Using silver nitrate solution as the silver source, sodium borohydride and tannic acid as co-reducing agents, and sodium citrate and polyvinylpyrrolidone as protective agents, a nano-silver solution with a narrow particle size distribution and small particle size is prepared, and the dispersion is good.

[0006] To achieve the above purpose, the present invention provides a preparation method for a nano-silver solution with small and adjustable particle size, comprising the following steps:

[0007] S1. Prepare a silver nitrate solution with a concentration of 0.01~0.05 mol / L as the silver source solution;

[0008] S2. Prepare a sodium borohydride solution with a concentration of 0.05~0.3 mol / L and a tannic acid solution with a concentration of 0.1~5 mol / L respectively. Mix the sodium borohydride solution and the tannic acid solution according to a predetermined ratio and stir evenly to obtain a reducing agent solution;

[0009] S3. Prepare a sodium citrate solution with a concentration of 0.1~0.5 mol / L and a polyvinylpyrrolidone solution with a concentration of 0.0001~0.0003 mol / L respectively as the protective agent solution;

[0010] S4. Add the silver source solution into the polyvinylpyrrolidone solution. After brief stirring, add the sodium citrate solution and the reducing agent solution, and continue stirring for a predetermined time to obtain a silver nanoparticle solution. Subject the obtained silver nanoparticle solution to ultrasonic cavitation treatment. The particle size of the silver nanoparticles in the silver nanoparticle solution is 5 - 30 nm.

[0011] As a further improvement of the present invention, in step S2, the molar ratio of the sodium borohydride solution to the tannic acid solution is 1:(0.3 - 15).

[0012] As a further improvement of the present invention, in step S4, the molar ratio of the silver source solution to the polyvinylpyrrolidone solution is (7 - 10):1.

[0013] As a further improvement of the present invention, the time for the brief stirring is 30 - 60 s.

[0014] As a further improvement of the present invention, the stirring speed is 300 - 500 rpm.

[0015] As a further improvement of the present invention, the time for the continuous stirring is 5 - 10 min.

[0016] As a further improvement of the present invention, the volume ratio of the sodium citrate solution to the reducing agent solution is 1:(1.3 - 1.5).

[0017] As a further improvement of the present invention, the molar ratio of the silver source solution to the sodium citrate solution is 1:(10 - 15).

[0018] The present invention also provides a silver nanoparticle solution with a small and adjustable particle size, which is prepared by the preparation method of the silver nanoparticle solution with a small and adjustable particle size described above.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The present invention provides a silver nanoparticle solution with a small and adjustable particle size and its preparation method. By using silver nitrate solution as the silver source, sodium borohydride and tannic acid as co-reducing agents, and sodium citrate and polyvinylpyrrolidone as protective agents, a silver nanoparticle solution with a narrow particle size distribution and a small particle size is prepared, and the dispersion is good; by adjusting the dosage ratio of the two reducing agents, the size of the silver nanoparticle solution can be adjusted; the silver source crystal is pre-coated with polyvinylpyrrolidone in advance, and a method of sharing the double reducing agent and the protective agent is adopted during the reduction process to enhance the dispersion and stability of the silver nanoparticle solution. The preparation cost of the present invention is low, the energy consumption is small, and it meets the requirements of "green production"; the preparation conditions are mild, the operation is simple, and it is suitable for large-scale production.

[0021] 2. By the combined action of two reducing agents, the present invention can improve the concentration of the solution size, and by adjusting the ratio of the two reducing agents, the size of the silver nanoparticle solution can be adjusted; meanwhile, the occurrence of silver mirror reaction in the conventional chemical reduction method can be avoided.

[0022] 3. The present invention uses a polyvinylpyrrolidone solution as the bottom liquid, and the silver source solution is then added, which can achieve the pre-coating effect of the dispersant on the silver source crystal and improve the dispersibility of the silver nanoparticle solution; the subsequent addition of the sodium citrate solution forms a tiny protective shell on the surface of the generated silver nanoparticle solution, further improving the dispersibility and stability of the solution. With the cooperation of ultrasonic cavitation, no bubbles will be generated during the reaction, and the growth of nanoparticles is more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the TEM image of the silver nanoparticle solution with small and adjustable particle size provided in Example 1 of the present invention.

[0024] Figure 2 It is the SEM image of the silver powder synthesized from the silver nanoparticle solution provided in Example 1 of the present invention.

[0025] Figure 3 It is the TEM image of the silver nanoparticle solution provided in Comparative Example 1.

[0026] Figure 4 It is the SEM image of the silver powder synthesized from the silver nanoparticle solution provided in Comparative Example 1.

[0027] Figure 5 It is the SEM image of the silver powder synthesized from the silver nanoparticle solution provided in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the drawings and specific embodiments.

[0029] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0030] In addition, it should also be noted that the term "comprises", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0031] The present invention provides a preparation method of a silver nanoparticle solution with small and adjustable particle size, comprising the following steps:

[0032] S1. Prepare a silver nitrate solution with a concentration of 0.01 - 0.05 mol / L as the silver source solution.

[0033] S2. Prepare a sodium borohydride solution with a concentration of 0.05 - 0.3 mol / L and a tannic acid solution with a concentration of 0.1 - 5 mol / L respectively. Mix the sodium borohydride solution and the tannic acid solution according to a predetermined ratio and stir evenly to obtain a reducing agent solution.

[0034] Specifically, the molar ratio of the sodium borohydride solution to the tannic acid solution is preferably 1:(0.3 - 15). Through the combined action of the two reducing agents, the concentration of the solution size can be improved. By adjusting the dosage ratio of the two reducing agents, the size of the silver nanosol can be adjusted. When the dosage of tannic acid is too high, it will affect the dispersibility and stability of the silver nanosol, resulting in aggregation or precipitation of the silver nanosol.

[0035] S3. Prepare a sodium citrate solution with a concentration of 0.1 - 0.5 mol / L and a polyvinylpyrrolidone solution with a concentration of 0.0001 - 0.0003 mol / L respectively as the protective agent solution.

[0036] Using the polyvinylpyrrolidone solution as the bottom liquid and then adding the silver source solution can achieve the pre - coating effect of the dispersant on the silver source crystals and improve the dispersibility of the silver nanosol; the subsequent addition of the sodium citrate solution forms a tiny protective shell on the surface of the generated silver nanosol, further improving the dispersibility and stability of the solution.

[0037] S4. Add the silver source solution into the polyvinylpyrrolidone solution, add the sodium citrate solution and the reducing agent solution after a short - time stirring, stir continuously for a predetermined time to obtain a silver nanosol, and perform ultrasonic cavitation treatment on the obtained silver nanosol. The particle size of the silver nanoparticles in the obtained silver nanosol is 5 - 30 nm.

[0038] Specifically, the molar ratio of the silver source solution to the polyvinylpyrrolidone solution is preferably (7 - 10):1; the short - time stirring time is preferably 30 - 60 s; the stirring speed is 300 - 500 rpm; the volume ratio of the sodium citrate solution to the reducing agent solution is preferably 1:(1.3 - 1.5); the continuous stirring time is preferably 5 - 10 min; the molar ratio of the silver source solution to the sodium citrate solution is preferably 1:(10 - 15); the addition method is rapid pouring.

[0039] By adjusting the concentration of the silver solution, the occurrence of the silver mirror reaction in the conventional chemical reduction method can be avoided. Pre - coat the silver source crystals with polyvinylpyrrolidone in advance, and use the combined method of two reducing agents and a protective agent during the reduction process to enhance the dispersibility and stability of the silver nanosol. With the cooperation of ultrasonic cavitation, no bubbles will be generated during the reaction process, and the growth of nanoparticles is more uniform.

[0040] The following is a description of the nano - silver solution with small and adjustable particle size and its preparation method provided by the present invention in combination with specific embodiments.

[0041] Example 1

[0042] Example 1 provides a preparation method of a nano - silver solution with small and adjustable particle size, including the following steps:

[0043] S1. Using ultrapure water as a solvent, prepare 100 mL of silver nitrate solution with a concentration of 0.01 mol / L.

[0044] S2. Using ultrapure water as a solvent, prepare 100 mL of sodium borohydride solution with a concentration of 0.1 mol / L and 30 mL of tannic acid solution with a concentration of 0.1 mol / L respectively. Mix the sodium borohydride solution and the tannic acid solution, and stir evenly to obtain a reducing agent solution.

[0045] S3. Using ultrapure water as a solvent, prepare 100 mL of sodium citrate solution with a concentration of 0.1 mol / L and 1.5 L of polyvinylpyrrolidone solution with a concentration of 0.0001 mol / L respectively.

[0046] S4. Add 100 mL of the silver source solution to 1.5 L of polyvinylpyrrolidone solution. After stirring for 1 min, add the sodium citrate solution and the reducing agent solution simultaneously, and continue stirring for 5 min to obtain a nano - silver solution. The obtained nano - silver solution is subjected to ultrasonic cavitation treatment. The TEM image of the obtained nano - silver solution is as Figure 1 shown, and the particle size distribution is shown in Table 1.

[0047] The obtained nano - silver solution is used for the preparation of silver powder: Dissolve 75 g of silver nitrate in 200 mL of water, dissolve 40 g of ascorbic acid in 130 mL of water, and dissolve 6 g of polyvinylpyrrolidone in 500 mL of water as the bottom solution. Add 3 g of ascorbic acid to the bottom solution. After dissolution, add 100 mL of the nano - silver solution to the bottom solution. Pump the silver nitrate solution and the ascorbic acid solution into the bottom solution simultaneously at a speed of 60 mL / min, stop stirring after 5 min. After the solid sediment settles, remove the supernatant, wash it 6 times with ultrapure water and 3 times with ethanol; After drying, the silver powder synthesized with this nano - silver solution is obtained, and its SEM image is as Figure 2 shown.

[0048] After testing, the size of the silver powder prepared with this nano - silver solution is distributed in the range of 400 - 600 nm, with good dispersion, narrow particle size distribution, and the tapped density is 4.9 g / cm 3 , Mix the silver powder obtained in this example with flake silver powder and organic components to make a conductive silver bar with a size of 4 cm * 1 cm * 0.4 cm, and conduct a resistance test. The test result is 1.92 mΩ.

[0049] Example 2

[0050] Example 2 provides a method for preparing a nano-silver solution with small and adjustable particle sizes. Compared with Example 1, the only difference is that the concentration of the tannic acid solution is 0.5 mol / L, and other experimental parameters and conditions are basically the same as those in Example 1, which will not be elaborated here. The particle size distribution is shown in Table 1.

[0051] Example 3

[0052] Example 3 provides a method for preparing a nano-silver solution with small and adjustable particle sizes. Compared with Example 1, the only difference is that the concentration of the tannic acid solution is 5 mol / L, and other experimental parameters and conditions are basically the same as those in Example 1, which will not be elaborated here. The particle size distribution is shown in Table 1.

[0053] Comparative Example 1

[0054] Comparative Example 1 provides a method for preparing a nano-silver solution with small and adjustable particle sizes. Compared with Example 1, the only difference is that the tannic acid solution is not added, and other experimental parameters and conditions are basically the same as those in Example 1, which will not be elaborated here. The particle size distribution of the obtained nano-silver is shown in Table 1, and the TEM image is as Figure 3 shown.

[0055] The obtained nano-silver solution is used for the preparation of silver powder: 75 g of silver nitrate is dissolved in 200 mL of water, 40 g of ascorbic acid is dissolved in 130 mL of water, and 6 g of polyvinylpyrrolidone is dissolved in 500 mL of water to be used as the base solution. 3 g of ascorbic acid is added to the base solution. After dissolution, 100 mL of the nano-silver solution is added to the base solution. The silver nitrate solution and the ascorbic acid solution are simultaneously pumped into the base solution at a speed of 60 mL / min. After stirring for 5 min, the stirring is stopped. After the solid sediment settles, the supernatant is removed, and it is washed 6 times with ultrapure water and 3 times with ethanol; after drying, the silver powder synthesized with this nano-silver solution is obtained, and its SEM image is as Figure 4 shown.

[0056] After testing, the size of the silver powder prepared with this nano-silver solution is distributed in the range of 300 - 700 nm, and there are several phenomena of particle agglomeration, and the particle size distribution is relatively wide. The tapped density is 3.5 g / cm 3 ³. The silver powder obtained in this example is mixed with flake silver powder and organic components to form a conductive silver bar with a size of 4 cm * 1 cm * 0.4 cm, and the resistance is tested. The test result is 3.28 mΩ.

[0057] Compared with Example 1, tannic acid solution was not added in Comparative Example 1, and the obtained silver nanoparticles had a wider particle size distribution. Because the trace tannic acid solution in Example 1 contributed to the growth of silver nanoparticle nuclei, accelerating the growth rate of silver nanoparticle nuclei, a silver nanoparticle solution with a narrow particle size distribution could be obtained. The silver nanoparticle solution prepared in Comparative Example 1 was used to synthesize silver powder. The particle size distribution of the silver powder was wide, resulting in the aggregation and growth of particles of various sizes during the preparation process, reducing its tapped density and increasing the resistance value.

[0058] Comparative Example 2

[0059] Comparative Example 2 provided a method for preparing a silver nanoparticle solution with small and adjustable particle sizes. Compared with Example 1, the only difference was that sodium citrate solution was not added, and other experimental parameters and conditions were basically the same as those in Example 1, which will not be elaborated here. The particle size distribution of the obtained silver nanoparticles is shown in Table 1.

[0060] The obtained silver nanoparticle solution was used for the preparation of silver powder: 75 g of silver nitrate was dissolved in 200 mL of water, 40 g of ascorbic acid was dissolved in 130 mL of water, and 6 g of polyvinylpyrrolidone was dissolved in 500 mL of water as the base solution. 3 g of ascorbic acid was added to the base solution. After dissolution, 100 mL of silver nanoparticle solution was added to the base solution. The silver nitrate solution and ascorbic acid solution were simultaneously pumped into the base solution at a speed of 60 mL / min. After stirring for 5 min, the stirring was stopped. After the solid sediment settled, the supernatant was removed, and it was washed 6 times with ultrapure water and 3 times with ethanol; after drying, the silver powder synthesized with this silver nanoparticle was obtained, and its SEM image was as Figure 5 shown.

[0061] After testing, the size of the silver powder prepared with this silver nanoparticle was distributed between 300 - 600 nm, with obvious aggregation phenomenon, and the tapped density was 2.8 g / cm 3 , the silver powder obtained in this example was mixed with flake silver powder and organic components to make a 4 cm * 1 cm * 0.4 cm conductive silver bar, and the resistance was tested. The test result was 4.52 mΩ.

[0062] Compared with Example 1, in Comparative Example 2, sodium citrate protective agent was not added, and the obtained silver nanoparticle solution had a wide particle size distribution. And according to the D90 data, there was a certain aggregation phenomenon in the solution; the silver nanoparticle solution prepared in Comparative Example 2 was used to synthesize silver powder, and the silver powder had obvious aggregation phenomenon, low tapped density, resulting in an increase in the resistance value.

[0063]

[0064] In summary, the nano silver solution with small and adjustable particle size provided by the present invention and its preparation method can adjust the size of the nano silver solution by adjusting the dosage ratio of two reducing agents; the silver source crystal is pre-coated with polyvinylpyrrolidone in advance, and a double reducing agent and a protective agent are used together during the reduction process, enhancing the dispersibility and stability of the nano silver solution.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a nano silver solution with a small and adjustable particle size, characterized in that: The following steps are involved: S1. Prepare 0.01-0.05 mol / L silver nitrate solution as a silver source solution; S2. Prepare 0.05-0.3 mol / L sodium borohydride solution and 0.1-5 mol / L tannic acid solution respectively, mix the sodium borohydride solution and the tannic acid solution in a predetermined ratio, stir evenly, and obtain a reducing agent solution; the molar ratio of the sodium borohydride solution to the tannic acid solution is 1:(0.3-15); S3. Prepare 0.1-0.5 mol / L sodium citrate solution and 0.0001-0.0003 mol / L polyvinyl pyrrolidone solution as protective agent solutions; S4. Add the silver source solution to the polyvinyl pyrrolidone solution to pre-coat the silver source crystals, wherein the molar ratio of the silver source solution to the polyvinyl pyrrolidone solution is (7-10):1; after briefly stirring for 30-60 seconds, add the sodium citrate solution and the reducing agent solution by rapid pouring, wherein the volume ratio of the sodium citrate solution to the reducing agent solution is 1:(1.3-1.5), and continue stirring for 5-10 minutes to obtain a nanosilver solution, and subject the obtained nanosilver solution to ultrasonic cavitation treatment, wherein the particle size of the nanosilver in the nanosilver solution is 5-30 nm.

2. The method for preparing a nano silver solution with a small and adjustable particle size according to claim 1, characterized in that: In step S4, the stirring speed is 300-500 rpm.

3. The method for preparing a nano silver solution with a small and adjustable particle size according to claim 1, characterized in that: The molar ratio of the silver source solution to the sodium citrate solution is 1:(10-15).

4. A nanosilver solution with small and adjustable particle size, characterized in that: The nano silver solution is prepared by the method for preparing the nano silver solution with small and adjustable particle size as described in any one of claims 1 to 3.

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