A method for preparing ultra-long silver nanowires

Abstract

The present invention discloses a method for preparing ultra-long silver nanowires. By adopting a seed growth method and strictly controlling chemical reaction parameters, a silver nanowire is initially grown, which serves as a seed crystal. The modified growth process is then repeated to grow extremely long silver nanowires. In addition to the innovation of the seed growth method, the method also incorporates a nucleation inhibitor during the seed growth process. This inhibitor prevents the formation of new nuclei, promotes the continued attachment and reduction of silver nitrate to existing silver nanowire seed crystals, and subsequently causes the crystals to continue growing, thereby significantly increasing the length of the silver nanowires.

Description

Technical Field

[0001] The present invention relates to the technical field of silver nanomaterials, and in particular to a method for preparing ultra-long silver nanowires. Background Art

[0002] Transparent conductive films (TCFs) are an important component of devices such as tablets, readers, smartphones, touch screens, OLEDs, and organic solar cells. Silver nanowires (AgNWs) are one-dimensional metallic materials. Due to their excellent electrical and thermal conductivity, good mechanical stability, and relatively affordable price, AgNWs are considered to have the most potential to replace ITO as the raw material for the next generation of transparent conductive films, thus attracting widespread attention from many researchers. As far as current research is concerned, the properties of AgNWs are closely related to their diameter, length, and dispersion. However, it is difficult to achieve both light transmittance and electrical conductivity in flexible transparent conductive films based on AgNWs. Therefore, in order to effectively solve the above problems, the research on batch preparation technology of AgNWs with higher aspect ratios has become a difficult problem that scientists are currently trying to overcome.

[0003] Existing research shows that the smoother the surface and the longer the AgNWs, the lower the junction resistance between them. Consequently, the sheet resistance of the AgNW-based transparent conductor is lower and the conductivity is better. However, existing silver nanowires produced by conventional methods are relatively short, mostly ranging from 20 to 50 μm. For example, a method for preparing high-aspect-ratio silver nanowires, disclosed in Publication No. CN103537710A, produces silver nanowires as long as 40 to 60 μm, limiting their electrical and optical properties. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing ultra-long silver nanowires, wherein the length of the prepared silver nanowires is extended to 300-800 μm, which greatly increases the length of the silver nanowires.

[0005] In order to achieve the above object, the solution of the present invention is:

[0006] A method for preparing ultra-long silver nanowires comprises the following steps:

[0007] Step 1, preparation of seed crystals:

[0008] S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 0.08-2.4 g of PVP with an average molecular weight of 1,300,000 and 0.08-2.4 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until they are completely dissolved to obtain a mixed solution;

[0009] S2. Then, add 0.08-2.4 g of silver nitrate to the mixed solution obtained in S1. After it is completely dissolved, add 1-10 mL of 0.3-25 mM ethylene glycol solution of metal chloride to the mixed solution and stir for 1 min.

[0010] The metal chloride is one of NaCl, CuCl2 and FeCl3;

[0011] S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 110-170°C, stir for 10 minutes, stop stirring, react for 2-3 hours to obtain seed crystals, and store them in an oven at 95°C for later use;

[0012] Step 2: Preparation of crystal nucleation inhibitor:

[0013] Dissolve 0.1-0.2 g of surfactant in 50 mL of ethylene glycol / glycerol mixed solvent to obtain a crystal nucleation inhibitor for later use;

[0014] The surfactant is one of didodecyldimethylammonium bromide, hexadecyltrimethylammonium bromide and didodecyldimethylammonium bromide;

[0015] Step 3: Growth of seed crystals:

[0016] S1. Then, 50 mL of ethylene glycol was added to the flask, and the flask was suspended in an oil bath and heated under stirring. 10 to 15 mL of a crystal nucleus inhibitor was injected, followed by adding 0.08 to 2.4 g of PVP with an average molecular weight of 1,300,000 and 0.08 to 2.4 g of PVP with an average molecular weight of 40,000 and fully dissolving them uniformly. Then, 10 to 15 mL of the synthesized seed crystals were injected, and then 25 mL of AgNO3 solution was added using a syringe pump at an injection rate of 0.5 to 2 mL / min. As the growth progressed, the color of the reaction solution changed from bright ivory to opaque gray-green. After the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature.

[0017] S2, then adding 100-500 mL of acetone solution to the synthesized silver nanowires to remove excess chemicals;

[0018] S3. The mixture obtained after impurity removal is then centrifuged to obtain a precipitate, which is then redispersed in 100 to 500 mL of ethanol and centrifuged several times to wash away the remaining PVP and other chemicals, and finally dispersed in ethanol to obtain ultra-long silver nanowires with a length of 300 to 800 μm.

[0019] In S1 of step 1, the usage ratio of PVP with an average molecular weight of 1,300,000 to PVP with an average molecular weight of 40,000 is 1:2 to 2:1.

[0020] In step 2, the mass ratio of the ethylene glycol / propylene glycol mixed solvent is 2 to 1:1.

[0021] In S1 of step 3, the heating temperature is 110-170° C., and the concentration of the AgNO 3 solution is 0.32-9.6 g / 100 mL.

[0022] In S1 of step 3, the usage ratio of PVP with an average molecular weight of 1,300,000 to PVP with an average molecular weight of 40,000 is 1:2 to 2:1.

[0023] In S2 of step 3, the volume ratio of the acetone solution is 1:8-9.

[0024] By adopting the above technical solution, the present invention provides a method for preparing ultra-long silver nanowires. By using a seed growth method and strictly controlling chemical reaction parameters, a silver nanowire is initially grown, which is used as a seed crystal. The modified growth process is then repeated to grow very long silver nanowires. However, simply adding chemicals and repeating the conventional silver nanowire growth process cannot achieve the growth of longer silver nanowires; instead, many nanoparticles are produced as byproducts. In addition to the innovative seed growth method, the present invention also incorporates a nucleation inhibitor during the seed growth process to prevent the formation of new nuclei, promote the continued attachment and reduction of silver nitrate to the existing silver nanowire seed crystals, and thus promote further crystal growth. This significantly increases the length of the silver nanowires. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the ultra-long silver nanowires prepared in Example 1;

[0026] Figure 2 This is the SEM image of the ultra-long silver nanowires prepared in Example 2;

[0027] Figure 3 This is the SEM image of the ultra-long silver nanowires prepared in Example 3;

[0028] Figure 4 This is the SEM image of the silver nanowires prepared in the comparative example. DETAILED DESCRIPTION

[0029] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0030] Example 1

[0031] A method for preparing ultra-long silver nanowires comprises the following steps:

[0032] Step 1, preparation of seed crystals:

[0033] S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 1.2 g of PVP with an average molecular weight of 1,300,000 and 1.6 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until completely dissolved to obtain a mixed solution;

[0034] S2, then add 1.2g of silver nitrate to the mixed solution obtained in S1, and after it is completely dissolved, add 10mL of 12mMFeCl3 ethylene glycol solution to the above mixed solution and stir for 1min;

[0035] S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 170°C, stir for 10 minutes, stop stirring, react for 3 hours to obtain seed crystals, and store them in an oven at 95°C for later use;

[0036] Step 2: Preparation of crystal nucleation inhibitor:

[0037] Dissolve 0.1 g of didodecyldimethylammonium bromide in 50 mL of a 2:1 ethylene glycol / glycerol mixed solvent to obtain a nucleation inhibitor for later use.

[0038] Step 3: Growth of seed crystals:

[0039] S1. Then, 50 mL of ethylene glycol was added to a clean flask, and the flask was suspended in an oil bath and heated to 130°C under continuous magnetic stirring. 10 mL of a nucleation inhibitor was injected, and then 1.2 g of PVP with an average molecular weight of 1,300,000 and 1.6 g of PVP with an average molecular weight of 40,000 were added to the above ethylene glycol in sequence until completely dissolved. Then, 15 mL of the synthesized seed crystals were injected, and then 25 mL of a 1.2 g / 100 mL AgNO3 solution was added using a syringe pump at an injection rate of 1 mL / min. As the growth progressed, the color of the reaction solution changed from bright ivory to opaque gray-green. After the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature.

[0040] S2, then adding 400 mL of acetone solution with a volume fraction of 1:9 to the synthesized silver nanowires to remove excess chemicals such as ethylene glycol and PVP;

[0041] S3. The mixture obtained after impurity removal was then centrifuged to obtain a precipitate, which was redispersed in 200 mL of ethanol and centrifuged several times to wash away the remaining PVP and other chemicals. Finally, the mixture was dispersed in ethanol to obtain ultra-long silver nanowires with a length of 300 to 500 μm. The SEM image of the silver nanowires is shown in FIG. Figure 1 shown.

[0042] Example 2

[0043] A method for preparing ultra-long silver nanowires comprises the following steps:

[0044] Step 1, preparation of seed crystals:

[0045] S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 0.16 g of PVP with an average molecular weight of 1,300,000 and 0.08 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until completely dissolved to obtain a mixed solution;

[0046] S2. Then, 0.24 g of silver nitrate was added to the mixed solution obtained in S1. After it was completely dissolved, 1 mL of 2 mM CuCl2 ethylene glycol solution was added to the mixed solution and stirred for 1 min.

[0047] S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 150°C, stir for 10 minutes, stop stirring, react for 3 hours to obtain seed crystals, and store them in an oven at 95°C for later use;

[0048] Step 2: Preparation of crystal nucleation inhibitor:

[0049] Dissolve 0.2 g of hexadecyltrimethylammonium bromide in 50 mL of a 1:1 ethylene glycol / glycerol mixed solvent to obtain a nucleation inhibitor for later use.

[0050] Step 3: Growth of seed crystals:

[0051] S1. Then, 50 mL of ethylene glycol was added to a clean flask, which was then suspended in an oil bath and heated to 150°C under continuous magnetic stirring. 10 mL of a nucleation inhibitor was injected, followed by the addition of 0.16 g of PVP with an average molecular weight of 1,300,000 and 0.08 g of PVP with an average molecular weight of 40,000 to the above ethylene glycol until completely dissolved. 15 mL of the synthesized seed crystals was then injected, followed by the addition of 25 mL of a 0.64 g / 100 mL AgNO3 solution using a syringe pump at an injection rate of 1 mL / min. As the growth progressed, the color of the reaction solution changed from bright ivory to opaque gray-green. After the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature.

[0052] S2, then adding 500 mL of acetone solution with a volume fraction of 1:9 to the synthesized silver nanowires to remove excess chemicals such as ethylene glycol and PVP;

[0053] S3. The mixture obtained after impurity removal was centrifuged to obtain a precipitate, which was redispersed in 200 mL of ethanol and centrifuged several times to wash away the remaining PVP and other chemicals. Finally, the mixture was dispersed in ethanol to obtain ultra-long silver nanowires with a length of 500 to 800 μm. The SEM image of the silver nanowires is shown in FIG. Figure 2 shown.

[0054] Example 3

[0055] A method for preparing ultra-long silver nanowires comprises the following steps:

[0056] Step 1, preparation of seed crystals:

[0057] S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 0.42 g of PVP with an average molecular weight of 1,300,000 and 0.84 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until completely dissolved to obtain a mixed solution;

[0058] S2. Then, 0.56 g of silver nitrate was added to the mixed solution obtained in S1. After it was completely dissolved, 5 mL of 2 mM NaCl in ethylene glycol was added to the mixed solution and stirred for 1 min.

[0059] S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 170°C, stir for 10 minutes, stop stirring, react for 2.5 hours to obtain seed crystals, and store them in an oven at 95°C for later use;

[0060] Step 2: Preparation of crystal nucleation inhibitor:

[0061] Dissolve 0.1 g of dihexadecyldimethylammonium bromide in 50 mL of a 1:1 ethylene glycol / glycerol mixed solvent to obtain a crystal nucleation inhibitor for later use.

[0062] Step 3: Growth of seed crystals:

[0063] S1. Then, 50 mL of ethylene glycol was added to a clean flask, and the flask was suspended in an oil bath and heated to 170°C under continuous magnetic stirring. 10 mL of a nucleation inhibitor was injected, and then 0.64 g of PVP with an average molecular weight of 1,300,000 and 0.32 g of PVP with an average molecular weight of 40,000 were added to the above ethylene glycol in sequence until completely dissolved. Then, 15 mL of the synthesized seed crystals were injected, and then 25 mL of a 1.2 g / 100 mL AgNO3 solution was added using a syringe pump at an injection rate of 0.5 mL / min. As the growth progressed, the color of the reaction solution changed from bright ivory to opaque gray-green. After the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature.

[0064] S2, then adding 400 mL of acetone solution with a volume fraction of 1:8 to the synthesized silver nanowires to remove excess chemicals such as ethylene glycol and PVP;

[0065] S3. The mixture obtained after impurity removal was then centrifuged to obtain a precipitate, which was redispersed in 200 mL of ethanol and centrifuged several times to wash away the remaining PVP and other chemicals. Finally, the mixture was dispersed in ethanol to obtain ultra-long silver nanowires with a length of 300 to 500 μm. The SEM image of the silver nanowires is shown in FIG. Figure 3 shown.

[0066] Comparative Example

[0067] A method for preparing silver nanowires comprises the following steps:

[0068] Step 1, preparation of seed crystals:

[0069] S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 1.2 g of PVP with an average molecular weight of 1,300,000 and 1.6 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until completely dissolved to obtain a mixed solution;

[0070] S2, then add 1.2g of silver nitrate to the mixed solution obtained in S1, and after it is completely dissolved, add 10mL of 12mMFeCl3 ethylene glycol solution to the above mixed solution and stir for 1min;

[0071] S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 170°C, stir for 10 minutes, stop stirring, react for 3 hours to obtain seed crystals, and store them in an oven at 95°C for later use;

[0072] Step 2: Growth of seed crystals:

[0073] S1. Then, 50 mL of ethylene glycol was added to a clean flask, and the flask was suspended in an oil bath and heated to 130°C under continuous magnetic stirring. Then, 1.2 g of PVP with an average molecular weight of 1,300,000 and 1.6 g of PVP with an average molecular weight of 40,000 were added to the above ethylene glycol in sequence until completely dissolved. Then, 15 mL of the synthesized seed crystals were injected. Then, 25 mL of 1.2 g / 100 mL AgNO3 solution was added using a syringe pump at an injection rate of 1 mL / min. As the growth progressed, the color of the reaction solution changed from bright ivory to opaque grayish white. After the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature.

[0074] S2, then adding 400 mL of acetone solution with a volume fraction of 1:9 to the synthesized silver nanowires to remove excess chemicals such as ethylene glycol and PVP;

[0075] S3. The mixture obtained after impurity removal was centrifuged to obtain a precipitate, which was redispersed in 200 mL of ethanol and centrifuged several times to wash away the remaining PVP and other chemicals. Finally, the mixture was dispersed in ethanol to obtain silver nanowires with a length of less than 50 μm. The SEM image of the silver nanowires is shown in FIG. Figure 4 shown.

[0076] The reagents used in the present invention are all commercially available reagents.

[0077] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for preparing ultra-long silver nanowires, characterized by: The following steps are involved: Step 1, preparation of seed crystals: S1. First, add 100 mL of ethylene glycol into a round-bottom flask at room temperature, and then add 0.08-2.4 g of PVP with an average molecular weight of 1,300,000 and 0.08-2.4 g of PVP with an average molecular weight of 40,000 to the ethylene glycol in sequence until they are completely dissolved to obtain a mixed solution; S2. Then, add 0.08-2.4 g of silver nitrate to the mixed solution obtained in S1. After it is completely dissolved, add 1-10 mL of 0.3-25 mM ethylene glycol solution of metal chloride to the mixed solution and stir for 1 min. The metal chloride is one of NaCl, CuCl2 and FeCl3; S3, then transfer the round-bottom flask containing the mixed solution obtained in S2 to an oil bath preheated to 110-170° C., stir for 10 minutes, stop stirring, react for 2-3 hours to obtain seed crystals, and store them in an oven for later use; Step 2: Preparation of crystal nucleation inhibitor: Dissolve 0.1-2 g of surfactant in 50 mL of ethylene glycol / glycerol mixed solvent to obtain a crystal nucleation inhibitor for later use; The surfactant is one of didodecyldimethylammonium bromide, hexadecyltrimethylammonium bromide and didodecyldimethylammonium bromide; Step 3: Growth of seed crystals: S1. Then, 50 mL of ethylene glycol was added to the flask, and the flask was suspended in an oil bath and heated under stirring. 10 to 15 mL of a nucleation inhibitor was injected, followed by adding 0.08 to 2.4 g of PVP with an average molecular weight of 1,300,000 and 0.08 to 2.4 g of PVP with an average molecular weight of 40,000 and fully dissolving them uniformly. Then, 10 to 15 mL of the synthesized seed crystals were injected, and then 25 mL of AgNO3 solution was added at an injection rate of 0.5 to 2 mL / min using a syringe pump. As the growth progressed, after the silver nanowires were formed, the reaction was terminated by cooling the flask in a water bath at room temperature. S2, then adding 100-500 mL of acetone solution to the synthesized silver nanowires to remove excess chemicals; S3. The mixture obtained after impurity removal is then centrifuged to obtain a precipitate, which is redispersed in 100 to 500 mL of ethanol, centrifuged several times to wash away the remaining chemicals, and finally dispersed in ethanol to obtain ultra-long silver nanowires with a length of 300 to 800 μm.

2. The method for preparing ultra-long silver nanowires according to claim 1, wherein: In S1 of step 1, the usage ratio of PVP with an average molecular weight of 1,300,000 to PVP with an average molecular weight of 40,000 is 1:2 to 2:

1.

3. The method for preparing ultra-long silver nanowires according to claim 1, wherein: In step 2, the mass ratio of the ethylene glycol / propylene glycol mixed solvent is 2 to 1:

1.

4. The method for preparing ultra-long silver nanowires according to claim 1, wherein: In S1 of step 3, the heating temperature is 110-170° C., and the concentration of the AgNO 3 solution is 0.32-9.6 g / 100 mL.

5. The method for preparing ultra-long silver nanowires according to claim 1, wherein: In S1 of step 3, the usage ratio of PVP with an average molecular weight of 1,300,000 to PVP with an average molecular weight of 40,000 is 1:2 to 2:

1.

6. The method for preparing ultra-long silver nanowires according to claim 1, wherein: In S2 of step 3, the volume ratio of the acetone solution is 1:8-9.

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