A silver nanowire preparation method giving consideration to high yield and high aspect ratio

Abstract

The application discloses a kind of silver nanowire preparation methods with high yield and high aspect ratio, (1) the precursor mixed solution of preparing silver nanowire is blown bubble under nitrogen for a period of time at room temperature, (2) the two mouth flask is closed in the heating process of 120 DEG C to 170 DEG C, (3) after reaching 170 DEG C, it is changed to condenser tube reflux air, and silver nanowire is obtained after a period of reaction.The oxygen content of nucleation stage and growth stage of silver nanowire is controlled separately in the application, the formation of nanoparticles is reduced, the yield of silver nanometer is greatly improved, and can reach 90%, and the diameter of prepared silver nanometer is 28 nanometers, and the aspect ratio is 2500, the method is simple in operation, and can be scaled up.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial preparation, and particularly relates to a silver nanowire preparation method with high yield and high aspect ratio. BACKGROUND

[0002] Silver nanowire (AgNW) transparent conductive film has excellent light transmittance, conductivity, thermal conductivity, and low surface resistance, and has wide application prospects in flat panel displays, large-size touch screens, solar cells, anti-fog heaters, etc. Due to its low preparation cost and excellent flexibility, it is considered to be the most promising electrode material to replace the current traditional ITO electrode. In order to increase the light transmittance and conductivity of the AgNW transparent conductive film, the AgNW is required to have a smaller diameter and a higher aspect ratio. Because the AgNW with a diameter of less than 30 nm has a surface plasmon absorption peak at about 370 nm, most of the visible light can pass through the conductive film, thereby increasing the light transmittance. In addition, the AgNW with a high aspect ratio indicates that the silver nanowire is very long, and the lapping between the lines can form a good network structure, the electron transmission path is more, and the conductive performance is good. Therefore, the slender AgNW with a high aspect ratio is an effective way to improve the light transmittance and reduce the resistance of the conductive film.

[0003] However, in the actual preparation process, when the conditions for preparing the slender silver nanowire are met, the yield of the silver nanowire is often low, that is, there are more silver nanoparticles in the product. The light transmittance of the conductive film prepared from such silver nanowire will be greatly reduced, because the nanoparticles have strong light scattering and light absorption. In 2015, Wiley et al. used chloride ions and bromide ions as additives to prepare silver nanowires with a diameter of 20 nm and an aspect ratio of 2000, but the yield of the nanowires was only 58% (Nano Lett. 2015, 15, 6722). In 2020, Wang et al. used the synergistic effect of chloride ions, bromide ions and iron ions to synthesize silver nanowires with a diameter of 29 nm and an aspect ratio of 3100, but did not give the yield of the nanowires (Nanomaterials 2020, 10, 237). Therefore, the low-yield silver nanowires need to be centrifuged and filtered in the later stage to prepare films, which greatly increases the production cost. Therefore, the existing silver nanowire preparation technology still needs to be improved.

[0004] Searches have found that Chinese patents 201310491884.0, 201911022163.9 and 201811496679.2 have disclosed related technologies for improving the yield of silver nanowires. However, analysis shows that although these existing technologies have improved the yield of silver nanowires, the parameters of the diameter and aspect ratio of the lines have decreased. In addition, the control of the temperature and nitrogen flow during the preparation of the AgNW is too complex, which is not conducive to operation and is difficult to meet the needs of large-scale production. SUMMARY

[0005] The purpose of this invention is to address the shortcomings of the existing technology by proposing a method for preparing silver nanowires that combines high yield and high aspect ratio, enabling the practical application of this technology in the preparation of transparent conductive films.

[0006] Therefore, the present invention adopts the following technical solution:

[0007] A method for preparing silver nanowires that achieves both high yield and high aspect ratio includes the following steps:

[0008] (1) Prepare a precursor mixture for preparing silver nanowires; the solvent of the mixture is ethylene glycol (EG), and the solutes include NaCl, NaBr, silver nitrate (AgNO3), and polyvinylpyrrolidone (PVP).

[0009] (2) Blow the mixture with nitrogen at room temperature for a period of time.

[0010] (3) Seal the two-necked flask, raise the temperature of the mixture from 100-120℃ to 160-170℃, and stir magnetically.

[0011] (4) When the temperature reaches 160-170℃, stop stirring, replace the mouth of the flask with a condenser to reflux air, and react for a period of time to obtain silver nanowires that combine high yield and high aspect ratio.

[0012] Preferably, the order of adding the solution in the mixture is as follows: (1) Silver nitrate is stirred thoroughly in ethylene glycol solution; (2) The prepared EG solution of NaCl and NaBr is added to the previous solution and stirred for 20 min; (3) The prepared EG solution of PVP is added to the previous solution and stirred for 20 min.

[0013] Preferably, the molar ratio of AgNO3, PVP, NaCl, and NaBr in the mixture is 80:300:2:1.

[0014] Preferably, in step (2), the mixture is bubbled with nitrogen for more than 30 minutes at room temperature and the flow rate is 200 mL / min.

[0015] Preferably, during the process of heating the mixture from 120°C to 170°C in step (3), the two openings of the flask are sealed to ensure a low-oxygen state.

[0016] Preferably, the heating time of the mixture in step (3) is controlled within 15-17 minutes.

[0017] Preferably, when the temperature reaches 170°C in step (4), the large and small bottle stoppers are removed, the large bottle opening is replaced with a condenser tube, and air is refluxed.

[0018] The mixed solution is magnetically stirred at a speed of 200-300 r / min before the temperature reaches 170 DEG C, and the stirring is stopped after the temperature reaches 170 DEG C.

[0019] The air refluxing of the condenser tube lasts for 30-40 min, the reaction is terminated when the green solution is observed, and the solution is centrifuged and washed to obtain silver nanowires with high yield and high aspect ratio.

[0020] The preparation method and the product of the present application have the following advantages and beneficial effects:

[0021] After the mixed solution is bubbled with nitrogen, the temperature is raised from 100-120 DEG C to 160-170 DEG C, the mouth of the flask is closed to ensure a low-oxygen state, and the proportion of crystal nuclei that are oxidized and etched is reduced, and more importantly, the crystal nuclei grown in a low-oxygen environment have a smaller diameter, which lays a foundation for the subsequent slender silver nanowires. During the growth stage at 160-170 DEG C, the air is refluxed to provide a certain oxidation etching capacity, reduce the number of nanoparticles in the solution, and increase the content of AgNW, so that the obtained silver nanowires have the advantages of high yield and high aspect ratio.

[0022] The solution configuration, mixing and stirring of the present application are all carried out at room temperature, the nitrogen is bubbled to reduce the oxygen content in the mixed solution, and the operation is simple.

[0023] Compared with the prior art 201310491884.0, the silver nanowires obtained by the present application have a smaller diameter of 28 nm while ensuring a higher efficiency of 90%. Compared with the prior art 201911022163.9, the aspect ratio of the silver nanowires obtained by the present application is as high as 2500. Compared with the prior art 201811496679.2, the nucleation and growth process of the silver nanowires of the present application is relatively simple in temperature control, the N2 protection is not throughout the process but only for bubbling N2 for more than 30 min before heating, and the N2 flow control is single, so the overall operation of the present application is simple and convenient, has good repeatability, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The silver nanowire preparation flowchart of the present application is shown.

[0025] In the figure: 1, two-mouth flask, 2, large mouth of the flask, 3, rubber plug of the large mouth, 4, nitrogen gas inlet pipe, 5, small mouth of the flask, 6, glass plug of the small mouth, 7, condenser tube.

[0026] Figure 2 The SEM image of the silver nanowires prepared in Example 1 of the present application is shown.

[0027] Figure 3 The SEM image of the silver nanowires prepared in Example 1 of the present application is shown.

[0028] Figure 4 SEM image of silver nanowires prepared under the whole process of N2 protection for the present application comparative example 2.

[0029] Figure 5 SEM image of silver nanowires prepared under the whole process of N2 protection for the present application comparative example 2. DETAILED DESCRIPTION

[0030] The application will be further described in detail by the accompanying drawings and specific examples.

[0031] The preparation process of the silver nanowires with high efficiency and high aspect ratio is shown in the schematic diagram of the application, as shown in the figure. Figure 1

[0032] Example 1:

[0033] (1) Prepare NaCl and NaBr EG solution in advance, the concentration is 300 mM; Prepare PVP EG solution in advance, the concentration is 270 mM.

[0034] (2) Take 0.25 g of silver nitrate and add it to 10 mL of EG solution, and magnetically stir for 20 min; Add 120 microliters of NaCl solution; Then add 60 microliters of NaBr solution, continue to stir for 20 min; Next, add 20 mL of PVP solution, and magnetically stir for 20 min. At this time, the molar ratio of AgNO3, PVP, NaCl, and NaBr in the solution is 80:300:2:1.

[0035] (3) Pour the resulting mixture into two flasks, plug the large bottle mouth 2 with a rubber plug 3, insert a nitrogen gas inlet tube 4, and blow bubbles for 30 min to reduce the oxygen content in the solution.

[0036] (4) After the bubbling is finished, pull out the nitrogen gas inlet tube 4, plug the large bottle mouth 2 with a rubber plug 3, and plug the small bottle mouth 5 with a glass plug 6.

[0037] (5) Put it into a preheated oil bath, and heat the solution from 120℃ to 170℃, magnetically stir at a speed of 200 r / min, and complete the nucleation and hatching process of silver nanowires.

[0038] (6) When the solution temperature reaches 170℃, stop stirring, remove the glass plug 6 from the small bottle mouth, and use a condenser tube 7 instead of the large bottle mouth. Reflux the air to ensure that there is an appropriate amount of oxygen during the growth of the nanowires, which will be oxidized and etched to consume excess silver nanoparticles.

[0039] (7) The 170℃ growth process lasts for a period of time, and every 10 min, 1 ml of silver nanowire reaction solution is taken from the small bottle mouth with a pipette for centrifugal analysis. ​

[0040] The reaction product is transferred to a centrifuge tube, ethanol is added to dilute to 8 times the original volume, shaken evenly, and centrifuged at 6000 rpm for 15 min; the supernatant is removed, and the bottom precipitate is reserved. This centrifugal purification process is repeated 3 times. Finally, the product is redispersed in ethanol. Figure 2 , Figure 3 The sample morphology at 30 min is shown. Through statistics, the diameter of the AgNW is 28 nm, the aspect ratio is 2500, there are fewer particles, and the yield of the wire is as high as 90%.

[0041] Example 2 (N2 protection throughout the process):

[0042] (1) An EG solution of NaCl and NaBr is prepared in advance, with a concentration of 300 mM; an EG solution of PVP is prepared in advance, with a concentration of 270 mM.

[0043] (2) 0.25 g of silver nitrate is weighed into 10 mL of EG solution, and is magnetically stirred for 20 min; 120 microliters of NaCl solution is added; then 60 microliters of NaBr solution is added, and stirring is continued for 20 min; next, 20 mL of PVP solution is added, and is magnetically stirred for 20 min. At this time, the molar ratio of AgNO3, PVP, NaCl, and NaBr in the solution is 80:300:2:1.

[0044] (3) The resulting mixture is poured into two flasks, the large flask mouth 2 is plugged with a rubber plug 3, a nitrogen gas inlet tube 4 is inserted, N2 is introduced, and bubbling is performed for 30 min to reduce the oxygen content in the solution.

[0045] (4) After bubbling is completed, the nitrogen gas inlet tube 4 is removed, the large flask mouth 2 is plugged with a rubber plug 3, and the small flask mouth 5 is plugged with a glass plug 6.

[0046] (5) The solution is warmed from 120°C to 170°C in a preheated oil bath, and is magnetically stirred at a speed of 200 r / min to complete the nucleation and incubation process of the silver nanowires.

[0047] (6) When the solution temperature reaches 170°C, stirring is stopped, and the state of the small flask mouth being plugged with a glass plug and the large flask mouth being plugged with a rubber plug is maintained.

[0048] (7) The 170°C growth process lasts for a period of time, and every 10 min, 1 ml of silver nanowire reaction solution is drawn from the rubber plug of the large flask mouth with a long stainless steel needle tube, and is subjected to centrifugal analysis.

[0049] The reaction product is transferred to a centrifuge tube, ethanol is added to dilute to 8 times the original volume, shaken evenly, and centrifuged at 6000 rpm for 15 min; the supernatant is removed, and the bottom precipitate is reserved. This centrifugal purification process is repeated 3 times. Finally, the product is redispersed in ethanol. Figure 4 ,Figure 5 The sample morphology at 30 min. It is statistically obtained that the diameter of the AgNW is 30 nm, the aspect ratio is 1500, there are many particles, and the yield of the wire is only 72%.

[0050] It can be seen that the oxygen has a great influence on the yield of the silver nanowire at 170 DEG C, the nitrogen protection process can prepare the silver nanowire with high aspect ratio, but the yield of the wire is low. Thus it can be proved that the present application provides a new technical path, that is, a low oxygen content atmosphere is used in the nucleation of the silver nanowire to ensure that the crystal nucleus has a small size, and in the growth stage, the appropriate oxygen backflow etches the excess nanoparticles, so that the silver nanowire with high yield and high aspect ratio is obtained.

[0051] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing silver nanowires that balances high yield and high aspect ratio, characterized in that, include: (1) Prepare a mixture for preparing silver nanowires; the solvent of the mixture is ethylene glycol (EG), and the solutes include NaCl, NaBr, silver nitrate (AgNO3), and polyvinylpyrrolidone (PVP); (2) Blow the mixture with nitrogen gas at room temperature for a period of time; (3) Seal the two-necked flask and heat the mixture from 100-120℃ to 160-170℃; (4) When the temperature reaches 160-170℃, replace the mouth of the flask with a condenser to reflux air, and react for a period of time to obtain silver nanowires that combine high yield and high aspect ratio.

2. The method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1, characterized in that, The order of adding the solutions in the mixture is as follows: (1) Silver nitrate is stirred thoroughly in ethylene glycol solution; (2) EG solutions with a concentration of 250-350mM NaCl and 250-350mM NaBr are added to the previous solution and stirred for 20-30 minutes; (3) EG solutions with a concentration of 250-300mM PVP are added to the previous solution and stirred for 20-30 minutes.

3. A method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1 or 2, characterized in that, The molar ratio of AgNO3, PVP, NaCl, and NaBr in the mixture is 60-100:280-320:4-2:

1.

4. The method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1, characterized in that, The mixture is bubbled with nitrogen at room temperature for 10-60 min at a flow rate of 200-300 mL / min.

5. The method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1, characterized in that, During the process of heating the mixture from 100-120℃ to 160-170℃, the two openings of the flask are sealed to ensure a low-oxygen environment.

6. A method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1 or 5, characterized in that, The heating process of the mixture is controlled within 15-25 minutes.

7. The method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1, characterized in that, When the temperature reaches 160-170℃, remove the large and small bottle stoppers, replace the large bottle opening with a condenser tube, and allow air to flow back.

8. A method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1, 5, or 7, characterized in that, The mixture is magnetically stirred at a speed of 200-300 r / min until the temperature reaches 160-170℃. Once the temperature reaches 160-170℃, stirring is stopped.

9. A method for preparing silver nanowires that combines high yield and high aspect ratio according to claim 1 or 7, characterized in that, The air is refluxed through the condenser for 30-40 minutes. When a green solution is observed, the reaction is terminated, the solution is centrifuged, washed, and silver nanowires with both high yield and high aspect ratio are obtained.

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