Preparation method of high-purity silver nanowire and topological conductive network

Abstract

The invention discloses a preparation method of a high-purity silver nanowire and a topological conductive network, and the method comprises the following steps: S1, dispersing PVP in a glycerol mixed solution, heating and stirring to obtain a solution a, adding AgNO3, and stirring to obtain a solution b; s2, NaCl and FeCl3 are added into water to be dissolved, then glycerol is added, and a halide additive / water / glycerol mixed solution c is prepared; s3, after the solution b is cooled to the room temperature, adding the solution c into the solution b, heating to the high temperature, reacting and stirring, stopping heating after the reaction is finished, and cooling to the room temperature to obtain a silver nanowire aqueous solution; and S4, high-purity silver nanowire aqueous solutions are obtained through graded centrifugation and solvent replacement and are blended into high-purity silver nanowire aqueous solutions with different concentrations, drying treatment is conducted in the high-vacuum and low-temperature environment, and then the silver nanowire topological conductive network is obtained. According to the method, the compounded halide additive is adopted and is centrifuged step by step, so that the high-purity silver nanowire with the high length-diameter ratio can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of one-dimensional nanomaterials, and particularly to a method for preparing high-purity silver nanowires and a topological conductive network. Background Art

[0002] Metal nanowires are a type of nanomaterial that has emerged in recent years. Their diameter is generally below 100 nm, and there is no limit in the length direction. Among them, silver nanowires are the most widely used metal nanowires. As a nanostructured material, silver nanowires not only inherit the excellent heat transfer performance, electrical conductivity, and mechanical properties of the metal bulk material, but also have some unique properties of nanoparticles, such as quantum size effect, small size effect, surface effect, and macroscopic quantum tunneling effect, etc. Therefore, silver nanowires show great application potential in fields such as touch screens, solar cells, heaters, and LEDs. The synthesis methods of silver nanowires mainly include polyol method, CVD method, electrochemical method, and template method, etc.

[0003] The polyol method is a currently popular method for preparing silver nanowires. It can control the morphology and size of silver nanowires by using a suitable solvent, setting a suitable reaction temperature, adding an effective reducing agent, selecting an anisotropic growth agent, a capping agent, etc. During the process of preparing silver nanowires by the polyol method, polyvinylpyrrolidone (PVP) is the most commonly used surfactant, which has a great influence on the shape, diameter, and aspect ratio of the obtained silver nanowires. In addition, halide additives also play a key role in the large-scale synthesis of nanosilver wires. Halide salts generate Cl - anions in the reaction solution, thereby forming AgCl colloids, which is convenient for controlling the concentration of free silver in the initial stage of the reaction to promote the formation and growth of AgNWs. The polyol method for preparing silver nanowires has mild reaction conditions, simple preparation process, no need for templates, environmentally friendly, short reaction time, suitable for large-scale synthesis, and the prepared silver nanowires can be easily dispersed in various solvents. However, in the actual reaction process, the silver nanowires prepared by the polyol method contain more silver nanoparticles and short silver nanowires. To obtain high-purity and high-aspect-ratio silver nanowires, further separation and purification are required. Summary of the Invention

[0004] In view of the above deficiencies, the present invention proposes a method for preparing high-purity silver nanowires and a topological conductive network. The use of a compound halide additive and step-by-step centrifugation helps to obtain high-purity and high-aspect-ratio silver nanowires.

[0005] To achieve the above object, the present invention provides the following technical solution: A method for preparing high-purity silver nanowires and a topological conductive network, comprising the following steps: S1: Disperse the capping agent and the growth control agent PVP in a glycerol mixed solution. After heating and stirring to obtain solution a, add AgNO3 and stir to obtain solution b; S2: Add the halide additive composed of NaCl and FeCl3 to water to dissolve it, and then add glycerol to prepare a halide additive / water / glycerol mixed solution c; S3: After solution b is cooled to room temperature, add solution c to solution b, heat to a high temperature for reaction and maintain gentle stirring. After the reaction ends, stop heating until the solution cools to room temperature to obtain an aqueous silver nanowire solution; S4: Obtain a high-purity aqueous silver nanowire solution through fractional centrifugation and solvent replacement. The product is formulated into aqueous silver nanowire solutions with different concentrations, placed in a petri dish, and dried under a high-vacuum and low-temperature environment to obtain a highly disordered and complex topological conductive network of silver nanowires.

[0006] As an improvement, in step S1, PVP is 1 part by weight, the mass fraction of the glycerol mixed solution is 1.5 - 3.5 wt%, the heating temperature is 50 °C, the heating duration is 3 hours, and AgNO3 is 0.1 - 0.4 part by weight.

[0007] As an improvement, in step S2, the halide additive is 0.005 - 0.02 part by weight, water is 0.02 - 0.15 part by weight, and glycerol is 1 - 3 parts by weight.

[0008] As an improvement, in step S2, the mass ratio of NaCl to FeCl3 is 3:2.

[0009] As an improvement, in step S3, heat to 140 - 250 °C, and the reaction duration is 0.5 - 4 hours.

[0010] As an improvement, in step S4, the diameter of the silver nanowires in the topological conductive network of silver nanowires is 140 - 160 nm, and the length is 70 - 100 μm.

[0011] As an improvement, in step S4, the fractional centrifugation includes a low-speed stage, a medium-speed stage, and a high-speed stage. The low-speed stage rotation speed is 1200 rpm - 1800 rpm, the medium-speed stage rotation speed is 2700 rpm - 3300 rpm, and the high-speed stage rotation speed is 4700 rpm - 5300 rpm.

[0012] Compared with the prior art, the advantages of the present invention are as follows: (1) By using a compounded halide additive and adding FeCl3 to traditional NaCl, it helps to obtain silver nanowires with a high aspect ratio. However, FeCl3 is insoluble in glycerol. Using a water / glycerol mixed solution as the halide additive solution facilitates the dissolution and uniform dispersion of FeCl3; (2) The hierarchical centrifugation method is adopted to separate silver nanoparticles and short silver nanowires successively through the centrifugal rotation speeds of low speed, medium speed, and high speed, obtaining silver nanowires with high purity and high aspect ratio. The obtained silver nanowires have uniform sizes, with a diameter of about 150 nm and a length of 70 - 100 μm, and there are no obvious silver nanoparticles and short silver nanowires. The silver nanowire topological conductive network prepared by high vacuum and low temperature drying treatment is highly disordered and complex; (3) Heat to 140 - 250 °C and maintain gentle stirring, enabling the reaction to proceed efficiently while avoiding the breakage or aggregation of silver nanowires caused by violent stirring. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments: Figure 1 It is a flow chart of a preparation method for high-purity silver nanowires and a topological conductive network; Figure 2 It is a scanning electron microscope image of silver nanowires provided in Examples 1 to 4; Figure 3 It is a scanning electron microscope image of silver nanowires provided in Example 5; Figure 4 It is a scanning electron microscope image of silver nanowires provided in Example 6; Figure 5 It is a scanning electron microscope image of the silver nanowire topological conductive network provided in Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0014] Example 1 S1: Disperse 1 part by weight of a capping agent and a growth control agent PVP in a round-bottom flask containing a 41-part-by-weight glycerol mixed solution with a mass fraction of 2.5 wt%. Transfer it to an oil bath and heat and mechanically stir at 50 °C for 3 hours to obtain solution a. Then, add 0.27 part by weight of AgNO3 as the Ag source to solution a and stir for 0.5 hour to obtain solution b; S2: Dissolve a halide additive composed of NaCl and FeCl3 in a mass ratio of 3:2 in 0.09 part by weight of water at 0.005 part by weight, where NaCl is 0.003 part by weight and FeCl3 is 0.002 part by weight. Then, add 2.16 parts by weight of glycerol and disperse evenly to prepare a halide additive / water / glycerol mixed solution c; S3: After solution b is cooled to room temperature, add solution c to solution b. Raise the temperature of the system to 210 °C and react at this temperature for 1 hour while maintaining gentle stirring. After the reaction ends, stop heating until the solution cools to room temperature to obtain an aqueous solution of silver nanowires; S4: Add 26.97 parts by weight of ethanol to the aqueous silver nanowire solution and centrifuge at 5000 revolutions for 5 minutes. Repeat the washing process three times to remove the residual PVP on the surface. Disperse the collected silver nanowires in an ethanol solution for subsequent use.

[0015] Drop the dispersion evenly onto a silicon wafer and observe its morphology by SEM, as Figure 2 shown. It can be seen from the figure that there are many silver nanoparticles and short silver nanowires in the silver nanowires prepared without the fractional centrifugation process.

[0016] Example 2 S1: Disperse 1 part by weight of the capping agent and the growth control agent PVP in a round-bottom flask containing a mixed solution of 41 parts by weight of glycerol with a mass fraction of 2.5 wt%. Transfer it into an oil bath and heat and mechanically stir at 50 °C for 3 hours to obtain solution a. Then add 0.27 part by weight of AgNO3 as the Ag source to solution a and stir for 0.5 hour to obtain solution b; S2: Dissolve a halide additive composed of NaCl and FeCl3 in a mass ratio of 3:2 in 0.09 part by weight of water at 0.01 part by weight, where NaCl is 0.006 part by weight and FeCl3 is 0.004 part by weight. Then add 2.16 parts by weight of glycerol and disperse evenly to prepare a halide additive / water / glycerol mixed solution c; S3: After solution b is cooled to room temperature, add solution c to solution b. Raise the system temperature to 210 °C and react at this temperature for 1 hour while maintaining gentle stirring. After the reaction is completed, stop heating until the solution cools to room temperature to obtain an aqueous silver nanowire solution; S4: Add 26.97 parts by weight of ethanol to the aqueous silver nanowire solution and centrifuge at 5000 revolutions for 5 minutes. Repeat the washing process three times to remove the residual PVP on the surface. Disperse the collected silver nanowires in an ethanol solution for subsequent use.

[0017] Drop the dispersion evenly onto a silicon wafer and observe its morphology by SEM, as Figure 2 shown. It can be seen from the figure that there are many silver nanoparticles and short silver nanowires in the silver nanowires prepared without the fractional centrifugation process.

[0018] Example 3 S1: Disperse 1 part by weight of the capping agent and the growth control agent PVP in a round-bottom flask containing a mixed solution of 41 parts by weight of glycerol with a mass fraction of 2.5 wt%. Transfer it into an oil bath and heat and mechanically stir at 50 °C for 3 hours to obtain solution a. Then add 0.27 part by weight of AgNO3 as the Ag source to solution a and stir for 0.5 hour to obtain solution b; S2: Dissolve the halide additive composed of NaCl and FeCl₃ with a mass ratio of 3:2 by adding 0.015 parts by weight of it to 0.09 parts by weight of water, where NaCl is 0.009 parts by weight and FeCl₃ is 0.006 parts by weight. Then add 2.16 parts by weight of glycerol and disperse evenly to prepare the halide additive / water / glycerol mixed solution c; S3: After the solution b is cooled to room temperature, add the solution c to the solution b, raise the temperature of the system to 210 °C and react at this temperature for 1 hour while maintaining gentle stirring. After the reaction is completed, stop heating until the solution cools to room temperature to obtain the silver nanowire aqueous solution; S4: Add 26.97 parts by weight of ethanol to the silver nanowire aqueous solution and centrifuge at 5000 rpm for 5 minutes. Repeat the washing process three times to remove the residual PVP on the surface, and disperse the collected silver nanowires in the ethanol solution for subsequent use.

[0019] The dispersion was evenly drop-coated on a silicon wafer, and its morphology was observed by SEM, as Figure 2 shown. It can be seen from the figure that there are many silver nanoparticles and short silver nanowires in the silver nanowires prepared without the fractional centrifugation process.

[0020] Example 4 S1: Disperse 1 part by weight of the capping agent and growth control agent PVP in a round-bottom flask containing a 41 parts by weight glycerol mixed solution with a mass fraction of 2.5 wt%. Transfer it to an oil bath and heat and mechanically stir at 50 °C for 3 hours to obtain solution a. Then add 0.27 parts by weight of AgNO₃ as the Ag source to solution a and stir for 0.5 hours to obtain solution b; S2: Dissolve the halide additive composed of NaCl and FeCl₃ with a mass ratio of 3:2 by adding 0.01 parts by weight of it to 0.09 parts by weight of water, where NaCl is 0.006 parts by weight and FeCl₃ is 0.004 parts by weight. Then add 2.16 parts by weight of glycerol and disperse evenly to prepare the halide additive / water / glycerol mixed solution c; S3: After the solution b is cooled to room temperature, add the solution c to the solution b, raise the temperature of the system to 210 °C and react at this temperature for 1 hour while maintaining gentle stirring. After the reaction is completed, stop heating until the solution cools to room temperature to obtain the silver nanowire aqueous solution; S4: Add 26.97 parts by weight of ethanol to the silver nanowire aqueous solution and centrifuge at 5000 rpm for 5 minutes. Repeat the washing process three times to remove the residual PVP on the surface, and disperse the collected silver nanowires in the ethanol solution for subsequent use.

[0021] The dispersion was evenly drop-coated on a silicon wafer, and its morphology was observed by SEM, as Figure 2As shown. It can be seen from the figure that there are many silver nanoparticles and short silver nanowires in the silver nanowires prepared without the fractional centrifugation process.

[0022] Example 5 S1: Disperse 1 part by weight of the capping agent and the growth control agent PVP in a round-bottom flask containing a mixed solution of 41 parts by weight of glycerol with a mass fraction of 2.5 wt%. Transfer it into an oil bath and heat it with mechanical stirring at 50 °C for 3 hours to obtain solution a. Then add 0.27 part by weight of AgNO3 as the Ag source to solution a and stir for 0.5 hour to obtain solution b. S2: Dissolve the halide additive composed of NaCl and FeCl3 in a mass ratio of 3:2 in 0.09 part by weight of water at 0.01 part by weight, where NaCl is 0.006 part by weight and FeCl3 is 0.004 part by weight. Then add 2.16 parts by weight of glycerol and disperse evenly to prepare a halide additive / water / glycerol mixed solution c. S3: After solution b is cooled to room temperature, add solution c to solution b. Raise the temperature of the system to 210 °C and react at this temperature for 1 hour while maintaining gentle stirring. After the reaction is completed, stop heating until the solution cools to room temperature to obtain an aqueous solution of silver nanowires. S4: Add 26.97 parts by weight of ethanol to the aqueous solution of silver nanowires. First, centrifuge at 3000 rpm for 5 minutes, then increase the speed to 5000 rpm and centrifuge for 5 minutes. Disperse the dispersion at the bottom of the centrifuge tube in 26.97 parts by weight of ethanol. After brief ultrasonic treatment, finally centrifuge at 5000 rpm for 5 minutes. Disperse the collected silver nanowires in an ethanol solution for subsequent use.

[0023] Drop the dispersion evenly on a silicon wafer and observe its morphology by SEM, as Figure 3 shown. It can be seen from the figure that after centrifugation at 3000 rpm for 5 minutes, there are still small silver nanoparticles in the ethanol dispersion of the prepared silver nanowires, but the amount of short silver nanowires has decreased.

[0024] Example 6 S1: Disperse 1 part by weight of the capping agent and the growth control agent PVP in a round-bottom flask containing a mixed solution of 41 parts by weight of glycerol with a mass fraction of 2.5 wt%. Transfer it into an oil bath and heat it with mechanical stirring at 50 °C for 3 hours to obtain solution a. Then add 0.27 part by weight of AgNO3 as the Ag source to solution a and stir for 0.5 hour to obtain solution b. S2: Add a halide additive composed of NaCl and FeCl₃ in a mass ratio of 3:2 in an amount of 0.01 parts by weight to 0.09 parts by weight of water to dissolve it, where NaCl is 0.003 parts by weight and FeCl₃ is 0.002 parts by weight, and then add 2.16 parts by weight of glycerol and disperse evenly to prepare a halide additive / water / glycerol mixed solution c; S3: After solution b is cooled to room temperature, add solution c to solution b, raise the temperature of the system to 210 °C and react at this temperature for 1 hour, and maintain gentle stirring. After the reaction is completed, stop heating until the solution cools to room temperature to obtain an aqueous silver nanowire solution; S4: Add 26.97 parts by weight of ethanol to the aqueous silver nanowire solution. First, centrifuge at 1500 revolutions per minute for 5 minutes, disperse the bottom dispersion of the centrifuge tube in 26.97 parts by weight of ethanol, after brief ultrasonic treatment, increase the speed to 3000 and centrifuge for 5 minutes, disperse the bottom dispersion of the centrifuge tube in 26.97 parts by weight of ethanol, after brief ultrasonic treatment, and finally increase the speed to 5000 revolutions per minute and centrifuge for 5 minutes. Collect the silver nanowires and disperse them in the ethanol solution for subsequent use.

[0025] Drop the dispersion evenly on the silicon wafer and observe its morphology by SEM, as Figure 4 shown. It can be seen from the figure that after fractional centrifugation at 1500, 3000, and 5000 revolutions per minute, the obtained silver nanowires have uniform sizes, a diameter of about 150 nm, a length of 70 - 100 μm, a high aspect ratio, and no obvious silver nanoparticles and short silver nanowires.

[0026] Replace the purified silver nanowire ethanol dispersion into an aqueous silver nanowire dispersion by a solvent replacement method. Then take a small part of the dispersion and place it in a petri dish, and dry it under a high vacuum and low temperature environment to obtain a highly disordered and complex silver nanowire topological conductive network. Observe the morphology of the dried product by SEM, as Figure 5 shown. It can be seen from the figure that the silver nanowire topological conductive network dried under high vacuum and low temperature is highly complex and disordered, and has broad application prospects in the field of flexible electronics.

[0027] The above only illustrates the best embodiments of the present invention, but it should not be construed as a limitation to the claims. The present invention is not limited to the above embodiments, and its specific structure allows changes. All changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing high-purity nano silver wires and topological conductive networks, characterized in that: The following steps are involved: S1: dispersing the capping agent and the growth control agent PVP in a propylene glycol mixed solution, heating and stirring to obtain solution a, and then adding AgNO3 and stirring to obtain solution b; S2: adding a halide additive composed of NaCl and FeCl3 into water to dissolve it, and then adding glycerol to prepare a halide additive / water / glycerol mixed solution c; S3: After solution b is cooled to room temperature, solution c is added to solution b, and the mixture is heated to a high temperature for reaction while being gently stirred. After the reaction is completed, heating is stopped until the solution is cooled to room temperature, thereby obtaining a silver nanowire aqueous solution; S4: A high-purity silver nanowire aqueous solution is obtained by fractional centrifugation and solvent replacement. The product is formulated into high-purity silver nanowire aqueous solutions of different concentrations, placed in a culture dish, and dried in a high vacuum and low temperature environment to obtain a highly disordered and complex nanosilver wire topological conductive network.

2. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: The PVP in step S1 is 1 part by weight, the mass fraction of the propylene glycol mixed solution is 1.5-3.5 wt%, the heating temperature is 50°C, the heating time is 3 hours, and the AgNO3 is 0.1-0.4 parts by weight.

3. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: The halide additive in step S2 is 0.005-0.02 parts by weight, the water is 0.02-0.15 parts by weight, and the glycerol is 1-3 parts by weight.

4. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: The mass ratio of NaCl to FeCl3 in step S2 is 3:

2.

5. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: In the step S3, the temperature is heated to 140-250° C., and the reaction time is 0.5-4 hours.

6. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: The diameter of the nanosilver wires in the nanosilver wire topological conductive network in step S4 is 140-160 nm, and the length is 70-100 μm.

7. The method for preparing a high-purity nano silver wire and a topological conductive network according to claim 1, characterized in that: The graded centrifugation in step S4 includes a low-speed stage, a medium-speed stage, and a high-speed stage. The low-speed stage has a rotation speed of 1200rpm-1800rpm, the medium-speed stage has a rotation speed of 2700rpm-3300rpm, and the high-speed stage has a rotation speed of 4700rpm-5300rpm.

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