A green method for the preparation of silver nanowires

Abstract

The application discloses a green preparation method of silver nanowires, which comprises the following steps: adding silver powder with a purity of greater than or equal to 99.9% into a polyvinylpyrrolidone aqueous solution, stirring for 20-40 min, adding metal halide MX n , uniformly mixing, reacting under an oxidizing condition at 70-90 DEG C for 7-9 h under a pH of 1-3, centrifuging the silver halide colloid, washing to obtain a precipitate, dispersing the precipitate in water to obtain a silver halide dispersion, adding a surfactant aqueous solution and a reducing agent aqueous solution into the silver halide dispersion in sequence to obtain a mixed solution, sealing the mixed solution for reaction at 100-130 DEG C for 20-24 h, and obtaining silver nanowires; the silver nanowires prepared by the green preparation method have an average diameter of 20-60 nm, a length-diameter ratio of 400-4000, a uniform morphology and a large length-diameter ratio.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanomaterials, and particularly relates to a green preparation method of silver nanowires. BACKGROUND

[0002] For a long time, indium tin oxide (ITO) has been widely used in the fields of liquid crystal display, touch screen and solar cell due to its low resistance and high light transmittance. However, ITO is brittle in texture, and indium is rare and expensive, which is difficult to meet the demand of the development of transparent conductive films. In order to overcome the limitations of ITO, researchers have explored various conductive materials, such as metal mesh, carbon nanotube, graphene and metal nanowire. However, these materials have their own shortcomings: metal mesh is prone to moire fringes, carbon nanotube is difficult to disperse uniformly, and the conductivity of graphene is weak. In contrast, metal nanowire, especially silver nanowire, is considered as an ideal material for preparing flexible transparent electrodes due to its unique five-fold twin crystal structure, significant surface plasmon resonance characteristics and excellent photoelectric performance.

[0003] Silver nanowire is a typical one-dimensional nanostructured material, with a diameter of usually 10-200 nm and a length of up to several hundred microns. At present, the methods for preparing silver nanowires in China include polyol method, hydrothermal method, template method, electrochemical method and microwave-assisted method. Among them, the polyol method is the mainstream process for industrial production of silver nanowires, but a large amount of organic solvent is needed in the preparation process, which not only causes environmental burden, but also makes the subsequent purification more complex. In contrast, the hydrothermal method has shown significant advantages in environmental friendliness and process cleanliness, and the silver nanowires prepared by the hydrothermal method have uniform morphology, controllable aspect ratio and good application prospect.

[0004] In the synthesis system of silver nanowires, commonly used silver sources include silver nitrate, silver acetate and silver trifluoroacetate. Among them, silver nitrate is the most widely used silver source due to its good water solubility and high reactivity. However, its industrial production needs to use metallic silver and concentrated nitric acid as raw materials, which not only involves strong corrosive reagents, but also releases toxic nitrogen oxide gas (such as nitrogen dioxide), and the subsequent waste liquid treatment is difficult, which is easy to cause environmental residues. Silver acetate is usually prepared by reacting silver nitrate with sodium acetate, or by reacting silver oxide with glacial acetic acid, but silver oxide is also prepared from silver nitrate; the synthesis of silver trifluoroacetate is also mainly based on the reaction of silver nitrate with sodium trifluoroacetate, or the reaction of silver oxide with trifluoroacetic acid. As can be seen, the two kinds of silver sources are essentially still based on silver nitrate as raw material for secondary processing, which not only increases the preparation steps and cost, but also may introduce new toxicity, increase instability and even increase the risk of explosion. Therefore, the commonly used silver sources in their production and use processes are accompanied by significant environmental risks and safety hazards. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a green preparation method of silver nanowires, which directly uses metal silver powder as a silver source to avoid the generation of harmful gases from the source, and uses water as a solvent to greatly reduce the use of organic solvents and significantly reduce the risk of environmental pollution.

[0006] Another purpose of the present application is to provide silver nanowires obtained by the above green preparation method.

[0007] The purpose of the present application is achieved by the following technical solutions.

[0008] A green preparation method of silver nanowires comprises the following steps:

[0009] Step 1: adding silver powder with a purity of ≥99.9% to a polyvinylpyrrolidone (PVP) aqueous solution, stirring for 20-40 min, and then adding a metal halide MX n , mixing uniformly, and reacting under oxidation conditions at pH=1-3 and 70-90°C for 7-9 h to obtain a silver halide colloid, wherein the ratio of polyvinylpyrrolidone (PVP), silver powder and metal halide MX n in the polyvinylpyrrolidone (PVP) aqueous solution is (20-30):1:(13-15) by mass fraction;

[0010] In the step 1, M in the metal halide MX n is one of Na + , K + , Cu 2+ , Fe 3+ and Al 3+ , X is Cl - or Br - , and n is an integer of 1-3.

[0011] In the step 1, the oxidation conditions are achieved by adding an oxidizing agent or creating an oxidizing environment.

[0012] In the step 1, the concentration of polyvinylpyrrolidone in the polyvinylpyrrolidone (PVP) aqueous solution is 0.0086-0.013 g / mL.

[0013] In the above technical solution, the oxidizing agent is an aqueous hydrogen peroxide solution, and the concentration of hydrogen peroxide in the aqueous hydrogen peroxide solution is 20-40 volume fraction.

[0014] In the above technical solution, when the oxidation conditions are achieved by adding an oxidizing agent, the ratio of the mass fraction of silver powder to the volume fraction of the oxidizing agent is 0.0431:(0.95-1.10), with the mass fraction being g and the volume fraction being mL.

[0015] In the above technical solution, when the oxidation condition is achieved by creating an oxidation environment, the reaction is carried out in an ozone atmosphere, and the reaction time is at least 8 hours.

[0016] In the step 1, the uniform mixing comprises stirring at a rotating speed of 700-1500 rpm for 20-40 min, and then ultrasonic treatment at a frequency of 30000-40000 Hz for 10-30 min.

[0017] In the step 2, the silver halide colloidal obtained in the step 1 is centrifuged and washed to obtain a precipitate, the precipitate is dispersed in water to obtain a silver halide dispersion, a surfactant aqueous solution and a reducing agent aqueous solution are sequentially added to the silver halide dispersion to obtain a mixed solution, the mixed solution is sealed and reacted at 100-130 ℃ for 20-24 h to obtain silver nanowires, wherein the surfactant aqueous solution comprises a surfactant, the reducing agent aqueous solution comprises a reducing agent, and the ratio of silver element, surfactant and reducing agent in the silver halide dispersion is (3-20) : (2-25) : (10-50) in terms of mass fraction.

[0018] In the step 2, 0.0172-0.1147 mass fraction of the precipitate is dispersed in 10-30 volume fraction of water to obtain the silver halide dispersion, the unit of mass fraction is g, and the unit of volume fraction is mL.

[0019] In the step 2, after the surfactant aqueous solution and the reducing agent aqueous solution are added, they are stirred for 20-40 min respectively.

[0020] In the step 2, the surfactant is a mixture of one or more of polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC).

[0021] In the step 2, the reducing agent is a mixture of one or more of ascorbic acid, hexamethylenetetramine and glucose.

[0022] In the step 2, the rotating speed of centrifugation is 5000-8000 rpm, and the centrifugation time is 5-15 min.

[0023] In the step 2, deionized water is used for washing, and the washing is performed 3-5 times.

[0024] In the step 2, the concentration of the reducing agent in the reducing agent aqueous solution is 7-30 mg / mL, and the concentration of the surfactant in the surfactant aqueous solution is 14-30 mg / mL.

[0025] The silver nanowires obtained by the above green preparation method.

[0026] In the technical scheme, the silver nanowire has a diameter of 20-60 nm and an aspect ratio of 400-4000.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. The green preparation method of the present application uses silver powder with a purity of ≥99.9% as a silver source and water as a main solvent, thereby avoiding the environmental impact caused by the conventional preparation process using silver nitrate as a silver source and ethylene glycol as a solvent, eliminating the generation of nitrogen oxide pollutants from the source, and providing a more sustainable solution for large-scale, environmentally friendly silver nanowire preparation methods.

[0029] 2. The silver nanowire prepared by the green preparation method of the present application has an average diameter of 20-60 nm and an aspect ratio of 400-4000, and has uniform morphology and a large aspect ratio, which has a wide application prospect in the preparation of transparent conductive films. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 XRD pattern of the silver nanowire prepared in Example 1 of the present application;

[0031] Figure 2 a is the SEM image of the silver halide colloid prepared in Example 1, Figure 2 b and Figure 2 c is the SEM image of the silver nanowire prepared in Example 1, wherein c is an enlarged view of b;

[0032] Figure 3 a is the SEM image of the silver halide colloid prepared in Example 6, Figure 3 b and Figure 3 c is the SEM image of the silver nanowire prepared in Example 6, wherein c is an enlarged view of b;

[0033] Figure 4 SEM images of the silver nanowire prepared in Examples 2-5 and Examples 7-8, wherein, Figure 4 a is the SEM image of the silver nanowire prepared in Example 2; Figure 4 b is the SEM image of the silver nanowire prepared in Example 3; Figure 4 c is the SEM image of the silver nanowire prepared in Example 4; Figure 4 d is the SEM image of the silver nanowire prepared in Example 5; Figure 4 e is the SEM image of the silver nanowire prepared in Example 7; Figure 4 f is the SEM image of the silver nanowire prepared in Example 8;

[0034] Figure 5 SEM images of the silver nanowire prepared in Comparative Examples 1-3, wherein,Figure 5 a is a SEM image of the silver nanomaterial prepared in Comparative Example 1; Figure 5 b is a SEM image of the silver nanomaterial prepared in Comparative Example 2; Figure 5 c is the SEM image of the silver nanomaterial prepared in Comparative Example 3. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] The water used in the following examples is deionized water.

[0037] The sources and purities of the reagents and materials involved in the following examples are as follows:

[0038]

[0039] The model and manufacturer information of the instruments used in the following examples are as follows:

[0040]

[0041] In the following embodiments, stirring was achieved using a magnetic stirrer at a speed of 1000 rpm.

[0042] Examples 1-5

[0043] A green preparation method for silver nanowires includes the following steps:

[0044] Step 1: Add silver powder with a purity ≥99.9% to a three-necked flask containing an aqueous solution of polyvinylpyrrolidone (PVP), stir for 20 min, then add sodium chloride, stir for another 20 min, and sonicate at a frequency of 40000 Hz for 10 min to obtain the first mixture. Adjust the pH of the first mixture to 1.0 using hydrochloric acid (HCl concentration of 12 mol / L), then place the flask in a water bath and connect one neck of the three-necked flask to an ozone generator. The neck on the other side is sealed, and the middle neck is connected to a straight condenser. The top of the straight condenser is connected to a gas collecting bottle to ensure good airtightness of the device. The temperature of the water bath is set to 80°C, and ozone is continuously introduced into the three-necked flask. The reaction is carried out for 8 hours to obtain silver halide colloid (silver chloride colloid). The ratio of polyvinylpyrrolidone (PVP), silver powder and sodium chloride in the polyvinylpyrrolidone (PVP) aqueous solution is 1:0.0431:0.5844 by mass.

[0045] The method for preparing an aqueous solution of polyvinylpyrrolidone (PVP) includes: mixing 1g of polyvinylpyrrolidone (PVP) and 100mL of deionized water, stirring and dissolving at 60°C to obtain an aqueous solution of polyvinylpyrrolidone (PVP).

[0046] Step 2: Centrifuge the silver halide colloid obtained in Step 1 at 8000 rpm for 10 min, discard the supernatant, and wash three times with deionized water to reduce the influence of PVP, excess halide ions, pH, and other factors on the purity of the product, obtaining a precipitate. Disperse 0.0573 g of the precipitate in 20 mL of water, sonicate for 10 min, and stir for 20 min to obtain a silver halide dispersion. Add an aqueous surfactant solution (CTAB aqueous solution) to the silver halide dispersion and stir for 30 min. Then add an aqueous reducing agent solution (ascorbic acid aqueous solution). Stir for 30 min to obtain a mixed solution. Seal the mixed solution in a reaction vessel and place the reaction vessel in an oven at 120℃ for 24 h. After the reaction is completed, allow the reaction vessel to cool naturally to room temperature, take out the mixed solution and repeat centrifugation 3 times. Each centrifugation is performed at a speed of 3000 rpm for 10 min to obtain silver nanowires. The ratio of silver element in the silver halide dispersion, surfactant (CTAB) in the surfactant aqueous solution and reducing agent (ascorbic acid) in the reducing agent aqueous solution is X, and the value of X is shown in Table 1.

[0047] The method for preparing the surfactant aqueous solution includes: weighing surfactant (CTAB) and dissolving it in water, stirring at 60°C for 10 minutes to obtain a clear surfactant aqueous solution, wherein the concentration of surfactant in the surfactant aqueous solution is c1, and the value of c1 is shown in Table 1;

[0048] The method for preparing the reducing agent aqueous solution includes: weighing the reducing agent (ascorbic acid) and dissolving it in deionized water, stirring for 20 minutes to obtain the reducing agent aqueous solution, wherein the concentration of the reducing agent in the reducing agent aqueous solution is c2, and the value of c2 is shown in Table 1.

[0049] Table 1

[0050]

[0051] Example 6

[0052] A green preparation method for silver nanowires includes the following steps:

[0053] Step 1, adding silver powder with purity ≥ 99.9% into polyvinylpyrrolidone (PVP) aqueous solution, stirring for 20 min, then adding metal halide (sodium chloride), stirring for 20 min, ultrasonic for 10 min under the condition of frequency 40000 Hz, adding oxidant (hydrogen peroxide aqueous solution), obtaining second mixture, using hydrochloric acid (the concentration of HCl in hydrochloric acid is 12 mol / L) to adjust the pH of the second mixture to 1.0, transferring to an oven, reacting for 8 h at 80℃, obtaining silver halide colloid, wherein, the ratio of polyvinylpyrrolidone (PVP), silver powder and metal halide in polyvinylpyrrolidone (PVP) aqueous solution is 1:0.0431:0.5844 by mass fraction, the ratio of mass fraction of silver powder to volume fraction of oxidant is 0.0431:1.02, the unit of mass fraction is g, and the unit of volume fraction is mL;

[0054] The method for preparing the polyvinylpyrrolidone (PVP) aqueous solution comprises the following steps: mixing 1 g of polyvinylpyrrolidone (PVP) and 98.98 mL of deionized water, stirring to dissolve at 60℃, and obtaining the polyvinylpyrrolidone (PVP) aqueous solution;

[0055] The oxidant (hydrogen peroxide aqueous solution) is a mixture of hydrogen peroxide and water, and the concentration of hydrogen peroxide in the hydrogen peroxide aqueous solution is 30% (volume fraction);

[0056] Step 2, centrifuging the silver halide colloid obtained in step 1 at a speed of 8000 rpm for 10 min, discarding the supernatant, washing the precipitate with deionized water for 3 times to reduce the influence of PVP, excessive halogen ions, pH and other factors on the purity of the product, obtaining the precipitate, dispersing 0.0573 g of the precipitate in 20 mL of water, ultrasonic for 10 min, stirring for 20 min, obtaining silver halide dispersion, adding surfactant aqueous solution (CTAB aqueous solution) into the silver halide dispersion, stirring for 30 min, then adding reducing agent aqueous solution (ascorbic acid aqueous solution), stirring for 30 min, obtaining a mixed solution, sealing the mixed solution in a reaction kettle, placing the reaction kettle in an oven at 120℃ and reacting for 24 h, after the reaction is completed, naturally cooling the reaction kettle to room temperature, taking out the mixed solution and repeating the centrifugation for 3 times, each time centrifuging at a speed of 3000 rpm for 10 min, obtaining silver nanowires, wherein, the ratio of silver element in the silver halide dispersion, surfactant (CTAB) in the surfactant aqueous solution and reducing agent (ascorbic acid) in the reducing agent aqueous solution is 10:15:25 by mole fraction.

[0057] The method for preparing the surfactant aqueous solution comprises the following steps: weighing the surfactant (CTAB) and dissolving it in water, stirring at 60℃ for 10 min, and obtaining a clear surfactant aqueous solution, wherein the concentration of the surfactant in the surfactant aqueous solution is 21.87 mg / mL.

[0058] The method for preparing the reducing agent aqueous solution includes: weighing the reducing agent (ascorbic acid) and dissolving it in water, stirring for 20 minutes to obtain the reducing agent aqueous solution, wherein the concentration of the reducing agent in the reducing agent aqueous solution is 17.61 mg / mL.

[0059] Example 7

[0060] A green preparation method for silver nanowires is basically the same as that in Example 1, except that in step 2 of this example, the temperature of the mixed solution reaction is 130°C.

[0061] Example 8

[0062] A green preparation method for silver nanowires is basically the same as that in Example 1, except that in step 2 of this example, the temperature of the mixed solution reaction is 100°C.

[0063] Comparative Example 1

[0064] A green preparation method for nano-silver materials is basically the same as that in Example 1, except that in step 2 of this comparative example, the ratio of silver element in the silver halide dispersion, surfactant in the surfactant aqueous solution, and reducing agent in the reducing agent aqueous solution is 10:40:25 by molar amount, wherein the concentration of surfactant in the surfactant aqueous solution is 58.31 mg / mL.

[0065] Comparative Example 2

[0066] A green preparation method for nano-silver materials is basically the same as that in Example 1, except that in step 2 of this comparative example, the ratio of silver element in the silver halide dispersion, surfactant in the surfactant aqueous solution, and reducing agent in the reducing agent aqueous solution is 10:15:60 by molar amount, wherein the concentration of reducing agent in the reducing agent aqueous solution is 42.27 mg / mL.

[0067] Comparative Example 3

[0068] A green preparation method for nano-silver materials is basically the same as that in Example 1, except that the reaction temperature of the mixed solution in step 2 of this comparative example is 80°C.

[0069] The XRD pattern of the silver nanowires obtained in Example 1 was detected using an X-ray diffractometer, and the XRD pattern is shown below. Figure 1 As shown. Figure 1 The XRD patterns of the standard silver spectrum (JCPDS NO.04-0783) were compared simultaneously. Figure 1It can be seen that the four diffraction peaks of the silver nanowires obtained in Example 1 correspond to the (111), (200), (220) and (311) crystal planes of the standard silver spectrum (JCPDS NO. 04-0783) respectively, and there is no other impurity peak, indicating that the silver nanowires prepared by the green preparation method of Example 1 have high purity.

[0070] The microstructure of the silver halide colloid and the silver nanowires obtained in Example 1 and Example 6 were observed by scanning electron microscopy, and the SEM images are shown in Figures 2-3 . Among them, Figure 2 a is the SEM image of the silver halide colloid obtained in Example 1, Figure 2 b and Figure 2 c are the SEM images of the silver nanowires obtained in Example 1 at different magnifications. It can be seen from Figure 2 that the silver nanowires prepared by the green preparation method of Example 1 have uniform morphology, less impurities, an average diameter of 35 nm, and a high aspect ratio of 4000.

[0071] Figure 3 a is the SEM image of the silver halide colloid obtained in Example 6, Figure 3 b and Figure 3 c are the SEM images of the silver nanowires obtained in Example 6 at different magnifications. It can be seen from Figure 3 that the silver nanowires prepared by the green preparation method of Example 6 have uniform morphology, less impurities, an average diameter of 38 nm, and an aspect ratio of 3600.

[0072] The microstructure of the silver nanowires obtained in Example 2~5 and Example 7~8 was observed by scanning electron microscopy, and the SEM images are shown in Figure 4 . Among them, Figure 4 a is the SEM image of the silver nanowires prepared in Example 2; Figure 4 b is the SEM image of the silver nanowires prepared in Example 3; Figure 4 c is the SEM image of the silver nanowires prepared in Example 4; Figure 4 d is the SEM image of the silver nanowires prepared in Example 5; Figure 4 e is the SEM image of the silver nanowires prepared in Example 7; Figure 4 f is the SEM image of the silver nanowires prepared in Example 8. It can be seen from Figure 5 that the green preparation methods of Example 2~5 and Example 7~8 can all prepare silver nanowires. The average diameter and aspect ratio of each silver nanowires prepared in Examples 1~8 are shown in Table 2.

[0073] Table 2

[0074]

[0075] The microstructure of the nano-silver materials obtained in Comparative Examples 1-3 was observed by a scanning electron microscope, and SEM images are shown in Figure 5 , wherein, Figure 5 a is the SEM image of the nano-silver material prepared in Comparative Example 1; Figure 5 b is the SEM image of the nano-silver material prepared in Comparative Example 2; Figure 5 c is the SEM image of the nano-silver material prepared in Comparative Example 3. It can be seen from ​ that the nano-silver materials prepared in Comparative Examples 1-3 have many impurities and almost no silver nanowires.

[0076] The above has described the present application by way of examples, and it should be noted that any simple modification, change or equivalent replacement which does not deviate from the core of the present application and can be made by those skilled in the art without creative effort falls within the protection scope of the present application.

Claims

1. A green method for the preparation of silver nanowires, characterized in that, The method comprises the following steps: Step 1, adding silver powder with purity ≥99.9% into polyvinylpyrrolidone aqueous solution, stirring for 20~40 min, and then adding metal halide MX n , mixing uniformly, and reacting for 7~9 h under oxidation condition at pH=1~3 and 70~90 ℃ to obtain silver halide colloid, wherein the ratio of polyvinylpyrrolidone, silver powder and metal halide MX n in the polyvinylpyrrolidone aqueous solution is (20~30):1:(13~15) by mass fraction. Step 2, centrifuging the silver halide colloid obtained in step 1, washing to obtain a precipitate, and dispersing the precipitate in water to obtain a silver halide dispersion, adding an aqueous surfactant solution and an aqueous reducing agent solution into the silver halide dispersion in sequence to obtain a mixed solution, and sealing the mixed solution for reaction at 100-130 ℃ for 20-24 h to obtain silver nanowires, wherein the aqueous surfactant solution comprises a surfactant, the aqueous reducing agent solution comprises a reducing agent, and the ratio of silver element in the silver halide dispersion, the surfactant and the reducing agent is (3-20):(2-25):(10-50) in terms of mass fraction.

2. The green manufacturing method of claim 1, wherein, In the step 1, a metal halide MX n wherein M is one of Na + , K + , Cu 2+ , Fe 3+ and Al 3+ , X is Cl - or Br - , and n is an integer of 1 to 3.

3. The green manufacturing method of claim 1, wherein, In the step 1, the oxidation condition is achieved by adding an oxidant or creating an oxidizing environment.

4. The green manufacturing method of claim 1, wherein, In the step 1, the concentration of polyvinylpyrrolidone in the aqueous polyvinylpyrrolidone solution is 0.0086-0.013 g / mL.

5. The green manufacturing method of claim 3, wherein, The oxidant is an aqueous hydrogen peroxide solution, and the ratio of the mass fraction of silver powder to the volume fraction of the oxidant is 0.0431:(0.95-1.10), wherein the unit of the mass fraction is g and the unit of the volume fraction is mL.

6. The green manufacturing method of claim 3, wherein, When the oxidation condition is achieved by creating an oxidizing environment, the reaction is carried out in an ozone atmosphere, and the reaction time is at least 8 h.

7. The green manufacturing method of claim 1, wherein, The surfactant is a mixture of one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, and the reducing agent is a mixture of one or more of ascorbic acid, hexamethylenetetramine and glucose.

8. The green manufacturing method of claim 1, wherein, In the step 2, 0.0172-0.1147 mass fraction of the precipitate is dispersed in 10-30 volume fraction of water to obtain the silver halide dispersion, wherein the unit of the mass fraction is g and the unit of the volume fraction is mL.

9. The green manufacturing method of claim 1, wherein, In the step 2, the concentration of the reducing agent in the aqueous reducing agent solution is 7-30 mg / mL, and the concentration of the surfactant in the aqueous surfactant solution is 14-30 mg / mL.

10. The silver nanowires obtained by the green preparation method according to any one of claims 1-9.

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