Preparation method of silver nanowire with high length-diameter ratio

Abstract

The invention discloses a preparation method of a high-length-diameter-ratio silver nanowire, and aims to solve the technical problem of how to obtain a silver nanowire which is uniform in morphology and higher in length-diameter ratio. The silver nanowire is prepared through a hot solvent method, the concentration of AgNO3 in a reaction solution D is 70-80 mmol / L, the volume ratio of a reaction solution A to the reaction solution D is 45-55: 23-33, the reaction temperature is 165-175 DEG C, and the reaction time is 145-155 min. The silver nanowire synthesized through the method is good in uniformity, high in purity and large in length-diameter ratio, the average diameter of the silver nanowire is 38.88 nm, the average length of the silver nanowire exceeds 100, the length-diameter ratio of the silver nanowire exceeds 2500, and the silver nanowire can be used for preparing the silver nanowire. The method has important guiding significance in application of the silver nanowires in the fields of transparent electrode materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a method for preparing silver nanowires with a high aspect ratio. Background Art

[0002] Transparent electrodes are widely used in various fields, including organic light-emitting diodes, wearable electronic devices, display panels and touch screens, and flexible solar cells. Indium tin oxide (ITO), a traditional electrode material, is in urgent need of new alternative materials due to its shortcomings such as shortage of indium resources, high manufacturing cost, and strong rigidity. Silver nanowires (Ag NWs) are considered to be an ideal substitute for ITO due to their high conductivity, affordable price, excellent optical properties, stable chemical properties, and excellent resistance to bending deformation. They have become a transparent electrode material with great potential in commercial applications. In the application process of silver nanowires (AgNWs), the smaller the diameter and the higher the aspect ratio, the better the light transmittance, conductivity, and sensitivity of the flexible transparent electrode material; therefore, how to prepare Ag NWs with uniform morphology and higher aspect ratio to improve the performance of flexible transparent electrodes is a key challenge currently faced by researchers.

[0003] The information disclosed in this background technology section is only used to deepen the understanding of the background technology of the present disclosure, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0004] The inventors found in the long-term research process that in order to obtain silver nanowires with uniform morphology and high aspect ratio, on the one hand, it is necessary to generate seeds with a five-fold twin structure as much as possible during the crystal nucleus formation stage: that is, by controlling the precursor AgNO 3 The concentration, type of nucleation controller and its concentration, reaction temperature, reaction time and other conditions can be used to regulate the type of nucleus formation; on the other hand, measures need to be taken during the nucleus growth stage to prevent the lateral growth of quintuple twinned seeds (MTPs): that is, to regulate the concentration of the structure directing agent polyvinyl pyrrolidone to control the longitudinal growth of the nucleus.

[0005] In view of this, the present disclosure provides a method for preparing silver nanowires with high aspect ratio, by reacting AgNO in a reaction solution D 3 The effective identification and selection of the effects of parameters such as concentration, reaction temperature, reaction time and the volume ratio of reaction solution A to reaction solution D can reduce the number of silver nanoparticles and the diameter of silver nanowires, increase the number and length of silver nanowires during the preparation process, and thus obtain silver nanowires with uniform morphology and higher aspect ratio. Specifically, the following steps are included: (1) dissolving polyvinyl pyrrolidone in ethylene glycol solvent to form a reaction solution A having a polyvinyl pyrrolidone concentration of 40 to 50 g / L; (2) NaBr, NaCl and Fe(NO 3 ) 3 Dissolved in ethylene glycol solvent respectively to form solutions with concentrations of 8-12 mmol / L, 8-12 mmol / L, and 0.8-1.2 mmol / L, respectively, and then mixed in a molar ratio of 65-75:270-280:1-2 to form a reaction solution B; (3) adding the reaction solution B to the reaction solution A at a volume ratio of 1-3:48-52 to form a reaction solution C; (4) Weigh AgNO 3 Dissolved in ethylene glycol solvent to form AgNO 3 Reaction solution D with a concentration of 70 to 80 mmol / L; (5) adding the reaction solution D dropwise to the reaction solution C while stirring, with the mixing volume ratio of the two being 23-33:47-57; (6) reacting the mixed solution obtained in step (5) at 165 to 175° C. under dry conditions for 145 to 155 minutes; (7) After the reaction is completed, the reaction product is cooled to room temperature, and then washed and purified, and finally dispersed in anhydrous ethanol to obtain silver nanowires with a high aspect ratio.

[0006] In some embodiments of the present disclosure, in step (1), the polyvinyl pyrrolidone is PVP-K90.

[0007] In some embodiments of the present disclosure, in step (5), the stirring is magnetic stirring.

[0008] In some embodiments of the present disclosure, in step (6), the reaction is carried out in an electric heated forced air drying oven.

[0009] In some embodiments of the present disclosure, the reaction volume ratio of the reaction solution A to the reaction solution D is 45-55:23-33.

[0010] In some embodiments of the present disclosure, in step (7), the cleaning and purification method is to centrifuge the reaction product at a speed of 4500-5000 rpm for 15-25 min, remove the supernatant, and then wash with acetone, anhydrous ethanol, and deionized water at a speed of 4500-5000 rpm for 15-25 min respectively.

[0011] One or more technical solutions provided in the embodiments of the present application have at least any of the following technical effects or advantages: In this application, polyvinyl pyrrolidone is used as a structure-directing agent, ethylene glycol is used as a solvent and a reducing agent, and AgNO 3 As the precursor, Cl- etc. were used as nucleation control agents to prepare silver nanowires using a hot solvent method, in which AgNO 3 The concentration is 70-80 mmol / L, the volume ratio of reaction solution A (polyvinyl pyrrolidone ethylene glycol solution) to reaction solution D (silver nitrate ethylene glycol solution) is 45-55:23-33, the reaction temperature is 165-175°C, and the reaction time is 145-155 min. The silver nanowires synthesized by this method have good uniformity, high purity, and a large aspect ratio. The average diameter is 38.88 nm, the average length exceeds 100 μm, and the aspect ratio exceeds 2500. It has important guiding significance for its application in the fields of transparent electrode materials and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the mechanism of preparing silver nanowires by solvothermal method in one embodiment of the present application.

[0013] Figure 2 This is a diagram of the coordination complex and three-dimensional structure of Ag-PVP (polyvinyl pyrrolidone) nanowires in one embodiment of the present application.

[0014] Figure 3 This is a SEM image of silver nanowires prepared under optimized process parameters and a distribution diagram of AgNWs diameters in an embodiment of the present application.

[0015] Figure 4 Magnified images of the silver nanowires prepared in one embodiment of the present application under an optical microscope; (a) 100 times; (b) 400 times.

[0016] FIG. 5 shows different AgNO in the reaction solution D in one embodiment of the present application. 3 SEM images of silver nanowires prepared at different concentrations; among them, (a) 70mmol / L; (b) 75mmol / L; (c) 80mmol / L.

[0017] FIG6 is an SEM image of silver nanowires prepared at different volume ratios of reaction solution A to reaction solution D in one embodiment of the present application; wherein, (a) 45:33; (b) 50:28; (c) 55:23.

[0018] FIG7 is a SEM image of silver nanowires prepared at different reaction temperatures in one embodiment of the present application; wherein, (a) 160° C.; (b) 170° C.; and (c) 180° C.

[0019] FIG8 is an SEM image of silver nanowires prepared at different reaction times in one embodiment of the present application; wherein, (a) 140 min; (b) 150 min; (c) 160 min. DETAILED DESCRIPTION

[0020] The specific implementation methods of the present invention are described below in conjunction with examples, but the following examples are only used to illustrate the present application in detail and do not limit the scope of the present application in any way.

[0021] Unless otherwise specified, the instruments and equipment involved in the following examples are all conventional instruments and equipment; the test materials and reagents involved are all commercially available unless otherwise specified; the tests and detection methods involved are all conventional methods unless otherwise specified.

[0022] Example 1 Synthesis mechanism and preparation of high aspect ratio silver nanowires 1. Synthesis mechanism of silver nanowires In the first step, ethylene glycol (EG) was used as a solvent and a reducing agent to prepare Ag NWs. EG was first decomposed into acetaldehyde at high temperature, and then acetaldehyde slowly converted AgNO 3 Silver ions (Ag + ) is reduced to silver atoms (Ag 0 ); In the second step, the newly formed Ag atoms aggregate to form silver clusters; In the third step, single crystal, single twin crystal and five-fold twin crystal (MTP) seeds are formed through uniform nucleation or non-uniform nucleation of silver atoms; In the fourth step, under the guidance of the structure-directing agent polyvinylpyrrolidone, the five-fold twinned seeds (MTPs) were directionally grown into Ag NWs, such as Figure 1 , Figure 2 shown.

[0023] 2. Preparation of Silver Nanowires (1) Weigh polyvinyl pyrrolidone (PVP-K90) and fully dissolve it in 250 ml of ethylene glycol solvent to form a reaction solution A with a polyvinyl pyrrolidone concentration of 45 g / L.

[0024] (2) NaBr, NaCl and Fe(NO 3 ) 3 They were dissolved in ethylene glycol solvent respectively to form solutions with concentrations of 10 mmol / L, 10 mmol / L, and 1 mmol / L, respectively, and then mixed in a molar ratio of 70:275:1 to form reaction solution B.

[0025] (3) Place 50 ml of reaction solution A obtained in step (1) in a beaker and uniformly add 2 ml of reaction solution B obtained in step (2) to form reaction solution C.

[0026] (4) Weigh AgNO 3 , dissolved in 28 ml of ethylene glycol solvent to form AgNO 3The concentration of reaction solution D is 75mmol / L.

[0027] (5) Using a dropper, add all of the reaction solution D obtained in step (4) to the reaction solution C at a uniform rate, and stir magnetically until the mixture is fully mixed.

[0028] (6) The mixed solution obtained in step (5) is transferred to a polytetrafluoroethylene-lined autoclave, and the autoclave is placed in an electric heated blast drying oven for heating. The reaction is carried out at a reaction temperature of 170° C. for a reaction time of 150 min.

[0029] (7) After the reaction is completed, the autoclave is taken out and cooled naturally to room temperature. The polytetrafluoroethylene liner is then taken out, the reaction product is poured out, and the reaction product is centrifuged at 4800 rpm for 20 min. The supernatant is removed and the remaining 10 ml of the centrifuge is collected. The centrifuge is then washed with 5 times acetone, anhydrous ethanol, and deionized water according to the above method to remove EG and excess PVP. Finally, it is dispersed in 10 ml of anhydrous ethanol to obtain high aspect ratio silver nanowires.

[0030] The silver nanowires prepared by the above method have good uniformity, an average diameter of 38.88nm, an average length of more than 100㎛, and an aspect ratio of more than 2500. Figure 3 , Figure 4 shown.

[0031] Example 2: AgNO in reaction solution D 3 Study on the effect of concentration on the preparation of silver nanowires The relationship between the precursor concentration and the five-fold twinned seed (thermodynamically more stable, usually decahedral) is very close; therefore, based on the preparation method in Example 1, this example studies the AgNO in the reaction solution D under the premise that other conditions and parameters remain unchanged. 3 The effect of concentration on the preparation of silver nanowires is shown in Figure 5.

[0032] It can be seen from Figure 5 (a), (b), and (c) that AgNO 3 Too low or too high a concentration will result in a decrease in the number of Ag NWs and a relative increase in the number of silver nanoparticles. This is because AgNO 3 At low concentrations, the chemical potential decreases, resulting in more thermodynamically stable MTPs rather than single crystal seeds (kinetically stable). If the precursor concentration is too small, the Ag precipitated on the seeds 0 The number of Ag NWs formed also decreases, which leads to a decrease in the yield of Ag NWs. 3 When the concentration is high, although the number of generated MTPs decreases, due to Ag 0The growth rate of different crystal faces of the seed crystal is isotropic, so the generated product is a large number of silver nanoparticles. Therefore, considering various factors, the AgNO 3 The concentration may preferably be 75 mmol / L.

[0033] Example 3: Study on the effect of the volume ratio of reaction solution A (polyvinyl pyrrolidone ethylene glycol solution) to reaction solution D (silver nitrate ethylene glycol solution) on the growth of silver nanowires The {100} crystal face of the five-fold twinned seed has a strong binding force with the strong polar groups (such as carboxyl) of polyvinyl pyrrolidone, and the steric hindrance effect also leads to a high coverage rate of the crystal face, thereby preventing Ag from 0 Lateral growth; while the {111} crystal plane, which has poor binding with polyvinyl pyrrolidone and maintains high activity, has more Ag 0 Ag NWs are deposited on the crystal plane, thereby growing vertically. It can be seen that the crystal plane selective adsorption characteristics of the structure-directing agent polyvinyl pyrrolidone can induce anisotropic growth and achieve the regulation of the morphology of Ag NWs.

[0034] This example is based on the preparation method in Example 1. In the reaction solution D, AgNO 3 Under the premise of the same conditions such as the concentration of 75 mmol / L, the effect of the volume ratio of reaction solution A to reaction solution D on the preparation of silver nanowires was studied, and the results are shown in FIG6 .

[0035] As can be seen from Figure 6, as the volume ratio of reaction solution A to reaction solution D gradually increases, the number of silver nanoparticles gradually decreases, and the number and length of silver nanowires gradually increase. However, when the volume ratio is 55:23, the length of Ag NWs becomes shorter and some particles appear. This is because when the amount of polyvinyl pyrrolidone is relatively insufficient, it is difficult to completely cover the {100} face of the seed crystal, resulting in isotropic growth of the seed crystal, resulting in a decrease in the number of Ag NWs, a shortening of the length, and even becoming particles. When the amount of polyvinyl pyrrolidone is too much and the seed crystal is severely coated, polyvinyl pyrrolidone not only loses its selective adsorption on different crystal faces of the seed crystal, but also prevents Ag from adsorbing on the surface of the seed crystal. 0 When deposited on the {111} surface, the viscosity of the system will also increase, thereby slowing down the diffusion rate of silver nanoparticles, and ultimately resulting in the anisotropic growth of the seed being restricted to varying degrees, and the resulting Ag NWs will become shorter or contain more silver nanoparticles. Therefore, in order to obtain Ag NWs with a high aspect ratio and uniform morphology, the volume ratio of reaction solution A to reaction solution D can be preferably 50:28.

[0036] Example 4: Study on the effect of reaction temperature on the growth of silver nanowires Solvothermal synthesis of silver nanowires is a thermodynamically controlled process, and the reaction temperature has a significant effect on the reduction rate of silver ions, the nucleation rate of silver atoms, and the growth rate of crystal nuclei. Therefore, based on the preparation method in Example 1, in the reaction solution D, AgNO 3 When the concentration was 75 mmol / L, the volume ratio of reaction solution A to reaction solution D was 50:28, and other conditions were the same, the effects of different reaction temperatures on the preparation of Ag NWs were compared and the results are shown in FIG7 .

[0037] As can be seen from Figure 7 (a) and (b), as the reaction temperature increases, the product gradually changes from a large number of irregular silver nanoparticles to silver nanowires with fewer particles, longer lengths and uniform diameters; when the reaction temperature is raised to 180°C (as shown in Figure 5 (c)), the yield of Ag NWs decreases, their lengths become uneven, and a certain amount of silver nanoparticles are produced. This is because when the reaction temperature is low, the energy of the reaction system is insufficient for the growth of silver nanowires, especially the anisotropic growth of MTPs, so it is more inclined to generate a large number of silver nanoparticles; and as the reaction temperature gradually increases, the effective heat energy of the reaction system increases, which not only promotes the growth of seed crystals, but also reduces the number of crystal nuclei in the reaction solution, which means that each silver nanowire can be allocated more silver sources, thereby promoting the growth of the length of Ag NWs; however, when the reaction temperature is further increased, even exceeding 180°C, the activity of the reaction system becomes too strong, resulting in intense movement of nanoparticles and agglomeration of crystal nuclei. In this case, the proportion of MTPs will decrease, while the generation of shorter silver nanowires or silver nanoparticles will increase, ultimately leading to a decrease in the yield of silver nanowires. In summary, the reaction temperature is preferably controlled at around 170°C.

[0038] Example 5: Study on the effect of reaction time on the growth of silver nanowires The preparation process of silver nanowires is nucleation first, then aggregation and growth, so it takes a certain reaction time. The length of the reaction time not only affects the production efficiency and morphology of Ag NWs, but also determines whether it can be mass-produced.

[0039] In this case, AgNO 3 Under the same conditions of concentration of 75 mmol / L, volume ratio of reaction solution A to reaction solution D of 50:28, reaction temperature of 170°C, etc., the effect of different reaction times on the preparation of silver nanowires was studied, and the results are shown in FIG8 .

[0040] As can be seen from Figure 8, when the reaction time is too short or too long, the coexistence of silver nanoparticles with different amounts and silver nanowires with reduced average lengths will be obtained. This is because due to the short reaction time, Ag+ is not completely reduced to silver, which cannot meet the Ag 0Nucleation and Ag NWs growth: Most of the seeds do not have time to grow into silver nanowires, resulting in more impurities such as silver nanoparticles in the product; and as the reaction time continues to increase, Ag + Gradually reduced to Ag 0 The continuously formed MTPs are selectively adsorbed by the polyvinylpyrrolidone molecules to form silver nanowires; however, as the reaction time continues to increase, the silver nanoparticles in the system agglomerate and cause the crystal form to reform: the proportion of non-MTPs increases, and then some silver nanoparticles are gradually generated, and the product length does not increase significantly. Taking various factors into consideration, the reaction time is preferably controlled at about 150 minutes.

[0041] Although some preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0042] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the inventive concept. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for preparing silver nanowires with high aspect ratio, characterized in that: The steps include: (1) dissolving polyvinyl pyrrolidone in ethylene glycol solvent to form a reaction solution A having a polyvinyl pyrrolidone concentration of 40 to 50 g / L; (2) dissolving NaBr, NaCl and Fe(NO3)3 in ethylene glycol solvent respectively to form solutions with concentrations of 8-12 mmol / L, 8-12 mmol / L and 0.8-1.2 mmol / L, respectively, and then mixing them in a molar ratio of 65-75:270-280:1-2 to form a reaction solution B; (3) adding the reaction solution B to the reaction solution A at a volume ratio of 1-3:48-52 to form a reaction solution C; (4) Weigh AgNO3 and dissolve it in ethylene glycol solvent to form a reaction solution D with an AgNO3 concentration of 70 to 80 mmol / L; (5) adding the reaction solution D dropwise to the reaction solution C while stirring, with the mixing volume ratio of the two being 23-33:47-57; (6) reacting the mixed solution obtained in step (5) at 165 to 175° C. under dry conditions for 145 to 155 minutes; (7) After the reaction is completed, the reaction product is cooled to room temperature, and then washed and purified, and finally dispersed in anhydrous ethanol to obtain silver nanowires with a high aspect ratio.

2. The preparation method according to claim 1, characterized in that: In the step (1), the polyvinyl pyrrolidone is PVP-K90.

3. The preparation method according to claim 1, characterized in that: In step (5), the stirring is magnetic stirring.

4. The preparation method according to claim 1, characterized in that: In the step (6), the reaction is carried out in an electric heated forced air drying oven.

5. The preparation method according to claim 1, characterized in that: The reaction volume ratio of the reaction solution A to the reaction solution D is 45-55:23-33.

6. The preparation method according to claim 1, characterized in that: In the step (7), the cleaning and purification method is to centrifuge the reaction product at a speed of 4500-5000 rpm for 15-25 minutes, remove the supernatant, and then wash with acetone, anhydrous ethanol, and deionized water at a speed of 4500-5000 rpm for 15-25 minutes.

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