A method for synthesizing high-purity silver nanowires

Abstract

The present invention discloses a method for synthesizing high-purity silver nanowires, which includes: dissolving silver nitrate in polyol to form solution a; dissolving a surface capping agent in polyol to form solution b; fully mixing the above solutions a and b under stirring conditions to obtain a mixed solution c; transferring the mixed solution c into a high-pressure reaction kettle, heating it to a specific temperature, and keeping it at this temperature for a certain period of time to obtain a silver nanowire stock solution; centrifuging and washing the silver nanowire stock solution to obtain high-purity silver nanowires. The present invention does not require the addition of halide additives, does not require inert gas protection, and does not require additional seeds. By only controlling the ratios of AgNO3, PVP, and polyol, the reaction temperature, and the volume of the reaction system, high-purity silver nanowires with a controllable aspect ratio and high uniformity can be obtained, and the yield can reach more than 90%. The silver nanowires prepared by this method can be used in fields such as flexible transparent conductive devices, electronic skin, biosensors, and nanomedicine.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of one-dimensional nanomaterials, and relates to a method for synthesizing high-purity silver nanowires, and particularly relates to a method for synthesizing high-purity silver nanowires without a promoter. Background Art

[0002] Silver nanowires have attracted great attention in the academic and industrial communities due to their unique electronic, optical, and thermal properties. Due to their unique properties, silver nanowires can be widely used in fields such as transparent conductive devices, electronic skin, solar cells, flexible circuits, biosensors, and nanomedicine.

[0003] In recent years, with the development of various electronic products towards intelligence and refinement, higher quality requirements for silver nanowires have been put forward in various application fields, such as high purity, halogen-free, and good uniformity. In order to meet the technical requirements of various application fields, researchers have proposed various methods for synthesizing silver nanowires, such as the polyol method, the seed method, the template method, the wet chemical method, the photoreduction method, the electrochemical method, and the green synthesis method. Among them, the polyol synthesis method is the main method for preparing silver nanowires. At present, silver nanowires of different sizes have been successfully prepared by the above methods. It is worth noting that in many reports, the method of introducing halide promoters (such as NaCl, NaBr, KBr, CuCl 2 , FeCl 3 etc.) is an important factor determining the structural characteristics of silver nanowires. For example, in the experiment of synthesizing silver nanowires by Patil et al. (Chemical Engineering Journal. 2021, 414, 128711.), the importance of NaCl and FeCl 3 was emphasized, that is, etching through chloride ions and removing adsorbed oxygen by Fe 3+ . For example, Chinese Patent CN112643044A discloses a method for preparing silver nanowires with a high aspect ratio. The polyol method is used, and bromide salts and chloride salts are used as promoters. By dropping a silver nitrate solution, silver nanowires are synthesized at 160°C. Another example is Chinese Patent CN107639236A, which discloses a method for preparing silver nanowires. The polyol method is used, and under nitrogen protection, FeCl 3Silver nanowires were successfully prepared with the addition of halide salts. However, although the addition of halide salts is beneficial to the synthesis of silver nanowires, the synthesized silver nanowires have deficiencies in some application fields, such as optoelectronics, sensors, biomedical materials, etc. Because the halogens or metal ions contained in the additives will be adsorbed on the silver crystal surface or lattice during the growth of silver nanowires, and it is difficult to completely remove them during the washing treatment of silver nanowires, thus affecting the electrical conductivity, thermal conductivity and biocompatibility of the material. In addition, halogens are very sensitive to humidity, temperature, light and electrical stress. If the residual halogens are exposed to the air for a long time, they are very likely to be corrosive, thereby reducing the service life of the material. In addition, its reaction temperature is mostly above 150°C, and there are deficiencies such as complex preparation process, difficult to control process steps, low yield, and high impurity content, which will bring challenges in large-scale mass production, application and cost. Therefore, the method of directly synthesizing silver nanowires without additives is considered to be one of the most effective methods to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing high-purity silver nanowires by directly synthesizing them without auxiliary agents in a one-pot process, which can effectively solve the problems existing in the existing preparation of silver nanowires, such as residual halogens will reduce the photoelectric properties of silver nanowires, increase corrosiveness, reduce service life, and the process is complex, difficult to control and low yield during the preparation process. In the present invention, the inventor uses propylene glycol or its corresponding mixed alcohol as a reducing agent and solvent, and only uses PVP as a surface capping agent to synthesize high-purity silver nanowires in a one-pot process at a relatively low temperature (90-130°C). The high-purity silver nanowires prepared by this method can be widely used in optoelectronics, sensors, biomedicine and other fields.

[0005] In order to achieve the above object, the present invention provides a method for synthesizing high-purity silver nanowires, which adopts the following technical scheme:

[0006] A method for synthesizing high-purity silver nanowires comprises the following steps:

[0007] (1) AgNO 3 Dissolve in polyol to prepare solution a for later use;

[0008] (2) dissolving PVP in polyol to prepare solution b for later use;

[0009] (3) the solutions prepared in steps (1) and (2) are fully mixed under stirring to obtain a mixed solution c;

[0010] (4) transferring the mixed solution obtained in step (3) into a high-pressure reactor, heating it to a specific temperature, and keeping it at this temperature for a certain period of time to obtain a silver nanowire stock solution;

[0011] (5) The silver nanowire stock solution obtained in step (4) is centrifuged, washed, and purified multiple times with deionized water and absolute ethanol to obtain the silver nanowires.

[0012] The polyol is one of propylene glycol, butylene glycol, and glycerol, or a mixed alcohol solution prepared by mixing propylene glycol with butylene glycol and glycerol respectively in a certain proportion.

[0013] The surface capping agent PVP is one of PVP-K15 (Mw: ~10000), PVP-K30 (Mw: 45000 - 58000), PVP-K60 (Mw: 360000), and PVP-K90 (Mw: 1300000), or a capping agent solution prepared by mixing one or two of them in a certain proportion.

[0014] The mass concentration of AgNO 3 in solution a is 10 - 40 g / L.

[0015] When preparing solution a, the dissolution temperature is 20 - 30 °C, the stirring speed is 150 - 250 rpm, and the stirring time is 10 - 30 min;

[0016] The mass concentration of PVP in solution b is 1 - 4 g / L.

[0017] When preparing solution b, the dissolution temperature is 30 - 50 °C, the stirring speed is 150 - 250 rpm, and the stirring time is 20 - 40 min.

[0018] The mass ratio of AgNO 3 to PVP in solution c is 1:0.05 - 1:0.4.

[0019] The stirring speed of the mixed solution c is 150 - 250 r / min, and the mixing and stirring time is 5 - 20 min.

[0020] The volume of the mixed solution c accounts for 30 - 70% of the total volume of the high-pressure reactor.

[0021] The heating rate is 1 - 10 °C / min.

[0022] The heat preservation temperature is 90 - 130 °C, and the heat preservation time is 5 - 30 h.

[0023] The mechanism involved in the present invention includes:

[0024] Different from the traditional method of synthesizing silver nanowires by adding halide additives, the present invention does not require adding halide additives and only uses PVP as the surface capping agent, and can directly synthesize silver nanowires in a polyol system. Taking propylene glycol as an example, its reaction mechanism is as follows;

[0025]

[0026] HCOOH + Ag → HCOOAg + H + (2)

[0027] CH 3 COOH + Ag → CH 3 COOAg + H + (3)

[0028] 3Ag + 4HNO 3 → 3AgNO 3 + NO + 2H 2 O (4)

[0029] As can be seen from Reaction Formula (1), when propylene glycol is heated under acidic conditions containing silver ions, successive oxidation reactions occur, ultimately producing formic acid (HCOOH) and acetic acid (CH 3 COOH) and their corresponding salts. The intermediate products include hydroxyacetone (CH 3 CHOCH 2 OH), methylglyoxal (CH 3 COCHO), and pyruvic acid (CH 3 COCOOH). Meanwhile, silver ions are continuously reduced to silver atoms. When the concentration of silver atoms in the reaction system reaches supersaturation, they aggregate and nucleate to form silver seeds, which may have any structure of single crystals, polycrystalline nanoparticles, and five-fold twinned nanoparticles. Among them, five-fold twinned silver nanoparticles are a necessary prerequisite for synthesizing silver nanowires. When the free silver ions in the reaction system are low enough and under thermodynamically stable conditions, silver nanoparticles with a five-fold twinned structure will preferentially form. In the present invention, a closed polytetrafluoroethylene is used as the reaction vessel, and the formic acid, acetic acid, and nitric acid generated in the reactor can be kept in the reactor under reflux. Nitric acid and carboxylic acids can be used as etchants to dissolve some nanoparticles with surface defects and polycrystalline nanoparticles, thereby resulting in a lower concentration of free silver ions in the reaction system (Reaction Formulas (2), (3), and (4)), which will help silver atoms nucleate and evolve into silver nanoparticles with a five-fold twinned structure. Secondly, by utilizing the property that the surface capping agent PVP can form Ag-O bonds with silver and preferentially cover the

[100] plane of five-fold twinned silver nanoparticles, the deposition of silver atoms on the

[111] plane is promoted, thereby realizing the unidirectional growth of silver nanowires, as Figure 2 shown. Based on the above reaction mechanism, the present invention successfully prepares high-purity silver nanowires without halide additives only by controlling conditions such as the ratio of AgNO 3 , PVP, and polyol in the reaction system, the reaction temperature, and the volume of the reaction system.

[0030] In the present invention, the reaction rate and the surface capping agent PVP are particularly important for regulating the aspect ratio of silver nanowires. The reaction rate determines the concentration of silver atoms in the reaction system, the generation of five-fold twinned crystal seeds, and the growth rate of silver nanowires. Here, the reaction rate can be precisely regulated by controlling the types and ratios of polyols, the reaction temperature, and the heating rate in the reaction system. The characteristics of the surface capping agent PVP in covering the (100) crystal plane of silver nanoparticles and promoting the unidirectional growth of silver nanowires along the (111) crystal plane direction are crucial for the preparation of silver nanowires with a high aspect ratio. Here, by selecting PVP with different molecular weights and the corresponding addition ratios to regulate the coating degree of silver nanowires during the growth process, the length and diameter of silver nanowires can be further controlled. In summary, by synergistically regulating the types and ratios of polyols, the reaction temperature, the heating rate, and the molecular weight and addition ratio of PVP in the reaction system, the controllable preparation of silver nanowires with a high aspect ratio and high purity can be achieved.

[0031] The beneficial effects of the present invention are as follows:

[0032] (1) The method of the present invention does not require the addition of halide additives, inert gas protection, or the additional addition of crystal seeds. The preparation process is simple, the reaction temperature is low, and the yield can reach more than 90%, making it easy to achieve batch production.

[0033] (2) The present invention can control the preparation parameters such as the length and diameter of silver nanowires, and silver nanowires with a high aspect ratio can be prepared.

[0034] (3) The halogen ion-free silver nanowires prepared by the present invention can be widely applied in fields such as flexible circuits, biosensors, and nanomedicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0036] Figure 1 is the process flow chart of the present invention.

[0037] Figure 2 is the reaction principle diagram of the present invention.

[0038] Figure 3 is the scanning electron microscope (SEM) image of the silver nanowires prepared in Example 1 of the present invention. The scale bar in the figure is 20 μm, and the average diameter of the silver nanowires is 100 - 20 nm, and the average length is 20 - 170 μm.

[0039] Figure 4This is a scanning electron microscope (SEM) image of the silver nanowires prepared in Example 2 of the present invention. The scale in the image is 20 μm. The average diameter of the silver nanowires is 50-200 nm, and the average length is 50-300 μm.

[0040] Figure 5 This is a scanning electron microscope (SEM) image of the silver nanowires prepared in Example 3 of the present invention. The scale in the image is 20 μm. The average diameter of the silver nanowires is 200-400 nm, and the average length is 30-200 μm. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figure 1 As shown, the present invention provides a method for synthesizing high-purity silver nanowires, comprising the following steps:

[0043] (1) AgNO 3 Dissolve in polyol to prepare solution a for later use;

[0044] (2) dissolving PVP in polyol to prepare solution b for later use;

[0045] (3) the solutions prepared in steps (1) and (2) are fully mixed under stirring to obtain a mixed solution c;

[0046] (4) transferring the mixed solution obtained in step (3) into a high-pressure reactor, heating it to a specific temperature, and keeping it at this temperature for a certain period of time to obtain a silver nanowire stock solution;

[0047] (5) The silver nanowire stock solution obtained in step (4) is subjected to multiple centrifugal washing and purification treatments with deionized water and anhydrous ethanol to obtain the silver nanowires.

[0048] The technical solutions and beneficial effects of the present invention are further described below in conjunction with specific embodiments.

[0049] Example 1

[0050] (1) Dissolve 1 g of silver nitrate in 50 mL of propylene glycol to prepare solution a, wherein the dissolution temperature is 25° C., the stirring speed is 250 rpm, and the stirring time is 20 min; set aside;

[0051] (2) Dissolve 0.08 g of polyvinylpyrrolidone (PVP, K90) in 50 mL of propylene glycol to prepare solution b. The dissolution temperature is 40 °C, the stirring speed is 250 rpm, and the stirring time is 30 min. Set aside for later use.

[0052] (3) Pour solution a into solution b and mix well at 25 °C with a stirring speed of 250 rpm for 10 min to obtain mixed solution c.

[0053] (4) Transfer mixed solution c into a 150 - 500 mL high-pressure reactor, heat it to 100 °C at a heating rate of 5 °C / min, and keep it at 100 °C for 8 h.

[0054] (5) Centrifuge and wash the prepared silver nanowire stock solution with deionized water and absolute ethanol for multiple times and perform purification treatment to obtain the high-purity silver nanowires.

[0055] Example 2

[0056] (1) Prepare a mixed alcohol solution by mixing propylene glycol and glycerol at a volume ratio of 1:1 - 1:10. Set aside for later use.

[0057] (2) Dissolve 1 g of silver nitrate in 50 mL of the mixed alcohol solution to prepare solution a. The dissolution temperature is 25 °C, the stirring speed is 250 rpm, and the stirring time is 15 min. Set aside for later use.

[0058] (3) Dissolve 0.1 g of polyvinylpyrrolidone (PVP, K90) in 50 mL of the mixed alcohol solution to prepare solution b. The dissolution temperature is 40 °C, the stirring speed is 250 rpm, and the stirring time is 30 min. Set aside for later use.

[0059] (4) Pour solution a into solution b and mix well at 25 °C with a stirring speed of 250 r / min for 10 min to obtain mixed solution c.

[0060] (5) Transfer mixed solution c into a 150 - 500 mL high-pressure reactor, heat it to 95 °C at a heating rate of 2 °C / min, and keep it at 95 °C for 30 h.

[0061] (6) Centrifuge and wash the prepared silver nanowire stock solution with deionized water and absolute ethanol for multiple times and perform purification treatment to obtain the high-purity silver nanowires.

[0062] Example 3

[0063] (1) Prepare a mixed alcohol solution by mixing propylene glycol and ethylene glycol at a volume ratio of 1:5 - 1:10. Set aside for later use.

[0064] (2) Dissolve 2 g of silver nitrate in 50 mL of a mixed alcohol solution to prepare solution a. The dissolution temperature is 25 °C, the stirring speed is 250 rpm, and the stirring time is 10 min; set aside for later use.

[0065] (3) Dissolve 0.4 g of polyvinylpyrrolidone (PVP, K60) in 50 mL of a mixed alcohol solution to prepare solution b. The dissolution temperature is 40 °C, the stirring speed is 250 rpm, and the stirring time is 30 min; set aside for later use.

[0066] (4) Pour solution a into solution b and mix well at 25 °C with a stirring speed of 250 r / min for 10 min to obtain a mixed solution c.

[0067] (5) Transfer the mixed solution c into a 150 - 500 mL high-pressure reactor, heat it to 120 °C at a heating rate of 5 °C / min, and keep it at 120 °C for 6 h.

[0068] (6) Centrifuge, wash, and purify the prepared silver nanowire stock solution with deionized water and absolute ethanol multiple times to obtain the high-purity silver nanowires.

[0069] In this specification, each embodiment is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0070] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for synthesizing high-purity silver nanowires, characterized in that, it includes the following steps: (1) Dissolve AgNO 3 in polyol to prepare solution a for standby; the AgNO 3 is dissolved in polyol to prepare solution a, the dissolution temperature is 20 - 30 °C, the stirring speed is 150 - 250 rpm, and the stirring time is 10 - 30 min; (2) Dissolve the surface capping agent PVP in polyol to form solution b for standby; the mass concentration of PVP in solution b is 1-4 g / L; when forming solution b, the dissolution temperature is 30-50 °C, the stirring speed is 150-250 rpm, and the stirring time is 20-40 min; (3) Solution a and solution b are fully mixed under stirring conditions to obtain a mixed solution c; wherein the solution c contains AgNO 3 The mass ratio of PVP is 1:0.05 to 1:0.1; the mixing temperature of the mixed solution c is 20 to 30°C, the stirring speed is 150 to 250 rpm, and the mixing time is 5 to 20 min; (4) Transfer the mixed solution c obtained in step (3) into a high-pressure reactor, raise the temperature to a specific temperature, and keep it at this temperature for a certain period of time to obtain a silver nanowire stock solution; in step (4), the heating rate is 1-10 o °C / min, the heat preservation temperature is 95-120 o °C, and the heat preservation time is 5-30 h; the volume of the mixed solution c accounts for 30-70% of the total volume of the high-pressure reactor. (5) Centrifuge, wash and separate the silver nanowire stock solution obtained in step (4) with deionized water and absolute ethanol to obtain the high-purity silver nanowires; The surface capping agent PVP is selected from one or two of PVP-K15, PVP-K30, PVP-K60 and PVP-K90; Of the PVP-K15 Mw: is 10,000, of the PVP-K30 Mw: is 45,000 to 58,000, of the PVP-K60 Mw: is 360,000, of the PVP-K90 Mw: is 1,300,000.

2. The method for synthesizing high-purity silver nanowires according to claim 1, characterized in that, the polyol is selected from one of propylene glycol and butylene glycol or a mixed alcohol solution prepared by mixing propylene glycol and butylene glycol in a certain proportion.

3. The method for synthesizing high-purity silver nanowires according to claim 1, characterized in that, The mass concentration of AgNO in the solution a is 3 10 to 40 g / L.

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