CN114433865A - Synthesis method of high-purity silver nanowires - Google Patents

Abstract

The invention discloses a method for synthesizing high-purity silver nanowires. The solution is fully mixed under stirring conditions to obtain a mixed solution c; the mixed solution c is transferred into an autoclave, raised to a specific temperature, and kept at this temperature for a certain period of time to obtain a silver nanowire stock solution; the silver nanowire stock solution is After centrifugal washing, high-purity silver nanowires can be obtained. The invention does not need to add halide additives, inert gas protection, and additional crystal seeds, and only by controlling the ratio of AgNO ₃ , PVP and polyol, the reaction temperature and the volume of the reaction system, a controllable and uniform aspect ratio can be obtained. The yield of high purity silver nanowires can reach more than 90%. The silver nanowires prepared by this method can be used in the fields of flexible transparent conductive devices, electronic skin, biosensors, and nanomedicine.

Description

A kind of synthetic method of high-purity silver nanowire

technical field

The invention relates to the technical field of one-dimensional nanomaterial preparation, relates to a method for synthesizing high-purity silver nanowires, and particularly relates to an additive-free synthesis method for high-purity silver nanowires.

Background technique

Silver nanowires have attracted great attention from academia and industry due to their unique electronic, optical, and thermal properties. Due to their unique properties, silver nanowires can be widely used in transparent conductive devices, electronic skin, solar cells, flexible circuits, biosensors, and nanomedicine.

In recent years, with the development of various electronic products towards intelligence and refinement, various application fields have put forward higher quality requirements for silver nanowires, such as high purity, halogen-free and good uniformity. In order to meet the technical requirements of various application fields, researchers have proposed a variety of synthesis methods for silver nanowires, such as polyol method, seed method, template method, wet chemical method, photoreduction method, electrochemical method and green synthesis method, etc. , among which the polyol synthesis method is the main method for the preparation of 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 in determining the structural properties of silver nanowires. For example, in the experiments of Patil et al. (Chemical Engineering Journal. 2021, 414, 128711.) to synthesize silver nanowires, the importance of _NaCl and FeCl was emphasized, i.e., etching by chloride ions and ^Fe removal of adsorbed oxygen . For example, Chinese patent CN112643044A discloses a preparation method of high aspect ratio silver nanowires, which adopts polyol method, uses bromide salt and chloride salt as auxiliary agents, and drips silver nitrate solution at 160 ° C. Silver nanowires were synthesized. Another example is Chinese patent CN107639236A, which discloses a method for preparing silver nanowires. The silver nanowires are successfully prepared by using the polyol method under nitrogen protection and using _FeCl3 as an auxiliary agent. However, although the addition of halide salts is beneficial for the synthesis of silver nanowires, the synthesized silver nanowires have shortcomings in some application fields, such as optoelectronics, sensors, and biomedical materials. Due to the halogen or metal ions contained in the additives, some of them will be adsorbed on the silver crystal plane or lattice during the growth of silver nanowires, and it is difficult to completely remove them during the washing process of silver nanowires, thus affecting the material. properties of electrical conductivity, thermal conductivity and biocompatibility. In addition, halogen is very sensitive to humidity, temperature, light and electrical stress. If the residual halogen is exposed to the air for a long time, it is very easy to be corrosive, thereby reducing the service life of the material. In addition, most of the reaction temperatures are above 150 °C, and the preparation process is complicated, the process steps are difficult to control, the yield is low, and the impurity content is high, which will bring challenges in large-scale batch 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

The object of the present invention is to provide a preparation method for directly synthesizing high-purity silver nanowires by one-pot method without additives, which can effectively solve the problems existing in the existing preparation of silver nanowires, such as residual halogen can reduce silver nanowires The photoelectric properties, increase corrosion, reduce service life, and the preparation process is complicated, difficult to control and low yield. In the present invention, the inventors use propylene glycol or its corresponding mixed alcohol as reducing agent and solvent, and only use PVP as surface capping agent to synthesize high-purity silver in a one-pot method at a relatively low temperature (90-130° C.). Nanowires. The high-purity silver nanowires prepared by this method can be widely used in fields such as optoelectronics, sensors, and biomedicine.

In order to achieve the above object, the present invention provides a kind of synthetic method of high-purity silver nanowire, adopts the following technical scheme:

A method for synthesizing high-purity silver nanowires, comprising the steps of:

( ₁ ) AgNO is dissolved in polyol and is made into solution a, for subsequent use;

(2) PVP is dissolved in polyol and is made into solution b, for subsequent use;

(3) fully mixing the solutions prepared in steps (1) and (2) under stirring conditions to obtain mixed solution c;

(4) transfer the mixed solution obtained in step (3) into the autoclave, rise to a specific temperature, and keep the temperature for a certain period of time to obtain a silver nanowire stock solution;

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

The polyol is one of propylene glycol, butanediol and glycerol, or a mixed alcohol solution prepared with propylene glycol and butanediol and glycerol in a certain proportion respectively.

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 two kinds of capping agent solutions prepared in a certain proportion.

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

In the preparation solution a, the dissolution temperature is 20-30° C., the stirring speed is 150-250 rpm, and the stirring time is 10-30 min;

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

For the prepared solution b, the dissolving temperature is 30-50° C., the stirring speed is 150-250 rpm, and the stirring time is 20-40 min.

The mass ratio of AgNO ₃ and PVP in the solution c is 1:0.05-1:0.4.

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

The volume of the mixed solution c accounts for 30-70% of the total volume of the autoclave.

The heating rate is 1-10°C/min.

The holding temperature is 90-130° C., and the holding time is 5-30 h.

The mechanisms involved in the present invention include:

Different from the traditional method of synthesizing silver nanowires by adding halide auxiliary agent, the present invention does not need to add halide auxiliary agent, and only uses PVP as the surface end-capping agent, which can realize the direct synthesis of silver nanowires in the polyol system. The reaction mechanism of propylene glycol as an example is shown below;

HCOOH+Ag→HCOOAg+H ⁺ (2)

CH ₃ COOH+Ag→CH ₃ COOAg+H ⁺ (3)

3Ag+4HNO ₃ →3AgNO ₃ +NO+2H ₂ O (4)

It can be seen from the reaction formula (1) that under the acidic conditions containing silver ions, heating propylene glycol will undergo continuous oxidation reaction, and finally generate formic acid (HCOOH) and acetic acid (CH ₃ COOH) and their corresponding salts, and the intermediate products These include hydroxyacetone ( _CH3CHOCH2OH ), methylglyoxal ( _CH3COCHO ) and pyruvic _acid ( _CH3COCOOH ). At the same time, silver ions are continuously reduced to silver atoms. When the concentration of silver atoms in the reaction system reaches supersaturation, it will aggregate and nucleate into silver seeds. The silver seeds may have any structure of single crystal, polycrystalline nanoparticles and five-fold twinned nanoparticles, among which five-fold twinned crystals Silver nanoparticles are a necessary prerequisite for the synthesis of silver nanowires. When the free silver ions in the reaction system are low enough and thermodynamically stable, silver nanoparticles with five-fold twinned structure will be preferentially formed. In the present invention, the 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 the action of reflux. Nitric acid and carboxylic acid can be used as etchants to dissolve some nanoparticles with surface defects and polycrystalline nanoparticles, resulting in the formation of lower concentrations of free silver ions in the reaction system (reactions (2), (3) and ( 4)), which will facilitate the nucleation and evolution of silver atoms into silver nanoparticles with a fivefold twinned structure. Secondly, the surface capping agent PVP can form Ag-O bonds with silver and preferentially cover the [100] surface of the five-fold twinned silver nanoparticles to promote the deposition of silver atoms on the [111] surface, thereby realizing The unidirectional growth of silver nanowires is shown in Figure 2. Based on the above reaction mechanism, the present invention successfully prepares high-purity silver nanoparticles without halide additives only by controlling the ratio of AgNO ₃ , PVP and polyol in the reaction system, the reaction temperature and the volume of the reaction system. Wire.

In the present invention, the control of the aspect ratio of the silver nanowires by the reaction rate and the surface capping agent PVP is particularly important, wherein the reaction rate determines the concentration of silver atoms in the reaction system, the formation of quintuple twin crystal seeds and the growth of silver nanowires Here, the reaction rate can be precisely regulated by adjusting the type and proportion of polyols in the reaction system, the reaction temperature and the heating rate; the surface capping agent PVP covers the [100] crystal face of the silver nanoparticles and promotes silver The unidirectional growth of nanowires along the [111] crystal plane direction is very important for the preparation of high aspect ratio silver nanowires. Here, PVP with different molecular weights and corresponding addition ratios are used to coat the silver nanowires during the growth process. The length and diameter of the silver nanowires can be further controlled. In conclusion, the controllable preparation of high aspect ratio and high purity silver nanowires can be achieved by coordinating the types and proportions of polyols in the reaction system, the reaction temperature and heating rate, and the molecular weight and addition proportion of PVP.

The beneficial effects of the present invention are as follows:

(1) the method of the present invention does not need to add halide auxiliary agent, inert gas protection, does not need to add additional crystal seed, the preparation process is simple, the reaction temperature is low, the yield can reach more than 90%, and it is easy to realize batch production;

(2) The present invention can control the parameters such as the length and diameter of the silver nanowires, and can prepare the silver nanowires with high aspect ratio.

(3) The silver nanowires without halide ions prepared by the present invention can be widely used in the fields of flexible circuits, biosensors, nanomedicine and the like.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 is a process flow diagram of the present invention.

Fig. 2 is the reaction principle diagram of the present invention.

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

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

5 is a scanning electron microscope (SEM) image of the silver nanowires prepared in Example 3 of the present invention, the scale in the figure is 20 μm, the average diameter of the silver nanowires is 200-400 nm, and the average length is 30-200 μm.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Figure 1, the synthetic method of a kind of high-purity silver nanowire provided by the present invention comprises the following steps:

( ₁ ) AgNO is dissolved in polyol and is made into solution a, for subsequent use;

(2) PVP is dissolved in polyol and is made into solution b, for subsequent use;

(3) fully mixing the solutions prepared in steps (1) and (2) under stirring conditions to obtain mixed solution c;

(4) transfer the mixed solution obtained in step (3) into the autoclave, rise to a specific temperature, and keep the temperature for a certain period of time to obtain a silver nanowire stock solution;

(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 nanowire.

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

Example 1

(1) 1g silver nitrate is dissolved in the propylene glycol of 50mL and is made into solution a, and its dissolving temperature is 25 ℃, and stirring speed is 250rpm, and stirring time is 20min; Standby;

(2) 0.08g of polyvinylpyrrolidone (PVP, K90) was dissolved in 50mL of propylene glycol to prepare solution b, and its dissolution temperature was 40°C, and the stirring speed was 250rpm, and the stirring time was 30min, for subsequent use;

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

(4) Transfer the mixed solution c into a 150-500 mL autoclave, raise the temperature to 100°C at a heating rate of 5°C/min, and keep at 100°C for 8h;

(5) The high-purity silver nanowires can be obtained by performing multiple centrifugal washing and purification treatments on the prepared silver nanowire stock solution with deionized water and absolute ethanol.

Example 2

(1) Propylene glycol and glycerol are made into mixed alcohol solution by volume ratio of 1:1～1:10, for subsequent use;

(2) 1g silver nitrate is dissolved in the mixed alcohol solution of 50mL and is made into solution a, and its dissolution temperature is 25 ℃, and stirring speed is 250rpm, and stirring time is 15min; Standby;

(3) 0.1g of polyvinylpyrrolidone (PVP, K90) is dissolved in 50mL of mixed alcohol solution to prepare solution b, and its dissolution temperature is 40 ° C, the stirring speed is 250rpm, and the stirring time is 30min, for subsequent use;

(4) Pour solution a into solution b, and at 25°C, fully mix for 10 minutes at a stirring speed of 250 r/min to obtain mixed solution c;

(5) Transfer the mixed solution c into a 150-500 mL autoclave, raise the temperature to 95°C at a heating rate of 2°C/min, and keep at 95°C for 30h;

(6) The high-purity silver nanowires can be obtained by performing multiple centrifugal washing and purification treatments on the prepared silver nanowire stock solution with deionized water and absolute ethanol.

Example 3

(1) Propylene glycol and ethylene glycol are made into a mixed alcohol solution in a volume ratio of 1:5 to 1:10, for subsequent use;

(2) 2g silver nitrate is dissolved in the mixed alcohol solution of 50mL and is made into solution a, and its dissolution temperature is 25 ℃, and the stirring speed is 250rpm, and the stirring time is 10min; for subsequent use;

(3) 0.4g of polyvinylpyrrolidone (PVP, K60) is dissolved in 50mL of mixed alcohol solution to prepare solution b, and its dissolution temperature is 40°C, the stirring speed is 250rpm, and the stirring time is 30min; for subsequent use;

(4) Pour solution a into solution b, and at 25° C., fully mix for 10 minutes at a stirring speed of 250 r/min to obtain mixed solution c;

(5) transfer the mixed solution c into a 150-500 mL autoclave, raise the temperature to 120°C at a heating rate of 5°C/min, and keep at 120°C for 6 hours;

(6) The high-purity silver nanowires can be obtained by performing multiple centrifugal washing and purification treatments on the prepared silver nanowire stock solution with deionized water and absolute ethanol.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant part can be referred to the description of the method.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for synthesizing high-purity silver nanowires is characterized by comprising the following steps:

(1) AgNO is added₃Dissolving in polyol to prepare solution a for later use;

(2) dissolving a surface end-capping reagent PVP in polyalcohol to prepare a solution b for later use;

(3) fully mixing the solution a and the solution b under the stirring condition to obtain a mixed solution c;

(4) transferring the mixed solution c obtained in the step (3) into a high-pressure reaction kettle, heating to a specific temperature, and preserving heat for a certain time at the temperature to obtain a silver nanowire stock solution;

(5) and (4) carrying out centrifugal washing and separation treatment on the silver nanowire stock solution obtained in the step (4) by using deionized water and absolute ethyl alcohol to obtain the high-purity silver nanowire.

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

3. The method for synthesizing high-purity silver nanowires of claim 1, wherein the surface blocking agent PVP is one or two selected from PVP-K15, PVP-K30, PVP-K60 and PVP-K90, the blocking agent solution is prepared according to a certain proportion, the Mw of PVP-K15 is: 10000, Mw of PVP-K30: 45000-58000, Mw of PVP-K60: 360000, Mw of PVP-K90: 1300000.

4. the method for synthesizing high-purity silver nanowires of claim 1, wherein AgNO in the solution a₃The mass concentration of (A) is 10-40 g/L.

5. The method for synthesizing the high-purity silver nanowires according to claim 1, wherein the mass concentration of PVP in the solution b is 1-4 g/L.

6. The method of claim 1 wherein the high purity silver nanowires are combinedThe method is characterized in that AgNO in the solution c₃The mass ratio of the PVP to the PVP is 1: 0.05-1: 0.1.

7. The method for synthesizing the high-purity silver nanowires according to claim 1, wherein the solution a is prepared at a dissolving temperature of 20-30 ℃, a stirring speed of 150-250 rpm and a stirring time of 10-30 min; preparing a solution b, wherein the dissolving temperature is 30-50 ℃, the stirring speed is 150-250 rpm, and the stirring time is 20-40 min.

8. The method for synthesizing a high-purity silver nanowire according to claim 1, wherein the mixing temperature of the mixed solution C is 20 to 30 ℃, the stirring speed is 150 to 250rpm, and the mixing and stirring time is 5 to 20 min.

9. The method for synthesizing high-purity silver nanowires according to claim 1, wherein the volume of the mixed solution c is 30-70% of the total volume of the high-pressure reaction kettle.

10. The method for synthesizing high-purity silver nanowires according to claim 1, wherein in the step (4), the temperature rise rate is 1-10 ℃/min, the temperature preservation temperature is 90-130 ℃, and the temperature preservation time is 5-30 h.

Images