A method for preparing silver nanowires by a soft template method

Abstract

The present invention relates to the technical field of silver nanowire preparation, and specifically relates to a method for preparing silver nanowires by a soft template method, which comprises the following steps: adding tea polyphenols, lactose and a control agent into deionized water in sequence, ultrasonically mixing evenly, then adding silver nitrate thereto, and reacting under hydrothermal conditions to obtain a mother liquor containing silver nanowires, and obtaining silver nanowires after washing treatment. The method for preparing silver nanowires by the soft template method of the present invention uses lactose as a template agent and tea polyphenols as a reducing agent, and reduces silver ions by a hydrothermal method under the action of a control agent through a suitable ratio. The overall process flow is simple, easy to operate, the prepared silver nanowires have high purity, good uniformity, are easy to disperse, and have good application value.

Description

Technical Field

[0001] The present invention relates to the technical field of silver nanowire preparation, and specifically relates to a method for preparing silver nanowires by a soft template method. Background Art

[0002] Nanowires, also known as one-dimensional nanomaterials, refer to materials with a scale of 1-100 nm in one dimension. When metal particles enter the nanoscale, they exhibit special effects different from macroscopic metals or single metal atoms, such as small size effect, interface effect, quantum size effect, macroscopic quantum tunneling effect, and dielectric confinement effect. Therefore, metal nanowires have great application potential in the fields of electricity, optics, thermotics, magnetics, and catalysis. Among them, silver nanowires have excellent electrical conductivity of silver and excellent light transmittance, flexural resistance, etc. due to the nanoscale size effect, and have a wide range of applications in many fields such as energy, catalysis, biology, and electronics.

[0003] Silver nanowires are generally synthesized by physical methods or chemical methods and are widely used in drug delivery, nanomedicine, chemical sensing, photocatalysis, etc. As an effective method for preparing nanomaterials, the main characteristics of the template method and its difference from the direct synthesis method are that the chemical reactions occurring either in the liquid phase or in the gas phase are carried out within an effectively controlled region. The synthesis of nanomaterials by the template method has many advantages compared with direct synthesis, mainly manifested in: ①Precisely controlling the size, shape, structure, and properties of nanomaterials with the template as a carrier; ②Integrating the synthesis and assembly of nanomaterials, and at the same time solving the problem of the dispersion stability of nanomaterials; ③The synthesis process is relatively simple, and many methods are suitable for mass production.

[0004] According to the different template materials, the template method is divided into the hard template method and the soft template method. Among them, the hard template method usually selects porous membranes, carbon nanotubes, DNA, etc. as templates for the growth of silver nanowires. For example, Chinese Patent CN103752850B discloses a method for preparing silver nanowires using an alumina template. Using porous alumina as a template, after ultrasonic treatment, it is immersed in an aqueous solution of a reducing agent containing a surfactant, washed, dried, and then placed on the surface of a soluble silver salt solution. The silver salt solution slowly enters the pores of the template by capillary action to undergo a reduction reaction to generate silver nanowires. After the reaction is completed, the alumina template is dissolved and removed with hydrochloric acid to obtain silver nanowires. This method has high requirements for the morphology of the alumina template, and the preparation process has many technological steps. The template needs to be removed, and at the same time, the capillary effect is used to adsorb the solution to synthesize silver nanowires. Due to the low adsorption efficiency, the yield is low, and industrial production cannot be carried out.

[0005] To overcome the shortcomings of the hard template method, researchers have constructed soft templates using substances such as biological proteins, plant somatic cells, and polymers to control the synthesis of nanomaterials with certain morphologies and sizes. However, most of the existing methods for preparing silver nanowires by the soft template method use organic reagents such as ethylene glycol and glycerol as solvents, and polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) as templates to reduce silver salts by the alcohol reduction method to prepare silver nanowires. For example, Chinese Patent CN105665742A discloses a method for controllably preparing a dispersion of silver nanowires with a high aspect ratio in batches. Using polyvinylpyrrolidone or polyvinyl alcohol as a templating agent and a halide as a controlling agent, soluble silver salts are reduced by liquid polyhydric alcohols to prepare silver nanowires. This method consumes a large amount of alcohol reagents, and using polyvinylpyrrolidone or polyvinyl alcohol as a templating agent is not environmentally friendly and increases costs at the same time. Chinese Patent CN110181074B discloses a method for green preparation of silver nanowires with a high aspect ratio by a composite soft template method. Using organic diacids and polyvinyl alcohol as a composite soft template and gallic acid as a reducing agent to reduce silver salts to obtain silver nanowires. Although this method provides a new type of soft template material - organic diacids, it still needs to be combined with polyvinyl alcohol as a composite template, consumes a large amount of organic reagents, and the reaction time of this method is 1 - 3 days, with a long preparation cycle, which is not conducive to improving production efficiency. Summary of the Invention

[0006] To solve the above problems, the present invention provides a method for preparing silver nanowires by the soft template method, using lactose as a template and tea polyphenols as a reducing agent, and directly carrying out a hydrothermal reaction with silver nitrate under the action of a controlling agent to obtain silver nanowires. The reaction is mild, and each reaction raw material is cheap and easily available, without the need to add other chemical reagents, meeting the requirements of green synthesis.

[0007] A method for preparing silver nanowires by the soft template method includes the following steps:

[0008] Add tea polyphenols, lactose, and a controlling agent to deionized water in sequence, ultrasonically mix evenly, then add silver nitrate thereto, and carry out a reaction under hydrothermal conditions to obtain a mother liquor containing silver nanowires, and obtain silver nanowires after washing treatment.

[0009] In the present invention, tea polyphenols are selected as the reducing agent and lactose as the templating agent. Both are natural organic raw materials, which are widely sourced, low-cost, and have no toxic side effects, greatly reducing the production cost of silver nanowires and the wastewater treatment cost. Tea polyphenols are the general term for polyphenolic substances in tea leaves, which are rich in catechins with reducing properties and can act as a reducing agent to reduce free silver ions to silver atoms. Lactose is a unique carbohydrate in human and mammalian milk, a disaccharide composed of glucose and galactose. Using lactose as a template, under hydrothermal conditions, lactose gradually decomposes to release glucose and galactose, and glucose and galactose hydrothermally carbonize at an appropriate release rate to form a one-dimensional tubular soft template with open channels. The soft template adsorbs free silver ions. Therefore, the silver atoms generated by the reduction of catechins in tea polyphenols grow along the one-dimensional direction under the induction of the one-dimensional tubular soft template, resulting in silver nanowires.

[0010] The conventional hydrothermal synthesis method for preparing silver nanowires usually follows the Ostwald ripening mechanism, that is, smaller crystals or sol particles in the solute dissolve and redeposit onto larger crystals or sol particles, similar to the recrystallization process. The applicant's research found that the synthesis mechanism of this method is different from the Ostwald ripening mechanism. In this application, the soft template method is used to prepare silver nanowires. Silver ions are first reduced by tea polyphenols and simultaneously wrapped by a gel formed by a small amount of lactose. As the reaction proceeds, the diameter of silver nanoparticles gradually increases, and lactose also forms a one-dimensional tubular soft template with a definite shape. The silver nanoparticles grow into discontinuous silver nanorods. As the reaction proceeds, the silver nanorods fuse with each other, and finally well-shaped silver nanowires are formed. Due to the presence of the template, there is a spatial confinement and directional induction effect on the growth of silver nanowires, and the length of the material is extended through the fusion of silver nanorods, thus obtaining a one-dimensional nanowire material with a certain aspect ratio.

[0011] Furthermore, the mass ratio of the tea polyphenols, the lactose, the controlling agent, and the silver nitrate is (1 - 2):(2 - 4):(2 - 3):4.

[0012] Preferably, the mass ratio of the tea polyphenols, the lactose, the controlling agent, and the silver nitrate is 1:2:2:4.

[0013] Furthermore, the concentration of the silver nitrate in the reaction solution is 5.0 - 6.0 mg / mL.

[0014] Furthermore, the controlling agent is selected from one of potassium chloride, sodium chloride, iron(III) chloride, and copper(II) chloride. Preferably, the controlling agent is selected from potassium chloride.

[0015] Furthermore, the time for ultrasonic mixing is 5 - 10 min, and the power is 100 - 200 W. Preferably, the time for ultrasonic mixing is 8 min, and the power is 150 W.

[0016] Furthermore, the reaction time under hydrothermal conditions is 5 - 6 h, and the temperature is 140 - 160 °C. Preferably, the reaction time is 5 h and the reaction temperature is 150 °C.

[0017] Furthermore, the washing treatment is to wash successively with deionized water and ethanol, and then perform centrifugation.

[0018] Furthermore, the centrifugation time is 3 - 5 min, and the maximum rotation speed is 7000 - 10000 rpm.

[0019] Furthermore, the average diameter of the prepared silver nanowires is 90 - 100 nm, the average length is 8 - 10 μm, and the purity is greater than 92%.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The method for preparing silver nanowires by the soft template method of the present invention uses lactose as a template agent and tea polyphenols as a reducing agent, and reduces silver ions by hydrothermal method under the action of a controlling agent to obtain silver nanowires. The overall process flow is simple and easy to operate; the template agent and the reducing agent are natural animal and plant extracts, which are widely sourced and inexpensive and easy to obtain. Water is used as a solvent in the reaction process, and no additional alcohol organic reagents or surfactants need to be added, greatly reducing the production cost of silver nanowires and the wastewater treatment cost. The prepared silver nanowires have high purity, good uniformity, are easy to disperse, and have good application value.

[0022] (2) The method for preparing silver nanowires by the soft template method of the present invention uses lactose as a template. Lactose wraps around the surface of silver particles and gradually hydrolyzes during the hydrothermal reaction to slowly release glucose and galactose, forming a one-dimensional tubular template with a definite shape, thereby providing spatial confinement and directional induction effects, enabling the generated silver nanorods to fuse radially to obtain one-dimensional silver nanowires with a certain aspect ratio. Using a disaccharide as a template agent, controlling the release rate of glucose and galactose during the reaction process by its slow hydrolysis, and then regulating the formation of a tubular soft template to ensure the obtained silver nanowires have a one-dimensional structure.

[0023] (3) The method for preparing silver nanowires by the soft template method of the present invention has an appropriate ratio of lactose and tea polyphenols, which can balance the formation rate of the template and the reduction rate of silver ions, thereby fully exerting the guiding role of the template to obtain silver nanowires with uniform shapes; and the present invention uses the conventional hydrothermal method for preparation, which is applicable to the existing production system and is suitable for large-scale industrial production applications. Description of the Drawings

[0024] 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 some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 SEM image of the silver nanowires prepared in Example 1 of the present invention;

[0026] Figure 2 Diameter distribution diagram of the silver nanowires prepared in Example 1 of the present invention;

[0027] Figure 3 Length distribution diagram of the silver nanowires prepared in Example 1 of the present invention;

[0028] Figure 4 SEM image of the reaction solution at different reaction stages in Example 1 of the present invention, where Figure 4 a, b, c, d, e, f respectively correspond to the SEM images of the reaction solution at 25 min, 50 min, 75 min, 100 min, 150 min, and 300 min in the reaction of Example 1;

[0029] Figure 5 Schematic diagram of the reaction mechanism for preparing silver nanowires by the soft template method of the present invention;

[0030] Figure 6 SEM image of the silver nanowires prepared in Example 2 of the present invention;

[0031] Figure 7 SEM image of the silver nanowires prepared in Example 3 of the present invention;

[0032] Figure 8 SEM image of the product prepared in Comparative Example 1 of the present invention;

[0033] Figure 9 SEM image of the product prepared in Comparative Example 2 of the present invention;

[0034] Figure 10 SEM image of the product prepared in Comparative Example 3 of the present invention;

[0035] Figure 11 SEM image of the product prepared in Comparative Example 4 of the present invention;

[0036] Figure 12 SEM image of the product prepared in Comparative Example 5 of the present invention;

[0037] Figure 13SEM image of the product prepared in Comparative Example 6 of the present invention;

[0038] Figure 14 SEM image of the product prepared in Comparative Example 7 of the present invention. Detailed implementation manners

[0039] In the following examples of the present invention, the experimental methods without specific conditions noted are generally in accordance with conventional conditions or in accordance with the conditions recommended by the manufacturers. All common chemical reagents used in the examples are commercially available products.

[0040] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0041] The terms "comprising" and "having" and any variations thereof in the present invention are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product or device that comprises a series of steps is not limited to the listed steps or modules, but optionally further includes steps not listed, or optionally further includes other steps inherent to these processes, methods, products or devices.

[0042] As used in the present invention, "a plurality of" means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0043] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Example 1

[0045] 50 mg of tea polyphenols, 100 mg of lactose and 100 mg of potassium chloride were successively added to 35 mL of deionized water and sonicated for 8 min at a power of 150 W; then 200 mg of silver nitrate was dissolved in the sonicated solution to obtain a reaction mixture, and the reaction mixture was transferred to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reactor. The reactor was sealed and reacted in a constant temperature air blast oven. The temperature of the hydrothermal reaction was set at 150 °C and the reaction time was 5 h. After the reaction, a mother liquor containing silver nanowires was obtained. The mother liquor was washed successively with deionized water and ethanol, and then centrifuged at 8000 rpm for 3 min to obtain silver nanowires.

[0046] As Figure 1 , Figure 2 and Figure 3 shown are the SEM image, diameter distribution diagram and length distribution diagram of the silver nanowires prepared in Example 1 respectively. It can be seen from Figure 1 that the product prepared in Example 1 is a nanowire-like structure with uniform size and good dispersibility; further from Figure 2 , Figure 3 it can be known that the average diameter of the silver nanowires prepared in Example 1 is 91 nm, the average length is 10 μm, and the purity is 96%.

[0047] As Figure 4 shown is the scanning electron micrograph of the reaction solution at different reaction stages in Example 1. Figure 4 a, b, c, d, e, f correspond to the SEM images of the reaction solution at 25 min, 50 min, 75 min, 100 min, 150 min, and 300 min of the reaction respectively; as Figure 5 shown is the schematic diagram of the reaction mechanism for the preparation of silver nanowires by the soft template method of the present invention. Figure 5 The reaction times represented by a, b, c, d, e, f are the same as Figure 4 . It can be seen from Figure 5 a that at 25 min, i.e., the initial stage of the reaction, some small spherical silver nanoparticles are covered by a gauze-like colloid. This indicates that free silver ions are first adsorbed and then reduced to silver atoms by the biomass, thus aggregating into silver nanoparticles covered by the biomass; Figure 5 b shows that when the reaction proceeds to 50 min, the number of silver nanoparticles increases significantly and shows a regular arrangement; Figure 5 c shows that when the reaction proceeds to 75 min, the average particle size of the silver nanoparticles increases, and the biomass layer tightly wraps around the silver nanoparticles. And the organic layer is gradually hydrothermally carbonized into a one-dimensional tubular soft template; Figure 5d shows that when the reaction proceeds to 100 min, one-dimensional tubular soft templates about 100 nm wide appear, and a small amount of silver nanoparticles are adsorbed on the tubes. In addition, in the tubular soft templates, discontinuous silver nanorods with a width of about 50 nm can be observed (indicated by arrows), which indicates that the one-dimensional soft tube templates induce the growth of silver nanowires along the one-dimensional direction. Therefore, there is no need to additionally add the inducer PVP; Figure 5 e shows that when the reaction proceeds to 150 min, these discontinuous nanorods merge to form silver nanowires with V-shaped notches (indicated by arrows); Figure 5 f shows that when the reaction proceeds to 300 min, silver nanowires with definite shapes are obtained.

[0048] Example 2

[0049] 50 mg of tea polyphenols, 200 mg of lactose and 100 mg of sodium chloride were successively added to 35 mL of deionized water and sonicated for 10 min at a power of 100 W; then 200 mg of silver nitrate was dissolved in the sonicated solution to obtain a reaction mixture, and the reaction mixture was transferred to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle. The reaction kettle was sealed and reacted in a constant temperature air blast oven. The temperature of the hydrothermal reaction was set at 160 °C and the reaction time was 6 h. After the reaction, a mother liquor containing silver nanowires was obtained. The mother liquor was washed successively with deionized water and ethanol, and then centrifuged at 10000 rpm for 4 min to obtain silver nanowires.

[0050] As Figure 6 shown is the SEM image of the silver nanowires prepared in Example 2. The average diameter of the silver nanowires prepared in Example 2 is 96 nm, the average length is 9 μm, and the purity is 92%.

[0051] Example 3

[0052] 100 mg of tea polyphenols, 100 mg of lactose and 100 g of ferric chloride were successively added to 35 mL of deionized water and sonicated for 5 min at a power of 200 W; then 200 mg of silver nitrate was dissolved in the sonicated solution to obtain a reaction mixture, and the reaction mixture was transferred to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle. The reaction kettle was sealed and reacted in a constant temperature air blast oven. The temperature of the hydrothermal reaction was set at 140 °C and the reaction time was 5 h. After the reaction, a mother liquor containing silver nanowires was obtained. The mother liquor was washed successively with deionized water and ethanol, and then centrifuged at 7000 rpm for 5 min to obtain silver nanowires.

[0053] As Figure 7 shown is the SEM image of the silver nanowires prepared in Example 3. The average diameter of the silver nanowires prepared in Example 3 is 100 nm, the average length is 8 μm, and the purity is 93%.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that tea polyphenols are not added to the raw materials, and at the same time, the amount of lactose is correspondingly increased to supplement the lack of tea polyphenols. The specific preparation steps are as follows:

[0056] Add 150 mg of lactose and 100 mg of potassium chloride to 35 mL of deionized water in sequence, and perform ultrasonic treatment for 8 min at a power of 150 W; then dissolve 200 mg of silver nitrate in the ultrasonically treated solution to obtain a reaction mixture, transfer the reaction mixture to the inner lining of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle, seal the reaction kettle and carry out the reaction in a constant temperature blast drying oven, set the temperature of the hydrothermal reaction to 150 °C, and the reaction time to 5 h. After the reaction, a mother liquor containing silver nanowires is obtained, and the mother liquor is washed with deionized water and ethanol in sequence, and then centrifuged at 8000 rpm for 3 min to obtain the product.

[0057] As Figure 8 shown is the SEM image of the product obtained in Comparative Example 1. It can be seen from the figure that the product obtained in Comparative Example 1 is mainly a tubular structure, with an average diameter of 1 μm and an average length of 10 μm. There are also irregular small particles dispersed within the visible range; through analysis, it can be known that the product with a tubular structure is a one-dimensional soft template, and the irregular particles are reduced silver particles. This is because the reducing component tea polyphenols are not added, and the rate of lactose hydrolysis and carbonization to form a tubular soft template is greater than the rate of lactose and its hydrolysis products as reducing sugars to reduce silver ions to obtain elemental silver, resulting in most silver ions being unable to be reduced, and thus silver materials cannot be obtained.

[0058] Comparative Example 2

[0059] The difference between this comparative example and Example 1 is that lactose is not added to the raw materials, and at the same time, the amount of tea polyphenols is correspondingly increased to supplement the lack of lactose. The specific preparation steps are as follows:

[0060] Add 150 mg of tea polyphenols and 100 mg of potassium chloride to 35 mL of deionized water in sequence, and perform ultrasonic treatment for 8 min at a power of 150 W; then dissolve 200 mg of silver nitrate in the ultrasonically treated solution to obtain a reaction mixture, transfer the reaction mixture to the inner lining of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle, seal the reaction kettle and carry out the reaction in a constant temperature blast drying oven, set the temperature of the hydrothermal reaction to 150 °C, and the reaction time to 5 h. After the reaction, a mother liquor containing silver nanowires is obtained, and the mother liquor is washed with deionized water and ethanol in sequence, and then centrifuged at 8000 rpm for 3 min to obtain the product.

[0061] As Figure 9The SEM image of the product obtained in Comparative Example 2 is shown. It can be seen from the figure that the product obtained in Comparative Example 2 is in the form of aggregated particles with poor dispersibility, and one-dimensional silver nanowires cannot be obtained. Analysis shows that due to the excessive amount of tea polyphenols, the reduction rate of silver ions is greater than the formation rate of the soft template. Without the induction of the soft template, silver ions are rapidly reduced to form silver nanoparticles, and one-dimensional silver nanowires cannot be formed.

[0062] Comparative Example 3

[0063] The difference between this comparative example and Example 1 is that lactose in the raw materials is replaced with its hydrolysis products glucose and galactose, and the molar ratio of glucose to galactose is 1:1. The specific preparation steps are as follows:

[0064] 50 mg of tea polyphenols, 34.5 mg of glucose, 65.5 mg of galactose and 100 mg of potassium chloride were successively added to 35 mL of deionized water, and ultrasonic treatment was carried out for 8 min at a power of 150 W; then 200 mg of silver nitrate was dissolved in the ultrasonically treated solution to obtain a reaction mixture, and the reaction mixture was transferred to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle. The reaction kettle was sealed and reacted in a constant temperature air blast oven. The temperature of the hydrothermal reaction was set at 150 °C and the reaction time was 5 h. After the reaction, a mother liquor containing silver nanowires was obtained. The mother liquor was washed successively with deionized water and ethanol, and then centrifuged at 8000 rpm for 3 min to obtain the product.

[0065] As Figure 10 The SEM image of the product obtained in Comparative Example 3 is shown. It can be seen from the figure that the product obtained in Comparative Example 3 is in the form of irregular large particles, and small-sized particles are attached to the surface of the large particles. One-dimensional silver nanowires cannot be obtained. This is because when lactose is replaced with the corresponding monosaccharides, no hydrolysis process will occur in the hydrothermal reaction, and no template can be formed to induce the anisotropic growth of silver nanowires.

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is the different proportion of lactose used in the raw materials. The specific preparation steps are as follows:

[0068] 50 mg of tea polyphenols, 300 mg of lactose and 100 mg of potassium chloride were successively added to 35 mL of deionized water, and ultrasonic treatment was carried out for 8 min at a power of 150 W; then 200 mg of silver nitrate was dissolved in the ultrasonically treated solution to obtain a reaction mixture, and the reaction mixture was transferred to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle. The reaction kettle was sealed and reacted in a constant temperature air blast oven. The temperature of the hydrothermal reaction was set at 150 °C and the reaction time was 5 h. After the reaction, a mother liquor containing silver nanowires was obtained. The mother liquor was washed successively with deionized water and ethanol, and then centrifuged at 8000 rpm for 3 min to obtain the product.

[0069] As Figure 11 shown is the SEM image of the product obtained in Comparative Example 4. It can be seen from the figure that the product obtained in Comparative Example 4 is aggregated silver nanoparticles. This is because the increased amount of monosaccharides released by the hydrolysis of excessive lactose makes it impossible to form a template, so silver nanowires cannot be formed.

[0070] Comparative Example 5

[0071] The difference between this comparative example and Example 1 lies in the different proportion of lactose used in the raw materials. The specific preparation steps are as follows:

[0072] Add 50 mg of tea polyphenols, 20 mg of lactose and 100 mg of potassium chloride to 35 mL of deionized water in sequence, and ultrasonically treat for 8 min at a power of 150 W; then dissolve 200 mg of silver nitrate in the ultrasonically treated solution to obtain a reaction mixture. Transfer the reaction mixture to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle, seal the reaction kettle and carry out the reaction in a constant temperature air blast oven. Set the hydrothermal reaction temperature to 150 °C and the reaction time to 5 h. After the reaction, a mother liquor containing silver nanowires is obtained. Wash the mother liquor with deionized water and ethanol in sequence, and then centrifuge at 8000 rpm for 3 min to obtain the product.

[0073] As Figure 12 shown is the SEM image of the product obtained in Comparative Example 5. It can be seen from the figure that the product obtained in Comparative Example 4 is irregular granular. This is because the decreased amount of monosaccharides released by the hydrolysis of too little lactose makes it impossible to form a template, so silver nanowires cannot be formed.

[0074] Comparative Example 6

[0075] The difference between this comparative example and Example 1 lies in the different proportion of tea polyphenols used in the raw materials. The specific preparation steps are as follows:

[0076] Add 200 mg of tea polyphenols, 100 mg of lactose and 100 mg of potassium chloride to 35 mL of deionized water in sequence, and ultrasonically treat for 8 min at a power of 150 W; then dissolve 200 mg of silver nitrate in the ultrasonically treated solution to obtain a reaction mixture. Transfer the reaction mixture to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle, seal the reaction kettle and carry out the reaction in a constant temperature air blast oven. Set the hydrothermal reaction temperature to 150 °C and the reaction time to 5 h. After the reaction, a mother liquor containing silver nanowires is obtained. Wash the mother liquor with deionized water and ethanol in sequence, and then centrifuge at 8000 rpm for 3 min to obtain the product.

[0077] As Figure 13The SEM image of the product obtained in Comparative Example 6 is shown. It can be seen from the figure that the product obtained in Comparative Example 5 is aggregated silver nanoparticles. This is because the excessive tea polyphenols rapidly reduce silver ions and quickly accumulate on the lactose-formed template, resulting in the aggregation of silver nanoparticles.

[0078] Comparative Example 7

[0079] The difference between this comparative example and Example 1 lies in the different dosage ratios of tea polyphenols in the raw materials. The specific preparation steps are as follows:

[0080] Add 20 mg of tea polyphenols, 100 mg of lactose, and 100 mg of potassium chloride to 35 mL of deionized water in sequence, and perform ultrasonic treatment for 8 min at a power of 150 W; then dissolve 200 mg of silver nitrate in the ultrasonically treated solution to obtain a reaction mixture. Transfer the reaction mixture to the inner liner of a 50 mL polytetrafluoroethylene hydrothermal reaction kettle, seal the reaction kettle, and carry out the reaction in a constant-temperature forced-air oven. Set the temperature of the hydrothermal reaction to 150 °C and the reaction time to 5 h. After the reaction, a mother liquor containing silver nanowires is obtained. Wash the mother liquor with deionized water and ethanol in sequence, and then centrifuge at a speed of 8000 rpm for 3 min to obtain the product.

[0081] As Figure 14 The SEM image of the product obtained in Comparative Example 7 is shown. It can be seen from the figure that the product obtained in Comparative Example 6 is irregularly shaped silver nanoparticles. This is because the relatively small amount of tea polyphenols cannot reduce silver ions in time, resulting in their agglomeration with biomass to form large particles.

[0082] The above examples and comparative examples are further analyzed. Among them, Examples 1-3 use the soft template method of the present invention to prepare silver nanowires. Using tea polyphenols as a reducing agent and lactose as a templating agent, silver nanowires with uniform size, good dispersibility, and relatively high purity are obtained through appropriate ratios; Comparative Examples 1-7 are comparative experiments relative to Example 1. Among them, only lactose is added in Comparative Example 1 and only tea polyphenols are added in Comparative Example 2, and silver nanowires of nanoscale size cannot be obtained; In Comparative Example 3, glucose and galactose, the hydrolysis products of lactose, are directly used to replace lactose. Since the content of glucose and galactose in the reaction system cannot be controlled by the slow-release effect of stepwise hydrolysis, directly using the hydrolyzed products results in too high a content, and it is impossible to form a template by coating, and thus silver nanowires or silver particles cannot be obtained; In Comparative Examples 4-5 and Comparative Examples 6-7, the contents of lactose and tea polyphenols are too high and too low respectively, and silver nanowires cannot be obtained.

[0083] In summary, the soft template method of the present invention is simple to operate and low in cost. The prepared silver nanowires have uniform size and relatively high purity, and have good popularization and application value.

[0084] The above further describes the present invention with reference to specific embodiments. However, it should be understood that this specific description should not be construed as limiting the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A method for preparing silver nanowires by a soft template method, characterized in that, It includes the following steps: adding tea polyphenols, lactose and a controlling agent into deionized water in sequence, ultrasonically mixing them evenly, then adding silver nitrate thereto, and carrying out a reaction under hydrothermal conditions to obtain a mother liquor containing silver nanowires, and obtaining silver nanowires after washing treatment; The controlling agent is selected from one of potassium chloride, sodium chloride, ferric chloride and copper chloride; The mass ratio of the tea polyphenols, the lactose, the controlling agent and the silver nitrate is 1:2:2:

4.

2. The method for preparing silver nanowires by the soft template method according to claim 1, wherein, The concentration of the silver nitrate in the reaction solution is 5.0 - 6.0 mg / mL.

3. The method for preparing silver nanowires by a soft template method according to claim 1, wherein, The time for ultrasonic mixing is 5 - 10 min, and the power is 100 - 200 W.

4. The method for preparing silver nanowires by a soft template method according to claim 1, wherein, The time for carrying out the reaction under hydrothermal conditions is 5 - 6 h, and the temperature is 140 - 160 °C.

5. A method for preparing silver nanowires by a soft template method according to claim 1, characterized in that, The washing treatment is to wash with deionized water and ethanol in sequence, and then carry out centrifugation treatment.

6. The method for preparing silver nanowires by a soft template method according to claim 5, wherein The time for centrifugation treatment is 3 - 5 min, and the maximum rotation speed is 7000 - 10000 rpm.

7. A method for preparing silver nanowires by a soft template method according to claim 1, characterized in that, The average diameter of the prepared silver nanowires is 90 - 100 nm, the average length is 8 - 10 um, and the purity is greater than 92%.

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