Method for preparing micro-sized hollow silver spheres using plant protein and application thereof

Abstract

The application discloses a method for preparing micro-sized hollow silver balls by using plant protein and application thereof, and the method comprises the following steps: firstly, adding plant protein solution into silver nitrate solution and reducing agent solution respectively to obtain solution A and solution B; secondly, adding solution A into solution B in an ice water bath under stirring to obtain a mixed solution; thirdly, stirring the mixed solution, and then separating, washing and drying the mixed solution to obtain the micro-sized hollow silver balls; and the micro-sized hollow silver balls are applied to the preparation of a flexible conductive film. The application can reduce the reaction rate, make silver atoms quickly nucleate and grow into nano silver particles, and make the nano silver particles gather to form the micro-sized hollow silver balls from the shell layer under the action of plant protein and stirring, so that the micro-sized hollow silver balls have high dispersity, the consumption of silver is small, and the micro-sized hollow silver balls are easy to be produced on a large scale; and the micro-sized hollow silver balls are applied to the preparation of the flexible conductive film, the film has good conductivity and high stability, can respond to pressure changes, and can be further used as a flexible pressure sensor for wearable electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of micro- and nano-silver materials technology, specifically relating to a method for preparing micron-sized hollow silver spheres using plant proteins and its application. Background Technology

[0002] Micro- and nano-silver, as important noble metal functional materials, are widely used in the electronics industry and photovoltaic field. In recent years, to enable electronic components to simultaneously meet the characteristics of miniaturization, flexibility, and high integration, and to cater to the trend of cost reduction and efficiency improvement in solar cells, researchers have developed various types of micron-sized silver materials. These include spherical, linear, sheet-like, and dendritic highly dispersed micron-sized silver powders. Pastes prepared from these silver powders have been applied in numerous electronic components, exhibiting excellent electrical properties. Particularly in some electronic sensors, micron-sized silver can be uniformly dispersed in the matrix, enabling the sensors to exhibit high sensitivity and a wide detection range. However, most reported micron-sized silver structures are dense, have a large proportion of the material, and consume relatively high amounts of energy. Most importantly, achieving conductivity in silver materials only requires continuous contact of the outer layer of micron-sized silver. Therefore, developing a simple and efficient method to produce highly dispersed micron-sized silver materials with a dense surface, porous internal structure, or even cavities, will significantly reduce the consumption of silver sources, thereby potentially reducing the manufacturing costs of electronic devices or photovoltaic cells. This type of silver material will receive increasing attention from researchers and entrepreneurs. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing micron-sized hollow silver spheres using plant protein. This method involves dispersing plant protein into silver raw materials and a reducing agent, followed by mixing and reaction in an ice-water bath. By reducing the reaction rate, silver atoms rapidly nucleate and grow into silver nanoparticles, which then aggregate from the shell to form micron-sized hollow silver spheres under the influence of the plant protein and stirring, exhibiting high dispersibility. This solves the problem of the lack of existing technology for preparing highly dispersed micron-sized silver materials with hollow structures.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing micron-sized hollow silver spheres using plant protein and its application, characterized in that the method includes the following steps:

[0005] Step 1: Add equal volumes of plant protein solution to equal volumes of silver nitrate solution and equal volumes of reducing agent solution, respectively, to obtain solution A and solution B.

[0006] Step 2: While stirring, add solution A obtained in Step 1 to solution B, which is in an ice-water bath at 2℃~5℃, in steps to obtain a mixture;

[0007] Step 3: Stir the mixture, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0008] The above-described method for preparing micron-sized hollow silver spheres using plant protein is characterized in that the plant protein in the plant protein solution in step one is soybean globulin, canavaglinin, amygdalin, whey protein, or maltodextrin, and the concentration of the plant protein solution is 3 mg / mL to 10 mg / mL, while the concentration of the silver nitrate solution is 80 mg / mL to 120 mg / mL. All of the above proteins are inexpensive spherical proteins, readily available, and highly water-soluble, making them easy to wash away after use. Furthermore, under the acidic reduction system of this invention, the spherical proteins carry a positive charge and exhibit strong electrostatic repulsion, resulting in uniform dispersion in the system and improved dispersibility between the generated silver spheres. Additionally, due to the large intermolecular gaps and strong interactions of the spherical proteins, rapid directional aggregation of silver nanoparticles is promoted, leading to the formation of micron-sized hollow spherical particles through secondary growth, thus obtaining micron-sized hollow silver spheres.

[0009] The method for preparing micron-sized hollow silver spheres using plant proteins described above is characterized in that the reducing agent in the reducing agent solution in step one is tartaric acid, ascorbic acid, or citric acid, and the concentration of the reducing agent solution is 50 mg / mL to 80 mg / mL. All of the above reducing agents can provide acidic conditions, ensuring that the reduction system is an acidic reduction system, thereby enhancing the electrostatic repulsion between plant proteins.

[0010] The method for preparing micron-sized hollow silver spheres using plant protein described above is characterized in that the stirring speed in step two is 300 r / min; the stepwise addition process is as follows: first, 1 / 5 of solution A is slowly added dropwise to solution B, and then the remaining portion is quickly added. This invention first slowly adds a small amount of solution A to generate a large number of silver nuclei, and then quickly adds the remaining large amount of solution A, so that the silver nuclei only grow into fine silver nanoparticles, which is beneficial for directional aggregation to form micron-sized silver spheres. This avoids the situation where adding solution A all at once results in larger silver particles, which is not conducive to secondary aggregation to form spherical silver particles.

[0011] The above-mentioned method for preparing micron-sized hollow silver spheres using plant protein is characterized in that the stirring speed of the mixture in step three is 50 r / min to 100 r / min.

[0012] Meanwhile, this invention also discloses an application of the micron-sized hollow silver spheres prepared by the above method, characterized in that the micron-sized hollow silver spheres are dispersed in a polyvinyl alcohol aqueous solution, and then a uniform flexible conductive film is formed on the surface of a mold by solvent evaporation; the mass ratio of the micron-sized hollow silver spheres to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 0.01 to 1:20, and the concentration of the polyvinyl alcohol aqueous solution is 8 mg / mL to 25 mg / mL.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. In this invention, plant protein is first added to silver raw material and reducing agent to ensure full combination with both, thereby uniformly dispersing in the reduction system and improving the dispersibility of the silver spheres. Then, the reaction is controlled under an ice-water bath. Silver ions and reducing agent react in a low-temperature environment filled with plant protein. The silver atoms formed by reduction rapidly nucleate and grow into silver nanoparticles. Due to the reduced reaction rate of the ice-water bath, under the action of large intermolecular gaps and strong electrostatic repulsion of plant protein, combined with the driving force of stirring and shearing, the silver nanoparticles regularly aggregate to form independent micron-sized spherical particles. This avoids the reaction under high temperature conditions, which would cause the silver particles to aggregate into irregular morphologies and reduce the dispersibility of the product. Furthermore, during the process of silver nanoparticles aggregating into isotropic spherical particles, because the nanoparticles are polyhedral rather than spherical, the size matching degree between particles is low. Aggregation begins from the shell rather than the center, thus forming a hollow porous structure, resulting in micron-sized hollow silver spheres. At the same time, because the plant protein carries a positive charge in the acidic reduction system and has strong intermolecular electrostatic repulsion, the micron-sized hollow silver spheres exhibit high dispersibility.

[0015] 2. This invention uses a simple and efficient method to prepare highly dispersed micron-sized hollow silver spheres with dense surfaces and porous or even cavity structures inside, which greatly reduces the consumption of silver source. Moreover, the preparation method is highly controllable, green and environmentally friendly, does not require the use of organic solvents, and is easy to scale up for production.

[0016] 3. The hollow silver spheres prepared by this invention have uniform particle size, high sphericity, and good dispersibility, making them suitable for the rapid preparation of uniform flexible conductive films. These films have good conductivity, high stability, and can respond to stress changes. They can be further used as flexible pressure sensors for wearable electronic sensors, while reducing the manufacturing cost of electronic devices or photovoltaic cells.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the micron-sized hollow silver spheres prepared in Example 1 of the present invention.

[0019] Figure 2 This is a scanning electron microscope image of a single cross-section of a micron-sized hollow silver sphere prepared in Example 1 of the present invention.

[0020] Figure 3 This is a scanning electron microscope image of the micron-sized hollow silver spheres prepared in Example 2 of the present invention.

[0021] Figure 4 The image shows a single X-ray diffraction pattern of a micron-sized hollow silver sphere prepared in Example 2 of this invention.

[0022] Figure 5 This is a scanning electron microscope image of the flexible conductive film prepared in Example 6 of the present invention.

[0023] Figure 6 The graph shows the change in sheet resistance of the flexible conductive film prepared in Example 6 of this invention before and after ultrasonic cleaning and 3M tape peeling treatment.

[0024] Figure 7 The graph shows the change of current over time in the flexible conductive film prepared in Example 6 of this invention during the cyclic application and release of pressure. Detailed Implementation

[0025] The method for preparing micron-sized hollow silver spheres using plant protein is described in detail in Examples 1 to 5.

[0026] Example 1

[0027] This embodiment includes the following steps:

[0028] Step 1: Add equal volumes of 10 mg / mL soybean globulin solution to equal volumes of 100 mg / mL silver nitrate solution and 80 mg / mL tartaric acid solution, respectively, to obtain solution A and solution B.

[0029] Step 2: While stirring at 300 r / min, slowly add 1 / 5 of the solution A obtained in Step 1 to solution B which is in an ice-water bath at 2℃~5℃, and then quickly add the remaining part to obtain a mixture;

[0030] Step 3: Stir the mixture at 50 r / min for 20 min, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0031] The micron-sized hollow silver spheres prepared in this embodiment were characterized by scanning electron microscopy, and the results are shown in the figure. Figure 1 and Figure 2 . Figure 1 Here is a scanning electron microscope image of the micron-sized hollow silver spheres prepared in this embodiment. Figure 1 It can be seen that the silver sphere is composed of stacked silver particles, with good overall dispersion and a particle size of 2.1μm to 3.9μm; Figure 2 This is a scanning electron microscope (SEM) image of a single cross-section of a micrometer-sized hollow silver sphere prepared in this embodiment. Figure 2 It can be seen that the silver sphere has a hollow structure. The outer layer is about 1.5 μm thick and is a spherical shell formed by silver particles. The inner layer is a spherical cavity with a radius of about 0.3 μm.

[0032] Comparative Example 1

[0033] The difference between this comparative example and Example 1 is that the soybean globulin solution in step one is replaced with an equal volume of water, and the silver product is obtained in step three.

[0034] Upon testing, the silver product prepared in this comparative example showed irregular morphology, severe agglomeration, and silver particles bonded together to form an irregular whole without a hollow structure, which is completely different from the highly dispersed micron hollow silver in Example 1.

[0035] Comparing Example 1 of the present invention with Comparative Example 1, it can be seen that the method of using plant protein in the present invention can prepare highly dispersed micron-sized hollow silver spheres with a dense surface and a porous internal structure.

[0036] Example 2

[0037] This embodiment includes the following steps:

[0038] Step 1: Add an equal volume of 5 mg / mL concanavalin A solution to an equal volume of 120 mg / mL silver nitrate solution and an equal volume of 80 mg / mL ascorbic acid solution, respectively, to obtain solution A and solution B.

[0039] Step 2: While stirring at 300 r / min, slowly add 1 / 5 of the solution A obtained in Step 1 to solution B which is in an ice-water bath at 2℃~5℃, and then quickly add the remaining part to obtain a mixture;

[0040] Step 3: Stir the mixture at 100 r / min for 20 min, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0041] Figure 3 Here is a scanning electron microscope image of the micron-sized hollow silver spheres prepared in this embodiment. Figure 3 It can be seen that the silver spheres have high sphericity, good dispersibility, little agglomeration, and a particle size of 2.8 μm to 5.1 μm.

[0042] Figure 4 The X-ray diffraction pattern of a single micrometer-sized hollow silver sphere prepared in this embodiment is shown below. Figure 4 It can be seen that the silver sphere has a very high degree of crystallinity and high purity, with no impurities.

[0043] Combination Figure 3 and Figure 4 As can be seen, the micron-sized hollow silver spheres prepared in this embodiment are polycrystalline spheres formed by the stacking of numerous nano-silver particles.

[0044] Example 3

[0045] This embodiment includes the following steps:

[0046] Step 1: Add an equal volume of amygdalin solution with a concentration of 3 mg / mL to an equal volume of silver nitrate solution with a concentration of 80 mg / mL and an equal volume of citric acid solution with a concentration of 50 mg / mL, respectively, to obtain solution A and solution B.

[0047] Step 2: While stirring at 300 r / min, slowly add 1 / 5 of the solution A obtained in Step 1 to solution B which is in an ice-water bath at 2℃~5℃, and then quickly add the remaining part to obtain a mixture;

[0048] Step 3: Stir the mixture at 80 r / min for 20 min, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0049] Testing revealed that the micron-sized hollow silver spheres prepared in this embodiment have a particle size of approximately 2.1 μm to 3.9 μm, exhibit good dispersibility, and the internal cavity radius of a single hollow silver sphere is approximately 0.3 μm.

[0050] Example 4

[0051] This embodiment includes the following steps:

[0052] Step 1: Add equal volumes of 8 mg / mL globulin solution to equal volumes of 90 mg / mL silver nitrate solution and 60 mg / mL citric acid solution, respectively, to obtain solution A and solution B.

[0053] Step 2: While stirring at 300 r / min, slowly add 1 / 5 of the solution A obtained in Step 1 to solution B which is in an ice-water bath at 2℃~5℃, and then quickly add the remaining part to obtain a mixture;

[0054] Step 3: Stir the mixture at 60 r / min for 20 min, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0055] Testing revealed that the micron-sized hollow silver spheres prepared in this embodiment have a particle size of approximately 2.8 μm to 4.5 μm, exhibit good dispersibility, and the internal cavity radius of a single hollow silver sphere is approximately 0.4 μm.

[0056] Example 5

[0057] This embodiment includes the following steps:

[0058] Step 1: Add equal volumes of 7 mg / mL wheat albumin solution to equal volumes of 90 mg / mL silver nitrate solution and 70 mg / mL tartaric acid solution, respectively, to obtain solution A and solution B.

[0059] Step 2: While stirring at 300 r / min, slowly add 1 / 5 of the solution A obtained in Step 1 to solution B which is in an ice-water bath at 2℃~5℃, and then quickly add the remaining part to obtain a mixture;

[0060] Step 3: Stir the mixture at 100 r / min for 20 min, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

[0061] Testing revealed that the micron-sized hollow silver spheres prepared in this embodiment have a particle size of approximately 2.1 μm to 3.9 μm, exhibit good dispersibility, and the internal cavity radius of a single hollow silver sphere is approximately 0.3 μm.

[0062] The application of the micron-sized hollow silver spheres of the present invention is described in detail through Example 6.

[0063] Example 6

[0064] The process of this embodiment is as follows: 10 mg of the micron-sized hollow silver spheres prepared in Example 1 are ultrasonically dispersed in 10 mL of a polyvinyl alcohol aqueous solution with a concentration of 25 mg / mL, and then transferred to a polytetrafluoroethylene mold (length × width × height is 20 mm × 10 mm × 0.2 mm). The mold is then placed in a 60°C oven and dried for 30 min to form a uniform flexible conductive film on the surface of the polytetrafluoroethylene mold.

[0065] Figure 5 This is a scanning electron microscope image of the flexible conductive thin film prepared in this embodiment. Figure 5 It can be seen that the flexible conductive film is formed by encapsulating micron-sized silver spheres with polyvinyl alcohol, and the silver spheres are uniformly dispersed within the film. Tensile testing shows that the flexible conductive film has a strength of 35 MPa and a toughness of 12 MJ / m. 3 It exhibits excellent flexibility.

[0066] Figure 6 This is a graph showing the change in sheet resistance of the flexible conductive film prepared in this embodiment before and after ultrasonic cleaning and 3M tape peeling treatment. Figure 6 It can be seen that after ultrasonic cleaning and repeated tearing of 3M tape, the sheet resistance of the flexible conductive film remains basically unchanged compared with that before the treatment, providing a stable guarantee for subsequent applications.

[0067] The flexible conductive film prepared in this embodiment was connected to an electrochemical workstation, and its current change was tested during the application and release of pressure. The results are as follows: Figure 7 As shown.

[0068] Figure 7This is a graph showing the change in current over time of the flexible conductive film prepared in this embodiment during cyclic application and release of pressure. Figure 7 It is observed that when pressure is gradually applied to the flexible conductive film, its current continuously increases, and when the pressure is slowly removed, its current decreases back to its initial value. In repeated pressure application and release cycles, its current maintains a stable and reversible change. Therefore, the flexible conductive film prepared by this invention can respond to pressure changes and possesses good flexibility, making it a promising candidate for application in wearable electronic sensors.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing micron-sized hollow silver spheres using plant protein, characterized in that, The method includes the following steps: Step 1: Add equal volumes of plant protein solution to equal volumes of silver nitrate solution and reducing agent solution, respectively, to obtain solution A and solution B. The plant protein in the plant protein solution is soybean globulin, concanavalin A, amygdalin, whey protein, or maltodextrin, and the concentration of the plant protein solution is 3 mg / mL to 10 mg / mL. The concentration of the silver nitrate solution is 80 mg / mL to 120 mg / mL. The reducing agent in the reducing agent solution is tartaric acid, ascorbic acid, or citric acid, and the concentration of the reducing agent solution is 50 mg / mL to 80 mg / mL. Step 2: While stirring, add solution A obtained in Step 1 to solution B, which is in an ice-water bath at 2℃~5℃, in steps to obtain a mixture; the step-by-step addition process is as follows: first, slowly add 1 / 5 of solution A to solution B, and then quickly add the remaining part; Step 3: Stir the mixture, then separate the solid and liquid phases, wash and dry the precipitate to obtain micron-sized hollow silver spheres.

2. The method for preparing micron-sized hollow silver spheres using plant protein according to claim 1, characterized in that, The stirring speed in step two is 300 r / min.

3. The method for preparing micron-sized hollow silver spheres using plant protein according to claim 1, characterized in that, The stirring speed of the mixture in step three is 50 r / min to 100 r / min.

4. An application of the micron-sized hollow silver spheres prepared by the method according to any one of claims 1 to 3, characterized in that, Micron-sized hollow silver spheres are dispersed in a polyvinyl alcohol aqueous solution, and then a uniform flexible conductive film is formed on the surface of a mold by solvent evaporation. The mass ratio of the micron-sized hollow silver spheres to the polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 0.01~1:20, and the concentration of the polyvinyl alcohol aqueous solution is 8mg / mL~25mg / mL.

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