KR20240114301A - Method For Producing Silver Nanoparticle, And Silver Nanoparticle Produced By This Method - Google Patents

Abstract

The present invention includes the steps of preparing a silver oxalate dispersion solution by adding silver oxalate and a dispersant to a solvent; Preparing a reducing solution by adding a reducing agent to a solvent; and adding the reducing solution to the silver oxalate dispersion solution. A method for manufacturing Ag fine particles can be provided, including a step.
The present invention can provide Ag microparticles manufactured by the above manufacturing method.

Description

Method for producing Ag microparticles and Ag microparticles produced thereby {Method For Producing Silver Nanoparticle, And Silver Nanoparticle Produced By This Method}

The present invention relates to a method for manufacturing Ag microparticles and Ag microparticles produced thereby, and more specifically, to Ag microparticles that can stably control the shape and size of Ag particles using a reduction process of silver oxalate. It relates to a particle manufacturing method and Ag microparticles produced thereby.

Typically, in the production of Ag particles, a reduction manufacturing method that directly reduces Ag ions is used. In this regard, Patent Document 1 describes a wet reduction process in which Ag ions are reduced by preparing an Ag ion solution using silver nitrate, adding NaOH as a pH adjuster, adding L-tryptophan as a surfactant, and then adding formalin as a reducing agent. It has a relatively simple process. However, due to the solubility limit of Ag ions, a large reactor is required for mass production, and it is difficult to finely control the shape and size of the particles due to the rapid reduction reaction of Ag ions freely dispersed in the Ag ion aqueous solution. there was.

까지 가열하는 것이 필요하므로 오토클레이브 (Autoclave)라는 압력가열 반응기를 사용해야만 한다. 이에, 반응기의 압력 한계에 따라 큰 용량의 반응기 제작이 어려우며, 대량 생산에는 적합하지 못한 공정이며 공정 시간도 1시간 이상으로 긴 단점이 있었다.Patent Document 2 relates to a method of producing Ag particles by thermally decomposing silver oxalate, unlike the conventional Ag particle production method. Although it is relatively advantageous to control the shape of the particles compared to the method of reducing Ag ions, thermal decomposition of silver oxalate 130 under high pressure of 2 to 10 kgf/cm ²

Since heating is necessary, a pressure heating reactor called an autoclave must be used. Accordingly, it is difficult to manufacture a large capacity reactor due to the pressure limit of the reactor, the process is not suitable for mass production, and the process time is long, over 1 hour.

Japanese Registered Publication JP 6900357B (2021.06.18) Japanese Registered Publication JP 6467542B (2019.01.18)

The present invention relates to a method for manufacturing Ag fine particles that can stably control the shape and size of the particles using a reduction process of silver oxalate.

The present invention relates to plate-shaped Ag microparticles produced by the above production method and having a particle size of 1 μm or less.

The present invention includes the steps of preparing a silver oxalate dispersion solution by adding silver oxalate and a dispersant to a solvent; Preparing a reducing solution by adding a reducing agent to a solvent; and adding the reducing solution to the silver oxalate dispersion solution. A method for manufacturing Ag fine particles can be provided, including a step.

The oxalic acid may further include the step of dissolving a transition metal after preparing the dispersion solution.

The solvent may be ion-exchanged water or distilled water.

The dispersant may be one or more selected from the group consisting of acetic acid, polyacrylic acid, polyethylene glycol, and polycarboxylic acid.

The reducing agent may be one or more selected from the group consisting of hydrazine, hydroquinone, formic acid, sodium percarbonate, citric acid, and ascorbic acid.

The transition metal may be scandium (Sc) or yttrium (Y).

The transition metal may be 0.05 to 1% by weight based on the weight of silver oxalate.

The present invention can provide Ag microparticles manufactured by the Ag microparticle production method.

The Ag fine particles may have a particle size of 1㎛ or less.

The Ag fine particles may have a ratio of plate-shaped particles of 95% or more.

By the manufacturing method of the present invention, the size and shape of Ag particles can be effectively controlled, the process can be completed effectively in a short time without using high energy or pressure reaction vessels, etc., and mass production of Ag fine particles is possible. do.

Ag microparticles produced by the production method of the present invention have a submicron particle size.

Figure 1 schematically shows the method for producing Ag microparticles of the present invention.
Figure 2 schematically shows the forms of silver nitrate dissociated in water and silver oxalate dispersed in water.
Figure 3 schematically shows the process of forming particles from Ag ions in water and the case of forming particles from silver oxalate.
Figure 4 shows CO ₂ gas escaping from silver oxalate and plate-shaped Ag particles being generated on the silver oxalate matrix.
Figure 5 shows SEM photographs of Ag particles prepared in Examples 1 to 3.
Figure 6 shows SEM photographs of Ag particles prepared in Examples 1 and 2 in more detail.
Figure 7 shows SEM photographs of Ag particles prepared in Example 1 and Comparative Example 1.
Figure 8 shows SEM photographs of Ag particles prepared in Example 1 and Comparative Example 2.

It should be noted that the technical terms used in this specification are only used to describe specific embodiments and are not intended to limit the present invention. In addition, the technical terms used in this specification, unless specifically defined in a different way in this specification, should be interpreted as meanings commonly understood by those skilled in the art in the technical field to which the present invention pertains, and are not overly comprehensive. It should not be construed in a literal or excessively reduced sense. Additionally, if the technical terms used in this specification are incorrect technical terms that do not accurately express the spirit of the present invention, they should be replaced with technical terms that can be correctly understood by those skilled in the art.

In addition, general terms used in the present invention should be interpreted according to the definition in the dictionary or according to the context, and should not be interpreted in an excessively reduced sense.

Additionally, as used herein, singular expressions include plural expressions, unless the context clearly dictates otherwise. In this application, terms such as “consists of” or “comprises” should not be construed as necessarily including several components or steps described in the specification, and some of the components or steps are included. It may not be possible, or it should be interpreted as including additional components or steps.

Hereinafter, the present invention will be examined in more detail through examples, but the scope of the present invention is not limited to the examples below.

The present invention includes the steps of preparing a silver oxalate dispersion solution by adding silver oxalate and a dispersant to a solvent; Preparing a reducing solution by adding a reducing agent to a solvent; and adding the reducing solution to the silver oxalate dispersion solution.

Figure 1 schematically shows the method for producing Ag microparticles of the present invention.

For example, when comparing the reduction potential (reduction driving force) between reducing Ag ions using ascorbic acid as a reducing agent and reducing silver oxalate, the case of reducing silver oxalate is compared to the case of reducing Ag ions. It can be confirmed that reduction of Ag particles is possible with a reduction potential that is 5 times lower ([Reference Figure 1]).

[Reference 1]

When the reduction potential is high, Ag ions or Ag atoms are generated into Ag particles with high energy, so nucleation and reaction occur rapidly and growth is accelerated, making it difficult to control the size or shape of the particles.

However, in the present invention, by using silver oxalate to lower the reduction potential, the reaction proceeds at a low nucleation and growth rate, thereby greatly expanding the scope for controlling the growth rate, and the size and shape in the particle generation step. It is much more advantageous to control.

For reference, Ag has a crystal structure called face centered cubic (FCC) ([Reference Figure 2]).

[Reference Figure 2]

The FCC model consists of one atom located at each vertex (eight locations) of a cube and six atoms located at the center of each face.

In the reduction process of making actual Ag particles, before reduction, Ag atoms exist freely in ions or other forms, but when they are reduced and become a solid, they basically have an FCC crystal structure.

Accordingly, as the basic unit cell (unit cell) atomic bond form and repetitive bond form, atoms combine and overlap repeatedly to form a certain, identifiable shape (spherical, rod-shaped, polygonal, plate-shaped, wire-shaped, etc.). It will be achieved. At this time, 'constant form' is related to the surface energy and reduction potential of each crystal plane in the FCC crystal structure.

As can be seen in [Reference Figure 2], the FCC crystal structure has a hexahedral structure, but since the bonding strength (distance between atoms, number of atoms on the surface, etc.) of the atoms on each side (top, front, diagonal, etc.) is different, each The surface energy values of the faces are different.

Specifically, each plane is defined as the (001) plane, (100) plane, and (111) plane using a notation method called the Miller index ([Reference Figure 3]).

[Reference Figure 3]

In order to manufacture plate-shaped particles, the triangular (111) plane crossing the diagonal direction of the hexahedron is important, and the (111) plane has the lowest surface energy value of 1.62206 eV ([Reference Figure 4]).

[Reference 4]

Meanwhile, reduction potential is defined as the force that induces a reduction reaction in which metal ions are reduced to become metal solid particles. To reduce metal ions, a reducing agent may be used, or various energies such as heat energy or metal substitution reaction may be used. However, when a reducing agent is used, the difference in reduction potential of the reducing agent mainly constitutes the reduction potential of the entire reaction.

[Reference 5]

It is in the high potential energy state of the blue curve in [Reference 5], and when it exceeds the energy barrier value represented by the orange curve due to a certain driving force, it enters a low potential energy state and changes from a metal ion to a solid particle.

In order for a metal ion to become a solid particle, a driving force that can overcome a certain energy barrier must be provided, and the energy barrier value of each face in the FCC crystal structure is usually different from the surface energy value of each face. , Unlike other surfaces, the (111) surface has a low surface energy value and a low energy barrier value, so it can be reduced to form metal particles even at low driving force.

For example, in an environment where a sufficiently high reduction potential is provided, all other surfaces with high surface energy will also be reduced, so all surfaces of the FCC basic unit cell will be reduced and combined to form spherical particles at the basic unit cell level. Even at the atomic level, it will have a spherical model ([Reference Figure 6]).

[Reference 6]

On the other hand, if the metal ion is reduced with a low reduction potential by creating reaction conditions that provide a low reduction potential, only the (111) surface with a low surface energy value and a low energy barrier value will be selectively reduced to a metal particle, and in this case, the spherical model will be Instead, triangular or hexagonal plate-shaped metal particles will be formed ([Reference Figure 7]).

[Reference Figure 7]

In this regard, since the silver oxalate used in the present invention has a low reduction potential, it will reduce Ag ions with a low reduction potential, and selectively form metal particles only on the (111) surface, which has a low surface energy value and a low energy barrier value. Since it will be reduced to , plate-shaped Ag microparticles rather than spherical shapes will be formed by the manufacturing method of the present invention.

Figure 2 schematically shows the forms of silver nitrate dissociated in water and silver oxalate dispersed in water. Specifically, the use of silver oxalate is more advantageous than the use of silver nitrate in controlling the shape of the particles, because the form in which Ag ions exist before they are reduced to Ag particles is different.

Ag metal salts such as silver nitrate or silver chloride are easily dissociated in water, so they exist in water by dissociating into Ag ⁺ cations and anions such as NO ^3- and Cl ^- . In this case, Ag ⁺ positive ions present in water are freely dispersed and moving in the water, and negative ions such as NO ^{3 -} and Cl ^- also exist and remain as final impurities. On the other hand, silver oxalate is in the solid form of Ag ₂ C ₂ O ₄ and is insoluble in water, so even when placed in water, it does not dissociate into Ag ⁺ cations and C ₂ O ₄ ^- anions but remains in a solid state.

For example, silver nitrate dissociates into ions in water, resulting in a transparent solution, while silver oxalate exists in a solid state, resulting in a white solution that resembles flour dissolved in water.

In addition, there is a difference in the reduction process to Ag particles when Ag ⁺ cations exist freely in water and when an Ag source exists in Ag ₂ C ₂ O ₄ solid.

In this regard, Figure 3 schematically shows the process in which particles are formed from Ag ions in water and the case in which Ag particles are formed from silver oxalate.

If Ag ions exist freely in water and then nuclei are created at a certain point and grow into particles, the Ag ions will flock to the nucleation point and grow into a crystal structure called face centered cubic (FCC). In the process of gathering irregularly existing Ag ions to one point, irregular particle shapes and growth occur.

On the other hand, in the case of silver oxalate, the Ag source exists in the form of Ag ₂ C ₂ O ₄ combined with C ₂ O ₄ rather than in ionic form. As C ₂ O ₄ decomposes into CO ₂ , the remaining Ag source is instantly It becomes an Ag ion and is immediately reduced to form Ag particles ([Reference Figure 8]).

[Reference 8]

In particular, each face of solid silver oxalate already has a crystal structure of (011), (142), (253), etc., and the Ag sources present therein are already arranged according to the crystal structure (see also 9]).

In other words, with each face and Ag source arranged according to the crystal structure, C and O atoms escape in the form of gas, and the regularly arranged Ag sources become irregular because nuclei are generated at that location and grow into particles. It is much more advantageous in controlling the shape and growth of particles compared to the case where Ag ions flock together to form particles.

[Reference Figure 9]

Figure 4 shows CO ₂ gas escaping from silver oxalate and plate-shaped Ag particles being generated on the silver oxalate matrix.

The method for producing Ag microparticles of the present invention includes a reduction process. As in the present invention, the case of producing Ag particles through a reduction process without thermal decomposition of silver oxalate is suitable for mass production because a pressure vessel is not used compared to the case of producing particles by thermal decomposition of silver oxalate.

In the thermal decomposition process, Ag particles are generated when excessive heat energy is supplied, so particle growth occurs rapidly. In addition, since water must be heated to 140°C for the pyrolysis process, a reactor in the form of a pressure vessel such as an autoclave must be used. When CO ₂ gas is released through pyrolysis, the pressure inside the vessel is about 100 psi (about 7 atm). Because very high pressure is generated, a pressure-resistant design reaction vessel made of thick material must be used, so there is a limit to increasing the volume of the vessel for mass production ([Reference Figure 10]).

[Reference 10]

In contrast, when using the reduction process, there is no need for processes such as heating and pressurization, so there is no difficulty in designing a mass production process by increasing the volume of the reaction vessel. In addition, in the reduction process, the overall reduction potential can be finely controlled by adjusting the concentration of the reducing agent, reaction temperature, etc., but in the case of the thermal decomposition process, an instantaneous explosive reaction is induced by excessive heat energy, so there is no variable to control the energy contributing to particle formation. Rather than controlling the overall reduction potential, the shape induction phenomenon of the large amount of added dispersant is the main mechanism for particle shape control.

In other words, the reduction process is easy to control variables that can make the size of Ag particles smaller or larger, while the thermal decomposition process has limitations in controlling the particle size during the process because thermal decomposition occurs only at a certain temperature (e.g., 140°C). There is.

The solvent may be ion-exchanged water or distilled water.

The dispersant may be one or more selected from the group consisting of acetic acid, polyacrylic acid, polyethylene glycol, and polycarboxylic acid.

The reducing agent may be one or more selected from the group consisting of hydrazine, hydroquinone, formic acid, sodium percarbonate, citric acid, and ascorbic acid.

The method for producing Ag microparticles of the present invention uses a transition metal as a catalyst. Because of this, the reduction potential can be adjusted to a lower or desired level, which is advantageous for controlling particle shape and size.

In this regard, the step of dissolving the oxalic acid by adding a transition metal after preparing the dispersion solution may be further included. For example, the transition metal may be scandium (Sc) or yttrium (Y).

In general, noble metals such as Pd, Pt, and Au are widely used as catalyst materials. Pd, Pt, and Au have a higher reduction potential than Ag, so the force to be reduced is large, but the force to be oxidized is small. Having a high reduction potential means that the metal ion has a strong ability to receive electrons and be reduced to metal particles. Pd, Pt, Au, etc. used as catalysts have a higher reduction potential than Ag and will want to be reduced before Ag, so the catalyst Elements react before the main elements, increasing the reactivity of the overall reaction and acting as a reaction initiator to accelerate the reaction.

On the other hand, the transition metal used in the present invention, for example, yttrium, is not an element with a high reduction potential compared to Pd, Pt, Au, etc., but rather is a material with a negative reduction potential ([Reference Figure 11]) .

[Reference 11]

In other words, yttrium, by being added after preparing the silver oxalate dispersion solution, plays the role of inducing the orientation of Ag particles due to bonding with the dispersant and providing nucleation sites.

Specifically, when Ag exists as an ion, it exists in the form of a monovalent cation that can bind to one anion, so when polycarboxylic acid is used as a dispersant, one carboxyl group and one Ag ion are bonded, When yttrium exists as an ion, it exists in the form of a trivalent cation that can bind to three anions, allowing the binding of three carboxyl groups and three Ag ions, so yttrium plays a role in inducing Ag particles to grow in a plate shape. can be performed ([Reference 12]).

[Reference 12]

The presence of yttrium ions primarily aligns the carboxyl groups, and when Ag ions are bonded to them, nucleation has already started with directionality compared to the case where Ag ions exist alone, thus increasing the probability of growth in a plate shape. It can be raised.

The transition metal may be 0.05 to 1% by weight based on the weight of silver oxalate. If the amount of transition metal added is small (less than 0.05% by weight), the number of bonds with the dispersant is small and the effect on particle shape is minimal. If the amount is excessive (more than 1% by weight), the transition metal ions may combine with many dispersants, causing Ag ions to bind. Control of shape and size may become difficult as space is lost.

The present invention relates to Ag microparticles produced by the above production method.

The Ag fine particles may have a particle size of 1㎛ or less. If the particle size of Ag microparticles exceeds 1㎛, dispersibility decreases during paste production and there is a risk of defects occurring in the printed electrode. On the other hand, if the particle size is less than 1㎛, dispersibility is excellent and defects occur during electrode printing. can be significantly reduced, and may preferably be 0.3 ㎛ or more and 1 ㎛ or less.

The Ag fine particles may have a ratio of plate-shaped particles of 95% or more. Specifically, the proportion of plate-shaped particles among all Ag microparticles may be 85% or more, preferably 90% or more, and more preferably 95% or more. Manufacturing plate-shaped Ag microparticles at high yield means that the proportion of plate-shaped particles among certain identifiable shapes (spherical, rod-shaped, polygonal, plate-shaped, wire-shaped, etc.) is high.

Example 1

A silver oxalate dispersion solution was prepared by adding 10 g of polycarboxylic acid to a solution in which 50 g of silver oxalate was dispersed in 2 L of distilled water and dispersing it evenly. A reducing solution was prepared by adding 25 g of ascorbic acid to 0.5 L of distilled water and dissolving it. The reduction solution was added to the silver oxalate dispersion solution to prepare Ag particles.

Example 2

A silver oxalate dispersion solution was prepared by adding 10 g of polycarboxylic acid to a solution in which 50 g of silver oxalate was dispersed in 2 L of distilled water and dispersing it evenly. A reducing solution was prepared by adding 25 g of ascorbic acid to 0.5 L of distilled water and dissolving it. 0.05 g of yttrium nitrate (Y(NO ₃ ) ₃ ) was added and dissolved in the silver oxalate dispersion solution being stirred at 500 to 700 rpm. The reduction solution was added to the silver oxalate dispersion solution to prepare Ag particles.

Example 3

A silver oxalate dispersion solution was prepared by adding 10 g of polycarboxylic acid to a solution in which 50 g of silver oxalate was dispersed in 2 L of distilled water and dispersing it evenly. A reducing solution was prepared by adding 25 g of ascorbic acid to 0.5 L of distilled water and dissolving it. 0.1 g of yttrium nitrate (Y(NO ₃ ) ₃ ) was added and dissolved in the silver oxalate dispersion solution being stirred at 500 to 700 rpm. The reduction solution was added to the silver oxalate dispersion solution to prepare Ag particles.

Comparative Example 1

A solution in which Ag ions were dissociated was prepared by adding 10 g of polycarboxylic acid to a solution in which 50 g of silver nitrate was dispersed in 2 L of distilled water and dispersing uniformly. A reducing solution was prepared by adding 25 g of ascorbic acid to 0.5 L of distilled water and dissolving it. Ag particles were prepared by adding the reducing solution to the solution in which the silver oxalate Ag ions were dissociated.

Comparative Example 2

A silver oxalate dispersion solution was prepared by adding 10 g of polycarboxylic acid to a solution in which 50 g of silver oxalate was dispersed in 2 L of distilled water and dispersing it evenly. The silver oxalic acid dispersion solution was introduced into an autoclave, pressurized at a pressure of 0.5 MPa, and heated to 130°C while stirring at a speed of 150 rpm. Ag particles were prepared by further stirring at this temperature for 30 minutes.

Figure 5 shows SEM photographs of Ag particles prepared in Examples 1 to 3. The particle size of the Ag particles prepared in Example 1 is 2 to 3㎛, the particle size of the Ag particles prepared in Example 2 is 0.5 to 0.9㎛, and the particle size of the Ag particles prepared in Example 3 is 0.3 to 0.3㎛. It is 0.5㎛.

Additionally, Figure 6 shows SEM photographs of Ag particles prepared in Examples 1 and 2 in more detail. It can be seen that when a small amount (0.05% by weight) of yttrium is added to oxalic acid, the number of small polygonal particles in addition to plate-shaped particles is significantly reduced compared to when no yttrium is added.

Figure 7 shows SEM photographs of Ag particles prepared in Example 1 and Comparative Example 1. It can be seen that in the case of the Ag particles prepared in Comparative Example 1, there are more small polygonal particles in addition to the plate-shaped particles, and in the case of the Ag particles prepared in Example 1, there are almost no polygons and the proportion of plate-shaped particles is high. You can check that.

In the case of Comparative Example 1, NO ^{3 -} anions remain as impurities in the solution after manufacturing Ag particles, but in Example 1, since they escape as CO ₂ gas, no impurities remain, so the washing process is reduced, and generation occurs during the washing process. As the loss of particles is reduced, the final Ag particle yield also increases.

Figure 8 shows SEM photographs of Ag particles prepared in Example 1 and Comparative Example 2. The average particle size of the Ag particles prepared in Comparative Example 2 was 4 to 6㎛, but it can be seen that the average particle size of the Ag particles prepared in Example 1 was smaller at 2 to 3㎛.

Claims (10)

Preparing a silver oxalate dispersion solution by adding silver oxalate and a dispersant to a solvent;
Preparing a reducing solution by adding a reducing agent to a solvent; and
A method for producing Ag microparticles, comprising: adding the reducing solution to the silver oxalate dispersion solution.
According to clause 1,
After preparing the silver oxalic acid dispersion solution, the method further includes adding a transition metal to dissolve it.
According to clause 1,
A method for producing Ag microparticles, wherein the solvent is ion-exchanged water or distilled water.
According to claim 1,
The method of producing Ag microparticles, wherein the dispersant is at least one selected from the group consisting of acetic acid, polyacrylic acid, polyethylene glycol, and polycarboxylic acid.
According to clause 1,
The method of producing Ag microparticles, wherein the reducing agent is at least one selected from the group consisting of hydrazine, hydroquinone, formic acid, sodium percarbonate, citric acid, and ascorbic acid.
According to clause 2,
A method of producing Ag microparticles, wherein the transition metal is scandium (Sc) or yttrium (Y).
According to clause 2,
A method for producing Ag fine particles, wherein the transition metal is 0.05 to 1% by weight based on the weight of silver oxalate.
Ag fine particles produced by the production method of any one of claims 1 to 7.
According to clause 8,
The Ag fine particles are Ag fine particles having a particle size of 1㎛ or less.
According to clause 8,
The Ag fine particles are Ag fine particles in which the ratio of plate-shaped particles is 95% or more.