KR20140058893A - Method of preparing nano particles having core-shell structure and nano particles prepared from the same - Google Patents

Abstract

The present invention relates to a nanoparticle having a core-shell structure including a shell layer formed using a precursor represented by the following formula 1, and to a method for preparing the same. [Formula 1] In the formula 1, X indicates hydrogen, alkyl group having 1-6 carbons, or halogen, and n indicates an integer of 0 to 23. According to the present invention, adjustment of particle size and synthesis of core nanoparticles having a uniform shape can be possible by controlling reduction using partition equilibrium of an organic phase (nonpolar solvent) and water phase (polar solvent). Also, the present invention can adjust thickness of the shell layer by controlling reaction temperature and concentration using the shell layer forming precursor capable of controlling oxidation-reduction reaction by high solubility and partition equilibrium.

Description

[0001] The present invention relates to a method for preparing nanoparticles of core-shell structure and nanoparticles prepared therefrom,

The present invention relates to a method for producing nanoparticles having a core-shell structure and nanoparticles prepared therefrom.

The importance of Transparent Conductive Electrodes (TCEs) is becoming increasingly important for applications such as touch panels, flat panel displays, and other optoelectronic devices. ITO is the most widely used transparent electrode in the field of organic solar cell, but because it is a sintered material, its process temperature is high and it is easily broken by external physical stimulation and is vulnerable to bending deformation. Also, when the substrate is coated on the polymer substrate, the film is broken when the substrate is bent. And, moreover, the price is increasing due to the scarcity of In, and there is a problem in supply.

Recently, conductive polymer, carbon nanotube, graphene, and metal nanowire and nanoparticles have been attracting attention as a flexible transparent electrode and a substitute for ITO as a solution to solve the problems of ITO.

However, carbon nanotubes or graphenes have low conductivity and difficult to improve the permeability. In addition, since the metal nanowires typified by Ag nanowires are expensive, the cost of manufacturing transparent electrodes is high due to only the Ag nanowire, and the roughness of the surface during the production of transparent electrodes is very difficult to perform lamination printing of the following materials for implementing devices such as TFTs . In addition, it has a limited process such as difficulty in ink jet printing and high temperature process, and the conductivity is decreased with stretching.

On the other hand, metal nanoparticles are produced in the form of conductive ink and used in the manufacture of electrodes by processes such as inkjet. Such metal nanoparticles may include particles of gold, silver, platinum, copper, nickel, iron, cobalt, zinc, chromium, manganese and the like. Among these, copper, nickel, iron, cobalt, zinc, chromium, and manganese particles are inexpensive to manufacture compared to noble metal nanoparticles, but have a low oxidation stability.

Especially copper (Cu) has good conductivity with low price. However, in the nanoparticle state, it is difficult to use it as a conductive ink because the surface is easily oxidized and the conductivity is greatly lowered. There is also a problem in that the conductivity may be lowered by an antioxidant used for preventing surface oxidation. In addition, silver (Ag), which is currently used as a nanoparticle of conductive ink, is very expensive, and as the price has recently surged, a substitute material that is relatively inexpensive and capable of ensuring high electric conductivity is desperately required.

Nanoparticles of the core-shell structure have been proposed to prevent oxidation of the metal particles forming the core portion and to improve the electrical conductivity of the particles. A representative example is a structure in which a shell layer is formed of silver (Ag) on the surface of core nanoparticles of copper (Cu). In the particles of such a structure, the shell layer made of silver prevents oxidation of copper in the core portion and improves the electrical conductivity of the whole particles.

Conventionally used methods for producing nanoparticles of the core-shell structure include a method in which core nanoparticles are prepared by reducing a precursor of core particles with a reducing agent in a single phase, that is, in a single solvent, and forming a shell layer The material was slowly charged and subjected to reduction reaction to form a shell layer on the surface.

The problem with the above method is that it is not easy to control the particle size of the nanoparticles formed when a single phase is reduced in order to prepare core particles and separation of formed particles is not easy. In addition, when the diluted silver (Ag) salt solution is dropped to synthesize the core-shell structure, it is not easy to control the rate of the solution input, so that the reduced silver (Ag) is not formed on the surface of the core particles, aggregation. And the thickness of the formed shell layer is not easy to control.

The present invention provides a method for manufacturing nanoparticles having a core-shell structure, which can easily control the particle size at room temperature, can be easily separated from particles, and can be uniformly formed at room temperature.

The present invention also provides a method for forming a shell layer which is capable of adjusting the thickness of the shell layer and does not cause agglomeration of the shell layer forming material.

It is another object of the present invention to provide nanoparticles which are prevented from oxidation, have excellent electric conductivity and are economically advantageous.

The present invention provides a core-shell structure nanoparticle characterized by comprising a shell layer formed from a precursor represented by the following formula on the surface of a metal particle of a core:

[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23.

Preferably, the core metal particles are copper, nickel, iron, cobalt, zinc, chromium or manganese particles.

Preferably, the core metal particles are made from a metal precursor having a structure represented by the following formula:

[Formula 2]

M is Cu, Ni, Fe, Co, Zn, Cr, or Mn, m is 1 to 5,

이며, 복수의 R은 동일 또는 상이할 수 있다.R is

, And a plurality of Rs may be the same or different.

(Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or a halogen, and n is an integer of 0 to 23.)

Preferably, the core metal particles are made from metal hexanoate.

The present invention provides a method for producing nanoparticles of a core-shell structure, characterized in that a shell layer is formed by reducing a precursor represented by the following formula at the surface of a metal particle of a core:

[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23.

Preferably, the metal particles of the core are prepared by reducing an organic phase of metal hexanoate with a reducing agent of an aqueous phase.

Preferably, the precursor is added dropwise to the metal particles of the core in the form of a solution comprising an organic phase solvent.

Preferably, the feed rate of the solution is in the range of 1 ml / min to 30 ml / min.

Preferably, the solution comprises an amine having an alkyl group of 4 to 18 carbon atoms.

Preferably, the precursor is used in an amount of 100 to 200 parts by weight based on the metal particles of the core.

According to the present invention, it is possible to synthesize nanoparticles of a core having a uniform shape and capable of controlling particle size by controlling the reduction reaction by an equilibrium distribution in an organic phase (nonpolar solvent) and an aqueous phase (polar solvent). Next, the thickness of the shell layer can be adjusted by adjusting the reaction temperature and concentration by using a shell layer formation precursor capable of controlling the redox reaction by high solubility and distribution equilibrium.

In addition, the nanoparticles of the core-shell structure manufactured according to the present invention are oxidized and improved in electric conductivity of the particles by shelling the easily oxidizable core particles into particles having high electrical conductivity and having high electrical conductivity.

The present invention also has the advantage of being economical compared to the case where the entire particles are provided as such particles by providing particles containing only expensive shells in the shell layer.

FIG. 1 shows a process for preparing core particles and a shell layer formation according to the production method of the present invention.
2 is an SEM photograph of copper nanoparticles and Cu @ Ag particles prepared in the examples.
3 is an SEM photograph of the particles produced in the comparative example.
4 is an SEM photograph of a coating film formed from the ink containing Cu @ Ag particles prepared in the example.

The present invention is characterized in that it comprises a shell layer formed from a precursor represented by the following formula on the surface of the metal particles of the core in order to improve the oxidation stability thereof and improve the electrical conductivity when the nanoparticles are produced from the metal having a strong oxidizing property The nanoparticles of the core-shell structure are provided:

[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23.

As the metal constituting the core particles, copper, nickel, iron, cobalt, zinc, chromium, and manganese having low oxidation stability may be used. In order to prepare the metal particles of the core therefrom, a metal precursor having a structure represented by the following formula can be used:

[Formula 2]

M is Cu, Ni, Fe, Co, Zn, Cr, or Mn, m is 1 to 5,

이며, 복수의 R은 동일 또는 상이할 수 있다.R is

, And a plurality of Rs may be the same or different.

(Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or a halogen, and n is an integer of 0 to 23.)

It is a substance with the property of being highly soluble in a non-polar solvent. Therefore, it is easy to prepare a reaction liquid for producing core metal particles.

In one embodiment of the present invention, a reaction liquid is prepared by dissolving metal hexanoate in a solvent and a capping agent. The capping agent participates in the reduction reaction of the metal hexanoate and surrounds the formed nanoparticles to stabilize the particles. The capping agent also serves to prevent the oxidation of the prepared metal nanoparticles. It also serves to control the particle size of the produced particles. Therefore, the capping agent preferably has an appropriate chain length.

In the present invention, an amine is used as a capping agent in one embodiment. The amine preferably contains an alkyl group having 4 to 18 carbon atoms. In the present invention, as a capping agent, butylamine, octylamine, dodecylamine, oleylamine and the like may be preferably used. More preferably, oleylamine is used as a capping agent. The oleylamine is an oleic acid amine which is a fatty acid. Due to its relatively high molecular weight, it can bind to metal nanoparticles and form a layer on the surface of the particles. As a result, oxidation stability of the metal nanoparticles can be increased by preventing external oxygen from diffusing into the core of the metal nanoparticles. In addition, the olefinic amines combined with the metal nanoparticles can facilitate the dispersion of the nanoparticles in the solvent.

In the process of preparing metal nanoparticles from metal hexanoate, as shown in section (1) of FIG. 1, the metal hexanoate is reduced to a reducing agent of an aqueous phase. The metal hexanoate is transported by the equilibrium distribution between the organic phase and the water phase and is reduced by the reducing agent present in the aqueous phase to be distributed and present in the aqueous phase and the organic phase as shown in section (2). According to the above process, aggregation phenomenon of particles formed from a rapid reaction can be prevented. It can also prevent the oxidation of metals that may occur during the reaction. Therefore, in the above process, the particle size can be easily controlled and uniform nanoparticles can be obtained according to the type of the capping agent used at a relatively low temperature (preferably room temperature to 60 ° C).

A shell layer is formed by reducing the precursor represented by the following formula on the surface of the metal particles of the thus formed core:

[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23.

The precursor has a high solubility for the nonpolar solvent and provides a distribution equilibrium between the nonpolar solvent and the polar solvent. This is a means to prevent aggregation, which has been a problem when compared to other precursor materials that have been used to form shell layers on metal particle surfaces. That is, with respect to the precursor, it is possible to control the rate of the redox reaction so as not to cause aggregation by controlling the distribution equilibrium between the non-polar and polar solvents. Accordingly, the precursor of the present invention, which is administered to the surface of the metal particles, is adsorbed only on the surface of the particles without being agglomerated to form a shell layer. Accordingly, the present invention can provide a core-shell structure in which a uniform shell layer is formed on the surface.

Further, when the shell layer is formed, the shell layer having a desired thickness can be formed by controlling the reaction temperature and the concentration of the precursor. Therefore, the particles of the core-shell structure of the present invention can control the thickness of the shell layer according to the reaction temperature and precursor concentration. The reaction temperature is preferably in the range of room temperature to 40 ° C, and the precursor is preferably used in the range of 100-200 parts by weight based on the metal particles of the core. At low temperatures, the activity of the surface of the core particles is greatly reduced and the reaction does not proceed. On the contrary, when the reaction temperature is higher than the above range, the reaction rate becomes too fast, so that the particles are agglomerated and a uniform shell layer can not be formed. When the precursor is used in an amount of less than 100 parts by weight based on the weight of the core particles, the precursor is present as a free molecule and does not react with the surface of the core particles or the shell layer is not formed in a sufficient thickness for improving conductivity. There is a possibility that the viscosity of the solution is increased and a uniform shell layer is not formed on the whole surface of the core particle, and local coagulation phenomenon occurs.

As shown in FIG. 1, the core particles synthesized by the dispersion equilibrium between the polar and non-polar solvents are distributed in a polarity and a non-polar phase. The precursor solution on the non-polar solvent phase is slowly added dropwise thereto to conduct the reduction reaction. At this time, the feed rate of the precursor solution is preferably in the range of 1 ml / min to 30 ml / min. If the feed rate is less than 1 ml / min, the reaction proceeds too slowly. If the feed rate exceeds 30 ml / min, the reduction reaction speeds up and coagulation phenomenon may occur.

On the other hand, in the reaction in which the shell layer is formed, the metal particles of the core act as a reducing agent for the precursor. That is, even if there is no additional reducing agent, the metal particles directly reduce the precursor to form a shell layer on the surface. Therefore, the shell formation reaction in the present invention is easier to control the reaction rate than that in the case of forming a shell layer from a reducing reaction by a separate reducing agent, and has a characteristic that bonding between the core and the shell layer formed therefrom becomes robust.

The precursor solution preferably contains an amine having an alkyl group having 4 to 18 carbon atoms. As examples, triethylamine, butylamine, octylamine, dodecylamine, and oleylamine can be used.

The amine controls the ionization of the precursor by reaction equilibrium as follows.

In the ionized state, the precursor forms a shell layer by the oxidation-reduction reaction on the surface of the metal particle as follows. In this case, the amine functions as an anion dopant as shown in an embodiment as shown below. Thus allowing the shell layer to form well from the precursor.

Thus, adjusting the amine concentration is a means of controlling the rate of shell formation reaction and the thickness of the shell layer. In the present invention, the amine is preferably used in a concentration of more than 0 wt% and 10 wt% or less in the precursor solution.

In the present invention, by using the precursor represented by the above formula and adjusting the concentration of the precursor solution, the reaction temperature, the feed rate, and the amount of the amine, a uniform shell layer having a desired thickness can be formed on the core particle surface.

Hereinafter, the present invention will be described in detail with reference to examples. However, it should be understood that the present invention is not limited to this because it is intended to facilitate understanding of the invention.

Example

(1) Production of copper nanoparticles

1.1 g of copper 2-ethylhexanoate (Cu (II) 2-ethylhexanoate), 0.7 g of butylamine and 30 mL of xylene were dissolved in a 100-mL round bottom flask. The solution was heated to 60 ° C and a solution of 0.2 g of hydrazine (using a reagent of 80% purity) as a reducing agent was added to a mixed solution of 12 mL of ethanol and 18 mL of water at once. After the addition, copper (Cu) nanoparticles were formed by allowing the reaction solution to stand at 60 ° C for 4 hours.

(2) Formation of a shell layer

The solution containing the copper nanoparticles was cooled to room temperature. Then, 0.6 g of acetaldehyde (using a reagent of 85% purity) was added to quench the reduction reaction of the reducing agent. Next, a solution containing copper nanoparticles was placed in a constant temperature bath set at 25 캜. A solution prepared by dissolving 150 parts by weight of silver 2-methylhexanoate and 0.1 part by weight of triethylamine relative to the nanoparticles in 30 mL of xylene was slowly dropped at a rate of 10 mL / Respectively. Then, it was allowed to stand at room temperature for 1 hour to form a shell layer.

Comparative Example

In the above example, (2) 0.6 g of silver nitrate (AgNO ₃ ) was used instead of silver 2-methylheptanoate for the shell layer formation reaction. However, silver nitrate did not dissolve well and was added to a solution containing copper nanoparticles in that state. It was observed that silver nitrate falls into this water layer.

Evaluation example

1. Identification of particles

Scanning Electron Microscope (SEM) photographs were taken to identify copper nanoparticles and Cu @ Ag particles prepared in Examples and Comparative Examples, respectively. The results are shown in Figures 2 and 3.

2, the copper nanoparticles of the core prepared according to the present invention had an average particle size of 100 nm, and it was confirmed that the copper nanoparticles were formed into a uniform spherical shape. Also, the grain size became larger as the Ag shell was formed thereon.

On the contrary, as shown in FIG. 3, aggregation generated in the shell layer formation process was found on the surface of the particles prepared in the comparative example.

2. Film formation and observation

The synthesized Cu @ Ag nanoparticles were prepared with 25 wt.% Of anhydrous octane ink and then spin-coated on a glass substrate at a speed of 2000 rpm for 30 seconds. Treated at 300 캜 for 15 minutes in an inert atmosphere (H ₂ (5%) + Ar (95%)).

The surface of the film was scanned by Scanning Electron Microscope (SEM). 4, it can be seen that a coating film is formed in a state where Ag is melted on the particles of the core. From these results, it can be seen that the particles prepared in the examples have a shell layer formed well on the core surface, and when the heat treatment is performed on the shell layer, the shell layer component is melted to form a coating film. The Ag coating film formed on the core particles from the shell layer thus prevents oxidation of the core particles and exhibits excellent electrical conductivity.

Claims (9)

And a shell layer formed from a precursor represented by the following formula on the surface of the metal particles of the core:
[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23. The method of claim 1,
Wherein the core metal particles are copper, nickel, iron, cobalt, zinc, chromium or manganese particles. The method according to claim 1,
Wherein the core metal particles are formed from a precursor represented by the following formula:
[Formula 2]

M is Cu, Ni, Fe, Co, Zn, Cr, or Mn, m is 1 to 5,
R is

, And a plurality of Rs may be the same or different.
(Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or a halogen, and n is an integer of 0 to 23.) The method of claim 1,
Wherein the core metal particles are made from a metal hexanoate. Wherein the shell layer is formed by reducing a precursor represented by the following formula on the surface of the metal particles of the core:
[Formula 1]

Wherein X is hydrogen, an alkyl group having 1 to 6 carbon atoms, or halogen, and n is an integer of 0 to 23. The method of claim 5,
Wherein the metal particles of the core are prepared by reducing an organic metal hexanoate with a reducing agent of an aqueous phase. The method of claim 5,
Wherein the precursor is added dropwise to the metal particles of the core in the form of a solution containing an organic phase solvent. 8. The method of claim 7,
Wherein the solution comprises an amine having an alkyl group of 4 to 18 carbon atoms. The method of claim 5,
Wherein the precursor is used in an amount of 100 to 200 parts by weight based on the metal particles of the core.

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