WO2014073772A1

WO2014073772A1 - Method for preparing nanoparticles having core-shell structure, and nanoparticles prepared thereby

Info

Publication number: WO2014073772A1
Application number: PCT/KR2013/006880
Authority: WO
Inventors: 김미영; 유의현; 임민기; 박찬혁; 연경열
Original assignee: 삼성정밀화학 주식회사
Priority date: 2012-11-07
Filing date: 2013-07-31
Publication date: 2014-05-15
Also published as: TW201422339A; KR20140058893A

Abstract

The present invention relates to nanoparticles having a core-shell structure comprising a shell layer formed using a precursor represented by formula 1, and a preparation method therefor. According to the present invention, core nanoparticles, the size of which can be controlled and which have a uniform shape, can be synthesized by controlling a reduction reaction by means of partition equilibrium in an organic phase (non-polar solvent) and a water phase (polar solvent). Next, the thickness of the shell layer can be controlled by controlling a reaction temperature and concentration by using the shell layer forming precursor which allows the control of an oxidation-reduction reaction by means of high solubility and partition equilibrium.

Description

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 to nanoparticles prepared therefrom.

The importance of Transparent Conductive Electrodes (TCEs) is increasing in importance for applications in touch panels, flat panel displays, and other optoelectronic devices. Indium Tin Oxide (ITO) is the most widely used material as a transparent electrode in the field of organic solar cells, but since it is a plastic material, the process temperature is high, it is fragile by external physical stimuli, and is vulnerable to bending deformation. In addition, there is a disadvantage that the film is broken when the substrate is bent when coated on a polymer substrate. And, above all, due to the scarcity of In, the price is gradually increasing, and a problem arises in the supply.

Recently, as a solution to solve the problems of ITO, a flexible transparent electrode and attracting attention as a material that can replace ITO are conductive polymers, carbon nanotubes, graphene, and metal nanowires and nanoparticles.

However, carbon nanotubes or graphene have low conductivity and are difficult to improve permeability. In addition, the metal nanowires represented by Ag nanowires are high in price and are expensive in the manufacture of transparent electrodes only with Ag nanowires, and the surface of the transparent electrodes is rough. . In addition, inkjet printing is difficult and high temperature process is impossible, and the process is limited and conductivity decreases with stretching.

On the other hand, the metal nanoparticles are prepared in the form of a conductive ink is used for electrode production by a process such as inkjet. Such metal nanoparticles may include particles of gold, silver, platinum, copper, nickel, iron, cobalt, zinc, chromium, manganese and the like. Among them, copper, nickel, iron, cobalt, zinc, chromium, manganese particles have a lower manufacturing cost than noble metal nanoparticles, but has a problem of low oxidation stability.

In particular, copper (Cu) has excellent conductivity with low price. However, in the nanoparticle state, as the surface is easily oxidized, the conductivity is greatly reduced, so it is difficult to use as a conductive ink. In addition, there is a problem that the conductivity may be reduced by the antioxidant used to prevent surface oxidation. In addition, silver (Ag), which is mainly used as a nanoparticle of a conductive ink, is very expensive, and as the recent price skyrockets, there is an urgent need for an alternative material that is relatively inexpensive and has high electrical conductivity.

Core-shell structured nanoparticles have been proposed to prevent oxidation of the metal particles forming the core portion and to improve the electrical conductivity of the particles. A typical one is a structure in which a shell layer is formed of silver (Ag) on the surface of core nanoparticles of copper (Cu). The shell layer made of silver in the particles having such a structure prevents oxidation of copper in the core portion and improves electrical conductivity of the whole particle.

The conventionally used method for producing the core-shell structured nanoparticles is to reduce the precursor of the core particles with a reducing agent in a single phase, i.e., a single solvent, to produce core nanoparticles and form a shell layer for the particles. The material was slowly added and reduced to form a shell layer on the surface thereof.

The problem with the method is that it is not easy to control the particle size of the nanoparticles formed when the reduction reaction in a single phase to prepare the core particles and the separation of the formed particles is not easy. In addition, when synthesizing the core-shell structure by dropping a salt solution of dilute silver (Ag), it is not easy to control the rate of addition of the solution. aggregation is often achieved. In addition, there is a disadvantage that the thickness of the shell layer formed is not easy to control.

The present invention provides a method for preparing nanoparticles having a core-shell structure at room temperature, particle size control, particle separation, and uniform production.

The present invention also provides a method of forming a shell layer which can control the thickness of the shell layer and does not cause aggregation of the shell layer forming material.

In addition, an object of the present invention is to provide nanoparticles that are prevented from oxidation, excellent in electrical conductivity, and advantageously economically.

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

[Equation 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 prepared from metal precursors having a structure represented by the following formula:

[Equation 2]

In the above formula, M is Cu, Ni, Fe, Co, Zn, Cr or Mn, m = 1-5,

R is

And R may be the same or different.

(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 made from metal hexanoate.

The present invention provides a method for producing a core-shell structured nanoparticle, wherein the shell layer is formed by reducing a precursor represented by the following formula on the surface of the metal particle of the core:

[Equation 1]

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

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

Preferably, the feed rate of the solution ranges from 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 the range of 100 to 200 parts by weight based on the metal particles of the core.

According to the present invention, the reduction reaction is controlled by distribution equilibrium in the organic phase (non-polar solvent) and the water phase (polar solvent), so that the particle size can be controlled and nanoparticles of the core having a uniform shape can be synthesized. Next, the thickness of the shell layer can be adjusted by controlling the reaction temperature and concentration by using the shell layer forming precursor which can control the redox reaction by high solubility and distribution equilibrium.

In addition, the core-shell structured nanoparticles prepared by the present invention are prevented from being oxidized by shelling core particles that are susceptible to oxidation and having high electrical conductivity, thereby preventing oxidation and improving electrical conductivity of the particles.

In addition, the present invention is advantageous in terms of economics compared to the case where the entire particle is provided by such particles by providing the particles containing the expensive metal only in the shell layer.

1 illustrates a process of preparing core particles and forming a shell layer according to the manufacturing method of the present invention.

Figure 2 is a SEM photograph of the copper nanoparticles and Cu @ Ag particles prepared in the example.

Figure 3 is a SEM photograph of the particles produced in the comparative example.

4 is a SEM photograph of a coating film formed from an ink including Cu @ Ag particles prepared in the Examples.

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 metal particles of the core in order to improve its oxidation stability and improve electrical conductivity when preparing nanoparticles from highly oxidizable metals. Core-shell structured nanoparticles are provided:

[Equation 1]

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

[Equation 2]

In the above formula, M is Cu, Ni, Fe, Co, Zn, Cr or Mn, m = 1-5,

R is

And R may be the same or different.

It is a material that is characterized by high solubility in nonpolar solvents. Therefore, the preparation of the reaction solution for producing the core metal particles is easy.

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

In the present invention, amine is used as an example as a capping agent. It is preferable that the said amine contains a C4-C18 alkyl group. In the present invention, a capping agent may preferably be butyl amine (butylamine), octylamine (octylamine), dodecylamine (dodecylamine), oleyl amine (Oleylamine) and the like. More preferably, oleylamine is used as the capping agent. Oleyl amine is an amine of oleic acid, a fatty acid, and because of its relatively high molecular weight, can be combined with metal nanoparticles to form a layer on the particle surface. As a result, the 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 oleamine amine combined with the metal nanoparticles may facilitate the dispersion of the nanoparticles in a solvent.

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

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

[Equation 1]

The precursor has high solubility in nonpolar solvents and is in equilibrium with the distribution between nonpolar and polar solvents. This is a means to prevent aggregation which has been a problem when compared to other conventional precursor materials that have been used to form shell layers on metal particle surfaces. In other words, by controlling the distribution equilibrium between the non-polar and polar solvents for the precursor, it is possible to control the rate of the redox reaction so that aggregation does not occur. Therefore, the precursor of the present invention administered to the metal particle surface is adsorbed only on the particle surface without forming agglomerates among them 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.

In addition, when the shell layer is formed, the reaction temperature and the concentration of the precursor may be adjusted to form a shell layer having a desired thickness. Therefore, the core-shell structured particles of the present invention can control the thickness of the shell layer according to the reaction temperature and the precursor concentration. It is preferable to perform reaction temperature in the range of room temperature-40 degreeC, and to use a precursor in the range of 100-200 weight part with respect to the metal particle of a core. At low temperatures, the activity of the surface of the core particles decreases a lot and the reaction does not proceed. On the contrary, when the reaction temperature is higher than the above range, the reaction rate is so fast that aggregation of particles occurs and a uniform shell layer cannot be formed. In addition, when the precursor is used in an amount less than 100 parts by weight relative to the core particles, the precursor does not react with the surface of the core particles or forms a shell layer with a sufficient thickness to improve conductivity. There is a possibility that the viscosity of the solution rises so that a uniform shell layer is not formed over the entire surface of the core particles, and local aggregation occurs.

Referring to the shell layer formation process, as an example, the core particles synthesized by the distribution equilibrium between the polar and nonpolar solvents are distributed in the polar and nonpolar phases as shown in FIG. 1. The precursor solution on the nonpolar solvent is slowly added dropwise thereto to proceed with the reduction reaction. At this time, the input rate of the precursor solution is preferably in the range of 1ml / min to 30ml / min. This is because if the feed rate is less than 1 ml / min, the reaction proceeds too slowly, and if the feed rate proceeds faster than 30 ml / min, the reduction reaction speeds up, which may cause aggregation.

On the other hand, the metal particles of the core act as a reducing agent on the precursor in the reaction in which the shell layer is formed. That is, even without a separate reducing agent, the metal particles directly reduce the precursor to form a shell layer on the surface thereof. Therefore, compared with the case of forming the shell layer from the reduction reaction by a separate reducing agent, the shell formation reaction in the present invention has the characteristics that the reaction rate is easily controlled and the bond between the core and the shell layer prepared therefrom is firm.

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

The amines control the ionization of the precursor by the reaction equilibrium as follows.

In addition, the precursor forms a shell layer by redox reaction on the surface of the metal particles as described below in the ionized state, in which the amine acts as an anionic dopant as shown below. Thus, the shell layer can be well formed from the precursor.

Therefore, controlling the concentration of amines is one means of controlling the speed of the shell formation reaction and the thickness of the shell layer. In the present invention, the precursor solution is preferably used by including the amine at a concentration of more than 0% by weight and 10% by weight or less.

In the present invention, by using the precursor represented by the above formula, by controlling the concentration of the precursor solution, the reaction temperature, the feeding rate and the amount of the amine, it is possible to form a uniform shell layer with a desired thickness for the core particle surface.

The invention is described in detail by the following examples. However, this is to aid the understanding of the invention and should not be construed as limiting the invention.

Example

(1) Preparation 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 added and dissolved in a 100 ml round bottom flask. The solution was heated to 60 ° C., and then a solution containing 0.2 g of hydrazine (using 80% purity reagent) as a reducing agent was rapidly added to a mixture of 12 mL of ethanol and 18 mL of water at a time. After the addition, the reaction solution was allowed to stand for 4 hours while maintaining a temperature of 60 ℃ to form copper (Cu) nanoparticles.

(2) the formation of the 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, the solution containing copper nanoparticles was installed in the thermostat set to 25 degreeC. Here, a solution of 150 parts by weight of silver 2-methylhexanoate and 0.1 parts by weight of triethylamine dissolved in 30 mL of xylene was slowly added dropwise at a rate of 10 ml / min. It was. The shell layer was then formed by standing for 1 hour at room temperature.

Comparative example

In the above example, (2) 0.6 g of silver nitrate (AgNO ₃ ) was used instead of silver 2-methyl heptanoate for the shell layer formation reaction. However, silver nitrate did not dissolve well and was added to the solution containing copper nanoparticles as it was. It was observed that silver nitrate fell into the water layer.

Evaluation example

1. Identification of Particles

Scanning Electron Microscope (SEM) photographing was performed to confirm the copper nanoparticles and Cu @ Ag particles prepared in Examples and Comparative Examples, respectively. The results are shown in FIGS. 2 and 3.

In FIG. 2, the copper nanoparticles of the core prepared according to the present invention had an average particle diameter of 100 nm, and it was confirmed that the shape was formed into a uniform spherical shape. In addition, the size of the particles increased as the Ag shell formed thereon.

On the other hand, the aggregation produced during the shell layer formation was found on the particle surface prepared in the comparative example as shown in FIG. 3.

2. Film formation and observation

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

The film surface was photographed by Scanning Electron Microscope (SEM). 4, it can be seen that a coating film is formed in a state in which Ag is melted on the particles of the core. From this, it can be seen that the particles prepared in Examples form a shell layer on the surface of the core, and when the heat treatment is performed, the shell layer is melted to form a coating film. This Ag coating film formed from the shell layer onto the core particles prevents oxidation of the core particles and exhibits excellent electrical conductivity.

Claims

A core-shell structured nanoparticle comprising a shell layer formed from a precursor represented by the following formula on the surface of a metal particle of a core:

[Equation 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.
In claim 1,

The core metal particle is a core-shell structured nanoparticles, characterized in that the copper, nickel, iron, cobalt, zinc, chromium or manganese particles.
The method of claim 1,

The core metal particles are core-shell nanoparticles, characterized in that formed from a precursor represented by the following formula:

[Equation 2]

In the above formula, M is Cu, Ni, Fe, Co, Zn, Cr or Mn, m = 1-5,

R is
And R may be the same or different.

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

The core metal particles are core-shell structured nanoparticles, characterized in that prepared from metal hexanoate.
A method for producing a core-shell structured nanoparticle, characterized in that to form a shell layer by reducing the precursor represented by the following formula on the surface of the metal particle of the core:

[Equation 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.
In claim 5,

The metal particles of the core is a core-shell structure of the nanoparticles manufacturing method characterized in that the metal hexanoate (metal hexanoate) of the organic phase is prepared by reducing the reducing agent of the aqueous phase.
In claim 5,

The precursor is dropwise added to the metal particles of the core in the form of a solution containing a solvent of the organic phase core-shell structure nanoparticles manufacturing method.
In claim 7,

The solution comprises a core-shell structure nanoparticles manufacturing method comprising an amine having an alkyl group having 4 to 18 carbon atoms.
In claim 5,

The precursor is a core-shell structure nanoparticles manufacturing method, characterized in that used in the range of 100 to 200 parts by weight based on the metal particles of the core.