阅读说明：本技术 金属氧化物纳米颗粒的制造方法 (Method for producing metal oxide nanoparticles ) 是由 都筑秀和 若江真理子 久留须一彦 阿部英树 于 2018-06-06 设计创作，主要内容包括：本发明的金属氧化物纳米颗粒的制造方法具有下述工序：第1工序,制作含有金属络合物、醇和水的反应溶液；第2工序,对上述反应溶液进行加热,在上述反应溶液的体积膨胀率为5～15％的密闭气氛下,使上述反应溶液发生相分离；第3工序,将在上述第2工序中加热的上述反应溶液保持30分钟以上,对上述金属络合物进行脱水,使金属氧化物纳米颗粒析出；和第4工序,在将上述金属氧化物纳米颗粒冷却后,收集上述金属氧化物纳米颗粒。(The method for producing metal oxide nanoparticles of the present invention comprises the steps of: a step 1 of preparing a reaction solution containing a metal complex, alcohol and water; a step 2 of heating the reaction solution to cause phase separation of the reaction solution in a closed atmosphere in which the volume expansion rate of the reaction solution is 5 to 15%; a 3 rd step of maintaining the reaction solution heated in the 2 nd step for 30 minutes or longer to dehydrate the metal complex and precipitate metal oxide nanoparticles; and a 4 th step of collecting the metal oxide nanoparticles after cooling the metal oxide nanoparticles.)

1. A method for producing metal oxide nanoparticles, characterized in that,

comprises the following steps:

a step 1 of preparing a reaction solution containing a metal complex, alcohol and water;

a step 2 of heating the reaction solution to cause phase separation of the reaction solution in a closed atmosphere in which the volume expansion rate of the reaction solution is 5% to 15%;

a 3 rd step of maintaining the reaction solution heated in the 2 nd step for 30 minutes or longer to dehydrate the metal complex and precipitate metal oxide nanoparticles; and

and a 4 th step of collecting the metal oxide nanoparticles after cooling the metal oxide nanoparticles.

2. The method for producing metal oxide nanoparticles according to claim 1, wherein the reaction solution has a pH of 4.0 to 6.0 in the step 1.

3. The method for producing metal oxide nanoparticles according to claim 1 or 2, wherein in the 3 rd step, the temperature in the sealed atmosphere is 130 ℃ to 190 ℃ and the holding time is 12 hours or more.

4. The method for producing metal oxide nanoparticles according to any one of claims 1 to 3, wherein the 1 st step comprises the steps of:

a step of preparing a solution containing the metal complex;

a step of preparing a mixed solution in which the alcohol and water are uniformly mixed; and

and mixing a solution containing the metal complex with the mixed solution.

Technical Field

The present invention relates to a method for producing metal oxide nanoparticles.

Background

In recent years, metal oxide nanoparticles have been used in various fields such as various catalysts, wiring materials and electrode materials by nano-inking, additive materials for electronic parts such as capacitors, and sensors using optical properties. Such metal oxide nanoparticles are particularly required to be made finer.

For example, as a Nitrogen Oxide (NO)_x) Purification catalyst for purification (the above Nitrogen Oxides (NO)_x) Which is a main toxic component of exhaust gas emitted from automobiles and the like using fossil fuel, it is known that copper oxide nanocrystalline powder oriented in the (001) plane exhibits excellent catalytic performance (patent document 1).

However, in the hydrothermal reaction which has been generally used in the past as shown in patent document 1, the target copper oxide cannot be obtained depending on the temperature. In addition, even if the target copper oxide is obtained, it is difficult to obtain the crystalline powder efficiently and in high yield. In addition, in the conventional hydrothermal reaction, metal ions are surrounded by hydrated ions in a solution, hydrate-based nanoparticles are easily precipitated, and hydrate nanoparticles are also mixed after metal oxide nanoparticles are generated by dehydration of hydrates. Therefore, it is difficult to separate and recover the metal oxide nanoparticles and hydrate-based nanoparticles, and it is not possible to obtain an aggregate of metal oxide nanoparticles having high purity.

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a method for producing metal oxide nanoparticles, which enables the metal oxide nanoparticles to be synthesized stably and in high yield.

Means for solving the problems

As a result of intensive studies, the present inventors have found that metal oxide nanoparticles can be synthesized stably and in high yield by providing a method for producing metal oxide nanoparticles with the following steps: a step for preparing a reaction solution containing a metal complex, alcohol and water; heating the reaction solution in a closed atmosphere so that the volume expansion rate of the reaction solution is 5 to 15%; maintaining the heated reaction solution for 30 minutes or more to precipitate metal oxide nanoparticles; and a step of collecting the metal oxide nanoparticles after cooling the solution containing the precipitated metal oxide nanoparticles. The present invention has been completed based on the above technical idea.

That is, the gist of the present invention is configured as follows.

[1] A method for producing metal oxide nanoparticles, comprising the steps of: a step 1 of preparing a reaction solution containing a metal complex, alcohol and water; a step 2 of heating the reaction solution to cause phase separation of the reaction solution in a closed atmosphere in which the volume expansion rate of the reaction solution is 5 to 15%; a 3 rd step of maintaining the reaction solution heated in the 2 nd step for 30 minutes or longer to dehydrate the metal complex and precipitate metal oxide nanoparticles; and a 4 th step of collecting the metal oxide nanoparticles after cooling the metal oxide nanoparticles.

[2] The method for producing metal oxide nanoparticles according to [1], wherein in the step 1, the reaction solution has a pH of 4.0 to 6.0.

[3] The method for producing metal oxide nanoparticles according to the above [1] or [2], wherein in the step 3, the holding temperature in the sealed atmosphere is 130 to 190 ℃ and the holding time is 12 hours or more.

[4] The method for producing metal oxide nanoparticles according to any one of the above [1] to [3], wherein the 1 st step includes the steps of: a step of preparing a solution containing the metal complex; a step of preparing a mixed solution in which the alcohol and water are uniformly mixed; and mixing a solution containing the metal complex with the mixed solution.

ADVANTAGEOUS EFFECTS OF INVENTION

The method for producing metal oxide nanoparticles of the present invention comprises the steps of: a step 1 of preparing a reaction solution containing a metal complex, alcohol and water; a step 2 of heating the reaction solution to cause phase separation of the reaction solution in a closed atmosphere in which the volume expansion rate of the reaction solution is 5 to 15%; a 3 rd step of maintaining the reaction solution heated in the 2 nd step for 30 minutes or longer to dehydrate the metal complex and precipitate metal oxide nanoparticles; and a 4 th step of collecting the metal oxide nanoparticles after cooling the solution in which the metal oxide nanoparticles are precipitated.

Drawings

FIG. 1 is a graph showing the relationship between the heating time and the heating temperature of the reaction solution in example 1.

FIG. 2 is an external view of the reaction solution in example 1 during heating.

Detailed Description

Hereinafter, preferred embodiments of the method for producing metal oxide nanoparticles of the present invention will be described in detail.

The method for producing metal oxide nanoparticles of the present invention comprises the steps of: a step 1 of preparing a reaction solution containing a metal complex, alcohol and water; a step 2 of heating the reaction solution to cause phase separation of the reaction solution in a closed atmosphere in which the volume expansion rate of the reaction solution is 5 to 15%; a 3 rd step of maintaining the reaction solution heated in the 2 nd step for 30 minutes or longer to dehydrate the metal complex and precipitate metal oxide nanoparticles; and a 4 th step of collecting the metal oxide nanoparticles after cooling the metal oxide nanoparticles.

The metal oxide nanoparticles obtained by the production method of the present invention contain a metal oxide containing at least one metal. Here, the at least one metal is preferably at least one metal selected from the group consisting of copper, nickel, cobalt, zinc, iron, cerium, titanium, silver, palladium, molybdenum, niobium, and zirconium, more preferably at least one metal selected from copper, nickel, cobalt, zinc, iron, cerium, and titanium, and particularly preferably copper. Such a metal oxide containing at least one metal may be an oxide containing one metal, or may be a composite oxide containing two or more metals.

The metal oxide nanoparticles obtained by the production method of the present invention are particles having a size of the order of nanometers, specifically, particles having a size of 100nm or less, for example, having a particle diameter of 5 to 50 nm. According to the production method of the present invention, not only an aggregate of particles having different particle sizes but also an aggregate of particles having a uniform particle size can be obtained depending on the synthesis conditions. The shape of the metal oxide nanoparticles obtained is not particularly limited, and examples thereof include a spherical shape, a cubic shape (cube shape), a rectangular parallelepiped shape, a rod shape, and a linear shape. In particular, the metal oxide nanoparticles obtained by the production method of the present invention are preferably nanoparticles formed by aggregation of single nanocrystalline sheets or a plurality of nanocrystalline sheets having a nano-plane structure. In addition, the metal oxide nanoparticles obtained by the production method of the present invention are preferably formed by aggregating a plurality of nanoparticles to form a nanoparticle aggregate.

1. Step of preparing reaction solution (step 1)

First, a reaction solution containing a metal complex, alcohol and water is prepared.

The metal complex can be prepared by reacting a metal salt containing at least one metal and a compound serving as a ligand of the metal salt in an aqueous solution. Examples of the metal salt include chlorides, bromides, iodides, sulfates, acetates, nitrates and the like of at least one of the metals, and chlorides are preferable. In particular, in the case where the at least one metal is copper, the copper salt is preferably copper chloride dihydrate.

Examples of molecules other than water constituting the ligand include ammonia, urea, thiourea, thiosulfuric acid, and a cyano compound (such as hydrogen cyanide), and urea is preferable.

In addition, the mixing ratio (molar ratio) of the metal salt to the compound as a ligand is preferably 1: 2-1: 6.

examples of the reaction solvent used for producing the metal complex include a mixed solution of water and alcohol. In the case where alcohol and water are not used as the reaction solvent, the reaction solution containing the metal complex, alcohol and water can be prepared by separating the metal complex and then mixing the separated metal complex with alcohol and water. When alcohol and water are used as the reaction solvent, a reaction solution containing a metal complex, alcohol and water can be prepared without separating the metal complex. The reaction temperature for producing the metal complex is, for example, 10 to 40 ℃.

Examples of the alcohol include methanol, ethanol, butanol, ethylene glycol, polyethylene glycol, isopropyl alcohol, propylene glycol, 1-propanol, 2-butanol, and 1, 3-butanediol. The alcohol is preferably a dihydric lower alcohol, and particularly preferably ethylene glycol, from the viewpoint of producing a nanocrystalline sheet having good orientation by a dehydration reaction using a hydrogen bond between a metal complex and the alcohol.

From the viewpoint of obtaining a reaction solution in which a metal complex is homogeneously compatible with alcohol and water, the ratio (volume ratio) of alcohol to water is preferably 1: 0.5-1: 1.5. in addition, the pH of the reaction solution is adjusted so that the metal salt in the reaction solution becomes a metal ion, and the metal ion reacts with a compound as a ligand to produce a metal complex, whereby the metal complex can stably exist. When the metal ion is a copper ion, the pH of the reaction solution is preferably 4.0 to 6.0, more preferably 4.2 to 5.2. The pH of the reaction solution can be adjusted by, for example, adding an acid (hydrochloric acid, nitric acid, or the like) or a base (sodium hydroxide, or the like) to the reaction solution.

The concentration of the metal in the reaction solution is preferably 0.1 to 5.0 wt%. If the concentration of the metal is less than 0.1 wt%, the weight of the resulting metal oxide nanoparticles becomes extremely small. On the other hand, if the concentration of the metal exceeds 5.0 wt%, the precipitated metal oxide nanoparticles become coarse, and it becomes difficult to obtain metal oxide nanoparticles having a desired structure.

The step of preparing such a reaction solution preferably includes the steps of: a step of preparing a solution containing a metal complex; a step of preparing a mixed solution in which alcohol and water are uniformly mixed; and mixing a solution containing the metal complex with the mixed solution. By preparing a solution containing a metal complex and a mixed solution in which an alcohol and water are uniformly mixed, and then mixing them, the amount of the solution increases as a whole after mixing, and the metal complex is easily dispersed in the solution, so that the stirring time can be shortened. The respective steps may be managed so that the state of the metal complex is managed by a solution containing the metal complex, and the phase separation state is managed by a mixed solution in which alcohol and water are uniformly mixed.

2. Step of heating the reaction solution (step 2)

Then, the reaction solution prepared in the above step is heated, and the reaction solution is phase-separated in a sealed atmosphere so that the volume expansion rate of the reaction solution is 5 to 15%. Specifically, the heating temperature and the pressure in the sealed atmosphere are set so that the volume expansion rate of the reaction solution is 5 to 15% in addition to the effect of phase separation by heating the reaction solution.

The heating of the reaction solution is preferably performed at a temperature equal to or higher than the temperature at which the reaction solution evaporates in the atmosphere. The "temperature at which the reaction solution is evaporated in the atmosphere" varies depending on the ratio of the alcohol to water constituting the reaction solution. For example, ethylene glycol has a boiling point of 189 ℃ and water has a boiling point of 100 ℃, but when the ratio of ethylene glycol to water (volume ratio) is 3: 2, the temperature at which the reaction solution is evaporated is about 120 ℃. In this case, the heating temperature is more preferably 130 to 190 ℃.

The heating of the reaction solution was performed under a closed atmosphere. The reaction solution is heated in a closed vessel (heating tank) such as an autoclave. When heating is performed in a sealed atmosphere, the pressure in the sealed container increases to a pressurized state as the reaction solution evaporates. The pressure in the closed container is, for example, 1 atmosphere or more. As another method for producing nanoparticles, there is a supercritical hydrothermal synthesis method. The supercritical fluid is a fluid exceeding the critical temperature and the critical pressure, and in the case of water, the critical temperature is 374 ℃ and the critical pressure is 22.1 MPa. In this synthesis method, the dielectric constant of water is greatly changed in the vicinity of the critical point, the supersaturation degree becomes large, and a large number of nuclei are generated, whereby nanoparticles can be synthesized. When the supercritical hydrothermal synthesis method is applied to produce nanoparticles in a supercritical state, the pressure in the closed container is preferably in the range of 4 to 600 MPa. In contrast, the production of the metal oxide nanoparticles of the present invention can be carried out in a low-pressure (less than 4MPa) atmosphere, and it is sufficient to use a simple closed vessel, and the control of the conditions is easy.

The thus-heated reaction solution expands 5 to 15% in terms of a volume expansion ratio [ { (volume of reaction solution at the time of heating-volume of reaction solution before heating)/volume of reaction solution at room temperature } x 100 (%) ] as compared with the reaction solution before heating.

It is known that: in the mixed solution composed of ethylene glycol and water, the ratio (volume ratio) of ethylene glycol to water is 1: 1, the volume expansion rate under heating at 150 ℃ was about 4%. In contrast, in the case of the reaction solution used in the production method of the present invention containing a metal complex, alcohol and water, the volume expansion rate increases to about 10% under heating at 150 ℃ even if the ratio (volume ratio) of ethylene glycol to water is about the same. It is presumed that the volume expansion generated in the reaction solution of the present invention is a different phenomenon from the volume expansion caused by heating in a generally known mixed system of ethylene glycol and water.

Such specific volume expansion is influenced by phase separation of the reaction solution, which is presumed to contribute to the production of metal oxide nanoparticles in the present invention. The volume expansion ratio is considered as an index for causing dehydration reaction, and at a volume expansion ratio of less than 5%, no phase separation is observed, and substantially no nanoparticles are obtained. In addition, in view of the realistic volume expansion of the reaction solution, the upper limit value of the volume expansion rate is less than 15%.

The phase separation in the present invention means two or more states including a microscopic phase separation in which the turbidity of the reaction solution is observed and a macroscopic phase separation in which the liquid phase is separated into 2 layers.

In particular, in the production method of the present invention, when the reaction solution is heated, the temperature of the reaction solution itself is gradually increased. With this, phase separation of the reaction solution started, and the reaction solution started to be cloudy. Then, this specific volume expansion occurs as the reaction solution is clouded. This phenomenon of phase separation is a phenomenon specific to the production method of the present invention. When the temperature of the reaction solution itself is further increased by heating the reaction solution, the phase separation of the reaction solution further proceeds, and the cloudiness of the reaction solution becomes more remarkable. Then, when the temperature of the reaction solution exceeds a certain temperature, the liquid phase separates into 2 layers, and the reaction solution starts to become transparent. Then, at the time when the reaction solution reached the heating temperature, the reaction solution became completely transparent.

3. A step of precipitating metal oxide nanoparticles (step 3)

The heated reaction solution is kept for 30 minutes or more, and the metal complex is dehydrated to precipitate metal oxide nanoparticles. Here, "holding the heated reaction solution" means that the reaction solution is maintained by controlling the temperature of the reaction solution heated to a predetermined temperature to be constant and by maintaining the reaction solution under a pressure in a closed state (in a closed atmosphere such as a closed container).

In the production method of the present invention, the phase separation of the reaction solution is performed in two stages (clouding and transparentization), whereby the dehydration reaction of the metal complex is promoted, and the metal oxide nanoparticles can be synthesized stably and in high yield.

The mechanism of this reaction system is not necessarily clear, but the present inventors speculate as follows. Namely, it is considered that: the effect of the reaction solution to undergo phase separation serves as a driving force for dehydration reaction to occur around the metal complex, and metal oxide nanoparticles are obtained in high yield.

In this step, the holding temperature in the sealed atmosphere is preferably 130 to 190 ℃, and more preferably 145 to 185 ℃. By setting the holding temperature to 130 to 190 ℃, the pressurized state in the closed container can be maintained, and phase separation can be promoted.

The holding time is preferably 30 minutes or more, more preferably 12 hours or more. By setting the holding time to 30 minutes or more, the dehydration reaction of the metal complex can be promoted in the entire reaction solution, and the metal oxide nanoparticles can be efficiently produced. The upper limit of the holding time is not particularly limited, but is preferably 120 hours (5 days) from the viewpoint of practical use. In particular, the combination of the holding temperature and the holding time in the sealed atmosphere is preferably 130 to 190 ℃ and the holding time is preferably 12 hours or more.

4. Step (4) of collecting the metal oxide

After the metal oxide nanoparticles are cooled, the metal oxide nanoparticles are collected.

The solution containing the precipitated metal oxide nanoparticles is cooled to a temperature around room temperature (15 to 25 ℃). The cooling method is not particularly limited, and examples thereof include: a method of natural cooling in a state of being disposed in a heating tank; a method of taking out from the heating tank and performing air cooling; a method of cooling with running water after being taken out from the heating tank; and so on.

After cooling, the precipitated metal oxide nanoparticles (precipitates) were collected from the solution, washed, and dried, thereby obtaining metal oxide nanoparticles. The washing solution may be appropriately selected, and for example, a mixed solution of methanol and water may be used.

In particular, in view of obtaining metal oxide nanoparticles with high yield from among the collected precipitates, it is preferable to quickly collect the precipitates and wash them after the sealed vessel after cooling is opened. When the sealed container is opened, the solution is exposed to the atmosphere, and thus, when left in this state, another product different from the metal oxide nanoparticles may be generated in the solution. In order to prevent the solution from contacting the atmosphere, it is more preferable to collect the precipitates in an inert gas atmosphere such as nitrogen or argon.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention, including all the embodiments included in the concept of the present invention and claims.