JPH06271905A - Production of monodisperse gold superfine particle - Google Patents

Abstract

PURPOSE:To produce the monodisperse gold superfine particle which is stable in a high-temp. region by heat treating an amorphous alloy compounded with Zr and Au and Ni, etc., at specific ratios at a specific temp. in an oxygen-contg.. atmosphere. CONSTITUTION:The amorphous alloy is produced by compounding Zr and Au and M (>=1 kinds among Cr, Mo, Fe, Co, Ni, Pt, Cu, Al, Si, etc.) so as to attain (ZraAU100-a)bM100-b (where 50>=a>=90, 1<=b<=30) and melting the mixture in an atmosphere of argon or helium in a vessel from which oxygen is removed. The amorphous alloy produced in such a manner is heat treated at 200 to 1000 deg.C in the atmosphere of about 1 to 50vol.% oxygen partial pressure diluted with argon, helium or nitrogen, by which the amorphous alloy is oxidized. As a result, the monodisperse gold superfine particle having much better high-temp. stability than by the conventional methods is obtd. with a simple process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing monodisperse ultrafine particles.

[0002]

2. Description of the Related Art Generally, there are a liquid phase method and a gas phase method for producing ultrafine gold particles. The liquid phase method is a method in which, for example, a suitable precipitating agent is added to a chloroauric acid solution or the like to precipitate ultrafine gold particles. In order to monodisperse the gold ultrafine particles, a carrier such as hematite or titanium oxide is mixed in the solution and a gold precipitation reaction is caused to produce monodispersed gold ultrafine particles on the carrier.

On the other hand, the vapor phase method includes, for example, a method of heating and evaporating a gold ingot at a high temperature to produce ultrafine gold particles in a vapor phase. The gold ultrafine particles recovered for monodispersion are dispersed in, for example, ethyl alcohol by using ultrasonic waves, and a carrier is put into the dispersion and supported.

Good monodisperse gold ultrafine particles can be obtained by any of these methods, but they have the following drawbacks. The liquid phase method is
1) In order to obtain ultrafine particles, it is necessary to extremely dilute the gold concentration in the solution so that the ultrafine gold particles do not collide with each other and aggregate. 2) Therefore, a large-scale container is required for mass production. 3) Since the solution after the precipitant is added cannot be reused, a large amount of waste liquid is generated. The vapor phase method requires 1) a lot of electric power to evaporate gold. 2) It is necessary to make the density of gold in the vapor phase extremely small in order to prevent aggregation of ultrafine particles. 3) Therefore, in mass production, an evaporator having many spaces and many evaporators are required. 4) A supporting step is required separately.

Further, the ultrafine particles produced by these methods are not suitable for use in the high temperature region because gold particles are extremely likely to sinter in the high temperature region.

In recent years, a method using an amorphous material has been reported as a method for producing ultrafine gold particles. This is Z
The ultrafine gold particles are dispersed in ZrO ₂ by oxidizing an amorphous material composed of r and Au in air or in high humidity. This method is excellent because it does not have the drawbacks of the liquid phase method and the gas phase method and does not require a supporting step, but it is not preferable because it easily sinters at high temperatures.

[0007]

The ultrafine gold particles produced by the above-mentioned conventional techniques have a great problem in stability at high temperature. Therefore, the ultrafine gold particles are used in a high temperature range, for example, in a catalyst body. Was a major cause of slowing down the industrialization of.
Therefore, an object of the present invention is to provide a method for producing monomolecular gold ultrafine particles which is stable even in a high temperature range.

[0008]

The present inventors have conducted various studies to solve the problems of the prior art, and as a result, Zr and A
u and M (where M is Sc, Y, La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, Lu, Ti, Hf, V, Ta, Cr, Mo,
W, Mn, Re, Fe, Ru, Os, Rh, Ir, C
o, Ni, Pd, Pt, Cu, Ag, Zn, Cd, H
g, B, Al, Ga, In, Si, Ge, Sn, Pb,
It has been found that a material in which ultrafine gold particles are held in a monodisperse state can be produced even in a high temperature range by heat-treating an amorphous alloy composed of P, Sb and at least one selected from Bi) in an atmosphere containing oxygen. Completed the invention.

That is, according to the present invention, Zr, Au, and M (where M is Sc, Y, La, Ce, Pr, Nd, Sm, E).
u, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
u, Ti, Hf, V, Ta, Cr, Mo, W, Mn, R
e, Fe, Ru, Os, Rh, Ir, Co, Ni, P
d, Pt, Cu, Ag, Zn, Cd, Hg, B, Al,
Ga, In, Si, Ge, Sn, Pb, P, Sb and B
A method for producing monodisperse gold ultrafine particles, which comprises heat-treating an amorphous alloy consisting of at least one selected from i) in an atmosphere containing oxygen.

[0010]

The metal used in the present invention is preferably Zr, Au or M having a purity of 99.5% or more.

The amorphous alloy made of Zr, Au and M preferably has a composition represented by the following formula. (Zr _a Au _100-a ) _b M _100-b (however, 50 ≦ a ≦ 90, 1 ≦ b ≦ 30) Here, a and b represent the range in which the alloy becomes amorphous, and other than this range. It is difficult to make it amorphous.

M and b are appropriately selected depending on the temperature range used. That is, in general, the larger b is, the more M is Zr.
The higher the affinity with, the less the gold loses its ultrafine particle properties even at high temperatures. However, in selecting M and b that are stable around a temperature that is too high, gold does not become ultrafine particles at a relatively low temperature, so it is preferable to select an optimum combination with reference to the examples described later.

The monodisperse gold ultrafine particles of the present invention are manufactured as follows. First, Zr, Au and M are melted and alloyed. For melting, a heating source capable of melting each metal raw material and a container capable of adjusting the atmosphere are required. Since a DC arc or a high frequency can be used as the heating source, it is most convenient to use an arc melting furnace or a high frequency melting furnace which is generally commercially available.

The atmosphere is melted by introducing argon or helium into a container from which oxygen has been removed so that the metal is not oxidized.
Zr is easily nitrided to zirconium nitride in the presence of nitrogen in the atmosphere, and since this does not contribute to the formation of amorphous, it means that Zr is actually reduced. Therefore, melting in a nitrogen atmosphere is inappropriate. is there.

Next, the produced alloy is made amorphous. For the amorphization, a single roll type liquid quenching method using a high frequency heat source, a gas atomizing method, a rotating electrode method using a direct current arc heat source, or the like is used. When using a method other than these, the amorphous alloy to be obtained should be selected in the form of ribbon or fine powder. This is to increase the amount of ultrafine gold particles finally obtained per unit weight.

When the alloy has a relatively high melting point, the rotating electrode method having a high melting temperature is used. The rotating electrode method uses arc discharge at a temperature higher than high frequency as a heat source, and is capable of melting a metal having a higher melting point. However, it should be noted that the rotating electrode method requires processing the alloy into a rod shape.

Finally, the formed amorphous alloy is heat-treated and oxidized in an atmosphere containing oxygen. The atmosphere is an oxygen partial pressure of 1 to 50 diluted with argon, helium, or nitrogen gas.
It is in the range of volume%, preferably 5 to 30 volume%. If the oxygen partial pressure is less than 1% by volume, the oxidation reaction is extremely difficult to proceed, which is not preferable. Heat is generated along with the general oxidation reaction and the temperature becomes higher than the set temperature, which is not preferable because the ultrafine particles may melt. As the atmosphere, the oxidation treatment in air is the simplest and economically superior.

The heat treatment temperature is 200 ° C to 1000 ° C, preferably 300 ° C to 800 ° C. If the temperature is lower than 200 ° C., no oxidation occurs, which is not preferable, and if the temperature is higher than 1000 ° C., the melting point is very close to the melting point of gold (1063 ° C.) and melting is started. It should be noted that Zr nitriding reaction does not occur in the temperature range of 200 ° C to 1000 ° C.
Through the above steps, monodispersed gold ultrafine particles that maintain a stable ultrafine particle size even at high temperature can be obtained. Moreover, it is well known that by making an amorphous alloy, the oxidation resistance is improved as compared with the normal alloy state.
This is also an advantage of the method of the present invention.

Although the mechanism of obtaining monodisperse gold ultrafine particles by the method of the present invention has not been completely clarified, Zr
The metal composed of M and M is an alloy having a very high oxidation resistance, and when it is oxidized under the above conditions, Zr and M are slightly oxidized, and gold is exposed to the surface layer as monodispersed ultrafine particles. Since the ultrafine gold particles are surrounded by an alloy composed of Zr and M, there is no contact between the ultrafine particles, and it is presumed that a stable particle size can be obtained even at 300 ° C. or higher where coarsening of the particles occurs in the conventional technique. It

[0020]

【Example】

Example 1 A metal raw material having a purity of 99.9% was added (Zr ₇₀ Au ₃₀ ).
₉₀ Ni ₁₀ was weighed and alloyed in an arc melting furnace. High-purity argon was used as the atmosphere gas. Next, this alloy was made amorphous by a single roll type liquid quenching device. The obtained product was in the form of a tape having a width of 5 mm and a thickness of 10 μm, and it was confirmed by X-ray diffraction that it was amorphized. This amorphous alloy was oxidized in air at 500 ° C. for 1 hour. From the X-ray diffraction of the material after oxidation treatment, it was composed of an amorphous phase and a crystal, and the crystal phase was gold and Zr.
It was a mixture of O ₂ . According to electron microscope, gold is 5
It was present as monodisperse ultrafine particles of 30 nm. According to the differential thermogravimetric analysis, this material has a Zr value of about 70.
% Remained Zr.

Example 2 An amorphous alloy was prepared and oxidized in the same manner as in Example 1 except that the composition ratio of Zr and Au was Zr ₆₀ Au ₄₀ . The particle size of the gold ultrafine particles was slightly larger than that obtained in Example 1 and was 10 to 50 nm, but it was confirmed that the monodisperse ultrafine particles were stably retained even at high temperatures.

Example 3 As shown in Table 1, various kinds of M and b were changed, an amorphous alloy was prepared in the same manner as in Example 1, and then an oxidation treatment was performed at the temperature shown in the table. The average particle size of the ultrafine gold particles after the oxidation treatment is shown in the same table. It was confirmed that all of the obtained products were monodisperse gold fine particles.

[0023]

[Table 1]

Example 4 Example 1 was repeated except that the heat treatment time was changed to 5 hours and 24 hours.
Ultrafine gold particles were obtained under the same conditions as above. The particle size did not change at 5 hours and increased by 5% at 24 hours.

Example 5 Ultrafine gold particles were obtained in the same manner as in Example 1 except that the oxidation treatment was carried out in an argon atmosphere containing 30% by volume of oxygen. It was confirmed that the particle size and the state of existence of gold in the obtained material were almost the same as in Example 1 and that there was no difference due to the atmospheres of the two.

Comparative Example 1 Chloroauric acid was dissolved in distilled water to a concentration of 0.1 mol / L. Titanium oxide fine powder (particle size 0.5 μm) was dispersed therein using ultrasonic waves, and then 10% by volume of ammonia solution was added dropwise to adjust the pH of the solution to 9 and gold ultrafine particles were formed on titanium oxide. Was carried. The supported gold particle size is 20-5
It was 0 nm. When this was heated in air at 400 ° C. for 30 minutes, the grain size of gold was coarsened to 80 to 100 nm or more, and gold was sintered.

Comparative Example 2 Zr and Au having a purity of 99.9% were weighed so as to be Zr ₇₀ Au _30, and then a tape-shaped amorphous alloy was prepared in the same manner as in Example 1. When this was kept at 100 ° C. for 5 hours in an atmosphere of 90% relative humidity, it was completely oxidized. From X-ray diffraction, it was confirmed to be a mixture of ZrO ₂ and Au. The gold particle size of this product was 10-50 nm, which was relatively small and good, but when heated in air at 400 ° C. for 1 hour, the gold particle size became 100-200 nm or more, and gold sintering occurred. Further, when the amorphous alloy was directly oxidized at 400 ° C. for 1 hour without being oxidized at a low temperature, gold sintering occurred although the grain size was slightly smaller than the above.

[0028]

According to the method of the present invention, it is possible to easily produce ultrafine monodispersed gold particles having excellent high-temperature stability as compared with the conventional method in a simple process. Therefore, since the gold obtained by the method of the present invention can maintain the state of ultrafine particles, it is expected to be used as a catalyst, for example. Until now, gold was less active and was not used as a catalyst like other noble metals, but this is because ultrafine gold particles easily contact each other and the melting point of gold is very low, so sintering starts at high temperature. It was to do.

In order to solve this, it was necessary to make gold monodisperse and to create an environment in which ultrafine particles do not come into contact with each other so as not to sinter even at high temperature.
Since the ultrafine gold particles produced by the method of the present invention are surrounded by the alloy having high oxidation resistance in a monodisperse state, they do not sinter even when exposed to a high temperature. Therefore, the catalytic activity at high temperature is also improved, so that it is possible to realize a high temperature catalyst by utilizing the excellent characteristics of the ultrafine gold particles even in a high temperature range which could not be used conventionally.

Further, CO ₂ , NO _X , SO _X , Freon,
Catalyst for decomposition reaction of halon, etc., compound production reaction catalyst using these as raw materials (for example, catalyst for producing methane or ethane from CO ₂ and hydrogen), catalyst for complete combustion reaction of unburned waste gas of automobiles, petroleum It can be applied as various industrial catalysts for refining, heavy oil desulfurization, petrochemical production, polymer polymerization, inorganic chemical production, oil and fat processing, pharmaceutical production, food production, atmospheric gas production, etc.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akihisa Inoue Kawauchi Muzen, Aoba-ku, Sendai City, Miyagi Prefecture Kawauchi House 11-806 (72) Inami Masami Uwazawa 2-3-9-201 Wakabayashi, Wakabayashi-ku, Sendai City, Miyagi Prefecture

Claims (3)

[Claims] 1. Zr, Au and M (where M is Sc, Y,
La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, D
y, Ho, Er, Tm, Yb, Lu, Ti, Hf, V,
Ta, Cr, Mo, W, Mn, Re, Fe, Ru, O
s, Rh, Ir, Co, Ni, Pd, Pt, Cu, A
g, Zn, Cd, Hg, B, Al, Ga, In, Si,
A method for producing monodisperse gold ultrafine particles, which comprises heat-treating an amorphous alloy composed of Ge, Sn, Pb, P, Sb and Bi) in an atmosphere containing oxygen. 2. The composition of the amorphous alloy is (Zr _a Au
_100-a ) _b M _100-b (provided that 50 ≦ a ≦ 90,
The method for producing monodisperse ultrafine gold particles according to claim 1, which is represented by 1 ≦ b ≦ 30). 3. The method for producing monodisperse gold ultrafine particles according to claim 1, wherein the heat treatment is performed at 200 ° C. to 1000 ° C.