JPH0610015A - Production of superfine particles of gold - Google Patents

Abstract

PURPOSE:To obtain the superfine particles of gold having excellent distribution state, large surface area and surface activity by extracting aqua regia dissolved liq. of gold with org. phase, then back-extracting the extract with the aq. soln. containing prescribed amount of a reductant. CONSTITUTION:The aqua regia dissolved liq. of gold obtained by dissolving gold in aqua regia, etc., and the hydrochloric acid or nitric acid dissolved liq. of gold chloride acid are prepared. The org. phase containing a solvating extractant (e.g. keton, ether, alkohl, etc.) or a neutral extractant (e.g. neutral phosphoric ester, trialkylphosphin oxide) is prepared. The org. phase is allowed to contact with the dissolved liq. of gold and gold is extracted into the org. phase. Then, the extract is back-extracted with the aq. soln. containing the reductant (e.g. HCHO, H2C2O4, Na2SO3, etc.) whose amount is below equivalent weight of gold reducing reaction and superfine particles of gold is obtained.

Description

Detailed Description of the Invention

The present invention relates to a method for producing ultrafine gold particles.

Ultrafine gold particles having a particle size of 1 μm or less are widely used as materials for decorative water gold, pastes and catalysts. As a method for producing ultrafine gold particles for such use, a reduction method in an aqueous solution, a hydrogen gas reduction method in an organic solvent, an emulsion type liquid film solvent extraction method (JP-A-3-253506) is used depending on the use. The microemulsion method has been proposed and put to practical use.

However, the gold particles obtained by the conventional manufacturing method as described above are relatively large particles having a particle size of about several μm, and when used for applications such as catalysts, the surface area is small and the surface is small. Since it has a weak activity, it has been desired to solve these problems.

The present invention provides a method for producing ultrafine gold particles having a good distribution state, a large surface area and a large surface activity, which solves the above problems. That is, the present invention comprises a step of extracting an aqua regia solution of gold or a hydrochloric acid or nitric acid solution of chloroauric acid into an organic phase containing a solvating extractant or a neutral extractant, and an equivalent amount of gold reduction reaction or less. And a method for producing ultrafine gold particles, which comprises a step of back-extracting with an aqueous solution containing a reducing agent. Further, the present invention, a gold aqua regia solution, or hydrochloric acid or nitric acid solution of chloroauric acid,
Extracting into an organic phase containing a solvating extractant or a neutral extractant, partially reducing gold using a photochemical reaction in the organic phase, and an aqueous solution containing a reducing agent in an amount equal to or less than the equivalent amount of the gold reduction reaction. The present invention relates to a method for producing ultrafine gold particles, which includes a step of back-extracting with.

In the present invention, gold is used as an aqua regia solution or a hydrochloric acid or nitric acid solution of chloroauric acid, but it can also be used in the form of a solution of gold in chlorine.

The concentration of gold can be widely selected according to need, but is preferably 6 × 10 ^{−4 to} 6 × 10.
^-3 mol / liter range.

[0007] In the present specification, the solvating extractant refers to an extractant such as ketone, ether or alcohol, and for example, methyl isobutyl ketone (MIBK) or diethylene glycol dinormal butyl ether (DBC) is preferably used. The neutral extractant refers to an extractant such as neutral phosphoric acid ester and trialkylphosphine oxide, and for example, tributyl phosphoric acid (TBP) is preferably used.

The extraction and back extraction may be performed by known methods. The conditions are not particularly limited,
For example, it is performed by mixing and contacting both phases with a shaker at room temperature. The back extraction is performed for about one day and night, for example.

Gold dissolved in aqua regia is easily extracted into an organic phase containing a solvation extractant, whereas metal ions such as platinum and iridium are not extracted, so gold and other noble metals are separated. be able to. Next, when gold in the organic phase is back-extracted with an aqueous solution containing a reducing agent, the back-extracted gold is reduced in water to form ultrafine metal particles. In addition to gold, precious metals such as platinum are also extracted into the organic phase containing the neutralizing extractant, but no precious metal other than gold is reduced even if back-extracting with an aqueous solution containing a reducing agent. Other precious metals can be separated. For example, gold extracted with MIBK can be easily extracted by back-extracting with an aqueous sodium thiosulfate solution.
Transferred to the aqueous phase as u (S ₂ O ₃ ) ₂ ^3- .

At this time, a suitable gold reducing agent, such as HCHO, H ₂ C ₂ O ₄ , HCOOH, CH ₃ 0H, is added to the aqueous solution.
C ₂ H ₅ OH, Na ₂ SO ₃ , (COONa) ₂ , and H
When COONa or the like is present, gold ions are reduced to gold at the same time as back extraction, and are recovered in the aqueous phase as ultrafine gold particles. The amount of the reducing agent added may be equal to or less than the equivalent required for the reduction reaction of gold, for example, 0.2 molar equivalent or less. The reduction reaction rate is not affected by the amount and type of the reducing agent contained in the aqueous solution during the back extraction, and the obtained ultrafine gold particles are not affected.

In the present invention, it is possible to carry out partial reduction by utilizing a photochemical reaction in the organic phase, and then back-extract with an aqueous solution containing a reducing agent in an amount equivalent to or less than the gold reduction reaction. Has an effect that the back extraction speed becomes extremely high. Note that no significant difference was found in the obtained ultrafine gold particles.

The light source for the photochemical reaction may be sunlight, or any other known light source can be used. Partially reducing means, for example, reducing gold until the yellow color of the organic phase extracted from gold becomes colorless. For example, Au extracted from a 3 mol / cc hydrochloric acid aqueous solution of chloroauric acid by MIBK
Although (III) has a yellow color, it is completely colorless and partially reduced under a condition of not blocking light for about 10 days. Also, using an ultraviolet lamp, the wavelength is 290-4
Irradiation at 00 nm and a density of 2.6 mW / cm ² is performed for 4 to 5 hours to obtain completely colorless.

Further, in the back extraction, the presence of a surfactant can reduce the particle size. Examples of the surfactant include sodium dodecyl sulfate (SD
S), sodium pyrophosphate (NaPP), and sodium hexametaphosphate (NaHMP) can be preferably used.

The present invention will be described in more detail below with reference to examples, but these are merely examples of preferred embodiments of the present invention, and do not limit the scope of the present invention in any way. Example 1 . A shaker at room temperature with a concentration of 3 × 10 ⁻³ mol · dm ⁻³ of 3 mol · dm ⁻³ HCl aqueous solution of chloroauric acid and MIBK (organic phase) / (aqueous phase) (O / A) = 1. When both phases were mixed and contacted with each other, Au (III) was easily extracted into the organic phase and exhibited a yellow color. When this liquid was allowed to stand at room temperature for several days in a colorless and transparent glass bottle, the yellow color of the liquid almost disappeared and the liquid became colorless.

When this solution was back-extracted at room temperature with an aqueous solution containing 0.1 molar equivalent of H ₂ C ₂ O ₄ in the organic phase, 18
After time, 100% of the Au in the organic phase was back-extracted,
Ultrafine particles of were obtained. A transmission electron micrograph (30,000 times) of the obtained ultrafine particles is shown in FIG. The obtained particles are ultrafine particles having a uniform particle size of 0.2 to 0.3 μm and surface active particles that are easily aggregated by the strength of an electric field under an electron microscope observation. The X-ray diffraction image is shown in FIG. From this, it can be seen that it is a single phase of Au metal. Example 2 . When the MIBK solution having an Au concentration of 2.8 × 10 ⁻³ mol · dm ⁻³ was irradiated with ultraviolet rays having a density of 2.6 mW / cm ² for 5 hours, the yellow color disappeared and the material became colorless. When this was back-extracted with an aqueous sodium thiosulfate solution containing 0.1 molar equivalent of H ₂ C ₂ O ₄ in the organic phase, 98% was transferred to the aqueous phase in 6 hours of back-extraction and was 0.1 μm or less. As a result, ultrafine gold particles were obtained. It was confirmed to be an Au crystal by a selected area electron diffraction method. Example 3 . When a 3 mol · dm ⁻³ HCl aqueous solution of chloroauric acid having a concentration of 3 × 10 ⁻³ mol · dm ⁻³ was extracted with DBC, Au (III) was easily extracted into the organic phase, and the liquid became yellow. When this solution was left in a colorless and transparent glass bottle for several days, the yellow color almost disappeared. 0.2 in Au in this organic phase
Back extraction with an aqueous solution containing molar equivalents of HCOOH gives 6
Back extraction in time gave 78% pure 0.2-0.3 μm ultrafine gold particles. Example 4 . A TBP solution with an Au concentration of 2.6 × 10 ⁻³ mol · dm ⁻³ was washed once with water, and then the density was 2.6 mW / cm ^2.
UV irradiation was performed for 7 hours. Next, A in the organic phase
When back-extracted with an aqueous sodium thiosulfate solution containing 0.2 molar equivalent of u ₂ of Na ₂ SO ₃ , 98% was obtained by back-extraction for 12 hours.
Was transferred to the water phase and could be deposited as ultrafine gold particles. Example 5 . The organic phase in which ³ mol · dm ⁻³ HCl aqueous solution of chloroauric acid having an Au concentration of 5 × 10 ⁻³ mol · dm ⁻³ was extracted with MIBK and the yellow color disappeared after standing for several days was adjusted to 0. Back-extraction with 1 molar equivalent of H ₂ C ₂ O ₄ and 3% by weight of sodium pyrophosphate (NaPP) gave a dark blue color and then back-extraction into the aqueous phase. After 24 hours of back extraction, 100% was recovered in the aqueous phase as ultrafine particles of Au. Transmission electron micrograph of FIG. 2 (30,000
The obtained particles have an average particle size of 0.1 μm.
It can be seen that they are the following ultrafine particles. Example 6 . MI in Au in HNO ₃ aqueous solution of chloroauric acid
After extraction with BK and back-extraction at room temperature with an aqueous solution containing 0.2 molar equivalent of HCOOH of the reducing agent necessary for the reduction of Au (III), it was 51% after 6 hours of back-extraction and 98% after 24 hours. Au is back-extracted into the aqueous phase and 0.2-0.3
μm Au single-phase ultrafine particles were recovered. Even if the amount of HCOOH in the back extraction liquid was 2 molar equivalents, the reduction and back extraction ratio of Au after 18 hours was the same as that in the case of 0.1 molar equivalents.

On the other hand, the organic phase was kept in a transparent bottle for several days, and after the liquid became colorless, 0.2 molar equivalent of HCOO was used.
When back-extracted with an aqueous solution containing H, the reduction back-extraction ratio after 6 hours was 81%.

[Brief description of drawings]

FIG. 1 is an electron micrograph of gold particles obtained in Example 1.

FIG. 2 is an electron micrograph of gold particles obtained in Example 4.

FIG. 3 is an X-ray diffraction image of the gold particles obtained in Example 1.

Claims (3)

[Claims] 1. A step of extracting a gold aqua regia solution or a hydrochloric acid or nitric acid solution of chloroauric acid into an organic phase containing a solvation extractant or a neutral extractant, and an amount equal to or less than the equivalent of the gold reduction reaction. A method for producing ultrafine gold particles, comprising the step of back-extracting with an aqueous solution containing a reducing agent. 2. A step of extracting a gold aqua regia solution or a hydrochloric acid or nitric acid solution of chloroauric acid into an organic phase containing a solvating extractant or a neutral extractant, and utilizing a photochemical reaction in the organic phase. And partially reducing the gold, and back-extracting with an aqueous solution containing a reducing agent in an amount equal to or less than the equivalent amount of the gold reduction reaction. 3. The method for producing ultrafine gold particles according to claim 1, wherein the aqueous solution containing a reducing agent used in the step of back-extracting further contains a surfactant.