JP4364692B2 - Method for producing hydrogen concentrated water and hydrogen concentrated water - Google Patents

Description

  The present invention relates to a high-concentration hydrogen concentration method and hydrogen-enriched water having a high-reactive oxygen species reduction-erasing ability or high anti-oxidation ability by absorbing and concentrating hydrogen in metal ultrafine particles.

It is well known that platinum group metal particles such as platinum and palladium store hydrogen remarkably. Furthermore, it is well known that it has SOD activity: the ability to eliminate active oxygen species such as superoxide anion (O ₂ ⁻ ) and hydrogen peroxide (H ₂ O ₂ ) generated in the body by the reducing power of hydrogen storage. It has been. Patent Document 1 describes a method for producing electrolytic reduced water by blowing hydrogen gas into water. In Patent Document 2, what is used as a raw material is recognized as a food additive, and an aqueous solution containing ultrafine metal particles is produced using a treatment liquid in which glycerin fatty acid ester as a surfactant is added to water. A method is described.

In Non-Patent Document 1, dissolved hydrogen is measured in alkaline ionized water or electrolytically reduced water produced by electrolyzing water on the cathode side, and this water is described as water that is good for the body. Non-Patent Document 2 explains that there is SOD activity on the assumption that electrolyzed water has active hydrogen. In order to increase the reactive oxygen species reduction and elimination ability, it is necessary to concentrate more hydrogen.
JP 2002-301383 A Japanese Patent Application No. 2003-404273: (2003/12/03) Functional Water Society: 7th Functional Water Symposium (2000 Tokyo Conference) “Physicochemical Properties of Alkaline Ionized Water” Kenji Kikuchi et al. Kyushu University Central Analysis Center News No. 75 “Science of reduced water with active oxygen scavenging ability and its application to medicine” Kyushu University Yasutaka Shirahata.

  The problem to be solved is that it is necessary to concentrate more hydrogen in order to increase the active oxygen scavenging ability of electrolytic reduced water, but it is difficult to concentrate hydrogen with electrolytic reduced water.

  The present invention is to produce hydrogen-enriched water having high active oxygen species reduction and elimination ability or high antioxidant ability by absorbing and concentrating hydrogen in platinum group metal ultrafine particles contained in an aqueous solution containing ultrafine platinum group metals. . In order to occlude and concentrate hydrogen in the platinum group metal ultrafine particles, hydrogen gas is arbitrarily injected into the platinum group metal ultrafine particle-containing aqueous solution, but the timing of the injection is not a particular problem. For example, in the aqueous solution before the metal salt reduction reaction treatment or in the aqueous solution after the start of the metal salt reduction reaction treatment, of course, when the nucleation of platinum group metal ultrafine particles such as platinum and palladium is generated, the reaction is completed. At any time, it may be after washing and purification of the produced platinum group metal ultrafine particles. The injection of hydrogen gas is preferably performed under high pressure because the hydrogen storage reaction is more efficient.

  The reducing power of an aqueous solution containing platinum group metal fine particles is measured using a redox dye: DCIP dye (2,6 dichloroindophenol sodium dihydrate) and DPPH dye (1,1-diphenyl-2-picrylhydrazyl). As a result, the hydrogen-enriched water according to the present invention, which occludes hydrogen, instantly changes these dyes from the oxidized form to the reduced form and greatly improves the reducing power compared to the original aqueous solution containing platinum group metal particles Was confirmed. As a result, the reactive oxygen species scavenging ability and antioxidant ability could be greatly improved.

  The present invention performs a metal salt reduction reaction process and a hydrogen gas injection process. The metal salt reduction reaction treatment is a treatment for producing platinum group metal fine particles by reducing a platinum group metal salt in an aqueous solution in the presence of a polymer such as a surfactant or a polymer. The injection process is a process in which hydrogen gas is arbitrarily injected into the aqueous solution containing the platinum group metal ultrafine particles generated by the aqueous solution before the metal salt reduction reaction treatment or the metal salt reduction reaction treatment, and hydrogen is occluded and concentrated in the metal ultrafine particles. . The metal salt reduction reaction treatment further includes a reduction reaction treatment for precipitating metal fine particles and a purification treatment for filtering the generated metal fine particles and washing with purified water.

The reduction reaction treatment further includes a metal salt such as chloroplatinic acid (H ₂ PtCl ₆ ) as a raw material, a reducing agent such as ethanol (CH ₃ CH ₂ OH) as a reaction solution, and a pH such as sodium hydrogen carbonate (NaHCO ₃ ). Weighing process to weigh the compensator, polymer such as surfactant and polymer to stably disperse the generated metal colloid, purified water used in the reaction, and heat the reaction liquid while stirring It consists of a reaction process that reacts.

  As for the hydrogen gas injection treatment, hydrogen gas can be arbitrarily injected into the aqueous solution containing the platinum group metal ultrafine particles, but the hydrogen gas injection in the reduction reaction treatment is performed from the start of the reaction of the reduction reaction treatment. The method of blowing after the nucleation where the color of the reaction liquid starts to change and the method of blowing after the completion of the reaction are conceivable. Next, as a method of blowing hydrogen gas in the purification treatment, there is a method of blowing hydrogen gas to the concentrate side when concentrating and washing with an ultrafiltration membrane. Another method may be a method in which hydrogen gas is blown into an aqueous solution containing ultrafine metal particles as a finished product after the purification treatment is completed.

Next, as a method of confirming that hydrogen has been occluded and concentrated in the aqueous solution containing metal ultrafine particles by hydrogen gas injection treatment, in addition to a method of measuring the remaining hydrogen by drying and vacuuming / degassing the aqueous solution, In order to utilize the reducing power in the aqueous solution containing metal ultrafine particles, that is, in the state of aqueous solution, the method for measuring the amount of dissolved hydrogen with a dissolved hydrogen meter, oxidation for evaluating reactive oxygen species scavenging ability and antioxidant ability by reduction reaction in oxidation / reduction reaction Reversible and reversible oxidation / reduction reactions with reducing dyes to observe the reducing power of DCIP (2,6-Dichlorindophenol Sodium Salt Dihydrate) dyes and DPPH ( 1,1-Diphenyl-2-picrylhydrazyl) dye method and superoxide anion _{(O 2} ^-) HPX-XOD system used in scavenging activity (hypoxanthine - hexa There is a method of comparative evaluation Chin oxidase system) or the like, in the present invention, performed per experiment radical scavenging reducing power in DPPH radical was evaluated by reducing power by DCIP dye.

In the evaluation, first, as DCIP dye evaluation stock solution, (1) 0.05 g DCIP was dissolved in 70 ml ethanol (2) 1 ml was collected and injected into 24 ml ethanol (3) 5 ml was collected to obtain 2.13 mg disodium hydrogen phosphate Was poured into 15 ml of a solution dissolved in 180 ml of purified water to make a stock solution. The oxidation / reduction reaction of the DCIP dye is shown in FIG. The DPPH radical is shown in FIG. As shown in FIG. 1, oxidized DCIP is supplied with electrons (e ⁻ ) or hydrogen (H ⁺ ), and is reduced and decolored to form reduced DCIPH ₂ . Therefore, in the case of this method in which hydrogen gas is blown, the reduction rate increases in proportion to the amount of hydrogen. In other words, it can be said that the reductive decolorization time is proportional to the amount of hydrogen.

Further, as shown in FIG. 2, the oxidized DPPH radical is radical-erased by electrons (e ⁻ ) or hydrogen (H ⁺ ), and is reduced and decolored to become reduced DPPH. Similar to the DCIP, the reductive decolorization time is proportional to the amount of hydrogen.

(Example)
Examples of the present invention will be described below.
In the following examples, when hydrogen gas is blown during the reaction of the reduction reaction treatment, the case where hydrogen gas is blown from the start of the reaction (1) and the case where hydrogen gas is blown from the time when generation of metal fine particle nuclei starts. (2) is considered. At that time, the reaction temperature, the stirring speed and the amount of hydrogen gas were changed. As a result, in both (1) and (2), there was almost no significant difference in the reduction decoloration time of the DCIP and DPPH in the stirring rotation speed and the hydrogen gas amount.

  Therefore, it can be said that there was no significant difference in the amount of hydrogen occlusion between the stirring speed and the amount of hydrogen gas. However, the higher the reaction temperature, the faster the reductive decoloration time of the DCIP and DPPH. Therefore, it can be said that the reaction temperature is preferably slightly higher than the normal temperature in consideration of economy. In addition, since the color of the reaction solution began to change when the metal fine particle nuclei began to be generated, a method was adopted in which hydrogen gas was blown in by capturing the change in color tone.

  Next, in order to blow in hydrogen gas during the purification process, hydrogen gas is blown into the concentrate side when concentrating and washing with an ultrafiltration membrane. Case (3) and the permeate side are washed and replaced with purified water for an additional 10 minutes after no salinity is detected by a salinity meter, but hydrogen gas is blown in during this 10-minute washing and replacement. Although (4) was performed, almost no significant difference was recognized in the reductive decoloration time of the DCIP and DPPH in (3) and (4).

  Therefore, it can be said that there was no significant difference in hydrogen storage amount between (3) and (4). In consideration of economy, hydrogen gas was blown in for 10 minutes for final cleaning with an ultrafiltration membrane. Furthermore, when hydrogen gas was blown into the aqueous solution containing ultrafine metal particles as a finished product after the purification treatment was completed, the same results as in the above-described finish cleaning with the ultrafiltration membrane described above were obtained.

Note that the hydrogen gas blowing amount shows a tendency for the DCIP reductive decoloration time to be extended when the hydrogen blowing amount with respect to the amount of the aqueous solution to be treated is 1/100 or less, and when it is 1/10 or more. There was no significant difference in DCIP reductive decolorization time. Therefore, since 1/10 or more is economically wasteful, the amount of hydrogen blown with respect to the amount of aqueous solution to be treated is set to 1/100 to 1/10.

In the present invention, as the platinum group element, six elements of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt) are well known, all of which are hydrogen. Although the behavior considered to be an occlusion phenomenon is exhibited, an aqueous solution containing platinum (Pt) colloid or palladium (Pd) colloid, which is often used industrially, has an excellent hydrogen occlusion effect. The particle diameters of these platinum colloids and palladium colloids were 1 to 20 nanometers (nm) depending on the production conditions.

Example 1
A. The metal salt reduction reaction treatment and the hydrogen gas injection treatment were performed in the following procedure.
(1) Preparation of treated water <Water A> Purified water was filtered through a 1 μm filter paper to prepare 4500 ml.
<Reducing agent B> 450 ml of ethanol (CH ₃ CH ₂ OH) was weighed.
<Surfactant C> As a glycerin fatty acid ester, 0.5 g of “L-10D” manufactured by Mitsubishi Chemical Foods and 1.5 g of “J-0381V” manufactured by Riken Vitamin Co., Ltd. were weighed and mixed.

<Metal ion solution D> A chloroplatinic acid solution (H ₂ PtCl ₆ ) was prepared, and 5 ml (containing Pt 1 g) of this chloroplatinic acid solution was weighed.
<PH compensator E> 5 g of sodium hydrogen carbonate (NaHCO ₃ ) was prepared, and 5 g of this sodium hydrogen carbonate (NaHCO ₃ ) was dissolved in 100 ml of purified water filtered.
<Hydrogen gas> A pressure reducing valve and a flow meter were prepared using a high purity hydrogen gas (grade G210L: purity (99.999%)) cylinder.

(2) Reduction treatment The water A was put in a container as a treatment solution, and the temperature was raised while stirring the solution. When the temperature of the water reached 60 ° C., the reducing agent B and the surfactant C were added to the water A. After addition of reducing agent B and surfactant C, the temperature is increased while stirring water A, and metal ion solution D and pH compensator E are added simultaneously when the temperature of the treatment liquid reaches 70 ° C. did.

(3) The processing liquid is continuously stirred while the temperature is maintained at 70 ° C., and the color tone of the processing liquid starts to change when platinum ions are reduced and nuclei begin to be generated. From that time, 400 ml / min of hydrogen gas was blown in from the lower part of the treatment liquid for 20 minutes, and when the reaction was completed, stirring and heating were stopped to obtain a platinum colloid. The particle size of the platinum fine particles in the platinum colloid was 2 to 3 nanometers (nm).

(4) Filtration treatment After completion of stirring, the platinum colloid was filtered through a 1 μm filter paper and allowed to stand for 12 hours. After standing, the mixture was filtered through an ultrafiltration membrane with a molecular weight cut-off of 10,000 while adding 15,000 ml of purified water to obtain an aqueous solution containing platinum ultrafine particles. An aqueous solution containing ultrafine metal platinum particles was used for the redox dye experiment. The activity of the obtained aqueous solution containing platinum ultrafine particles was tested using a Hitachi spectrophotometer (U3210).

(5) In the test, first, 3 ml of redox dye: DCIP sample was injected into a glass cell with a lid of Hitachi spectrophotometer, and then 150 μl of the aqueous solution containing platinum ultrafine particles was injected, and gently shaken 5 times. And set in an absorptiometer and measured at a wavelength of 600 nm.

B. Discussion of results The measurement results are shown in FIG.
(1) As shown in FIG. 3, the absorption intensity (I _O ) is changed from 0.73 to 0.18 instantaneously, and the measurement cell containing the measurement solution is set to 5 It can be confirmed that the oxygen concentration in the air is dissolved in the treatment liquid by shaking about once and returned to the oxidized DPIC, and the time change of the absorption intensity (I _O ) of reductive decolorization is instantaneously reduced and decolorized in the same way as the initial one. It was. Further, FIG. 3 shows the same oxidation / reduction repeated four times. Similarly, the reduction and decolorization are instantaneously performed. As a result, it was found that the aqueous solution containing ultrafine metal particles produced in the treatment liquid by blowing hydrogen gas had high activity and was stable.

Although hydrogen gas was blown simultaneously with the start of the reaction of the treatment liquid, the same pattern as that in FIG. 3 was obtained using the absorptiometer. Therefore, it is considered that the hydrogen gas reaction has contributed from the time of nucleation. Furthermore, when the reaction temperature from the time of nucleation was increased to 75 ° C., the change and decolorization of the absorption intensity (I 2 _{O 3} ) was further accelerated.

(2) In the case of an aqueous solution containing platinum ultrafine particles, a chloroplatinic acid solution (H ₂ PtCl ₆ ) was prepared in the metal ion solution D, and 5 ml of this chloroplatinic acid solution was weighed and reacted. In the case of an aqueous solution containing palladium ultrafine particles, prepare a chloropalladium acid solution (H ₂ Pdcl ₄ ), measure 5 ml of this chloropalladium acid solution, and confirm that it has high activity in any hydrogen gas treatment. did. In addition, it was confirmed that aqueous solutions containing noble metal ultrafine particles such as an aqueous solution containing gold ultrafine particles and an aqueous solution containing silver ultrafine particles also became highly active by hydrogen gas treatment.

(Comparative Example 1)
FIG. 4 shows the result of measuring the platinum metal ultrafine particle-containing aqueous solution obtained by carrying out the same reaction without blowing hydrogen gas in Example 1 with an absorptiometer in exactly the same manner. . As shown in FIG. 4, the absorption intensity (I _O ) changed from 0.73 to 0.18 instantaneously and decolorization took nearly 13 minutes, and the hydrogen gas blown in Example 1 was instantaneously reduced and decolorized. It takes a long time. Furthermore, when measured by gently shaking 5 times, the measurement time is as short as about 2.5 minutes, but the reaction time is longer than that of the hydrogen gas blowing sample being instantaneously reduced and decolored.

  The first decoloration change is that the dissolved oxygen is in a saturated state, and the next one that was gently shaken five times is considered to have accelerated the reductive decoloration because the dissolved oxygen was not saturated.

(Example 2)
In the purification treatment of the reaction completion liquid of Comparative Example 1, the reaction liquid was filtered through a 1 μm quantitative filter paper and allowed to stand for 12 hours. After standing, in the process of filtering through an ultrafiltration membrane with a molecular weight cut off of 10,000, hydrogen gas is introduced from the lower part of the concentrated liquid side where ultrafine metal platinum particles are concentrated after the salt concentration in the permeated water is not detected. Of 300 ml / min. Purified water used at that time was 2,000 ml for about 20 minutes, and filtration and hydrogen blowing were continued to obtain an aqueous solution containing ultrafine metal platinum particles.

In the same manner as in Example 1, 3 ml of redox dye: DCIP sample was injected into a glass cell with a lid of a Hitachi spectrophotometer (U3210), and 150 μl of the aqueous solution containing ultrafine metal particles was further injected. . Further, as in Example 1, the measurement cell was gently shaken 5 times and set in an absorptiometer, and measurement was repeated 5 times at a wavelength of 600 nm. The measurement results are shown in FIG. As shown in FIG. 5, as in Example 1, the absorption intensity (I 2 _{O 3} ) is reduced and decolorized from 0.73 to 0.18 instantaneously, and the amount of metallic platinum produced in the treatment liquid is higher. It was found that the aqueous solution containing fine particles had high activity and was stable.

(Comparative Example 2)
In the purification step, the reaction completed solution of Comparative Example 1 was filtered through a 1 μm quantitative filter paper and allowed to stand for 12 hours. After standing, in the step of filtering with an ultrafiltration membrane with a molecular weight cut off of 10,000, after the salt concentration in the permeated water is not detected, hydrogen gas is not blown, and 2,000 ml of purified water is further added. Filtration was continued while adding for about 20 minutes to obtain an aqueous solution containing ultrafine metal platinum particles. The result was the same as the result shown in FIG.

(Example 3)
An aqueous solution containing ultrafine metal platinum particles adjusted to have a platinum concentration of 500 ppm is obtained by purifying an aqueous solution containing ultrafine metal platinum particles produced in the reduction reaction step in Comparative Example 1 using an ultrafiltration membrane. Prepare 2,000 ml. Hitachi gas 300 ml / min was blown from the bottom of the aqueous solution, and 150 μl was sampled after 1 minute, 3 minutes, and 10 minutes, respectively. Inject 3 ml of redox dye: DCIP sample into a glass cell with a lid of a spectrophotometer (U3210), inject 150 μl of each of the sampling solutions, and gently shake the measurement cell 5 times to absorb light. It set to the photometer and measured at wavelength 600nm.

The measurement results are shown in FIGS. FIG. 6A shows the control, FIG. 6B shows the case where H ₂ was blown for 1 minute, FIG. 6C shows the case where H ₂ was blown for 3 minutes, and FIG. 6D shows the case where H ₂ was blown for 10 minutes. As a result, as in the results obtained in Example 1 and Example 2, sufficient high activity was obtained by blowing hydrogen gas into the third quantile.

Next, the radical scavenging ability of the DPPH radical was measured in the same manner as the DCIP dye. Samples of control and hydrogen gas blowing time after 1 minute, 3 minutes, and 10 minutes were each sampled in 20 ml, diluted 10 times (indicated by 1/10) and diluted 100 times (1/100) Display) and inject into 2 ml of 50 μMol of DPPH into the absorptiometer cell, gently shake it about 5 times and leave to stand to visually observe the decoloration change with a spectrophotometer (wavelength: 600 nm). It was measured. The absorption intensity (I _O ) after 10 minutes is shown in Table 1 and FIG. In Table 1, as in Comparative Example 3 below, 300 ml / min of hydrogen gas was blown into 2,000 ml of purified water for 1 minute, 3 minutes, and 10 minutes, and the DPPH solution after 10 minutes was also listed.

(Comparative Example 3)
FIG. 8 shows the measurement result of DCIP dye of purified water obtained by blowing hydrogen gas at 300 ml / min for 30 minutes into 2,000 ml of purified water.
It was confirmed that even when hydrogen gas was blown into purified water, the reduction reaction to DCIP dye and DPPH radical dye, which are redox dyes, did not occur at all as shown in Table 2.

Table 1 shows the radical scavenging ability in terms of the absorption intensity (I _O ) at a wavelength (600 nm) depending on the amount of DPPH radical added in an aqueous solution containing platinum ultrafine particles and the time for blowing hydrogen gas into the aqueous solution containing platinum ultrafine particles. It is. As the addition amount of the aqueous solution containing platinum ultrafine particles, 20 μl, 10 μl, 5 μl and 1/100 diluted 20 μl, 5 μl of the diluted ultrafine platinum-containing aqueous solution are added to the DPPH solution. . The hydrogen gas blowing time was assumed to be blown for 1 minute, 3 minutes, and 10 minutes, with the hydrogen gas not blown as a control. Each measured value is the value of the light absorption intensity (I 2 _{O 3} ) after 10 minutes from the addition to the DPPH solution.

  As a comparative example, the control of purified water and hydrogen gas blown in for 1 minute, 3 minutes, and 10 minutes are listed at the bottom. It was confirmed that purified water had no DPPH radical scavenging ability regardless of whether hydrogen gas was blown in or not. It was confirmed that the radical scavenging ability was proportional to the hydrogen gas blowing time and the amount added.

  Further, Table 2 is a visual observation of the radical scavenging ability observed in the reductive decolorization of DPPH radicals. Like Table 1, the amount of platinum fine particle-containing aqueous solution added, hydrogen gas blowing time, and radical scavenging ability are in a proportional relationship. It shows that there is. Moreover, it was confirmed that purified water has no radical scavenging ability regardless of hydrogen gas blowing.

(Example 4)
An aqueous solution containing ultrafine metal platinum particles adjusted to have a platinum concentration of 500 ppm is obtained by purifying an aqueous solution containing ultrafine metal platinum particles produced in the reduction reaction step in Comparative Example 1 using an ultrafiltration membrane. 500 ml was prepared, poured into a 1 liter pressure vessel, and a high activity equivalent to the 10 minute treatment in Example 3 was obtained in about 2 minutes by blowing with 100 ml / min at a pressure of ² Kg / cm ² .

Further, pressurization was carried out at 2.5 kg / cm ² and 3 kg / cm ² , but no significant difference was observed from that with a DCIP reductive decoloration time of 2 kg / cm ² . Therefore, the maximum is 2 Kg / cm ² from the economical viewpoint.

From the results of these examples, the platinum metal particles originally having catalytic ability form an electric double layer by ion dissociation (H ⁺ , OH ⁻ ) of the surrounding water molecules H ₂ O to form electrons (e ⁻ ) or Although it is said that it has hydrogen (H ⁺ ) donating-type reducing properties, as shown in the schematic diagram of FIG. 9, since hydrogen H ₂ is occluded in the nano-sized metal platinum fine particles P, the surface energy is increased. As a result, it is estimated that the reducing power is improved. Furthermore, it is considered that the stored hydrogen is activated hydrogenated by the catalytic ability of the metal platinum fine particles, and the reducing power is improved.

In the medical field that utilizes the improvement effect of reactive oxygen species scavenging ability and antioxidant ability on diseases caused by reactive oxygen species such as superoxide anion (O ₂ ⁻ ) and hydrogen peroxide (H ₂ O ₂ ) generated in the body First, it can be used in the field of catalysts such as organic compound synthesis utilizing high activity catalytic ability.

It is an oxidation-reduction reaction diagram of DCIP dye. It is a radical elimination diagram by DPPH radical and reduction. It is a figure which shows the decoloring change curve of the DCIP pigment | dye by the platinum ultrafine particle containing aqueous solution addition which injected hydrogen gas from the time of the nucleation in the reaction process. It is a figure which shows the decoloring change curve of the DCIP pigment | dye by the platinum ultrafine particle containing aqueous solution addition which does not blow hydrogen gas in the comparative example of FIG. It is a figure which shows the decoloring change curve of the DCIP pigment | dye by the platinum ultrafine particle containing aqueous solution addition which blown in hydrogen gas from the completion | finish of the refinement | purification by the salinity meter in a refinement | purification process. (A)-(d) is a figure which shows the reduction | decrease decoloration change curve of the DCIP pigment | dye by adding platinum ultrafine particle containing aqueous solution from which control and hydrogen gas blowing-in time (1 minute, 3 minutes, 10 minutes) differ. It is a figure which shows the graph of the change of the reductive decoloring reaction to the DPPH radical pigment | dye by hydrogen-blown platinum ultrafine particle containing aqueous solution addition. It is a figure which shows the reductive decoloring reaction to the DPPH radical pigment | dye of hydrogen blowing purified water. It is an assumption figure of the nanosize metal platinum fine particle containing aqueous solution which occluded hydrogen.

Explanation of symbols

P Nano-sized platinum fine particle H ₂ Hydrogen H ⁺ , OH ^- Water molecule

Claims (4)

A method for producing hydrogen-enriched water containing platinum fine particles ,
Including a step of generating platinum fine particles by reducing a platinum salt in an aqueous solution ,
A method comprising injecting hydrogen gas into an aqueous solution during the reduction reaction in the step .   The method according to claim 1, wherein hydrogen gas is injected into the aqueous solution before the start of the reduction reaction, at the start of the reduction reaction, or from the start of platinum fine particle nucleation.   The method according to claim 2, wherein hydrogen gas is injected into the aqueous solution from the start of the reduction reaction or the start of platinum fine particle nucleation.   The method according to claim 1, wherein a platinum ion solution, a reducing agent, a surfactant, and a pH compensator are used.