JP2020037537A - Method for producing gold nanoparticle-supported powder - Google Patents

Abstract

To efficiently produce a gold nanoparticle-carrying powder that has only a minimum amount of an additive such as a dispersant, and is free of impurities.SOLUTION: The present invention provides a method for producing gold nanoparticle-carrying powder that is obtained by: adding a base powder for carrying gold nanoparticles thereon, to a mixture solution having an ammonia solution added to a solution containing gold ions; disposing at least two electrodes in a gas above the liquid level of the mixture solution; applying voltage to between electrodes in a rare gas atmosphere; and generating plasma between the electrodes and the liquid level. There is also provided a gold nanoparticle-carrying powder thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing gold nanoparticle-supported powder by liquid level plasma, and is applied to the field of cosmetics and toiletries as an antibacterial agent and a coloring material.

  Silver nanoparticles and silver ions used as antibacterial materials are likely to be safe for living organisms due to the penetration of nanoparticles into the skin, exposure to the lungs, and elution of silver ions. Often have been. Therefore, it is important to develop a material form that dispels concerns about the nanoparticles and a material that suppresses elution due to ionization.

  From these needs, it is important to fix nanoparticles to submicron or micron-sized mother powder or to form aggregates with other powders, etc., for scattering of nanoparticles. For elution by ionization, it is conceivable to substitute a metal that is harder to ionize, such as platinum or gold.

  Under these circumstances, it is known that gold nano-sized particles, which are difficult to ionize, exhibit a chemical activity not found in bulk gold, and are used in fields such as catalysts and biosensors. ing. Further, it is known that the color development of gold nanoparticles by surface plasmon resonance exhibits a vivid color tone from red to purple, and the gold nanoparticles are also used in the field of color materials.

  As a method for producing the gold nanoparticles, there are known a method of reducing gold ions using a reducing agent and a dispersant and protecting the generated gold particles, a method of plasma discharge into an aqueous solution containing gold ions, and the like. Have been.

  As a method of reducing gold ions, there is a method using an alkali metal borohydride as a reducing agent (Non-Patent Document 1). However, in order to stably disperse gold nanoparticles, which are fine particles that are easily aggregated, it is necessary to use thiol or polyvinylpyrrolidone, which has a strong interaction with gold and forms a monomolecular film on the gold surface, as a protective agent. . As described in Non-Patent Document 2, there is a method in which gold ions are reduced by heating in a mixed solvent of ethanol and water, but the reaction requires a long time.

  On the other hand, a technique has been reported in which a pair of metal electrodes are arranged in an aqueous solution containing gold ions, and gold ions are reduced by performing plasma discharge to generate gold nanoparticles (Patent Document 1). However, this method also uses a surfactant to stabilize the dispersion of gold ions and gold nanoparticles, and there is a concern about electrode deterioration due to discharge in an aqueous solution.

  In order to apply gold nanoparticles in a wide range of fields, it is necessary to efficiently generate fine gold nanoparticles. However, if a reducing agent, a dispersant, a protective agent, or the like is used, a step of removing an additive such as a washing step is required when finally extracting the gold nanoparticles. Also, considering the application to the cosmetics field and the like as a vivid red-purple coloring material by surface plasmon coloring, the use of additives such as dispersants that are irritating to human skin and the like was suppressed, and the scattering of nanoparticles was suppressed. In order to obtain a good color development, it is necessary to control the particles to be fine and uniform in particle diameter.

  Among them, an electron beam irradiation reduction method for obtaining metal nanoparticles by irradiating a metal ion aqueous solution with an electron beam under the condition that there is no additive such as a reducing agent has been developed, but an electron beam irradiation apparatus is large-scale, A facility for shielding the wires is required, and the work is not safe (Patent Document 2).

JP-A-2006-27184 Patent 4069193

M. Brust, M .; Walker, D.W. Bethell, D.M. J. Schiffrin, R .; Wyman, J .; Chem. Soc. Chem. Commun, p801-802 (1994) N. Toshima, K .; Kushihashi, T .; Yonezawa, H .; Hirai, Chem. Lett. , 18 (10), p1769-1772 (1989).

  In view of the above background, the problem to be solved by the present invention is to use a small-sized device to safely carry gold nanoparticle-supported powder with less impurities without using an additive that requires a process for removing a dispersant or the like. In addition, there is a need for efficient generation.

  In the present invention, plate-like alumina as a base powder is added to a mixed aqueous solution obtained by adding an aqueous ammonia solution to an aqueous chloroauric acid solution (trivalent gold), and at least two electrodes are placed in the air above the liquid surface of the mixed aqueous solution. A method of obtaining a gold nanoparticle-supporting powder by arranging and applying a voltage between the electrodes in a rare gas atmosphere to generate plasma between the electrode and the liquid surface, and a gold nanoparticle-supporting powder. FIG. 1 shows a basic configuration of a plasma processing apparatus of the present invention.

  In the present invention, as shown in FIG. 1, since the electrodes do not come into contact with the mixed aqueous solution of the chloroauric acid aqueous solution and the ammonia aqueous solution, the plasma processing can be performed regardless of the concentration or pH of the liquid to be processed. Low contamination from electrodes due to electrode deterioration. Furthermore, since plasma is generated between a plurality of electrodes and the liquid surface, compared to a plasma generation method in which one of the electrodes is in the air and the other is in an aqueous solution, or a method in which plasma is generated between a pair of electrodes in an aqueous solution. Thus, more efficient plasma processing can be performed.

  In the present invention, it is easy to increase the efficiency of the gold nanoparticle loading process by increasing the number of power supplies and a pair of electrodes as shown in FIG. 2 and by increasing the number of batch processes in FIGS. It is.

  The shape of the electrode used in the present invention is not particularly limited, but may be a needle shape, a hollow needle shape, a linear shape, a flat plate shape, among others, and among them, an uneven electric field is generated, thereby lowering a dielectric breakdown voltage. A needle-like one that facilitates generation of plasma even at a low voltage is preferable. Also, the material of the electrode is not particularly limited as long as it can maintain a stable discharge state. In addition to metals and alloys such as platinum, tungsten, copper, copper tungsten, silver, graphite, titanium, stainless steel, molybdenum, aluminum, iron, etc., the surfaces of these metals and alloys are coated with dissimilar materials for the purpose of improving electrode performance You may.

  In the plasma processing method according to the present invention, various types of power sources, such as a DC power source, a pulse power source, a low-frequency / high-frequency AC power source, and a microwave power source, can be used as a power source for generating plasma. Circuits may be combined. Among them, considering the production efficiency of gold nanoparticles, a wound neon transformer, a pulse power supply combining a rectifier circuit, and an inverter neon transformer combining a rectifier circuit are good, because they are inexpensive and easy to use. Wound neon transformers are best.

  Therefore, it is a cheaper and simpler device than the method of obtaining gold nanoparticles by the electron beam irradiation method, and can safely work without the need to shield the electron beam.

  In the plasma generation method of the present invention, the distance between the electrode disposed in the air above the liquid surface and the liquid surface, the distance between the electrode and the electrode of the electrode disposed in the air, and the applied voltage are determined between the electrode and the liquid surface. Any condition may be used, and there is no particular limitation. It is performed under the condition that no discharge occurs between the electrodes in the air. Regarding the relationship between the electrode-to-electrode distance L and the electrode-to-liquid surface distance D that can generate a discharge between the electrode and the liquid level, L> 3D is preferable (when the number of electrodes is three or more, , The shortest distance between the different polarity electrodes is L, and the longest electrode-liquid level distance is D.) The distance between the electrode disposed in the air and the liquid surface is usually sufficient as long as the electrode is slightly away from the liquid surface, and the distance is larger than 0 mm and 50 mm or less. D = 1 to 30 mm is particularly preferable as a range in which a stable discharge state is maintained. Further, the distance between each electrode arranged in the air and the liquid surface is preferably such that D of all the electrodes is equal to obtain a stable discharge. The applied voltage required for plasma generation is affected by the arrangement of the electrodes, the material of the electrodes, and the like. Further, 1 to 5 kV is most preferable from the viewpoint of easy application of a voltage.

  In the present invention, the atmosphere inside the container for generating plasma is a rare gas in order to suppress a change in pH or the like of a mixed aqueous solution of chloroauric acid aqueous solution and ammonia aqueous solution due to generation of plasma. Helium, neon, argon, and xenon are listed as rare gases that can be used, but argon is preferable from an economic viewpoint.

  In the present invention, plasma is discharged to a mixed aqueous solution of a chloroauric acid aqueous solution and an ammonia aqueous solution. The chloroauric acid concentration (gold ion concentration) in the mixed aqueous solution is preferably 0.01 to 100 mM (M = mol / L). In consideration of the yield efficiency, the price of gold, and the cost in consideration of antibacterial properties from the processing capability of the power supply, 0.1 to 10 mM is more preferable. The concentration of ammonia in the mixed aqueous solution to which the aqueous ammonia solution is added and added also depends on the concentration of the chloroauric acid charged, but is preferably 0.1 to 100 mM, and more preferably 1 to 50 mM.

  By mixing the aqueous solution of chloroauric acid and the aqueous solution of ammonia, gold nanoparticles can be efficiently produced in the mixed aqueous solution within the concentration range of gold and ammonia as described above. If the concentration is limited, it is optimal to carry out the reaction in a molar ratio of chloroauric acid and ammonia charged in the range of 1:10 to 1: 100.

  In the present invention, a mixed aqueous solution of a chloroauric acid aqueous solution and an ammonia aqueous solution is used, and the above-described process is performed in the charged concentration range and the molar ratio of the chloroauric acid and the ammonia. Since it is considered to be a condition under which good gold nanoparticles are generated, when a mixed aqueous solution of both is used (before the plasma treatment), the pH of the mixed aqueous solution from which a good product is obtained is 6.0 to 11.0. As a range in which fine gold nanoparticles can be obtained more efficiently, pH 9.0 to 11.0 is preferable. In addition, although the pH tends to decrease due to the generation of gold nanoparticles by the plasma treatment, the change in pH after the plasma treatment is preferably small. That is, the pH after the plasma treatment is preferably in the range of 3.0 to 11.0, and more preferably 8.5 to 10.5.

  In the present invention, before generating plasma, a plasma treatment is performed by adding a base powder for supporting gold nanoparticles to a mixed aqueous solution obtained by adding an aqueous ammonia solution to an aqueous chloroauric acid solution. By adding the base powder before the plasma treatment, the base powder serves as a scaffold for gold nanoparticle generation, promotes the generation of gold nanoparticles, and suppresses the aggregation of gold particles to reduce the gold nanoparticles. It can be carried on.

  Metal oxides, metal hydroxides, metal oxyhydroxides, and clay minerals can be used as the base powder for supporting the gold nanoparticles in the present invention. Among them, alumina, aluminum hydroxide, iron oxide, titanium oxide, zinc oxide, sericite, and talc are preferable, and in particular, alumina, iron oxide, and titanium oxide are used in view of the surface characteristics of gold nanoparticles generated by the method using plasma of the present invention. Considering that zinc oxide is good, and furthermore, taking advantage of the red-violet coloration of the gold nanoparticles, alumina and titanium oxide are particularly preferable, and alumina is most preferable. Also, as for the shape of these powders, plate-like powders more easily carry gold nanoparticles.

  The surface charge of the gold nanoparticles obtained by the method using the plasma of the present invention is negative.

  The charge concentration of the base powder for supporting the gold nanoparticles is 0.5 to 20% by weight based on the weight of the mixed aqueous solution of the aqueous solution of chloroauric acid and the aqueous ammonia, and the gold nanoparticles are dispersed in a good dispersion state. In order to support and obtain good antibacterial properties, 1 to 10% by weight is preferable.

  Further, in order to suppress the aggregation of the generated gold nanoparticles and to disperse the base powder in the mixed aqueous solution, it is preferable to use a mechanical stirring force in combination. For example, an ultrasonic disperser, a magnetic stirrer, a propeller stirrer, a disper mixer, a homomixer and the like can be used.

  The gold nanoparticle-supported powder produced according to the present invention has few additives and impurities, and it is easy to remove these unnecessary components. Therefore, it can contribute to the development of a safe and low-cost antibacterial material. Furthermore, since the addition of the base powder and the generation of the gold nanoparticles and the loading of the gold nanoparticles on the base powder can be performed in one step by the plasma treatment, the number of steps is small and there is an advantage in terms of manufacturing cost, Furthermore, it can be said that the manufacturing method is advantageous in terms of simplicity of manufacturing equipment and safety management.

FIG. 1 is a schematic diagram of a basic configuration of a plasma processing apparatus. FIG. 2 is a schematic diagram of a basic configuration of the plasma processing apparatus when four pairs of electrodes are added.

  Next, the method for obtaining the gold nanoparticle-supported powder of the present invention and the gold nanoparticle-supported powder will be described in detail with reference to examples, but the present invention is not limited thereto.

A gold nanoparticle-supporting powder was prepared by performing a plasma treatment under the following conditions using the plasma generator shown in FIG.
<Aqueous mixed solution used for gold nanoparticle supporting treatment>
Chloroauric acid (trivalent) concentration (gold concentration): 0.2 mM (M = mol / L), ammonia concentration: 4 mM, volume of mixed aqueous solution: 0.25 L
<Mother powder>
Alumina (RonaFlare White Sapphire made by Merck, plate-like powder): 1% by weight based on the total amount of the mixed aqueous solution (about 250 g of 0.25 L of the mixed aqueous solution and 2.5 g of alumina were charged)
<Reaction vessel>
Uses separable flask and separable cover <Plasma processing conditions>
Power supply: Winding type neon transformer (60Hz, manufactured by Reship LSP)
Electrode: Tungsten wire (needle, diameter 0.7 mm), a distance between the electrode and the liquid surface is about 5 mm, and a distance between the electrodes is about 50 mm, and a pair of electrodes is arranged in the air. Applied voltage: 3 kV
Mechanical stirring power: Propeller stirring, preliminary stirring for 10 minutes before plasma processing <Processing time> 60 minutes <Liquid temperature> 25 ° C
<Atmosphere> An argon atmosphere was supplied at 1 L / min into the vessel in an argon atmosphere. From the viewpoint of examining the generation efficiency of gold nanoparticles in the plasma treatment, the pH before and after the plasma treatment was measured.
Under the above conditions, the plasma treatment was performed, the appearance of the treated sample was observed, the sample for the gold loading was sampled, and then the treatment liquid was filtered, washed with ion-exchanged water, and dried to obtain the gold nanoparticle-supported powder. I got

(Comparative Example 1)
Plasma treatment was performed in the same manner as in Example 1 except that ammonia was not added.

  In Example 1, the solution before the plasma treatment was clouded by the mother powder, but immediately after the plasma treatment, the solution gradually began to turn reddish purple. The color of the suspension became darker with the treatment time, and became a magenta suspension after the treatment for 60 minutes. When the suspension was stopped and the mixture was allowed to stand, the colored particles immediately began to settle, and after standing for 30 minutes, the supernatant became colorless and transparent. On the other hand, in Comparative Example 1, although it was slightly reddish after the plasma treatment for 60 minutes, it was almost cloudy.

  The powder was taken out of these suspensions by filtration and observed by an electron microscope (SEM). As a result, fine particles of about 10 nm were observed in Example 1, whereas in Comparative Example 1, the particles were larger than 100 nm. Coarse particles of gold were scattered.

<Evaluation of gold loading>
Initial gold concentration [Au, ini. ] Was determined by collecting the solution before adding the mother powder, diluting the solution with diluted nitric acid, and performing ICP emission spectroscopy. The gold concentration [Au] in the suspension was determined by filtering the suspension with a syringe filter (pore size 0.8 μm), diluting the filtrate with diluted nitric acid, and performing ICP emission spectroscopy. . Using these values of the gold concentration, the gold loading ratio on the mother powder (the following formula) and the gold loading amount per gram of the mother powder were determined.
Loading ratio [%] = 100 × (1- [Au] / [Au, ini.])

  For the suspension obtained in Example 1, the gold carrying ratio and the amount of gold carried per gram of the mother powder were determined. The loading ratio was extremely high at 100%, indicating that almost all of the gold chloride in the solution could be recovered as gold nanoparticles. The amount of gold carried per gram of the powder was 3.8 mg / g. (See Table 1).

(Comparative Example 2)
In Example 1, the plasma treatment was performed in the same manner except that alumina as a base powder was not added.

  About 5 minutes after the start of the plasma discharge, a dark gold thin film began to float on the water surface. After 60 minutes, a dark gold foil-like substance was floating. Although it was a gold product, the particle size was not controlled to a nano size, and it was present as a precipitate.

  Therefore, in order to obtain good gold nanoparticles supported on alumina and obtain a vivid red-purple coloring material, adjust the pH to about 10 by adding an aqueous ammonia solution to an aqueous chloroauric acid solution before the treatment. Also, it is necessary to add a base powder such as alumina which serves as a scaffold for gold nanoparticle deposition.

<Differences in contamination depending on the discharge method>
(Comparative Example 3)
Subsequently, a pair of tungsten wire electrodes in Example 1 were placed in water with a distance between the electrodes of 1 mm, and the power supply was changed to an inverter type neon transformer, and plasma treatment was similarly performed at a voltage of 4.8 kV.

<Contamination evaluation>
In order to confirm the contamination of the obtained gold-nanoparticle-supported powder, X-ray fluorescence measurement was performed on the alumina of the base powder used in Example 1 and the gold-nanoparticle-supported powder prepared in Example 1. The measurement was carried out using a wavelength-dispersive X-ray fluorescence analyzer (Rigaku RIX2000, Rh bulb, tube voltage 50 kV, tube current 50 mA) and pressure molded into a shape having a diameter of 30 mm and a thickness of about 2 mm.

  From the fluorescent X-ray measurement, no element other than the components contained in the gold and the base powder was detected from the gold nanoparticle-supported powder of Example 1. On the other hand, in Comparative Example 3, a very small amount of tungsten was detected, which proved the superiority regarding the contamination derived from the electrode in the present invention.

  In Example 2, the power supply and the electrodes under the plasma processing conditions of Example 1 were increased by four power supplies and four pairs of electrodes as shown in FIG. 2, and the processing time was set to 30 minutes. Was done.

  By increasing the number of electrodes in four pairs, the generation rate of the gold nanoparticle-supported powder was reliably increased. The results after the last 30 minutes are shown in Table 2. The loading rate reaches 98.2% after 15 minutes and reaches 100% after 30 minutes. Improved. Observation of the appearance showed a vivid reddish purple appearance, and observation of the SEM revealed that fine gold nanoparticles of about 10 nm were supported on alumina.

<Difference in production by pH>
The concentration of chloroauric acid was set to 0.20 mM, and the concentration of ammonia was changed to examine the loading of gold nanoparticles. In Example 3, a plasma treatment was performed in the same manner as in Example 2 except that the ammonia concentration was changed to 1 mM.

  Plasma treatment was performed in the same manner as in Example 2 except that the ammonia concentration was 8 mM.

  Plasma treatment was performed in the same manner as in Example 2 except that the ammonia concentration was changed to 16 mM.

Table 2 shows the results of supporting gold nanoparticles in Examples 2 to 5.

  The chloroauric acid concentration was set to 0.20 mM, and the concentration of the aqueous ammonia solution was changed to confirm the conditions for forming gold nanoparticles. According to Examples 1, 2, 4, and 5, the pH when the aqueous chloroauric acid solution and the aqueous ammonia solution are mixed before the plasma treatment is set to 9.0 to 11.0. A powder supporting fine gold nanoparticles of several tens of nm is preferably obtained. That is, in order to carry fine gold nanoparticles, the pH of the aqueous solution is set to a pH range in which ammonia is present in excess of chloroauric acid, which is acidic.

<Confirmation of antibacterial property>
Next, among the gold nanoparticle-supported powders prepared according to the present invention, the antibacterial properties of Examples 1, 2 and Comparative Example 1 were evaluated. Escherichia coli, which is a standard strain used in the preservative efficacy test of cosmetics, and acne bacteria, which are indigenous to human skin, were used as test strains. A sample for evaluation was prepared by adding 0.1 g of the gold nanoparticle-supported powder to 1 mL of the test bacterial solution (the number of inoculated bacteria: 1.0 × 10 ⁵ CFU / mL), and a blank sample was prepared by adding 1 mL of the test bacterial solution alone. did. After a predetermined time, the number of viable bacteria was measured by a standard method, and the antibacterial activity was evaluated from the survival rate of the bacteria.

  Regarding Escherichia coli, the viability was 0% after 6 hours in Examples 1 and 2, whereas the number of bacteria in Comparative Example 1 was increased to 100% or more. In Examples 1 and 2, among the Acne bacteria, the survival rate of the Acne bacteria was 0% after one week, whereas about 10 to 20% of the bacteria were alive in Comparative Example 1. Therefore, in order to exhibit antibacterial properties, it is necessary that fine gold nanoparticles of several tens of nm, not coarse particles, be supported on the alumina powder as the base powder.

(Comparative Example 4)
Comparative Example 4 was the same as Example 2 except that alumina of the base powder was not added and the other conditions were the same.

  From Example 2, the base powder was changed to 1 to 10% by weight based on the weight of the mixed aqueous solution of chloroauric acid aqueous solution and ammonia aqueous solution, and the other conditions were the same as Example 6.

  From Example 2, the base powder was changed from 1% by weight to 20% by weight based on the weight of the mixed aqueous solution of chloroauric acid aqueous solution and ammonia aqueous solution, and the other conditions were the same as Example 7.

Table 3 shows the results of Comparative Example 4, Examples 6 and 7 in which the presence and amount of the mother powder were examined.

  From the results of Comparative Example 4, it was confirmed that even when the electrodes were added in four pairs, gold nanoparticles were not generated without alumina as the base powder, and foil-like pieces and coarse particles floated. . Therefore, the alumina base powder is important as a place for supporting the gold nanoparticles, and when there is no base powder, the generated gold nanoparticles are aggregated with each other because there is no place for supporting the gold nanoparticles, and the alumina base powder is large. It was again confirmed that the particles became coarse particles.

  In Examples 6 and 7 in which the amount of the mother powder was increased, the loading ratio was reduced, so that the magenta color and the antibacterial property were reduced. By the time of Example 7, the redness was considerably reduced, and the antibacterial property also began to be significantly reduced with respect to P. acnes. Therefore, the amount is preferably 1 to 10% by weight in order to support the gold nanoparticles in a good dispersion state to obtain a red-purple supported powder and obtain good antibacterial properties.

  By using the present invention, it is possible to efficiently produce a gold nanoparticle-supporting powder with few impurities. In addition, since the production of the gold nanoparticles and the loading on the mother powder are performed in one step, the number of production steps is reduced, and there is also an advantage in cost. The technology of the present invention is supposed to provide catalytic performance by supporting metal nanoparticles on powders such as metal oxides, as well as on metal oxides, and can be used in a wide range of fields as well as cosmetics. It is.

DESCRIPTION OF SYMBOLS 1 Storage tank which stores liquid to be processed 2 Liquid to be processed 3 Power supply 4 Electrode installed in the air above liquid level 5 Insulating tube 6 Plasma 7 Argon gas 8 Constant temperature water 9 Water tank 10 Stirrer

Claims (5)

  To a mixed aqueous solution obtained by adding an aqueous ammonia solution to an aqueous chloroauric acid solution, a base powder for supporting gold nanoparticles is added, and at least two electrodes are arranged in the air above the liquid surface of the mixed aqueous solution to form a rare gas atmosphere. A method for producing a gold nanoparticle-supported powder obtained by applying a voltage between the electrodes below to generate plasma between the electrodes and the liquid surface.   The method of claim 1, wherein the rare gas is argon.   The method for producing a gold nanoparticle-supported powder according to claim 1 or 2, wherein the pH of the mixed aqueous solution of the aqueous chloroauric acid solution and the aqueous ammonia solution before the plasma treatment is 9.0 to 11.0.   The method for producing a gold nanoparticle-supported powder according to any one of claims 1 to 3, wherein the mother powder is alumina. A gold nanoparticle-supported powder produced by the method for producing a gold nanoparticle-supported powder according to claim 1.