JP2002028487A - Catalyst for generating atomic oxygen, producing method thereof and method for generating atomic oxygen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a complex which is useful as a new catalyst which enables generating atomic oxygen by facilitating the decomposition for hypochlorite such as sodium hypochlorite, a producing method thereof and a method for generating atomic oxygen under the presence of the said complex. SOLUTION: This catalyst for generating atomic oxygen comprises the complex which carries gold fine particles on a carbon type carrier. The complex can be produced by the method containing that an Au-containing compound is adsorbed by the carbon type carrier, subsequently, the carbon type carrier which adsorbs the Au-containing compound is subjected to plasma treatment and, thereby, the Au-containing compound is converted to Au fine particles. As a result, the method for generating atomic oxygen which contains the decomposition of hypochlorite under the presence of the complex is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly active atomic oxygen generating catalyst comprising a composite in which gold particles are supported on a carbon-based carrier, a method for producing the catalyst, and atomic oxygen using the catalyst. The present invention relates to a method for oxidatively decomposing organic substances and microorganisms and a method for sterilizing the same using a method for generating atomic oxygen. INDUSTRIAL APPLICABILITY The catalyst and method of the present invention are useful for environmental purification, food sterilization, and the like.

[0002]

BACKGROUND OF THE INVENTION Hypochlorites, such as sodium hypochlorite, are oxidizing agents and are widely used for applications such as sterilization and bleaching. However, the oxidizing power is not so high, and when the concentration in the aqueous solution decreases, the oxidizing power decreases. On the other hand, sodium hypochlorite is used in fields such as the decomposition of organic matter in wastewater and the sterilization of food, but even low-concentration sodium hypochlorite is decomposed into atomic If oxygen is generated and high oxidizing power (decomposing power, bactericidal power) is obtained, its usefulness is enhanced. However, few catalysts for accelerating the decomposition and producing atomic oxygen for hypochlorite such as sodium hypochlorite are known.

[0003] Incidentally, a catalyst using a carbon-based carrier such as activated carbon as a carrier is known. The main such catalysts are nickel on cobalt and cobalt on activated carbon, known as nickel and cobalt. These catalysts make use of the high surface area of activated carbon and carry nickel and cobalt acting as catalysts on the surface, thereby increasing the reaction field and increasing the activity of the metal catalyst per unit amount. . However, when high concentrations of sodium hypochlorite are used,
When a carbon-based carrier carrying these metals is used as a catalyst, the catalyst is deteriorated due to oxidation of the metal or changes to chlorides, resulting in a problem that the catalyst activity is reduced.

[0004] If a highly active gold-supported catalyst utilizing the high surface area of activated carbon can be obtained, its use is considered to be wide, and it is considered that the catalyst for promoting the decomposition of hypochlorite such as sodium hypochlorite described above is used. Is expected to be useful as a catalyst, but such a catalyst has not been put to practical use. Gold has traditionally been considered not to exhibit catalysis by itself. However, it has recently been gradually revealed that gold also exhibits a catalytic action when used as fine particles. However, the particle size of the fine gold particles having a catalytic action is considered to be several tens nm or less, and it is not easy to produce such fine gold particles.

[0005] Usually, a catalyst in which a metal is supported on a suitable carrier is
It is prepared by supporting a metal compound on a carrier, converting the metal compound into an oxide, and further reducing the oxide with hydrogen or the like. However, hydrogen reduction is performed at relatively high temperatures. Therefore, even if the reduced metal is fine particles immediately after the reduction, the particles grow during the reduction operation, and it is difficult to produce the fine particles. The same applies when the metal is gold. In addition, when the carrier is a carbon-based material such as activated carbon, the carbon-based material may burn, etc., depending on conditions during the reduction treatment at a high temperature, and a carbon-based material such as activated carbon is used as a carrier. ,
It was very difficult to support the metal fine particles thereon.

Accordingly, an object of the present invention is to convert gold fine particles, such as activated carbon, useful as a new catalyst capable of accelerating the decomposition of hypochlorite such as sodium hypochlorite to generate atomic oxygen. To provide a composite supported on a carbon-based substance. It is a further object of the present invention to provide a method for generating atomic oxygen using the above catalyst, and a method for decomposing, sterilizing, etc. using this method.

[0007]

Means for Solving the Problems The present inventors plasma-treat a carbon-based carrier on which a gold-containing compound has been adsorbed,
The present invention was completed by finding that a composite in which gold fine particles were supported on a carbon-based carrier was obtained, and that this composite had a catalytic action to promote the decomposition of hypochlorite.

[0008] That is, the present invention relates to a catalyst for generating atomic oxygen comprising a composite in which gold is supported on a carbon-based carrier. Furthermore, the present invention relates to a method for producing the above-mentioned catalyst of the present invention, and a method for generating atomic oxygen including decomposing hypochlorite in the presence of the above-mentioned catalyst of the present invention. In addition, the present invention includes oxidizing decomposed substances contained in or adhered to the object by bringing the atomic oxygen generated by the method of the present invention into contact with the object. It relates to an oxidative decomposition method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Catalyst The composite of the present invention is a composite in which gold fine particles are supported on a carbon-based carrier. The carbon-based carrier is, for example, activated carbon, and examples of other carbon-based carriers include fibrous carbon.
As the activated carbon, conventional activated carbon can be used as it is. The carbon material used as the raw material of the activated carbon is usually coconut shell, but other than coconut shell, charcoal, sawdust, lignite, coal, pitch, rice hull, old tires and the like may be used. Furthermore, there is no particular limitation on the activation method at the time of producing activated carbon, and activated carbon activated by either gas activation or chemical activation can be used. In addition, activated carbon usually contains
Depending on the shape, there are granulated coal, crushed charcoal, granular charcoal, spherical charcoal, and the like. In the present invention, any shape of activated carbon can be treated.

The gold carried on the composite of the present invention is a fine particle. For example, the average particle diameter of the primary particles determined based on Scherrer's formula (Formula 1) is in the range of 5 to 30 nm, preferably The range of 10 to 25 nm is preferable because the dispersibility is good and the formed composite exhibits high catalytic activity.

[0011]

(Equation 1) (D: particle diameter of crystallite, λ: wavelength of X-ray used for measurement,
θ: Bragg angle, β: spread of half width (rad))

The amount of the fine gold particles carried on the carbon-based carrier is not particularly limited, and can be appropriately adjusted according to the desired catalytic activity. For example, it can be in the range of 0.1 to 5 parts by weight per 100 parts by weight of the carbon-based carrier. However, it is not limited to this range.

Method for Producing Catalyst The catalyst of the present invention can be produced by the following method. That is, by adsorbing the gold-containing compound on the carbon-based carrier and then subjecting the carbon-based carrier to plasma treatment, the adsorbed gold-containing compound can be converted into fine gold particles.

The adsorption of the gold-containing compound onto the carbon-based carrier can be carried out, for example, by immersing the carbon-based carrier in an aqueous solution containing the gold-containing compound and drying. Gold-containing compound, from the viewpoint of easily adsorbing to the carbon-based carrier,
Suitably, the compound has high solubility in an aqueous solution. However, even if the compound has low solubility, a desired amount of the gold-containing compound can be adsorbed by repeatedly immersing in an aqueous solution and drying. Further, the type of the gold-containing compound can be selected in consideration of the adsorptivity to the carbon-based carrier, the ease of conversion to the fine gold particles, and the like. As the gold-containing compound, for example, chloroauric acid, gold hydroxide, gold carbonate,
Examples thereof include gold nitrate, organic acid salt, gold alkoxide, and organic gold complex.

The concentration of the gold-containing compound in the aqueous solution containing the gold-containing compound and the immersion conditions (time, temperature, etc.) can be appropriately determined in consideration of the type of the gold-containing compound, the desired amount of adsorbed gold, and the like. Further, in order to promote the adsorption of the gold-containing compound to the activated carbon, it is preferable that the activated carbon is immersed in an aqueous solution containing the gold-containing compound, stirred, and further allowed to stand for a certain period of time.
The carbon-based support that has been subjected to the adsorption treatment is subjected to a plasma treatment after removing water.

Before the adsorption of the gold-containing compound, the activated carbon to be treated is dehydrated by, for example, heating it under vacuum to promote the adsorption of the gold-containing compound. This vacuum heat treatment is performed, for example, at a temperature of 50 to 600 ° C. and a vacuum
The processing can be performed under the condition of a processing time of 1 to 5 hours or less.

By subjecting the carbon-based carrier to which the gold-containing compound has been adsorbed to a plasma treatment, a composite (catalyst) carrying fine gold particles can be obtained. By this plasma treatment, the gold-containing compound adsorbed on the carbon-based carrier can be converted into gold fine particles. The plasma processing method itself can be a conventionally known method, for example,
A plasma processing method using an electromagnetic wave such as a microwave and an RF plasma processing method described in JP-A-5-220530 and JP-A-9-52042 can be used. Such a plasma treatment can be performed either under reduced pressure or normal pressure. Further, from the viewpoint of converting the gold-containing compound into fine gold particles, the plasma treatment is
It is appropriate to carry out the reaction under reduced pressure, or under reduced pressure or normal pressure and under the flow of an inert gas or a reducing gas such as hydrogen.

The plasma processing using an electromagnetic wave can be performed using, for example, an apparatus as shown in FIG. In the figure,
1 is a microwave generator, 2 is a waveguide, 3 is a processing chamber made of quartz glass, 4 is an isolator, 5 is a three-stub tuner, 6 is a microwave power meter, 7 is a microwave power meter. It is a reflection plunger.
The microwave reflecting plunger 7 is used to reflect the microwave and concentrate the microwave in the processing chamber 3.
A carbon-based carrier on which a metal-containing compound is adsorbed is placed in the processing chamber 3, and a microwave is applied to the carbon-based carrier to generate plasma, whereby the carbon-based carrier is subjected to plasma processing.

The plasma is a group of particles including charged particles such as excited molecules, atoms, ions, and electrons, and as a whole, almost electrically neutral. The plasma is usually 1
It is generated when a gas in the range of about Pa to 1 atm is brought to an extremely high temperature state or is placed under a strong magnetic field or an electromagnetic wave. In the present invention, plasma processing refers to placing a target material in such an environment for a certain period of time.

In the apparatus shown in FIG. 1, plasma can be generated by, for example, reducing the pressure in the processing chamber 3 and irradiating it with electromagnetic waves such as microwaves. It is appropriate to set the degree of vacuum of the processing chamber 3 to about 1 Torr or less from the viewpoint of maintaining the generation of plasma. The electromagnetic wave is preferably in a range from a radio wave to a microwave, and the frequency is approximately 1 GHz to 1000 GHz.
The range of z, usually 1 to 10 GHz, is appropriate. This plasma is a so-called low-temperature plasma utilizing electromagnetic waves such as radio waves and microwaves under reduced pressure.

The catalyst of the present invention prepared as described above is
Gold is supported in the form of fine metal particles and can be used as a catalyst for generating atomic oxygen. Gold is inactive when it has a normal particle size, but exhibits excellent catalytic activity when used as fine particles, as obtained by the method of the present invention.

Atomic Oxygen Generation Method Atomic oxygen can be generated by contacting the above-described catalyst of the present invention with hypochlorite to decompose hypochlorite. The contact between the catalyst and hypochlorite can be performed, for example, by adding the catalyst to an aqueous solution of hypochlorite or by flowing the aqueous solution of hypochlorite through a column filled with the catalyst. . As hypochlorite, for example,
It can be sodium hypochlorite or calcium hypochlorite. In addition, sodium hypochlorite and calcium hypochlorite are commercially available as chemicals. In the case of sodium hypochlorite, it may be generated by electrolyzing a saline solution. The concentration of the hypochlorite as an aqueous solution, the amount of the catalyst used, and the like can be appropriately determined depending on the use.

Atomic oxygen generated by the above method of the present invention has a strong oxidizing power, and by bringing this into contact with the object to be processed, the oxygen contained in or adhered to the object to be decomposed is oxidized. Can be disassembled. As the object to be treated,
For example, drainage, food, tableware, kitchenware, kitchenware, a catering facility, and the like can be given. Examples of the clothes to be decomposed include organic substances, microorganisms (for example, Escherichia coli), and the like. According to the oxidative decomposition method of the present invention, sterilization, deodorization, and the like can be more effectively performed using hypochlorite. That is, various articles can be sterilized using the atomic oxygen generated by the method of the present invention.

[0024]

According to the present invention, it is possible to obtain a catalyst in which gold fine particles are supported on a carbon-based carrier such as activated carbon. The catalyst obtained according to the present invention can generate atomic oxygen from hypochlorite with high efficiency, and is useful for sterilization, deodorization, and the like. Further, according to the present invention, it is possible to obtain a catalyst that maintains good catalytic activity for a long period of time.

[0025]

The present invention will be further described with reference to the following examples. Example 1 Preparation of Activated Carbon Supporting Gold Fine Particles Using a device schematically shown in FIG. 1, a carbon-based carrier on which gold was adsorbed was subjected to plasma treatment. That is, 15 g of commercially available activated carbon was weighed and azeotroped with ion-exchanged water to wash the activated carbon. The washed activated carbon was dried and degassed at 110 ° C. for 3 hours. Tetrachlorogold (III) on the obtained activated carbon
Acid tetrahydrate HAuCl ₄ / 4H ₂ O aqueous solution (0.24 M)
Was added and stirred for 3 hours, and then left at room temperature for 110 hours. Further, the solution was evaporated to dryness and dried at 110 ° C. for 10 hours to obtain activated carbon carrying 1 wt% of gold.

The obtained activated carbon was charged into the processing chamber 3, and the pressure in the processing chamber 3 was reduced to 0.1 torr by a vacuum pump. After the pressure was reduced to a predetermined pressure, the processing chamber was irradiated with a microwave (2.45 GHz) of 300 W for 1 minute to bring the processing chamber into a plasma state. FIG. 2 shows the results of analyzing a sample obtained by irradiation with microwaves for 2 minutes with an X-ray diffractometer RAD-B (manufactured by Rigaku Denki). FIG. 2 confirmed the presence of gold in the metallic state.

Example 2 Measurement of Particle Diameter of Supported Gold A composite was prepared in the same manner as in Example 1 except that the plasma treatment time was changed to 1, 2, 3, or 5 minutes, and gold was added. A composite (catalyst) supporting 1 wt% was obtained. The particle size of the gold supported on the obtained composite (catalyst) was measured by an X-ray powder diffraction method. The crystallite particle size was determined using an X-ray diffractometer RAD-B (manufactured by Rigaku Denki). Table 1 shows the results
Shown in From Table 1, it was confirmed that fine gold particles having a particle size of about 20 nm were supported on activated carbon by the method of the present invention.

(Equation 2) (D: particle diameter of crystallite, λ: wavelength of X-ray used for measurement,
θ: Bragg angle, β: spread of half width (rad))

[0028]

[Table 1]

Example 3 Catalytic activity of atomic oxygen generation The gold loading was carried out in the same manner as in Example 1 except that the concentration of tetrachlorogold (III) tetrahydrate, the immersion time and the number of times of drying were appropriately changed. The amount is 0.1 wt%, 1 wt%, 3 wt%
% Or 5 wt% of the composite was prepared. For each of the prepared composites (catalysts), the ability to generate atomic oxygen from sodium hypochlorite was examined. (1) Examination of supported amount of gold and catalytic ability A round bottom flask and a cooling tube are set in a constant temperature water bath. 3%
0.5 L of a NaCl-containing aqueous NaClO solution (1 ppm) is placed in the flask, and immersed in a 27 ° C. water bath for 30 minutes. Next, each of the composites (catalysts) prepared by the above method is put into an aqueous solution in a 0.1 g flask, and stirring is immediately started. The concentration of NaClO in the reaction solution was quantified by iodine titration. The measurement was performed 5 times in total every hour, the average value was obtained, and the conversion was calculated. The results are shown in FIG. still,
Higher conversion means that the catalyst has better catalytic activity. For reference, the conversion of activated carbon measured by performing a plasma treatment under the same conditions as in Example 1 without carrying gold was about 50%. (2) Time-dependent change in catalytic activity Further, the time-dependent change in catalytic activity of the composite (catalyst) supporting 1 wt% or 3 wt% of gold prepared by the above method was observed. Set the solution tank and the reaction tube in the constant temperature water bath. 0.5 g of each of the above complexes (catalysts) was packed in a reaction tube, and 3% Na was added at a flow rate of 50 ml / min.
A Cl-containing NaClO aqueous solution (1 ppm) was flowed. The solution flowing at regular intervals was collected, the concentration of NaClO was quantified by iodometric titration, and the change in conversion with time was observed. FIG. 4 shows the results. As shown in FIG.
Each of the composites (catalysts) of 3 wt% to 3 wt% converts the plasma-treated activated carbon (not carrying gold) to a conversion rate (about 50%).
%), And was confirmed to have good catalytic activity. Further, as shown in FIG.
It was confirmed that the composite (catalyst) of t% or 3 wt% shows high conversion even after passing through the reaction solution for a long time, that is, maintains high catalytic activity.

Example 4 Examination of Catalyst Durability The catalyst activity durability of the composite (catalyst) supporting 1 wt% of gold prepared in Example 3 was examined. Under the same conditions as in Example 3 (1), the concentration of NaClO in the reaction solution was measured every hour, and this operation was repeated for 30 hours to determine the conversion. FIG. 5 shows the results. FIG.
Thus, it was confirmed that the composite (catalyst) obtained according to the present invention exhibited good catalytic activity over a long period of time. For comparison, the active durability of a composite (catalyst) plasma-treated with nickel and cobalt loaded on activated carbon at 1 wt% each was measured in the same manner. Table 2 shows the results.

[0031]

[Table 2]

Example 5 Difference in catalytic activity depending on the presence or absence of plasma treatment The same as in Example 3 except that the composite carrying 1 wt% of gold prepared in Example 3 (plasma treated) and no plasma treatment were applied. The catalytic activity of each of the composites supporting 1 wt% of gold prepared by the method was measured. Evaluation of the catalyst activity was performed in the same manner as in Example 3 (1). FIG. 5 shows the results. From FIG. 6, it was confirmed that the catalytic activity was significantly improved by performing the plasma treatment.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a plasma processing apparatus used for producing a catalyst of the present invention.

FIG. 2 is a diffraction pattern by RAD-B of the sample obtained in Example 1.

FIG. 3 is a graph showing the correlation between the supported amount of gold fine particles and the catalytic activity.

FIG. 4 is a graph showing the change over time in the catalytic activity of the catalyst of the present invention.

FIG. 5 is a graph showing the catalyst durability of the catalyst of the present invention.

FIG. 6 is a graph showing a difference in catalytic activity before and after plasma treatment.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 1/72 C02F 1/72 Z F term (Reference) 4B021 MC01 MK01 MK08 MP05 4C080 AA07 BB05 MM09 MM40 NN05 QQ11 4D050 AA12 AA15 AB06 AB11 BB07 BC05 BC06 4G042 BA08 BB07 BC06 4G069 AA03 AA08 BA08A BA08B BC33A BC33B CD10 DA05 EA02X EA02Y EA03X EB18X EB18Y FA01 FA02 FB14 FB58

Claims (15)

[Claims] 1. An atomic oxygen generating catalyst comprising a composite in which gold particles are supported on a carbon-based carrier. 2. The catalyst according to claim 1, wherein the average primary particle size of the gold fine particles determined based on the Scherrer's formula is in the range of 5 to 30 nm. 3. The catalyst according to claim 1, wherein the carbon-based support is activated carbon or fibrous carbon. 4. A method for adsorbing a gold-containing compound on a carbon-based carrier,
Next, a method for producing a composite in which gold particles are supported on a carbon-based carrier, comprising converting the gold-containing compound into fine gold particles by subjecting the carbon-containing carrier to which the gold-containing compound is adsorbed to plasma treatment. 5. The method according to claim 4, wherein the carbon-based carrier is activated carbon or fibrous carbon. 6. The production method according to claim 4, wherein the carbon-based carrier is immersed in an aqueous solution containing a gold-containing compound and dried to adsorb the gold-containing compound on the carbon-based carrier. 7. The method according to claim 4, wherein the plasma treatment is performed under reduced pressure or normal pressure. 8. The method according to claim 4, wherein the plasma treatment is performed in an inert gas atmosphere. 9. The manufacturing method according to claim 4, wherein the plasma processing is microwave plasma or RF plasma. 10. A method for generating atomic oxygen, comprising decomposing hypochlorite in the presence of the catalyst according to claim 1. Description: 11. The method according to claim 10, wherein the hypochlorite is sodium hypochlorite or calcium hypochlorite. 12. A method comprising contacting atomic oxygen generated by the method according to claim 10 with an object to oxidize a substance contained in or adhered to the object. Oxidative decomposition method. 13. The method according to claim 12, wherein the object to be treated is drainage, food, tableware, kitchenware, kitchenware, or a catering facility. 14. The method according to claim 12, wherein the substance to be decomposed is an organic substance or a microorganism. 15. A sterilization method using atomic oxygen generated by the method according to claim 10.