JP2006088069A - Photocatalytic body, manufacturing method for the same and photocatalytic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalytic body showing high activity when a substance to be decomposed is decomposed by irradiating the photocatalytic body with light of a visible light range, a method for manufacturing the photocatalytic body and a photocatalytic device. <P>SOLUTION: The photocatalytic body is manufactured by mixing 0.01-1.0 mass% manganese dioxide having 1-50 nm average particle size with titanium oxide having 1-100 nm average particle size. A desired activity result can be achieved when the substance to be decomposed is decomposed by irradiating the photocatalytic body with light of the visible light range. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photocatalyst having a high decomposition activity not only in the ultraviolet region but also in the visible light region, a photocatalyst apparatus using the photocatalyst, and a method for producing the photocatalyst.

  Conventionally, titanium oxide has been known as a photocatalyst, but the light that can impart decomposition activity to titanium oxide is visible light that is near ultraviolet light of 380 nm or less included as part of sunlight or indoor illumination light. (400 to 750 nm) cannot be used, and thus there is a problem that the light utilization efficiency is low.

  As a means for solving such a problem, an invention is proposed in which a part of the oxygen site of the titanium oxide crystal is replaced with a nitrogen atom, thereby absorbing visible light and decomposing an organic substance adhering to or contacting the photocatalyst. (See Patent Document 1).

However, in this method, it is necessary to perform heat treatment in a reducing atmosphere in the photocatalyst formation process. For this reason, the primary particle of the photocatalyst grows, the specific surface area of the photocatalyst is reduced, the contact area with the organic substance is reduced, and there is a problem that the decomposition activity on the organic substance is reduced.
Japanese Patent Laid-Open No. 2004-988

  The present invention has been made to solve such problems, and an object thereof is to provide a photocatalyst exhibiting a high decomposition activity even in the visible light region, a photocatalyst apparatus using the photocatalyst, and a method for producing the photocatalyst. And

The photocatalyst according to claim 1 is characterized in that 0.01 to 1.0 mass% of manganese dioxide having an average particle diameter of 1 to 50 nm is mixed with titanium oxide having an average particle diameter of 1 to 100 nm.
A photocatalyst device according to claim 2 is characterized in that the photocatalyst body according to claim 1 is attached to a porous support substrate.
The method for producing a photocatalyst according to claim 3 includes a solution step in which manganese carbonate is dissolved in a dilute solution of a strong acid, and slurry formation in which titanium oxide is dispersed in the sol obtained in the solution step. And a pulverization step in which the slurry obtained in the slurrying step is dried to form powder.

Titanium oxide includes anatase type, brookite type, and rutile type due to the difference in crystal structure. The anatase type and brookite type titanium oxide has a band gap energy of about 3.20 eV, which is 388 nm in terms of wavelength.
However, the present inventors have confirmed through experiments that when manganese dioxide is added to the anatase-type and brookite-type titanium oxide, the band gap energy is reduced and the degradation activity is exhibited even in the visible light region.

The present invention has been made based on such findings, and is characterized by mixing a small amount of manganese dioxide with titanium oxide.
The photocatalyst of the present invention is activated and exhibits photocatalytic activity in any region of visible light having a wavelength of 400 nm or more and ultraviolet light having a wavelength of 380 nm or less.
In addition, when titanium oxide alone is irradiated with light, electrons and holes appear on the surface, but when titanium dioxide is mixed with manganese dioxide and irradiated with light, electrons appear on the surface of manganese dioxide, and on the surface of titanium oxide. Holes appear and electrons and holes are less likely to recombine than with titanium oxide alone.

  Therefore, in the present invention, electrons and holes can exist for a longer time than in the case of titanium oxide alone, and the decomposition activity can also be enhanced by this.

  The average particle diameter of the titanium oxide used in the present invention is 1 to 100 nm, preferably 5 to 30 nm. If the average particle size is less than 1 nm, production becomes difficult, and if the average particle size exceeds 100 nm, the specific surface area becomes small and sufficient decomposition activity cannot be obtained.

The average particle diameter of manganese dioxide used in the present invention is 1 to 50 nm, preferably 3 to 10 nm. If the average particle size is less than 1 nm, production becomes difficult, and if the average particle size exceeds 50 nm, the specific surface area becomes small and sufficient decomposition activity cannot be obtained.
The compounding quantity of manganese dioxide is 0.01-1.0 mass% of a photocatalyst body (total amount of titanium oxide and manganese dioxide).

  The photocatalyst of the present invention can be produced, for example, by the following method.

First, manganese carbonate (MnCO ₃ .nH ₂ O) is dissolved in a dilute acid of strong acid such as sulfuric acid, hydrochloric acid or nitric acid so as to be 10 to 20% by mass to obtain a sol in which colloidal particles of manganese dioxide are dispersed. Nitric acid is suitable as the strong acid, and the pH of the dilute acid of the strong acid is about 0 to 1.
At this time, a chelating agent or a surfactant may be added in order to disperse the colloidal particles generated in the liquid medium to obtain a stable sol.

  Titanium oxide particles are dispersed in the manganese dioxide sol thus obtained to prepare a 2.5 to 10% by mass slurry. Thereafter, the slurry is washed with water as necessary, and is heat-dried at 100 to 300 ° C. with an acid resistant dryer to obtain the photocatalyst of the present invention as powder.

  This photocatalyst body can be provided with photocatalytic activity by placing it together with an object to be processed in a glass container that transmits visible light and irradiating visible light having a wavelength of 400 nm or more with a light source. The irradiation time may be appropriately selected according to the light intensity of the light source and the type and concentration of the object to be processed. The light source is not limited as long as it can irradiate visible light having a wavelength of 400 nm or more. For example, sunlight, fluorescent lamp, halogen lamp, black light, xenon lamp, mercury lamp, sodium lamp or cold cathode lamp Etc. can be used.

  Moreover, this photocatalyst body can be dispersed in an appropriate dispersion medium to form a slurry, which can be attached to a porous support substrate having an arbitrary shape and dried to form a photocatalyst device. As a solvent for adjusting the photocatalyst body, a solvent that does not dissolve manganese dioxide present on the surface of titanium oxide and does not evaporate after coating and remains in the photocatalyst body is preferable. Specific examples of the solvent include water or alcohol.

  What is necessary is just to select photocatalyst body content suitably according to the kind of support base material which is application object, the film thickness to apply | coat, etc., and is about 2.5-10 mass%.

In this slurry, an appropriate amount of an appropriate binder can be mixed in order to bind the fine particles of the photocatalyst to increase the mechanical strength of the photocatalyst film. Such binder include a silicone _resin, may be used one or more of such SiO 2, ZrO _2, and _Al 2 _{O 3.} Although these substances bind well between the fine particles of the photocatalyst, they have a high transmittance with respect to ultraviolet light and visible light, so that the decomposition activity of the photocatalyst film is hardly inhibited.

  If the amount of the binder is too large, the photocatalyst fine particles are embedded in the binder and it is difficult to exert the photocatalytic action. If the amount is too small, the required binding force cannot be obtained. %, Preferably 7 to 15% by mass.

  The binder may be in the form of being melted and solidified to bind between photocatalyst fine particles and a support such as a lighting product, or in the form of being bonded by van der Waals force in an ultrafine particle state. It may be.

  By mixing the binder in this manner, it is possible to form a photocatalytic film having high mechanical strength while maintaining strong decomposition activity.

  The film thickness of the photocatalyst formed on the support substrate of the photocatalyst device is preferably about 0.1 to 10 μm. When the film thickness of the photocatalyst is less than 0.1 μm, sufficient decomposition activity cannot be obtained, and when it exceeds 10 μm, sufficient mechanical strength, light transmittance, and decomposition activity cannot be obtained.

  Next, it is applied to a porous support substrate by a flow coating method or a dipping method, and dried to form a photocatalytic film of about 1 to 10 μm. The photocatalyst film can be applied by using various known film forming methods, for example, spraying, dipping, brushing, electrostatic adsorption, or the like, by room temperature, low temperature heating or high temperature heating baking. .

  Specific examples of the porous support substrate include filters such as an air cleaner and a vacuum cleaner. Specific examples include a ceramic filter, an alumina filter, and an aluminum expanded metal. By coating such a household appliance filter, for example, formaldehyde generated from a new building material can be decomposed and removed.

  The photocatalytic film formed on the porous support substrate has an ultraviolet light transmittance of 20 to 50% at a wavelength of 360 nm, a visible light transmittance of 40 to 80% at a wavelength of 400 nm, and a visible light transmittance of 80 to 95 at a wavelength of 450 nm. % Range is desirable.

According to the photocatalyst of the present invention, sufficient decomposition activity can be obtained for ultraviolet light and visible light.
The photocatalyst of the present invention is effective not only for decomposition of organic gas but also for antifouling. In particular, since the unevenness of the surface of the photocatalyst film is fine, there is an effect that dirt particles are difficult to adhere, which contributes to the antifouling effect.

  According to the photocatalyst body of the present invention, it is possible to obtain a decomposition activity effect of a desired substance to be decomposed when irradiated in the visible light region.

  Next, the present invention will be described more specifically with reference to the following examples and evaluation results thereof. However, the present invention is not limited to this embodiment.

  The physical properties of the photocatalyst were measured by the following method.

  First, 10 g of manganese carbonate was dissolved in 90 g of nitric acid. Next, a chelating agent or a surfactant was added to prepare a manganese sol. 20 g of titanium oxide fine particles (ST-01 manufactured by Ishihara Sangyo Co., Ltd.) were added to 100 g of the manganese sol, and stirred at normal temperature and pressure. The mixture was further reduced in pressure with stirring, dried by evaporating moisture, baked in air at 300 ° C. for 1 hour, and then slowly cooled to room temperature in air to carry manganese oxide on the surface of the titanium oxide particles. A photocatalyst was obtained. This photocatalyst had a water content of 10% by mass.

[Evaluation of photocatalyst]
The photocatalyst thus obtained was irradiated with visible light to evaluate the decomposition activity of acetic acid.

First, a glass petri dish was placed in a 1 m ³ hermetic glass container, and 200 g of the photocatalyst was placed thereon. The container was filled with 100 ppm formaldehyde and irradiated with visible light from the outside. For irradiation with visible light, a light source device equipped with a 10 W cold cathode lamp (manufactured by Harrison Toshiba Lighting Co., Ltd.) and a filter that cuts off ultraviolet light having a wavelength of about 400 nm or less was used as a light source.

  Since carbon dioxide is generated when acetic acid is decomposed by irradiation with visible light, the carbon dioxide concentration in the container was measured by gas chromatography to evaluate the catalytic activity of the photocatalyst against acetic acid. The carbon dioxide concentration in the container after light irradiation for 1 hour was 50 ppm.

  In this example, the decomposition activity of the photocatalyst is evaluated by irradiating visible light. However, when visible light and ultraviolet light are irradiated without cutting the ultraviolet light, a higher photocatalytic effect can be obtained.

  The photocatalyst body of the present invention can be applied to filters such as air cleaners, air conditioners, and vacuum cleaners. In the unit, a filter coated with this photocatalyst is combined with a visible light lamp and placed in an air flow path to exhibit an air cleaning function.

Claims (3)

  A photocatalyst obtained by mixing 0.01 to 1.0 mass% of manganese dioxide having an average particle diameter of 1 to 50 nm with titanium oxide having an average particle diameter of 1 to 100 nm.   A photocatalyst device comprising the photocatalyst body according to claim 1 attached to a porous support substrate. A solution process for dissolving manganese carbonate in a dilute solution of strong acid;
A slurrying step in which titanium oxide is dispersed in the sol obtained in the solution step to form a slurry;
A method for producing a photocatalyst, comprising: a step of drying the slurry obtained in the slurrying step to obtain a powder.