JP4125819B2 - Photocatalyst - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocatalyst for the field of oxidation of an organic compound suspended in a gas or liquid (referred to as fluid).
[0002]
[Prior art]
Petrochemical products are increasing and complex pollution of harmful organic compounds has become a problem both inside and outside the living environment. As means for solving this, there is a purification method using oxidative decomposition by a photocatalytic semiconductor.
[0003]
For example, there is a method in which a photocatalytic semiconductor is supported on the surface of a gas constituting an apparatus or device, and the harmful organic substance is brought into contact with the photocatalytic semiconductor by placing the apparatus or apparatus in a fluid in which the harmful organic substance floats. In this case, in order to exert a high photocatalytic function, it is necessary that the surface area of the photocatalytic function layer is large and that the photocatalytic semiconductor is sufficiently activated by electromagnetic waves having excitation wavelengths.
[0004]
For this reason, various proposals have conventionally been made regarding techniques for increasing the surface area of a substrate and film-forming techniques for forming a photocatalytic functional layer (see, for example, JP-A-5-309267 and JP-A-8-196903).
[0005]
[Problems to be solved by the invention]
However, these methods simply increase the surface area, and even if the area of the photocatalytic functional layer increases, the activation rate by the electromagnetic wave of the excitation wavelength is low, or the contact efficiency between the fluid and the photocatalytic semiconductor is poor. .
In addition, in order to form devices and instruments, it is preferable that the base supporting the photocatalytic semiconductor has a flexibility that can be molded, such as press working, or can be rolled or bent. In particular, there is no substrate having such a condition for a substrate made of an inorganic material, and the range in which the photocatalyst can be used is narrow.
[0006]
Accordingly, an object of the present invention is to provide a photocatalyst that can enlarge the surface area of the substrate and can activate the photocatalytic functional layer formed on the surface thereof almost uniformly, and that increases the contact efficiency between the fluid and the photocatalytic semiconductor. It is to be.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention employs a technical means of having a base having a plain woven wire mesh and a metal nonwoven fabric fixed to the surface thereof, and a photocatalytic functional layer formed on the surface of the base. .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be described below with reference to the drawings.
FIG. 1 is a front view of a photocatalyst according to an embodiment of the present invention.
In the figure, 1 is a photocatalyst, 2 is a substrate, 3 is a plain woven wire mesh, 4 is a metallic nonwoven fabric, and 5 is a photocatalytic functional layer. A cross section of the metallic nonwoven fabric is shown in FIG.
[0009]
The base 2 is a plain weave wire mesh 3 made of a metal material and a metal wire or metal fiber having a diameter of 10 to 50 μm cut into a length of several millimeters to several tens of millimeters to form a short fiber having a density ratio on the metal mesh. For example, it is sprayed so as to be 90%, and a load of 5 to 50 g / cm ² is applied thereto (or the area of the fiber intersection may be increased by rolling before sintering the short fiber as another method), for example And a metal nonwoven fabric 4 formed by sintering at 1000 to 1150 ° C. for 30 minutes to 8 hours in a hydrogen atmosphere (even in vacuum). In addition, the metallic nonwoven fabric may be rolled after sintering (rolling ratio 20 to 50%), thereby improving the mechanical strength. In the metal nonwoven fabric, the crossed portion of the short fibers is sintered and fixed, so that a strong nonwoven fabric can be obtained. Further, since the metallic nonwoven fabric is supported by a wire mesh, the substrate has a high mechanical strength. As the metal material, for example, austenitic stainless steel, or any one selected from Al, Ti, Cu and alloys thereof can be used. Cu itself has antibacterial properties, Ti and stainless steel are excellent in rust prevention and durability, and an aluminum alloy is rust prevention and lightweight at the same time.
The metal nonwoven fabric has a thickness of 0.1 to 4 mm, has a fiber structure equivalent to the surface direction in the cross-sectional direction, and the size of the opening in the surface direction is larger than 10 μm.
If the thickness of the metal nonwoven fabric is too thick, the weight increases. On the other hand, if the thickness is too thin, the mechanical strength decreases. Moreover, as for the opening of a metal nonwoven fabric, it is desirable that the hole diameter is 50-1000 micrometers.
[0010]
The photocatalytic functional layer 5 is made by adhering a sol solution mixed with a photocatalytic semiconductor such as TiO _{2 to} the surface of the substrate by spraying or dipping, drying, and baking at a temperature of 50 ° C. to less than 500 ° C. Can be formed.
It should be noted that in addition to the photocatalytic semiconductor, amorphous titanium peroxide or titanium oxide in the sol is mixed at a titanium weight ratio (dry amount) of 1: 1 or 1: 5 at a relatively low temperature. The particles can be firmly supported.
[0011]
Furthermore, in order to improve the decomposition performance by oxidation reduction by adding a small amount of particles of Pt, Ag, Rh, RuO ₂ , Nb, Cu, Sn, and NiO to supplement functions such as antifungal sterilization and adding an adsorption function One or more inorganic materials such as zeolite, silica (silicon dioxide), alumina, zinc oxide, magnesium oxide, rutile type titanium oxide, zirconium phosphate, or various activated carbons, porous phenol resin or melamine resin can do.
[0012]
Alternatively, the photocatalytic functional layer can be formed after a surface treatment for forming a protective film by spraying a protective material such as a titanium peroxide aqueous solution on the surface of the substrate. In any case, if a film is formed in advance with PTA (oxysan tynic / titanium / acid ... titanium peroxide aqueous solution), the adhesion and ductility of the TiO ₂ sol solution will be improved and it will be easy to get wet. The photofunctional layer can be formed uniformly and widely. PTA has excellent spreadability even when the substrate is a metal such as stainless steel, and is effective for applying a TiO ₂ sol solution widely and uniformly. PTA also functions as a binder, but it does not include ceramic materials in composition and has good compatibility with metals, so the photocatalytic functional layer formed on the surface of the substrate peels even if the substrate is bent or vibrated There are few things.
[0013]
ZnO are other as a photocatalyst _{semiconductor, SrTiO 3, CdS, CdO,} CaP, InP, In 2 O 3, CaAs, BaTiO 3, K 2 NbO 3, Fe 2 O 3, Ta 2 O 5, WO 3, SaO 2, Examples include Bi ₂ O ₃ , NiO, Cu ₂ O, SiC, SiO ₂ , MoS ₂ , MoS ₃ , InPb, RuO ₂ , and CeO ₂ . Of these, titanium oxide TiO ₂ (anatase type) is inexpensive, has stable characteristics, is harmless to the human body, and is the most excellent as a photocatalyst.
[0014]
The catalytic function of the photocatalytic semiconductor is that electron cleavage occurs in the semiconductor by irradiating an excitation wavelength (electromagnetic wave of excitation wavelength, ultraviolet region in the case of TiO ₂ ) that is higher than the band gap of a semiconductor such as metal oxide, and OH is formed on the surface. An active radical hydroxyl group or active oxygen of-or O _2- is generated, and an organic compound in contact with these is decomposed by oxidation or reduction action. This makes it possible to clean off bad odors and oil stains. Moreover, bacteria and viruses can be killed (sterilized) by the same function.
[0015]
With the structure of the present invention, the surface area of the photocatalytic functional layer is large, and electromagnetic waves with an excitation wavelength irradiated from the outside easily reach particles in the deep part of the photocatalytic functional layer, and the photocatalytic functional layer is activated in a wide range. Is done. In addition, since the fluid passing through such a layered structure portion hits the wall of the layered structure and is reflected or enters the recess and temporarily stays there, there are many opportunities for the organic matter floating in the fluid to come into contact with the photocatalytic semiconductor. . For this reason, a photocatalyst body becomes a high performance thing.
[0016]
The photocatalyst body configured as described above can be used in various forms, but may be used by forming a photocatalytic functional layer on both surfaces of a single flat substrate. In this case, an electromagnetic wave supply source with an excitation wavelength is arranged along both side edges of the flat plate, one surface (front) of the flat plate is irradiated with the electromagnetic wave supply source with one excitation wavelength, and the other electromagnetic wave supply source with an electromagnetic wave with the other excitation wavelength. The surface (back) can be irradiated.
[0017]
In the present invention, the photocatalyst can be used as various filters because the substrate has a large number of fine through holes. Not only a filter as an element, but also an inner wall of a cabinet that is sealed like a refrigerator, and when used as a gas filter that circulates in the cabinet, vegetables and fruits such as ethylene gas are extracted from the air in the cabinet. It can remove harmful gases that are worn out, and can remove unpleasant odors such as hydrogen sulfide and mercaptans. In this case, since the inner wall functions as a filter, the volume in the cabinet is not reduced and the filter does not get in the way compared to the case where the filter is separately provided in the cabinet.
[0018]
In addition, such a photocatalyst can have a silencing function, a visual shielding function, or a function of wave suppression and defoaming when the fluid is in a liquid phase, as well as a cleaning function.
Silencing is, for example, the case where the photocatalyst is used as a boundary wall plate that separates the roadway and the human road on the road, and NOx and SOx are decomposed and removed by the photocatalytic functional layer, and at the same time, the base is made of a metal nonwoven fabric. The sound wave is guided to the complicated internal space of the metal nonwoven fabric and the propagation energy is absorbed.
The visual shielding function is a function of blocking the passage of light, and this makes it possible to use the photocatalyst body as a partition or the like. In addition, wave quenching is similar to sound wave absorption. The wave of the liquid makes the opportunity of contact between the organic compound floating in the liquid and the photocatalytic semiconductor nonuniform, but the fluid temporarily stops in the internal space of the metal nonwoven fabric due to the metal nonwoven fabric, and the contact with the photocatalytic semiconductor. Contact opportunities are almost uniform.
[0019]
In addition, the photocatalyst body of the present invention can be used for an air conditioner, an exhaust gas processing apparatus body or filter, a toilet wall, an indoor wall board for construction, an algae-proof aquarium wall, a swimming pool wall, and the like.
[0020]
【Example】
Example of production of photocatalyst (Example 1)
As a substrate, a metal nonwoven fabric (thickness: 0.00%) was prepared by spreading SUS fibers having a diameter of 20 μm and a length of 5 mm on a plain woven wire mesh made of SUS316, sintering at 1100 ° C. for 5 hours, and rolling (rolling ratio 50%). The one having a size of 2 mm and an opening size of 70 μm (average value) in the surface direction was used. FIG. 3 is a schematic view showing SUS fibers, and FIG. 4 is a schematic view showing SUS fibers rolled after sintering. It can be seen from FIG. 4 that the crossed portions of the sintered SUS fibers are fixed to each other.
[0021]
Next, as a photocatalytic functional material, an armofas type titanium peroxide aqueous solution (0.84 w%): anatase type titanium oxide aqueous solution (0.84 w%): colloidal silica aqueous solution (0.84 w%) was used in a ratio of 3: 7: 0.1. Mixing at a ratio, spraying 0.7 g / 25 cm ² (wet state) on the surface of the substrate. Then, after drying at room temperature, it was dried by heating (300 ° C. × 1 hr) to obtain a photocatalyst.
[0022]
(Example 2)
As an adsorption / photocatalyst functional material, amorphous titanium peroxide aqueous solution (0.84%): anatase titanium oxide aqueous solution (0.84%): colloidal silica aqueous solution (0.84%): coconut shell activated carbon (in terms of weight of other aqueous solution) ) At a ratio of 3: 3: 0.1: 0.3 and spraying 0.6 g / 25 cm ² (wet state) on the surface of the substrate of Example 1. The whole was heat-dried (300 ° C. × 1 hr) to obtain a photocatalyst.
[0023]
FIG. 5 shows a photocatalyst device 9 in which a photocatalyst body 1 configured as a flat plate is fitted in a frame 7 and a fluorescent lamp 8 is integrated as an electromagnetic wave supply source of excitation wavelength. The photocatalyst body 1 is the same as that shown in Example 1, and the frame 7 is made of stainless steel and has a rectangular shape. The frame material constituting the vertical frames on both sides includes a space for storing the fluorescent lamp 8.
Therefore, when the frame 7 is viewed from above, it becomes a long rectangle corresponding to the cross-sectional shape, but the flat photocatalyst 1 is disposed along the diagonal line. With this structure, one fluorescent lamp 8 irradiates one surface (front) of the photocatalyst body 1 and the other fluorescent lamp 8 irradiates the other surface (back) to activate the photocatalytic functional layer on each surface. . The ultraviolet light from the fluorescent lamp 8 is irradiated to the surface of the photocatalyst body 1 from one side, but the surface of the photocatalyst body 1 is reflected by the uneven surface of the metal nonwoven fabric, and the ultraviolet light is also applied to the shadowed portion when viewed from the fluorescent lamp side. The front surface of the photocatalytic function layer on the surface of the photocatalyst body is almost activated, and an efficient photocatalytic function is exhibited.
Since this photocatalyst device 9 has air permeability, it can be used not only as a filter but also as a partition that also serves as a purifier for indoor air.
[0024]
FIG. 6 shows a low-temperature storage chamber 10 for storing vegetables and the like in cross section. The low temperature storage chamber 10 is hermetically sealed by a door (not shown), but the flat photocatalyst 1 shown in the first embodiment is attached in the form of a lining with a space 12 inside a box-shaped outer wall 11. ing. In the space 12 of the ceiling portion, a flat plate-like reflector 13 is arranged in a diagonal arrangement, and fluorescent lamps 8 as ultraviolet ray supply sources are arranged on both sides thereof.
As shown in FIG. 7A, the flat reflector 13 is formed with reflecting pieces 14 on both sides, and reflects the ultraviolet rays from the fluorescent lamps 8 on both sides in the same direction, that is, the direction of the photocatalyst 1 on the ceiling. In addition, when a photocatalyst functional layer exists on both surfaces of the panel as in the central partition, a reflecting plate 13 having a reflecting layer 18 on both surfaces is used as shown in FIG. 7B.
The reflective layer 18 is constituted by, for example, a stack of SUS particles baked on both surfaces of a stainless steel plate 19. The particles are densely arranged with a small diameter on the steel plate 19 side and a large diameter on the side away from the substrate.
In the space 15 of the wall portion, an elliptically curved reflecting plate 16 having a mirror surface inside, and a fluorescent lamp 8 as an ultraviolet ray supply source are arranged inside the central portion. The spaces 13 and 15 communicate with ducts 17 on both sides of the ceiling, and the internal air of the storage chamber 10 circulates through the photocatalyst body 1 that is an inner wall by a circulation pump. Then, when passing through the photocatalyst 1, an organic compound which is inconvenient for preservation of vegetables such as ether and odor floating in the air is decomposed by oxidation / reduction action.
The photocatalyst body 1 as the inner wall can be formed into a container shape all at once by press working, instead of combining the flat plates when the substrate 2 has moldability as in the embodiment. If peeling of the photocatalytic functional layer becomes a problem, the photocatalytic functional layer may be formed after pressing the substrate 2.
[0025]
FIG. 8 shows an example in which the photocatalyst body 1 is used as a countermeasure against deodorization in a toilet, and the photocatalyst body 1 that is a flat plate is attached to the ceiling. Reference numeral 8 denotes a fluorescent lamp, which is an ultraviolet ray supply source. In the indoor space of the toilet, indoor air is always flowing by a normal ventilation device, and the floating organic compound that is the source of odor on the airflow collides with the photocatalyst 1 and is decomposed by the photocatalytic functional layer. Since the surface of the photocatalyst body 1 has an uneven laminated structure with voids, the photocatalyst body 1 is easily decomposed during contact with floating organic compounds or passing through the pores, thereby receiving a photocatalytic function, thereby improving the deodorizing effect.
[0026]
【The invention's effect】
According to the present invention, the photocatalyst body has many voids and irregularities in the surface layer portion, the photocatalyst functional layer has a large area, a large oxidation / reduction power, and a contact opportunity between the organic compound floating in the fluid and the photocatalyst functional layer. Therefore, a photocatalyst with high performance can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view of a photocatalyst according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a cross section of a metallic nonwoven fabric.
FIG. 3 is a schematic view showing a SUS fiber.
FIG. 4 is a schematic view showing a sintered SUS fiber.
FIG. 5 is a perspective view showing a flat photocatalytic device.
FIG. 6 is a front view showing the cryogenic storage in a cut state.
7A and 7B are plan views showing examples of reflectors.
FIG. 8 is a front view schematically showing a use form in a toilet.
[Explanation of symbols]
1 Photocatalyst body, 2 substrate, 3 wire mesh, 4 metal nonwoven fabric, 5 photocatalyst functional layer

Claims (3)

A photocatalyst comprising a substrate having a plain woven wire mesh and a metal nonwoven fabric fixed to the surface thereof, and a photocatalytic functional layer formed on the surface thereof. The photocatalyst body according to claim 1, wherein the metal nonwoven fabric has a pore diameter of 50 to 1000 μm. The plain weave wire mesh is formed of stainless steel or a wire made of any one metal material selected from Al, Ti or Cu and alloys thereof, and the metal nonwoven fabric is made of stainless steel or Al, Ti or Cu and The photocatalyst body according to claim 2, wherein the photocatalyst body is produced by spraying and sintering fibers made of any one metal material selected from the alloys.

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