JP2009219958A - Oxidative decomposition method using photocatalyst and water purification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxidative decomposition method using a photocatalyst the photocatalytic function of which can be improved, and to provide a water purification apparatus. <P>SOLUTION: When oxidative decomposition is performed by using a photocatalyst layer consisting of a carbon-doped metal oxide layer arranged on the surface of a metal-made base body, the photocatalyst layer is kept in an electric potential-imparted state. The photocatalyst layer is a carbon-doped titanium oxide layer or a carbon-doped titanium alloy oxide layer and is formed by heat-treating the surface of the base body, the surface layer of which consists of titanium, a titanium alloy, a titanium alloy oxide, titanium oxide or the like at the least, in such an atmosphere that chemical pieces containing carbon and oxygen are supplied to the surface of the base body. The photocatalyst layer thus formed is a dense layer, is integrated with the base body and has excellent electrical conductance with the base body. As a result, an overvoltage can be restrained and an energy loss can be decreased when an electric potential is imparted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photocatalyst, in particular, an oxidative decomposition method and a water purification apparatus using a photocatalyst for improving the oxidative decomposition ability of a photocatalyst composed of a carbon-doped metal oxide layer provided on the surface of a metal substrate.

Conventionally, titanium dioxide TiO ₂ (simply referred to as titanium oxide in the present specification and claims) is known as a substance exhibiting a photocatalytic function. In addition, when manufacturing photocatalyst products that can provide deodorizing, antibacterial, antifogging and antifouling effects by such photocatalytic function, titanium oxide sol is generally applied to the substrate by spray coating, spin coating, dipping, etc. Film formation.

  In addition, in order for titanium oxide to function as a photocatalyst, ultraviolet light having a wavelength of 400 nm or less is necessary. In order to improve the photocatalytic function or to exhibit the photocatalytic function by visible light, titanium oxide doped with other elements Various photocatalysts have been studied, a titanium compound obtained by substituting the oxygen site of titanium oxide with an atom such as nitrogen or an anion X, a titanium compound obtained by doping an atom such as nitrogen or an anion X between the lattices of the titanium oxide crystal, Or the photocatalyst which consists of titanium compound Ti-O-X which arrange | positions atoms, such as nitrogen, or anion X to the grain boundary of the polycrystalline aggregate of a titanium oxide crystal is proposed (refer patent documents 1-4 etc.). For practical use, it is necessary to further improve the characteristics.

  On the other hand, the present applicant has found that carbon-doped titanium oxide, carbon dome hafnium oxide, carbon-doped zirconium oxide produced by a special production method has a photocatalytic function that also responds to visible light, and filed earlier. (Refer patent documents 5-8 etc.).

  However, of course, there is a demand for improving the photocatalytic function as much as possible for practical use.

JP 2001-205103 A (Claims) JP 2001-205094 A (Claims) JP 2002-95976 A (Claims) WO 01/10553 pamphlet (claims) Japanese Patent No. 3948738 (Claims) Japanese Patent No. 4010558 (Claims) JP 2007-270316 A (Claims) JP 2007-270318 A (Claims)

  This invention makes it a subject to provide the oxidative decomposition method and water purification apparatus by a photocatalyst which can improve a photocatalytic function in view of the situation mentioned above.

  A first aspect for solving the above-described problem is that a potential is applied to the photocatalyst layer when oxidative decomposition is performed using a photocatalyst layer made of a carbon-doped metal oxide layer provided on the surface of a metal substrate. It is in the oxidative decomposition method by the photocatalyst characterized by the above-mentioned.

  In the first aspect, the oxidative decomposition power can be improved by performing the oxidative decomposition in a state where a potential is applied to the photocatalyst layer formed of the carbon-doped metal oxide layer provided on the surface of the metal substrate.

  According to a second aspect of the present invention, there is provided the photocatalytic oxidative decomposition method according to the first aspect, wherein the photocatalyst layer is irradiated with ultraviolet to visible light from a light source.

  In the second aspect, the photocatalytic function of the photocatalyst layer can be reliably functioned by irradiating ultraviolet to visible light from the light source.

  According to a third aspect of the present invention, in the oxidative decomposition method using the photocatalyst according to the first or second aspect, the photocatalyst layer is immersed in the water to be treated to purify the water to be treated. It is in the oxidative decomposition method.

  In the third aspect, the water to be treated can be efficiently purified.

  According to a fourth aspect of the present invention, in the oxidative decomposition method using a photocatalyst according to any one of the first to third aspects, the metal is at least selected from titanium, hafnium, zirconium, and an alloy mainly composed of these. It is in the oxidative decomposition method by the photocatalyst characterized by being 1 type.

  In the fourth aspect, the oxidative decomposition can be efficiently performed by the photocatalyst layer on the surface of the metal substrate that is at least one selected from titanium, hafnium, zirconium, and alloys mainly composed of these.

  According to a fifth aspect of the present invention, in the method for oxidative decomposition using a photocatalyst according to the fourth aspect, the photocatalyst layer contains carbon in a state of metal-carbon bonds. It is in the decomposition method.

  In the fifth aspect, since the carbon contained in the photocatalyst layer is contained in a metal-carbon bond state, the durability and the photocatalytic function of the photocatalyst layer are further improved.

  According to a sixth aspect of the present invention, in the oxidative decomposition method using a photocatalyst according to the fourth or fifth aspect, the photocatalyst layer supplies the surface of the metal substrate with a chemical species containing carbon and oxygen. The photocatalytic oxidative decomposition method is characterized by being formed by heat treatment in an atmosphere.

  In the sixth aspect, the photocatalyst layer composed of the carbon-doped metal oxide layer provided on the surface of the metal substrate can be more reliably manufactured by the predetermined heat treatment.

  7th aspect of this invention is the water purification apparatus which purifies the to-be-processed water, Comprising: The processing container which hold | maintains to-be-processed water at least temporarily, The carbon dope metal oxide provided in the surface of metal base | substrates A water purification apparatus comprising: a photocatalyst layer comprising a layer and arranged to contact water to be treated held in the treatment vessel; and a power source for applying a potential to the photocatalyst layer.

  In such a seventh aspect, by treating the water to be treated with a potential applied to the photocatalyst layer composed of the carbon-doped metal oxide layer provided on the surface of the metal substrate, impurities contained therein can be efficiently removed. Therefore, the water to be treated can be purified with certainty.

  An eighth aspect of the present invention is the water purification apparatus according to the seventh aspect, further comprising a light source that irradiates the photocatalyst layer with ultraviolet to visible light.

  In the eighth aspect, by irradiating ultraviolet to visible light from the light source, the photocatalytic function of the photocatalyst layer can be reliably functioned, and purification can be performed more reliably.

  According to a ninth aspect of the present invention, in the water purification apparatus according to the seventh or eighth aspect, the treatment container includes an introduction port for introducing the water to be treated and a discharge port for discharging the treated water. It is in the water purification apparatus characterized by comprising.

  In the ninth aspect, the water to be treated can be introduced from the inlet of the processing container and discharged from the outlet, so that the water to be treated can be purified efficiently.

  According to a tenth aspect of the present invention, there is provided the water purification apparatus according to the ninth aspect, further comprising means for continuously introducing the water to be treated into the treatment container.

  In the tenth aspect, a large amount of water to be treated can be continuously purified by continuously introducing the water to be treated into the treatment container, and the purification rate can be increased by circulating treatment. Can do.

  The photocatalyst layer composed of the carbon-doped metal oxide layer provided on the surface of the metal substrate used in the present invention is described in Patent Documents 5 to 7 described above, and detailed description thereof is omitted. Briefly described.

  Examples of such a photocatalytic layer include carbon-doped carbon-doped titanium oxide layers or carbon-doped titanium alloy oxide layers, carbon-doped carbon-doped zirconium oxide layers or carbon-doped zirconium alloy oxide layers, and carbon-doped carbon. Examples thereof include a doped hafnium oxide layer or a carbon-doped hafnium alloy oxide layer. Such a photocatalyst layer has, for example, at least a surface layer of titanium, titanium alloy, titanium alloy oxide, titanium oxide, zirconium, zirconium alloy, zirconium alloy oxide, zirconium oxide, hafnium, hafnium alloy, hafnium alloy oxide, oxidation The surface of the substrate made of hafnium or the like can be formed by heat treatment in an atmosphere in which chemical species including carbon and oxygen are supplied to the surface. Such a photocatalyst layer is a dense layer unlike a coating layer formed by thermal spraying of ceramic, and is integrated with the substrate, and has good electrical conductance with the substrate. Thereby, there is an advantage that an overvoltage at the time of applying a potential can be suppressed and energy loss can be reduced.

Moreover, it is preferable that this photocatalyst layer is doped in a state where carbon is in a metal (M) -C bond. That is, in the photocatalyst layer, carbon is doped so as to replace oxygen of the metal oxide M _x O _y , and an MC bond is generated. The presence of the MC bond in this way significantly improves the durability and improves the characteristics as a photocatalyst.

  In addition, about the shape of a base | substrate, it can select according to the use to be used, and plate shape, a wire, or a rod shape etc. can be mentioned. Moreover, the shape which increases a surface area, for example, the shape which has many fins on the surface, and a powder form may be sufficient if the state which can apply an electric potential is ensured.

  Further, the photocatalyst layer is, for example, disclosed in Japanese Patent No. 4010558, where a layer in which fine columns made of titanium oxide or titanium alloy oxide are exposed is exposed, or titanium oxide or titanium alloy is formed on the thin film. A large number of continuous narrow protrusions made of oxide and fine pillars standing on the protrusions are exposed, and the protrusions, for example, the fine pillars and the narrow protrusions are carbon-doped. It is good also as such. In this case, there is an advantage that the surface area can be remarkably increased.

  The photocatalyst layer of the present invention can be formed, for example, by subjecting the surface of the substrate as described above to heat treatment in an atmosphere in which chemical species containing carbon and oxygen are supplied to the surface.

  Here, heat treatment in an atmosphere in which chemical species including carbon and oxygen are supplied to the surface means, for example, a gas containing a compound containing carbon and oxygen (if carbon atoms and oxygen atoms exist in the gas atmosphere). Heat treatment using a combustion flame containing a compound containing carbon and a gas containing oxygen, a compound containing both carbon and oxygen, and a gas containing oxygen if necessary), or It is heat-treating as needed while supplying the atmosphere gas of such a combustion flame to the surface. That is, carbon, chemical species including oxygen, that is, activated carbon atoms or atomic groups including carbon atoms, activated oxygen or atomic groups including oxygen atoms, atomic groups including carbon and oxygen, and the like are present on the surface. Heat treatment may be performed in the supplied state, and preferably the surface is oxidized by directly heat-treating the surface using a combustion flame, or by heat treatment while supplying the atmosphere gas of the combustion flame to the surface. A complicated surface modification of carbonization is realized, and carbon is doped on the surface to form a carbon-doped metal oxide layer.

  Specifically, a gas combustion flame may be directly applied to the surface of the substrate and heat treatment may be performed at a high temperature, or such a substrate surface may be heat-treated in a combustion gas atmosphere. It can be carried out in a furnace. When heat treatment is performed at a high temperature by directly applying a combustion flame, the above gas may be burned in a furnace, and the combustion flame may be applied to the surface of the substrate. When heat treatment is performed in a combustion gas atmosphere, the above gas is burned in a furnace and the high-temperature combustion gas atmosphere is used.

  As a preferred method for forming such a photocatalyst layer, it is desirable to perform heat treatment using a combustion gas containing a gas containing a compound containing carbon or oxygen, for example, a gas containing a gas containing an alcohol compound or hydrocarbon.

  When the photocatalyst layer of the present invention is obtained by heat treatment using such a combustion flame, in particular, a gas mainly composed of hydrocarbons, preferably hydrocarbons containing unsaturated bonds, particularly acetylenes having triple bonds. It is desirable to use a combustion flame, particularly a reducing flame. When a fuel having a low hydrocarbon content is used, the carbon doping amount is insufficient or not at all, and as a result, the hardness becomes insufficient.

  Here, the hydrocarbon-based gas means a gas containing at least 30% by volume, preferably at least 50% by volume of hydrocarbon, preferably unsaturated hydrocarbon, particularly acetylene, for example, acetylene. It means a gas containing 30% by volume or more, preferably 50% by volume or more and appropriately mixed with air, hydrogen, oxygen or the like. In the production of such a multifunctional material, the gas containing hydrocarbon as a main component preferably contains 50% by volume or more of acetylene, and the hydrocarbon is most preferably 100% acetylene. When unsaturated hydrocarbons, especially acetylene having a triple bond, are used, in the process of combustion, especially in the reducing flame part, the unsaturated bond part decomposes to form an intermediate radical substance. It is considered that carbon doping is likely to occur because of its high activity.

  When producing a photocatalyst layer using a combustion flame in this way, if the surface layer of the substrate to be heat-treated is a metal (including an alloy), oxygen that oxidizes the metal is required, and accordingly Need only contain air or oxygen.

  Such a photocatalyst layer exhibits a photocatalytic function by the action of ultraviolet to visible light, that is, ultraviolet light, visible light, or ultraviolet light and visible light. In the present invention, a potential is applied to the photocatalytic layer. In this state, it functions as a photocatalyst in a state where the original oxidative decomposition power is remarkably improved. The photocatalyst layer responds to ultraviolet rays or visible light as well as short-wavelength radiation, and may exhibit a photocatalytic function by radiation irradiation.

  Here, the state where a potential is applied to the photocatalyst layer is a state where a positive voltage is applied to the photocatalyst layer or a substrate having the photocatalyst layer on the surface. In this way, when a potential is applied to the photocatalyst layer, charge separation efficiency is improved by polarization, so that the oxidative decomposition power of the photocatalyst layer is remarkably improved.

  In addition, since the photocatalyst layer is used in a polarized state in this way, even if the electrode overvoltage changes, the function that the photocatalytic characteristics can be controlled to the same efficiency by increasing the polarization voltage positively. Have

  Since the method of the present invention is used in a state in which the photocatalyst layer is polarized, it can be applied to oxidative decomposition in the gas phase. For example, it can be applied to the removal of organic substances in the gas phase, but is applied to oxidative decomposition in the liquid phase. Is preferred.

  When performing oxidative decomposition according to the method of the present invention, the photocatalyst layer may be placed in an environment exposed to natural light. However, in order to perform oxidative decomposition stably and efficiently, the photocatalyst layer is irradiated with ultraviolet rays from the light source. It is preferable to irradiate with visible light.

  In addition, the method of the present invention is suitable for performing oxidative decomposition in the liquid phase, that is, in water as described above. Therefore, the method of the present invention is suitable for application to decomposition and removal of organic substances in the liquid phase in addition to purification of water. It is.

  Furthermore, the photocatalyst layer used in the present invention has the advantage of being excellent in durability (high hardness, scratch resistance, abrasion resistance, chemical resistance, heat resistance). It can be applied to various uses.

  Hereinafter, an example of the water purification apparatus which processes to-be-processed water by this invention method is demonstrated. FIG. 1 shows a schematic plan view of a water purification apparatus according to this embodiment and a cross-sectional view taken along the line AA ′.

  As shown in FIG. 1, the water purification apparatus includes a metal cylindrical treatment container 1 that temporarily holds water to be treated. The treatment container 1 includes an introduction port 2 for introducing treated water and a discharge port 3 for discharging treated treated water. The treated water is introduced from the introduction port 2, and treated water is fed from the discharge port 3. It comes to discharge. A photocatalyst 4 is disposed in the processing container 1. The photocatalyst 4 is formed by forming a base made of a metal plate in a spiral shape, and a photocatalyst layer made of a carbon-doped metal oxide layer is provided on the surface of the metal base, and is fixed to the central portion of the processing vessel 1. The water to be treated introduced from the introduction port 2 is arranged so as to come into contact.

  Here, a positive electrode of a DC power source 5 is connected to the photocatalyst 4, and a negative electrode of the DC power source 5 is connected to the processing container 1. As a result, the photocatalyst layer of the photocatalyst 4 can be polarized with the potential applied.

  In addition, the form of the photocatalyst 4 is not limited to the above-mentioned thing, The metal plate may be used instead of the metal plate, and the metal plate may be processed into a shape other than the spiral. In addition, the metal plate may be obtained by sintering metal particles, and any metal plate may be used as long as the photocatalyst layer is effectively provided on the surface.

  In addition, four light sources 6 are provided around the photocatalyst 4 in the processing container 1. Such a light source 6 irradiates the photocatalyst 4 with ultraviolet or visible light, and thus the photocatalyst layer of the photocatalyst 4 can effectively function as a photocatalyst.

  In this water purification apparatus, the processing vessel 1 is made of metal and the negative electrode of the DC power source 5 is connected to the processing vessel 1. However, a separate negative electrode is provided in the processing vessel 1 to connect the negative electrode of the DC power source 5. May be. In this case, it goes without saying that the processing container 1 may not be made of metal.

  In addition, in order to increase the contact efficiency between the water to be treated in the treatment container 1 and the photocatalyst 4, a member that causes turbulent flow is provided near the inlet 2 or the fluid collides with the catalyst surface in the flow path of the water to be treated. You may devise so that a to-be-processed water stirring means may be provided.

  Further, although the light source 6 is disposed in the processing container 1, the light source 6 may be disposed outside the processing container 1 when the processing container 1 can be formed of a transparent material.

  According to such a water purification apparatus, water to be treated is introduced from the introduction port 2, a potential is applied to the photocatalyst 4, and ultraviolet light or visible light is irradiated from the light source 6, so that the water to be treated is in contact with the photocatalyst 4. Impurities and the like in the water are oxidatively decomposed, and the water to be treated can be purified and discharged from the outlet 3 as treated water.

  Such purification treatment of the water to be treated may be performed in a batch system, or may be carried out by a continuous treatment in which the water to be treated is continuously passed, and furthermore, the water to be treated is provided by providing a circulation path. It is good also as a circulation system introduce | transduced in the processing container 1 in multiple times.

The results of actual testing of the present invention will be described below as examples and comparative examples.
Example 1
As a test material, a combustion flame of acetylene (flow rate 5 NL / min) was brought into contact with one side of a JIS type 1 titanium plate 32 mm × 64 mm × t 0.4 mm for 300 seconds to make a photocatalyst layer made of carbon-doped titanium oxide. The back and end surfaces were sealed with an epoxy resin (Nichiban Co., Ltd. Araldai Rapid). As a result, the electrode area becomes 30 mm × 43 mm.

This test piece was immersed in a 50 mL aqueous solution. This solution contains 0.05 M sodium sulfate (Na ₂ SO ₄ , Wako Pure Chemical Industries, Ltd., reagent special grade) as an electrolyte, and 10 μM methylene blue (methylene blue trihydrate, Wako Pure Chemical Industries, Ltd.) as a decomposition product. Is.

  While applying voltage to the test piece to polarize it, a methylene blue fading test was performed. The methylene blue fading test is generally used as a water purification effect by oxidative decomposition of a photocatalyst.

A UV lamp EDF15BLB manufactured by Toshiba Lighting & Technology Co., Ltd. was used for irradiation with ultraviolet light. The ultraviolet intensity was about 3 mW / cm ² (measured with a custom-made UVA-365).

  For the polarization of the photocatalyst layer, HSV-100 manufactured by Hokuto Denko Co., Ltd. was used as voltammetry. The polarization potential is 0.6 V vs. SSE.

  As a comparison object, a platinum plate was used instead of carbon-doped titanium oxide.

  FIG. 2 shows the test results (methylene blue fading speed). The vertical axis is the concentration of methylene blue, and the horizontal axis is the elapsed time. 0 hour indicates the ultraviolet irradiation start and polarization start time. The methylene blue concentration was measured using a spectrophotometer (Shimadzu Corporation UV-1650PC).

  FIG. 2 shows that the fading speed of methylene blue is low only by ultraviolet irradiation and polarization alone. On the other hand, the fading speed is remarkably improved by performing polarization while irradiating with ultraviolet rays. This is presumably because the charge separation efficiency was improved by polarization. That is, it is considered that this is because recombination between excited electrons and holes generated by light irradiation is suppressed and can be efficiently used for a reduction reaction and an oxidation reaction, respectively.

  For comparison, it was found that the platinum electrode was irradiated with ultraviolet rays and simultaneously polarized, but it did not function as a photocatalyst and methylene blue hardly faded.

  As a result, it was found that both polarization and ultraviolet irradiation act synergistically on the photocatalyst layer to promote the decomposition of methylene blue.

(Example 2)
The photocatalyst layer used in Example 1 was compared with a photocatalyst Type-B (comparative material) manufactured by Nippon Metal Industry Co., Ltd. The test surface area, end seal method, solution and other conditions were all the same and compared.

  The result of the corrosion resistance test for methylene blue is shown in FIG.

  When the comparative material is polarized, the concentration of methylene blue does not decrease. A remarkable methylene blue fading performance was obtained with the comparative material when irradiated with ultraviolet rays. Polarization was performed simultaneously with the ultraviolet irradiation, but a synergistic effect due to the polarization was not obtained.

  On the other hand, in the photocatalyst layer of the example, methylene blue fading performance higher than that of the comparative material was obtained by performing polarization simultaneously with ultraviolet irradiation. As a comparative material, a general photocatalyst is a method of coating a titanium oxide powder coating material by dipping, spraying or dipping, and the electrical conductance of the binder with the base material is lowered. On the other hand, the photocatalyst layer used in the examples is formed by a technique of simultaneously oxidizing and carbonizing titanium or a titanium alloy. It is considered that a synergistic effect due to polarization is brought about by the fact that the binder is not interposed and the conductance between the photocatalyst film and the base material (substrate) is good.

It is the schematic plan view and sectional drawing of the water purification apparatus which concern on one Embodiment. 2 is a graph showing the results of a methylene blue fading test in Example 1. 4 is a graph showing the results of a methylene blue fading test in Example 2.

Explanation of symbols

1 Processing Container 4 Photocatalyst 5 DC Power Supply 6 Light Source

Claims (10)

  A photocatalytic oxidative decomposition method, characterized in that a potential is applied to the photocatalyst layer when performing oxidative decomposition using a photocatalyst layer comprising a carbon-doped metal oxide layer provided on the surface of a metal substrate.   2. The photocatalytic oxidative decomposition method according to claim 1, wherein the photocatalytic layer is irradiated with ultraviolet to visible light from a light source.   3. The oxidative decomposition method using a photocatalyst according to claim 1, wherein the photocatalyst layer is immersed in water to be treated to purify the water to be treated. 4.   The oxidative decomposition method using a photocatalyst according to any one of claims 1 to 3, wherein the metal is at least one selected from titanium, hafnium, zirconium, and an alloy mainly composed of these. Oxidative decomposition method using photocatalyst.   5. The photocatalytic oxidative decomposition method according to claim 4, wherein carbon in the photocatalyst layer is contained in a metal-carbon bond state.   6. The oxidative decomposition method using a photocatalyst according to claim 4 or 5, wherein the photocatalyst layer heat-treats the surface of the metal substrate in an atmosphere in which chemical species including carbon and oxygen are supplied to the surface. A photocatalytic oxidative decomposition method characterized by being formed.   A water purification apparatus for purifying water to be treated, comprising a treatment container for at least temporarily holding the water to be treated, and a carbon-doped metal oxide layer provided on the surface of the metal substrate, and in the treatment container A water purification apparatus comprising: a photocatalyst layer disposed so as to be in contact with the water to be treated, and a power source for applying a potential to the photocatalyst layer.   The water purification apparatus according to claim 7, further comprising a light source that irradiates the photocatalyst layer with ultraviolet to visible light.   The water purification apparatus according to claim 7 or 8, wherein the treatment container includes an introduction port for introducing the water to be treated and a discharge port for discharging the treated water. . The water purification apparatus according to claim 9, further comprising means for continuously introducing water to be treated into the treatment container.

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