JP5565791B2 - Method for modifying visible light responsive photocatalyst, modified visible light responsive photocatalyst, method for decomposing organic substance using the photocatalyst, and apparatus for performing the modification - Google Patents
Method for modifying visible light responsive photocatalyst, modified visible light responsive photocatalyst, method for decomposing organic substance using the photocatalyst, and apparatus for performing the modification Download PDFInfo
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- 238000000034 method Methods 0.000 title claims description 41
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- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 claims description 33
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- 239000011368 organic material Substances 0.000 claims 1
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- 230000000052 comparative effect Effects 0.000 description 46
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 42
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Description
本発明は、可視光応答性光触媒の改質方法及び改質された可視光応答性光触媒並びに該光触媒を用いた有機物の分解方法と該該改質を実施する装置に関するものである。 The present invention relates to a method for modifying a visible light responsive photocatalyst, a modified visible light responsive photocatalyst, a method for decomposing an organic substance using the photocatalyst, and an apparatus for performing the modification.
近年、環境汚染物質を吸着し太陽光や室内光によって分解除去する光触媒が注目され、その研究が精力的に行われている。酸化チタンはその代表的なものであり強力な光触媒活性を示す。しかし、酸化チタンではバンドギャップが大きくて太陽光の大部分を占める可視光が吸収されず、紫外光にのみ活性なため、太陽光を十分に利用することができないことや紫外光が極めて弱い室内では機能しないことなどの問題があった。人工光源を使う場合でも、バンドギャップが小さいほど利用できる光子は増えるので理論上活性は向上できる。このための手法として、窒素ドープなどで可視光を吸収できるようにするなどの酸化チタンの改良研究や可視光で光触媒として活性を示す新規な酸化物半導体の探索研究が行われている（例えば、非特許文献１、２）。 In recent years, photocatalysts that adsorb environmental pollutants and decompose and remove them with sunlight or room light have attracted attention, and their research has been conducted energetically. Titanium oxide is a typical example and exhibits strong photocatalytic activity. However, titanium oxide has a large band gap and does not absorb visible light, which occupies most of sunlight, and is only active for ultraviolet light. Then there were problems such as not functioning. Even when using an artificial light source, the smaller the band gap, the more photons that can be used, so the activity can be improved theoretically. As a technique for this, improvement research of titanium oxide, such as allowing visible light to be absorbed by nitrogen doping or the like, and search research of new oxide semiconductors that exhibit activity as a photocatalyst by visible light (for example, Non-patent documents 1, 2).
酸化チタンと比較してバンドギャップが小さいために可視光を吸収することができる酸化タングステンなどの半導体は、可視光活性な光触媒（可視光応答性光触媒）として期待されている。これらの可視光応答性光触媒は、白金やパラジウム、銅化合物などの助触媒を利用して活性を促進させることが多い（例えば、特許文献１、２、３）。 A semiconductor such as tungsten oxide that can absorb visible light because it has a smaller band gap than titanium oxide is expected as a visible light active photocatalyst (visible light responsive photocatalyst). These visible light responsive photocatalysts often promote activity by using a cocatalyst such as platinum, palladium, or copper compound (for example, Patent Documents 1, 2, and 3).
一方、酸化チタンを光触媒として用いた場合には気相の有機物分解反応の反応性に湿度が影響を与えることが知られていた。例えば、光触媒に酸化チタンを用いて気相中のトルエンの分解反応を行った場合、湿度が高いとトルエンの分解速度が向上するという報告がある（非特許文献３、特許文献４）。どちらの報告も湿度６０％までの影響を酸化チタン光触媒で検討している。この湿度６０％までの条件では水は水蒸気として気相状態で存在し、触媒表面の一部には水分子が吸着しているが液相状態の水は定常的には存在していないと考えられる。 On the other hand, when titanium oxide is used as a photocatalyst, it has been known that humidity affects the reactivity of vapor phase organic substance decomposition reaction. For example, when the decomposition reaction of toluene in the gas phase is performed using titanium oxide as a photocatalyst, there is a report that the decomposition rate of toluene is improved when the humidity is high (Non-patent Documents 3 and 4). Both reports examine the effect of up to 60% humidity on titanium oxide photocatalysts. Under conditions up to this humidity of 60%, water is present in the vapor phase as water vapor, and water molecules are adsorbed on part of the catalyst surface, but liquid phase water is not steadily present. It is done.
酸化タングステンなどの酸化物半導体を用いた有機物の分解方法において、対象有機物がトルエンなどの芳香族の場合には、助触媒を利用しても、難分解性の反応中間体が生成して分解反応が進行しにくくなる場合がある。また、対象有機物が完全に二酸化炭素にまで酸化分解されない場合、生成する反応中間体が対象有機物と同等あるいはそれ以上に悪臭などの有害性を示す可能性があり、光触媒活性の向上が課題であった。 In the method for decomposing organic substances using oxide semiconductors such as tungsten oxide, if the target organic substance is aromatic such as toluene, even if a cocatalyst is used, a difficult-to-decompose reaction intermediate is generated and the decomposition reaction occurs. May be difficult to progress. In addition, if the target organic matter is not completely oxidatively decomposed to carbon dioxide, the reaction intermediate produced may be as harmful as the target organic matter or more harmful such as bad odor, and improvement of the photocatalytic activity is a problem. It was.
本発明は、こうした従来技術における課題を解決し、トルエンなどの難分解性芳香族化合物をはじめとした環境汚染物質を、可視光照射により、二酸化炭素にまで完全に分解することができる酸化タングステンなどのタングステン化合物又は助触媒を添加したそれらのタングステン化合物からなる可視光応答性光触媒を提供することを目的とするものである。 The present invention solves such problems in the prior art, and tungsten oxide that can completely decompose environmental pollutants such as a hardly decomposable aromatic compound such as toluene into carbon dioxide by irradiation with visible light. It is an object of the present invention to provide a visible light responsive photocatalyst comprising the tungsten compound or a tungsten compound to which a promoter is added.
前述のとおり、光触媒に酸化チタンを用いて気相中のトルエンの分解反応を行った場合、湿度が高いとトルエンの分解速度が向上するという報告があるが、可視光応答性のタングステン化合物光触媒に関しては湿度の影響などの水分の効果は知られておらず、水分が酸化チタン以外の光触媒反応にどのような影響を与えるかは不明であった。
また一方で、光触媒表面に液相状態で存在する水分の影響については、トルエンのような疎水性の有機物の分解の場合には、触媒の表面に水の液膜が存在すれば分解対象の有機物が接触しにくくなり、かえって活性が著しく低下するという考えもある。しかし可視光応答性のタングステン化合物光触媒に関してはこのような液相状態の水の影響も全く知られていない。
As mentioned above, when the decomposition reaction of toluene in the gas phase is performed using titanium oxide as the photocatalyst, there is a report that the decomposition rate of toluene improves when the humidity is high, but regarding the visible light responsive tungsten compound photocatalyst The effect of moisture, such as the effect of humidity, is not known, and it was unclear how the moisture affects photocatalytic reactions other than titanium oxide.
On the other hand, regarding the influence of moisture present in the liquid phase state on the photocatalyst surface, in the case of decomposition of hydrophobic organic matter such as toluene, if there is a liquid film of water on the surface of the catalyst, the organic matter to be decomposed There is also an idea that the activity is remarkably lowered. However, regarding the visible light responsive tungsten compound photocatalyst, the influence of such liquid phase water is not known at all.
本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、酸化タングステンなどのタングステン化合物、さらには助触媒を添加したそれらのタングステン化合物からなる可視光応答性光触媒については、水分添加または湿度の制御等により光触媒を改質することで可視光照射によってトルエン等の有機物を二酸化炭素にまで完全に分解する速度を著しく増加させることができることを見いだした。 As a result of intensive research to achieve the above object, the present inventors have found that a visible light responsive photocatalyst comprising a tungsten compound such as tungsten oxide, and further including such a tungsten compound to which a cocatalyst has been added, It was found that the rate at which organic substances such as toluene are completely decomposed into carbon dioxide by visible light irradiation can be remarkably increased by modifying the photocatalyst by controlling the humidity.
本発明はこれらの知見に基づいて完成に至ったものであり、本発明によれば、以下の発明が提供される。
［１］助触媒として貴金属及び／又は銅化合物を添加した酸化タングステンからなる可視光応答性光触媒に対して水分を直接添加することにより、可視光照射により気相中の有機物を光分解する速度を向上させることを特徴とする可視光応答性光触媒の改質方法。
［２］前記可視光応答性光触媒の表面に水を液相状態で存在させることを特徴とする上記［１］の可視光応答性光触媒の改質方法。
［３］助触媒として貴金属及び／又は銅化合物を添加した酸化タングステンからなる可視光応答性光触媒に加湿して周囲の湿度を６０％以上とすることにより、可視光照射により気相中の有機物を光分解する速度を向上させることを特徴とする可視光応答性光触媒の改質方法。
［４］前記有機物を含んだ被処理気体中に水分を飽和させることを特徴とする上記［３］の可視光応答性光触媒の改質方法。
［５］前記貴金属が、白金、パラジウム、ロジウム、銀から選ばれることを特徴とする上記［１］〜［４］のいずれかの可視光応答性光触媒の改質方法。
［６］前記銅化合物が、酸化銅、塩化銅、水酸化銅、及び銅複合酸化物から選択されることを特徴とする上記［１］〜［５］のいずれかの可視光応答性光触媒の改質方法。
［７］上記［１］〜［６］のいずれかの改質方法により改質を行った可視光応答性光触を用い、可視光照射により有機物を光分解する速度を向上させることを特徴とする有機物の光分解法。
［８］前記有機物の光分解反応が、気相中における揮発性有機物の分解反応であることを特徴とする上記［７］の有機物の光分解法。
［９］前記有機物が疎水性の化合物であることを特徴とする上記［７］又は［８］の有機物の光分解法。
［１０］前記疎水性の化合物が、疎水性芳香族化合物であることを特徴とする上記［９］の有機物の光分解法。
［１１］上記［１］〜［６］のいずれかの改質方法により可視光応答性光触媒を改質するための装置であって、助触媒として貴金属及び／又は銅化合物を添加した酸化タングステンからなる可視光応答性光触媒の表面に水分を放出する手段を有することを特徴とする光触媒改質装置。
［１２］上記［１］〜［６］のいずれかの改質方法により可視光応答性光触媒を改質するための装置であって、有機物を含んだ被処理気体中に水分を飽和させる手段、及び助触媒として貴金属及び／又は銅化合物を添加した酸化タングステンからなる可視光応答性光触媒の表面に水分を飽和した被処理気体を放出する手段を有することを特徴とする光触媒改質装置。
The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] by adding water directly to the cocatalyst as the precious metal and / or tungsten oxide emissions or Ranaru visible light responsive photocatalyst that the copper compound was added, the light decompose organic substances in the gas phase by irradiation of visible light A method for reforming a visible light responsive photocatalyst characterized by improving the speed.
[2] The method for modifying a visible light responsive photocatalyst according to the above [1], wherein water is present in a liquid phase state on the surface of the visible light responsive photocatalyst.
[3] By humidifying a visible light responsive photocatalyst composed of tungsten oxide to which a noble metal and / or a copper compound is added as a co-catalyst to increase the ambient humidity to 60% or more , organic matter in the gas phase is irradiated by visible light irradiation. method for modifying you, characterized in that to improve the optical decomposing rate the visible light responsive photocatalyst.
[4] The visible light responsive photocatalyst reforming method according to the above [ 3 ], wherein water is saturated in the gas to be treated containing the organic substance.
[ 5 ] The method for modifying a visible light responsive photocatalyst according to any one of [1] to [ 4 ], wherein the noble metal is selected from platinum, palladium, rhodium, and silver.
[ 6 ] The visible light-responsive photocatalyst according to any one of [1] to [ 5 ], wherein the copper compound is selected from copper oxide, copper chloride, copper hydroxide, and copper composite oxide. Modification method.
[ 7 ] Using the visible light responsive light touch modified by any of the modification methods of [1] to [ 6 ], and improving the rate of photodegradation of organic matter by visible light irradiation. Photolysis method of organic matter.
[ 8 ] The organic substance photodecomposition method according to [ 7 ], wherein the organic substance photodecomposition reaction is a decomposition reaction of a volatile organic substance in a gas phase.
[ 9 ] The method for photolyzing an organic substance according to [ 7 ] or [ 8 ] above, wherein the organic substance is a hydrophobic compound.
[ 10 ] The method for photolyzing an organic substance according to the above [ 9 ], wherein the hydrophobic compound is a hydrophobic aromatic compound.
[11] [1] to a device for modifying the visible light responsive photocatalyst by either modifying the method of [6], tungsten oxide emissions added a noble metal and / or a copper compound as cocatalyst or photocatalytic reformer, characterized in that it comprises a means for releasing the water to the surface of Ranaru visible light responsive photocatalysts.
[ 12 ] An apparatus for reforming a visible light responsive photocatalyst by any one of the reforming methods of [1] to [ 6 ], and means for saturating moisture in a gas to be treated containing an organic substance, and photocatalytic reformer, characterized in that it comprises a means for releasing a noble metal and / or gas to be treated to the moisture saturated in the surface of the tungsten oxide emissions or Ranaru visible light responsive photocatalyst that the copper compound was added as a cocatalyst.
本発明のとおり酸化タングステンなどのタングステン化合物または助触媒を添加したそれらタングステン化合物からなる可視光応答性光触媒を水分添加または湿度制御により改質して用いると可視光照射によりトルエンなどの難分解性化合物を二酸化炭素にまで分解する速度が著しく増加し、速やかに分解除去することが可能になる。本発明は、空気清浄機や浴室、キッチン、トイレなどにおいても使用することが期待できる。特に容易に乾燥する可能性がある環境で可視光応答性光触媒を作用させる場合は、乾燥によって性能が著しく低下する可視光応答性光触媒を本発明により改質することで有効・安定的に使用することができる。紫外光照射により酸化チタンを使用する場合に比較すると、特に分解反応が進行しにくい難分解性有機物を可視光応答性光触媒で可視光照射により分解除去する場合には本件発明は極めて重要である。 When a visible light responsive photocatalyst comprising a tungsten compound such as tungsten oxide or a tungsten compound added with a promoter as in the present invention is modified by moisture addition or humidity control, it is a hardly decomposable compound such as toluene by visible light irradiation. The rate of decomposing the carbon dioxide into carbon dioxide is remarkably increased, so that it can be rapidly decomposed and removed. The present invention can be expected to be used in air purifiers, bathrooms, kitchens, toilets, and the like. In particular, when a visible light responsive photocatalyst is allowed to act in an environment where it can be easily dried, the visible light responsive photocatalyst whose performance is significantly reduced by drying is effectively and stably used by modifying according to the present invention. be able to. Compared to the case where titanium oxide is used by irradiation with ultraviolet light, the present invention is extremely important particularly when a hardly decomposable organic substance that is difficult to undergo a decomposition reaction is decomposed and removed by irradiation with visible light using a visible light-responsive photocatalyst.
気相中のトルエン、ベンズアルデヒド、安息香酸等々の難分解性および疎水性の有機化合物を、酸化タングステンなどのタングステン化合物または助触媒を添加したタングステン化合物からなる可視光応答性光触媒を用いて二酸化炭素にまで速やかに分解して除去するためには、光触媒を作用させる環境の水分量制御が重要である。湿度６０％以下の気相条件下でも初期は反応が進行するが、活性が低下してしまう。活性が高いまま持続するためには、好ましくは、十分な加湿などで湿度を制御することによって乾燥を防ぎ、光触媒の表面に水が通常の空気中よりも多く存在した状態で反応を行うことが望ましい。このような条件として選択されるのは、分解の対象である有機化合物によるが、好ましくは湿度６０％以上、より好ましくは湿度８０％以上、さらにより好ましくは湿度１００％（飽和状態）において気相の揮発性有機物の分解反応を行うことである。また、液体の水を光触媒に直接に添加することにより十分な量の水分を存在させた状態で反応を行うことによっても活性を高いまま持続させることができる。この場合には光触媒表面には液相の水が液膜として存在していると考えられるが、疎水性の有機物の分解の場合であっても活性は高くなる。 Refractory and hydrophobic organic compounds such as toluene, benzaldehyde, and benzoic acid in the gas phase are converted into carbon dioxide using a visible light responsive photocatalyst composed of a tungsten compound such as tungsten oxide or a tungsten compound to which a promoter is added. Therefore, it is important to control the amount of water in the environment in which the photocatalyst acts. Although the reaction proceeds initially even under a gas phase condition of humidity 60% or less, the activity is lowered. In order to keep the activity high, it is preferable to prevent the drying by controlling the humidity by sufficient humidification or the like, and to carry out the reaction in a state where more water is present on the surface of the photocatalyst than in normal air. desirable. Such conditions are selected depending on the organic compound to be decomposed, but are preferably in the gas phase at a humidity of 60% or more, more preferably a humidity of 80% or more, and even more preferably a humidity of 100% (saturated state). It is to perform a decomposition reaction of volatile organic substances. Further, by adding liquid water directly to the photocatalyst, the activity can be maintained at a high level by carrying out the reaction in the presence of a sufficient amount of water. In this case, liquid phase water is considered to exist as a liquid film on the surface of the photocatalyst, but the activity is high even in the case of decomposing hydrophobic organic substances.
湿度を高い状態に制御することや水分を直接に添加することによって、酸化タングステンなどのタングステン化合物または助触媒を添加したそれらのタングステン化合物からなる可視光応答性光触媒の表面に水分が吸着して光触媒反応が生じやすい状態に改質されると考えられる。同じ光触媒を用いても分解される有機物により反応過程が異なっていることは、生成物である二酸化炭素の発生のパターン（発生量の時間変化）が分解される有機物ごとに異なっていることなどから明らかである。湿度制御や水分添加による分解反応の促進効果は反応過程の異なる多種多様な有機物の分解について観測されており、このことは湿度制御や水分添加によって、ただ単に特定の反応が促進されるのではなく、光触媒の表面が分解反応の進行しやすい状態に改質されることを示している。また、表面状態は物質により全く異なるため酸化タングステンなどのタングステン化合物にこのような現象が観測されることは固有のことであり、酸化チタンの例からは容易に類推することはできない。後述する実施例・比較例から分かるように、酸化タングステンなどのタングステン化合物を光触媒として用いる場合には、湿度制御や水分添加の光触媒活性への影響は非常に大きく、乾燥状態ではほとんど光触媒が機能しなくなる場合もある。これはタングステン化合物の固有の性質として、容易に水分の吸脱着により状態が変化するために周囲の水分量の影響を受けやすいことに起因すると考えられる。そのため、酸化チタンの場合と比較しても、酸化タングステンなどのタングステン化合物を光触媒として用いる場合には本件発明による改質は極めて重要である。 By controlling the humidity to a high level or adding water directly, water is adsorbed on the surface of the visible light responsive photocatalyst made of tungsten compounds such as tungsten oxide or those tungsten compounds added with promoters. It is considered that the reaction is likely to occur. Even if the same photocatalyst is used, the reaction process varies depending on the organic matter that is decomposed because the pattern of generation of carbon dioxide (time change in the amount of generation) differs depending on the organic matter that is decomposed. it is obvious. The effect of promoting the decomposition reaction by humidity control and water addition has been observed for the decomposition of a wide variety of organic substances with different reaction processes. This is not just a specific reaction accelerated by humidity control or water addition. This shows that the surface of the photocatalyst is modified to a state in which the decomposition reaction easily proceeds. In addition, since the surface state is completely different depending on the substance, it is inherent that such a phenomenon is observed in a tungsten compound such as tungsten oxide, and it cannot be easily inferred from the example of titanium oxide. As can be seen from the examples and comparative examples described later, when a tungsten compound such as tungsten oxide is used as a photocatalyst, the influence of humidity control and moisture addition on the photocatalytic activity is very large, and the photocatalyst functions almost in a dry state. It may disappear. This is considered to be due to the nature of the tungsten compound being easily affected by the amount of moisture in the surroundings because the state easily changes due to moisture adsorption and desorption. Therefore, even when using a tungsten compound such as tungsten oxide as a photocatalyst as compared with the case of titanium oxide, the modification according to the present invention is extremely important.
本発明における水分の添加は以下に示すような多彩な方法で実施することができる。すなわち粉末状または薄膜状の光触媒に水分を直接に添加し、その周辺の水分量を十分に増加させてその表面を改質することができる。
また別の方法としては、光触媒に導入される分解対象となる有機物を含んだ被処理気体に水分を飽和させること等により光触媒周辺の湿度を高い状態に保つことができれば作用させる光触媒を改質させることができる。
さらに、光触媒はまた水相中で作用させることでも改質を行うことができる。
光触媒の表面が乾燥すると状態が変化してその活性が著しく減少するので、乾燥を防止して水分がその周辺に十分に存在するようにできるならば、いずれの方法でも本件発明の改質を行うことができる。
The addition of moisture in the present invention can be carried out by various methods as shown below. That is, the surface can be modified by directly adding water to the powdered or thin film photocatalyst and sufficiently increasing the amount of water around the photocatalyst.
As another method, if the humidity around the photocatalyst can be kept high by, for example, saturating the gas to be treated containing the organic matter to be decomposed introduced into the photocatalyst, the photocatalyst to be acted on can be modified. be able to.
Furthermore, the photocatalyst can also be modified by acting in the aqueous phase.
When the surface of the photocatalyst is dried, its state changes and its activity is significantly reduced. Therefore, any method can be used to modify the present invention as long as it can be prevented from drying and sufficient moisture exists in the vicinity. be able to.
紫外光応答性半導体である酸化チタンもトルエン等の分解反応が可能であるが、紫外光の少ない室内環境においては反応が進行しにくい。可視光応答性光触媒はバンドギャップが酸化チタンと比較して小さくて可視光を吸収できるが光触媒活性はあまり強力ではないため、助触媒の利用および本件発明の改質によって反応速度の向上が見込まれる。本発明に関して可視光応答性光触媒として選択されるのは、タングステン化合物であり、そのうちより好ましくは酸化タングステンなどのタングステン酸化物であるである。具体的には、ＷＯ３、ＷＯｘ（ｘは３以下）、Ｂｉ２ＷＯ６などがある。 Although titanium oxide, which is an ultraviolet light-responsive semiconductor, can also be decomposed with toluene or the like, the reaction hardly proceeds in an indoor environment with little ultraviolet light. Visible light-responsive photocatalyst has a smaller band gap than titanium oxide and can absorb visible light, but its photocatalytic activity is not so strong, so the use of cocatalyst and modification of the present invention is expected to improve the reaction rate . For the present invention, a tungsten compound is selected as the visible light responsive photocatalyst, and more preferably a tungsten oxide such as tungsten oxide. Specifically, there are WO 3 , WO x (x is 3 or less), Bi 2 WO 6 and the like.
助触媒を用いることで可視光応答性光触媒の反応性が向上する。助触媒として選択されるのは、好ましくは貴金属および銅の化合物である。貴金属のうちより好ましく選択されるのは白金、パラジウム、ロジウム、銀である。また銅化合物のうちより好ましく選択されるのは酸化銅、塩化銅、水酸化銅、銅複合酸化物、銅イオンである。助触媒はできるだけ高分散に担持させることが好ましい。
また貴金属と銅の化合物の両方を組み合わせて同時に助触媒として用いることがより好ましく、どちらか片方だけを用いるより可視光応答性光触媒の反応性は大きく向上する。本件発明の改質についても貴金属と銅の化合物の両方を組み合わせて同時に用いることにより大きな効果を得ることができる。複数の助触媒は同時に担持しても良いし、逐次担持しても良い。
助触媒の可視光応答性光触媒への担持方法は、混練法や含浸法、イオン交換法、光電着法、ＣＶＤ法、蒸着法、スパッタ法など様々な方法が利用できる。また、塩化物イオンや硝酸アニオンの存在も触媒活性を向上させる。
The reactivity of the visible light responsive photocatalyst is improved by using the cocatalyst. The cocatalyst selected is preferably a noble metal and copper compound. Of the noble metals, platinum, palladium, rhodium and silver are more preferably selected. Of the copper compounds, copper oxide, copper chloride, copper hydroxide, copper composite oxide, and copper ions are more preferably selected. The cocatalyst is preferably supported as highly dispersed as possible.
It is more preferable to combine both noble metal and copper compounds and use them as a co-catalyst at the same time, and the reactivity of the visible light responsive photocatalyst is greatly improved compared to using only one of them. Also for the modification of the present invention, a great effect can be obtained by combining and using both noble metal and copper compound at the same time. A plurality of promoters may be supported simultaneously or sequentially.
Various methods such as a kneading method, an impregnation method, an ion exchange method, a photo-deposition method, a CVD method, a vapor deposition method, and a sputtering method can be used as a method for supporting the promoter on the visible light responsive photocatalyst. The presence of chloride ions and nitrate anions also improves the catalytic activity.
以下に酸化タングステン粉末にパラジウム粉末を添加する場合を例として説明する。
酸化タングステン粉末にパラジウム粉末を添加する場合では１重量％から０．０００１重量％が好ましく、より好ましくはおよそ０．１〜０．００１重量％である。添加量が０．０００１重量％より少なければ効果が小さく、また１重量％より大きければ助触媒が酸化タングステンの光吸収を妨げるので光分解反応の進行が遅くなる。
酸化タングステン粉末とパラジウム粉末を混合したものに少量の水分を滴下により添加し、気相のトルエン存在下で可視光を照射すると、水分を滴下により添加していない場合と比較してトルエンを二酸化炭素にまで効率よく分解できる。助触媒の添加量、照射光の強度・照射時間などの最適条件は添加する助触媒や光触媒の種類、形状などに依存する。
The case where palladium powder is added to tungsten oxide powder will be described below as an example.
When palladium powder is added to tungsten oxide powder, the content is preferably 1 to 0.0001% by weight, more preferably about 0.1 to 0.001% by weight. If the addition amount is less than 0.0001% by weight, the effect is small, and if it is more than 1% by weight, the cocatalyst hinders light absorption of tungsten oxide, so that the photolysis reaction proceeds slowly.
When a small amount of water is added dropwise to a mixture of tungsten oxide powder and palladium powder and irradiated with visible light in the presence of vapor phase toluene, toluene is added to carbon dioxide compared to when water is not added dropwise. Can be decomposed efficiently. Optimum conditions such as the amount of promoter added, the intensity of irradiation light, and the irradiation time depend on the type and shape of the promoter and photocatalyst to be added.
本発明における可視光応答性光触媒は粉末形状に限定されるものではなく、薄膜などに形成して使用することもできる。例えば、上記した可視光応答性光触媒粉末を薄膜形状に形成して使用することができる。薄膜の作製は通常に用いられているドクターブレード法やスピンコート法などによって行う。 The visible light responsive photocatalyst in the present invention is not limited to a powder form, and can be used by forming into a thin film or the like. For example, the visible light responsive photocatalyst powder described above can be used in the form of a thin film. The thin film is produced by a commonly used doctor blade method, spin coating method, or the like.
反応速度は温度によっても影響を受けるが、常温よりも高い方が望ましい。光照射により、触媒温度は上昇するが、光触媒として有効な波長の光以外の波長、例えば、バンドギャップ以上の波長の光や赤外線の照射で、触媒温度を上昇させることができる。また、別な熱源を使っても触媒温度を上昇できる。しかし、温度を上昇しすぎると、触媒表面が乾燥してしまうので、常に水分を供給することが望ましい。 Although the reaction rate is affected by temperature, it is preferably higher than room temperature. Although the catalyst temperature is increased by light irradiation, the catalyst temperature can be increased by irradiation with light or infrared light having a wavelength other than light having a wavelength effective as a photocatalyst, for example, light having a wavelength greater than the band gap. Also, the catalyst temperature can be increased by using another heat source. However, if the temperature is raised too much, the catalyst surface will dry out, so it is desirable to always supply moisture.
本発明における改質法は光触媒による空気清浄や廃水処理などに対して様々な形態で利用できる。気相における有機物の分解反応に対しては、初めに適切な湿潤状態を調製し、被処理気体の湿度を１００％近くにすれば、改質を容易に行うことができる。例えば、被処理気体を水中でバブリングしたり、水分を含んだスポンジ状のフィルターを通したりすることで十分な湿度を加えて、光触媒上の水分の蒸発を防ぐことにより光触媒の改質を行いながら被処理気体に含まれる有機物を光触媒反応により分解除去することができる。 The reforming method in the present invention can be used in various forms for air purification or wastewater treatment with a photocatalyst. For an organic substance decomposition reaction in the gas phase, an appropriate wet state is first prepared, and if the humidity of the gas to be treated is close to 100%, the modification can be easily performed. For example, while reforming the photocatalyst by adding sufficient humidity by bubbling the gas to be treated in water or passing it through a sponge-like filter containing water, preventing the evaporation of water on the photocatalyst Organic substances contained in the gas to be treated can be decomposed and removed by photocatalytic reaction.
図１は、分解対象物の有機物を含んだ被処理気体中に水分を飽和させることにより、可視光応答性光触媒を改質する装置の一例を模式的に示す図であり、図中、１は、基板上に薄膜状に形成された可視光応答性光触媒、２は、光照射部、３は、水分添加部、４は、被処理気体導入部、５は、被処理気体放部、をそれぞれ示している。該装置においては、被処理気体を水中でバブリングして水分を飽和させた後、この被処理気体を可視光応答性光触媒表面に供給することにより改質し、その状態で光照射を行うことにより、被処理気体中の有機物質を光分解するようにしたものである。 FIG. 1 is a diagram schematically showing an example of an apparatus for modifying a visible light responsive photocatalyst by saturating moisture in a gas to be treated containing an organic substance to be decomposed. The visible light responsive photocatalyst formed in a thin film on the substrate, 2 is a light irradiation part, 3 is a moisture addition part, 4 is a gas to be treated introduction part, and 5 is a gas release part to be treated, respectively. Show. In this apparatus, after bubbling the gas to be treated in water to saturate the moisture, the gas to be treated is modified by supplying it to the surface of the visible light responsive photocatalyst, and light irradiation is performed in that state. The organic substance in the gas to be treated is photodecomposed.
別の形態としては、光触媒薄膜上に、水や水蒸気、ミスト状水分を放出して改質を実施しながら有機物を光触媒反応により分解することができる。
図２は、可視光応答性光触媒に対して水分を放出供給して改質する装置の一例を模式的に示す図であり、図中、１は、基板上に薄膜状に形成された可視光応答性光触媒、２は、光照射部、６は、水分貯蔵部、７は、水分導入部、８は、水分放出部、をそれぞれ示している。該装置においては、水分貯蔵部の水分を、可視光応答性光触媒薄膜の表面に放出することにより改質し、その状態で光照射を行うことにより、大気中の揮発性有機物を光分解するようにしたものである。
As another form, organic substances can be decomposed by a photocatalytic reaction while water, water vapor, and mist-like moisture are released on the photocatalytic thin film and reforming is performed.
FIG. 2 is a view schematically showing an example of an apparatus for releasing and supplying moisture to the visible light responsive photocatalyst, in which 1 denotes visible light formed in a thin film on a substrate. The responsive photocatalyst, 2 is a light irradiation unit, 6 is a moisture storage unit, 7 is a moisture introduction unit, and 8 is a moisture release unit. In this apparatus, the moisture in the moisture storage part is modified by being released to the surface of the visible light responsive photocatalytic thin film, and light irradiation is performed in this state, so that volatile organic substances in the atmosphere are photolyzed. It is a thing.
また、光触媒を塗布したフィルターを水に浸して改質しておいて被処理気体を通過させることで処理気体中の有機物を光触媒反応により分解除去したりすることもできる。
また、光触媒膜を適度な多孔質状態にして、その多孔質の表面張力で水分を保持しても良い。シリカやアルミナ、粘土鉱物などの調湿材料を光触媒と組み合わせることで、光触媒上の水分を保持することも有効である。
さらに、温度差のある空間の低温になる部分に光触媒を設置することで、凝結や結露により自然に水を供給する方法も有効である。またさらに水中に有機物を含むガスや液体を通して有機物を水相中で光触媒反応により分解することもできる。
In addition, the filter coated with the photocatalyst can be modified by immersing it in water, and the gas to be treated can be passed through to decompose and remove organic substances in the treatment gas by a photocatalytic reaction.
Alternatively, the photocatalytic film may be in an appropriate porous state, and moisture may be held with the porous surface tension. It is also effective to retain moisture on the photocatalyst by combining a humidity control material such as silica, alumina, or clay mineral with the photocatalyst.
Furthermore, it is also effective to supply water naturally by condensation or condensation by installing a photocatalyst at a low temperature part of a space having a temperature difference. Furthermore, the organic substance can be decomposed by a photocatalytic reaction in the aqueous phase through a gas or liquid containing the organic substance in water.
以下、本発明を実施例及び比較例によりさらに具体的に説明するが、本発明はこの実施例によって何ら限定されるものではない。 EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by this Example.
酸化タングステン粉末（和光純薬工業、（６ｍ２／ｇ））にパラジウム粉末（シグマ アルドリッチ）を０．１重量％加え、乳鉢を用いてよく混合して可視光応答性光触媒粉末を作製した。この光触媒を４ｍｌのバイアル瓶（底面面積：約１ｃｍ２）におよそ１５０ｍｇ投入して、湿度約５０％の空気を入れて密栓し、水１０μｌおよびトルエン２μｌをシリンジでバイアル瓶の底面の触媒上に滴下した。この水１０μｌを添加した場合を実施例１とする。
３００Ｗのキセノンランプ（ＵＶカットフィルター無し、熱線カットミラー有り）から４２０ｎｍより短波長をフィルターによりカットした可視光を上述のバイアルに照射し、光分解で生じる二酸化炭素の量をガスクロマトグラフィーで定量し、時間変化をモニターした。
また比較例１として、水分添加や湿度制御をせずに本件発明の改質を行っていない、トルエン２μｌのみを注入したサンプル（湿度５０％前後）を用いて同様の実験を行った。
さらに比較例２として、光触媒を乾燥空気中で脱水し、トルエン２μｌのみを注入したサンプル（湿度０％）を用いて同様の実験を行った。
0.1 wt% of palladium powder (Sigma Aldrich) was added to tungsten oxide powder (Wako Pure Chemical Industries, (6 m 2 / g)) and mixed well using a mortar to prepare a visible light responsive photocatalyst powder. About 150 mg of this photocatalyst is placed in a 4 ml vial (bottom area: about 1 cm 2 ), air is sealed with about 50% humidity, and 10 μl of water and 2 μl of toluene are placed on the bottom of the vial with a syringe. It was dripped. A case where 10 μl of water is added is referred to as Example 1.
The above vial is irradiated with visible light, which is cut by a filter with a wavelength shorter than 420 nm, from a 300 W xenon lamp (without a UV cut filter and with a heat ray cut mirror), and the amount of carbon dioxide produced by photolysis is quantified by gas chromatography. The time change was monitored.
In addition, as Comparative Example 1, a similar experiment was performed using a sample (about 50% humidity) in which only 2 μl of toluene was injected without modification of the present invention without adding water or controlling the humidity.
Further, as Comparative Example 2, a similar experiment was performed using a sample (humidity 0%) in which the photocatalyst was dehydrated in dry air and only 2 μl of toluene was injected.
結果を、図３に示す。図中、●は、水分添加（実施例１）の場合、□は、水分添加や湿度制御なしの湿度５０％（比較例１）の場合、▲は、乾燥（比較例２）の場合、をそれぞれ示している。 The results are shown in FIG. In the figure, ● indicates moisture addition (Example 1), □ indicates humidity of 50% (Comparative Example 1) without moisture addition or humidity control, and ▲ indicates drying (Comparative Example 2). Each is shown.
また表１には、酸化タングステン粉末のみのものと酸化タングステン粉末にパラジウム、白金、酸化銅の各種助触媒を混合して調整した可視光応答性光触媒を用いてトルエンなどの様々な有機物を光分解したときの、光照射の初期２時間における二酸化炭素の生成量（ｐｐｍ）を、水分添加（湿度１００％）と、水分添加なし（湿度５０％前後）、および乾燥（湿度０％）の場合で比較した結果を示してある。可視光の場合はＵＶカットフィルターを付け、全光の場合はＵＶカットフィルターを付けていない。 Table 1 also shows the photolysis of various organic substances such as toluene using a visible light-responsive photocatalyst prepared by mixing only tungsten oxide powder and tungsten oxide powder with various promoters of palladium, platinum, and copper oxide. The amount of carbon dioxide produced (ppm) in the initial 2 hours of light irradiation when moisture was added (humidity 100%), no moisture added (humidity around 50%), and drying (humidity 0%) The comparison results are shown. In the case of visible light, a UV cut filter is attached, and in the case of all light, no UV cut filter is attached.
水１０μｌを滴下して本発明の改質を行った実施例１では、バイアル内部の湿度は非常に高く、液相の水が存在するとともに、底面の触媒は水で湿潤状態になる。図３に示すように乾燥により水分を取り除いた比較例２では全く反応が進行しなかったのに対して、本発明による改質を実施しなかった比較例１では、湿度がおよそ５０％しかなく、乾燥した比較例２と比較すると元から含まれる水分の影響によりある程度の速度で反応が進行している。しかし、水分添加によって本発明による改質を十分に実施した実施例１では比較例１に比較しても著しく速く反応が進行し、その効果は明らかである。
このように、水分添加や湿度制御による改質は光触媒活性に大きな影響を与えることが見出された。
また、表１に示すように、初期の二酸化炭素の発生速度は、実施例1が、３２００ｐｐｍ／２ｈ、比較例１が、１８００ｐｐｍ／２ｈ、比較例２が、＜１０ｐｐｍ／２ｈであり、トルエンが二酸化炭素まで酸化分解される速度が水分添加によって大幅に向上していることが確認できる。
In Example 1 in which 10 μl of water was dropped to perform the modification of the present invention, the humidity inside the vial was very high, liquid phase water was present, and the bottom catalyst was wetted with water. As shown in FIG. 3, in Comparative Example 2 in which moisture was removed by drying, the reaction did not proceed at all, whereas in Comparative Example 1 in which the modification according to the present invention was not performed, the humidity was only about 50%. Compared with the dried Comparative Example 2, the reaction proceeds at a certain rate due to the influence of moisture contained originally. However, in Example 1 in which the modification according to the present invention was sufficiently performed by addition of water, the reaction proceeded much faster than Comparative Example 1, and the effect is clear.
Thus, it was found that the modification by moisture addition or humidity control has a great influence on the photocatalytic activity.
Further, as shown in Table 1, the initial carbon dioxide generation rate is 3200 ppm / 2h in Example 1, 1800 ppm / 2h in Comparative Example 1, <10 ppm / 2h in Comparative Example 2, and toluene is It can be confirmed that the rate of oxidative decomposition to carbon dioxide is greatly improved by the addition of moisture.
また表１にはさらに実施例２〜１１及び比較例３〜１６を示している。
酸化タングステンにパラジウム粉末を助触媒として用いた場合に、トルエン以外にもベンズアルデヒド、ベンジルアルコール、クレゾールなどのトルエン分解の中間体として考えられる芳香族化合物や酢酸などの有機物の分解反応においても二酸化炭素にまで分解される速度が水分添加により水分を添加しない場合と比較して向上した。
また、酸化タングステンについて助触媒が白金、酸化銅の場合や助触媒を用いない場合にもトルエンの分解反応において二酸化炭素にまで分解される速度が水分を添加することにより水分を添加しない場合と比較して向上した。
さらに、酸化タングステンに酸化銅を助触媒として用いた場合に、ｍ−キシレン、ベンゼンなどの芳香族化合物やヘキサンなどの有機物の分解反応においても二酸化炭素にまで酸化分解される速度が水分添加により水分を添加しない場合と比較して向上した。
Table 1 further shows Examples 2 to 11 and Comparative Examples 3 to 16.
When palladium powder is used as a co-catalyst for tungsten oxide, carbon dioxide is also converted into carbon dioxide in the decomposition reaction of aromatic compounds such as benzaldehyde, benzyl alcohol, and cresol as well as organic compounds such as acetic acid. The rate of decomposition was improved by the addition of water compared to the case where no water was added.
In addition, when tungsten copromoter is platinum, copper oxide, or when no cocatalyst is used, the decomposition rate of toluene to carbon dioxide in the decomposition reaction of toluene is compared with the case where water is not added by adding water. And improved.
Furthermore, when copper oxide is used as a co-catalyst for tungsten oxide, the rate of oxidative decomposition to carbon dioxide in the decomposition reaction of aromatic compounds such as m-xylene and benzene and organic substances such as hexane is increased by the addition of moisture. Compared with the case where no is added.
また、実施例１２として、酸化タングステン粉末に助触媒としてパラジウム粉末０．００１重量％、酸化銅粉末０．１重量％を同時に加えて調整した可視光応答性光触媒に、実施例１と同様にして水分を添加した条件下でキセノンランプの全光照射によりトルエンを分解する実験を行った。助触媒がパラジウムのみのものを比較例１７、酸化銅のみのものを比較例１８、助触媒を添加しないものを比較例１９として同様の実験を行った。結果を図４に示す。図中、●は、実施例１２（Ｐｄ＋ＣｕＯ）、□は比較例１７（Ｐｄのみ）、△は比較例１８（ＣｕＯのみ）、◇は比較例１９（いずれもなし）、をそれぞれ示している。
図から明らかなように、パラジウムと酸化銅の両方を同時に助触媒として用いた実施例１２は、比較例１７〜１９に比較して分解反応が速く進行した。
Further, as Example 12, a visible light responsive photocatalyst prepared by simultaneously adding 0.001% by weight of palladium powder and 0.1% by weight of copper oxide powder as a co-catalyst to tungsten oxide powder was used in the same manner as in Example 1. An experiment was conducted in which toluene was decomposed by all-light irradiation of a xenon lamp under the condition of adding water. The same experiment was conducted with Comparative Example 17 in which the promoter was palladium only, Comparative Example 18 in which only the copper oxide was added, and Comparative Example 19 in which the promoter was not added. The results are shown in FIG. In the figure, ● represents Example 12 (Pd + CuO), □ represents Comparative Example 17 (Pd only), Δ represents Comparative Example 18 (CuO only), and ◇ represents Comparative Example 19 (none).
As is clear from the figure, in Example 12, in which both palladium and copper oxide were simultaneously used as promoters, the decomposition reaction proceeded faster than Comparative Examples 17-19.
さらに、実施例１３として、酸化タングステン粉末に助触媒としてパラジウム粉末０．００１重量％、酸化銅粉末０．１重量％を同時に加えて調整した可視光応答性光触媒に、実施例１と同様にして水分を添加した条件下でキセノンランプの全光照射によりベンズアルデヒドを分解する実験を行った。助触媒がパラジウムのみのものを比較例２０、酸化銅のみのものを比較例２１、助触媒を添加しないものを比較例２２として同様の実験を行った。結果を図５に示す。図中、●は、実施例１３（Ｐｄ＋ＣｕＯ）、□は比較例２０（Ｐｄのみ）、△は比較例２１（ＣｕＯのみ）、◇は比較例２２（いずれもなし）、をそれぞれ示している。
図から明らかなように、パラジウムと酸化銅の両方を同時に助触媒として用いた実施例１３は、比較例２０〜２２に比較して分解反応が速く進行した。
Further, as Example 13, a visible light responsive photocatalyst prepared by simultaneously adding 0.001% by weight of palladium powder and 0.1% by weight of copper oxide powder as a co-catalyst to tungsten oxide powder was used in the same manner as in Example 1. An experiment was conducted to decompose benzaldehyde by all-light irradiation of a xenon lamp under the condition of adding water. The same experiment was conducted with Comparative Example 20 in which the promoter was palladium only, Comparative Example 21 in which only the copper oxide was added, and Comparative Example 22 in which the promoter was not added. The results are shown in FIG. In the figure, ● represents Example 13 (Pd + CuO), □ represents Comparative Example 20 (Pd only), Δ represents Comparative Example 21 (CuO only), and ◇ represents Comparative Example 22 (none).
As is apparent from the figure, the decomposition reaction of Example 13 using both palladium and copper oxide as co-catalyst proceeded faster than Comparative Examples 20-22.
それに加えて、実施例１４として、酸化タングステン粉末に助触媒としてパラジウム粉末０．００１重量％、酸化銅粉末０．１重量％を同時に加えて調整した可視光応答性光触媒に、実施例１と同様にして水分を添加した条件下でキセノンランプの全光照射により安息香酸を分解する実験を行った。助触媒がパラジウムのみのものを比較例２３、酸化銅のみのものを比較例２４、助触媒を添加しないものを比較例２５として同様の実験を行った。結果を図６に示す。図中、●は、実施例１４（Ｐｄ＋ＣｕＯ）、□は比較例２３（Ｐｄのみ）、△は比較例２４（ＣｕＯのみ）、◇は比較例２５（いずれもなし）、をそれぞれ示している。
図から明らかなように、パラジウムと酸化銅の両方を同時に助触媒として用いた実施例１４は、比較例２３〜２５に比較して分解反応が速く進行した。
In addition, as Example 14, a visible light responsive photocatalyst prepared by simultaneously adding 0.001% by weight of palladium powder and 0.1% by weight of copper oxide powder as promoters to tungsten oxide powder was the same as in Example 1. An experiment was conducted in which benzoic acid was decomposed by the total light irradiation of a xenon lamp under the condition of adding water. The same experiment was conducted with Comparative Example 23 in which the promoter was palladium only, Comparative Example 24 in which only the copper oxide was added, and Comparative Example 25 in which the promoter was not added. The results are shown in FIG. In the figure, ● represents Example 14 (Pd + CuO), □ represents Comparative Example 23 (Pd only), Δ represents Comparative Example 24 (CuO only), and ◇ represents Comparative Example 25 (none).
As is clear from the figure, in Example 14 in which both palladium and copper oxide were simultaneously used as promoters, the decomposition reaction proceeded faster than Comparative Examples 23-25.
別の助触媒を添加した実施例１５として、酸化タングステン粉末に助触媒としてパラジウム粉末０．００１重量％加え、塩化銅水溶液（０．０１Ｍ）を同時に滴下により添加して調整した可視光応答性光触媒に、実施例１と同様にして水分を添加した条件下でキセノンランプの全光照射によりトルエンを分解する実験を行った。助触媒がパラジウムのみのものを比較例２６、塩化銅水溶液（０．０１Ｍ）の添加のみのものを比較例２７、助触媒を添加しないものを比較例２８として同様の実験を行った。結果を図７に示す。図中、●は、実施例１５（Ｐｄ＋ＣｕＣｌ２）、□は比較例２６（Ｐｄのみ）、△は比較例２７（ＣｕＣｌ２のみ）、◇は比較例２８（いずれもなし）、をそれぞれ示している。
図から明らかなように、パラジウムと塩化銅の両方を同時に助触媒として用いた実施例１５は、比較例２６〜２８に比較して分解反応が速く進行した。
As Example 15 in which another cocatalyst was added, a visible light responsive photocatalyst prepared by adding 0.001% by weight of palladium powder as a cocatalyst to tungsten oxide powder and simultaneously adding a copper chloride aqueous solution (0.01M) dropwise. In the same manner as in Example 1, an experiment was conducted in which toluene was decomposed by the total light irradiation of a xenon lamp under the condition of adding water. The same experiment was conducted with Comparative Example 26 in which the promoter was only palladium, Comparative Example 27 in which only the copper chloride aqueous solution (0.01 M) was added, and Comparative Example 28 in which the promoter was not added. The results are shown in FIG. In the figure, ● represents Example 15 (Pd + CuCl 2 ), □ represents Comparative Example 26 (Pd only), Δ represents Comparative Example 27 (CuCl 2 only), and ◇ represents Comparative Example 28 (none). Yes.
As is apparent from the figure, the decomposition reaction of Example 15 using both palladium and copper chloride as co-catalyst proceeded faster than Comparative Examples 26-28.
以上のとおり、貴金属と銅化合物の両方を同時に助触媒として用いると助触媒がいずれか一種の場合と比較して光触媒活性が著しく向上する。本件発明の水分添加による改質もこれら２種類の助触媒を用いることにより大きな効果を得ることができる。 As described above, when both the noble metal and the copper compound are used as a cocatalyst at the same time, the photocatalytic activity is remarkably improved as compared with the case where any one of the cocatalysts is used. The reforming by the addition of water in the present invention can also achieve a great effect by using these two types of promoters.
１：可視光応答性光触媒
２：光照射部
３：水分添加部
４：被処理気体導入部
５：被処理気体放出部
６：水分貯蔵部
７：水分導入部
８：水分放出部
1: Visible light responsive photocatalyst 2: Light irradiation unit 3: Water addition unit 4: Gas to be treated introduction unit 5: Gas treatment release unit 6: Water storage unit 7: Water introduction unit 8: Water release unit
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