JP4000374B2 - Semiconductor metal oxide photocatalyst and method for decomposing hazardous chemicals using the same - Google Patents
Semiconductor metal oxide photocatalyst and method for decomposing hazardous chemicals using the same Download PDFInfo
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- GNRSAWUEBMWBQH-UHFFFAOYSA-N nickel(II) oxide Inorganic materials [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 1
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- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
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- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Oxygen, Ozone, And Oxides In General (AREA)
- Catalysts (AREA)
Description
この出願の発明は、半導体金属酸化物光触媒およびそれを用いた有害化学物質の分解方法に関するものである。さらに詳しくは、この出願の発明は、正孔電荷が空間分離されることにより光触媒酸化分解作用が高効率となる、半導体金属酸化物光触媒およびそれを用いた有害化学物質の分解方法に関するものである。 The invention of this application relates to a semiconductor metal oxide photocatalyst and a method for decomposing harmful chemical substances using the same. More specifically, the invention of this application relates to a semiconductor metal oxide photocatalyst having a high efficiency of photocatalytic oxidative decomposition action due to space separation of hole charges and a method for decomposing a harmful chemical substance using the same. .
現在地球温暖化が世界的な問題となっているが、この原因は大気中の二酸化炭素の急増にある。いまのペースで増え続けると２１世紀末には世界平均で１．４〜５．８℃上昇し、地域的にはさらに大きな上昇が予測されている。また、海面水位の上昇で考えると、２１世紀末までに９〜８８センチに達するとの予測も示されており、地球の生態系や気候変動に大きな悪影響を及ぼすと考えられている。 Currently, global warming is a global problem, which is caused by the rapid increase in atmospheric carbon dioxide. If it continues to increase at the current pace, the global average will rise by 1.4 to 5.8 ° C at the end of the 21st century, and a larger increase is predicted in the region. In addition, when the sea level rises, it is predicted that it will reach 9 to 88 centimeters by the end of the 21st century, which is considered to have a serious adverse effect on the global ecosystem and climate change.
これを避けるため、二酸化炭素を排出しないクリーンなエネルギーとして、水素が最近注目されている。水素は、熱効率がガソリンの３倍程度と大きい上、燃焼後は水となるため、燃焼後に有害物質を発生させない点で理想的燃料と考えられる。また、水素は燃料電池の燃料ともなり、クリーンなエネルギー源としてその発生技術開発が急がれている。しかしながら、その水素を生成するために二酸化炭素や有害廃棄物を発生させたり、貴重な有限資源を大量に消費して枯渇させたりしては意味がない。 In order to avoid this, hydrogen has recently attracted attention as a clean energy that does not emit carbon dioxide. Hydrogen is considered to be an ideal fuel because it has a thermal efficiency about three times that of gasoline and becomes water after combustion, so that no harmful substances are generated after combustion. Hydrogen is also a fuel for fuel cells, and its generation technology is urgently being developed as a clean energy source. However, it does not make sense to generate carbon dioxide and hazardous waste to generate the hydrogen, or to consume and deplete valuable limited resources in large quantities.
そこで有望なのが、太陽エネルギーを活用した水素の生成技術である。一年間で地上に届く太陽エネルギーは人類の年間エネルギー消費量の１万倍に相当するほど莫大である。その太陽エネルギーの利用法のひとつとして、水と無尽蔵な太陽光から、半導体金属酸化物光触媒を用いて、クリーンな燃料となる水素や酸素を直接製造する人工光合成技術が考えられる。光触媒は、そのバンドギャップ以上のエネルギーを吸収すると、正孔と電子を生成し、これらがそれぞれ水と酸化反応、還元反応を行い、酸素や水素を発生させる。この光触媒の実用化を考えた場合、光源として太陽光を如何に効率よく利用するかは重要な問題である。 What is promising is hydrogen generation technology that uses solar energy. The solar energy that reaches the ground in one year is enormous, equivalent to 10,000 times the annual energy consumption of mankind. One of the methods of utilizing solar energy is an artificial photosynthesis technology that directly produces hydrogen and oxygen as clean fuels from water and inexhaustible sunlight using a semiconductor metal oxide photocatalyst. When the photocatalyst absorbs energy greater than its band gap, it generates holes and electrons, which respectively undergo an oxidation reaction and a reduction reaction with water to generate oxygen and hydrogen. When practical application of this photocatalyst is considered, how to efficiently use sunlight as a light source is an important issue.
一方で、光触媒の応用は有害化学物質の分解処理技術としても広く検討されて始めている。水中や土壌あるいは大気中の農薬や悪臭物質などの有機物の分解、触媒コーティングによるガラスや陶器などの固体表面のセルフクリーニングなどへの応用もその一例である。現在のところ、それらの技術の大半は二酸化チタンを用いるため、可視光線ではほとんど働かず、また紫外線に対しても効率の改善余地が非常に大きい。 On the other hand, the application of photocatalysts has begun to be widely studied as a technique for decomposing harmful chemical substances. Examples include the decomposition of organic substances such as pesticides and malodorous substances in water, soil or air, and self-cleaning of solid surfaces such as glass and ceramics by catalytic coating. At present, since most of these technologies use titanium dioxide, they hardly work with visible light, and there is much room for improving efficiency against ultraviolet light.
上記の応用のほとんどは光触媒中に励起される正孔と電子がスムーズに空間的に分離し、無駄な再結合が減らされれば、効率は格段に向上すると期待できる。金属酸化物光触媒系でその際重要になるのが価電子帯のポテンシャルの空間分布の設計である。従来の多くの半導体光触媒は光励起で生成された正孔と電子の空間的分離が十分ではなく、光励起で生じた正孔と電子が励起過程の逆過程を辿るなどして、対象化合物を酸化還元する前に無駄な再結合を起こして励起された正孔と電子が消滅してしまい、水素や酸素の生成効率や分子の分解効率が低いという難点があった。 In most of the above applications, if the holes and electrons excited in the photocatalyst are smoothly and spatially separated, and wasteful recombination is reduced, the efficiency can be expected to be greatly improved. What is important in metal oxide photocatalytic systems is the design of the spatial distribution of the valence band potential. Many conventional semiconductor photocatalysts do not have sufficient spatial separation of holes and electrons generated by photoexcitation, and the target compounds are oxidized and reduced by following the reverse process of the excitation process. In other words, useless recombination occurs before the excited holes and electrons disappear, resulting in low hydrogen and oxygen generation efficiency and low molecular decomposition efficiency.
励起された電子については白金などの貴金属を用いて空間的分離の促進を図っていたが、正孔については酸素原子をそのまま利用する場合が多かった。もともと多くの半導体金属酸化物の場合、電子に比べ正孔の移動能力は低く、光励起で発生した正孔を集合させる技術はほとんどなかった。 For excited electrons, a precious metal such as platinum was used to promote spatial separation, but for holes, oxygen atoms were often used as they were. Originally, many semiconductor metal oxides have a lower ability to move holes than electrons, and there has been almost no technique for collecting holes generated by photoexcitation.
この出願の発明者等も半導体金属酸化物を光触媒として用いる研究を行ってきたが（非特許文献１）、これまで光励起で発生した正孔を集合させることができ、光触媒酸化分解作用が高効率な半導体金属酸化物は得られていなかった。
そこで、この出願の発明は、以上のとおりの事情に鑑みてなされたものであり、従来技術の問題点を解消し、正孔の空間分離により、励起されて得られた正孔電子対の無効な再結合を防ぎ、実用化に重要な光触媒酸化分解作用が高効率な半導体金属酸化物光触媒とその応用方法を提供することを課題としている。 Therefore, the invention of this application has been made in view of the circumstances as described above, which eliminates the problems of the prior art and invalidates hole electron pairs obtained by excitation by spatial separation of holes. It is an object of the present invention to provide a semiconductor metal oxide photocatalyst that is highly effective in photocatalytic oxidative decomposition, which is important for practical use, and its application method.
この出願の発明は、上記の課題を解決するものとして、まず第１には、占有最高準位である価電子帯頂上に５０％以上１００％以下の組成率で酸素原子の２ｐ軌道が存在し、かつ非占有最低準位である伝導帯の底部にＣｕ、Ｎｉ、Ｃｏ以外の金属元素Ｘおよび遷移金属Ｔの少なくとも一方の原子軌道成分がＸとＴの成分合計５０％以上１００％の組成率で存在しているＴＯ化合物、ＸＯ化合物およびそれらの複合酸化化合物であるＸＴＯ化合物のうちのいずれかの半導体金属酸化物の結晶構造中に、酸素６個で囲まれている金属元素Ｘあるいは遷移金属Ｔが存在し、その酸素６個で囲まれている金属元素Ｘあるいは遷移金属Ｔの一部がＣｕ、ＮｉあるいはＣｏで置換されてＣｕ、ＮｉあるいはＣｏを酸素原子６個で囲むＣＮＣＯＨＤ八面体が形成されており、このＣＮＣＯＨＤ八面体により、母体であるＴＯ化合物、ＸＯ化合物およびそれらの複合酸化化合物であるＸＴＯ化合物のうちのいずれかの半導体金属酸化物より形成される光励起に寄与する金属酸素多面体の１個ないし２個を、その稜あるいは頂点を共有するように挟み込んだ構造を有していることを特徴とする半導体金属酸化物光触媒を提供する。 In order to solve the above problems, the invention of this application firstly has a 2p orbit of oxygen atoms at a composition ratio of 50% or more and 100% or less on the top of the valence band which is the highest occupied level. In addition, at the bottom of the conduction band that is the lowest unoccupied level, at least one atomic orbital component of the metal element X other than Cu, Ni, and Co and the transition metal T has a total composition ratio of 50% to 100%. The metal element X or transition metal surrounded by 6 oxygen atoms in the crystal structure of the semiconductor metal oxide of any one of the TO compound, XO compound, and XTO compound that is a complex oxide compound thereof There is a CNCOHD octahedron in which T is present and a part of the metal element X or transition metal T surrounded by six oxygen atoms is replaced by Cu, Ni or Co, and Cu, Ni or Co is surrounded by six oxygen atoms. A metal oxygen polyhedron that is formed by the CNCOHD octahedron and contributes to photoexcitation formed from a semiconductor metal oxide of any one of a parent TO compound, an XO compound, and an XTO compound that is a complex oxide compound thereof The semiconductor metal oxide photocatalyst is characterized in that it has a structure in which one or two of these are sandwiched so as to share the edges or vertices thereof.
第２には、この出願の発明は、第１の発明において、Ｃｕ、ＮｉあるいはＣｏ同士が、平均距離が６Å以上で離散的に配置されていることを特徴とする半導体金属酸化物光触媒を提供する。 Second, the invention of this application provides the semiconductor metal oxide photocatalyst according to the first invention, characterized in that Cu, Ni or Co are discretely arranged with an average distance of 6 mm or more. To do.
さらに、第３には、第１または２の発明において、貴金属、遷移金属、ＮｉＯ、ＩｒＯ２、ＮｉＯｘおよびＲｕＯ２のうちのいずれかの助触媒を担持していることを特徴とする半導体金属酸化物光触媒を提供する。 Further, thirdly, in the first or second invention, a semiconductor metal carrying a promoter of any of noble metal, transition metal, NiO, IrO 2 , NiO x and RuO 2 An oxide photocatalyst is provided.
また、第４には、第１ないし３いずれかの発明において、酸素製造用光触媒あるいは水素製造用光触媒として用いられることを特徴とする半導体金属酸化物光触媒を提供する。 According to a fourth aspect of the present invention, there is provided a semiconductor metal oxide photocatalyst used as the photocatalyst for oxygen production or the photocatalyst for hydrogen production in any one of the first to third inventions.
第５には、第１ないし３いずれかの発明において、水分解用光触媒として用いられることを特徴とする半導体金属酸化物光触媒を提供する。 Fifth, in any one of the first to third inventions, there is provided a semiconductor metal oxide photocatalyst characterized by being used as a water splitting photocatalyst.
第６には、第１ないし３いずれかの発明において、化学物質分解用光触媒または化学物質製造用光触媒として用いられることを特徴とする半導体金属酸化物光触媒を提供する。 Sixthly, in any one of the first to third inventions, there is provided a semiconductor metal oxide photocatalyst used as a photocatalyst for chemical substance decomposition or a photocatalyst for chemical substance production.
第７には、第６の発明の化学物質分解用光触媒としての半導体金属酸化物光触媒の存在下で、有害化学物質に光を照射することを特徴とする有害化学物質の分解方法をも提供す
る。
Seventh, the present invention also provides a method for decomposing a harmful chemical substance, characterized by irradiating the hazardous chemical substance with light in the presence of the semiconductor metal oxide photocatalyst as the photocatalyst for chemical substance decomposition of the sixth invention. .
この出願の発明により、正孔の空間分離により、励起されて得られた正孔電子対の無効な再結合を防ぎ、実用化に重要な光触媒酸化分解作用が高効率な半導体金属酸化物光触媒が得られる。 According to the invention of this application, a semiconductor metal oxide photocatalyst that has high efficiency in photocatalytic oxidative decomposition, which is important for practical use, prevents ineffective recombination of hole electron pairs obtained by excitation by space separation of holes. can get.
この出願の発明は上記のとおりの特徴をもつものであるが、以下にその実施の形態について説明する。 The invention of this application has the features as described above, and an embodiment thereof will be described below.
この出願の発明の半導体金属酸化物光触媒は、占有最高準位である価電子帯頂上に５０％以上１００％以下の組成率で酸素原子の２ｐ軌道が存在し、かつ非占有最低準位である伝導帯の底部にＣｕ、Ｎｉ、Ｃｏ以外の金属元素Ｘおよび遷移金属Ｔ少なくとも一方の原子軌道成分がＸとＴの成分合計５０％以上１００％の組成率で存在しているＴＯ化合物、ＸＯ化合物およびそれらの複合酸化化合物であるＸＴＯ化合物のうちのいずれかの半導体金属酸化物の結晶構造中に、酸素６個で囲まれている金属元素Ｘあるいは遷移金属Ｔが存在し、その酸素６個で囲まれている金属元素Ｘあるいは遷移金属Ｔの一部がＣｕ、ＮｉあるいはＣｏで置換されてＣｕ、ＮｉあるいはＣｏを酸素原子６個で囲む八面体（以下「ＣＮＣＯＨＤ八面体」とする）が形成されており、このＣＮＣＯＨＤ八面体により、母体であるＴＯ化合物、ＸＯ化合物およびそれらの複合酸化化合物であるＸＴＯ化合物のうちのいずれかの半導体金属酸化物より形成される光励起に寄与する金属酸素多面体の１個ないし２個を、その稜あるいは頂点を共有するように挟み込んだ構造を有していることを大きな特徴としている。 The semiconductor metal oxide photocatalyst of the invention of this application has a 2p orbit of oxygen atoms at the composition ratio of 50% or more and 100% or less on the top of the valence band, which is the highest occupied level, and is the lowest unoccupied level. TO compounds and XO compounds in which at least one atomic orbital component other than Cu, Ni, Co and transition metal T is present at the bottom of the conduction band at a composition ratio of 50% or more and 100% of the total components of X and T In addition, a metal element X or a transition metal T surrounded by six oxygen atoms is present in the crystal structure of the semiconductor metal oxide of any of the XTO compounds that are complex oxide compounds thereof. An octahedron (hereinafter referred to as “CNCOHD octahedron”) in which a part of the enclosed metal element X or transition metal T is replaced with Cu, Ni or Co and Cu, Ni or Co is surrounded by six oxygen atoms is formed. And a metal oxygen polyhedron that contributes to photoexcitation formed by the CNCOHD octahedron and is formed from a semiconductor metal oxide of any one of a parent TO compound, an XO compound, and an XTO compound that is a complex oxide thereof. The main feature is that it has a structure in which one or two of these are sandwiched so as to share the edges or vertices thereof.
このような構造を有する半導体金属酸化物光触媒は、光励起によってＣｕ、ＮｉあるいはＣｏ周辺の酸素原子上に生じた正孔を、Ｃｕ、ＮｉあるいはＣｏの３ｄエネルギー準位の性質を利用してＣｕ、ＮｉあるいはＣｏ元素周辺へ移動集中させて空間的に電荷の分離を図ることができ、正孔の無駄な再結合消失を防ぐことができ、その結果光触媒酸化分解作用が高効率な半導体金属酸化物光触媒となるのである。 The semiconductor metal oxide photocatalyst having such a structure uses holes generated on oxygen atoms around Cu, Ni, or Co by photoexcitation using Cu, Ni or Co 3d energy level properties, Cu, It is possible to separate the charges spatially by moving and concentrating around the Ni or Co element, preventing the loss of useless recombination of holes, and as a result, a highly efficient semiconductor metal oxide with a photocatalytic oxidative decomposition action It becomes a photocatalyst.
このときＴは一種類の遷移金属元素でも複数種の遷移金属元素でも良く、Ｘも一種類の金属元素でも複数種の金属元素であっても良い。また、結晶構造中にＴあるいはＸを酸素原子６個で囲む八面体構造が稜あるいは頂点を連ねて存在し、かつ、その物質が半導体金属酸化物であるという条件を満たせば、ＴＯ、ＸＯあるいはＸＴＯのＸ、Ｔ、Ｏの原子組成比自体に制限はない。 At this time, T may be one kind of transition metal element or plural kinds of transition metal elements, and X may be one kind of metal element or plural kinds of metal elements. In addition, if the crystal structure has an octahedral structure in which T or X is surrounded by six oxygen atoms, the ridges or vertices are continuous, and the material is a semiconductor metal oxide, TO, XO or There is no limitation on the atomic composition ratio of X, T, and O of XTO.
また酸素６個で囲まれた金属元素Ｘあるいは酸素６個で囲まれた遷移金属Ｔの一部をＣｕ、ＮｉあるいはＣｏで置換するとき、Ｃｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体の周辺には、できるだけ同様のＣＮＣＯＨＤ八面体を配置しないのが望ましい。ＣＮＣＯＨＤ八面体の周りには、その母体である半導体金属酸化物の電子構造上、価電子帯頂上と伝導帯の底部の原子軌道成分に寄与していて、かつ、Ｃｕ、ＮｉあるいはＣｏを含まない母体である金属酸素多面体（以下この多面体を「ＭＯＰＨＤ」とする）をその稜あるいは頂点を共有するように配置する必要がある。このＭＯＰＨＤは八面体でも四面体でもあるいは他の型でもかまわない。理想的には、ＣＮＣＯＨＤ八面体の正孔収集能力範囲を考慮して、Ｃｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体と最も近くに存在する別のＣｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体との間に１個から２個程度のＭＯＰＨＤが存在するように配置する。さらに、任意のＣｕ、ＮｉあるいはＣｏに対して、最も近いＣｕ、ＮｉあるいはＣｏまでの距離が５．７Å程度以上、平均距離にして６Å以上の距離になるように離散して配置することが望ましく、その上限としては９
Å以下程度であることが望ましい。
When a part of the metal element X surrounded by 6 oxygen atoms or the transition metal T surrounded by 6 oxygen atoms is replaced by Cu, Ni or Co, the periphery of the CNCOHD octahedron centered on Cu, Ni or Co It is desirable not to place the same CNCOHD octahedron as much as possible. Around the CNCOHD octahedron, it contributes to the atomic orbital components at the top of the valence band and the bottom of the conduction band, and does not contain Cu, Ni, or Co, due to the electronic structure of the base semiconductor metal oxide. The metal oxygen polyhedron (hereinafter, this polyhedron is referred to as “MOPHD”), which is a base material, needs to be arranged so as to share the edges or vertices thereof. This MOPHD may be octahedron, tetrahedron or other types. Ideally, in consideration of the hole collection capability range of a CNCOHD octahedron, a CNCOHD octahedron centered on Cu, Ni or Co and another CNCOHD octahedron centered on another Cu, Ni or Co closest to the CNCOHD octahedron Arranged so that about 1 to 2 MOPHDs exist between the face pieces. Furthermore, it is desirable that the distance to the nearest Cu, Ni, or Co is discretely arranged so that the distance to the nearest Cu, Ni, or Co is about 5.7 mm or more and the average distance is 6 mm or more with respect to any Cu, Ni, or Co. The upper limit is 9
It is desirable to be less than or equal to Å.
しかし理想的状況を実現することは必ずしも容易ではないため、厳密には上記の「Ｃｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体の周辺には、できるだけ同様のＣＮＣＯＨＤ八面体を配置しない」という条件を維持する必要はなく、製造技術と経済性を考慮して妥協点を探ればよい。触媒粒子中にＣＮＣＯＨＤ八面体が隣接して存在する部分が多少あっても触媒としては機能するが多すぎる場合は、母体結晶構造そのものを維持できなかったり、電子構造が激変したり、金属的性質が強くなったりして触媒機能が失われることがあるので注意が必要である。 However, since it is not always easy to realize the ideal situation, strictly speaking, the condition that “the same CNCOHD octahedron is not arranged as much as possible around the CNCOHD octahedron centered on Cu, Ni, or Co” is used. It is not necessary to maintain the system, and it is only necessary to search for a compromise with consideration of manufacturing technology and economy. Even if there are some adjacent CNCOHD octahedrons in the catalyst particles, it will function as a catalyst, but if it is too much, the host crystal structure itself cannot be maintained, the electronic structure may change drastically, or the metallic properties Care must be taken because the catalytic function may be lost due to an increase in the pressure.
なお、Ｃｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体において、酸素原子とＣｕ、ＮｉあるいはＣｏまでの距離は、通常概ね１．８Å〜２．３Å程度である。この出願の発明の半導体金属酸化物光触媒の電子構造の特徴は、その占有最高準位がＣｕ、ＮｉあるいはＣｏの３ｄ軌道準位に応じて変わることである。Ｃｕ、ＮｉあるいはＣｏを囲む酸素原子までの距離が仮に同じであると仮定すれば、この出願の発明の半導体金属酸化物光触媒の占有最高準位はＣｕ、Ｎｉ、Ｃｏの順で高くなる傾向がある。また、置換元素をＣｕ、Ｎｉ、Ｃｏのどれか一つに定めれば、酸素までの距離が短くなるほどその占有最高準位は高くなる傾向にある。５０％以上１００％以下の組成率で酸素の２ｐ軌道成分が存在する母体半導体金属酸化物光触媒の占有最高準位よりわずかに高くなるようにＣｕ、ＮｉあるいはＣｏのいずれかを選択することが望ましいが、分解する標的分子の性質にあわせて適宜調整してもよい。 In the CNCOHD octahedron centered on Cu, Ni or Co, the distance between the oxygen atom and Cu, Ni or Co is generally about 1.8 to 2.3 mm. The feature of the electronic structure of the semiconductor metal oxide photocatalyst of the invention of this application is that its occupied highest level changes according to the 3d orbital level of Cu, Ni or Co. Assuming that the distance to oxygen atoms surrounding Cu, Ni or Co is the same, the highest occupied level of the semiconductor metal oxide photocatalyst of the invention of this application tends to increase in the order of Cu, Ni and Co. is there. If the substitution element is set to any one of Cu, Ni, and Co, the occupied maximum level tends to increase as the distance to oxygen decreases. It is desirable to select either Cu, Ni, or Co so that it is slightly higher than the highest occupied level of the parent semiconductor metal oxide photocatalyst in which the oxygen 2p orbital component exists at a composition ratio of 50% to 100%. However, you may adjust suitably according to the property of the target molecule to decompose.
またこの出願の発明の半導体金属酸化物光触媒は、主に水素、炭素、窒素、酸素をその構成要素とする分子の分解や合成過程にも原理的に応用可能であるため、光による分子製造技術に多大な貢献をもたらすと考えられる。 In addition, the semiconductor metal oxide photocatalyst of the invention of this application can be applied in principle to molecular decomposition and synthesis processes mainly composed of hydrogen, carbon, nitrogen, and oxygen. It is thought to bring a great contribution to
なお、この出願の発明の半導体金属酸化物光触媒においては、酸化物ＸＴＯ化合物、ＸＯ、ＴＯを母体結晶として使用し、前述した条件を満たすようにＸあるいはＴを、Ｃｕ、ＮｉあるいはＣｏで置換した物質を使用するが、Ｃｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体の隣接条件は必ずしも厳密に満たされる必要はない。 In the semiconductor metal oxide photocatalyst of the invention of this application, the oxide XTO compound, XO, or TO is used as a base crystal, and X or T is substituted with Cu, Ni, or Co so as to satisfy the above-described conditions. Although materials are used, the adjacent conditions of the CNCOHD octahedron centered on Cu, Ni or Co do not necessarily have to be strictly met.
なお、酸素６個で囲まれたＸあるいはＴの一部をＣｕ、ＮｉあるいはＣｏに置換するには、例えば固相反応法による場合は、ＸＴＯ結晶を製作する出発原料物質の中にＣｕ、ＮｉあるいはＣｏまたはその化合物を微量に混入することで可能となる場合があるし、あるいはイオン注入技術、各種蒸着技術などを利用して実現することが可能であるが、その製法はここでは問題ではない。 In order to replace a part of X or T surrounded by 6 oxygen atoms with Cu, Ni or Co, for example, in the case of the solid phase reaction method, Cu, Ni in the starting material for producing the XTO crystal Alternatively, it may be possible by mixing a small amount of Co or a compound thereof, or can be realized by using ion implantation technology, various vapor deposition technologies, etc., but the manufacturing method is not a problem here. .
また、この出願の発明の半導体金属酸化物光触媒の形状は、光を有効に利用するために微粒子で表面積の大きいことが望ましい。例えば、固相反応法で調製した酸化物は粒子が大きく表面積が小さいが、ボールミルなどで粉砕を行うことで粒子径を小さくできる。一般には粒子の大きさは１０ｎｍ〜２００μｍ程度である。固相反応法で調製した酸化物微粒子であればそれを成型して板状として使用することも可能である。各種薄膜形成技術を駆使して薄膜薄片状に製造して使用することも可能であるし、他の材質に薄膜状にコーティングして使用することもできる。また、触媒物質を壁材などに練りこむなどしてセルフクリーニング技術に応用しても良い。 Further, the shape of the semiconductor metal oxide photocatalyst of the invention of this application is desirably a fine particle and a large surface area in order to effectively use light. For example, an oxide prepared by a solid phase reaction method has large particles and a small surface area, but the particle size can be reduced by grinding with a ball mill or the like. In general, the size of the particles is about 10 nm to 200 μm. Oxide fine particles prepared by a solid phase reaction method can be molded and used as a plate. Various thin film forming techniques can be used to manufacture and use in the form of a thin film, or it can be used by coating other materials into a thin film. Further, the catalyst material may be applied to a self-cleaning technique by kneading it into a wall material or the like.
更に、この出願の発明の半導体金属酸化物光触媒に対しては、励起された電子を空間的に分離する目的でＰｔなどの貴金属、Ｎｉなどの遷移金属、ＮｉＯやＩｒＯ２、ＮｉＯｘ、ＲｕＯ２といった酸化物を助触媒として担持させて触媒表面を修飾することもできる。その担持方法は含浸法や光電着法などで行うことが出来る。又、水の分解反応を行う際に
用いる反応溶液は、純水に限らず、通常、水の分解反応によく用いられるように、適宜、炭酸塩や炭酸水素塩、ヨウ素塩、臭素塩等の塩類を混ぜた水を用いてもよい。上記水溶液に本発明の光触媒を添加する。触媒の添加量は、基本的に入射した光が効率よく吸収できる量を選ぶ。照射する光の波長は半導体の吸収がある領域の波長の光を含むことが必要である。またこの出願の発明においては太陽光を照射してもよい。
Furthermore, for the semiconductor metal oxide photocatalyst of the present invention, noble metals such as Pt, transition metals such as Ni, NiO, IrO 2 , NiO x , RuO 2 for the purpose of spatially separating excited electrons. Such an oxide can be supported as a cocatalyst to modify the catalyst surface. The supporting method can be performed by an impregnation method or a photo-deposition method. In addition, the reaction solution used for the water decomposition reaction is not limited to pure water, and is usually appropriately selected from carbonates, hydrogen carbonates, iodine salts, bromine salts, etc. You may use the water which mixed salt. The photocatalyst of the present invention is added to the aqueous solution. The amount of catalyst added is basically selected so that incident light can be efficiently absorbed. The wavelength of the light to be irradiated needs to include light having a wavelength in a region where the semiconductor is absorbed. In the invention of this application, sunlight may be irradiated.
この出願の発明の半導体金属酸化物光触媒は、Ｃｕ、ＮｉあるいはＣｏの３ｄ原子軌道の性質とそれを６個の酸素原子で取り囲まれていること、そしてそのＣＮＣＯＨＤ八面体が、価電子帯頂上が主に酸素原子の２ｐ軌道で構成され、かつ、伝導体の底が主に金属元素Ｘあるいは遷移金属Ｔの原子軌道成分で構成される半導体金属酸化物であるＴＯ化合物、ＸＯ化合物あるいはそれらの複合酸化化合物ＸＴＯの結晶構造中、ある程度離散的に含まれていることが本質的に重要で、その母体半導体金属酸化物として適当なものはＴｉＯ２やＩｎＶＯ４以外にも多数存在し、本発明の適用範囲は極めて広く有望なものである。 The semiconductor metal oxide photocatalyst of the invention of this application is characterized by the nature of the 3d atomic orbital of Cu, Ni, or Co and that it is surrounded by six oxygen atoms, and its CNCOHD octahedron has a valence band top. A TO compound, a XO compound, or a composite thereof, which is a semiconductor metal oxide mainly composed of 2p orbits of oxygen atoms and the bottom of the conductor is mainly composed of atomic elements of the metal element X or transition metal T In the crystal structure of the oxide compound XTO, it is essential that the oxide compound XTO is included to some extent, and there are many suitable materials other than TiO 2 and InVO 4 as the base semiconductor metal oxide. The scope of application is extremely wide and promising.
また触媒粒子が比較的大きい場合、あるいは、触媒薄膜が比較的厚い場合、それらの内部においては必ずしもＣｕ、ＮｉあるいはＣｏを中心とするＣＮＣＯＨＤ八面体が存在する必要はなく、それらの表面近傍においてのみこの出願の発明の半導体金属酸化物触媒の構造を構築してもよい。 Also, when the catalyst particles are relatively large or the catalyst thin film is relatively thick, there is not necessarily a CNCOHD octahedron centered on Cu, Ni, or Co inside them, only in the vicinity of their surfaces. The structure of the semiconductor metal oxide catalyst of the invention of this application may be constructed.
この出願の発明の半導体金属酸化物光触媒は、水の分解だけでなく多くの光触媒反応に応用できる。たとえば有機物の分解の場合、アルコールや農薬、悪臭物質などは一般に電子供与体として働き、正孔によって酸化分解される。この出願の発明の半導体金属酸化物触媒においては高い酸化効率が期待できる。反応形態は、有機物を含む水溶液に触媒を懸濁して光照射しても良いし、触媒を基板に固定しても良い。悪臭物質の分解のように気相反応でも良い。また本発明は、光触媒反応の選択反応性を利用して、各種分子の製造工程における素反応過程に応用することも可能である。 The semiconductor metal oxide photocatalyst of the invention of this application can be applied not only to water decomposition but also to many photocatalytic reactions. For example, in the case of decomposing organic substances, alcohol, agricultural chemicals, malodorous substances, etc. generally act as electron donors and are oxidatively decomposed by holes. In the semiconductor metal oxide catalyst of the invention of this application, high oxidation efficiency can be expected. As a reaction form, the catalyst may be suspended in an aqueous solution containing an organic substance and irradiated with light, or the catalyst may be fixed to a substrate. A gas phase reaction may be used, such as decomposition of malodorous substances. The present invention can also be applied to elementary reaction processes in the production process of various molecules by utilizing the selective reactivity of the photocatalytic reaction.
以下、添付した図面に沿って実施例を示し、この出願の発明の実施の形態についてさらに詳しく説明する。もちろん、この発明は以下の例に限定されるものではなく、細部については様々な態様が可能であることは言うまでもない。 Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.
＜実施例１＞
以下、この出願の発明の半導体金属酸化物光触媒の構造について図面を用いて詳細に説明する。以下の実施例においては、母体半導体金属酸化物としてＴｉＯ２を用いており、その組成比はＴｉ（遷移金属Ｔのチタニウム）:Ｏ（酸素）＝１：２であり、その属する
空間群はＰ４２／ｍｎｍであり、ルチル構造と称される。この構造は図１に示すように、結晶構造中、Ｔｉが６個の酸素に囲まれ、ＴｉＯ６八面体（１）を形成しており、それらＴｉＯ６八面体（１）が密接に連なっている。その電子構造の特徴は第一原理理論により求められ、価電子帯頂上は主に（５０％以上の組成率で）Ｏの２ｐ軌道により構成され、伝導帯の底部は図２に示すように、主に（５０％以上の組成率で）Ｔｉの３ｄ軌道で構成されており、この出願の発明の半導体金属酸化物光触媒における母体の半導体金属酸化物の構造を有している。
<Example 1>
Hereinafter, the structure of the semiconductor metal oxide photocatalyst of the invention of this application will be described in detail with reference to the drawings. In the following examples, TiO 2 is used as the base semiconductor metal oxide, the composition ratio thereof is Ti (titanium of transition metal T): O (oxygen) = 1: 2, and the space group to which it belongs is P4. 2 / mnm, referred to as a rutile structure. As shown in FIG. 1, in this structure, Ti is surrounded by six oxygen atoms to form a TiO 6 octahedron (1), and these TiO 6 octahedrons (1) are closely connected. Yes. The characteristics of the electronic structure are determined by first-principles theory, the top of the valence band is mainly composed of 2p orbitals of O (with a composition ratio of 50% or more), and the bottom of the conduction band is as shown in FIG. It is mainly composed of 3d orbitals of Ti (with a composition ratio of 50% or more), and has the structure of the parent semiconductor metal oxide in the semiconductor metal oxide photocatalyst of the invention of this application.
そして、図１に示すような半導体金属酸化物ＴｉＯ２の結晶構造において６個の酸素に囲まれたＴｉの一部がＣｕに置換されたＣＮＣＯＨＤ八面体であるＣｕＯ６八面体（２）（色の濃い部分）を含む半導体金属酸化物Ｔｉ２３Ｃｕ１Ｏ４８の結晶構造を図３に示す。さらに、図１に示す半導体金属酸化物ＴｉＯ２と図３に示す半導体金属酸化物Ｔｉ２３Ｃｕ１Ｏ４８の電子構造を、それぞれ図２および図４に示しているが、図２および図４ともに伝導帯の構造に大きな違いはなく、その主成分はＴｉの３ｄ軌道成分である。しかし
、図４、は図２と異なり、図中ｅｆで示す占有最高準位は主にＣｕの３ｄ軌道で形成されている。かつこの準位は酸素の２ｐ軌道で形成される母体半導体金属酸化物の価電子帯より僅かに（約０．３５ｅＶだけ）高いことがわかる。
Then, a CuO 6 octahedron (2) (color) which is a CNCOHD octahedron in which a part of Ti surrounded by six oxygen atoms is replaced by Cu in the crystal structure of the semiconductor metal oxide TiO 2 as shown in FIG. FIG. 3 shows the crystal structure of the semiconductor metal oxide Ti 23 Cu 1 O 48 including the dark portion. Further, the electronic structures of the semiconductor metal oxide TiO 2 shown in FIG. 1 and the semiconductor metal oxide Ti 23 Cu 1 O 48 shown in FIG. 3 are shown in FIGS. 2 and 4, respectively. There is no significant difference in the structure of the conduction band, and the main component is the 3d orbital component of Ti. However, unlike FIG. 2, FIG. 4 differs from FIG. 2 in that the occupied highest level indicated by ef is mainly formed by a 3d orbit of Cu. This level is slightly higher (by about 0.35 eV) than the valence band of the base semiconductor metal oxide formed by the oxygen 2p orbital.
以上のことから、光励起により２ｐ価電子帯に正孔が生じると、その正孔はエネルギー的に得になるようにＣｕの３ｄバンドに移動することになる。これは実空間では酸素元素近辺に生じた正孔がＣｕに移動したことに相当し、正孔のＣｕ原子サイトへの集合作用を示すものである。この移動が起こらない通常の金属酸化物半導体ＴｉＯ２では、光励起で生じた正孔と電子の一部が自然放出や誘導放出現象のため、励起過程の逆過程を辿り無駄に消費されやすい。しかしこの出願の発明の半導体金属酸化物光触媒では、生成された正孔は速やかにＣｕのサイトに移動するため、その逆過程は大幅に抑制される。これは、構成原子間の距離や電子波動関数の性質から、ＴｉからＣｕへ遷移する緩和過程の遷移双極子モーメントが、酸素からＴｉに遷移における励起過程の遷移双極子モーメントよりずっと小さいためである。 From the above, when holes are generated in the 2p valence band by photoexcitation, the holes move to the 3d band of Cu so as to be obtained energetically. This corresponds to the movement of holes generated in the vicinity of the oxygen element to Cu in the real space, and shows the collective action of the holes at the Cu atom site. In a normal metal oxide semiconductor TiO 2 in which this movement does not occur, a part of holes and electrons generated by photoexcitation is spontaneously emitted or stimulated emission, and therefore tends to be wastefully consumed following the reverse process of the excitation process. However, in the semiconductor metal oxide photocatalyst of the invention of this application, the generated holes move quickly to the Cu site, and the reverse process is greatly suppressed. This is because the transition dipole moment of the relaxation process of transition from Ti to Cu is much smaller than the transition dipole moment of the excitation process in the transition from oxygen to Ti due to the distance between constituent atoms and the nature of the electron wave function. .
これにより光励起で生じた正孔と電子が励起過程の逆過程を辿るなどして、反応対象化合物を酸化する前に正孔と電子が消滅する無効再結合を大幅に低減させることが可能となる。いわば分子レベルの電極を構築して、励起された正孔を、励起された電子（この例ではＴｉ近傍に存在する）から空間的に引き離したことになる。 This makes it possible to significantly reduce the invalid recombination in which holes and electrons disappear before the reaction target compound is oxidized, for example, by holes and electrons generated by photoexcitation following the reverse process of the excitation process. . In other words, a molecular level electrode is constructed, and the excited holes are spatially separated from the excited electrons (in this example, near Ti).
Ｃｕを結晶構造中に比較的離散的に配置するため、それらの原子による３ｄのバンドの幅は狭くなり、さらに、そのバンドには非占有状態が多数存在するため、反応対象分子中の酸素原子や窒素原子が吸着しやすく、またその吸着安定性も高い。つまり、この出願の発明に基づきＣｕを配置すると、Ｃｕは、正孔を収集する役割と反応対象分子を捕らえる役割の両方をこなすため、酸化対象物質から電子をより確実に抜き取ることができるため、触媒の酸化効率は飛躍的に高められるのである。
＜実施例２＞
次に半導体金属酸化物ＩｎＶＯ４の組成比はＩｎ（金属元素Ｘのインジウム）:Ｖ（遷
移金属Ｔのヴァナジウム）:Ｏ（酸素）=１：１：４であり、その属する空間群はＣｍｃｍである。結晶構造中、Ｉｎが６個の酸素に囲まれたＩｎＯ６八面体と、Ｖは４個の酸素に囲まれたＶＯ４四面体が存在し、その電子構造の特徴は実施例１と同様第一原理理論により求められ、価電子帯頂上が主にＯの２ｐ軌道で構成され、図６に示すように伝導帯の底は主に（約６０％の組成率）Ｖの３ｄ軌道で構成されている（Ｉｎの５ｓ軌道の成分も約２０％ほど存在する。）。したがって、Ｖ３ｄ＋Ｉｎ５ｓ（Ｘ＋Ｔ成分）が約８０％の組成率となる。なお、図５においてはＩｎが６個の酸素に囲まれたＩｎＯ６八面体（３）と、Ｖは４個の酸素に囲まれたＶＯ４四面体（４）が存在し、さらにＩｎの一部がＮｉで置換されたＣＮＣＯＨＤ八面体であるＮｉＯ６八面体（５）が存在する結晶構造を有しており、組成比Ｉｎ７Ｎｉ１Ｖ８Ｏ３２を有しており、最短Ｎｉ−Ｎｉ距離は６．６Åである。
Since Cu is relatively discretely arranged in the crystal structure, the width of the 3d band due to those atoms becomes narrow, and furthermore, since there are many unoccupied states in the band, oxygen atoms in the reaction target molecule And nitrogen atoms are easily adsorbed, and their adsorption stability is high. That is, when Cu is arranged based on the invention of this application, since Cu performs both the role of collecting holes and the role of capturing reaction target molecules, electrons can be more reliably extracted from the oxidation target substance. The oxidation efficiency of the catalyst is dramatically increased.
<Example 2>
Next, the composition ratio of the semiconductor metal oxide InVO 4 is In (indium of the metal element X): V (vanadium of the transition metal T): O (oxygen) = 1: 1: 4, and the space group to which it belongs is Cmcm. is there. In the crystal structure, there are an InO 6 octahedron in which In is surrounded by 6 oxygen atoms, and a VO 4 tetrahedron in which V is surrounded by 4 oxygen atoms. Obtained by one-principles theory, the top of the valence band is mainly composed of 2p orbitals of O, and the bottom of the conduction band is mainly composed of 3d orbitals of V (composition ratio of about 60%) as shown in FIG. (The component of the 5s orbital of In is also about 20%.) Accordingly, the composition ratio of V 3d + In 5s (X + T component) is about 80%. In FIG. 5, there are an InO 6 octahedron (3) in which In is surrounded by six oxygen atoms, and a VO 4 tetrahedron (4) in which V is surrounded by four oxygen atoms. NiO 6 octahedron (5), which is a CNCOHD octahedron in which part is substituted with Ni, has a crystal structure, has a composition ratio In 7 Ni 1 V 8 O 32 , and has the shortest Ni—Ni The distance is 6.6 km.
そして、図５に示す半導体金属酸化物Ｉｎ７Ｎｉ１Ｖ８Ｏ３２の結晶構造よりもさらに高い割合で６個の酸素に囲まれたＩｎの一部がＮｉに置換された半導体金属酸化物Ｉｎ７Ｎｉ１Ｖ８Ｏ４の結晶構造を図７に示す。この結晶構造においては最短Ｎｉ−Ｎｉ距離は５．１Åである。 Then, a part of In surrounded by six oxygen atoms at a higher rate than the crystal structure of the semiconductor metal oxide In 7 Ni 1 V 8 O 32 shown in FIG. 5 is replaced with Ni. The crystal structure of 7 Ni 1 V 8 O 4 is shown in FIG. In this crystal structure, the shortest Ni-Ni distance is 5.1 km.
そして、半導体金属酸化物ＩｎＶＯ４の電子構造、配列したＩｎ７Ｎｉ１Ｖ８Ｏ４の電子構造、さらにＣＮＣＯＨＤ八面体をより高濃度に含有させ、理想条件からずらした場合の電子構造をそれぞれ、図６、図８、図９に示す。図６、図８、図９ともに伝導帯の構造に大きな違いはなく、その主成分はＶの３ｄ軌道成分である。しかし、図８、図９は図６と異なり、図中ｅｆで示す占有最高準位（価電子帯頂上）は主にＮｉの３ｄ軌道で形成さ
れている。かつこの準位は酸素の２ｐで形成される母体半導体金属酸化物の価電子帯より約０．６５ｅＶだけ高いことがわかる。
The electronic structure of the semiconductor metal oxide InVO 4 , the electronic structure of the arranged In 7 Ni 1 V 8 O 4 , and the CNCOHD octahedron are contained at a higher concentration and shifted from the ideal condition, FIG. 6, FIG. 8, and FIG. 6, 8 and 9, there is no significant difference in the structure of the conduction band, and the main component is the 3d orbital component of V. However, FIG. 8 and FIG. 9 are different from FIG. 6, and the occupied highest level (top of the valence band) indicated by ef in the figure is mainly formed by Ni 3d orbitals. This level is higher by about 0.65 eV than the valence band of the base semiconductor metal oxide formed with 2p of oxygen.
以上のことから、光励起により２ｐ価電子帯に正孔が生じた場合、実施例１同様にその正孔はＮｉの３ｄバンドに移動する。これは実空間では酸素元素近辺に生じた正孔がＮｉに移動したことに相当し、正孔のＮｉ原子サイトへの集合作用を示すものである。この移動が起こらない通常の金属酸化物半導体では、光励起で生じた正孔と電子の一部が自然放出や誘導放出現象のため、励起過程の逆過程を辿り無駄に消費されやすい。しかし本発明を導入することにより、生成された正孔は速やかにＮｉのサイトに移動するため、その逆過程は大幅に抑制される。これは、構成原子間の距離や電子波動関数の性質から、Ｖ（あるいはＩｎ）からＮｉへ遷移する緩和過程の遷移双極子モーメントが、酸素からＶ（あるいはIn）に遷移における励起過程の遷移双極子モーメントよりずっと小さいためである。これにより光励起で生じた正孔と電子が励起過程の逆過程を辿るなどして、対象化合物を酸化する前に正孔と電子が消滅する無効再結合を防ぐことが可能となる。 From the above, when holes are generated in the 2p valence band by photoexcitation, the holes move to the 3d band of Ni as in Example 1. This corresponds to the movement of holes generated in the vicinity of the oxygen element to Ni in real space, and shows the collective action of the holes at the Ni atom site. In a normal metal oxide semiconductor in which this movement does not occur, a part of holes and electrons generated by photoexcitation is spontaneously emitted or stimulated emission, so that it tends to be wasted due to the reverse process of the excitation process. However, by introducing the present invention, the generated holes quickly move to the Ni site, and the reverse process is greatly suppressed. This is because the transition dipole moment of the relaxation process in the transition from V (or In) to Ni is the transition dipole of the excitation process in the transition from oxygen to V (or In) due to the distance between constituent atoms and the nature of the electron wave function. This is because it is much smaller than the child moment. This makes it possible to prevent invalid recombination in which holes and electrons disappear before the target compound is oxidized, for example, by holes and electrons generated by photoexcitation following the reverse process of the excitation process.
Ｎｉを結晶構造中に比較的離散的に配置するため、それらの原子による３ｄのバンドの幅は狭くなり、さらに、そのバンドには非占有状態が多数存在するため、反応対象分子中の酸素原子や窒素原子が吸着しやすく、またその吸着安定性も高い。つまり、Ｎｉをこの出願の発明に基づいて配置すると、Ｎｉは、正孔を収集する役割と反応対象分子を捕らえる役割の両方をこなすため、酸化対象物質から電子をより確実に抜き取ることができるため、触媒の酸化効率は飛躍的に高められる。 Since Ni is relatively discretely arranged in the crystal structure, the width of the 3d band due to those atoms becomes narrow, and furthermore, since there are many unoccupied states in the band, oxygen atoms in the reaction target molecule And nitrogen atoms are easily adsorbed, and their adsorption stability is high. In other words, when Ni is arranged based on the invention of this application, since Ni performs both a role of collecting holes and a role of capturing molecules to be reacted, electrons can be more reliably extracted from the oxidation target substance. The oxidation efficiency of the catalyst can be dramatically increased.
なお、高濃度に置換した場合である図９は、一見、その電子構造が図８ときわめて似ているが、結晶構造中において、光エネルギーの捕獲の役割を果たすＭＯＰＨＤの存在割合が減少してしまい、高い効率が期待できない。また、Ｎｉの濃度を高くしＮｉ３ｄ軌道同士が密接に連結するような状況がおきると、その部分が金属的な電気伝導を発現するようになり、触媒結晶中への光の進入を妨げたり、その伝導性により光エネルギーを失ってしまったりして、触媒活性を著しく損なう可能性が高い。３ｄ軌道同士の連結性の強さは、この例ではＮｉ３ｄバンドの広がり大きさ（射影状態密度スペクトルＮｉ３ｄ成分の太さ）を見ることである程度理解でき、その連結性はＮｉ同士の距離を約６ないし７Å以上離すことによりほぼ断ち切ることができると考えてよい。このことはＣｕやＣｏの場合でもほぼ同様である。また、高濃度に置換すると、母体結晶構造や電子構造が大きく変わってしまい、もはや触媒として成り立たなくなる可能性がある。 In addition, FIG. 9 which is a case where it is replaced with a high concentration at first glance has an electronic structure very similar to that of FIG. 8, but the proportion of MOPHD that plays a role of capturing light energy in the crystal structure is reduced. Therefore, high efficiency cannot be expected. In addition, when the situation where Ni concentration is increased and Ni3d orbitals are closely connected to each other, the portion develops metallic electrical conduction, preventing light from entering the catalyst crystal, There is a high possibility of losing light energy due to its conductivity and significantly impairing the catalytic activity. In this example, the strength of connectivity between 3d orbitals can be understood to some extent by looking at the spread size of the Ni3d band (the thickness of the projected state density spectrum Ni3d component). It can be considered that it can be almost cut off by separating 7 mm or more. This is almost the same for Cu and Co. Moreover, if the substitution is performed at a high concentration, the host crystal structure and the electronic structure may be greatly changed, and there is a possibility that the catalyst can no longer be realized as a catalyst.
以上詳しく説明したとおり、この出願の発明の半導体金属酸化物光触媒においては、光励起によって酸素原子上に生じた正孔を、Ｃｕ、ＮｉあるいはＣｏ元素周辺へ移動集中させて空間的に正孔電荷の分離を図り、正孔の無駄な再結合消滅を防ぐことが可能となり、光触媒酸化分解作用の大幅な高効率化が可能となる。またこの出願の発明によれば、電子構造の性質上、その波長感度領域をも幾分か広げることが可能な場合もあり、太陽光エネルギーを利用して水分子を分解し水素や酸素を生成するより効率的な技術の発展に大きく貢献できるものと考えられる。また、これらの光触媒を水の分解反応でなく、例えば有機物の分解反応や金属イオンの還元反応にも応用可能であるし、有害有機物を分解することによる環境浄化などにも大きく貢献できる。新しい光励起化学反応技術の発展にも幅広く寄与できるものと考えられる。 As described in detail above, in the semiconductor metal oxide photocatalyst of the invention of this application, holes generated on the oxygen atoms by photoexcitation are moved and concentrated around the Cu, Ni or Co element to spatially generate hole charges. Separation can be achieved, so that unnecessary recombination of holes can be prevented, and the photocatalytic oxidative decomposition action can be greatly improved in efficiency. Also, according to the invention of this application, the wavelength sensitivity region may be able to be expanded somewhat due to the nature of the electronic structure, and hydrogen and oxygen are generated by decomposing water molecules using solar energy. Therefore, it is thought that it can greatly contribute to the development of more efficient technology. Moreover, these photocatalysts can be applied not only to the decomposition reaction of water but also to, for example, the decomposition reaction of organic substances and the reduction reaction of metal ions, and can greatly contribute to environmental purification by decomposing harmful organic substances. It is thought that it can contribute widely to the development of new photoexcited chemical reaction technology.
１ ＴｉＯ６八面体
２ ＣｕＯ６八面体
３ ＩｎＯ６八面体
４ ＶＯ４四面体
４ ＮｉＯ６八面体
1 TiO 6 octahedron 2 CuO 6 octahedron 3 InO 6 octahedron 4 VO 4 tetrahedron 4 NiO 6 octahedron
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