JP4528944B2 - Photocatalyst carrying Ir oxide cocatalyst in oxidative atmosphere in the presence of nitrate ion and method for producing the same - Google Patents
Photocatalyst carrying Ir oxide cocatalyst in oxidative atmosphere in the presence of nitrate ion and method for producing the same Download PDFInfo
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- 239000011941 photocatalyst Substances 0.000 title claims description 110
- 238000004519 manufacturing process Methods 0.000 title claims description 15
- 230000001590 oxidative effect Effects 0.000 title claims description 13
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 title description 6
- 229910002651 NO3 Inorganic materials 0.000 claims description 27
- 229910052741 iridium Inorganic materials 0.000 claims description 27
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 claims description 27
- -1 nitrate ions Chemical class 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 19
- 229910052784 alkaline earth metal Inorganic materials 0.000 claims description 18
- 150000001342 alkaline earth metals Chemical class 0.000 claims description 18
- 238000002256 photodeposition Methods 0.000 claims description 18
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- 239000002184 metal Substances 0.000 claims description 15
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- 229910052783 alkali metal Inorganic materials 0.000 claims description 11
- 150000001340 alkali metals Chemical class 0.000 claims description 11
- 150000001875 compounds Chemical class 0.000 claims description 9
- 239000007864 aqueous solution Substances 0.000 claims description 8
- 238000006243 chemical reaction Methods 0.000 description 58
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- 239000003054 catalyst Substances 0.000 description 32
- 230000000694 effects Effects 0.000 description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 24
- 239000001301 oxygen Substances 0.000 description 24
- 229910052760 oxygen Inorganic materials 0.000 description 24
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 20
- 229910000457 iridium oxide Inorganic materials 0.000 description 20
- 238000011068 loading method Methods 0.000 description 13
- 239000003426 co-catalyst Substances 0.000 description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 10
- 239000001257 hydrogen Substances 0.000 description 10
- 229910052739 hydrogen Inorganic materials 0.000 description 10
- 238000000354 decomposition reaction Methods 0.000 description 9
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- 238000013032 photocatalytic reaction Methods 0.000 description 5
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 5
- 238000000926 separation method Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000000084 colloidal system Substances 0.000 description 4
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- 239000002994 raw material Substances 0.000 description 4
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
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- 238000010532 solid phase synthesis reaction Methods 0.000 description 3
- 230000007306 turnover Effects 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000000862 absorption spectrum Methods 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
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- 229910001961 silver nitrate Inorganic materials 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 1
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 description 1
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910019899 RuO Inorganic materials 0.000 description 1
- 229910002367 SrTiO Inorganic materials 0.000 description 1
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- YGANSGVIUGARFR-UHFFFAOYSA-N dipotassium dioxosilane oxo(oxoalumanyloxy)alumane oxygen(2-) Chemical compound [O--].[K+].[K+].O=[Si]=O.O=[Al]O[Al]=O YGANSGVIUGARFR-UHFFFAOYSA-N 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
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- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
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- 230000007062 hydrolysis Effects 0.000 description 1
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- 150000002504 iridium compounds Chemical class 0.000 description 1
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- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000008204 material by function Substances 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052627 muscovite Inorganic materials 0.000 description 1
- GNRSAWUEBMWBQH-UHFFFAOYSA-N nickel(II) oxide Inorganic materials [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
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- 230000027756 respiratory electron transport chain Effects 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
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- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-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
Description
本発明は、タンタル酸アルカリ金属塩系光触媒、ＳｎＮｂ２Ｏ６系光触媒、Ｃｓ２Ｎｂ４Ｏ１１光触媒、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒またはＡｇＴａＯ３光触媒を用いての水の光完全分解または光酸化反応における活性、特に酸素生成反応活性を改善した硝酸イオン存在下の酸化的雰囲気において光電着により形成したＩｒ酸化物系助触媒を担持させたタンタル酸アルカリ金属塩系光触媒、特にアルカリ土類金属またはＬａをドープしたナノステップ構造のタンタル酸アルカリ金属塩系光触媒、ＳｎＮｂ２Ｏ６光触媒、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒またはＡｇＴａＯ３光触媒およびその製造方法に関する。 The present invention uses an alkali metal tantalate photocatalyst, SnNb 2 O 6 photocatalyst, Cs 2 Nb 4 O 11 photocatalyst, K 3 Ta 3 B 2 O 12 photocatalyst, Sr 2 Ta 2 O 7 photocatalyst or AgTaO 3 photocatalyst Alkaline metal tantalate supporting Ir oxide promoter formed by photo-deposition in an oxidative atmosphere in the presence of nitrate ion with improved activity in photo-complete decomposition or photo-oxidation reaction of all water, especially oxygen generation reaction activity Salt-based photocatalyst, especially alkali metal tantalate photocatalyst having a nanostep structure doped with alkaline earth metal or La, SnNb 2 O 6 photocatalyst, K 3 Ta 3 B 2 O 12 photocatalyst, Sr 2 Ta 2 O 7 photocatalyst or The present invention relates to an AgTaO 3 photocatalyst and a method for producing the same.
化石資源は無尽蔵とは言えないことから、これらを化学原料に振り向けることが資源の有効利用の観点から好ましい。また、地球温暖化などの環境問題などの観点から、ＣＯ２の発生を伴わないクリーンなエネルギーへの変換が熱望されている。また、石炭の燃焼の際にはＣＯ２の発生だけでなく、白雲母として石炭中に含まれている化合物からのフッ素の発生も有ると言われている。前記問題ないエネルギー供給手段として登場して来た原子力利用の発電技術も、燃料物質を製造する工程、及び使用後の処理において生成する物質の兵器としての使用などによる世界秩序の破壊が懸念されるという事態に至り、大きな問題を抱えることになった。このような中で、環境に優しく、安全性が高く、かつ設備コストも比較的かからないエネルギー資源の開発が望まれている。最近、風力発電に、無尽蔵なエネルギー資源の利用の観点、及び設備費も比較的小さいなどから、多くの投資が向けられている。また、太陽電池もクリーンで、利用性の高いエネルギーを生産することから、実用化され、かつ更に効率性の向上と、安定したエネルギー供給に向けて多数の研究が行われている。また、太陽光を利用するエネルギー変換技術として、光触媒を利用した水の光分解反応に興味が持たれている。ここで利用される水の光分解反応に活性を示す光触媒は、太陽光を構成する紫外光、可視光の光吸収、電荷分離、表面での酸化還元反応の一連の反応を進行させる機能を備えた高度な光機能材料であり、多くの系が提案されている。 Since fossil resources cannot be said to be inexhaustible, it is preferable to allocate them to chemical raw materials from the viewpoint of effective use of resources. In addition, from the viewpoint of environmental problems such as global warming, conversion to clean energy without generating CO 2 is eagerly desired. Further, it is said that not only the generation of CO 2 but also the generation of fluorine from a compound contained in the coal as muscovite when the coal is burned. The nuclear power generation technology that has emerged as a non-problematic energy supply means is also concerned about the destruction of the world order due to the use of substances produced in the process of manufacturing fuel materials and the processing after use as weapons. This led to a big problem. Under such circumstances, development of energy resources that are environmentally friendly, high in safety, and relatively low in equipment costs is desired. Recently, many investments have been directed to wind power generation because of its infinite use of energy resources and relatively low equipment costs. In addition, since solar cells produce clean and highly usable energy, they have been put into practical use, and many studies have been conducted for further improving efficiency and supplying stable energy. In addition, as an energy conversion technology using sunlight, there is an interest in water photolysis using a photocatalyst. The photocatalyst that is active in the photodecomposition reaction of water used here has the function of advancing a series of reactions including ultraviolet light, visible light absorption, charge separation, and oxidation-reduction reaction on the surface. Many advanced optical functional materials have been proposed.
このような中で、光触媒を高活性化するための種々の技術的改善の検討がなされている。前記検討の中で、触媒粒子径のナノサイズ化、ナノサイズ粒子の形態・構造の検討、基質と光生成キャリアとの電子授受に寄与する助触媒の検討が光活性の特性の改善に大きく寄与するものと考えられている。助触媒の役割は、助触媒を担持させることにより、電荷の分離の促進および活性点の導入が行われることにある。従って、助触媒担持物は光触媒の研究の中で重要な役割を担っている。これまでに、水の完全分解に有効に働く助触媒としてＰｔ、Ｒｈ、Ｐｄ、ＮｉＯ、ＲｕＯ２が良く知られている。しかし、これらの助触媒はいずれも水素生成の活性点として働いている。一方、均一系のＲｕ錯体光触媒に対する酸素生成活性点として働く助触媒としてＩｒＯ２コロイドが原らによって報告された（非特許文献１）。これは、Ｓｍ２Ｔｉ２Ｓ２Ｏ５の不均一系光触媒に対しても効果的である（非特許文献２）。しかしながら、このＩｒＯ２コロイド助触媒の担持には、［ＩｒＣｌ６］２−の加水分解によるＩｒＯ２コロイドの調製に続く吸着という手順を踏まなければならない。また、純水の完全分解反応の触媒にイリジウム系助触媒を担持させ高光活性化させる技術が特許文献１に報告されているが、イリジウム酸化物系助触媒を担持させた具体例はないし、水素生成の活性点として働くことの言及があるだけである。
Under such circumstances, various technical improvements for highly activating the photocatalyst have been studied. Among the above studies, the catalyst particle size nano-size, nano-sized particle shape and structure, and the co-catalyst that contributes to the electron transfer between the substrate and the photo-generated carrier greatly contribute to the improvement of the photoactive properties. It is thought to do. The role of the cocatalyst is to promote charge separation and introduce active sites by supporting the cocatalyst. Thus, the promoter support plays an important role in the research of photocatalysts. To date, Pt, Rh, Pd, NiO, and RuO 2 are well known as cocatalysts that work effectively for complete decomposition of water. However, all of these promoters serve as active sites for hydrogen production. On the other hand, IrO 2 colloid was reported by Hara et al. As a co-catalyst acting as an oxygen generation active site for a homogeneous Ru complex photocatalyst (Non-patent Document 1). This is also effective for the heterogeneous photocatalyst of Sm 2 Ti 2 S 2 O 5 (Non-patent Document 2). However, the loading of this IrO 2 colloid co-catalyst must follow the procedure of adsorption followed by the preparation of IrO 2 colloid by hydrolysis of [IrCl 6 ] 2− . Further,
触媒粒子径のナノサイズ化、ナノサイズ粒子の形態・構造（モルフォロジー）の検討に関しては、本発明者らは、高い光活性を示すタンタル酸アルカリ金属塩系の光触媒を得るために、この光触媒におけるナノサイズ化、およびアルカリ土類金属、Ｌａドープによるナノステップ構造の形成と光触媒活性、特にドープ構造と光活性の発現との相関を検討し、報告してきた（非特許文献３）。 Regarding the nano-sized catalyst particle size and the study of the morphology and structure (morphology) of the nano-sized particles, the present inventors have obtained a photocatalyst based on an alkali metal tantalate with high photoactivity. We have investigated and reported the relationship between nano-sizing and formation of nanostep structures by alkaline earth metal and La doping and photocatalytic activity, particularly the dope structure and the expression of photoactivity (Non-patent Document 3).
本発明の解決しようとする課題は、基本的には、今まであまり提案されていない酸化反応（酸素生成）のより高い活性点を提供する助触媒を提供することである。０２ｐからなる深い価電子帯は、酸化反応に対して助触媒を必要としない。これに対して、可視光応答性光触媒の開発が盛んに行われている中、浅い価電子帯に対しては、前記助触媒の必要性が増すと予想され、価電子帯が０２ｐより浅いＳｎ３ｄからなるＳｎＮｂＯ６系の活性を向上させるには、酸素生成反応を活性化する助触媒の開発が必要であることは明らかである。また，水の完全分解に対して水素生成反応を活性化する助触媒を用いて高い光触媒活性を実現した前記タンタル酸塩系においても酸素生成反応を活性化する助触媒の開発が必要であることは明らかであるから、これらの要求を満たすために酸素生成反応を活性化する助触媒を提供することである。そこで、本発明者らは、前記酸素生成反応を触媒することが報告されているＩｒＯ２触媒を採用することを考えたが、そのままでは全く適用できないことが分かった。従って、前記光触媒活性の高いタンタル酸塩系の光触媒等において酸素生成反応の活性点として機能する助触媒をどのような手法を用いたら形成できるかを検討することが必要であった。そこで、ＩｒＯ２助触媒を形成するのに、助触媒を形成する方法として知られている1つの方法である光電着法を用いることを試みた。すなわち、水溶性のイリジウム化合物（ＮＨ４）２［ＩｒＣｌ６］を純水中に溶解した溶液に、前記本発明者らが開発したタンタル酸塩系光触媒などを分散し、紫外線を照射してＩｒ系助触媒の担持を試みた。その結果、前記方法による助触媒の担持により光触媒活性は向上した。しかしながら、時間経過により活性が低下するという現象が現れ、そして、前記活性の低下の原因が生成したＨ２とＯ２間の逆反応が進行すること起こり、それがＩｒ系助触媒によることが分かった。 The problem to be solved by the present invention is basically to provide a co-catalyst that provides a higher active point of the oxidation reaction (oxygen generation), which has not been proposed so far. The deep valence band consisting of 02p does not require a promoter for the oxidation reaction. On the other hand, while the development of visible light responsive photocatalysts is being actively conducted, it is expected that the need for the promoter will increase for shallow valence bands, and Sn3d whose valence band is shallower than 02p. Clearly, it is necessary to develop a co-catalyst that activates the oxygen-producing reaction in order to improve the activity of the SnNbO 6 system. In addition, it is necessary to develop a co-catalyst that activates the oxygen-producing reaction even in the tantalate system that achieves a high photocatalytic activity using a co-catalyst that activates the hydrogen-producing reaction for complete water decomposition. It is obvious to provide a co-catalyst that activates the oxygen production reaction to meet these requirements. Therefore, the present inventors considered adopting an IrO 2 catalyst that has been reported to catalyze the oxygen generation reaction, but it was found that this is not applicable at all. Therefore, it has been necessary to examine what method can be used to form a co-catalyst functioning as an active site of the oxygen generation reaction in the tantalate photocatalyst having high photocatalytic activity. Therefore, in order to form the IrO 2 promoter, an attempt was made to use a photo-deposition method, which is one of the methods known as a method for forming a promoter. That is, a tantalate photocatalyst developed by the present inventors is dispersed in a solution in which a water-soluble iridium compound (NH 4 ) 2 [IrCl 6 ] is dissolved in pure water, and irradiated with ultraviolet rays to give Ir. An attempt was made to support the system promoter. As a result, the photocatalytic activity was improved by supporting the promoter according to the above method. However, the phenomenon that the activity decreases with the lapse of time appears, and the cause of the decrease in activity occurs because the reverse reaction between the generated H 2 and O 2 proceeds, and it is understood that this is due to the Ir-based promoter. It was.
この逆反応の原因はＩｒ金属の逆反応触媒作用によるものと考えることができる。そこで、ＩｒＯ２助触媒を光電着法により効率的に形成するにはどうすればよいかと考え、イリジウムが酸化物を形成する酸化的雰囲気を提供することが重要と考え、種々検討する中で、前記光電着水溶液に硝酸イオンを存在させ、酸化的雰囲気下で光電着反応を進行させることにより、前記逆反応を抑制し、かつ光触媒活性の向上したタンタル酸塩系光触媒が得られることを確認し、ＩｒＯ２助触媒を担持した光触媒活性の高いタンタル酸塩系の光触媒を提供すること可能であることが確認され、前記課題を解決することができた。また、前記ＩｒＯ２助触媒の形成を本来水素生成光触媒であるＳｎＮｂ２Ｏ６系光触媒に適用したところ、酸素生成反応に活性な助触媒となることを確認できた。 The cause of this reverse reaction can be attributed to the reverse reaction catalysis of Ir metal. Therefore, considered that what can I efficiently formed by photoelectrodeposition method IrO 2 promoter, considered important that iridium provide oxidizing atmosphere to form an oxide, in the various studies, the photoelectric It was confirmed that a tantalate photocatalyst that suppresses the reverse reaction and has an improved photocatalytic activity can be obtained by allowing nitrate ions to be present in the aqueous solution and allowing the photodeposition reaction to proceed in an oxidative atmosphere. 2 It was confirmed that it is possible to provide a tantalate photocatalyst having a high photocatalytic activity carrying a promoter, and the above problems could be solved. Moreover, when the formation of the IrO 2 cocatalyst was applied to a SnNb 2 O 6 photocatalyst that was originally a hydrogen generation photocatalyst, it was confirmed that it became an active cocatalyst for the oxygen generation reaction.
本発明第１は、（１）０．１重量％以上５重量％以下のアルカリ土類金属およびＬａからなる群から選択される少なくとも1つの金属をドープしたＡＴａＯ３：Ｂ（ｘ）〔Ａはアルカリ金属、Ｂはアルカリ土類金属またはＬａ、ｘは０．１≦x≦５％である。〕の光触媒、ＳｎＮｂ２Ｏ６光触媒、ＳｒをドープしたＳｎＮｂ２Ｏ６光触媒、Ｃｓ２Ｎｂ４Ｏ１１光触媒、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒またはＡｇＴａＯ３光触媒に硝酸イオンの存在下の酸化的雰囲気において水溶性のイリジウム供給化合物を用いて光電着法によりＩｒ酸化物系助触媒を担持させた光触媒である。好ましくは、（２）０．１重量％以上５重量％以下のアルカリ土類金属およびＬａからなる群から選択される少なくとも1つの金属をドープしたＡＴａＯ３：Ｂ（ｘ）〔Ａはアルカリ金属、Ｂはアルカリ土類金属またはＬａ、ｘは０．１≦x≦５％である。〕の光触媒がＳＥＭによりナノステップ構造が観察されるものであることを特徴とする前記（１）に記載のＩｒ酸化物助触媒を担持させた光触媒であり、より好ましくは、（３）光電着法が硝酸イオンを溶かした水溶液の酸化的雰囲気においてイリジウム供給源として（ＮＨ４）２［ＩｒＣｌ６］またはＮａ３［ＩｒＣl６を用いて進行させたことを特徴とする前記（１）または（２）に記載のＩｒ酸化物助触媒を担持させた光触媒である。
本発明の第２は、（４）０．１重量％以上５重量％以下のアルカリ土類金属およびＬａからなる群から選択される少なくとも1つの金属をドープしたＡＴａＯ３：Ｂ（ｘ）〔Ａはアルカリ金属、Ｂはアルカリ土類金属またはＬａ、ｘは０．１≦x≦５％である。〕のナノステップ構造の光触媒、ＳｎＮｂ２Ｏ６光触媒、ＳｒをドープしたＳｎＮｂ２Ｏ６光触媒、Ｃｓ２Ｎｂ４Ｏ１１光触媒、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒またはＡｇＴａＯ３光触媒を硝酸イオンおよびＩｒ酸化物助触媒を形成する水溶性のイリジウム供給化合物が存在する酸化性雰囲気の水溶液中に分散し２５０ｎｍ以上７４０ｎｍ以下の紫外から可視領域内の光を照射して前記光触媒にＩｒ酸化物助触媒を担持させるＩｒ酸化物助触媒を担持させた光触媒の製造方法である。好ましくは、（５）０．１重量％以上５重量％以下のアルカリ土類金属およびＬａからなる群から選択される少なくとも1つの金属をドープしたＡＴａＯ３：Ｂ（ｘ）〔Ａはアルカリ金属、Ｂはアルカリ土類金属またはＬａ、ｘは０．１≦x≦５％である。〕の光触媒がＳＥＭによりナノステップ構造が観察されるものであることを特徴とする前記（４）に記載のＩｒ酸化物助触媒を担持させた光触媒の製造方法であり、より好ましくは、イリジウム供給源として（ＮＨ４）２［ＩｒＣｌ６］またはＮａ３［ＩｒＣl６］を用いことを特徴とする前記（４）または（５）に記載のＩｒ酸化物助触媒を担持させた光触媒の製造方法である。
The first aspect of the present invention is (1) ATaO 3 : B (x) [A is doped with at least one metal selected from the group consisting of 0.1% by weight or more and 5% by weight or less of an alkaline earth metal and La Alkali metal, B is alkaline earth metal or La, and x is 0.1 ≦ x ≦ 5%. Photocatalyst], SnNb 2 O 6 photocatalyst, SnNb 2 O 6 photocatalyst doped with Sr, Cs 2 Nb 4 O 11 photocatalyst, K 3 Ta 3 B 2 O 12 photocatalyst, the
A second aspect of the present invention is (4) ATaO 3 : B (x) [A which is doped with at least one metal selected from the group consisting of 0.1% to 5% by weight of an alkaline earth metal and La. Is an alkali metal, B is an alkaline earth metal or La, and x is 0.1 ≦ x ≦ 5%. Photocatalytic nano step structure], SnNb 2 O 6 photocatalyst, SnNb 2 O 6 photocatalyst doped with Sr, Cs 2 Nb 4 O 11 photocatalyst, K 3 Ta 3 B 2 O 12 photocatalyst,
発明の効果として、先ず、硝酸イオン存在下で（ＮＨ４）２［ＩｒＣｌ６］からの光電着という簡便な手法にて担持したイリジウム系助触媒が、光触媒を用いた水の分解反応の活性を向上させたこと、およびこのようにして担持したイリジウム系助触媒は、硝酸銀水溶液からの酸素生成反応に対しても反応促進の効果を発揮したことを挙げることができる。特に、可視光に活性を示す光触媒を用いた水の分解反応においても酸素生成反応に対しても反応促進の効果示すことは、水の光完全分解に大きく貢献するものである。 As an effect of the invention, first, an iridium-based cocatalyst supported by a simple method of photodeposition from (NH 4 ) 2 [IrCl 6 ] in the presence of nitrate ions has an activity of water decomposition reaction using a photocatalyst. It can be mentioned that the improvement and the iridium-based cocatalyst thus supported exerted a reaction promoting effect on the oxygen generation reaction from the silver nitrate aqueous solution. In particular, showing the effect of promoting the reaction for both the decomposition reaction of water and the oxygen generation reaction using a photocatalyst active in visible light greatly contributes to the complete photolysis of water.
Ａ，本発明の大きな特徴は可視光領域に光触媒活性を示す触媒に対して、酸素生成反応を促進する助触媒を前記光触媒に形成する方法を提供できたことである。
１，前記助触媒の形成は、Ｉｒ供給水溶性化合物を溶解した硝酸イオンを含む酸化的雰囲気下の水溶液に前記光触媒を懸濁させ、２５０ｎｍ以上７４０ｎｍ以下の紫外から可視領域の光を照射し光電着により前記光触媒にイリジウム酸化物系助触媒を担持させて行うことができる。
２，前記酸素生成反応を促進する助触媒が有効に機能する光触媒としては、請求項１に記載の光触媒を特に有効な光触媒として挙げることができるが、他の光触媒、特に可視光領域に活性を示す触媒に有用である。
３，Ｉｒ供給水溶性化合物としては（ＮＨ４）２［ＩｒＣｌ６］を特に好ましい化合物として挙げることができる。イリジウム酸化物系助触媒の好ましい担持量は光触媒によっても異なるが、０．１２重量％〜０．７８重量％、好ましくは０．１３重量％〜０．５２重量％である。
４，イリジウム酸化物系助触媒の効果は、水素生成サイトおよび酸素生成サイトの分離が効率よくなされている光触媒において、例えば前記非特許文献３に記載のナノステップ構造の形成された光触媒において効果を発揮する。
A, A major feature of the present invention is that it can provide a method for forming a cocatalyst for promoting an oxygen generation reaction on the photocatalyst with respect to a catalyst exhibiting photocatalytic activity in the visible light region.
1. The promoter is formed by suspending the photocatalyst in an aqueous solution containing nitrate ions in which an Ir-supplied water-soluble compound is dissolved, and irradiating light in the ultraviolet to visible region from 250 nm to 740 nm. The photocatalyst can be loaded with an iridium oxide promoter on the photocatalyst.
2. As a photocatalyst in which the co-catalyst that promotes the oxygen generation reaction functions effectively, the photocatalyst according to
As the Ir-supplied water-soluble compound, (NH 4 ) 2 [IrCl 6 ] can be mentioned as a particularly preferable compound. The preferred loading of the iridium oxide-based cocatalyst varies depending on the photocatalyst, but is 0.12 wt% to 0.78 wt%, preferably 0.13 wt% to 0.52 wt%.
4. The effect of the iridium oxide-based cocatalyst is effective in the photocatalyst in which the separation of the hydrogen generation site and the oxygen generation site is efficiently performed, for example, in the photocatalyst having the nanostep structure described in Non-Patent Document 3. Demonstrate.
Ｂ，光触媒反応特性、および触媒の特性の測定機器；
（１）光触媒反応は、閉鎖循環系にて行った。前記閉鎖循環系を備えた装置を図６に示す。反応管は、紫外光照射では石英製内部照射型反応管を、可視光照射ではＰｙｒｅｘ製上方照射型反応管を用いた。紫外光照射では４００Ｗ高圧水銀灯（ＳＥＮ；ＨＬ４００ＥＨ−５）を，可視光照射ではカットオフフィルター（Ｋｅｎｋｏ：Ｌ４２）を取り付けた３００Ｗキセノンランプ（パーキンエルマー：CERMAX-LX300F）を用いた。
（２）生成したＨ２およびＯ２は、前記に閉鎖循環系を備えた装置に接続されたガスクロマトグラフ(Shimadzu; GC-8A, MS-5A column, TCD, Ar carrier)で測定した。
（３）触媒のキャラクタリゼーション
１．光触媒粉末は、Ｘ線回折（リガク：MiniFlex）によって同定した。
２．拡散反射スペクトルを吸光光度分光計（日本分光：Ubest-V570）で測定した。
B, measuring device for photocatalytic reaction characteristics and catalyst characteristics;
(1) The photocatalytic reaction was performed in a closed circulation system. An apparatus provided with the closed circulatory system is shown in FIG. As the reaction tube, a quartz internal irradiation type reaction tube was used for ultraviolet light irradiation, and a Pyrex upward irradiation type reaction tube was used for visible light irradiation. A 400 W high-pressure mercury lamp (SEN; HL400EH-5) was used for ultraviolet light irradiation, and a 300 W xenon lamp (Perkin Elmer: CERMAX-LX300F) equipped with a cutoff filter (Kenko: L42) was used for visible light irradiation.
(2) The produced H 2 and O 2 were measured by a gas chromatograph (Shimadzu; GC-8A, MS-5A column, TCD, Ar carrier) connected to the apparatus provided with the closed circulation system.
(3) Characterization of catalyst The photocatalytic powder was identified by X-ray diffraction (Rigaku: MiniFlex).
2. The diffuse reflection spectrum was measured with an absorptiometer (JASCO: Ubest-V570).
（１）光触媒の調製；
Ｌａを２％ドーピングしたＮａＴａＯ３（以後ＮａＴａＯ３：Ｌａ（２％））を以下の手順で調製した。
ＮａＴａＯ３：Ｌａ(２％) 粉末の調製（Kato，H．；Asakura，K．；Kudo，A．J．Am．Chem．Soc．2003，125，3082．による。）
ＮａＴａＯ３：Ｌａ(２％)は、固相法で調製した。原料（Ｎａ２ＣＯ３(Kanto Chemical；９９．５％)、Ｔａ２Ｏ５(Rare metallic；９９．９％)およびＬａ２Ｏ３をＮａ：Ｌａ：Ｔａ＝１．０５：０．０２：１で混合した。Ｎａは焼成時の揮発による損失を補うため、過剰にした。この混合物を、白金るつぼを用いて空気中１４２３Ｋで１０ｈ焼成した。過剰のアルカリは、焼成後水で洗浄し、その後乾燥させることでＮａＴａＯ３：Ｌａ(２％)粉末を得た。
(1) Preparation of photocatalyst;
NaTaO 3 doped with 2% La (hereinafter referred to as NaTaO 3 : La (2%)) was prepared by the following procedure.
Preparation of NaTaO 3 : La (2%) powder (according to Kato, H .; Asakura, K .; Kudo, AJ Am. Chem. Soc. 2003, 125, 3082.)
NaTaO 3 : La (2%) was prepared by a solid phase method. The raw materials (Na 2 CO 3 (Kanto Chemical; 99.5%), Ta 2 O 5 (Rare metallic; 99.9%)) and La 2 O 3 were used as Na: La: Ta = 1.05: 0.02: 1. Na was added in an excess amount to compensate for loss due to volatilization during firing, and this mixture was fired in air using a platinum crucible for 10 h at 1423 K. The excess alkali was washed with water after firing, and then By drying, NaTaO 3 : La (2%) powder was obtained.
（２）助触媒担持法；
イリジウム系助触媒の担持；比較のために純水を用いた場合も示す。
純水中（比較例）および硝酸イオンを含む水溶液中に（ＮＨ４）２［ＩｒＣｌ６］（ヘキサクロロイリジウム酸アンモニウム; Wako）を所望の担持量になるように配合して調製した反応溶液に、前記（１）で調製したＮａＴａＯ３：Ｌａ（２％）光触媒を仕込み、光（２５０ｎｍ以上）を照射して光電着反応を進行させた。前記反応溶液には、純水および硝酸イオン供給源として硝酸アルカリ（ＮａＮＯ３,(Kanto、９９％)、ＫＮＯ３またはＣｓＮＯ３）を使用した。また、必要に応じて光電着後に触媒を遠心分離法にて洗浄、回収した。
(2) Cocatalyst loading method;
Loading of iridium-based cocatalyst; the case of using pure water for comparison is also shown.
In a reaction solution prepared by blending (NH 4 ) 2 [IrCl 6 ] (ammonium hexachloroiridate; Wako) in pure water (comparative example) and an aqueous solution containing nitrate ions so as to have a desired loading amount, The NaTaO 3 : La (2%) photocatalyst prepared in the above (1) was charged, and light (250 nm or more) was irradiated to advance the photodeposition reaction. In the reaction solution, pure water and alkali nitrate (NaNO 3 , (Kanto, 99%), KNO 3 or CsNO 3 ) were used as a nitrate ion source. Further, if necessary, the catalyst was washed and collected by centrifugal separation after the photodeposition.
（３）光触媒特性；
イリジウム系助触媒の光触媒的水分解反応での効果；ここでは、前記（２）で純水を用いて調製したものも比較例として示した。
前記（１）〜（２）で調製した光触媒の性能を前記光触媒反応特性を測定する閉鎖循環系装置を用いて測定した。
図３に純水中（比較例）で調製したイリジウム酸化物助触媒を光電着したＮａＴａＯ３：Ｌａ（２％）の光触媒を分散させ水の完全分解反応を行った結果を示す。この場合では、初期には助触媒未担持に比べ３倍程度活性の向上が見られたが、すぐに失活した。これは、水分解に対して生成したＨ２とＯ２が水にもどる逆反応の割合が大きくなったためである。この触媒では、ＮａＴａＯ３：Ｌａ（２％）中に光生成した電子により反応溶液中のＩｒ４＋が還元されることで触媒表面上にＩｒメタルとして担持され、このＩｒメタル表面で逆反応が早く進行したと考えられる。このことは、光照射をやめた後に、生成したＨ２とＯ２がほぼ２：１で減少することから示された。
(3) Photocatalytic properties;
The effect of the iridium-based cocatalyst in the photocatalytic water splitting reaction; Here, the one prepared using pure water in the above (2) is also shown as a comparative example.
The performance of the photocatalyst prepared in the above (1) to (2) was measured using a closed circulation system that measures the photocatalytic reaction characteristics.
FIG. 3 shows the result of a complete decomposition reaction of water by dispersing a NaTaO 3 : La (2%) photocatalyst photocatalyzed with an iridium oxide promoter prepared in pure water (comparative example). In this case, the activity was improved by about 3 times in comparison with the unsupported cocatalyst, but it was immediately deactivated. This is because the ratio of the reverse reaction in which H 2 and O 2 generated for water splitting return to water has increased. In this catalyst, Ir 4+ in the reaction solution is reduced by the electrons photogenerated in NaTaO 3 : La (2%), so that it is supported as Ir metal on the catalyst surface, and the reverse reaction is fast on this Ir metal surface. It seems that it has progressed. This was shown by the fact that the generated H 2 and O 2 decreased by approximately 2: 1 after the light irradiation was stopped.
（４）ここでは、光水分解系に硝酸イオンを存在させ、反応系中でイリジウム酸化物系助触媒が生成する系での光触媒特性を示す。
図２に、硝酸イオン存在下の、光触媒測定系に、すなわち、反応場でイリジウム酸化物助触媒を担持させつつ水分解反応を行った結果を示す。この反応では、以下に示す硝酸イオンの還元反応が水の還元反応と競争して進行している。
２Ｈ＋＋２ｅ−→Ｈ２ （１）
２ＮＯ３ −＋２Ｈ＋＋２ｅ−→ ２ＮＯ２ −＋Ｈ２Ｏ （２）
このときＨ２活性は、イリジウム酸化物助触媒未担持のときの約６倍に向上した。また、純水中で光電着した場合とは異なり、光照射下で定常的に水素および酸素が生成した。さらに，７時間（ｈ）での水素生成量は７．１７ｍｍｏｌとなり、下記の式（３）に示されるＮａＴａＯ３：Ｌａ（２％）に対する反応電子数のターンオーバー数は３．７に、またイリジウムに対する反応電子数のターンオーバー数は５９８に達した。
［ターンオーバー数］＝［反応した電子の物質量］／［触媒の物質量] （３）
また、ダーク時における逆反応は抑制されていた。これは、硝酸イオンが酸化剤として働くために、光生成した電子によるＩｒ４＋の還元を抑制し、Ｉｒ４＋が酸化イリジウムとして担持されたためであると考えられる。
この酸化イリジウムは、酸素生成反応を触媒するが、逆反応を触媒しない。この特性は、水分解光触媒のための助触媒に求められている特性である。このように、簡便な手法で担持できる酸素生成促進型の水分解用イリジウム酸化物系助触媒を開発できることが予想させる実験である。
(4) Here, the photocatalytic characteristics in a system in which nitrate ions are present in the photohydrolysis system and an iridium oxide promoter is generated in the reaction system are shown.
FIG. 2 shows the result of the water splitting reaction carried out in the photocatalyst measurement system in the presence of nitrate ions, that is, while supporting the iridium oxide promoter in the reaction field. In this reaction, the nitrate ion reduction reaction shown below proceeds in competition with the water reduction reaction.
2H + + 2e − → H 2 (1)
2NO 3 − + 2H + + 2e − → 2NO 2 − + H 2 O (2)
At this time, the H 2 activity was improved about 6 times that when the iridium oxide promoter was not supported. Also, unlike the case of photo-deposition in pure water, hydrogen and oxygen were constantly generated under light irradiation. Furthermore, the amount of hydrogen generated in 7 hours (h) was 7.17 mmol, the turnover number of the number of reaction electrons for NaTaO 3 : La (2%) shown in the following formula (3) was 3.7, The turnover number of the reaction electrons for iridium reached 598.
[Turnover number] = [Amount of reacted electron] / [Amount of catalyst] (3)
Moreover, the reverse reaction at the time of darkness was suppressed. This is considered to be because the nitrate ions act as an oxidant, so that the reduction of Ir 4+ by photogenerated electrons is suppressed, and Ir 4+ is supported as iridium oxide.
This iridium oxide catalyzes the oxygen production reaction but not the reverse reaction. This characteristic is a characteristic required for a promoter for a water-splitting photocatalyst. Thus, it is an experiment that predicts that an oxygen generation promoting type iridium oxide promoter for water splitting that can be supported by a simple technique can be developed.
（５）イリジウム酸化物系助触媒を担持させた後、ＮａＴａＯ３：Ｌａ（２％）を回収した触媒の光触媒活性の測定；
前記（４）のイリジウム酸化物系助触媒の硝酸イオンの競争的反応を除外し、水分解に対する効果を調べるために、イリジウム酸化物系助触媒を光電着させた後、触媒を遠心分離法による洗浄、回収を行い硝酸イオンを取り除き、純水中で再度反応を行った（図１）。２回の反応の純水中における反応では、水素と酸素が量論比でそれぞれ１０００および５００μｍｏｌ／ｈで生成した。そして、再排気後も定常的な活性が得られた(３回反応)、更にダークで逆反応の進行が見られなかったことから、一度硝酸イオン存在下で光電着されたイリジウム助触媒は、光水分解系の硝酸イオンを取り除いても（３）でのようにメタルに還元されることなく高い助触媒能を維持することが明らかとなった。
(5) Measurement of the photocatalytic activity of a catalyst in which NaTaO 3 : La (2%) was recovered after supporting an iridium oxide-based cocatalyst;
In order to exclude the competitive reaction of nitrate ions of the iridium oxide promoter of the above (4) and investigate the effect on water splitting, the iridium oxide promoter is photoposited, and then the catalyst is centrifuged. Washing and recovery were performed to remove nitrate ions, and the reaction was performed again in pure water (FIG. 1). In the two reactions in pure water, hydrogen and oxygen were produced at a stoichiometric ratio of 1000 and 500 μmol / h, respectively. And even after re-evacuation, steady activity was obtained (reaction 3 times), and since the progress of reverse reaction was not seen in the dark, the iridium promoter once photo-deposited in the presence of nitrate ions was It was clarified that even when nitrate ions in the photo-water splitting system were removed, a high cocatalyst ability was maintained without being reduced to metal as in (3).
図４にＮａＴａＯ３：Ｌａ（２％）に担持されたイリジウム系助触媒の拡散反射スペクトルを示す。硝酸イオン存在下で光電着したイリジウム助触媒では６００ｎｍ付近に吸収バンドが見られたのに対し、純水中で担持したイリジウムメタル助触媒では、この吸収が見られなかった。このように、光電着の際の硝酸イオンの有無によって、担持されたイリジウム助触媒はまったく異なった吸収スペクトルを示した。このことからも、純水中での光電着と酸化的雰囲気での光電着では、まったく違った形態のイリジウム系助触媒が担持されていることが明らかとなった。表１、２に、イリジウムの担持条件及び担持量を変化させたときのＮａＴａＯ３：Ｌａ（２％）の活性を示す。表１で酸素が過剰に生成しているのは、硝酸イオンの光分解による酸素生成のためである。純水を用いた表１の測定ではこのような現象は見られない。イリジウムの最適担持量は、硝酸溶液中の光電着時およびその後の純水での反応においても０．２６重量％であった(表１、２)。これより低い担持量では、助触媒担持により導入される活性点の数が不十分であると考えられる。一方、これより多い担持量では、担持されたＩｒが表面を覆ってしまい水素生成の活性サイトがつぶされたり、ＮａＴａＯ３：Ｌａ（２％）光触媒自身に届く光の量が減少してしまったりしたために活性が低くなったと考えられる。また，出発原料としてＮａ３［ＩｒＣｌ６］を用いても、同様の効果が見られた。
今まで、ＮｉＯ、ＲｕＯ２などのＨ２生成助触媒を担持することにより活性の向上が計られてきた。今回の、Ｏ２生成助触媒を担持することによっても、活性を向上せさることができることが明らかとなった。
FIG. 4 shows a diffuse reflection spectrum of an iridium-based promoter supported on NaTaO 3 : La (2%). The iridium promoter photo-deposited in the presence of nitrate ions showed an absorption band near 600 nm, whereas the iridium metal promoter supported in pure water did not show this absorption. Thus, the supported iridium promoter exhibited a completely different absorption spectrum depending on the presence or absence of nitrate ions during photodeposition. This also revealed that iridium-based cocatalysts of different forms were supported between the photodeposition in pure water and the photodeposition in an oxidizing atmosphere. Tables 1 and 2 show the activity of NaTaO 3 : La (2%) when the iridium loading conditions and loadings are changed. The excessive generation of oxygen in Table 1 is due to oxygen generation by photolysis of nitrate ions. Such a phenomenon is not observed in the measurement of Table 1 using pure water. The optimum amount of iridium supported was 0.26% by weight during photodeposition in a nitric acid solution and in the subsequent reaction with pure water (Tables 1 and 2). When the loading is lower than this, it is considered that the number of active sites introduced by the loading of the promoter is insufficient. On the other hand, if the loading is larger than this, the supported Ir may cover the surface and the active site for hydrogen generation may be crushed, or the amount of light reaching the NaTaO 3 : La (2%) photocatalyst itself may be reduced. Therefore, the activity is considered to have decreased. The same effect was observed even when Na 3 [IrCl 6 ] was used as the starting material.
Up to now, the activity has been improved by supporting a H 2 production promoter such as NiO or RuO 2 . It has been clarified that the activity can also be improved by supporting the O 2 production co-catalyst this time.
実施例１のＬａに代えてＳｒ（５重量％）ドープしたＮａＴａＯ３系触媒、ＮａＴａＯ３：Ｓｒ（５％）触媒に実施例１と同様の方法でＩｒ酸化物助触媒を担持させた場合における光水分解活性の特性を表３に示す。顕著な光触媒活性の向上が見られる。 In the case where an Ir oxide promoter is supported on the NaTaO 3 -based catalyst doped with Sr (5 wt%), NaTaO 3 : Sr (5%) catalyst in the same manner as in Example 1 instead of La in Example 1. Table 3 shows the characteristics of the photohydrolysis activity. Significant improvement in photocatalytic activity is observed.
ＳｎＮｂ２Ｏ６触媒を用いた場合；
（１）ＳｎＮｂ２Ｏ６粉末の調製；（Hosogi，Y．；Tanabe，K．；Kato，H．；Kobayashi，H．；Kudo，A．Chem．Lett．2004, 33，28．参照）
ＳｎＮｂ２Ｏ６は、不活性ガス中での固相法で調製した（８７３−１２７３Ｋ）。原料としてＳｎＯ( Wako、９９．９％)、およびＮｂ２Ｏ５（Kanto、 ９９．９５％）を用いた。Ｓｎ０．９５Ｓｒ０．０５Ｎｂ２Ｏ６は前記ＳｎＮｂ２Ｏ６触媒にＳｒをドープすることにより得られる。
（２）助触媒担持及び光触媒反応の結果；
実施例１と同様にイリジウムを硝酸イオン存在下で担持させた。表４にイリジウム酸化物助触媒を担持した触媒を硝酸銀水溶液に分散し酸素生成反応の活性を測定した結果を示す。ＳｎＮｂ２Ｏ６触媒は水素生成反応の触媒として活性を示すが、酸素の生成反応には活性を示さないが、イリジウム酸化物助触媒の担持により酸素生成反応に活性を示すことが表３の結果から分かる。
When using SnNb 2 O 6 catalyst;
(1) Preparation of SnNb 2 O 6 powder (see Hosogi, Y .; Tanabe, K .; Kato, H .; Kobayashi, H .; Kudo, A. Chem. Lett. 2004, 33, 28.)
SnNb 2 O 6 was prepared by a solid phase method in an inert gas (873-1273K). SnO (Wako, 99.9%) and Nb 2 O 5 (Kanto, 99.95%) were used as raw materials. Sn 0.95 Sr 0.05 Nb 2 O 6 can be obtained by doping the SnNb 2 O 6 catalyst with Sr.
(2) Results of cocatalyst loading and photocatalytic reaction;
As in Example 1, iridium was supported in the presence of nitrate ions. Table 4 shows the results of measuring the activity of the oxygen generation reaction by dispersing a catalyst carrying an iridium oxide promoter in an aqueous silver nitrate solution. The results of Table 3 show that SnNb 2 O 6 catalyst shows activity as a catalyst for hydrogen generation reaction, but does not show activity for oxygen generation reaction, but shows activity in oxygen generation reaction by supporting an iridium oxide promoter. I understand.
ここでは、光触媒として、Ｃｓ２Ｎｂ４Ｏ１１光触媒、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒またはＡｇＴａＯ３光触媒を用いて、これにＩｒ酸化物助触媒を担持させた光触媒の活性の改善について示す。
（１）Ｃｓ２Ｎｂ４Ｏ１１粉末の調製（三石雄悟, 加藤英樹, 工藤昭彦 日本化学会第81春季年会予稿集 2002，480．参照）；
Ｃｓ２Ｎｂ４Ｏ１１は、固相法で調製した。原料（Ｃｓ２ＣＯ３（Kanto Chemical、９８％）、Ｎｂ２Ｏ５（Kanto、９９．９９％）を混合し、白金るつぼを用いて空気中１１２３Ｋで５ｈ焼成した。過剰のアルカリは、焼成後水で洗浄し、その後乾燥させることでＣｓ２Ｎｂ４Ｏ１１粉末を得た。
（２）助触媒担持法；
イリジウム系助触媒の担持は、目的担持量（ＮＨ４）２［ＩｒＣｌ６］（ヘキサクロロイリジウム酸アンモニウム; Wako）を光触媒とともに反応溶液に仕込み、光（紫外光）を照射する光電着法で行った。反応溶液には、純水および硝酸アルカリ溶液（ＮａＮＯ３,(Kanto、９９％)、ＫＮＯ３、ＣｓＮＯ３）を使用した。また、必要に応じて光電着後に触媒を遠心分離法にて洗浄、回収した。
（３）Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒の触媒調製（奥富太陽・加藤英樹・工藤昭彦 触媒討論会 ２００２， ４０．参照）。
Ｓｒ２Ｔａ２Ｏ７光触媒の触媒調製（Kudo, A.; Kato, H.; Nakagawa, S. J. Phys. Chem. B, 2000, 104, 571. 参照）。
ＡｇＴａＯ３光触媒の調製（Kato, H.; Kobayashi, H.; Kudo, A. J. Phys. Chem. B, 2002, 106, 12441. 参照）。
前記文献記載の手法により調製した、Ｋ３Ｔａ３Ｂ２Ｏ１２光触媒、Ｓｒ２Ｔａ２Ｏ７光触媒及びＡｇＴａＯ３光触媒を用い、実施例１と同様の方法でＩｒ酸化物助触媒を担持させて光触媒を調製した。図５は、Ｓｒ２Ｔａ２Ｏ７光触媒、ＳｒＴｉＯ３触媒、ＮａＴａＯ３触媒にイリジウム酸化物系助触媒を担持させた触媒の拡散反射スペクトルを示す。
（４）光触媒反応；
前記各実施例と同様の閉鎖循環系装置にて行った。結果を表５に示す。Ｉｒ酸化物助触媒を担持させることにより光活性が見られた。
Here, a Cs 2 Nb 4 O 11 photocatalyst, a K 3 Ta 3 B 2 O 12 photocatalyst, a Sr 2 Ta 2 O 7 photocatalyst, or an AgTaO 3 photocatalyst is used as a photocatalyst, and an Ir oxide promoter is supported on this. The improvement of the activity of the photocatalyst will be described.
(1) Preparation of Cs 2 Nb 4 O 11 powder (see Yugo Mitsuishi, Hideki Kato, Akihiko Kudo, The 81st Annual Meeting of the Chemical Society of Japan 2002, 480);
Cs 2 Nb 4 O 11 was prepared by a solid phase method. Raw materials (Cs 2 CO 3 (Kanto Chemical, 98%)) and Nb 2 O 5 (Kanto, 99.99%) were mixed and calcined in air at 1123 K for 5 h using a platinum crucible. Cs 2 Nb 4 O 11 powder was obtained by washing with water and then drying.
(2) Cocatalyst loading method;
The iridium-based cocatalyst was supported by a photodeposition method in which a target supported amount (NH 4 ) 2 [IrCl 6 ] (ammonium hexachloroiridate; Wako) was charged into a reaction solution together with a photocatalyst and irradiated with light (ultraviolet light). . Pure water and alkaline nitrate solution (NaNO 3 , (Kanto, 99%), KNO 3 , CsNO 3 ) were used as the reaction solution. Further, if necessary, the catalyst was washed and collected by centrifugal separation after the photodeposition.
(3) Catalyst preparation of K 3 Ta 3 B 2 O 12 photocatalyst (Refer to Taiyo Okutomi, Hideki Kato, Akihiko Kudo Catalysis Forum 2002, 40).
Catalyst preparation of Sr 2 Ta 2 O 7 photocatalyst (see Kudo, A .; Kato, H .; Nakagawa, SJ Phys. Chem. B, 2000, 104, 571.).
Preparation of AgTaO 3 photocatalyst (see Kato, H .; Kobayashi, H .; Kudo, AJ Phys. Chem. B, 2002, 106, 12441.).
Using the K 3 Ta 3 B 2 O 12 photocatalyst, the Sr 2 Ta 2 O 7 photocatalyst and the AgTaO 3 photocatalyst prepared by the method described in the above literature, an Ir oxide promoter is supported in the same manner as in Example 1. A photocatalyst was prepared. FIG. 5 shows a diffuse reflection spectrum of a catalyst in which an iridium oxide-based cocatalyst is supported on a Sr 2 Ta 2 O 7 photocatalyst, a SrTiO 3 catalyst, or a NaTaO 3 catalyst.
(4) Photocatalytic reaction;
The same closed circulatory system as in the above examples was used. The results are shown in Table 5. Photoactivity was observed by loading an Ir oxide promoter.
本発明の硝酸イオンの存在下の酸化的雰囲気下において光電着によりＩｒ酸化物助触媒を担持させた光触媒は、従来にない酸化反応の活性を向上させ、更に前記特性の向上に伴って光触媒の活性を改善することができるという、全く新しい触媒の活性化技術を提供できた点で、酸化反応を利用する、特に光触媒を用いた酸化反応を利用する産業において多大の貢献をすることは明らかである。 The photocatalyst on which an Ir oxide promoter is supported by photodeposition in an oxidative atmosphere in the presence of nitrate ions according to the present invention improves the activity of an oxidation reaction that has not been heretofore, and further, with the improvement of the above characteristics, It is clear that we can provide a completely new catalyst activation technology that can improve the activity, and that it will make a great contribution in the industry using oxidation reaction, especially using photocatalyst. is there.
Claims (6)
6. The method for producing a photocatalyst carrying an Ir oxide promoter according to claim 4 , wherein (NH 4 ) 2 [IrCl 6 ] or Na 3 [IrCl 6 ] is used as an iridium supply source.
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| JP2021013890A (en) * | 2019-07-11 | 2021-02-12 | 国立大学法人 東京大学 | Photocatalyst and method of producing the same |
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