JP5755093B2 - Method for producing composite oxide having perovskite crystal structure - Google Patents
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- 239000013078 crystal Substances 0.000 title claims description 78
- 239000002131 composite material Substances 0.000 title claims description 29
- 238000004519 manufacturing process Methods 0.000 title claims description 29
- 239000002244 precipitate Substances 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 22
- 229910052783 alkali metal Inorganic materials 0.000 claims description 21
- 150000001340 alkali metals Chemical class 0.000 claims description 21
- 230000000737 periodic effect Effects 0.000 claims description 20
- 229910021478 group 5 element Inorganic materials 0.000 claims description 19
- 239000011941 photocatalyst Substances 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 14
- 150000001339 alkali metal compounds Chemical class 0.000 claims description 13
- 150000002736 metal compounds Chemical class 0.000 claims description 13
- 239000000470 constituent Substances 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 11
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052700 potassium Inorganic materials 0.000 claims description 10
- 229910052708 sodium Inorganic materials 0.000 claims description 10
- 229910052715 tantalum Inorganic materials 0.000 claims description 10
- 239000000047 product Substances 0.000 claims 1
- 239000003054 catalyst Substances 0.000 description 39
- 230000000694 effects Effects 0.000 description 25
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 22
- 239000001257 hydrogen Substances 0.000 description 22
- 229910052739 hydrogen Inorganic materials 0.000 description 22
- 238000001027 hydrothermal synthesis Methods 0.000 description 22
- 238000010304 firing Methods 0.000 description 19
- 238000006243 chemical reaction Methods 0.000 description 17
- 238000010335 hydrothermal treatment Methods 0.000 description 15
- 239000011734 sodium Substances 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 14
- 238000005259 measurement Methods 0.000 description 13
- 239000010955 niobium Substances 0.000 description 13
- 239000002243 precursor Substances 0.000 description 13
- 230000001699 photocatalysis Effects 0.000 description 12
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 239000000463 material Substances 0.000 description 8
- 239000007864 aqueous solution Substances 0.000 description 7
- 239000002585 base Substances 0.000 description 7
- 238000005406 washing Methods 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 229910002367 SrTiO Inorganic materials 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 150000001768 cations Chemical class 0.000 description 5
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- 230000004913 activation Effects 0.000 description 4
- 239000003513 alkali Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910010413 TiO 2 Inorganic materials 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 229910000484 niobium oxide Inorganic materials 0.000 description 3
- URLJKFSTXLNXLG-UHFFFAOYSA-N niobium(5+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Nb+5].[Nb+5] URLJKFSTXLNXLG-UHFFFAOYSA-N 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 238000003746 solid phase reaction Methods 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 229910052792 caesium Inorganic materials 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
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- 229910052701 rubidium Inorganic materials 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 125000004429 atom Chemical group 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
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- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 230000004298 light response Effects 0.000 description 1
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- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000013081 microcrystal Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
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- 230000033116 oxidation-reduction process Effects 0.000 description 1
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- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 238000006303 photolysis reaction 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
- 229910052726 zirconium Inorganic materials 0.000 description 1
Description
本発明は、例えば、Ｚ−スキーム型光水分解触媒系に利用することが期待できる、ペロブスカイト型結晶構造を有する複合酸化物の製造方法に関する。 The present invention is, for example, can be expected to be utilized in the Z- Scheme type light water decomposition catalyst systems relates to the method for producing a composite oxide having a perovskite crystal structure.
従来から、光触媒としては酸化物半導体であるＴｉＯ２やＳｒＴｉＯ３などのペロブスカイト型酸化物がよく知られている。このＴｉＯ２やペロブスカイト型酸化物に代表される触媒を用いて、可視光下で水分解によって水素が製造できれば、太陽という無限のエネルギーを利用することが可能となり、またＧＨＧ削減にも寄与できるため研究が盛んに行われてきている。しかしながら、これらの酸化物半導体からなる触媒の価電子帯はＯ２ｐ（約３Ｖ）であるため、水分解に必要な光触媒のバンドギャップは必然的に３ｅＶを超える値が必要となる。すなわち、紫外光に対しては活性を有するが、太陽光の大部分を占める可視光に対しては可視光吸収ができないため活性を持たない。そのため、可視光応答型酸化物光触媒の開発を進めるためには、水の酸化還元電位（１．２３ｅＶ）を挟みこみ、Ｏ２ｐに代わる新たな価電子帯あるいはドナー準位を形成することが必要であった。 Conventionally, perovskite oxides such as TiO 2 and SrTiO 3 which are oxide semiconductors are well known as photocatalysts. If hydrogen can be produced by water splitting under visible light using a catalyst typified by this TiO 2 or perovskite type oxide, it will be possible to use the infinite energy of the sun and contribute to GHG reduction. Research has been actively conducted. However, since the valence band of these oxide semiconductor catalysts is O2p (about 3 V), the band gap of the photocatalyst necessary for water splitting inevitably requires a value exceeding 3 eV. That is, it has activity for ultraviolet light, but it has no activity for visible light, which occupies most of sunlight, because it cannot absorb visible light. Therefore, in order to proceed with the development of a visible light responsive oxide photocatalyst, it is necessary to sandwich a redox potential (1.23 eV) of water and form a new valence band or donor level in place of O2p. there were.
このような、価電子帯を制御する方法として、Ｏ２ｐに代わって価電子帯を形成する可能性がある元素の探索や、ドナー準位を形成させるために、既に開発されている紫外光応答型光触媒の中で、Ｔｉと同様にｄ０電子配置をとるＶ、Ｚｒ、Ｎｂ、Ｍｏ、Ｔａ、Ｗなどの金属を含んだｄ０系酸化物半導体に遷移金属、例えばＣｒをドーピングする方法（非特許文献１）、また、可視光応答化するため、紫外光応答型光触媒と同じ結晶構造を有し、かつ可視光を吸収できる元素を添加して固溶体を形成する方法など、多くの検討がなされてきた。 As a method for controlling the valence band, an ultraviolet light response type that has already been developed in order to search for an element that may form a valence band instead of O2p and to form a donor level. In a photocatalyst, a method of doping a transition metal such as Cr into a d 0 -based oxide semiconductor containing a metal such as V, Zr, Nb, Mo, Ta, and W having a d 0 electron configuration similar to Ti In order to make visible light responsive, many studies have been made such as a method of forming a solid solution by adding an element having the same crystal structure as an ultraviolet light responsive photocatalyst and capable of absorbing visible light. I came.
例えば、ＳｒＴｉＯ３にＲｈをドープすることによりエネルギーギャップを小さくし、
Ｐｔを担持した触媒が、可視光分解活性を有する高活性触媒として開示されている。（特許文献１） この触媒は、少なくとも水の光分解によるＨ２の生成において効率の良い触媒であり、この触媒を利用して効率的に水素を生成する反応系として、Ｚ−スキーム型光触媒系が開示されている。（特許文献２） このＺ−スキーム型触媒系は酸素生成系触媒と水素生成系触媒とからなり、電子伝達剤を仲介して酸化還元を行うことによって、水素生成能力あるいは酸素生成能力のどちらか一方しか持たない材料でも水分解反応（２Ｈ２Ｏ→２Ｈ２＋Ｏ２）のための光触媒として使用できる反応系である。
For example, the energy gap is reduced by doping Rh into SrTiO 3 ,
A catalyst supporting Pt is disclosed as a highly active catalyst having visible light decomposition activity. (Patent Document 1) This catalyst is an efficient catalyst at least in the production of H 2 by photolysis of water, and a Z-scheme type photocatalytic system is used as a reaction system that efficiently generates hydrogen using this catalyst. Is disclosed. (Patent Document 2) This Z-scheme type catalyst system comprises an oxygen generation system catalyst and a hydrogen generation system catalyst, and either of hydrogen generation capacity or oxygen generation capacity is achieved by performing oxidation-reduction via an electron transfer agent. Even a material having only one is a reaction system that can be used as a photocatalyst for a water splitting reaction (2H 2 O → 2H 2 + O 2 ).
紫外光活性の高いＳｒＴｉＯ３にＲｈをドープすることによる可視光活性化は太陽光を利用できるようになる点で非常に有効な手段であるが、現状はまだまだ十分な可視光活性を得られていないのが実情である。その原因の１つは、可視光化の効率が低いこともあるが、母材となる酸化物触媒そのものの活性が未だ不十分ということである。従って、母材の光活性を改良する方法も活発に研究されており、ＲｈをドープしたＳｒＴｉＯ３触媒においては、更なる高活性化を狙って、母材中にＳｒを過剰に添加することが有効であることも開示されている。（非特許文献２）Ｓｒ添加量を増やすことで、Ｓｒ欠陥が減少し、また、Ｒｕがより高分散に担持されることで高活性化できることが示唆されている。 Visible light activation by doping Rh into SrTiO 3 having high ultraviolet light activity is a very effective means in that sunlight can be used, but at present, sufficient visible light activity is still obtained. There is no actual situation. One of the causes is that although the efficiency of visible light is low, the activity of the oxide catalyst itself as a base material is still insufficient. Accordingly, a method for improving the photoactivity of the base material has been actively researched. In the SrTiO 3 catalyst doped with Rh, it is possible to add excessive Sr to the base material for further activation. It is also disclosed that it is effective. (Non-patent document 2) It is suggested that Sr defects are reduced by increasing the amount of Sr added, and that Ru can be highly activated by being supported in a highly dispersed state.
このように、太陽光エネルギーの利用を目指した水の光触媒的分解反応系開発のために触媒の可視光活性化は不可欠ではあるが、母材となるペロブスカイト型酸化物触媒そのものの活性を上げることも重要であり、その性能が上がれば、水の光触媒的分解反応活性のポテンシャルを上げることが可能となる。 In this way, visible light activation of the catalyst is indispensable for developing a photocatalytic decomposition reaction system of water aiming at the use of solar energy, but the activity of the perovskite oxide catalyst itself that is the base material should be increased. It is also important, and if the performance is improved, the potential for photocatalytic decomposition activity of water can be increased.
一般的に光触媒活性が高いペロブスカイト型酸化物（母材）としてよく知られているのはＳｒＴｉＯ３等の複合金属酸化物などである。例えば、ペロブスカイト構造のＳｒＴｉＯ３は、ＴｉＯ２、ＳｒＣＯ３の金属化合物を原料として、これらを混合後、焼成による固相反応により一般に製造されている。固相法は操作が簡便であるという理由によって、母材の製造ではよく採用される技術であるが、焼成による結晶形成では結晶形態まで制御することは通常困難であった。一方で、結晶形態を制御できる製造法として水熱合成法が知られており、結晶成長を液相でゆっくりと行うことにより、形成される結晶は非常に微細にもかかわらず、その水熱条件によって、さまざまな結晶形態を形成させることが可能であることが知られている (例えば、非特許文献３)。本発明者らはこの水熱合成技術をベースにして、微細なペロブスカイト構造の結晶を得るための調製方法、すなわち小さい結晶でかつ高結晶性の触媒を得るための製造条件について種々検討した結果、従来にない小さな結晶子径を有するペロブスカイト構造の複合酸化物母材と、それを調製するための新しい製造方法を見出すに至った。 In general, composite metal oxides such as SrTiO 3 are well known as perovskite oxides (base materials) having high photocatalytic activity. For example, SrTiO 3 having a perovskite structure is generally manufactured by using a metal compound of TiO 2 and SrCO 3 as a raw material and mixing them, followed by solid-phase reaction by firing. The solid-phase method is a technique often used in the production of a base material because it is easy to operate, but it is usually difficult to control the crystal form in crystal formation by firing. On the other hand, a hydrothermal synthesis method is known as a production method capable of controlling the crystal form, and by performing crystal growth slowly in the liquid phase, the hydrothermal conditions are formed even though the crystals formed are very fine. It is known that various crystal forms can be formed by (for example, Non-Patent Document 3). Based on this hydrothermal synthesis technique, the present inventors have conducted various studies on a preparation method for obtaining a fine perovskite structure crystal, that is, a production condition for obtaining a small crystal and a highly crystalline catalyst. The present inventors have found a composite oxide base material having a perovskite structure having a small crystallite diameter and a new manufacturing method for preparing the same.
本発明は上記のような状況に鑑みてなされたもので、Ｚ−スキーム型可視光活性水分解触媒系への展開が期待できるペロブスカイト型の酸化物とその製造方法、およびそのペロブスカイト型の酸化物からなる光触媒を提供することを目的とする。 The present invention has been made in view of the above situation, and a perovskite oxide that can be expected to develop into a Z-scheme type visible light active water decomposition catalyst system, a method for producing the same, and a perovskite oxide. It aims at providing the photocatalyst which consists of.
本発明は、ペロブスカイト型の結晶構造を有する複合酸化物とその製造方法に関するものであり、更に、従来から知られている触媒に比較して高活性なペロブスカイト型の酸化物からなる光触媒に関する。 The present invention relates to a composite oxide having a perovskite-type crystal structure and a method for producing the same, and further relates to a photocatalyst composed of a perovskite-type oxide having a higher activity than conventionally known catalysts.
すなわち、本発明は、アルカリ金属（Ｍ１）と周期律表第５族元素（Ｍ５）を構成成分とする、結晶子径が１０〜３５ｎｍの範囲にあるペロブスカイト型結晶構造を有する複合酸化物、並びに当該複合酸化物からなる光触媒に係る。 That is, the present invention relates to a composite oxide having a perovskite crystal structure having a crystallite diameter in the range of 10 to 35 nm, comprising alkali metal (M 1 ) and Group 5 element (M 5 ) of the periodic table as constituent components. And a photocatalyst comprising the composite oxide.
ここで、結晶子径が１０〜３５ｎｍの範囲にあるペロブスカイト型結晶構造を有する複合酸化物は、アルカリ金属（Ｍ１）、好ましくはＮａおよびＫから選ばれる一種以上を構成成分とするアルカリ金属化合物（Ａ）と周期律表第５族元素（Ｍ５）、好ましくはＮｂおよびＴａから選ばれる一種以上を構成成分とする金属化合物（Ｂ）を含有する混合物を水熱処理してペロブスカイト構造ではない結晶性の沈殿物を形成させた後、次いで当該沈殿物を焼成することによって調製される。 Here, the composite oxide having a perovskite crystal structure having a crystallite diameter in the range of 10 to 35 nm is an alkali metal compound (M 1 ), preferably an alkali metal compound containing at least one selected from Na and K as a constituent component A crystal that does not have a perovskite structure by hydrothermally treating a mixture containing (A) and a group 5 element (M 5 ) in the periodic table, preferably a metal compound (B) containing at least one member selected from Nb and Ta. After the formation of a neutral precipitate, the precipitate is then calcined.
水熱処理は１４５〜１７８℃の温度で実施し、金属化合物（Ｂ）中の周期律表第５族元素（Ｍ５）に対するアルカリ金属化合物（Ａ）中のアルカリ金属（Ｍ１）の仕込み原子比が２．１〜５．５を満たすように、アルカリ金属化合物（Ａ）の水溶液中で金属化合物（
Ｂ）を処理することが望ましい。
更に、焼成は３６０〜８３０℃で実施することが望ましい。
本発明はまた、このペロブスカイト型結晶構造を有する複合酸化物からなる光触媒である。
The hydrothermal treatment is performed at a temperature of 145 to 178 ° C., and the charged atomic ratio of the alkali metal (M 1 ) in the alkali metal compound (A) to the Group 5 element (M 5 ) in the periodic table in the metal compound (B) Of the metal compound (A) in an aqueous solution of the alkali metal compound (A) so as to satisfy 2.1 to 5.5.
It is desirable to process B).
Furthermore, it is desirable to perform baking at 360-830 degreeC.
The present invention is also a photocatalyst comprising a complex oxide having this perovskite crystal structure.
更に本発明は、アルカリ金属（Ｍ１）、好ましくはＮａおよびＫから選ばれる一種以上を構成成分とするアルカリ金属化合物（Ａ）と周期律表第５族元素（Ｍ５）好ましくはＮｂおよびＴａから選ばれる一種以上を構成成分とする金属化合物（Ｂ）を含有する混合物を水熱処理して、ペロブスカイト構造を持たない結晶性の沈殿物を形成させた後、次いで当該沈殿物を焼成することによってペロブスカイト型結晶構造を有する複合酸化物を製造する方法に係る。 Furthermore, the present invention relates to an alkali metal compound (A) comprising at least one selected from alkali metals (M 1 ), preferably Na and K, and a Group 5 element (M 5 ), preferably Nb and Ta, of the periodic table. By hydrothermally treating a mixture containing a metal compound (B) containing at least one selected from the group consisting of 1 to form a crystalline precipitate having no perovskite structure, and then firing the precipitate The present invention relates to a method for producing a composite oxide having a perovskite crystal structure.
従来得られていた複合酸化物に比較して、紫外光による水素生成活性が高いペロブスカイト型結晶構造を有する複合酸化物が提供される。 Provided is a composite oxide having a perovskite crystal structure that has a higher hydrogen generation activity by ultraviolet light than a conventionally obtained composite oxide.
本発明の、例えばＺ−スキーム型光水分解触媒系に利用することが期待できるペロブスカイト型結晶構造を有する複合酸化物は、アルカリ金属（Ｍ１）と周期律表第５族元素（Ｍ５）を構成成分とする、結晶子径が１０〜３５ｎｍの範囲にある。アルカリ金属（Ｍ１）としては、Ｎａ、Ｋ、Ｒｂ、Ｃｓを挙げることができるが、後述するように当該複合酸化物を調製する際に用いられるアルカリ金属化合物（Ａ）の安全性や入手容易性の視点からＮａとＫが好ましく、光触媒活性の視点からはＮａが特に好ましい。アルカリ金属（Ｍ１）は一種類のみであっても二種以上の複数種であってもよい。周期律表第５族元素（Ｍ５）としては、Ｖ、Ｎｂ、Ｔａ、Ｄｂが挙げられるが、後述する当該複合酸化物を調製する際に用いられる金属化合物（Ｂ）の安全性や入手容易性の視点からＮｂとＴａが好ましく、光触媒活性の視点からはＮｂが特に好ましい。周期律表第５族元素（Ｍ５）は一種類のみであっても二種以上の複数種であってもよい。本発明のペロブスカイト型結晶構造を有する複合酸化物の結晶子径は、通常１０〜３５ｎｍ、好ましくは２０〜３５ｎｍである。結晶子径が小さいほど光触媒活性は高まるが、１０ｎｍ未満の複合酸化物を調製するためには全工程時間が長くなり経済的ではない。また結晶子径が３５ｎｍを超える場合では十分な光触媒活性を得ることができない。本発明においては光触媒活性の点から、本発明の複合酸化物は全てがペロブスカイト型結晶構造を有することが好ましいが、本発明は非
ペロブスカイト型結晶構造を有する複合酸化物の混入を排除するものでない。後述するようにペロブスカイト型結晶構造の純度よりも当該複合酸化物の調製速度を優先する場合は、一般的に光触媒活性は多少低下する。このような光触媒活性低下が許容される場合であっても、ペロブスカイト型結晶構造のＸＲＤピーク強度および非ペロブスカイト型結晶構造のＸＲＤピーク強度から算出される、非ペロブスカイト型結晶構造複合酸化物混入量の上限値は全体の複合酸化物量に対して１５％とするのが好ましい。
The composite oxide having a perovskite type crystal structure that can be expected to be used in, for example, a Z-scheme type photohydrolysis catalyst system of the present invention includes an alkali metal (M 1 ) and a periodic table Group 5 element (M 5 ). The crystallite diameter is in the range of 10 to 35 nm. Examples of the alkali metal (M 1 ) include Na, K, Rb, and Cs. As will be described later, the safety and easy availability of the alkali metal compound (A) used when preparing the composite oxide. Na and K are preferable from the viewpoint of the property, and Na is particularly preferable from the viewpoint of the photocatalytic activity. The alkali metal (M 1 ) may be only one type or two or more types. Examples of the Group 5 element (M 5 ) in the periodic table include V, Nb, Ta, and Db. The safety and easy availability of the metal compound (B) used when preparing the composite oxide described later. Nb and Ta are preferable from the standpoint of safety, and Nb is particularly preferable from the viewpoint of photocatalytic activity. The periodic table Group 5 element (M 5 ) may be only one type or two or more types. The crystallite diameter of the composite oxide having a perovskite crystal structure of the present invention is usually 10 to 35 nm, preferably 20 to 35 nm. The smaller the crystallite size, the higher the photocatalytic activity. However, in order to prepare a composite oxide of less than 10 nm, the entire process time is increased, which is not economical. Further, when the crystallite diameter exceeds 35 nm, sufficient photocatalytic activity cannot be obtained. In the present invention, from the viewpoint of photocatalytic activity, it is preferable that all the complex oxides of the present invention have a perovskite crystal structure, but the present invention does not exclude the inclusion of a complex oxide having a non-perovskite crystal structure. . As described later, when priority is given to the preparation rate of the composite oxide over the purity of the perovskite crystal structure, the photocatalytic activity generally decreases somewhat. Even when such a decrease in photocatalytic activity is allowed, the amount of mixed non-perovskite crystal structure complex oxide calculated from the XRD peak intensity of the perovskite crystal structure and the XRD peak intensity of the non-perovskite crystal structure The upper limit is preferably 15% with respect to the total amount of complex oxide.
ペロブスカイト型構造は、一般にＡＢＸ３の結晶構造で表される。このペロブスカイト型構造は、Ａサイトの陽イオンとＸサイトの陰イオンが同程度の大きさを有し、このＡとＸで構成される立方晶系単位格子の中にＡサイトより小さい陽イオンがＢサイトとして位置している。したがって、Ａサイトの陽イオンは１２配位となり、Ｂサイトの陽イオンは６配位、Ｘサイトの陰イオンは６配位となる。 The perovskite structure is generally represented by the crystal structure of ABX 3 . In this perovskite structure, the cation at the A site and the anion at the X site have the same size, and a cation smaller than the A site is present in the cubic unit cell composed of A and X. It is located as B site. Therefore, the cation at the A site is 12-coordinated, the cation at the B-site is 6-coordinated, and the anion at the X site is 6-coordinated.
本発明のペロブスカイト型結晶構造を有する複合酸化物は、まず初めにアルカリ金属（Ｍ１）を構成成分とするアルカリ金属化合物（Ａ）と周期律表第５族元素（Ｍ５）を構成成分とする金属化合物（Ｂ）を含有する混合物を水熱処理して、ペロブスカイト構造を持たない結晶性の沈殿物を形成させた後、次いで当該沈殿物を焼成処理することによって得られる。水熱処理（以下の説明では「水熱合成」と呼称する場合もある）法は、高圧の水蒸気の存在下で行なわれる無機化合物の合成および結晶を成長させる方法であり、その条件は特に限定されるものではないが、本発明においては、この水熱合成は通常塩基性条件下で行われることが特徴である。そのため、Ａサイトとしては、塩基性水溶液中でイオンとして安定に存在するアルカリ金属が好ましく、かつ、１２配位を取りうる原子が必要なことから、Ｎａ、Ｋ、Ｒｂ、Ｃｓが好ましいのである。ここで、Ｘサイトは酸素原子であり、ＡサイトとＸサイトは同程度の大きさであることからＡサイトとしては、ＮａまたはＫのいずれかが好ましい。この条件で、Ｂサイトには６配位を取る５価の陽イオンが候補となるが、安全性や価格を考慮すれば、ＮｂまたはＴａのいずれかが好ましい。
以下、水熱処理（水熱合成）、次いで焼成処理の順に本発明の製造方法を詳細に説明する。
The composite oxide having a perovskite crystal structure according to the present invention first comprises an alkali metal compound (A) containing an alkali metal (M 1 ) as a constituent and a Group 5 element (M 5 ) in the periodic table as constituents. The mixture containing the metal compound (B) to be obtained is hydrothermally treated to form a crystalline precipitate having no perovskite structure, and then the precipitate is calcined. Hydrothermal treatment (sometimes referred to as “hydrothermal synthesis” in the following description) is a method of synthesizing inorganic compounds and growing crystals in the presence of high-pressure steam, and the conditions are particularly limited. Although not intended, the present invention is characterized in that this hydrothermal synthesis is usually carried out under basic conditions. Therefore, as the A site, an alkali metal that is stably present as an ion in a basic aqueous solution is preferable, and an atom capable of taking 12-coordination is necessary, and therefore Na, K, Rb, and Cs are preferable. Here, since the X site is an oxygen atom, and the A site and the X site are of the same size, the Na site is preferably either Na or K. Under this condition, a pentavalent cation having 6-coordination is a candidate for the B site, but either Nb or Ta is preferable in consideration of safety and price.
Hereinafter, the production method of the present invention will be described in detail in the order of hydrothermal treatment (hydrothermal synthesis) and then baking treatment.
〔水熱処理〕
本発明に係る、水熱合成で得られるペロブスカイト構造を持たない前駆体は具体的には、非常に微細な針状結晶が形成されることが好ましく、このペロブスカイト構造を持たない針状結晶が形成された場合、その次の工程の焼成処理によって、針状が分断されると同時にこの前駆体は熱をかけることによってペロブスカイト構造に変化しやすいために、最終的に結晶子径の小さい、かつ結晶性の高いペロブスカイト構造を有する複合酸化物からなる触媒が得られると考えている。
[Hydrothermal treatment]
Specifically, the precursor having no perovskite structure obtained by hydrothermal synthesis according to the present invention preferably forms very fine needle-like crystals, and the needle-like crystals not having this perovskite structure are formed. In this case, the precursor is easily changed to a perovskite structure by applying heat at the same time as the needle shape is divided by the firing process of the next step. It is believed that a catalyst composed of a complex oxide having a highly perovskite structure can be obtained.
本発明による水熱合成と焼成を経て得られたペロブスカイト構造を有する結晶は、前記のように、ＡサイトはＮａまたはＫ、ＢサイトはＮｂまたはＴａとするペロブスカイトである。 As described above, the crystal having a perovskite structure obtained through hydrothermal synthesis and baking according to the present invention is a perovskite in which the A site is Na or K and the B site is Nb or Ta.
水熱合成は塩基性条件下で行うため、Ａサイトの金属（Ｍ１）の原料であるアルカリ金属化合物（Ａ）としては水溶液中で塩基性を示す化合物が好ましく、特にはアルカリ金属水酸化物が好ましい。Ｂサイトの金属（Ｍ５）は水熱条件下で溶解するのであれば、原料である金属化合物（Ｂ）としては特に制限はないが、酸化物あるいは水酸化物が操作上好ましい。 Since hydrothermal synthesis is performed under basic conditions, the alkali metal compound (A) that is the raw material for the metal (M 1 ) at the A site is preferably a compound that exhibits basicity in an aqueous solution, and in particular, an alkali metal hydroxide. Is preferred. As long as the metal (M 5 ) at the B site is dissolved under hydrothermal conditions, the metal compound (B) as a raw material is not particularly limited, but an oxide or hydroxide is preferable in terms of operation.
本発明の特徴の１つは水熱合成で形成される微結晶は、その時点では未だ基本的にペロブスカイト構造を有しないということである。すなわち、本発明においては、水熱合成では、ペロブスカイトとは異なる水和物の結晶形成に留めるのが好ましい。特にこの段階の
結晶形態は針状結晶であることが望ましく、これは、ペロブスカイト構造の結晶が得られたときの立方晶の形状とは異なる。水熱合成の時点でペロブスカイト結晶構造が形成されてしまうと、そのあとの焼成では、得られたペロブスカイト構造の結晶性を改善はできても、結晶子径を小さくすることは出来ない。
One of the features of the present invention is that the microcrystal formed by hydrothermal synthesis still does not basically have a perovskite structure at that time. That is, in the present invention, hydrothermal synthesis is preferably limited to crystal formation of a hydrate different from perovskite. In particular, it is desirable that the crystal form at this stage is a needle crystal, which is different from the cubic shape when a crystal having a perovskite structure is obtained. If a perovskite crystal structure is formed at the time of hydrothermal synthesis, the crystallite size of the obtained perovskite structure can be improved by subsequent firing, but the crystallite diameter cannot be reduced.
一方で、本発明によれば、水熱合成を終わった段階で、ペロブスカイト構造ではない前駆体構造の結晶を形成できれば、そのあとに行う焼成段階において、ペロブスカイト構造への結晶変態が起こり、前駆体構造の結晶は小さく細分化されることを見出した。またそのときにペロブスカイト構造に変態し易い前駆体構造であるためにより低温でのペロブスカイト構造への変態も可能となる。その結果として、従来に比較して、結晶子径は小さいにもかかわらず、高結晶性の結晶が得られるため、本発明による得られたペロブスカイト型の酸化物は高い光触媒活性を示すことができるのである。 On the other hand, according to the present invention, if a crystal having a precursor structure that is not a perovskite structure can be formed at the end of hydrothermal synthesis, crystal transformation to the perovskite structure occurs in the subsequent firing step, and the precursor It has been found that the crystals of the structure are small and fragmented. In addition, since the precursor structure is easily transformed into a perovskite structure at that time, the transformation to the perovskite structure at a low temperature is also possible. As a result, a highly crystalline crystal can be obtained in spite of a small crystallite diameter compared to the conventional case, and thus the perovskite oxide obtained according to the present invention can exhibit high photocatalytic activity. It is.
水熱合成においてペロブスカイト構造ではない前駆体の特に望ましい結晶形態は針状結晶である。前駆体が好ましい針状結晶構造であるかどうかについては、その針状結晶のＸＲＤによる構造解析、走査電子顕微鏡（ＳＥＭ）による形態観察によって判断可能である。本発明においては、ＳＥＭ観察により直径が０．５μｍ以下、好ましくは０．１μｍ 以下の針状結晶が得られることが望ましい。 A particularly desirable crystal form of a precursor that does not have a perovskite structure in hydrothermal synthesis is an acicular crystal. Whether or not the precursor has a preferable acicular crystal structure can be determined by structural analysis by XRD of the acicular crystal and morphological observation by a scanning electron microscope (SEM). In the present invention, it is desirable to obtain a needle-like crystal having a diameter of 0.5 μm or less, preferably 0.1 μm or less by SEM observation.
このような、針状結晶が得られる水熱合成条件について次に述べる。水熱合成の際の原料仕込みについては、Ｂサイトに入る周期律表第５族元素（Ｍ５）に対するＡサイトに入るアルカリ金属（Ｍ１）の仕込原子比が１以上であれば、その水熱条件にも左右される場合があるが、通常は望ましい結晶が形成される。また、一般に塩基性を示すアルカリ金属（Ｍ１）はＡサイトの金属と同じであることが望ましく、そのため、前記の仕込原子比は２．１以上であることが好ましい。仕込原子比の上限値は特に制限されないが、その溶解度や、結晶析出速度などを考慮すれば、不必要に高くすることはあまり意味がなく、従って、仕込原子比は通常２．１〜５．５、好ましくは２．１〜５．０、更に好ましくは２．５〜５．０の範囲である。 The hydrothermal synthesis conditions for obtaining such needle-like crystals will be described next. Regarding the preparation of raw materials in hydrothermal synthesis, if the charged atomic ratio of alkali metal (M 1 ) entering the A site to the Group 5 element (M 5 ) in the periodic table entering the B site is 1 or more, the water Usually, the desired crystal is formed, although it may depend on the thermal conditions. In general, the alkali metal (M 1 ) that exhibits basicity is desirably the same as the metal at the A site, and therefore, the charged atomic ratio is preferably 2.1 or more. The upper limit of the charged atomic ratio is not particularly limited, but considering its solubility, crystal precipitation rate, etc., it is not meaningful to make it unnecessarily high. Therefore, the charged atomic ratio is usually 2.1 to 5. 5, Preferably it is 2.1-5.0, More preferably, it is the range of 2.5-5.0.
本発明においては、水熱処理する溶液中の[ＯＨ−]イオン濃度も結晶成長には影響する。
[ＯＨ−]イオン濃度は低すぎると結晶生成に時間がかかり、高すぎると短時間で結晶変態が進みすぎて構造制御が困難となり、ペロブスカイト構造にまで進んでしまうこともあるので、経済性や操作性を考慮すれば[ＯＨ−]濃度は通常、０．２〜２．５モル／リットル、好ましくは０．２〜２．５モル／リットルである。更に、結晶を形成する金属原料の仕込み量も同様に結晶形態に影響する。Ｂサイトの金属は酸化物などの化合物で仕込むため、仕込み時には懸濁液となるが、水熱反応後に得られる前駆体結晶として５０〜２００ｇ／リットルの濃度範囲とするのが生産効率、及び再現性を考慮すれば望ましい。
In the present invention, the [OH − ] ion concentration in the hydrothermally treated solution also affects the crystal growth.
If the [OH − ] ion concentration is too low, it takes time to produce crystals, and if it is too high, the crystal transformation proceeds in a short time, making the structure control difficult, and may lead to a perovskite structure. Considering operability, the [OH − ] concentration is usually 0.2 to 2.5 mol / liter, preferably 0.2 to 2.5 mol / liter. Furthermore, the charged amount of the metal raw material forming the crystal similarly affects the crystal form. Since the metal at the B site is charged with a compound such as an oxide, it becomes a suspension at the time of charging. However, the precursor crystal obtained after the hydrothermal reaction has a concentration range of 50 to 200 g / liter, and production efficiency and reproduction are achieved. It is desirable to consider the characteristics.
本発明において、水熱合成温度は重要な因子の１つである。この温度が低すぎると結晶成長が進まないので好ましくないが、逆に高すぎると、結晶変態の速度を制御できなくなり、望ましい結晶構造が得られない場合がある。実生産での操作を考慮すれば、水熱合成温度は、１４５〜１７８℃、好ましくは１５０〜１７５℃とすることが望まれる。この温度であれば低すぎて結晶生成が進まないということもなく、また、結晶がペロブスカイト構造を取るということもなく、目的とする前駆体結晶が得られるので好ましい。この水熱温度が決まると圧力は自己発生蒸気圧よって従属的に決まるが、更に、加圧することは結晶成長には大きく影響しないため加圧操作は任意である。但し、通常は経済性を考えて、温度上昇による自己発生蒸気圧で反応を行う。水熱合成時間は、短すぎると、結晶化が不十分となり好ましくないが、長くする分には特に影響はない。反応の効率や操作性等を考慮すれば、好ましい反応時間は８〜２００時間、更に好ましくは１０〜５０時間である。
水熱合成で得られた前駆体結晶を含む沈殿溶液は、このあと、溶液から沈殿物を分離・回収するためにろ過する。ここで回収された沈殿物は余剰のアルカリ分を除去するため、得られた沈殿物重量の４０〜２００倍の水で洗浄した後、再びろ過・回収される。洗浄方法としては、洗浄水量を数回分に分けて洗浄・ろ過を繰り返す方法でもよく、最終的にこの水洗浄の際の濾液のｐＨが８以下となればよい。このようにして回収された結晶は、６０〜１２０℃で一晩乾燥された後、焼成で温度が均一になるよう、適宜、解砕する。
In the present invention, the hydrothermal synthesis temperature is one of the important factors. If the temperature is too low, crystal growth does not proceed, which is not preferable. However, if the temperature is too high, the rate of crystal transformation cannot be controlled, and a desired crystal structure may not be obtained. Considering operation in actual production, the hydrothermal synthesis temperature is desired to be 145 to 178 ° C, preferably 150 to 175 ° C. This temperature is preferable because it is too low and crystal formation does not proceed, and the crystal does not have a perovskite structure and the desired precursor crystal can be obtained. When the hydrothermal temperature is determined, the pressure is dependently determined by the self-generated vapor pressure, but further, pressurization is optional because pressurization does not significantly affect crystal growth. However, the reaction is usually carried out with a self-generated vapor pressure due to temperature rise in consideration of economy. If the hydrothermal synthesis time is too short, crystallization becomes insufficient and this is not preferable, but there is no particular effect on the length of the hydrothermal synthesis time. In view of the efficiency and operability of the reaction, the preferred reaction time is 8 to 200 hours, more preferably 10 to 50 hours.
The precipitation solution containing the precursor crystals obtained by hydrothermal synthesis is then filtered to separate and recover the precipitate from the solution. The precipitate collected here is filtered and collected again after washing with 40 to 200 times the weight of the obtained precipitate in order to remove excess alkali. As a washing method, a method of repeating washing and filtration by dividing the amount of washing water into several times may be used, and the pH of the filtrate at the time of this water washing should finally be 8 or less. The crystals recovered in this manner are dried at 60 to 120 ° C. overnight, and then appropriately crushed so that the temperature becomes uniform by firing.
〔焼成処理〕
このようにして得られた前駆体結晶は、次に目的とするペロブスカイト構造にするために焼成処理が行われる。一般に、固相反応によってペロブスカイト構造の結晶を得るためには、少なくとも６００℃以上の温度で２０時間以上焼成することが必要であるが、本発明においては、ペロブスカイト構造に変化しやすい前駆体構造を予め形成させているため、その焼成温度は必ずしも結晶成長が起こるような高温を必要としない。本発明においては、その焼成温度は、固相反応に必要な温度より低くすることが可能であり、通常３６０〜８３０℃、好ましくは３７０〜８００℃で行えばよい。水熱合成で得られた前駆体結晶の焼成は、この温度の範囲であれば、ペロブスカイト構造への変化が十分に起こらないということもなく、また、ペロブスカイト構造が結晶成長して、結晶子径が大きくなるということもない。焼成時間は特に限定されないが、結晶変態に十分な時間を与え、かつ経済的な時間を考慮すれば、通常５〜２０時間、好ましくは５〜１２時間焼成するのが好ましい。焼成雰囲気については特に制限はなく、還元雰囲気でも、不活性雰囲気でも、酸化性雰囲気でも行うことは可能である。一般的には、設備が最も簡単な大気中での焼成が好んで採用される。
[Baking treatment]
The precursor crystal thus obtained is then subjected to a firing treatment in order to obtain the desired perovskite structure. In general, in order to obtain a crystal having a perovskite structure by a solid phase reaction, it is necessary to calcinate at a temperature of at least 600 ° C. for 20 hours or more. In the present invention, a precursor structure that easily changes to a perovskite structure is used. Since it is formed in advance, the firing temperature does not necessarily require a high temperature at which crystal growth occurs. In the present invention, the calcination temperature can be lower than the temperature required for the solid-phase reaction, and is usually 360 to 830 ° C, preferably 370 to 800 ° C. The firing of the precursor crystal obtained by hydrothermal synthesis does not cause a sufficient change to the perovskite structure within this temperature range, and the perovskite structure grows and the crystallite diameter grows. Does not increase. Although the firing time is not particularly limited, it is usually preferable to fire for 5 to 20 hours, preferably 5 to 12 hours, given sufficient time for crystal transformation and considering economic time. The firing atmosphere is not particularly limited, and can be performed in a reducing atmosphere, an inert atmosphere, or an oxidizing atmosphere. In general, firing in the atmosphere with the simplest equipment is preferred.
得られたペロブスカイト型酸化物を光触媒として使用する場合には、適宜、その使用形態に応じて粉砕工程にかけるなどした後、水素生成反応に用いられる。
本発明のペロブスカイト型の酸化物（母材）は、このままでは、可視光活性を持たないが、その紫外光活性は非常に高く、先に述べた可視光活性化の方策を施すことにより、可視光化することは可能である。本発明によるペロブスカイト型の酸化物の可視光化の処方については、従来から知られている処方が特に問題なく適用可能である。
以下、参考形態の例を付記する。
＜１＞
アルカリ金属（Ｍ １ ）と周期律表第５族元素（Ｍ ５ ）を構成成分とする、結晶子径が１０〜３５ｎｍの範囲にあることを特徴とするペロブスカイト型結晶構造を有する複合酸化物。
＜２＞
アルカリ金属（Ｍ １ ）が、ＮａおよびＫから選ばれる１種以上であることを特徴とする＜１＞記載の酸化物。
＜３＞
周期律表第５族元素（Ｍ ５ ）が、ＮｂおよびＴａから選ばれる１種以上であることを特徴とする＜１＞記載の複合酸化物。
＜４＞
アルカリ金属（Ｍ １ ）を構成成分とするアルカリ金属化合物（Ａ）と周期律表第５族元素（Ｍ ５ ）を構成成分とする金属化合物（Ｂ）を含有する混合物を水熱処理して、ペロブスカイト構造を持たない結晶性の沈殿物を形成させた後、次いで焼成処理して得られることを特徴とする＜１＞〜＜３＞のいずれか１項に記載の複合酸化物。
＜５＞
水熱処理を１４５〜１７８℃の温度で実施することを特徴とする、＜４＞に記載の複合酸化物。
＜６＞
周期律表第５族元素（Ｍ ５ ）に対するアルカリ金属（Ｍ １ ）の仕込み原子比が、２．１〜５．５となるように、アルカリ金属化合物（Ａ）の水溶液中で金属化合物（Ｂ）を水熱処理することを特徴とする、＜４＞または＜５＞に記載の複合酸化物。
＜７＞
焼成処理を３６０〜８３０℃で実施することを特徴とする＜４＞〜＜６＞のいずれか一項に記載の複合酸化物。
＜８＞
＜１＞〜＜７＞に記載のペロブスカイト型結晶構造を有する複合酸化物からなる光触媒。
＜９＞
アルカリ金属（Ｍ １ ）を構成成分とするアルカリ金属化合物（Ａ）と周期律表第５族元素（Ｍ ５ ）を構成成分とする金属化合物（Ｂ）を含有する混合物を水熱処理して、ペロブスカイト構造を持たない結晶性の沈殿物を形成させた後、焼成することを特徴とするペロブスカイト型結晶構造を有する複合酸化物の製造方法。
＜１０＞
アルカリ金属（Ｍ １ ）が、ＮａおよびＫから選ばれる１種以上であることを特徴とする＜９＞記載の製造方法。
＜１１＞
周期律表第５族元素（Ｍ ５ ）が、ＮｂおよびＴａから選ばれる１種以上であることを特徴とする＜９＞に記載の製造方法。
＜１２＞
水熱処理を１４５〜１７８℃の温度で実施することを特徴とする、＜６＞に記載のペロブスカイト構造の酸化物の製造方法。
＜１３＞
周期律表第５族元素（Ｍ ５ ）に対するアルカリ金属（Ｍ １ ）の仕込み原子比が、２．１〜５．５となるように、アルカリ金属化合物（Ａ）の水溶液中で金属化合物（Ｂ）を水熱処理することを特徴とする、＜９＞〜＜１２＞のいずれか１項に記載の製造方法。
＜１４＞
焼成処理を３６０〜８３０℃で実施することを特徴とする、＜６＞に記載のペロブスカイト構造の酸化物の製造方法。
When the obtained perovskite type oxide is used as a photocatalyst, it is used in a hydrogen generation reaction after being subjected to a pulverization step depending on the usage form.
The perovskite oxide (matrix) of the present invention does not have visible light activity as it is, but its ultraviolet light activity is very high, and it can be made visible by applying the above-mentioned visible light activation strategy. It is possible to make it light. As the formulation for making the perovskite oxide visible according to the present invention, a conventionally known formulation can be applied without any particular problem.
Hereinafter, examples of the reference form will be added.
<1>
A composite oxide having a perovskite type crystal structure, characterized in that the crystallite diameter is in the range of 10 to 35 nm, comprising alkali metal (M 1 ) and Group 5 element (M 5 ) of the periodic table as constituent components.
<2>
<1> The oxide according to <1>, wherein the alkali metal (M 1 ) is at least one selected from Na and K.
<3>
The complex oxide according to <1>, wherein the Group 5 element (M 5 ) of the periodic table is at least one selected from Nb and Ta.
<4>
Perovskite is obtained by hydrothermally treating a mixture containing an alkali metal compound (A) containing alkali metal (M 1 ) as a constituent and a metal compound (B) containing group 5 element (M 5 ) as a constituent of the periodic table. The composite oxide according to any one of <1> to <3>, which is obtained by forming a crystalline precipitate having no structure and then performing a baking treatment.
<5>
The composite oxide according to <4>, wherein the hydrothermal treatment is performed at a temperature of 145 to 178 ° C.
<6>
The metal compound (B) in the aqueous solution of the alkali metal compound (A) so that the charged atomic ratio of the alkali metal (M 1 ) to the Group 5 element (M 5 ) in the periodic table is 2.1 to 5.5. The composite oxide according to <4> or <5>, which is hydrothermally treated.
<7>
The composite oxide according to any one of <4> to <6>, wherein the baking treatment is performed at 360 to 830 ° C.
<8>
<1>-<7> The photocatalyst which consists of complex oxide which has the perovskite type crystal structure.
<9>
Perovskite is obtained by hydrothermally treating a mixture containing an alkali metal compound (A) containing alkali metal (M 1 ) as a constituent and a metal compound (B) containing group 5 element (M 5 ) as a constituent of the periodic table. A method for producing a composite oxide having a perovskite crystal structure, wherein a crystalline precipitate having no structure is formed and then fired.
<10>
The production method according to <9>, wherein the alkali metal (M 1 ) is at least one selected from Na and K.
<11>
The production method according to <9>, wherein the Group 5 element (M 5 ) of the periodic table is one or more selected from Nb and Ta.
<12>
The method for producing an oxide having a perovskite structure according to <6>, wherein the hydrothermal treatment is performed at a temperature of 145 to 178 ° C.
<13>
The metal compound (B) in the aqueous solution of the alkali metal compound (A) so that the charged atomic ratio of the alkali metal (M 1 ) to the Group 5 element (M 5 ) in the periodic table is 2.1 to 5.5. ) Is subjected to hydrothermal treatment. The production method according to any one of <9> to <12>.
<14>
The method for producing an oxide having a perovskite structure according to <6>, wherein the baking treatment is performed at 360 to 830 ° C.
以下、実施例に基づいて本発明によるペロブスカイト型の酸化物、およびその光触媒としての活性評価結果について、さらに具体的に説明するが、本発明はこれら実施例に限定されるものではない。 Hereinafter, the perovskite type oxide according to the present invention and the activity evaluation result as a photocatalyst according to the present invention will be described more specifically. However, the present invention is not limited to these examples.
次に、本発明のペロブスカイト型結晶構造を有する複合酸化物を光触媒として用いる場合の活性評価活性評価方法について説明する。本発明の実施例および比較例で得られた複合酸化物は、図１に示すような閉鎖循環式のガラス製水素生成反応装置を用いて、メタノールを犠牲剤とした酸化還元反応での水素生成反応（２Ｈ＋＋２ｅ−→Ｈ２）に対する触媒活性で評価した。 Next, an activity evaluation activity evaluation method when the composite oxide having a perovskite crystal structure of the present invention is used as a photocatalyst will be described. The composite oxides obtained in the examples and comparative examples of the present invention produced hydrogen in oxidation-reduction reactions using methanol as a sacrificial agent, using a closed-circulation glass hydrogen production reactor as shown in FIG. The catalytic activity for the reaction (2H + + 2e − → H 2 ) was evaluated.
まず、３００ｍｌの反応容器に水を１０８ｍＬとメタノール１２ｍＬを入れ、１０体積％の濃度になるようにメタノール水溶液を調製した後、ペロブスカイト型酸化物の光触媒を１００ｍｇ加えて、反応溶液を十分に撹拌した。次に、助触媒としてＰｔをこの光触媒に光析出担持させるため、塩化白金酸水溶液をＰｔとして０．１重量％担持できるよう添加後、反応容器を閉鎖循環式の水素生成反応装置に接続し、攪拌しながら系内を真空脱気した後、Ａｒガスを４００Ｔｏｒｒ導入し、３００Ｗキセノンランプ（朝日分光：ＭＡＸ−３０２、ＵＶタイプミラーモジュール、石英製ファイバー、石英製ロッドレンズ）を光源として、溶液の上から石英製ガラス窓を通して光照射を行った。光照射により生成した気体は、オンラインのガスクロマトグラフ（島津：ＧＣ−８Ａ、ＭＳ−５Ａカラム、ＴＣＤ、Ａｒキャリアー）で分析し、水素発生量を定量した。 First, 108 mL of water and 12 mL of methanol were placed in a 300 mL reaction vessel, and after preparing an aqueous methanol solution to a concentration of 10% by volume, 100 mg of a perovskite oxide photocatalyst was added and the reaction solution was sufficiently stirred. . Next, to add Pt as a cocatalyst to the photocatalyst by photoprecipitation, after adding an aqueous chloroplatinic acid solution to support 0.1% by weight as Pt, the reaction vessel was connected to a closed circulation type hydrogen generation reactor, After the system was vacuum degassed while stirring, Ar gas was introduced at 400 Torr, and a 300 W xenon lamp (Asahi Spectroscopy: MAX-302, UV type mirror module, quartz fiber, quartz rod lens) was used as a light source. Light was irradiated from above through a quartz glass window. The gas generated by light irradiation was analyzed by an online gas chromatograph (Shimadzu: GC-8A, MS-5A column, TCD, Ar carrier), and the amount of hydrogen generation was quantified.
〔実施例１〕
２００ｍＬのテフロン（登録商標）コートしたステンレス製反応容器に、水１００ｍＬおよび水酸化ナトリウム（関東化学製）４．００ ｇからなる水溶液と 、酸化ニオブ：Ｎｂ２Ｏ５（アルドリッチ製）４．６１ｇを入れて、十分に攪拌する。（Ｎａ：Ｎｂ=１．００：０．３５(原子比)、アルカリイオン[ＯＨ−]濃度＝１．０モル／リットル）次に、反応容器を水熱反応装置に入れ、１６０℃、２０時間、水熱処理する。水熱処理で得られた沈殿物は、ろ液のｐＨが８以下になるまで水洗浄、ろ過を行い、８０℃で一晩乾燥、解砕した。
[Example 1]
In a stainless steel reaction vessel coated with 200 mL of Teflon (registered trademark), 100 mL of water and an aqueous solution consisting of 4.00 g of sodium hydroxide (manufactured by Kanto Chemical Co., Ltd.) and 4.61 g of niobium oxide: Nb 2 O 5 (manufactured by Aldrich) And stir well. (Na: Nb = 1.00: 0.35 (atomic ratio), alkali ion [OH − ] concentration = 1.0 mol / liter) Next, the reaction vessel was placed in a hydrothermal reactor, and 160 ° C., 20 hours. , Hydrothermal treatment. The precipitate obtained by hydrothermal treatment was washed with water and filtered until the pH of the filtrate became 8 or less, dried at 80 ° C. overnight and crushed.
得られた沈殿物はＸＲＤ測定、及びＳＥＭ観察により、ペロブスカイト構造ではない針状結晶であることを確認した。ＸＲＤの結果を図２、ＳＥＭ写真を図３に示す。
得られた針状結晶を、大気中、４００℃、１０時間焼成した。焼成後、室温まで放冷、解砕した。その後、ろ液のｐＨが８以下になるまで水洗浄、ろ過を行い、乾燥後、触媒を得た。水熱処理、及び焼成条件を表１に示す。
It was confirmed by XRD measurement and SEM observation that the resulting precipitate was a needle-like crystal having no perovskite structure. The results of XRD are shown in FIG. 2, and the SEM photograph is shown in FIG.
The obtained needle crystal was fired in the atmosphere at 400 ° C. for 10 hours. After firing, the mixture was allowed to cool to room temperature and crushed. Thereafter, water washing and filtration were performed until the pH of the filtrate was 8 or less, and after drying, a catalyst was obtained. Table 1 shows the hydrothermal treatment and firing conditions.
得られた触媒は、ＸＲＤ測定において、結晶子径が２５ｎｍで、単一のペロブスカイト構造を示した。ＸＲＤの結果を図４、ＳＥＭ写真を図５に示す。結晶子径は、ＸＲＤ測定で得られた回折ピークの半値幅から、シェラーの式を使って計算した。
先に述べた触媒の活性評価方法に従って、水素生成反応を５時間行った。得られた水素生成反応の経時変化から、水素が定常的に生成したときの速度を水素生成速度とした。
水素生成活性とＸＲＤ測定の結果を、表２に示す。
The obtained catalyst showed a single perovskite structure with a crystallite diameter of 25 nm in XRD measurement. The results of XRD are shown in FIG. 4, and the SEM photograph is shown in FIG. The crystallite diameter was calculated from the half width of the diffraction peak obtained by XRD measurement using the Scherrer equation.
According to the catalyst activity evaluation method described above, the hydrogen generation reaction was performed for 5 hours. From the change over time of the obtained hydrogen generation reaction, the rate at which hydrogen was constantly generated was defined as the hydrogen generation rate.
Table 2 shows the hydrogen production activity and the results of XRD measurement.
〔実施例２〜８〕
表１に記入した条件の変更以外は実施例１と同様にして、触媒調製を行った。
各実施例の結果を表２に示す。
[Examples 2 to 8]
A catalyst was prepared in the same manner as in Example 1 except that the conditions entered in Table 1 were changed.
The results of each example are shown in Table 2.
〔比較例１〕[固相法製造触媒]
炭酸ナトリウム：Ｎａ２ＣＯ３（関東化学製）粉末を１．１１ｇ、酸化ニオブ：Ｎｂ２Ｏ５（アルドリッチ製）粉末を２．６６ｇ（Ｎａ：Ｎｂ＝１．０５：１．００の原子比）秤量、混合後、大気中、６００℃、２０時間焼成する。焼成後、室温まで放冷してから、解砕する。未反応のアルカリを除去するために、解砕した粉末を、１００ｍＬの水に懸濁させ、３０分間攪拌する。この懸濁液から、粉末を分離・回収した後、８０℃で一晩乾燥させて、触媒を得た。焼成条件を表１に示す。
[Comparative Example 1] [Solid-phase production catalyst]
1.11 g of sodium carbonate: Na 2 CO 3 (manufactured by Kanto Chemical), 2.66 g of niobium oxide: Nb 2 O 5 (manufactured by Aldrich) (atomic ratio of Na: Nb = 1.05: 1.00) After weighing and mixing, it is fired in the atmosphere at 600 ° C. for 20 hours. After firing, the mixture is allowed to cool to room temperature and then crushed. In order to remove the unreacted alkali, the crushed powder is suspended in 100 mL of water and stirred for 30 minutes. The powder was separated and collected from this suspension, and then dried at 80 ° C. overnight to obtain a catalyst. The firing conditions are shown in Table 1.
得られた触媒は、ＸＲＤにおいて、結晶子径が３７ｎｍで、単一のペロブスカイト構造を示す。ＸＲＤの結果を図６、ＳＥＭ写真を図７に示す。
実施例１と同様にして水素生成活性評価を行った。水素生成活性とＸＲＤ測定の結果を、表２に示す。
The obtained catalyst has a crystallite diameter of 37 nm in XRD and shows a single perovskite structure. The result of XRD is shown in FIG. 6, and the SEM photograph is shown in FIG.
The hydrogen generation activity was evaluated in the same manner as in Example 1. Table 2 shows the hydrogen production activity and the results of XRD measurement.
〔比較例２〕[水熱法製造触媒]
２００ｍＬテフロン（登録商標）コートしたステンレス製反応容器に、水１００ｍＬと水酸化ナトリウム（関東化学製）８．００ ｇからなる水溶液と 、酸化ニオブ：Ｎｂ２Ｏ５（アルドリッチ製）４．６１ｇを入れて、十分に攪拌する。（Ｎａ：Ｎｂ=２．００：０．３５(原子比)、アルカリイオン[ＯＨ−]濃度＝２．０モル／リットル）次に、反応容器を水熱反応装置に入れ、１６０℃、２０時間、水熱処理する。水熱処理で得られた沈殿物は、ろ液のｐＨが８以下になるまで水洗浄、ろ過を行い、８０℃で一晩乾燥、解砕した。得られた沈殿物はＸＲＤ測定により、結晶子径が４１ｎｍの単一のペロブスカイト構造であることを確認した。ＸＲＤの結果を図８、ＳＥＭ写真を図９に示す。
[Comparative Example 2] [Hydrothermal production catalyst]
In a stainless steel reaction vessel coated with 200 mL Teflon (registered trademark), 100 mL of water and an aqueous solution consisting of 8.00 g of sodium hydroxide (manufactured by Kanto Chemical) and 4.61 g of niobium oxide: Nb 2 O 5 (manufactured by Aldrich) are placed. Stir well. (Na: Nb = 2.00: 0.35 (atomic ratio), alkali ion [OH − ] concentration = 2.0 mol / liter) Next, the reaction vessel was placed in a hydrothermal reactor, and 160 ° C., 20 hours. , Hydrothermal treatment. The precipitate obtained by hydrothermal treatment was washed with water and filtered until the pH of the filtrate became 8 or less, dried at 80 ° C. overnight and crushed. The obtained precipitate was confirmed by XRD measurement to have a single perovskite structure with a crystallite size of 41 nm. The XRD result is shown in FIG. 8, and the SEM photograph is shown in FIG.
得られたペロブスカイト構造の沈殿物を、大気中、４００℃、１０時間焼成した。焼成後、室温まで放冷、解砕した。その後、ろ液のｐＨが８以下になるまで水洗浄、ろ過を行い、乾燥後、触媒を得た。水熱処理、及び焼成条件を表１に示す。
得られた触媒は、ＸＲＤ測定において、単一のペロブスカイト構造を維持しており、結晶子径が４１ｎｍだった。ＸＲＤの結果を図１０、ＳＥＭ写真を図１１に示す。
実施例１と同様にして水素生成活性評価を行った。水素生成活性とＸＲＤ測定の結果を、表２に示す。
The resulting perovskite structure precipitate was calcined in the atmosphere at 400 ° C. for 10 hours. After firing, the mixture was allowed to cool to room temperature and crushed. Thereafter, water washing and filtration were performed until the pH of the filtrate was 8 or less, and after drying, a catalyst was obtained. Table 1 shows the hydrothermal treatment and firing conditions.
The obtained catalyst maintained a single perovskite structure in XRD measurement and had a crystallite diameter of 41 nm. The XRD result is shown in FIG. 10, and the SEM photograph is shown in FIG.
The hydrogen generation activity was evaluated in the same manner as in Example 1. Table 2 shows the hydrogen production activity and the results of XRD measurement.
〔比較例３〜１２〕
表１に記入した条件の変更以外は比較例２と同様にして、触媒調製を行った。
各実施例の結果を表２に示す。
[Comparative Examples 3 to 12]
A catalyst was prepared in the same manner as in Comparative Example 2 except that the conditions entered in Table 1 were changed.
The results of each example are shown in Table 2.
添付した図１２からも明瞭に理解されるように、本願発明の結晶子径が３５ｎｍ以下に制御された複合酸化物を用いた紫外光下での水分解触媒活性は、比較例（水熱処理でペロブスカイトができたもの、比較例２〜５、１０、１１）に比べて高活性である。 As clearly understood from FIG. 12 attached, the water splitting catalytic activity under the ultraviolet light using the composite oxide in which the crystallite diameter of the present invention is controlled to 35 nm or less is shown in Comparative Example (hydrothermal treatment). It is more active than those obtained from perovskite, Comparative Examples 2-5, 10, 11).
本発明によるペロブスカイト型の酸化物からなる光触媒は、従来得られていた触媒に比較して、紫外光による水素生成活性が高い。 The photocatalyst comprising a perovskite oxide according to the present invention has a higher hydrogen generation activity by ultraviolet light than a conventionally obtained catalyst.
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